Symposium Organizers
John J. Boeckl Air Force Research Laboratory
Liming Dai Case Western Reserve University
Weijie Lu Fisk University
Mark H. Ruemmeli Leibniz Institute
IFW Dresden
Jamie Warner University of Oxford
C3: Poster Session: Mechanism, Growth, and Processes of Low-dimensional Carbon Nanostructures
Session Chairs
Tuesday AM, November 30, 2010
Exhibition Hall D (Hynes)
C1: Growth of Graphene/Substrate Structures
Session Chairs
Monday PM, November 29, 2010
Room 304 (Hynes)
9:00 AM - C1.1
Epitaxial Growth of Single-layer Graphene over Crystalline Metal Films Deposited on Sapphire.
Hiroki Ago 1 2 3 , Yoshito Ito 2 , Baoshan Hu 1 , Masaharu Tsuji 1 , Noriaki Mizuta 2 , Seigi Mizuno 2
1 Inst. Mater. Chem. Eng., Kyushu Univ., Fukuoka Japan, 2 Grad. Shcl. Eng. Sci., Kyushu Univ., Fukuoka Japan, 3 , PRESTO-JST, Kawasaki Japan
Show AbstractGraphene is emerging as a new building block of future nanoelectronics and microelectro-mechanical systems. Recently, catalytic CVD growth has attracted considerable interest as an effective means to produce large-area graphene films. However, because most of the CVD growth has been done over a polycrystalline metal film that is deposited on a SiO2/Si substrate, as-grown graphene has relatively small grain size and its orientation is not controlled. We studied the growth of graphene films over crystalline metal films deposited on single crystalline substrates and reported an interesting formation of square and triangular-shaped graphene films on such crystalline metal catalyst [1]. Here, we performed CVD growth over crystalline Co and Cu films deposited on sapphire substrates. Interestingly, the preferential formation of uniform single-layer graphene is also observed for the Co film. More than 90% area of the graphene film is found to be single-layer with Co. Furthermore, we discuss the orientation of graphene films on Co and Cu that was grown by atmospheric CVD. Our study offers a new route to grow high-quality single-layer graphene even on Co metal and gives new insights into the growth mechanism of graphene.Reference[1] H. Ago, I. Tanaka, C. M. Orofeo, M. Tsuji, Small, 6, 126 (2010).
9:15 AM - C1.2
Dimensional Changes of Cabon Nanostructure Growth on SiC by Controlling Pressure.
Adrienne Williams 1 , Edwina Clarke 1 , Roland Barbosa 1 , W. Collins 1 , Weijie Lu 1 , John Boeckl 2 , William Mitchel 2
1 Department of Chemistry, Fisk University, Nashville, Tennessee, United States, 2 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, United States
Show AbstractCarbon nanotubes (CNTs) and graphene exhibit extraordinary and unique physical properties that make them potentially useful in many applications in nanotechnology, electronics, optics, and other fields of material science. Both CNTs and grapheme can be produced by silicon carbide (SiC) decomposition by controlling growth temperature and pressure. Our preliminary results have demonstrated that graphene and single walled nanotubes (SWNTs) were produced by annealing the SiC samples at 1450°C under 5.0 x 10e-8 Torr and 5.0 x 10e-6 Torr, respectively. During the heating process, the partial pressure of oxygen was monitored using a Residual gas analyzer (RGA). Low-dimensional morphological and structural features were analyzed by Raman Spectroscopy, Atomic Force Microscopy, and X-ray photoelectron spectroscopy. Graphene layer is produced at the total pressure at 10e-8 Torr while SWNTs are produced at 10e-6 Torr at 1450°C. The introduction of oxygen after the grown process results in the formation of structural defects.
9:30 AM - C1.3
Catalytic Graphene Growth from Solid and Gaseous Carbon Sources.
Robert Weatherup 1 , Daiyu Kondo 1 , Bernhard Bayer 1 , Raoul Blume 2 , Robert Schloegl 2 , Stephan Hofmann 1
1 Electronic Engineering, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom, 2 Inorganic Chemistry, Fritz-Haber-Institut, Berlin Germany
Show AbstractCatalytic chemical vapour deposition (CVD) on metal film templates offers a low-cost method of producing graphene across large areas, but at present the growth mechanism(s) are not well understood. We compare (few-layer) graphene precipitation based on a solid C source to graphene CVD based on low acetylene exposures on poly-crystalline transition metal films. Time-resolved, high-pressure X-ray photoelectron spectroscopy (XPS)[1] allows a detailed record of transient C/metal core level signatures prior to and during graphene formation for the different experimental conditions, based on which we model the growth process. We assess the uniformity and domain sizes of as-grown and transferred graphitic layers by optical/scanning electron microscopy, Raman mapping and electrical transport measurements.[1] Hofmann et al., J. Phys. Chem. C 113, 1648 (2009)
9:45 AM - C1.4
Macroscopic Monolayer Graphene on Ruthenium Thin Films.
Peter Albrecht 1 , Eli Sutter 1 , Peter Sutter 1
1 , Brookhaven National Laboratory, Upton, New York, United States
Show AbstractEpitaxy on noncarbide-forming transition-metal substrates has emerged as a scalable alternative to micromechanical cleavage for the synthesis of high-quality graphene [1, 2]. On the Ru(0001) surface, for example, epitaxial growth can produce macroscopic (>100 microns), single-crystalline graphene domains having uniform monolayer thickness [1, 3]. Potential applications in microelectronics, photonics, and sensing will demand graphene synthesis on low-cost substrates or sacrificial templates that permit facile transfer to insulating supports. This talk will describe the synthesis and characterization of graphene on Ru thin films deposited on SiO2/Si(001) which possess significant advantages over alternative metal films if qualities such as macroscopic monocrystalline domains with perfect rotational alignment, a very low defect density, and precise thickness control proven for Ru single crystals can be retained. Through a combination of cross-sectional transmission electron microscopy (XTEM) and scanning tunneling microscopy (STM), we establish that the Ru films have columnar structure with strongly aligned grains exposing flat (0001) surface facets [4]. We observe small (3-4 degree) relative tilts of the [0001] axes between neighboring Ru grains as well as variations in in-plane orientation. In addition, we find that such a thin-film template yields a graphene layer that is continuous across the entire sample and of uniform monolayer thickness. Analysis of the graphene/Ru moire structure reveals that single-crystalline graphene domains are coherent across multiple Ru grains each on the order of 0.5 microns in size [4]. Thus the lateral expansion of the monolayer graphene domains is not restricted by grain boundaries in the polycrystalline Ru template.Moreover, we demonstrate graphene epitaxy on metal surfaces of arbitrary geometry. We report the synthesis of graphene on Ru thin films deposited on fused silica substrates containing arrays of micron-scale concave, three-dimensional structures milled via focused ion beam. Based again upon a combined XTEM/STM study, we conclude that monolayer graphene completely and uniformly covers the Ru films in microscopic off-axis planar and continuously curved areas, indicating that the synthesis of graphene on polycrystalline Ru is not restricted to flat surfaces but can be extended to more complex, topologically irregular substrates without sacrificing coverage uniformity or thickness control. In addition, we demonstrate that monolayer graphene passivates the underlying metal surface against reaction with ambient gases, which is critical for applications such as concave focusing mirrors and nonplanar microelectrode arrays. [1] P. Sutter et al., Nature Mater. 7, 406 (2008).[2] P. Sutter et al., Phys. Rev. B 80, 245411 (2009).[3] E. Sutter et al., Appl. Phys. Lett. 94, 133101 (2009).[4] E. Sutter et al., Appl. Phys. Lett. 95, 133109 (2009).
10:00 AM - **C1.5
MBE Growth of Graphene Using a C60 Carbon Source.
William Mitchel 1 , Jeongho Park 1 , Howard Smith 1 , John Boeckl 1 , Shin Mou 1 , D. Tomich 1 , Kurt Eyink 1
1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson AFB, Ohio, United States
Show AbstractDirect epitaxial growth of graphene on SiC substrates using thermally evaporated solid C60 is reported. Carbon source molecular beam epitaxy (CSMBE) provides an additional control parameter and can produce high quality graphene at significantly lower temperatures than conventional SiC decomposition in ultra-high vacuum (UHV) or in atmospheric pressure argon. Atomic force microscopy, X-ray photoemission spectroscopy, Raman spectroscopy, transmission electron microscopy and electrical transport measurements were used to compare material grown at 1400°C by CSMBE and by both forms of thermal decomposition. CSMBE has significantly improved surface quality with a very low Raman D to G band ratio. Graphene growth under a C60 flux has been observed at temperatures as low as 1200°C.
10:30 AM - **C1.6
Graphene Growth and Formation of Free Standing Graphene Membranes.
Michael Spencer 1
1 Electrical and Computer Engineering, Cornell University, Ithaca, New York, United States
Show Abstract Graphene is a single atomic layer of graphite and consists of sp2 bonded carbon atoms arranged in 2-dimensional honeycomb lattice. Extremely high carrier mobility and ballistic carrier transport in graphene makes it an attractive candidate for high frequency electronic devices. High quality graphene can be directly formed on SiC surface as a result of Si evaporation at high temperature. At Cornell we have been able to produce material (by sublimation) on the Si face of SiC with mobility as high as 1,400 cm2/Vsec. On the C face of SiC we have been able to obtain similar mobility. We have demonstrated a technique for producing free-standing graphene on SiC using a photoelectrochemical (PEC) etch process and characterized the nanomechanical graphene resonators formed from this material. In order to enable electron transport studies of suspended epitaxial graphene (SEG) on SiC we have modified our earlier process. Our earlier work reported on SEG produced on n-doped SiC substrates. The PEC etch process requires a doped substrate for the etching reaction to proceed. The conducting substrate, however, rendered transport measurements in graphene difficult. In the current configuration, semi-insulating SiC substrates are implanted using nitrogen in order to produce a thin doped top sacrificial layer for the PEC etch. Graphene is now grown on the implanted substrates at a growth temperature of 1700oC in an argon atmosphere. The growth process also provided sufficient energy for activation of the implanted donors. Graphene thickness is estimated to be ~1.3 monolayers using X-ray photoelectron spectroscopy and AFM. Graphene is then photolithographically patterned using an oxygen plasma and then the devices are exposed to the PEC etch. Raman spectroscopy showed that the suspended devices are not chemically modified during the PEC process. Transport measurements showed no conduction between contact pads in the absence of graphene.
11:30 AM - **C1.7
Steps Towards Controlling Epitaxial Graphene Growth
David Gaskill 1 , L. Nyakiti 1 , J. Hite 1 , N. Garces 1 , V. Wheeler 1 , J. Tedesco 1 , J. Culbertson 3 , F. Bezares 1 , G. Jernigan 2 , R. Myers-Ward 1 , E. Imhoff 1 , C. Eddy 1
1 Code 6882, U.S. Naval Research Laboratory, Washington, District of Columbia, United States, 3 Code 6876, U.S.Naval Research Laboratory, Washington, District of Columbia, United States, 2 Code 6812, U.S.Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractIn the last two years, tremendous progress has been realized in the fabrication of epitaxial graphene (EG) RF devices [1]. However, improving the control of EG growth – thickness and doping uniformity - is crucial for continued success. It is natural to think that understanding the initial steps of graphene growth is paramount to future development of control strategies. In this regard, we present recent results in two areas of EG growth synthesis: graphene island formation on (000-1) 6H-SiC and single layer graphene growth on (0001) 4H-SiC step-free mesas (SFMs).Through control of temperature and Ar pressure, graphene epitaxy can be slowed, resulting in island growth on the C-face of SiC [2]. The islands are thought to represent early stages in graphene growth, and in nearly all cases appear to originate from threading screw dislocations associated with the substrate. We followed the growth process from island to complete film using optical and scanning electron microscopies and Raman spectroscopy. Island centers were generally thicker than the edges. During island expansion, coalescence of adjacent islands naturally occurred, which resulted in thickness inhomogenieties. The island crystallite length scale was extracted using the ratio of the Raman D and G band intensities; this length scale was found to increase with increasing island lateral dimension, eventually achieving the values associated with complete films.To aid in understanding EG growth without the impact of substrate defects, we investigated growth on SFMs. SFMs were formed by a kinetically-controlled lateral step-flow SiC growth process at 1580°C on (0001) 4H-SiC substrates patterned with mesas [3]. When threading screw dislocations are not present, the SiC growth process results in atomically flat mesas. Subsequently, EG was grown in a 100 mbar Ar ambient at 1620°C on an array of SFMs with side lengths ranging from 40µm to 200µm. For short growth times, partial graphene coverage of SFMs was observed suggesting a growth mechanism limited, in part, by C surface diffusion. For long growth times, complete EG mesa coverage was established and the step bunching morphology typically observed on conventional basal plane substrates was not found. For the long growth time case, analysis of the 2D Raman signal implied a single layer of graphene was present in the central area of the mesa. In contrast, analysis of the 2D Raman signal from mesa edges suggested up to 2 layers were present. In addition, the graphene in the central region of the SFMs was approximately strain-free whereas the graphene at the edges was more strained. These latter properties differ substantially from EG grown on conventional basal plane substrates which exhibit significant strain.References[1] J.S. Moon, et al, IEEE Electron Device Letters 31, 260, (2010).[2] J.L.Tedesco, et al, Appl. Phys. Lett. 96, 222103 (2010).[3] P.Neudeck, et al, Mater. Res. Soc. Symp. Proc. 911, 85 (2006).
12:00 PM - C1.8
The Surface Evolution and Growth Mode of Graphene on Polycrystalline Cu Using Real Time Analysis.
Joseph Wofford 1 , S. Nie 2 , N. Bartelt 2 , K. McCarty 2 , O. Dubon 1
1 , UC Berkeley, Lawrence Berkeley National Lab, Berkeley, California, United States, 2 , Sandia National Laboratories, Livermore, California, United States
Show AbstractGraphene synthesis on polycrystalline Cu foil has been shown to consistently produce monolayer films of relatively high quality, which has significantly enhanced its potential as a technologically relevant material. Despite this, little is understood about both the growth kinetics of this system or the morphology of the resulting heterostructure. We have used low-energy electron microscopy to observe in situ the UHV growth of monolayer graphene on polycrystalline Cu foil by electron-beam evaporation of C.The temperatures required to synthesize graphene simultaneously induce significant Cu sublimation and step flow, leading to a dynamic growth surface. As a result a complex interdependence develops between the graphene growth behavior and Cu surface morphology: the graphene islands limit Cu step mobility, while Cu step bunching distorts the propagation of the graphene growth front. This relationship becomes increasingly dramatic over time as the inhomogeneous sublimation of Cu leads to considerable surface roughening, resulting in a Cu mound developing beneath each graphene island. The graphene islands show preferential nucleation at step edge clusters, pinning sites, and other surface imperfections indicating that heterogeneous nucleation is dominant. Additionally, although initially compact in shape, the islands become increasingly ramified over time, eventually developing several distinct lobes.Low-energy electron diffraction reveals that each island lobe is a single crystal, differentiated from its neighbors by its orientation relative to the Cu grain below. Dark field imaging exposes the spatial distribution of these rotational variants, and shows that the constituent grains of the polycrystalline islands share a common nucleation site. The morphological evolution of the graphene islands is explained through a growth mode with a two-fold symmetric, orientation-dependent growth velocity, which sculpts the islands into an equilibrium growth shape. This growth velocity symmetry suggests a dependence on the atomic geometry at the crystal front, which is dictated by the orientation of both the graphene and the Cu crystals. The incommensurate structural relationship between the graphene and the Cu, in combination with the demonstrated growth mode, indicate that graphene films interact more weakly with the Cu substrate than in many other graphene-metal systems. Finally, the implications of this unexpected nucleation and growth mechanism on the formation of high-quality graphene films on Cu foils are evaluated.Work at Sandia was supported by the Office of Basic Energy Sciences, Division of Materials Sciences, U. S. Department of Energy under Contract No. DE-AC04-94AL85000. Work at LBNL was supported by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. JMW acknowledges the support from an NSF fellowship.
12:15 PM - C1.9
Layer-by-layer Growth of Graphene on Copper by Chemical Vapor Deposition.
Murari Regmi 1 , Matthew Chisholm 1 , Gyula Eres 1
1 , Oak Ridge National Lab, Oak Ridge, Tennessee, United States
Show AbstractThe growth of graphene on copper is believed to occur by a surface-limited process that self-terminates at a single layer thickness. Our results show that graphene growth on copper occurs by a process similar to the layer-by-layer (LBL) growth mode familiar in epitaxial growth of metal and semiconductor thin films. Different graphene samples were prepared by systematically varying the process parameters including the temperature, pressure, and methane concentration. The optimal temperature window was found to be very narrow (950-1000 °C) with the pressure and methane concentration being less critical. Single layer graphene domains nucleate, grow and coalesce to form a continuous sheet. In addition, small second layer flakes appear in the center of the single layer domains before they coalesce. The appearance of second layer nucleation is indicative of LBL growth in which a critical island size exists for nucleation of the second layer before the growing layer is complete. The size of the second layer flakes changes very little in 30 minutes of growth suggesting very slow lateral growth. Graphene sheets were transferred on SiO2/Si and lacey carbon on copper grids after removing the copper substrate by chemical etching. Raman spectroscopy, optical microscopy and scanning electron microscopy were used to characterize the as grown or transferred graphene sheets. The structure of the graphene layers was studied by aberration corrected scanning transmission electron microscopy (STEM). The atomic resolution images show carbon atoms arranged in a perfect hexagonal honeycomb lattice with no pentagon heptagon (5-7) defects introduced during growth.
12:30 PM - C1.10
Direct Graphene Growth on Insulating Weak Interacting Substrates.
Gunther Lippert 1 , Olaf Seifarth 1 , Dabrowski Jaroslaw 1 , Grzegorz Lupina 1 , Wolfgang Mehr 1
1 Materials Research, IHP, Frankfurt (Oder) Germany
Show AbstractGraphene, an outstanding material with two-dimensional structure and zero band gap, is in focus of intensive efforts to revolutionise high-frequency microelectronic applications. Conception and realization of graphene based devices are often hindered by the fact, that no technology-relevant layer growth method except the decomposition of hexagonal SiC is available. Other techniques like layer-transfer from natural graphite are restricted because of the uncertainty of the position of the graphene flake on the wafer. CVD grown graphene on Cu, Ni, Ir, Ru etc. exhibits a direct bond of the graphene layer with the metal and in addition the conducting behaviour of the metal beneath induces a short circuit with the substrate, making a formation of a transistor difficult. A step forward is the direct growth of graphene on materials with insulating nature. In our presentation we demonstrate graphene growth on insulating silicate substitutes with high electronic band gap by solid-phase epitaxy in UHV. Graphene film evaluation is performed with Raman microspectroscopy, XPS, SEM, AFM and electrical measurements. In a last step we introduce electrical characterizations of the graphene on insulator in a field effect transistor configuration. The stability of graphene growth on this insulator was simulated by DFT calculations within the LDA approximation. With Raman microscopy the growth of few layer graphene was identified on islanding positions determined by the substrate. The quality of the graphene was probed by high-resolution Raman area and line-scans and the spatial distribution of the spectroscopic features like the distortion derived D-line or the graphene associated G and G’ emissions. The few layer graphene flakes are distributed over the substrate and show the size between 1µm to 50 µm. The chemical bonding of the few layer graphene with the silicate substrate is probed using XPS.
12:45 PM - C1.11
CVD Growth of Graphene on Three Types of Epitaxial Metal Films on Sapphire Substrate.
Katsuya Nozawa 1 , Nozomu Matsukawa 1 , Kenji Toyoda 1 , Shigeo Yoshii 1
1 Advanced Technology Research Laboratories, Panasonic Corporation, Kyoto Japan
Show AbstractGraphene growth by chemical vapor deposition (CVD) on three types of epitaxial metal films with different crystal structures on sapphire was studied. Epitaxial metal film on a single crystal substrate can offer both large substrate size and large metal crystal domain for graphene growth, while poly metal film deposited on substrate [1] [2] or bulk metal crystal substrate [3] [4] used in former studies can offer only either of them. Although it is very important for high quality graphene growth to select appropriate metal material, report on it is limited [5]. In this study, we report graphene growth on three types of epitaxial metal films with different crystal structures, which are quite important for epitaxial growth of metal film.Ni (fcc), Ru (hcp) and Co (fcc at temperature for graphene growth and hcp at R.T.) were deposited on c-plane sapphire substrate and annealed in a furnace for solid phase epitaxial (SPE) growth. Graphene layer was grown by CVD with methane gas on the epitaxial metal film. In all cases, both epitaxial growth of metal film on substrate and epitaxial growth of graphene on the metal film were confirmed. In the case of Ru, only one domain is created in the metal film, while two types of domains are created in Ni film. The difference comes from crystal structures. The two domains in Ni film correspond to different stacking sequences in fcc crystal, while hcp has only one stacking sequence. Both fcc region and hcp region were found in the Co film. Carbon atoms dissolved in the Co film suppressed the phase transition from fcc to hcp.Ru sample has good uniformity in graphene layer number, while Co sample has poor uniformity. In the case of Ni sample, layer number is uniform on each metal domain, but layer number at domain boundary is larger than on each domain.Only in the case of Ni film samples, additional peaks are observed around G-line in Raman spectra. Neither Co nor Ru film samples have the peaks. It suggests strong interaction between graphene layer and Ni crystal which has been expected by theoretical study.[1]L.G. De Arco et al., IEEE Trans. Nanotechnol. 8 (2009) p.135[2]A. Reina et al., Nano Lett. 9 (2009) p.30[3]P.W. Sutter et al., Nat. Mater.7 (2008) p.406[4]J. Wintterlin and M.-L. Bocquet, Surf. Sci.603 (2009) p.1841[5] H. Ago et al., Small 6 (2010) p.1226
C2: Low-dimensional Graphitization and Structural Transformations
Session Chairs
Monday PM, November 29, 2010
Room 304 (Hynes)
2:30 PM - **C2.1
Graphene and Its Chemical Derivatives.
Konstantin Novoselov 1
1 School of Physics and Astronomy, University of Manchester, Manchester United Kingdom
Show AbstractThe strictly two dimensional material called graphene was presumed not to exist in the free state until only a few years ago. The most amazing things about graphene probably is that its electrons move with little scattering over huge (submicron) distances as if they were completely insensitive to the environment only a couple of angstroms away. Moreover, whereas electronic properties of other materials are commonly described by quasiparticles that obey the Schrödinger equation, electron transport in graphene is different: It is governed by the Dirac equation so that charge carriers in graphene mimic relativistic particles with zero rest mass. Graphene opens a new direction of research: quasi-relativistic experiments in condensed-matter set-up.Another way of looking at graphene is to think of it as a giant molecule with a possibility of altering it by chemical means. To this end, we have found that can react with atomic hydrogen, which transforms this zero-overlap semimetal into an insulator. Transmission electron microscopy reveals that the obtained graphene derivative (graphane) is crystalline and retains the hexagonal. The reaction with hydrogen is reversible, so that the original metallic state, the lattice spacing and even the quantum Hall effect can be restored by annealing. This illustrates the concept of graphene as a robust atomic-scale scaffold, on the basis of which new two-dimensional crystals with designed electronic properties can be created by attaching other atoms and molecules.
3:00 PM - C2.2
Low Temperature CVD Graphene Formation over MgO.
Mark Ruemmeli 1 2 , Alicja Bachmatiuk 1 , Arezoo Dianat 2 , Felix Boerrnert 1 , Jamie Warner 3 , Andrew Scott 1 , Shasha Zhang 1 , Gianaurelio Cuniberti 2 , Bernd Buechner 1
1 , IFW Dresden, Dresden Germany, 2 , Technische Universität Dresden, Dresden Germany, 3 , University of Oxford, Oxford United Kingdom
Show AbstractGraphene ranks highly as a possible material for future high-speed and flexible electronics. Current fabrication routes, which rely on metal substrates, require post synthesis transfer of the graphene onto a Si wafer or in the case of epitaxial growth on SiC, temperatures above 1000°C are required. Both the handling difficulty and high temperatures are not best suited to present day silicon technology. A possible alternative route is the use of oxides to directly form graphene layers via CVD. This is attractive because most of today’s transistor technology uses complementary metal-oxide semiconductor (CMOS) technology in which an oxide layer insulates the transistor gate from the channel. Hence, the ability to synthesize graphene directly on an oxide crucially removes the need to transfer the graphene after synthesis and can remove the need for large area synthesis as required with metal substrates. Moreover, in order that the technique could easily be adapted for use in Si based technology low temperature reactions (400-450°C) are required to maintain the mechanical integrity of low dielectric constant (K) intermetal dielectrics. In this presentation we demonstrate MgO is suitable for the direct fabrication of graphene and few layer graphene (FLG) via CVD. Moreover, adjusting the reaction time or temperature allows one to switch between FLG and graphene formation. We have achieved synthesis temperatures down to 325°C using acetylene as the feedstock. The experimental data suggest step sites are key catalytic sites. Early theoretical DFT calculations corroborate step sites on MgO (100) as catalytically active centers for acetylene decomposition and carbon adsorption.
3:15 PM - C2.3
Understanding the Graphitisation via SiO2 Catalyst Systems in CVD.
Alicja Bachmatiuk 1 , Felix Boerrnert 1 , Bernd Buechner 1 , Mark Ruemmeli 1 2
1 , IFW Dresden, Dresden Germany, 2 , Technische Universität Dresden, Dresden Germany
Show AbstractMetal free carbon nanostructures are desirable materials for wide potential applications in composites, drug delivery, electronic circuits, especially for the silicon industry. The general requirement for the silicon industry for metal free carbon nanotubes is well known. Metals reduce chip lifetime because they react unfavourably with many materials found in circuits. Hence, the use of non-metallic catalysts is desirable for silicon compatibility (and also composites). Recently various investigations have successfully implemented ceramic catalyst particles, for example, SiO2, ZrO2, SiC, MgO or Al2O3. The use of SiO2 as a catalyst for graphitic nanostructure formation, such as carbon nanotubes and graphene, is particularly attractive for integration into Si based technology. A key question is whether carbide phases form in the reaction. We show the formation of SiC from SiO2 nanoparticles for the synthesis of graphitic carbon nanostructures via chemical vapor deposition (CVD) at 900°C. Our findings point to the carbothermal reduction of SiO2 in the CVD reaction. Moreover, the inclusion of triethyl borate accelerates the carbothermal reduction process improving the availability of SiC species and hence leads to improved yields. The formation of graphitic carbon is best explained through a carbon dissolution mechanism. The studies improve our understanding of the growth mechanisms at play in sp2 carbon formation when using SiO2 catalysts.
3:30 PM - C2.4
Structural Transformations of Carbon Nanomaterials Studied with High Spatial and Temporal Resolution.
Jamie Warner 1 , Yasuhiro Ito 1 , Franziska Schaeffel 1 , Alicja Bachmatiuk 2 , Neil Young 1 , Bernd Buechner 2 , Mark Ruemmeli 2 , Angus Kirkland 1 , Hisanori Shinohara 3 , Andrew Briggs 1
1 Department of Materials, University of Oxford, Oxford United Kingdom, 2 , IFW Dresden, Dresden Germany, 3 , Nagoya University, Nagoya Japan
Show AbstractElectron beam irradiation is used to locally modify the structure of graphitic based carbon nanomaterials, such as graphene, nanotubes and peapods (fullerenes inside nanotubes). Recent results on studying this process with atomic resolution using low-voltage aberration-corrected transmission electron microscopy will be presented. An accelerating voltage of 80 kV is used and this minimizes knock-on structural damage. We find that at 80 kV, metallofullerenes inside SWNTs rapidly fuse together to form DWNTs with metal atoms confined to the interior. We examine how the e-beam interacts with the edges and defect sites of few-layer graphene sheets to modify the local structural properties. We capture the movement of atoms and molecules within these graphtic nanostructures in real time with 80 ms temporal resolution to reveal the detailed dynamics. These results provide insights into the stability, growth mechanisms and bonding in sp2 carbon systems.
3:45 PM - C2.5
Chemical Vapor Deposition (CVD) for Industrial-scale Production of Graphene Films.
Elena Polyakova 1 , Daniel Stolyarov 1 , Wey Zhang 2 , Thomas Salagaj 2 , Karlheintz Strobl 2 , Kirill Bolotin 3
1 , Graphene Laboratories Inc., Reading , Massachusetts, United States, 2 , CVD Equipment Corporation, Ronkonkoma, New York, United States, 3 Physics and Astronomy, Vanderbilt University, Nashville, Tennessee, United States
Show AbstractGraphene materials are considered for use in a wide variety of practical applications including electronics, solar cells, MEMS and NEMS, chemical and biological sensors. Reproducible and cost effective manufacturing of wafer scale graphene films is one of the major roadblocks on the commercialization of the graphene nanomaterials. Our team has successfully grew graphene films on Ni and Cu using Chemical Vapor Deposition approach for the commercial production of CVDGraphene™ products including CVDGraphene™ TEM grids, CVDGraphene™ wafers, etc. We report both on the commercial scale up progress and on the exploration and testing of the CVDGraphene™ films for various applications. We will also show examples from our customers and collaborators who benefited from using CVDGraphene™ products.
4:30 PM - C2.6
Large Scale Homogeneous Bilayer Graphene Film.
Seunghyun Lee 1 , Kyunghoon Lee 1 , Zhaohui Zhong 1
1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Ann Arbor, Michigan, United States
Show AbstractSince its discovery, graphene has attracted broad attentions across disciplines due to its superior electrical and optical properties. However, pristine single and few-layer graphene are intrinsically semimetals; introducing energy bandgap requires patterning nanometer-width graphene ribbons, or utilizing special substrates. The recent discovery of electric field induced bandgap opening in bilayer graphene opens new door for making semiconducting graphene without aggressive size scaling, or using expensive substrates, and makes bilayer graphene particularly attractive for graphene based electronics. Despite intensive research, synthesizing homogeneous bilayer graphene in large size has proven extremely difficult and most bilayer graphene samples are fabricated by mechanical exfoliation, limiting their sizes at micrometer scale. Here we demonstrate homogeneous bilayer graphene films over at least square cm area, synthesized by chemical vapor deposition (CVD) on thin copper foil and subsequently transferred to arbitrary substrates. Bilayer coverage of over 99% is confirmed by spatially resolved Raman spectroscopy. The result is further supported by electrical transport measurements on dual-gate bilayer graphene transistors, where field induced bandgap opening is observed in 98% of the devices. The size of our bilayer graphene film is only limited by the synthesis apparatus and can be readily scaled up, thus enabling wafer scale graphene electronics and photonics.
4:45 PM - C2.7
Molecular Motions from Single C60 Jumps to Collective Transport and Rotation of C60s Chain Stimulated by Electron Beam Irradiation.
Ke Ran 1 3 , Qing Chen 3 , Zujin Shi 4 , Jian-Min Zuo 1 2
1 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing China, 4 College of Chemistry and Molecular Engineering, Peking University, Beijing China, 2 Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractElectron beam irradiation stimulated motions of carbon nanostructures from single C60 to C60s chain inside C60@CNT peapods are investigated by low voltage and high resolution TEM. In a fully filled carbon nanotube with a regular zigzag packing C60s chain inside it, single C60’s motion along and perpendicular to the tube axis is observed. A cluster of C60s in an isolated partially filled carbon nanotube is found to translate back and forth within the hollow space of the host nanotube for several times and can pick up more C60s when it reaches either end of the hollow space. Intermediate state of the translation is recorded as well, in which the moving cluster is temporarily trapped at some middle places of the hollow space. Continuous rotation of a long zigzag C60s chain in an overloaded carbon nanotube results in expansion and contraction of the host nanotube as observed in TEM images, and the maximum CNT expansion is measured up to 29%. Potential simulation of different peapod systems taking into consideration of the van der Waals interactions between carbon atoms is performed. Activation energy around hundreds of meV is estimated to stimulate the various nanostructure’s motions which probably can be accomplished in tens of picoseconds. Under our experimental condition, motivation of these observed motions is attributed to the elastic scattering between incident electrons and carbon atoms. After being scattered by a carbon atom, part of the incident electron’s energy is imparted to the carbon atom, of which the probability is depend on the amount of energy that is transferred, and considering the beam density of incident electrons, more than one motions are expected to take place within the 0.5s exposure time for each image. These studies demonstrate the potential of precise controlling of nanostructure’s dynamic behavior by electron irradiation and show the potential of nanoscale motors based on pure carbon material that can be integrated into various nanodevices.
5:00 PM - C2.8
Low Temperature Synthesis of Carbon Nanomarerials.
Vladimir Novikov 1 , Sergey Kyrik 1
1 , SSPA “Scientific-Practical Material Research Centre of NAS of Belarus, Minsk Belarus
Show AbstractWe have demonstrated a possibility of cryogenic synthesis of some low-dimensional materials such as linear carbon, carbon nanotubes, nanodispersed diamond-like carbon and graphens at temperature below minus 30C. Liquid ammonia was used as media, as solvent and as reagent for production of all this carbon materials. 1.Graphene.The method of graphene preparation was based on two main stages. First one was an intercalation of graphite by alkali metal-ammoniac complex and second one was decomposition of the complex by water. The presence of individual graphene sheets we confirm by electron diffraction. Owing to high reduced condition at all stages of synthesis the are no any structural defects of graphene sheets Raman and IR spectroscopic analysis of these films suggests the flakes to be largely free of defects and oxides. High aspect ratio graphite nanoplatelets offer promise as reinforcements for high strength Polymer carbon composites2.Linear carbon (carbyne).The method is based on defluorination of (poly) tetrafluoroethylene by solution alkali metals in liquid ammonium. The starting material was PTFE films. The product of such a reaction under the optimal concentration of alkali metals was black paper-like, flexible porous material. According to FITR and Raman spectra this substance was a chain of carbon atoms connected by sp-hybrid bonds.3. Diamond-like carbon nanopowders.Diamond-like carbon was synthesize by transformation of acetylene-nickel-ammonium complexes in medium of liquid ammonium. Product of the synthesis represents yellow-brawn powders size of 10 nmRaman spectra and functional chemical analysis indicate prevalence of sp3 bonds in such structure.
5:15 PM - C2.9
Reduction of Graphene Grain Boundaries and Synthesis of Single-crystalline Graphene by Chemical Vapor Deposition.
Qingkai Yu 1 , Wei Wu 1 , Zhihong Liu 1 , Luis Jauregui 2 , Jiming Bao 1 , Yong Chen 2
1 , Univ of Houston, Houston, Texas, United States, 2 , Purdue University, West Lafayette, Indiana, United States
Show AbstractThe extraordinary properties and vast potential applications of graphene are strongly stimulating the development of the technology for graphene synthesis with controllable layers, large size and low defects. Recently, significant progresses happened in the synthesis of grapheme both on metal foils and SiC substrates. However, the grain boundaries (GBs) of graphene, where the defects concentrate, have not been controlled well during graphene synthesis. Defects, especially GBs, can severely negatively affect the electrical and mechanical properties. Furthermore, growth of single-crystalline graphene (SCG), which has no grain boundary, has not been developed yet, except on single-crystalline metal substrate, which is impossible to be used in a large scale. So far, the performance of exfoliated graphene is still significantly superior to that of graphene on metals by CVD and on SiC substrates by Si sublimation. One of the reasons of the measured superior performance of exfoliated graphene is that all the properties were measured on a small piece of graphene flake lack of GBs. It is expected that the performance of large-size graphene by CVD or sublimation of SiC substrates can significantly improved by reducing the density of GBs. In this report, we demostrate the large graphene film with domain size as large as 100 um by fine tuning the growth condition with thermodynamic and kinetic analysis. We will also discuss the SCG growth on polycrystalline metal substrates.
5:30 PM - C2.10
A Fully Atomistic Reactive Molecular Dynamics Study on the Formation of Graphane from Graphene Hydrogenated Membranes.
Marcelo Flores 1 , Pedro Autreto 1 , Sergio Legoas 2 , Douglas Galvao 1
1 Applied Physics, State University of Campinas, Campinas, Sao Paulo, Brazil, 2 Centro de Ciencias e Tecnologia, Federal University of Roraima, Boa Vista, Roraima, Brazil
Show AbstractRecently, Elias et al. [1] performed a series of elegant experiments which resulted on the formation of graphane from the graphene membranes under cold plasma exposure. Graphane is a two-dimensional system consisting of a single layer of fully saturated (sp3 hybridization) carbon atoms. In an ideal graphane structure C–H bonds exhibit an alternating pattern (up and down with relation to the plane defined by the carbon atoms) [2]. In this work we have investigated, using ab initio and reactive molecular dynamics simulations [3], the role of H frustration (breaking the H atoms up and down alternating pattern) in graphane-like structures. Such frustrations determine the lattice parameter value as a consequence of the different contributions of graphene, chairlike (hydrogen atoms alternating on both sides of the plane) and boatlike (hydrogen alternating in pairs) graphane motifs [4]. Our results show that a significant percentage of uncorrelated H frustrated domains are formed in the early stages of the hydrogenation process leading to membrane shrinkage and extensive membrane corrugations. These results also suggest that large domains of perfect graphane-like structures are unlikely to be formed, as H frustrated domains are always present. The number of these domains seems to be sensitive to small variations of temperatures and H gas densities. This can perhaps explain the significant broad lattice parameter distribution values experimentally observed [1].[1] D. C. Elias, R. R. Nair, T. M. G. Mohiuddin, S. V. Morozov, P. Blake, M. P. Halsall, A. C. Ferrari, D. W. Boukhvalov, M. I. Katsnelson, A. K. Geim, K. S. Novoselov., Science v323, 610 (2009); arXiv:08104706.[2] J. O. Sofo, A. S. Chaudhari, and G. D. Baker, Phys. Rev. B v75, 153401 (2007); arXiv:condmat/ 0606704.[3] A. C. T. van Duin, S. Dasgupta, F. Lorant, and W. A. Goddard III, J. Phys. Chem. A v105, 9396 (2001).[4] M. Z. S. Flores, P. A. S. Autreto, S. B. Legoas and D. S. Galvao, Nanotechnology v20, 465704 (2009); arXiv:condmat/ 0903.0278v1.
C3: Poster Session: Mechanism, Growth, and Processes of Low-dimensional Carbon Nanostructures
Session Chairs
Tuesday AM, November 30, 2010
Exhibition Hall D (Hynes)
9:00 PM - C3.1
Metal-catalyzed Graphitization in Ni-C Alloys and Amorphous-C/Ni Bilayers.
Katherine Saenger 1 , Christian Lavoie 1 , Roy Carrruthers 1 , Ageeth Bol 1 , Jack Chu 1 , James Tsang 1 , Alfred Grill 1
1 , IBM T.J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractMetal-catalyzed graphitization from vapor phase sources of carbon is now an established technique for producing few-layer graphene, a candidate material for post-silicon electronics. Here we describe two alternative metal-catalyzed graphene formation processes utilizing solid phase sources of carbon. In the first, carbon is introduced as one of the layers in an amorphous carbon (a-C)/Ni bilayer stack; in the second, carbon is introduced as part of a co-sputtered Ni-C alloy. We examine the quality and characteristics of the resulting graphene as a function of starting film thicknessses, Ni-C alloy composition or a-C deposition method (physical or chemical vapor deposition), and annealing temperature/ambient. In addition, we will review recent evidence showing that the graphitic carbon in the a-C/Ni system initially forms by a metal-induced crystallization mechanism (analogous to what is seen with Al-induced crystallization of amorphous Si) rather than by the dissolution/precipitation mechanism seen in graphene growth by metal-catalyzed chemical vapor deposition methods.
9:00 PM - C3.10
Influence of Graphene on Chain and Segmental Dynamics of Polyisoprene.
Derrick Stevens 1 , Wen Yin 2 , Alexander Kisliuk 1 , Alexi Sokolov 1 2
1 , ORNL, Oak Ridge, Tennessee, United States, 2 Chemistry, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractProduction and characterization of polymer composites, specifically those utilizing carbon based nanoparticles, has seen continual interest by the materials science community. Graphene, in particular, has showed promise as a composite filler due to its excellent physicochemical properties and unique morphology. This research investigates the dynamics in composites of polyisoprene and graphene by dielectric relaxation spectroscopy. Polyisoprene with its dielectric response provides an ideal model to observe the influence of graphene additives on the polymer dynamics, from global chain modes to more local segmental and secondary relaxations. Composites are produced at a variety of graphene loading weights and levels of dispersion, as characterized by optical and electron microscopy, through a combination of mechanical mixing and/or solution precipitation methods. Additionally, graphenes at differing stages of production (e.g. annealed, non-annealed, oxidized) were utilized. Changes of the composite dynamics, such as change in the glass transition temperature, segmental and chain relaxation, as a function of these graphene properties are reported.
9:00 PM - C3.11
Hole or Electron Doped C60 Polymer Using Free Electron Laser Irradiation.
Nobuyuki Iwata 1 , Daiki Koide 1 , Syouta Katou 1 , Eri Ikeda 1 , Hiroshi Yamamoto 1
1 Electronics & Computer Science, CST, Nihon Univ., Chiba Japan
Show AbstractThe aim of our study is to develop a novel photopolymerization process for C60 molecules and synthesize an amorphous three dimensional (3D) C60 polymer at the bulk scale for various application fields. The C60 polymer is expected to have features of stiffness, low-density as well as flexibility like organic material owing to the amorphous phase of C60 polymer, and the density lower than that of metal alloys[1-3]. We chose a free electron laser (FEL) as a light source, which has unique features: a tunable wavelength in the infrared range, and a micropulses with a pulse width less than one ps. H. Nakayama et al. demonstrated that a hole doping in graphite induces the same effect as applying pressure[4]. In this study the hole and/or electron doped C60 crystals were pressed, and the FEL was irradiated to promote the polymerization from hybridized orbital sp2.278 of C60 to diamond-like sp3. The I2 dissolved for hole doping and/or Ca(OCH3)2 dissolved for electron doping alcohol was gently added to the C60 saturated solution to grow crystals by liquid-liquid interfacial precipitation (LLIP) method[5]. The layered solution was maintained approximately at 34K for one week. The LLIP grown C60 crystals were filtered and pressed at 600MPa and/or 7GPa. The 500 nm-FELwas irradiated at 2Hz with the energy density of 1 mJ/cm2 for one hour in vacuum. Polymerization degree was analyzed using a micro-Raman spectroscopy, especially Ag(2)-derived mode was observed. Raman spectra of the specimen pressed at 7GPa using o-xylene and I2 dissolved butyl alcohol showed only Ag(2)-derived mode at 1457 cm-1, revealed that the FEL-irradiated area was completely polymerized. This result indicated that the F (fcc structure, space group : Fm3m) phase with the lattice constant of approximately 13.6Å was present.[6] Considering that the lattice constant of pristine C60 is 14.17Å, the distance between centers of molecules shrunk with approximately 4%. Appearence of only this peak also suggested that the polymerization degree was higher than that of traditional photopolimerization, represented by the peak at 1460 cm-1. [1]H. Yamamoto, N. Iwata, R. Hashimoto, and S. Ando: Appl. Surf. Sci. 253, (2007)7977.[2] Shingo Ando, Ryo Nokariya, Reou Koyaizu, Nobuyuki Iwata and Hiroshi Yamamoto, Molecular Crystals and Liquid Crystals, 472 (2007) 255-262.[3]N. Iwata, S. Ando, R. Nokariya, and H. Yamamoto, Jpn. J. Appl. Phys. 47,(2007) 1412.[4]H.Nakayama, H. Katayama-Yoshida, Jpn. J. Appl. Phys. 41 (2002) L817.[5]K. Miyazawa, and K. Hamamoto, Materials Research Society 17, 2205-2208 (2002)[6]P. C. Eklund, A. M. Rao (eds.), Fullerene Polymers and Fullerene Polymer Composites (Springer, 1999), p.169-178.
9:00 PM - C3.13
Palladium Based Synthesis of Carbon Nanotube Materials.
Florian Nitze 1 , Thomas Wagberg 1
1 Dept. of Physics, Umeå Universitet, Umeå Sweden
Show AbstractThe use of palladium as catalyst for different processes has lately attracted the attention of more and more research groups. Carbon materials as support for nano particles, such as palladium decorated carbon nanotubes (CNTs), have shown excellent oxygen reduction properties in fuel cells at a reduced cost compared to platinum-based techniques. However, usually the support material contains a high level of unwanted impurity metals originating from the synthesis. A more desirable approach, which we have examined in our studies, is to synthesize carbon nanotubes with the same metal catalyst as later used for functionalization and/or decoration. We present results showing that Pd in various appearances has the ability to synthesize a broad range of different carbon nanotube materials. Depending on the synthesis conditions we can synthesize helical, Y-shaped, regular straight CNTs or combinations of the mentioned out of the same catalyst material. Temperature plays a key role and can be used to tune the properties of the desired product. We discuss about the growth mechanism and the relation between catalyst structure and the structural properties of the grown nanotube structures. For our material characterization we use transmission and scanning electron microscopy as well as Raman spectroscopy.
9:00 PM - C3.14
Nanoscale Lithograpy: Local Oxidation on Graphene.
Ik-Su Byun 1 , Jin-Sik Choi 1 , Duk-hyun Lee 1 , Mi-Jung Lee 1 , Seung-Woong Lee 1 , Bae-Ho Park 1
1 Division of Quantum Phases & Devices, Department of Physics, Konkuk University, Seoul Korea (the Republic of)
Show AbstractSingle layer graphene, with two linear bands crossing at the Dirac point, is a zero-gap material [1]. Therefore, much effort has been devoted to creating an energy gap in graphene-based materials for device applications. Among its applications, Graphene nanoribbon (GNR) is one of the most effective methods to open the gap by confining the carriers into a quasi-one-dimensional system. In this work, we have fabricated and investigated a nano size oxidized graphene lines for the purpose of manipulating structure of graphene. The nano-oxidation process was carried out using local anodic oxidation (LAO) method by atomic force microscopy (AFM) [2-3]. A monolayer exfoliated graphene on SiO2 (300 nm)/Si substrate were used for nano-oxidation. Single-layer graphene are identified by their color contrast under an optical microscope and then Raman spectroscopy is used to confirm that sample is single-layer graphene. A Pt-coated conductive AFM cantilever was used. The graphene surface was oxidized by anodization using AFM cantilever as a cathode through the water that adhered to the surface of graphene from the atmosphere, and the oxidized graphene line of nanometer size was formed. We successfully controlled the width of oxidized graphene line from 30 to 90 nm by changing a bias voltage (5 ~10V) and a scan speed (0.1~ 10um/s). Furthermore we have successfully fabricated sub-10 nm wide GNR with two oxidized graphene barrier lines using LAO nano fabrication method. We also confirmed that two separated graphene area by thick oxidized graphene barrier was electrically blocked. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (MEST) (KRF-2008-314-C00111). [1] K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Gregorieva, and A.A. Firsov, Science, 306, 666 (2004). [2] L. Weng, L. Zhang, Y.P. Chen, and L.P. Rokhinson, Appl. Phys. Lett. 93, 093107 (2008). [3] S. Masubuchi, M. Ono, K. Yoshida, K. Hirakawa, and T. Machida, Appl. Phys. Lett. 94, 082107 (2009).
9:00 PM - C3.15
Rehybridization of Few-layer Graphene as a Route to Novel Materials: Theoretical Aspects.
Ana Barboza 1 , Marcos Guimaraes 1 , Leonardo Campos 1 , Rodrigo Lacerda 1 , Helio Chacham 1 , Mario Mazzoni 1 , Bernardo Neves 1
1 Department of Physics, Universidade Federal de Minas Gerais, Belo Horizonte - MG, Minas Gerais, Brazil
Show Abstract We predict, by means of first-principles calculations, that few layer graphene may undergo a rehybridization process under pressure, generating a 2D ferromagnetic insulator material. Our model is based on the application of pressure by an Atomic Force Microscopy tip (for instance) in the presence of a water layer on top of the graphene material. In these conditions, we show that hydroxyl groups may stabilize the sp3 hybridization of the two topmost carbon layers, creating a single layer of hydroxylated hexagonal diamond, or diamondol, We alsopresent experimental results based on Electric Force Microscopy (EFM) measurements which give support this idea.The calculations made use of the Pseudopotential Density Functional Theory (DFT) as implemented in the SIESTA code.
9:00 PM - C3.17
A Compositional Island of Colloidal Nanorod Kinetic Stability Using Amphiphilic Polymers.
Esther S. Jeng 1 , Chih-Jen Shih 1 , Paul W. Barone 1 , Michael S. Strano 1
1 , MIT, Cambridge, Massachusetts, United States
Show AbstractAmphiphilic polymers are often used to disperse nanoparticles in aqueous solution. Polymer adsorption theory predicts that there exists a narrow compositional range of hydrophobic groups on the polymer chain that allows for kinetic stabilization. Too few groups limit polymer adsorption, while too many allow aggregation of polymer coated nanoparticles for lack of entropic repulsion. We experimentally validate the existence of this compositional range using a high throughput screening method, and the resulting stability 'island' is demonstrated using phenoxy-dextran polymer to disperse single walled carbon nanotubes. Although much work has been devoted to the design of polymers for suspending SWNT, this work is the first attempt to model the ability of a polymer to suspend SWNT, based on the chemical structure of the polymer. We develop a theory to connect polymer interaction, adsorption, and structure to the colloidal stability of the polymer coated SWNT. The results should provide a theoretical basis for the design of nanoparticle dispersants.
9:00 PM - C3.18
Ni-catalyzed Carbon Nanotubes Synthesis by Diffusion of Amorphous Carbon.
Willie Matthews 1 , Roland Barbosa 1 , Edwina Clarke 1 , W. Collins 1 , Weijie Lu 1
1 Department of Chemistry and Center for Physics and Chemistry of Materials, Fisk University, Nashville, Tennessee, United States
Show AbstractChemical vapor deposition (CVD) is a common method to produce carbon nanotubes (CNTs) and graphene. The carbon source is from the gas phase in CVD technique. In this study, we are presenting a novel method to produce CNTs structures by diffusion controlled metal catalytic graphitization. A thin layer of carbon is placed on oxidized Si wafer, and a metal catalyst then is deposited on top of the carbon then annealed at high temperatures and low pressures. Depending on the conditions, carbon structures are diffused through the Ni layer and CNTs are formed on the surface. When the multi-layered Ni/C/SiO2/Si samples are annealed at 600° C under 10e-8 Torr and aligned CNTs are produced. X-ray photoelectron spectroscopy (XPS) analysis has shown a significant increase in the sp2 carbon component. Raman analysis showed prominent CNT peaks corresponding to G, D and 2D bands with ID/IG equal to 0.53. A peak at 194 cm-1 is also present indicating the formation of single-walled nanotubes. The effect of oxygen on the sample was also investigated by annealing under different O2 partial pressures (10e-9, 10e-7 and 10e-5 mbar). AFM images displayed similar morphologies but with larger diameter tubes and formation of agglomerates with higher oxygen pressure. Raman spectra showed upward shift of G peak as a function of increasing O2 concentration in the chamber suggesting bond expansion and other structural changes which will be examined further with XPS.
9:00 PM - C3.19
Fabrication of Hexagonal Pattern Arrays of Metal Nanodots via Direct Metal Contacting Process with Carbon Nanopost Arrays.
Sang Ho Lee 1 , Hyung-Gu Jeong 1 , Byungjin Cho 1 , Seung Ha Yoon 1 , Heesoo Jung 1 , Gun-Young Jung 1 , Beong Ki Cho 1 , Takhee Lee 1 , Dong-Yu Kim 1 , Won Bae Kim 1
1 , Gwangju Institute of Science & Technology (GIST), Gwangju Korea (the Republic of)
Show AbstractUniformly aligned metal nanoparticles have attracted much attention for diverse applications in nanotechnology including optical devices, magnetic data storage, biological sensors, and catalysts for one-dimensional nanostructure growths [1-4]. The ability to prepare uniformly ordered and highly patterned metal nanodot arrays is essential for practical implementation. In this research, we report a novel stamping platform for an efficient nanoprinting process. Vertically-aligned and hexagonally-patterned carbon nanopost arrays, supported by the straight nano-channels of anodic aluminum oxide templates, are used as a stamp for transferring metal nanodot patterns. The carbon nanopost stamps are fabricated by a simple chemical self-assembly process, and the size, density, and interval of the individual nanopost can be precisely defined by adjusting the pore dimension of the alumina nanochannels [5]. Using these nano-stamps, hexagonally-oriented metal nanodot patterns such as gold, copper, nickel, silver, platinum, titanium and aluminum are successfully printeded in the laboratory environments at room temperature. The transferred metal nanoparticle arrays are replicated to the mother stamp geometries, where the size, density and inter-dot distance of the transferred metal nanoparticles are readily engineered via nanoprinting, implying that these carbon-based nanopost stamps could be an excellent platform for transferring metal nanodot array to substrates.References[1]S. -S. Kim, S. -I. Na, J. Jo, D. -Y. Kim, Y. -C. Nah, Appl.Phys.Lett. 93, 073307 (2008).[2]S. Sun, C. B. Murray, D. Weller, L. Folks, A. Moser, Science 287, 1989 (2000).[3]W. Fritzsche, T. A. Taton, Nanotechnology 14, R63 (2003).[4]A. I. Hochbaum, R. F. R. He, P. Yang, Nano Lett. 5, 457 (2005).[5]S. H. Lee, G. Jo, W. Park, S. Lee, Y. -S. Lee, B. K. Cho, T. Lee, W. B. Kim, ACS NANO 4, 1829 (2010).
9:00 PM - C3.2
Chirality Sorting of Single-walled Carbon Nanotubes Using Their Redox Potentials.
Yuichi Kato 1 , Yasuro Niidome 1 , Naotoshi Nakashima 1 2
1 Applied Chemistry, Kyushu Univ., Fukuoka Japan, 2 , Japan Science and Technology Agency CREST, Fukuoka, Tokyo, Japan
Show Abstract Due to the difficulty in the synthesis of Single-Walled Carbon Nanotubes (SWNTs) with a specific chirality, SWNT chirality sorting has been an anticipated technique for realizing practical applications of SWNTs especially in the field of nanoelectronic devices. Density-gradient ultracentrifugation (DGU) is a powerful technique to sort SWNTs having a different diameter, while fine sorting of SWNTs, whose diameters are close, is still difficult. In this work, we present a novel strategy for chirality sorting of SWNTs; that is, a method using “nanometal sinkers” that adsorb on specific SWNTs, resulting in the separation of nanometal sinker-adsorbed SWNTs and the other SWNTs by DGU. HiPco-SWNTs were dispersed in a sodium cholate aqueous solution. The HAuCl4 was then added to the solution, and then the DGU procedure using indixanol was carried out. We have succeeded in the separation of the (6,5)-SWNTs from the other SWNTs including (8,3)-SWNTs whose diameter was very close to that of (6,5)-SWNTs. This result suggests that the AuCl4- reacted (8,3)-SWNTs and formed Au(0) on the surfaces of the (8,3)-SWNTs, which acted as the “sinker”. It is proved that our method is useful for the separation of the SWNTs whose diameters are very close and therefore their separation is unable using conventional DGU.
9:00 PM - C3.20
Nuclear Quantum Effect on Hydrogen Adsorption Site for Zeolite Templated Carbon (ZTC) Using Path Integral Molecular Dynamics.
Kimichi Suzuki 1 , Megumi Kayanuma 1 , Masanori Tachikawa 2 , Hiroshi Ogawa 1 , Hirotomo Nishihara 3 , Takashi Kyotani 3 , Umpei Nagashima 1
1 , National Institute of Advanced Industrial Science and Technology, Tsukuba Japan, 2 , Quantum Chemistry Division, Graduate School of Science, Yokohama City University, Yokohama Japan, 3 , Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan
Show Abstract Carbon materials of large surface area, such as activated carbons, graphene sheets, carbon nanotubes, and zeolite templated carbon (ZTC), have attracted attention as hydrogen storage materials by physisorption. Among them, ZTC using Zeolite Y as a template has some structural features. It has a larger surface area than other materials, uniform micropores, and its hydrogen storage up to 2.2 wt% at 34 MPa at 303 K [1]. This hydrogen storage amount has been highest among any pure carbon materials. However, it has to increase the hydrogen storage capacity for practical use. To improve hydrogen storage capacity, it is indispensable to understand for the hydrogen diffusion process and its adsorption site on carbon. In this study, we have performed path integral molecular dynamics (PIMD) simulation at 300 K to accurately evaluate the hydrogen adsorption site on ZTC. In this simulation method, nuclei are treated as quantum mechanical particles, and can take account of quantum and thermal fluctuations with respect to molecular vibrational and rotational degree of freedom. The minimum unit (C36H12) of ZTC which has a buckybowl structure including three pentagonal carbons was employed as a model structure [2]. Five carbons inside of buckybowl were selected from innermost to edge as the adsorption site for additional hydrogen atom. All PIMD simulations were done with the imaginary time slices P=24 using PM3 potential. The conventional MD simulation was also performed with P=1 condition. It is found that hydrogen in conventional MD simulation has adsorbed on each carbon. On the other hand, stable hydrogen adsorption site in PIMD simulation has been only four, except for innermost carbon. Stable adsorption site is not appeared on innermost carbon, since additional hydrogen atom in PIMD simulation is easy to go over the potential barrier between innermost and other carbons by thermal effect and zero point vibration of the CH stretching mode. This work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under “Advanced Fundamental Research Project on Hydrogen Storage Materials”.[1] H. Nishihara, et al., J. Phys. Chem. A, 113, 3189 (2009). [2] H. Nishihara, et al., Carbon, 47, 1220 (2009).
9:00 PM - C3.21
Growth Control of Carbon Nanopearls by Variation of the Ni Catalyst Size.
Shanee Pacley 1 , Merlin Theodore 2 , Thomas Ekiert 2
1 , Air Force Research Laboratory/Wright Patterson Air Force Base, Wright Patterson, Ohio, United States, 2 , Universal Technology Corporation, Dayton, Ohio, United States
Show AbstractCarbon nanopearls (CNP) were grown using a chemical vapor deposition (CVD) furnace, acetylene carbon source, and a Ni catalyst at 850°C. We previously reported the growth of CNP on a Si substrate, with a diameter of 500-700nm, using a 150nm Ø Ni catalyst. Our experiments have shown that by varying the size of the Ni catalyst, the diameter of the carbon nanopearls can be controlled. Controlling the size of the CNP makes them ideal for electronic applications. The size of the Ni catalysts used were: 10nm, 20nm, and 150nm. Scanning electron microscopy (SEM) revealed that the size of the carbon nanopearls was dependent on the diameter of the Ni catalyst. Raman spectra showed a change in the G band intensity as the carbon nanopearl size varied. The magnetic properties, as a result of the catalyst variation, was investigated using a superconductor quantum interface device (SQUID).
9:00 PM - C3.22
Carbon Nanoscroll Formation Initiated by Carbon Nanotube.
Zhao Zhang 1 , Teng Li 1 2
1 Department of Mechanical Engineering, University of Maryland, College Park, Maryland, United States, 2 Maryland NanoCenter, University of Maryland, College Park, Maryland, United States
Show AbstractA carbon nanoscroll (CNS) is formed by rolling up a graphene sheet into a spiral multilayer structure. The unique topology and exceptional properties of carbon nanoscrolls (CNSs) have inspired novel nano-device concepts, such as hydrogen storage medium, water and ion channels, nano-oscillators, and nano-actuators. However, the fabrication of CNSs remains rather challenging. Using molecular dynamics simulations, we demonstrate the spontaneous formation of a CNS from graphene on a substrate, initiated by a carbon nanotube (CNT). The rolling of graphene into a CNS is modulated by the CNT size, the carbon-carbon interlayer adhesion, and the graphene-substrate interaction. A phase diagram emerging from the simulations can offer quantitative guideline toward a feasible and robust physical approach to fabricating CNSs.
9:00 PM - C3.23
Carbon Nanotube Growth on Annealed Copper Iron (Cu 97.5 – Fe 2.5 wt%) Substrates without Additional Catalysts or Processing.
Jack Burke 1 3 , Chakrapani Varanasi 2 , Betty Quinton 3 , Lyle Brunke 1 3 , Jared Petry 4 3 , Yongli Xu 5 3 , Paul Barnes 3
1 , University of Dayton Research Institute, Dayton, Ohio, United States, 3 , U.S. Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 2 , U.S. Army Research Office, Durham, North Carolina, United States, 4 , 46th Operations Group, Wright-Patterson AFB, Ohio, United States, 5 , UES, Inc., Dayton, Ohio, United States
Show AbstractAs-rolled copper iron substrates (Cu 97.5 – Fe 2.5 wt%) were annealed in-situ under varying conditions to yield different surface morphologies. No catalysts were deposited and no extra processing steps were used beyond heat treatment. Samples were analyzed using scanning electron microscopy (SEM), and under certain processing conditions, large (~1 μm) precipitates were shown to form across the surface along with smaller (~20 nm) particles. Energy dispersive x-ray spectroscopy (EDS) shows these large particles to be composed mostly of iron. Initial studies show growth of carbon nanotubes (CNTs) on copper iron substrates using thermal chemical vapor deposition (CVD) at 750 °C with acetylene. This is significant since the small amount of iron alloyed into the Cu serves as the catalyst for growth, thus minimizing the Cu-CNT interface. SEM of copper iron samples indicate a high density of CNTs grown directly on the substrate, with most ranging in diameter from 20 nm to 200 nm. Raman spectroscopy was conducted, and peaks corresponding to the D and G band (~1320 cm-1 and ~1580 cm-1) were observed, with initial samples showing a D to G ratio of 1.89. Transmission electron microscopy (TEM) of the interface will be provided and all microstructural details will be presented.
9:00 PM - C3.25
Probabilistic Model for Growth Mechanism of Single and Few Layer Graphene, Grown Using CVD on Metal Substrates.
Abhishek Rishabh 1
1 , IIT Kanpur, Kanpur India
Show AbstractLarge area single and few layer has been recently grown on metal substrates which has again boosted up the Graphene community. Growth mechanism of graphene on Cu and Ni substrates was first explained by Li et al by using isotope labelling. In this method underlying concept was of separation of 12C and 13 C Raman modes to observe the spatial distribution of graphene domain. Here we present a model to explain the growth mechanism of single layer and few layer graphene which is finally related to Langmuir and BET isotherms, which would lead to a mathematical understanding of the growth mechanism.
9:00 PM - C3.26
Fabrication of Graphene-alumina Ceramic Composites.
Lianjun Wang 1 , Yuchi Fan 1 , Wan Jiang 1
1 College of Material Science & Engineering, Donghua University, Shanghai China
Show AbstractGraphene is the thinnest known material in the universe and the strongest ever measured. Its charge carriers exhibit giant intrinsic mobility, have zero effective mass, and can travel for micrometers without scattering at room temperature. Graphene can sustain current densities six orders of magnitude higher than that of copper, shows record thermal conductivity and stiffness, is impermeable to gases, and reconciles such conflicting qualities as brittleness and ductility. Hence there is a great prospect to apply these excellent properties of graphene as reinforcement in composites and lighten the weight of materials. Because graphene has so many wonderful physical properties and is easy to disperse in matrix compared with carbon nanotubes, the main focus of this research is to prepare graphene and incorporate it in a ceramic matrix. In this paper, we adapted a new method to prepare graphene/alumina composites using mechanical exfoliation. Fully dense graphene nanosheet/alumina composites have been fabricated from ball milled expanded graphite and alumina by SPS. The graphene nanosheets after ball milling are 2.5–20 nm in thickness and homogeneously dispersed in the ceramic matrix. The percolation threshold of the as-prepared graphene nanosheet/alumina composites is around 3 vol.%. The conductivity achieves 5709S/m when composite has 15 vol.% graphene nanosheets, which was 170% higher compared to the best result previously reported in carbon nanotube/alumina composites. The as-prepared composites behaved as semimetal as indicated by the temperature dependence of electrical conductivity in a temperature range from 2 to 300 K. The present work paves a new way to fabricate graphene nanosheet/ceramic composites with much improved electrical properties.
9:00 PM - C3.27
Modeling Liquid-phase Graphene Exfoliation.
Olga Pupysheva 1 , Cory Knick 1 , Amir Farajian 1
1 Mechanical and Materials Engineering, Wright State University, Dayton, Ohio, United States
Show AbstractUltrasonication of graphite nanoparticles dispersed in water in the presence of a surfactant is a promising way to produce pristine graphene nanoplatelets. Possible mechanisms of graphene exfoliation, specifically those involving sodium dodecylbenzenesulfonate surfactant, are studied. A combined Lennard-Jones/molecular-mechanics model is used, that includes the effects of charged surfactant and solvent. The energetics of exfoliation and exposure to the surfactant are compared. Our calculations reveal the significant role of the surfactant in liquid-phase graphene production.This work is supported by the National Science Foundation through NSF STTR Phase I grant No. 0930342.
9:00 PM - C3.28
Experimental Study of Molecule-pore Wall Collisions in Carbonized Ultrathin Porous Membranes.
Maryna Kavalenka 1 , Christopher Striemer 2 , David Fang 1 , Thomas Gaborski 2 , James McGrath 3 , Philippe Fauchet 1
1 Department of Electrical and Computer Engineering, University of Rochester, Rochester, New York, United States, 2 , SiMPore Inc., West Henrietta, New York, United States, 3 Department of Biomedical Engineering, University of Rochester, Rochester, New York, United States
Show AbstractExperiments and MD simulations of fluid transport through carbon nanotubes reported flow enhancement over other porous materials and existing theories [1-2]. This enhancement was explained by the difference in the nature of molecule collisions with the crystalline carbon wall compared to other wall materials. It was proposed that collisions with carbon nanotube walls scatter in the forward direction and not randomly as in other materials. We have tested this hypothesis by measuring the flow of various gases through short (~15nm) nanopores whose walls are made of either silicon or crystalline carbon. We used high temperature carbonization to create highly ordered graphene layers [3] inside the pores of an ultrathin template membrane. The template material is an ultrathin porous nanocrystalline silicon (pnc-Si) membrane with pore sizes from 5 to 50 nm and a thickness of 15 nm [4]. The wide distribution of available pore sizes allows us to directly compare flow through carbonized and non-carbonized pores of the same diameters and aspect ratios, and thus to study the influence of the nature of the molecule-pore wall collisions on the flow. The molecularly thin nature of the membranes allows us to separate for the first time the two constituent components of molecular flow: molecules that undergo no collisions (ballistic transport) and molecules that collide with the wall. Our results confirm that Knudsen theory for gas flow through nanopores is correct down to nanometer lengths and diameters, and that molecular collisions with crystalline carbon walls are predominant in the forward direction.This work was supported by the NIH, NYSTAR and SiMPore Inc.1. S. Kim et al., Nano Lett., 7, 2806, 2008; B. Hinds et al., Science, 303, 62, 2004; J. Holt et al., 312, 1034, 20062. S. Bhatia et al., Molecular Simulation, 9, 643, 2005; A. Skoulidas et al., PRL 89, 185901, 2002; V. Sokhan et al., J. Chem. Phys., 117, 8531, 20023. D. Fang, C. Striemer, T. Gaborski, J. McGrath, P. Fauchet, “Pore size control of ultra-thin silicon membranes by rapid thermal carbonization," (2010), Nano Lett. (submitted)4. C. Striemer, T. Gaborski, J. McGrath, and P. Fauchet, Nature, 445, 749, 2007
9:00 PM - C3.29
Dynamic Superlubricity of Graphene Flake on Graphite Surface.
Irina Lebedeva 1 2 3 , Andrey Knizhnik 2 3 , Andrey Popov 4 , Olga Ershova 1 , Yurii Lozovik 1 4 , Boris Potapkin 2 3
1 , Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region, Russian Federation, 2 , Kintech Lab Ltd, Moscow Russian Federation, 3 , RRC Kurchatov Institute, Moscow Russian Federation, 4 , Institute of Spectroscopy, Troisk, Moscow Region, Russian Federation
Show AbstractDifferent mechanisms of diffusion and drift of a graphene flake on a graphite surface are systematically analyzed using ab initio calculations and calculations with empirical potentials. On the basis of this study, a new mechanism of diffusion, “dynamic superlubricity”, is proposed. According to the proposed mechanism, rotational transition of the flake to incommensurate states takes place with subsequent simultaneous rotation and translational motion until the commensurate state is reached again, and so on. Due to the significant barrier for rotation of the flake, these events are rare. However, this factor is compensated by long distances passed by the flake before it returns to the commensurate state.The molecular dynamics simulations demonstrate that the proposed diffusion mechanism can be dominant under certain conditions. According to analytic expressions derived for the diffusion coefficient and mobility of the flake, the relative contribution of rotation to incommensurate states should be the most significant at temperature associated with the barrier for transition of the flake between adjacent energy minima in the commensurate state and should correspond to an increase of the diffusion coefficient by more than an order of magnitude. The results obtained can be also useful for study of dynamics of polyaromatic molecules on a graphite surface and should be qualitatively valid for a set of commensurate adsorbate-adsorbent systems.The methods of control over the diffusion and drift of graphene components in nanoelectromechanical systems are discussed. Moreover, the possibility to experimentally measure the barriers to relative motion of graphene layers is considered.
9:00 PM - C3.3
Rippling Instability in Carbon Nanotube Forest Growth and the Resulting Diffraction of Visible Light.
Phillip Vinten 2 1 , Jeffery Bond 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 AbstractAt low magnification, nanotubes in vertically aligned carbon nanotube forests appear straight and well aligned; however, on the micrometer scale, nanotubes wander significantly in a seemingly random manner. Under certain conditions, the wandering can become highly ordered, coherent, and synchronized over forest-sized length scales as a result of a periodic growth instability (rippling). The coordinated nature of this rippling pattern reveals the importance of nanotube-nanotube interactions within forests. These interactions play a role in the growth and termination of forests. We grow forests on silicon:silicon dioxide samples patterned with thin film alumina:cobalt catalyst islands in a cold-walled chemical vapor deposition reactor that is operated at atmospheric pressure using acetylene as the carbon source and water vapor as a growth enhancer. We identify the reactor conditions that promote the reproducible formation of ripples, and, based on our observations, we propose a formation mechanism. The ripples are regular enough and synchronized over a sufficient area of the forest that they create a remarkable and easily observable optical effect: the diffraction of visible light via a surface grating effect. This effect provides a method of optical observation of these structures that are too small for direct optical imaging and can be observed in situ to reveal important information about the ripple formation mechanism.
9:00 PM - C3.30
Shrinkage Induced Self-localized Electronic States in Trans-polyacetylene.
Andre Botelho 2 1 , Minghai Li 2 1 , Xi Lin 2 1
2 Mechanical Engineering, Boston University, Boston, Massachusetts, United States, 1 Division of Materials Science and Engineering, Boston University, Brookline, Massachusetts, United States
Show AbstractThe self-localized electronic states beyond the solitonic state are demonstrated to arise from the soliton induced shrinkage in the one dimensional Su-Schrieffer-Heeger (SSH) model of trans-polyacetylene. The numerical solution to the SSH model using the Hartree-Fock (HF) approximation for the spring constant K=21 eV/A^2 clearly show both shrinkage around the soliton region and extra localized states at the bottom of the valence band and top of the conduction band. These localized states are also found in HF ab-initio calculations. The shrinkage increases the effective hopping integral causing a broadening of the band width that brings the aforementioned states into the complex band region where the states become localized. In contrast, removing the shrinkage by constraining the order parameter to the hyperbolic tangent function eliminates the extra localized states.
9:00 PM - C3.31
Kinetics of Oxygen Removal in Reduced Graphite Oxide Using Infrared Spectroscopy.
Muge Acik 1 , Rodolfo Guzman 1 , Cheng Gong 1 , Kyeongjae Cho 1 , Yves Chabal 1
1 Materials Science and Engineering, The University of Texas at Dallas, Dallas, Texas, United States
Show AbstractA potential method to produce defect-free graphene sheets or ribbons from graphite is to change the interlayer distance by intercalation using a combination of chemical treatment and heat. The intercalated species not only affect the chemical reactivity of the materials but also alters their band gap. For this reason, it is important to understand the interlayer chemistry of graphite and its derivatives such as graphite oxide (GO). In the case of GO, the insertion of oxygen functionalities such as epoxides and hydroxyls on the basal plane opens up the interlayer spacing and plays a crucial role through intercalation to tailor the electrical, optical and mechanical properties. Chemical or electrochemical functionalization of these interlayer groups also triggers the variations in film properties for applications such as layer by layer assembly in batteries and molecular recognition for sensor applications. In addition, its synthesis in aqueous media creates lots of water molecules trapped in between the intersheets where the oxygen functionalities stay in contact within the hydrogen bond network of these water molecules. Therefore, the disturbance of this network with various chemical species is possible and requires further mechanistic understanding. We therefore focus on the interlayer chemistry of reduced GO performing in-situ infrared spectroscopy (FTIR) to examine the kinetics of oxygen removal as a function of intercalated species. We perform experiments with different alcohols to explain their role for chemical reactivity in the interlayer spacing of GO, such as methanol, ethanol, 1-propanol, 2-propanol and 1-butanol. The introduction of these organic liquids in the presence of water in the interlayers of GO is studied using XRD analysis as a function of annealing temperature. DFT simulations are used to estimate the activation energies for selected chemical reactions within the graphene plane. Time resolved spectroscopy is used to analyze the time dependence of the structural changes in reduced GO during annealing at 60-200°C. Additionally, we use static contact angle measurements to determine the surface wettability of these alcohol intercalated GO samples compared with that of pure GO (49.5°). The experimental results show that wettability of these GO surfaces decreases and that the interlayer separation increases when they are exposed to alcohols with longer chains such as 1-propanol and 1-butanol in comparison to methanol, ethanol and 2-propanol. In addition, the interlayer chemistry is affected by the nature of the intercalated species (i.e. alcohol vs. water). This information is useful for future use of GO for device fabrication.*The authors acknowledge funding from the SWAN/NRI program and Texas Instruments.
9:00 PM - C3.32
Patterned Gold Nanoparticles Effects on Graphene.
Sung Huh 1 , Jae Sung Park 1 , Byung Hee Hong 2 3 , Kwang Su Kim 1 , Seung Bin Kim 1
1 Chemistry, Pohang University of Science and Technology, Pohang Korea (the Republic of), 2 SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon Korea (the Republic of), 3 Chemistry, Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractA newly developed gold nanoparticles film was patterned on a single layer graphene, which was synthesized by novel thermal chemical vapor deposition (CVD) method. The gold nanoparticles were coated on the graphene surface and patterned in a few micrometer scales by the fast and easy UV irradiation system. We observed the selective enhancement of Raman signals in graphene prepared on SiO2 (300nm)/Si substrate at 514nm and 633nm excitation on the patterned area. Furthermore, the graphene can be p-type doped via coated gold nanoparticles, which was result in remarkable doping on the patterned area compared to the nonpatterned area. The combined effects of the gold nanoparticles on the graphene provide modification of optical and electric properties of graphene due to the modification of electronic structure on graphene for electrical application. We suggest that this new hybrid nanomaterial combined of graphene and gold nanoparticles can be applied to manufacture graphene based nanoelectronic devices and circuits, solar cells, diode, and optical sensor.
9:00 PM - C3.33
Single-crystalline C60 Hollow Nanostructures by Sonophysical Preparation.
Louzhen Fan 1
1 Department of Chemistry, Beijing Normal University, Beijing China
Show Abstract Fullerene[60] (C60) has attracted much attention in materials chemistry owing to its versatile functionalities. The assembly of fullerenes as super-atoms into controlled morphology, size and dimensions allows their physical and chemical properties to be tuned. Low-dimensional C60 nanostructures, such as nanowires or nanorods, demonstrated fantastic performance in optical devices. And the preparation of C60 nanodisks has also been reported recently.8 However, such complex C60 nanostructures as hollow bowls/cups have not been realized experimentally up till now. We ventured to use a mixture of two incompatible organic solvents to produce C60 hollow nanostructures by a sonophysical method: this is so called because there is no chemical reaction involved here. By using this method with simple ultrasonication, we demonstrate, for the first time, that large quantities of single-crystalline C60 hollow nanostructures, particularly nanobowls, can be prepared in a binary organic solution of m-xylene and acetonitrile. Significantly, by judiciously adjusting the concentration of C60/m-xylene solution and the volume ratio of m-xylene to acetonitrile, we readily tuned pure and large-scale C60 nanostructures from nanorods, nanowires into nanoplates, nanorings and nanobowls. To gain an insight into applications of the C60 hollow nanostructures, their unique use as a catalyst support for direct methanol fuel cells (DMFC) was further investigated. The C60 nanobowls, after deposition with Pt nanoparticles, significantly promoted catalytic activity toward methanol oxidation, portending their use in designing fuel cell electrodes.
9:00 PM - C3.35
Desktop Continuous Growth of Vertically Aligned Carbon Nanotubes.
Roberto Guzman de Villoria 1 , Brian Wardle 1
1 Aeronautics and Astronautics, MIT, Cambridge, Massachusetts, United States
Show AbstractVertically aligned carbon nanotubes (VACNTs), sometimes called forests or carpets, are a promising material due to their unique physical and scale-dependent physical properties. Continuous production of VACNTs is required for large-scale applications in electronic devices, fuel cells and structural materials among others. Chemical vapour deposition (CVD) is the only available technique to produce large areas of VACNTs, nevertheless most of the studies done for this technique are done for stationary growth in batch CVD processing. Recently, it has been demonstrated that there is no significant difference between the VACNTs grown at different velocities up to 1.1 mm/s in terms of quality, morphology and length using a CVD process in a custom cold wall reactor [1].In the present work, a desktop continuous growth apparatus has been designed and implemented to grow VACNTs on different substrates continuously. Substrates include planar silicon wafers coated with a Fe/Al2O3 catalyst and three-dimensional ceramic fibres (tow and cloth) substrates dip coated with an iron nitrate solution. The particular CVD process studied in this work is performed at ambient pressure employing a mixture of ethylene (C2H4), hydrogen (H2), without intentionally introducing oxidizing agents. No significant differences are noted between static and moving growth as characterized by SEM and Raman spectroscopy, although overall growth height is marginally reduced at the highest substrate velocity (6.8 cm/min) which is attributed to the overall time of the substrate in the heated zone (1 cm wide). Thus, we have demonstrated and reported for first time the ability to manufacture VACNT arrays in a continuous fashion, reducing significantly time, energy consumed, and reaction products relative to batch processing.[1] R Guzmán de Villoria et al., “High-yield growth of vertically aligned carbon nanotubes on a continuously moving substrate,” Nanotechnology 20, no. 40 (2009): 405611 (8pp).
9:00 PM - C3.37
Spinnable Carbon Nanotube Forests Produced by RF Induction Heating.
William Holmes 2 , Anvar Zakhidov 1
2 , Solarno, Inc, Coppell, Texas, United States, 1 , University of Texas at Dallas, Richardson, Texas, United States
Show AbstractSpinnable carbon nanotube forests provide a novel way to create by simple dry-draw process conductive transparent sheets [1] for various applications, such as photovoltaics, OLEDs [2], and many more. These tubes are typically grown in atmospheric CVD systems on silicon substrate materials. Heating of the substrate is normally achieved by resistive element heating inside quarts tubes of three-zone tube furnaces. The spinability of CVD forests strongly depend on the rate of furnace heating, which effects the catalyst treatment and density/height of the forest itself. We will present an innovative way to heat the substrate with very high and controllable rate, which we developed using inductive RF heating [3]. Such process allows not only to quickly heat the substrate to growth temperatures, but also to control the catalyst nanoclusters proper formation. Various samples on substrates can be heated to growth temperatures over 700C in less than 2 minutes. This quick heating and control over the heat rate aids in catalyst particle formation and minimizes the process of Ostwald Ripening of catalyst which limits the CVD growth. This produces Multiwall carbon nanotube forests with very good spinnability and uniformity. The acetylene, ethylene or other feedstock gas heating via a standard tube furnace is used to heat the incoming gasses mixtures separately from the substrate. This gives fine control over the substrate and gas temperatures independently. Moreover the CVD growth can be visually controlled through RF coils of induction systems. We will describe other advantages of this CVD process, such as ability to grow continuously the CNT forests on arbitrary shaped surfaces for advanced applications. The financial support of Texas Emerging Technology fund under ETF grant is appreciated. [1] M. Zhang, S. Fang, A.A. Zakhidov, S.B. Lee, A.E. Aliev, C. D. Williams, K.R. Atkinson, and R.H. Baughman, Science, 309, 1215 (2005). [2] C.D. Williams, R.O. Robles, M. Zhang, S. Li, R.H. Baughman and A.A. Zakhidov, Appl. Phys. Lett. 93, 1 (2008). [3] W.A. Holmes, US patent application, No. 61333327.1 Solarno Inc, 153 Hollywood Drive, Coppell, Tx 75019, USA.2 NanoTech Institute, University of Texas at Dallas, Richardson, TX 75083–0688, USA.* To whom correspondence should be addressed. E-mail:
[email protected]9:00 PM - C3.4
Synthesis of Single-walled Carbon Nanotubes by a Submarine-style Substrate Heating Method.
Hiroyuki Yokoi 1 , Hiroshi Momota 2 , Chihiro Iwamoto 3
1 Department of Materials Science and Engineering, Kumamoto University, Kumamoto Japan, 2 Faculty of Engineering, Kumamoto University, Kumamoto Japan, 3 Department of Mechanical System Engineering, Kumamoto University, Kumamoto Japan
Show AbstractA new method for the synthesis of carbon nanotubes (CNTs) is reported. Our method is based on the liquid-phase deposition method [1], in which a catalyst-coated silicon substrate is heated electrically to high temperatures around 1000 K in liquid hydrocarbon. The liquid-phase deposition method has realized simple and rapid growth of CNTs. However, this method has not been very successful in producing single-walled CNTs (SWCNTs) as the catalyst coating which is required to be as thin as 1 nm for the synthesis of SWCNTs is peeled off easily during the synthesis in liquid. This aspect has prevented one from applying zeolite-supported catalysts, which are recognized to be excellent catalysts for the synthesis of SWCNTs. We have resolved the demerit by attaching a cover over the catalyst-coated substrate and leaving a vapor area around the substrate under the liquid surface (‘submarine-style substrate heating method’). In the experiments, iron-cobalt composite catalyst supported on ultra-stable Y-type zeolite was employed [2]. Catalyst-dispersed ethanol was dropped on a silicon substrate and dried to form a catalyst coating. The substrate was installed in a cover, and then inserted into ethanol liquid (99.5% in purity) with the inside of the cover being filled with argon gas. The substrate was heated electrically to 1173 K for 10 min. The bottom of the cover was left open in order that ethanol vaporized by radiation heat may be supplied to the catalyst. Products on the substrate were analyzed through scanning electron microscopy, transmission electron microscopy (TEM) and Raman scattering spectroscopy. SWCNTs with the diameters around 1 nm were observed with TEM and corresponding radial breathing modes were also detected. These results suggest that the submarine-style substrate heating method could be one of the simplest methods to synthesize SWCNTs on a macro scale. [1] M. Nishitani-Gamo et al., Jpn. J. Appl. Phys., 46, 6329 (2007).[2] K. Mukhopadhyay et al., Chem. Phys. Lett., 303, 117 (1999).
9:00 PM - C3.40
Temperature Dependence of Epitaxial Graphene Formation on C-face SiC.
Shin Mou 1 , J. Boeckl 1 , J. Park 1 , K. Eyink 1 , D. Tomich 1 , L. Grazulis 2 , H. Smith 2 , L. Hoelscher 3 , Weijie Lu 4 , W. Mitchel 1
1 AFRL/RXPS, Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 2 , University of Dayton Research Institute, Dayton, Ohio, United States, 3 , Wright State University, Dayton, Ohio, United States, 4 , Fisk University, Nashville, Tennessee, United States
Show AbstractThe formation of epitaxial graphene on SiC (000-1) surface (C-face) is studied using Hall measurement, atomic force microscopy (AFM), Raman spectroscopy, ellipsometry, and X-ray photoemission spectroscopy (XPS). Epitaxial graphene films are grown on 10x10 mm2 samples diced from polished (000-1) semi-insulating SiC wafers without hydrogen etching. Argon atmospheric pressure sublimation process is used over a range of growth temperatures and times. At about 1500°C, graphene starts to form with only part of the SiC C-face surface covered by graphene. At higher temperatures around 1600°C, the coverage is better but still incomplete where the Hall mobility is low with values smaller than 100 cm2/Vs. When the growth temperature is raised up to 1700°C, the SiC C-face appears to be covered by graphene completely with wrinkles on the surface. The maximal Hall mobility is higher than 800 cm2/Vs. Compared to the graphene formation on SiC (0001) surface (Si-face) where the nucleation mostly starts from terrace step edges, the growth mechanism seems to be different on the C-face where the nucleation sites spread more randomly across the surface from the observation of AFM morphology at different temperatures.
9:00 PM - C3.5
Experimental Determination of Electronic Potentials of Individual (n,m)Single-walled Carbon Nanotubes.
Yasuhiko Hirana 1 , Yasuhiko Tanaka 1 , Yasuro Niidome 1 , Naotoshi Nakashima 1 2
1 Department of Applied Chemistry, Kyushu University, Fukuoka Japan, 2 CREST, Japan Science and Technology Agency, Tokyo Japan
Show AbstractEver since the discovery of carbon nanotubes (CNTs), many groups have endeavored to understand the fundamental properties of the CNTs. The redox properties (i.e. electronic densities, the Fermi levels, redox potentials) of single-walled carbon nanotubes (SWNTs) are related to the structures of SWNTs that have a specified diameter and chirality angle uniquely related to a pair of integers (n,m); the so-called chiral indices. For many practical applications of CNTs, redox behavior of CNTs plays a central role. We now describe a simple method for the determination of the electronic potentials of many individual (n,m)SWNTs using near-IR PL spectroelectrochemistry.
9:00 PM - C3.7
Enhanced Anisotropic Growth of Graphene on Vicinal SiC Surfaces - Formation of Graphene Nanoribbons.
Kouhei Morita 1 , Satoru Tanaka 1 , Naoya Uehara 1 , Kan Nakatsuji 2 , Tsuguo Yoshimura 2 , Fumio Komori 2
1 Applied Quantum Physics, Kyushu Univ., Fukuoka Japan, 2 ISSP, Univ. of Tokyo, Chiba Japan
Show AbstractWe have studied epitaxial graphene on vicinal SiC surfaces. After H2-gas etching the vicinal SiC surfaces exhibited self-ordered nanofacet structures consisting of pairs of a (0001) plane and a (11-2n) nanofacet with a characteristic distance of 10/20 nm [1, 2]. Such unique vicinal SiC surfaces would play a significant role in obtaining self-ordered graphene nanostructures (e.g. nanoribbons). The vicinal 4H or 6H-SiC (Si-face) substrates afterH2-gas etching were loaded into an UV chamber and were heated by direct current to the temperatures at 1700C for various times. The samples were then investigated ex-situ by AFM, micro-Raman, and ARPES. We have found the growth in this system indicates anisotropic layer-by-layer mode [3]. As a function of growth time we could achieve fractional layer thickness, which is, in another words, periodically (1D) fluctuate layer thickness in nano-scale. After forming a 1-ML-thick graphene nucleation for the second layer takes place along nanofacets and preferentially grows in one-direction with strong anisotropic growth mode, resulting in graphene nanoribbons underneath a graphene layer. AFM-phase images indicate such features with typically 10-20nm widths of such nanoribbons. Micro-Raman analyses show clear D-band features, possibly originated by the edges at nanoribbons. We also discuss electronic states observed by ARPES on these nanoribbons.[1] H. Nakagawa et al., Phys. Rev. Lett. 91, 226107(2003). [2] M. Fujii and S. Tanaka, Phys. Rev. Lett. 99, 016102(2007). [3] S. Tanaka et al., Phys. Rev. B 81, 041406(R)(2010).
9:00 PM - C3.9
Effect of the Supporting Substrate on Graphene Etching Using Fe Nanoparticles.
Takahiro Tsukamoto 1 , Toshio Ogino 1
1 , Yokohama National University, Yokohama Japan
Show Abstract Graphene is one of the most notable materials in the recent progress of nanomaterial science and technology owing to its remarkable properties, such as extremely high mobility of charged carriers. Toward its device applications, control of the size, morphology, edge states, and shape is required because the electronic properties of graphene depend on those parameters. One of the methods for control of graphene shapes is crystallographic etching using metal nanoparticles. Carbon atoms of graphene sheets are removed through a reaction between graphene and hydrogen catalyzed by the metal nanoparticles during annealing in a hydrogen atmosphere. In this process, graphene is etched along particular directions of the graphene lattice. In this paper, we propose a new etching technique that is controlled by atomic structures on the substrate surface. Single-stepped sapphire (1-102) substrates were chemically cleaned using a H2SO4 and H2O2 mixed solution (H2SO4:H2O2=3:1). Graphene films were deposited on the sapphire surface by mechanical exfoliation of graphite. To form Fe nanoparticles on the sapphire surfaces with graphene films, a solution of Fe(NO3)3*9H2O in isopropyl alcohol was uniformly spin-coated. The samples were then annealed at 1173 K in a hydrogen (320 sccm) and argon (600 sccm) mixed gas in a furnace for 10 min. The surface morphology was observed by AFM. Graphene sheets tightly adhere to the sapphire surface with regularly ordered terrace/step structure, and the buried step arrangement on the sapphire surface clearly appears on the graphene surface [1]. Deformation on the few layer graphene (FLG), which is introduced from the substrate surface, influences the direction of the etching using Fe nanoparticles [2]. A single layer graphene, on the other hand, was selectively etched in the direction perpendicular to the sapphire steps. We found that comb-patterns form on the present sapphire (1-102) surface after the annealing. The observed controlled etching is attributed to the direct interaction between the metal nanoparticle and the supporting substrate. When a sapphire (0001) surface is used for the supporting substrate, ordered structure such as the comb-pattern does not form, and the graphene etching is performed in random directions. These results indicate that surface structures of the supporting substrate are essential to control the movement of metal nanoparticles and that various shape of graphene can be obtained by designing atomic structures on the supporting substrate surface. [1] T. Tsukamoto and T. Ogino, Appl. Phys. Express 2 (2009) 075502. [2] T. Tsukamoto and T. Ogino, J. Phys. D (2010) in press.
Symposium Organizers
John J. Boeckl Air Force Research Laboratory
Liming Dai Case Western Reserve University
Weijie Lu Fisk University
Mark H. Ruemmeli Leibniz Institute
IFW Dresden
Jamie Warner University of Oxford
C4: CNTs Growth, Exploring Novel CNT Growth Techniques and Growth Mechanisms I
Session Chairs
Tuesday AM, November 30, 2010
Room 304 (Hynes)
9:00 AM - **C4.1
Synthesis and Characterization of Hybrid Graphene Layers.
Pulickel Ajayan 1
1 Mechanical Engineering and Materials Science, Rice University, Houston, Texas, United States
Show AbstractGraphene has several outstanding properties based on its electronic structure but the ability to tailor its bandgap is crucial for many applications. In addition to graphene there are other layered structures such as hexagonal BN which can be synthesized as single layers. This in turn allows the co-deposition of such layered materials which could lead to layered phases containing all the three components of carbon, boron and nitrogen. The way these elements are distributed in the atomic layers of CBN depends of synthesis parameters and there could be a large number of layered phases that could be produced from different compositions of these components. Here we will describe the synthesis and characterization of phases that contains hybridized layers of C, B and N and their properties. These 2D layered materials provide a number of new phases that could be important in preparing band gap engineered structures for applications.
9:30 AM - **C4.2
Metal-catalyst-free Growth and Mechanism of Single-walled Carbon Nanotubes from SiOx Nanoparticles.
Hui-Ming Cheng 1 , Bilu Liu 1 , Wencai Ren 1
1 , Institute of Metal Research, CAS, Shenyang China
Show AbstractCatalyst is very important for the growth of carbon nanotubes (CNTs), especially single-walled CNTs (SWNTs), which can remarkably affect the diameter and wall number of CNTs, and the chirality distribution of SWNTs. Initially, only iron group metals (Fe, Co, Ni) were used as catalysts for SWNT growth via a vapor-liquid-solid (VLS) mechanism. But recently it has been found that many other metals and some semiconductors are also able to grow SWNTs. We have recently developed a simple and effective metal-catalyst-free chemical vapor deposition (CVD) method for the growth of SWNTs from SiOx nanoparticles (NPs),1 and a “scratching growth” approach for the patterned growth of SWNTs on silica substrate without any metal species.1 It was also found that SWNTs grow from SiOx with an extremely slow growth speed of 8.3 nm/s in this CH4 CVD process, ~300 times slower than commonly used Co catalyst at the same growth condition.2 Thanks to this slow growth speed of SWNTs from SiOx NPs, direct length-sorted growth of short SWNTs was achieved.2 To study the nature of catalyst (e.g., oxide vs carbide, liquid vs solid) and understand the SWNT growth mechanism in this process, detailed CVD and in situ TEM studies, together with density functional theory calculations, were performed. It is interesting to find that oxygen in SiOx plays a remarkable role in the nucleation and growth of SWNTs. The in situ TEM monitoring reveals that SiOx NPs keep solid during growth, implying a vapor-solid-solid growth mechanism for SiOx catalysts. An oxygen-enabled growth is suggested to be a common feature for many other nontraditional catalysts developed recently. Lastly, epitaxial growth of SWNTs with discrete diameter distribution from BN nanofibers will be reported.Reference:1. B.L. Liu, et al., J. Am. Chem. Soc. 2009, 131, 2082.2. B.L. Liu, et al., ACS Nano, 2009, 3, 3421.
10:00 AM - C4.3
Controlling Carbon Nanotube Structures at Low Growth Temperatures.
Michael Siegal 1 , Thomas Beechem 1 , Paula Provencio 1 , David Tallant 1 , Donald Overmyer 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractThe structural properties of carbon nanotubes (CNTs) are explored as a function of growth parameters using thermal chemical vapor deposition (CVD) at low temperatures. There exist two independent, and critical, temperatures in the CVD process: (1) the reduction anneal temperature to remove oxygen from the catalyst layer, and (2) the growth temperature used to crack the hydrocarbon feed gas to produce CNTs. For example, we find that high crystalline quality single (SWNT) and multiwall (MWCNT) CNTs grow at temperatures ranging from 530 – 630C. Using identical 2.5 nm thick Ni catalyst layers on W-coated Si(100) and a constant CO reduction annealing process at 600C, the number of walls in the resulting CNTs increase linearly from one to eight over this growth temperature range. However, the highest temperature used during CVD growth appears to control the resulting inner core diameter, which is ~ 1 nm for all CNTs grown ≤ 610C, near the 600C CO reduction anneal temperature used for these samples. The corresponding CNT outer diameters also increase linearly from 1 – 5 nm up to 610C. Using growth temperatures measurably higher than that of the reduction anneal results in both larger inner and outer diameters, inferring that the Ni catalyst islands grow with increasing temperature. These results suggest that independent control of the number of walls and the inner core diameter in CNTs is possible.This hypothesis will be explored by growing CNTs at increasingly lower temperatures, reproducibly as low as ~ 350C, and by varying the temperature of the reduction anneal to independently set the highest temperature experienced by the catalyst layers. Resulting inner and outer wall diameters, number of walls, and chirality (for SWNTs) will be determined as a function of growth conditions. Raman spectroscopy is used to identify SWNT chirality and the representative C-C bonding for MWCNTs. High-resolution transmission electron microscopy is used to independently measure wall thickness, wall diameters, and crystalline quality.Supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.
10:15 AM - C4.4
Supergrowth of Nitrogen-doped Single-walled Carbon Nanotube Arrays: Active Species, Dopant Characterization, and Doped/Undoped Heterojunctions.
Cary Pint 1 2 , Zhengzong Sun 2 , Sharief Moghazy 2 , Ya-Qiong Xu 3 , James Tour 2 , Robert Hauge 2
1 Physics, Rice University, Houston, Texas, United States, 2 Chemistry, Rice University, Houston, Texas, United States, 3 Physics and Electrical Engineering, Vanderbilt University, Nashville, Tennessee, United States
Show AbstractWe demonstrate the water-assisted supergrowth of vertically aligned single-walled carbon-nitrogen nanotubes (SWNNT). In-situ characterization of gas-phase nitrogen containing precursors identifies HCN as the most active precursor for SWNNT growth, analogous to C2H2 for single-walled carbon nanotubes (SWNTs). Optical characterization reveals sensitivity of SWNNT optical transitions to N-doping through absorbance characterization, and XPS and mass spectrometry are combined to quantitatively assign N-content. Finally, we fabricate tunable SWNT/SWNNT molecular heterojunctions in the self-assembled carpet morphology. This leads to printable SWNT/SWNNT hierarchical structures with tunable built-in potential differences that can be useful in the development of a variety of energy harvesting applications.
10:30 AM - C4.5
Multiple-cycle Chemical Vapor Deposition Growth for the Synthesis of High-density Aligned Arrays of Single-walled Carbon Nanotubes on Quartz Surface.
Weiwei Zhou 1 , Lei Ding 1 , Jie Liu 1
1 Chemistry Department, Duke University, Durham, North Carolina, United States
Show AbstractSingle-walled carbon nanotubes(SWNTs), as a typical one-dimensional molecular system, have been attracted enormous attentions for their remarkable electrical properties. Currently a key challenge is to obtain high-density aligned array of SWNTs for the applications in highly integrated carbon nanotube-based circuits and especially high frequency electronics where impedance matching is a necessity. Significant progresses have recently been achieved on single-crystal quartz wafers by chemical vapor deposition (CVD).Here, we will present our multi-cycle CVD method which can greatly enhance the catalyzing efficiency of catalyst particles for growing ultra-high-density aligned arrays. This method is based on our previous methanol/ethanol CVD method and dividing a normal one-step CVD growth process to multiple CVD growth cycles. In scanning electron microscope (SEM) images, the nanotubes uniformly covered the whole surface, and the density of the aligned SWNTs is so high that we are not able to distinguish the isolated SWNTs on the surface using SEM characterization. We further use atomic force microscope (AFM) which has a higher resolution to characterize the SWNT arrays and found that SWNTs almost form a continual monolayer film and the density is around 30~40 SWNTs/μm. We believe that the formation of this continual monolayer SWNT film is due to the high efficiency of catalyst particles. The amount of catalyst nanoparticles activated in a three-cycle CVD growth is much larger than in normal one-cycle CVD growth. We further confirm this hypothesis by in-situ comparing SEM images of the same catalyst areas on a quartz wafer after the first growth and after the second growth. Some new SWNTs after the second growth grown from the same catalyst area on the wafer directly verify that more catalyst particles can be activated in multiple-cycle CVD growth.
10:45 AM - C4.6
Bi-Metallic Catalyst Composition, Morphology and Reaction Pathway in the Growth of ``Super-Long'' Carbon Nanotubes.
Joerg Schneider 1
1 Fachbereich Chemie, Technische Universität Darmstadt, Darmstadt Germany
Show AbstractThe discovery of “super-long” growth of carbon nanotubes (CNTs) by the catalyst driven water assisted chemical vapor deposition by Hata et al. has represented a major synthetic breakthrough for the integration of CNTs in future device architectures such as chemical and physical sensors, heterogeneous catalyst arrays, or 3D micro- and nano-electromechanical sytems (MEMS and NEMS).Herein we report on our findings regarding nature, role and mechanism of the catalyst composition in the “super long” growth of CNTs. Our studies allow an understanding of the morphology and structure of the catalyst nanoparticles by high resolution scanning transmission electron microscopy (STEM) tomograms and of their chemical composition by a combination of spectroscopic (EELS, XPS) and diffraction techniques (GIXRD). Our studies allow new insight and understanding in the nature of the chemical composition of the bimetallic Fe/Al catalyst responsible for ultralong CNT growth.
11:30 AM - C4.7
Growth of Diameter-modulated Single-walled Carbon Nanotubes through Instant Temperature Modulation in Laser-assisted Chemical Vapor Deposition.
M. Mahjouri-Samani 1 , Y. Zhou 1 , W. Xiong 1 , Y. Gao 1 , M. Mitchell 1 , Yongfeng Lu 1
1 , University of Nebraska, Lincoln, Nebraska, United States
Show AbstractThe diameter of individual single-walled carbon nanotubes (SWNTs) was successfully modulated along their axes by instant temperature control in a laser-assisted chemical vapor deposition (LCVD) process. SWNTs were grown using different temperature profiles to investigate the effects of temperature variation on the growth. Due to the inverse relationship between the SWNT diameter and the growth temperature, SWNTs with ascending diameters were obtained by reducing the LCVD temperature from high to low. The diameter-modulated SWNTs were grown across a pair of Mo electrodes to form field-effect transistors (FETs) for investigation of their electronic transport properties. Fabricated devices demonstrated properties similar to Schottky-barrier diodes, implying different bandgap structures at the ends of the SWNTs. Raman spectroscopy, transmission electron microscopy, and electronic transport characteristics were studied to investigate the influence of the temperature variation on the structural and electronic characteristics of the SWNTs.
11:45 AM - C4.8
Aerosol-assisted CCVD Process: From the Reactive Aerosol to the Formation of Aligned Multi-walled Carbon Nanotube Carpets.
Celia Castro 1 , Mathieu Pinault 1 , Servane Coste-Leconte 2 1 , Rodrigo Fernandez Pachecco 3 , Odile Stephan 3 , Cecile Reynaud 1 , Martine Mayne-L'Hermite 1
1 laboratoire Francis Perrin, CEA-Saclay, Gif sur Yvette France, 2 INSTN, UEINE, CEA-Saclay, Gif sur Yvette France, 3 Laboratoire de Physique des Solides, CNRS UMR 8502, Université Paris Sud, Orsay France
Show AbstractThe excellent mechanical, physical and chemical properties of carbon nanotubes (CNT), are the origin of various potential applications. In this context, one of the challenges of CNT synthesis is the ability to grow uniform and calibrated products in a reproducible way regarding their length, diameter and structure. Among the synthesis techniques, catalytic chemical vapor deposition (CCVD) appears as the most promising one for scaling up at industrial levels. CCVD using gaseous precursors has been used by several groups [1-2] who succeeded in obtaining well controlled CNT. However, these techniques often require the use of precisely designed layered substrates. Our aerosol assisted CCVD process [3] enables rapid and continuous growth of aligned multi-walled CNT (MWNT) directly on substrates (silicon, quartz,…) by injecting simultaneously and continuously carbon and catalyst precursors together (toluene and ferrocene). However, this one-step technique is more complicated to understand since catalyst particle formation, nucleation and growth of CNT take place simultaneously in the reactor. Also, the reactants are submitted to a strongly inhomogeneous temperature profile along the cylindrical reactor which is expected to act differently on the precursors. The aim of this study is to determine and understand CNT growth mechanisms from the aerosol reactive phase to the nucleation and growth of aligned MWNT. Therefore, from analysis of Fe and carbon profile all along the heated reactor coupled to microscopy analysis of collected samples, we will demonstrate that aligned MWNT growth is divided into 3 steps:1 – Gas phase nucleation of Fe-based catalyst particles from the aerosol reactive phase [4];2 – Gradual deposition of Fe-based catalyst particles all along the reactor walls [4];3 – Nucleation and growth of carbon nanotubes through a base-growth mechanism [5]We will also report how carbon and catalyst species feed continuously aligned CNT growth. In particular, we will focus on the diffusion of both carbon and Fe-based species along the aligned CNT carpets in order to react on the reactor walls where the catalyst particle layer is active for the CNT base-growth mechanism.References[1] K. Hasegawa et al., J. Nanosci. Nanotechnol. (2007).[2] T. Yamada et al., Nature Nanotech. 1, 131 (2006).[3] M. Pinault, et al., Nano Lett., 5, 12, 2394-2398 (2005).[4] C. Castro et al., accepted for publication in Carbon. [5] M. Pinault et al. Carbon 43, 2968 (2005)
12:00 PM - C4.9
Gas Composition and Trace Gas Impurities Controlled Growth Kinetics of Vertically Aligned Carbon Nanotube Arrays.
Jung Bin In 1 2 3 , Costas Grigoropoulos 1 , Alexander Chernov 3 , Aleksandr Noy 2 4
1 Mechanical Engineering, UC Berkeley, Berkeley, California, United States, 2 The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 3.Physics and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States, 4 4.School of Natural Sciences, UC Merced, Merced, California, United States
Show AbstractAlthough there has been a tremendous improvement in the yield and quality of the CVD synthesis of vertically aligned carbon nanotubes, the details of the growth kinetics still remain ambiguous. Several studies have suggested different growth models that match their experimental growth kinetics with good accuracy, but often do not reconcile with one another. In this study, we conducted growth experiments using a CVD synthesis system equipped with a high resolution optical micrometer for detailed in-situ kinetic monitoring. We have explored the effect of gas composition on growth kinetics of vertically aligned multi-walled carbon nanotubes (VA-MWNTs) by varying concentrations of ethylene and hydrogen. We show that catalyst lifetime and the final length of nanotube array are greatly influenced by process gas concentrations as well as ethylene. Surprisingly, we show that growth of VA-MWNTs is so sensitive to gaseous impurities such as water and oxygen that even traces (<2ppm) of the impurities could have a large effect on the catalyst lifetime. We have removed the effects of these impurities by adding high performance deoxo purifiers to our gas delivery system, and for the first time were able to observe the true kinetics of the carbon nanotube growth. Typically, we have observed abrupt termination of VA-MWNTs growth and we show that this behavior correlates well with a simple kinetic model.
12:15 PM - C4.10
Scalable Flame Synthesis of Carbon Nanotubes on Substrates.
Nasir Memon 1 , Jafar Al-Sharab 2 , Yogesh Jaluria 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 AbstractAn experimental study using a novel setup is undertaken to investigate the direct flame-synthesis of carbon nanotubes (CNTs) on metal-alloy substrates. When utilizing flames, the combustion of hydrocarbon gas provides both the high temperature and carbon species necessary for the growth of CNTs, resulting in an efficient and robust process. In previous studies, vertically well-aligned multi-walled CNTs with uniform diameters (<15 nm) were grown in 1 and 2-D diffusion flame configurations, which were excellent for fundamental investigation, but were limited in their potential for scale up. Our novel setup includes the use of a multi-element diffusion burner (MEDB), capable of producing a quasi-one-dimensional flow field of radially uniform temperature and species concentrations, while also providing conditions ideal for the growth of CNTs over large areas in open environments. Moreover, the setup still allows for fundamental investigations on the local growth conditions corresponding to specific CNT morphologies, which are compared to that produced in other flame geometries, so that universal growth mechanisms can be identified. Specifically, we examine the influence of local temperature, relevant carbon-based species, and other parameters in the formation of CNTs. Gas-phase spontaneous Raman scattering is used to determine the axial temperature profile and to map CO, C2H2, CH4, and H2 species. Analytical electron microscopy techniques and resonant Raman spectroscopy are used to characterize the as-synthesized CNTs.
12:30 PM - C4.11
A CMOS Compatible Carbon Nanotube Growth Approach.
Daire Cott 1 , Nicolo Chiodarelli 1 2 , Philipe Vereecken 1 3 , Bart Vereecke 1 , Sven Van Elshocht 1 , Stefan De Gendt 1 4
1 , IMEC, Leuven Belgium, 2 Electrical Engineering, Katholieke Universiteit Leuven, Leuven Belgium, 3 Center for Surface Chemistry and Catalysis, Katholieke Universiteit Leuven, Leuven Belgium, 4 Chemistry, Katholieke Universiteit Leuven, Leuven Belgium
Show AbstractIn future technology nodes, 32nm and below, Carbon Nanotubes (CNTs) may provide a viable alternative to Cu as an interconnect material. CNTs exhibit a current carrying capacity (up to 109 cm2), whilst also providing a significantly higher thermal conductivity (SWCNT ~ 5000 WmK) over Copper (106 A/cm2 and ~400WmK). However, exploiting such properties of CNTs in small vias is a challenging endeavor. In reality, to outperform Cu in terms of a reduction in via resistance alone, densities in the order of 1013 CNTs/cm2 are required. At present, conventional thermal CVD of carbon nanotubes is carried out at temperatures far in excess of CMOS temperature limits (400 °C). Furthermore, high density CNT bundles are most commonly grown on insulating supports such as Al2O3 and SiO2 as they can effectively stabilize metallic nanoparticles at elevated temperatures but this limits their application in electronic devices. To circumvent these obstacles we employ a remote microwave plasma to grow high density CNTs at temperatures below 450 °C on conductive underlayers such as TiN and transition metal silicides. As CNT growth is a catalytic process the energy required to form graphene tubular structures from a hydrocarbon gas comes exclusively from the heat supplied to the catalyst particle. We identify the critical factors important for high-quality CNTs at low temperatures such as control over the amount of charged species and radicals in the plasma growth environment and present a fully CMOS compatible carbon nanotube synthesis approach
C5: CNTs Growth, Exploring Novel CNT Growth Techniques and Growth Mechanisms II
Session Chairs
Tuesday PM, November 30, 2010
Room 304 (Hynes)
2:30 PM - **C5.1
A Quantitative Study of Ostwald Ripening Induced Termination of Carbon Nanotube Growth.
Benji Maruyama 1 , Placidus Amama 4 1 , Gordon Sargent 5 1 , Tonya Cherukuri 1 , Neal Pierce 4 1 , Eric Stach 2 , Seung-Min Kim 2 , Cary Pint 3 , Robert Hauge 3 , Kent Weaver 1 , Pablo Caceres 1 , Roberto Accosta 1 , Lee Semiaten 1
1 AFRL/RXBN, Air Force Research Laboratory, Wpafb, Ohio, United States, 4 , University of Dayton Research Institute, Dayton, Ohio, United States, 5 , UES Inc., Dayton, Ohio, United States, 2 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 3 Smalley Institute, Rice University, Houston, Texas, United States
Show AbstractAir Force applications of carbon nanotubes span structural, energy storage, power transmission, field emission and electronics. Despite their importance, synthesis of nanotubes remains poorly understood and poorly controlled. Specifically, early termination of growth leads to reduced yield, purity and low aspect ratio, all of which increase cost and reduce properties. Ostwald ripening of catalyst particles has been shown to cause termination of nanotube growth. A quantitative assessment of Ostwald ripening of nanotube catalysts under conditions mimicking growth will be presented, along with implications of the finding on the structure and kinetics of carpet growth. Finally the impact of substrate composition and morphology on catalyst lifetime will be presented.
3:00 PM - **C5.2
Metal-free Growth of Single-walled Carbon Nanotubes.
Shaoming Huang 1
1 , Wenzhou University , Wenzhou China
Show Abstract Selective growth of SWNT with specific helicity is one of the main challenges towards controlled growth of SWNTs for various applications Metal nanoparticles (NPs) are indispensable for the growth of SWNTs by chemical vapor deposition (CVD) and Fe family of elements were regarded as the most effective catalysts in the past. However, in recent years many other metal NPs such as Au, Ag, Cu, Pd, Rh,, Mg, Mn, Cr, Sn and Al, semiconductors NPs such as Si, Ge, Te, carbides such as SiC, Fe3C etc have been reported to be active for nanotube growth although these materials were regarded as inactive catalysts for CNTs. One problem raising from the metal catalysts is that the chemical, redox, magnetic properties of the metal NPs involved in the nanotube materials will interfere the corresponding nanotube properties and performances. In this talk, recent progress in the growth of SWNTs from metal-free catalysts will be summarized and the possible grow mechanism is discussed. The strategy for realizing the controlled growth of SWNTs, particularly for helicity, is also proposed.
3:30 PM - C5.3
On the Formation of Carbon Nanotube Serpentines: Insights from Multi-million Atom Molecular Dynamics Simulation.
Leonardo Machado 1 , Sergio Legoas 2 , Jaqueline Soares 3 , Nitzan Shadmi 4 , Ado Jorio 3 , Ernesto Joselevich 4 , Douglas Galvao 1
1 Departamento de Física Aplicada, Unicamp, Campinas, São Paulo, Brazil, 2 Física, UFRR, Boa Vista, Roraima, Brazil, 3 Física, UFMG, Belo Horizonte, Minas Gerais, Brazil, 4 Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot Israel
Show AbstractIn this work we present results from molecular dynamics simulations of carbon nanotube serpentine formation. These S-like nanostructures consist of a series of carbon nanotube segments arranged in a parallel, straight and regularly spaced geometry, connected by alternating U-turn shaped curves. These serpentines were firstly synthesized in 2008 [1], but up to now no atomistic simulations have been carried out to address the dynamics of formation of these nanostructures. Their formation has been explained based on the 'falling spaghetti mechanism' [1]. The serpentines would be formed in a two-step process, where the isolated nanotubes are first grown standing up from the silicon oxide stepped substrates, and at a second stage, the tube would fall down preferentially along the steps, creating the oscillatory patterns, like spaghetti falling on a tilted bamboo mat [1]. The force that would be primarily responsible for the tube fall is the strong nanotube-surface interactions (mainly van der Waals forces).In order to address the processes of serpentine formation we have carried out fully atomistic molecular dynamics simulations using the well-known NAMD code [2]. We have considered graphite and quartz stepped substrates with the nanotubes placed on top of them. We have considered very long tubes (about 1 micron length) of different diameters, with and without a nanoparticle on the free tube end. A force was applied to the upper part of the tube during a short period of time and then turned off and the system let free to evolve in time.Our results showed that these conditions are sufficient to form robust serpentines and validate the general features of the ‘spaghetti model’ [1]. We observed well formed serpentine on both types of substrates (graphite and quartz) and with different tube diameters. Different U-turns (lengths and spacings) can be produced as a consequence the oscillatory tube movement induced by thermal fluctuations. Our results also showed that the nanoparticle has an active role on the serpentine formation. It helps to damp large amplitude tube oscillations that would prevent more uniform shaped serpentines.[1] N. Geblinger, A. Ismach, E. Joselevich, Nature Nanotech. v3, 195 (2008). [2] NAMD, http://www.ks.uiuc.edu/Research/namd/.
3:45 PM - C5.4
Revealing the Population Kinetics of Carbon Nanotube Growth.
Mostafa Bedewy 1 , Michael Reinker 1 , Eric Meshot 1 , Erik Polsen 1 , Arthur Woll 2 , A. John Hart 1
1 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 , Cornell University, Ithaca, New York, United States
Show AbstractA vertically aligned carbon nanotube (CNT) “forest” grown by chemical vapor deposition is a polydisperse population of over 109 CNTs/cm2. Previous studies used either ex situ or in situ height measurements to explain, and mathematically model, the growth kinetics. However, we have recently shown that the time evolution of mass is an important complement to height data, due to the decay of CNT density [1] that occurs as catalyst particles deactivate [2], which eventually leads to abrupt termination of growth [3]. Likewise, due to the inherent tortuosity of CNTs within a forest, the forest height does not equal the CNT length, and time-resolved height measurements do not accurately represent the lengthening kinetics [4]. We herein demonstrate a comprehensive nondestructive characterization methodology for quantifying the population kinetics of CNT forest growth, which can be implemented ex situ after growth or in situ during growth. Our approach combines real-time height measurement with spatial mapping of CNT alignment using small angle X-ray scattering (SAXS), to calculate the time evolution of CNT average length. Differential X-ray absorption is used to obtain a height-resolved map of mass density, which is then integrated to obtain the spatial variation of mass. The spatial mapping and distribution of the diameter is obtained from fitting of linescans in SAXS patterns with a lognormally distributed form factor model. Combining these with the height kinetics gives the time evolution of mass, diameter, and number density during CNT forest growth. This methodology provides a framework for quantifying the lifetime distribution of catalyst particles in CNT films, therefore providing a complete measure of the growth kinetics. Using this technique, we determine that the lengthening of CNTs is linear with time; thus, CNT forest growth is essentially reaction-limited under the tested conditions, with the variation in alignment being responsible for the sub-linear curvature observed in height kinetics. Moreover, the time-resolved decay in number density indicates that the deactivation of catalyst particles causes growth termination of individual CNTs, and then collective forest termination happens at a critical density threshold. This CNT density decay during growth, which is up to 10-fold in some cases, has crucial implications for electronic and thermal transport properties of CNTs that may be used in future interconnects and thermal interfaces. 1. Bedewy, M., et al. Journal of Physical Chemistry C, 2009. 113(48): p. 20576–20582.2. Kim, S.M., et al. Journal of Physical Chemistry Letters, 2010. 1(6): p. 918-922.3. Meshot, E.R. and A.J. Hart. Applied Physics Letters, 2008. 92(11).4. Meshot, E.R., et al. Nanoscale, 2010. 2(6): p. 896–900.
4:30 PM - C5.5
Critical Structural and Compositional Changes in Iron Catalyst During Carbon Nanotube Growth.
Andre Mkhoyan 1 , Michael Behr 1 , Eray Aydil 1
1 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractDuring carbon nanotube (CNT) growth, hydrocarbon molecules and radicals from the gas phase decompose on the catalyst surface and provide the source of carbon atoms, which diffuse and add to the base of the growing CNT walls. However, the exact location where and how carbon atoms incorporate into the growing nanotube still remains unclear. This information is critical for catalyst selection and control of CNT growth. When Fe-based catalysts were used, CNT have been reported to grow not only from metallic iron in BCC and FCC phases, but also from the cementite (Fe3C) phase that forms in situ when Fe catalyst is exposed to carbon during the growth. It was speculated that Fe3C plays only an intermediate role, as the surface of the Fe3C catalyst would decompose into Fe metal and graphite producing the CNT walls. To understand diffusion processes occurring inside Fe catalyst during CNT growth the catalyst nanoparticles were examined using atomic-resolution scanning transmission electron microscopy combined with electron energy-loss spectroscopy. The CNT walls emanate from completely modified and chemically complex nanoparticles consisting of three sections: cementite, 5 nm amorphous FeOx layer and 2-3 nm carbon-rich interfacial region. Nonuniform distribution of carbon throughout these sections reveals that carbon from the gas phase decomposes on Fe3C near the multisection junction where the CNT walls also terminate. It was found that carbon-rich interfacial region formed between the FeOx cap and the Fe3C crystal is the essential carbon source for CNT growth.
4:45 PM - C5.6
Selective Growth of Aerosol Carbon Nanotubes with Straight-, Coiled-, and Sea Urchin-like Structures in the Gas Phase.
Whi Kim 1 , Ji Ahn 1 , Soo Kim 2
1 Nano fusion technology, Pusan national university, Milyang Korea (the Republic of), 2 Nano mechatronics engineering, Pusan National University, Miryang Korea (the Republic of)
Show AbstractWe demonstrate a gas-phase one-step method for selectively growing aerosol carbon nanotubes (CNTs) with different shapes, including straight-, coiled- and sea urchin- CNTs. The growth of aerosol CNTs in this approach was made by the combination of spray pyrolysis and thermal CVD, in which Ni-Al bimetallic nanoparticles were first formed and subsequently reacted with acetylene and hydrogen gases. On the basis of SEM analysis for the mixture of straight-, coiled-, and sea urchin-CNTs, we proposed that the diameter of seeded bimetallic particles played a key role in growing aerosol CNTs with various nanostructures. In order to identify the role of bimetallic particle size, several groups of spray-pyrolyzed bimetallic nanoparticles with the average size of ~60, ~200, and ~300 nm, respectively, were electrically classified using a differential mobility analyzer, and then each group of size-selected bimetallic nanoparticles was subsequently introduced into a thermal CVD reactor to continuously grow aerosol CNTs. We found that coiled-CNTs (C-CNTs) were formed on the entire surface of a seeded bimetallic nanoparticle with the average size of smaller than ~100 nm at medium temperature ranges of 500~650oC. However, straight-CNTs (S-CNTs) can be easily obtained with relatively high temperature ranges of 650~800oC, which result in melting the Al matrix sites in the seeded bimetallic nanoparticles so that the liquid-like Al matrix was then consumed by subsequent CNT precipitation. Therefore, the presence of Al components in the seeded bimetallic particles with the average size of smaller than ~100 nm is the most important in developing the desired morphology for C-CNTs and S-CNTs. However, sea urchin-CNTs (SU-CNTs) are mostly grown on the seeded bimetallic particles with average size of larger than ~100 nm, in which Ni sites sufficiently isolated by Al sites are seeded to radially grow multiple CNTs with the average diameter of ~ 60±13 nm under the medium reaction temperature ranges of 500~650°C. If the processing takes place at relatively high temperature ranges of 650~800°C, this makes Al molten and results in significant size reduction of available Ni sites by thermal expansion of non-catalytic Al matrix sites so that one can obtain SU-CNTs with the average diameter of ~10±4 nm. The results demonstrate that isolating catalytic Ni sites by thermal expansion of non-catalytic Al matrix sites embedded in the bimetallic particles is the key factor to determine the desired nanostructures of aerosol CNTs.
5:00 PM - C5.7
Catalyst Evolution and Carbon Nanotube Growth Studies Performed Using a Custom-built Rapid Experimentation and In-situ Spectroscopy System.
Rahul Rao 1 , Kent Weaver 1 2 , Gordon Sargent 1 3 , Lee Semiatin 1 , Benji Maruyama 1
1 Nanostructured and biological materials branch, Air Force Research Laboratory, wpafb, Ohio, United States, 2 , Southwestern Ohio Council for Higher Education, Dayton, Ohio, United States, 3 , University of Dayton Research Institute, Dayton, Ohio, United States
Show AbstractWe have developed a unique system that incorporates a chemical vapor deposition (CVD) chamber for single-walled carbon nanotube (SWNT) growth with micro-Raman and near-infrared fluorescence spectrometers. Growth occurs when catalyst nanoparticles deposited on thermally isolated silicon islands are irradiated with the micro-Raman excitation laser (532 nm), which also serves as a localized heat source. Automated control of substrate temperature, position, feed gas composition, and chamber pressure enable rapid real-time exploration of SWNT growth parameter space. In this study we use thin (0.5 – 2nm) films of nickel and iron which form nanoparticles upon exposure to the Raman laser under typical CVD conditions. We first investigate the change in catalyst particle size and density due to Ostwald ripening [1] as a function of laser power (temperature) and exposure time. The average particle size distribution and density are obtained ex-situ via electron microscopy and atomic force microscopy. Next we evaluate the impact of Ostwald ripening on subsequent SWNT growth. Growth kinetics are obtained by analyzing the evolution of the Raman signal the nanotubes in-situ. We can rapidly compare the growth kinetics of iron and nickel catalysts, and will discuss the origins of these differences. In addition, changes in the Raman D/G ratios and reaction time constants with respect to various catalyst particle distributions will be compared. Finally, the effect of Ostwald ripening-induced termination of growth [2] will be discussed with regards to controlled growth of SWNTs.[1] S.M. Kim et al., J. Phys. Chem. Lett., 1(6), 918, 2010[2] P.B. Amama et al., Nano Lett., 9, 44, 2009
5:15 PM - C5.8
Control of Carbon Nanotube Size and Structure by Precursor Gas Chemistry.
Eric Meshot 1 , Desiree Plata 2 4 , Gilbert Nessim 3 , Matteo Seita 3 , Yongyi Zhang 1 , Christopher Reddy 4 , Philip Gschwend 2 , Carl Thompson 3 , A. John Hart 1
1 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 , Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, United States, 3 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractControlling the size and topology of carbon nanostructures, from amorphous carbon nanofibers (CNFs), to crystalline carbon nanotubes (CNTs), to graphene, is critical for perhaps every possible application of these important materials. Myriad studies show that catalyst size and composition determine the diameter and affect the chirality of CNTs; however, little is known about how the chemistry of hydrocarbon precursors may affect these attributes. Although gas-structure correlations are not predicted by classical CNT nucleation and growth models involving metal catalysts, findings using new (e.g, semiconductor, oxide) CNT catalysts and oxygen-assisted growth ambients indicate that more complex mechanisms determine the structure of CNTs. Herein, we demonstrate that both the crystallinity and size of CNTs is indeed controlled by the chemistry of the reaction ambient, in both “hot-wall” and “cold-wall” CVD systems featuring decoupled heating of the precursor and growth substrate. At low substrate temperatures (500 C) facilitating growth on CMOS-compatible substrates, we find that the gas chemistry determines the crystal structure of carbon filaments. An abrupt transition from amorphous nanofibers to crystalline nanotubes is observed as thermal decomposition of the feedstock is controlled to create an increasing population of PAHs and VOCs [1]. At higher substrate temperatures (700-900 C), CNTs always form, and varying the hydrocarbon population does not change the CNT diameter yet significantly affects the CNT purity and structural quality [2]. However, under these conditions adding a small quantity of ethanol to the feedstock selectively reduces the number of walls without changing the CNT diameter, and this method, in combination with tuning of the catalyst film thickness is used to selectively produce double-wall CNT forests with a 5-fold yield increase over the baseline conditions [3]. Possible roles of specific thermally-generated hydrocarbon precursors are quantified by gas chromatography with a flame ionization detector (GC-FID) and GC-mass spectroscopy (GC-MS), at detection levels of subparts per trillion (10-12) for certain species [4]. Further study of the detailed decomposition pathways of hydrocarbons and oxygen-containing additives will give important insights on how the chemistry of the precursor can affect the atomic-scale processes of CNT growth, and may be important pieces of the chirality control puzzle.1. Nessim, G.D., et al. Submitted for publication, 2010.2. Meshot, E.R, et al. ACS Nano, 2009. 3(9): p. 2477-2486.3. Zhang, Y.Y., et al. Journal of Physical Chemistry C, 2010. 114(14): p. 6389-6395.4. Plata, D.L., et al. Environmental Science & Technology, 2009. 43(21): p. 8367-8373.
5:30 PM - C5.9
Role of Plasma Activation in Kinetics of CNT Growth in PECVD Process.
Irina Lebedeva 1 , Andrey Knizhnik 1 , Alexey Gavrikov 1 , Alexey Baranov 1 , Boris Potapkin 1 , Steven Aceto 2 , Pierre-Andre Bui 2 , Ulrike Grossner 2 , David Smith 2 , Timothy Sommerer 2
1 , Kintech Lab Ltd, Moscow Russian Federation, 2 , GE Global Research Center, Niskayuna, New York, United States
Show AbstractThe work presents kinetic modeling of the effect of acceleration for the growth kinetics of carbon nanotubes by hydrocarbon gas mixture modification with plasma discharge. The plasma activation creates active species in hydrocarbon gas mixture, which can easily adsorb and dissociate on the catalyst surface. So plasma treatment of the gas mixture in the CVD process allows to increase the carbon supply rate by a few orders of magnitude compared to than in thermal CVD process. On the other hand, plasma can also provide etching of carbon species from the catalyst surface. To correctly reproduce both of these effects of plasma, the kinetic model of growth of carbon nanotubes is developed based on first-principles analysis of heterogeneous processes on the catalyst surface and detailed kinetics of gas phase chemistry. The model is used to compare the growth rates of carbon nanotubes in thermal and plasma-enhanced CVD processes and to determine critical gas pressures, at which CNT growth switches from the adsorption limitation to the limitation by reaction and diffusion on the catalyst.
5:45 PM - C5.10
Structural and Chemical Analysis of Carbon Nanotubes Grown on Diamond Substrate Using Three Different Techniques.
Betty Quinton 1 2 , Paul Barnes 2 , Sharmila Mukhopadhyay 1 , Pani Varanasi 3 , Bob Wheeler 4 , Yongli Xu 4
1 Mechanical and Materials Engineering, Wright State University, Dayton, Ohio, United States, 2 Propulsion Directorate, Air Force Research Laboratory, Dayton, Ohio, United States, 3 Materials Science Division, Army Research Office, Research Triangle Park, North Carolina, United States, 4 Surface Engineering, UES, Inc., Dayton, Ohio, United States
Show AbstractDue to the allotropic nature of carbon, diamonds exist with a SP3 hybridized bonding structure and carbon nanotubes (CNTs) exist with a SP2 bonding structure. In our study, three different growth methods were used to grow CNTs onto commercial polished freestanding chemical vapor deposited (CVD) diamond substrates. The three growth methods were: thermal CVD with pre-sputtered metal catalyst, microwave plasma enhanced CVD with pre- sputtered metal catalyst, and floating catalyst thermal chemical vapor deposition with xylene and ferrocene liquid mixture without any prior catalyst deposition. The scanning electron microscope images show that all three different methods produce multiwall CNTs with varying diameters. Thin foil samples for transmission electron microscopy (TEM) studies were made from the samples grown by using each of the growth methods to compare and contrast different growth mechanisms. The energy dispersive spectroscopy maps and TEM images of the samples grown by thermal CVD shows that a transition layer is present at the CNT and diamond interface. The images indicated a carbon layer and detached Ni catalyst particles in this layer. The detached and carbon encapsulated Ni particles were found to be located close to CNT roots suggesting that root growth is predominant. Cross-sectional TEM data of all the samples processed by different routes will be presented and the growth mechanisms will be discussed.
C6: Electronic, Optical, and Magnetic Properties of Carbon Nanomaterials I
Session Chairs
Wednesday AM, December 01, 2010
Back Bay A (Sheraton)
9:00 PM - C6.1
Rational Engineering and Magnetotransport Study of Graphene Nanostructures.
Jingwei Bai 1 , Xiangfeng Duan 2 , Yu Huang 1
1 Material Science and Engineering, University of California, Los Angeles, Los Angeles, California, United States, 2 Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California, United States
Show AbstractGraphene and graphene nanostructures have attracted considerable interest for fundamental studies and potential applications because of their unique electronic properties. It has been demonstrated that a conduction band gap can be achieved in graphene nanoribbons (GNRs) due to size confinement and edge effect. Theoretical studies have also suggested interesting magneto-electronic properties in GNRs originated from the magnetic edge states or the Hall-edge states under a perpendicular magnetic field, with very large magnetoresistance (MR) predicted. Here we demonstrate a rational method to fabricate GNRs with sub-10 nm width by employing nanowire as etch mask. Taking a step further, we demonstrate a new graphene nanostructure-graphene nanomesh as a mimic of GNR network. This nanomesh structure introduces finite size effect into a large sheet of graphene while retaining the two-dimensional nature, and therefore may be advantageous in practical device fabrication and integration. Based on the advance of our fabrication method, we report the first experimental observation of a dramatic enhancement of the conductance in a GNR field-effect transistor by a perpendicular magnetic field. Very large negative MR of nearly 100% with conductance enhanced over 10,000 times was observed at low temperatures; and more than 50% remained at room temperature. Similar magnetotransport behavior was also observed in graphene nanomesh device. The observed large MR was attributed to the complex interplay between edge roughness, quantum confinement and the formation of cyclotron orbits. These findings demonstrate interesting magnetotransport properties in graphene nanostructures, and can open up exciting new opportunities for a new generation of magneto-electronic devices.
9:15 PM - C6.2
Graphene for Magnetoresistive Junctions.
Junichiro Inoue 1 , Tomohiro Hiraiwa 1 , Ryuichi Sato 1 , Syuta Honda 2 , Hiroyoshi Itoh 2
1 , Nagoya University, Nagoya Japan, 2 , Kansai University, Suita Japan
Show AbstractGraphene is a two dimensional honeycomb lattice made of carbon atoms. Although the carbon is the well known element, the graphene is a novel material which attracts much interest recently because of its characteristic features. The graphene is a gapless semiconductor, and electrons in the graphene behave as massless Dirac fermions. The massless electrons give rise to distinguished features of electrical transport properties from those in conventional metals and semiconductors. Furthermore, the graphene is expected to be an alternative to silicon in the contemporary electronics, because of its high mobility, long spin diffusion length and planer structure. When two electrodes attached to the graphene are ferromagnets (FMs), the junction works as a spin field effect transistor with magnetoresistive effects. Because MR ratios observed are not large enough for device applications, and no clear mechanism for the MR has been presented, theoretical study of MR in two-terminal graphene junctions with ferromagnetic (FM) electrodes is desirable to clarify the mechanism and to provide a guiding principle for junction design.We perform tight-binding (TB) calculations of the conductance and MR in FM/graphene/FM junctions adopting several models for the electronic structure and the contact structure between the graphene and FM electrodes, and examine in detail the change in the electronic states near DPs caused by the contacts. It is shown that spin dependent shift of effective DPs caused by band mixing between the graphene and the electrodes plays an important role on MR. That is, the MR originates from a conflict between the DP shift in the up- and down-spin states in the antiparallel alignment of the FM magnetization. The MR ratio is independent of the graphene length because of a characteristic dependence of the tunneling conductance via states near the DP. The mechanism of the MR effect is different from those previously described, in that it is caused by contact with the electrodes. We further show that a huge MR effect may appear in junctions with electrodes made of FeCo, FeCr, and FeV alloys. The result is attributed to a suppression of conducting states in the majority spin state near the junction contacts, which indicates matching between DPs and conduction channel of electrodes becomes worse in the spin state.
9:30 PM - C6.3
Room Temperature Superparamagnetism Observed in Foam-like Carbon Nanomaterials.
Shunji Bandow 1 , Hirohito Asano 1 , Susumu Muraki 1 , Takahiro Mizuno 1 , Makoto Jinno 1 , Sumio Iijima 1
1 Materials Science and Engineering, Meijo University, Nagoya, Aichi, Japan
Show AbstractStable carbon nanomagnet can be formed by vaporizing the pure carbon target using a pulsed Nd:YAG laser (10 Hz) in H2 containing balance gas at 1000°C. Similar carbon nanomagnet was first developed by Rode et al in 2004 by using the high repetition rate (2-25 kHz) pulsed laser vaporization in pure Ar. However, the strong magnetism was observable only at low temperatures (< ~90 K). In the present sample, the magnetism was quite stable in open air, and the attraction of whole powder to the commercial magnet can be seen at room temperature. On the other hand, the carbon powder produced in pure Ar, no such magnetic attracting powder can be obtained. This control experiment guarantees that the observed magnetism is not from the spurious extrinsic origins, such as transition metals. Magnetic measurement by using SQUID showed that the magnetization at room temperature was easily saturated by ~10 kG with no hysteresis and the magnitude of the saturation magnetization (Ms) was in the range ~1 emu G/g. This corresponds to the spin concentration of 0.002μB per carbon atom. High temperature heat treatment in 1 atm of H2 flux (50 sccm) up to 800°C decreased the magnitude of Ms without changing the structure (XRD pattern), but the Ms was again recovered above 900°C H2 treatment. TEM observation cleared up the structural difference between the samples prepared in H2 containing environment and in pure Ar. Former sample probably has a structure illustratable by the sterically overlapped graphitized nanosheets. On the other hand, the latter one resembles the amorphous carbon. We consider the observed magnetism is fundamentally originated in the magnetic states of the zigzag edge of graphene, which is protected by air oxidation due to the sterically overlapped structure. Electron micrographs showed that that the structural morphology resembles the foam and the mean diameter of the powder is about 10 nm, but individual particles agglutinate through a part of the graphene sheets. Ultrasonic agitation in ethanol partially disintegrates such agglutination and only the magnetic active isolated foam-like nanoparticles can be obtained by the centrifugal separation.
9:45 PM - C6.4
WITHDRAWN 12/27/10 Current Enhancement by Compression of Buckled Carbon Nanotube Bundles.
Laishram Singh 1 , Karuna Kar Nanda 1
1 Materials Research Centre, Indian Institute of Science, Bangalore, Karnataka, India
Show Abstract A carbon nanotube (CNT) can be either metallic or semiconducting depending on the orientation between the atomic lattice and the tube axis. A strain can induce a band gap in a metallic NT and can modify the band gap in a semiconducting CNT. Here, we report on the synthesis and the current (I) - voltage (V) characteristics of semiconducting multiwall CNT bundles by compressing them. Millimeter long buckled CNTs are synthesis by co-pyrolysis of benzene and THF precursors using ferrocene as a source of catalyst. A special arrangement has been made to investigate the IV characteristics by compressing the bundles. Interestingly, it has been shown that the current through CNTs increases with compression and is believed to be due to the conversion of sp2 to some other form of hybridization. It has also been shown that the band gap can be evaluated from the IV curves and the band gap increases with compression. Overall, the band gap of CNTs can be tuned by twisting or compressing them. Raman study reveals that the characteristic frequencies of CNT shift to higher frequency side. In the compressed state, the walls come closer to each other, Raman peaks shifted to higher frequency due to the van der Waals interaction between the layers and walls. There is also increase in the intensity of disorder peak compared to graphitic peak. The detail results and discussion will be presented.
10:00 PM - C6.5
Intrinsic Twisting and Electronic Properties of Carbon Nanotubes : A First-principles Study.
Koichiro Kato 1 , Takashi Koretsune 1 , Susumu Saito 1
1 Department of Physics, Tokyo Institute of Technology, Meguro, Tokyo, Japan
Show AbstractIt is often thought carbon nanotubes (CNTs) are perfect cylinders made by rolling up a graphene sheet. In reality, however, there are undeniable possibilities that they possess structural deformations including twisted regions. As for chiral nanotubes, they may be twisted even at their ground state geometries because of their inherent helical structures. According to a density functional study, the electronic structures of CNTs sensitively depend on their geometry such as bond lengths and bond angles [1, 2]. Hence, electronic properties of deformed nanotubes should be of high interest and importance. In the present work, we study the energetics and electronic structures of twisted single-walled CNTs in the framework of the density functional theory (DFT) with the local density approximation. As for quite thin CNTs, we use conventional plane-wave DFT computational code [3]. In order to utilize the periodic boundary condition implemented in the plane-wave DFT code, we study CNTs under several discretized twisting conditions, and perform geometrical optimizations at each twisting conditions. On the other hand, because of a huge number of atoms in a translational unit cell for not only frequently synthesized chiral CNTs but also most kinds of twisted CNTs, we develop a real-space DFT computational code with helical-symmetry operation, and apply it to several kinds of nanotubes including experimentally abundant (6,5) nanotube. Their diameters are about 0.8 nm. In this computational code, the number of atoms in a unit cell becomes two for any type of nanotube. Therefore, we are able to perform geometrical optimizations including quasi-continuous twisting conditions for any type of nanotube in principle.As a result, it is found that chiral CNTs become more stable in slightly twisted geometry. This effect should be significant in CNTs with realistic length. Therefore, our results suggest that chiral nanotubes would possess the intrinsic twisting. We also report the twisting-level dependence of the electronic structures. It is found that the fundamental gaps of most kinds of CNTs sensitively depend on twisting level. Importantly, the directions of the intrinsic twisting are the same as the directions of enlarging the fundamental gap except for quite thin CNTs. The nearly free electron states play important roles in the electronic structures of quite thin nanotubes.This work was supported by the Global Center of Excellence Program by MEXT, Japan through the "Nanoscience and Quantum Physics" Project of the Tokyo Institute of Technology. K.K. also acknowledges JSPS Research Fellowship for Young Scientists.[1] K.Kanamitsu and S. Saito, J. Phys. Soc. Jpn 71, 483 (2002)[2] K. Kato and S. Saito, to appear in Physica E.[3] P. Giannozzi et al., http://www.quantum-espresso.org
10:15 PM - C6.6
The Mechanical Properties of Functionalized Graphene.
Qing-Xiang Pei 1 , Yong-Wei Zhang 1 , Vivek Shenoy 2
1 , Institute of High Performance Computing, Singapore Singapore, 2 Division of Engineering, Brown University, Providence, Rhode Island, United States
Show AbstractChemical functionalization of graphene via attachment of atoms or atomic clusters can serve as an effective means to modify, manipulate or control its physical, chemical, and mechanical properties. Chemical functionalization is also relevant for using graphene as hydrogen storage medium and for applications as a strengthening agent in composite materials. Although there is a considerable literature on chemical functionalization of graphene, most studies have focused on the effect of adsorbed atoms on the electronic and chemical properties of graphene. To the best of our knowledge, the influence of chemical functionalization on the mechanical properties of graphene remains almost unexplored. This is particularly important for applications of graphene as sensors or nanoresonators and in composite materials. Molecular dynamics simulations have been performed to investigate the mechanical properties of both hydrogen- and methyl- functionalized graphene. For H- functionalization, the coverage spans the entire range from graphene (H-0%) to graphane (H-100%). We find that the Young’s modulus, tensile strength, and fracture strain of the functionalized graphene deteriorate drastically with increasing H-coverage up to about 30%. Beyond this limit the mechanical properties remain insensitive to H-coverage. While the Young’s modulus of graphane is smaller than that of graphene by 30%, the tensile strength and fracture strain show a much larger drop of about 65%. We show that this drastic deterioration in mechanical strength arises both from the conversion of sp2 to sp3 bonding and due to easy-rotation of unsupported sp3 bonds. Our results suggest that the coverage-dependent deterioration of the mechanical properties must be taken into account when analyzing the performance characteristics of nanodevices fabricated from functionalized graphene sheets. For methyl functionalization, it is found that the mechanical properties of functionalized graphene greatly depend on the location, distribution and coverage of CH3 radicals on graphene. Surface functionalization exhibits a much stronger influence on the mechanical properties than edge functionalization. For patterned functionalization on graphene surfaces, the radicals arranged in lines perpendicular to the tensile direction lead to larger strength deterioration than those parallel to the tensile direction. For random functionalization, the elastic modulus of graphene decreases gradually with increasing CH3 coverage, while both the strength and fracture strain show a sharp drop at low coverage. When CH3 coverage reaches saturation, the elastic modulus, strength and fracture strain of graphene drop by as much as 18%, 43% and 47%, respectively.
10:30 PM - C6.7
Tailoring Graphene Band Structure by Strain.
Cocco Giulio 1 , Cadelano Emiliano 1 , Colombo Luciano 1
1 Department of Physics, University of Cagliari, Monserrato (Ca) Italy
Show AbstractThe zero-gap semiconductor nature of graphene is detrimental for its use in nanoelectronics, since it prevents the pinch off of charge current as requested in conventional devices. Different attempts have been therefore tried in order to induce a gap, including: quantum confinement of electrons and holes in graphene nanoribbons or quantum dots; growing graphene sheets on an appropriately chosen substrate, inducing a strain field controllable by temperature.In this work we exploit the concept of strain-induced band structure engineering in graphene through the calculation of its electronic band structure under uniaxial, shear, and combined uniaxial-shear deformations. We show that by combining shear deformations to uniaxial strains it is possible to modify the gapless nature of graphene, by inducing a tailored energy gap varying from zero to 0.9 eV.We also discuss the strain-driven drift and merging of Dirac points, which is involved into the gap opening process. Interestingly enough, the use of a shear component allows for a gap opening and Dirac points migration at moderate absolute deformations, safely smaller than the graphene failure strain.We finally discuss how strain affects the total electronic density of states and, in particular, the occurrence and position of its van Hove singularites, which are knwo to affect electron transport features and, possibly, the occurrence of superconductivity as well.
Symposium Organizers
John J. Boeckl Air Force Research Laboratory
Liming Dai Case Western Reserve University
Weijie Lu Fisk University
Mark H. Ruemmeli Leibniz Institute
IFW Dresden
Jamie Warner University of Oxford
C7: Structural Characterization
Session Chairs
Wednesday AM, December 01, 2010
Room 304 (Hynes)
9:30 AM - C7.1
Atomic Resolution Imaging of Defects in Free-standing, Single-layer CVD Graphene.
Pinshane Huang 1 , Arend van der Zande 2 , Carlos Ruiz-Vargas 1 , Ye Zhu 1 , Jiwoong Park 3 , Paul McEuen 4 , David Muller 1 4
1 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 2 Department of Physics, Cornell University, Ithaca, New York, United States, 3 Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States, 4 Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York, United States
Show AbstractWe demonstrate that using annular dark field (ADF) scanning transmission electron microscopy (STEM), we can both image graphene defects with atomic resolution and quickly characterize their densities on the scale of microns. Single-layer graphene (SLG) can be grown on metal substrates using chemical vapor deposition (CVD) and transferred onto arbitrary substrates, enabling practical graphene-based devices[1]. For these applications, it is critical to understand the structure of CVD grown SLG membranes and how this structure affects graphene’s properties. Defects in graphene may have interesting electronic[2], magnetic[3], chemical[4, 5], and mechanical properties, and thus the properties of graphene membranes may be strongly affected or even dominated by atomic-scale defects.In order to examine the structure of defects in single-layer CVD graphene grown on Cu, we make two key improvements. First, we utilize a fifth-order aberration-corrected NION ultra-STEM operated at 60kV. Low-voltage ADF STEM is an ideal technique with which to study atomic-scale defects because ADF images are high resolution, directly interpretable, and non-destructive. Therefore, with ADF-STEM we can detect each kind of possible graphene defect, including vacancies, substitutions in the graphene lattice[6], pentagon-heptagon rings, and extended dislocations. Second, we develop novel fabrication and cleaning methods to produce single sheets of suspended graphene with high yield (over 95% of the TEM grid) and/or extremely clean surfaces (atomically clean SLG for hundreds of nanometers). In previous studies [7], both large-scale characterization of defects and imaging of CVD graphene in the TEM have been hampered by the difficulty of suspending and cleaning a single layer of graphene on a TEM grid. Combined, our techniques enable both atomic-resolution defect imaging in the electron microscope and easy characterization at unprecedented large scales. We apply these methods to characterize defect density and other key issues regarding the properties of graphene defects and dislocations. We find that defect density varies by up to an order of magnitude between different growths, suggesting that defect formation depends strongly on growth conditions. Our fabrication and characterization techniques may thus provide an avenue toward the eventual control of the properties of single-layer graphene via defects.1.Li, X., et al., Science, 2009. 324(5932): p. 1312-1314.2.Lahiri, J., et al., Nature Nanotechnology, 2010. 5(5): p. 326-329.3.Cervenka, J., M.I. Katsnelson, and C.F.J. Flipse, Nat Phys, 2009. 5(11): p. 840-844.4.Boukhvalov, D.W. and M.I. Katsnelson, Nano Lett., 2008. 8(12): p. 4373-4379.5.Malola, S., H. Hakkinen, and P. Koskinen, Phys Rev B, 2010. 81(16): p. 165447.6.Krivanek, O.L., et al., Nature, 2010. 464(7288): p. 571-574.7.Gass, M.H., et al., Nature Nanotechnology, 2008. 3(11): p. 676-681.
9:45 AM - C7.2
In-situ Observations of Restructuring Carbon Nanotubes via Low-voltage Aberration-corrected Transmission Electron Microscopy.
Felix Boerrnert 1 , Alicja Bachmatiuk 1 , Sandeep Gorantla 1 , Jamie Warner 2 , Bernd Buechner 1 , Mark Ruemmeli 1 3
1 , IFW Dresden e. V., Dresden Germany, 2 , University of Oxford, Oxford United Kingdom, 3 , Technische Universität Dresden, Dresden Germany
Show AbstractThe molecular structureand dynamics of carbon nanostructures is much discussed throughout the literature, mostly from the theoretical side because of a lack of suitable experimental techniques to adequately engage the problem. A technique that has recently become available is low-voltage aberration-corrected transmission electron microscopy. It is a valuable tool with which to directly observe the atomic structure and dynamics of the specimen in situ. Time series aberration-corrected low-voltage transmission electron microscopy is used to study the dynamics of single-wall carbon nanotubes in situ. Stable junctions between a single carbon chain and two single-wall carbon nanotubes were produced via coalescence of functionalized fullerenes filled into a single-wall carbon nanotube and directly imaged. We also confirm experimentally previous theoretical predictions for the agglomeration of adatoms forming protrusions and subsequent ejection. In addition, the complete healing of an approximately 20 atom multi-vacancy in a nanotube wall is followed providing key insight into graphitisation phenomena at the atomic scale.
10:00 AM - **C7.3
Structure Control of Carbon Nanotube Films and Graphene on SiC.
Michiko Kusunoki 1 , Wataru Norimatsu 1
1 , Nagoya University, Nagoya Japan
Show AbstractCarbon nanotube (CNT) and graphene1) have attracted many researchers’ attention with the anomalous electronic properties for a long period. For actual application and further development of these superior materials, it is important to attain to perfection of control the crystallinity, structures and alignment. We have firstly reported that well-aligned and highly-dense CNT films are self-organized on SiC(000-1)C-face and graphene on (0001)Si-face by surface decomposition of SiC.2) In these phenomena, Si atoms are selectively removed from the surface by annealing SiC at high temperature (1300~1700°C) in a vacuum, and remaining carbon atoms construct well controlled CNTs or graphene on SiC without any metal catalysts. Transmission electron microscopy and electron diffraction patterns revealed that the CNTs on SiC(000-1) formed by controlling heating rate are mainly double-walled and mostly of zigzag-type.3) This is caused by that the CNT structure grown along the [0001]SiC direction inherits the crystalline skeleton of the pristine SiC.3, 4) On the other hand, stacking sequence of homogeneous several layers of graphene formed on SiC(0001) were also investigated by high-resolution transmission electron microscopy5). Graphene layers basically exhibited an ABC-type stacking. This is considered to be caused by the interaction between graphene and SiC.5) Furthermore, a multi-layered CNT/SiC stack structure was fabricated by repeated alternate deposition and surface decomposition of SiC.6) The newly deposited 3C-SiC layer on the CNT film was well crystalline; the CNTs produced by the decomposition of the 3C-SiC were as well aligned as the CNTs produced from pristine 6H-SiC. By appropriate choice of deposition and decomposition conditions we were able to produce alternating CNT and SiC layers of a controlled thickness.6)These nano-carbon structures on SiC formed by the surface decomposition method will be of great advantage to develop novel devices through further control of the structures in the near future. References1) K. S. Novoselov et al., Science 306, 666 (2004). 2) M. Kusunoki et al., Appl. Phys. Lett., 77, 531 (2000).3) S. Irle et al., J Chem. Phys., 125, 1 (2006).4) M. Kusunoki et al., Chem. Phys. Lett., 366, 458 (2002).5) W. Norimatsu and M. Kusunoki, Phys. Rev. B, 81,161410 (2010).6) T. Maruyama et al., Physica E 42, 767 (2010).
10:30 AM - C7.4
STM and STS Study of CVD Grown Graphene Nanoribbons.
Xiaoting Jia 1 , Minghu Pan 2 , Sreekar Bhaviripudi 3 , Vincent Meunier 2 , Jing Kong 3 , Mildred Dresselhaus 3 4
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractGraphene nanoribbons (GNRs) are quasi one dimensional structures which have unique transport properties, and have a potential to open a bandgap at small ribbon widths. They have been extensively studied in recent years due to their high potential for future electronics applications. We have experimentally found some GNRs in our CVD grown graphene layers. In this work, we investigated the morphology and electronic properties of these GNRs on top of a graphene layer transferred to a SiO2 substrate. Our results suggest that the GNRs have a surprisingly high crystallinity and a clean surface. We observed both folded and open edges in GNRs, as well as large diameter single wall carbon nanotubes. We have also studied the electronic properties of the GNRs using both room temperature and low temperature (at ~10K) STS. Our findings suggest that different electronic states may exist at GNR edges, when compared to the ribbon interior regions. Future investigations are needed to understand the mechanism for the formation of these CVD-grown ribbons and edge structures on the graphene layers.
11:15 AM - C7.5
Annular Dark Field Imaging of Chemical and Structural Defects in Single-layer Materials.
Matthew Chisholm 1 , Murai Regmi 1 , Gyula Eres 1 , Veena Krishnan 2 1 , Gerd Duscher 2 1 , Valeria Nicolosi 3
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials Science Department, University of Tennessee, Knoxville, Tennessee, United States, 3 Department of Materials, University of Oxford, Oxford United Kingdom
Show AbstractAberration correction has lead to remarkable improvements in scanning transmission electron microscopy in the last few years. It is now possible to reach probe sizes close to 0.1 nm at 60 keV, an operating energy that avoids direct knock-on damage in materials consisting of light atoms such as B, C, N, and O.1 Annular dark field imaging, because of its strong dependence on atomic number, allows the chemical identification of individual atoms, both heavy and light. We present images of graphene, monolayer boron nitride and carbon nanotubes in perfect form, with impurity substitution and with dislocations. The results show that an atom-by-atom structural and chemical analysis of all radiation-damage resistant atoms present in and on top of ultra-thin sheets has now become possible.This research was sponsored by the Materials Sciences and Engineering Division of the US Department of Energy.1 O.L. Krivanek et al., Nature 464 571 (2010).
11:30 AM - **C7.6
In-situ Evaluation of the Factors Controlling Carbon Nanotube Synthesis.
Renu Sharma 1
1 Center for Nanoscale Science and Technology and National Institute of Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractCarbon nanotubes (CNTs) are being investigated for a wide variety of applications; ranging from biotechnology to nanotechnology. Tremendous progress has been made in understanding their formation, for large scale synthesis and building CNT based devices. Generally CNTs are synthesized by catalytic chemical vapor deposition (C-CVD) using transition metal catalysts such as Ni, Fe, Co and hydrocarbons as carbon source. During the last five years, in situ observations using environmental transmission microscopy (ETEM) have played a crucial role in revealing atomic level structural transformations occurring during their nucleation and growth. We have combined in situ and ex situ measurements to demonstrate the importance of temperature and precursor pressure in controlling the structure and morphology of the CNTs. We have also used the column of the ETEM for site-specific deposition of Fe catalyst particles and revealed the atomic-level structural transformations occurring during nucleation and growth of CNTs. We have recently observed increased activity in tubular structure formation for samples with low amounts of Au (~20% nominal composition). Atomic resolution videos reveal that the graphene layers (the essential topological form of carbon for tubular growth) form at facets of the crystalline catalyst particles. Both in situ and ex situ analysis of the composition of the catalyst particles, effect of temperature and pressure on the morphology and structural mechanism for the formation of various morphologies observed will be presented.
12:00 PM - C7.7
Influence of Chirality and Environment on the Asymmetry of Raman Resonance Windows of Individual Single-walled Carbon Nanotubes.
Mario Hofmann 1 , Ya-Ping Hsieh 1 , Jing Kong 1 , Martin Kalbac 3 , Ado Jorio 2 , Mildred Dresselhaus 1
1 , MIT, Cambridge, Massachusetts, United States, 3 , Academy of Sciences of the Czech Republic, Prague Czechia, 2 , Universidade Federal de Minas Gerais, Belo Horizonte Brazil
Show AbstractResonance Raman excitation profiles (REPs) of individual single-walled carbon nanotubes were investigated.An asymmetry in these profiles was observed. This asymmetry is related to different intensities of the resonant scattering processes contributing to the REP. The chiral angle (θ) dependence of the asymmetry was found to be caused by variations in the defect density with θ. Our analysis suggests that the doping of nanotubes by adsorbates is the reason for changes to the REP shape. Consequently the resonance window width could be smaller than predicted, and could also be affected by environmental changes. Implications of these observations for nanotube metrology are discussed.
12:15 PM - C7.8
Calculation of the D band Raman for Armchair-edged Graphene Nanoribbons.
Eduardo Barros 1 , Kentaro Sato 2 , Antonio Souza Filho 1 , Riichiro Saito 2
1 Physics, Universidade Federal do Ceará, Fortaleza`, Ceara, Brazil, 2 Physics, Tohoku University, Sendai, Tohoku, Japan
Show AbstractOne of the main problems concerning the application of graphene for nanoelectronic devices is the defect scattering at the edges. For this reason, a good comprehension of the electron-defect scattering processes at the edges of graphene nanoribbons is of great importance. In this sense, Raman spectroscopy has been widely used to access information on the presence of structural defects through the analysis of the defect-related Raman peak known as the D band. To better understand the role of the defect on the D band intensity within the double resonance Raman scattering it is necessary to calculate the elastic scattering amplitude between electronic states of different eigenvectors. The elastic scattering amplitude can be obtained using the T-matrix formalism through the calculation of the eigenfunctions for the perturbed system by direct diagonalization of the perturbed Hamiltonian. This calculation results in a scattering amplitude which includes all multiple scattering processes, and not only the single scattering process (which corresponds to the first Born approximation for the scattering amplitude). In a previous publication, the D band intensity dependence on excitation energy and crystallite size was calculated within the first Born approximation for a nearest-neighbors tight-binding approach in armchair edged graphene ribbons.[2] Although this approximation can give insight to the overall properties of the D band Raman peak, the Born approximation only considers a single scattering event. Although for some systems this is known to give a good approximation, the question of the importance of the contribution or multiple scattering processes to the total scattering amplitude needs to be addressed. In this work we calculate the D band Raman peak for armchair-edge scattering in graphene. The T matrix is calculated an armchair-edged graphene ribbon using an extended tight-binding and model with density-functional-theory-based parameters and considering contributions from up to 7 nearest neighbors. Our results show that the contribution from the multiple scattering is of the same order of magnitude as the first born approximation thus confirming the importance of considering such processes. The D band intensity is shown to depend on the inverse of the ribbon width, as experimentally observed, and on the inverse cube of the laser excitation energy.[1] M. A. Pimenta, et al, Phys. Chem. Chem. Phys., 9, 1276, (2007).[2] K. Sato, et al, Chem. Phys. Lett. 427, 117 (2006).[3] D. Porezag, et al, Phys. Rev. B 51, 12947 (1995).
12:30 PM - C7.9
Raman Spectroscopy Study of Graphene and Few-layer Graphene Grown by Chemical Vapor Deposition.
Xuesong Li 1 , Shanshan Chen 1 , Carl Magnuson 1 , Weiwei Cai 1 , Richard Piner 1 , Luigi Colombo 2 , Rodney Ruoff 1
1 , UT Austin, Austin, Texas, United States, 2 , Texas Instruments Incorporated, Dallas, Texas, United States
Show AbstractXuesong Li1, Shanshan Chen1, Carl Magnuson1, Weiwei Cai1, Richard Piner1, Luigi Colombo2, and Rodney S. Ruoff11Dept. of Mech. Engineering and the Texas Materials Institute, The University of Texas at Austin2Texas Instruments Incorporated, Dallas, TXGraphene and few-layer graphene (FLG) have attracted increasing attention over the last few years.1-3 Accurate determination of the carbon atom stacking order and number of layer determination is important since both the number of layers and stacking order are closely related to the electrical properties. Raman spectroscopy is a commonly used technique for probing the number of graphene layers, the stacking order, evaluation of crystal quality, charged impurity detection, mechanical strain measurement, and more.4, 5 Most of graphene and FLG films characterized to date were formed by exfoliation of bulk graphite. Recently, chemical vapor deposition (CVD) of hydrocarbons on metal substrates has shown promise for large area and scaled production of graphene and FLG. 6-10 Recently, we have also succeeded growing large area FLG with various number of layers and stacking orders using CVD of methane on Cu foils. Given the growing importance of CVD-grown graphene and FLG, we thought it important to systematically study these films by Raman spectroscopy. Raman spectroscopy of the CVD grown films shows features that have not been reported in graphene and FLG obtained by micromechanical exfoliation. Our results are important in teaching about the use of Raman spectroscopy for characterization of CVD-grown graphene and FLG.References1.Geim, A. K.; Novoselov, K. S. Nat. Mater. 2007, 6, 183-191.2.Geim, A. K. Science 2009, 324, (19), 1530-1534.3.Orlita, M.; Potemski, M. Semiconductor Science and Technology 2010, 25, (6).4.Ferrari, A. C. Solid State Communications 2007, 143, (1-2), 47-57.5.Malard, L. M.; Pimenta, M. A.; Dresselhaus, G.; Dresselhaus, M. S. Physics Reports-Review Section of Physics Letters 2009, 473, (5-6), 51-87.6.Yu, Q.; Lian, J.; Siriponglert, S.; Li, H.; Chen, Y. P.; Pei, S.-S. Appl. Phys. Lett. 2008, 93, 113103.7.Reina, A.; Jia, X.; Ho, J.; Nezich, D.; Son, H.; Bulovic, V.; Dresselhaus, M. S.; Kong, J. Nano Lett. 2009, 9, 30-35.8.Sutter, P. W.; Flege, J.-I.; Sutter, E. A. Nat. Mater. 2008, 7, 406-411.9.Kim, K. S.; Zhao, Y.; Jang, H.; Lee, S. Y.; Kim, J. M.; Kim, K. S.; Ahn, J.-H.; Kim, P.; Choi, J.-Y.; Hong, B. H. Nature 2009, 457, 706-710.10.Li, X. S.; Cai, W. W.; An, J. H.; Kim, S.; Nah, J.; Yang, D. X.; Piner, R. D.; Velamakanni, A.; Jung, I.; Tutuc, E.; Banerjee, S. K.; Colombo, L.; Ruoff, R. S. Science 2009, 324, 1312-1314.
12:45 PM - C7.10
Structural Evolution During the Reduction of Chemically Derived Graphene Oxide.
Vivek Shenoy 1
1 , Brown University, Providence, Rhode Island, United States
Show AbstractWe present an atomistic description of progressively reduced graphene oxide (GO) using molecular dynamics simulations[1]. The calculations reveal that thermal annealing of GO leads to the formation of highly stable carbonyl and ether residual oxygen functional groups that hinder the complete regraphitization of rGO, even when annealed at very high temperatures. The thermally activated interplay between carbon and oxygen, responsible for incorporation of oxygen in- and out-of-plane, has been elucidated. Defects and crystallographic distortion of the hexagonal graphene structure are also studied as a function of the chemical composition and the heating temperature. The calculations are supported by infrared and X-ray photoelectron spectroscopy measurements on GO at different stages of reduction. The information regarding the atomic structure and configuration of residual oxygen groups provides insight into the fundamental electronic transport limitations of reduced GO. Finally, a scheme for more effective reduction treatment towards achieving complete regraphitization is proposed based on our detailed theoretical analysis. [1] A. Bagri, C. Mattevi, M. Acik, Y. J. Chabal, M. Chhowalla, V. B. ShenoyStructural evolution during the reduction of chemically derived graphene oxideNATURE CHEMISTRY DOI: 10.1038/NCHEM.686 JUNE 2010
C8/UU8: Joint Session: Optical Probes
Session Chairs
Lorenzo Marucci
Mark Rummeli
Wednesday PM, December 01, 2010
Room 304 (Hynes)
2:30 PM - C8.1/UU8.1
A Fully Automated Remote Controllable Microwave-based Synthesis Setup for Colloidal Nanoparticles with an Integrated Absorption and Photoluminescence Online Analytics.
Michael Krueger 1 2 , Simon Einwaechter 1 2
1 Freiburg Materials Research Centre (FMF), University of Freiburg, Freiburg Germany, 2 Institute for Microsystems Technology, University of Freiburg, Freiburg Germany
Show AbstractWe present a fully automated microwave-based synthesis setup for colloidal nanoparticles. An integrated absorption and photoluminescence online analytics opens the possibility to monitor the growth of various nanoparticles at any stage of the reaction. Spectroscopic investigation within the first seconds of a reaction is accessible opening the possibility to detect potential critical size nuclei as a function of the reaction conditions. Beside the possibility to perform systematic mechanistic studies, this system allows a high degree of synthesis control leading to a very good product reproducibility. In conjunction with an automated autosampler unit systematic multiple reactions can be performed one after each other and compared. The setup is intended to be remote-controllable allowing worldwide online control accessibility over the synthesis setup including data processing, visualisation and storage. The performance of the setup will be demonstrated by using the synthesis of CdSe nanocrystals as a model system and will be extended to the synthesis of various metallic and semiconducting nanoparticles.
2:45 PM - C8.2/UU8.2
Direct Measurements of Exciton Mobility in Single-walled Carbon Nanotubes Using Far-field Near-infrared Fluorescence Microscopy.
Dmitri Tsyboulski 1 , R. Bruce Weisman 1 , Anton Naumov 1
1 Chemistry, Rice Universtiy, Houston, Texas, United States
Show Abstract The discovered effect of stepwise quenching of photoluminescence (PL) signal from semiconducting single-walled carbon nanotubes (SWCNTs) by single molecule reactions suggested extensive mobility of excitons in these one-dimensional structures. The mobility of excitons can be assessed by measuring a change of SWCNT PL intensity ΔI after the single-molecule quenching event relative to its total PL intensity value I, normalized per unit of SWCNT length L. Thus, the average exciton mobility Λ will be given simply as Λ=L*ΔI/I. Using this method, the range of exciton mobility as high as 240 nm was reported for selected SWCNT structures. This measurement of Λ parameter is valid under assumption that reaction events quench excitons in the vicinity of a defect with a 100% probability. We note, that this underlying assumption has never been verified. In this report, we demonstrate a new method to directly measure exciton mobility with far-field near-infrared fluorescence microscopy. Within a framework of exciton diffusion model, the exciton quenching profile along the nanotube is given as exp(-|x|/Λ), where x is the distance from the defect location. The later function decays slower that the corresponding point spread function (PSF) of an optical system ~ exp(-x2). Hence, it is possible to partially resolve fluorescence quenching profile along SWCNT length. Indeed, when we compute differential images of SWCNTs before and after quenching reaction events, the asymmetric quenching profiles with aspect ratio ~ 2-3 become apparent. The measured profiles are numerically fitted with convolution of PSF and exp(-|x|/Λ) function to determine Λ values for a particular nanotube structure. The measured variations of exciton mobility for a range of SWCNT structures well be presented and discussed.
3:00 PM - **C8.3/UU8.3
Laser Interactions and Real-Time Diagnostics in Nanomaterial Synthesis.
David Geohegan 2 3 , Christopher Rouleau 2 3 , Gyula Eres 3 , Mina Yoon 3 , Murari Regmi 3 , Jeremy Jackson 3 , Junsoo Shin 3 , Amit Goyal 3 , Karren More 1 2 , Norbert Thonnard 3 , Jason Readle 3 2 , Gerd Duscher 4 2
2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 1 SHaRE Facility, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Dept. of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractLaser interactions with materials are explored for the growth of novel nanomaterials, both as sources of energy to provide unique, nonequilibrium synthesis conditions and also as spectroscopic probes for real-time diagnostics of the growth environment. Time-resolved, in situ spectroscopy and imaging techniques are described to investigate processes involved in thin film and nanomaterials synthesis through the remote characterization of species concentrations, the measurement of growth kinetics, and the development of growth models. Progress in the design of pulsed laser and pulsed gas-growth environments to explore the synthesis of novel nanomaterials such as carbon nanohorns, graphene, and vertically-aligned carbon nanotube arrays as well as functional oxide nanoparticles and nanowires will be described. Variations in the synthesized product distribution of nanostructures are shown to result from the competition between kinetic and thermodynamic pathways. Examples of laser-synthesized nanomaterials designed for enhanced functionality in energy applications of hydrogen storage and optoelectronics will be presented. This work supported by the U.S. Dept. of Energy, Office of Science, Basic Energy Sciences. Fundamental studies of synthesis are supported by the Division of Materials Sciences and Engineering, with materials characterization support from the Division of Scientific User Facilities. Hydrogen storage measurements provided through the Hydrogen Sorption Center of Excellence, U.S. DOE-EERE.
3:30 PM - C8.4/UU8.4
Temperature Dependence of Silver Nanoparticles Dielectric Function as Observed by in situ and Real Time Spectroscopic Ellipsometry.
Scott Little 1 , Sylvain Marsillac 1 , Robert Collins 1
1 Physics and Astronomy, University of Toledo, Toledo, Ohio, United States
Show AbstractA broadband analysis of silver nanoparticles optical properties was achieved as a function of temperature via in situ real-time spectroscopic ellipsometry (RTSE). The silver nanoparticles were deposited at room temperature by d.c. magnetron sputtering onto thermally oxidized Si (100) wafers using a high purity 2 in diameter silver target in argon. A 4 mTorr argon pressure and 10 W d.c. target power was maintained throughout the deposition process. Various deposition times were employed, varying from 30 seconds to 2 minutes. RTSE data were acquired in situ using a rotating-compensator multichannel ellipsometer spanning the photon energy range from 0.75 to 6.50 eV at an angle of incidence of 65°. The presence of nanoparticles was confirmed via the analysis of the imaginary part of the dielectric function, where no free electron behavior was observed while a particle plasmon polariton (PPP) transition as well as an interband transition were modeled by a Lorentzian oscillator and a generalized critical point oscillator, respectively. Ex situ measurements were also used to confirm the presence of nanoparticles. The temperature dependence of the dielectric function of these films was monitored in situ and in real time from room temperature up to 873 K, and back down to room temperature. A steep reduction in PPP oscillator strength and increase in PPP energy suggests an increase in void fraction which may arise due to melting of small particles and wetting of the surface, or suggests a change in the particle shape. The lifetime term of the PPP oscillator is also changing due to the temperature, in agreement with the Mayadas equation, which relates the lifetime term to the particle size. A more abrupt change in these parameters at specific temperatures, varying with particle size, suggests that the melting point of particles of average size has been reached. This lower melting temperature for the silver nanoparticles, compared to bulk material, is consistent with previous studies that demonstrate the depression of the melting point.
3:45 PM - C8.5/UU8.5
Absorption Backgrounds in Single-walled Carbon Nanotube Spectra.
Anton Naumov 1 , Saunab Ghosh 2 , Dmitri Tsyboulski 2 , R. Bruce Weisman 2
1 Applied Physics Program, Rice University, Houston, Texas, United States, 2 Chemistry, Rice University, Houston, Texas, United States
Show AbstractThe source of broad backgrounds in visible-near-IR absorption spectra of single-walled carbon nanotube (SWCNT) dispersions was explored through a series of controlled experiments. Chemical functionalization of nanotube sidewalls generates a background absorption while broadening and red-shifting resonant transitions. Extensive ultrasonic agitation can induce a similar background component that may reflect unintended chemical changes to the SWCNTs. Only minor spectral differences are seen among length-separated fractions with nanotube lengths down to ~50 nm. If present, amorphous carbon content contributes to background absorption. Samples containing many SWCNT structural species can have overlapping resonant absorption bands that lead to elevated backgrounds from spectral congestion. Nanotube aggregation broadens resonant bands and increases such congestion backgrounds. However, there is essentially no background in well-dispersed samples enriched in a specific pristine semiconducting(n,m) species. By contrast, samples enriched in metallic SWCNTs show broad absorption backgrounds that appear to be intrinsic. Knowledge of spectral background effects should enhance the value of absorption spectroscopy for analyzing the compositions and purity of SWCNT samples.
C9: Electronic, Optical, and Magnetic Properties of Carbon Nanomaterials II
Session Chairs
Wednesday PM, December 01, 2010
Room 304 (Hynes)
4:30 PM - C9.1
Transport and Optical Studies of Graphene Fluoride: A Wide Bandgap Material Derived from Graphene.
Bei Wang 1 , Shih-Ho Cheng 1 , Humberto Gutierrez 1 , Ke Zou 1 , Ning Shen 1 , Awnish Gupta 1 , Qingzhen Hao 1 , Peter Eklund 1 , Fujio Okino 2 , Jorge Sofo 1 , Jun Zhu 1
1 , Penn State University, University Park, Pennsylvania, United States, 2 , Shinshu University, Tokido, Ueda, Japan
Show AbstractWe report the synthesis, electrical and optical properties of graphite fluoride and graphene fluoride, a two-dimensional wide bandgap semiconductor derived from graphene. Graphite fluoride is synthesized by reacting graphite with fluorine gas at temperatures up to 600 C. X-ray diffraction, transmission electron microscope and electron diffraction measurements show the resulting compound consists of weakly coupled layers where the in-plane lattice displays hexagonal symmetry with a lattice constant that is 4.5% larger than that of graphene and a lateral nanocrystalline domain size of ~ 30 nm. The stoichiometry is predominantly graphite monofluoride, (CF)n. Similar to graphane (CH), crystalline CF is expected to be a wide bandgap material with a band gap greater than 3.5 eV and may be of significant technological import for electronic and electro-optical applications. We perform transport and photoluminescence measurements to explore these previously untapped potentials. Thin sheets of graphene fluoride are obtained by mechanical exfoliation of graphite fluoride and made into transport devices. Graphene fluoride exhibits strongly insulating behavior with resistance exceeding 10 GΩ at room temperature, confirming the large band gap. The electrical conduction in graphene fluoride is well described by variable-range hopping in two dimensions, which we attribute to the presence of mid-gap defect states. Highly conductive graphene (sheet resistance of 100 kΩ at room temperature) can be recovered by annealing CF in Ar/H2 to remove fluorine, resulting in a conductance change of five orders of magnitude. We further demonstrate through photoluminescence (PL) measurements using a range of excitation energies that CF emits in five distinct wavelength windows (1.7, 1.9, 2.1, 2.2, 2.9 eV) from near infrared to near ultraviolet. PL studies at variable temperatures from 5 K to 300 K again point to mid-gap defects as the origin of the emissions. We discuss possible sources, together with density functional theory calculations for a few candidates. Graphene fluoride offers an alternative pathway to control the band structure and conductivity of graphene. Further improvement of the crystalline quality and defect engineering may lead to optical applications currently lacking in graphene due to the absence of a band gap. References:S. Cheng, Z. Ke, F. Okino, H.R. Gutierrez, A. Gupta, N. Shen, P. Eklund, J.O. Sofo, and J. Zhu, “Reversible fluorination of graphene: towards a two-dimensional wide band gap semiconductor”, Phys. Rev. B 81, 205435 (2010)Wang et al, “Photoluminesence from graphite fluoride”, to be submitted
4:45 PM - C9.2
Correlating Domain Sizes with Carrier Mobility in Large-scaled Graphene Films: Raman Spectral Signatures for Domain Size Estimation.
Jeong-Yuan Hwang 1 , Chun-Chiang Kuo 2 , Li-Chyong Chen 1 , Kuei-Hsien Chen 2 1
1 Centre for Condensed Matter Sciences, National Taiwan University, Taipei Taiwan, 2 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei Taiwan
Show AbstractLarge-scaled graphene films have been successfully prepared by chemical vapor deposition (CVD) method. The layer number and the crystal quality are examined by using Raman spectroscopy. With careful control of growth parameters, such as gas compositions and the growth temperature, monolayer-dominant graphene films with different D peak intensity in Raman spectra can be obtained. Generally D peak indicates the existence of structural disorder and its intensity suggests the defect density, or the crystallite size. The graphene domain sizes are then estimated by the intensity ratios of D to G peak and the preliminary results show a good correspondence to the carrier mobility obtained by Hall measurement: the larger domain size, the higher mobility. In our observations, the CH4/H2 ration at growth stage and the H2 incorporation in cooling stage show the most important influences on graphene properties. With the best growth conditions, a cm-scaled graphene film with carrier mobility ~1350 cm2/Vsec (p-type in air) and a calculated crystallite size ~950 nm can be obtained. Further studies are underway for the electrical and optical characterizations of these domain-dependent graphene films.
5:00 PM - C9.3
Opening of a Tunable Bandgap in Graphene via Oxygen Plasma Treatment: A Building Block for Graphene-based Electronics.
Amirhasan Nourbakhsh 1 , Mirco Cantoro 1 , Geoffrey Pourtois 1 , Afshin Hadipour 1 , Francesca Clemente 1 , Tom Vosch 3 , Marleen van der Veen 1 , Marc Heyns 1 , Stefan De gendt 1 , Bert Sels 2
1 , IMEC, Leuven Belgium, 3 Department of Chemistry, Katholieke Universiteit Leuven, Leuven Belgium, 2 Department of Microbial and Molecular Systems, Katholieke Universiteit Leuven, Leuven Belgium
Show AbstractThe results of experiments devoted to the modification of the pristine electronic properties of single-layer graphene by means of an oxygen plasma will be illustrated. Electrical characterization and photoluminescence measurements are carried out to investigate the opening of a bandgap in plasma-treated graphene; such a bandgap can be tuned by changing the plasma parameters. Modified graphene exhibits a ~2 eV optical bandgap and p-type semiconducting behavior; back-gated FETs with modified graphene as active channel possess on/off ratio up to 4 orders of magnitude. The experimental results are explained in terms of a functionalization of the pristine sp2 graphene lattice with chemisorbed epoxy groups. The effects of epoxidation on graphene optoelectronic properties are further investigated by ab initio calculations carried out in a DFT framework. They confirm that progressively larger bandgaps are introduced in graphene upon functionalization with increasing amount of oxygen. Furthermore, we demonstrate the potential of metal-contacted plasma-treated graphene rectifying junctions to fabricate Schottky diodes with turn-on voltages below 0.5 V. The use of low- (Al, Yb) and high- (Pd, Pt) work function metals, directly in contact with modified graphene, allows for the modulation of the Schottky barrier. Our results suggest that an oxygen plasma treatment represents a valid approach to control graphene chemistry toward tunable-bandgap graphene-based electronics.
5:15 PM - C9.4
Local Density of States and Differential Conductance of Graphene After UV/Ozone and Oxygen Plasma Treatments.
Adi Wijaya Gani 1 , Adrianus Aria 2 , Morteza Gharib 2
1 Electrical Engineering, California Institute of Technology, Pasadena, California, United States, 2 Graduate Aeronautical Laboratories, California Institute of Technology, Pasadena, California, United States
Show AbstractIn recent years, a lot of investigations have been done to understand the electrical properties of graphene under various treatment conditions, but currently there exists only a few instances in literature that correlate electrical properties of graphene and its degree of oxidation. Here we present an investigation of electrical properties of oxidized graphene by utilizing the spectroscopy capability of Scanning Tunneling Microscopy (STM), namely Scanning Tunneling Spectroscopy (STS).In this study, two oxidizing methods were performed on graphene samples: UV/ozone and oxygen plasma treatment. UV/ozone treatment is a well-known process of oxidizing carbon-based structures that can be easily done at room temperature and atmospheric pressure. While its operational requirement is simpler, UV/ozone treatment generally provides lower oxidizing energy than the oxygen plasma treatment. As a result, oxygen plasma treatment can in general provide a higher degree of oxidation.Before the electrical properties of oxidized graphene were probed using STS, its surface was imaged using STM. In agreement with previous studies, atomic-resolution imaging of the surface of oxidized graphene showed rough topography with randomly-distributed defects. These defects were verified using Raman spectroscopy. The absolute intensity ratio of the D and G bands (ID/IG) was considerably higher for the samples that had been exposed to oxidation process. The sample that was treated by oxygen plasma showed higher ID/IG than the sample that was exposed to UV/ozone treatment. These findings indicate the degree of defects of oxidized graphene is proportional to the amount of oxidizing energy given during the treatments.In both oxidation treatments, the distribution of Local Density of States (LDOS) of graphene was observed to be more spread-out than the distribution of LDOS of untreated graphene, indicating more availability of higher energy states to be occupied by electrons. The degree of LDOS spreading was observed to be proportional to the amount of oxidizing energy. In addition, lower graphene conductance at low bias voltage was observed on a graphene sample that was exposed to stronger oxidizing energy. The damage done to graphene’s structural integrity caused by the treatments may contribute to the observed lower conductance values. In addition to the lower conductance, the differential conductance of treated graphene showed some degree of flattening around the zero-bias region, which indicates less variation of conductivity values at low bias voltage.We have shown that the degree oxidation of graphene influences its LDOS and differential conductance. This implies that the LDOS and differential conductance of graphene may be adjusted by varying the amount of oxidizing energy during the oxidation process. These findings are likely important for further understanding the electrical properties of graphitic structures and future applications of carbon-based electronics.
5:30 PM - C9.5
Electrons, Phonons and Electron-phonon Interactions in Bilayer Graphene Investigated by Resonance Raman Scattering.
Marcos Pimenta 1
1 Departamento de Fisica, UFMG, Belo Horizonte, Minas Gerais, Brazil
Show AbstractRaman spectroscopy is a very useful tool to study graphene samples, since it furnishes information about the graphene structure, presence of disorder, defects, charges, strain, etc. However, important information about electrons can be also obtained in a Resonance Raman investigation, where the energy of the laser excitation can be tuned. We will present experimental results of the dispersion of electrons and phonons in bilayer graphene obtained from a resonant Raman study using different laser energies in the visible and NIR range. The electronic structure will be discussed within the tight-binding approximation. We will show that the Kohn anomaly of the phonon branches near the K point is different for the symmetric and anti-symmetric branches, and results evidence the importance of considering electron-phonon and electron-electron interactions. We will also present results in gated graphene devices where the position of the Fermi level can be changed by applying a gate voltage, which splits the Raman G band. The dependence of the position, linewidth and intensity of these components on the charge concentration in the bottom and top layers will be presented and compared to theoretical predictions.
C10: Poster Session: Characterizations and Properties of Low-dimensional Nanocarbon Structures
Session Chairs
Thursday AM, December 02, 2010
Exhibition Hall D (Hynes)
9:00 PM - C10.1
Properties of Wrinkles in Graphene.
MiJung Lee 1 , Jin-Sik Choi 1 , Ik-Su Byun 1 , Duk-hyun Lee 1 , Seung-Woong Lee 1 , Bae-Ho Park 1
1 , konkuk university, Seoul Korea (the Republic of)
Show AbstractIn the past few years, considerable theoretical and experimental interest has been focused on the study of graphene which is two-dimensional structure of monolayer carbon atoms. Exfoliation methods provide us high quality two-dimensional graphene sheet for study its peculiar properties. The surface of exfoliated graphene has a nano scale local corrugations. To study properties of local corrugations is important because they exert influence on electrical properties of grapheme[1-2]. In our study, we have successfully formed wrinkles in exfoliated monolayer graphene intentionally and investigated their morphological, physical and chemical properties. The topography of graphene wrinkles were studied by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Moreover, the structural and electrical properties of graphene wrinkles were analyzed by friction mode of AFM, and electrostatic force microscopy (EFM), respectively. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (MEST) (KRF-2008-314-C00111). [1] Ke Xu,Peigen Cao, and James R. Heath. Nano Lett. 2009, 9, 4446-4451. [2] Zhang, Y. B.; Brar, V. W.; Wang, F.; Girit, C.; Yayon, Y.; Panlasigui, M.; Zettl, A.; Crommie, M. F. Nat. Phys. 2008, 4, 627
9:00 PM - C10.10
Electrogenerated Chemiluminescence from Carbon Dots.
Liangfeng Sun 1 3 4 , Md. Rashid 4 , Yue Wang 2 4 , Byung-Ryool Hyun 3 , Adam Bartnik 1 3 , George Malliaras 2 , Frank Wise 3 , Emmanuel Giannelis 2 4
1 Center for Nanoscale Systems, Cornell University, Ithaca, New York, United States, 3 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 4 KAUST-Cornell Center for Energy and Sustainability, Cornell University, Ithaca, New York, United States, 2 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractFluorescent semiconductor quantum dots have generated broad promising applications including biological labeling and solid-state lighting. Nanometer-size carbon dots which are the counterparts of silicon nanoparticles now light up. Although the typical photoluminescence quantum efficiency of carbon dots is not high yet, they are non-blinking [1] and have large two-photon absorption cross section [2] which are favorable for one-photon or two-photon bio-imaging. Here we report another interesting property of carbon dots: they emit light under charge injection. We synthesized carbon dots in diameter about 10 nm using wet chemistry methods [3]. The photoluminescence quantum efficiency of the carbon dots dissolved in water was about 3%. The experiment setup for measuring the luminescence through charge injection was similar to a typical cyclic voltammetry measurement [4]. A glassy carbon disk was used as the working electrode while a platinum wire was used as the counter electrode. The sample was prepared by dissolving carbon dots into an acetonitrile solution with tetra-n-butylammonium perchlorate (TBAP) as the electrolyte. As we scanned the voltage between -2V and +2V, we observed strong electrogenerated chemiluminescence (ECL) from the sample. We found the ECL from carbon dots is as strong as that from [Ru(bpy)3](PF6)2 (a textbook material for ECL) even though the injection current is much lower. This observation of ECL from carbon dots indicates that they could be a good candidate material for carbon-based electroluminescent devices. Reference:1.Y.-P. Sun et al, J. Am. Chem. Soc. 2006, 128, 77562.L. Cao et al, J. Am. Chem. Soc. 2007, 129, 113183.A. B. Bourlinos et al, Small 2008, 4, 4554.L. Sun et al, Nano Lett. 2009, 9, 789
9:00 PM - C10.11
The Role of the Dielectric Constant for the Excitonic Transition Energy of Single-Wall Carbon Nanotubes.
Paulo Araujo 1 , Ahmad Nugraha 2 , Kentaro Sato 2 , Mildred Dresselhaus 3 , Richiiro Saito 2 , Ado Jorio 1
1 Departamento de Física - ICEx, Universidade Federal de Minas Gerais, Belo Horizonte Brazil, 2 Department of Physics, Tohoku University, Senday Japan, 3 Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe measured optical transition energies Eii of single-wall carbon nanotubes are compared with bright exciton energy calculations. The Eii differences between experiment and theory are minimized by considering first, a diameter/chiral angle-dependent dielectric constant and second, a diameter/exciton size-dependent dielectric constant, which comprises the screening from the tube and from the environment. We discuss the main aspects of each approach and show that in the first case, different dependencies are obtained for (ES11, ES22, EM11) relative to (ES33, ES44) which is understood as follows: A changing environment changes the diameter dependence for (ES11, ES22, EM11), but for (ES33, ES44) the environmental effects are minimal. We show that in order to achieve a single dependence for all Eii, the exciton's size should be taken into account, as considered in the second approach. The resulting calculated exciton energies reproduce experimental Eii values within 50 meV for a diameter range (0.7< dt <3.8 nm) and 1.2 < Eii <2.7 eV, thus providing a theoretical justification for Eii, environmental effects and important insights on the dielectric screening in one-dimensional structures.
9:00 PM - C10.12
Modelling of Graphene-based NEMS.
Irina Lebedeva 1 2 3 , Andrey Knizhnik 2 3 , Andrey Popov 4 , Yurii Lozovik 1 4 , Boris Potapkin 2 3
1 , Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region, Russian Federation, 2 , Kintech Lab Ltd, Moscow Russian Federation, 3 , RRC Kurchatov Institute, Moscow Russian Federation, 4 , Institute of Spectrocopy, Troitsk, Moscow Region, Russian Federation
Show AbstractThe possibility of designing nanoelectromechanical systems (NEMS) based on the relative motion or relative vibrations of graphene layers is analyzed. Ab initio and empirical calculations are performed to study the potential relief of the interlayer interaction energy of bilayer graphene. A new potential based on the density functional theory calculations with dispersion correction is developed to reliably reproduce the potential relief of the interlayer interaction energy of bilayer graphene. Telescopic oscillations and small relative vibrations of graphene layers are investigated using molecular dynamics simulations. It is shown that these vibrations are characterized with small Q-factor values. For this reason, graphene is less suitable for the use in the gigahertz oscillator and nanoresonator than carbon nanotubes. However, this property makes graphene perfect for the use in fast-responding nanorelays and memory cells. Due to the small Q-factor values, no oscillations occur upon switching the position of the movable layer in graphene-based nanorelays and memory cells. Therefore, the graphene-based nanorelayers and memory cells should be characterized with the smallest possible switching times.
9:00 PM - C10.13
Are Oxygen-terminated Zigzag Graphene Nanoribbons Metallic or Semiconducting? A Hybrid Density Functional Theory Study.
Ashwin Ramasubramaniam 1
1 , University of Massachusetts, Amherst, Massachusetts, United States
Show AbstractThe size-dependent electronic structure of oxygen-terminated zigzag graphene nanoribbons is investigated using standard density functional theory (DFT) with an exchange-correlation functional of the generalized gradient approximation form as well as hybrid DFT calculations with two different exchange-correlation functionals. Hybrid DFT calculations, which typically provide more accurate band gaps than standard DFT, are found to predict semiconducting behavior in oxygen-terminated zigzag graphene nanoribbons; this is in distinct contrast to standard DFT with (semi)local exchange-correlation functionals, which have been widely employed in previous studies and shown to predict metallic behavior. (Semi)local exchange-correlation functionals employed in standard DFT calculations cause unphysical delocalization of lone pairs from the oxygen atoms due to self-interaction errors and lead to metallic behavior. Hybrid DFT calculations do not suffer from this spurious effect and produce a clear size-dependent band gap. Appreciable fundamental band gaps (~1 eV) are found for the smallest ribbons (two zigzag rows); the band gap decreases rapidly with increasing ribbon width, resulting eventually in a zero band-gap semiconductor at about 4 –5 zigzag rows. This finding could have useful implications for molecular electronics, in particular, since oxygen-terminated zigzag graphene nanoribbons are thermodynamically stable unlike their hydrogenated counterparts. More generally, through a concrete example, this study suggests caution when employing (semi)local functionals in DFT studies of functionalized graphene/graphene derivatives when the functional groups contain electron lone pairs.
9:00 PM - C10.14
Direct Measurement of Graphene Adhesion to Silicon Substrates.
Yung-Kong Fan 1 , Guangxu Li 1 , Zong Zong 1 , Mehmet Dokmeci 2 , Kai-tak Wan 1
1 Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractGraphene, the promising material for devices such as stretchable transparent electrodes and N/MEMS, has attracted great interest because of its novel and versatile materials properties. Its mechanical integrity and ability to integrate or to adhere to electronic substrates holds the key to success in nano-circuits and devices, despite the difficulties in experimentally measuring interfacial adhesion. We devised a novel method to directly measure graphene adhesion. Nano-particles of gold or silver are scattered randomly on the surface of an electronic grade silicon wafer, before a mechanically exfoliated graphene sheet is laid down by an adhesive tape. The wedging nano-particles support the graphene at the center to form circular blisters at the graphene-silicon interface. Knowing the particle diameter, one can measure the blister radius using scanning electronic microscope (SEM) to deduce the adhesion energy: the stronger the adhesion, the smaller the blister. The blister profile can also be measured by an atomic force microscope (AFM). We believe this is the first direct measurement of graphene adhesion reported in literature. Intricate geometry of coalesced blisters due to neighboring particles and particles trapped at the crystallographic ledge are observed in SEM. The method is useful in measuring adhesion at different locations of an interface. A continuum model based on classical linear elasticity for mixed plate-bending and membrane-stretching and an energy balance to account for long range intersurface forces (e.g. van der Waals) is constructed to relate the measurable quantities: applied load, central displacement (or particle height), contact radius and blister profile. Molecular dynamic simulation (MDS) is also conducted for better comprehension of underlying physics and mechanics. Two configurations are investigated: (i) graphene adhered to a rigid planar substrate with or without crystallographic registry, and (ii) adhesion of two graphene sheets clamped at the periphery. There is a reasonably good agreement between the continuum model, MDS, and our measurements.
9:00 PM - C10.15
Carbon Nanotube Solvents - The Critical Components.
Shane Bergin 1 , Jason Hallett 1 , Jonathan Coleman 2 , Milo S Shaffer 1
1 Chemistry, Imperial College London, London United Kingdom, 2 Physics, Trinity College Dublin, Dublin Ireland
Show AbstractSince their discovery, 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 and the diminished properties that result from this bundled state. Simple two-phase systems, of nanotube and dispersant, offer a very simplistic approach to overcoming this problem.Recently, work from these authors have demonstrated debundling by dilution in the amide solvent N-Methyl-Pyrrolidone(NMP)(1). This method demonstrated high populations of individual SWNTs confirmed by spectroscopic and microscopic techniques. Subsequent work showed spontaneous debundling of SWNTs in NMP (2); it should be stressed that this debundling occurred without sonication: spontaneity would suggest that the SWNTs are soluble in NMP. A rigorous investigation of the various components of the free energy of mixing for such a reaction was conducted, and SWNTs were shown to be soluble in NMP. The critical enthalapic component was modelled as an expression with a very similar form to the famous Scratchard-Hildebrand equation – the basis of the like-dissolves-like rule familiar to chemists. By matching the surface energy of the solvent to the surface energy of the SWNT, we obtained the optimum debundling of SWNTs. This has led, more recently, to the unearthing of a new family of solvents capable of exfoliating SWNT bundles: two of these novel solvents have been shown to demonstrate superior dispersability to surfactants (3).Thus far, we have only considered the dispersive, or London, interactions within solvents (as accounted for in the Scratchard-Hildebrand equation). However, it is well known that most systems are not well described by one solubility parameter. Most molecular interactions are a combination of dispersive, polar and Hydrogen-bonding interactions. Here we demonstrate the critical solvent – solute physical interactions necessary to exfoliate SWNT bundles (4). This has unearthed new solvents for SWNTs – two of which have been shown to have superior dispersibility to surfactant based systems (5). The question remains – why do some solvents with the correct physical solubility parameters not disperse SWNTs? Here, we question what specific solvent-nanotube chemical interactions make amide solvents such successful exfoliants; stressing the importance of these parameters, along with the correct physical parameters, when choosing solvents for nanotubes.(1)Giordani, S.; Bergin, S. D., et al. Journal of Physical Chemistry B 2006, 110, 15708.(2)Bergin, S. D.; Nicolosi, V., et al. Advanced Materials 2008, 20, 1876.(3)Bergin, S. D.; Nicolosi, V., et al. The Journal of Physical Chemistry C 2008, 112, 972.(4)Bergin, S. D.; Sun, Z., et al. ACS Nano 2009, 3, 2340.(5)Bergin, S. D.; Sun, Z., et al. Journal of Physical Chemistry C 2010, 114, 231.
9:00 PM - C10.16
Determination of the Local Chemical Structure of Graphene Oxide and Reduced Graphene Oxide Using Aberration Corrected Transmission Electron Microscopy.
Kris Erickson 1 2 , Rolf Erni 3 , Zonghoon Lee 2 4 , Alex Zettl 1 2
1 Physics, University of California - Berkeley, Berkeley, California, United States, 2 , Lawrence Berkeley National Lab, Berkeley, California, United States, 3 , Electron Microscopy Center, EMPA, Dübendorf Switzerland, 4 , National Center for Electron Microscopy, Berkeley, California, United States
Show AbstractThe local atomic structure and stability of a single layer of graphene oxide (GO) and reduced and annealed graphene oxide (raGO) are determined via ultra-high-resolution aberration corrected transmission electron microscopy. We find that the proposed and desired return to graphene from GO is not possible through the synthetic route employed. The detailed structure of GO, previously unknown, is revealed as mottled, with few square nanometer graphitic regions separated by highly oxidized regions and with occasional small holes. The structure of raGO is revealed to have a highly restored graphitic nature but is distinguished from graphene with the small numbers of remaining functionalities and the holes present within the sheet. Individual functionalities and other regions within both GO and raGO are imaged and compared to simulations of proposed structures. With these observations, a redefinition of the structure of GO is presented. We observe high mobility of oxygen functionalities in GO and overall structural instability in raGO under electron beam irradiation.
9:00 PM - C10.17
Curved Nanocarbons: Geometrical Interpretations, Curvature Distributions and Probing Topology Using Resonance Raman Spectroscopy.
Sanju Gupta 1 , A. Saxena 2
1 Chemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Theoretical Div., LANL, New Mexico, New Mexico, United States
Show AbstractCarbon is a unique element for its structural diversity and exotic geometries and more so in curvature and topology aspects, namely the spherical fullerenes or stable sp^2 C spherical carbon cages, spheroidal hyper-/hypofullerenes, cylindrical nanotubes, conical nanocarbons, and toroidal nanorings that have attracted a great deal of attention both experimentally and theoretically. Despite extensive structural and physical property characterization, they were not viewed as low-dimensional topologically distinct nanoscale materials albeit geometrical systems that opened a new research arena in materials science [1]. An additional interest in such systems stems from the fact that the exotic geometries are accompanied by (local) topological defects. In the virtues of defects, local violation by topological defects (violating nanoscale translational order inherent to periodic nanostructures) leads to novel curved nanocarbons, which in turn transcends to global topology thus global versus local topology inter-relationship. This work is prompted by our recent report [Gupta and Saxena, J. Raman Spectroscopy 40, 1127 (2009)], wherein we provided a detailed and systematic behavior of the phonon spectra through resonance Raman spectroscopy, which paved a way to an emergent paradigm of curvature / geometry/ topology --> property --> functionality relationship. To this end other than monitoring phonon spectra from a range of nanocarbons above mentioned, we determined the probability densities of the mean (H) and Gaussian (K) curvatures as pertinent observables for geometric characterization of various nanocarbons include tubular (single, double- and multi-walled nanotubes), spherical (hypo- and hyper-fullerenes) and complex (nanocones and nanotorus/nanoring) geometries to quantify the interplay of intrinsic curvature (geometric) and topology (global topology). We found various mathematical homologues such as catenoid and saddle-shaped surfaces in nanotorus and nanocones [2]. We compared these results with highly-oriented pyrolytic graphite and monolayer graphene as layered and planar systems, respectively and importantly, the nanoscale carbons discussed are their derivatives. We note that curvature leads to nonlinearity that manifests itself in some form of symmetry breaking that can be extrapolated to topological variations that may either close or open the bandgap reflected in the introduction of new Raman and absorption peaks, changes in mechanical property and electrical behavior as well as electronic density of states.These concepts are generally applicable to other distinct nanostructured materials such as boron-nitride (BN) nanotubes and nanotori, helical gold nanotubes and graphene nanoribbons and Möbius conjugated polymers. [1] Gupta and Saxena, J. Raman Spectroscopy 40, 1127 (2009); [2] ibid. (submitted, 2010).
9:00 PM - C10.18
Characterization of As-produced and Heat Treated Graphitic Nanoribbons.
Jessica Campos-Delgado 1 , Daniel Baptista 1 , Braulio Archanjo 1 , Mauricio Terrones 2 , Carlos Achete 1
1 DIMAT, INMETRO, Duque de Caxias, Rio de Janeiro, Brazil, 2 Department of Materials Science and Engineering & Chemical Engineering, Polytechnic School, Carlos III University of Madrid, Madrid Spain
Show AbstractGraphitic nanoribbons have been produced by the pyrolysis of ethanol-ferrocene-thiophene solutions at 950 °C. Previous experiments have shown that heat treatments on this material increase crystallinity and promote loop formation at the adjacent edges of graphene sheets. We have been able to study the morphology and structure of such nanoribbons by placing them on a TEM cupper grid with and without previous dispersion in alcohol by sonication. In order to observe the material as-produced, avoiding a dispersion process, we use a probe to manipulate the material inside a microscope and place it on a cupper grid. Our transmission electron microscopy results at low voltages (80 kV) show that the process of dispersion in alcohol and sonication modifies the morphology and structure of the material.
9:00 PM - C10.19
Universal Response of Single-wall Carbon Nanotubes to Radial Compression.
Ana Paula Barboza 1 , Helio Chacham 1 , Bernardo Neves 1
1 Física, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
Show AbstractSince the early 90's, the electronic and structural properties of single-wall carbon nanotubes (SWNTs) have been thoroughly investigated and some applications of those properties have been proposed. Regarding SWNT mechanical properties, most of the attention has been given to their large resistance to axial tension, even though several electromechanical effects have been observed on radially compressed SWNTs, such as the predicted [1], and recently observed [2], metal-insulator transition. The mechanical response of single-wall carbon nanotubes to radial compression is normally investigated via Atomic Force Microscopy (AFM). A universal and consistent understanding of the mechanical properties of SWNT under radial compression is, nevertheless, still missing: for instance, reported values of the radial Young modulus Er vary by up to three orders of magnitude. The present work [3] brings a unifying picture to the process of radial compression/deformation of SWNTs, where experimental data are analyzed through a rescaling model yielding a universal-type behavior. The developed experimental procedure (AFM imaging of the same SWNT region with increasing compressive forces) is quite simple, fast, and precise, allowing accurate monitoring of the deformation process. We observed height h of several SWNTs as a function of the compression force F exerted by the AFM tip. All SWNTs are deformed by the tip during the imaging process, with a pronounced decrease of SWNT height as the compression force is increased.Specifically, we find that the quantity Fd3/2(2R)-1/2, where F is the force applied by an AFM tip (with radius R) and d is the SWNT diameter, is a universal function of the compressive strain. Such universality is reproduced analytically in a model where the graphene bending modulus is the only fitting parameter. The application of the same model to the radial Young modulus Er leads to a further universal-type behavior, which explains the large variations of the SWNTs Er reported in the literature. Finally, the implications of such universal-type behavior to nanometrology are briefly discussed.References[1]M. S. C. Mazzoni et al., Appl. Phys. Lett. 76 (2000) 1561.[2]A. P. M. Barboza et al., Phys. Rev. Lett. 100 (2008) 256804.[3]A. P. M. Barboza et al., Phys. Rev. Lett. 102 (2009) 025501.
9:00 PM - C10.2
Probing Coupled Electronic and Vibrational States in Graphene Oxide Using Fluorescence Spectroscopy.
Aditya Mohite 1 2 , Charudatta Galande 3 , Anton Naumov 4 , Anchal Srivstava 5 , R. Weisman 6 , P. Ajayan 3
1 Center for Integrated Nanotechnologies, Los Alamos National Lab, Los Alamos, New Mexico, United States, 2 Chemistry and Applied Spectroscopy, Los Alamos National Lab, Los Alamos, New Mexico, United States, 3 2.Department of Mechanical Engineering and Materials Science , Rice University, Houston, Texas, United States, 4 Applied Physics, Rice University, Houston, Texas, United States, 5 4.Department of Physics, Banaras Hindu University, Banaras, Uttar Pradesh, India, 6 5.Department of Chemistry, Rice University, Houston, Texas, United States
Show AbstractGraphene Oxide (GO) is a functionalized derivative of graphene, obtained by chemical exfoliation and chemical oxidation of graphite. Recent NMR studies on GO have revealed presence of several functional groups - mainly hydroxyl, epoxy, carbonyl, carboxyl and lactols. Although there have been several studies on electronic and optical properties of GO, the role of functional groups in determining the electronic density of states is still unclear. Here we report pH-dependent fluorescence and excitation spectra of GO, with spectroscopic signatures indicating coupling of electronic transitions and vibrational modes of functional groups. At pH 1.7, a single, broad (~200 nm FWHM) fluorescence peak is observed near 660nm. Tuning the sample pH from acidic to basic results in complete quenching of this peak by pH 11. In addition, new emission features at lower wavelengths (480 nm - 515 nm) appear in a narrow pH range between 7.8 and 8.0 and completely dominate the spectrum by pH 11. In this basic environment, the excitation and emission spectra show several similar features in a mirror image pattern such as those seen in molecular spectroscopy. These suggest significant vibrational-electronic coupling related to the functional groups. Understandings how functional groups influence the optical properties of GO may enable controlled manipulation of the graphene electronic band structure.
9:00 PM - C10.21
Electronic Structure Studies of Graphene Oxide.
Sumit Saxena 1 , Trevor Tyson 1
1 Physics Department, New Jersey Institute of Technology, Newark, New Jersey, United States
Show AbstractThe electronic structure of graphene oxide has been studied using ground state density functional theory within the local density approximation. Comparisons of the site projected electron density of states with synchrotron based soft x-ray near edge absorption measurements have been made. The projected partial density of states indicates the presence of epoxide and diether bonds. Few layered graphene oxide (FLGO) is understood to be linked by the formation of weak peroxide like linkages. The electron localization function has been calculated to understand the bond formation in graphene oxide in a chemically intuitive way.
9:00 PM - C10.22
In-situ Study of the Atomic and Electronic Structural Evolution During the Reduction of Chemically Derived Graphene Oxide.
Cecilia Mattevi 0 , James Perkins 0 , Manish Chhowalla 0
0 Materials, Imperial College, London United Kingdom
Show AbstractGraphene oxide (GO), a chemical derivative of graphene, provides a high yield of covalently functionalized and atomically thin carbon sheets. Lately this material has emerged as a promising candidate for large-area electronics as it is a solution-processable and therefore can be readily and uniformly deposited on a variety of substrates. GO contains saturated sp3 carbon atoms bound to oxygen as well as sp2 carbon. It is an electrical insulator and through chemical or thermal removal of oxygen it is possible to tune its electrical conductivity over several orders of magnitude [1]. However, highly reduced GO (rGO) contains residual (8% at.) oxygen and lattice defects [1,2]. Hence a detailed description of the residual amount of sp3 carbon and the density of states of highly reduced GO are of fundamental importance. Here we present real time observations of fractional changes in the carbon sp2/sp3 content by measuring the fine structure of C K-edges using electron energy loss spectroscopy in an aberration corrected scanning transmission electron microscope. Observed changes of the oxygen distribution by annular dark field imaging of single and multilayer sheets during in-situ annealing up to 1000 C revealed remarkable structural changes around 500 C and at about 850 C. Electronic plasma excitations have also been measured, showing that the low-energy plasma excitations energies of the π electrons and the bulk plasma loss (π + σ excitation) of highly reduced GO are almost indiscernible from the values of mechanically exfoliated graphene [3].[1] Mattevi C. et al. Adv. Funct. Mater. 2009, 19, 2577–2583.[2] Bagri A., Mattevi C., Acik M., Chabal Y. J., Chhowalla M. and. Shenoy V. B., DOI: 10.1038/NCHEM.686 Nature Chem. 2010[3] Eberlein, T. et al. Phys. Rew. B 2008, 77, 233406.
9:00 PM - C10.23
Structural Analysis of Chemically Functionalized Epitaxial Graphene with High-resolution X-ray Reflectivity.
Jonathan Emery 1 , Qing Hua Wang 1 , Paul Fenter 2 , Mark Hersam 1 , Michael Bedzyk 1
1 Materials Science, Northwestern University, Evanston, Illinois, United States, 2 Chemical Sciences and Engineering, Argonne National Lab, Argonne, Illinois, United States
Show AbstractIn order for graphene to realize its potential in next-generation electronics it must be incorporated with a variety of materials to form devices. Recently, the use of self-assembled organic monolayers deposited on epitaxial graphene (prepared by graphitization of the 6H-SiC(0001) surface) has been effective in the functionalization of the bare graphene sheet, enabling the additional chemistry necessary for device fabrication. In this work, we present high-resolution X-ray Reflectivity (XRR) studies of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) on epitaxial graphene. Initially, a model-independent vertical electron density profile of the graphene/silicon carbide interface is retrieved with the use of Feinup-based error correction algorithms in order to minimize ambiguities that can arise from model-based methods. This retrieved structure is then used as the foundation for model-based analysis, from which the final structures are extracted. A series of structures comprising 0, 1, and 2MLs of PTCDA deposited on 1-2ML graphene are discussed. The interlayer spacing between the PTCDA and top graphene layer are revealed to be approximately 0.35 nm, which supports the view that the PTCDA molecules are interacting only weakly (van der Waals) with the graphene layer.
9:00 PM - C10.25
Far Infrared Absorption Measurements of Low Dimensional Carbon Materials.
Shin Chou 1 , Zeeshan Ahmed 1 , Georgy Samsonidze 2 3 , Ki Kang Kim 4 , Jing Kong 4 , Mildred Dresselhaus 4 5 , Jeeseong Hwang 1 , David Plusquellic 1
1 Optical Technology Division, NIST, Gaithersburg, Maryland, United States, 2 Physics, University of California at Berkeley, Berkeley, California, United States, 3 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 EECS, MIT, Cambridge, Massachusetts, United States, 5 Physics, MIT, Cambridge, Massachusetts, United States
Show AbstractIn this study, high resolution, variable temperature far infrared absorption measurements were carried out for single walled carbon nanotubes and CVD-grown graphene between 0 and 100 cm-1. At a temperature where kBT is significantly lower than the phonon energy, the broad absorption features as observed in room temperature become slightly blue-shifted, yet well-resolved, optical transitions. The energies of the transitions are consistent with the low energy acoustic phonon associated with lattice translation and deformation. First principle calculations are carried out to understand the phonon spectra and their temperature-induced blue shift.
9:00 PM - C10.26
Mpemba-like Behavior in Carbon Nanotube Resonators.
Alex Greaney 1 , Rajamani Raghunathan 1 , Jeffrey Grossman 1
1 Department of Materials Science and Engineering, Massechusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractWe observe unexpected dissipative behavior during molecular dynamics simulations of the ring-down of flexural modes of carbon nanotube resonators (CNTs). Simulating a CNT with a large initial excitation, it is found that the system equilibriates faster than a system with a smaller initial excitation that starts closer to equilibrium. We liken this to the Mpemba effect in which hot water freezes faster than cold water. We show that this seemingly counter intuitive effect is the result of a hidden variable in the form of a non-equilibrium phonon population. Using simple models of damped harmonic oscillators in a closed system we show that with the addition of an internal degree of freedom we can capture the full qualitative behavior of the CNT damping.
9:00 PM - C10.27
Highly Controllable Fabrication of CNT Arrays for Interfacial Mechanical Properties Investigation.
Yuqin Yao 1 , Quan Xu 2 , Jianyu Liang 1 , Zhenhai Xia 2
1 Mechanical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts, United States, 2 Mechanical Engineering, University of Akron, Akron, Ohio, United States
Show AbstractInterfacial properties of nanostructured materials have been vigorously studied by scientists and researchers because of their important role in understanding the unique behaviors and devising novel applications of those materials. In this report, arrays of carbon nanotubes( CNTs) embedded in anodized aluminum oxide (AAO) templates have been utilized as a platform to study mechanical interfacial properties of importance to nanoimprinting and nanostructured reinforced composites. In order to systematically and experimentally study the interfacial mechanical properties, a highly controllable fabrication protocol to create uniform and free standing CNT arrays with well-defined morphology has been developed based on the previously well-studied template-assisted chemical vapor deposition method (CVD). The microstructure and the morphology of the CNT based nanocomposite materials are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The influence of fabrication conditions on the microstructure and the morphology of the nanomaterials, such as the property of the AAO templates, the CVD growth conditions, and the post growth treatments will be reviewed in detail. The effect of the material morphology and microstructure on the measured interfacial mechanical properties will be reported.
9:00 PM - C10.28
Curvature-induced Symmetry Lowering and Anomalous Dispersion of Phonons in Carbon Nanotubes.
Jason Reppert 1 , Ramakrishna Podila 1 , Nan Li 2 , Codruta Loebick 2 , Steven Stuart 3 , Lisa Pfefferle 2 , Apparao Rao 1
1 Department of Physics and Astronomy; Center for Optical Material Science and Engineering Technologies, Clemson University, Clemson, South Carolina, United States, 2 Department of Chemical Engineering, Yale University, New Haven, Connecticut, United States, 3 Department of Chemistry, Clemson University, Clemson, South Carolina, United States
Show AbstractHere we report the effect of high curvature on the electronic and vibrational properties of one-dimensional systems. Sub-nanometer diameter single wall carbon nanotubes (sub-nm SWNTs; diameter < 1 nm) are used as a model system to show that such curvature-induced perturbation will lead to new and strong Raman and infrared (IR) features. Specifically, we show that the high curvature in sub-nm SWNTs leads to (i) an unusual S-like dispersion of the G band due to the strong electron-phonon coupling, (ii) an activation of diameter-selective intermediate frequency modes that are as intense as the radial breathing modes (RBMs), and (iii) a clear observation of the IR modes. Furthermore, we provide an alternate model to the existing excitonic picture of SWNTs by including the effects of curvature into the widely used tight-binding model. Lastly, we show that the phonon spectra for sub-nm SWNTs obtained from the molecular dynamic simulations which employ a curvature-dependent force field concur with our experimental observations. This study suggests new ways to interpret spectroscopic data and warrants further theoretical and experimental studies in strongly correlated systems.
9:00 PM - C10.3
On the Inner Double-resonance Raman Scattering Process in Bilayer Graphene.
Daniela Mafra 1 , Elie Moujaes 1 , Ricardo Nunes 1 , Marcos Pimenta 1
1 , Universidade Federal de Minas Gerais, Belo Horizonte Brazil
Show AbstractThe dispersion of phonons and the electronic structure of graphene systems can be obtained experimentally from the double-resonance (DR) Raman features by varying the excitation laser energy. In a previous resonance Raman investigation of graphene, the electronic structure was analyzed in the framework of the Slonczewski-Weiss-McClure (SWM) model, considering the outer DR process. In this work we analyze the data considering the inner DR process, and obtain SWM parameters that are in better agreement with those obtained from other experimental techniques. This result possibly shows that there is still a fundamental open question concerning the double resonance process in graphene systems.
9:00 PM - C10.30
Properties Modeling of Low-dimensional Carbon Nanostructures.
Andrew Basteev 1 , Leonid Bazyma 1 , Mykhaylo Ugryumov 1 , Yuriy Chernishov 1 , Margarita Slepicheva 1
1 , National Aerospace University, Kharkov Aviation Institute “KhAI”, Kharkov Ukraine
Show AbstractLow-dimensional carbon nanostructures properties have the great potential for application in different branches of industry. We need to achieve the understanding of correlation between these objects structure and properties and the mechanism of above properties control. It is well-known that chirality of carbon nanotubes has the significant influence on to their properties including the sorption ones [1]. In the same time enough high indexes of hydrogen mass content at relatively low pressures obtained in experiments [2] can be linked with structure defects in nanotubes walls. These defects generated for example by means of annealing procedure create the irregular surface shape and roughness which are associated with hydrogen binding energy [2]. The modeling of single wall carbon nanotubes properties (length, diameter, chirality, defective wall structure) influence on sorption capability at different thermodynamic conditions (T=80-273 K; P = 2-12 MPa) is presented in this work. The applied simulation procedure is the molecular dynamics (as has been applied in [2]) as well the new event-driven simulation algorithm has been used. In the frameworks of this event-driven simulation method the modeling of structure formation for carbon nanotubes have been done with different chirality and with wall defects presence. The analysis of obtained results and comparison with experiment and published data are performed. REFERENCES:[1] Lianquan GUO, Changxiang MA., Shuai Wang, He MA and Xin LI, Molecular simulation of hydrogen adsorption density in single-walled carbon nanotubes and multilayer adsorption mechanism // J. Mater. Sci. Technol. – 2005. – Vol. 21, No. 1. – P. 123 – 127.[2] Pradhan B.K., Harutyunyan A.R., Stojkovic D., J.C. Grossman, Zhang P., Cole M.W., Crespi V., Goto H., Fujiwara J. and Eklund P.C., Large cryogenic storage of hydrogen in carbon nanotubes at low pressures // J. Mater. Sci. Technol. – 2002. – Vol. 17, No. 9. – P. 2209 – 2216.
9:00 PM - C10.31
Electronic Sensing of Ions Passing through Porous Graphene Nanoribbons.
Artem Baskin 1 , Niladri Patra 1 , Petr Kral 1
1 Chemistry, University of Illinois at Chicago, Chicago, Illinois, United States
Show AbstractPorous graphene nanoribbons (PGN) might be excellent electronic sensors for molecular species passing through them [1]. To follow this challenging idea, we calculate ab initio the electronic structures in different types of PGNs in the presence of simple ions passing through them [2]. We perform systematic band gap analysis for various types of PGNs with pores of different sizes, shapes, and locations, in the presence of passing Na+ and Cl- ions. The pores can dramatically enlarge the bang gaps that are present in armchair PGNs, however they preserve the metallicity in zigzag PGNs. Similarly, the passing ions largely influence only the armchair PGNs. These results show that biased PGNs might be used as highly sensitive sensors of passing ions and molecules that could be detected from the electronic currents induced in them.[1] K. Sint, B. Wang and P. Král, JACS (Communication) 130, 16448 (2008)[2] A.I. Baskin, N. Patra. P. Král, Electronic Structure of Porous Graphene Nanoribbons, in preparation
9:00 PM - C10.32
DFT Studies on Surface Reactions of a Partially Hydrogenated Graphene.
Dong Hyun Jung 1 , Daejin Kim 1 , Areum Lee 1 , Noejung Park 2 , Seung-Hoon Choi 1
1 CRD, Insilicotech Co. Ltd., Seongnam-Shi, Gyeonggi-Do, Korea (the Republic of), 2 Department of Applied Physics, Dankook University, Yongin-si, Gyenggi-Do, Korea (the Republic of)
Show AbstractGraphene has been known to have novel properties so that it is expected to be applicable to diverse electronic devices in nanoscale. To control the electronic structure of graphene, hydrogenation of grapene has been suggested as a method for widening the band gap. Therefore, it is important for understanding the fundamental properties of hydrogenated states of graphene to study surface reactions happening on the hydrogenated graphene. We investigated the thermodynamics and kinetics of surface reactions of a partially hydrogenated graphene. Surface reactions we studied are desorption and diffusion of chemisorbed hydrogen atoms. We performed density functional theory calculations based on plane-wave basis set using CASTEP in Materials Studio 5.0. In order to obtain barriers for desorption and diffusion, transition state search method was adapted. The model used here is the most stable configuration of graphene sheet on which 24 hydrogen atoms are chemisorbed. Desorption of a hydrogen molecule is accompanied by the change of spin state: singlet to triplet, and the desorption barrier is 3.30 eV. For the diffusion, the activation barrier for concurrent diffusion of two adjacent hydrogen atoms is 5.36 eV and the diffusion barrier of one hydrogen atom is 3.19 eV. With these results, we can conclude that it is very difficult for the surface reactions including desorption and diffusion to take place on the graphene surface at the ambient temperature and the hydrogenated state of graphene is thermodynamically and kinetically very stable.
9:00 PM - C10.4
First Principles Study of Adsorption of Hydrogen Sulfide (H2S) on Graphene.
Heriberto Hernandez Cocoletzi 1 , Eduardo Castellanos Aguila 2 , Gregorio Hernandez Cocoletzi 2
1 Facultad de Ingeniería Química, Benemérita Universidad Autónoma de Puebla, Puebla, Puebla, Mexico, 2 Instituto de Física, Benemérita Universidad Autónoma de Puebla, Puebla, Puebal, Mexico
Show AbstractDensity Functional Theory, as implemented in the quantum ESPRESSO package [1], has been used to analyze the interaction between hydrogen sulfide and graphene. The electron-ion interaction is modeled using ultrasoft pseudopotentials, the exchange-correlation energy is approximated by the method of local density approximation (LDA) and the generalized gradient approximation (GGA) within the parameterization PZ (Perdew-Zunger) [2] and PBE (Perdew-Burke-Ernzerhof) [3], respectively. Four different coverages (one H2S molecule per 8, 16, 18 and 32 C atoms) have been studied; geometries, binding energies and Density of states (DOS) are calculated. We studied several preferential sites (top, bridge, center) where the molecule may be adsorbed. Our results show that the molecule H2S suffers a physisorption process; the DOS of graphene-H2S system shows a metallic behavior which coincides with the behavior of isolated graphene. Finally, the stability of the hydrogen sulfide remains when is adsorbed by the graphene. [1] S. Baroni, A. Dal Corso, S. de Gironcoli, P. Giannozzi, C. Cavazzoni, G. Ballabio, S. Scandolo, G. Chiarotti, P. Focher, A. Pasquarello, K. Laasonen, A. Trave, R. Car, N. Marzari, and A. Kokalj, http://www.pwscf.org.[2]. J.P. Perdew and A. Zunger, Phys. Rev. B 23, 5048 (1981).[3] Perdew J. P. Burke K., and Ernzerhof, M., Phys. Rev. Lett., 77, 3865-3868, 1996.This work was partially supported by CONACyT, Mexico (Grant No. 0083982).
9:00 PM - C10.6
UV Signatures of Carbon Nanocones.
Henning Heiberg-Andersen 1 , Arne Skjeltorp 1 2
1 Physics department, Institute for Energy Technology, Kjeller Norway, 2 Department of Physics, University of Oslo, Oslo Norway
Show AbstractCarbon nanocones are seamless, cone shaped graphene layers with five possible apex angles determined by the topology of the 3-coordinated network of sp2 hybridized carbon atoms[1]. The theoretical structures can be obtained by folding a flat graphene sheet after removal of one to five sectors of disclination angle 60°. Cones of all five apex angles have been synthesized, with sizes ranging from tens of nms to several μms. For the cones with four disclinations, we find a characteristic systematic in the theoretical UV spectra: Independent of size and detailed tip topology, for half of the cones with four disclinations and C2 point group symmetry the first peak in the UV spectrum is a B2 transition. This result was obtained by graph theoretical analysis of the relevant Hückel orbitals and confirmed by UV spectra calculated by Density Functional Theory.[1] H. Heiberg-Andersen, G.S. Walker, A.T. Skjeltorp and S. Nalum Naess, Graphene Cones, in Handbook of Nanophysics, Ed. K.D. Sattler, CRC Press 2010ISBN-10: 1420075381, ISBN-13: 978-1420075380
9:00 PM - C10.7
Deformation of Graphene Oxide Layers Probed by Electric Force Microscopy.
Camilla Karla Oliveira 1 , Ana Paula Barboza 1 , Mario Sergio Mazzoni 1 , Rodrigo Lacerda 1 , Bernardo Neves 1
1 Departamento de Fisica, Universidade Federal de Minas Gerais, Belo Horizonte Brazil
Show AbstractIn recent years, theoretical and experimental studies have shown that both structural and electronic changes occur when we apply forces to the different carbon materials such as carbon nanotubes [1]. In this work, we study the effects of the force applied by an AFM tip on graphene oxide (GO). The graphite oxide, known for more than 50 years [2], can be dispersed in various solvents giving rise to graphene oxide layers [3], which have been considered as a new route to produce graphene from the reduction of these oxide layers. Unlike graphene, GO behave as an insulator and its structure is presented as a graphene containing oxygen bonds in the form of functional groups like carboxyl, hydroxyl or epoxy, with the oxygen atoms randomly distributed over the layer [4]. We use Force Spectroscopy (FS) and Electric Force Microscopy (EFM) to study the electro-mechanical response of several few-layer graphene oxides, for different applied forces. A force curve is obtained whenever a force is applied by the AFM probe, perpendicular to the sample surface, and its deflection is monitored, while in EFM, the observed frequency shift in the probe oscillation is directly related to the gradient of the electric force, for a constant bias. We vary the applied force, with forces values up to μN, and for each force, an EFM image is performed and the electric response of the sample is measured. Our results show a variation of the EFM signal with the force applied to multi-layers and bilayers, while the electric response of the monolayer remains unchanged for any force value. A pressure-induced-rehybridization model, including ab initio calculations, is used to explain these experimental results.[1] A. P. M Barboza et al, Phys. Rev. Lett., 100 (2008) 256804 [2] W. S. Hummers and R. E. Offerman, J. Am. Chem. Soc., 80 (1958) 1339 [3] S. Park and R.S. Ruoff, Nature Nanotecnology, 4 (2009) 217[4] K. A. Mkhoyan et al, Nanoletters, 9 (2009) 1058-1063
9:00 PM - C10.8
Thermal, Chemical and Radiation Treatment Influence on Hydrogen Adsorption Capability in Single Wall Carbon Nanotubes.
Michail Obolensky 2 , Andrew Kravchenko 2 , Yury Petrusenko 3 , Valery Borysenko 3 , Andrew Basteev 1 , Leonid Bazyma 1
2 , V.N. Karazin Kharkov National University, Kharkov Ukraine, 3 , National Science Center Kharkov Institute of Physics and Technology, Kharkov Ukraine, 1 , National Aerospace University, Kharkov Aviation Institute “KhAI”, Kharkov Ukraine
Show AbstractThe main methods of carbon nanotubes (CNT) synthesis lead to formation of products mixture with various degree of imperfectness, structural and dimensional properties. The serious problem of results reproducibility is staying actual at practical CNT use. It is concerning with the requirement of identical or very close CNT properties after the procedure of their separation and purification. In spite of variety of applied methods no one method is able realize above identity. It means that purification and separation procedures have the primary importance. It is well-known that chemical CNT treatment increases the CNT adsorption capability eve at atmospheric pressures [1]. Chemical purification without thermal treatment can both increase the hydrogen percentage in CNT as well decrease the mass content [2]. The complex CNT treatment (chemical and thermal) allow obtaining the significantly large adsorption capability. The four time hydrogen percentage increasing comparatively with untreated sample is reported in [2] and hydrogen mass content more than 6 percent was obtained. The influences on CNT adsorption capability of above listed factors (chemical and thermal processing) as well the irradiation procedure were experimentally studied in this work. Two ways for CNT purification and separation were used. The SWNT (Carbon Solutions, amount about 1 g) was annealed on open air at temperature 350oC during 30 minutes and then was heated in 2.6 M HNO3 during 28 hours in accordance with the first method [2]. Accordingly with the second method the 0.5 ml of 10 percent solution of H[AuCl4] was added to CNT with the aim to increase the selectivity of amorphous carbon elimination. Then 100 ml mixture of concentrated H2SO4 + H2O2 (7:3) was added and heating with interfusing during 20 hours and at temperature 90oC was conducted. After above procedure the treated CNT were flushing in methanol and then in water till the neutral reaction achievement, dried in air and at last were annealed in deep vacuum (10-8 torr) during 20 hours at temperature 1000oC. The further CNT control evidences the second method advantage. The technology for SWNT treatment by electron beam (~2MeV) and also converted γ-quantum was elaborated. The electron beam bombardment was conducted in the interval 1011-1015 e-/cm2. The irradiation influence on to adsorption capability was studied as well other factors for SWNT treatment.References:[1] Anson A., Callejas M.A., Benito A.M., Maser W.K., Izquierdo M.T., Rubio B., Jagiello J., Thommes M., Parra J.B., Martinez M.T., Hydrogen adsorption studies on single wall carbon nanotubes // Carbon . – 2004 – 42 – P. 1243–1248.[2] Pradhan B.K., Harutyunyan A.R., Stojkovic D., J.C. Grossman, Zhang P., Cole M.W., Crespi V., Goto H., Fujiwara J. and P.C. Eklund, Large cryogenic storage of hydrogen in carbon nanotubes at low pressures // J. Mater. Sci. Technol. – 2002. – Vol. 17, No 9. – P. 2209 – 2216.
9:00 PM - C10.9
Mechanical and Thermal Properties of Low-dimensional Carbon Nanocomposites.
Sangil Hyun 1 , Joon-Hyun Byun 2
1 , KICET, Seoul Korea (the Republic of), 2 , KIMS, Changwon Korea (the Republic of)
Show AbstractCarbons can exist in many different forms in different dimensions; for example 0-dimensional buckyballs, 1-dimensional CNTs, 2-dimensional graphite sheets, and 3-dimensional diamonds. Well-designed hybrid composites consisting of different dimensional microstructures were sometimes known to enhance their properties significantly. One of the well-known examples would be the hybrid composite of carbon nanotubes (1D) and graphite sheets (2D). Graphite sheets can possess high mechanical strength but it is highly anisotropic as well. Thus, the polycrystalline graphite instead can enhance its mechanical performance by minimizing the anisotropy. However the polycrystalline structures are generally known to degrade mechanical performance because it can be highly dependent on the microstructures such as grain size and shape. In the present study, we employed classical molecular dynamics to address the mechanical and thermal properties of polycrystalline graphite and the property degradations for various microstructures. Also the hybrid composites in multi-dimensional structures were investigated to determine the sensitivity of the properties on the microstructures. The interfacial characteristics between CNTs and polycrystalline graphite sheets were particularly analyzed to address its enhancement of the properties.
Symposium Organizers
John J. Boeckl Air Force Research Laboratory
Liming Dai Case Western Reserve University
Weijie Lu Fisk University
Mark H. Ruemmeli Leibniz Institute
IFW Dresden
Jamie Warner University of Oxford
C11: Doping, Defects and Surface Chemistry
Session Chairs
Thursday AM, December 02, 2010
Room 304 (Hynes)
9:45 AM - **C11.1
Tuning the Structure and Properties of Carbon Nanotubes.
Antal Koos 1 , Frank Dillon 1 , Zabeada Aslam 1 , Alison Crossley 1 , Nicole Grobert 1
1 Department of Materials, University of Oxford, Oxford United Kingdom
Show AbstractCarbon nanotubes (CNTs) are the subject of widespread research due to their outstanding properties and are expected to have many applications across the length scales. These include CNTs as fillers in multifunctional composite materials, as building blocks in nanoelectronic devices, chemical sensors, etc. Unfortunately, for most products CNTs with well defined properties are needed at commercially viable price, but current production methods do not fulfill those requirements. However, theoretical and experimental studies have also shown that it is possible to tailor the electronic properties of CNTs by replacing some of the carbon atoms with hetero atoms.The doping allows us to tailor the density of states and produce CNTs with new chemical properties. In-situ transmission electron microscopy studies revealed crucial information on the stress and disorder caused by incorporation of foreign atoms. Hence, the dopants must be carefully selected and their incorporation well controlled. Herein we investigate and compare the effect of reaction parameters on the structure of multi-walled CNTs produced via aerosol chemical vapour deposition technique from boron, nitrogen, phosphorus and silicon containing precursors. We were able to control the structure, diameter distribution, defect density and oxidation resistance of the nanotubes. The findings pave the way CNTs with well defined properties for electronic components, composite materials or high performance chemical sensors.
10:15 AM - C11.2
Migration Mechanism of Self-localized Topological Defects in Conductive Polymers.
Yongwoo Shin 1 , Xi Lin 1
1 Department of Mechanical Engineering and Division of Materials Science and Engineering, Boston University, Brookline, Massachusetts, United States
Show AbstractConductive polymers have been widely studied in the last couple of decades. The fundamental factor of charge transport is known to be the migration of self-localized defects such as the soliton, polaron, and exciton. In our previous work, we searched for the activation energy barrier of the motion of these defects in trans-polyacetylene (t-PA), which we found to be on the order of 0.01 eV for a soliton and 0.001 eV for a polaron using ab initio Hartree-Fock (HF) calculations. Nevertheless, the mechanism of migration of defects has yet to be clearly explained theoretically. On the other hand, the mechanism for migration of defects is not clearly explained theoretically. In this project we present the migration mechanism of defects through the Goldstone mode, which is a break in the translational symmetry, as well as the other localized modes. Finally, the energy landscape of conductive polymers, restricted by the localized modes, is presented by the tight-binding method as well as HF calculations. Our systems included not only t-PA but also poly-phenylacetylene.
10:30 AM - C11.3
Room-temperature Tunable Fano Resonance by Chemical Doping in Few-layer Graphene Synthesized by Chemical Vapor Deposition.
Jiming Bao 1 , Zhihong Liu 1 , Xiaoxiang Lu 1 , Peng Peng 1 , Wei Wu 1 , Steven Pei 1 , Qingkai Yu 1
1 Electrical and Computer Engineering, University of Houston, Houston, Texas, United States
Show AbstractWe report the observation of Fano-like phonon resonance using infrared Fourier transform spectroscopy at room-temperature in few-layer (~3) graphene synthesized by chemical vapor deposition. We subsequently demonstrate a continuous tuning of Fano lineshape from anti-resonance to phonon-dominated by ammonia chemical doping. The few-layer Fano resonance exhibits a strong asymmetric characteristic between n-doped and p-doped graphene, different from that observed in double-layer graphene gated by external electrodes. This asymmetry probably arises from non-uniform charge-distribution in graphene due to the substrate and adsorbed ammonia molecules. Simultaneous measurements of Fano lineshape and infrared signature of adsorbed ammonia molecules have also revealed the orientation of ammonia molecules on graphene and confirmed the charge-transfer mechanism of chemical doping.
10:45 AM - C11.4
Focused Ion Beam Induced Damage in Highly Ordered Pyrolytic Graphite and Synthesis of Free-standing Graphite Nanosheets.
Rupert Langegger 1 , Alois Lugstein 1 , Emmerich Bertagnolli 1
1 Institute of Solid State Electronics, Vienna Institute of Technology, Vienna Austria
Show AbstractIn recent years, carbon nanostructures have attracted great attention as building blocks in nanotechnology. To get deeper insight into graphite processing in the nanoscale regime we intensively investigated HOPG under FIB exposure.Therefore, highly ordered pyrolitic graphite (HOPG) was irradiated with focussed Ga+-ions with a kinetic energy of 30 keV. The surface modifications are investigated as a function of anlge of ion beam incidence (θ=0° -55° ), fluence (Φ= 1,248*1015 - 2,996*1017ions/cm2) and substrate temperature up to 600°C by scanning electron microscopy and AFM imaging. At room temperature mainly physical sputtering was observed leading to flat bottomed boxes independent of the ion fluencies and angle of beam incidence.For a substrate temperature of 300°C ripples were observed on the HOPG surface. Pretreatment with small ion fluence allows us to modify the wavelike character of these ripples. At a substrate temperature of 600°C the HOPG surface transforms to cellular like structures. At these higher substrate temperatures we explored a process for nanosheet formation. With skillful use of FIB technique we created a self assembled free standing carbon nanosheet about 1 nm high and less than 80 nm thick.WE will present a SEM video which shows the assembling of these carbon nanosheets in situ and in real-time.
11:30 AM - C11.5
Two-dimensional Molecular Crystals of Phosphonic Acids on Graphene.
Mariana Prado 1 , Regiane Nascimento 1 , Luciano Guimaraes 1 , Matheus Matos 1 , Mario Sergio Mazzoni 1 , Luiz Gustavo Cancado 1 , Helio Chacham 1 , Bernardo Neves 1
1 Departamento de Física, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
Show Abstract Much attention has been drawn to graphene in the past years due to its remarkable properties and it is expected that this material will play a major role in nanotechnology and industrial applications [1]. In order to fulfill such great potential, some basic issues concerning graphene’s electronic properties such as control of bandgap and doping levels are in need. In this work, we report synthesis and characterization of two-dimensional (2D) molecular crystals from long and linear phosphonic acids atop graphene. These crystals deposited on graphene provide an easy way to determine the flake orientation and induce a well-defined shift in the Fermi-level. Scanning Probe Microscopy (SPM), Raman Spectroscopy and ab initio calculations were employed to characterize the self-assembled monolayers of two phosphonic acids OPA (octadecylphosphonic acid) and TPA (tetradecylphosphonic acid) atop graphene. Atomic Force Microscopy (AFM) measurements easily detect the period of the 2D crystal after deposition on graphene flake. Our calculations show a significant difference in the formation energy of OPA or TPA monolayers when different orientations of the molecule with respect to substrate are considered, clearly showing that the monolayer most stable configuration is along the graphene zigzag direction. Thus, a simple AFM measurement, with no need of atomic resolution, is all it takes to determine the graphene crystallographic orientation.In addition, Raman spectroscopy measurements, before and after monolayer deposition, confirm the results of our ab initio calculations regarding the doping effect of the OPA/TPA monolayer, where both show a hole doping of graphene with carrier concentration of about 1013cm-2. The 2D crystal formation on graphene flakes on top of Si/SiO2 is easily achieved via spread coating with ethanolic solution [2,3] making this a fast and practical method to discover flake orientation and achieve chemical doping of graphene.[1] – Schwierz, F. Graphene transistors. Nature Nanotechnol. doi: 10.1038/nnano.2010.89 (2010).[2] - Neves, B. R. A., Salmon, M. E., Russell, P. E. & Troughton, E. B. Spread coating of OPA on mica: From multilayers to self-assembled monolayers. Langmuir 17, 8193-8198 (2000).[3] - Fontes, G. N. & Neves, B. R. A. Effects of substrate polarity and chain length on conformational and thermal properties of phosphonic acid self-assembled Bilayers. Langmuir 21, 11113-11118 (2005).
11:45 AM - C11.6
Point and Line Defect-mediated Binding of Metal Nanoparticles to Graphene.
Ioanna Fampiou 1 , Ashwin Ramasubramaniam 1 , Nikhil Medhekar 2
1 , University of Massachusetts, Amherst, Massachusetts, United States, 2 , Monash University, Clayton, Victoria, Australia
Show AbstractThe synthesis of well dispersed, size-controlled metal nanoclusters on carbon supports is highly desirable since such clusters have been shown to possess enhanced catalytic activity and selectivity in a variety of chemical reactions. However, metal clusters interact rather weakly with defect-free carbon supports and can coarsen over time leading to loss of surface area and thence catalytic activity. Defects in carbon supports play an important role in enhancing metal-carbon bonding, thereby reducing the propensity for cluster coalescence. Using a combination of density functional theory and empirical potential simulations, we examine the interaction of metal (Pt, Pd) clusters with point (vacancies, holes) and line defects (dislocations, grain boundaries) in graphene. We compare and contrast the binding energies and diffusivities of clusters bound at defects and on pristine graphene. Our results suggest possible avenues for controlling the dispersion of catalyst clusters on carbon supports via defect engineering.
12:00 PM - C11.7
Effect of Sidewall Functionalization and Nitrogen Doping on the Deformation and Failure Mechanisms of Individual Catalytically Grown Multi-wall Carbon Nanotubes.
Yogeeswaran Ganesan 1 , Cheng Peng 1 , Yang Lu 1 , Lijie Ci 1 , Anchal Srivastava 1 , Pulickel Ajayan 1 , Jun Lou 1
1 MEMS, Rice University, Houston, Texas, United States
Show AbstractOwing to their small size and the magnitude of the forces and deformation involved, the knowledge of the mechanical strength, nature of inter-shell load transfer and failure mechanisms associated with catalytically grown MWNTs is currently limited even though these materials are routinely used for research and commercial applications. Here, we report on the usage of a simple microfabricated device, that works in conjunction with a quantitative Nanoindenter within a scanning electron microscope (SEM) chamber, for the in situ quantitative tensile testing of individual catalytically grown pristine, fluorine functionalized and nitrogen doped multi-wall carbon nanotubes (MWNTs). The stress vs. strain curves, extracted from nanoindenter load vs. displacement curves, for representative tensile specimens will be presented. The effect of sidewall functionalization and doping (nitrogen) on the load bearing capacity and on the failure mechanisms associated with the MWNTs will also be discussed.
12:15 PM - C11.8
Nitric Acid Doping of Single-walled Carbon Nanotubes under Mild and Harsh Conditions.
Katalin Kamaras 1 , Aron Pekker 1 , Bea Botka 1
1 , Research Institute for Solid State Physics and Optics, Budapest Hungary
Show AbstractAcid doping, mainly treatment with nitric acid, is a common procedure to get rid of catalysts in as-grown nanotubes. The acid also reacts with the sidewalls of the tubes, resulting in two types of effects: carboxylic groups attached to the tube ends and/or defects on the walls, and p-doping of the whole nanotube, similar to intercalated graphite. Wide-range optical spectroscopy is an ideal tool to study both effects: doping will result in the increase of far-infrared absorbance and dc conductivity, and carboxyl groups will show up as a specific signature in the infrared spectrum. We have performed a systematic study of several types of nanotubes,on both self-supporting thicker and substrate-supported thinner layers. We find that under harsh conditions (boiling in nitric acid for an extended period of time) both carboxyl substitution and p-doping occur, but for mild conditions (nitric acid vapor at room temperature) only p-doping is observed. We also studied the time evolution of the doping process.While doping occurs on the scale of minutes, and there is significant initial dedoping, the improvement remains over several weeks. Our spectroscopic data unambigously prove that the changes in conductivity are intrinsic, and not just a result of improving the contact between nanotubes. For self-supporting films, the dc conductivity of the networks is close to that extrapolated from the low-frequency optical conductivity.
12:30 PM - C11.9
Substantial Effect of Surface Doping on the Stone-wales Transformation in C60.
Swarnakamal Mukherjee 1 , Mukul Kabir 2 , Tanusri Saha-Dasgupta 1
1 , S. N. Bose National Centre for Basic Sciences, Salt Lake City, Kolkata, India, 2 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractIsomerization of C60 fullerene via the Stone-Wales transformation requires very high energy (the activation energy barrier is ~ 6.7 eV). However, it is know that this activation barrier can be reduced (at most by 0.80 eV) by endohedral La-doping. Here we study, through ab initio calculations, the effects of surface-doping on the activation energy of this Stone-Wales transformation for C60. Here we dope single and double boron (B) at the active Stone-Wales site since the B-doped C60 is believed to be a good candidate for hydrogen storage. In contrast to the endohedral metallofullerenes, we find that such surface doping substantially reduces the activation barrier by 2.03 eV and 4.30 3V for single and double B doping, respectively These implies a much higher probability of isomerization for these doped fullerenes. Further analysis of phonon frequencies and bonding charge densities suggests that these reductions in activation energies are due to the bond weakening at the active Stone-Wales site.
C12: Surface, Interface and Interactions
Session Chairs
Thursday PM, December 02, 2010
Room 304 (Hynes)
2:30 PM - **C12.1
Nano-Objects and Nanochemistry at Epitaxial Graphene/Silicon Carbide Surface and Interface.
Patrick Soukiassian 1
1 , CEA-Saclay and Universite de Paris-Sud/Orsay, Gif sur Yvette France
Show AbstractNanostructures and nanochemistry at epitaxial graphene on Si and C-faces silicon carbide (SiC) surfaces and interfaces, are investigated by synchrotron radiation-based photoemission spectroscopy, absorption spectroscopy, scanning tunneling microscopy/spectroscopy (STM/STS). SiC and graphene are advanced semiconductors having figures of merit scaling well above those of well-established semiconductors. SiC is a wide band gap semiconductor (2.4-3.3 eV depending on polytype). Strain/stress minimization is the driving force in SiC surface/interface organization leading to complex surface atomic structures and nano-objects, including sp2 or sp3 surface transformation. Indeed, among many others, an interesting feature of SiC is to be a very suitable substrate for epitaxial graphene growth. Graphene, a single atomic layer of graphite, is a semimetal or a “zero” band gap semiconductor. It could be exfoliated or epitaxialy grown on a substrate. It exhibits outstanding transport properties, with carriers moving at zero mass and constant velocity just like photons, leading to linear electronic structure dispersion forming Dirac cones. Also, graphene has the highest mechanical resistance ever measured. In this presentation, a special emphasis will be put on epitaxial graphene electronic properties, graphene/SiC interface investigation and hydrogen atoms interaction with graphene and/or SiC substrate surface. In the latter, hydrogen atoms are found to interact at the graphene/SiC interface and at the SiC surface leading to band-gap opening and to C-layer decoupling from the SiC surface. At the graphene/SiC interface, the results reveal nano-objects forming mesas with steep sides suggestive of C nanotubes at graphene/SiC interface, triggering electronic interface states possibly detrimental to carrier mobility. Nano-cracks are found at the SiC surface with the graphene layer going deep into the crack without any disruption and no resulting electronic interface states, in strong contrast to the nano-objects. The different mechanisms at the origin of these features will be discussed. The results directly impact the engineering of surface/interface properties. Research supported by Agence Nationale de la Recherche (ANR) and Partner University Funds (PUF)
3:00 PM - **C12.2
Growth of Carbon Nanotubes for Sensor and Instrumentation Applications.
Meyya Meyyappan 1
1 , NASA Ames Research Center, Moffett Field, California, United States
Show AbstractCarbon nanotubes have been considered for a wide range of applications from electronics, optoelectronics, composites, catalyst support, field emission to sensors and many others. While this literature is vast, commercial product development has been hindered in many cases due to numerous growth and practical issues such as reproducibility, interface resistance and adhesion problems on substrates, wafer scale growth uniformity etc. We have successfully developed over the last several years applications in chemical sensors, biosensors and x-ray tubes for instrumentation. Each of these presented their own unique growth and processing challenges which will be discussed along with application results. Our chemical sensors currently use bulk, purified SWCNTs across interdigitated electrodes through an ink-jetting process while an in situ CVD process across a 6” wafer over thousands of sensors is yet to materialize. The biosensors use in situ grown carbon nanofibers (~50 nm diameter MWCNTs with bamboo-like interior) by PECVD which are individual, freestanding and vertical. The process is highly amenable for large wafer production (6”) and further functionalization with probe molecules. The X-ray tube development uses MWCNT towers directly grown on metal substrates (ex: kanthal) to improve interface resistance, adhesion, stability at high current densities, life time and robustness. The author thanks Jing Li, Y. Lu, Jessica Koehne, P. Arumugam, and Cattien Nguyen for their contributions.
3:30 PM - C12.3
Quantum Interference Channelling at Graphene Edges.
Heejun Yang 1 2 3 , Andrew Mayne 2 , Mohamed Boucherit 2 , Genevieve Comtet 2 , Gerald Dujardin 2 , Young Kuk 3
1 , Samsung Advanced Institute of Technology, Yongin-si Korea (the Republic of), 2 , Univ Paris Sud, Orsay France, 3 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractGraphene nanoribbons have attracted much attention recently for their quasi-one dimensional electronic properties such as the opening of an energy gap. Moreover, graphene nanoribbons have applications in spintronics and as field-effect transistors. Resistivity measurements have highlighted the influence of edges in the electron transport properties for narrow graphene nanoribbons (width < 40 nm). However, the exact contributions of edges are still unknown, despite theoretical and experimental studies of edge states. These indicate a high electronic density near the Fermi level localized at edges, that could possibly affect the electrical properties of graphene nanoribbons. Electron scattering at graphene edges is also expected to make a crucial contribution by producing quantum interferences. This has not been investigated so far as it requires a real atomic-scale resolution control of the edge structure. In this presentation, we investigate quantum interferences at edges of monolayer graphene from atomic-scale scanning tunnelling microscopy (STM) topographies of different edge structures; irregular armchair, mixed armchair and zigzag, and regular armchair. We show that quantum interferences are channelled along the graphene carbon bond network. They form high electronic density of states (DOS) patterns along the C-C bonds, whose shapes depend only on the edge structure and not on the electron energy. We also discovered that the pseudo-spin from the graphene sublattice is perfectly conserved for perpendicular incident Dirac fermions while there is pseudo-spin mixing at other directions which corresponds partial pseudo-spin flip at graphene arm-chair edge. These results help us understand the unique physics at graphene edge where the most important symmetry of graphene, ‘sublattice symmetry’, is broken.
3:45 PM - C12.4
Reactivity of Single Graphene Layers and Edges toward Electron Transfer Chemistries.
Richa Sharma 1 , Michael Strano 1
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractThe reactivity of graphene and its various multilayers toward electron transfer chemistries with 4-nitrobenzene diazonium tetrafluoroborate is probed by Raman spectroscopy after reaction on-chip. Single graphene sheets are found to be almost 10 times more reactive than bi- or multilayers of graphene according to the relative disorder (D) peak in the Raman spectrum examined before and after chemical reaction in water. A model whereby electron puddles that shift the Dirac point locally to values below the Fermi level is consistent with the reactivity difference. Because the chemistry at the graphene edge is important for controlling its electronic properties, particularly in ribbon form, we have developed a spectroscopic test to examine the relative reactivity of graphene edges versus the bulk. We show, for the first time, that the reactivity of edges is at least two times higher than the reactivity of the bulk single graphene sheet, as supported by electron transfer theory. These differences in electron transfer rates may be important for selecting and manipulating graphitic materials on-chip. Electrical measurements of the chemically functionalized graphene are also done to understand the role of functional group in electron conduction.
4:30 PM - C12.5
A Novel Approach to Interface Eengineering of Reduced Graphene Oxide.
Muge Acik 1 , Cheng Gong 1 , Geunsik Lee 1 , Cecilia Mattevi 2 , Manish Chhowalla 2 , Kyeongjae Cho 1 , Yves Chabal 1
1 Materials Science and Engineering, The University of Texas at Dallas, Dallas, Texas, United States, 2 Department of Materials, Imperial College, London United Kingdom
Show AbstractThough graphite oxide (GO) has been mostly considered as a precursor for large area graphene production, understanding its formation and reduction mechanisms remains vital for many other applications. The challenge of dealing with a non-stoichiometric chemical structure with little information on its interface properties makes it difficult to expand the use of GO and graphene for a wide range of applications for devices such as capacitors, sensors, transistors and resonators. In particular, understanding the growth mechanism of defects in the graphene basal plane still remains elusive in terms of functionalization of graphene planes, which is believed to heal the sp2-hybridization resulting in higher conductivity. Up to now, the interface chemistry of GO has been of interest for many chemists and materials scientists to intercalate both chemically and electrochemically various metals, polymers, ceramics in the interlayers, which alter its electrical, mechanical and optical properties. Therefore, the interplay between these intercalated species and the defect site is of interest to understand the chemical interactions among various GO functional groups in the presence of water.Our approach to understanding the interfacial interactions is the evaluation of reduction chemistry of GO using in-situ infrared spectroscopy (FTIR). Specifically, we have studied the deoxygenation process of both single-layer and multilayered GO for comparison and focused on the pathways of thermal removal of oxygen both from the basal plane and the edges. We have performed a series of test experiments using x-ray diffraction technique (XRD), ex-situ raman scattering, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS), together with supportive theoretical methods such as density functional (DFT) calculations and molecular dynamic (MD) simulations. The key observation is that the formation of intermediate carbonyl groups in the graphene plane during thermal reduction (removal) of hydroxyls, carboxyls and epoxides. For multilayered GO, the carbonyl formation occurs as defects are produced as evidenced by the evolution of CO2 molecules at ~125oC. Intercalated water is shown to react with the defects to form carbonyls species. At higher annealing temperatures (~ 850oC), all carbonyl and carboxyl species are reacted, leaving oxygen at the edges in the form of ether. This oxygen configuration is highly stable and is characterized by an asymmetric stretch mode at 800 cm-1 that is greatly enhanced by induced electronic states. These findings highlight the role of intercalated water in the thermal evolution of GO and suggest methods for stabilizing graphene-based devices. *The authors acknowledge funding from the SWAN/NRI program and Texas Instruments.
4:45 PM - C12.6
Giant Interfacial Stress Transfer Between Single-layer Graphene Oxide and Polymers.
Minzhen Cai 1 , Hannes Schniepp 1
1 Applied Science, The College of William and Mary, Williamsburg, Virginia, United States
Show AbstractDue to the outstanding mechanical properties of the low-dimensional carbon materials, the idea of their application in high-performance nanocomposites has been long-standing. Recently, graphene-based materials have emerged as a very promising candidate in this respect, as they can be mass-produced at low cost and easily dispersed and processed in a great variety of media. Their theoretically expected, exceptionally high values for Young’s modulus and strength have already been experimentally confirmed. Nevertheless, a nanocomposite that rivals the mechanical properties of “traditional”, carbon fiber-based composites has yet to be demonstrated. We address the most significant fundamental difficulty that remains with respect to the realization of high-performance, graphene-based nanocomposites. In order to make full use of the sheets’ exceptional mechanical properties, their interface with the surrounding matrix needs to be strong enough that they are actually loaded up to their ultimate limit. In a very recent report it has been demonstrated that mechanically exfoliated graphene can be strained up to 0.5% through adhesion to polymer before it slips. While this result represents a significant progress, it falls one and a half orders of magnitude short of the maximally possible strain for graphene, which has experimentally been demonstrated to exceed 20%. We applied a newly developed, atomic force microscopy (AFM)-based method to measure the interfacial adhesion between graphene oxide sheets and polymers. We have identified some polymers to which these sheets adhere exceptionally well. Subsequently, we manufactured nanocomposites out of these materials, and we applied AFM to visualize individual, single-layer graphene oxide sheets embedded in the polymer. We selected 50 sheets and measured their dimensions when the sample was relaxed. We repeated the measurements on the very same set of sheets when the sample was under strain. We found that these sheets exhibited average strains significantly in excess of 5% with respect to the relaxed state, which establishes a lower limit for the strain at break of graphene oxide. Since the investigated sheets were smaller than one micrometer on average, our results also suggest that it is possible to make nanocomposites in which graphene sheets are strained up to their ultimate limit without introducing any covalent bonding between the sheets and the polymer. We hence envision a new generation of graphene-based nanocomposites with exceptional strength and toughness.
5:00 PM - C12.7
Tunable Surface Wetting in Transferable Films of Graphene Oxide.
Saad Hasan 1 , John Rigueur 1 , Robert Harl 2 , Bridget Rogers 2 , James Dickerson 3
1 Interdisciplinary Graduate Program in Materials Science, Vanderbilt University, Nashville, Tennessee, United States, 2 Department of Chemical & Biomolecular Engineering, Vanderbilt University, Nashville, Tennessee, United States, 3 Department of Physics & Astronomy, Vanderbilt University, Nashville, Tennessee, United States
Show AbstractGraphene, the single atomic layer sheet of carbon that constitutes graphite, is a material with exceptional electrical conductivity and mechanical strength. Graphene can be isolated by mechanical cleavage of graphite ("Scotch tape method") or can be grown by thermal decomposition of silicon carbide. Producing graphene on a larger scale has proved challenging. One promising, recently popularized approach entails (a) the conversion of graphite to graphite oxide, (b) the exfoliation of graphite oxide to yield separate graphene oxide sheets, and (c) the reduction of the graphene oxide sheets to graphene-like sheets [1]. The colloidal graphene resulting after steps (b) or (c) can be assembled into multilayered composites, using techniques like vacuum filtration and electrophoretic deposition. These multilayered materials demonstrate very good electrical conductivity, tensile strength, and flexibility, which make them promising components for electrical and optical devices.
In this presentation, we report the fabrication of multilayered films assembled from aqueous suspensions of graphene oxide using electrophoretic deposition. We address how to determine the stability of the colloidal system and how the suspension can be tuned over a range of pH values. We then show how macroscopic films of graphene oxide, with an assortment of microstructures, can be produced using electrophoretic deposition. The water contact angle for smooth graphene oxide films was 41.1° ± 1.2° while the inclusion of microscopic voids in the graphene oxide film raised the contact angle to 79.1° ± 3.5°. We hypothesize that the changes in surface wetting of these films resulted from changes in the microstructure, not changes in the chemical composition. X-ray photoelectron spectroscopy (XPS) measurements of the films revealed no appreciable differences in the chemical composition of the films. Finally, we demonstrate how to isolate these graphene oxide films as free-standing objects using a sacrificial layer [2] to facilitate their transfer to arbitrary substrates.
[1] S. Park and R. S. Ruoff. Nature Nanotechnology 4, 217-224 (2009).
[2] S. A. Hasan, D. W. Kavich, and J. H. Dickerson. Chemical Communications 3723-3725 (2009).
5:15 PM - C12.8
Tuning Electron-phonon Coupling in Carbon Nanotube Ensembles via Inter/Intra-tube Modifications.
Keqin Yang 1 , Dale Hitchcock 1 , Pooja Puneet 1 , Jian He 1 , Malcolm Skove 1 , Apparao Rao 1 2
1 Physics & Astronomy, Clemson University, Clemson, South Carolina, United States, 2 COMSET, Clemson University, Clemson, South Carolina, United States
Show AbstractThe electron-phonon coupling (EPC) in the carbon nanotube (CNT) ensemble is sensitive not only to intrinsic parameters such as the diameter and chirality but also to extrinsic parameters such as doping ratios and inter-tube interactions. In this work we study the EPC and its impact on the electrical and thermal transport properties of spark plasma sintered (SPSed) CNT ensembles via two approaches. The first approach concerns enhancing inter-tube bonding by increasing the SPS temperature from 500 °C to 1500 °C. A pronounced phonon drag peak in the thermopower, accompanied by a plateau in the resistivity, is only observed in the sample SPSed at 1500 °C. We conclude these features are due to strong EPC in the sample with strong inter-tube interactions. As a function of SPS temperature, the resistivity exhibits a percolation type behavior while the thermal conductivity shows a clear dimensionality crossover. The second approach concerns doping CNTs with boron in a SPS process at 1200 °C. With increasing nominal boron doping ratio, the magnitude of the resistivity systematically decreases while the magnitude of the thermopower at room temperature first decreases and then increases again after reaching the minimum in the sample with the nominal boron concentration of 7.5%. It is noted that the phonon drag peak and the accompanied resistance plateau are observed only in the sample with 7.5% doping ratio. These observations suggest that EPC is sensitive to the Fermi energy.
5:30 PM - C12.9
Theoretical Study of Hydrogen Adsorption on Flat and Curved Surfaces in Zeolite-templated Carbon (ZTC).
Megumi Kayanuma 1 2 , Kimichi Suzuki 1 , Umpei Nagashima 1 , Hiroshi Ogawa 1 , Hirotomo Nishihara 3 , Takashi Kyotani 3
1 , AIST, Tsukuba, Ibaraki, Japan, 2 , Université de Strasbourg, Strasbourg France, 3 Institute of Multidisciplinary Research for Advanced Materials, Tohoku Univ., Sendai Japan
Show AbstractZeolite-templated carbon (ZTC) synthesized by Kyotani et al. [1] has attractive structural features for hydrogen storage: large surface area up to 4100 m2/g, uniform pores with curved graphene-like structure units of about 1.2 nm. [2] The structure is favorable for both hydrogen physorption and chemisorption, and recent experiments showed the possibility of increase in hydrogen uptake by spillover process. In this study, the authors evaluate the chemisorption of spillover hydrogen on flat and curved surfaces in ZTC by DFT calculation. Four flat and curved molecules, coronene, corannulene, pleiadannulene and triacenaphthotriphenylene, were assumed for structure units in ZTC. DFT calculation indicate that the adsorption energy of atomic hydrogen on the model molecules depends on both curvature and position of adsorption site. In the case of flat surface (coronene), adsorption energy at the edge is larger than that at the center. The adsorption energies increase in cases of curved surfaces, and the relation between the energy values at two sites is reversed in triacenaphthotriphenylene. [3] The authors also found that hydrogen chemisorption at the edge enhances the adsorption at inner sites. [3] These results suggest that hydrogen spillover in ZTC is effective for hydrogen storage and controllable by the curvature of structure units. This work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under "Advanced Fundamental Research Project on Hydrogen Storage Materials".[1] Kyotani et al., Chem. Mater., 9 (1997) 609. [2] Nishihara et al., Carbon 47 (2009) 1220. [3] Kayanuma et al, Chem. Phys. Let., in press.
C13: Thermal Properties
Session Chairs
Friday AM, December 03, 2010
Independence W (Sheraton)
9:00 PM - C13.1
Thermal Transport in 2D Hybrid Graphene-BN Nanostructures.
Jun Song 1 , Nikhil Medhekar 2
1 Division of Engineering, Brown University, Providence, Rhode Island, United States, 2 Department of Materials Engineering, Monash University, Clayon, Victoria, Australia
Show AbstractGraphene—a 2D structure with a honeycomb carbon lattice—has drawn tremendous attention as promising material for next generation optoelectronic and NEMS applications. Recent developments have shown that it is possible to obtain hybrid 2D structures by combining sp2-graphene lattice with sp2-lattice of non-carbon materials such as hexagonal Boron Nitrides. The atomically thin sheets containing both hexagonal-Boron Nitride and graphene can result in new materials with properties complementary to their individual properties and further enrich the potential applications. Here, using molecular dynamics simulations, we elucidate the characteristics of thermal transport in 2D hybrid h-BN and graphene materials. We find the thermal conductivity of the hybrid material is a strong function of the relative domain widths, interface type (e.g., zigzag and armchair) as well as the interface quality. Our results provide crucial insights on the role of the interfaces and defects in phonon scattering in the hybrid material and can potentially provide means to tailor its thermal properties.
9:15 PM - C13.2
Modeling of Thermal Transport in Pillared-graphene Architectures.
Ajit Roy 1 , Vikas Varshney 1 2 , Soumya Patnaik 4 , Barry Farmer 1 , George Froudakis 3
1 Materials & Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 2 , Universal Technology Corp, Dayton, Ohio, United States, 4 Propulsion Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 3 Dept of Chemistry & Materials Science and Technology, University of Crete, Crete Greece
Show AbstractDue to their superior thermal properties, allotropic forms of carbon such as CNTs and graphene are considered as potential future candidates for many nano-/micro-scale integrated devices. However, both systems exhibit significant anisotropy in their thermal conduction that limits their performance as 3-dimensional thermal transport material systems. From thermal management perspective, one way to tailor this anisotropy is to consider designing alternative carbon-based architectures. This presentation will discuss the thermal transport behavior in one such novel architecture –a Pillared-Graphene (PG) network nanostructure which combines graphene sheets and carbon nanotubes to create a three-dimensional network, having junction between CNT and graphene. We have carried out non-equilibrium molecular dynamics simulations using the AIREBO potential to calculate the thermal conductivity of Pillared-Graphene structures along parallel (in-plane) as well as perpendicular (out-of-plane) directions with respect to graphene plane. We also calculated the thermal conductivity for pure CNT and graphitic systems of similar length scales. The conductivity values for PG systems are analyzed and compared with simulated values for pure CNT and graphite. At studied length scales, our results suggest that minimum inter-pillar distance and the CNT-pillar length are two crucial parameters that govern thermal transport in these structures. This is primarily attributed to scattering of phonons occurring at the CNT-graphene junctions in these nanostructures, which are located at the distances corresponding to aforementioned parameters. Towards the end, affect of junction impurities on thermal transport will also be discussed briefly.
9:30 PM - C13.3
Thermal Conductivities of Carbon Nanotube Fibers from Pulsed Laser Thermal Relaxation Technique.
Hai Duong 1 2 , James Elliott 1 , Matthew James 1 , Agnieszka Lekawa-Raus 1 , Krzysztof Koziol 1 , Laurent Pambaguian 3 , Alan Windle 1
1 Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Mechanical Engineering, National University of Singapore, 117576 Singapore, 3 Materials Technology Section, European Space Agency , ESA-ESTEC Netherlands
Show AbstractCarbon nanotube fibres made by the direct spinning of an aerogel from the CVD reactor in which the nanotubes are synthesized [1] show the promise of high axial conductivity, and are the subject of this investigation.The measurement of thermal conductivity of very thin electrically conducting (<20 micron) fibres is especially challenging, on account of the heat loss by surface radiation. Several experimental techniques have been developed which include pulse laser thermal relaxation [2], transient electrothermal [3], and transient photoelectrothermal [4] methods. The pulse laser thermal relaxation method has been focused as this technique can overcome limitation of slow rising time for the current and consumes much less measurement time [2-4]. In this technique, a periodically modulated laser beam is used to irradiate the fibre, leading to periodical changes in temperature and electrical resistance, the latter being monitored using a small dc current. From the phase shift difference between the voltage variation and laser beam, the thermal conductivity of the fibre can be determined. As there currently no current experimental or computational work determining the sensitivity of this method for carbon nanotube fibres where the transverse thermal conductivity is likely to be much less than the axial value, we have developed a computational modeling approach to simulate the experiment and compare the derived thermal conductivity from the known values given to the fibre. The modeling has shown the effects of various frequencies of laser intensity variation, different fibre dimensions, different anisotropies of heat conduction, and different emissivities from the fibre surface on the closeness of the derived conductivities to the given values, enabling the choice of optimum parameters for the experiment. The validation between the developed model and experimental measurement is also discussed.[1] Y-L. Li, I. A . Kinloch and A H Windle, Science, 304, 276-278 (2004).[2] J. Guo et alia, J. Appl. Phys., 103, 113505 (2008).[3] J. Guo, X. Wang and T. Wang, J. Appl. Phys., 101, 063537 (2007).[4] T. Wang, et alia. Appl. Phys. A: Mater. Sci. Process., 87, 599 (2007).
9:45 PM - C13.4
Thermal Conductivity of Graphene Ribbons from Equilibrium Molecular Dynamics: Effect of Ribbon Width, Edge Roughness and Hydrogen Termination.
William Evans 1 , Lin Hu 2 1 , Pawel Keblinski 2 1
1 Rensselaer Nanotechnology Center, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractGraphene nanoribons (GNRs), which are narrow (typically < 20 nm) strips of graphene, have became the subject of significant research because of equally extraordinary electrical, thermal, and mechanical properties with significant application potential to future nano-electronic/mechanical devices. Several theoretical estimates place the thermal conductivity, k, of a graphene ribbons in the range of several thousand W/m K, i.e, comparable with k or in plane graphite or carbon nanotubes. However, several research groups using non-equilibrium molecular dynamics (NEMD) simulations found significantly lower values of k in the range of several hundred W/m K depending on the width, edge type (armchair or zigzag), and roughness. We have used equilibrium molecular dynamics (EMD) simulations to investigate the effect of GNR width on thermal conductivity for GNRs in widths ranging from 10 Å to 100 Å with both smooth and rough edges, and have included the effect of hydrogen termination (H-termination) of the edge atoms. For smooth edges without H-termination the conductivity is very high (~3000 W/m), quite strikingly, even for 10 Å width, and increases with increasing width, At a ribbon width of 100Å for either type of edge the thermal conductivity reaches values of ~6000 to 7000 W/m K with no (H)-termination; only about 25% less than the value calculated for graphene sheets. The conductivity for both edge types is quite similar for all ribbon widths. However, rough-edged GNRs exhibit conductivity which is proportional to the ribbon width and at narrowest widths have a much reduced conductivity, on the order of 500 W/m K. We also found that hydrogen termination of the edge atoms has significant effects on conductivity, particularly for smooth edges.
10:00 PM - C13.5
Regulating Vibrational Energy in Molecular Dynamics Simulations: A New Tool to Understand and Predict Heat Dissipation at the Nanoscale.
Rajamani Raghunathan 1 , P. Alex Greaney 1 , Jeffrey Grossman 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractControlling vibrational energy in a system is an uphill task in a Molecular Dynamics (MD) simulation since the internal degrees of freedom are highly inaccessible due to the strong coupling between various degrees of freedom. Usual thermostat algorithms in MD simulations maintain a system at an average temperature by regulating the atomic velocities rather than controlling the energy in internal degrees of freedom. Here, we present a “Phonostat” algorithm that can regulate total energy in a given internal degree of freedom. Our method relies on computing the modal energies in each step of the simulation and a reservoir of fictitious tuning forks drives a chosen vibrational mode in the system. This vibrational reservoir exchanges vibrational energy with a given internal mode rather than heat in contrast to a usual thermostat. The rate of exchange of vibrational energy between Phonostat and the system is controlled by two parameters: the magnitude of the external driving force F(t) and the damping parameter ζ’ of the Photostat. We present applications of this algorithm for test cases like a simple harmonic oscillator and carbon nanotubes.
10:15 PM - C13.6
Near-field Substrate Heating by a Carbon Nanotube under High Bias.
Kamal Baloch 1 2 , Norvik Voskanian 2 , Merijntje Bronsgeest 3 4 , John Cumings 2
1 Institute of Physical Science and Technology, University of Maryland, College Park, Maryland, United States, 2 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 3 Physics, University of Maryland, College Park, Maryland, United States, 4 , Laboratory for Physical Sciences, College Park, Maryland, United States
Show AbstractFor the utilization of carbon nanotubes in next-generation thermal management and thermal logic devices, a fundamental understanding of basic mechanisms that govern their thermal transport is required. Employing in-situ electron thermal microscopy, we investigate thermal transport mechanisms in current-carrying carbon nanotubes under high bias. We observe that even though the thermal conductivity of the nanotube is three orders of magnitude higher than that of the substrate, a large thermal contact resistance between the two limits the transport under typical conditions. However, under current-carrying conditions, thermal transfer between the nanotube and the substrate appears to be considerably more facile. The most straightforward explanation of this enhanced thermal transfer invokes near-field radiation that carries a significant fraction of generated heat directly from the electron system of the nanotube to the phonon system of the substrate. In this presentation we will explore the possible mechanisms for this enhanced thermal transport, integrating experimental results, simulations and a review of relevant theories.
10:30 PM - C13.7
WITHDRAWN 12/27/10 Effects of Nanoscale Defects and Phononic Structure on Thermal Conductivity in 2D Atomistic Systems.
Jean-Francois Robillard 1 , Nichlas Swinteck 1 , Krishna Muralidharan 1 , Pierre Deymier 1
1 Materials Science and Engineering, University of Arizona, Tucson, Arizona, United States
Show AbstractTwo-dimensional materials such as graphene and boron-nitride have generated much scientific interest due to their extraordinary structure/property relations. Indeed, these materials have remarkable electronic and thermal transport properties inherited from the 2D confinement of excitations. For example, graphene is found to have a very high thermal conductivity[1] and is expected as a thermal interface material in the next generation of microprocessor units. In contrast, materials with highly diminished thermal transport are required for thermo-electric applications. Thus, studying the effects of nanoscale phonon-diffusing structures is an important step towards the development of materials with appropriate thermal properties. Here, we report on Molecular Dynamics (MD) study of nanoscale phonon-diffusion effects in 2D atomistic systems: (i) Bragg scattering in a square lattice of nano-holes and (ii) thermal rectification by triangular shaped defects. We examine 2D Lennard-Jones (LJ) and graphene systems (modeled by the Tersoff potential[2]) respectively. The thermal conductivity is determined by equilibrium Green-Kubo and non-equilibrium formulations. In the case of Bragg scattering, the thermal conductivity was calculated as a function of the periodicity and the filling fraction of holes in the LJ and graphene systems. Introducing arrays of defects in a 2D atomic sheet realizes a so-called phononic crystal[3] in which the propagation of phonons is governed by Bragg scattering. Such a structure can introduce band-gaps, flattening of phonon bands or inhibition of inelastic phonon-phonon processes leading to a dramatic reduction in the thermal conductivity. These results are in agreement with previous thermal conductivity predictions of 3D semiconductor nano-composites[4]. Complementary lattice dynamics calculations of the phonon dispersion curves show that the 2D square Lennard-Jones phononic crystal exhibits bands with significant negative group velocities. These negative bands are analyzed in the context of phonon focusing. In the case of thermal rectification, we simulate the heat transport in an atomic sheet with a line of triangular defects under a thermal gradient. Results show that an asymetric thermal conduction results from the distribution of defects. This thermal rectification effect is studied as a function of the defects size and density and in ensembles of various size defects. These results suggest that recently proposed asymmetric shape nanostructures[5] and boron nitride mono-atomic layers with triangular defects[6] have enormous potential applications as thermal management materials.[1] A.A. Balandin et al., Nano Letters, 8, 902 (2008)[2]V. Perebeinos et al., Phys. Rev. B, 79, 241409 (2009)[3] J.O. Vasseur et al., Phys. Rev. Lett., 86, 3012 (2001) [4] J.-N. Gillet et al., J. of Heat Transfer, 131, 043206 (2009)[5] S. Chen et al., Nano Letters, 2, 1003 (2002)[6] C. Jin et al., Phys. Rev. Lett., 102, 195505 (2009)
10:45 PM - C13.8
The Effect of Defects on the Thermal Conductivity of Carbon Nano-ribbons : A Molecular Dynamics Study.
Justin Haskins 2 , Alper Kinaci 1 , Cem Sevik 1 2 , Tahir Cagin 1 2
2 Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas, United States, 1 Materials Science and Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractCarbon nano-ribbons have unique properties which open them to broad range of applications especially in microelectronics industry. Some of the proposed uses of nano-ribbons include thermal management devices and thermoelectrics. However, these applications require a full characterization of thermal properties and their dependence on the configuration of defect structures. To this end, simulations can provide necessary information for such small dimensional systems. In this study, we present lattice thermal conductivity (κl) calculations of carbon nano-ribbons having both edge defects and vacancies that commonly occur in experimental samples. We employ equilibrium molecular dynamics with Tersoff potential and Green-Kubo fluctuation dissipation theory for the calculations. We use a re-parametrized Tersoff potential that gives correct phonon dispersions to obtain accurate κl values. Ribbons as long as half a micron were simulated in order to avoid any size dependency. We investigate the effect of vacancy concentration, edge roughness and temperature on κl of the ribbons. It is concluded that the defects significantly affect the thermal conductivity and should be included in simulations in order to obtain realistic behavior.
Symposium Organizers
John J. Boeckl Air Force Research Laboratory
Liming Dai Case Western Reserve University
Weijie Lu Fisk University
Mark H. Ruemmeli Leibniz Institute
IFW Dresden
Jamie Warner University of Oxford
C14: Novel Structures and Properties of Low Dimensional Carbon Nanostructures
Session Chairs
Friday AM, December 03, 2010
Independence W (Sheraton)
9:30 AM - C14.1
Highly Selective Stress-induced Chemistry: How Does Unzipping of Carbon Nanotubes Work?
Alexander Sinitskii 1 , Dmitry Kosynkin 1 , Ayrat Dimiev 1 , James Tour 1
1 Chemistry, Rice University, Houston, Texas, United States
Show AbstractRecently, we reported on the simple approach to fabricate graphene nanoribbons (GNRs) by chemical unzipping of multiwalled carbon nanotubes (MWCNTs). (1) This approach employs very common reagents (potassium permanganate and sulfuric acid), is simple, straightforward, scalable and has a high yield approaching 100%, enabling large scale production of GNRs for research needs (2-5) as well as bulk applications, such as composites, fibers and thin films. However, two fundamentally important questions remain: how does unzipping of carbon nanotubes work and what makes this simple reaction so highly selective? It is well known that strong oxidants can cleave carbon-carbon bonds in the benzene rings of aromatic hydrocarbons. However, in our particular case there are millions of double bonds in MWCNTs and only those few are broken that enable longitudinal unzipping of the tubes. In order to address these questions, we have performed experiments where we monitored the appearance and electrical properties of selected MWCNTs during step-by-step oxidation by acidic potassium permanganate. We have observed the formation of the unzipping sites whose development results in the transformation of the outer shells of MWCNTs to GNRs. We found that mechanical stress in MWCNTs plays crucial role in this reaction making it very selective. Although simultaneous formation of several unzipping sites is very frequent, they develop in a concurrent manner due to the mechanical stress, yielding μm-long GNRs rather than small graphene nanoplatelets of irregular shape. Our SEM observations are in a good agreement with the results of the step-by-step electrical measurements. We also discuss the physical and chemical properties of the GNRs. Our findings on the importance of mechanical stress in chemical reactions could be applicable to other carbon allotropes and, more generally, other materials.[1] Kosynkin, D. V.; Higginbotham, A. L.; Sinitskii, A.; Lomeda, J. R.; Dimiev, A.; Price, B. K.; Tour, J. M. Nature 2009, 458, 872-876. [2] Sinitskii, A.; Fursina, A. A.; Kosynkin, D. V.; Higginbotham, A. L.; Natelson, D.; Tour, J. M. Appl. Phys. Lett. 2009, 95, 253108.[3] Sinitskii, A.; Dimiev, A.; Corley, D. A.; Fursina, A. A.; Kosynkin, D. V.; Tour, J. M. ACS Nano 2010, 4, 1949-1954.[4] Behabtu, N.; Lomeda, J. R.; Green, M. J.; Higginbotham, A. L.; Sinitskii, A.; Kosynkin, D. V.; Tsentalovich, D.; Parra-Vasquez, A. N. G.; Schmidt, J.; Kesselman, E.; Cohen, Y.; Talmon, Y.; Tour, J. M.; Pasquali. M. Nature Nanotech. 2010, 5, 406-411.[5] Sinitskii, A.; Kosynkin, D. V.; Dimiev, A.; Tour. J. M. ACS Nano 2010, 4, 3095-3102.
9:45 AM - C14.2
Nonlinear Mechanical Properties of Graphene Nanoribbons.
Qiang Lu 1 , Rui Huang 1
1 , University of Texas at Austin, Austin, Texas, United States
Show AbstractBased on atomistic simulations, the nonlinear elastic properties and the uniaxial fracture strength of graphene nanoribbons are predicted theoretically, emphasizing the effects of the edge structures. The excess edge energy and internal edge forces are determined as functions of the uniaxial strain. Under an infinitesimal strain, the edge force is compressive for both zigzag and armchair edges, leading to an intrinsic wavelength for edge buckling. A size-dependent Young's modulus is predicted for the graphene nanoribbons. Under a finite uniaxial strain, the stress-strain behavior of a graphene nanoribbon becomes highly nonlinear and anisotropic. A failure criterion based on the intrinsic lattice instability is proposed for brittle fracture of graphene at low temperatures. It is found that the critical strain to fracture is considerably lower for armchair graphene nanoribbons than that for zigzag ribbons, corresponding to two distinct fracture mechanisms. The effect of hydrogen passivation along the edges is found to be negligible for the zigzag ribbons but significant for the armchair ribbons.
10:00 AM - C14.3
Dynamics of Graphene Nanodrums.
Gustavo Brunetto 1 , Sergio Legoas 3 , Vitor Coluci 2 , Liacir Lucena 4 , Douglas Galvao 1
1 Departamento de Física Aplicada, Unicamp, Campinas, São Paulo, Brazil, 3 Departamento de Fisica, Universidade Federal de Roraima, Boa Vista, Roraima, Brazil, 2 Faculdade de Tecnologia, Unicamp, Limeira, São Paulo, Brazil, 4 Departamento de Física, Universidade Federal do Rio Grande do Norte, Natal Brazil
Show AbstractRecently Bunch et al. [1] demonstrated that graphene sheets deposited on silicon oxide can act as impermeable atomic membrane to standard gases, such as helium, argon, and nitrogen. It is assumed that graphene membrane is clamped over the surface only due to van der Waals forces [2].The leakage mechanism can be experimentally addressed only indirectly [1]. The gas leaking can occurs between the membrane and the substrate and/or through the substrate walls. In order to investigate these aspects we have carried out molecular dynamics simulations for model systems.We have considered silicon oxide cavities with dimension of 154x154x30 Å. The cavity is filled with different gases (helium and argon). Graphene membranes (single layer up to 3 layers) of different sizes (100x100 up to 400x400 Å) are deposited over the cavity. The largest system is composed of about 1.5 million atoms. The temperature of the gas is varied (in this way, the gas pressure is also varied) and the dynamics analyzed from the molecular dynamics (MD) trajectories. The MD simulations were carried out using the NAMD code [3].The obtained results are in good qualitative agreement with the experimental data [1]. We observe that the graphene membranes remain attached to the substrate for pressures up to 11 bar. This value is about two times the largest value experimentally investigated. We did not observe any gas leakage through the membrane/substrate interface until the critical limit is reached and then an abrupt membrane detachment occurs. This confirms the model proposed by Bunch et al. [1]. Possible applications exploiting these phenomena are also addressed.[1] J.S.Bunch, S.S. Verbridge, J.S. Alden, et al. Nano Letters. 8, 2458 (2008).[2] Z. Lu, M.L. Dunn. Journal of Applied Physics. 107, 044301 (2010).[3] J. Phillips, R. Braun, W. Wang, et al. Journal of Computational Chemistry. 26, 1781 (2005).
10:15 AM - C14.4
In-Situ Transfer of Monolayer Graphene Fluoride Flakes and Study by Scanning Tunneling Microscopy.
Scott Schmucker 1 2 , Joshua Wood 1 2 , Joseph Lyding 1 2
1 Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 , Beckman Institute, Urbana, Illinois, United States
Show AbstractThe production and characterization of graphene fluoride is of interest due to its retention of the layered structure of graphite and the introduction of a large (>3eV) band gap. Interest in graphene fluoride as an electronic material is extended by the possible reduction of multi-layer graphene fluoride to graphene[1,2]. In this work we demonstrate the exfoliation and characterization of predominantly monolayer graphene fluoride (CF)n flakes by an in-situ mechanical exfoliation process onto the Si(100)2x1:H surface and investigate these features by scanning tunneling microscopy (STM). By a dry-contact transfer (DCT) process [3], monolayer graphene fluoride islands are transferred to the passivated silicon surface with negligible substrate contamination, as seen in earlier examples of graphene exfoliation [4]. This ultrahigh vacuum (UHV) compatible transfer enables UHV-STM imaging and electronic characterization of monolayer graphene fluoride islands (12 – 38 nm lateral dimension). The resultingtopographic and spectroscopic data suggest local variations in fluorine coverage, which is manifested in variable topographic height, ranging from 5.3Å to 7.3Å (mean = 6.4 Å), and also in the small band gap measured in these islands when probed by scanning tunneling spectroscopy. However, the theoretically anticipated large gap (~3 eV) of graphene fluoride is demonstrated when small, weakly interacting (CF)n islands are removed from the substrate to the STM tip. Subsequent transport through captured flakes exhibits band gaps of 2.8 – 3.2 eV.For ex-situ investigation of transferred few-layer graphene fluoride, graphite fluoride powder is dispersed in N-Methylpyrrolidone (NMP), deposited onto silicon dioxide, and characterized by optical microscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX). We thereby verify the transfer of few-layer (CF)n from NMP and the decomposition and chemical modification of (CF)n under electron bombardment.1 N. Kumagai, et al., J. Appl. Electrochem. 25, 869 (1995)2 S.-H Cheng, et al., Phys. Rev. B 81, 205435 (2010)3 P.M. Albrecht and J.W. Lyding, Appl. Phys. Lett. 83, 5029 (2003).4 K.A. Ritter and J.W. Lyding, Nat. Mater. 8, 235 (2009).
10:30 AM - C14.5
Graphene Oxide and Chemically Modified Graphene – A Flame Retardant or Fire Hazard?
Jiaxing Huang 1
1 Materials Science and Engineerinjg, Northwestern University, Evanston, Illinois, United States
Show AbstractGraphite oxide (GO) has gained extensive interest as a precursor for bulk production of graphene based materials. Due to the highly energetic nature of GO, self-propagating thermal deoxygenating reaction can be observed in solid state. Although the resulting graphene product is quite stable against combustion even in a natural gas flame, its thermal stability is significantly reduced when contaminated with potassium salt by-products left from GO synthesis. In particular, the contaminated GO becomes highly flammable, which poses a serious fire hazard. This highlights the need for efficient sample purification methods. However, purification of GO is typically hindered by its tendency to gelate during rinsing. We proposed a two-step, washing procedure that was found to be effective for suppressing gelation and thus greatly facilitating purification. Salt induced flammability is alarming for the fire safety in large scale manufacturing, processing, and storage of GO materials. However, the energy released from the deoxygenation of GO can be harnessed to drive new reactions for creating graphene-based hybrid materials. Through such domino-like chain reactions, graphene sheets decorated with metal and metal oxide particles were synthesized using GO as the in-situ power source. For example, enhanced electrochemical capacitance was observed for graphene sheets loaded with RuO2 nanoparticles.
11:15 AM - C14.6
Fractionation of Single Wall Carbon Nanotubes by Length Using Cross Flow Filtration Method.
Shigekazu Ohmori 1 , Takeshi Saito 1 , Bikau Shukla 1 , Motoo Yumura 1 , Sumio Iijima 1
1 Nanotube Research Center, AIST, Tsukuba, Ibaraki, Japan
Show AbstractSingle wall carbon nanotubes (SWCNTs) are one of the most promising materials for the post silicon electronic applications because of their excellent electronic properties based on their chemical stability and mechanical strength. Particularly, the length of SWCNTs is important for applying to electronic devices with SWCNTs' interconnection networks of percolation. Beside this, it has been reported that the length of SWCNTs can also affect critically to their dispersing and optical properties. Thus sorting of SWCNTs by length is of great importance for both the fundamental understanding of their properties as well as for their applications. Recently, some techniques for sorting of SWCNTs by length, such as, size exclusion chromatography, centrifugation techniques, electrophoresis, and so on, have been reported to date. However, these methods have a problem of throughput due to their batch process. Therefore, developing an efficient method of sorting SWCNTs by length is still in demand for their applications.Motivated by this need, we have developed a novel technique for fractionating SWCNTs by length using multi-steps cross-flow filtration, in which three membrane filters of different pore sizes, 1.0, 0.45, and 0.2μm were used. SWCNTs dispersed in water with the help of sodium carboxymethyl cellulose detergents were successfully sorted into four fractions, and their atomic force microscopy observations confirmed that their length distribution peaks are within the expected ranges from pore sizes of used filters. However, the result of the similar filtration process using a different detergent, sodium dodecylbenzene sulfonate, showed no pronounced correlation between the length distribution of SWCNTs and the pore size. The observed difference in the sorting phenomena caused by the detergent type suggests that the permeation property of dispersed SWCNTs strongly depends on their complex structure with detergent molecules.
11:30 AM - C14.7
Rubberlike Viscoelastic Energy Dissipation from -196°C To 1000°C.
Ming Xu 1 , Don Futaba 1 , Takeo Yamada 1 , Motoo Yumura 1 , Kenji Hata 1 2
1 1Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan, 2 , Japan Science and Technology Agency (JST), Kawaguchi Japan
Show Abstract Viscoelasticity describes the ability of a material to both dissipate energy (viscous) and reversibly deform (elastic) and permeates all levels of our lives from human tissue, shoe soles, ear plugs, mattresses to vibration isolators. Within all viscoelastic materials there are elements providing both elasticity through their bonding and viscosity through their motion. The most common element, such as in rubber, is cross-linked long-chain molecules that move via intermolecular motion. Long-chain molecules limit temperature stability because below the glass transition temperature, molecular motion is frozen and at sufficiently high temperature, the material decomposes. This even holds true for silicone rubber, which is one of the best heat resistant viscoelastic materials. Here, we present a 100% CNT viscoelastic material that shows temperature invariant rubberlike energy dissipation ability from -196°C~1000°C [1], which was achieved by mimicking the rubber structure through creating a random network of long interconnected carbon nanotubes synthesized by water-assisted chemical vapor deposition [2,3]. Characterization at room temperature (RT) by dynamic mechanical analysis (DMA) revealed that the CNT rubber had same stiffness (storage modulus 1MPa) as silicone rubber, yet superior energy dissipation ability (Loss modulus (0.3 MPa) two times higher). Furthermore, not only did it exhibit similar viscoelastic properties from -140°C to 600°C, but also it demonstrated frequency stability (0.1-100Hz), the same level of reversible deformation (critical strain 5%) and fatigue resistance (1,000,000 cycles, 100Hz) similar to the RT behavior of silicone rubber. As far as we know, commercial DMAs are limited to 600°C as no existing viscoelastic materials required tests beyond ~300°C. The intertube structure resembling a three-dimensional highway network was the key for the energy dissipation and structural cohesiveness that allowed for large deformations, where each CNT made contact with innumerous other CNTs. It should be noted that this structure greatly differs from typical bundled CNT material where CNTs are straight and contacts the same CNTs over long spans. The energy dissipation of the CNT rubber through the zipping and unzipping at intertube contacts differs from that of rubber where energy is dissipated by molecular motion. The temperature invariance of the vdW interactions and the mechanical properties of CNTs explain these temperature invariant viscoelastic properties [1].[1] M. Xu, D. N. Futaba, T. Yamada, M. Yumura, K. Hata, Nature, Submitted (2010).[2] K. Hata, D. N. Futaba, K. Mizuno, T. Namai, M. Yumura and S. Iijima, Science, 306, 1362 (2004).[3] S. Yasuda, T. Hiraoka, D. N. Futaba, T. Yamada, M. Yumura, K. Hata, Nano Lett., 9, 769 (2009).
11:45 AM - C14.8
Engineering CNT Oriented Sheets for a Better Polarizer.
Julia Bykova 1 2 , Aleksey Arsenin 3 , Yakov Lesnichiy 3 , Anvar Zakhidov 1 2 4 , Jonathon Smith 1 2 , William Holmes 4 , Alexander Kuznetsov 2
1 Physics, University of Texas at Dallas, Richardson, Texas, United States, 2 The Alan G. MacDiarmid NanoTech Institute, University of Texas at Dallas, Richardson, Texas, United States, 3 , Moscow Institute of Physics and Technology, Moscow Russian Federation, 4 , Solarno Inc., Irving, Texas, United States
Show AbstractThe anisotropy of carbon nanotube (CNT) can absorb polarized light by varying amount, depending on its relative orientation to the incident light. It has been shown before that short single-wall carbon nanotubes (SWNT) in polyvinyl alcohol (PVA) composite oriented in certain direction can be a good polarizer with qualitative factor of polarization (QFP) ~2, with low total transparency (up to 15%) [1].Oriented aerogel of multi-wall carbon nanotubes (MWNT) created by dry-drawing of spinable CNT forests has also been showed to be a relatively good polarizer [2,3]. However the QFP of such CNT sheets once created was not quite understood in terms of the initial properties of CVD grown forest. In this presentation it is shown how the QFP depends on the CVD synthesis conditions, i.e. the height of the grown CNT forest, temperature of synthesis and specific process of densification of CNT sheet. The QFP is 2-3 times higher than that of short SWNT [1] and the transparency of CNT aerogel increased up to 80%, while sheet resistance can also be tuned.The free standing non-densified state of oriented CNT sheet is actually an oriented aerogel with very low density and namely this CNT aerogel is shown to have the highest QFP. We analyze the factors which control the physical processes of light absorption and scattering in CNT sheets and clarify the relationship between the optical polarizer QFP and the anisotropy of the ac and dc electrical conductivities and other parameters. Systematic characterization by UV-Vis and IR spectroscopy, elipsometry combined with SEM and Raman scattering showed that organic liquid densification of CNT aerogel (which compresses the fee standing aerogel of ~ 30 micron height to ~50-100 nm thin CNT film on glass substrate) creates mainly three types of reorientations of the sheet: broadening of bundles, reorientation of bundles in perpendicular direction and partial disorientation. This reorientations decrease QFP and we discuss the ways to keep QFP high, while strengthening CNT aerogel by appropriate methods.This work is supported by AFOSR grant FA 9550-09-1-0384 and AFRL/Rice grant via CONTACT consortium of Texas.[1] S. Shoji at al., Phys Rev B 77 (2008) 153407[2] M.Zhang, S.Fang et al., Science, V.309 (2005) 1215[3] A. Aliev, A.Kuznetsov, Phys Let A 372 (2008) 4938
12:00 PM - C14.9
Manipulation of Electrical Transport of Carbon Nanotube Films by Decorating Metal Nanoparticles.
Yeontack Ryu 1 , Choongho Yu 1
1 Mechanical Engineering, Material Science and Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractThis study demonstrates that electrical transport properties of carbon nanotube films can be dramatically altered by decorating nanoparticles on nanotubes. Depending on the reduction potential of nanoparticles, electrical conductance and Seebeck coefficient have been increased or decreased. The high susceptibility is believed to be due to electrical transport occurred only along the surface of tubes. Carbon nanotubes were first dispersed in water by using sodium dodecyl benzene sulfonate (SDBS). The solution was sprayed on a substrate to form transparent films. Subsequently, gold chloride or copper sulfate was used for precipitating nanoparticles on the films. The decoration process was performed by immersing the film into the metal salt solution. In order to facilitate the decoration process, silver paint for gold or zinc plate for copper was in contact with the film. The film immersion time in the metal salts and its concentration play a significant role in the particle precipitation, which changes electronic transport properties of nanotube films. Particularly, the two different nano-particles decorated films show opposite behaviors in electrical conductance and Seebeck coefficient. For instance, the electrical conductance was increased by a factor of ~2 via gold incorporation, whereas copper incorporation yielded reduction in conductance (a factor of ~0.8 decrease) with a large increase in Seebeck coefficient (a factor of ~2 enhancement). We believe that this study can be served as a basis to develop a material with desired properties for various applications including thermoelectric energy conversion.
12:15 PM - C14.10
Structural Properties of Pillard Graphene Structures.
Sangwook Sihn 1 2 , Vikas Varshney 1 3 , Ajit Roy 1 , Barry Farmer 1
1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, United States, 2 Multi-Scale Composites and Polymers Division, Univ. of Dayton Research Institute, Dayton, Ohio, United States, 3 , Universal Technology Corporation, Dayton, Ohio, United States
Show AbstractCarbon nanostructures such as carbon nanotube (CNT), graphite and diamond are known to have superior mechanical, thermal and electrical properties. However, unlike the diamond, these superior properties of other forms of carbon nanostructures (CNT and graphite) are limited to the directions parallel to the graphene sheet (e.g., length direction for CNT and graphene plane for graphite). Non-bonding van der Waals interactions result in poor properties in the transverse direction perpendicular to the graphene sheet. A pillared graphene structure (PGS) is a numerically designed carbon nanostructure with the graphene sheets bonded together with CNTs to form a CNT and graphite network. Not only because of the superior properties of graphite and CNTs, but because of low interfacial resistance at the CNT-graphene junctures due to the same constitutive carbon elements and the same hybridization among the carbon atoms, it is highly expected to enhance the transverse transport properties such as thermal and electrical conductivities. However, because of its column-like structure and curvature near CNT-graphene junctures, the structural properties might be compensated. Therefore, it is important to investigate the structural performance of the PGS.In the present study, we will investigate the structural integrity of the three-dimensionally reinforced carbon architecture, PGS, in terms of mechanical properties and buckling instability. We will conduct computational simulation using a finite element method based on a structural molecular mechanics approach using an energy equivalence. Various representative unit cell models will be developed for the PGSs having different values of pillar lengths and inter-pillar distances. These structures will be converted into the beam finite elements having nodal points on the carbon atom sites. Proper periodic boundary conditions will be applied to the unit cell of the PGS to obtain the effective mechanical properties such as Young’s modulus and Poisson’s ratio in three orthogonal directions (two planar and one out-of-plane). The results of the unit cell will be compared with those of the multi-cell model. Parametric study will be conducted with various CNT truss lengths to determine the critical parameters that affect the effective in-plane and through-thickness properties of the PGS. Eigen analysis will be conducted to obtain critical buckling loads for these various geometric parameters.
12:30 PM - C14.11
Vibrational Dynamics and Polymorphism in Deodesic Polyarene Crystals.
Rozenn LeParc 1 , Laurent Alvarez 1 , Jean Louis Bantignies 1 , Stephane Rols 2 , Patrick Hermet 3 , David Maurin 1 , Alexander Ivanov 2 , Vincent Jourdain 1 , Lawrence Scott 4
1 LCVN, Université Montpellier II, Montpellier France, 2 , ILL, Grenoble France, 3 Physique Théorique des Matériaux, Université de Liège, Liège Belgium, 4 Merkert Chemistry Center , Boston College, Boston, Massachusetts, United States
Show Abstract“Geodesic Polyarenes” belong to a new class of carbon materials intermediate between carbon nanotube and graphene. As a matter of fact these molecules are “bowls shaped” polycyclic aromatic hydrocarbon with curved convex or concave surfaces, composed by a carbon skeleton and “the edge of the bowls” is terminated by hydrogen atoms. Different molecules present different curvatures related to the number and the distribution of five numbered and six membered rings. Like flat PAH geodesic polyarenes form crystalline materials exhibiting different structures and intermolecular interactions.The general aim of our work is to bring a better understanding of these new molecules, particularly focusing on the influence of the molecules curvature and size on their structural organization (for flat PAH, it has been demonstrated that the size and shape of the molecule is influencing the crystalline organization) and on their dynamics. Thus infra-red absorption, neutron inelastic scattering have been performed between 10 and 300K in order to understand the dynamics in these crystalline materials. High pressure Raman and X-ray diffraction have also been performed on these crystalline materials in order detect polymorphism associated to possible molecular reorientation.