Symposium Organizers
Prabhakar Bandaru University of California-San Diego
Sonia Grego RTI International
Ian Kinloch University of Manchester
JJ1: Carbon Nanotube Synthesis
Session Chairs
Prabhakar Bandaru
Ian Kinloch
Monday PM, December 01, 2008
Room 302 (Hynes)
9:30 AM - **JJ1.1
Carbon Nanotubes and Their Applications.
Yuntian Zhu 1 , Qingwen Li 2 , Lianxi Zheng 4 , Xiefei Zhang 3
1 Materials Science & Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 , Suzhou Institute of Nanotech and Nanobionics, CAS, SuZhou China, 4 Mechanical & Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 3 , Los Alamos National Lab, Los Alamos, New Mexico, United States
Show AbstractCarbon nanotubes have many unique electronic and physical properties and are an order of magnitude stronger than any existing engineering materials. I’ll present the synthesis of long carbon nanotubes (CNTs), long CNTs with intramolecular junctions, long CNT arrays, the super strong CNT fibers, and CNT cottons. These CNTs were synthesized using catalytic chemical-vapour-deposition. Their growth mechanisms will be discussed. We have produced the longest individual CNTs, and the strongest CNT fibers with specific strength many times higher than current engineering fibers. Potential applications of these CNTs and CNT fibers include electronic devices, chemical and bio sensors, solar cells, filters, nano-composites, body armor, space shuttles, airplanes, etc.
10:00 AM - JJ1.2
Synthesis of Unique Carbon Nanotubes Inspired by the Allende Meteorite.
Satoshi Ohara 1 , Zhenquan Tan 1 , Kazuyoshi Sato 1 , Hiroya Abe 1
1 , Osaka University, Ibaraki Japan
Show AbstractTo fine-tune the properties of nanomaterials, they can now be processed into uniform-size nanocrystals with spherical, wire, rod, tadpole shapes. Despite the recent advances, controlling the shape, morphology, and surface characteristics of carbon nanomaterials is still a difficult task. Here, we have investigated the shock events inspired by the Allende meteorite for sophisticated tailor-made carbon nanomaterials. The formation of unique carbon nanotubes with bent, buckled, twisted nanostructures was observed by a novel collision process.
10:15 AM - JJ1.3
The Role of Water in Super Growth of Single-Walled Carbon Nanotube Carpets.
Placidus Amama 1 , Cary Pint 2 , Laura McJilton 2 , Seung Min Kim 3 , Eric Stach 3 , P. Terry Murray 4 , Robert Hauge 2 , Benji Maruyama 5
1 , Universal Technology Corporation, Dayton, Ohio, United States, 2 Department of Chemistry, Rice University, Houston, Texas, United States, 3 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 4 UDRI, University of Dayton, Dayton, Ohio, United States, 5 Materials & Manufacturing Directorate, Nanostructured and Biological Materials Branch, Air Force Research Laboratory, Dayton, Ohio, United States
Show AbstractVertically oriented single-walled carbon nanotube (SWNT) carpets grown by catalytic CVD have received enormous attention because of their suitability in a growing number of important technological applications [1]. Although the ultra-long, aligned SWNTS which can be attained by this growth method are promising for such applications, the lack of understanding associated with growth termination after micron-tall carpets are attained limits their widespread appeal. This problem is compounded by the limited understanding of the complicated process associated with carpet growth. To promote and sustain the growth of SWNT carpet, Iijima’s group advanced an approach whereby water was used as a protective agent against amorphous carbon coating [2]. The water-assisted CVD growth (also referred to as “super growth”) revealed that the activity and lifetime of the catalysts are dramatically enhanced by introducing a well-defined, limited amount of water into the growth chamber, resulting in the rapid growth of highly dense, vertically aligned SWNT carpets of high purity with heights up to 2.5 mm after 10 min. The main focus of our work is to understand the role water plays during super growth of SWNT carpets. We have studied the ripening behavior of the Fe catalyst film under typical CVD annealing conditions (with H2 pretreatment) and under super growth conditions (H2/H2O) at 750 °C, without the growth step. The TEM and AFM results demonstrate that water vapor impedes Ostwald ripening of catalysts, thus extending their life; this may be due to the ability of oxygen and hydroxyl species to reduce diffusion rates of catalyst atoms, and thus a delay in the collective termination of carpet growth. Our work explicitly shows the impact of typical carpet growth environments on catalyst film evolution, the termination of nanotube growth, and carpet growth in the context of Ostwald ripening. References(1) (a)Chattopadhyay, D.; Galeska, I.; Papadimitrakopoulos, F. J. Am. Chem. Soc. 2001, 123, 9451. (b) Jo, S. H.; Tu, Y.; Huang, Z. P. et al. Appl. Phys. Lett. 2003, 82, 3520. (c) Yildirim, T.; Ciraci, S. Phys. Rev. Lett. 2005, 94, 175501. (d) Hinds, B. J.; Chopra, N.; Rantell, T.; Andrews, R.; Gavalas, V.; Bachas, L. G. Science 2004, 303, 62.(2) (a) Hata, K.; Futaba, D. N.; Mizuno, K.; Namai, T.; Yumura, M.; Iijima, S. Science 2004, 306, 1362; (b) Futaba, D. N.; Hata, K.; Yamada, T.; Mizuno, K.; Yumura, M.; Iijima, S. Phys. Rev. Lett. 2005, 95, 056104.
10:30 AM - JJ1.4
Energetic and Entropic Considerations in the Synthesis of Helical Nanostructures.
Prabhakar Bandaru 1 , Apparao Rao 3 , Chiara Daraio 2
1 Materials Science program, Mechanical Engineering , UC, San Diego, La Jolla, California, United States, 3 Physics and Astronomy, Clemson University, Clemson, South Carolina, United States, 2 Applied Physics, California Institute of Technology, Pasadena, California, United States
Show AbstractThe synthesis of helical morphologies of nanotubes (NTs) and nanofibers (NFs), through Chemical Vapor Deposition (CVD) techniques, has been widely reported and can be made practical for a wide variety of applications, e.g., nanoscale mechanical springs and electrical inductors. Additionally, the observed nano-coils/-helices (NC/NH) could be pertinent for observing interesting variants of electronic architecture. NC/NH formation, mostly observed in carbon nano-tube/-fiber (CNT/CNF) syntheses, is also scientifically interesting in that helices abound in nature, e.g., DNA, proteins etc. and a connection is being made at the nanoscale between carbon based inorganic and organic structures. For application, it would be desirable to have control over the coil morphology and geometry- which has not been achieved, possibly due to an incomplete understanding of their growth mechanisms. Several models, none of them completely satisfactory, have been proposed to understand their synthesis. In this presentation, we first briefly review the models in vogue and point out their shortcomings. Second, we introduce a thermodynamic model, based on exclusion volume principles, common in chemical and biological systems, that could potentially explain coiling in nanostructures. Here, the observation of helices and coils in nano-tube/-fiber (NT/NF) syntheses is explained on the basis of the interactions between specific catalyst particles and the growing nanostructure. Third, we make specific predictions for the optimal growth of NC/NHs with the hope that these could be used as a guide for rational synthesis. Finally, our own experimental results conforming to the above model, on the role of Indium catalyst particles and local CVD reactor temperature in influencing the coil pitch in NT/NFs, will be presented.
10:45 AM - JJ1.5
Growth Mechanism, Characterization, and Structure Control of Aligned Carbon Nanotubes on Sapphire.
Hiroki Ago 1 2 3 , Naoki Ishigami 2 , Naoki Yoshihara 2 , Tetsushi Nishi 2 , Kenta Imamoto 2 , Carlo Orofeo 2 , Ken-ichi Ikeda 2 , Masaharu Tsuji 1 2 , Tatsuya Ikuta 4 , Koji Takahashi 4 , Nobutsugu Minami 5 , Konstantin Iakoubovskii 5
1 Inst. Mater. Chem. Eng., Kyushu University, Fukuoka Japan, 2 Grad. Schl. Eng. Sci., Kyushu University, Fukuoka Japan, 3 , PRESTO-JST, Kawasaki Japan, 4 Grad. Schl. Eng., Kyushu University, Fukuoka Japan, 5 , AIST, Tsukuba Japan
Show AbstractSapphire surfaces have enabled horizontally-aligned single-walled carbon nanotubes (SWNTs) based on the anisotropic interaction between the surface atomic arrangement of sapphire and SWNTs [1,2]. In this presentation, we show our recent progress on the aligned growth on the sapphire surfaces. We succeeded in visualizing the SWNT growth by using 13C/12C isotopes and found that the base-growth mode occurred mainly for the aligned SWNTs, which signifies the importance of the nanotube-sapphire interaction [3]. The Raman and photoluminescence (PL) measurements showed a strong crystal plane dependence of the nanotube growth. The diameter was narrower for the aligned SWNTs on R- and A-planes compared with the randomly-oriented SWNTs on C-plane [4]. Moreover, near armchair nanotubes showed strong PL on R-plane, while the PL from near zigzag structures was dominant on A-plane [4]. The atomic steps formed on sapphire surface are also important. Studies on the effects of surface atomic arrangement and step-terrace structure on the nanotube alignment indicate that there is a strong dependence of the nanotube direction on the step height [5]. Also, under specific conditions, we realized a unidirectional SWNT growth from the patterned catalyst. These findings offer a new method to control the nanotube structure by “epitaxial nanotube growth” and realize advanced nanotube architectures. Finally, we show our recent development of the aligned growth of SWNTs on a Si wafer with oxide layer, which is promising for electronic applications.[1] H. Ago et al., Chem. Phys. Lett., 408, 433 (2005).; [2] S. Han et al., J. Am. Chem. Soc., 127, 5294 (2005). [3] H. Ago et al., J. Phys. Chem. C, 112, 1735 (2008).; [4] N. Ishigami et al., J. Am. Chem. Soc. in press.; [5] H. Ago et al., Appl. Phys. Lett., 90, 123112 (2007).
JJ2: Carbon Nanotube Growth Mechanisms
Session Chairs
Prabhakar Bandaru
Sonia Grego
Ian Kinloch
Monday PM, December 01, 2008
Room 302 (Hynes)
11:30 AM - JJ2.1
In flight Dimensional and Compositional Tuning of Metal Nanocatalysts for Gas-phase Carbon Nanotube Growth.
Wei-Hung Chiang 1 , R. Mohan Sankaran 1
1 Chemical Engineeing, Case Western Reserve University, Cleveland, Ohio, United States
Show AbstractDespite the availability of a wide range of synthesis techniques including chemical vapor deposition and the floating catalyst method, the role of the catalyst in CNT growth remains unclear due to the complexity of the catalytic growth process. Here, we present a novel two-step, continuous-flow approach that effectively separates the formation of metal nanocatalysts from CNT nucleation and growth to enhance our understanding of the growth mechanism [1]. Nanometer-sized metal particles are produced in an atmospheric-pressure microplasma reactor. Vapor-phase precursors such as nickelocene or ferrocene are introduced into the microplasma and disassociated non-thermally by electron impact to homogenously nucleate particles. Particle growth is limited to a small reactor volume (less than 1 nL) allowing the preparation of narrow distributions of dimensionally-controlled metal particles. Mixing different vapor precursors in the microplasma leads to compositional tuning of metal particles independent of diameter. To study the catalytic properties of the as-grown metal particles, we continuously inject the particle flow into a heated tubular flow furnace and add acetylene (C2H2) and hydrogen (H2) gas. In situ monitoring of the reactor effluent allows us to “watch” nanotube nucleation and growth as process parameters such as catalyst diameter and material, furnace temperature, and gas composition are varied. Experiments show that the CNT structure can be tuned in flight from single-walled to double-walled to multi-walled with relatively high purity. Aerosol classification is used to perform kinetic studies on CNT growth and obtain activation energies of 119 and 73 kJ/mol for monometallic Fe and Ni nanoparticles, respectively. In comparison, NixFe1-x bimetallic nanoparticles are observed to have dramatically different activation energies as low as 34 kJ/mol [2]. Additionally, the nanoparticle alloys are found to catalyze CNT growth at 300oC, significantly lower than temperatures normally required for monometallic catalysts. These results suggest that the bimetallic catalyst particles are characterized by synergistic effects during the nucleation and growth of CNTs. A possible mechanism for CNT growth based on the diffusion of carbon on the catalyst particles will be discussed. Microcharacterization of the catalyst particles and CNTs by high-resolution TEM, X-ray diffraction, and micro Raman spectroscopy will also be presented. [1] W-H. Chiang and R. M. Sankaran, Appl. Phys. Lett. 91, 121503 (2007). [2] W-H. Chiang and R. M. Sankaran, submitted to Advanced Materials (2008).
11:45 AM - JJ2.2
In Situ Observation of Nucleation and Growth of Carbon Nanotubes from Iron Carbide Nanoparticles.
Hideto Yoshida 1 , Tetsuya Uchiyama 1 , Hideo Kohno 1 , Seiji Takeda 1
1 , Osaka Univ., Osaka Japan
Show AbstractCarbon Nanotubes (CNTs) are most important and promising materials for future nanotechnology. Recently, the growth methods of CNTs, in particular catalytic chemical vapor deposition (CVD), are developed and therefore we can obtain high purity, vertically aligned CNTs in large quantities. In the CVD growth of CNTs, it is inferred that metal nanoparticles act as catalyst; however the details of the role are still unknown. In order to elucidate the CVD growth mechanism of CNTs including the role of nanoparticle catalysts, in-situ observation of the CNT growth is necessary. In this study, we observe the nucleation and growth of single-walled CNTs (SWNTs) and multi-walled CNTs (MWNTs) in Fe catalyzed CVD by atomic-scale in-situ environmental transmission electron microscopy (ETEM). Experimental procedure is summarized as follows. As a catalyst, Fe was deposited on silicon substrates with thin SiO2 surface layer by vacuum evaporation. The substrates were set in a newly designed ETEM operated at 200 kV. The substrates were heated to 600 C in a vacuum, and then a mixture of C2H2:H2 = 1:1 was introduced into the ETEM. The pressure of the gas and the temperature of the substrates in the CVD condition in the ETEM were 10 Pa and 600 C, respectively. The growth of CNTs were recorded at a rate of 1 frame per 0.35 s using a CCD cameraOur atomic-scale in situ observation of Fe catalyzed CVD growth of CNTs has shown that iron carbide (Fe3C) nanoparticles act as catalyst. Iron carbide (Fe3C) nanoparticle catalysts fluctuate structurally in the CVD condition. In addition, we strongly suggest that carbon atoms migrate through the bulk of nanoparticle catalysts. These finding may bring general understanding of catalyzed CVD growth of CNTs at atomic scale. Based on the in-situ observations, we will discuss the structure of CNTs as well as that of nanoparticle catalysts in the CVD condition.
12:00 PM - JJ2.3
Mechanisms of Single-walled Carbon Nanotube Growth and Deactivation from in situ Raman Measurements.
Vincent Jourdain 1 , Matthieu Picher 1 , Eric Anglaret 1
1 , Université Montpellier 2, Montpellier France
Show AbstractCatalytic Chemical Vapor Deposition (CCVD) has recently emerged as an important method for the growth of nanotubes and nanowires. In this process, nanoparticles are used to catalyze the decomposition of a gaseous precursor and spatially constrain the growth of the nano-objects. CCVD stands at the interface between heterogeneous catalysis (HC) and thermal Chemical Vapor Deposition (TCVD), which are both industrial methods studied for many years.Surface diffusion is an important process in both HC and TCVD, which is notably described by the surface diffusion rate and the surface residence time of adspecies. In HC, the surface residence time affects the surface concentration of adspecies and hence the kinetics of the surface reactions. In TCVD, the ratio between the surface diffusion rate and the rate of precursor supply from the gas phase influences the crystalline order of the grown layer. Since CCVD combines catalyst nanoparticles of small surface area with growth conditions favoring the formation of a solid layer, encapsulation of the catalyst nanoparticles is a frequent cause of deactivation. The growth of carbon nanotubes (CNTs) by CCVD is particularly subject to this type of deactivation, which prevents the growth of nanotubes of arbitrary length. During the last years, valuable information on the kinetics and the deactivation of CNT growth were provided by in situ analyses [1,2]. However, a better understanding of the observed growth regimes is still required to address the deactivation problem. Here, we present a systematic study on the kinetics and deactivation of SWCNT growth in the temperature (T) - precursor pressure (P) parameter space by in situ Raman spectroscopy. With Raman spectroscopy, correlating kinetic data and structural information (e.g. crystalline order) on the growing nanotubes is made possible. Three growth regimes with different activation energies and reaction orders are thus observed as a function of T and P: a “high-disorder activated-growth regime” in the low T - high P region, a “low-disorder activated-deactivation regime” in the high T - low P region and an “intermediate-disorder unactivated-growth regime” in the intermediate T - P region. The determining steps of the three regimes are respectively attributed to the dissociative adsorption of the precursor, the desorption of reactive adspecies and the mass transport of the precursor from the gas phase . The evolution of the ratio between the Raman G and D peaks with (T, P) allows estimating the activation energy for the diffusion of carbon atoms and the reaction order for the formation of the disordered carbonaceous layer. In all regimes, the initial growth rate and the catalyst lifetime are anticorrelated demonstrating that the growth and the deactivation are both surface processes competing for the same source of adspecies.1. Puretzky et al., Applied Physics A (2005), 81, 223.2. Einarsson et al., Carbon (2008), 46, 923.
12:15 PM - JJ2.4
Control of the Diameter and Chiral Angle Distributions During Production of Single-wall Carbon Nanotubes.
Pavel Nikolaev 1 , Sivaram Arepalli 1 , William Holmes 1 , Edward Sosa 1 , Peter Boul 1 , Leonard Yowell 2
1 , ERC Inc./NASA-Johnson Space Center, Houston, Texas, United States, 2 , NASA-Johnson Space Center, Houston, Texas, United States
Show AbstractMany applications of single wall carbon nanotubes (SWCNT), especially in microelectronics, will benefit from use of certain (n,m) nanotube types (metallic, small gap semiconductor, etc.) However, as produced SWCNT samples are polydispersed, with many (n,m) types present and typical ~1:2 metal/semiconductor ratio. It has been recognized that production of SWCNTs with narrow “tube type populations” is beneficial for their use in applications, as well as for the subsequent sorting efforts. In the present work, SWCNTs were produced by a pulsed laser vaporization (PLV) technique. The nanotube type populations were studied with respect to the production temperature with two catalyst compositions: Co/Ni and Rh/Pd. The nanotube type populations were measured via photoluminescence, UV-Vis-NIR absorption and Raman spectroscopy.It was found that in the case of Co/Ni catalyst, decreased production temperature leads to smaller average diameter, exceptionally narrow diameter distribution, and strong preference toward (8,7) nanotubes. The other nanotubes present are distributed evenly in the 7-30° chiral angle range. In the case of Rh/Pd catalyst, a decrease in the temperature leads to a small decrease in the average diameter, with the chiral angle distribution skewed towards 30° and a preference toward (7,6), (8,6) and (8,7) nanotubes. However, the diameter distribution remains rather broad. These results demonstrate that PLV production technique can provide at least partial control over the nanotube (n,m) populations. In addition, these results have implications for the understanding the nanotube nucleation mechanism in the laser oven.
12:30 PM - JJ2.5
Determination of the Chirality of Composite Nanotubes by Electron Diffraction.
Hakan Deniz 1 , Anna Derbakova 1 , Letian Lin 2 , Lu-Chang Qin 1 2
1 Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States, 2 Curriculum in Applied and Materials Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Show AbstractThe chirality of a nanotube can be convenient expressed by its chiral indices (n,m) which define the chiral vector (perimeter vector) of the nanotubes. For a multishell nanotube, the determination of the chirality requires the knowledge of chirality of each and every shell of the nanotube. This exact chirality of a nanotube is very much desired for understanding and control of the properties of nanotube in connection with its atomic structure. However, it remains a great experimental challenge to determine accurately the chirality (chiral indices) of nanotubes, including both the elemental carbon nanotubes and the composite cylindrical nanotubes such as the BN and WS2 nanotubes. Basing on the helical electron diffraction method that we developed for the determination of the chiral indices of both single-shell and multishell carbon nanotubes, we have extended the analytical method to cylindrical composite nanotubes. While the electron scattering intensities o the layer lines from composite nanotubes will be different from elemental carbon nanotubes, the diffraction geometry remains the same and therefore the chirality of composite nanotubes can also be determined with a high accuracy using the established nano-beam electron diffraction method.We will present both the general analytical procedure and experimental practice of the helical electron diffraction method. Using a few selected BN and WS2 nanotubes as examples, we will also describe a systematic approach to demonstrate the applications to practical problems. When these nanotubes have multiple shells, the chial indices of each and every shell are determined unambiguously in these applications.
JJ3: Carbon Nanotube Processing
Session Chairs
Monday PM, December 01, 2008
Room 302 (Hynes)
2:30 PM - **JJ3.1
Growth and Manipulation of Carbon Nanotubes Toward Desirable Geometry and Properties.
Sungho Jin 1
1 Materials Science and Engineering, University of California at San Diego, La Jolla, California, United States
Show Abstract3:00 PM - JJ3.2
Chloride Mediated Chemical Vapor Deposition Growth of Aligned Bulk Ultra-long Multi-walled Carbon Nanotube.
Yoku Inoue 1 , Akihiro Ishida 1 , Hidenori Mimura 2
1 Department of Electrical and Electronic Engineering, Shizuoka University, Hamamatsu Japan, 2 Research Institute of Electronics, Shizuoka University, Hamamatsu Japan
Show Abstract Large scale production of carbon nanotube (CNT) often requires complicated and delicate techniques. We present a one-step simple and easy method for mass synthesis that yields ultra-long, vertically aligned multi-walled CNT. This method requires no additional process for catalyst thin film (pre-deposition), and only requires iron chloride powder and acetylene gas used [1]. The lengths of obtained multi-walled CNT ranged up to the millimeter-scale. Multi-walled CNTs can easily be spun into yarn by hand with the naked eyes. In addition, this method can be used to coat the entire surface of a target with MWCNT. Vertically aligned CNT (VACNT) was synthesized using a conventional thermal CVD system. A smooth quartz substrate was placed at a centre of horizontal quartz tube furnace with iron chloride powder. Typically, a thin metallic film deposited on a substrate is widely used as a catalyst; however, in the proposed method, such a film need not be pre-deposited. We refer to the proposed method as “chloride mediated CVD (CM-CVD)”. Features such as using a pure acetylene gas flow and not using a metallic film on the substrate, are peculiar to CM-CVD. Densely grown CNTs are vertically aligned on a quartz substrate throughout the surface, including the side and back surfaces. The length of the bulk VACNTs is 2.1 mm in 20 min. The obtained CNT sample was confirmed to contain very few Fe particles, and to be multi-walled from TEM image. For our VACNTs, one can easily spin a CNT yarn using tweezers or an adhesive tape. We obtained a 15.5-cm CNT yarn by pinching and pulling out CNTs. We got the idea of the CNT-coating growth from the entire surfaces growth. To demonstrate the CNT-coating ability, the CNT growth was examined using quartz fiber wool of 3–5 μm diameter. SEM observation revealed that the individual quartz fibers were completely coated with hair-like CNTs. The fibers increased to 30–50 μm in diameter due to the coating. The macroscopic coating morphology extended homogeneously from the surface to the inside of a quartz wool ball. The advantage of applying this technique is that it can easily be used to coat structurally complex samples. Our established one-step growth method, CM-CVD, offers a potentially viable VACNT mass production method. In the present system, we can grow 1 g of VACNT for a two hour process time including 20 minutes of growth time, and material cost performance is as low as US$0.5/g.[1] Y. Inoue et. al. Appl. Phys. Lett. 92, 213113 (2008).
3:15 PM - JJ3.3
Role of Optical Excitation in the Electric-field Assisted Assembly of Semiconductor Nanorods.
Emanuela Rossitto 1 2 , Tonggang Jiu 1 , Olivier Lecarme 2 , Laurence Latu-Romain 2 , Kevin Berton 2 , David Peyrade 2 , Peter Reiss 1
1 INAC/SPrAM, CEA Grenoble, Grenoble France, 2 CNRS-LTM, CEA Grenoble, Grenoble France
Show AbstractSemiconductor nanorods (NRs) are versatile nanostructures combining size-dependent optical and electrical properties, solution processability and high aspect ratio. One of the most demanding challenges for their study and application in nanoelectronics is the control of their assembly and integration in electronic devices. The oriented positioning of NRs is highly desirable for fundamental charge transport studies, as well as for the investigation of single NR electroluminescence in view of applications in optoelectronics. In contrast to spherical nanocrystals, NRs exhibit linearly polarized emission along the long axis. Furthermore, their geometric anisotropy facilitates their alignment: for this purpose an external electric field can be applied in order to drive their ordered assembly in nanoscale devices.In this work we illustrate how an external UV source can, under application of an external electric field during drop-cast deposition, enhance the lateral alignment of colloidal quantum rods across metal electrodes on silicon oxide substrates. CdSe (aspect ratio=10) and CdSe@CdS NRs were prepared by chemical synthesis, while Ti/Au interdigitated electrodes of different sizes have been pre-patterned by a photolithographic process. The influence of the applied voltage and NRs concentration were systematically investigated. In addition to SEM analysis, polarization anisotropy measurements and fluorescence spectroscopy have been used to characterize the assembly.An external static electric field leads to a preferential orientation of the long axis of the NRs along the field lines, as compared to the assembly obtained without applied voltage. The permanent dipole moment of the NRs is at the origin of this behaviour. The application of UV excitation in addition to the electric field induces the alignment of a much larger number of NRs parallel to the field lines. At the same time the bridging between neighbouring electrodes takes place through head-to-tail assembly of NRs, driven by dipole-dipole interactions between permanent and/or induced dipoles. We rationalize these findings with the fact that the electron-hole pairs (excitons) generated in the NRs upon UV irradiation present a very high polarizability due to the well-separated electronic energy levels in the quantum confinement regime. Therefore their dipolar character is increased under photo-excitation, enhancing the interaction with the external electric field.In conclusion, our study reveals the synergetic action of static electric fields and UV irradiation in the controlled assembly of semiconductor NRs between electrodes. Furthermore, the results suggest useful parameters for the development of nanoelectronic devices, in which nanoparticles are self-assembled to create complex structures of desired functionality.
3:30 PM - JJ3.4
Quantitative Characterization of the Semiconducting Fraction in Single-Walled Carbon Nanotube Samples.
Anton Naumov 1 , Oleg Kuznetsov 3 , Alexander Green 2 , Mark Hersam 2 , Avetik Harutyunyan 3 , R. Bruce Weisman 4
1 Physics, Rice University, Houston, Texas, United States, 3 , Honda Research Institute USA Inc., Columbus, OH, Columbus, Ohio, United States, 2 Materials Science & Engineering, Northwestern University, Evanston/Chicago, Illinois, United States, 4 Chemistry, Rice University, Houston, Texas, United States
Show AbstractStudies dedicated to revealing the fraction of semiconducting SWCNTs in various samples will be described. In a series of experiments, SWCNT samples produced by different growth and processing methods were dispersed in dilute aqueous SDS and spin-coated onto polished fused silica slides. To obtain the percentage of semiconducting SWCNTs in the sample, the total number of SWCNTs per unit area was counted from AFM images. This value was then compared to the number density of semiconducting nanotubes revealed by near-infrared fluorescence microscopy using an inverted Nikon microscope coupled to an InGaAs 2-D near-IR camera. An unseparated HiPco sample showed 63% semiconducting SWCNTs, near to the statistical expectation of 2/3. The semiconducting fraction was highest in an unprocessed, standard grade CoMoCat sample and lowest in a custom-prepared CVD sample. Density gradient processing to enrich semiconducting or metallic content was also quantitatively evaluated and confirmed. Our counting-based method provides important statistical information about the composition of SWCNT samples and can be used to calibrate bulk methods such as optical spectroscopy.
JJ4: Solution Based Processing and Electrochemistry
Session Chairs
Monday PM, December 01, 2008
Room 302 (Hynes)
4:15 PM - **JJ4.1
Liquid Processing of Carbon Nanotubes: Towards Structured Composites and Fibers.
Philippe Poulin 1
1 , Centre de Recherche Paul Pascal-CNRS, Pessac France
Show AbstractCarbon nanotubes have to be properly spatially distributed to be efficiently exploited. Processing nanotubes in liquid states offers a variety of opportunities to control their spatial organization. The use of dispersants such as low molecular weight surfactants or polymers allows the interactions between the nanotubes to be tuned from attractive to repulsive. As a consequence various states can be obtained from disordered dispersions with very low percolation thresholds to ordered liquid crystalline phases in which the nanotubes exhibit long range orientational ordering. Experimental observations (1-3) will be discussed and compared with recent theoretical models and simulations proposed in the literature (4, 5). Flow of nanotube dispersions is also the opportunity to orient nanotubes and develop new processes for the fabrication of structured composites and fibers with a large fraction of carbon nanotubes. We will discuss in particular the thermomechanical properties of fibers obtained by the coagulation of nanotubes in the flow of polymer solutions. Such fibers exhibit shape memory phenomena with a giant stress generation and a surprising temperature memory (6). This behavior is ascribed to gradients of the glass transition temperature of the polymer confined at the interface of the nanotubes.References: 1- S. Badaire, C. Zakri, M. Maugey, A. Derré, N. Barisci,, G. Wallace, P. Poulin. Adv. Materials 17, 1673-1676 (2005).2- B. Vigolo, C. Coulon, M. Maugey, C. Zakri, P. Poulin, Science 309, 920-923 (2005).3- C. Zakri, P. Poulin, J. Mat. Chem.16, 4095-4098 (2006).4- T. Schilling, S. Jungblut, M.A. Miller, Phys Rev Lett 98:108303 (2007).5- A. V. Kyrylyuk, P. van der Schoot PNAS 105, 8221-8226 (2008). 6- P. Miaudet, A. Derré, M. Maugey, C. Zakri, P. Piccione, R. Inoubli, P. Poulin Science 318, 1294-1296 (2007).
4:45 PM - JJ4.2
An Athermal Single-Walled Carbon Nanotube Solution.
Shane Bergin 1 4 , Valeria Nicolosi 1 , Alan Windle 3 , James Hamilton 2 , Jonathan Coleman 1 4
1 Physics, Trinity College Dublin, Dublin , Leinster, Ireland, 4 Centre for Reseach on Adaptive Nanostructures and Nanodevices, Trinity College Dublin, Dublin Ireland, 3 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Department of Chemistry and Engineering Physics, University of Wisconsin –Platteville, Platteville, Wisconsin, United States
Show AbstractSince their discovery in 1993, the much heralded properties of single walled carbon nanotubes (SWNTs) have not been realised to their full potential due to their propensity to bundle with one another via Van der Waals interactions and the diminished properties that result from this bundled state. The literature is peppered with various techniques to debundle SWNTs, most of which rely on covalent or non-covalent functionalisation of the SWNTs in order to change the solvent-nanotube interaction. This type of three phase system has had success. However, the effect of covalent attachments on the electronic properties of pristine SWNTs cannot be ignored. Neither too can we neglect the role this third dispersant phase may play in the implementation of the debundled SWNTs in any composite. Thus, we arrive at the situation where a simple two phase system of SWNTs being exfoliated in an appropriate solvent would be of great benefit to any possible user. Recently, work from our group has demonstrated debundling by dilution in the common amide solvent N-Methyl-Pyrrolidone (NMP) [1]. This demonstrated high populations of individual SWNTs confirmed by spectroscopic and microscopic techniques. The benefits accruing from this have been measured in various composite materials reported by our group. More recently, we have demonstrated spontaneous debundling of SWNTs in NMP: it should be stressed that this debundling occurred without the need for sonication. We compare the sonicated dispersions to the non-sonicated samples and show that after a period of approximatly 150hrs the non-sonicated dispersions are debundled to the same extent as the sonicated dispersions. This spontaneity would suggest that the SWNTs are soluble in NMP. To that end, we investigated the various components of the free energy of mixing for such a reaction. The entropic component was described using Flory’s model of mixing rigid rod-like molecules. Modelling the enthalapic element, we arrived at an expression with a very similar form to the famous Scratchard Hildebrand equation – the basis of the like-dissolves-like rule familiar to chemists. We show that by matching the surface energy of the solvent to the surface energy of the SWNT, we obtain optimum debundling of SWNTs: this match corresponds to a minimised enthalpy of mixing component which would again point toward a SWNT solution. To verify this, using Flory’s theory for mixing, we express the conditions required for a solution in terms of the Flory Huggins parameter. An absolute measure for the Flory Huggins parameter was obtained using dynamic light scattering. Comparing this experimental value to the theoretical requirement for a solution, we confirm that SWNTs are soluble in NMP. [1]S. Giordani, S.D. Bergin, et al., Journal of Physical Chemistry B,. 2006, 110, 15708.
5:00 PM - JJ4.3
Modification of Carbon Nanotube Architectures for Alternative Energy Applications.
Andrew Minett 1 , Peter Sherrell 1 , Jun Chen 1 , Gordon Wallace 1
1 Intelligent Polymer Research Institute, University of Wollongong, Wollongong, New South Wales, Australia
Show AbstractDue to their high surface area, electro-chemical stability and versatility, carbon nanotube electrodes have been attracting great interest for use in alternative energy applications such as supercapacitors, Li-ion batteries and fuel cells. In this presentation, we describe the production and modification of flexible pre-formed carbon nanotube architectures with various entities such as conducting polymers or metal nanoparticles for use as superior electrode materials. Recently, we have reported on the direct use of various carbon nanotube assemblies as electrodes for Li-ion batteries, supercapacitors or catalyst supports. In one process, a flexible aCNT/PEDOT/PVDF membrane electrode is prepared via conventional CCVD. This electrode structure was assembled into a lithium-ion battery for testing, by stacking a porous polypropylene separator containing liquid electrolyte between the aCNT/PEDOT/PVDF electrode and a lithium-foil counter electrode. While this assembly showed a large irreversible first cycle capacity, a highly stable discharge capacity of 265 mAh/g is observed for the second to fiftieth cycle. In a second related approach, a novel carbon composite electrode shows vastly superior reversible capacities of over 600mAh/g, stable over 100 cycles. What is remarkable with this electrode system is that there is no large drop in capacity during charge cycles. To demonstrate the versatility of these carbon composite electrodes, the introduction of metal nanoparticles for catalysis or enhanced electrochemical properties allows the use of these electrodes as either the anode or cathode in fuel cell applications or as supercapacitors. Eight different metals have been deposited by a simple method with nanoparticle sizes as small as 4nm. Energy densities of ~70Wh/kg and power densities up to ~10kW/kg for these composite electrodes highlight their promise for alternative energy applications.
5:15 PM - JJ4.4
The Role of Defects in Carbon Nanostructures Probed through Ion Implantation and Electrochemistry.
Mark Hoefer 1 , Jeffrey Nichols 1 , Prabhakar Bandaru 1
1 Materials Science program, Mechanical Engineering department, UC, San Diego, La Jolla, California, United States
Show AbstractWhile carbon nanotubes (CNTs) are known to contain various defects that can significantly influence their physical and chemical properties, a systematic investigation of the correlation has not yet been undertaken. The goal of this study is to quantify the effect of defect density on the electrochemical properties of multi-walled CNTs. Consequently, reactive ion etching, with argon and hydrogen (individually), under various conditions of power, pressure, and flow rate has been performed to systematically incorporate defects into vertically aligned MWCNTs. Raman spectroscopy was then used to characterize the amount of disorder within the nanotube samples. The electrochemical behavior of MWCNT samples with different defect densities was then subsequently observed through cyclic voltammetry (CV) measurements. Raman spectroscopy revealed an increase in the disorder in MWCNTs with the introduction of argon and hydrogen, as evidenced by an increase in the ID/IG peak intensity ratio. However, argon is intercalated into the CNTs, and charges the nanotubes (in the form of dangling bonds), while hydrogen treatment terminates residual dangling bonds in the CNTs. We have also seen a corresponding modification of the in-plane nanotube correlation length, from 2- 4 nm, by measuring the area ratios of the Raman peaks. In CV measurements, we have seen that only the Ar treated samples exhibit perfect reversible Nernstian behavior characteristic of ideal electrodes. However, hydrogen treated CNT electrode ensembles seem to exhibit quicker response, as glucose sensors, with exquisite (~ 1 microM) sensitivity
5:30 PM - JJ4.5
Platinum Nanoparticles on SWNT Nanopaper Support: Synthesis, Characterization and Application in Electrocatalysis.
Malka Bromberg 1 , Anatoly Frenkel 1 , Zafar Iqbal 2 , Anitha Patlolla 2 , Shiunchin Wang 2 , Qi Wang 1 , Rebecca Segal 1 , Weiqiang Han 3 , Fredy Zypman 4
1 Physics, Stern College for Women, Yeshiva University, New York, New York, United States, 2 Chemistry, New Jersey Institute of Technology, Newark, New Jersey, United States, 3 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States, 4 Physics, Yeshiva College, Yeshiva University, New York, New York, United States
Show AbstractSingle-walled carbon nanotubes (SWNTs) decorated with platinum have recently attracted much interest due to their potential for high electrocatalytic activity and application as fuel cell catalyst support. We studied different methods of depositing platinum nanoparticles on SWNTs and examined their effectiveness as electrocatalysts for hydrogen fuel cells. Commercially obtained SWNTs were characterized by Raman Spectroscopy, TEM, EDS, AFM, EXAFS and XANES. By quantifying both nanotubes' diameter and defects and size and composition of metal impurities, this multi-technique characterization allowed us to choose the purification method. After purification, we formed a substrate for depositing Pt atoms by synthesizing a “nanopaper”: a 10-20 micrometer thick free standing sheet of self-assembled SWNTs. The nanopaper was then characterized by AFM, SEM and Raman scattering in order to verify its microstructure, the average diameter of SWNTs, and level of sidewall defects in the SWNTs. Platinum was deposited onto the nanopaper by two methods: electrochemically and electroless deposition. We used TEM, XANES and EXAFS to measure the particles' sizes and charge states, and thus compare the two methods of deposition. In order to determine the effectiveness of these nanopapers as electrocatalysts in hydrogen fuel cells, cyclic voltammetry experiments were conducted in a fuel cell. In situ XANES and EXAFS measurements were also performed in a custom-designed electrochemical cell, and these results were correlated with the fuel cell experiments. M.B. would like to acknowdedge the H. Kressel research scholarship.
5:45 PM - JJ4.6
Three Dimensional (3D) Single-crystal, Oxide Nanofence for Epitaxial Growth of Electronic, Magnetic or Electromagnetic Devices.
Amit Goyal 1 , Sung-Hun Wee 1 , Karren More 1
1 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge , Tennessee, United States
Show AbstractJJ5: Poster Session: Carbon Nanotube Synthesis and Characterization
Session Chairs
Prabhakar Bandaru
Sonia Grego
Ian Kinloch
Tuesday AM, December 02, 2008
Exhibition Hall D (Hynes)
9:00 PM - JJ5.1
A Molecular Dynamics Study of the Graphitization Ability of Transition Metals for Catalysis of Carbon Nanotube Growth via Chemical vapor Deposition.
Yasushi Shibuta 1 , James Elliott 2
1 Department of Materials Engineering, The University of Tokyo, Tokyo Japan, 2 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show AbstractThe graphitization ability of several transition metals commonly used as catalysts for carbon nanotube growth (nickel, cobalt and iron) has been investigated via classical molecular dynamics simulation on planar crystalline surfaces and nanoclusters with short-range structural order. Bond-order type potentials [1], which were constructed by fitting the binding energy of the small clusters to DFT calculations, were used for describing the metal-carbon and metal-metal bonds. First, the stability of the graphene on the surfaces of the bulk crystalline metals was examined. A defect-free graphene sheet was deposited onto the Ni(111)fcc, Co(0001)hcp and Fe(100)bcc surfaces. After some initial bond breakage due to kinetic energy of impact with the metal surface, the hexagonal graphene network was rapidly reconstructed on the Ni(111)fcc and Co(0001)hcp surfaces, whereas the graphene structure was not readily recovered on the Fe(100)bcc surface. It was found that two dimensional closed-packed facets, such as (111)fcc and (0001)hcp, can act as a template for reconstructing the graphene structure since the hexagonal carbon network and the closed-packed facet exhibit some degree of epitaxy. Next, the interaction between graphene and transition metal nanoclusters was examined. A graphene sheet was deposited onto amorphous nickel, cobalt and iron nanoclusters with various sizes, ranging in diameter from 1.7 to 2.7 nm (256 to 864 atoms) [2]. Due to the relatively strong interactions with the predominantly {100}bcc type facets of the iron cluster, the surface energy of graphene on iron was calculated to be twice that of the cobalt and nickel clusters. Finally, we include a comparison of bulk and surface structures of iron particles with semi-empirical molecular orbital calculations on molybdenum, which is also an bcc metal.[1] Y. Shibuta, S. Maruyama, Comp. Mater. Sci. 39 (2007) 842-848. [2] Y. Shibuta, J.A. Elliott, Chem. Phys. Lett. 427 (2006) 365-370.
9:00 PM - JJ5.10
Spectroscopic Characteristics of Differently Produced Single-Walled Carbon Nanotubes.
Zhongrui Li 1 , Yang Xu 1 , Enkeleda Dervishi 1 , Viney Saini 1 , Meena Mahmood 1 , D. Oshin 1 , Alexandru Biris 1
1 , University of Arkansas at Little Rock, Little Rock, Arkansas, United States
Show AbstractSingle-walled carbon nanotubes (SWNTs) synthesized with different methods were investigated by using multiple characterization techniques, including Raman scattering, optical absorption, X-ray absorption near edge structure, along with X-ray photoemissions by following the total valence bands and C 1s core level spectra. Four different SWNT materials (produced by arc discharge, HiPco, laser ablation, and CoMoCat methods, respectively) containing nanotubes with diameters ranging from 0.7 to 2.8 nm were used. The vibrational spectroscopies revealed that the diameter distribution and the compositions of metallic and semiconducting tubes of the SWNT materials are strongly affected by the synthesis methods. Similar sp2 hybridization of carbon in the SWNT structure oxygenated can be found but different surface functionalities are introduced while the tubes are processed. All SWNTs demonstrated stronger plasmon resonance excitations, lower electron binding energy compared to graphite and multi-walled carbon nanotubes. These SWNT materials also exhibit different valence band X-ray photoemission features which are considerably affected by the nanotube diameter distribution and metallic/semiconducting composition.
9:00 PM - JJ5.11
Effect of Water Vapor on the Catalytic Growth of Carbon Nanotubes at Low Temperature.
Youngrae Kim 1 , Hong Jun Jeon 1 , Naesung Lee 1
1 Faculty of Nanotechnology and Advanced Materials Engineering, Sejong University, Seoul Korea (the Republic of)
Show AbstractCarbon nanotubes (CNTs) have attracted much attention as promising nano-materials in various applications such as flat panel displays, nanoelectronics, nanocomposites, energy device electrodes, via interconnect, etc, due to their unique and versatile properties. CNTs grow long nowadays even to several hundreds of micrometers at high temperatures. Many groups have reported the growth of such long CNTs, so-called super-growth, by adding a small amount of water vapor during the CNT growth. The water-assisted synthesis seems to suppress the formation of amorphous carbon and then grow CNTs faster, producing high-quality, millimeter-long CNTs. As lowering the temperature, however, CNTs grow slower, and thus the super-growth has not yet been achieved at low temperature. Furthermore, rarely has the effect of water vapor on the CNT growth been investigated at low temperature. This study has elucidated the beneficial effect of water vapor on the low-temperature growth of CNTs. We synthesized multi-walled CNTs at temperature as low as 360°C by introducing water vapor. The water addition caused CNTs to grow ~3 times faster. Moreover, the water-assisted growth prolonged the termination of CNT growth, implying the enhancement of catalyst lifetime by water vapor. In general, a thinner catalyst layer is likely to produce smaller-diameter, longer CNTs. In a similar manner, the water vapor had a greater effect on the growth of CNTs for a smaller thickness of catalyst in this study. To figure out the role of process gases, CNTs were grown in the first stage and then exposed to each of process gases in the second stage. It was shown that water vapor and hydrogen did not etch CNTs while acetylene led to the additional growth of CNTs even faster in the second stage. As-grown CNTs were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and Raman spectroscopy.
9:00 PM - JJ5.12
Growth of Single-walled Carbon Nanotubes from Non-metal Materials.
Huaping Liu 1 , Daisuke Takagi 1 , Shohei Chiashi 1 , Tomohito Chokan 1 , Yoshikazu Homma 1
1 Department of Physics, Tokyo University of Science, Tokyo Japan
Show Abstract9:00 PM - JJ5.13
Study of Chloride Mediated Chemical Vapor Deposition for Ultra-long Multi-walled Carbon Nanotube.
Yoku Inoue 1 , Akihiro Ishida 1 , Hidenori Mimura 2
1 Department of Electrical and Electronic Engineering, Shizuoka University, Hamamatsu Japan, 2 Research Institute of Electronics, Shizuoka University, Hamamatsu Japan
Show Abstract Chemical vapor deposition (CVD) methods for carbon nanotube (CNT) growth usually require pre-deposition of iron-related catalyst thin film. Recently, we found a new method using iron chloride powder as a catalyst material for aligned ultra-long multi-walled CNT [1]. This method requires no additional process for the catalyst thin film (pre-deposition), and only requires iron chloride (FeCl2) powder and acetylene gas. We refer to the proposed method as “chloride mediated CVD (CM-CVD)”. The lengths of obtained aligned MWNT ranged up to the millimeter-scale (2.1 mm) in 20-min-growth. In addition, this method can be used to coat the entire surface of a target with MWCNT. These features are considered to be due to high dehydrogenation activity and high vapor pressure of FeCl2. In this study, we present some properties and growth mechanism model of our aligned ultra-long MWNT. The MWNT was synthesized on a quartz substrate with acetylene source gas using a conventional thermal CVD system. Densely grown CNTs are vertically aligned on a substrate throughout the surface, including the side and back surfaces. To understand the growth mechanism in CM-CVD, the MWNT samples were grown under various conditions, such as growth time, temperature, pressure, gas flow rate. The growth morphology was drastically changed depending on the pressure. With decreasing growth pressures, growth density of CNTs increased. Since FeCl2 is completely vaporized at growth temperature (820 °C), formation of CNT growth sites is thought to result from vapor phase reaction between FeCl2 and acetylene, and nucleation of iron carbide nanoparticles as a result of multi collisions. The pressure dependence result supports this growth initiation model. This growth initiation process is also responsible for the CNT coating growth. During heating process, FeCl2 vapor spreads across the entire heated space. Since acetylene flow may cause the sublimation of iron carbide nanoparticles on the entire surfaces, CNTs can be grown everywhere. Our growth mechanism model will be discussed in detail with experimental results including Raman measurements and quadrupole mass analysis.[1] Y. Inoue et. al. Appl. Phys. Lett. 92, 213113 (2008).
9:00 PM - JJ5.15
Solubilization and Separation of Single Wall Carbon Nanotubes with Genomic DNA.
Steve Kim 1 , Kristi Singh 1 , Fahima Ounchen 2 3 , James Grote 2 , Rajesh Naik 1
1 Materials and Manufacturing Directorate, AFRL/RXBN, Wpafb, Ohio, United States, 2 Materials and Manufacturing Directorate, AFRL/RXPS, Wpafb, Ohio, United States, 3 Electrical Engineering, University of Dayton, Dayton, Ohio, United States
Show AbstractDeoxyribo nucleic acid (DNA) has been recognized as one of efficient dispersion media that individually exfoliate and fractionate single wall carbon nanotubes (SWCNTs) according to their diameter and metallicity. Single stranded d(GT)n DNA oligomers have been known to efficiently stabilize carbon nanotube in aqueous media and enable one to obtain chirality separated fractions, when eluted from an anion exchange column at various salt concentrations. In this work, we present a solubilization and chirality separation study of SWCNTs by using genomic salmon DNA (SaDNA), which is a byproduct from the fishing industry and costs ~$20/gm. We show that the SaDNA disperses SWCNTs on a comparable level to d(GT)n oligomer. The NIR, PLE emission and resonance Raman analysis from the SaDNA solubilized nanotube samples will be presented along with their chirality dependent separation results.
9:00 PM - JJ5.16
Synthesis of Carbon Nanostructures by AC Arc Discharge at Atmospheric Pressure.
Marco Vittori Antisari 1 , Daniele Mirabile Gattia 1 , Renzo Marazzi 1 , Amelia Montone 1 , Emanuela Piscopiello 1
1 FIM, ENEA, Rome, Rome, Italy
Show AbstractIn this communication we report about the synthesis of single wall carbon nanohorns and highly convoluted graphite sheets by arc discharge carried out between pure graphite electrodes in gas environment at atmospheric pressure. The arc is powered by an AC power supply. The symmetry in the thermal situation of the two electrodes avoids the formation of the classical hard cathode crust and the whole synthesized material is in the form of nano-powder ejected from the arc plasma. The arc is surrounded by a cylindrical collector which, besides collecting the synthesized material, is particularly useful in controlling the synthesis environment. In our previous studies on the use of an AC arc discharge at the fixed voltage of 50 Hz, we have ascertained that this kind of setup is suitable to the purpose and that this kind of carbon nano-particles can be synthesized with a good yield. The purpose of this paper is to explore the effect of the frequency at which the voltage is applied to the carbon electrodes on the structure of the material produced and on the yield of production of soot respect to the sublimated material. To this purpose the arc is powered by an AC supply with variable frequency in the range 30 Hz-2000 Hz. In fact, the frequency at which the power is applied to a surface affects the heat conduction toward the material bulk and the thermal gradient near the surface. Consequently, at fixed power, the temperature of the electrodes is expected to change with the frequency of the feeding current: at low frequencies the heating of the core of the electrodes is expected to be favored and low evaporation rate are achieved, while at high frequencies the opposite takes place. These phenomenon influences the synthesis environment and in particular some parameters which are known to influence the microstructure of the synthesized powders like the sublimation rate and the temperature gradient near the arc zone. First results show that mainly two kinds of particles are found in a TEM observation of the produced soot, and namely highly convoluted graphene sheets, having locally the nanohorn morphology, and better organized nano-balls constituted by concentric graphene sheets. The experimental results clearly show that the relative abundance of the two kinds of particles can be easily controlled by the frequency of the power applied at the arc even without changing the heat input. A detailed TEM analysis of the synthesized materials will be reported.
9:00 PM - JJ5.17
Synthesis of Carbon Nanotubes in Different Shapes: Straight, Wavy, and Spiral.
Mei Zhang 1 2
1 Industrial and manufacturing Engineering, Florida State University, Tallahassee, Florida, United States, 2 High-Performance Materials Institute, Florida State University, Tallahassee, Florida, United States
Show AbstractCarbon nanotubes (CNTs) are an attractive material for wide potential applications. Controlling the growth of CNTs is one of the challenges to the successful application of CNTs. In this work, the CNTs were deposited on substrate by controlled thermal chemical vapor deposition using acetylene as carbon source. The substrates were seeded with a thin film of composite metal catalysts. By controlling the kind and the ratio of components in such a composite catalyst, the CNTs grown on substrate can be obtained in number of various shapes: straight, wavy, or spirals. The morphologies and the properties of the tubes in different shapes are investigated by high resolution TEM and SEM. In the case of “wavy tubes”, more than 80% CNTs were bended with the same period of several hundred nanometers through their whole length. When using compound metals as catalyst, most of the tubes grow as spiral ones. The diameter of the spiral is in the range of tens to hundreds nanometers. The growth mechanism will be discussed.
9:00 PM - JJ5.18
Effective Parameters For Growing Vertically-Aligned Individual Freestanding Carbon Nanotubes/Nanofibers (CNs) using Plasma Enhanced Chemical Vapor Deposition (PECVD).
Hyung Woo Lee 1 , Soohyung Kim 1 , Sang-Gook Kim 1
1 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show Abstract9:00 PM - JJ5.19
Diameter Dependence of the Charge Transfer Between CNTs and a Chemical P-type Dopant.
Damien Casterman 1 , Premlal Pillai 1 , Merlyne De Souza 1
1 Electronic and Electrical Engineering, The University of Sheffield, Sheffield United Kingdom
Show AbstractIntroductionControlling the type of carrier propagating through carbon nanotube field effect transistors is one of the major challenges in the quest for nanotube-based electronics. Different approaches ranging from multi-gate design to exposure to gases have been investigated to control the ambipolar operation of CNTFETs and consequently drive only one particular type of carriers. Particularly, the use of one electron oxidant hexachloroantimonate as chemical p-type dopant was demonstrated to degenerately dope the nanotube and enhance the operation of the CNTFET [1].In this regard, the present theoretical study investigates for the first time the diameter dependence of the charge transferred from various semiconducting carbon nanotubes to hexachloroantimonate. MethodThis study employs the Density Functional Theory (DFT) implemented in the Vienna Ab initio Simulation Package [2] to model the interaction between CNTs and the chemical dopant. The charge transfer is evaluated using the Bader charge analysis which consists of partitioning the charge density to evaluate the atomic charge and, thereby, the transfer doping [3].ResultsThe charge exchanged has been calculated for a large range of zigzag (n, 0) CNT having diameters ranging from 0.5 to 1.3 nm. These calculations show that the number of electrons increase with diameter, varying from 0.48 to 0.56 electrons per molecule. However, this trend is marked by an oscillating pattern which insinuates a family like dependence (n=1mod(3)and n=2mod(3)). This behaviour is a consequence of the effect hybridization on the Ionization potential of the nanotube which then modulates the exchange of charge.ConclusionNumerical values of the net charge exchanged between CNT and its chemical dopant have been presented. The diameter-to-diameter discrepancy observed highlight the importance of controlling the CNT properties (in particular its diameter and its chirality) in order to control the influence of the dopant and to obtain a reproducible doping process which is crucial for the manufacture of such devices. Acknowledgement: This work, as part of the European Science Foundation EUROCORES Programme FoNE, was supported by funds from the EPSRC and the EC Sixth Framework Programme, under Contract N. ERAS-CT-2003-980409.References[1] J. Chen, C. Klinke, A. Afzali and Ph. Avouris, Appl. Phys. Lett. 86, 123108 (2005).[2] G. Kresse and J. Hafner, Phys. Rev. B 47, 558 (1993)G. Kresse and J. Furthmuller, Comput. Matter. Sci. 6.16 (1996).[3]W. Tang, E. Sanville, and G. Henkelman, J. Phys.: Compute Mater. (in press, 2008).
9:00 PM - JJ5.2
The Apparent Paradox of the Gibbs-Thompson Phenomenon is the Thermodynamic Limit for the Growth of Single Walled Carbon Nanotubes from Fe and Fe:Mo Catalysts.
Stefano Curtarolo 1 , Neha Awasthi 1 , Wahyu Setyawan 1 , Toshio Tokune 2 , Elena Mora 2 , Avetik Harutyunyan 2 , Kim Bolton 3
1 Materials Science, Duke University, Durham, North Carolina, United States, 2 , Honda RI, Columbus, Ohio, United States, 3 , University College of Boraas and Physics Dept., Göteborg University , Göteborg Sweden
Show Abstract9:00 PM - JJ5.20
Carbon Alewives: Highly Aligned and Monodispersed Self Aggregates of Single Walled Carbon Nanotubes.
Budhadipta Dan 1 , Natnael Behabtu 2 , Howard Schmidt 2 , Matteo Pasquali 2
1 Applied Physics, Rice University, Houston, Texas, United States, 2 Chemical and Biomolecular Engineering, Rice University, Houston, Texas, United States
Show Abstract9:00 PM - JJ5.25
Nanotube-Tubulin Interaction: From Assembly to Transport.
Shyam Sundhar Bale 1 , Cerasela Dinu 1 , Jonathan Dordick 1
1 Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractThere is a growing interest in the preparation and design of functional nanoscale hybrid materials with properties derived from both nanomaterials and biomolecules. Carbon nanotubes are attractive components of such hybrid functional materials due to their interesting mechanical and surface properties (i.e. high surface area). However, carbon nanotubes are difficult to solubilize and organize into architectures, which limits their ultimate use in electronic displays, and nanoscale actuators, as well as in biological applications e.g. protein-nanotube conjugates as sensor elements. Herein, we explore two approaches for the interaction of tubulin, a major cytoskeleton protein of eukaryotic cells with cut multi walled nanotubes (MWNTs) to form supramolecular structures for use in bioengineering applications.(i)In one approach, cut-MWNTs were complexed with tubulin to form nanotube-based conjugate assemblies in a concentration dependent manner. Specifically, at lower tubulin loading (~ 10 nM), linear bundles of MWNTs were formed while higher concentrations of tubulin (5-100 µM) led to regular morphologies of aligned MWNTs in petal like conformations. The immobilized tubulin retained its ability to polymerize into microtubular structures that encapsulated the nanotubes when free tubulin was added. The polymerized structures inherited the functionality of tubulin specifically, motility in a gliding assay when using immobilized kinesin molecules. (ii)In the second approach we tested the ability of the microtubules to transport MWNTs attached as “cargo” to their lattices. Specifically, streptavidin functionalized cut-MWNTs were attached to biotinylated microtubules and the assembly was driven by the kinesin immobilized on engineered surfaces. Furthermore, when other nanoparticles were attached to the nanotube (i.e. silver) and subsequently to the motile microtubule, the complex hybrid structures were also glided by the immobilized kinesin. These studies show the ability to modulate protein-nanomaterial interactions to direct the formation of functional structures with varied properties ranging from cargo transport to preparing higher-order assemblies of nanotube-based conjugates. We envision applications ranging from nanoelectronics to drug delivery systems.
9:00 PM - JJ5.26
Growth and Properties of Sn Doped Ga2O3 Nanowires.
Lena Mazeina 1 , Nelson Garces 1 , Evan Glaser 1 , Serguei Maximenko 1 , Keith Perkins 1 , Yoosuf Picard 1 , Sharka Prokes 1
1 , Naval Research Laboratory, Washington, District of Columbia, United States
Show Abstract Gallium oxide, due to its high thermal and chemical stability, is suitable for many applications including as high temperature gas sensors. At lower temperatures, however, sensing applications are impractical due to the low conductivity of Ga2O3. One of the methods to enhance sensitivity at lower temperatures is to increase the conductivity by creating a greater number of surface defects and oxygen vacancies appropriate growth or through impurity doping. Since, Sn is known to increase Ga2O3 thin film conductivity [1] and improve the optical [2] and sensing properties [2,3], the focus of this work is doping of Ga2O3 nanowires (NWs) with Sn. Growth of low Sn-doped Ga2O3 NWs was performed by the vapor-liquid-process in a manner analogous to the growth method of pure Ga2O3 NWs, i.e. a quartz tube was inserted into a horizontal furnace using silicon as a substrate and gold as a catalyst. Instead of pure gallium, Ga-Sn alloys were used as sources. Growth of highly Sn doped Ga2O3 NWs was performed by the vapor-solid process using pure Ga and Sn as sources placed at different distances from the source. The samples were analyzed and characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron and high resolution transmission microscopies (SEM and TEM, respectively) both coupled with energy dispersive spectroscopy (EDS), cathodo- and photoluminescence (CL and PL, respectively), electron paramagnetic resonance(EPR) and by electrical measurements. Nanowires synthesized using the Sn-Ga alloy have low concentration (0.1-0.6 wt%, based on growth conditions) of incorporated Sn and have straight morphologies similar to pure Ga2O3 NWs. Broad PL emission bands observed from these Sn-doped samples at 510 nm were red-shifted by 40 nm relative to pure Ga2O3 NW. Nanowires with high concentration of Sn (15-20 wt%, based on EDS measurements) have bent morphologies. Real color imaging CL imaging and high spatial resolution CL spectroscopy showed that the structures are optically inhomogeneous due to the non-uniform incorporation of Sn. Electrical properties, TEM, FTIR and EPR results will be discussed as well. In general, these results showed that Ga2O3 can be successfully doped by Sn. References.1.Frank,J., Fleischer M., Meixner H., Feltz A. 1997. Enhancement of sensitivity and conductivity of semiconducting Ga2O3 gas sensors by doping with SnO2. Transducers 97, International Conference on Solid-State Sensors and Actuators, 2, 955-958.2.Trinchi A., Li Y. X., Wlodarski W., Galatsis K. 2002. Zn and Ce doped Ga2O3 thin films for oxygen gas sensing. Sensors and Microsystems, Proceedings of the Italian Conference, 7th, Bologna, Italy, 173-179.3.Li Y., Trinchi A., Wlodarski W., Galatsis K., Kalantar-Zadeh K. 2003. Investigation of the oxygen gas sensing performance of Ga2O3 thin films with different dopants. Sensors and Actuators, B: Chemical, B93 (1-3), 431-434.
9:00 PM - JJ5.27
Role of Iodine in the Creation of Nanowires and Nanotubes in CdX and HgX Thin Films.
RangaRao Arnepalli 1 , Viresh Dutta 1
1 Centre for Energy Studies, Indian Institute of Technology, Delhi, New Delhi, Delhi, India
Show Abstract9:00 PM - JJ5.28
Nanotube Fabrication Based on the Kirkendall Effect: Basic Concept and Selected Examples.
Margit Zacharias 1 , Hongjin Fan 2 , Yang Yang 3 , Mato Knez 3 , Roland Scholz 3 , Kornelius Nielsch 4 , Dietrich Hesse 3
1 IMTEK, FAW, University of Freiburg, Freiburg Germany, 2 Department of Earth Sciences, University of Cambridge, Cambridge United Kingdom, 3 Department II, MPI of Microstructure Physics, Halle Germany, 4 Institute of Applied Physics, University of Hamburg, Hamburg Germany
Show AbstractThere has been increasing interest in intentional synthesis of nanowires and nanotubes based on a large variety of materials. A deeper understanding and a sufficient control of the growth of nanowires and nanotubes are in the center of current research interest. We demonstrated the transfer of core-shell nanowires into spinel nanotubes via Kirkendall effect and solid-state reaction.[1] We will show that the nanoscaled Kirkendall effect provides a general fabrication route to hollow nanostructures, including high aspect ratio Nanotubes and complex hierarchical structures.[2,3] Our nanotubes are 30-40 nm in diameter, smooth with excellent monocrystallinity, and up to 20 micrometer long. In our study, the starting object is a core-shell nanowire in which the crystalline ZnO core and the amorphous Al2O3 shell have an initially smooth interface. Atomic layer deposition (ALD) was used which assures a uniform thickness of the Al2O3 shell. As a result of the conformal characteristics of ALD, a uniform coating of the amorphous alumina surrounding the single-crystal ZnO core is evident. After annealing, the structure transforms into hollow tubes. A conceptual extension for the formation of hollow nanostructures initiated by the Kirkendall effect is proposed, suggesting that surface diffusion processes might be the dominant mass flow mechanism responsible for the enlargement of the interior pores after their initial nucleation and formation induced by the Kirkendall effect.[4] We will show results of the spinel-forming solid-state reaction of ZnO-Al2O3 core-shell nanowires to illustrate the influence of surface diffusion on the morphology evolution. Finally, we will demonstrate a simple and efficient pathway to design complex hollow hierarchical nanostructures, which are expected to have applications in catalysis.[1] H.J. Fan, M. Knez, R. Scholz, K. Nielsch, E. Pippel, D. Hesse, M. Zacharias; U. Goesele, Monocrystalline spinel nanotube fabrication based on Kirkendall effect. Nature Materials 5 (2006) 627.[2] H.J. Fan, U. Goesele, M. Zacharias, Formation of nanotubes and hollow nanoparticles based on Kirkendall and diffusion processes: A review, Small 3 (2007) 1660.[3] Y. Yang, D.S. Kim, R. Scholz, M. Knez, S.M. Lee, U. Gösele, M. Zacharias, Hierarchical three-dimensional ZnO and their shape-preserving transformation into hollow ZnAl2O4 nanostructures, Chemistry of Materials 20 (2008) 3487.[4] H.J. Fan, M. Knez, R. Scholz, D. Hesse, K. Nielsch, M. Zacharias, and U. Goesele, Influence of surface diffusion on the formation of hollow nanostructures induced by the Kirkendall effect: The basic concept, Nano Letters 7 (2007) 993.
9:00 PM - JJ5.29
Structures of Complex TiSi2 Nanostructures.
Xiaohua Liu 1 , Sa Zhou 1 , Yongjing Lin 1 , Dunwei Wang 1
1 Chemistry, Boston College, Chestnut Hill, Massachusetts, United States
Show AbstractAs one of the most conductive silicides, TiSi2 has been widely used in microelectronics as a contacting material. It was recently demonstrated as a good photo-catalyst for water-splitting, as well, opening new avenues to producing clean energy carrier of H2 using solar lights. For both electronic and energy-related applications, nanometer-scaled structures are desirable, either for device miniaturizations or for high surface-to-volume ratios. This motivates us to investigate TiSi2 nanomaterials, and we present here our success in synthesizing TiSi2 nanostructures, including one-dimensional (1D) nanowires, 2D nanonets and 3D complexes, all in single-crystalline forms. Interestingly, the microstructure of TiSi2 nanowire is drastically different from their 2D and 3D counterparts, with the former assumes a C54 structure and the latter two are C49. The structures are confirmed by X-ray diffraction, electron microscopy and Raman spectroscopy. Combining the synthesis chemistry, we present evidence that the difference results from different surface terminations. Strikingly, C49 TiSi2 nanonets exhibit extremely low resistivity of 10 µΩ●cm, comparable to bulk C54 TiSi2 and significantly better than bulk C49. This is attributed to the lack of stacking faults, benefited from the nanometer-scales. Details of the structural analysis and device measurements will be presented. Results reported here are significant in both complex nanostructure synthesis and the potential applications. Promising preliminary results of TiSi2 nanostructures for nanoelectronics and solar hydrogen generations will be discussed, too.
9:00 PM - JJ5.3
The Fabrication of Carbon Nanotubes with Corona Discharge.
Ching Chen Li 1 , Ya Chu Chang 1 , Ching Tung Hsu 1 , Wen Kung Hsu 1
1 Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan
Show Abstract9:00 PM - JJ5.30
Chemical Synthesis of TiSi2 Nanostructures: Influence of Growth Conditions on Morphology and Crystal Structures.
Sa Zhou 1 , Xiaohua Liu 1 , Dunwei Wang 1
1 Chemistry, Boston College, Chestnut hill, Massachusetts, United States
Show AbstractBottom-up chemical synthesis is a promising approach toward nanomaterials. It offers potential controls over chemical composition, morphology and structure of targeted materials, and therefore is advantageous to other competing preparation methods. Lately, attentions have been attracted to synthesize complex nanostructures that are composed of one-dimensional (1D) features joined together by single crystalline junctions, to enhance charge transport between branches. Various three-dimensional (3D) structures, including hierarchical and hyperbranched structures, have been synthesized. We present here our success in chemical synthesis of 2D complex TiSi2 networks. The unique shape renders it a formidable challenge to chemically synthesize 2D complex structures. We show that the key to the growth is careful controls over precursor reaction conditions. Chemical passivation on {010} planes plays critical roles, the hindered growth of which leads to the overall 2D feature. When the ratios of the precursors are adjusted, either nanowires or 3D structures can be obtained. It is also found that subtle growth conditions variations can produce either C54 or C49 TiSi2, both of which are remarkably stable, drastically different from their bulk counterparts. We will discuss the details of our studies and their implications. We will also show encouraging preliminary results of photoelectrochemical and electrical measurements of as-synthesized TiSi2, as our main motivation is to explore the applications of TiSi2 in the field of solar energy conversion and nanoelectronics.
9:00 PM - JJ5.31
Synthesis and Characterization of AuNi Core-shell Nanowires.
Jin-Hee Lim 1 , John Wiley 1
1 Department of Chemistry and Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractBoth nanowires and nanotubes have attracted great interest due to their distinctive physical properties and potential applications. The combination, a core-shell structure, is also of great interest in that it may be possible to exploit the synergistic properties of the combined materials. We are investigating the formation of core-shell structures within anodic alumina membranes (AAM) starting with the simple metals, Ni and Au. Initially, Ni nanotubes are prepared by electrodeposition, and then the cores of the tubes are filled with gold by a second electrodeposition step. In depth studies were carried out to better understand this process in particular, how to control the shell thicknesses and consequently the diameter of the core. Details on important electrochemical parameters as well as the effect of these on the morphology of the Au core will be presented and a possible growth mechanism discussed.
9:00 PM - JJ5.32
Mechanism of Asymmetric Growth of Wurtzite Nanostructures: A Case Study of CdSe Through Ab Initio Computations.
Ghanshyam Pilania 1 , Thomas Sadowski 1 , Rampi Ramprasad 1
1 Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States
Show AbstractAn interesting and potentially useful phenomenon observed in wurtzite semiconductor nanocrystals is asymmetric anisotropic growth, i.e., a strong preference to grow along only one of the two complementary anisotropic axes. This property has been exploited (through control of surfactants, ambient atmosphere and temperature) in the preferential creation of nanorods, nanoribbons and nanosaws over spherical nanocrystals. However, the details of the mechanism underlying this phenomenon of asymmetric anisotropic growth remain poorly understood. Here, we use CdSe as a prototypical wurtzite system, and oxygen as an agent that encourages asymmetric anisotropic growth. The choice of oxygen was motivated by recent experimental work in which low temperature annealing in the presence of oxygen leads to the conversion of spherical CdSe nanocrystals to nanorods through asymmetric anisotropic growth. Our ab initio computations were performed using density functional theory (DFT). Several nonpolar and polar surface facets of CdSe in the wurtzite phase were considered, and their surface energies computed. The impact of the ordering of the surface energies as a function of (i) the chemical potential of Cd (i.e., precursor concentration), (ii) the presence of oxygen adsorbates, (iii) the binding modes of oxygen at the surface, and (iv) the density of oxygen adsorbates on the surfaces, were critically assessed. Our results show that oxygen adsorption (in its most favored binding mode) is exothermic on all polar and nonpolar facets. On nonpolar facets, which contain both Cd and Se atoms, adsorption of oxygen takes place preferentially on Se resulting in very stable surface configurations with large drops in surface energy (relative to the clean surfaces). This renders all nonpolar facets passive towards growth in the presence of oxygen. Among the four major polar surface facets which are either Cd- or Se-terminated, two facets (the Cd-terminated and the Se-terminated (0001) surfaces) can be successively created on the same side of the nanocrystal and two other facets (the Cd-terminated and the Se-terminated (000-1) surfaces) can be successively created on the opposite side of the nanocrystal. We find that for appropriate choices of the Cd chemical potential and oxygen coverage, the surface energies of the two (0001) facets are far higher than any of the other surfaces, thereby making (0001) facets relatively unstable and prone to rapid growth along only that direction (resulting in the observed asymmetric anisotropic growth). Thus, by controlling the ordering of the surface energies (e.g., though proper choices of precursor concentration, temperature, and surfactants), novel growth modes such as asymmetric growth can be made possible.
9:00 PM - JJ5.33
Strain Engineering of Band Structure and Doping of Silicon Nanowires.
Ki-Ha Hong 1 , Jongseob Kim 1 , Jae Kwang Shin 1
1 Semiconductor Lab., Samsung Advanced Institute of Technology, Yongin city, Gyeonggi-Do, Korea (the Republic of)
Show AbstractSilicon nanowires (SiNWs) have been considered as one of the most manufacturable nano-structured building blocks. As photonic materials, the usage of the bulk silicon is limited due to its indirect bandgap character. Although many theoretical investigations predict that SiNWs can have wide direct band gap and emit visible light, there has been no experimental evidence as yet. Therefore band structure modification to enhance direct band gap characteristic of SiNWs is necessary for efficient light emission. There is one more issue on using nanowires as building block for devices. It is well known that nano-structured materials such as quantum dots and nanowires are hardly doped although doping is essential to make efficient electronic devices.Lattice strain is a useful method for modulating band structures. In designing electronic devices, it has been widely studied to enhance the device performance by modifying the band structure of silicon. Applying strain is a very economical way for improving the performance of devices and has the advantage of being compatible with conventional CMOS processes for device fabrication.We report that lattice strain can manipulate band structure and dopant formation energy of Si-nanowire using the density functional theory. Strain dependence of band structure change is strongly dependent upon the crystallography of SiNW and the direction of strain. Tensile strain enhances direct band gap character and compressive strain enhances indirect band gap character in case of [100] and [111] SiNWs, whereas both tensile and compressive strain make [110] SiNWs have indirect band gap. We compare formation energies of Phosphorus, Boron, and Arsenic in SiNWs with lattice strain variation.
9:00 PM - JJ5.34
Nanoparticle-Guided Assembly of Silicon Nanotubes at Low Temperatures.
Beri Mbenkum 1 2 , Gunther Richter 1 , Andreas Schneider 1 , Hefin Griffiths 3 , Peter Kopold 1 , Kersten Hahn 1 , Peter van Aken 1 , Joachim Spatz 1 2
1 , Max Planck Institute for Metals Research, Heisenbergstr. 3, D-70569, Stuttgart Germany, 2 Department of Biophysical Chemistry, Im Neuenheimer Feld 253, University of Heidelberg, D-69120, University of Heidelberg, Heidelberg Germany, 3 , Oxford Instruments Plasma Technology, North End, Bristol, BS494AP, Yatton United Kingdom
Show AbstractLow dimensional silicon (Si)-based materials are of particular relevance due to the eminence of Si-based devices in contemporary microelectronics and the prospect of becoming the most versatile building materials for nanoelectronic devices. Among the Si-based nanomaterials successfully produced, the synthesis of silicon nanotubes (SiNTs) has posed a great challenge. Carbon easily forms strong π bonds through sp2 hybridization which results in molecules with a stable trigonal planar coordination and promotes the 2-D crystallization of carbon into tubular structures. Silicon on the other hand is sp3 hybridized and typically favours a diamond-like structure. SiNTs have been synthesized via hydrothermal self-assembly and laser ablation routes. These techniques however lack precise control over SiNT diameter and SiNT yield is low. Also, the direct growth of SiNTs on substrates which is a pre-requisite for direct device integration processes has not been demonstrated.We present an alternate, economical and well controlled method for SiNT synthesis with high yield from nanoparticle templates. Growth proceeds via a chemical vapour deposition route by catalyst-mediated fragmentation of silane at temperatures as low as 350°C. High resolution transmission electron microscopy confirms the presence of multi-walled silicon nanotubes which adopt diameters on the order of 10 - 20 nm depending on the nanoparticle size used. The silicon nanotubes have aspect ratios as high as 660. The low synthesis temperatures enable highly selective synthesis and are beneficial for direct circuit integration processes.
9:00 PM - JJ5.36
Fabrication of ZnS Nanowires by the use of Alpha Synuclein Protein Template.
Sonal Padalkar 1 2 , John Hulleman 3 , Seung Min Kim 1 2 , Jean-Cristophe Rochet 3 , Eric Stach 1 2 , Lia Stanciu 1 2
1 Material Science and Engineering, Purdue University, West Lafayette, Indiana, United States, 2 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 3 Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana, United States
Show AbstractZnS nanowires are of great interest due to their semiconducting, photoluminescent and field emission properties. The present research exploits the nature of alpha synuclein protein fiber for the synthesis of ZnS nanowires. The diameter of the ZnS nanowires was tuned in range of ~50nm to ~200nm by varying the process variables. The nanowires were characterized by field emission scanning electron microscopy, UV-VIS spectroscopy, transmission electron microscopy, electron energy loss spectroscopy and high resolution transmission electron microscopy. The UV Vis absorption peak for ZnS nanowires was obtained at ~355nm, which later shifted to higher wavelength, of ~375nm, with increase in the diameter of the nanowire. The UV Vis results were confirmed by transmission electron microscopy. A colloidal sample of ZnS was also prepared for a comparison with the ZnS nanowires. Further, the effect of incubation temperature on the morphology of the nanowires was also studied. High resolution images and diffraction patterns, of ZnS nanowires, were obtained for complete characterization.
9:00 PM - JJ5.37
Fabrication of Highly Porous Zinc and Zinc Oxide Nanostructures.
Joshua LaForge 1 , Michael Brett 1 2
1 Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada, 2 , National Institute for Nanotechnology, Edmonton, Alberta, Canada
Show AbstractPorous, large surface area zinc oxide thin films[1] are desirable for several applications, including sensors, catalysts, and photovoltaic solar cells[2]. Glancing angle deposition (GLAD) is a physical vapour deposition technique that depends on a highly oblique flux angle to create porous, large surface area thin films via self-shadowing. Control of the deposition angle may provide a means to tune film porosity for zinc oxide sensors and photovoltaic devices. However, the self-shadowing mechanism depends on a collimated particle flux, and therefore GLAD performs best under high vacuum. Creating structured films with sputtered GLAD[3] is difficult since the high-chamber pressure (>1 mTorr) necessary to maintain the sputter plasma reduces the mean-free-path of flux particles to less than 100 mm. By using an aperture to reduce the angle subtended by the target from the perspective of the substrate, maintaining an argon plasma pressure of 1.4 mTorr, and reducing the throw distance to within 50 mm we were able to produce structured, poly-crystalline, zinc thin films via GLAD. At oblique flux angles, highly porous films consisting of a convoluted arrangement of randomly oriented nanorods are grown. The nanorods that make up the film have diameters between 10-100 nanometers with lengths up to several micrometers. Annealing at temperatures up to 250°C in air produces poly-crystalline zinc oxide with minimal changes to the film structure. We present details of the thin film fabrication process and explore the growth mechanism of the convoluted nanorod film morphology. We report characterization results for films produced at several incident angles films before and after thermal processing using scanning electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction.1. Wang, Z. L. (2004), 'Zinc oxide nanostructures: growth, properties and applications', Journal of Physics: Condensed Matter 16(25), R829--R858.2. Peiro, A. M.; Ravirajan, P.; Govender, K.; Boyle, D. S.; O'Brien, P.; Bradley, D. D. C.; Nelson, J. & Durrant, J. R. (2006), 'Hybrid polymer/metal oxide solar cells based on ZnO columnar structures', Journal of Materials Chemistry 16(21), 2088--96.3. Sit, J. C.; Vick, D.; Robbie, K. & Brett, M. J. (1999), 'Thin film microstructure control using glancing angle deposition by sputtering', Journal of Materials Research 14, 1197--1199.
9:00 PM - JJ5.38
Effect of Seed Layer on Hydrothermal Synthesis of Zno Nanostructures and Their Properties.
Harish Bahadur 1 2 , Jeong Cho 1 2 , D. Haranath 1 2 , Jinkyoung Yoo 1 2 , Gyu Yi 1 2
1 Materials Characterization, National Physical Laboratory, New Delhi, Delhi, India, India, 2 Materials Science and Engineerin, POSTECH, Pohang Korea (the Republic of)
Show Abstract9:00 PM - JJ5.39
Flame Synthesis of ZnO Nanostructures: Morphology and Local Growth Conditions.
Fusheng Xu 1 , Cassandra D'Esposito 1 , Xiaofei Liu 1 , Bernard Kear 2 , Stephen Tse 1
1 Mechanical and Aerospace Engineering, Rutgers University, Piscataway, New Jersey, United States, 2 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States
Show AbstractNanostructured ZnO materials have attracted much interest in recent years due to their unique semiconducting, piezoelectric, and pyroelectric properties, as well as bio-safety and biocompatibility characteristics. Possessing a wurtzite lattice structure of non-central symmetry and a combination of three sets of fast growth directions (along with polar surfaces), ZnO can manifest itself in wide range of diverse structures, such as nanowires, nanorods, nanoneedles, nanotubes, nanobelts, nanodisks, nanorings, and hierarchical and networked nanostructures. Within this group, several techniques for the fabrication of one-dimensional ZnO nanowires have been explored using different starting materials, e.g. zinc metal powder, ZnO powder, and metal organic precursor.In this work, various ZnO nanostructures are produced from counterflow diffusion flames, which include nano- wires, ribbons, rods, and networked structures. The synthesis is carried out at one atmosphere pressure using a Zn-plated metal substrate. As described in a previous work, various ZnO nanostructures were obtained in inverse jet diffusion flames (IJDFs), given the appropriate local growth conditions (e.g. temperature and growth-related chemical species). However, the large radial gradients in IJDFs can result in non-uniformity of ZnO nanostructures, making it somewhat difficult to properly assess the growth conditions for specific ZnO nanostructures. To better correlate ZnO morphologies with local conditions, counterflow diffusion flames (CDFs) with quasi-one-dimensionality are employed, where the gradients vary mainly in the axial direction. The axial separation of fuel side and air side with respect to the reaction zone in CDFs also makes it easier to evaluate the roles of H2O (or CO2) versus O2 in the synthesis of ZnO nanostructures. Laser-based diagnostics are used to map local chemical species concentrations and gas-phase temperature with ZnO growth morphology, helping to divulge the growth mechanisms. Results for ZnO nanostructures and their corresponding local conditions are then compared between IDFs and CDFs to assess the translatability of local growth parameters between different flame configurations, as well as the establishment of reference conditions that may be used for other methods of gas-phase synthesis in general.
9:00 PM - JJ5.41
Synthesis of Highly Ordered Arrays of Nanowires of Complex Functional Oxides.
Barnali GhoshSaha 1 , A. Raychaudhuri 1 , V. Subramanian 2
1 Department of Materials Science, S.N.Bose National Centre For Basic Sciences, Kolkata, West Bengal, India, 2 Department of Physics, Indian Institute of Technology Madras, Chennai India
Show Abstract9:00 PM - JJ5.42
Synthesis of Metal Nanotube Ordered Arrays by Programmed Motion of Ions.
Venkata Mutta 1 , Arup Raychaudhuri 1
1 Department of Material Science, DST Unit for Nanosciences, S. N. Bose National Centre for Basic Sciences, Kolkata, West Bengal, India
Show Abstract9:00 PM - JJ5.43
Lithographically Patterned Nanowire Electrodeposition: A Method for Patterning Electrically Continuous Metal Nanowires on Dielectrics.
Chengxiang Xiang 1 , Aleix Guell 2 , Reginald Penner 1
1 Department of Chemistry, University of California,Irvine, Irvine, California, United States, 2 Department of Physical Chemistry, Unversity of Barcelona, Barcelona Spain
Show Abstract9:00 PM - JJ5.44
Ab-initio Study of Structural and Electronic Properties of Zigzag Single Wall GaN Nanotubes.
Uma Shankar Sharma 1 , Udai Pratap Verma 2
1 Engg. Physics, RJIT Tekanpur, Gwalior India, 2 Physics department, School of Studies in Physics Jiwaji Univ., Gwalior India
Show Abstract9:00 PM - JJ5.45
Aqueous Dispersion and Self-Limiting Assembly of Large Diameter Single-Walled Carbon Nanotubes.
Brian Burg 1 , Matthias Muoth 1 , Lukas Durrer 1 , Timo Schwamb 1 , Niklas Schirmer 1 , Christofer Hierold 1 , Dimos Poulikakos 1
1 Department of Mechanical Engineering, ETH Zurich, Zurich Switzerland
Show AbstractThe dispersion of large diameter (2-3 nm) single-walled carbon nanotubes (SWNTs) in surfactant stabilized solutions and subsequent controlled dielectrophoretic assembly is presented. SWNTs are grown in a low-pressure chemical vapor deposition (LPCVD) oven and by a short ultrasonic pulse dispersed in sodium dodecylbenzene sulfonate (SDBS) aqueous solution. Very low energies are required for SWNT removal from the sample surface, with iron (Fe) catalyst particles remaining on the growth support chip. Ultra-pure and long term stable SWNT solutions are achieved with no bundling observed. SWNT enriched solutions (1 ng/ml) are used in the following self-limiting dielectrophoretic deposition of SWNTs between photolithographically pre-fabricated electrodes. The process allows the deposition of individual, suspended, large diameter, and long SWNTs, enabling improved electrode contacting. Short ultrasonic treatment times of SWNTs further reduce the risk of cavitation-induced scission and defect occurrence during processing. Scale up of the introduced parallel fabrication technique permits large scale assembly of SWNT devices, one of the biggest limitations in conventional carbon nanotube device fabrication.
9:00 PM - JJ5.47
Carbon Nanotube Growth on Diamond Substrates.
Chakrapani Varanasi 1 , J. Petry 2 , J. Bulmer 2 , J. Burke 1 , Lyle Brunke 1 , K. Yost 2 , William Lanter 3 , J. Scofield 2 , Paul Barnes 2
1 , University of Dayton Research Institute (UDRI), Dayton, Ohio, United States, 2 , Airforce Research Laboratory (AFRL), WPAFB, Ohio, United States, 3 , Innovative Scientific Solutions, Inc. (ISSI), Dayton, Ohio, United States
Show AbstractCarbon nanotubes (CNTs) have very high thermal conductivity (~3000 W/m-K) at room temperature and so are very attractive to use them as thermal interface materials in electronic applications. It is widely known that diamonds films are also being considered for dissipating heat in these applications. However, a structure consisting of both CNTs and diamonds is not studied in detail so far. In this study, results of initial efforts to grow CNTs on diamonds will be presented. Diamond films on Si were grown at 1100 oC in 5KW microwave plasma enhanced chemical vapor (PECVD) reactor using CH4 as carbon precursor. Free standing diamond films were obtained by removing Si substrates through chemical etching. Free standing diamond films as well as diamond films on Si were used to grow CNTs on them using a separate thermal CVD reactor. CNTs were grown using C2H2 as carbon precusor at 700 C in a tube furnace. Various catalyst nanoparticles were investigated to assist CNT growth on diamonds. Substrates were decorated with nanoparticles of various metal/alloy particles (Ni, Ni-Mo, Ni-W-Fe) prior to CVD. Both magnetron sputtering and pulsed laser ablation approaches were taken to create catalyst nanoparticles on diamonds. Out of the materials investigated so far, Ni- W- Fe, was found to be most suitable to grow CNTs on diamond. Microstructural and Raman characterization of CNTs grown on diamonds will be presented and growth mechanisms will be discussed.
9:00 PM - JJ5.49
Growth of Single Strand Carbon Nanotube Arrays on Foldable Titanium Nitride Membranes.
Hyung Woo Lee 1 , Hyun Jin In 1 , George Barbastathis 1 , Sang-Gook Kim 1
1 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractFolding of nano-patterned membranes has been proposed as a method for assembling three-dimensional (3D) nanostructures. Carbon nanotubes (CNTs) can be used for folding nanostructured devices serving as mechanical tethers as well as electrical or optical interconnects between the folded members of multi-layered nanostructures.In this paper, we describe and show the growth of vertically-aligned CNTs on foldable titanium nitride (TiN) membranes. Although various materials can be used as CNT catalysts, nickel (Ni) was used mainly in this work. We first pattern the TiN membrane including such features as serpentine hinges that will allow easy folding of the membrane along predefined lines. In order to define the location of each CNT, we then pattern Ni dots (150~250 nm in diameter) on top of the TiN layer. Titanium nitride was chosen since it is an excellent diffusion barrier material and prevents the formation of unwanted alloys or diffusion into silicon during the high-temperature (>500 C) CNT growth process. Additionally, TiN has excellent electrical conductivity especially in comparison to other substrates like glass and silicon on which CNTs are typically grown. The nanoscale Ni dots were formed by using electron beam patterning of PMMA (polymethyl methacrylate) coated on top of the titanium nitride/silicon wafer and subsequently depositing a 20 nm thick layer of evaporated Ni. A series of experiments confirmed 500 µAs/cm2 of the optimal e-beam area dose for making dots ranging from 50 to 200 nm in diameter. In the growth of CNTs using PECVD, we identified typical parameters such as ammonia etching time, the ratio of carbon source gas and dilution gas, and plasma power,. Through repeated experiments, we obtained optimal growth parameters for both CNT forests and single strands of vertically-aligned CNTs. Finally, we showed the membrane folding by applying magnetic fields onto the CNTs and utilizing the ferromagnetic catalyst tip encapsulated within each PECVD-grown CNT.
9:00 PM - JJ5.5
Higher Yield of Short Multiwall Carbon Nanotubes by Catalytic Growth.
Vladimir Mordkovich 1 , Svetlana Zaglyadova 1 , Aida Karaeva 1 , Igor Maslov 1 , Eduard Mitberg 1 , Alexey Don 1 , Dmitry Kharitonov 1
1 Advanced Materials, YRD Center, Moscow Russian Federation
Show AbstractThe research works in the field of carbon nanotube (CNT) catalytic growth are mostly devoted to one of the three major challenges, i.e. (a) selective growth of certain fractions; (b) growth of longer CNT for technological fibers or (c) growth of short CNT with maximum yield. The latter task is most closely related to the emerging industry of multi-ton CNT production for polymer-CNT composites and other applications. The yields of lower than 300 g/g, which were typical for earlier catalytic growth works reported before 2003 are no longer interesting for future development. The future of higher-yield CNT growth is related to satisfaction of three major requirements, i.e. (a) yield higher than 1000 g/g; (b) impurities of non-CNT as low as possible for easier purification and (c) cheaper catalyst. This work is dedicated to formulation of growth conditions for higher yield CNT growth on relatively simple and cheap Fe/Al2O3 catalysts. It is necessary to note that the Fe/Al2O3 catalysts of seemingly identical composition are reported to give wildly varying CNT yields. We are set to confirm that it is possible to reach reproducible, high yields of high quality CNT on these catalysts. The catalysts were prepared by impregnation of Al2O3 powder supports with aqueous or ethanol solutions of Fe(NO3)3×9H2O to provide 1, 5, 10 or 20 % Fe content in the support. The impregnated supports were then dried and fired. The supports were prepared by thermal treatment of boehmite AlO(OH). Depending on the temperature of the treatment we received γ-Al2O3 or δ-Al2O3 or Θ-Al2O3 or α-Al2O3, which was confirmed by X-ray diffraction. All the prepared catalysts were activated by hydrogen at 600°C and then the catalytic growth of CNT was carried out in a reaction gas mixture flow at the temperature from 650°C to 950°C. The reaction gas mixtures contained CH4, H2, N2, benzene or toluene in various ratios. The reaction time was varied from 0.5 hr to 3 hr in order to confirm additionally the reproducibility. Experiments with all the catalysts led to formation of black powders of short CNT. The best results were reached for the catalyst 10 % Fe/δ-Al2O3 prepared with the use of ethanol solution of Fe(NO3)3×9H2O. The yield of 19100 g/gcatal was reached at 650°C in 3-hour experiment with the use of benzene-saturated hydrogen gas (saturation temperature 20°C) as a precursor. The catalyst was not desactivated after these 3 hr run. Characterization with TEM, TGA and XRD showed that the product is dominated by short multiwall CNT with relatively narrow size distribution (20-50 nm diameter. 500-600 nm length) and nearly cylindrical layer stacking. No non-CNT carbon was observed. Carbon content was 97 to 98 % weight, TGA manifested a single peak of CNT oxidation at 615°C.The results witness very high yield of carbon nanotubes suitable as filler material for composites. The absence of non-CNT carbon in the product of catalytic growth makes final purification much easier.
9:00 PM - JJ5.50
Unidirectional Growth of Single-Walled Carbon Nanotubes on Sapphire.
Naoki Ishigami 1 , Hiroki Ago 1 2 3 , Tetsushi Nishi 1 , Ken-ichi Ikeda 1 , Masaharu Tsuji 1 2 , Tatsuya Ikuta 4 , Koji Takahashi 4
1 Graduate School of Engineering Sciences, Kyushu University, Fukuoka Japan, 2 Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka Japan, 3 PREST, Japan Science and Technology Agency, Saitama Japan, 4 Graduate School of Engineering, Kyushu University, Fukuoka Japan
Show AbstractHorizontally-aligned single-walled carbon nanotubes (SWNTs) grown on single crystal sapphire (α-Al2O3) has attracted a great interest, because of their orientation to specific crystallographic axes of the sapphire according to a specific surface atomic arrangement. This alignment is attributed to the anisotropic van der Waals interaction between SWNTs and the atomic surface [1,2]. Recently, we found that the crystal plane affects not only the nanotube orientation but also the diameter and chirality, which potentially leads to the development of “epitaxial nanotube growth” [3]. It is known that the catalyst patterning offers a better alignment of longer SWNTs. Generally, the SWNTs grow to both directions from the patterned catalyst. Here, we report a new growth mode in which the SWNTs grow to only one side of the patterned catalyst, providing a unidirectional growth on sapphire. This unidirectional growth occurred irrespective of the gas-flow direction. Our study suggests that the growth direction is determined in the initial stage of nanotube growth. The new unidirectional growth mode would contribute to the formation of advanced nanotube architectures for device applications.[1] H. Ago et al., Chem. Phys. Lett., 408, 433 (2005). [2] S. Han et al., J. Am. Chem. Soc., 127, 5294 (2005). [3] N. Ishigami et al., J. Am. Chem. Soc. in press
9:00 PM - JJ5.51
Nanostructural Evolution During Emission from CsI Coated Carbon Fiber Cathodes.
Lawrence Drummy 1 2 , Daivd Liptak 1 2 , Richard Vaia 1 , Vasilios Vlahos 3 , John Booske 4 , Dane Morgan 3 , Don Shiffler 5
1 AFRL/RXBN, Air Force Research Laboratory, Wright Patterson AFB, Ohio, United States, 2 , UES Inc., Dayton, Ohio, United States, 3 Department of Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States, 4 Department of Electrical and Computer Engineering, University of Wisconsin, Madison, Wisconsin, United States, 5 AFRL/RDHP, Air Force Research Laboratory, Kirtland AFB, New Mexico, United States
Show AbstractCarbon-based nano and microfiber cathodes exhibit very low voltages for the onset of emission, and thus provide exciting opportunities for applications ranging from high power microwave sources to field emission displays. CsI coatings have been shown to enhance the emission properties of carbon fibers, but the mechanisms underlying this enhancement are not clearly understood. Notwithstanding these successes, little is known about the microstructure of the fibers themselves in their as-received state, after coating with CsI, or after being subjected to high voltage cycling. Understanding the evolution of the fiber microstructure is critical to ascertaining the long-term failure processes limiting emission lifetimes. Recent advances in sample preparation techniques for transmission electron microscopy (TEM), such as focused ion beam (FIB) lift-out techniques, have allowed for thin sectioning of materials with varying geometries including fibers. Longitudinal cross sections produced by FIB lift-out reveal a nanostructured graphitic core with a 400 nm amorphous layer. As the cathodes fibers are cycled at high voltage, aberration-corrected high resolution TEM demonstrates the graphitic ordering increases with the number of cycles, however the amorphous layer remains unchanged. These results are consistent with micro-Raman measurements of the fiber D/G band ratios. Vapor deposited bulk CsI is segregated into sub-micron sized islands on the outside of the amorphous layer. A detailed study of the electronic properties of CsI-coated graphitic surfaces by means of ab initio quantum mechanical modeling reveals a significant reduction in the work function of the system associated with the CsI coating. The 4.5 eV initial work function value of the purely graphitic surface is reduced to ~ 1.3 eV when the former is covered by thin ( ~ 0.8nm) vertical CsI dimers at a surface density of 1.6 x 1014 dimers / cm2. This lowering is accomplished by a mechanism of induced surface dipoles, suggesting that work function modification is a major contribution to the improved emission properties of CsI coated graphitic fibers. Ongoing work is aimed at relating these experimental and computational results to the measured drop in carbon fiber emission voltage associated with CsI coatings.
9:00 PM - JJ5.52
Kinetics of Single Walled Carbon Nanotube Growth from In Situ Optical Microscopy.
Phillip Vinten 2 1 , Paul Marshall 1 , Jacques Lefebvre 1 , Paul Finnie 1 2
2 Department of Physics, University of Ottawa, Ottawa, Ontario, Canada, 1 Institute for Microstructural Sciences, National Research Council Canada, Ottawa, Ontario, Canada
Show AbstractChemical vapor deposition (CVD) is a leading approach for the synthesis of single walled carbon nanotubes (SWNTs). However, to advance our understanding and thereby synthesize higher quality nanotubes, the underlying physical and chemical steps of the microscopic growth process must be better understood. In situ observation is a promising approach, as it can directly reveal the growth kinetics and can provide insight into the basic growth mechanisms. Here, we report the use of in situ optical microscopy to observe growing nanotube forests, record videos of the growth, and obtain detailed information about the growth kinetics. The functional form of the instantaneous forest height versus growth time is extracted experimentally for a wide range of growth parameters and the initial growth rate, growth lifetime, and final height are determined from this data. Ex situ Raman spectral data shows that the D band, G band, integrated D/G ratio, and statistical radial breathing mode (RBM) abundances are closely linked to the in situ growth kinetics data. The activation energies associated with the kinetic processes are extracted and are used to suggest associated mechanisms. Critical conditions for the optimal feeding of SWNTs during growth are thus obtained.
9:00 PM - JJ5.53
Directed Assembly of Carbon Nanotubes via Photosensitive Self-Assembled Monolayer.
Ali Afzali 1 , Julie Bardecker 1 , George Tulevski 1 , James Hannon 1
1 , IBM Research, Yorktown Heights, New York, United States
Show AbstractCarbon nanotubes (CNTs) are playing an increasing important role in development of nanotechnology. For example, filed-effect transistors incorporating CNTs as channel have demonstrated superior device performance compared to conventional Si devices. However, a major barrier to large-scale integration of CNT devices in circuits is lack of control in placement and orientation of nanotubes on substrates. In this talk, we present several approaches to selective placement of CNTs on an oxide substrates. These approaches include functionalization of CNTs for directed assembly on metal oxide, use of photosensitive monolayers to divide the surface into hydrophilic and hydrophobic regions and assembly of CNTs on prepatterned substrates.
9:00 PM - JJ5.54
Thermodynamics Behind the Nanotube Growth via Endothermic Reaction.
Elena Pigos 1 , Gugang Chen 1 , Trenton Mueller 1 , Avetik Harutyunyan 1
1 , Honda Research Institute USA Inc, Columbus, Ohio, United States
Show AbstractInherited contradictions in carbon nanofilaments growth models postulated in the 1970s have become essential in understanding the growth of carbon nanotubes. The commonly accepted mechanism based on the heat liberated during the exothermic hydrocarbon dehydrogenation reaction followed by the temperature gradient driven carbon atoms diffusion, does not explain the growth via endothermic reactions (e.g. methane). By using in situ calorimetric measurements during nanotube growth and Raman studies of the samples produced we found that nanotube growth is, in fact, associated with a superimposed exothermic reaction. Further analysis by mass spectrometry and gas chromatography revealed that this exothermic process originates from the partial decomposition of the methane followed by coupling to generate higher order carbon species and the radiative heat transfer from the surroundings. The role of the radiation heat flow, as well as the growth mechanism and optimal synthesis conditions, are discussed.
9:00 PM - JJ5.55
Electronically Homogeneous, Photonic Semiconducting Single-Walled Carbon Nanotubes Bundles In Solid Phase.
Jae-Hee Han 1 2 , Ryuichiro Maruyama 3 , Woo-Jae Kim 1 , Chang Young Lee 1 , Jong Hyun Choi 1 , Daniel Heller 1 , Paul Barone 1 , Michael Strano 1 2
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Institute of Soldier Nanotechnologies, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Solid State Ionics Lab., Advanced Material Laboratories, Sony Corporation, Kanagawa Japan
Show AbstractThe ability to synthesize and manipulate uniform bundles of electronically pure single walled carbon nanotubes (SWNTs) remains central to the advancement of these systems in nano-electronic applications. The assembly of separated SWNT into bundles (parallel aggregates) that are electronically homogeneous and of controlled size is currently beyond engineering capabilities. Using the advance of both density gradient1,2 and dielectrophoresis methods,3 we have performed the first synthesis and measurements of electronically homogeneous bundles of SWNTs in solid state.4 Several interesting properties are noted. We find that bundles of semi-conducting SWNT that are free of all metallic impurities emit photoluminescence (PL) in the near infrared, as anticipated by theory.5 The emission is an important quality control metric, and allows for photophysical characterization of such systems. TEM image reveals a dielectrophoretically synthesized 36 nm bundle of (6,5)-enriched SWNTs bundle attached to the very end of a supporting chemically etched tungsten tip. A vertical conductance measurement characterizes the resistance with length and reveals non-ohmic, step changes in current at constant potential characteristic of ballistic conductance. A scattering length, L, of approximate 4 to 18 nm is calculated from the trace. We also find that such solid bundles show unprecedented significantly bright PL emission as imaged using an InGaAs camera at both 658 and 785 nm laser excitations, confirming a high degree of semiconductor purity. Controls with un-enriched samples show no emission. The G/G0, where G and G0 are conductance and quantum conductance 2e2/h ≈ 1/13 (kΩ)-1 respectively, ranges from 0.3 to 2.2 for a typical un-enriched SWNT bundle. High purity semi-conducting bundles exhibit significantly low ratios at about 0.002 to 0.004. Some interesting applications involving environmentally-related PL shift from these semiconducting solid bundles will be discussed.References1. Arnold, M. S.; Green, A. A.; Hulvat, J. F.; Stupp, S. I.; Hersam M. C. Nature Nanotech. 2006, 1, 60-65. 2. Kim, W. -J.; Usrey M. L.; Strano, M. S. Chem. Mater. 2007, 19, 1571-1576. 3. Lee, C. Y.; Baik, S.; Zhang, J.; Masel, R. I.; Strano, M. S. J. Phys. Chem. B 2006, 110, 11055-11061. 4. Han, J. H.; Maruyama, R.;, Kim, W. -J.; Lee, C. Y.; Choi, J. H.; Heller, D. A.; Strano, M. S. 2008 (submitted). 5. Graff, R. A.; Swanson, J. P.; Barone, P. W.; Baik, S.; Heller, D. A.; Strano, M. S. Adv. Mater. 2005, 17, 980-984.
9:00 PM - JJ5.56
Thermal CVD Synthesis of Carbon Nanotubes for Lateral Field Emission Devices.
Andrew Monica 2 1 , George Coles 1 , Stergios Papadakis 1 , Robert Osiander 1 , Makarand Paranjape 2
2 , Georgetown University, Washington, District of Columbia, United States, 1 , Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, United States
Show AbstractWe report the fabrication of lateral carbon nanotube (CNT)-based field emission devices using a thermal CVD growth method. We describe the device fabrication process, which allows the creation of functional triode devices from quartz, titanium, nickel, and carbon nanotubes only. These techniques are promising for the creation of integrated electronics capable of operating over a very wide temperature range and in the presence of ionizing radiation. The devices consist of CNT emitters grown laterally from an etched quartz sidewall. The lateral CNT growth process is facilitated by a novel two-step angled evaporation technique. This method allows the selective deposition of Ni catalyst along the cathodic sidewall while simultaneously preventing unwanted CNT growth on other surfaces of the device. Electrical and thermal results are reported. In a diode configuration the devices demonstrate low turn-on fields and achieve current densities approaching Amps/cm2. Triode operation of the devices demonstrate the effectiveness of the gate electrodes by the successful modulation of the emission current. Thermal testing of the diodes reveal that device performance does not change over a wide temperature range.
9:00 PM - JJ5.57
Controlled Growth of Super-aligned Carbon Nanotube Arrays and their Applications.
Kaili Jiang 1 , Kai Liu 1 , Xiaobo Zhang 1 , Lina Zhang 1
1 Department of Physics, Tsinghua University, Beijing , Beijing, China
Show Abstract9:00 PM - JJ5.59
Chemistry of Reverse Micelles: A Versatile Route to the Synthesis of Nanorods and Nanoparticles.
Tokeer Ahmad 1
1 Chemistry, Jamia Millia Islamia (Central University), New Delhi, Delhi, India
Show Abstract9:00 PM - JJ5.6
The Structure of Carbon Cones and Disks.
Geir Helgesen 1 2 , Kenneth Knudsen 1 3 , Patrick Pinheiro 1 , Arne Skjeltorp 1 2 , Arnljot Elgsaeter 3 , Torgunn Garberg 3 , Stine Naess 3
1 Physics Department, Institute for Energy Technology, Kjeller Norway, 2 Department of Physics, University of Oslo, Oslo Norway, 3 Department of Physics, Norwegian University of Science and Technology, Trondheim Norway
Show AbstractLarge-scale production of perfect conical carbon nanostructures that are fundamentally different from the other nanocarbon materials, such as buckyballs and nanotubes, can be made using the so-called Kvaerner Carbon Black & Hydrogen Process. This involves pyrolysis of hydrocarbons using a proprietary plasma torch process. The carbon cones (CC) that occur appear in five distinctly different forms. In addition, disk-shaped particles may be produced. The carbon cones consist of curved graphite sheets formed as open cones with one to five carbon pentagons at the tip with successively smaller and discrete cone angles, respectively. The structure and properties of these carbon cones and disks have been relatively little explored until now. We present results from our experimental research on the structure of carbon cones and disks using scanning- and transmission electron microscopy and neutron-, X-ray- and electron diffraction. The disk-shaped particles have diameters of 0.5-4 μm and are typically about 20 nm thick, but can have thicknesses in the range 2-60 nm. The particles show 12-fold faceting along the edges, and their crystalline cores are usually coated with amorphous layers. Heat treatment of the as-produced CC raw material improves the crystalline quality. The work was supported in part by the EU project HYCONES (NMP3-CT-2006-032970).
9:00 PM - JJ5.60
Selective Photo-oxidation of Surfactant-Dispersed Single-Walled Carbon Nanotubes in Water.
Noe Alvarez 1 4 , Carter Kittrell 1 4 , Howard Schmidt 2 4 , Robert Hauge 1 4 , Paul Engel 1 4 , James Tour 1 3 4
1 Chemistry, Rice University, Houston, Texas, United States, 4 The Richard E. Smalley Institute for Nanoscale Science and Technology, Rice University, Houston, Texas, United States, 2 Chemical and Biomolecular Engineering, Rice University, Houston, Texas, United States, 3 Mechanical Engineering and Materials Science, Rice University, Houston, Texas, United States
Show AbstractSelective covalent functionalized single-walled carbon nanotubes (SWCNTs) are critical for applications in a wide variety of technological fields including separations. Ultraviolet (UV) irradiation of single-walled carbon nanotubes (SWCNTs) individually dispersed in surfactants leads to diameter and type-selective photo-oxidation of the nanotubes. Progressive photoreaction of semiconductors and small diameter metallic SWCNTs was confirmed after 254 nm UV irradiation in acidic, neutral and basic aqueous solutions at ambient and elevated temperatures. The increased oxygen content of the SWCNTs after UV irradiation, as detected by X-ray photoelectron spectroscopy, suggests that SWCNTs were oxidized by reaction with water. Attenuated total reflectance Fourier transform infrared analysis provides evidence of hydroxyl functional groups on their surface. This photochemical reaction is impeded by molecular oxygen and appears to involve a reactive intermediate generated in the vicinity of semiconducting SWCNTs. This selective reaction in liquid phase utilices an intrinsic property of the tubes, its absorbance, does not generate chemical contaminantes and it is a promising route to generate hydroxylated SWCNTs.
9:00 PM - JJ5.61
Kinetics of Fe Ion Release and Deposition in Ferritin by Electrochemical Stimulus.
KwangMin Shin 1 , Richard Watt 2 , Gerald Watt 2 , Sang H. Choi 3 , Sun I. Kim 1 , Seon Jeong Kim 1
1 Center for Bio-Artificial Muscle and Dept. of Biomedical Engineering, Hanyang University, Seoul, Seoul, Korea (the Republic of), 2 Dept. of Chemisty and Biochemistry, Brigham Young University, Provo, Utah, United States, 3 Advanced Materials and Processing Branch, NASA Langley Research Center, Hampton, Virginia, United States
Show AbstractThe redox reactions of iron storage protein1, ferritin is intimately involved in both the oxidation of iron during the process of iron storage and the reduction of iron during iron release. The ferritin with an artificially reconstituted core were used to characterize the mass change during electrochemical redox reactions, and the kinetics of metal release and deposition from, or to the cavities of ferritin and ferritin in SWNT composite by an electrochemical redox stimulus was characterized by electrochemical quartz crystal microbalance (EQCM). Unlike ferritin, ferritin/SWNT composites show a reversible mass change and an initial mass increase at the first oxidation because of the double layer charging effect of the SWNT. By using a coreless apoferritin/SWNT composite, the actual mass change related to the core of ferritin was characterized. By using Fe2+ chelating agent2, mass change of Fe-ferritin core was calculated by EQCM. The dependency of metal core release and deposition of ferritin core during electrochemical redox reaction on pH was characterized. It is clear that ferritin in the SWNT composite shows a stable mass change at pH = 7.4, whereas it did not at pH = 6.0 and 8.0. The Fe ion in core release and deposition kinetics of ferritin will be helpful for applications based on electron transfer and electrochemical reconstitution of a ferritin core.
9:00 PM - JJ5.62
The Effect of Molybdenum Addition on the Phase Composition of Fe/MgO System as a Catalyst for CVD Synthesis of Carbon Nanotubes.
Ana Paula Teixeira 1 , José Ardisson 1 , Clascídia Furtado 1 , Waldemar Macedo 1 , Luiz Ladeira 2 , Adelina Santos 1
1 Materials Research and Nuclear Fuel, CDTN/CNEN, Belo Horizonte - MG, Minas Gerais, Brazil, 2 Department of Physics, UFMG, Belo Horizonte - MG, Minas Gerais, Brazil
Show Abstract9:00 PM - JJ5.63
Hydrocarbon Feedstock Decomposition Limited Growth of SWCNTs.
Elena Pigos 1 , Gugang Chen 1 , Avetik Harutyunyan 1
1 , Honda Research Institute USA Inc, Columbus, Ohio, United States
Show AbstractUtilization of the unique properties of single-walled carbon nanotubes (SWCNTs), particularly in electronics, requires in situ controlled growth of the material at a targeted area and possible lowest temperature. Several works have reported on the growth of SWCNTs at very low temperatures, even as low as 350 oC [1]. We notice that, in most cases, the reported low temperature growth was achieved by using active hydrocarbon sources with low catalytic decomposition temperature. In the case of CH4, the lowest temperature reported when using alumina supported Fe/Mo catalysts was 680 oC. Here, we show that by especial activation treatment of this catalyst, which enables it to decompose CH4 at lower temperatures; we were able to grow SWCNT at significantly lower temperature (560 oC). Our studies suggest that the decomposition of the carbon feedstock limits the CNT growth. Hence, by using more active carbon feedstock or somehow facilitating its decomposition (e.g. especial activation treatment of the catalyst or with assistance of plasma) one could enable the synthesis of SWCNT at even lower temperature.[1] M. Cantoro et al. Nano Lett. 2006, 6, 1107.
9:00 PM - JJ5.64
Diameter Selective Growth of Vertically Aligned Single Walled Carbon Nanotubes by Ethanol Flow Control.
Myung Gwan Hahm 1 , Eunah Lee 2 , Sungjong Woo 3 , Chiwon Ahn 4 , Young-Kyun Kwon 3 , Yung Joon Jung 1
1 Mechanical and Industrial, Northeastern University, Boston, Massachusetts, United States, 2 Molecular and Microanalysis Division, HORIBA Jobin Yvon Inc., Edison, New Jersey, United States, 3 Physics, University of Massachusetts Lowell, Lowell, Massachusetts, United States, 4 NEMS and Bio , National NanoFab Center, Dajeon Korea (the Republic of)
Show Abstract9:00 PM - JJ5.65
RCL Model and Extremely Quality Factor in Single-Walled Carbon Nanotubes.
Yu-Hsien Lin 1 , Ching-Chin Lee 1 , Yi-Fan Li 1 , Tung-Wen Cheng 1
1 Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractMore and more electrical properties of carbon nanotubes (CNTs) are investigated. CNTs not only have exceptional dc characteristics but also are promising in ac circuit. In this work, we especially focus on the ac behavior in single-walled carbon nanotubes (SCNTs). An as-prepared chip with coated electrodes and dilute SCNTs/ methyl benzene solution are used for few SCNTs dispersed between electrodes. We set up a RCL model of SCNTs and get an extremely high quality factor (Q) at low frequency (<1MHz). Therefore, by illuminating SCNTs, we can change the electronic characteristics of SCNTs with photocurrent effect and get larger Q values.
9:00 PM - JJ5.66
Exceptional Intertube Cohesion.
Tung-Wen Cheng 1 , Sen-Hong Syue 1 , Wen-Kuang Hsu 1
1 Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractTortuous carbon nanotube bundle is transformed into a rigid rod by the electric field application and the underlying mechanism involves the reorganization of carbon nanotubes into closed-packed bundles via field induced intertube displacement. Three different stages caused by electric field during the field treatment were observed and the mechanism that enhances the stiffness of the carbon nanotube bundle is also discussed. The theory calculation reveals that the cohesive energy and the elastic modulus of the reorganized carbon nanotube bundle are greater than the values observed in the pristine structure by two orders of magnitudes.
9:00 PM - JJ5.67
Fast Hydrophilization of Carbon Nanotubes.
Yi-Fan Li 1
1 Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractBecause of low surface tension of CNTs, the wetting property of CNTs is limited to liquid. We had introduced a simple and fast approach to make CNTs hydrophilic. Through EUV irradiation for short time, various oxygenated functional groups are introduced on the surface of CNTs, such as C=O stretching mode (1750 cm-1 from acid), C-O-H bending mode (1450 cm-1 from acid), and C-O stretching mode (1050 cm-1. It is duo to ozone is produced during EUV irradiation. Ozone is a type of strong oxidant, and it will react with CNTs at defect sites (either existed originally or due to EUV irradiation). Oxygenated groups were formed without destroying the tubular structure of CNTs, and hence the polar groups contribute the surface tension. The overall surface tension has boosted from 20.49 to 76.11 (mN / m). And through annealing in N2 atmosphere for 4 hours, SWNT film recovers from hydrophilic to hydrophobic. The method developed here allows the applications in reinforced polymer, adsorption of heavy metal.
9:00 PM - JJ5.7
Enhancement of Single-Walled Carbon Nanotube Formation Using Aluminum Oxide Buffer Layer in Alcohol Gas Source Method.
Takahiro Maruyama 1 , Kuninori Sato 1 , Tomoyuki Shiraiwa 1 , Shigeya Naritsuka 1
1 Department of Materials Science and Engineering, Meijo University, Nagoya, Aichi, Japan
Show AbstractRecently, we have been reporting carbon nanotube (CNT) growth by a gas source method in an ultra-high vacuum (UHV) chamber using ethanol gas [1]. This growth technique enables CNT growth in a high vacuum, which is useful for investigation of the growth mechanism and can reduce the growth temperature below 400°C. In spite of these advantages, the yields of CNTs grown by the gas source method have been insufficient, because of a low carbon supply. In this study, we utilized an Al2Ox layer in CNT growth from an ethanol gas source, attaining a drastic enhancement of yield. We also characterized both the Al2Ox layers and Co particles in detail, further clarifying the activation mechanism. Co/Al2Ox catalysts were formed on SiO2(100 nm)/Si substrates and Mo grids for TEM observation. The nominal thickness of the Al was varied from 0 to 60 nm, whereas the Co thickness was set to a constant 0.1 nm. Subsequently, CNT growth was carried out by gas source technique using ethanol. The sample temperature was maintained at 700°C during CNT growth. The supply of ethanol gas was controlled by monitoring the ambient pressure, and was kept at 1×10-1 Pa.As the thickness of the Al layer increased, the RBM peak intensities increased, reaching a maximum at an Al thickness of 30 nm, then decreasing when Al thickness was further increased to 60 nm. At an Al thickness of 30 nm, highly-dense web-like CNTs were grown on the substrate surface, and vertically aligned CNTs were also observed in some areas. The diameters of CNTs were distributed between 0.8 and 1.5 nm. Regardless of Al thickness, the D band intensity was fairly low, and the G/D ratio of the CNTs was about 48 at an Al thickness of 30 nm, where the G band reached its maximum. The Raman results demonstrate that the quality of grown CNTs was improved by the Al2Ox buffer layers, and the optimal Al thickness, in regard to both yield and quality, was about 30 nm. AFM results indicate that no distinct increase of Al2Ox layer surface area occurred during the growth. TEM observations showed most of the grown CNTs were SWNTs and that the Al2Ox layer produced Co catalyst particles of 2-3 nm in diameter, which are favorable for high efficient SWNT growth. SIMS measurements indicate that, after annealing, Co diffused from the surface into the Al2Ox layer, leading to Co accumulation at the interface. This suggests that for samples with 60 nm thick Al, this diffusion reduced the Co concentration on the Al2Ox surface, thus lowering CNT yield. Therefore, it is important to optimize Al2Ox thickness, taking into account both the growth temperature and Co thickness.[1] K. Tanioku, T. Maruyama and S. Naritsuka, Diamond Relat. Mater. 17 (2008) 589.
9:00 PM - JJ5.8
Evolution of the SWCNTs Structure as a Function of the Growth Time and Parameters from in Situ and ex Situ Raman Measurements.
Matthieu. Picher 1 , Eric Anglaret 1 , Vincent Jourdain 1
1 LCVN, CC026, Université de Montpellier 2, Montpellier France
Show AbstractOwing to their outstanding electronic properties, single-walled carbon nanotubes (SWCNTs) stand among the potential materials for the future electronics and optoelectronic technologies. Depending on its diameter and chiral angle, a SWCNT can be either an excellent electrical conductor demonstrating room-temperature ballistic conduction or a direct bandgap semiconductor whose energy can be tuned in the near-infrared range. The main hurdle in the development of a SWCNT-based technology is that nanotube samples are generally a mixture of nanotubes with different structures (diameter and chiral angle). Although sorting nanotubes as a function of their types showed significant progress, controlling the SWCNT structure (diameter, chirality, defects) directly at the synthesis stage would be much more effective. This critically depends on a detailed understanding and control of the nucleation and growth mechanisms. During the last years, considerable progress has been achieved in measuring and controlling the chirality of SWCNT samples. In particular, several groups [1, 2, 3] reported a selectivity in favor of high chiral angles. However, the origin of this selectivity remains unknown.Raman spectroscopy is a very convenient tool for characterizing the structure of SWCNTs: the atomic structure can be derived by combining the frequency of the Radial Breathing mode (RBM) and the resonance energy; the crystalline order is related to the intensity of the ratio between the G and D bands.Here, we combined in situ and ex situ Raman measurements to study the evolution of the structure of SWCNTs grown by Catalytic Chemical Vapor Deposition as a function of time and growth parameters.Concerning the crystalline order, we report on the influence of the growth temperature and precursor partial pressure on the G/D ratio: we determined the reaction order for the D band formation and the activation energy for the conversion of carbon atoms from the D band to the G band. The temporal evolution of the G/D ratio during the growth was also investigated as a function of the growth parameters.Concerning the chiral distribution, we performed a systematic study on the evolution of the RBMs as a function of the growth parameters. The temporal evolution of the RBMs was also investigated to determine whether the growth kinetics were dependent on the chiral structure. To do so, we combined in situ measurements and ex situ measurements on samples grown for different durations.[1] Wang et al., J. Phys. Chem. C. 111, 14612 (2007).[2] Y. Miyauchi et al., Chem. Phys. Lett. 387, 198 (2004).[3] X. Li et al.,J. Am. Chem. Soc., 129
9:00 PM - JJ5.9
Carbon Nanotubes Growth on Calcium Carbonate Supported Molybdenum-Transition Metal Catalysts.
Zhongrui Li 1 , Enkeleda Dervishi 1 , Yang Xu 1 , Viney Saini 1 , Meena Mahmood 1 , D. Oshin 1 , Alexandru Biris 1 , Alexandru Biris 2 , Dan Lupu 2
1 , University of Arkansas at Little Rock, Little Rock, Arkansas, United States, 2 , National Institute for Research and Development of Isotopic and Molecular Technologies, Cluj-Napoca Romania
Show AbstractA comparison of different catalyst systems (Ni, Co, Fe/Mo nanoparticles supported on calcium carbonate) has been performed in order to optimize the carbon nanotubes (CNTs) growth. The influences of the reaction temperature, metal loading and carbon source on the synthesis of CNTs were systematically investigated. Dense CNT networks have been synthesized by thermal chemical vapor deposition (CVD) of acetylene at 720 °C using Co-Mo/CaCO3 catalyst. The dependence of the CNT growth on the most important parameters will be discussed exemplarily on the Co catalyst system. Based on the experimental observations, a phenomenological growth model for CVD synthesis of CNTs is proposed. The synergy effect of Mo and active metals was also discussed.
Symposium Organizers
Prabhakar Bandaru University of California-San Diego
Sonia Grego RTI International
Ian Kinloch University of Manchester
JJ6: Graphene: Synthesis
Session Chairs
Prabhakar Bandaru
Sonia Grego
Ian Kinloch
Tuesday AM, December 02, 2008
Room 302 (Hynes)
9:15 AM - JJ6.1
All-semiconducting Armchair Graphene Nanoribbons: A Band Structure Study.
Hassan Raza 1 , Edwin Kan 1
1 School of Electrical and Computer Engineering, Cornell University, Ithaca, New York, United States
Show AbstractOne-third armchair graphene nanoribbons (acGNRs) are metallic within a pz-orbital tight-binding theory due to the transverse momentum crossing of the Dirac point, where the band gap is zero, and the transverse momentum for every one-third of the boundary conditions. One finds that the “metallic” acGNRs actually have a small band gap of a few tens of meV using a more sophisticated theory [1]. However, these are still not useful as transistor material for logic and memory applications. Thus, acGNRs suffer from the same bottleneck as carbon nanotubes that parametric yields will be low unless we have exact control of the ribbon width or the nanotube chirality to the atomic precision. We analyze the acGNR for obtaining an all-semiconducting material, as suggested by recent experiments [2], and find that by mixing different boundary configurations of acGNRs, 1.4 eV band gap can be opened for a 1 nm wide acGNR. Our objective is to study the electronic structure of these mixed acGNRs to ensure significant band gap opening. Such mixing may be present in nature, governed by thermodynamics when the ribbon is formed by etching or oxidation. We use a semi-empirical extended Hückel theory (EHT) with non-orthogonal Slater-type orbital basis set and transferable parameter set [3]. EHT has been applied successfully to study electric field modulation in acGNRs [1] and bilayer graphene [4]. One can categorize acGNRs into three types – alpha, beta and gamma. Alpha-acGNRs are metallic and the rest are semiconducting. However, if the unit cell consists of an alpha-acGNR and a beta-acGNR, e.g. N=8 and N=9 acGNRs, the transverse momentum does not necessarily cross the Dirac point. As a result, a band gap will be observed. The same should hold for a mixed acGNR consisting of an alpha- and a gamma-acGNR or a beta- and a gamma-acGNR. However, not all such configurations are stable due to possibility of open benzene rings. We find that the for an even N, if the next segment of the unit cell is N+1, [e.g. (8,9)-acGNRs, (10,11)-acGNRs, etc], the structure consists of closed benzene rings. For these mixed acGNRs, a band gap is always observed, which still varies inversely with the width in three different trends. Furthermore, unpassivated acGNRs also exhibit this band gap opening. However, the dangling bond states lie in the band gap close to the valence band and reduce the band gap slightly. For the rest of the combinations, still a band gap is observed, but the open benzene rings lead to trap state like bands within the band gap. This analysis is extended to bigger unit cells of different combinations of acGNRs, and the general trend of band gap opening is observed. [1] H. Raza and Edwin C. Kan, Phys. Rev. B, 77, 245434 (2008).[2] X. Li et al., Science 319, 1229 (2008); M. Y. Han et al., Phys. Rev. Lett. 98, 206805 (2007).[3] H. Raza and Edwin C. Kan, J. Comp. Elec., in press (arXiv:0801.1125).[4] H. Raza and Edwin C. Kan, unpublished (arXiv:0806.3128).
9:30 AM - **JJ6.2
Magic of Flat Carbon.
Andre Geim 1
1 , University of Manchester, Manchester United Kingdom
Show AbstractFirst found in 2004, a free standing strictly two-dimensional crystal of carbon (also known as graphene) is now one of the brightest stars on the horizon of materials science and condensed matter physics, revealing a cornucopia of new physics. I will overview our experimental work on graphene concentrating on its next-to-magic electronic and optical properties and speculate about future applications.
10:00 AM - JJ6.3
Large-area, Few-layer Graphene Films on Arbitrary Substrates by Ambient Pressure Chemical Vapor Deposition.
Alfonso Reina 1 , Xiaoting Jia 1 , John Ho 1 , Daniel Nezich 1 , Hyungbin Son 1 , Vladimir Bulovic 1 , Midred Dresselhaus 1 , Jing Kong 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractLarge-area (~cm2) graphene films are grown by ambient pressure chemical vapor deposition (CVD) on evaporated Ni films. We show that proper engineering of the Ni film properties, such as grain structure and surface roughness, and the use of ultra-diluted hydrocarbon flow yield films consisting of 1 to ~10 graphene layers in thickness. Regions with 1-2 layers in thickness can be up to 20 μm in lateral size. Furthermore, the produced films can be transferred, by wet-etching the underlying Ni, to a variety of substrates allowing graphene coverage over large areas on different materials, such as glass, polymers or other semiconductors. Possible growth mechanisms and the structural characterization of the produced graphene will also be discussed. This technique allows the synthesis of graphene patterns on non-specific substrates by bottom-up and top-down approaches. Opto-electronic properties and ambipolar transfer characteristics of the produced material are also demonstrated. This technique may be a viable route towards the large-scale production and integration of graphene in future electronics applications.
10:15 AM - JJ6.4
Chemically Derived Graphene Nanoribbons and Large-scale High Quality Graphene Sheets.
Xiaolin Li 1 , Xinran Wang 1 , Guangyu Zhang 1 , Hongjie Dai 1
1 Chemistry Department, Stanford University, Stanford, California, United States
Show AbstractGraphene (single layer graphite) has emerged as a material with interesting low-dimensional physics and potential applications in electronics. We developed a chemical route to produce graphene nano-ribbons (GNR) with width below 10 nanometers, as well as single ribbons with varying widths along their lengths or containing lattice-defined graphene junctions for potential molecular electronics. The GNRs are solution-phase derived, stably suspended in solvents with non-covalent polymer functionalization, and exhibit ultra-smooth edges with possibly well-defined zigzag or arm-chair edge structures. Electrical transport experiments show that unlike single-walled carbon nanotubes, all of the sub-10 nanometer GNRs produced are semiconductors and afford graphene field effect transistors (FET) with on-off ratios ~107 at room temperature. We also developed a method of exfoliation-reintercalation-expansion of graphite to produce large-scale high quality single-layer graphene sheets (GS) stably suspended in organic solvents. The GS exhibit high electrical conductance at room and cryogenic temperatures. Large amounts of GS in organic solvents are made into large transparent conducting films by Langmuir-Blodgett (LB) assembly in a layer-by-layer manner. The chemically derived high quality graphene sheets could lead to future scalable graphene devices.
10:30 AM - JJ6.5
High Yield Production of Graphene by Liquid Phase Exfoliation of Graphite.
Yenny Hernandez 1 , Valeria Nicolosi 5 , Mustafa Lotya 1 , Fiona Blighe 1 , Zhenyu Sun 1 2 , Sukanta De 1 2 , Iggy McGovern 1 , Brendan Holland 1 , Michele Byrne 3 , Yurii Gunko 2 3 , Boland John 2 3 , Peter Niraj 2 3 , Georg Duesberg 2 3 , Robbie Goodhue 4 , Andrea Ferrari 6 , Jonathan Coleman 1 2
1 School of Physics, Trinity College Dublin, Dublin Ireland, 5 Department of Materials, University of Oxford, Oxford United Kingdom, 2 Centre for research on adaptive nanostructures and nanodevices (CRANN), Trinity College Dublin, Dublin Ireland, 3 School of Chemistry, Trinity College Dublin, Dublin Ireland, 4 Department of Geology, Trinity College Dublin, Dublin Ireland, 6 Engineering Department, University of Cambridge, Cambridge United Kingdom
Show AbstractGraphene is at the centre of nanotechnology research. In order to fully exploit its outstanding properties, a mass production method is necessary. Here we demonstrate graphene dispersions with concentrations up to ~0.01mg/ml by dispersion and exfoliation of graphite in organic solvents. This occurs because the energy required to exfoliate graphene is balanced by the solvent-graphene interaction for solvents whose surface energy matches that of graphene. We confirm the presence of individual graphene sheets with yields up to 12% by mass, using absorption spectroscopy, transmission electron microscopy and electron diffraction. The absence of defects or oxides is confirmed by XPS, IR and Raman spectroscopies.
10:45 AM - JJ6.6
Formation of Graphene Nanowires on Vicinal SiC Surfaces.
Satoru Tanaka 1 , Srey Chenda 1
1 Applied Quantum Physics, Kyushu Univ., Fukuoka Japan
Show AbstractGraphene is an idealistic form of two-dimensional (2D) systems and thus has recently been enthusiastically investigated from the views of low dimensional physics and electronic applications. Fabrication of graphene by the common method using a “Scotch tape”, however, is still an elaborative work [1]. Vacuum heating of SiC substrate is rather simple and easy to obtain thin layers of graphene [2]. Nanostructures of graphene are of significance to control electronic states, by which semiconductor characteristics are achieved by quantum size effects. For the field effective transistor (FET) application the band-gap control is a crucial matter for the gate-controlled operation. It is so far performed by an elaborative lithographic technique, which limits the lower size of the wire width. Self-organization processes are therefore desired in this regard and also for the higher structural/electronic quality of graphene.The use of vicinal surfaces, which consist of step/terraces or facets, is one of the promising ways to fabricate nanowires via self-organization. We have found self-organized nano-facet formation on vicinal SiC(0001) by high temperature H2 gas etching [3, 4], that can be applicable to nanostructure formation. A 6H-SiC(0001) substrate with a vicinal angle of 4.0° (vicinal toward <11-20>, Si face) was first etched by H2 gas at 1320°C for 30 min. followed by the N2 gas treatment at the same temperature, resulting in periodic nanofacets consisting of (0001) and (11-2n) with an epitaxial SiON superlattice as shown in Figs. 1. Loading into the UHV chamber the sample was first checked by RHEED, showing (√3x√3)R30° which is characteristic of the SiON superlattice [5]. The sample was then heated up to 800~1050°C. The initial (√3x√3)R30° due to the SiON superlattice was thermally destroyed at ~800-900°C and (√3x√3)R30° was again appeared, which is due to ad-atom Si. At ~1030-1050°C in addition to the √3x√3 structure new steak lines were appeared at slightly outside of (±2/3) streaks as shown in Fig. 2. The new lines are due to graphene, estimated by those lattice constants. Moreover, the surface morphology checked by atomic force microscopy indicated the periodic structure similar to the surface shown in Fig. 1. From the facts that two phases, consisting of (√3x√3)R30°-Si and graphene, are present on the surface and well-ordered surface morphology, we can infer that graphene was preferentially formed at/along (11-2n) nanofacets. This can be considered as graphene nanowires. The further results of characterizations using STM, AFM, micro-Raman, and ARPES will be given and the formation mechanisms of graphene nanowires will be discussed.References:[1] K. S. Novoselov et al., Nature 438, 197 (2005[2] C. Berger et al., Science 312, 1191 (2006)[3] H. Nakagawa, S. Tanaka, and I. Suemune, Phys. Rev. Lett. 91, 226107 (2003).[4] M. Fujii and S. Tanaka, Phys. Rev. Lett. 99, 016102(2007).[5] T. Shirasawa et al., Phys. Rev. Lett. 98, 136105(2007).
JJ7: Graphene Characterization
Session Chairs
Tuesday PM, December 02, 2008
Room 302 (Hynes)
11:30 AM - JJ7.1
Investigation of Chemically Doped Graphene and Graphene p-n Junctions.
Damon Farmer 1 , Roksana Golizadeh-Mojarad 2 , George Tulevski 1 , Vasili Perebeinos 1 , Yu-Ming Lin 1 , James Tsang 1 , Ali Afzali-Ardakani 1 , Phaedon Avouris 1
1 TJ Watson Research Center, IBM, Yorktown Heights, New York, United States, 2 School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana, United States
Show AbstractDue to its linear dispersion relation and the predicted chiral nature of its quasiparticles, graphene has become a material of intense experimental and theoretical investigation. There has been rapid progress in the fabrication and understanding of graphene devices. However, many key issues still need to be addressed in order to fully exploit graphene for technological applications. Controlled doping of graphene with stable chemical dopants is one such issue. Here, we investigate the use of polyethylene imine (PEI) and diazonium compounds as molecular dopants and functionalizing agents. PEI is an amine-rich, electron-donating polymer that is found to be an effective n-dopant on graphene. Conversely, diazonium salts are observed to cause p-type behavior. The interaction of diazonium with graphene appears to be noncovalent in nature. This is in contrast to what is observed with carbon nanotubes, where covalent bonding with the diazonium cation occurs. Reasons for this disparity are discussed. PEI and diazonium exposure is found to produce an asymmetrical change in graphene carrier mobility, preserving the mobility of one carrier type (electron or hole) while decreasing the mobility of the other. Theoretical models are developed and simulations are carried out to elucidate the mechanism behind this observed asymmetry. A graphene p-n junction is fabricated to demonstrate the compatibility of these dopants. The nonclassical transport characteristics exhibited by this device are discussed and compared to simulations.
11:45 AM - JJ7.2
Uniaxial Strained Graphene: Bandgap Opening and Raman Mapping Investigation.
Ting Yu 1 , Zhenhua Ni 1 , YingYing Wang 1 , Yumeng You 1 , Zexiang Shen 1
1 Division of Physics and Applied Physics, Nanyang Technological University, Singapore Singapore
Show AbstractGraphene consists of one flat layer of carbon atoms arranged in a honeycomb lattice, it has attracted intensive interest since experimentally discovered in 2004. Due to its special properties such as the massless relativistic Dirac fermions, the quantum Hall effect, and the ballistic transport even at room temperature, graphene provides a promising future for fundamental studies and practical applications. In order to make graphene a real technology, a special issue must be solved: creating an energy gap at K and K′ points in the Brillouin zone. Different attempts have been made by researchers, such as patterning graphene into nanoribbon, forming graphene quantum dots, making use of multilayer graphene sheets, and applying an external electrical field. Here, we propose a practical way to open the bandgap on graphene: application of uniaxial strain. Our first principle calculation predicted a bandgap opening of ~300 meV for 1% uniaxial tensile strained single layer graphene, mainly due to the breaking of sublattice symmetry under uniaxial strain. Experimentally, we report Raman mapping investigation of strain effects on graphene on transparent and flexible substrate. Raman mappings reveal significant red-shift of 2D mode with introduction of tensile strain, distribution of local strain in the strained graphene, and immediate recovery after strain relaxation. The systematic fitting and statistical analysis quantify tensile strain sensitivity of graphene for the first time, which is comparable to the single-walled carbon nanotubes (SWNTs) and implies the potential of graphene as an ultrasensitive strain sensor. Strained graphene based field effect transistor (FET) will also be fabricated to measure the transport properties. Our results on strained graphene suggest that (1) band gap engineering is possible by applying uniaxial strain on graphene. (2) The strained graphene can be realized by depositing graphene on flexible substrate. (3) Raman spectroscopy can be used an ultra-sensitive way to determine the strain in graphene.
12:00 PM - JJ7.3
Electrical Characterization of Graphene Films Fabricated by Chemical Vapor Deposition Method.
Daniel Nezich 1 , Alfonso Reina 2 , Joel Yang 3 , Karl Berggren 3 , Jing Kong 3
1 Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Material Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractAn electronic characterization of graphene films grown by chemical vapor deposition (CVD) is presented. This CVD growth process is an alternative route toward graphene fabrication that is both scalable and economical. The graphene films contain a variety of domains of differing thickness, ranging from one layer up to about 12 layers. Arrays of two-terminal devices using standard fabrication techniques were obtained and the electrical measurement data are analyzed statistically for an overall evaluation of the quality of the graphene films. Measured properties include the film conductivity and mobility, as well as their temperature dependence both above and below room temperature. Device operation under electrical stress conditions is also observed, with current densities above 108 A/cm2.
12:15 PM - JJ7.4
Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene.
Xiaoding Wei 1 , Changgu Lee 1 , Jeffrey Kysar 1 , James Hone 1
1 Mechanical Engineering, Columbia University, New York, New York, United States
Show AbstractThe elastic properties and intrinsic breaking strength of free-standing monolayer graphene membranes are measured. The free-standing films are suspended above circular wells in a silicon substrate and are fabricated by exfoliating single atomic layers of graphene from a graphite source. The mechanical properties of the graphene are characterized via nanoindentation with an atomic force microscope by measuring the force and displacement relationship upon indenting the graphene film in the center of the suspended film. The force-displacement behavior is interpreted within a framework of non-linear elastic stress-strain response, from which the second- and third-order elastic moduli are determined. In addition, we show that the breaking strength of the monolayer graphene represents the intrinsic strength of a defect free sheet. These experiments establish graphene as the strongest material ever measured, and show that atomically perfect nanoscale materials can be mechanically tested to deformations well beyond the linear regime.
JJ8: Nanowires: Synthesis and Characterization I
Session Chairs
Prabhakar Bandaru
Sonia Grego
Ian Kinloch
Tuesday PM, December 02, 2008
Room 302 (Hynes)
2:30 PM - **JJ8.1
Nanowire Nanopiezotronics.
Zhong Lin Wang 1
1 School of Materials Science and Engineering, Georgia Tech, Atlanta , Georgia, United States
Show AbstractNanopiezotronics is a new field that was introduced based on using the coupled piezoelectric and semiconducting properties of nanowires/nanobelts for fabbricating unique and novel electronic devices and components [1]. For a ZnO nanowire/nanobelt that is piezoelectric n-type semiconductor, it creates an asymmetric strain distribution across its width when being bent laterally by an external force, which results in an asymmetric potential distribution across the nanowire width, with the tensile and compressive sides being positive and negative, respectively. The magnitude of this potential is proportional to the degree to which the nanowire is bent and it can reach a couple of volts depending on the size of the nanowire/nanobelt [2, 3]. As a result, the potential drop across the two sides is effectively a gate voltage that can trap the charge carriers, thus, controlling the current flowing from one end of the nanowire to the other end. This presentation will feature the piezoelectric field effect transistor [3], piezoelectric diode [4] and piezoelectric chemical sensors [5] that were fabricated based on the principle of nanopiezotronics. A prospective will be given about its future applications.[1] Z.L. Wang “Nano-piezotronics”, Adv. Mater., 19, 889 (2007).[2] Z.L. Wang and J.H. Song “Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays”, Science, 312, 242 (2006).[3] Yifan Gao and Z.L. Wang “Electrostatic Potential in a Bent Piezoelectric Nanowire – The Fundamental Theory of Nanogenerator and Nanopiezotronics”, Nano Letters, 7, 2499 (2007).[4] Jr H. He, C. H. Hsin, L.J. Chen, Z.L. Wang* ”Piezoelectric Gated Diode of a Single ZnO Nanowire”, Adv. Mater., 19 (2007) 781-784.[5] C.S. Lao, Q. Kuang, and Z.L. Wang, M.C. Park and Y.L. Deng “Polymer Functionalized Piezoelectric-FET as Humidity/Chemical Nanosensors”, Appl. Phys. Letts., 90 (2007) 262107. [6] Research supported by DARPA, BES DOE, NSF, NASA and Emory-Georgia Tech CCNE from NIH.[7] for details: http://www.nanoscience.gatech.edu/zlwang/
3:00 PM - JJ8.2
Nanowire Templated Lateral Epitaxial Growth (NTLEG) of Low Dislocation Density GaN.
George Wang 1 , Qiming Li 1 , J. Randall Creighton 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractWe present here a novel application of vertically aligned GaN nanowire arrays as 3D strain-compliant templates for the lateral growth and coalescence of high quality GaN films on lattice-mismatched sapphire. In contrast to current epitaxial lateral overgrowth techniques used to reduce dislocation densities, this approach, referred to here as “nanowire templated lateral epitaxial growth” (NTLEG), requires no growth interruption or costly patterning. Using metal-catalyzed MOCVD, we have achieved the growth of highly aligned and dense arrays of single crystalline GaN nanowires uniformly on unpatterned 2-inch diameter sapphire. Surprisingly, the nanowire density and the degree of alignment were found to be highly sensitive to changes in the Ni catalyst film thickness below 1 nm, a regime rarely explored in catalyzed nanowire growth. For submonolayer Ni films, the formation of high-density and ultra-small Ni islands with a narrow size distribution is attributed to the high activation energy for Ni diffusion on sapphire, which in turn leads to high-density and highly aligned GaN nanowires. From these nanowire arrays, we have been able to demonstrate fully coalesced, nonpolar a-plane GaN NTLEG films. The growth and characterization of the nanowire arrays and NTLEG films will be discussed. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000. This work is supported by DOE EERE/NETL.
3:15 PM - JJ8.3
Metal-Semiconductor Hybrid Micro- and Nanotubes: Large Area Assembly, Dispersion, Functionalization and Characterization.
Ik Chun 1 , Xiuling Li 1
1 Electrical and Computer Engineering, University of Illinois, Urbana, Illinois, United States
Show Abstract3:30 PM - JJ8.4
High aspect ratio GaAs nanowires grown by Hydride Vapour Phase Epitaxy.
Mohammed Ramdani 1 , Evelyne Gil 1 , Yamina Andre 1 , Dominique Castelluci 1 , Agnes Trassoudaine 1 2 , Audrey Bodin 1 , Christine Leroux 3 , Luc Bideux 1 , Guillaume Monier 1 , Oscar Awitor 1 2 , Christine Robert-Goumet 1
1 , LAboratoire des Sciences et Materiaux pour l'Electronique et d'Automatique LASMEA UMR CNRS 6602, Aubiere France, 2 Departement Mesures Physiques, Institut Universitaire de Technologie, Aubiere France, 3 , Institut Materiaux Microelectronique Nanosciences de Provence IM2NP UMR CNRS 6242, La Garde France
Show AbstractSemiconductor nanowires (NWs) of III-V compounds have received much interest in recent years due to their potential use as nano-building blocks for electronic, optoelectronic and biological applications. Nanowires can be achieved by a several techniques based on photolithography and selective area epitaxy, but a most successful approach to the bottom-up approach is the catalyst-assisted vapour-liquid-solid (VLS) mechanism. In VLS growth, a suitable metal catalyst alloys with the group III metal atoms introducing a local liquid solid interface with a growth rate similar to that of liquid-phase epitaxy (LPE). The constituent materials are supplied from the vapour phase and incorporated into the metal-catalyst which acts as seed for the NWs growth. In most cases, Au is the metal-catalyst used for the NWs formation. Many successful NWs growth studies were performed by metal-organic vapour phase epitaxy (MOVPE) or molecular beam epitaxy (MBE).In this work, we present the first study of GaAs NWs grown by hydride vapour phase epitaxy (HVPE). The use of chloride molecules as element III growth precursors gives to HVPE its main feature: the dechlorination frequency is high enough so that there is no kinetic limitation and conditions for equilibrium are quickly reached. A wide range of growth rates (from 3 to 100 µm/h) can then be set depending on the state of advancement of the growth reaction with respect to equilibrium. The main advantage of the bottom-up near-equilibrium HVPE process, compared to the other techniques for micro and nano-structuration, is the possibility of processing large-area surfaces (1–3 in wafers) in a few minutes exhibiting defect-free crystal-defined grown motifs with unusually high aspect ratios, the growth morphologies being mainly governed by surface kinetics.GaAs NWs were grown on GaAs (100) and (111)B substrates in a hot wall horizontal HVPE reactor kept at atmospheric pressure (AP-HVPE) using Au particles as catalytic agents. The Au surface structuration and growth parameters (temperature, partial pressures, growth duration) were investigated to establish the mechanisms that govern the wire growth in the HVPE process. We synthesized NWs with lengths beyond 90 µm for diameters below 200 nm at a mean rate of 200 µm/h, and microwires (MWs) with lengths beyond 400 µm. These results emphasize that the growth mechanism of GaAs NWs and MWs by HVPE is mainly based on solidification after direct impingement of the growth species from the vapour phase through the liquid alloy catalyst, facilitated by the high dechlorination frequency. This is the first demonstration of very long semiconductor NWs opening the way to new applications which were not imaginable before the synthesis of such lengthy nanowires.
JJ9: Nanowires: Synthesis and Characterization II
Session Chairs
Tuesday PM, December 02, 2008
Room 302 (Hynes)
4:45 PM - JJ9.2
Synthesis, Properties and Applications of Transition Metal Silicide Nanowires.
Song Jin 1
1 , University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractNanowire materials extensively studied so far usually are made of elements or prototypical compound semiconductors with simple stoichiometries. In contrast, intermetallic compounds such as metal silicides have multiple and unpredictable stoichiometries and complex phase behavior, making them challenging to synthesize and rarely explored so far. However, nanowires of silicides have many new physical properties and significant applications in nanoelectronics, nanophotonics, nanospintronics, and thermoelectrics. We have developed general synthetic approaches to nanowires of silicides to overcome such previously unaddressed complexity. Our first approach utilizes chemical vapor deposition (CVD) of single source organometallic precursors (SSPs) to reproducibly deliver both silicon and metals with stoichiometric control. We have also developed a complementary chemical vapor transport (CVT) method to synthesize nanowires of semiconducting silicides for which suitable organometallic precursors are not readily accessible. We discovered a new and general nanowire growth mechanism that is different from the typical vapor-liquid-solid (VLS) nanowire growth and critically depends on the oxide thickness. A total of eight different new silicide nanowires have been synthesized by us so far. We will discuss our systematical investigation of families of metal-silicon organometallic complexes as SSPs, our current understanding on the detailed nanowire growth mechanism and the chemical rules governing the formation of the nanoscale silicide phases. The applications of silicide nanowires will be discussed using magnetic semiconducting silicide alloys for spintronics and semiconducting silicides for thermoelectric applications.
5:00 PM - JJ9.3
Elastic Strain Relaxation in Axial Si/Ge Nanowhisker Heterostructures.
Michael Hanke 1 , Christian Eisenschmidt 1 , Peter Werner 2 , Nikolai Zakharov 2 , Frank Syrowatka 3 , Frank Heyroth 3 , Peter Schaefer 4 , Oleg Konovalov 5
1 Institute of Physics, Martin-Luther-University Halle-Wittenberg, Halle /Saale Germany, 2 , Max-Planck-Institut fuer Mikrostrukturphysik, Halle Germany, 3 Center for Materials Science, Martin-Luther-University Halle-Wittenberg, Halle Germany, 4 , Humboldt-University, Berlin Germany, 5 , European Synchrotron Radiation Facility, Grenoble France
Show AbstractOne-dimensional semiconductor structures, also referred to as nanowires and nanowhiskers (NWs), have attracted much interest during recent years due to their many-fold potential applications in novel electronics, photonics and sensing devices. Regarding characterization most groups, however, still rely on direct imaging techniques like electron microscopy, whereas x-ray scattering techniques quite recently emerge in the NW field. We will report on a combined approach including direct and indirect analytical techniques to probe composition, strain and elastic relaxation within heteroepitaxial Si/Ge NWs.The elastic behavior of MBE-grown SiGe/Si(111) nanowhiskers (NWs) has been studied by means of electron microscopy, x-ray scattering and numerical linear elasticity theory (Finite Element Method)[1]. Highly brilliant synchrotron radiation was applied to map the diffusely scattered intensity near the asymmetric (115) reciprocal lattice point. The larger lattice parameter with respect to the Si matrix causes a lateral lattice expansion within embedded Ge layers. This enables a clear separation of scattering due to NWs and laterally confined areas aside. Finite element calculations prove a lateral lattice compression in the Si matrix close to the NW apex above buried three-fold and single Ge layer stacks. This suggests an incorporation probability, which additionally depends on the radial position within heteroepitaxial NWs.[1] M.Hanke et al., Phys. Rev. B 75, 161303(R) (2007)
5:15 PM - JJ9.4
Hybrid Nanocoil Sculptured Thin Films.
Daniel Schmidt 1 , Tino Hofmann 1 , Mathias Schubert 1 , Eva Schubert 1
1 Electrical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
Show AbstractThree-dimensional structure design of chiral materials on the nanoscale are in the focus of modern material science and engineering because intriguing applications are foreseen in various fields ranging from optics, electromechanics or electromagnetic. Glancing angle physical vapor deposition is a technique, which allows for “bottom-up” fabrication of 3D shaped and tailored chiral nanostructures arranged in sculptured thin films (STFs). We will present a study of STFs from various conducting and magnetic materials grown on highly p-doped silicon substrates by using ion beam sputtering or electron beam evaporation. Various growth schemes have been used to obtain films with different nanostructure shapes such as posts, screws or spirals. Furthermore, in order to achieve hybrid chiral STFs with advanced dielectric or magnetic functionality, nano cluster deposition and spin-on techniques were used to partly or completely fill the voids in the films with magnetic nanoparticles or polymer-based compounds.The films have been characterized regarding their morphological, optical, and electrical properties by means of SEM, AFM, Mueller Matrix Ellipsometry, IR Spectroscopic Ellipsometry and electrical measurements. Whereas Mueller Matrix Ellipsometry reveals an optical response which can be related to the symmetry of the three-dimensional nanostructures [1], the IR data give hint to electron or lattice absorption effects. We found that the IR optical response depends on the shape of the nanostructures. Sculptured thin films from aluminum (Al) posts, for example, show a bulk-like behavior, whereas STFs containing Al nanocoils show multiple resonances with a periodic spectral distance between neighboring absorption features. The IR Ellipsometry spectra were analyzed by using a Drude term to account for free electron mobility. Additionally, each of the resonances in the nanocoil STFs was modeled by a Lorentz oscillator approach. The Drude term reveals significant differences in free carrier mobility between STFs from different nanostructure geometries, which is also supported by electrical measurements under DC conditions.The resonance features in the nanocoil STFs are discussed in terms of coupled inductance and capacitance pairs. Here, the inductance and the capacitance are created from nanocoils and the depletion layer at the interface between coils and p-type Si substrate, respectively.
Reference
[1]D. Schmidt, E. Schubert, and M. Schubert, phys. stat. sol. (a) 205, 748 (2008).
5:30 PM - JJ9.5
Fabrication of and Electrical Measurements on Integrated Single-Crystal Silicon Nanowires.
Chung Hoon Lee 1 3 , Clark Ritz 2 , Max Lagally 2
1 ECE, California State University, Fresno, Fresno, California, United States, 3 EECE, Marquette University, Milwaukee, Wisconsin, United States, 2 , University of Wisconsin, Madison, Wisconsin, United States
Show AbstractSilicon is the dominant material for current electronics because the fabrication technology is mature and electrical properties can be precisely controlled by doping. As dimensions shrink to the nanoscale, many new opportunities arise for devices using nanomembranes, ribbons, or wires. Because the surface-to-volume ratio becomes very high, one class of devices relates to using the surface as the active element in electronic –readout nanosensors. The surface conditions of the nanostructure can contribute significantly to the electrical conduction. We demonstrate a method to fabricate integrated free-standing single-crystal Si nanowires that is scalable from a single nanowire to wafer size, and which produces nanowires with specific, well defined, and controllable surface orientations and with controllable metal contacts [1]. We measure electron transport characteristics of a single SiNW with various metal contacts and for different surface conditions. The fabricated structures are metal-semiconductor-metal with Schottky contacts at each end, and exhibit the expected non-linear I-V behavior. We describe the relevant contributions to conduction in these nanowires, including contributions from the surface. The latter may trap charge (e.g. Si/oxide interface), making the wire an insulator, or may pin the Fermi level to provide conduction of different degrees. For example, it is believed [2] that HF dipped Si causes the Fermi level to be pinned 0.2~0.3eV below the conduction band minimum. We demonstrate the resulting electrical conduction in a single 50nm x 30nm x 5um nanowire. With exposure to atmosphere, bonds at the H-terminated surface are replaced by O-Si bonds. We observe the resulting reduction of the current due to formation of Si/oxide interface states. The effect is similar to having a gate all around the wire, with the potential on the gate provided by surface charges and changing over time. We will describe how one can extract, from the rate of change of the current with time and from known oxidation kinetics, the effective range of interface defects in modifying the surface potential.Research supported by DOE and AFOSR[1] C. H. Lee, C. S. Ritz and M. G. Lagally, to be published.[2] R. Schlaf, R. Hinogami, M. Fujitani, S. Yae, and Y. Nakato, J. Vac. Sci. Technol. A 17, 164 (1999).
5:45 PM - JJ9.6
Low-Threshold Two-Photon Pumped ZnO Nanowire Lasers.
Jian Xu 1 , Chunfeng Zhang 1 , Jong-in Hahm 3 , Zhonglin Wang 2
1 Engineering Science and Mechanics, Penn State University, University Park, Pennsylvania, United States, 3 Chemical Engineering, Penn State University, University Park, Pennsylvania, United States, 2 Department of Material Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractRecently, nanoscale ultraviolet (UV) lasers based on ZnO nanowires have commanded much attention for their potential applications in integrated photonics, sensing and photochemotherapy. As promising as the emerging ZnO nanolasers are, ZnO nanowires require optical excitation or pumping with deep-UV, coherent light to produce stimulated emission via a linear optical process. The excitation photon energy has to be larger than the band gap (~3.37 eV) of ZnO nanowires in order to pump them in the one-photon absorption (OPA) regime. The dependence on expensive, deep-UV pumping sources could significantly hinder the applications of ZnO nanolasers in view of the overall cost, complexity, and incompatibility for chip-level integration.We report in this conference the two-photon absorption (TPA)-induced room-temperature lasing performance of ZnO nanowires. Under femtosecond pulse-excitation at λ=700nm, a remarkably low threshold of 160µJ/cm2 was observed for the TPA-induced lasing action, which is of the same order of magnitude as was measured for the linear lasing process. Time-resolved photoluminescence characterization of two-photon pumped ZnO nanowires reveals the presence of a fast decay (3-4 ps) in the stimulated emission as compared to the slow decay (50-70 ps) for the spontaneous emission. The TPA process in ZnO nanowires was characterized with the nonlinear transmission measurement, which uncovers an enhanced TPA coefficient, about 14.7 times larger than that of bulk ZnO samples. The observed TPA enhancement in ZnO nanowires accounts for the low threshold lasing behavior, and has been attributed to the intensified optical field confined within the nanowire waveguides.
JJ10: Poster Session: Carbon Nanostructure Processing
Session Chairs
Prabhakar Bandaru
Sonia Grego
Ian Kinloch
Wednesday AM, December 03, 2008
Exhibition Hall D (Hynes)
9:00 PM - JJ10.1
Surface Oxidation of Single-walled Carbon Nanotubes with Oxygen Atoms.
Luciana Oliveira 1 , Thomas Debies 2 , Gerald A. Takacs 1
1 Chemistry, Center for Materials Science and Engineering, RIT, Rochester, New York, United States, 2 , Xerox Corporation, Webster, New York, United States
Show Abstract Liquid-phase oxidizing agents are often used to surface oxidize carbon nanotubes in order to achieve adhesion to the nanotubes. Gas-phase oxidation processes would eliminate liquid waste and may assist with the manufacture of nanoelectronic devices. Single-walled carbon nanotube (SWNT) powder was surface oxidized with gaseous oxygen atoms produced by low-pressure (1) plasma-generated vacuum UV (VUV) photo-oxidation (λ= 104.8 and 106.7 nm) and (2) microwave plasma discharge of an Ar-O2 mixture in the absence of radiation from the plasma. X-ray Photoelectron Spectroscopy (XPS) was used to detect the carbon- and oxygen-containing functional groups in the top 2-5 nm of the sample’s surface. The results are compared to our previous results using atmospheric pressure, UV photo-oxidation (λ= 184.9 and 253.7 nm) where ozone was primarily reacted with SWNT powder [1] and SWNT paper [2].1. M. Krysak, A. Jayasekar, B. Parekh, L. Oliveira, T. Debies, K. S. V. Santhanam, R. A. DiLeo, B. J. Landi, R. P. Raffaelle and G. A. Takacs, presented at the Sixth International Symposium on Polymer Surface Modification, Cincinnati, OH, June 11-13 (2007) in: Polymer Surface Modification: Relevance to Adhesion, K. L. Mittal (Ed.), VSP/Brill, Leiden, accepted for publication (2008).2. B. Parekh, T. Debies, C. M. Evans, B. J. Landi, R. P. Raffaelle and G. A. Takacs, Mater. Res. Soc. Symp. Proc. 887, 3-8 (2006).
9:00 PM - JJ10.10
Single Wall Nanotube Type-specific Functionalization and Separation.
Peter Boul 1 , Pavel Nikolaev 1 , Edward Sosa 1 , Sivaram Arepalli 1 , Leonard Yowell 1
1 , NASA, Houston, Texas, United States
Show AbstractMetallic single-wall carbon nanotubes were selectively solubilized in THF and separated from semiconducting nanotubes. Once separated, the functionalized metallic tubes were defunctionalized to restore their metallic band structure. Absorption and Raman spectroscopy of the enriched samples support conclusions of the enrichment of nanotube samples by metallic type.
9:00 PM - JJ10.11
Centerline Placement and Alignment of Single Carbon Nanotubes In Cylindrical Droplets of Nanometer Diameter.
Richa Sharma 1 , Michael Strano 1
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractThe hydrodynamic flow patterns inside high aspect ratio evaporating cylindrical droplets have utility for parallel alignment, positioning and placement of nanoparticles. We successfully create ~200 nm diameter cylindrical droplets for the first time using alternating hydrophobic and hydrophilic SAM layers made by a micro-contacting printing technique. We find that as the diameter of the droplet is reduced below 1000 nm (950-175 nm), a reversal of the internal flow is evident with highly accurate parallel alignment and placement of single walled carbon nanotubes along the centerline with 95 % precision. In contrast deposition is along the edges for droplets larger than 3 μm in diameter. This flow reversal is a direct consequence of the evaporation mode switching for the narrow droplets. A model is developed to describe the transition from radially outward to inward flow. This technique should be useful for precisely aligning and placing individual or bundled anisotropic nanoparticles (i.e. carbon nanotubes) with arbitrary surface chemistries.
9:00 PM - JJ10.12
Aggregation Kinetics of Novel Carbon Nanotube and Ruthenium Metallodendrimer Supramolecular Assemblies Under Various Solvent Conditions.
Michael Forney 1 , Andrea Giordano 2 , Jordan Poler 1
1 Department of Chemistry, University of North Carolina at Charlotte, Charlotte, North Carolina, United States, 2 , Pennsylvania State University, State College, Pennsylvania, United States
Show AbstractSingle Walled Carbon Nanotubes (SWCNTs) show effective binding with varying ruthenium complexes in N, N-Dimethylformamide (DMF). Enantiomerically pure ruthenium metallodendrimer [Λ6Δ3Λ-Ru10]20+[PF6-]20 (Ru(dec)) is shown to bind strongly and specifically to the SWNTs. Our previous studies show that in varying concentrations of coagulants, stable dispersions of carbon nanotubes aggregate and flocculate. The critical coagulation concentrations (CCC) have been determined for +1, +2, and +3 inorganic salts, the +2 Ru(phen)3, and the +20 ruthenium coagulants. It has been found that the water content of DMF is significant and modifies the CCC. Our current studies investigate the effect of water in DMF on the CCC for varying ruthenium oligomers as a function of morphology and charge state. The CCC is studied using UV-Vis spectroscopy. Analysis of current theoretical models is given with regard to these experimental data. Multiparticle interactions and solvent effects will be discussed. Potential applications toward 3-dimensional nano-manufacturing will be discussed.
9:00 PM - JJ10.13
Solution-Plasma Synthesis of FePt Nanoparticles Supported onto CNTs.
Kyoung-hee Lee 1 , Nagahiro Saito 1 , Osamu Takai 1
1 , Nagoya University, Nagoya Japan
Show Abstract9:00 PM - JJ10.14
Transparent and Conducting Uniform Solution Processed Reduced Graphene Oxide Thin Films for Large Area Electronics.
Goki Eda 1 , Giovanni Fanchini 1 , Manish Chhowalla 1
1 , Rutgers University, Piscataway, New Jersey, United States
Show Abstract9:00 PM - JJ10.15
Synthesis of Isolated Graphene Sheets and its Application in Composite Materials.
Yongchao Si 1 , Edward Samulski 1
1 Chemistry Department, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Show Abstract9:00 PM - JJ10.16
Controlled Carbon Nanostructures Fabricated by Electrical Pulse Induced Evaporation Method.
Hyunjung Kim 1 , Hyeyun Park 1 , Hyunwook Kim 1 , Sikyung Choi 1
1 Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of)
Show Abstract9:00 PM - JJ10.17
Probing the Crystallographic Orientation of Graphene by Raman Spectroscopy.
Mingyuan Huang 1 , Hugen Yan 1 , Changyao Chen 1 , Tony Heinz 1 , James Hone 1
1 , Columbia University, New York, New York, United States
Show Abstract9:00 PM - JJ10.18
Electron Backscatter Diffraction Pattern Measurements of Grain-size of Multi-layer Graphene Grown by Low Temperature CVD for Future LSI Graphene Interconnects.
Motonobu Sato 1 2 5 , Mizuhisa Nihei 1 2 5 , Daiyu Kondo 1 2 5 , Shintaro Sato 1 2 5 , Yuji Takakuwa 3 5 , Eiji Ikenaga 4 5 , Mari Ohfuti 2 , Yuji Awano 1 2 5
1 Nanotechnology Research Center, Fujitsu Laboratories LTD, Atsugi Japan, 2 , Fujitsu Limited, Atsugi Japan, 5 , CREST-JST, Tokyo Japan, 3 , Tohoku Univ., Sendai Japan, 4 , JASRI, Hyogo Japan
Show Abstract9:00 PM - JJ10.19
In-situ Edge Formation and Edge Motion of Graphene Nanoribbons by Joule Heating.
Xiaoting Jia 1 , Mario Hofmann 2 , Jessica Campos-Delgado 3 , José Manuel Romo-Herrera 3 , Hyungbin Son 2 , Ya-Ping Hsieh 2 , Alfonso Reina 1 , Jing Kong 2 , Mauricio Terrones 3 , Mildred Dresselhaus 2 4
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Advanced Materials Department, IPICYT, San Luis Potosí, San Luis Potosí, Mexico, 4 Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractEdge study in graphene nanoribbons has attracted lots of interest in recent years, due to the different electronic properties of the ribbons arising from zigzag and armchair edges. Here we demonstrate a crystallization process of graphite nanoribbons by joule heating inside a TEM-STM integrated system. During the joule heating process, the resistance continuously drops, the layers of graphite evaporate and a few-layered graphene ribbon is formed. After Joule annealing, long smooth edges and edge arrays are formed, most of which are in either a zigzag or armchair configuration. Detailed study of the edge evolution and motion confirmed that both current and joule heating are playing a role in the edge formation. This work shows the possibility of self-eliminating defects by applying a high bias, and an effective way to produce clean zigzag and armchair edges, which could be useful for both fundamental study and future electronics applications. *Support for this work was provided by NSF-NIRT Grant number CBET-05-06830.
9:00 PM - JJ10.21
Theoretical Study of Single Graphene-like Semiconductor Layer Made of Si and Transition Metal Atoms.
Takehide Miyazaki 1 , Noriyuki Uchida 2 , Toshihiko Kanayama 3
1 Research Institute for Computational Sciences, AIST, Tsukuba Japan, 2 Nanodevice Innovation Research Center, AIST, Tsukuba Japan, 3 Nanodevice Innovation Research Center, AIST, Tsukuba Japan
Show AbstractA recent trend in downsizing of field effect transistors (FETs) is pointing sub-10-nm regimes, where the physical gate length and channel thickness should be ~6 nm and less than ~2nm, respectively [1]. The fabrication of those aggressively miniaturized FETs should be performed with atomic scale accuracies. This has prompted researchers to envisage bottom-up approaches that introduce new materials with one dimensional and two dimensional anisotropies. Graphene is a typical example of two dimensional materials, which has been extensively studied as a candidate for the channel layer in the ultra-scaled FETs [2]. It is semimetallic in nature while the FET channel regions should be semiconducting. Although several experiments have demonstrated that graphene bilayers can be semiconducting by the application of electric field [3,4] or by cutting into nanoribbons [5,6], it is worth attempting to search for other layered materials, particularly those mainly composed of Si.A purpose of this theoretical study is to propose Si-based ultra-thin semiconductor layers as a possible candidate for channel regions of nano-scale FETs. We have so far studied Si thin films resembling the graphene bilayers, in which transition metal atoms are intercalated. We have shown that (MoSi12)n and (ZrSi12)n have the energy gaps of ~0.5 eV and ~0.3 eV, respectively, in generalized gradient approximation (GGA) to density functional theory (DFT) [7,8]. The structure of these films are characterized by the MSi12 building blocks (M: transition metal atom) which have a hexagonal prism shape with the M atom inside of the prism cavity [9].In the present study, we show that it is possible to make a semiconducting state even in a single graphene-like Si layer, provided that the transition metal atoms are attached to the Si layer. For example, we have found that a (MoSi6)n film has the indirect GGA band gap of ~0.3 eV. The structure is obtained by removing a six-membered ring of Si in the unit cell of (MoSi12)n mentioned above and relaxing the positions of all remaining atoms. The thickness of this film is ~0.2 nm. Three highest valence and three lowest conduction bands across the energy gap are both characterized by the mixture of the d components of Mo and the p components of Si6. This suggests that the gap opening is mainly due to a substantial overlap among these orbitals. [1] International Technology Roadmap for Semiconductors, SIA, EECA, EIAJ, KSIA, TSIA, 2005.[2] K. S. Novoselov et al., Science 306, 666 (2004).[3] T. Ohta et al, Science 313, 951 (2006).[4] J. B. Oostinga, et al., Nature Mat. 7, 151 (2008).[5] X. Wang et al., Phys. Rev. Lett 100, 206803 (2008).[6] X. Li et al., Science 319, 122 (2008).[7] T. Miyazaki and T. Kanayama, Mater. Res. Soc. Proc. 0958, L01-07 (2007).[8] T. Miyazaki and T. Kanayama, Appl. Phys. Lett. 91, 082107 (2007).[9] H. Hiura, T. Miyazaki and T. Kanayama, Phys. Rev. Lett. 86, 1733 (2001).
9:00 PM - JJ10.22
Atomistic Fracture Mechanisms of Graphene Sheets under Mode I Loading.
Dipanjan Sen 1 , Markus Buehler 2
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe recent development of technologies based on the use of individual graphene sheets has sparked much interest in their applications in the micro- and nanotechnologies, for example due to their exceptional electronic properties. Their high thermal conductivity, along with crystallinity and mechanical strength also makes them good candidates for composite materials with integrated mechanical and thermal applications. The study of the mechanics of defects in graphene sheets, such as cracks, under loading is essential to understand atomistic mechanisms and failure strength of the material. Here we study crack mechanisms in graphene sheets under mode I loading through direct atomistic simulation. We report a detailed analysis of fracture propagation mechanism, including the formation of metastable defects at crack tips that strongly influence crack dynamics.
9:00 PM - JJ10.23
Silica Nanocoils Induced by Partial Melting of Co3O4 Cubic Nanoparticles at Lower Temperature.
Yongquan Qu 1 , Daniel Masiel 1 , Ting Guo 1
1 Chemistry Department, UC Davis, Davis, California, United States
Show AbstractTo understand the interface between nanoparticle catalyst and 1D nanostructure is the key to control growth of nanomaterials. We have explored the growth of silica nanowires and silica nanocoils by using different nanoparticle catalysts under various conditions. It was discovered that lower temperature (1050 deg C) tends to catalyze the growth of nanocoils and higher temperature (1100 deg C) favors the formation of straight silica nanowires. Besides the temperature, the size of nanoparticles catalysts can affect the synthesis of nanostructures. For 3 nm cobalt nanoparticles, only a small amount of silica nanocoils (below 5% yield) was synthesized under 1050 deg C. Large nanoparticle catalysts tend to high yield of nanocoils. Using 60 nm cubic Co3O4 nanoparticles, large quantity of silica nanocoils (100% yield) was synthesized at 1050 deg C. At 1100 deg C, straight nanowires were formed by using the same cubic Co3O4 nanoparticles. The most important difference between nanocoils and nanowires is the nanoparticles at the tips of coiled nanowires are faceted, whereas those at the tips of straight silica nanowires are spherical. Based on experimental results, a growth mechanism of nanocoils is proposed. At 1100 deg C the nanoparticles completely melt (isotropic or spherical), causing straight silica nanowires to grow. At lower temperatures, the nanoparticles are only partially molten, leading to be highly anisotropic, which promotes the synthesis of silica nanocoils. The nanocoils have non-circular cross sections and the edges are clearly visible in each nanocoil, suggesting that these non-cylindrical nanocoils have sharp edges. The anisotropic and faceted nanoparticle catalysts caused this non-cylindrical cross section of silica nanocoils.
9:00 PM - JJ10.24
Fabrication of Helical and Post Nanotube Arrays.
Zhifeng Huang 1 , Ken Harris 2 , Michael Brett 1 2
1 Electrical and Computer Engineering , University of Alberta, Edmonton, Alberta, Canada, 2 , National Institute for Nanotechnology, Edmonton, Alberta, Canada
Show AbstractA new method to grow nanotube arrays derived from GLAD (Glanced Angle Deposition) porous films on silicon wafers has been developed recently. Combining the control of deposition angle and substrate motion, GLAD employs e-beam evaporation to deposit porous films composed of a matrix of individual columns with different shapes, e.g. slanted post, chevron, helix and vertical post. Serving as a template, GLAD porous films are covered with a second layer of material using Low Pressure Chemical Vapor Deposition (LPCVD) and Atomic Layer Deposition (ALD). After ion milling to unveil the GLAD columns on their tops, an appropriate etchant is used to wet-chemically dissolve the internal GLAD columns and leave the tube arrays standing on the wafer. The approach has been demonstrated for the fabrication of tube arrays (a-Si, poly-Si, nitride) with the shape of vertical post and helix. For example, a-Si post tubes, with lengths of 1 to 2 μm, have an interior diameter of 149±64 nm and a tube thickness of 60.5±7.2 nm, which can be adjusted by LPCVD reaction time. The planar post tube density in the array is 8.8 μm-2. An extension of this technique has been demonstrated earlier in the fabrication of perforated thin films.(1) The nanotube arrays could potentially have application in biosensors, optics, storage and energy devices. The initial characterization of structural, mechanical and optical properties of the tube architecture will be reported.Reference:1. A.L. Elias, K.D. Harris, M.J. Brett, J. Microelectromechanical Systems, 13, (2004) 808
9:00 PM - JJ10.25
Synthesis and Formation Mechanism of Light Emitting ZnO Nanobrushes.
Shubra Singh 1 , Mamidanna Rao 1
1 Department of Physics, Materials Science Research Centre and Nano Functional Materials Technology Centre, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India
Show Abstract9:00 PM - JJ10.26
Mass-Productive Synthesis of Free-Standing ZnO Nanotripods in a Thermal Chemical Deposition Process.
Min-Yeol Choi 1 , Hyun-Kyu Park 1 , Jae-Young Choi 2 , Sang-Woo Kim 1
1 School of Advanced Materials and System Engineering, Kumoh National Institute of Technology, Gumi Korea (the Republic of), 2 , Samsung Advanced Institute of Technology, Yongin Korea (the Republic of)
Show AbstractRecently, ZnO multipod nanostructures have attracted much attention recently due to many advantages of free-standing ZnO multipod nanostructures in networked or branched nano-scale device applications. For example, branched nanostructures provide enhanced electron extraction in inorganic-organic hybrid photovoltaic devices due to their more large surface area compared with one-dimensional nanostructures such as nanowires and nanotubes. Moreover, the multipod structure is strongly effective to realize the formation of branched or linear homo/hetero-junctions by self-assembly in successive growth processes, leading to arbitrary branching nanostructure building blocks. Especially, a number of research works regarding the synthesis and characterization of ZnO nano-scale tetrapod structures were reported because the tetrapod structure is the simplest, while ZnO tripod nanostructures were rarely investigated. Thus, formation mechanism and characteristics of ZnO tripod nanostructures are not clear. In this presentation, we report mass production of free-standing ZnO nanotripods obtained by thermal chemical vapor deposition without introduction of catalysts and substrates. Three arms of ZnO nanotripods had lengths ranging from 300 nm – 1.0 μm and a single-crystalline hexagonal structure. It was found that an inverted triangle-shaped zinc-blende ZnO core is located at the center of the grown ZnO nanotripod and a twin structure exists at the interface between each arm. The three arms with extremely narrow diameters below 20 nm were grown along to the [0001] c-axis and the twin boundary was identified as (01-13). ZnO nanotripods exhibited a relatively weak deep-level emission band as well as strong near band-edge emission in the room-temperature photoluminescence measurement, indicating the high optical quality and low defect density of the ZnO nanotripods.
9:00 PM - JJ10.28
Single Crystalline Boron Nanocones.
Xing Jun Wang 1 2 , Jifa Tian 1 , Tianzhong Yang 1 , Lihong Bao 1 , Cao Hui 1 , Chengmin Shen 1 , Hongjun Gao 1
1 , Institute of Physics, Chinese Academy of Sciences, Beijing China, 2 , University of Electro-communications, Tokyo Japan
Show Abstract9:00 PM - JJ10.29
Thermally-Induced GaSb Core-Shell Nanofibers: Evidence of Nanoscale Phase Instability.
Alejandro Perez-Bergquist 1 , Kai Sun 2 , Yanwen Zhang 3 , Lumin Wang 1 2
1 Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Ann Arbor, Michigan, United States, 3 , Pacific Northwest National Laboratories, Richland, Washington, United States
Show AbstractIon irradiation of GaSb is known to form porous nanostructures that upon a high enough ion dose can form dense networks of distinct nanofibers. The irradiation induced nanofibers show potential for exciting applications in nanoscale optoelectronic devices, but the nanofibers, which are amorphous as a result of radiation damage, need to be crystalline for implementation in a variety of devices. In this study, we investigate the crystal structure and composition of GaSb nanofibers before and after thermal annealing.Both unannealed and annealed fibers were analyzed primarily by transmission electron microscopy (TEM) techniques. TEM analysis revealed that the as-formed fibers were mostly amorphous, although the fibers contained some small, discrete nanocrystals, and the fibers contained a uniform distribution of Ga and Sb with some slight surface oxidation. Thermal annealing of the fibers was performed at 250°C for 600 seconds in an oxygen-free environment, and the annealed fibers were also analyzed via TEM techniques. Interestingly, the annealed fibers showed selective recrystallization of the cores over the shells. In addition, spectroscopy techniques revealed the crystalline fiber cores were composed of pure Sb, while the amorphous shells were composed of gallium oxide.Bulk GaSb does not exhibit any anomalous annealing behavior, and low temperature annealing of amorphous GaSb should result in uniform, crystalline β-phase GaSb. Our data suggests that the observed core-shell fiber formation process is a function of size-dependent oxidation, evaporation, and diffusion effects that only become significant at the nanoscale. Due to their small size, the GaSb fibers are able to oxidize rapidly in air at room temperature to a proportionately high extent. Similarly, during the annealing process, the small size of the fibers leads to a large loss of volatile Sb through evaporation, even at very low temperature, leading to a fully Sb-depleted shell. Finally, the small size of the fiber core allows Ga, which is highly mobile in GaSb, to quickly diffuse from the core to the core-shell interface and react with excess oxygen. The result is a thermally-induced, size-dependant nanoscale phase separation process that results in core-shell antimony-gallium oxide nanofibers.
9:00 PM - JJ10.3
Functionalization of Metal Nanoparticle-Decorated Single-Walled Carbon Nanotubes.
Yi Lin 1 , John Connell 2
1 , NASA Postdoctoral Fellow, Hampton, Virginia, United States, 2 Advanced Materials and Processing Branch, NASA Langley Research Center, Hampton, Virginia, United States
Show AbstractMetal nanoparticle-decorated single-walled carbon nanotubes (SWNTs) were prepared in a facile process at gram-quantity level using the corresponding metal acetate as the thermal decomposable precursor. The resultant nanohybrid could be readily functionalized with organic molecules such as octadecylamine (ODA) or amine-terminated oligomeric polyethylene glycol (PEG) in procedures similar to those used for neat nanotubes without metal nanoparticles attached. The solubilities of the nanohybrids in organic solvents and/or water were significantly enhanced as a result of functionalization, enabling solution processing for a variety of electrical and catalytic applications. The preparation and characterization of these materials will be presented.
9:00 PM - JJ10.30
Synthesis of β-Ga2O3 Nanowires and Nanobelts using GaAs Evaporation.
Seoung-Bum Son 1 , Seul Cham Kim 1 , Hee-Suk Chung 1 , Do Hyun Kim 1 , Kyu Hwan Oh 1
1 , Seoul National Univ., Seoul Korea (the Republic of)
Show Abstract One dimensional nanostructured materials based on bottom-up paradigm can exhibit unique optical, electronic, and structural properties as compared to their bulk forms owing to quantum confinement effects and a high fraction of chemically similar surface sites. These remarkable physical and chemical properties due to their unique size and dimensionality have drawn extensive attraction. Among various 1D nanostructures, monoclinic(β)-Ga2O3, a wide-band gap compound with a band gap of approximately 4.9eV at room temperature, is a promising transparent conductor for the coming generation of optoelectric devices in the deep-ultraviolet wavelength region. Recently, β-Ga2O3 have been synthesized via arc discharge, laser ablation, powder evaporation, etc. However, little literature is only available with regard to understanding the vapour-liquid-solid (VLS) via oxygen atmosphere on β-Ga2O3 nanowires synthesis. In this letter, we report fabrication and characterization of β-Ga2O3 nanowires synthesized through GaAs physical evaporation. As-synthesized nanowires were characterized with scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman analysis. This work was supported by the Korea Science and Engineering Foundation (KOSEF) granted by the Korea government (MOST) (No.R11-2005-065).
9:00 PM - JJ10.31
Electrochemical Growth of Copper Nanobelts.
TingKai Huang 1 , Ta-Ming Cheng 1 , I-Chung Chang 1 , Chi-Young Lee 2 , Hsin-Tien Chiu 1
1 Applied Chemistry, National Chiao Tung University, HsinChu Taiwan, 2 Center for Nanotechnology, Materials Science and Microsystems, National Tsing Hua University, HsinChu Taiwan
Show AbstractWe demonstrated previously the growth of Cu nanobelts (NBs) on Al(s) surface from galvanic reduction of Cu2+(aq) by Al(s) in the presence of cetyltrimethylammonium chloride (CTAC) and HNO3(aq). Now we have modified the process so that Cu NBs can be deposited electrochemically on printed carbon electrodes at 2.0 V at 290 K. The average width, thickness and length of the NBs were about 50 nm, 20 nm and several tens of micrometers, respectively. Microstructure characterization indicated that the NB’s basal plane was {111} and growth direction of the NB was along [-110] direction. The belt width could be adjusted by varying the reaction mixture concentration and the applied potential. Other experimental conditions, such as temperature, presence or absence of CTAC and HNO3, also affected NB growth. Cyclic voltammetric (CV) experiments showed that the Cu NB electrode could enhance glucose oxidation ability. This is an essential character for a high-sensitivity glucose sensor.
9:00 PM - JJ10.33
Tailoring Conductivity of Carbon Nanotubes Network by Selective Oxidation with Halogen Oxoanions.
Seon-Mi Yoon 1 , Sung Jin Kim 2 , Hyeon-Jin Shin 1 2 , Anass Benayad 1 , JongMin Kim 1 , Young Hee Lee 2 , Jae-Young Choi 1
1 , Samsung Advanced Institute of Technology, Yongin-Si, Gyunggi-do, Korea (the Republic of), 2 , Sungkyunkwan University, Suwon, Gyeonggi-do, Korea (the Republic of)
Show AbstractChlorine oxoanions with the chlorine atom at different oxidation states were introduced in an attempt to systematically tailor the electronic structures of single-walled carbon nanotubes (SWCNTs). The degree of selective oxidation was controlled systematically by the different oxidation state of the chlorine oxoanion. Selective suppression of the metallic SWCNTs with a minimal effect on the semiconducting SWCNTs was observed at a high oxidation state. The adsorption behavior and charge transfer at a low oxidation state were in contrast to that observed at a high oxidation state. These results concurred with the experimental observations from X-ray photoelectron spectroscopy. In general, the sheet resistance of the random network SWCNTs is determined by the sum of resistances of the intrinsic SWCNT network and tube-tube contact. The tube-tube contact is composed of metal-metal and semiconductor-semiconductor junctions that give ohmic behavior, and a metal-semiconductor junction that forms a Schottky barrier. The conversion of metallic SWCNTs to semiconducting ones at high oxidation state might result in an increase in the resistance of the intrinsic SWCNTs but reduces the contact resistance significantly by decreasing the number of metal-semiconductor junctions. The sheet resistance of the SWCNT film decreased significantly at high oxidation states, which was explained in terms of a p-doping phenomenon that is controlled by the oxidation state.
9:00 PM - JJ10.34
Reactivity Enhancement via Defects on Carbon Nanotubes.
Seungmuk Ji 1 , Hyunung Yu 1 , Dong Han Ha 1 , Ja-Yong Koo 1
1 , Korea Research Institute of Standards and Science, Daejeon Korea (the Republic of)
Show AbstractWe have investigated acid reactivity enhancement of carbon nanotube film due to defect generation by confocal Raman spectroscopy measurement. A red-shift of tangential G-band in the Raman spectra is observed for carbon nanotubes suggesting defects generated by thermal heating in ambient air flow. In contrast, G-band is blue-shifted by acid treatment due to chemical doping effect. The defects on carbon nanotubes can function as binding sites of acid molecules which give carriers to nanotubes. As a result, defective carbon film shows good conductivity than the pristine one after acid treatment. Features in the Raman spectra have been identified and assigned to doping status of single-walled carbon nanotube. Implications on the effects of acid treatment on carbon nanotube film and its reactivitiy will be also discussed.
9:00 PM - JJ10.35
Photon Enhanced Aggregation in Metallodendrimer ``Docked" Single Walled Carbon Nanotubes.
Harsh Chaturvedi 1 , Jordan Poler 1 2
1 Center for Optoelectronics and Optical Communications, UNCC, Charlotte, North Carolina, United States, 2 Chemistry, UNCC, Charlotte, North Carolina, United States
Show AbstractSingle Walled Carbon Nanotubes (SWNT) has been shown to have significant potential as a material for applications in optoelectronics and photovoltaics. The presence of delocalized π electrons in nanotubes makes them interesting materials for applications involving charge transfer and charge transport. We will be presenting “mechanical docking” of an optically active rigid molecule, ruthenium metallodendrimer (decamer) to single walled carbon nanotubes with some diameter selectivity. Atomic force and scanning electron micrographs indicating binding of these molecules specifically to the end of nanotubes have been reported earlier. Near-IR absorption and radial breathing mode Raman spectra of these “end-functionalized” SWNTs show preferential diameter-selective separation, along with a red-shift of the optical transitions. A concentration dependent red-shift is observed for the NIR absorption for decamer bound nanotubes. Spectral shifts and intensity variations in specific radial breathing mode bands of the functionalized SWNTs are consistent with our observations of the UV-Vis-NIR absorption spectra and AFM data; indicating strong interaction between selective SWNTs and the decamer. These supramolecular systems absorb strongly in the UV and provide a rigid stable architecture for the desired nanostructures. This mechanical rigidity provides structural advantages over polymer and nucleic acid wrapping which are too flexible to sustain a morphologically rigid assembly. Effects of this binding mechanism on the electrical, vibrational and structural properties of the nanotubes will be presented. Moreover, we observe a photon enhanced aggregation of dispersed single walled carbon nanotubes in the presence of electron transfer reagents. Upon optical excitation, of the metal to ligand charge transfer absorption, of various ruthenium complexes, the nanotubes rapidly coagulate. Our electron transfer mechanism is consistent with observed photon enhancement process. Photon induced aggregation of selective nanotubes and using optical excitations for controlled self-assembly of these nanotubes indicate a novel paradigm for building supramolecular assembly “bottom – up”. Field effect transistors using these functionalized SWNTs have been fabricated and characterized. Their potential application as an optoelectronic device and sensor will also be discussed. Kinetics of this photon enhanced aggregation phenomenon is understudy and will be presented.
9:00 PM - JJ10.36
A Novel Method to Fabricate Carbon Nanotube AFM-Probes using the Langmuir-Blodgett Technique.
Jae-Hyeok Lee 1 , Won-Seok Kang 1 , Hyo-Sop Kim 1 , Jae-Ho Kim 1 , Kwang-nak Koh 2
1 Molecular Science and Technology, Ajou University, Suwon Korea (the Republic of), 2 Department of Nanomedical Engineering, Pusan National University, Miryang Korea (the Republic of)
Show Abstract9:00 PM - JJ10.37
Geometrical Factor Dependent Brewster Angle Shift of Silicon Nano-Pillars.
Fan-Shuen Meng 1 , Yi-Hao Pai 1 , Gong-Ru Lin 1
1 Graduate Institute of Photonics and Optoelectronics, National Taiwan University , Taipei Taiwan
Show Abstract9:00 PM - JJ10.38
Self-aligned Growth of Single-walled Carbon Nanotubes using Optical Near-field Effects.
Yunshen Zhou 1 , Wei Xiong 1 , Masoud Samani 1 , Weiqing Yang 1 , Kaijun Yi 1 , Xiangnan He 1 , Yong Feng Lu 1
1 Electrical Engineering, University of Nebraska, Lincoln, Nebraska, United States
Show AbstractDue to the superior electronic and physical properties, single-walled carbon nanotubes (SWNTs) are ideal candidates for fabricating next-generation electronics. Since the first SWNT-based field-effect transistor (FET) was reported, tremendous efforts have been devoted to the study of SWNT-based devices. Two approaches are generally used to fabricate SWNT devices. One is post-growth manipulation, which requires exquisite equipment hence is time consuming. The other approach is in-situ growth which involves the controlled growth of SWNTs on a pre-defined substrate. Compared with post-growth manipulation, in-situ growth is more suitable for large-scale device fabrication. Nevertheless, precise control of SWNT growth remains to be a key issue for industry-scale applications. In this study, we introduced a novel strategy using optical near-field effects for controlled SWNT growth. Due to the optical near-field effects, significant optical field enhancement occurs at the electrode tip apexes and induces localized high temperatures at the tip apex areas, which stimulate the selective growth of SWNTs bridging the tip apexes. Numerical simulation using High-frequency Structure Simulator demonstrates that the local temperatures can reach one order of magnitude higher at the tip apexes than the rest of the electrodes. The technique promises mass production of next-generation SWNT-based electronics at low substrate temperatures in a precisely-controlled manner.
9:00 PM - JJ10.39
Single-Walled Carbon Nanotube Networks with Precisely Runed Metal/semiconductor Ratios.
Jeff Blackburn 1 , Teresa Barnes 1 , Matthew Beard 1 , Chaiwat Engtrakul 1 , Bobby To 1 , Jeremy Bergeson 1 , Nikos Kopidakis 1 , Andrew Ferguson 1 , Timothy Coutts 1 , Michael Heben 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractTransparent, conductive networks of single-walled carbon nanotubes (SWNTs) are being studied extensively for possible application in solution processed solar cells, field effect transistors, touch-screens, and EMI shielding. In photovoltaic applications, the SWNTs can be utilized as the transparent conducting electrodes or as electron acceptors in polymer-based organic photovoltaic cells. Thus, understanding the fundamental electronic and optical properties of SWNTs is tantamount to producing efficient SWNT-based PV devices.A large number of factors affect the optical and electrical properties of a SWNT network, which is essentially a three-dimensional inter-connected network of quantum wires. These factors include the intrinsic resistance of SWNTs within the network, the resistance associated with junctions in between SWNTs, the specific optical signatures of the SWNTs, and the degree to which intentional and unintentional redox doping modifies each of these parameters. Additionally, when used as electron acceptors in polymer devices, the intrinsic band structure determines charge transfer energetics and efficiency. Underlying all of these aspects is the electronic poly-dispersity inherent in all SWNT samples of a given diameter range. Semiconducting (S-SWNTs) are characterized by optical gaps in the range of ~0.5 – 1.0 eV, with a complete absence of states within this gap, while metallic (m-SWNTs) have much larger optical gaps of ~2 – 2.5 eV with a non-zero density of states within this gap. In this presentation, we explore the fundamental electronic and optical properties of transparent, conductive SWNT films with precisely tuned ratios of s- and m-SWNTs. A combination of optical spectroscopy and electrical and optical conductivity measurements allows us to carefully evaluate the impacts of SWNT electronic structure and redox doping on the intrinsic SWNT resistance, inter-nanotube junction resistance, and ultimate performance of these thin film electrodes. We will also discuss the use of time-resolved terahertz spectroscopy to characterize the electrical properties of the SWNT films as a function of the various experimental parameters. This non-contact method provides complimentary information to the DC electrical measurements helps to provide a more complete mechanistic understanding of the opto-electronic film properties.Finally, we report on preliminary electrochemical and charge transfer measurements on the precisely tuned SWNT electrodes. These studies elucidate the charge transfer mechanisms for metallic and semiconducting SWNT networks with photo-excited molecules relevant to photovoltaics. As a whole, these studies guide the judicious selection of tailored SWNT mixtures for specific photovoltaic applications.J. L. Blackburn, T. M. Barnes, M. Beard, C. Engtrakul, T. J. McDonald, T. J. Coutts and M. J. Heben. ACS Nano, 2, 1266 (2008).
9:00 PM - JJ10.4
Effects of Fe2SiO4 Cluster Formation on the Electric Properties of Single Walled Carbon Nanotubes During Camera Flash.
Shih-Hao Tseng 1 , Nyan-Hwa Tai 1
1 Department of Materials Science and Engineering, National Tsing Hua University, Hsin-chu Taiwan
Show AbstractPhotoacoustic and ignition effects of fluffy single-walled carbon nanotubes (SWCNTs) under camera flash were reported in our previous work. It is found that heat converted from flash may ignite carbon nanotubes (CNTs) depending on the amount of iron catalyst involved in the material system. Under flash exposure, local CNT temperature increases rapidly up to over 475 °C within 0.03 second, which results in the generation of an acoustic wave exceeding 110 db and the oxidation of the CNTs. It was also found that Fe2SiO4 particles covered with several layers of amorphous carbon were generated when unpurified CNTs were exposed under flash. Moreover, the ratio of disordered band (ID)and graphitized band (IG) in Raman spectrum varied indicating the change of CNT microstructure during flash exposure. Electric resistance of the SWCNT film extracted from the fluffy SWCNTs was in-situ measured during flash exposure. The electric resistance increases stepwise from 233.92 (original) to 422.61Ω after fifty flash exposures was detected, which is due to breakage of the conductive pathways between adjacent nanotubes. On the other hand, the amorphous carbon shells covered on Fe2SiO4 particles provide pathways for electron transport via hopping or tunneling. A detailed feasible mechanism on the influence of Fe2SiO4 particle formation on electric resistance variation of the SWCNTs will be discussed in this study.
9:00 PM - JJ10.40
Andreev Tunneling in Single and Bilayer Graphene.
Michele Zaffalon 1 , Joel Wang 1 , Pablo Jarillo-Herrero 1
1 Physics, MIT, Cambridge, Massachusetts, United States
Show Abstract9:00 PM - JJ10.41
Anharmonic Phonon Lifetimes in Graphene and Carbon Nanotubes.
Nicola Bonini 1 , Michele Lazzeri 2 , Francesco Mauri 2 , Nicola Marzari 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 IMPMC, Universités Paris 6 et 7, Paris France
Show AbstractIn this work we present a detailed first-principles investigation of the anharmonicphonon lifetimes in graphene and carbon nanotubes—a fundamental issue tounderstand and engineer the thermal and electronic transportproperties of these materials.The vibrational properties and the cubic anharmonic terms in theinteratomic potential are calculated using density-functional theoryand density-functional perturbation theory. These computationallydemanding calculations are performed on selected structures and theresults for carbon nanotubes of arbitrary dimensions and chiralitiesare obtained using an accurate anharmonic force field based oninternal coordinates and fitted on our ab initio data.Our results provide a microscopic characterization of the energyrelaxation processes and of the relative importance of the individualdecay channels. We will discuss the relevance of these findings tounderstand the thermal transport properties of these materials and toelucidate the role of non-equilibrium phonon populations in high-fieldelectronic transport.
9:00 PM - JJ10.42
Growth of InN Whiskers and Nanowires by Direct Reaction of Indium with NH3.
Gary Harris 1 , Josha Halpern 2 , James Mitchell 3 , Maoqi He 1
1 HNF, Howard University , Washington, District of Columbia, United States, 2 Department of Chemistry, Howard University, Washington, District of Columbia, United States, 3 Chemical Eng-CREST, Howard University, Washington, District of Columbia, United States
Show Abstract9:00 PM - JJ10.44
Synthesis of Iron(III) Phosphate Nanostructures and Their Lithium Electroactivities.
Gwang-Hee Lee 1 2 , Dong-Wan Kim 1 , Jae-Gwan Park 1 , Yun-Mo Sung 2
1 Nano-materials Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 2Department of Materials Science and Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractWe report on the preparation of iron(III) phosphates, FePO4 by a wet chemistry method involving two steps; formation of FePO4 2H2O (orthorhombic metastrengite–type hydrated iron phosphate) using a hydrothermal route without any templates or surfactants and subsequent thermal decomposition to FePO4 at 200oC. Initially, FePO4 2H2O nuclei are formed through the reaction of FeCl3 and PCl5 (or H3PO4) in an aqueous solution containing Na2SO4. The concentrations of each phosphate (PO43-) and chlorine ion (Cl-) play an important role on the crystallinity, morphology, and crystallite sizes of the FePO4 2H2O. Typical FePO4 2H2O powders are composed of microspheres of self-assembled nanorods with diameter of 50 nm and length of 200 nm. FePO4 2H2O is completely dehydrogenated and converted to the tridymite-type FePO4 at 200oC, and then transformed to another polymorph, quartz-type FePO4 at over 600oC preserving the initial morphology.The electrochemical properties of FePO4 2H2O and each FePO4 are evaluated using a cyclic voltammetry and galvanostatic cycling in the low-voltage range. The mechanism for the lithium electroactivities of FePO4 nanostructures is also discussed.
9:00 PM - JJ10.45
The Influence of Reaction Temperature on the Size of the Catalyst Nano-particle and the Carbon Nanotube Diameter Distributions.
Enkeleda Dervishi 1 2 , Zhongrui Li 1 , Yang Xu 1 , Viney Saini 1 2 , Fumiya Watanabe 1 , Alexandru Biris 3 , Dan Lupu 3 , Meena Mahmood 1 2 , Alexandru Biris 1 2
1 Nanotechnology Center, University of Arkansas at Little Rock, Little Rock, Arkansas, United States, 2 Applied Science Department, University of Arkansas at Little Rock, Little Rock, Arkansas, United States, 3 , Institute for Research and Development of Isotopic and Molecular Technologies, Cluj-Napoca Romania
Show AbstractNanotubes with narrow diameter distributions are excellent candidates for nano-electronic devices, and especially for field emitter transistors (FETs). High quality carbon nanotubes (CNTs) were synthesized on the MgO supported Fe-Co catalyst system using inductive Radio Frequency (RF) chemical vapor deposition method. In this work, methane was utilized as a hydrocarbon source and the reaction temperature was varied between 700 to 1000 oC. The influence of the temperature on the size of the metal nano-particles and the morphology of CNTs was systematically studied. The catalyst system Fe:Co:MgO (2.5:2.5:95 wt.%) was exposed to different temperatures and its structural and morphological properties were analyzed by Scanning Transmission Electron Microscopy (STEM), X-ray diffraction technique and surface area analyzer. It was found that as the temperature increases to 1000 oC, the nanotubes have a wider diameter distribution when compared to the ones grown at lower temperatures. These results correlated well with the STEM analysis of the catalyst system indicating a variation in the size of the active metal nanoclusters of Fe/Co. Furthermore, the morphological changes of the catalysts were directly found to influence the properties of the corresponding carbon nanotubes, as obtained from electron microscopy (SEM and TEM), Raman spectroscopy, and thermogravimetric analysis.
9:00 PM - JJ10.46
Highly Ordered Free-standing Magnetic Nanotubes.
Mats Boman 1 , Inna Soroka 1 , Anders Harsta 1 , Marten Rooth 1
1 Dep. of Materials Chemistry, Uppsala University, Uppsala Sweden
Show AbstractHighly ordered nanostructures of a wide variety of materials have been fabricated using nanoporous alumina as a template and the use of atomic layer deposition (ALD). The alumina template, which was synthesized as a membrane, was made by anodization of aluminium in two steps. The pores, typically 60 nm in diameter, were parallel and well ordered in a hexagonal pattern.ALD is a gas phase method, which can evenly coat the pore walls of nanoporous alumina. In ALD the precursors are not mixed but are introduced into the reactor in a sequential way. This means that the chemical reactions occur sequentially on adsorbed layers. In the present paper, different metal oxide nanotubes were manufactured by ALD using nanoporous alumina as a template. Results from single layered nanotubes of Nb2O5, Fe2O3 and TiO2 will be presented as well as results from multi-layered TiO2/Fe2O3 nanotubes.The magnetic characterization of the iron-containing multilayered nanotubes deposited at different temperatures was performed using Superconducting Quantum Interference Device (SQUID) magnetometer. The measurements reveal that the nanotubes exhibit weak ferromagnetism at room temperature and peculiar magnetic anisotropy behavior: The sign of the magnetic anisotropy energy (MAE) was shown to be strongly dependent on the temperature at which the samples were manufactured. Such magnetic behavior can be addressed to the varied structural properties/composition of the iron oxide nanotubes at different deposition temperatures.
9:00 PM - JJ10.47
Synthesis Mechanism of CeO2 Nanotubes under Alkaline Route.
Xusheng Wu 1 , Sibudjing Kawi 1
1 Chemical and Biomolecular Engineering, National University of Singapore, Singapore Singapore
Show AbstractCeO2 nanotubes have been successfully synthesized using hydrothermal synthesis method under alkaline route for the formation of Ce(OH)3 nanotubes, and then calcined at 450°C for 5 hours. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) have been applied to characterize the synthesized CeO2 nanotubes. TEM images show that CeO2 nanotubes have outer diameters ranging from 30 nm to 70 nm, and inner diameters ranging from 20 nm to 30 nm. Furthermore, based on TEM images, two forms of growth mechanism for CeO2 nanotubes have been observed: upward growth over Ce(OH)3 compound and simultaneous multidirectional growth on one core.
9:00 PM - JJ10.5
Optical Properties of Nanoparticle-doped Liquid Crystals.
Richard Osgood 1 , Brian Kimball 1 , Diane Steeves 1 , Lauren Belton 1 , Nagarajan Ramanathan 1 , Gary Walsh 1 , James Welch 1
1 , US Army NSRDEC, Natick, Massachusetts, United States
Show AbstractLiquid crystals are anisotropic fluids exhibiting orientational order, whose director can be controlled with an applied electric field. Nanoparticles, such as carbon nanotubes, have been shown to align with the liquid crystal molecules in the nematic phase, and the addition of nanoparticles has the potential for modifying the liquid crystal’s electro-optical properties. Previous studies have shown modifications of the liquid crystal’s nematic-isotropic phase transition temperature by the addition of carbon nanotubes. We have dispersed single-wall and multi-wall carbon nanotubes in liquid crystal cells at the level of 0.1% by weight, and discuss techniques for debundling the nanotubes. We find that carbon nanotubes, added to liquid crystal cells, enhance linear and nonlinear transmission in the blue-green part of the visible spectrum. We study experimentally the effect of the dispersed nanotubes on the nematic-isotropic phase transition of various liquid crystals, induced by visible-light illumination and/or electric fields.
9:00 PM - JJ10.6
Sorting Carbon Nanotubes by Number of Sidewalls.
Sungwoo Yang 1 , Jie Liu 1
1 Chemistry, Duke University, Durham, North Carolina, United States
Show AbstractCarbon nanotubes (CNTs) have fascinated numerous scientists over the last two decades due to their outstanding material properties, such as high electric conductivity and high Young’s modulus. These electronic and mechanical properties vary with the type of CNT depending on the diameter and the number of sidewalls. Over the last decade, many methods have been developed to control the type of CNT and its diameter to some degree. However, structural heterogeneity in terms of diameter and the number of sidewalls is still unavoidable. Therefore, the separation of CNTs in terms of diameter and the number of sidewalls is one of the great challenges to realize CNT’s applications, including CNT composite and transparent conductive films. Recently, several methods to sort CNTs by their diameter have been reported. However, sorting CNTs by their number of sidewalls has not been reported yet. Hereby, we report sorting CNTs by their number of sidewalls, such as single, double and triple walled carbon nanotubes (SWNTs, DWNTs and TWNTs). In our report, UV-vis NIR, Raman and TEM were used to study different types of CNT. Furthermore, comparative studies in terms of transparent conductive coating and material strength were also conducted on different types of CNT. Few walled carbon nanotubes (FWNTs) were synthesized by chemical vapor deposition method using a metal mixture of cobalt and molybdenum, supported by titanium silicalite (TS-1). Ethanol was a carbon feeding source. After purifying steps, including oxidation in the air and treatment with NaOH, highly pure FWNTs were successfully synthesized, and the major species of as-synthesized CNTs were DWNTs and TWNTs. Well dispersed CNT solutions were achieved using the surfactant sodium cholate. The density gradient separation method using ultracentrifugation was used to sort FWNTs by their number of sidewalls. UV-vis NIR, Raman and TEM were studied to distinguish different types of CNTs. These studies were used to demonstrate sorting of synthesized CNTs by their number of sidewalls. In addition, spectroscopic study of TWNTs is valuable due to its scarcity. Furthermore, uniform transparent films with various types of CNT were produced by the spraying method. The conductivity of each uniform transparent film was measured to demonstrate different electrical properties of various types of CNTs. DWNT shows the best conductivity compared to other types of CNT. This result confirms DWNT as the best candidate for conductive films application. In addition, Young’s modulus on various types of CNTs was also studied to demonstrate different mechanical properties of CNTs depending on their number of sidewalls. TWNT demonstrates the highest Young’s modulus, which suggests TWNT as the best candidate for CNT composite applications.
9:00 PM - JJ10.7
Modeling Sustained Energetic Chain Reactions in Carbon Nanotubes.
Nitish Nair 1 , Michael Strano 1
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractWe have developed a computational technique for tracking chain reactions along functionalised one-dimensional lattices, specifically single walled carbon nanotubes (SWNT). A hybrid Molecular Dynamics/Monte Carlo algorithm has been used for a coarse-grained model of a SWNT. The parametric space comprises the activation energies of the functional groups, and the fraction of enthalpy released during the reaction which is converted into translational kinetic energy. With the help of these two handles, we have estimated the stabilities of the proposed nanostructures and explored boundaries within which a reaction that has been initiated at one end of the nanotube will be sustained along its length. Finally, the effect of the density of loading of the functional groups has been studied with respect to the aforementioned details.
9:00 PM - JJ10.8
Controlling Single-walled Carbon Nanotube Bundling by Employing Co-surfactant Titration.
Darlington Abanulo 1 , Sang-Yong Ju 1 , Fotios Papadimitrakopoulos* 1 2
1 Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States, 2 Department of Chemistry, University of Connecticut , Storrs, Connecticut, United States
Show Abstract9:00 PM - JJ10.9
Impact of Hexacholorantimonate as a Dopant on the Physical and Electrical Properties of CNTFETs.
Premlal Pillai 1 , Damien Casterman 1 , Maria De Souza 1 , Abbes Tahroui 2 , Colm Durkan 2 , William Milne 2
1 EEE, University of Sheffield, Sheffield United Kingdom, 2 Engineering, University of Cambridge, Cambridge United Kingdom
Show AbstractSingle wall Carbon Nanotubes (SWCNTs) are considered one of the most promising candidates among emerging research devices to push the limits of integrated circuits beyond CMOS. Their main advantages include room temperature operation, suppression of short channel effects and promising perspectives for bottom up fabrication techniques. However, the main challenges of carbon nanotube-based electronics are in achieving controlled growth of metallic or semi-conducting configurations, the control of ambipolar conduction [1], and reduction of the Schottky barriers at the contacts [2]. One of the techniques to achieve p-type doping of CNTFETs is via the one electron oxidant hexachloroantimonate shown to enhance the operation of the CNTFET [3]. In this work a statistical analysis of the influence of this dopant on the subthreshold and on-state properties of bottom gated CNTFETs as a function of dopant concentration is presented. The SWCNTs used in this work were grown by the chemical vapor deposition method on Highly doped n-type silicon substrates coated by a 100 nm thermal oxide, The SWCNTs were grown from prepatterned catalyst islands followed by the fabrication of metallic Cr/Au or Pd contacts on the SWCNT using electron-beam lithography, metal sputtering, and lift off. The substrate was used as the back gate for the SWCNT devices. The spacing between the metal contacts defined the channel length—this was fixed at 1 micron. The diameters of the nanotubes (average 1.3 nm) are determined via non-contact AFM with an accuracy of about 10%. The analysis includes the dependence of the turn-on voltage, subthreshold slope and on/off ratio as a function of the diameter. A study of Pd contacted devices indicates a deterioration of the contact via erosion in the presence of hexachloroantimonate. This is confirmed by AFM analysis. However the Cr/Au contacts are unaffected by this dopant.References:[1] Avouris et al, APL 83, 2435 (2003).[2] Avouris et al, page 508, CP633, Structural and Electronic Properties of Molecular Nanostructures, edited by H. Kuzmany et al. © 2002.[3] J. Chen et al, Appl. Phys. Lett. 86 (2005) 123108.
Symposium Organizers
Prabhakar Bandaru University of California-San Diego
Sonia Grego RTI International
Ian Kinloch University of Manchester
JJ11: Electronic and Optical Properties:I
Session Chairs
Prabhakar Bandaru
Sonia Grego
Wednesday AM, December 03, 2008
Room 302 (Hynes)
9:00 AM - **JJ11.0
Nanoelectronic devices based on branched nanowires and nanotubes.
Hongqi Xu 1
1 Mesoscopic Physics and Devices Group, Division of Solid State Physics, Lund University, Lund Sweden
Show Abstract9:30 AM - **JJ11.1
Reversible Metal-Insulator Transitions in Metallic Single-Walled Carbon Nanotubes.
Christoph Marquardt 1 , Simone Dehm 1 , Aravind Vijayaraghavan 1 , Sabine Blatt 1 , Frank Hennrich 1 , Ralph Krupke 1
1 , Forschungszentrum Karlsruhe, Eggenstein-Leopoldshafen Germany
Show AbstractScanning electron microscopy (SEM) is an established technique for imaging of carbon nanotubes with nanometer spatial resolution. The technique is rapid, has a large zoom range, and allows localizing individual single-walled carbon nanotubes (SWCNT), even if their diameter is below the microscope resolution limit[1].For these reasons SEM is commonly used as a standard characterization tool for carbon nanotube devices. Moreover it is the only technique that allows rapid screening of SWCNT locations in high-density device arrays[2]. Recently scanning electron microscopy has been advanced to image the metallic versus semiconducting character of carbon nanotubes in device architectures[3].On the other hand it is known that electron irradiation can cause structural damage to SWCNTs, in particular if the electron energy is above the threshold value for knock-on damage (E > 86 keV), characteristic for transmission electron microscopy[4]. Here we report on the first evidence of reversible metal to insulator transitions in metallic SWCNT devices that have been induced by local electron irradiation[5]. The transition from a low resistive, metallic state into a high resistive, insulating state was monitored by electron transport measurements. The key observation is that a transition back into the original metallic state can be induced by application of a voltage bias to the nanotube. Both metallic and insulating states are stable in time and transitions between them are fully reversible and reproducible. Our data is evidence for a local perturbation of the nanotube electronic system by removable trapped charges in the underneath substrate, which opens a new way of patterning quantum dot structures. Moreover we can conclusively exclude structural damage to play a role in this study.[1] T. Brintlinger, Yung-Fu Chen, T. Dürkop, E. Cobas, M. S. Fuhrer, J. D. Barry, J. Melngailis, Appl. Phys. Lett. 2002, 81, 2545-2456.[2] A. Vijayaraghavan, S. Blatt, D. Weissenberger, M. Oron-Carl, F. Hennrich, D. Gerthsen, H. Hahn, R. Krupke, Nano Letters 2007, 7, 1556-1560.[3] A. Vijayaraghavan, S. Blatt, C. Marquardt, S. Dehm, R. Wahi, F. Hennrich, R. Krupke, "Imaging Electronic Structure of Carbon Nanotubes by Voltage-Contrast Scanning Electron Microscopy" submitted to Nano Research 2008.[4] B. W. Smith, D. E. Luzzi, J. Appl. Phys. 2001, 90, 3509-3515.[5] C. W. Marquardt, S. Dehm, A. Vijayaraghavan, S. Blatt, F. Hennrich, R. Krupke, "Reversible local metal-insulator transitions in metallic single-walled carbon nanotubes" submitted to Nano Letters 2008.
10:00 AM - JJ11.2
Tunneling Transport for Metal - Carbon Nanofiber - Metal Structures.
Toshishige Yamada 1 , Tsutomu Saito 1 , Patrick Wilhite 1 , Xuhui Sun 1 , Drazen Fabris 1 , Cary Yang 1
1 Center for Nanostructures, Santa Clara University, Santa Clara, California, United States
Show AbstractCarbon nanostructures such as nanotubes and nanofibers have been extensively studied for interconnect applications because of their excellent electrical, thermal, and mechanical properties. In these materials, electric and thermal transport across the interfaces between nanostructure and electrodes is often more influential than transport in the nanostructure itself 1, and understanding the interplay between electronic and thermal transport is essential for interconnect applications.We study a system of a horizontal carbon nanofiber (CNF) bridging two Au electrodes, one of the simplest configurations for interconnect applications. In these structures, passing high current (current stressing) reduces the total resistance Rtot, consisting of CNF resistance RCNF and CNF-Au contact resistance Rc, by two to three orders of magnitude2. The CNF is typically ~4 μm long and ~200 nm in diameter, and the initial Rtot is in the MΩ range, but after current stressing, it is in the KΩ range. The CNF resistivity is estimated to be 4 × 10-5 Ωm with four-probe measurement, and a typical RCNF of the present dimension is ~5 KΩ. Therefore, it is concluded that Rc » RCNF and thus Rtot ~ Rc except for the very final stage (just before breakdown) of current stressing. Thus, the Rtot reduction with current stressing is mainly due to the change in interfacial properties at the CNF-Au contact. With additional current stressing, Rtot decreases further and nonlinearity in the current-voltage (I-V) characteristics also lessens, but there is a limitation for improvement. This nonlinearity reduction with decreasing Rtot is a signature of tunneling transport3. The current stressing is modeled as a process to reduce the interfacial tunneling gap between the CNF and Au electrode (several Å). The gap reduction with current stressing is possible because Joule heating anneals out chemical residues in the interfacial region, resulting in reduction of the gap between CNF and Au via van der Waals attractive interaction. According to this model, when the van der Waals equilibrium separation is reached, the improvement in contact resistance would stop. This is consistent with the experimental observation that the improvement does not continue indefinitely after multiple cycles of current stressing. The model explains measured I-V characteristics satisfactorily, and also confirms the observed trend for nonlinearity reduction with decreasing Rtot. 1T. Yamada, Appl. Phys. Lett. 78, 1739 (2001).2H. Kitsuki, T. Yamada, D. Fabris, J. R. Jameson, P. Wilhite, M. Suzuki, and C. Y. Yang, Appl. Phys. Lett. 92, 173110 (2008).3T. Yamada, M. Suzuki, P. Wilhite, H. Kitsuki, X. Sun, D. Fabris, and C. Y. Yang, submitted.
10:15 AM - JJ11.3
Imaging Electronic Structure of Carbon Nanotubes by Voltage Contrast Scanning Electron Microscopy.
Aravind Vijayaraghavan 1 , Sabine Blatt 1 , Christoph Marquardt 1 , Ralph Krupke 1
1 Institut für Nanotechnologie, Forschungszentrum Karlsruhe, Eggenstein-Leopoldshafen Germany
Show AbstractThe most common technique to observe Single-Walled Carbon Nanotubes (SWCNTs) is Scanning Electron Microscopy (SEM). However, this is limited to locating the nanotube, and is unable to provide structural or electronic information. We present Voltage Contrast SEM (VC-SEM) as a powerful technique for electronic characterization of large arrays of SWCNT devices [1] and to visualize the voltage-profile and charge-distribution in a single nanotube.The most significant result is to distinguish between metallic and semiconducting SWCNTs in a SEM. This is achieved by observing the difference in contrast profile arising from potential-distribution when the nanotube is subjected to a gate-field. The observed charge-distribution will be explained through finite-element modeling of the device electrostatics under the influence of an asymmetric gate-field generated by our electrode configuration.VC-SEM can also be used to locate, image and charactarize defects along a nanotube, such as stone-wales defects, current-induced breakdown, and defects engineered by electron irradiation of the nanotube. VC-SEM is many orders of magnitude quicker in comparison to Kelvin force or near-field microscopy. It can simultaneously characterize a large array of devices and sort them into metallic and semiconducting varieties and give an indication of the turn-on voltage required for the nanotube devices.1.Vijayaraghavan, A., et al., Ultra-Large Scale Directed Assembly of Single-Walled Carbon Nanotube Devices. Nano Letters, 2007. 7(6): p. 1556-1560.
10:30 AM - JJ11.4
Characterization of Carbon Nanotubes Array for Radio Frequency Applications.
Mahmoud Al Ahmad 1 , Mohamad Al Bahri 1 , Ian Bu 2 , Bill Milne 2 , Robert Plana 1
1 , LAAS CNRS, Toulouse France, 2 , University of Cambridge, London United Kingdom
Show Abstract10:45 AM - JJ11.5
Vertically Aligned Arrays of Templated Single-Walled Carbon Nanotubes for Nanoelectronics.
Aaron Franklin 1 2 , Jonathan Claussen 1 3 , Robert Sayer 1 3 , Timothy Sands 1 2 4 , David Janes 1 2 , Timothy Fisher 1 3
1 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 2 Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana, United States, 3 Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States, 4 Materials Engineering, Purdue University, West Lafayette, Indiana, United States
Show AbstractSingle-walled carbon nanotubes (SWCNTs) have shown great promise for many nanoelectronic applications, from field-effect transistors (FETs) to biological sensors. However, difficulty in controlling the placement and properties of SWCNTs has encumbered their integration into commercial applications. In the near term, if the placement and density of SWCNTs could be controlled, then the opportunity for multi-channel nanoelectronic devices may become feasible. Using highly ordered porous anodic alumina (PAA) thin films, we have developed techniques for not only synthesizing vertical SWCNTs (v-SWCNTs) in precise locations, but also for embedding independently addressable fields of these v-SWCNT arrays in an insulating support. These customizable v-SWCNT/PAA templates have been used to fabricate nanoelectronics ranging from surround gated FETs (SG-FETs) to ultra-sensitive biological sensors.In a thin film PAA template with hexagonally arranged 20 nm diameter pores, v-SWCNTs are synthesized at a yield of no more than one nanotube per pore (achievable density of 100 SWCNTs/µm2). Electrodeposited Pd nanowires contact the v-SWCNTs within their nanopores and a dielectric is deposited into the PAA using either spin-on glass or atomic layer deposition, to surround each nanotube. Using a combination of selective etches, the dielectric-wrapped nanotube channels are exposed as pillars and subsequently coated with a gate metal. The channel length for the final vertical SG-FET devices is controlled using an inert gas ion bombardment etch in a reactive ion etcher at a rate of 40 nm/min. Control of the channel length using this ion etch has enabled the definition of sub 100 nm nanotube channels over an entire wafer in a single step without the use of any lithographic patterning. The number of pores containing a v-SWCNT is varied primarily by adjusting the nanotube growth time between 30 sec and 10 min, which yields a v-SWCNT occupancy as low as one nanotube and as high as thousands of nanotubes per 100 µm2. In order to achieve currents capable of driving CMOS circuitry, and to improve upon the consistency of device-to-device characteristics, multi-channel SG-FETs are defined by using the appropriate growth time and covering the desired number of highly ordered nanotube channels with a top contact. In the context of biological sensing, the Pd nanowire contacted v-SWCNTs are decorated with Pd-Au nanoparticles on the PAA surface. These functionalized fields of PAA are embedded in SiO2 on independently addressable electrodes for potential multiplexed sensing of various biological species. The glucose-sensitivity of the nanoparticle-decorated nanotubes has reached the micro-molar regime in preliminary tests performed thus far. Ultimately, the ability to customize these PAA/v-SWCNT fields provides a means for realizing nanotube-driven nanoelectronic applications, such as the SG-FETs and biological sensors demonstrated herein.
JJ12: Electronic and Optical Properties: II
Session Chairs
Prabhakar Bandaru
Ralph Krupke
Wednesday PM, December 03, 2008
Room 302 (Hynes)
11:30 AM - **JJ12.1
Electrons, Holes, and Spins in Carbon Nanotubes.
Paul McEuen 1
1 Department of Physics, Cornell University, Ithaca, New York, United States
Show Abstract12:00 PM - JJ12.2
Relaxation and Restoration of Spin Signals in Carbon Nanotube Spin Valve Devices.
Chen-Wei Liang 1 , Serhat Sahakalkan 1 , Siegmar Roth 1
1 , Max-Planck-Institute, Stuttgart Germany
Show AbstractCarbon-based low-dimensional materials like carbon nanotubes (CNT) and graphene have spin coherent length larger than hundreds of nm. When contacting these materials with ferremagnetic leads, spin-polarized current can be injected from one lead and its spin states are analyzed by the other. However, various factors like structural defects or adsorbates do not behave only as momentum-scattering centers but also spin relaxation center. This debases of the superiority of carbon-based materials as spin transporter. In this experiment we use ferromagnetically contacted CNT devices to demonstrate the imperfections of the nanotubes are responsible for the spin relaxation centers. We also observed that the spin signal is restored after rectifying the imperfections. By comparing our results and other reported studies on CNT and graphene, a dimension-dependent scattering model is suggested to explain the relation between momentum- and spin-relaxation inside the carbon-based materials.
12:15 PM - JJ12.3
Massively Parallel Solution Phase Processing of Carbon Nanotubes with Optoelectronic Tweezers.
Peter Pauzauskie 1 , Arash Jamshidi 2 , Joseph Zaug 1 , Justin Valley 2 , Yong Han 1 , Joe Satcher 1 , Ming Wu 2
1 Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Electrical Engineering, Univeristy of California, Berkeley, Berkeley, California, United States
Show AbstractCarbon nanotube (CNT) processing will require a massively parallel technique to enable high-throughput separations and the assembly of large-scale nanostructured architectures. Optoelectronic tweezers [1] (OET) have emerged in recent years as a powerful tool for highly parallel manipulation of micron scale particles, including solid-state nanowires [2]. In this presentation we demonstrate that aqueous dispersions of both carboxylic-functionalized-CNT bundles and sodium dodecyl benzene sulfonate (SDBS) coated multiwalled-CNTs are addressable with forces generated by optoelectronic tweezers (OET). Dynamic virtual electrodes defined by optical images enable the translation and patterning of carbon nanotubes in two dimensions. Due to the large aspect ratio of carbon nanotubes, OET is capable of transporting CNTs in solutions with conductivites ranging from 10 – 100 mS/m while using 100,000x less optical power density than optical tweezers. AFM images are used to characterize nanotube diameters and `in situ’ Raman spectroscopy is presented as a way to monitor nanotube ensembles trapped within individual OET potential wells. Digital video microscopy is used to quantify nanotube dynamics resulting from dipole-dipole interactions. Potential applications involving nanotube separations and optically-patterned nanotube arrays will be discussed.[1] Chiou, P. Y.; Ohta, A. T.; Wu, M. C. Nature 2005, 436, 370-372.[2] Jamshidi, A.; Pauzauskie, P. J.; Schuck, P. J.; Ohta, A. T.; Chiou, P. Y.; Chou, J.; Yang, P. D.; Wu, M. C. Nature Photonics 2008, 2, 85-89.
12:30 PM - JJ12.4
Size Matters: Length-Dependent Photoconductivity of Single-Walled Carbon Nanotubes.
Andrew Ferguson 1 , Jeffrey Blackburn 1 , Robert Tenent 1 , Bobby To 1 , Teresa Barnes 1 , Nikos Kopidakis 1 , Michael Heben 1 , Garry Rumbles 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show Abstract12:45 PM - JJ12.5
Carbon Nanotube Based Photocathodes.
Le Sech Nicolas 1 , Hudanski Ludovic 1 , Minoux Eric 1 , Gangloff Laurent 1 , Schnell Jean-phillipe 1 , Cojocaru Costel-Sorin 1 , Teo Kenneth B K 2 , Robertson John 2 , Milne William 2 , Legagneux Pierre 1 , Pribat Didier 1
1 , Thales R&T, Palaiseau France, 2 , Electrical Engineering Division, University of Cambridge, Cambridge United Kingdom
Show AbstractA novel photocathode is presented, consisting in arrays of vertically aligned multi-walled carbon nanotubes (MWCNTs), each MWCNT being associated with one p–i–n photodiode. Unlike conventional photocathodes, the functions of photon–electron conversion and subsequent electron emission are physically separated. Photon–electron conversion is achieved using p–i–n photodiodes whereas the electron emission occurs from the MWCNTs. The current modulation is highly efficient as it uses an optically controlled reconfiguration the electric field at the MWCNTs locations. We have made the first carbon nanotube based photocathode using silicon p–i–n photodiodes and MWCNT bunches.Using a green LASER excitation, the photocathode delivers a current intensity of 0.5 mA with an internal quantum efficiency of 10% and an ION/IOFF ratio of 30. The first result about the analog modulation of the photocathode at a few hundred MHz will be presented.Finally, we consider the carbon nanotube based photocathode perspectives. We plan to replace the silicon photodiodes with high frequency p–i–n photodiodes on III-V semiconductor substrate. The goal is to obtain a 10-30GHz modulated electron beam operated by a 1.55µm LASER diode. The carbon nanotube growth technology process on III-V substrate, at low temperature (550°C) associated with GaInAs p-i-n photodiodes and field emission results is also discussed.The use of these new photocathodes as optically modulated electron sources could lead to new generation of highly compact, high efficiency and large bandwidth microwave amplifiers.
JJ13: Optical Properties and Raman Spectroscopy
Session Chairs
Wednesday PM, December 03, 2008
Room 302 (Hynes)
2:30 PM - **JJ13.1
Influence of Dopant-induced Defects on the Optical, Mechanical and Electronic Properties of Carbon Nanotubes.
A. Rao 1
1 Department of Physics and Astronomy, Clemson University, Clemson, South Carolina, United States
Show AbstractA carbon nanotube is an ideal prototype for probing the role of defects in nanoscale systems. Improved methods permit the synthesis of carbon nanotubes with controlled dopant (e.g., boron, nitrogen) concentrations. Using a fully electrical actuation and detection method for measuring mechanical oscillation in cantilevered multi-walled carbon nanotubes (MWNTs), the bending modulus of chemical vapor deposition-grown MWNTs has been measured. Different precursors were used to produce the MWNTs with differing densities of defects in the tube walls. A correlation between the defect density and the bending modulus suggests that the bending modulus is relatively more sensitive to wall defects than the nanotube diameter. Raman scattering, has been largely used to study defects in sp2 carbon materials, including doping. Defects usually break the selection rules, so that broadening and new peaks can be observed in the Raman spectra mostly related to specific phonons in the interior of the Brillouin zone that are enhanced by a double-resonance process. Besides usual symmetry breaking effects, the presence of charged defects will renormalize the electron and phonon energies. We find that near a negatively charged defect the electron velocity is increased, which influences the atomic vibrations locally. Finally, evidence for superconductivity in SWNTs and its correlation with dopant concentration will be presented. The Meissner effect exhibiting a Tc = 12 K is found in thin films consisting of assembled boron-doped SWNTs. The first-principles electronic-structure study of boron-doped SWNTs strongly supports these results.This work is supported by NSF and jointly performed with Profs. Malcolm Skove, Ado Jorio and Junji Haruyama.
3:00 PM - **JJ13.2
Raman Studies of Exciton Behavior in Single-Walled Carbon Nanotubes.
Stephen Doorn 1 , Erik Haroz 1 , Paulo Araujo 2 , Ado Jorio 2 , Kenji Hata 4 , Sergei Bachilo 3 , Bruce Weisman 3
1 Chemistry Division, Los Alamos National Lab, Los Alamos, New Mexico, United States, 2 Departamento de Física, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil, 4 , Research Center for Advanced Carbon Materials, Tsukuba Japan, 3 Department of Chemistry, Richard E. Smalley Institute for Nanoscale Science and Technology, and Center for Biological and Environmental Nanotechnology, Rice University, Houston, Texas, United States
Show AbstractThe realization of photonic, optoelectronic, sensing, and other applications of carbon nanotubes requires a complete understanding of their electronic structure, nature of the optical excited states, and how electronic and phonon structure couple. We present here a scaling law analysis of E33 and E44 energies for small diameter (0.7 to 1.2 nm) nanotubes probed with resonance Raman and photoluminescence excitation spectroscopy in the deep blue to UV (488 nm to 280 nm) excitation regions. We demonstrate that the E33 and E44 scaling behavior for nanotubes with diameter < 0.9 nm deviates significantly from that previously observed for larger diameter nanotubes. The scaling analysis allows a first demonstration that the E33 and E44 energy trend lines for a given 2n+m branch do in fact cross over each other. Additionally, our observation of a pronounced negative trend in scaling behavior at small diameters represents a breakdown in the scaling-law physics that may be interpreted as a many-body exciton effect that becomes significant only at high curvatures. Application of the scaling law analysis to transition energies for metallic nanotubes suggests that the transitions are excitonic in nature and that relative scaling of electron self-energies and exciton binding energies in metallic nanotubes closely matches that found in semiconductors. This similarity in behavior can be understood in terms of similar regions of the Brillouin zone being sampled by E11M and E11S and E22S (and by E22M and E33S and E44S). Additionally, for large diameter nanotubes (> 1.3 nm) we now observe the previously elusive upper branch signatures for several chiralities for both E11M and E22M excitation. These results are discussed as a consequence of the nodal behavior of exciton-phonon coupling. Finally, while theoretical calculations for the (n,m) dependent matrix elements predict the RBM intensity should decrease with increasing diameter, the opposite behavior is observed experimentally. We show this to be a consequence of an increase in the resonance Raman broadening factor gamma as diameter decreases.
3:30 PM - JJ13.3
Raman Spectroscopy of Isolated Double Wall Carbon Nanotubes (DWNT).
Federico Villalpando 1 , Hyungbin Son 2 , Ya-Ping Hsieh 2 , Jing Kong 2 , Kim Yoong Ahm 4 , Endo Morinobu 4 , Mauricio Terrones 5 , Mildred Dresselhaus 2 3
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Electrical Engineering, MIT, Cambridge, Massachusetts, United States, 4 Faculty of Engineering, Shinshu University, Shinshu Japan, 5 Advanced Materials Department, IPICYT, San Luis Potosi, San Luis Potosi, Mexico, 3 Physics, MIT, Cambridge, Massachusetts, United States
Show AbstractWe have developed a method to perform Raman spectroscopy on isolated double wall carbon nanotubes (DWNT). By identifying isolated DWNTs and obtaining their Raman spectra using different laser lines, we are able to find DWNTs whose inner and outer walls are in resonance with the same laser line or with more than one laser line. The inner and outer walls of a DWNT can be metallic (M) or semiconducting (S) and each of the four possibleconfigurations (M/M, M/S, S/S, S/M) is expected to have different electronic properties. The obtained Raman spectra show simplified radial breathing mode(RBM), G and G' line shapes that allow us to study the inter layer interactions and make comparisons to previous experiments on DWNT bundles.
JJ14: Optical and Thermal Properties
Session Chairs
Wednesday PM, December 03, 2008
Room 302 (Hynes)
4:15 PM - **JJ14.1
Thermoelectric and Photovoltaic Particle Heat Engines Based on Silicon Nanostructures.
Akram Boukai 1
1 Department of Chemistry, University of California, Berkeley, Berkeley, California, United States
Show AbstractGrowing concerns of global warming due to rising CO2 levels necessitates the search for highly efficient renewable energy alternatives. Thermoelectrics and photovoltaics are two attractive alternatives. Thermoelectric materials convert temperature differences into electricity and vice versa. Photovoltaics convert light energy into electricity and vice versa. Such materials are non-polluting and use no moving parts. Currently, they find only limited use because of their poor efficiency. Nanostructured materials, however, offer a route to enhance thermoelectric and photovoltaic efficiencies above that of bulk materials. This talk will explain our recent work on silicon nanowire thermoelectrics that has shown a 100 fold improvement in the efficiency over bulk. Phonon effects are responsible for this improved efficiency. In addition, silicon nanostructures may also be used to enhance photovoltaic properties. Finally, this talk will elucidate the mechanism that characterizes thermoelectrics and photovoltaics as "particle heat engines".
4:45 PM - JJ14.2
Nanotube Based Thermal Motors.
Riccardo Rurali 1 , Amelia Barreiro 2 , Eduardo Hernandez 3 , Adrian Bachtold 2
1 Departament d'Enginyeria Electrònica, Universitat Autonoma de Barcelona, Bellaterra (Barcelona) Spain, 2 , CIN2 Barcelona and CNM-CSIC, Bellaterra (Barcelona) Spain, 3 , ICMAB-CSIC, Bellaterra (Barcelona) Spain
Show Abstract5:00 PM - JJ14.3
Tunable Thermal Conductivity in CNT Assembly.
Ali Aliev 1 , Gautam Hemani 1
1 NanoTech Institute, University of Texas at Dallas, Richardson, Texas, United States
Show AbstractExtremely high thermal conductivity of single carbon nanotubes predicted theoretically and recently obtained experimentally never was achieved in macroscopic assemblies. The low quality of CVD grown nanotubes, interconnections in ropes and quenching of phonon modes in bundles substantially reduce the transport properties of carbon nantotubes. In this presentation we emphasize on quenching of phonon modes in bundles created during growing process and assembling in particular devices. Recently we found that the thermal conductivity of single MWNT grown by CVD method do not exceed of 600±100 W/m*K. The coupling in the ropes decreases the thermal conductivity to 100±15 W/m*K. The further decrease of effective thermal conductivity to 50±5 W/m*K comes from the imperfection of MWNT sheet like dangling terminals, loops and misalignment of tubes. The unbundling of MWNT ropes can substantially increase the thermal conductivity of assembly. Using electrostatic potential and dynamic resonance shacking we have demonstrated the unbundling which lead to increase the thermal conductivity of whole assembly.
5:15 PM - JJ14.4
Thermal Conductance and Bolometric Response of Individual Single-Walled Carbon Nanotubes.
Daniel Santavicca 1 , Joel Chudow 1 , Yan Yin 1 , Anthony Annunziata 1 , Luigi Frunzio 1 , Daniel Prober 1 , Meninder Purewal 2 , Philip Kim 2
1 Dept. of Applied Physics, Yale University, New Haven, Connecticut, United States, 2 Depts. of Physics and Applied Physics, Columbia University, New York, New York, United States
Show AbstractWe have studied the response of individual metallic single-walled carbon nanotubes to dc and rf Joule heating at temperatures between 4 and 300 K. These measurements enable us to determine the nanotube thermal conductance, and also to clearly distinguish between thermal and non-thermal nonlinearities in the I-V curve, both of which give rise to a heterodyne mixing response. Distinguishing between thermal and non-thermal nonlinearities is critical in understanding the high frequency performance of nanotube devices. Using Johnson noise thermometry, we establish that the low-bias increase in the differential resistance with increasing bias current corresponds to self-heating of the electron system in the nanotube. Thus the device resistance can be used as a direct probe of the nanotube temperature. Dc Joule heating measurements are used to determine the thermal conductance as a function of the nanotube temperature. Nanotubes between 2 and 20 microns were measured. The thermal conductance scales linearly with the length, suggesting a relatively uniform temperature profile along the tube and cooling predominantly into the substrate. We also measure the rf heterodyne mixing response. The response at bath temperatures above 20 K agrees well with a linear response bolometric model using the thermal conductance determined from dc measurements. Below 20 K, the I-V curve exhibits an increase in the differential resistance at zero bias that is attributed to Schottky barrier contacts. At very low current bias, these Schottky contacts provide the dominant heterodyne response, while at higher bias the bolometric response dominates.
5:30 PM - JJ14.5
Experimental Observation of an Extremely Dark Material Made By Low-Density Nanotube Array.
Zu-Po Yang 1 2 , Shawn-Yu Lin 1 2
1 Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Future Chips Constellation, Rensselaer Polytechnic Institute, Troy, New York, United States
Show Abstract An ideal black material absorbing light perfectly at all angles and over all wavelengths is an important element for the applications such as solar thermophotovoltaic, infrared detection, and astronomical observation. However, the experimental realization of a truly black material has been hindered by our inability to reduce the index of refraction of a material to unity and thus eliminate its optical reflection. Here, we report the low-density vertically aligned carbon nanotube (VA-CNT) array can be engineered to have integrated total reflectance 0.045% which is three times lower than lowest-ever reported value. In addition, VA-CNT array shows ultra-low diffuse reflectance of 1x10-7 for a collection angle of ΔΩ=8.2x10-4 Sr. This observation of extremely dark of VA-CNT is due to the combination of its high porosity nanostructure and surface randomness. A theoretical calculation predicted recently that the well-aligned VA-CNT has an extremely low index of refraction (n=1.01-1.10) and a finite absorption constant. Hence, our VA-CNT array not only reflects light weakly but also absorbs light strongly. In addition, several surface diffuser models suggest that the surface roughness can suppress the reflection as well as change the diffuse reflection profile. From our total reflection measurement and diffuse profile measurement, we show that VA-CNT array is a stronger diffuser and, at the same time, can absorb light over wide spectrum range and large angle-of-incidence. In summary, our data suggest that the VA-CNT array is a super black material, and can be used as a near-perfect sunlight absorber over all-angles and all-wavelength of interest. S.Y.L. acknowledges the financial support from DOE. This work is result of joint collaboration with Dr. Lijie Ci and Prof. P. M. Ajayan at Rice University.
5:45 PM - JJ14.6
Crystal Orientation-ordered ZnS Nanobelt Arrays: Enhanced Field-emission More Than 20 Times.
Xiaosheng Fang 1 , Yoshio Bando 1 , Dmitri Golberg 1
1 World Premier International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Ibaraki, Japan
Show AbstractJJ15: Poster Session: Nanowires and Nanotubes: Electrical, Optical and Thermal properties
Session Chairs
Prabhakar Bandaru
Sonia Grego
Ian Kinloch
Thursday AM, December 04, 2008
Exhibition Hall D (Hynes)
9:00 PM - JJ15.1
Gold-supported Titania Nanotubes for Catalytic Applications.
Mohamed Abdelmoula 1 , Minh Phan 2 , R. Willey 2 , Laura Lewis 2 , Latika Menon 1
1 Physics, Northeastern University, Boston, Massachusetts, United States, 2 Chemical Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractGold particles have been deposited on electrochemically synthesized high-aspect ratio titania nanotubes. Titania nanotubes with very long aspect ratio as long as 50microns are synthesized by means of electrochemical anodization of titanium foils in chlorine containing electrolytes. The tube dimensions (diameter, wall thickness and length) of the tubes can be controlled in our fabrication approach. The gold particles are deposited on the tubes by means of a deposition-precipitation method in HAuCl4 solution under controlled pH and concentration of the solution. We show that by adjusting the fabrication conditions, we can obtain a high deposition density of the gold particles over the nanotube surface and also have good control over the size of the gold nanoparticles (<5 nm). The samples have been characterized by means of scanning and transmission electron microscopy. The optical and preliminary catalytic properties of such gold-supported titania nanotubes will also be reported.
9:00 PM - JJ15.10
Electrical Properties of Carbon Nanofiber Interconnect Vias.
Wen Wu 1 , Xuhui Sun 1 , John Jameson 1 , Dinh Nguyen 1 , Patrick Wilhite 1 , Shoba Krishnan 1 , Cary Yang 1
1 Center for Nanostructures, Santa Clara University, Santa Clara, California, United States
Show Abstract Carbon-based nanostructures such as carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are receiving increasing attention as alternatives to copper (Cu) for sub-30nm on-chip interconnects. As the minimum feature size scales down, Cu interconnects encounter challenges including electromigration, dramatically increasing resistivity, and excessive power dissipation with increasing on-chip clock frequencies. Our previous work showed strong evidence that horizontal CNF interconnects have metallic properties under both DC and radio-frequency (RF) operations, and they exhibit high current capacity and excellent thermal conductivity characteristics. In this work, we measure the electrical properties of CNFs for interconnect via applications. With a nickel (Ni) catalyst layer on a silicon (100) wafer coated with a base-electrode layer, vertically aligned CNFs are grown in a plasma-enhanced chemical vapor deposition (PECVD) system. Individual CNFs are characterized using atomic force microscopy (AFM) current-sensing technique. We analyze the relationships between CNF structural parameters such as length and diameter and via resistance. Using a scheme based on these relationships, we extract the contact resistance between CNF and different electrode materials. Following the bottom-up approach of interconnect processes in the semiconductor industry, we design and fabricate patterned via structures with each containing bundles of vertically aligned CNFs. The via diameter varies from 400 to 1000 nm. The high current capacity of each via is demonstrated using constant-current stress experiments.
9:00 PM - JJ15.11
Tuning 1/f Noise in Metallic Nanowires by Electrochemical Growth Parameters.
Amrita Singh 1 , Arindam Ghosh 1
1 Physics Department, Indian Institute of Science, Bangalore, karnataka, India
Show AbstractNanowire hybrids with single molecule or nano /CMOS based design have been suggested to significantly enhance the integration density with higher operating speeds. Although a great deal has been known about the electrical properties of metallic nanowires, little is known about their noise characteristics. Hence if these nanowires are to be used in nanoelectronic circuits as interconnects, it is very important to investigate the microscopic origin of electrical noise in this system which is not yet understood clearly. The excess noise in single crystal systems can be due to the defect diffusion along the dislocations, movement of dislocations etc, which are highly crystal structure dependent. To study the effect of defect dynamics on electrical noise in single-crystalline nanowires, here we have used silver nanowires realized in both hcp and fcc crystal structures. We employed a modified electrodeposition technique [1], in which an inter-electrode potential, much smaller than the Nernst potential, was applied across a highly concentrated electrolyte and the resulting nanowires acquired hcp structure. Using conventional over potential electrodeposition (OPD) technique, where the inter-electrode potential is slightly higher than the Nernst potential, nanowires with fcc crystal structure were also grown and their noise characteristics were compared with those having hcp crystal structure. Electrical noise was measured with ac multiprobe technique in an electromagnetically shielded set-up that is sensitive to voltage fluctuations with power spectral densities as low as 10-20V2/Hz. We found that the noise magnitude at room temperature in fcc nanowires is three orders of magnitude higher than that of hcp nanowires [2]. This can be attributed to the dislocation dynamics as fcc crystal has more number of slip systems as compared to the hcp crystal, which results in more number of ways for dislocations to propagate. Moreover, point defects are thought to lock the dislocation motion by forming Cottrell atmosphere around the dislocations, which in turn can reduce the noise. The hcp nanowires generally displayed lower residual resistivity ratio, which suggests the presence of more number of disorders which impedes the motion of dislocation and decreases the noise significantly. Thus, the observed temperature independent behavior of noise in hcp silver nanowires can be explained in terms of locking of dislocation motion. The results thus pave a new understanding of the crystal structure dependent microscopic origin of noise in single crystal nanowires.[1] A. Singh and A. Ghosh, J. Phys. Chem. C, 112, 3460-3463, 2008.[2] A. Singh, T.P Sai and A. Ghosh, manuscript submitted for publication.
9:00 PM - JJ15.13
Investigation of Transport Properties of Schottky Carbon Nanotube FET Devices using a Dual-diode Model.
David Perello 1 , Dong Jae Bae 2 , Seung Yol Jeong 2 , Bo Ram Kang 2 , Woo Jong Yu 2 , Young Hee Lee 2 , Dong K. Cha 3 , Moon J. Kim 3 , Minhee Yun 1
1 Electrical and Computer Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 , SungKyunKwan University, Suwon Korea (the Republic of), 3 , University of Texas at Dallas, Dallas, Texas, United States
Show AbstractSingle- wall carbon nanotubes (SWCNT) have changed from a novel material in the early 1990’s to being mass-produced commercially and implemented in multiple types of electronic devices by various lab groups [1-2]. As reported by our group and others in recent years, consistency and an accurate theory describing the schottky transport are major difficulties. Most reported devices display near-symmetric conduction for positive and negative applied source-drain bias; but the fact is that even using a heat-treatment step in fabrication does not always produce this result. This factor is especially true for devices consisting of multiple metal types or diode-like devices in which neither the source or drain contact is ohmic. The presence of an ohmic contact on a single side allows for the consideration of a commonly studied metal – semiconductor schottky contact at the other side of the channel. In typical carbon nanotube transistors, however, both the source and drain are Schottky contacted and a carrier is forced to traverse two barriers – synonymous with two diodes. Before leaving the drain (source), a hole must first surmount a reverse-biased Schottky diode, cross the semiconducting nanotube channel, and then exit the device by once again thermionically overcoming a potential-dependent barrier at the source (drain) end.We present here an experimental analysis of carbon nanotube Schottky transistors using this double-diode method to find parameters associated with a metal-semiconductor contact. Due to the complexity of the equations involved, nonlinear curve fitting was employed to decompose the I-V and temperature curves of the device into that of two separate diodes with differing potential differences and characteristics.Metals that are analyzed by this method include Cr, Ti, Pd, Hf, and Ti/Au. For best comparison, devices with channel lengths between 200 nm and 1 μm are used (near ballistic transport). Also, multiple devices of with different contact metals are fabricated on nanotubes longer than 5 mm to allow more consistent diameter-dependent transport characteristics – as well as the placement of more than 50 devices per tube. This type of device fabrication also allows for devices with different metal contacts exhibiting diode-like I-V curves due to asymmetric barriers on the contacts. Preliminary results thus far are indicative that metal contact is strongly dependent on the metal type, and that the presence of a metal contact on the tube, even if not connected electrically to an external probe, can alter the Fermi level of the nanotube – allowing a researcher to create a logic device without altering source-drain contacts or doping. We believe this can allow for easier device analysis and fabrication as a result.
9:00 PM - JJ15.14
Gate Controlled Negative Differential Resistance and Photoconductivity Enhancement in Carbon Nanotube Addressable Intra-connects.
Seon Woo Lee 1 , Haim Grebel 1 , Andrei Sirenko 2 , Daniel Lopez 3 , Avi Kornblit 3
1 Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, New Jersey, United States, 2 Physics, New Jersey Institute of Technology, Newark, New Jersey, United States, 3 New Jersey Nanotechnology Consortium (NJNC), Lucent Technologies Bell Labs, Murray Hill, New Jersey, United States
Show AbstractWe have observed gate-controlled N-shaped negative differential resistance (NDR) and photoconductivity enhancement in carbon nanotube (CNT) based addressable intra-connects. The intra-connects – bridges spanning across planar electrodes – were measured at room temperature. Individual single-walled CNT (SWCNT) channels were grown using chemical vapor deposition (CVD) precisely between very sharp metal tips on the pre-fabricated electrodes without post-processing. The electrodes were made of cobalt. Methane and H2 gas mixture were introduced into quartz tube for an hour at 900 C, with flow rate of 1900 sccm for methane and 20 sccm for H2. We have investigated two different cases: in one case, the source-drain current-voltage, Ids-Vds, characteristics were linear. The other case exhibited nonlinear Ids-Vds characteristics. Raman scattering of the intra-connects indicated that each were made of SWCNT with radial breathing mode (RBM) at 191.9 cm-1 and 176.2 cm-1, respectively. Current-voltage Ids-Vds characteristics were measured for various Vgs from -10 V to +10 V. Negative differential resistance (NDR) was found in the Ids-Vgs curves for gate bias in the region of -3>Vgs>-6 V. The NDR peak was shifted to the negative side as the source-drain voltage was increased from Vds=0 to 0.75 V. Otherwise, the intra-connects exhibited characteristics of an ordinary p-type channel. The experiments were repeated under white light illumination. The light increases the carrier density in the channel but not in the metal electrodes and allowed us to study the effective doping of the channel without affecting the work function of the SWCNT/metal contact. The overall channel conductance increased under the light irradiation. Under illumination, the devices became more stable, as well. In summary, we have investigated contact properties between a SWCNT intra-connect and metal electrodes in a well controlled layout settings.
9:00 PM - JJ15.15
Electrical Characterization of Vertically-aligned Carbon Nanotube Bundles with Metallic End Contacts.
Zhengchun Liu 1 , Lijie Ci 2 , Zheng Xu 1 , Pulickel Ajayan 2 1 , Jian-Qiang Lu 1
1 Center for Integrated Electronics, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Mechnical Engineering & Materials Science, Rice University, Houston, Texas, United States
Show AbstractVertically-aligned carbon nanotubes (VACNTs) are promising for various electrical and electronic applications. For example, VACNT bundles were grown on IC chips for interconnect vias. It is important to know the electrical properties of these CNT bundles. In this paper, we investigated the electrical resistance of VACNT bundles versus their bundle lengths. As-grown VACNT bundle arrays were filled with a polymer resin. After polymer curing, a mechanical polishing process is used to expose the CNT ends. VACNTs were then metallized at one end. The CNT/polymer composite film was then flipped over and transferred to a metallized substrate. Repeating the polishing and metallization process, we obtained the samples ready for electrical testing. We found that the resistance-length plot deviates from the linear relation over the whole bundle length. But it is linear in certain sections. Metal/CNT end contact resistances were extracted using the extrapolation of these linear sections. The nonlinear behavior of resistance versus length indicates the conductivity variation along the CNT growth direction, implying that the alignment or defect level may vary at different growth stage.
9:00 PM - JJ15.16
Single-Walled Carbon Nanotube as nanoelectrodes for molecular level detection of DNA hybridization.
Harindra Vedala 1 , Taehyung Kim 1 , Wonbong Choi 1
1 Mechanical and Materials Engineering, Florida International University, Miami, Florida, United States
Show AbstractIn this work we demonstrate a unique nanoelectronic platform for detection of single DNA molecules. Single walled carbon nanotubes are utilized as nanoscale electrodes for measuring and comparing electrical conductivity of 80 base pair single and double-stranded DNA of various sequences. About 25-40 pA current was measured for the genomic dsDNA molecule covalently attached to the SWNT electrode at its termini.In the absence of base pair stacking, a ssDNA carries a feeble current of few pA or less. Gate-voltage-dependent I-V characteristics revealed that the bridging dsDNA molecule acts as a p-type channel between SWNT source and drain electrodes.
9:00 PM - JJ15.17
Piezoelectric Nanorod-Based Flexible Nanogenerators.
Mi-Jin Jin 1 , Sam-Dong Lee 1 , In-Soo Kim 1 , Sang-Hyeob Kim 2 , Jae-Young Choi 3 , Sang-Woo Kim 1
1 School of Advanced Materials and System Engineering, Kumoh National Institute of Technology, Gumi Korea (the Republic of), 2 IT Convergence Technology Research Laboratory, Electronics and Telecommunications Research Institute, Daejeon Korea (the Republic of), 3 , Samsung Advanced Institute of Technology, Yongin Korea (the Republic of)
Show AbstractRecently, some of research groups have reported the development and characteristics of high power nanogenerators by using piezoelectric material-based nanostructures such as ZnO and BaTiO nanowires. However, the piezoelectric ZnO nanostructure-based nanogenerators ever reported are hard to give any flexibility and large area fabrication because the nanostructures have been synthesized on rigid GaN and sapphire substrates with a small size. In this presentation, we report fully flexible high-power nanogenerators by introducing ZnO-nanorod and PdAu-nanodot arrays. The ZnO nanorods acting as an active layer for current generation were grown on ITO/PES substrates using an aqueous solution route. Ordered PdAu nanorods and nanodots for the Schottky contact to the ZnO nanorods were prepared on flexible PES films using anodic aluminum oxide templates in watt solution by an electroplating method. All fabrication processes were established at low temperature below 100°C. Each flexible layer with PdAu nanostructures and ZnO nanorods was stacked and packaged to prevent fluid from penetrating into the nanogenerators under ultrasonic wave. Output currents obtained from our flexible nanogenerators were in tens of μA ranges, indicating high efficiency of our flexible nanogenerators. We strongly believe that these novel nanogenerators for flexible and wearable device applications as a unique self-power source can replace existing consumable energy sources such as batteries.
9:00 PM - JJ15.18
In-situ Resistometry Studies of Carbon Nanotube Films and Fibres.
Krzysztof Koziol 1 , Gregory Kozlowski 1 2 , Stuart Fraser 1 , Simon Hopkins 1 , Ian Pong 1 , Bartek Glowacki 1 , Alan Windle 1
1 Department of Materials Science, University of Cambridge, Cambridge United Kingdom, 2 Department of Physics, Wright State University, Dyton, Ohio, United States
Show AbstractCarbon nanotube films and fibres consisting exclusively of highly oriented nanotube bundles, spun directly from a CVD reaction zone, were the subject of this study. Measurements of resistance versus temperature were conducted by using resistometry. In this system we could measure small changes in the resistance of the samples with a four-terminal alternating current (AC) technique, with a lock-in amplifier. The AC current was used with amplitude range from 3 µA up to 30 mA and at frequencies of 63 Hz and 126 Hz.The measurements using carbon nanotube films and fibres were conducted in air and vacuum (up to 10-6 Torr) to eliminate oxidation effects and isolate the sample from external disturbances. The temperature range from 193K to 773K was used with different ramping rate and dwelling time.Difference between virgin and conditioned samples was clearly observed. We show that different chemical species adsorbed on the surface of nanotubes have a prominent effect on the resistance. After conditioning a minimum was observed in the case of nanotube films around 400K, which divided the region of resistance from semiconducting to metallic character.
9:00 PM - JJ15.19
Imaging Dielectric Properties of Silicon Nanowire Oxide by Conductive Atomic Force Microscopy Complemented with Femtosecond Laser Illumination.
Nipun Misra 1 , Emmanuel Stratakis 2 3 4 , David Hwang 1 , Emmanuel Spanakis 2 3 4 , Costas Fotakis 2 5 , Panagiotis Tzanetakis 2 5 , Costas Grigoropoulos 1
1 Mechanical Engineering, University of California, Berkeley, Berkeley, California, United States, 2 , Institute of Electronic Structure and Laser, Foundation for Research and Technology Hellas, Crete Greece, 3 Material Science and Technology Department, University of Crete, Crete Greece, 4 , Technological Educational Institute of Crete, Crete Greece, 5 Physics Department, University of Crete, Crete Greece
Show AbstractSilicon and its oxide have enabled the continued scaling of microelectronic devices and in most nanowire applications the silicon oxide forms an insulating barrier or a medium of controlled electron tunneling. We report conductive atomic force microscopy based imaging of the dielectric properties of silicon nanowire oxide layers. The current measurements were complemented with femtosecond laser illumination to determine the band offsets of the nanowire silicon core and oxide shells through multiphoton photoelectron emission. Our work reveals both similarities and differences between silicon nanowire oxides and planar oxides on silicon. The threshold electric field and interface barrier for electron transit were similar to planar oxide. The conductive-AFM based imaging shows non-uniform currents from the nanowire oxide indicating variations in trap densities of the oxide. Additionally, repeated scans under dark and illuminated conditions show trapping and detrapping of injected electrons in the oxide suggesting a high non-uniform distribution of traps in the oxide.
9:00 PM - JJ15.20
A Scalable Method to fabricate High Quality Suspended Carbon Nanotube Devices.
Vinod Sangwan 1 2 , Vincent Ballarotto 2 , Michael Fuhrer 1 , Ellen Williams 1 2
1 Department of Physics, University of Maryland, College Park, Maryland, United States, 2 , Laboratory for Physical Sciences, College Park, Maryland, United States
Show AbstractA novel scalable method has been developed to fabricate suspended carbon nanotube (CNT) field effect transistors using as-grown CNTs without chemical processing. A printing process is used to transfer CVD-grown CNTs onto specially configured electrode sets fabricated on SiO2 and sapphire substrates. The versatility and ease of the technique is demonstrated by controlling the number of suspended CNTs per device, and by re-using the same electrode set multiple times to produce the desired device characteristics. In addition, simultaneous transfer of CNTs to a set of multiple electrodes resulted in at least 10 suspended single-CNT devices in 8 minutes. The technique allows incorporation of different materials, and devices have been fabricated using Au and Pd source-drain electrodes. The quality of suspended CNTs is characterized by electrical transport as well as 1/f noise measurements. Standard resist-processed CNTs on SiO2 substrates show unipolar behavior and strong gate voltage hysteresis associated with doping by the SiO2 surface and charge trapping in the SiO2, respectively. In contrast, suspended CNTs show ambipolar behavior with negligible hysteresis. Low frequency noise measurements on suspended CNT show 1/f behavior with Hooge’s constant 3 x 10-3, a factor of 3 to 10 times less than that of CNTs lying on SiO2, consistent with reduced effect of the SiO2 charge traps, responsible for the bulk of the noise in CNTs on SiO2. **Work supported by the Laboratory for Physical Sciences. The SEFs of the UMD NSF- MRSEC were used in this work .
9:00 PM - JJ15.21
Effect of Cathode Material on the Morphology and Photoelectrochemical Properties of Vertically Oriented TiO2 Nanotube Arrays.
Nageh Allam 1 , Craig Grimes 1 2
1 MATERIALS Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Electrical Engineering, Pennsylvania State University, State College, Pennsylvania, United States
Show Abstract9:00 PM - JJ15.22
Design Rules and Modeling of Photodetectors Based on Individual Nanowires.
Juan Daniel Prades 1 , Roman Jimenez-Diaz 1 , Francisco Hernandez-Ramirez 1 , Luis Fernandez-Romero 1 , Teresa Andreu 1 , Albert Cirera 1 , Albert Cornet 1 , Juan Ramon Morante 1 , Sven Barth 2 3 , Sanjay Mathur 2 3 , Albert Romano-Rodriguez 1
1 EME-IN2UB, Dept. Electronics, University of Barcelona, Barcelona Spain, 2 Institute of Inorganic Chemistry, University of Cologne, Cologne Germany, 3 CVD/PVD Technologies, Leibniz Institute of New Materials, Saarbruecken Germany
Show AbstractSeveral semiconducting nanowires exhibit outstanding performances as photodetectors. To date, most of the works devoted to evaluate the sensing properties of these nanomaterials have not focused on determining the best design rules to obtain optimized devices.In this contribution, we present a theoretical description of the charge generation into the bulk of semiconductor nanowires by incident photons, and a set of design rules to improve the quality of the final prototypes [1]. It is demonstrated that the geometry of the electrical contacts as well as the surface passivation of the nanowires are extremely important parameters to significantly increase the response and stability of these nanodevices., This theoretical discussion has been experimentally validated with the help of individual ZnO nanowires, electrically contacted by means of the use of FIB lithography and exposed to different oxidizing or reducing atmospheres, either unpassivated as well as passivated with a PMMA layer. The here-presented results may pave the way to a new generation of optoelectronic devices based on semiconductor nanowires, either on individual or on bunches of them, whose expected performances will be also discussed.1. J. D. Prades et al. J. Phys. Chem. 2008 (in press).
9:00 PM - JJ15.23
Chirality-dependent Replacement of Flavin Mononucleotide onto Carbon Nanotube using Various Surfactants.
Ity Sharma 1 2 , Sang-Yong Ju 1 , Fotios Papadimitrakopoulos 1 2
1 , university of connecticut, Storrs, Connecticut, United States, 2 chemistry, University of Connecticut, storrs, Connecticut, United States
Show Abstract9:00 PM - JJ15.24
Optical Studies of Single Wall Carbon Nanotubes Wrapped with Different Surfactants.
Cristiano Fantini 1 , José Cassimiro 1 , Valdirene Peressinotto 1 , Flavio Plentz 2 , Antônio Souza Filho 3 , Marcos Pimenta 2 , Clascídia Furtado 1 , Adelina Santos 1
1 Materials Research and Nuclear Fuel, CDTN/CNEN, Belo Hrizonte - MG, Minas Gerais, Brazil, 2 Department of Physics, UFMG, Belo Horizonte, MG, Minas Gerais, Brazil, 3 Department of Physics, UFC, Fortaleza, CE, Ceará, Brazil
Show Abstract9:00 PM - JJ15.25
Electronic, Structural and Transport Properties of Nicotinamide and Ascorbic Acid Interacting with Carbon Nanotubes.
Solange Fagan 1 , Vivian Menezes 2 , Ivana Zanella 1 , Ronaldo Mota 2 , Alexandre Rocha 4 , Adalberto Fazzio 3 4
1 Nanociências, UNIFRA, Santa Maria - RS, RS, Brazil, 2 Física, UFSM, Santa Maria, RS, Brazil, 4 Centro de Ciências Naturais e Humanas, UFABC, São Paulo, SP, Brazil, 3 Física, USP, São Paulo, SP, Brazil
Show AbstractSince their discovery by Iijima [1], carbon nanotubes (CNT) have attracted great interest due to their prominent features. CNTs associated with pharmaceutical compounds can develop promising systems for drug dissemination. However, to successfully use CNTs in drug delivery, there are some points one needs to be aware of such as, for example, the biological compatibilities of the carbon nanostructures and the type of the chemical binding between the drugs and the CNTs [2]. Meanwhile, the nicotinamide (VTB) is necessary for good blood circulation and skin health. In the same view, ascorbic acid (VTC) is important in the immune response system, acting as triglycerides and cholesterol reducer. Both vitamins are soluble in water and part of many other chemical complexes and they present certain instability that can be controlled by the association with other chemical species such as, for example, CNTs. These results are extremely relevant in order to identify the applications of CNTs as drug delivery or molecule sensors. Specifically, in this work, ab initio simulations of the VTB and VTC molecules adsorbed on (8,0) single-walled CNT (SWCNTs) are studied based on density functional theory (DFT) implemented on the SIESTA code [3]. Using a combination of DFT and non-equilibrium Green’s function methods we also performed electronic transport calculations of VTB and VTC molecules adsorbed onto semiconducting SWCNTs. The adsorptions of the molecules are observed to depend strongly on the functionalization of the adsorbed molecules. The results demonstrate that the interactions between the VTC or VTB pristine molecules and the SWCNTs occur in a physiosorption regime. This adsorption is interesting because the molecules can be easily removed from the SWCNT surface, keeping their original properties, which are one of the fundamental conditions for drug release systems. At the same time, the functionalized VTC or VTB molecules, when adsorbed on the SWCNT, via a strongly covalent bond, result on significant changes on the electronic properties. This strong chemical bond demonstrates that the resulting systems could be manipulated in a rather stable way resulting in interesting possibilities for drug carrier under appropriate circumstances. In this regime we also observe significant changes to the electronic transport properties of the CNTs. In all cases we observe a significant reduction of the total transmission both at the valence and conduction bands of the CNT. In some cases we also observe sharp Fano-type resonances which are an indication weak coupling between sharp states of the molecule and the block states belonging to the nanotube. Hence, it is verified that SWCNTs could result in a promising vitamin carriers in both, pristine or functionalized, forms.
[1] Iijima, S.; Nature 1991, 354, 56.
[2] Zanella, I. et al. Chem. Phys. Lett. 2007, 439, 348.
[3] Soler, J. M. et al. Phys.: Condens. Matter. 2002, 14, 2745.
9:00 PM - JJ15.26
Biomimetically Synthesized Silica-Carbon Nanofiber Nanocomposites for the Development of Highly Stable Electrochemical Biosensor Systems.
Nikos Chaniotakis 1 , Maria Hatzimarinaki 1 , Vicky Vamvakaki 1
1 Chemistry, University of Crete, Iraklion, Crete, Greece
Show AbstractPoly(L-lysine) templated silica/carbon nanofiber nanocomposites are used for the encapsulation of Acetylcholinesterase and the development of a novel electrochemical biosensor system. Detailed conformational analysis of poly(L-lysine), Dm. AChE and their interactions with the silica and carbon nanofibers is conducted using ATR-FTIR and Micro-Raman spectroscopy, while electrochemical impedance spectroscopy is used to probe the rotational mobility of the enzyme within the poly(L-lysine) templated silica nanocomposites. It is concluded that the enzyme is highly mobile in its active form within the nanocomposites. Carbon nanofibers allow the efficient electron transfer from the enzyme to the electrode. The silica/carbon nanofiber based biosensor can withstand exposure to extreme operational conditions, such as high temperature, or the presence of proteases and presents high operational stability. This stabilization effect is attributed to the direct interaction of the protein with the silica backbone, as well as to the nanostructured enzyme confinement.
9:00 PM - JJ15.27
Study of the Interaction of Single-stranded DNA Homopolymers with Single Wall Carbon Nanotubes.
Valdirene Peressinotto 1 , Clascídia Furtado 1 , Antônio Cláudio Braga 2 , Adelina Santos 1
1 Materials Research and Nuclear Fuel, CDTN/CNEN, Belo Hrizonte - MG, Minas Gerais, Brazil, 2 Institut of Chemistry, UNICAMP, Campinas, SP, São Paulo, Brazil
Show Abstract9:00 PM - JJ15.28
Addressable Carbon Nanotube Intra-connects With Conductive Polymers.
Seon Woo Lee 1 , Haim Grebel 1 , Daniel Lopez 2 , Avi Kornblit 2
1 Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, New Jersey, United States, 2 New Jersey Nanotechnology Consortium (NJNC), Lucent Technologies Bell Labs, Murray Hill, New Jersey, United States
Show AbstractWe have measured the electrical and optical properties carbon nanotube (CNT) based addressable intra-connects which were deposited with conductive polymer such as, polycarbazole (PCZ). Individual, single-walled CNT (SWCNT) channel was grown by chemical vapor deposition (CVD) precisely between very sharp metal tips on pre-fabricated circuit without post-process. The metal electrodes served as the catalytic seed for the SWCNT growth. Methane and H2 gas mixture was introduced into quartz tube at 900 oC for one hour to enable the tube growth. Polycarbazole (PCZ) was deposited on top of the as-grown individual SWCNT bridge using electrochemical deposition in a three-electrode cell configuration. The quality and type of the SWCNT was assessed by the radial breathing mode of the CNT intra-connect. Electrical properties such as Ids-Vds and Ids-Vgs characteristics were measured in darkness and under white light illumination. The channel conductance increased as a function of white light irradiation. Both the CNT only and PCZ channels were sensitive to the white light exposure, exhibiting approximately 10% conductance increase at intensity values of 0.25W/cm2. Yet, the CNT/PCZ channel exhibited a photo-conductance change of 400% by the same white light intensity.
9:00 PM - JJ15.30
Nanowire Reads a Nanowire Information.
Joondong Kim 1 , Young-Hyun Shin 1 , Moon Seop Hyun 2 , Wayne Anderson 3 , Eung-Sug Lee 1 , Chang-Soo Han 1
1 Nano-Mechanical Systems Research Center, Korea Institute of Machinery and Materials, Daejeon Korea (the Republic of), 2 Measurement and Analysis Division, National Nanofab Center, Daejeon Korea (the Republic of), 3 Electrical Engineering, University at Buffalo, The State University of New York, Buffalo, New York, United States
Show AbstractElectric conductive Ni silicide nanowire (NiSi NW) was used as an electric force microscopy (EFM) probing tip and obtained electric information through the NiSi NW interconnect. NiSi NWs grown by chemical vapor deposition were positioned by dielectrophoretic (DEP) method on a Si cantilever to fabricate the NiSi NW sitting EFM probe and NiSi NW interconnects between Pt metal electrodes. DEP manipulation modulates the number of NW interconnects and controls the position of the NW sitting on a cantilever apex. Lead zirconate titanate (PZT) ferroelectric thin film was positive and negative polarized and the polarities were obtained by probing of the NiSi NW EFM tip to give distinctive charging information of the PZT film. Moreover, the NiSi NW EFM probing was adopted to achieve the electric signal from the NW interconnect. The NiSi NW EFM probe revealed the uniform electric-potential distribution through the single crystalline NiSi NW interconnect. These results demonstrate the high feasibility of the electric excellent NiSi NW to be a functional microscopy probing entity and to be a reliable nanoscale wire-embedding interconnection as well.
9:00 PM - JJ15.31
Confocal Raman Microscopy of One Dimensional ZnO Nanostructures.
Srikanth Singamaneni 1 , Maneesh Gupta 1 , Benjamin Weintraub 1 , Zhong Wang 1 , Vladmir Tsukruk 1
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractZnO nanostructures with various shapes (vertically aligned nanorods, nanobelts, nanohelixes, nanorings) have been synthesized using both vapor phase and solution growth methods. In the simplest example of a nanobelt, the fast growth direction can be either (2 0) or (01 0) or (0001). Here, we show that confocal Raman microscopy can be employed as a fast and nondestructive analytical technique to identify the crystal planes and reveal the relative orientation of the ZnO nanostructure. Various features of the Raman spectrum of ZnO nanostructures (presence of the A1(TO) mode, width of the E2 mode) were found to be sensitive to relative orientation of the incident source laser and the crystal plane. Furthermore, owing to the optical anisotropy of ZnO, Raman scattering from the substrate is modulated (either enhanced or suppressed with respect to the background) depending on the polarization of the incident light with respect to orientation of the nanobelt. The results presented here describe a novel method to nondestructively identify the growth, relative orientation, and the waveguiding properties of the ZnO nanostructures which is important to a wide variety of piezotronic devices, sensors, and waveguides based on ZnO nanstructures.
9:00 PM - JJ15.33
Mechanical and Electrical Properties of Single LaB6 Nanorods.
Han Zhang 1 , Jie Tang 1 , Zheng Ren 1 2 , Lu-Chang Qin 2 3
1 1D Nanomaterials Research Group, National Institute for Materilas Science, Tsukuba, Ibaraki, Japan, 2 Curriculum in Applied and Materials Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States, 3 Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Show AbstractLanthanum hexaboride (LaB6) has been used as a thermal electron emission cathode material for more than fifty years. The low work function and structural integrity of the LaB6 nanowires / nanorods offer a great promise as field-emission point sources for applications where high performance requirements including high emission brightness, high emission stability, low energy spread, and long service life are desired as in the applications as the electron emitters utilized in electron-beam analytical instruments like the transmission electron microscopes and/or scanning electron microscopes. When the dimensions of the LaB6 nanowires / nanorods are reduced to the nanoscale, many properties, including mechanical, electrical, electronic, and magnetic properties, often exhibit unique features different from their bulk form. Using the lithographic and manipulation techniques, we have fabricated structures where individual LaB6 nanorods are positioned at desired locations for property measurements. We have measured the mechanical and electrical properties of individual LaB6 nanorods synthesized using a chemical vapor deposition method that we have established recently. In the measurement of the mechanical properties, we employed the three-point method as well as the nano-indentation method. The Young’s modulus and the indentation hardness of single-crystalline LaB6 nanorods were measured using the three-point bending method by an atomic force microscope (AFM) with a custom-designed AFM probe. The Young’s modulus was obtained to be E = 467.1 ± 15.8 GPa and the indentation hardness H = 70.6 ± 2.1 GPa.In the measurement of the transport properties of individual LaB6 nanowires, we designed and fabricated a microcircuit using lithographic techniques. Results will be reported and discussed in connection with the morphology of the nanowires and the potential applications as field-emission point electron sources.
9:00 PM - JJ15.35
Electron-Phonon Coupling in GaAs and AlGaAs Nanowires.
Megan Brewster 1 , Oliver Schimek 2 , Stephanie Reich 2 , Silvija Gradecak 1
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Applied Physik, Freie Universitat Berlin, Berlin Germany
Show AbstractSemiconductor nanowires play a promising role in nano-scale electronic devices, due in part to inherent quantum confinement effects of electronic transport in quasi-one dimensional structures. Phonon quantum interference with electrons in crystalline semiconductors further complicates the action of electronic transport in these systems. However, despite the relevance of electron-phonon coupling at the nanoscale, there is little workreported on the quantum interference effects in these novel quasi-one dimensional systems. Here we investigate the Fröhlich- and Fano-type electron-phonon couplings in individual semiconductor nanowires using micro-Raman spectroscopy as a function of materials composition, excitationwavelength, and wire diameter. We observe unusually strong LO multiphonon modes up to the fourth orderin single GaAs and AlGaAs nanowires due to a cascade scatteringprocess of electrons with 1LO phonons by Fröhlich coupling. The 2LO:1LO elastic scattering cross-section exhibits a sharp resonance at energies equal to one LO-phonon energy above the bandgap for both GaAs and AlGaAs systems, with ratiosreaching beyond 6.0 in AlGaAs at the resonance condition. The2LO:1LO peak intensity ratio decreases with wire diameter in GaAs nanowires; a result that is contrary to expectations, as the bandgap is blue-shifted due to quantum confinement at small diameters towards resonance conditions. We alsoobserve asymmetric phonon modes in AlGaAs nanowires, suggesting that Fanoquantum interference between excitation to a continuum of energystates and to a discrete energy level is occurring. These resultsimply that electron-phonon coupling in GaAs and AlGaAs nanowires isrich with interesting physics, and that further investigation willaide in the description of electronic transport in nanowire electronic devices.
9:00 PM - JJ15.36
Electroluminescence from Electrolyte Gated Carbon Nanotube Arrays.
Jana Zaumseil 1 , Xinning Ho 2 , Jeffrey Guest 1 , John Rogers 2 , Gary Wiederrecht 1
1 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 2 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractCarbon nanotubes are of great interest for nanoscale optoelectronic devices, due to their high charge carrier mobility and emission at telecommunications wavelengths. In order to further develop this opportunity, it is important to understand the large impact that the chemical and physical environment of carbon nanotubes has on their charge transport and light-emitting properties. For example, the photoluminescence yield of suspended nanotubes is significantly higher than when in contact with a substrate, and fluorescence from solvent dispersed nanotubes is quenched by metal cations. Successful implementation of carbon nanotubes in optoelectronic devices requires an understanding of these quenching processes. Here we demonstrate near-infrared electroluminescence from carbon nanotube field-effect transistors that are gated via a polymer electrolyte or ionic liquid. Due to the high effective capacitance of up to 50 μF/cm2 electrolyte gating achieves large carrier densities at low gate voltages with minimal current hysteresis. Efficient injection of holes and electrons leads to ambipolar device characteristics and associated light-emission where holes and electrons recombine even for nanotubes with larger bandgaps.We used aligned, high density arrays of carbon nanotubes, which enable spatial and spectral resolution of electroluminescence from dozens of nanotubes in a single device, one nanotube at a time. The unusual environment of an electrolyte with high ion concentrations allows us to study the impact of surrounding mobile charges on exciton confinement and quantum yield for nanotubes of various diameters and chiralities. While we use parallel arrays to observe electroluminescence from nanotubes with no or little interaction, we also use low and high density random networks to study charge and energy transfer between semiconducting and metallic nanotubes, as well as different semiconducting nanotubes. The prospects for future optoelectronic applications of carbon nanotubes are discussed.
9:00 PM - JJ15.37
Visible Blind Photocathode Based on MgZnO Thin Film Alloys and Nanostructures for Space Applications.
R. Vispute 1 , T. Venkatesan 1 , D. Pugel 2 , B. Woodgate 2 , G. Hilton 2 , T. Norton 2
1 Physics, Center for Nanophysics and Applied Materials (CNAM), University of Maryland, College Park, Maryland, United States, 2 , NASA-Goddard Space Flight Center, Greenbelt, Maryland, United States
Show Abstract9:00 PM - JJ15.38
Theoretical Study of Current-Voltage Characteristics of Carbon Nanotube Wire Functionalized with Hydrogen Atoms.
Hiroyuki Fueno 1 , Yoshikazu Kobayashi 1 , Yoshitaka Kato 1 , Kazuyoshi Tanaka 1
1 Department of Molecular Engineering, Kyoto University, Kyoto Japan
Show AbstractCarbon nanotubes (CNTs) have been attracting much attention for making molecular devices, since CNTs are expected to afford intriguing nano devices such as, for instance, high-speed transistors due to ballistic conduction. It has been suggested that individual metallic single-walled CNT (SWCNT) with tunneling barriers of the short sections can be used for the single-electron transistor (SET). Although a part containing a quantum dot function is necessary to realize the SET function, it is desirable not to come from accidental fact such as defects. In the present study, we suggested that functionalized SWCNT could be expected to be used for a quantum dot. We theoretically investigated the electronic transport of the SWCNT(6,6) wire and that functionalized with hydrogen atoms on the side wall (H-CNT), the latter modeling nano-device with a quantum dot inside. We calculated the current-voltage (I-V) characteristics by means of the conventional non-equilibrium Green’s function approach based on the density functional theory using the ATK(Atomistix ToolKit) program package. A gate electrode was introduced into a system and the gate-voltage depending characteristics were examined as well as an effect of the bias voltage. In the presentation, we will report that the peaks of the I-V spectrum of H-CNT indicate a resonant tunneling effect and its related results. We conclude that H-CNT model is of interest for such a nano-device. The current-voltage characteristics of the CNT wires between the silicon electrodes with Si (111) surface will be also reported.
9:00 PM - JJ15.39
Schottky Contacted Nanomaterials for UV Detection.
Joondong Kim 1 , Ju-Hyung Yun 1 , Chang-Soo Han 1 , Yun Chang Park 2 , Jeunghee Park 3
1 Nano-Mechanical Systems Research Center, Korea Institute of Machinery and Materials, Daejeon Korea (the Republic of), 2 Measurement and Analysis Division, National Nanofab Center, Daejeon Korea (the Republic of), 3 Chemistry, Korea University, Seoul Korea (the Republic of)
Show AbstractNanomaterials (such as carbon nanotubes, nanowires, and nanoparticles) embedded Ultraviolet (UV) detectors were fabricated and presented distinctive responses to UV light. Nanomaterial containing solution was firstly prepared and then dropped in pre-patterned Pt (Platinum) interdigitated electrode fingers with an applying electric field. Thermal treatment was performed to ensure the contact formation between nanomaterials and Pt electrodes. Transmission electron microcopy was adopted to investigate the structures of nanomaterials and decoration of nanoparticles. The detector unit of nanomaterial-embedding on Pt electrodes was observed in scanning electron microscopy. In UV responses, the single wall carbon nanotubes (SWCNTs) embedded sensor showed the increase of electric resistance and no significant change was obtained from the multi wall carbon nanotubes (MWCNTs) sensor. Otherwise, Tin oxide nanowires (SnO2 NWs) sensor gave the decrease of resistance, which is different to the performance of SWCNT. Moreover, the Palladium (Pd) doping in CNT may enhance the responsivity to UV light comparing to the performance of the bare CNT detector. We present the mechanism of UV responses of various nanomaterials with discussing in Schottky contact formation between the nanomaterials and electrode metal. It also covers the schemes of the selective UV detection.
9:00 PM - JJ15.4
Flexural Vibration Spectra of Various Nanowires Measured using Laser Doppler Vibrometry.
Laura Biedermann 1 2 , Ryan Tung 1 3 , Arvind Raman 1 3 , Ronald Reifenberger 1 2
1 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 2 Physics Department, Purdue University, West Lafayette, Indiana, United States, 3 Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States
Show AbstractReliable estimates for the moduli of nanowires are of interest for potential applications in ultra-high frequency resonators, sensors, and nanoelectronics. We have used laser Doppler vibrometry to measure the oscillation spectra of individual nanowires including multiwalled carbon nanotubes. An advantage of this technique is that the eigenfrequencies between 0 and 20 MHz can be measured with 156 Hz frequency resolution. This high frequency resolution allows the quality factors and resonant frequencies of the nanowires to be accurately determined. Using Euler-Bernoulli beam theory, the Young’s modulus can be calculated from the resonance frequencies of the oscillation spectrum and the dimensions of the nanowires, which are obtained from parallel SEM studies. Mie scattering is used to estimate lower limits for the diameters of nanowires, below which, the scattered light is undetectable. Furthermore, techniques to increase the effective scattering efficiency of the nanowires will be presented. Under ambient conditions, the low quality-factor characterizing each measured vibrational resonance is due to gas damping in the transition or free molecular regime. To determine the intrinsic quality factor of the nanowires, the oscillation spectra of the nanowires will be measured under low-vacuum conditions. The techniques developed can be used to measure the vibrational spectra of any suspended nanowire with high frequency resolution.
9:00 PM - JJ15.40
A Simple Manipulation of Single Wall Carbon Nanotubes Network as Infrared Detector.
Li-Chun Wang 1 2 , I-Ju Teng 2 , Cheng Tzu Kuo 3 , Han-Wen Kuo 1 , Yuh Sung 1 , Shau-Ray Lin 1 , Shiang-Feng Tang 4 , Yan-Ten Ho 5
1 Chemistal Systems Research Division, Chung-Shan Institute of Science and Techanlogy, Tao-Yuan Taiwan, 2 Dept. of Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan, 3 Institutes of Materials and Systems Engineering, Ming Dao University, Changhua Taiwan, 4 Materials & Electro-Optics Research Division, Chung-Shan Institute of Science & Technology, Taoyuan Taiwan, 5 Electronic Research Division, Chung-Shan Institute of Science & Technology, Taoyuan Taiwan
Show Abstract9:00 PM - JJ15.41
A New Thermionic Cathode Based on Carbon Nanotubes with a Thin Layer of Low Work Function Barium Strontium Oxide. surface coating.
Feng Jin 1 , Little Scott 1
1 Department of Physics and Astronomy, Ball State University, Muncie, Indiana, United States
Show Abstract9:00 PM - JJ15.42
Characterization of Pt Nanocontacts to ZnO Nanowires using Focused-Ion-Beam Deposition.
Pei-Hsin Chang 1 , Kun-Tong Tsai 1 , Cheng-Ying Chen 1 , Jr-Hau He 1
1 , Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei Taiwan
Show Abstract9:00 PM - JJ15.5
First-principles Phase Diagram of Ultrathin Silica-germania Nanotubes: Negatives Poisson Ratio and Thermal Expansion, High Dielectric Constant and Wide Tunable Band Gap.
Caetano Miranda 1 , Tomohiro Kabashima 1 , Yasuhiro Fukunaka 2 , Toshifumi Matsuoka 1
1 JAPEX - Energy Resources Engineering, Kyoto University, Kyoto Japan, 2 Institute for Nanoscience & Nanotechnology, Waseda University, Tokyo Japan
Show AbstractWe have applied full range of first-principles characterization to predict and calculate the thermo-mechanical and optical properties of ultrathin silica-germania nanotubes. The optimal structures and energetics of silica-germania nanotubes have been calculated for different lengths and radii within Density Functional Theory using the GGA functional. The basic structure is formed by SiO2[x]GeO2[1-x] rings connected by Oxygen bridge atoms with Si/Ge atoms fully coordinated. We found that nanotubes formed by 5 and 6-member Silica-Germania rings have the lowest energy structures. The phase diagram for of SiO2[x]GeO2[1-x] optimal structures was determined. The electronic structure of these systems show a tunable band gaps for different Silica-Germania amount going from wide band gap (> 5eV) to lower ones (1.5 eV). The Born effective charges, piezoelectric coefficients and static dielectric constants have been also obtained. The calculations reveal the importance of O-bridge atoms on the thermal and mechanical properties. Unusual properties such as negatives Poisson ratio and thermal expansion have been observed. Bulk crystalline phases of Silica such as crystobalite and quartz also show some of these unusual properties. In the same way, apparent negative thermal expansion has been suggested to occur in Carbon nanotubes. We are going to discuss the nature of those phenomena regarding the dimensionality and the intrinsic material properties of Silica – Germania bulk systems. Our findings suggests a potential use of silica-germania nanotubes as mechanical absorbent and nanostructures electric generator and can guide on the synthesis of these interesting nanostructures.
9:00 PM - JJ15.6
New Precursors for Boron Nanotubes: A Novel Bonding Picture.
Hui Tang 1 , Sohrab Ismail-Beigi 1 2
1 Department of Applied Physics, Yale University, New Haven, Connecticut, United States, 2 Center for Research on Interface Structures and Phenomena (CRISP), Yale University, New Haven, Connecticut, United States
Show AbstractBoron nanotubes(BNT) have attracted a great deal of attention since their first fabrication in experiments. In contrast to carbon nanotubes, all BNT were expected to be metallic with large densities of states at their Fermi energies regardless of their chirality or diameters, which may provide excellent and robust conducting systems for one-dimensional electronics. In order to study BNT, researchers have proposed several two-dimensional atomically thin boron sheets as precursors and investigated various properties of BNT and their possible applications. Based on first principles density functional theory calculations, we present a new class of boron sheets, composed of mixtures of triangular and hexagonal motifs, that are more stable than any sheet-structures considered to date and thus are more likely to be the precursors of single-walled BNT [1]. We describe the nature of bonding in these new sheets and explain their stability based on a balance of two-center and three-center bonding. Our bonding picture is also crucial for the stability of other boron nanostructures. Moreover, we discuss the asymmetric buckling behavior of boron sheets and show that the electronic kinetic energy is the driving force for the buckling. We apply this knowledge to understand the buckling of BNT, the stability of the buckling and their effects on the BNT electronic properties. [1] H. Tang, and S. Ismail-Beigi, Phys. Rev. Lett. 99, 115501 (2007).
9:00 PM - JJ15.7
Theoretical Analysis of the Spontaneous Bending of Piezoelectric Nanobelts.
Carmel Majidi 1 , Mikko Haataja 2 1 , David Srolovitz 3
1 Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey, United States, 2 Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States, 3 Yeshiva College, Yeshiva University, New York, New York, United States
Show AbstractA comprehensive free energy-based analysis explains the experimentally observed spontaneous bending of ±(0001) faceted zinc oxide (ZnO) nanobelts into nanoarcs and nanorings [1,2]. These structures are semiconducting and piezoelectric and will have an important role in a variety of applications, including nanoelectromechanical systems (NEMS) and energy harvesting [3]. Understanding the physical mechanisms that govern the morphologies of nanoscale structures with reduced dimensionality is key in developing novel materials for a wide range of applications.
The nanobelt is treated as a planar elastic rod that is capable of stretching and bending about its widthwise axis. The free energy F is derived in terms of the bending curvature κ, extensional stretch γ, and electric potential Φ. F includes the energetic contributions of elastic deformation, surface tension, electrostatics, polarization-induced surface charge, non-uniform space charge, and piezoelectric interactions. The constitutive laws for linear piezoelasticity along with symmetries of the free energy functional with respect to variations in κ, γ, and Φ furnish the balance laws for mechanical stress (linear and angular momentum) and electric displacement (Gauss’s Law).
At equilibrium, the analysis suggests that experimentally observed curvatures are only possible through piezoelectric interactions induced by non-uniformly distributed space charge. Such distributions can be created by the accumulation of free charge carriers, which leave behind opposite charge in the depletion zone. Our predictions for spontaneous curvature are markedly different from those of previous model for spontaneous bending, which neglect piezoelectricity and space charge and instead compare the effects of elasticity, surface tension and polarization-induced surface charge [1,2].
[1] X. Y. Kong and Z. L. Wang, Nano Lett. 3, 1625-1631 (2003).
[2] W. L. Hughes and Z. L. Wang, J. Am. Chem. Soc. 126, 6703-6709 (2004).
[3] Z. L. Wang, J. Phys.: Condens. Matter 16, R829-R858 (2004).
9:00 PM - JJ15.9
Improved Contact for Thermal and Electrical Transport in Carbon Nanofiber Interconnects.
Tsutomu Saito 1 , Toshishige Yamada 1 , Drazen Fabris 1 , Hirohiko Kitsuki 1 , Patrick Wilhite 1 , Cary Yang 1
1 , Santa Clara University, Santa Clara, California, United States
Show AbstractCarbon nanotubes (CNTs) and carbon nanofibers (CNFs) are seriously considered as next-generation interconnect materials because of their high electrical and thermal conductivities and superior reliability over copper. To make the most of these excellent properties, their performance and reliability as interconnects must be examined in great depth. This paper focuses on one reliability aspect, electrical transport and breakdown in these materials. To study reliability of carbon nanofibers (CNFs) under high-current stress, the optimization of contact with metal is critically important. In this work, systematic characterization of CNF under high-current stress has been performed for four different configurations. These are: (1) CNFs suspended between two pre-patterned planar electrodes on a SiO2/Si substrate, (2) CNFs resting on a SiO2/Si substrate between two pre-patterned electrodes, (3) CNFs suspended between two pre-patterned electrodes with W deposited on top of the CNFs and electrodes to reduce contact resistance, and (4) CNFs supported between two pre-patterned electrodes with W deposited on top of the CNFs. For configurations (3) and (4), the contact resistance with deposited W is typically a few kΩs, representing one to two orders of magnitude reduction from configurations (1) and (2). By examining and comparing CNF breakdown in these four configurations, a better understanding of the role of contact resistance is obtained. Using scanning electron microscopy, we observe W contact under high-current stressing. The results for configurations (1) and (3) for suspended nanofibers are satisfactorily explained with a heat transport model taking into account Joule heating and heat dissipation along the CNF, while the supported cases show a consistently larger current density just before breakdown, confirming effective heat dissipation to the substrate. The results obtained using these four configurations provide an enhanced understanding of the electrothermal transport and breakdown mechanisms in carbon nanofiber interconnects.
Symposium Organizers
Prabhakar Bandaru University of California-San Diego
Sonia Grego RTI International
Ian Kinloch University of Manchester
JJ16: Mechanical Properties: I
Session Chairs
Sonia Grego
Sonia Grego
Ian Kinloch
Thursday AM, December 04, 2008
Room 302 (Hynes)
9:30 AM - **JJ16.1
Why might Fibres made from Carbon Nanotubes be Strong?
Alan Windle 1 , James Elliot 1 , Krzysztof Koziol 1 , Anna Moisala 1 , Marcelo Motta 1 , Kelly Stano 1 , Juan Vilatela 1
1 , University of Cambridge, Cambridge United Kingdom
Show Abstract10:00 AM - JJ16.2
Tunable Poisson's Ratio for Carbon Nanotube Sheets.
Vitor Coluci 1 , Lee Hall 2 , Mikhail Kozlov 2 , Mei Zhang 3 , Socrates Dantas 4 , Douglas Galvao 5 , Ray Baughman 2
1 , Center for High Education on Technology, University of Campinas , Limeira, SP, Brazil, 2 , Alan G. MacDiarmid NanoTech Institute and Dep. of Chemistry, University of Texas, Richardson, Texas, United States, 3 , Department of Industrial and Manufacturing Engineering, Florida State University, Tallahassee, Florida, United States, 4 , Universidade Federal de Juiz de Fora, Juiz de Fora, MG, Brazil, 5 , Applied Physics Department, Institute of Physics, University of Campinas, Campinas, SP, Brazil
Show Abstract10:15 AM - JJ16.3
Stress Transfer in Double Walled Carbon Nanotubes in Composites.
Shuang Cui 1 , Ian Kinloch 1 , Robert Young 1 , Laure Noe 2 , Marc Monthioux 2
1 School of Materials, University of Manchester, Manchester United Kingdom, 2 CEMES, UPR 8011 CNRS, Toulouse France
Show AbstractThe level to which stress is transferred between the different layers or walls in multi-walled carbon nanotubes (MWNT) is of profound significance for their use in composites. It has been shown theoretically that the effective modulus of the MWNT reinforcement is reduced dramatically if the stress transfer between the layers is poor [1]. In this study well-characterized double-walled nanotubes (DWNT) have been prepared from single walled nanotubes (SWNT) using the peapod route with C60. In particular it has been possible to use Raman spectroscopy to identify bands from the outer and inner walls of the DWNTs. Composites have been prepared by dispersing small quantities of the DWNTs in an epoxy resin. Stress transfer to the DWNTs during deformation of the composite has been monitored from the relative shift of the Raman G’ bands [2] from the inner and outer nanotube walls. It has been found that the stress transfer from the outer to the inner walls is poor such that the inner walls in the DWNTs are virtually unstressed during both tensile and compressive deformation. The implication of this result is that the anticipated levels of reinforcement by MWNTs in composites cannot be achieved.[1] L. Zalamea, H. Kim and R.B. Pipes, Composites Science and Technology, 67 (2007) 3425-3433.[2] C.A. Cooper, R.J. Young and M. Halsall, Composites A: Applied Science and Manufacturing, 32 (2001) 401-411.
10:30 AM - JJ16.4
The Mechanical Response of Aligned Carbon Nanotube Mats via Transmitted Laser Intensity Measurements.
Christian Deck 1 , Chinung Ni 1 , Kenneth Vecchio 2 , Prabhakar Bandaru 1
1 Materials Science, UC San Diego, San Diego, California, United States, 2 Nanoengineering, UC San Diego, San Diego, California, United States
Show AbstractMany recently discovered nanostructures have been shown to possess exceptional material properties and are thought to hold great potential for many possible applications. Carbon nanotubes remain one of the more widely studied nanostructures today, with ongoing attempts to exploit their small size, large aspect ratio, and combination of mechanical, optical, and electronic properties. In this work, a chamber was designed to pass a laser through a mat of aligned carbon nanotubes and monitor the variation in transmitted light intensity in response to different mechanical deformations. This approach specifically takes advantage of the scale and mechanical and optical properties of carbon nanotubes, particularly their high elastic limit and anisotropic light absorption. In the first study, we measure the flexural rigidity (the product EI) of carbon nanotube arrays. Vertically aligned nanotubes were grown in periodic arrays with lengths up to 100µm, and fluid flow was applied normal to the nanotube axis. These nanotubes deflect due to shear caused by fluid drag, and this deflection is monitored experimentally with high accuracy by measuring a decrease in transmitted light intensity as a function of increasing fluid velocity and density. This response was also simulated, using a model based on the Stokes-Oseen equations with a correction for the small length scales associated with nanotube mats. The experimental data on the deflections and the estimated force on the tubes from simulations are used for determining the flexural rigidity of CNTs, to be of the order of 10^(-15) Nm^2. Using this method, we also demonstrate a carbon nanotube-based fluid flow and shear force sensor that offers fast response, repeatability, and that can measure forces in very close proximity to surfaces (such as in boundary layer flow). In addition to our investigation of the shear response of aligned nanotube arrays, deformation due to compressive stresses was also studied using a variation on our transmitted laser intensity method. Absorption of light by aligned nanotube mats was found to be anisotropic, with the intensity of transmitted light varying as a function of the angle of polarization of the laser and the angle of incidence of the laser with the nanotube axis. This effect is strongest when the nanotube mats are highly aligned, and decreases with increasingly random nanotube orientation within the mat. Under compressive loading, nanotubes strain and buckle; the resulting loss of alignment leads to a more isotropic light absorption which can be measured by monitoring the transmitted light intensity. In addition to correlating this variation in polarization with the magnitude of the loading, light intensity was also monitored as a function of time following the removal of the applied force, and a time dependent recovery was studied.
10:45 AM - JJ16.5
Difference in the Electromechanical Response of Isolated Metallic and Semiconducting Nanotubes Observed by Raman Spectroscopy.
Hootan Farhat 1 , Martin Kalbac 2 3 , Hyungbin Son 2 , Mildred Dresselhaus 2 , Jing Kong 2
1 DMSE, MIT, Cambridge, Massachusetts, United States, 2 EECS, MIT, Cambridge, Massachusetts, United States, 3 J. Heyrovky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Prague Czechia
Show AbstractWe report on the shifting of the G’ band (~2700cm-1) frequency of isolated single-walled carbon nanotubes as a function of electrochemical doping. Large variations were observed in the doping response of different isolated nanotubes. Most notably, there is a distinction in the doping dependence of the G’ band of metallic and semiconducting nanotubes. Using the radial breathing mode frequency we identify the observed nanotubes and classify their behaviors. Our observations are explained in terms of the charge induced structural deformation of different nanotubes.
JJ17: Mechanical Properties: II
Session Chairs
Thursday PM, December 04, 2008
Room 302 (Hynes)
11:30 AM - **JJ17.1
Diverse Carbon Nanotube Artificial Muscles Meet an Exciting New Family Member.
Ali Aliev 1 , Jiyoung Oh 1 , Mikhail Kozlov 1 , Alexander Kuznetsov 1 , Shaoli Fang 1 , Alexandre Fonseca 1 , Raquel Robles 1 , Márcio Lima 1 , Mohammad Haque 1 , Yuri Gartstein 1 , Mei Zhang 2 , Anvar Zakhidov 1 , Ray Baughman 1
1 , NanoTech Institute, Universty of Texas at Dallas, Richardson, Texas, United States, 2 , Department of Industrial Engineering, Florida State University , Tallahassee, Florida, United States
Show AbstractHumankind has had little success in replicating the wondrous properties of natural muscle, which has meant that the most advanced prosthetic limbs, exoskeletons, and humanoid robots lack critically needed capabilities. Use of electrical input power, instead of nature’s choice of high energy density fuel, is a problem for autonomous operation, which severely limits operational lifetime between recharge. Another problem is the inability to crowd sufficient motors into available space to provide natural movement. Probably no other material has been described for so many fundamentally different types of actuators than carbon nanotubes. Demonstrated electrically powered and fuel powered nanotube actuators provide up to a few percent actuator stroke and a hundred times higher stress generation than natural muscle. Large stroke pneumatic nanotube actuators have been demonstrated that use electrochemical gas generation within nanotube sheets. In other studies, nanotubes have been used either as electrodes or as additives to profoundly modify the response of other actuating materials – like dielectric, ionically conducting, photoresponsive, shape memory, and liquid crystal polymers. All of these advances will be discussed, together with most recent improvements. Most important, totally new types of carbon nanotube muscles will be described. These nanotube muscles provide over 300% actuator stroke, over 10^4 %/minute stroke rate and can be operated from near 0 K to far above the demonstrated 1900 K.
12:00 PM - JJ17.2
Liquid Phase Dispersion of Nanotubes and Graphene: The First Step on the Path to Functional Composites.
Jonathan Coleman 1 2
1 Physics, Trinity College Dublin, Dublin Ireland, 2 CRANN, Trinity College Dublin, Dublin Ireland
Show AbstractSingle walled carbon nanotubes have been limited from fulfilling their extraordinary potential by their tendency to aggregate. Due to their high surface energy they are generally found in bundles containing hundreds of nanotubes. We demonstrate that nanotubes can be efficiently exfoliated form these bundles in certain solvents simply by control of the concentration. Atomic force microscopy measurements show that the mean bundle diameter falls with decreasing concentration while the fraction of individual tubes increases with decreasing concentration. At low concentrations the fraction of individuals approaches 70%. This phenomenon is universal and has also been observed for nanotubes dispersed with the aid of surfactants, DNA, peptides as well as inorganic nanowires in solvents. In addition we have also observed this behaviour for functionalsed nanotubes dispersed in common solvents. By working with low concentration solutions of nanotubes we can fabricate high quality composites where the nanotubes remain extremely well dispersed in polymer matrices even at high volume fraction. We use these techniques to make composites with electrical conductivities in the range of tens of thousands of S/m. In addition we can mechanically reinforce composites. By adding less than one percent nanotubes we can strengthen and stiffen polyvinylchloride by ~50%. More importantly we can dramatically increase the ductility resulting in a tenfold increase in toughness. By electro-spinning composite membranes we can produce materials with strength, stiffness and toughness approaching that of normal plastics, but with densities as low as 300 kg/m3. Finally we can apply some of these ideas to graphite leading to the liquid phase exfoliation of graphite in certain solvents to give graphene dispersions with high yield. We have produced monolayer graphene with yields of up to 1wt%. Raman and X-ray photoelectron spectroscopy shows this graphene to be defect and oxide free. These dispersions can be used to produce graphene thin films and composites. These structures have novel optical and electrical properties.
12:15 PM - JJ17.3
Composites Reinforced with Continuous Carbon Nanotubes.
Lijie Ci 1 , J. Suhr 2 , P. Ajayan 1
1 MEMS, Rice University, Houston, Texas, United States, 2 Department of Mechanical Engineering, The University of Nevada-Reno, Reno, Nevada, United States
Show AbstractRecent advances in fabrication of carbon nanotubes allow us to grow them up to several millimeters at length, and this provides an opportunity for fabricating continuous nanotube reinforced composites. It has been reported that free-standing arrays of millimeter long, vertically aligned multiwalled nanotubes exhibit super-compressibility, outstanding fatigue resistance and viscoelastic characteristics. In this study we attempt to utilize the free-standing arrays of the nanotubes as continuous reinforcements in polymer composites. Here, we study the compressive mechanical behavior of the continuous nanotubes composites, and report that under compressive loadings, the nanotube composites can generate more than an order of magnitude improvement in the longitudinal modulus (up to 3,300%) as well as damping capability (up to 2,100%). It is also observed that composites with random distribution of nanotube of same length and similar filler fraction provide three times less effective reinforcement in composites. In addition to the mechanical properties, excellent electrical and thermal conductivity of the continuous nanotubes in the composites also add promise for light-weight, multi-functional composites suitable for a variety of engineering applications.
12:30 PM - JJ17.4
Reinforcement of Phenolic Resin with Carbon Nanotubes: A Multiscale Study.
Padraig Moloney 1 , Pasha Nikolaev 2 , Peter Boul 2 , Mary Jane O'Rourke 1 , Edward Sosa 2 , Sivaram Arepalli 2 , Leonard Yowell 1
1 Applied Nanotechnology Team, NASA Johnson Space Center, Houston, Texas, United States, 2 Applied Nanotechnology Team, ERC Inc., Houston, Texas, United States
Show AbstractAn interest in nanocomposites based on phenolic resin has been sparked by their application in ablative thermal protection system (TPS) materials used for atmospheric reentry. Phenolic resin is a component in Phenolic Impregnated Carbon Ablator (PICA), a TPS material developed at NASA Ames Research Center in the mid-90’s for Discovery class missions [1]. Previous work has reported large Raman response under strain in phenylsulfonated SWCNT dispersed in SC-1008 phenolic resin films which was interpreted as an improvement in stress transfer [2]. The current study extends this to explore the stress transfer and mechanical properties of surface–modified single-wall and multi-wall carbon nanotubes in phenolic resin. Nanocomposite samples were fabricated by a solution-processing method. Test coupons were cast and cured in appropriate molds. Two functionalization approaches (with unfunctionalized nanotubes as a control) were adopted, with potential scalability to multi-gram quantities in mind. The extent of functionalization was monitored by XPS and TGA-MS. Mechanical testing included Dynamic Mechanical Analysis (DMA) and tensile tests. Stress transfer was studied by measurements of SWCNT Raman G-band shift dependence on the strain in the matrix. Nanotube dispersions were evaluated by optical and electron microscopy. Conclusions on the relative importance of nanotube dispersion vs. bonding to the matrix, and the nature of the mechanisms of reinforcement in this particular system will be discussed. [1] “Phenolic Impregnated Carbon Ablators (PICA) as Thermal Protection Systems for Discovery Missions”, Huy K. Tran, Christine E. Johnson, Daniel J. Rasky, Frank C. L. Hui, Ming-Ta Hsu, Timothy Chen, Y. K. Chen, Daniel Paragas, and Loreen Kobayashi, NASA Technical Memorandum 110440, April 1997[2] P. Nikolaev, M. Stackpoole, W. Fan, B. A. Cruden, M. Waid, P. Moloney, S. Arepalli, J. Arnold, H. Partridge, and L. Yowell, “Carbon nanotube-enhanced carbon-phenolic ablator material”, presented at MRS fall meeting, November 2006, Boston, MA.
12:45 PM - JJ17.5
Interfacial and Morphology Studies in Polyvinyl Alcohol/Single-Wall Carbon Nanotube Composites to produce High-Performance Materials.
Marilyn Minus 1 , Satish Kumar 1
1 Polymers, Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractThis study illustrates the ability of single-wall carbon nanotubes (SWNT) to nucleate and template polymer crystallization and orientation at the interface. Polymer crystallization in the near vicinity of SWNT (interphase) has been studied to understand the capability of SWNT in influencing polymer morphology in bulk films and fibers. Gel-spinning was used to produce polyvinyl alcohol (PVA), and PVA/SWNT fibers. With 1 wt% SWNT loading in PVA, the fiber tensile strength increased from 1.6 GPa for the control PVA to 2.6 GPa for PVA/SWNT. Analysis of this data suggests stress of up to ~120 GPa on the SWNT. This is the highest reported stress on the SWNT to date and confirm excellent reinforcement and load transfer of SWNT in the PVA matrix. Raman spectroscopy data show high SWNT alignment in the fiber where the ratio is measured to be 106.In addition to PVA/SWNT fiber spinning work, fibrillar and folded-chain single crystal growth of PVA in the presence of SWNT was also studied to look in detail at PVA-SWNT interfacial interactions. PVA/SWNT fibrillar crystals exhibit SWNT templated PVA extended-chain crystals at the interphase. PVA fold-chain single crystals were also grown in PVA solutions as well as PVA/SWNT dispersions over a different time scales at various temperatures. PVA single crystal growth in PVA/SWNT dispersions is templated by SWNT, and show the presence of new morphologies and crystal structure for PVA. Furthermore, PVA single crystals grown at various temperatures show morphology dependant electron beam irradiation resistance.
JJ18: Nanocomposites
Session Chairs
Thursday PM, December 04, 2008
Room 302 (Hynes)
2:30 PM - **JJ18.1
Nanotube as a Specimen Cell, - Individual Molecular Imaging Inside Carbon Nanotubes.
Kazu Suenaga 1
1 , AIST, Central 5, Tsukuba Japan
Show Abstract3:00 PM - JJ18.2
STEM-HAADF Tomography Studies of Carbon Nanotubes-quantum Dots Nanocomposites.
Ana Hungria 1 2 , Beatriz Juarez 3 , Christian Klinke 3 , Horst Weller 3 , Paul Midgley 1
1 Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Inorganic Chemistry, University of Cadiz, Puerto Real, Cadiz, Spain, 3 Institute of Physical Chemistry, University of Hamburg, Hamburg Germany
Show AbstractNovel applications in nanotechnology rely on the design of tailored nano-architectures. For this purpose, carbon nanotubes (CNTs) and nanoparticles (NPs) or so called quantum dots are intensively investigated. The integration of semiconductor nanoparticles and nanoparticle-nanotube composites in solar cells and photovoltaics continues to attract great interest. The combined properties of light harvesting nanoparticles together with the high conductivity of carbon nanotubes (CNTs) can lead to improvements in the efficiency of photoelectric devices. In previous studies, semiconductor NPs have been grown on CNTs by generation of defects in the CNT lattice structure by means of covalent functionalization or ozonolysis [1]. The drawback of such covalent functionalizations is that they modify the response of the CNTs in terms of conductivity, optical behaviour, and mechanical stability, a disadvantage for further applications.In this work we study the influence of non-functionalised carbon nanotubes on the synthesis of CdSe nanoparticles by means of organometallic colloidal routes [2]. A new property of CNTs has been observed for the first time during the synthesis in which CNTs trigger a morphological transformation of CdSe nanorods into pyramidal-shaped nanoparticles and a tight attachment to the CNTs. The morphology of the nanoparticles has been elucidated in 3D by means of high-resolution transmission electron microscopy (HRTEM) and STEM tomography [3]. The presented non-covalent attachment (according to Raman spectroscopy) should, furthermore, be most advantageous in order to combine the outstanding electrical properties of CNTs with the unique possibility of bandgap tuning of quantum dots. The attachment is observed for CdSe quantum dot particles on both, singlewall and multiwall carbon nanotubes (MWCNTs) and the obtained composite materials exhibit promising photoelectrical response. These nanocomposites may have a strong impact in optoelectronics and photovoltaics.References[1] S. Banerjee, S. S. Wong, J. Am. Chem. Soc. 125, 10342 (2003); [2] B. H. Juarez, C. Klinke, A. Kornowski, H. Weller, Nano Lett. 2007, 7(12), 3564 3568[3] A.B. Hungría, B. H. Juarez, C. Klinke, H. Weller, P.A. Midgley, Submitted
3:15 PM - **JJ18.3
Load Transfer Mechanism between Carbon Nanotubes and Amorphous Polymers.
Karen Winey 1 , Minfang Mu 1 , Sebastian Osswald 2 , Yury Gogotsi 2
1 Materials Science and Engineering, Univ. of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractPolymer nanocomposites based on carbon nanotubes have not yet reached the high expectations held for their mechanical properties, because the dispersion of nanoparticles and the load transfer between the filler and the matrix are less than idea. This presentation focuses on the load transfer mechanism is nanocomposites containing single wall carbon nanotubes (SWCNTs) and an amorphous polymer. Mechanical interactions between SWCNTs and poly(methyl methacrylate) (PMMA) were probed by measuring the tensile moduli of nanocomposite fibers with aligned SWCNTs. Polymer chains provide better load transfer and thereby higher tensile moduli when the polymer size is large relative to the diameter of the filler. By comparing the mechanical properties with carbon nanofiber composites, we found that the specific interfacial area of the filler was not sufficient to explain the observed increase in elastic modulus. The load transfer mechanism of the applied stress on single wall carbon nanotube (SWCNT)/polymer nanocomposites to SWCNTs was further studied using in situ Raman spectrometry. In these amorphous polymer composites with non-specific interactions, the effective stress transfer to SWCNTs is limited to a small strain region. At higher strain, the stress on SWCNTs decreases due to the debonding between the nanotube surface and polymer and the nanotube fiber was pulled out at the facture surface. A longer polymer chain transfers the stress more effective and we attribute this to a higher probability of nanotube-polymer chain entanglement.
3:45 PM - JJ18.4
Carbon Nanotube Aerogels: A Novel Class of Robust Ultralow-Density Nanoporous Carbons.
Sergei Kucheyev 1 , M. Worsley 1 , T. Baumann 1 , J. Satcher 1 , A. Hamza 1
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractMechanical properties of porous solids exhibit strongly superlinear dependencies on the material density. Hence, ultralow-density nanoporous materials have poor mechanical properties. This remains the major factor limiting many potential energy-related applications of these materials. For example, silica aerogels with densities below ~100 mg/cm3 typically have a very low Young’s modulus of ~1 MPa. In this presentation, we will discuss synthesis and mechanical properties of a novel class of robust ultralow-density nanoporous sp2-bonded carbons. These materials, with monolithic densities of ~10 mg/cm3 and above, are made of single-walled carbon nanotubes decorated and interconnected by carbon nanoparticles. Such nanofoams exhibit unprecedented mechanical properties, including high stiffness, fracture toughness, and effective yield stress. Deformation is characterized by strain-dependent elastic properties and viscoelastic energy dissipation. These findings are compared with deformation modes of better studied nanoporous systems such as silica, alumina, and conventional carbon aerogels.This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344.
JJ19: Device Applications
Session Chairs
Prabhakar Bandaru
Sonia Grego
Thursday PM, December 04, 2008
Room 302 (Hynes)
4:15 PM - **JJ19.1
Ultrathin Films of Single Walled Carbon Nanotubes for Analog RF and Digital Electronics.
John Rogers 1
1 Materials Science and Engineering, University of Illinois-Urbana Champaign, Urbana, Illinois, United States
Show Abstract4:45 PM - JJ19.2
Medium-scale Carbon Nanotube Thin-film Integrated Circuits on Flexible Plastic Substrates.
Qing Cao 1 3 4 , John Rogers 2 3 4
1 Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Frederick-Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 4 Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractThe ability to form integrated circuits (ICs) on flexible sheets of plastic enables attributes (e.g. conformal and flexible formats, lightweight and shock resistant construction) in electronic devices that are difficult or impossible to achieve with technologies that use semiconductor wafers or glass plates as substrates. Organic small molecule and polymer based materials represent the most widely explored types of semiconductors for such flexible ICs. Although these materials and those that use films or nanostructures of inorganics have promise for certain applications, existing demonstrations of them in ICs on plastic indicate modest performance characteristics that might restrict the application possibilities. Here we report advanced implementations of a comparatively high-performance carbon-based semiconductor consisting of sub-monolayer, random networks of single-walled carbon nanotubes (SWNTs) to yield small-scale to medium-scale, integrated digital circuits, composed of up to nearly one hundred transistors on plastic substrates. Transistors in these ICs demonstrate excellent properties: mobilities as high as 80 cm2/Vs, subthreshold slopes as low as 140 mV/dec, operating voltages <5 V together with deterministic control over the threshold voltages, on/off ratios as high as 105, switching speeds well in the kilohertz range even for coarse (~100 μm) device geometries and good mechanical bendability, all with levels of uniformity and reproducibility that enable high yield fabrication of ICs. Theoretical calculations, ranging from heterogeneous percolative transport through the networks to compact models for the transistors to circuit level simulations, provide quantitative and predictive understanding of these systems. Taken together, these results suggest that sub-monolayer films of SWNTs represent an attractive type of carbon-based semiconductor for flexible ICs, with many potential areas of application in consumer and other areas of electronics.
5:00 PM - JJ19.3
Self-Sorted, Aligned Nanotube Networks for Thin Film Transistors and Transparent Electrodes.
Zhenan Bao 1 , Melburne LeMieux 1 , Mark Roberts 1 , Soumendra Barman 1 , Justin Opatkiewicz 1
1 , Stanford University, Stanford, California, United States
Show AbstractFor single walled carbon nanotubes to find use in electronics there is a need to efficiently separate them by electronic type, and align them to ensure optimal and reproducible electronic properties. Here, we report SWNT network field effect transistors, deposited from solution, possessing controllable topology and on/off ratio as high as 900,000. The spin-assisted alignment and density of the SWNTs is tuned by different surfaces that effectively vary the degree of interaction with surface functionalities in the device channel. This leads to a self-sorted SWNT network whereby nanotube chirality separation and simultaneous control of density/alignment occurs in one step during device fabrication. Micro-Raman experiments corroborates device results as a function of surface chemistry indicating enrichment of specific SWNT electronic type absorbed onto the modified dielectric.[ref] 1)M. LeDuex, M. Roberts, S. Barmann, Y.W. Jin, J.M. Kim, Z. Bao, Science, in press.
5:15 PM - JJ19.4
Smart Dust Built from Hybrid Nanowires.
Fung Suong Ou 1 , Manikoth Shaijumon 2 , Pulickel Ajayan 2
1 Department of Applied Physics, Rice University, Houston, Texas, United States, 2 Department of Mechancial Engineering and Materials Science, Rice University, Houston, Texas, United States
Show AbstractSmart dust, a millimeter size mote with the ability to monitor its surrounding and communicate with the outside world is a bold vision that was first projected by experts in wireless communication. The possibility of such a structure will have profound impact for applications such as communications, drug delivery and microfludics. Even a decade after the concept was first projected, only limited progress has been made in assembling such smart structures. The main difficulty has been the inability to have complex functionalities controllably installed into building blocks that would assemble into smart dust. Taking advantage of the multiple functionalities available in hybrid nanotubes, we demonstrate the assembly of smart particles from nanostructures consisting of contiguous metal and carbon nanotube components. The hybrid nanotubes are amphiphilic, consisting of hydrophobic nanotube tails and hydrophilic gold nanowire heads, allowing them to be assembled into massive micellar structures via interaction with their surrounding medium. Further, we show that, when properly designed, the assembled particles can carry out specific actions based on external stimuli such as ultrasound, magnetic force or optical irradiation. For example, the amphiphilic nanowires can be modified by inserting pieces of magnetic nanowires into the middle, making the structure magnetic and hence allowing large assemblies to be manipulated by external field. The assembly sequences can also be manipulated by modifying the hydrophobicity of the respective components via chemical functionalization and optical irradiation. In short, the nanowire elements act as independent smart components, akin to nanoscale robots, and interact with their surrounding and external stimuli in a concerted and controlled fashion to produce massive ordered aggregates. The observations suggest that multi-component hybrid nanotubes could be the perfect building blocks in the making of smart material, which could find applications in a variety of technologies.
5:30 PM - JJ19.5
Reprogrammable Circuits based on Carbon Nanotubes.
Sung Myung 1 , Sungjong Woo 2 , Jiwoon Im 1 , Yosep Min 3 , Young-Kyun Kwon 2 , Seunghun Hong 1
1 Department of Physics and Astronomy, Seoul National Univ, Seoul Korea (the Republic of), 2 Department of Physics and Applied Physics, University of Massachusetts, Lowell, Massachusetts, United States, 3 Chemical & Biological Engineering, Konkuk University, Seoul Korea (the Republic of)
Show AbstractThe “learning” process of a human brain, one of the most efficient information processor, is based on the capability of reconfiguring individual neural networks in real-time. However, such capability has been extremely difficult to implement in conventional solid-state devices. Herein, we report a large-scale assembly method for reprogrammable circuits based carbon nanotubes. In our reprogrammable circuits, the charges in nanoparticles adjacent to ambipolar carbon nanotube channels were adjusted to control the carrier type and density in the channels. We demonstrated the real-time reconfiguration of individual field effect transistors, logic gates, and diodes. Theoretical simulation of a model system was provided to explain the characteristics of the carbon nanotube-based reprogrammable circuits. This work should be a major breakthrough in building reconfigurable electronics and may enable new device architecture for highly-efficient information processing.
5:45 PM - JJ19.6
Molecular-Linear-Motor System Consisting of Carbon Nanotubes.
Kaori Hirahara 1 2 , Hiroshi Somada 2 3 , Seiji Akita 3 , Yoshikazu Nakayama 2
1 Frontier research base for grobal young researchers, School of Engineering, Osaka University, Suita Japan, 2 Dept. of Mechanical Engineering, Osaka University, Suita Japan, 3 Dept. of Physics and Electronics, Osaka Prefecture University, Sakai, Osaka, Japan
Show AbstractMolecular motor system seen in nature, which transfers given energy to mechanical motion on a single molecule scale, would have valuable application in nanotechnology; that is, it would evolve into components of information transportation in a nanodevice. Designing the synthetic molecular motor systems is therefore essential. There are two types of motions in natural molecular motors: rotary and linear motions. Some synthetic molecular motors providing rotary motion have been reported (1). Linear motion, however, has not yet been found experimentally for synthetic molecular motors, although some theoreticians have predicted (2). In this paper, we present experimental evidence that a capsule-like short carbon nanotube (CNT) worked as a “molecular-linear-motor” as well as a “molecular-rotary-motor” in the interior space of a host CNT, by means of transmission electron microscopy (3).
CNT capsules were obtained by coalescence of fullerene molecules encapsulated in carbon nanotubes assisted by heat treatment in vacuo, as preparing double wall CNTs (4). In the present study, we obtained CNT capsules with 3–10 nm lengths encapsulated in the interior of host CNTs by heating at 1073–1373 K for 8 hours. We observed a CNT capsule is ca. 0.95 nm in diameter and ca. 3.2 nm in length by a transmission electron microscope with 90 kV acceleration voltage at room temperature. The both ends of the hollow space are closed by hemisphere-like caps of the other encapsulated CNTs or capsule-like materials. Initially, the CNT capsule is located on one side of the hollow space. After several seconds, we find the capsule quickly travels to the other side. The capsule then travels back to the initial place after a couple of seconds. Namely, the capsule showed the “linear-motion”. In an observation of 150 seconds, the capsule travels back and forth seven times. In addition, we found the CNT capsule has not only linear motion but also simultaneous rotary motion.
The “linear motor”-like motion of the CNT capsule observed in this study has two characteristics: second-scale time interval and very quick movement faster than the video frame rate (1/60 s). With aid of molecular dynamics simulations, the mechanism are discussed by considering an equilibrium among the thermal energy and the energy gain due to the van der Waals energy at the ends of the hollow space as well as resistance originating in lattice fluctuation due to heating; that is, the thermal-energy-derived motor. The present system operates around room temperature and this opens up the possibility of designing novel nanodevices such as oscillators and switching memory devices.
(1) A. M. Fennimore et al. Nature 424, 408-410 (2003).
(2) Y. K. Kwon et al., Phys. Rev. Lett. 82, 1470 (1999).
(3) H. Somada, K. Hirahara, et al. submitted.
(4) S. Bandow et al., Chem. Phys. Lett. 337, 48 (2001).
JJ20: Poster Session: Mechanical Properties and Energy applications
Session Chairs
Prabhakar Bandaru
Sonia Grego
Ian Kinloch
Friday AM, December 05, 2008
Exhibition Hall D (Hynes)
9:00 PM - JJ20.1
Platform for Continuous Manufacture of Vertically-Aligned Carbon Nanotubes.
Stacy Figueredo 1 , Stephen Steiner III 2 , Aria Reynolds 1 , A. John Hart 3 , Alexander Slocum 1 , Brian Wardle 2
1 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Department of Mechanical Engineering, University of Michigan, Cambridge, Michigan, United States
Show Abstract9:00 PM - JJ20.10
The Coin Type and the Coiled Electric Double Layer Capacitors Formed with Carbon Nanotube.
M. Imano 1 , H. Ino 1 , Y. Totani 1 , H. Yoshida 1 , Yoshiyuki Show 1
1 Dept. of Electrical and Electronic Engineering, Tokai University, Hiratsuka, Kanagawa, Japan
Show Abstract9:00 PM - JJ20.12
Nanostructured High Surface Area Materials for Actuation and Energy Storage.
Brian Gardina 1 , Carter Haines 1 , Theja Lanka 1 , Anand Chamarthy 1 , Phuong Huynh 1 , Jiyoung Oh 1 , Marcio Lima 1 , Raquel Robles 1 , Ray Baughman 1 , Mikhail Kozlov 1
1 NanoTech Institute, Universty of Texas at Dallas, Richardson, Texas, United States
Show Abstract9:00 PM - JJ20.13
Study of the Interaction between Hydrogen and Carbon-based Nanomaterials.
Roberto Felix 1 , Ich Tran 1 , Lothar Weinhardt 1 2 , Marcus Baer 1 , Timo Hofmann 1 , Yufeng Zhang 1 , Clemens Heske 1
1 Chemistry, University of Nevada, Las Vegas, Las Vegas, Nevada, United States, 2 Experimentelle Physik 2, Universität Würzburg, Würzburg Germany
Show Abstract9:00 PM - JJ20.14
Electrochemical Characterization of Lipid Bilayers on Single Silicon Nanowire Electrodes.
Julio Martinez 1 2 , Nipun Misra 3 , Jay Huang 1 , Alexander Artyuhkin 1 , Costas Grigoropoulos 3 , Pieter Stroeve 2 , Aleksandr Noy 1
1 Chemistry, Materials, Earth, & Life Science Directorate, Lawrence Livemore National Laboratory, Livermore, California, United States, 2 Department of Chemical Engineering and Materials Science, University of California, Davis, California, United States, 3 Department of Mechanical Engineering, Univeristy of California, Berkeley, California, United States
Show AbstractThe next generation of biomimetic devices and sensors will benefit from the possibility of using biological molecules embedded in biomimetic matrices such as lipid membranes. Silicon nanowires represent one of the promising material platforms for such devices due to their unique combination of geometry, and surface and electronic properties. The formation of a highly insulating lipid membrane barrier to the passive diffusion of solution ions on the nanowire surface could represent an important step towards creating a biomimetic nanowire-based detection platform.We present nanowire-based 1-D lipid bilayer structures where single silicon nanowire electrode surfaces are shielded by a lipid bilayer. Electrochemical characterization of the bare and coated single nanowire electrodes by cyclic voltammetry shows that lipid bilayers strongly modify the ion transport efficiency in this system. We compare the insulating properties of 1-D bilayers with the properties of highly insulating lipid membranes supported on flat silicon electrodes. We also discuss the use of nanowire electrodes for detecting the presence of pore forming ion channels in lipid bilayers.Julio Martinez acknowledges the financial support by the Lawrence Scholar Program fellowship, University Relations Program, LLNL.This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
9:00 PM - JJ20.15
Double-walled Nanotube Network Based Hydrogen Sensors.
Hau Wang 1 , Francisco Rumiche 1 2 , Ernesto Indacochea 2 , Yugang Sun 3 , Wei-Shan Hu 4
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Department of Civil and Materials Engineering, University of Illinois at Chicago, Chicago, Illinois, United States, 3 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 4 Department of Chemistry, National Tsing-Hua University, Hsin-Chu Taiwan
Show AbstractHydrogen sensors are playing an important role in the forthcoming hydrogen economy in safety devices, fuel cells, environmental control, manufacturing and security industries. Carbon nanotubes due to their small sizes, high surface areas, modest electrical conductivity, etc., became an ideal substrate for various sensing materials. In our current studies, random network of single-walled carbon nanotubes (SWNTs) and double-walled nanotubes (DWNTs) were used to build a percolation pathway for charge transport. We have studied both commercial CVD SWNT and DWNT drop coated thin films as well as SWNT network prepared with use of dry-transfer technique. Typical SWNTs have diameters between 1.5 and 2.5 nm as measured with AFM. When these SWNTs and DWNTs were thermally evaporated or electrochemically decorated with Pd nanoparticles, they became ultra-sensitive ambient temperature hydrogen sensors (Appl. Phys. Lett. 90, 213107 2007, Adv. Mater. 19 2818 2007). We found the responsivities are much higher than those of the pure Pd thin film or Pd nanotube H2 sensors. The Pd nanoparticles appear to be gating the hole transport in carbon nanotubes. Therefore, our two-terminal CNT network devices perform as well as the traditional three-terminal field effect transistor devices. In addition, our preliminary results indicate that the DWNTs are also excellent sensing materials. These results will be presented. Work at Argonne National Laboratory as well as FESEM carried out at EMC are supported by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357.
9:00 PM - JJ20.16
A Nano-Micro-Macro Integrated Device Structure Based on Highly Aligned Carbon Tubes for Sensor Applications.
Joerg Schneider 1 , Dimitris Pavlidis 1 , Alexander Popp 1 , Oktay Yilmazoglu 1 , Oktay Kaldirim 1
1 Chemistry, TU Darmstadt, Darmstadt Germany
Show AbstractThe integration of carbon nanotubes (CNTs) into micro-components is one of the main challenges concerning their future technical implementation in higher organized device architectures. Creating a reliable connection of massively parallel aligned CNTs in order to make use of the special features CNTs offer in electronic microscaled component devices, is currently the limiting factor. Efforts in addressing this limitation include the use of interdigital structures [2] or transistors[3] with CNTs placed randomly on the contacts of such structures. CNTs are promising candidates for sensing small concentration of gases, DNA, nerve agents, vitamin/proteins. For gas detection, single-walled CNTs due to their semiconducting properties have demonstrated already high sensitivity. They typically exhibit a fast response and a higher sensitivity than observed for existing solid-state sensors at room temperature. Moreover CNT-based nanoelectromechanical systems (NEMS) are becoming important for pressure, vibration and acceleration sensing with unique sensitivities and resolutions. In this regard sensor configurations involving disordered CNTs are only of limited applicability due to the non-uniformity of length, diameter and density of the individual CNTs. Sensitivity of CNTs is further handicapped by the simultaneous presence of metallic and semiconducting electrical features of CNTs. For gas sensors this results in a response where the gas influence is averaged and the inner tubes contribute very little to gas detection. Herein we report on a novel approach for fabricating freestanding, highly aligned multiwalled CNT arrays in between a top and bottom carbon layer via a template approach. The resulting monolithic all carbon structure is highly flexible with integrated micro-nano-features and allows an addressing of nanoscopic CNT bundles by electrical contacting. Due to the contacting it can be used as a macroscopic gas sensor device. Besides synthesis, characterization, nano-micro integration and electrical contacting we present results towards sensing of various gases.
9:00 PM - JJ20.17
Carbon Nanotube-Based Dual Mode Biosensors for Electrical and SPR measurements.
Seunghwan Yoo 1 , Jeseung Oh 3 , Young Wook Chang 1 , Dong Jun Kim 2 , Soon Joon Yoon 2 , Donghyun Kim 2 3 , Kyung-Hwa Yoo 1 3
1 Physics, Yonsei University , Seoul Korea (the Republic of), 3 National Core Research Center for Nanomedical Technology, Yonsei University, Seoul Korea (the Republic of), 2 Electrical & Electronic Engineering, Yonsei University, Seoul Korea (the Republic of)
Show AbstractWe have fabricated carbon nanotube (CNT)-based biosensors on transparent quartz substrates, which can detect biomolecules by measuring the conductance change and the surface plasmon resonance (SPR). The device has a metal-semiconductor-field-effect transistor (MESFET) structure with a metal (Au) island between source and drain electrodes. Since this metal island acts as a Schottky metal gate, the conductance of the device is controlled by the metal gate. In order to see whether it is possible to detect biomolecules adsorbed on the metal island using the CNT-MESFET, thiol-modified single strand DNA molecules are immobilized on the metal island and then DNA molecules with the complementary base sequence are added. When DNA hybridization occurs, the CNT conductance is observed to decrease, suggesting that biomolecules adsorbed on the metal islands can be detected by measuring the conductance change. In addition, the metal island is also able to be utilized for SPR measurements, which detects the change in refractive index induced by binding of biomolecules on the metal surface. Indeed, we have demonstrated that DNA hybridization can be detected using the CNT-MESFET by measuring the SPR angle shift. Since the sensitivity of biosensors measuring the conductance change is higher than SPR biosensors, whereas the reproducibility and the reliability is better in SPR biosensors. Therefore, this dual mode CNT biosensor are expected to provide high sensitivity reinforced with more reliability.
9:00 PM - JJ20.18
Suspended Single-Walled Carbon Nanotube Vacuum Sensors.
Huiyan Pan 1 , Chia-Ling Chen 1 , Mehmet Dokmeci 1
1 Electrical and Computer Engineering , Northeastern University, Boston, Massachusetts, United States
Show Abstract9:00 PM - JJ20.19
Heterogeneous Integration of Single-Walled Carbon Nanotubes with CMOS Circuitry.
Chia-Ling Chen 1 , Vinay Agarwal 2 , Huiyan Pan 1 , Sameer Sonkusale 2 , Mehmet Dokmeci 1
1 ECE, Northeastern University, Boston, Massachusetts, United States, 2 ECE, Tuft University, Medford, Massachusetts, United States
Show AbstractIn this paper, we demonstrate the integration of Single-Walled Carbon Nanotubes (SWNTs) with CMOS circuitry as a first step toward realizing highly sensitive nanosystems. The proliferation of technologies to create nanoscale materials coupled with the funding from the government and industry is yielding a plethora of fascinating nanomaterials which are increasingly being used in high performance novel devices. For instance, SWNT based molecular wires have been utilized as chemical sensors with a fast response. The nanotube or nanowire based sensors have very high sensitivity yet are also prone to noise, hence require the electronics to be near. Accordingly, the implementation of nanostructures directly on a CMOS electronic chip not only improves the signal to noise ratio, but also provides an opportunity for signal conditioning and storage leading to highly sensitive single chip nanomaterial based systems. The SWNT assembly technology utilized dielectrophoresis which is low temperature, versatile and wafer scale and is applicable for post-CMOS integration of numerous nanostructures. The CMOS chip containing assembly microelectrodes and the interface circuitry is designed and fabricated using the AMI 0.5µm CMOS process, provided by MOSIS. After receiving the fabricated chips, we first etched the oxide layer (Al2O3) on top of the Al metal electrodes and then coated them with a Zn layer using an electroless plating process. Next, we deposit a 2-3 µl droplet of an aqueous solution containing the nanotubes on to the microelectrodes. An AC voltage of 5Vpp with a frequency of 10 MHz was utilized during the DEP assembly. A high gain op-amp circuitry was designed to demonstrate the integration of nanotubes with CMOS electronics. The SWNTs are into the feedback resistor of the op-amp. The small signal gain of the op-amp with CNT feedback resistors was measured as ~-1.95. The thermal response of SWNTs have been measured and has a negative temperature coefficient of resistance (TCR) ~ -0.4%. In summary, we have successfully integrated SWNTs on to functional CMOS circuitry utilizing a low temperature wafer scale process. The technique is simple, versatile and high yield with potential applications for the realization of nanotube and nanowire based bio and chemical sensors.
9:00 PM - JJ20.20
Control of NEMS Based on Carbon Nanotube.
Andrey Knizhnik 1 , Irina Lebedeva 2 , Olga Ershova 2 , Yurii Lozovik 4 , Andrey Popov 4 , Boris Potapkin 1 3
1 , Kintech Lab Ltd, Moscow Russian Federation, 2 , Moscow Institute of Physics and Technology, Moscow Russian Federation, 4 , Institute of Spectroscopy, Moscow Russian Federation, 3 , RRC "Kurchatov Institute", Moscow Russian Federation
Show AbstractRecently, a number of nanoelectromechanical systems (NEMS) that employ carbon nanotube walls as movable elements were proposed. The crucial issue for the practical use of such devices is the ability to control the motion of the nanotube walls.We propose a new method for controlling the motion of the nanotube-based NEMS. In this method, chemical adsorption of atoms and molecules at the open ends of a carbon nanotube wall leads to the appearance of an electric dipole moment. In this case the nanotube wall can be actuated by a non-uniform electric field. Possibility of the method proposed is examined by the example of a gigahertz oscillator based on a double-walled nanotube.The gigahertz oscillator is characterized by a strong dependence of the frequency on the oscillation amplitude. Thus, the application of this NEMS with a constant frequency requires that the oscillation be sustained at a constant amplitude. We showed that the minimum amplitude of the control force which is required to sustain the oscillation at a constant amplitude (the critical amplitude) is determined by the Q-factor of the oscillator. The molecular dynamics calculations revealed that the Q-factor of defect-free oscillators with the interwall distance of about 3.4 Å is inversely proportional to temperature. So it is possible to design the NEMS with a desirable Q-factor by decreasing temperature. However, the Q-factor of nanotubes containing defects or with the interwall distance above 3.4 Å is relatively small and displays almost no dependence on temperature. A mechanical model was applied to investigate the oscillator behavior at a long simulation time. Due to the oscillator non-linearity, the possibility of establishment of the stationary operation mode is determined by the initial phase shift between the control force and the oscillator. Nevertheless, at a large control force amplitude, the stable region of the initial phase shift is large and the switching of the control force is possible at an arbitrary moment.With the critical amplitude of the control force calculated by means of the mechanical model, molecular dynamics simulations of controlled oscillations were carried out. The inner wall of the nanotube was hydrogen-functionalized and the system was exposed to the electric field of a spherical capacitor. The charge distribution in the functionalized wall was found using the density functional theory. These molecular dynamics simulations demonstrated the possibility of the proposed method for controlling the NEMS motion. Furthermore, the influence of thermodynamic fluctuations on the operation of nanotube-based NEMS was investigated. Significant fluctuations were revealed for the oscillator under consideration. These fluctuations were shown to have the critical effect on the possibility of controlling the oscillator operation.
9:00 PM - JJ20.21
From Electrical to Fuel Powered Artificial Muscles.
Mikhail Kozlov 1 , Jiyoung Oh 1 , David Novitski 1 , Brian Gardina 1 , Carter Haines 1 , Mei Zhang 2 , Shaoli Fang 1 , John Ferraris 1 , Ray Baughman 1 , Tissaphern Mirfakhrai 3 , John Madden 3
1 NanoTech Institute, Universty of Texas at Dallas, Richardson, Texas, United States, 2 Department of Industrial Engineering, Florida State University, Tallahassee, Florida, United States, 3 Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, British Columbia, Canada
Show Abstract9:00 PM - JJ20.22
Fabrication and Selective Microwave Absorption of Annealed Fe-filled Carbon Nanotube/epoxy Composites.
Kunlin Wang 1 , Xuchun Gui 1 , Ruitao Lv 2 , Jinquan Wei 1 , Dehai Wu 1
1 Department of Mechanical Engineering, Tsinghua University, Beijing China, 2 Department of Materials Science and Engineering, Tsinghua University, Beijing China
Show Abstract Carbon nanotubes (CNTs) have been explored for applications such as electromagnetic interference (EMI) shielding and microwave absorption. Although different types of CNTs (e.g. single-walled, multi-walled) have been investigated in recent time, only a few works has tapped on the magnetic particles (Fe) filled CNTs. In this paper, we directly fabricated the microwave absorber by uniform dispersing annealed Fe-filled CNTs in the epoxy by controlling the concentration of CNTs in the composites. The annealed Fe-filled CNTs have stronger saturation magnetization and weaker coercivity, due to the filled iron nanowires was mainly in ferromagnetic α-Fe. The annealed Fe-contained CNTs were dispersed in acetone by sonication for half an hour, and then a certain weight percentage of epoxy resin was added into the solvent to mix with CNTs. After sonication for another 30 minutes, hardener was added at specified ratio. And the mixture was molded as a square sheet (180mm × 180mm × 2 mm) on an aluminum substrate for reflection loss measurement. Microwave absorbers with different concentrations of annealed Fe-filled CNTs were fabricated by the same method. The reflection loss spectra in the range of 2 to 18 GHz shown that the annealed Fe-filled CNTs/epoxy composites have better microwave absorption properties. And the maximum reflection loss reached 16.5 dB at 7.7 GHz for the samples with the CNTs concentration of 10 wt %. The reflection loss is over 5 dB between 9.0 GHz and 15.5 GHz for the CNT concentration of 4.5 wt %. The value of frequency corresponding to the maximum reflection loss peak shifts toward lower frequency region with increasing concentration of CNTs. And the frequency value at the maximum reflection loss drops from about 16 GHz to less than 8 GHz when the concentration of CNTs increases from 0.1 wt % to 10 wt%. Such character should facilitate control of reflection behavior by tuning the CNT concentrations during the fabrication stage. The use of annealed Fe-filled CNTs concentration to control the absorption selectivity could facilitate potential higher-frequency applications of CNTs.
9:00 PM - JJ20.23
Tailoring Carbon Nanotube Dispersion in Water using PH-responsive Polymers.
Krishna Etika 1 , Jaime Grunlan 1
1 Department of Mechanical Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractDespite their immense potential, the ability to control the dispersion and microstructure of carbon nanotubes remains a hurdle for widespread use of nanotube-filled polymer composites. Stimuli responsive or “smart” polymers show a significant conformational change with applied stimulus (pH, temperature, ionic strength etc.). Significant tailoring of carbon nanotube dispersion in water can be achieved by making use of pH responsive polymers (e.g., poly(acrylic acid)), which can enable macroscopic control of carbon nanotube dispersion with pH. Microstructural changes as a function of pH were observed with cryo–TEM of aqueous SWNT-filled suspensions. pH dependent interaction of PAA with carbon nanotubes in water were confirmed by Raman spectroscopy and liquid suspension conductivity. In poly(acrylic acid), the bundling of nanotubes increases with increasing pH and these microstructurally induced changes are reversible (i.e., highly aggregated at high pH and exfoliated at low pH). Smart polymers induced dispersion of carbon nanotubes has significant influence on processing and properties of polymer nanocomposites. Many of the relationships described here could also be applied with other smart polymers and for the tailored dispersion of other types of nanoparticles (e.g., inorganic nanotubes and nanowires).
9:00 PM - JJ20.24
Study of the Orientational Order in Stretch-aligned Single Wall Carbon Nanotubes/polymer Photoluminescent Films.
Camilo Zamora-Ledezma 1 2 , Christophe Blanc 1 , Eric Anglaret 1
1 Laboratoire des Colloïdes,Verres et Nanomatériaux, Université Montpellier 2, Montpellier, Montpellier, France, 2 Laboratorio de Física de la Materia Condensada, Instituto Venezolano de Investigaciones Científicas, Caracas, Caracas, Venezuela, Bolivarian Republic of
Show AbstractAligning carbon nanotubes (CNTs) on a large scale is an important challenge to prepare nanotube based materials with novel or enhanced properties (mechanical, electronic, optical). A remarkable improvement of their properties is expected by controlling their orientational order, with possible applications as reinforced composites [1], actuators [2] or optoelectronic devices [3]. We prepared anisotropic polyvinylalcohol (PVA) films doped with individualized single wall carbon nanotubes (SWCNT), stabilized with denaturated DNA [4]. SWCNT alignment was achieved by mechanical stretching (hot-drawing technique). We evidence the effectiveness of nanotube exfoliation and study their orientational order as a function of the film elongation using Raman and Photoluminescence spectroscopies [5]. A good agreement is found with a simple model considering only stretching-indueced geometric changes of the films.Bibliography[1] J. N. Coleman, U. Khan, W. J. Blau, Y. K. Gun’ko. Carbon, 2006, 44 (9), 1624.[2] R. H. Baughman, C. Cui, A. A. Zahidov, Z. Iqbal, J. N. Barisci, G. M. Spinks, G. G. Wallace, A. Mazzoldi. D. De Rossi, A. G. Rinzler, O. Jaschinski, S. Roth, M. Kertesz, Science, 1999, 284, 1340.[3] Y. Kim, N. Minami, S. Kazaoui. Appl. Phys. Lett., 2005, 86, 73103. [4] S. Badaire, C. Zakri, M. Maugey, A. Derré, J. N. Barisci, G. Wallace, P. Poulin. Adv. Mater. 2005, 17, 1673.[5] M.J. O’Connell, S. M. Bachilo, C. B Huffman, V. C. Moore, M. S. Strano, E. H. Haroz, K. L. Rialon, P. J Boul, W. H. Noon, C. Kittrell, J. Ma, R. H. Hauge, R. B. Weisman, R. E. Smalley. Science 2002, 297, 593.
9:00 PM - JJ20.25
Chemical Vapor Deposition As a Route for the Fabrication of Variable Volume Fraction Aligned Carbon Nanotube Polymeric Nanocomposites.
Hulya Cebeci 1 , Sreeram Vaddiraju 2 , Karen Gleason 2 , Brian Wardle 1
1 Aeronautics and Astronautics Engineering, MIT, Cambridge, Massachusetts, United States, 2 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractChemical Vapor deposition (CVD) was employed for the conformal deposition of polymers on vertical arrays of aligned carbon nanotubes (CNTs) toward the realization of engineered polymer-CNT composites. Aligned MWCNT forests were grown by a method developed at MIT [1, 2]. As grown CNT forests (1% volume fraction) were mechanically densified to desired high volume fractions up to 20% (approaching theoretical and practical limits) [3] Mechanical densifications allows the fabrication of high volume fraction polymer-CNT composites where spacing between the nanotubes approaches to the characteristic length of polymer chains. This mode of engineering polymer-CNT composites helps in the fabrication of multifunctional materials (e.g. electrically conducting and hydrophobic). Oxidative chemical vapor deposited (oCVD) was employed to deposit poly(3,4-ethylenedioxythiophene) (PEDOT) conducting films on CNTs. Iron chloride (FeCl3) is used as the oxidizing agent for the oCVD process. Morphological analysis indicated that the CNTs were coated conformally with the conducting polymer by the oCVD process. Directional dependant wetting behavior (top surface vs. sides) is also observed in such composites. The engineering of these multifunctional composites along with possible application will be discussed in detail. References: 1.A. J. Hart, A. H. Slocum, Journal of Physical Chemistry B. 2006, 110.2.Garcia, E.J., Hart, J., and B.L. Wardle, “Long Carbon Nanotubes Grown on the Surface of Fibers for Hybrid Composites”, AIAA Journal, Vol. 46, No.6, 2008, pp.1405-1412.3.Wardle, B.L., Saito, D.S., Garcia, E.J., Hart, A.J., deVilloria, R.G.,, Fabrication and Characterization of Ultra-High Volume Fraction Aligned Carbon-Nanotube-Polymer Composites. Advanced Materials on-line June, 2008.
9:00 PM - JJ20.26
Spectroelectrochemical Behaviour of Polyaniline-Single-Wall-Carbon-Nanotubes Nanocomposites Monitored by Resonance Raman Spectroscopy.
Paola Corio 1 , Gustavo Nascimento 1 3 , Tilana Silva 1 , Mildred Dresselhaus 2 3
1 Chemistry, University of São Paulo, São Paulo, São Paulo, Brazil, 3 Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractCarbon nanotubes (CNTs) are one of the most promising materials for applications ranging from low-cost circuits, nanoscale devices, sensors for mechanical devices, mainly owing to their unique mechanical, electrical, and thermal conductivity properties. However, it will be necessary to address questions concerning the low solubility of CNTs in most organic solvents, their relatively low reactivity and poor chemical compatibility within a polymer matrix in order to make their use a reality. Several approaches have been proposed to make solubilized nanotubes, such the interaction with polymers. This work reports on the synthesis, spectroscopic and electrochemscal study of highly dispersed and stable nanocomposites of polyaniline (PANI) and single wall carbon nanotubes (SWNTs) by in situ polymerization using dodecylbenzenesulfonic acid (DBSA) as a dispersant. The materials were characterized via resonance Raman using three laser lines (Elaser = 488.0 nm or 2.56 eV, 632.8 nm or 1.96eV, 1064.0 nm or 1.17eV) and electronic absorption spectroscopy (UV-VIS-NIR). The behaviour of the composites as a function of the applied potential was also investigated using in situ Raman electrochemical measurements. The results obtained in this work suggest that a charge-transfer process occurs between the polymer and metallic and semiconducting nanotubes in the PANI/SWNT composite, but with different intensities. The charge-transfer between semiconducting SWNTs and PANI occur to a lesser extent than for metallic SWNTs. However, the charge-transfer between PANI and metallic SWNTs is reduced by the amount of defects on the surface of metallic nanotubes. Resonance Raman results suggest that the interaction between PANI and CNT surfaces occurs mainly through the polymer quinoid rings. Such an interaction between nanotubes and polymers may act to stabilize the quinoid structure after protonation (polaron and/or bipolaron segments) and in this way contribute to the increase of the conductivity of the composite. The spectroelectrochemical results, obtained at 488.0 nm, indicate that the presence of SWNTs prevents the oxidation of PANI rings. It can be concluded that the interactions between the PANI backbone with the carbon surface stabilize the polaronic/bipolaronic structure of PANI.
9:00 PM - JJ20.27
Fabrication and Characterization of Aligned-CNT Polymer Nanocomposites (PNCs).
Hulya Cebeci 1 , Roberto De Villoria 1 , Brian Wardle 1 , A. John Hart 2
1 Aeronautics and Astronautics Engineering, MIT, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractAligned, as opposed to randomly-oriented, long aligned-CNT polymer nanocomposites (PNCs) are fabricated, characterized, and tested to assess mechanical, thermal, and electrical property effects of the CNTs. Such PNCs approach the ideal morphology for greatest benefit from the CNT properties due to the long (~1 mm) CNT alignement in the matrix, and have application directly as well as form a constitutent in larger-scale nano-engineered composites containing advanced fibers such as carbon. Aligned-CNT PNCs are fabricated using capillarity-driven wetting [1], avoiding dispersion issues. The effect of CNT alignment on nanocomposite mechanical properties is significant (220% vs. <100%) [2]. In this study, aligned CNTs were used and mechanically densified [3] to obtain desired volume fractions in order to dominate composite properties. The prior-reported mechanical densification process was improved with an effective wetting induced by capillarity driven forces depending on properties of CNT forest (volume fraction) and polymer (contact angle, viscosity). Low viscosity thermoset resins were used to wet forests where CNT alignment is preserved as determined quantitatively using SAXS. Cured samples machined to mm scale PNC samples and several techniques were used to characterize such as optical, scanning and transmission microscopy, small- and wide-angle x-ray scattering (SAXS and WAXS) to study alignment, dispersion, voids, and the effect of the closely-packed CNTs on polymer curing. Mechanical and electrical properties are assessed with nanoindentation and impedance spectroscopy, respectively, demonstrating clear trends with CNT volume fraction. Multifunctional properties and characterization techniques will be discussed in detail. References:1.Garcia, E.J., Hart, A. J., Wardle, B. L., Slocum, A. H., Fabrication of composite microstructures by capillarity-driven wetting of aligned carbon nanotubes with polymers. Nanotechnology, 2007. 18(16): p. -.2.Garcia, E.J., et al., Fabrication and nanocompression testing of aligned carbon-nanotube-polymer nanocomposites. Advanced Materials, 2007. 19(16): p. 21513.Wardle, B.L., Saito, D.S., Garcia, E.J., Hart, A.J., deVilloria, R.G.,, Fabrication and Characterization of Ultra-High Volume Fraction Aligned Carbon-Nanotube-Polymer Composites. at press Advanced Materials May, 2008.
9:00 PM - JJ20.28
Polyacrylonitrile/carbon Nanotube Composite Fibers for Next Generation Carbon Fiber.
Han Gi Chae 1 , Satish Kumar 1
1 School of Polymer, Textile & Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractPolyacrylonitrile (PAN)/carbon nanotube (CNT) composite fibers were made using various processing methods such as conventional solution spinning, gel spinning, and bi-component gel spinning. The detailed characterization exhibited that the smaller and longer CNT will reinforce polymer matrix mostly in tensile strength and modulus, respectively. Gel spinning combined with CNT also showed the promising potential of PAN/CNT composite fiber as precursor fiber of the next generation carbon fiber. High resolution transmission electron microscopy showed the highly ordered PAN crystal layer on the CNT, which attributed to the enhanced physical properties. The subsequent carbonization study revealed that carbonized PAN/CNT fibers have at least 50% higher tensile strength and modulus as compared to those of carbonized PAN fibers. Electrical conductivity of CNT containing carbon fiber was also 50% higher than that of carbonized PAN fiber. In order to have carbon fiber with high tensile strength, the smaller diameter precursor fiber is preferable. Bi-component gel spinning produced 1-2 µm precursor fiber, resulting in ~1 µm carbon fiber. The tensile strength of the carbonized bi-component fiber (islands fibers) is as high as 6 GPa with tensile modulus of ~500 GPa. Further processing optimization may lead to the next generation carbon fiber.
9:00 PM - JJ20.29
Electrically Conductive Composite Film Made from CNT and PTFE.
Y. Nishimura 1 , K. Takahashi 1 , K. Kohara 1 , T. Heishi 1 , Yoshiyuki Show 1
1 Dept. of Electrical and Electronic Engineering, Tokai University, Hiratsuka, Kanagawa, Japan
Show AbstractCarbon nanotube (CNT) is chemically stable and electrically conductive material. One of the applications of the CNT is filler into insulating materials in order to develop electrical conduction. In this study, the CNT and the polytetrafluoroethylene (PTFE) were mixed. This composite material is electrically conductive and chemically stable due to the CNT. The composite film was formed from CNT and PTFE dispersion fluids. The CNT dispersion fluid with concentration of 3% was made from multi-walled type CNTs. Cellulose derivatives were added to the water to disperse the CNT. Water-based commercial PTFE dispersion was used in this study. The PTFE particles in the water were 0.20–0.40 micrometer in diameter. The PTFE concentration was 60%. The separate CNT and PTFE dispersion fluids were mixed and stirred by ultrasonic wave application. The CNT concentration in this mixed fluid was varied from 0 (pure-PTFE dispersion) to 100% (pure-CNT dispersion). An additional separate dispersion fluid, formed from PTFE dispersion fluid and CNT powder instead of CNT dispersion fluid, was also prepared as a reference. The CNT-added PTFE dispersion was applied at a 50μm thickness to a glass substrate. The sample was dried in a 40 °C atmosphere for 30 min and then was heated at 350 °C for 10 min. When CNT power was mixed with PTFE dispersion, the CNT and the PTFE was precipitated. Therefore, no composite film of them was observed. On the other hand, the smooth composite film of the CNT and the PTFE was successfully formed by using CNT dispersion. Pure PTFE showed the low conductivity below measuring limit. The composite material of 5% CNT showed high conductivity of 0.1S/cm. The conductivity increased with an increase in the CNT concentration in the film up to 10S/cm. This result indicates that the CNTs form the electrical network in the material and modify the PTFE into electrically conductive material.Both CNT and PTFE are chemically stable materials. Therefore this composite film fabricated from them is also chemically resistant. In this study, this electrically conductive and chemically stable composite film will be applied to the anti-corrosion coating of bipolar plates (electrodes) for a fuel cell.
9:00 PM - JJ20.3
Functionalization of Single-wall Carbon Nanotubes for Nanocarbon Composites.
Peter Zapol 1 3 , David Horner 2 , Paul Redfern 3 , Michael Sternberg 4 , Larry Curtiss 1 3 4
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Dept of Chemistry and Physics, North Central College, Naperville, Illinois, United States, 4 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractA quantum chemical study of the reactivity of the 7-5-5-7 topological defect, corresponding to a carbon ad-dimer, or di-interstitial, on a (5, 5) armchair nanotube was performed. Calculated energies indicate that nanotubes with the defect is more reactive by 46–70 kcal/mol towards adsorbates containing pi-bonds, such as C2H4, O2, and O3, than are pristine nanotubes or the Stone–Wales 5-7-7-5 defect. The enhanced reactivity of this defect was also obtained for other sizes and types of carbon nanotubes using tight-binding calculations. We explore computationally different configurations of carbon nanotubes on diamond surface to take advantage of enhanced reactivity in making nanocarbon composites. We discuss potential applications of these composites. This work is supported by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357.
9:00 PM - JJ20.31
An NMR Study of C13 Labeled Single Wall Nanotubes with Phenolic Resin.
Peter Boul 1 , Edward Sosa 1 , Pavel Nikolaev 1 , Sivaram Arepalli 1 , Leonard Yowell 1
1 , NASA, Houston, Texas, United States
Show Abstract9:00 PM - JJ20.32
Interlaminar Fracture Toughness of Nano-engineered Composites Reinforced with Aligned Carbon Nanotubes (CNTs).
Sunny Wicks 1 , Roberto Guzman de Villoria 1 , Namiko Yamamoto 1 , Brian Wardle 1
1 Department of Aeronautics and Astronautics, MIT, Cambridge, Massachusetts, United States
Show Abstract9:00 PM - JJ20.33
Growth of Aligned Carbon Nanotubes on Carbon Fibers and Nanotube Yarns: Hierarchal Fiber Architectures for Advanced Composites.
Stephen Steiner III 1 , Megan Tsai 1 , Kyoko Ishiguro 1 , Roberto Guzman de Villoria 1 , A. John Hart 2 , Brian Wardle 1
1 Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show Abstract9:00 PM - JJ20.34
Elastic Properties and Buckling of Silicon Nanowires.
Wenjie Mai 1 , Cheng-lun Hsin 1 2 , Yudong Gu 1 , Yifan Gao 1 , Chi-Te Huang 2 , Yuzi Liu 1 , Lih-Juann Chen 2 , Zhong-lin Wang 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan
Show Abstract9:00 PM - JJ20.37
``Textured" Carbon Nanotube Network Channel for High-Performance Nanoscale Transistors.
Minbaek Lee 1 , Meg Noah 2 , June Park 3 , Maeng-Je Seong 3 , Young-Kyun Kwon 2 , Seunghun Hong 1
1 Department of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of), 2 Department of Physics and Applied Physics, University of Massachusetts, Lowell, Massachusetts, United States, 3 Department of Physics, Chung-Ang University, Seoul Korea (the Republic of)
Show AbstractThin film devices based on single-walled carbon nanotube (swCNT) networks were extensively studied for various practical applications such as high-performance transistors. However, such devices have been suffering from various fundamental limitations such as ‘poor on-off ratio’ due to metallic swCNTs and ‘low mobility and conductance’ with nanoscale channel width due to the percolation problem. Herein, we present a simple but efficient strategy to achieve high performance nanoscale FET devices with large on-off ratio by controlling the ‘network structures’ in their channels. In this strategy, surface molecular patterns were utilized to prepare “textured” swCNT network channels with aligned swCNTs along the channel direction. The textured network structures significantly improved the on-off ratio and allowed us to prepare high-performance devices with high yield. Importantly, unlike randomly-oriented network transistors, our devices exhibited ‘improved mobility and conductivity with reduced channel width.’ It indicates that this strategy is an ideal solution for high-performance nanoscale device fabrication.
9:00 PM - JJ20.38
Ordered Single Walled Carbon Nanotube Networks: Formation Processes and Mechanical Properties.
Vitor Coluci 1
1 , Center for High Education on Technology, University of Campinas , Limeira, SP, Brazil
Show AbstractMany attempts have been made to develop procedures to controllably assemble large number of single walled carbon nanotubes (SWCNTs) in terms of position and orientation, which would allow the fabrication of ordered SWCNT networks and their use in designing of new materials with desirable electronic and mechanical properties. We present results of molecular dynamics simulations of the formation processes involved on the network ordering and formation onto SiC surfaces and the mechanical responses of carbon nanotube networks under different types of mechanical tests. The interactions between carbon atoms were described by the adaptive intermolecular reactive empirical bond-order potential. Tight-binding molecular dynamics simulations were also used to investigate the initial stages of nanotube formation on SiC surfaces. We show that the nanotube arrangement is dependent on the crystallographic orientation of the SiC surface. In order to analyze the mechanical properties of ordered networks, they were constructed connecting SWCNTs through Y- or X-like junctions yielding to hexagonal and crossbar networks, respectively [1]. The tensile tests indicated that rupture occurs basically at regions near the SWCNT junctions. Our results showed that the networks exhibit very high flexibility, showing elasticity modulus ~10-100 GPa and bulk modulus ~10 GPa and may represent interesting candidates for novel porous, flexible, and high-strength materials. Work supported by FAPESP.References[1] V. R. Coluci, S. O. Dantas, A. Jorio, D. S. Galvão, Phys. Rev. B 75 075417 (2007).
9:00 PM - JJ20.4
Processing Dependence of Thermal and Mechanical Behavior of Nanotube Reinforced Polyethylene Composite.
Ananta Adhikari 1 , Karen Lozano 1
1 Department of Mechanical Engineering, University of Texas-Pan American, Edinburg, Texas, United States
Show Abstract9:00 PM - JJ20.41
Acoustic/Mechanical Properties of Slanted Nanorod Arrays.
Masashi Yamaguchi 1 , Jianxun Liu 1 , Dexian Ye 1 , Toh-Ming Lu 1
1 Physics, Rensselaer Polytechnic Institute, Troy, New York, United States
Show Abstract9:00 PM - JJ20.42
A Mechanochemical Model of Growth Termination in Vertical Carbon Nanotube Forests and Experimental Approaches toward Infinite Film Synthesis.
Jae-Hee Han 1 2 , Charles Welch 3 , Charles Marsh 4 , Thomas Carlson 4 , Michael Strano 1 2
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 The Shock and Vibration Information and Analysis Center, Information Technology Laboratory, U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi, United States, 4 Construction Engineering Research Laboratory (CERL), U.S. Army Engineer Research and Development Center, Champaign, Illinois, United States
Show AbstractUnderstanding the mechanisms by which vertical carbon nanotubes (CNTs) array terminate their growth may lead to the production of aligned materials of infinite length. Both single- and doubled-walled carbon nanotubes (SWNTs and DWNTs) films demonstrate characteristic yet unexplained deflections of the top surface near the edges and corners of the film. We show that this upturn in the surface can be explained by assuming a mechanical coupling between neighboring nanotubes.1 A Monte Carlo simulation of film growth is able to qualitatively reproduce the shape by assuming that the coupling is limited by the enthalpy of the carbon forming reaction. The shape of the surface is approximately conic with hyperbolic cross sections that allow for the calculation of a threshold force (Fmax = 34 to 51 nN for SWNTs, 25 to 27 nN for DWNTs) and elastic constant (k = 384 to 547 N/m for SWNTs and 157 to 167 N/m for DWNTs) from the images of experimentally synthesized films. Despite differences in nanotube type and precursor chemistry, the values appear consistent. The origin of the mechanical coupling will be discussed. With this theoretical hypothesis, up to now, we have experimentally synthesized the millimeter-thick vertical CNTs array via water injection route during synthesis to circumvent the growth termination of the film in chemical vapor deposition system. Notably we observed such characteristic deflections of the top surface of the films grown and were able to control the degree of both deflections and straightness, possibly originated from the mechanical coupling between arrays of CNTs in the forests. For the further detailed quantitative analysis, small angle X-ray scattering (SAXS) studies on different forests grown under various water injection modes will be presented. Reference 1. Han, J. H.; Graff, R. A.; Welch, B.; Marsh, C. P.; Franks, R.; Strano, M. S. ACS Nano 2008, 2, 53-60.
9:00 PM - JJ20.43
The Stress and Dislocation Core Controlled Plasticity of Graphene-based Systems.
Shuo Chen 1 , Elif Ertekin 2 , Daryl Chrzan 1 3
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Berkeley Nanoscience and Nanoengineering Institute, University of California, Berkeley, California, United States, 3 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show Abstract9:00 PM - JJ20.44
Electronic Detection and Influence of Environmental Factors on Conductivity of Single DNA Molecule using Single-walled Carbon Nanotube Electrodes.
Harindra Vedala 1 , Taehyung Kim 1 , Sookhyun Hwang 2 , Minhyon Jeon 2 , Wonbong Choi 1
1 Mechanical and Materials Engineering, Florida International University, Miami, Florida, United States, 2 Department of Nano Systems Engineering, Inje University, Gimhae Korea (the Republic of)
Show AbstractRapid detection of ultra low concentration or even single DNA molecules are essential for medical diagnosis and treatment, pharmaceutical applications, gene sequencing as well as forensic analysis. In this work we demonstrate the use of single walled carbon nanotubes as nanoscale electrodes for electronic detection of single DNA molecules. A detailed study on electrical conductivity and influence of environmental factors on a double-stranded DNA molecule bridging a single-walled carbon nanotube (SWNT) gap is presented. The amine terminated DNA molecule was trapped between carboxyl functionalized SWNT electrodes by dielectrophoresis. Typically, a current of tens of picoamperes at 1 V was observed at ambient conditions, with a decrease in conductance of about 30% in high vacuum conditions. As the intrinsic conductivity of the DNA molecule is strongly influenced by environmental factors we study the conductivity of DNA under the influence of salt concentration, counterion variation, pH and temperature. The counterion variation was analyzed by changing the buffer type. A reversible shift in the current signal was observed for pH variation. An increase in conductivity of the DNA was also observed at high salt concentrations.
9:00 PM - JJ20.45
CMOS-analogous Wafer-scale Nanotube-on-insulator Approach for Devices and Integrated Circuits using Aligned Nanotubes.
Koungmin Ryu 1 , Alexander Badmaev 1 , Chuan Wang 1 , Lewis Gomez 1 , Akshay Kumar 1 , Chongwu Zhou 1
1 Department of Electrical Engineering, University of Southern California, Los Angeles, California, United States
Show AbstractThe nanotube-on-insulator (NOI) approach based on massively aligned nanotubes offers many advantages including high device yield, registration-free fabrication, high current outputs, reasonable mobility, as well as good uniformity over wafer scale. This shows a route toward large-scale and truly integrated nanotube electronics. In this presentation, we present essential technological components for wafer-scale (4-inch) integrated CMOS nanotube circuits, including wafer-scale nanotube synthesis, wafer-scale nanotube transfer, wafer-scale circuit fabrication, device tuning with automated electrical breakdown, and n-type doping. We demonstrated the synthesis of massively aligned carbon nanotube arrays, with uniform density (2-3 tubes/micrometer) on entire 4” quartz or sapphire substrates followed by the transfer to 4” Si/SiO2 wafer using our facile transfer imprinting method, which has a transfer yield of close to 100%. Based on the transferred aligned nanotubes, wafer-scale fabrication of high performance field effect transistors with submicron active channel as well as many kinds of integrated CMOS circuits such as inverters, NAND, and NOR logic gates were demonstrated. With the above-mentioned devices, we carried out in-depth device study as well as device tuning using automated electrical breakdown to remove metallic nanotubes while retain good wafer-scale uniformity in terms of on-off ratio and current density. We also demonstrated multiple transfers as a method to increase the nanotube density, delivering high current outputs. In addition, three kinds of doping techniques, including Hydrazine, Potassium, and electrostatic doping were successfully demonstrated to convert the p-type aligned nanotube devices to n-type. Based on those doping techniques, truly integrated CMOS inverters, NAND, and NOR logic gates were also demonstratedOur full-wafer-scale approach using many parallel nanotubes showed huge advantage over conventional and small scale processes based on individual nanotube, and proposed a practical and realistic process for the large-scale integrated nanotube circuits.
9:00 PM - JJ20.46
Carbon Nanotubes and Their Composites with Nanodiamond for Thermal Packaging: Syntheses, Characterization and Modeling.
Sanju Gupta 1 , A. Schuttler 1
1 ECE, UMC, Columbia, Missouri, United States
Show Abstract9:00 PM - JJ20.47
Modeling of Contact Mechanics in Carbon Nanotube Array Interfaces.
Baratunde Cola 1 2 , Timothy Fisher 1 2
1 Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States, 2 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States
Show AbstractSubstrate-supported carbon nanotube (CNT) and nanofiber arrays represent one of the most versatile and promising platforms for CNT integration into functional devices and systems. Such CNT arrays have demonstrated gecko-like dry adhesion to a mating surface and have been employed as highly conductive thermal and electrical contacts. The high mechanical compliance of CNT arrays can create intimate interface contact and is central to the efficacy of these applications. Recent studies have demonstrated the extent of CNT array compliance; however, no analytical model has been proposed to explain the mechanics of CNT array deformation and to relate compliance to the real contact area created in CNT array interfaces. Inspired by observations of CNT deformation at interfaces, we apply here a semi-empirical wool fiber compression theory, which was developed for the textile industry more than 60 years ago, to describe CNT array deformation under loading. The wool compression theory applied to substrate-supported CNT arrays agrees well with recent force-displacement measurements, accurately predicting that the CNT array thickness under loading scales as one over the cube root of pressure. Utilizing classical contact mechanics and considering the effect of van der Waals forces at the nanoscale, we demonstrate that the wool compression theory can be extended to predict the real contact area in CNT array interfaces based on data obtained from experiments involving compression measurements, thermal contact resistance, and electrical contact resistance. We show that mechanical compliance and CNT number density are explicit array metrics that can be optimized in the fabrication process to produce CNT array interfaces that enhance real contact area for a variety of applications spanning tribology, electronics packaging, and energy transport and conversion.
9:00 PM - JJ20.48
Interface-controlled Carbon Nanotubes for Polymer and Copper Matrix Composites.
Youngseok Oh 1 , Seyoung Oh 1 , Byengsoo Lim 2 , Young-jin Kim 1 2 , Seunghyun Baik 1 2
1 SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon Korea (the Republic of), 2 School of Mechanical Engineering, Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractNumerous attempts have been made to develop advanced composites by the incorporation of carbon nanotubes (CNTs) due to the remarkable mechanical and electrical properties such as high strength, stiffness, flexibility, thermal and electrical conductivity. To utilize the excellent properties of carbon nanotubes in the matrix material, it is important to achieve homogeneous dispersion of CNTs and improve interfacial bonding. In this study, we developed copper matrix composites and silver/conducting polymer matrix composites by the incorporation of interface-controlled carbon nanotubes. The homogeneous dispersion of nanotubes was achieved by acid treatment process and the interfacial bonding was improved by electroless metal plating around nanotubes. The significantly improved mechanical and electrical properties were demonstrated by the displacement rate tests and four-point probe measurements. For the copper matrix composites, nickel plating on CNTs increased mechanical properties whereas copper plating improved electrical conductivity. The resistivity of the silver/conducting polymer composite was decreased by an order of magnitude by the addition of silver-plated CNTs.
9:00 PM - JJ20.5
Electronic Properties of Multiwall Carbon Nanotubes Studied by Frequency Dependent Rotation in Suspension in AC Electric Fields.
Donglei Fan 1 , Frank Zhu 2 , Robert Cammarata 1 , Chia-Ling Chien 2 1
1 Materials Science and Engineering, Johns Hopkins Univ, Baltimore, Maryland, United States, 2 Physics and Astronomy, Johns Hopkins Univ, Baltimore, Maryland, United States
Show AbstractWe have studied the electronic properties of the multiwall-carbon nanotubes (MWCNT) by characterizing the frequency dependent rotation of MWCNT in solution exposed to AC electric fields. The rotation angle, speed, and chirality can be precisely controlled by the electric field strength and frequency. From the rotation spectrum, the imaginary part of the Clausius-Mossotti factor can be readily determined from 0.05 to 1MHz, which depends on the material, the geometry, and the AC frequency. This approach can be used as a non-contact and non-destructive method to determine and differentiate the electronic properties of nanoparticles.
9:00 PM - JJ20.6
High Electrochemical Performances of Tin Sulfide Nanosheet Electrodes Directly Grown on Current Collectors.
Jin-Gu Kang 1 , Dong-Wan Kim 1 , Kyung Jin Choi 1 , Jae-Gwan Park 1
1 Nano-materials Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractSelf-supported low-dimensional nanostructuring of electrode materials on current collectors is one of attractive strategies for advanced Li ion battery by providing shorter path length for both electronic and Li ionic transport, higher electrode/electrolyte contact area, better accommodation of the strain of volume change during cycling, and especially good electrical contact between each array and the current collector. Herein, we fabricated two-dimensional (2-D) nanosheet arrays of high-capacity tin sulfide (SnS) directly grown on metallic current collector via the one-step pulsed laser ablation method. It was found that nanosheets have tens of nanometers thickness and hundreds of nanometers width. The preferential formation of sheet-like morphologies originates from weak Van der Waals force between two layers along the <010> direction in orthorhombic SnS structure. Electrochemical measurements such as cyclic voltammetry and galvanostatic cycling were performed to evaluate lithium reactivity of nanosheet electrodes. Indeed, SnS nanosheet electrodes show high reversible capacity and superior rate capability compared to its powder counterpart with lamellar structure. The origin of improved electrochemical performance and reaction mechanism upon cycling in SnS nanosheet electrodes are also investigated using high resolution transmission electron microscopy.
9:00 PM - JJ20.7
Enhanced Reduction of Oxygen at Pt electrodes modified with Conducting Polymer/Single Walled Carbon Nanotube Composite.
Santhisagar Vaddiraju 1 , Patrick Tshilenge 1 , Diane Burgess 2 , Faquir Jain 3 , Fotios Papadimitrakopoulos 1 4
1 Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States, 2 Department of Pharmaceutical Sciences, University of Connecticut, Storrs, Connecticut, United States, 3 Electrical and Computer Engineering, University of Connecticut, Storrs, Connecticut, United States, 4 Department of Chemistry, University of Connecticut, Storrs, Connecticut, United States
Show AbstractCarbon nanotubes (CNTs) because of their excellent mechanical, electrical, chemical and electrochemical properties have found a tremendous potential for use in a range of diverse fields including biosensors, flexible optoelectronics and high performance materials. In particular because of their enhanced catalytic activities, they have been widely used for detection of various electrochemical analytes. We herein report on the fabrication of oxygen sensors based on the incorporation of single walled carbon nanotubes (SWNT) as dopant within an electropolymerized conducting polymer (CP) film. Cyclic voltammetry and optical absorbance spectra have been used to confirm the incorporation of SWNT within the growing film of CP. The reduction of oxygen at the CP/SWNT composite electrode displayed enhanced sensitivities and a favorable shift in over potential, attributed to the catalytic activity of both SWNTs and the CP acting in tandem. This electropolymerization avenue to incorporate CNTs in a biosensor represents a simple, one-step route for the fabrication of high performance oxygen sensors and can be easily extended to other types of biosensors and biofuel cell applications.
9:00 PM - JJ20.8
Polymer Electrolyte Membrane Fuel Cell with Vertically Aligned Carbon Nanotube Electrode.
Di-Jia Liu 1 , Junbing Yang 1 , Nancy Kariuki 1 , Gabriel Goenaga 1 , Ann Call 1
1 Chemical Sciences & Engineering Div, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractSince its discovery, carbon nanotube (CNT) has been considered as a promising material for various applications. Electro-catalyst support for polymer electrolyte membrane fuel cells is one of them. The desirable attributes of CNT include its unique geometric shape, high surface area, graphitic structure with better stability in the oxidative environment. Although there have been a number of reports on CNT based membrane electrode assembly (MEA) in fuel cell, the CNTs in these electrodes oriented randomly. The advantages associated with the distinctively structural properties of CNTs such as similar diameter, length and orientation were not fully utilized.We report here our progresses in fabricating and evaluating MEA made of catalyst decorated, vertically aligned carbon nanotube (ACNT) layers. The advantages of ACNT-based MEA include improved thermal and charge transfers through direct contact between the electrolyte and current collectors without percolation and the maximum exposure of the catalyst site to gas reactant through uniform support geometry and parallel alignment. Furthermore, a MEA of 3-D nanoarchitecture with improved mass-transport, water management and fuel utilization can be fabricated through patterning the substrate with micron precision for ACNT growth. Our ACNT-MEAs were prepared by nanotube growth through chemical vapor deposition (CVD), followed by catalyzing and transfer processes. The aligned CNT layer was decorated with highly dispersed platinum crystallites either by modified solution chemistry or gas phase co-CVD process to keep the alignment intact. Alternatively, N-containing compounds were introduced during the CVD process to form non-precious metal electrocatalytically sites on the surface of ACNT. The catalyzed ACNT layer was transferred over the ion-conducting polymer film such as Nafion® through hot-press method. The ACNT-MEA thus prepared was tested in a single cell test assembly using hydrogen as the feed in the anode and air or oxygen in the cathode. For comparison, a commercial MEA prepared through the ink-based process was also tested under the similar conditions. Improved performance, particularly at high current region, was observed for ACNT-MEA, suggesting the enhancement in mass transport and better water management. This work was supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. The electron microscopy was performed at the Electron Microscopy Center for Materials Research at Argonne National Laboratory, a U.S. Department of Energy Office of Science Laboratory operated under Contract No. DE-AC02-06CH11357 by UChicago Argonne, LLC. The authors are grateful to Drs. D. Myers, S. Niyogi, M. Ferrandon and J. Mawdsley for their helpful discussions and the experimental supports.
9:00 PM - JJ20.9
Improved Long-term Stability of Pt Nanocatalysts on CNT-Electrode Grown by Oxygen-containing Plasma.
He-Yun Du 1 , Hsin-Cheng Hsu 1 , Chien-Chu Chen 2 , Chen-Hao Wang 4 , Sun-Tang Chang 1 , Shi-Chern Yen 1 , Li-Chyong Chen 4 , Kuei-Hsien Chen 3 4
1 Chemical Engineering Department, National Taiwan University , Taipei Taiwan, 2 Department of Chemistry, National Taiwan Normal University, Taipei Taiwan, 4 Center for Condensed Matter Sciences, National Taiwan University, Taipei Taiwan, 3 Institue of Atomic and Molecular Science, Academia Sinica, Taipei Taiwan
Show AbstractThe carbon nanotubes (CNTs) were directly grown on the carbon cloth (CNT-electrode) by the microwave plasma-enhanced chemical vapour deposition (MPECVD) and the subsequently platinum catalysts were deposited on the as-grown CNTs (Pt/CNTs-CC) by the chemical ion-exchange method. The Pt/CNTs-CC electrodes exhibit excellent electrochemical activity of methanol oxidation, because of the high conductivity of the CNT as well as the low interfacial resistance between the catalyst and the CNT, which has been demonstrated in our previous work. The nitrogen doping in the CNT served as the active sites for the subsequently electrocatalyst deposition, which resulted in highly dispersion of electrocatalysts on the CNT. In order to strengthen the interaction between catalysts and CNTs, the additional oxygen precursor was participated in the growth of the CNT-electrode, which was expected to functionalize the surface of the CNT with oxygen group. The mixture precursors of CH4/H2/N2/O2 as the flow rates of 80/20/80/0.8 were introduced into the growth under the plasma power of 1500 W for 10 min. The electrocatalysts were deposited on the CNT-electrode with oxygen-containing plasma (Pt/oCNT-electrode) by means of the chemical ion-exchange method. For comparison, the electrocatalysts were also deposited on the CNT-electrode without the oxygen introducing into the growth (Pt/CNT-electrode). According to the high-resolution scanning electron microscopy (HRSEM) results, the length of oCNT-electrode is around 2.5 μm, which is shorter than that of CNT-electrode. The oxygen incorporation may inhibit the CNT length-growth due to part of the hydrocarbon (CHx) radicals and ions reacting with the oxygen. Cyclicvoltammetry results show the activities of methanol oxidation of Pt/CNT-electrode and Pt/oCNT-electrode, respectively, in 1 M methanol and 1 M sulfuric acid for 500 cycles. In the initial cycle, the peak current density of Pt/CNT-electrode is almost equal to that of Pt/oCNT-electrode, interpreting that both of them have the even activity of methanol oxidation at the beginning. However, after 300 cycles, the peak current of Pt/CNT-electrode is almost half of the initial cycle, but the peak current of Pt/oCNT-electrode is nearly the same as the initial cycle. This indicates that the Pt electrocatalysts are not easily poisoned by carbon monoxides during the methanol oxidation. The oxygen-containing functional group on the CNT surface have ability to provide the hydroxide near the Pt-CO, and therefore the carbon monoxides can be released to form the gaseous CO2. The mechanism of the enhanced activity of Pt/oCNT-electrode needs to study in the future.