Symposium Organizers
Manish Chhowalla Rutgers University
John A. Rogers University of Illinois, Urbana-Champaign
Carey M. Tanner SRI International
Pagona Papakonstantinou University of Ulster
Andrea C. Ferrari University of Cambridge
L1: Chemically Derived Graphenes I
Session Chairs
Monday PM, November 30, 2009
Room 310 (Hynes)
9:30 AM - **L1.1
Graphene-based Materials.
R. Ruoff 1
1 Mechanical Engineering, University of Texas, Austin, Texas, United States
Show AbstractOur top-down approaches [1,2] inspired physicists to study individual layers of graphite obtained by micromechanical exfoliation, and one of our current approaches has been to convert graphite to graphite oxide (GO), generate aqueous colloidal suspensions containing individual layers of GO (we call them ‘graphene oxide’), and to use these ‘graphene oxide sheets’ in a variety of ways. For example, we have embedded individual and reduced graphene oxide sheets in polymers such as polystyrene and evaluated their dispersion, morphology, and the electrical percolation and thus conductivity of the resulting composites. In parallel paths, we have: (i) undertaken studies of individual graphene oxide and reduced graphene oxide sheets, to elucidate their chemical, optical, and electrical properties, (ii) embedded graphene oxide sheets in glass by a sol-gel route and made electrically conductive and transparent glass coatings, and (iii) produced 'graphene oxide paper', a material with intriguing mechanical properties (iv) produced reduced graphene oxide powder with moderately high surface area and used this to study electrochemical double layer capacitance (v) made carbon-13 labeled graphite and thus carbon-13 labeled graphite oxide, and studied its detailed chemical structure with SS NMR. Finally, (vi) I will talk about recent work in our group on growing and characterizing graphene and few layer graphene films on metal substrates, and their transfer to other substrates for device fabrication and characterization. This survey talk about graphene and its chemical derivatives will present an overview of these various results. Support of our work by the NSF, ONR/NRL, NASA, and DARPA is appreciated. 1. Lu XK, Yu MF, Huang H, and Ruoff RS, Tailoring graphite with the goal of achieving single sheets, Nanotechnology, 10, 269-272 (1999).2. Lu XK, Huang H, Nemchuk N, and Ruoff RS, Patterning of highly oriented pyrolytic graphite by oxygen plasma etching, Applied Physics Letters, 75, 193-195 (1999).See also papers on http://bucky-central.me.utexas.edu/publications.htm such as #139,146, 150,155, 160, 164, 166, 168, 169, 174, 179, 180, 181, 182, etc.
10:00 AM - L1.2
Probing the De-oxidation and Electronic Structure of Graphene Oxide by in situ High Resolution X-ray Photoelectron Spectroscopy.
Surbhi Sharma 1 , Jeremy Hamilton 1 , Pagona Papakonstantinou 1
1 School of Engineering, Nanotechnology and Integrated BioEngineering Centre, NIBEC, University of Ulster, Newtownabbey United Kingdom
Show AbstractCurrent interest in graphene oxide (GO) sheets has been sparkled by the recent discovery of graphene. Graphene oxide is the most promising precursor for bulk production of graphene. Graphene oxide sheets are heavily oxidised layers, which contain a large number of oxygen groups within the graphene structure. These oxygen functional groups can be partially removed by deoxidation either thermally or by chemical reduction, yielding a partially reduced structure, which is of interest as a filler to polymer composites; as transparent conducting films for low cost photovoltaics and energy –storage materials, liquid crystal devices as well as a potential component for biosensing and nanoelectronics devices. Although graphene derived from graphene oxide holds significant technological promise the evolution of its fundamental electronic structure at different reduction steps remains largely unexplored. There is also controversy in the literature which groups are dominant in graphene oxide or after its conversion to graphene. To address these points, we have studied the progressive loss of oxygen functional groups and the electronic structure of graphene oxide at various stages of ultra high vacuum thermal annealing process by in situ high resolution X ray photoelectron spectroscopy, XPS (conducted at the NCESS facility in Daresbury, UK). In particular temperature dependent XPS and valence band studies revealed that the majority of oxygen species in thermally deoxidized GO consist of hydroxyl C-OH groups; followed by contributions from carbonyl and carboxylic C=O, COOH groups, whereas the epoxy/ether C-O-C groups are the least thermally stable. Annealing up to 1000C is able to remove oxygen content from 32 at% to 3at% (C:O ratio 11.3). The valence band spectrum of the de-oxygenated film via heating to 1000 C resembles significantly that of graphite. After thermal treatment to 1000 C the intensity ratio of D to G Raman peaks slightly decreased and both peaks exhibited a reduction in FWHM suggesting improvement in the graphitization. The thermal treatment process can increase the sp2 bonding fraction up to ~70% and functionalize the surface to meet application demands. Our study shows that the graphene oxygen functional groups can be decreased in a controllable manner using high temperature annealing. Our findings provide useful information, critical to graphene device engineering and fabrication.
10:15 AM - L1.3
Evolution of Electrical, Chemical and Structural Properties of Graphene Oxide Upon Annealing.
Cecilia Mattevi 1 , Goki Eda 1 , Stefano Agnoli 2 , Steve Miller 1 , Andre Mkhoyan 3 , Ozgurd Celik 4 , Daniel Mastrogiovanni 4 , Gaetano Granozzi 2 , Eric Garfunkel 4 , Manish Chhowalla 1
1 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States, 2 Department of Chemical Science, University of Padova, Padova Italy, 3 Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States, 4 Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey, United States
Show AbstractSingle sheets of graphite oxide are emerging as starting materials providing alternative path to graphene. The exfoliation of graphite oxide in aqueous solution allows deposition of single sheets, referred to as graphene oxide (GO), or multilayer films on virtually any substrate. The stoichiometry, atomic and electronic structures of GO are largely unknown. GO is an insulator but controlled reduction provides tunability of the electronic properties, allowing the possibility of accessing zero-band gap graphene. We present a detailed description of opto-electronic properties, chemical state [1] and structure [2] of single and few-layered of GO at different stages of reduction. Particular attention has been given to understanding the atomic structure of pristine GO before investigating its transformation upon annealing. The sp2/sp3 fraction for single and multilayered pristine GO have been elucidated using comparative X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) measurements of the fine structure of C and O K-edges. The distortion of carbon basal plane induced by sp3 C-O bonds in pristine GO has been observed by annular dark filed imaging [2].We found that the electrical characteristics of reduced GO do not approach those of intrinsic graphene obtained by mechanical cleaving because the materials remains significantly oxidized. In fully reduced GO, the carbon-carbon sp2 bonding fraction is ~ 0.80 while the residual oxygen still forms sp3 bonds with carbon atoms in the basal plane. The oxygen disrupts the transport of carriers delocalized in the sp2 network, limiting the mobility and conductivity of reduced GO thin films. Our analysis reveals that removal of oxygen to achieve sp2 carbon fraction of > 0.95 in GO should lead to properties that are comparable to graphene.[1] C. Mattevi et al.“Evolution of electrical, chemical, and structural properties of transparent and conducting chemically derived graphene thin films” Adv. Funct. Mater. Vol 19, (2009) p.1.[2] K. A. Mkhoyan et al.” Atomic and electronic structure of graphene oxide” Nano Lett. vol.9, (2009), p 1058.
10:30 AM - L1.4
Photothermal Deoxygenation of Graphene Oxide for Patterning and Distributed Ignition Applications.
Scott Gilje 1 , Sergey Dubin 2 , Alireza Badakhshan 3 , Jabari Farrar 1 , Stephen Danczyk 3 , Richard Kaner 2
1 Aerospace Research Laboratories, Northrop Grumman Aerospace Systems, Redondo Beach, California, United States, 2 Department of Chemistry and Biochemistry and California NanoSystems Institute, University of California Los Angeles, Los Angeles, California, United States, 3 AeroPhysics Branch, Combustion Devices Group, Air Force Reserach Laboratory, Edwards Air Force Base, California, United States
Show AbstractExposing nanostructured graphene oxide (GO) to a camera flash results in a photothermally activated reaction. This process is accompanied by a pronounced photoacoustic effect along with a rapid temperature increase, which initiates a deoxygenation reaction to yield graphitic carbon. SEM images of the product reveal that an expanded graphite with an accordion type structure forms. Nitrogen absorption measurements (BET), carried out before and after exposure to the flash, yield a surface area that increases from 6 m2/g up to 980 m2/g. X-ray photoelectron spectroscopy (XPS) indicates a substantial increase in intensity of the C=C signal, while the oxygen content decreases markedly after flashing. XRD analysis shows a single peak at 26.4° 2θ, confirming conversion to graphitic carbon. Hydrogen gas uptake of 0.5 wt % was measured at 77 K. Thin films of GO can be patterned using a mask to selectively control exposure to the flash. This holds potential for future conducting graphene and insulating GO-based electronics. Another potential application involves using a photo-initiated reaction to achieve the simultaneous ignition of multiple nucleation sites. This type of “distributed ignition” has applications in liquid fuel rockets and in high efficiency homogeneous charge compression ignition (HCCI) engines.
10:45 AM - L1.5
Infrared Absorption Study of the Thermal Reduction of Graphene Oxide.
Muge Acik 1 , Cecilia Mattevi 2 , Geunsik Lee 1 , SeongYong Park 1 , Carlo Floresca 1 , Adam Pirkle 1 , Robert Wallace 1 , Moon Kim 1 , Kyeongjae Cho 1 , Manish Chhowalla 2 , Yves Chabal 1
1 Materials Science and Engineering, The University of Texas at Dallas , Dallas, Texas, United States, 2 Materials Science and Engineering, Rutgers - the State University of New Jersey, Piscataway, New Jersey, United States
Show AbstractTo characterize graphene oxide (GO) and understand how it is thermally reduced, we have carried out a series of experiments using in-situ IR absorption spectroscopy and ex-situ atomic force microscopy, Raman scattering, transmission electron microscopy, and x-ray photoelectron spectroscopy. The in-situ transmission Fourier Transform Infrared Spectroscopy (FTIR) measurements focus on the reduction of GO via thermal annealing to understand the deoxygenation process. Indeed, the manner in which oxygen might be incorporated into the structure (e.g. into the basal plane or the edges of graphene and graphite sheets) would help tailor the properties for optimum device performance. Therefore, GO samples of different thicknesses (single layer, three layers, five layers and multi-layers) were deposited on doped Si substrates coated with native SiO2 double sided polished, approximately 15Å thick layer). Ex-situ Raman scattering data and TEM images make it possible to determine the number of layers, and XPS is used to examine the binding configuration of carbon to oxygen. Thermal annealing of GO upon gradual heating was performed at various temperatures (30-900°C) under vacuum (10−3-10−4 Torr) in a reaction cell. As prepared, the absorbance spectrum of GO at room temperature shows a complex structure including a high concentration of functional groups, such as hydroxyls, carboxyls, sp2-hybridized C=C, epoxides and ethers. Using differential spectra, the reduction process was monitored in detail to determine the change in functional groups at each temperature with 25°C increments up to 850°C. Our observations reveal the formation of ketones, ethers and sp2-hybridized C=C as well as a loss of hydroxyls, carboxyls and epoxides upon gradual annealing. After high temperature annealing at 850°C, there is still oxygen remaining in the structure of GO. At that point the DC electrical conductivity as well as the AC conductivity (IR absorbance) increase, consistent with the presence of graphene domains. Yet, there is a clear incorporation of oxygen into the basal plane. *The authors acknowledge funding from the NRI SWAN program.
11:30 AM - **L1.6
Electronic Transport in Chemically Derived Graphene.
Klaus Kern 1 2
1 Nanoscale Science Department, Max Planck Institute for Solid State Research, Stuttgart Germany, 2 , Ecole Polytechnique Federale de Lausanne , Lausanne Switzerland
Show AbstractGraphene, consisting of a layer of carbon atoms just one atom thick, is the ultimate in thin conducting sheets. The charge carriers can be tuned from electron-like to hole-like by the application of a gate voltage, and very high carrier mobilities have been reported. Future electronics applications envisage the creation of diverse nanoscale elements of electronic circuits on a single graphene sheet. However, progress in this direction is hampered by the limited availability of high-quality, large size graphene sheets. A very promising low-cost, up-scalable synthetic approach comprises the reduction of graphene oxide (GO) sheets, which can be deposited with controllable density onto a wide range of substrates. Chemical reduction converts the close-to-insulating GO into sheets with up to four orders of magnitude higher electrical conductivity. Such chemically derived graphene is a versatile basis for fabricating thin conductive films on solid support, thus opening access to transparent flexible electrodes. For the electrical conductivity of monolayers of reduced GO, only moderate values of 0.1-50 Scm-1 have been found. The observed temperature- and electric field-dependence of conductance can be consistently interpreted in the framework of two-dimensional variable-range hopping in parallel with electric field-driven tunneling. The latter mechanism is found to dominate the electrical transport at very low temperatures and high electric fields. Our results are consistent with a model of highly conducting graphene regions interspersed with disordered regions, across which charge carrier hopping and tunneling are promoted by strong local electric fields. Strategies to heal these defects are thus needed for more demanding device applications. We demonstrate that this task can be approached by a CVD process which enables substituting carbon atoms contained within the defective areas. In this manner, chemically derived graphene sheets of large dimensions and two orders of magnitude enhanced conductivity compared to the merely reduced GO can be obtained.
12:00 PM - L1.7
Ultra-Large Graphene Membranes as Flexible and Transparent Electronic Material.
Hisato Yamaguchi 1 , Goki Eda 1 , Cecilia Mattevi 1 , HoKwon Kim 1 , Manish Chhowalla 1
1 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States
Show AbstractPreparation of single- to few-layered graphene thin films in ultra-large scale is one necessary step towards utilizing graphene as a practical electronic material. However, large-area deposition of graphene is still in the progress with deposition on the order of few cm [1-3] being demonstrated. Although chemical vapor deposition (CVD) process and annealing of SiC substrates are potentially promising routes for achieving pristine graphene films, solution-based process using chemically derived graphene has important advantage in the preparation of large-area thin films and membranes.We report the use of chemically derived graphene for deposition of single- to few-layered ultra-large graphene thin films, which are compatible with CMOS device manufacturing standards. The thin films were deposited using a modified version of the method proposed by Robinson et al. [4]. By optimizing the conditions, we succeeded in deposition of uniform graphene thin films on 300 mm SiO2 on Si wafers. Single- to few-layered thin films were achieved. Furthermore, deposited films were transferred on to arbitrary substrates such as PET films or left as free-standing membranes. Detailed characterization using AFM, Raman spectroscopy, XPS, transmittance and electrical measurements as a function of reduction will be presented. We demonstrate that by using appropriate reduction conditions, it is possible to achieve mobility values of 10 – 15 cm2/Vs. Our results provide a pathway for integration of graphene into ultra-large area flexible electronics.[1] K. S. Kim et al. “Large-scale pattern growth of graphene films for stretchable transparent electrodes” Nature 457, 706-710 (2009).[2] X. Li et al. “Large-Area Synthesis of High-Quality and Uniform Graphene Films on Copper Foils” Science 324, 1312-1314 (2009).[3] K. V. Emtsev et al. “Towards wafer-size graphene layers by atmospheric pressure graphitization of silicon carbide” Nature Materials 8, 203 - 207 (2009).[4] J. T. Robinson et al. “Wafer-scale Reduced Graphene Oxide Films for Nanomechanical Devices” Nano Lett. 8, 3441–3445 (2008).
12:15 PM - L1.8
Graphene as a Transparent Electrode.
Ki-Bum Kim 1 , Chang-Mook Lee 1 , Jaewu Choi 1
1 Information Display, Kyung Hee University, Seoul Korea (the Republic of)
Show AbstractIn this talk, we will present the strength and the weakness of graphene as a transparent electrode for future electro-optic devices such as displays, solar cells, and light emitting diodes. The electro-optical properties of the graphene transparent electrodes, which were prepared by mechanical cleavage from a highly ordered pyrolytic graphite and chemical vapor deposition, are compared.
12:30 PM - L1.9
Fabrication of Large Area Graphene Sheets by Chemical Exfoliation for Transparent Conductive Films.
Takeshi Fujii 1 , Ryosuke Shimizu 1 , Yoshiyuki Yonezawa 1 , Yukimi Ichikawa 1
1 Electron Device Technology Center, Fuji Electric Advenced Technology, Hino-city Japan
Show AbstractGraphene sheet is a promising candidate for a low-cost and rare-metal free transparent conductive film (TCF) with a high transparency in wide wavelength range. Recently, the TCF composed of densely stacked graphene sheets by chemical exfoliation have been reported [1]. However, conductance of the graphene TCF was not high enough for electrical applications such as solar cells and flat panel displays, because the size of graphene sheet was as small as several micrometers, and carrier transport was limited by contact among adjacent graphene sheets. To improve the conductivity of graphene TCF, we have fabricated large area chemical exfoliated graphene sheets by using large size graphite oxide (GO) without coercive exfoliation by an ultrasonication process. Large size GO was prepared by modified Hummer’s method [2] using natural graphite flakes with a size of around 400 μm. Then, obtained GO was dispersed into methanol, which results in grahpene oxide naturally exfoliated to single layer. Graphene sheet was deposited on hydrophilically treated SiO2/Si substrate by casting the obtained graphene oxide dispersion and then reduced by hydrazine-monohydrate. From optical microscope image, the measured size of grahene sheet was over 100 μm, and, the thickness was about 1nm from AFM measurement. From both results, obtained graphene sheet was suggested to be mono-layer graphene with a dimension of over 100 μm. Electrical properties of the obtained graphene sheet will also be discussed in the presentation. This work was supported in part by the New Energy and Industrial Technology Development Organization (NEDO) under the Ministry of Economy, Trade and Industry (METI) of Japan.[1] X. Wang et al., Nano Letters 8, 323 (2008). [2] M.Hirata et al., Carbon 42, 2929 (2004).
12:45 PM - L1.10
High Performance of Graphene-based Flexible Transparent Conducting Film by Chemical Doping.
Ki Kang Kim 1 , Alfonso Reina 1 , Hyesung Park 1 , Yumeng Shi 2 , Jing Kong 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 School of Materials Science and Engineering, Nanyang Technological UniVersity, Nanyang Singapore
Show AbstractGraphene based transparent conducting films were transferred to SiO2, glass, and PET substrates after their growth by ambient pressure chemical vapor deposition (CVD). Here, we show that the sheet resistance of the sample was significantly decreased after chemical doping with metal halide such as AuCl3, PtCl2 and PdCl2. Furthermore, the reduction of the sheet resistance was related to the reduction potential of cation of metal halides. Finally, we discuss the transmittance of those films in terms of doping and film morphology. The sheet resistance and transmittance obtained after doping of such films were measured to be between 150-1500 ohms/sq at 80-90% transmittance. Lastly, the adhesion energy between target substrates and the graphene was different due to the hydrophobicity of the substrates.
L2: Chemically Derived Graphenes II
Session Chairs
Monday PM, November 30, 2009
Room 310 (Hynes)
2:30 PM - **L2.1
Large-Area Graphene Films for Sensor, MEMs and RF Applications.
Eric Snow 1
1 , Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractThe recent discovery of graphene and its extraordinary electrical, mechanical and chemical properties has stimulated an intensive effort to exploit these properties in potential applications. Recently, this effort has taken on increased interest and importance, because researchers have demonstrated the ability to form large-area sheets of single- to few-layer graphene and to deposit them on arbitrary substrates. In this presentation, we present initial results obtained at NRL on the formation and use of large-area films of graphene for sensor, microelectromechanical and radio-frequency device applications. We have investigated both transferred films of CVD-grown graphene and spin-on (or spray-deposited) films of chemically modified graphene. We find that the active surface of chemically modified graphene produces high-performance sensors with demonstrated part-per-billion detection of trace chemical vapors [1]. We find that this same chemically active surface also improves the performance of micromechanical resonators where we have demonstrated ~ 100 MHz drum resonators with quality factors ~ 3,000, which is comparable to nanocrystalline diamond thin films [2]. For high-frequency electronic devices pure graphene is optimal because of its high electron mobility and saturation velocity. Using this material we have demonstrated RF amplifiers with an fT*Lg product of 9 GHz-μm [3], which is comparable to Si NMOS. These initial promising results coupled with the low-cost and simplicity of graphene material growth indicate that graphene has a promising future for large-area electronics applications.[1] JT Robinson, FK Perkins, ES Snow, ZQ Wei and PE Sheehan, NanoLetters 8, 3137 (2008).[2] JT Robinson, M Zalalutdinov, JW Baldwin, ES Snow, ZQ Wei, PE Sheehan and BH Houston, Nanoletters 8, 3441 (2008).[3] J.S. Moon, et al., IEEE Electr. Dev. Lett. 30, 650 (2009).
3:00 PM - L2.2
Development of Conductometric Sensors and Supercapacitors from Aqueous Suspensions of Functionalized Graphene.
Xiaohong An 1 , Trevor Simmons 2 , Rakesh Shah 3 , Morris Washington 1 , Saroj Nayak 1 , Saikat Talapatra 3 , Swastik Kar 1
1 Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Chemistry and Chemical Biology, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Department of Physics, Southern Illinois University Carbondale, Carbondale, Illinois, United States
Show AbstractWe have developed a new method for producing large quantities of graphene flakes in aqueous suspensions. Using this, we present simple methods for large-scale applications of graphene such as conductometric sensors and supercapacitors. In both cases, the graphene flakes are transferred onto nanoporous membranes which then form thin films of large specific area. These films show large changes in resistance upon exposure to gases/vapors. In particular, the sensor films are extremely sensitive to the presence of alcohol vapors (dR/R >10,000%), which make them suitable for breathalyzers. Further, electrolytic double-layer capacitors fabricated from these graphene-film membrane structures show impressive specific capacitance (over 100 F/gm) at high energy densities (>9 Wh/kg) and are capable of delivering high power (operating at > 100 kW/kg) making them suitable for high surge-power applications.
3:15 PM - L2.3
Gas Sensors Based on Thermally Reduced Graphene Oxide.
Ganhua Lu 1 , Junhong Chen 1 , Leonidas Ocola 2
1 Department of Mechanical Engineering, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractNanoscaled materials are attractive candidates for gas detection elements due to their unique and outstanding properties (e.g., extremely high surface-to-volume ratio) which can potentially lead to novel sensors with exceptional performance. Graphene is a two-dimensional monolayer of sp2-bonded carbon atoms and has been reported as a promising sensing material because of its excellent mechanical, thermal, and electrical properties. A variety of physical and chemical routes have been employed to produce graphene. A potential strategy to cost-effectively mass produce graphene-based devices is to first generate graphene oxide and then reduce it to obtain graphene for device applications. Here, we demonstrate a high-performance gas sensor using partially-reduced graphene oxide sheets. The sensing device was fabricated by dispersing the graphene oxide suspension onto gold interdigitated electrodes. The partial reduction of graphene oxide was achieved through low-temperature step annealing (300 °C at maximum) of the device in argon flow at atmospheric pressure. The electrical conductance of graphene oxide was measured after each heating cycle to evaluate the level of reduction. The thermally reduced graphene oxide showed p-type semiconducting property in ambient environment and were highly responsive to low-concentration NO2 and NH3 diluted in air at room temperature. The NO2 sensing mechanism of the fabricated sensor is attributed to the electron transfer from the reduced graphene oxide to adsorbed NO2 (electron acceptor), which leads to enriched hole concentration and enhanced electrical conduction in the reduced graphene oxide sheet. In the case of NH3 detection, the electron transfer is from adsorbed NH3 (electron donor) to the reduced graphene oxide, lowering hole concentration and electrical conduction in the reduced graphene oxide. The contact between the reduced graphene oxide and the electrode could also contribute to the sensing response. The simple and low-cost manufacturing process and the wide availability of graphene oxide could lead to cost-effective graphene-based gas sensors.
3:30 PM - **L2.4
Exfoliation of Graphene in Common Solvents and Other Systems: The Route to Useful Nano-structured Materials?
Jonathan Coleman 1 , Paul King 1 , Arlene O'Neill 1 , Mustafa Lotya 1 , Valeria Nicolosi 1 , Zhenyu Sun 1 , Shane Bergin 1 , Fiona Blighe 1 , Sukanta De 1 , Umar Khan 1 , Yenny Hernandez 1
1 Physics, Trinity College Dublin, Dublin Ireland
Show AbstractWe have built on our recent discovery of a small family of solvents to disperse and exfoliate graphite to give graphene. This simple process uses sonic energy to break up graphite powder in certain solvents. Due to the balance of graphene-graphene and graphene-solvent interactions, exfoliation occurs without any net energy cost. This process does not result in oxidation or defect formation and so no thermal or chemical reduction is required. Early results confirmed that this resulted in dispersions of well-exfoliated graphene at concentrations of up to 0.01 mg/ml. We have now demonstrated over 30 solvents for graphene. By measuring the concentration of graphene dispersed after centrifugation for all solvents we can estimate the Hansen solubility parameters for graphene. This allows us to show that the dispersability decreases as the enthalpy of mixing of the dispersion increases. In addition we have demonstrated a method to improve the concentration of graphene dispersed. We can attain up to 2 mg/ml of graphene dispersed in N-methylpyrrolidone. Even at this high concentration, the degree of exfoliation is excellent with 17% of flakes consisting of a single graphene layers and 83% of flakes containing <5 layers. These high concentration dispersions can be formed into mechanically strong, electrically conductive, free standing films. We have also developed methods to exfoliate graphene using surfactants which give graphene dispersions with concentration approaching 1 mg/ml. These dispersions can be used to prepare thin, transparent, conducting films with DC and optical conductivities of ~1.5*10^4 S/m and ~4*10^4 S/m respectively. This results in films with sheet resistance of <4 kOhm/Sq for transmittance ~75%. These films are electromechanically stable under flexing for at least 2000 bend cycles.
4:30 PM - **L2.5
Transparent Conducting Nanomaterials from Chemically Converted Graphene: Synthesis, Deposition and Selective Patterning.
Yang Yang 1 , Richard Kaner 2 , Vincent Tung 1 , Matthew Allen 2 , Steven Jonas 1 , Kitty Cha 1 , Jonathan Wassei 2
1 Materials 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 has been shown to exhibit extraordinary electrical characteristics that have caused a dramatic increase in interest and research into this material. Several methods have emerged for producing high quality large-area graphene for electrode applications. The advantages of chemically converted graphene (CCG) include the ability to be solution-cast, an essential property for roll-to-roll processing. Transparent electrodes comprised of a nano-composite of CCG and single-walled carbon nanotubes have been successfully fabricated from solution and applied to optoelectronic devices. Our method does not require surfactants, preserving the intrinsic electronic and mechanical properties of both components. This low temperature process is completely compatible with flexible substrates and does not require a sophisticated transfer process. Chemical doping further enhances the conductivity of the hybrid films. Recent progress in transfer patterning and selective area registration using straightforward soft lithographic methods is also presented.
5:00 PM - L2.6
Electrical and Materials Characterization of Large Area, Transparent, Conductive Graphene Film Networks and Their Potential for Gas Sensing.
Jason Johnson 1 , Ashkan Behnam 1 , Ant Ural 1
1 Electrical and Computer Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractWe investigate the fundamental electrical and structural properties of room temperature processed, large area, transparent, conductive graphene film networks and demonstrate their ability to detect ammonia at low ppm levels. Several groups have obtained graphene in individual sheets or few-layers by either liquid exfoliation from expandable graphite, chemical conversion from graphene oxide (GO), or CVD grown graphene. In this talk, we show that expandable graphite (EG) can be treated with surfactant solutions and high energy sonication to obtain few-layer graphene sheets, which can then be filtered and transferred onto large area silicon substrates with excellent repeatability and with little time and cost. In order to investigate the electrical properties of the few-layer graphene (FLG) film networks fabricated using this method, we pattern the material into various structures using simple photolithography techniques and plasma etching; similar to what has been done for carbon nanotube films. We find that the graphene film networks have reasonable conductivity in the range from 25 to 65 S/cm at room temperature, and demonstrate excellent transmittance, greater than 80% in the visible regime and over 90% in the IR and near IR range. We determine the mechanisms responsible for transport in the FLG film network by measuring its four point probe resistance at various temperatures. The weak insulating behavior observed in the cryogenic regime suggests that 3D variable range hopping is the dominant transport mechanism at low temperatures. In addition to the above results, magneto-resistance measurements reveal a weak inverse dependence of resistivity on magnetic field at higher temperatures while at lower temperatures the dependence becomes stronger and changes sign as the magnetic field increases. Together with AFM and TEM analysis, these results enable us to better understand both the physical structure and the percolative nature of the transport in FLG film networks. Finally, we experimentally demonstrate the application of graphene film networks for gas sensing. Due to its large surface to volume ratio and large number of edge defects, graphene is highly sensitive to its environment. We fabricate a simple and efficient gas sensor based on FLG film networks and demonstrate large changes in its resistance upon exposure to both oxygen and ammonia. In addition, upon functionalizing the surface of our FLG film networks, we can achieve even higher changes in the film resistance. This works provides further insight into possible applications of large area graphene film networks and their potential in device applications.
5:15 PM - L2.7
Highly Sensitive Gas Sensors Using Graphene Thin Films as Sensing Materials.
Jinwoo Lee 1 , Byeonghyeon Kang 1 , Kyongsoo Lee 1 , Cheoljin Lee 1 , Byeongkwon Ju 1
1 Electrical Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractAfter the 1st separation from graphites in 2004 by mechanical exfoliation method, graphene is regarded as one of promising new nano-materials required for future electronics. Graphene is an unfolded single-walled nanotube. Like carbon nanotubes, graphene is consisted of carbon honeycomb structure. However, it is a two dimensional material, while a nanotube is one dimensional. Both surface areas (upper and lower) of a graphene sheet have the same possibility for gas molecule adhesion, while the internal surface area inside a nanotube are limited for gas adhesion than the outer surface. Therefore, graphene is expected to offer wider surface area compared with nanotubes, and is more suitable for gas sensor applications.In this study, we obtained graphene sheets by chemical vapor deposition and also by mechanical exfoliation of a HOPG (Highly ordered pyrolitic graphite). In chemical vapor deposition method, graphene sheets were directly grown over Ni substrate using CH4 and H2 gas mixture and separated from the substrate to SiO2/Si surface using FeCl3 (aq). In mechanical exfoliation method, a HOPG mass was rubbed over SiO2/Si surface several times repeatedly until we obtain enough amounts of graphene thin layers for sensor applications. For each graphene sheet, the thickness was measured by Raman spectroscopy. Gas sensors were fabricated by E-beam deposition of electrodes over the pre-deposited graphene sheets. Several hazardous gases including NH3, NO2, and O3 were applied for the test of sensor performance in room temperature. NH3 and NO2 gases were purchased and ozone gas was obtained directly from an O3 generator. 5 ppm of NH3, 1 ppm of NO2, and 1 ppm O3 were measured, which shows that our graphene based gas sensor is highly sensitive.
5:30 PM - L2.8
New Insights into the Structure and Reduction of Graphite Oxide.
Wei Gao 1 , Lawrence Alemany 1 , Lijie Ci 1 , Pulickel Ajayan 1
1 , Rice University, Houston, Texas, United States
Show AbstractGraphite oxide (GO) is one of the main precursors of graphene-based materials, highly promising for various technological applications because of their unusual electronic properties. But although epoxy and hydroxyl groups are widely accepted as its main functionalities, its complete structure has remained elusive. Interpreting spectroscopic data in the context of the major functional groups believed to be present in GO, we now show evidence for the presence of 5- and 6-membered-ring lactols. Based on this chemical composition, we devised a complete reduction process through chemical conversion by sodium borohydride and sulfuric acid treatment, followed by thermal annealing. Only small amounts of impurities are present in the final product (less than 0.5 wt% of sulphur and nitrogen, compared with about 3 wt% with other chemical reductions). This method is particularly effective in the restoration of the π conjugated structure, and leads to highly soluble and conductive graphene materials.
5:45 PM - L2.9
Oligo (Polyethylene Glycol) Functionalized Reduced Graphene Oxide and Its Water Solubility.
Shifeng Hou 1 , Robert Cuellari 1 , Najeeb Hoshang Hakimi 1 , Krutika Patel 1 , Pratik Shah 1 , Matthew Gorring 2 , Stefanie Brachfeld 2
1 Chemistry & Biochemistry, Montclair State University, Montclair , New Jersey, United States, 2 Department of Earth & Environmental Studies, Montclair State University, Montclair , New Jersey, United States
Show AbstractSince first discovered in 2004, graphene has shown various unique properties, including superior mechanical strength and low density and high heat conductance. Many potential applications are based its unique mechanical and electrical properties: graphene–polymer composites, electronic devices, drug delivery and biosensors. Graphene oxide is water soluble with low conductivity and the reduced graphene oxide is good conductivity with poor solubility in water. Several techniques have been developed to enhance the solubility of reduced graphene oxide and most of these are based on physically absorbed functional molecules onto graphene sheets. In this report, a chemical modification process was developed to functionalize reduced graphene oxide with specific groups. Graphene oxide was obtained from graphite powder through a modified Hummers method and then reduced by NH2-NH2, LiAlH4 or NaBH4. The reduced graphene oxide had been functionalized with amine and halogen successfully firstly and these graphene sheets can be used as precursors for further functionalization. Oligo (Polyethylene glycol) molecules were linked to single-layer graphene sheets through covalent bond. The FT-IR, X-Ray diffraction, TEM, SEM and Uv-spectroscopy techniques were used to characterize polyethylene glycol modified reduced graphene oxide (PEG-RGO). PEG-RGO could be dispersed in water, tetrahydrofuran, and ethylene glycol, with individual, single-layer graphene sheets automatically. The dispersion behavior of PEG-RGO in aqueous solvent has been investigated. It was demonstrated that the addition of PEG groups to the surface reduced graphene can enhance the solubility of RGO in water. PEG-RGO was well-dispersed as individual sheets in water. A series of solutions of PEF-RGO with concentrations of 0.001% to 1.5% were prepared and the PEG-RGO dispersions exhibited long-term stability, similar to the case of graphene oxide dispersions in water. In addition, a PEG-RGO film with layered structure and high conductivity has been successfully prepared by filtration, spin-coating or evaporation technique. We have further characterized the compatibility of PEG-RGO with a series of polymer matrixes. Our results demonstrate the feasibility of combining conventional organic synthesis techniques with techniques for the modification of reduced graphene oxide. The technique developed here can be extended to synthesize various functionalized graphene dispersions by using other functional groups and provides a general route for preparing solutions and conducting films based on functional graphene and seeks different applications of graphene-based materials.1.K. S. Novoselov, A. K.Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, A. A. Firsov, Science, 2004, 306, 666-669.2.S. Park, R. S. Ruoff, Nature Nanotechnology, 2009, 4, 217 - 224.3.Y. Xu, H. Bai, G. Lu, C. Li and G. Shi, J. Am. Chem. Soc., 2008, 130, 5856–5857.
L3: Poster Session: Chemically Derived Graphenes III
Session Chairs
Tuesday AM, December 01, 2009
Exhibit Hall D (Hynes)
9:00 PM - L3.1
Efficient Reduction of Graphite Oxide by Sodium Borohydride and its Effect on Electrical Conductance.
Hyeon-Jin Shin 1 2 , Ki Kang Kim 2 , Anass Benayad 1 , Seon-Mi Yoon 1 , Hyeon Ki Park 2 , In-Sun Jung 1 , Mei Hua Jin 2 , Hae-Kyung Jeong 2 , Jong Min Kim 1 , Jae-Young Choi 1 , Young Hee Lee 2
1 Samsung Advanced Institute of Technology, Samsung Electronics Co., LTD., Youngin-si Korea (the Republic of), 2 Sungkyunkwan Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon-si Korea (the Republic of)
Show AbstractWe systematically modulated the conductivity of graphite oxide film by using reducing agents. We found that the sheet resistance of graphite oxide film reduced by sodium borohydride (NaBH4) was much lower than that reduced by hydrazine (N2H4). This was attributed to the formation of C-N groups in the case of N2H4 that may act as a donor state and as a consequence, compensate the hole carriers in the reduced graphite oxide. In the case of reduction by NaBH4, the interlayer distance was slightly expanded first by the formation of intermediate boron oxide complex and then contracted by the gradual removal of carbonyl and hydroxyl groups together with boron oxide complex. The fabricated transparent conducting film with the reduced graphite oxide by NaBH4 revealed the sheet resistance comparable to that of the dispersed graphene.
9:00 PM - L3.10
Graphene Growth Based on Dissolution and Segregation of C in Ni.
Ageeth Bol 1
1 TJ Watson Research Center, IBM, Yorktown Heigths, New York, United States
Show AbstractWe developed a scalable process to synthesize large area graphene films based on dissolution/segregation of Carbon in Nickel. A thin film of Ni (typically 300 nm) is exposed to ethylene at 1000°C at low pressure (500 mTorr) and subsequently cooled down in inert atmosphere. In this way we obtain a continuous film consisting of overlapping graphene flakes. HRTEM, LEED, XPS and Raman spectroscopy show that the flakes consist of 1-10 layers of graphene. The graphene films are rather robust and can easily be lifted off from the Ni films and placed on any desirable substrate. Hall mobility measurements show very uniform electrical characteristics. Over a piece of 0.5 cm2 the Hall mobility varies from 940 to 990 cm2/Vs with a stable carrier density of 8.5x10.12 cm-2 (channel width 200 um, channel length 460 um). With in-situ LEEM we demonstrate that our growth technique is based on dissolution and segregation of Carbon in Nickel rather than chemical vapor deposition. At high temperatures ethylene breaks down on the Ni surface and C dissolves into the Ni and saturates the film. In-situ LEEM shows that by cooling the C-saturated Ni film in inert atmosphere, the Ni becomes over-saturated with C and the C crystallizes out on the surface of the Ni in the form of graphene.With in-situ XRD we show that controlling the cooling down rate is important in this process. The cooling down rate has a large influence on how the Ni film orders and therefore how the graphene grows.
9:00 PM - L3.11
A Magneto-Catalytic Technique for Writing Complex Patterns in Graphene.
Lutfiye Bulut 1 , Robert Hurt 1
1 , Brown University, Providence, Rhode Island, United States
Show AbstractThere is tremendous interest in the patterning of graphene and other carbon films for a variety of applications. In addition to lithographic methods, graphene patterning may be possible through selective etching by catalytic gasification. Several studies have created single-particle channels in graphite or graphene using gasification catalyzed by iron, nickel, cobalt, or silver particles. It has been reported that channeling catalyst particles follow preferred crystallographic directions, which if fully understood could lead to precise patterning through rule-based etching protocols. Nevertheless, this class of technique would be much more powerful and flexible if one had a method to explicitly control the channeling directions, or to change direction dynamically to produce complex and preselected channel patterns. Here we explore the use of the dioxygen reaction (C + O2 -> CO/CO2) to reduce reaction temperature below the Curie point of magneto-catalytic particles allowing them to be steered in situ by externally applied magnetic fields. We demonstrate that graphene can be etched into arbitrarily complex and preset patterns using cobalt-based catalyst particles for dioxygen gasification at temperatures near 550 oC using a close-proximity Sm2Co17 magnet. We demonstrate vertical pitting, horizontal unidirectional channeling, bidirectional channeling, and tridirectional channeling under identical reaction conditions by varying only the position and motion of the external magnetic. Etch rates as high as 2 um/min are achieved and the etch tracks and XRD studies suggest the gradual decrease in magneto-catalytic activity over the course of the reaction through cobalt oxide formation. The results suffice to demonstrate active steering for particles/channels down to about 200 nm. This is to our knowledge the first demonstration of a magneto-catalytic writing technique for graphene, and it may find application in the massively parallel production of uniform flow channels, pores, ribbons, devices, or circuits.
9:00 PM - L3.12
Electrochemical Synthesis of CdSe Quantum Dot Array on Graphene Basal Plane using Mesoporous Silica Thin Film Templates.
Yong Tae Kim 1 , Jung Hee Han 2 , Byung Hee Hong 1 2 , Young-Uk Kwon 1 2
1 Chemistry, BK-21 School of Chemical Materials Science, Sungkyunkwan University, Suwon Korea (the Republic of), 2 Chemistry, SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractSince the discovery of microscale single-layer graphene, graphene and related materials have received intensive attention as promising materials for nanoelectronics due to their fascinating electrical, mechanical, and chemical properties. In addition, the recent large-scale synthesis of high-quality graphene films suggests their applications to bendable and/or stretchable transparent electrodes for solar cells, sensors and displays. Surface grafting on the graphene with functional materials will be an indispensable technique towards these directions of progress. This, however, requires the problems arising from the lack of reactivity of the graphene basal plane to be resolved. A perfect graphene does not have dangling bonds on the basal plane for chemical bond formation. The chemical potential of the basal plane is lower than the edges or defects. Therefore, deposition directly on graphene results in grafting on the edges and defects only. In case of using vacuum deposition techniques, this problem has been solved by modifying the graphene surface i.e., ozone treatment, forming metal underlayer, and attaching organic molecules with functional groups. On the contrary, there has been no report on grafting on the basal plane by electrochemistry. Here, we demonstrate that the use of a nanoporous mask can be a viable means to form a uniform nanostructured film on the graphene basal plane. We applied a mesoporous silica thin film whose pore structure is composed of about 8 nm sized vertical channels in a hexagonal symmetry on the graphene surface as a nanoporous mask. The nanochannels exert resistance against the diffusion of electrolytes and, thus, function as a potential-equalizer to suppress the preference for the edge and defect sites. By depositing CdSe, we formed CdSe quantum dots into a hexagonal array structure.
9:00 PM - L3.13
Formation of Graphene Nanostructures on Vicinal SiC(000-1) Surfaces.
Chenda Srey 1 , Seigi Mizuno 2 , Satoru Tanaka 1
1 Applied Quantum Physics, Kyushu Univ., Fukuoka Japan, 2 Molecular and Material Sciences, Kyushu Univ., Fukuoka Japan
Show AbstractGraphene, a single sheet of sp2-bonded carbon arranged in a honeycomb structure has attracted a lot research interests due to its superior electronic properties [1]. Graphene can be epitaxially grown either on Si or C face of SiC surface by heating at high temperatures in vacuum [2].The self-organized nanofacet formation was found by high temperature H2 gas etching on vicinal SiC surfaces consisting of step/terraces or facets and that is the one of the promising ways to be applicable to nanostructure formation. The high temperature etching on 4° (vicinal toward [11-20]) C-terminated 6H-SiC(000-1) at 1360°C result in a periodic surface structure [3]. In our experiments, we focus on the growth of graphene layers, in vacuum, with SiC nanofacet surface, which can be a good template for the nanostructure formation. First, the growth of graphene has been carried out on Si face of SiC (0001) surfaces with nanofacet structure. The surfaces exhibited the (√3×√3)R30° due to silicate adlayer [4]. After annealing to higher temperature than 1100°C, the surface structure was changed to (6√3×6√3)R30° [5] before the monolayer or few layers of graphene were grown . The nanofacet structure was thermally destroyed at the temperature higher than 1050°C confirmed by atomic force microscope (AFM). Thus, the nanostructure was conclusively difficult to form on Si face of SiC substrate.On the other hand, the C face of SiC(000-1) surface initially exhibited (√3×√3)R30° by reflection high electron energy diffraction (RHEED) due to silicate adlayer [4] after H2 etching. Then, the surface was changed to (3×3) when annealed to 1000°C, and the mixure of (3×3) and (2×2) phases were appeared after annealing at 1050°C. Further anneal to 1100°C for 5 minutes, a faint streak of graphene was only observed outside of the (+2/3) streak (invisible at the (-2/3) streak), viewed with [1-100] azimuth parallel to the facet/step edges. This asymmetric pattern indicates site-selective formation of graphene on (11-2n) nanofacets. This was confirmed by the detailed RHEED analysis, showing a ~8° inclined graphene streak from SiC rods. Importantly, the surface morphology checked by AFM indicated the periodic structure similar to the SiC nanofacet surface. We can here infer that the nucleation of graphene takes place at the facet region, resulting in the formation of the nano-structure of graphene at (11-2n) nanofacets. The further results of characterizations using LEED, STM, AFM, and micro-Raman will be given and the formation mechanisms of graphene nanowires will be discussed.References[1] K. S. Novoselov et al., Nature 438, 197 (2005)[2] I. Forbeaux et al.,Surf. Sci. 442, 9 (1999)[3] H. Nakagawa et al., Phys. Rev. Lett. 91, 226107 (2003)[4] J. Bernhardt et al., Appl. Phys. Lett. 74, 1084 (1996)[4] L.I Johansson et al., Phys. Rev. B. 53, 13793 (1996)
9:00 PM - L3.14
Morphology of Graphene Surfaces on Hydrophobic/Hydrophilic Domain Nanopatterns.
Takahiro Tsukamoto 1 , Toshio Ogino 1
1 , Yokohama National University, Yokohama Japan
Show Abstract Graphene attracts much interest as a new material for the next generation of electronic devices owing to its remarkable electrical and mechanical properties. In many studies, graphene samples have been prepared using mechanical exfoliation of graphite and its deposition onto a SiO2 substrate. Substrate-induced structures or mesoscopic corrugations on the deposited graphene are important for their transport. Since a well-defined graphene layer on a solid substrate is necessary for device applications, a well-defined surface is also required to tightly attach the graphene to the substrate. Therefore, the selection of the substrate is one of the important issues. Previously, we have reported on a graphene sheet on a sapphire surface with a terrace/step structure [1]. Graphene is closely adhered on the sapphire surface and the height of a single layer graphene is estimated to be approximately 0.36 nm when using atomic force microscopy (AFM) in air. In the present study, we report on a graphene sheet on the sapphire surface on which hydrophilic and hydrophobic domain nanopatterns coexist. Sapphire substrates with step bunches accompanied with crossing steps were treated by a H2SO4 and H2O2 mixed solution (H2SO4:H2O2=3:1) for 10 min followed by an ultrasonic treatment in water for 5 min to clean the surface. Graphene was deposited on the sapphire surface by mechanical exfoliation of graphite. The surface morphology of the graphene was observed using the contact mode in AFM in air. Previously, we found that a graphene sheet tightly adheres to a sapphire surface with regularly ordered terrace/step structure and the buried step structure on the sapphire surface clearly appeared on the graphene surface. In the case of a sapphire surface with elliptical hydrophobic domains surrounded with hydrophilic areas, graphene adhered on the hydrophobic domains and did not closely attach to the surrounding hydrophilic areas. The weaker adhesion on the hydrophilic areas is believed to be owing to water or gas molecules confined at the interface. The graphene is hydrophobic. When the graphene attaches to the hydrophobic domains, the confined water or gas molecules are transferred from the hydrophobic domains to the hydrophilic areas. The water or gas molecules are concentrated in the hydrophilic areas. Our experimental results indicate that, for a good contact of graphene with a solid surface, hydrophobicity is important in addition to the flatness. [1] T. Tsukamoto et al., Appl. Phys. Express, 2 (2009) 075502.
9:00 PM - L3.15
Electric Transport in Epitaxial Graphene on Vicinal SiC Substrate with Periodic Atomic-scale Facets.
Shunsuke Odaka 1 2 3 , Hisao Miyazaki 1 3 , Akinobu Kanda 3 4 , Kouhei Morita 5 , Satoru Tanaka 5 , Yasumitsu Miyata 6 , Hiromichi Kataura 6 , Kazuhito Tsukagoshi 1 3 6 , Yoshinobu Aoyagi 3 7
1 , MANA, NIMS, Tsukuba Japan, 2 , Tokyo Institute of Technology, Yokohama Japan, 3 , JST-CREST, Kawaguchi Japan, 4 , Institute of Physics and TIMS, University of Tsukuba, Tsukuba Japan, 5 , Kyushu University, Fukuoka Japan, 6 , AIST, Tsukuba Japan, 7 , Ritsumeikan University, Kusatsu Japan
Show AbstractHigh mobility in single or multiple carbon atomic sheets of graphene have been revealed in theoretical and experimental studies. For a development of the field-effect transistors (FETs) fabricated in graphene sheet, large-area sheet of an epitaxial graphenes on SiC substrate were grown at high temperatures on a vicinal SiC substrate. However, the vicinal SiC surface was corrugated with atomic-scale facet arrays. The atomic-scale facets caused an anisotropic transport in the graphene sheets, depending on current flow direction. A series of graphene FETs were fabricated on vicinal SiC substrates with the channels parallel (parallel-channel FET) or perpendicular to the facet (perpendicular-channel FET). The graphene with a few layers were grown on the Si face of vicinal 4H-SiC substrates by thermal decomposition at 1600 °C in vacuum. Cross-sectional transmission electron microscopy revealed that the epitaxial graphene layers continuously covered the facets. The graphene was composed of two regions: flat regions with atomic flatness and slop regions on facets. The typical period of the flat and slop cycle was 30 nm. The graphene layers were patterned by dry etching with O2 plasma. Source and drain electrodes, and a top gate structure were formed on the graphene layers. The sheet resistivity as a function of the gate voltage was measured at room temperature in parallel or perpendicular configuration. Ambipolar resistance modulation with respect to the gate voltage change was observed in the both FETs. In comparison of the two FETs, the parallel-channel FET reproducibly exhibited lower sheet resistivity. Based on the observed result, we could clarify the resistivity and gate-voltage response of the graphene in facet regions and atomic flat regions. As the most probable case, the resistivity of terrace region could be smaller than the resistivity of the facet region. This is because the Si atom was decomposed from the facet region, resulting in introducing the defects in the graphene. Furthermore, since graphitization must be started from the facets, there would be disconnection at the facets. More details of the graphene transport with atomic-scale corrugation will be discussed.
9:00 PM - L3.16
Graphene-on-insulator Substrates by In-place Bonding of Graphene Grown on Si/SiO2/Metal Templates.
Katherine Saenger 1 , James Tsang 1 , Jack Chu 1 , Ageeth Bol 1 , Conal Murray 1 , Alfred Grill 1
1 , IBM T.J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractGraphene synthesis by chemical vapor deposition on metallic template layers is a potentially promising route to large-area electronic-quality graphene, providing that workable methods can be found for post-growth removal of the metal and transfer of the graphene sheets to an insulating substrate. The in-place bonding approach presented here, in which the metal template layer under a multilayer graphene (MLG) film is removed while the graphene layer is still attached to the substrate, is both low-cost and scalable. Metal/MLG layers on an insulating substrate are first patterned to form die-sized regions having edges bordered by exposed regions of insulating substrate. Some edges are then tacked to the substrate (with drops of PMMA, for example) while others are left exposed to provide access to a selective etchant for removing the metal. Once the metal is gone, the MLG film spontaneously bonds to the underlying insulator. Substrates produced from Si/SiO2/Ni/MLG structures by this technique will be described along with qualitative data on the technique's sensitivity to tacking geometry and the initial thicknesses of the Ni and MLG films. This work is supported by DARPA under contract FA8650-08-C-7838 through the CERA program.
9:00 PM - L3.17
Graphene Nanoelectronic Devices in Superconducting Regime.
Michele Zaffalon 1 , Joel Wang 1 2 , Pablo Jarillo-Herrero 1
1 Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractGraphene, a single atom-thick sheet of graphite discovered in recent years,has attracted tremendous attention due to its exotic properties. At low energy,its gapless linear band structure results in transport properties described bythe Dirac equation. Graphene is also expected to exhibit many novel transport characteristics in the superconducting (SC) regime. New phenomena, such as pseudo-diffusive dynamics of ballistic electrons, the relativistic Josephson effect,and specular Andreev reflection are predicted by theoretical models combining relativistic quantum mechanics and superconductivity.We study these phenomena experimentally in SC-graphene-SC junctions. Superconductivity in graphene is induced by means of the superconducting contacts through proximity effect. In particular, we use reactive sputtering of NbNto fabricate SC leads which exhibit high SC critical temperature and critical magnetic field. Preliminary results indicate transparent electrical contact withgraphene and induced superconductivity. This combined with the possibility of ballistic transport in graphene may open up the way to the study exotic quantum phenomena.
9:00 PM - L3.18
Photoluminescence in Graphene Oxide Suspensions.
Cecilia Mattevi 1 , Goki Eda 1 , Hisato Yamaguchi 1 , Manish Chhowalla 1
1 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States
Show AbstractGraphene oxide (GO) is emerging as a material with tunable photoluminescence (PL) [1] in the visible range, opening up the prospect of pursuing photonics applications. We have found that GO suspensions obtained by different sedimentation-centrifugation processes reveal PL at different energies and intensities in the visible range. We have carefully investigated the chemical and structural properties of the GO sheets contained in the suspensions. We have found that GO suspensions consisting of poorly exfoliated graphite oxide (i.e containing multilayered flakes) gives rise to a PL peak at 670 nm, while single layered GO suspensions under UV illumination yields a peak at 440 nm. The absorbance spectra of multilayered GO are remarkably affected by the functional groups at the edges attached to the sheets while this effect is negligible in single layered suspensions. No emission energy shifts have been observed for different degree of oxidation. The role of concentration of peripheral functional groups in connection with the average lateral size of the flakes and the exfoliation level on determining the PL energy will also be presented.[1]Z.Luo et al., Appl.Phys.Lett.(2009),94,p.111909.
9:00 PM - L3.2
Lateral Uniformity of Few Layers Graphene Grown on 4H-SiC by Nanoscale Current Measurements.
Filippo Giannazzo 1 , Sushant Sonde 2 1 , Vito Raineri 1 , Jean-Roch Huntzinger 3 , Antoine Tiberj 3 , Jean Camassel 3 , Mikael Syvaejaervi 4 , Rositza Yakimova 4
1 , CNR-IMM, Catania, 95121 Italy, 2 , Scuola Superiore di Catania, Catania, 95123 Italy, 3 , GES, CNRS and Université Montpellier 2, Montpellier, 34095 cedex 5 France, 4 , IFM, Linkoping University, Linkoping Sweden
Show AbstractBecause of its outstanding transport properties, graphene is currently the object of intense research interests. Epitaxial graphene (EG) grown by solid state graphitization of SiC surface has the potential to get wafer size layers for large area electronic applications. To date, few layers graphene (FLG) have been grown both on the Si or C-faces of 6H and 4H-SiC wafers by high temperature treatments (1300-2000°C) in ultra-high vacuum or under atmospheric pressure in Ar ambient. In both cases, the growth starts from large reconstructed terraces that form upon high temperature annealing. The crystal quality of EG is still not as good as that of deposited graphene (DG) obtained by mechanical exfoliation of HOPG. In fact, epitaxial layers are superficially non uniform and a transition/buffer layer in between the reconstructed SiC surface and the first graphene layer is always present in EG grown on the Si face of hexagonal SiC. This charged buffer layer typically affects the electrostatic properties of EG, causing also a shift in the Fermi level with respect to the Dirac point. Low doped 4H-SiC epilayers grown on (0001), 8°-off oriented wafers were used as substrates. Graphene growth was carried out in an inductively-heated reactor, operating at minimal pressure of 5×10-6 mbar. The growth temperature was 2000 °C and, to lower the Si out-diffusion process, a confining argon pressure of 1 atm was used [1]. The aims of this work are: (i) to quantify the SiC surface coverage by EG with nanometric resolution and (ii) to locally determine the Fermi level shift in EG. An innovative scanning probe microscopy technique, torsion resonant conductive atomic force microscopy (TRCAFM), was applied for non-destructive mapping of the current flowing at graphene-SiC interface. Analyses were carried out on two kinds of samples: (i) SiC treated to obtain EG on the surface and (ii) identical pristine SiC with DG. The latter is used as reference sample, because DG can be distinctly identified by optical microscopy and AFM, and because no buffer layer is present at the interface with SiC. TRCAFM on reference samples showed a higher current level on the regions covered by DG than on bare SiC surface, allowing to distinctly determine the graphene covered areas. Local I-V curves showed a Schottky contact-like behaviour, with the DG/SiC barrier height (ΦB~0.9±0.1 eV) much lower than that of Pt tip on SiC (~1.6±0.1eV). A rectifying contact was also found for EG on SiC, but with lower barrier heights than for DG. The difference between the local barrier height and the average value measured on DG gave the local shift in the Fermi level due to the buffer layer charge. Furthermore, current maps on EG samples allowed to quantitatively determine the fraction of area covered by graphene and the bare SiC fraction.[1] C. Virojanadara et al., Phys. Rev B 78 245403 (2008).
9:00 PM - L3.20
On the Formation Graphane from Graphene: A Molecular Dynamics Study.
Sergio Legoas 2 , Pedro Autreto 1 , Marcelo Flores 1 , Douglas Galvao 1
2 Centro de Ciencias e Tecnologia, Federal University of Roraima, Boa Vista, Roraima, Brazil, 1 Applied Physics, State University of Campinas, Campinas, Sao Paulo, Brazil
Show AbstractRecently, a new carbon-based structure named graphane was theoretically proposed [1] and experimentally realized this year [2]. Ideal graphane is a two-dimensional non-flat system consisting of a single layer of fully saturated carbon atoms (sp3 hybridization) with H atoms attached to it in an alternating pattern (up and down with relation to the plane defined by the carbon atoms). Graphane was obtained from hydrogenation of graphene membranes with cold plasmas [2]. In this work we have theoretically investigated the mechanisms of graphane formation from molecular dynamics simulations. We have carried out the simulations using a binding energy bond-order (BEBO) method as developed by A. C. T. van Duin and collaborators and implemented in ReaxFF code [3]. In contrast to more standard molecular force fields ReaxFF can handle making/breaking chemical bonds and the atomic hybridizations are allowed to change during the simulations. Considering the stochastic nature of the experiments, there is a significant probability of the existence of H frustration. H frustration is a configuration where the sequence of alternating up and down H atoms is broken (frustrated). This is similar to spin frustration in magnetic materials. We have considered finite and infinite (cyclic boundary conditions) structures of different sizes and at different temperatures. Our results show [4] that significant percentage of uncorrelated H frustrated domains are formed in the early stages of the hydrogenation process leading to lattice decreased values and extensive membrane corrugations. These results also suggest that large domains of perfect graphane-like structures are unlikely to be formed, 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 [2].[1] J. O. Sofo, A. S. Chaudhari, and G. D. Baker, Phys. Rev. B 75, 153401 (2007); arXiv:cond-mat/0606704.[2] D. C. Elias et. al., Science 323, 610 (2009); arXiv:08104706.[3] A. C. T. van Duin, S. Dasgupta, F. Lorant, and W. A. Goddard III, J. Phys. Chem. A 105, 9396 (2001).[4] S. B. Legoas, P. A. S. Autreto, M. Z. S. Flores, and D. S. Galvao, arXiv:cond-mat/0903.0278v1.
9:00 PM - L3.21
Local Manipulation of Graphene Using Atomic Force Microscopy: Effects on Electronic Properties.
Romaneh Jalilian 1 2 , Luis Jauregui 2 4 , Caleb Roecker 3 , John Coy 2 , Mehdi Yazdanpanah 5 6 , Robert Cohn 6 , Igor Jovanovic 3 , Yong Chen 1 2 4
1 Department of Physics, Purdue University, West Lafayette, Indiana, United States, 2 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 4 School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana, United States, 3 School of Nuclear Engineering, Purdue University, West Lafayette, Indiana, United States, 5 , NaugaNeedles LLC, Louisville, Kentucky, United States, 6 Department of Electrical engineering, University of Louisville, Louisville, Kentucky, United States
Show AbstractGraphene (a single atomic layer of graphite) is a two dimensional hexagonal lattice of sp2 bonded carbon atoms. Graphene shows exceptional properties (e.g. high electrical conductivity, carrier mobility and ballistic electron transport) that are appealing in nanoelectronics and electrically-detected sensors. It is known that charge carriers (both the type and density) in graphene can be tuned by an electric field from p-type to n-type through a charge neutrality point (CNP) (also known as the “Dirac point”). Nearby the CNP, the resistance of graphene is very sensitive to even a small and local change in the carrier density or electrostatic potential.In this work, we have exfoliated graphene from bulk graphite onto 300nm-thick SiO2 and fabricated standard field effect transistor devices using doped Si as the back gate. We have explored how local mechanical or electrical manipulation by various atomic force microscope (AFM) tips may affect the electronic properties of graphene. For example, we have found that both scratching the graphene and brushing off the dusts on the graphene can shift the CNP, possibly through a change in the chemical doping. We have also explored modulating the resistance of graphene by a local “top gate” electric field applied through the AFM tip (using air gap and/or a parylene coating as dielectric). In this work, we have also developed flexible and conductive AFM tips by growing metallic Ag¬2Ga nanoneedles (diameter 50-500 nm, length 1 to 10 μm) on AFM cantilevers for top gating and for gentle mechanical manipulation of graphene.
9:00 PM - L3.22
Measurement of Carrier Recombination Dynamics in Epitaxially-Grown and CVD-Grown Graphene.
Jared Strait 1 , Paul George 1 , Haining Wang 1 , Shriram Shivaraman 1 , Virgil Shields 1 , Mvs Chandrashekhar 1 , Carlos Ruiz-Vargas 2 , Farhan Rana 1 , Michael Spencer 1 , Jiwoong Park 2
1 Electrical and Computer Engineering, Cornell University, Ithaca, New York, United States, 2 Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States
Show AbstractWe present results on the measurement of electron and hole recombination rates in few-layer and multi-layer epitaxial graphene grown on the silicon and carbon faces of silicon carbide [1] and also in graphene grown via chemical vapor deposition (CVD) on nickel [2] using ultrafast optical-pump THz-probe spectroscopy. We find that recombination times can be shorter than 1 ps and longer than 10 ps, depending on the number of graphene layers, the growth technique, and the substrate. We compare our results with theoretical predictions based on recombination mechanisms such as optical phonon emission and electron-electron interactions and find good agreement provided the background carrier density in the graphene layers is taken into consideration. High mobility and unusual band structure of graphene promise high speed electronic and optical devices [3]. Graphene has been proposed for the use of active THz devices, photodetectors, and solar cells [4]. The performance of many of these technologies depends sensitively on the electron-hole recombination rates in graphene. The realization of graphene based technologies for commercial applications relies on the development of scalable methods for the growth of large-area graphene layers. The most promising candidates for this are epitaxially-grown graphene [1] and graphene grown by CVD on metal substrates [2]. The similarities and differences in the optical and electronic properties of these materials are not well understood. In particular, it is not known how many parameters important for devices, such as the carrier cooling and recombination times, vary from one material growth technology to another. In our experiments, optical pulses with 780 nm wavelength, ~90 fs duration, and 1-12 nJ energy were used to photoexcite carriers within the samples. Few-cycle THz pulses generated and detected with a THz time-domain spectrometer were used to probe the carrier distribution and density at various temperatures. It is well known that impurities and the substrate potential can dope exfoliated and CVD grown graphene to densities on the order of 1E12 1/sq-cm. Similarly, the first few layers of epitaxially-grown graphene are doped due to their strong interaction with the SiC substrate [5]. We measure that near-intrinsic graphene layers have recombination times that are carrier density dependent, as predicted by theory, and are in the few-10 ps range. The measured recombination times are found to be shorter and independent of the photoexcited carrier density in doped graphene layers. This latter observation is also in line with the theoretical models. Our results shed light on the most suitable graphene growth technologies for different device applications. [1] W. A. de Heer et. al., Science, 312 , 1191–1196 (2006) [2] J. Kong et. al., Nano lett., 9, 30 (2009) [3] I. Meric et al., Nat. Nanotechnol. 3, 654 (2008) [4] F. Rana, IEEE Trans. Nanotech. 7, 91, (2008) [5] Varchon et al., Phys. Rev. Lett. 99, 126805 (2007)
9:00 PM - L3.23
Ultrafast Hot Phonon Dynamics in CVD-Grown and Epitaxially-Grown Graphene.
Haining Wang 1 , Jared Strait 1 , Paul George 1 , Shriram Shivaraman 1 , Virgil Shields 1 , Mvs Chandrashekhar 1 , Carlos Ruiz-Vargas 1 , Farhan Rana 1 , Michael Spencer 1 , Jiwoong Park 1
1 , Cornell University, Ithaca, New York, United States
Show AbstractWe present measurement and theoretical results on the ultrafast dynamics of hot phonons and hot carriers in few-layer and multi-layer epitaxial graphene grown on the silicon and carbon faces of silicon carbide [1] and also in graphene grown via chemical vapor deposition (CVD) on nickel [2]. We find that the cooling rates of photoexcited carriers are largely independent of the graphene growth technique. The carrier cooling times are found to be limited by the generation of hot optical phonons and their subsequent relaxation. We find that hot phonons decay with a time constant of 3-4 ps which is independent of the number of graphene layers as well as the type of the substrate indicating that energy transport among the graphene layers or from the graphene layers into the substrate is not the bottleneck for hot optical phonon relaxation. The theoretical results obtained from first principles show an excellent agreement with the experimental results. The unique electronic and optical properties of graphene, including high electron and hole mobility and wideband optical absorption, have made graphene a promising candidate for high-speed electronic and optical devices, such as transistors, terahertz oscillators, optical detectors, and sensors. The performance of most of these devices depends on the dynamics of hot phonon and hot carrier relaxation [3,4]. We use ultrafast optical pump-probe spectroscopy that is sensitive to the tail of the hot photoexcited carrier distribution. Immediately after photoexcitation with an optical pulse, the carriers thermalize in 10-100 fs and acquire a Fermi-Dirac distribution with carrier temperatures in the 1200-2000 K range. In the next 300-500 fs the carriers loose energy to the optical zone-center and zone-edge phonons via both intravalley and intervalley scattering. As a result, the optical phonons heat up until the carrier and phonon temperatures are nearly the same and in the 600-900 K range. After that the bottleneck for hot carrier relaxation is hot phonon relaxation. Optical phonons loose energy to acoustic phonons via the anharmonic decay mechanism. We measure hot optical phonon decay rates in the 3-4 ps range in good agreement with theoretical predictions. The dynamics of carrier and phonon temperatures can be described by coupled rate equations which give two distinct time constants; one associated with the initial exchange of energy between the hot carriers and cold phonons and is of the order of 100-150 fs and the other associated with the subsequent relaxation of both hot phonons and hot carriers. These two different time constants are observed in all our experiments. Our experiments conducted on different types of graphene demonstrate the generality of the results. [1] W. A. de Heer et. al., Science, 312 , 1191–1196 (2006). [2] J. Kong et. al., Nano lett., 9, 30 (2009) .[3] A. K. Geim et. al., Rev. Mod. Phys. 81, 109 (2009).[4] R. Bistritzer et.al., arXiv:0906.2992 (2009).
9:00 PM - L3.24
Synthesis of Multilayer Graphene and its Electrical Properties.
Daiyu Kondo 1 2 3 , Katsunori Yagi 1 , Motonobu Sato 1 2 3 , Mizuhisa Nihei 1 2 3 , Shintaro Sato 1 2 3
1 , Fujitsu Laboratories Ltd., Atsugi Japan, 2 , Fujitsu Limited, Atsugi Japan, 3 , CREST-JST, Atsugi Japan
Show AbstractGraphene, an atomically thin carbon film, has been reported to have excellent electrical properties, such as a high carrier mobility and robustness over a high-density current. These properties, however, have been mainly obtained using graphene exfoliated from a graphite crystal. Recently, synthesis of graphene by chemical vapor deposition (CVD) has been reported [1,2]. The quality and electrical properties of the graphene, however, are not yet as good as those of graphene obtained from graphite. In this study, we performed CVD synthesis of graphene to obtain a high-quality graphene film. We also measured electrical properties of multilayer graphene thus obtained.Multilayer graphene was synthesized by hot-filament CVD and thermal CVD. In both cases, an Fe film was first deposited on a Si substrate with a SiO2 layer, and graphene was synthesized using C2H2 diluted by Ar. The pressure was kept at 1 kPa. The Fe film thicknesses ranged from 2.5 nm to 200 nm. In hot filament CVD, the temperature of the filament located 5mm above the substrate was 1000°C, while the substrate temperature was kept at 620°C. In thermal CVD, the substrate temperature was 650°C. The typical synthesis time was 60 min. We have found by scanning and transmission electron microscopy that multilayer graphene tends to be synthesized on a substrate with a thick Fe film, while carbon nanotubes (CNTs), with a thin Fe film. Actually, in hot filament CVD, only CNTs were obtained from Fe films thinner than 7.5 nm, while multilayer graphene was formed from Fe films thicker than 20 nm. Moreover, the thickness of multilayer graphene can be controlled by the Fe thickness. In fact, we obtained 6-nm multilayer graphene from a 200-nm Fe film. On the other hand, 80-nm graphene was formed from a 50-nm Fe film. The results also indicate that the thickness of multilayer graphene was inversely proportional to that of the iron film in hot filament CVD. Raman analyses further showed that the ratio of G band to D band for the multilayer graphene by hot filament CVD was as high as 10. The ratio was improved to 40 for graphene by thermal CVD.For electrical property measurements, a graphene film was transferred to another substrate by etching the iron film under the graphene. The graphene film was then patterned by photolithography followed by dry etching to form a graphene channel. Electrodes consisting of Ti and Au layers were finally made on both ends of the channel by the standard lift-off procedures. It has been found that the graphene channel can sustain a current density higher than 107 A/cm2, which is close to the limit of the current density Cu wiring can sustain. Furthermore, by using a thin graphene channel, we found that the channel current can be modulated by the gate voltage.The authors thank Dr. N. Yokoyama, Fellow of Fujitsu Laboratories Ltd., for his support and useful suggestions.[1] Kim et al., Nature 457, 707 (2009)[2] Li et al., Science 324, 1312 (2009)
9:00 PM - L3.25
The Direct Fabrication of Mechanically Stable Reduced Graphene Oxide/Multi-walled Carbon Nanotube Double Layer Thin Films as a Transparent Electrode.
Young-Kwan Kim 1 , Dal-Hee Min 1
1 chemistry, KAIST, Deajeon Korea (the Republic of)
Show AbstractGraphene is recently considered as a promising candidate for fabrication of highly transparent and conductive electrode. Therefore, many approaches have been tried to synthesize highly crystallized graphene by “peeling off”, epitaxial growth and chemical vapor deposition method. However, these methods are not scalable. For mass production, chemical oxidation and reduction of graphite is a scalable and cost effective method. Nevertheless, this method still requires cumbersome post transfer process and showed relatively poor conductivity. In this work, we describe a novel and simple self-assembly route for direct construction of mechanically stable reduced graphene oxide (RGO)/aminated multi-walled carbon nanotube (MWNT) double layer on transparent substrates without post transfer process. The RGO/MWNT double layer was fabricated by formation of uniform GO thin films on the substrate and following incorporation of aminated MWNTs as a highly conductive bridge to improve poor junction of individual GO sheets. Finally, The GO/MWNT double layer was reduced by hydrazine monohydrate treatment and following thermal annealing process. The fabricated RGO/MWNT double layer thin film on the transparent substrates showed the uniform one to three layered structure without aggregated GO sheet and significantly improved electrical conductivity compared to RGO thin film with high transparency over 90 % at 550 nm. To the best of our knowledge, this work is the first example of construction of large area and highly transparent double layer films consisted of RGO and aminated MWNT on transparent substrates by transfer free process. We believe this self-assembly approach will be a general tool to fabricate hybrid thin films composed of RGO and other important nanomaterials for various applications.
9:00 PM - L3.3
Dielectrophoretic Assembly of Graphene Oxide and Few-Layer Graphene.
Brian Burg 1 , Julian Schneider 1 , Simon Maurer 1 , Niklas Schirmer 1 , Timo Schwamb 1 , Dimos Poulikakos 1
1 Department of Mechanical and Process Engineering, ETH Zurich, Zurich Switzerland
Show AbstractA major drawback in advanced processing technology is the absence of mature and reliable parallel assembly techniques for the large-scale assembly of individual nanoscale structures at predefined locations. Dielectrophoresis (DEP), allowing the site-selective, out of solution deposition of micro- and nanoscale objects in non-uniform electric fields, provides this prospect. A very critical element is the solution quality of the dispersed nanostructures, which is investigated for the dielectrophoretic deposition of graphene oxide and few-layer graphene. Graphene oxide solutions are prepared by a very long acid oxidation period, combined with a thorough purification process to obtain highly oxidized, exfoliated, and extremely pure aqueous dispersions. Pristine graphene solutions on the other side are prepared by ultrasonification and centrifugation of graphite flakes in N-methyl-pyrrolidone (NMP) and water-surfactant solutions, thus avoiding chemical treatment. After DEP, individual sheets of graphene oxide are found between the electrodes, which, initially insulating, recover their electrical conductivity after thermal reduction at 450°C. From the graphene solutions, the directed parallel assembly of electrically active few-layer graphene flakes is realized, with the NMP solutions providing flake thicknesses in the range of 10-50 nm. Liquid phase exfoliation in water-surfactant solutions yields thicker flake dimensions due to the higher enthalpy of mixing in the dispersion. The reported research permits the nonintrusive, parallel, large-scale assembly of soluble two-dimensional nanostructures and is an important framework for the integration of carbon nanostructure based nanoelectromechanical systems (NEMS), sensors and applications.
9:00 PM - L3.4
Strategies for Graphene Layers Achievement by SiC Sublimation Under Various Atmospheres.
Loic Becerra 1 , Aziz Zenasni 1 , Pierre Mur 1 , Denis Rouchon 2 , Denis Mariolle 2 , Nicolas Chevalier 2 , Dominique Lafond 2 , Gerard Lapertot 3 , Thierry Poiroux 4
1 D2NT / L2MA, CEA-LETI, Grenoble France, 2 DPTS / SCPIO, CEA-LETI, Grenoble France, 3 INAC / SPSMS, CEA, Grenoble France, 4 D2NT / LDI, CEA-LETI, Grenoble France
Show AbstractGraphene, thanks to its fascinating hexagonal honeycomb lattice structure, became since its insulation in 2004 by Geim’s team [1] a fashion material studied by numerous laboratories and industrials across the world. Indeed, this crystalline bi-dimensional carbon atoms monolayer could revolutionize many areas of research ranging from nanoscale electronic applications to basic science. Among all its promising characteristics, its high mobility (up to 20 m2/V.s [2] at room temperature) and its transparency combined to its electrical conduction properties make graphene an attractive candidate for potential applications such as transistors, sensors or solar cells.Nowadays, different ways of producing graphene layers are investigated: micromechanical cleavage, chemical elaboration, carbon nanotubes opening, CVD on metallic layers and SiC sublimation [3]. But for the moment, none of these methods provides a reliable technique for large and uniform graphene areas. Since two years, CEA-LETI is engaged in the sublimation of SiC under controlled atmospheres to decrease the temperature of formation of high cristallinity graphene on the SiC surface. Our goal is to develop a microelectronic compatible SiC sublimation process. Thermodynamical simulations have been used in order to investigate possible environments for decomposition at lower temperatures and first experiments in such atmospheres have been carried out.In this contribution, we will present our work on bulk 6H-SiC(0001) and 3C-SiC/Si(111) substrates. Graphene epitaxial growth has been carried out for temperatures ranging from 1200 to 1400°C. Different gaseous atmospheres have been investigated, comparing vacuum and the pure argon atmosphere in terms of structure and topological aspects of graphene. H2 high diluted HCl has been also used since the thermodynamical simulations show a significant impact of Si-etchant atmosphere on the carbon rearrangement at lower temperature. Graphene integrity has been evidenced by Raman spectroscopy and surface morphology has been studied by AFM-KFM and TEM microscopies. Effects of growth time, temperature and gaseous environment will be discussed. Depending of the elaboration conditions used, the sublimation rate can be controlled and it could provide smoother, more homogeneous and bigger domains of graphene on SiC. The obtained results show that graphene films are fast approaching wafer-scale dimensions.[1] K.S. Novoselov et al., Science 306 (2004) 666[2] S.V. Morozov et al., Phys. Rev. Lett. 100 (2008) 016602[3] J. Hass et al., J. Phys.: Condens. Matter. 20 (2008) 323202Keywords: graphene, SiC, sublimation, carbon, crystal, Raman, AFM-KFM, TEM
9:00 PM - L3.5
Focused Ion Beam Etching of Suspended Graphene Devices.
Britt Baugher 1 , Pablo Jarillo-Herrero 1
1 Physics, MIT, Cambridge, Massachusetts, United States
Show AbstractIn this talk we will present our achievements etching nanostructured devices into suspended graphene using a focused ion beam (FIB). Nanoscale devices were recently etched into graphene on a substrate using an FIB, but unfortunately, severe contamination from the beam and the substrate all but completely masked graphene’s unique electrical properties in those devices. Suspended devices, however, may be able to escape this fate. Their separation from the substrate keeps the largest source of impurities at a distance and makes annealing far more effective. Annealed, suspended devices have been shown to survive a myriad of fabrication procedures while still achieving the highest mobilities found in graphene. Here we elucidate the effects of etchings in graphene by two different ion beams: a standard gallium focused ion beam and the recently developed helium ion beam. We will be presenting extensive electrical measurements on the devices we created, in addition to characterizations of the graphene after etching down to the atomic scale, as seen by TEM measurements.
9:00 PM - L3.6
Transport Measurements in Dual-gated Bilayer Graphene.
Thiti Taychatanapat 1 , Pablo Jarillo-Herrero 2
1 Physics, Harvard University, Cambridge, Massachusetts, United States, 2 Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe ability to control the band gap in bilayer graphene by applying a perpendicular electric field has attracted a lot of interest for its potential in nanoelectronic devices based on this material. Here, we examine the electronic properties of top-and-bottom gated bilayer graphene devices. The local top gate and global back gate enable us to control the size of the band gap and the Fermi energy separately and hence create PN junctions and an insulating state in bilayer graphene. In addition, we use quantum point contact geometries to study transport in laterally confined bilayer graphene constrictions. We observe a non-monotonic resistance behavior as the transverse electric field is increased, which we attribute to the onset of conductance through the nanoconstriction.
9:00 PM - L3.7
Large Area Single Crystal Substrates for Growing Graphene.
Meifang Li 1 , Jae Wook Shin 2 , Eric Chason 1
1 Division of Engineering, Brown University, Providence, Rhode Island, United States, 2 Metallurgy Division, B-160/224, Mail Stop 8551, National Institute of Standards and Technology, Gaithersburg, 20899, Maryland, United States
Show AbstractA method for producing large-area, inexpensive single crystal substrates through electrochemical processing is described, which could be used to make substrates for large area graphene. The method uses a sequence of electropolishing, epitaxial electrodeposition and selective etching to create freestanding foils from an initial template crystal that can then be reused to make more material. We have shown that the starting single crystal (Ni) can be reconditioned using electropolishing so that we have been able to produce nine generations of ~80 mm2 freestanding films from the same starting sample with the same crystalline quality. The process has been demonstrated for both Ni(100) and Ni(111) orientations. This method can be turned into a continuous process for making long ribbons or large areas of single crystal films to provide inexpensive substrates for growing graphene layers.
9:00 PM - L3.8
Inelastic Electron Scattering from Graphene on SiC(0001), Ni(111), and Polycrystalline Nickel.
Roland Koch 1 2 , Katharina Kloeckner 1 , Thomas Haensel 1 , S. Imad-Uddin Ahmed 1 , Vladimir Polyakov 3 , Jing Kong 2 , Thomas Seyller 4 , Juergen Schaefer 1 5
1 Institut für Physik and Institut für Mikro- und Nanotechnologien, TU-Ilmenau, Ilmenau Germany, 2 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 , Fraunhofer Institute for Applied Solid State Physics, Freiburg Germany, 4 Institut für Physik der Kondensierten Materie, Universität Erlangen-Nürnberg, Erlangen-Nürnberg Germany, 5 Department of Physics, Montana State University, Bozeman, Montana, United States
Show AbstractThe recent experimental realization of single-layer graphene sheets has led to intense efforts to understand its electronic and vibrational properties in the context of solid state materials physics. Fundamental as well as technological aspects are of high interest for designing future graphene-based devices. In this context it is important to gain new insights about the properties, origin and effects of extrinsic sources upon graphene. Among them the influence of the substrate with respect to growth and electron as well as phonon and plasmon interaction is particularly relevant.In this contribution we investigate the interaction of graphene with SiC(0001), Ni(111), and polycrystalline nickel using inelastic electron scattering. In particular, new results are presented that relate the coupling of charge carriers in semi-metallic graphene with the optical phonons of SiC(0001). Due to this coupling the surface optical phonons, the so called Fuchs-Kliewer phonons, are completely quenched and two new modes ω- and ω+ appear. The energetic position and intensity of these modes depend strongly upon the incoming primary electron beam energy which has been varied from 2.5eV up to 200eV. Simulating our high resolution electron energy loss spectroscopy(HREELS)-data using dielectric theory and solving the Poisson- and Schrödinger equations self consistently allows us to determine the carrier density distribution and the conduction band edge normal to the plane of the graphene/SiC heterostructure. Both change drastically by varying the sample temperature from 130K up to 600K. A comparison with new temperature dependent HREELS data from highly oriented pyrolytic graphite(HOPG) will be presented. There a strong increase in carrier concentration is observed with increasing sample temperature.
Symposium Organizers
Manish Chhowalla Rutgers University
John A. Rogers University of Illinois, Urbana-Champaign
Carey M. Tanner SRI International
Pagona Papakonstantinou University of Ulster
Andrea C. Ferrari University of Cambridge
L4: Electronics from Solution Exfoliated Graphite I
Session Chairs
Tuesday AM, December 01, 2009
Room 310 (Hynes)
9:30 AM - **L4.1
Graphene and Its Chemical Derivatives.
Kostya Novoselov 1
1 School of Physics and Astronomy, University of Manchester, Manchester United Kingdom
Show AbstractWhen one writes by a pencil, thin flakes of graphite are left on a surface. Some of them are only one angstrom thick and can be viewed as individual atomic planes cleaved away from the bulk. This strictly two dimensional material called graphene was presumed not to exist in the free state and remained undiscovered until the last year. In fact, there exists a whole class of such two-dimensional crystals. 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. The very unusual electronic properties of this material as well as the possibility for it’s chemical modification make graphene a promising candidate for future electronic applications.
10:00 AM - L4.2
Large-scale Exfoliation of Graphite into Stable Aqueous Solutions of Graphene Using a Non-covalent Functionalization.
Xiaohong An 1 , Trevor Simmons 2 , Morris Washington 1 , Saroj Nayak 1 , Saikat Talapatra 3 , Swastik Kar 1
1 Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Chemistry and Chemical Biology, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Department of Physics, Southern Illinois University Carbondale, Carbondale, Carbondale, Illinois, United States
Show AbstractWe report a novel “molecular wedging” method for directly exfoliating graphite into stable aqueous suspensions of graphene using 1-pyrenecarboxylic acid (PCA). Electron microscopy investigations reveal large quantities of graphene flakes in the aqueous dispersion, while Raman and AFM investigations confirm the presence of monolayer graphene amongst the exfoliated species. Absorption measurements at the UV region confirm that the exfoliated flakes are functionalized with PCA. This non-covalent functionalization is superior to existing covalent functionalization techniques that disrupt the sp2 hybridization of the carbon network, and facilitates the production of large quantities of high-quality graphene. The exfoliation mechanism will be discussed within the framework of the physicochemical interactions of PCA and graphitic surfaces in the presence of appropriate polar solvents, with the help of control experiments and characterization steps. The PCA-functionalized graphene flakes can be transferred onto a variety of substrates for characterization as well as diverse applications development.
10:15 AM - L4.3
Synthesis of Large Graphene Nanostructures Through Solution Chemistry.
Liang-shi Li 1 , Xin Yan 1
1 Chemistry Department, Indiana University , Bloomington, Indiana, United States
Show AbstractGraphene is a new type of material with great potential in electronic and optical applications. When made into structures with nanometer size in one or both dimensions, graphenes have tunable properties including bandgap that depend not only on the size but also on the geometry and the chemical nature of the edges. Thus to make graphene nanostructures, methods based on solution chemistry have a unique advantage because they enable control of the nanostructures with atomic precision.Despite the recent progress in chemical synthesis of aromatic compounds, the rapidly decreasing solubility of graphenes with increasing size poses a major challenge in attempts to synthesize them through solution chemistry. Herein we present a novel solubilization scheme for large graphenes that involves introducing long flexible chains to block the inter-graphene face-to-face interaction. It has enabled us to synthesize stable colloidal graphenes that are large enough to absorb light in the whole visible range. The colloidal graphenes have identical size, shape, and chemical identify because they are synthesized through well-controlled stepwise chemical reactions from benzene derivatives. The large solubility and large extinction efficient for visible light of the colloids suggest that they could serve as a new type of light absorber in organic or hybrid photovoltaic devices. More importantly, the new solubilization method makes it possible to synthesize even larger graphene such as graphene nanoribbons. The latest progress in our group toward this goal will also be discussed.
10:30 AM - L4.4
Low Temperature Highly–yielded Preparation of Fully Exfoliated Graphite.
Vladimir Novikov 1 , Sergei Kirik 1
1 , SSPA “Scientific-Practical Material Research Centre of NAS of Belarus, Minsk Belarus
Show AbstractThe most common technique for exfoliated graphite preparation has been the oxidization and subsequent exfoliation of graphite to give graphene oxide. However the oxidization process results in the formation of structural defects. These defects reduce as electric and mechanical properties of this material. These defects are impossible to remove completely; even after annealing at 1000C. We proposed a new method of exfoliated graphite preparation to give defect-free monolayer graphene. The method 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 powder of purified natural graphite size of 30 microns was used in all experiments as starting material The first stage (intercalation of graphite) was carried out in Dewar vessel at -30 C using solution of alkali metal in liquid ammoniac as reagent. The second stage of the process was realized by putting intercalated of graphite in liquid water. Process of decomposition of intercalated of graphite finished in a second and accompanied by colloidal solution of exfoliated graphite formation. 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 composites.
10:45 AM - L4.5
Large Area Deposition of Graphene Thin Films by Langmuir-Blodgett Assembly.
HoKwon Kim 1 , Cecilia Mattevi 1 , Goki Eda 1 , Hisato Yamaguchi 1 , Manish Chhowalla 1
1 Materials Science and Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States
Show AbstractA challenge in exploiting the electrical properties of graphene is the realization of large area thin films in a scalable and inexpensive manner. The lack of a reliable and simple graphite exfoliation procedure has hindered the possibility of making films starting from pure graphene. Recently it has suggested that organic solvents with surface energies close to the graphene, are able to exfoliate flakes by ultrasonication [1], generating a stable suspension of graphene sheets. Of these, exfoliation with 1-Methyl-2-pyrrolidinone (NMP) yielded the highest concentration of 1-5 graphene layers [1]. Here we present a scalable manner to obtain films of pure graphene on virtually any substrate with reproducible nanometric control over the number of layers. By minimizing the sonication time and alternating several cycles of mild centrifugation followed by sonication of the precipitate, we were able to increase the yield of exfoliated flakes avoiding the excessive reduction in lateral size of the sheets. Suspension of 1 mg/mL containing 1 to 5 layer graphene, as determined by Raman spectroscopy, were prepared. Moreover, a narrow distribution of lateral sheet dimensions has been obtained by imparting a final centrifugation at higher force. Dropping the as obtained suspension onto water forms a Langmuir-Blodgett (LB) film of graphene floating on top of water surface because of its hydrophobicity. The thickness can be tuned from 1 nm up to 20nm. Films of 20 nm display sheet resistance of 5 KOhm/sq and transmittance of 75% at wavelength of 550nm and therefore conductivity of 100 S/cm. These values demonstrate a significant improvement over films of similar thickness reported in Ref 1. Field effect devices using NMP exfoliated graphene exhibit mobility values that are better than those for chemically derived graphene.[1] Hernandez, Y.; Nicolosi, V.; Lotya, M.; Blighe, F. M.; Sun, Z.; De, S.; McGovern, I. T.; Holland, B.; Byrne, M.; Gun’kp, Y. K.; Boland, J. J.; Niraj, P.; Duesberg, G.; Krishnamurthy, S.; Goodhue, R.; Hutchison, J.; Scardaci, V.; Ferrari, A. C.; Coleman, J. N. Nat. Nanotechnol. 2008, 3, 563.
11:30 AM - **L4.6
Solutions of Negatively Charged Graphene Sheets.
Alain Penicaud 1 , Cristina Valles 5 1 , Amelie Catheline 1 , Carlos Drummond 1 , Hassan Saadaoui 1 , Cecile Zakri 1 , Maryse Maugey 1 , Clascidia Furtado 2 1 , Luca Ortolani 4 3 , Marc Monthioux 3
1 CNRS-CRPP, University of Bordeaux, Pessac France, 5 Instituto de Carboquimica, CSIC, Zaragoza Spain, 2 Centro de desenvolvimento da tecnologia nuclear, CDTN-CNEN, Belo Horizonte Brazil, 4 CNR-IMM Bologna, University of Bologna, Bologna Italy, 3 CEMES, CNRS, Toulouse France
Show AbstractNegatively charged graphene layers from a graphite intercalation compound (GIC) spontaneously dissolve in N-methylpyrrolidone, without the need for any sonication, yielding stable, air-sensitive, solutions of atom-thick graphene sheets and ribbons.[1,2] Yield, after centrifugation to remove insoluble material, is as high as 50% of the starting GIC and concentration is as high as 1.0 mg/ml. Raman and absorption spectroscopies show the presence of material of graphitic origin within the homogeneous, aggregate free, solutions whereas light scattering experiments indicate 2D nature of the dissolved species. Graphene flakes and ribbons deposited on a variety of substrates have been imaged by STM, AFM, HRTEM and multiple beam interferometry, demonstrating deposits of atomically thin material. Noteworthy, AFM height measurements on mica give the actual height of graphene (ca 0.4 nm).References (1)C. Vallés, A. Pénicaud, Patent filing FR 07/05803, August 9, 2007.(2)C. Vallés, C. Drummond, H. Saadaoui, C. A. Furtado, M. He, O. Roubeau, L. Ortolani, M. Monthioux, A. Pénicaud, J. Am. Chem. Soc., 2008, 130 (47), 15802-15804.
12:00 PM - L4.7
Highly Ordered Monolayer Films of Graphene Nanosheet by Self-assembly at the Liquid-liquid Interface.
Sanjib Biswas 1 , Lawrence Drzal 1
1 Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States
Show AbstractTransparent and electrically conductive glasses have a wide range of applications in solar cells, sensor devices, and electrostatic charge dissipating coatings. The use of metal oxides such as indium tin oxide (ITO) and fluorine tin oxide (FTO) have limitations such as shortages in the availability of materials, susceptibility to ion diffusion in polymers and reduced transparency in the infra-red (IR) region. Carbon nanotubes and graphene nanosheets are possible alternatives to these metal oxides. Graphene, a single layer of graphite is a two dimensional aromatic macromolecule with the requisite properties and is potentially available from one of the most abundant elements on earth, graphite. Exfoliated graphene nanosheets, developed in the Drzal research group in Michigan State University, consisting of a stack of a few layers of graphene are prepared from natural graphite through a simple intercalation and exfoliation process. These nanosheets contain the aromaticity of the graphite basal plane without extensive chemical treatments and thus these are highly hydrophobic. The average thickness of these nanosheets can be varied from 3 to 10 nm and the size can be varied from submicron to a lateral dimension as large as 100 μm in diameter. Transparent, conductive and highly ordered monolayer of graphene nanosheets was prepared on a large area substrate via self assembly at the liquid-liquid interface. Driven by the minimization of interfacial energy these planar shaped nanosheets produce a closed packed monolayer structure at the liquid-liquid interface without any agglomeration and restacking. This research has shown that the highly hydrophobic nature of the graphene nanosheet can be used to self assemble at the hydrophobic liquid - hydrophilic liquid interface into a close packed monolayer. The large microscopic size of the nanosheets that comprise the film reduces the number of contacts between sheets and hence the contact resistance of the film. This monolayer film shows high electrical conductivity of more than 1000 S/cm and an optical transmission of more than 70% at a wavelength of 550 nm. The graphene nanosheets are inexpensive to produce and the process to form a monolayer is easily scalable to very large areas offering a new material and method to replace ITO and FTO coatings for optoelectronics applications.References: 1.Gan, Y.; Liu, J. X.; Zeng, S. N. Surf. Coat. Technol. 2006, 201, 25-292.Biswas. S, Drzal. L.T, Nano Lett., 2009, 9 (1), pp 167–1723.Goki Eda; Giovanni Fanchini; Manish Chhowalla. Nature Nanotechnology 2008, 270 – 2744.Héctor A. Becerril; Jie Mao; Zunfeng Liu; Randall M. Stoltenberg; Zhenan Bao; and Yongsheng Chen; ACS Nano 2008, 2, 463-470
12:15 PM - L4.8
Exfoliation and Sorting of Graphene in Aqueous Solutions via Density Gradient Ultracentrifugation.
Felice Torrisi 1 , Francesco Bonaccorso 1 , Calogero Sciascia 2 , Giulia Privitera 1 , Tawfique Hasan 1 , Andrea Ferrari 1
1 Department of Engineering, University of Cambridge, Cambridge United Kingdom, 2 Department of Physics, Politecnico di Milano, Milano, MI, Italy
Show AbstractMicro-mechanical cleavage is the most popular technique to produce high quality individual graphene samples [1]. However, this is not suitable for large scale applications. Alternative approaches are based on CVD growth or thermal treatment of carbon containing substrates, such as SiC. Another option is to pursue large-scale exfoliation [2-5]. Here, we apply density gradient ultracentrifugation (DGU), analogously to what done for the separation of carbon nanotubes [6], for exfoliation and sorting of graphene layers. We use a mild ultrasonication treatment on graphite flakes dispersed in water-surfactant solutions. The surfactant covering the flakes stabilizes the repulsion between their hydrophobic surface and water, preventing subsequent re-aggregations. This also results in a variation of buoyant density dependent on the flake thickness. This enables the separation of single-layer graphene from multi-layer and bulk graphite [7]. We find that bile salts and polymers provide better surface coverage compared to linear chain surfactants resulting in better DGU separation. The resulting material is characterized by absorption, Raman spectroscopy and atomic force microscopy [7]. We then use the sorted flakes to prepare polymer-composites to be used in optical and electrical applications. 1. K. S. Novoselov et al. Science 306, 666 (2004)2. S. Stankovich et al. Nature 442, 282 (2006)3. X. Li et al. Science 319, 1229 (2008)4. C. Vallés et al. J. Am. Chem. Soc. 130, 15802 (2008)5. Y. Hernandez et. al. Nature Nanotech. 3, 563 (2008)6. M. S. Arnold et al. Nature Nano 1, 60 (2006)7. C. Sciascia et al. submitted (2009)
12:30 PM - L4.9
Graphene Dispersion at High Concentrations and Formation of Liquid Crystals.
Natnael Behabtu 1 3 , Jay Lomeda 2 3 , Micah Green 1 3 , Amanda Higginbotham 2 3 , Nicholas Parra-Vasquez 1 3 , Dmitri Kosynkin 2 3 , Ellina Kesselman 4 , Judith Schmidt 4 , Yeshayahu Talmon 4 , James Tour 2 3 , Matteo Pasquali 1 2 3
1 Chemical Engineering, Rice University, Houston, Texas, United States, 3 Smalley Institute for nanoscale science and technology, Rice University, Houston, Texas, United States, 2 Chemistry, Rice University, Houston, Texas, United States, 4 Chemical Engineering, Technion-Israel Institute of Technology, Haifa Israel
Show AbstractGraphene is a promising new material with a wide number of potential applications, including electronics and nanocomposites, which often require that the graphene be dispersed and processed in a fluid phase. Here we show that in chlorosulfonic acid, graphene is spontaneously exfoliated from graphite and dissolved at isotropic concentrations as high as ~2 mg/ml without the need for covalent functionalization, surfactant stabilization, or sonication. At higher concentrations, a liquid-crystalline phase forms spontaneously. The dissolution mechanism in superacids is protonation forming charge transfer complexes facilitating electrostatic repulsion, similar to nanotubes in superacids. Cryo-TEM and HR-TEM show evidence for graphene. Novel forms of graphene such as carbon nanoribbons can be dispersed as well. High concentration isotropic and liquid crystalline phases are particularly useful for the processing of flexible
12:45 PM - L4.10
Dispersions of Exfoliated Hexagonal Boron Nitride Nanosheets.
Yi Lin 1 , John Connell 2
1 , National Institute of Aerospace, Hampton, Virginia, United States, 2 Advanced Materials and Processing Branch, NASA Langley Research Center, Hampton, Virginia, United States
Show AbstractTwo-dimensional graphene nanosheets have attracted much attention recently due largely to their unique transport properties as a result of their planar crystalline structure. Although structurally similar to graphite, the layered hexagonal boron nitride (h-BN) crystals were reported to be much more inert and are not readily exfoliated using the oxidative treatments commonly used with graphite. Here we report a facile method to exfoliate bulk h-BN particles into nanosheets of one to several layers thick. These h-BN nanosheets are soluble in common organic solvents and/or water allowing for solution processing and mixing with polymeric as well as other matrices. The soluble h-BN nanosheets were characterized using a variety of microscopic and spectroscopic techniques. The results of this study will be presented.
L5: Electronics from Solution Exfoliated Graphite II
Session Chairs
Tuesday PM, December 01, 2009
Room 310 (Hynes)
2:30 PM - **L5.1
Chemically Tailored Carbon-Based Nanoelectronic Materials and Devices.
Mark Hersam 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractCarbon-based nanoelectronic materials have attracted significant attention due to their potential to enable and/or improve applications such as transistors, transparent conductors, solar cells, and biosensors [1]. This talk will delineate chemical strategies for enhancing the electronic and optical properties of these promising nanomaterials. For example, we have recently developed a scalable technique for sorting single-walled carbon nanotubes (SWNTs) by their physical and electronic structure using density gradient ultracentrifugation (DGU) [2,3]. The resulting monodisperse SWNTs possess unprecedented uniformity in their electronic and optical properties, thus enabling the fabrication of high performance thin film field-effect transistors [4,5] and transparent conductors [6]. The DGU technique also enables multi-walled carbon nanotubes to be sorted by the number of walls, which facilitates the preparation of high purity solutions of double-walled carbon nanotubes (DWNTs). Monodisperse DWNT samples yield enhanced performance in transparent conductors and help elucidate the fundamental photophysics of DWNTs [7]. As a final example, this talk will discuss the preparation and characterization of highly ordered self-assembled monolayers on graphene. In particular, self-assembled monolayers of perylene-3,4,9,10-tetracarboxylic-dianhydride (PTCDA) can be formed on graphene surfaces via gas-phase deposition in ultra-high vacuum environments at room temperature [8]. Molecular-scale resolution scanning tunneling microscopy images reveal long-range order in the PTCDA monolayers, while scanning tunneling spectroscopy measurements yield distinct electronic features associated with the PTCDA that are not observed on pristine graphene. Ultimately, organic functionalization allows the chemical properties of graphene to be tailored for subsequent materials deposition in addition to presenting opportunities for graphene-based molecular electronic and sensing devices.[1] M. C. Hersam, Nature Nanotechnology, 3, 387 (2008).[2] M. S. Arnold, et al., Nature Nanotechnology, 1, 60 (2006).[3] A. A. Green, et al., Nano Research, 2, 69 (2009).[4] M. Engel, et al., ACS Nano, 2, 2445 (2008).[5] L. Nougaret, et al., Applied Physics Letters, 94, 243505 (2009).[6] A. A. Green and M. C. Hersam, Nano Letters, 8, 1417 (2008).[7] A. A. Green and M. C. Hersam, Nature Nanotechnology, 4, 64 (2009).[8] Q. H. Wang and M. C. Hersam, Nature Chemistry, 1, 206 (2009).
3:00 PM - L5.2
A Breakthrough Toward Wafer-size Graphene Transfer.
Akihiro Hashimoto 1 , Hiromitsu Tearsaki 1 , Kouhei Morita 2 , Satoru Tanaka 2 , Hiroki Hibino 3
1 Graduate School of Electrical & Electronics Engineering, University of Fukui, Fukui Japan, 2 Applied Quantum Physics & Nuclear Engineering, Kyushu University, Fukuoka Japan, 3 NTT Basic Research Laboratories, NTT Corporation, Atsugi Japan
Show Abstract Uniform ordered formation of graphene on an insulating substrate is extremely necessary for all technological applications as a successor of Si in the beyond Moore’s law era. Vacuum decomposition of vicinal insulating Si-terminated silicon carbide (SiC) (0001) surfaces by high-temperature annealing after formation of step-ordered surface by H2 high-temperature surface cleaning was previously proposed to open a road for large-scale production of graphene-based devices. However, the lack of transfer technique of few mono-layer graphene (FLG) from the graphitized SiC surface to an insulating substrate is a large barrier to promote more extended basic and/or application research of graphene. In spite of many efforts for these years, nobody has been succeeding to transfer a large area FLG with several mm2 to an insulating substrate like SiO2/Si. On the contrary, even the exfoliation of the epitaxial graphene from the graphitized SiC substrate has not been established, yet. Here, we first successfully show that a new proposed exfoliation method of the graphene from graphitized vicinal SiC substrate provides an exfoliated larger area graphene with several mm2 than previously attainable. Raman spectroscopy and low energy electron microscopic (LEEM) measurements confirm to be able to obtain the uniform and large area graphene layers for the transfer to an insulating substrate by the proposed new exfoliation method. The new exfoliation introduced here establishes a method for the large area graphene technology.
3:15 PM - L5.3
Natural Dye Sensitized Solar Cells based on Graphene as Counter Electrode.
Francesco Bonaccorso 1 , Giuseppe Calogero 2 , Pietro Gucciardi 2 , Giulia Privitera 1 , Gaetano Di Marco 2 , Andrea Ferrari 1
1 Engineering, Cambridge University, Cambridge, Cambridgeshire, United Kingdom, 2 , Istituto per i Processi Chimico-Fisici, Messina Italy
Show AbstractDye-sensitized solar cells (DSSCs) [1] have attracted much attention due to their good light to electricity conversion efficiency, simple fabrication and low cost. The counter electrode employed for the regeneration of electrolyte is commonly constituted by a platinum film deposited on a conductive glass. Carbonaceous materials, and graphene in particular, are quite attractive due to the potential to simultaneously replace both the platinum catalyst and the conductive glass, yielding cells with higher corrosion resistance, higher catalytic activity and lower costs. Natural dyes extracted from fruits, flowers, leaves, as new ecological sensitizers are ideally suited for environmentally friendly and low cost DSSCs [2]. Such dyes are, in fact, very abundant, easy to prepare and non-toxic. Here we show that solution-processed graphene thin films can be used as conductive electrodes for DSSCs employing natural dyes sensitizers, replacing the brittle and expensive transparent conductive oxides (Indium Tin oxide, ITO, or Fluorine Tin Oxide, FTO). We also demonstrate that graphene layers can be used as counter-electrodes, allowing us to replace the Platinum catalyst, preventing the DSSC efficiency reduction over time, caused by the Pt-catalyst degradation when in contact with iodide/tri-iodide liquid electrolyte. Graphene dispersions are produced by liquid phase exfoliation of graphite [3]. The graphene electrodes are prepared either by directly spin coating the dispersion on quartz substrates or embedding graphene in a host polymer matrix [4]. The combination of graphene and natural sensitizers opens up new scenarios for totally green, natural, environmentally friendly and low cost DSSCs.1.B. O'Regan, M. Gratzel, Nature 353, 737 (1991).2.G. Calogero, G. Di Marco, Solar Energy Material & Solar Cells 92, 1341 (2008).3.Y. Hernandez et al., Nat Nanotech 3, 563 (2008). 4. F. Bonaccorso et al. submitted (2009).
3:30 PM - L5.4
Transferring and Multi-stage Cutting Graphene Patterns.
Li Song 1 , Lijie Ci 1 , Deep Jariwala 2 , Wei Gao 1 , Ana-Laura Elias 1 , Mauricio Mauricio Terrones 3 , Pulickel Ajayan 1
1 Department of Mechanical Engineering and Materials Science, Rice University, Houston, Texas, United States, 2 Department of Metallurgical Engineering, IT-BHU, Varanasi India, 3 Advanced Materials Department, IPICYT, San Luis Potosí Mexico
Show AbstractCutting graphene layers through catalytic hydrogenation process can create graphene pieces with smooth edges of atomic precision and well-defined shapes. Recently, nanocutting of graphene sheets have been realized by using nano-sized nickel and iron particles in hydrogen atmosphere at high temperature. It is note that the edges of these tailored graphene pieces are along specific crystallographic orientation. Here we present a facile way for easily transferring and multi-stage cutting of graphene patterns. In specially, we successfully exfoliate pre-fabricated graphene patterns from HOPG surface by using gold film as a transfer-stamp. As followed, the controlled cutting of graphene can be accomplished by manually creating graphene step edges via an oxidation or a plasma etching process.
3:45 PM - L5.5
Electronic Devices Based on Graphene Ribbons Produced by Unzipping of Carbon Nanotubes.
Alexander Sinitskii 1 , Ayrat Dimiev 1 , Dmitry Kosynkin 1 , James Tour 1
1 Chemistry, Rice University, Houston, Texas, United States
Show AbstractWe report on the large-scale fabrication of electronic devices based on graphene ribbons produced by the recently discovered chemical unzipping of carbon nanotubes [1]. We show that unzipped carbon nanotubes have numerous advantages for the device fabrication, as they can be produced in large quantities with a 100% yield, their thickness can be estimated by conventional SEM, they all have similar dimensions, rarely exhibit wrinkles on Si/SiO2 substrates and can be easily aligned in a parallel fashion. Though the conductivity of thus prepared graphene ribbons is lower than that of graphene produced by micromechanical cleavage technique, it is shown to be significantly higher than that reported for reduced GO. With the available alignment techniques, hundreds of graphene-based devices can be easily fabricated on a single chip. We discuss the possible applications of these devices as field-effect transistors, ultracompact gas sensors and nonvolatile memories. [1] D.V. Kosynkin et al. Longitudinal unzipping of carbon nanotubes to form graphene nanoribbons. Nature 458, 872-876 (2009).
4:30 PM - **L5.6
Effect of Functionalized Single Wall Carbon Nanotube and Graphene Oxide Electrodes on the Performance of Polymer Photovoltaic Devices.
Yun-Yue Lin 1 , Kun-Hua Tu 1 , Chun-Wei Chen 1 , Manish Chhowalla 2
1 Materials Science and Engineering, National Taiwan University , Taipei Taiwan, 2 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States
Show AbstractIn this talk, we would like to present the effect of functionalized transparent and conducting single walled carbon nanotube (SWNT) and graphene oxide (GO) electrodes on the performance of polymer photovoltaic devices. By different chemical treatments in the SWNT electrodes, the short circuit current (Jsc) and open circuit voltage (Voc) of photovoltaic devices can be varied systematically. The origin of shift in the open circuit voltage with different functionalized SWNT electrodes is mainly attributed to the significant charge transfer between polymer and SWNT electrodes, which was further revealed by the first principles, density functional theory calculations. A systematic investigation of carrier transport and recombination of the photovoltaic devices deposited on the SWNT network electrodes has also been performed, indicating that transparent and conducting SWNT electrodes can act as an “active” electrode in the polymer photovoltaic applications. In addition, the recent progress using GO electrodes for photovoltaics will also be addressed.
5:00 PM - L5.7
Using Large Area Graphene as an Electrode for Photovoltaic Application.
Ping Loh 1 , Yu Wang 1 , Xiaohong Chen 1 , Shuai Wang 1
1 chemistry, national university of singapore, Singapore Singapore
Show AbstractLarge-area, continuous, highly transparent and conducting graphene films with sheet resistance of 200 ohms/square were produced by chemical vapor deposition (CVD) method. The CVD grown graphene films can be readily transferred onto glass using polydimethylsiloxane (PDMS) stamp approach and were used as the anode for application in organic photovoltaic cells. After non-covalent modification with pyrene buanoic acid succidymidyl ester (PBASE), the power conversion efficiency (PCE) of organic solar cells increased from 0.21% of the unmodified films to 1.71 %. This performance corresponds to ~55.2 % of the PCE of an identical device made with indium tin oxide (ITO) anode, e.g., ITO/PEDOT-PSS/P3HT/PCBM/Al (PCE=3.1%). This finding paves the way for the substitution of the ITO anode with low cost graphene film in photovoltaic and electroluminescent devices.
5:15 PM - L5.8
Chemical Vapor Deposition of Single- and Few-layer Graphene Film and its Application in Solar Cells.
Lewis Gomez De Arco 1 , Yi Zhang 1 , Cody Schlenker 2 , Koungmin Ryu 1 , Mark Thompson 2 , Chongwu Zhou 1
1 Electrical Engineering, University of Southern California, Los Angeles, California, United States, 2 Chemistry, University of Southern California, Los Angeles, California, United States
Show AbstractWe report the implementation of a simple, scalable and cost-efficient method to prepare single and few-layer graphene films by chemical vapor deposition (CVD). Synthesized graphene films were transferred to transparent substrates for solar cell fabrication. Solar cells obtained from the synthesized graphene films showed comparable performance to those fabricated with indium tin oxide (ITO) on rigid substrates but outperformed ITO solar cells when built on flexible substrates. Synthesis of graphene by CVD constitutes a significant advance towards the production of transparent conductive films of graphene at large scale and has great implications for future graphene-related electronic devices.
5:30 PM - L5.9
Large-Scale Directed Assembly and Rapid Characterization of Carbon Nanotube and Graphene Devices.
Aravind Vijayaraghavan 1 , Frank Hennrich 1 , Christoph Marquardt 1 , Ninette Stuerzl 1 , Calogero Sciascia 2 3 , Simone Dehm 1 , Sharali Malik 1 , Andrea Ferrari 2 , Ralph Krupke 1 4
1 Institut für Nanotechnologie, Forschungszentrum Karlsruhe, Karlsruhe Germany, 2 Engineering Department, University of Cambridge, Cambridge United Kingdom, 3 INFM-CNR Physics Department, Politecnico di Milano,, Milano Italy, 4 , DFG Center for Functional Nanostructures (CFN), Karlsruhe Germany
Show AbstractIn the recent years, significant strides have been made in demonstrating unique and high-performance functionality in single-walled carbon-nanotube (SWCNT) and graphene electronic devices. However, high-density directed assembly, integration and rapid characterization of a large number of devices for statistical analysis remains major challenges. Here, I present our recent developments in our group towards achieving these goals.First, I will discuss the fabrication of high-density arrays of single-chirality SWCNT [1] and of graphene [2] devices. Recently, we have demonstrated that dielectrophoresis can be used to fabricate high-density arrays of SWCNT devices, and that the process is self limiting to one nanotube per device. [3] Single-chirality nanotube suspensions are obtained by selective polymer wrapping and density gradient ultracentrifugation. Graphene solutions are made by exfoliating graphite in aqueous and organic solvents. The arrays are characterized by spatial Raman and photoluminescence maps and electronic transport measurements.In the second part, I will present Voltage-Contrast Scanning Electron Microscopy (VC SEM) as a new metrology technique for the rapid, parallel and visual electronic characterization of carbon nanotube devices and arrays. This technique is based on the fact that the secondary electron yield depends on surface potentials. VC-SEM is demonstrated to distinguish metallic and semiconducting nanotubes in the SEM, [4] and the mechanism of contrast evolution is discussed. Furthermore, the contrast profile along a nanotube changes abruptly in the presence of defects, and this can be used to locate and characterize them. VC-SEM is demonstrated in the characterization of typical defects, [5] such as Stone-Wales defects, high-current breakdown, electron-beam induced metal-insulator transition and charge-injection into the dielectric substrate.[1] Vijayaraghavan, A.; Hennrich, F.; Engel, M.; Marquardt, C.; Dehm, S.; Krupke, R. Submitted, 2009.[2] Vijayaraghavan, A.; Dehm, S.; Sciascia, C.; Lombardo, A.; Bonetti, A.; Ferrari, A. C.; Krupke, R. ACS Nano, 2009, Article ASAP.[3] Vijayaraghavan, A.; Blatt, S.; Weissenberger, D.; Oron-Carl, M.; Hennrich, F.; Gerthsen, D.; Hahn, H.; Krupke, R. Nano Letters 2007, 7, 1556-1560.[4] Vijayaraghavan, A.; Blatt, S.; Marquardt, C.; Dehm, S.; Wahi, R.; Hennrich, F.; Krupke, R. Nano Research 2008, 1, 321-332.[5] Vijayaraghavan, A.; Marquardt, C.; Dehm, S.; Hennrich, F.; Krupke, R. Submitted, 2009.
5:45 PM - L5.10
Large Area Single- and Bi-layer Graphene on Single Crystalline Nickel by Chemical Vapor Deposition.
Yi Zhang 1 , Lewis Gomez De Arco 1 , Chongwu Zhou 1
1 , University of Southern California, Los Angeles, California, United States
Show AbstractGreat effort has been made on the synthesis of graphene but achieving large graphene domains with uniform thickness remains a challenge. In this work we will present our approach to large-scale, single- and bilayer graphene synthesis. The graphene synthesis was achieved by using single crystalline nickel as substrates via chemical vapor deposition. The formation of the graphene layers were confirmed by micro Raman spectroscopy analysis. AFM, SEM, x-ray diffraction and Raman spectroscopy was employed to fully characterize the as-grown graphene on both single-crystal nickel substrates and nickel film over large areas. Our results demonstrate that single-crystal nickel substrates have a great advantage in terms of yielding graphene layers with more uniform, fewer layers and larger domain size than nickel films.
L6: Poster Session: Graphene
Session Chairs
Wednesday AM, December 02, 2009
Exhibit Hall D (Hynes)
9:00 PM - L6.1
Graphene as Saturable Absorber for Ultrafast Lasers.
Daniel Popa 1 , Felice Torrisi 1 , Zhipei Sun 1 , Tawfique Hasan 1 , Fengqiu Wang 1 , Francesco Bonaccorso 1 , Andrea Ferrari 1
1 Department of Engineering, University of Cambridge, Cambridge, Cambridge, United Kingdom
Show AbstractSingle and few layer Graphene display strong nonlinear optical properties with ultrafast response over a broad spectral range. Here, we report the linear and nonlinear optical characterization of graphene-polymer composites prepared using wet chemistry techniques [1,2]. Their nonlinear optical absorption decreases for increasing incident laser power, with the characteristic behavior of saturable absorbers. The composites are then integrated in a fiber laser cavity, to generate ultrafast pulses. We obtain pulse duration of ~800fs [3, 4] at 1557nm with a 3.2nm spectral bandwidth [3, 4]. The time-bandwidth product is 0.317, close to the theoretical value of 0.314 for Fourier-transform limited sech2 pulses, indicating that the pulse is as short as allowed by the spectral bandwidth. These composites are expected to mode-lock from visible to IR due to the broad absorption range of graphene, with the potential to overcome the wide tunability offered by nanotubes [5].1. Y. Hernandez, et al. Nat Nanotech. 3, 563 (2008).2. F. Torrisi, et al. Submitted (2009)3. T. Hasan, et al. Adv. Mat. in press (2009)4. Z. Sun et al. Submitted (2009)5. F. Wang et al. Nature Nano. 3, 738 (2008).
9:00 PM - L6.2
All Graphene Electromechanical Switch Fabricated by Chemical Vapor Deposition.
Kaveh Milaninia 1 , Alfonso Reina 1 , Jing Kong 2 , Marc Baldo 2
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, California, United States
Show AbstractWe demonstrate an electromechanical switch comprising two polycrystalline graphene films, each deposited using ambient pressure chemical vapor deposition (CVD). Large area graphene sheets facilitate the use of straight forward “top-down” fabrication of electromechanical switches. The top film is pulled into electrical contact with the bottom film by application of approximately 5V between the layers. Contact is broken by mechanical restoring forces after bias is removed. The device switches several times before tearing. Demonstration of multiple switching at low voltage and large on currents confirms that graphene is an attractive material for electromechanical switches. Reliability may be improved by scaling the device area to within one crystalline domain of the graphene films.
9:00 PM - L6.3
Tuning the Electronic Structure of Graphene Nanoribbons by Chemisorption.
Felipe Cervantes Sodi 1 , Gabor Csanyi 1 , Stefano Piscanec 1 , Andrea Ferrari 1
1 Engineering Department, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom
Show AbstractGraphene nanoribbons (GNRs) are the counterpart of nanotubes in graphene-based nanoelectronics. The electronic properties of GNRs are determined by their geometry and functionalisation of the edges [1, 2]. In graphene, OH, O and H chemisorption alter its electronic and magnetic properties [3, 4]. Previous theoretical works show that at low concentrations chemisorbed graphene keeps its semi-metal character [4], while at high, a band gap develops [4]. Indeed, C-OH and C-O groups are present in semiconducting graphene oxide [5], and insulating hydrogenated graphene was recently produced [5]. Here we study by Density Functional Theory the electronic properties of chemisorbed GNRs. Low density adsorption of H and OH gives impurity levels in the gap of armchair GNRs, while H or OH saturation widens the gap[3]. In zigzag GNRs OH chemisorption lifts the spin degeneracy, leading to half-semiconducting ribbons, while H and OH saturation opens the gap [2].1. Y.W. Son et. al., Phys. Rev. Lett. 97, 216803 (2006).2. F. Cervantes-Sodi et. al., Phys. Rev. B 77, 165427 (2008).3. F. Cervantes-Sodi et. al., submitted (2009).4. J. O. Sofo et. al., Phys. Rev. B 75, 153401 (2007).5. W. Cai et. al., Science 321, 1815 (2008).6. D.C. Elias et al, Science, 323, 610 (2008).
9:00 PM - L6.4
Conductance Modulation Upon Layer Stacking in Graphene Nanoribbons.
Kirti Kant Paulla 1 , Amir Farajian 1
1 Mechanical and Materials Engineering, Wight State University, Dayton, Ohio, United States
Show AbstractWe calculate the quantum conductance of single- and bi-layer graphene nanoribbons, of both zigzag and armchair types. The electronic structures of the nanoribbons are calculated using density functional theory with gradient-corrected exchange and correlation functionals. The electronic structures are used to derive conductance characteristics based on the Green's function approach to Landauer's theory. Our results show, in agreement with previous studies, that the band gap of a single-layer armchair graphene nanoribbon is reduced when another layer is stacked on top of it. The conductance characteristics of bilayer armchair and zigzag nanoribbons are shown to be different from those obtained by superimposing single-layer characteristics. In particular, the conductance characteristics strongly depend on stacking order (AA or AB). These interesting modulation effects are shown to arise from inter-layer interactions between electronic states. We discuss possible applications of these results in characterization of and device design based on graphene nanoribbons.
9:00 PM - L6.5
Gating Effects and Three-terminal Quantum Transport in Multi-layer Graphene Nanoribbons.
Amir Farajian 1
1 Mechanical and Materials Engineering, Wright State University, Dayton, Ohio, United States
Show AbstractWe theoretically investigate the two- and three-terminal quantum transport characteristics of multi-layer graphene nanoribbons, under gate bias. In addition to conventional two-terminal transport, three-terminal transport characteristics of these materials are particularly interesting, as their layered structures can be advantageous for effective gate modulation. The calculations are based on ab initio electronic structures combined with the Green's function formalism and Landauer's method. By addressing the nanoribbons using separate electrodes, we investigate the gating and screening effects in these nanoscale field effect transistors, and calculate their gate leakage currents. For different geometries of the nanoribbons and the electrodes, it is possible to have unscreened or screened gate modulations. The effects of these modulations on the transport characteristics, in particular the switching performance, will be discussed.
9:00 PM - L6.6
Fabrication of Graphene Devices with a Helium Ion Beam.
Max Lemme 2 , David Bell 1 , Lewis Stern 3 , Britt Baugher 4 , Pablo Jarillo-Herrero 4 , Jimmy Williams 2 , Charels Marcus 2
2 Department of Physics, Harvard University, Cambridge, Massachusetts, United States, 1 School of Enginnering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 3 ALIS Business Unit, Carl Zeiss SMT, Peabody, Massachusetts, United States, 4 Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractWe report on the etching of graphene devices with a helium ion beam, including in situ electrical measurement during lithography. The etching process can be used to nanostructure and electrically isolate different regions in a graphene device, as demonstrated by etching a channel in a suspended graphene device with etched gaps down to about 10nm. Graphene devices on SiO2 substrates etch with lower He ion doses and are found to have a residual conductivity after etching, which we attribute to contamination by hydrocarbons.Helium ion microscopy (HeIM) has recently been introduced as high-resolution imaging technology for nanoscale structures and materials. In this work we use a helium ion microscope (Zeiss ORION) as a lithography tool to controllably modify electrical properties of graphene devices. We further demonstrate in situ electrical measurement during lithography. The HeIM is particularly well suited for this purpose because it produces a high-brightness, low-energy-spread, sub-nanometer size beam. Themicroscope benefits from the short de Broglie wavelength of helium, ~ 100 times smaller than the corresponding electron wavelength. This gives the beam an ultimate resolutionof 0.5nm or better, making it an attractive tool for precision lithography of graphene devices. While process details are published elsewhere, this paper focuses on themodification of electrical properties of graphene.
9:00 PM - L6.7
Quantum States in Graphene-Based Josephson Junctions.
Steve Carabello 1 , Joseph Lambert 1 , Zechariah Thrailkill 1 , Roberto Ramos 1
1 Physics, Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractGraphene, a one- or few-layer thick carbon lattice, has demonstrated great promise for a wide variety of applications. Recently, supercurrents have been measured in graphene-based Josephson junctions. These devices consist of parallel superconducting leads deposited onto single- and few-layer graphene flakes; the graphene near the leads becomes superconducting due to the proximity effect. Experiments have demonstrated the Josephson effects in such devices, revealing similarities to conventional SNS and SIS junctions, together with some novel characteristics. Using graphene as the weak link in the Josephson junction offers some appealing characteristics. These include the ability to tune the critical current by applying a gate voltage, and the potential for increased coherence times due to graphene’s pristine crystal structure.
We report the current-voltage characteristics of our graphene junctions. Additionally, we propose the existence of quantum metastable states trapped in the well of the washboard potential of a current-biased, graphene-based Josephson junction. We report the results of microwave spectroscopy measurements to detect these states.
9:00 PM - L6.8
Few Layer Graphene Based CO and NO2 Gas Sensors.
Rakesh Joshi 1 , Gomez Humberto 1 , Kumar Ashok 1 , Denis Kitenge 1 , Farah Alvi 1
1 mechanical Engineering, ENB118, University of South florida, Tampa, Florida, United States
Show AbstractWe report the gas sensor performance of few layer graphene grown on Ni coated Si substrates. Graphene is special because it is all surfaces with no bulk which can be very important for surface dependent gas sensor phenomenon. The graphene layers for gas sensor application were grown using microwave plasma enhanced chemical vapor deposition method. Hydrogen and methane in a ratio of 8:1 were used as gaseous mixture in presence of 2 kW microwave plasma to grow graphene on the Ni coated substrates at 700C. Few layer graphene was characterized using Raman Spectroscopy, Scaning Electron Microscopy, Transmission Electron Microscopy and Atomic Force Microscopy. Gas sensing properties of the few layer graphene structures were studied at room temperature for 100 to 500 ppm of CO and NO2 in synthetic air mixture. Effect of Ni layer thickness as well as roughness on graphene morphology, and subsequently on gas sensing behavior will be presented. Increase in the number of graphene layers results into improvement in gas sensing characteristics. The gas sensor mechanism is consistent with charge carrier donation to conducting graphene surfaces in presence of the target gases.
Symposium Organizers
Manish Chhowalla Rutgers University
John A. Rogers University of Illinois, Urbana-Champaign
Carey M. Tanner SRI International
Pagona Papakonstantinou University of Ulster
Andrea C. Ferrari University of Cambridge
L7: Graphene by Chemical Vapor Deposition
Session Chairs
Wednesday AM, December 02, 2009
Room 310 (Hynes)
9:30 AM - **L7.1
Graphene Synthesis and Its Device Application for Future Carbon Based Electronics.
Jae-Young Choi 1 , Seon-Mi Yoon 1 , Hyeon-Jin Shin 1 , Byung Hong 2 , Ji-Beom Yoo 2 , Young Hee Lee 2 , Sang Yoon Lee 1 , Jong Min Kim 1
1 , Samsung Advanced Institute of Technology, Yongin-si, Gyeonggi-do Korea (the Republic of), 2 , Sungkyunkwan University, Suwon, Gyeonggi-do, Korea (the Republic of)
Show AbstractGraphene has been attracting much attention owing to its fascinating physical properties such as quantum electronic transport, a tunable band gap, extremely high mobility, high elasticity and electrochemical modulation. CNT has been one of the leading materials in the carbon-based nanotechnologies. But we have many difficulties to make product level devices because we don’t have feasible methodologies to select specific type of CNT and bring the CNT to exact position in highly integrated device structure. On the other hand, graphene can give us strong opportunity to make future nano electronic devices. Graphene is a 2-dimensional carbon sheet, that is, a sort of atomically thin film. Therefore, the graphene can be very easily fabricated into the highly integrated devices by currently well developed photo litho technology. For the realization of commercial application of graphene in the future, following key technologies should be developed: (1) synthesis of large single crystalline graphene, (2) direct growth of graphene on device substrate, and (3) simple doping process to control electronic properties. In this talk, we will present new synthesis methods of large area graphene by CVD and solution chemistry and their device application.
10:00 AM - L7.2
Patterned Growth of Graphene on Epitaxial Catalyst.
Hiroki Ago 1 2 3 , Izumi Tanaka 1 , Masaharu Tsuji 1 2 , Ken-ichi Ikeda 2
1 Inst. Mater. Chem. Eng., Kyushu University, Fukuoka Japan, 2 Grad. Schl. Eng. Sci., Kyushu University, Fukuoka Japan, 3 , PRESTO-JST, Kawasaki Japan
Show AbstractGraphene is emerging as a new building block of future nanoelectronics and microelectro-mechanical systems. Catalytic growth has attracted recent interest as a powerful means to produce highly crystalline large-area graphene sheets [1-3]. Here, we studied the growth of graphene films over the epitaxial metal films deposited on single crystalline substrates. The epitaxial metal film gave the unique micro-pits with rectangular and triangular shape, reflecting the crystallographic orientation of the substrate. Thin films of graphene were observed inside these pits. This patterned graphene was transformed on SiO2/Si substrates, and their Raman spectra and AFM data showed the formation of thin layers (1-5 layers) of graphene.References[1] A. Reina, NanoLett., 9, 30 (2009). [2] K. S. Kim, Nature, 457, 706 (2009). [3] X. Li, Science, 324, 1312 (2009).
10:15 AM - L7.3
Large-Area Patterning of Arrays of Graphene Nanostructures for Electronics and Optoelectronics Applications.
Nathaniel Safron 1 , Michael Arnold 1
1 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractGraphene nanostructures are promising materials for future electronics and optoelectronics applications due to their size-tunable electrical and optical band gaps and their potentially high carrier mobility, current density, and thermal conductivity. Research has primarily focused on laterally confining graphene monolayers into narrow nanoribbons using time-intensive lithographic techniques such as electron-beam lithography in order to open up a band gap in the graphene. Here, we demonstrate the nanopatterning of graphene and graphitic nanostructures using two facile and scalable bottom-up lithographic techniques: (1) traditional nanosphere lithography, and (2) inverted honeycomb nanosphere lithography. Large-area periodic arrays of sub-20 nm graphene quantum dots and graphene nanoribbons, respectively, can be easily fabricated using these techniques.In (1) traditional nanosphere lithography, 72 nm polystyrene (PS) nanospheres are self-assembled into hexagonal close-packed arrays onto mono-, few-, and many-layered graphene. Arrays of sub-20 nm islands of dielectrics or metals are then thermally evaporated through the vertices of the PS template. Subsequent oxygen reactive ion etching is then utilized to transfer the island pattern into the underlying graphene, resulting in the formation of arrays of sub-20 nm graphene quantum dots. On HOPG, we have demonstrated the fabrication of arrays of nanopillars of stacked graphene quantum dots etched 200 nm into the HOPG with <10 degree taper that are expected to have applications in optoelectronics.In (2) inverted honeycomb nanosphere lithography, arrays of PS nanospheres are also self-assembled onto graphene. An aluminum precursor is then deposited from solution onto the graphene between the crevices of the nanospheres. After the PS nanospheres are removed and the precursor is annealed, an interconnected hexagonal honeycomb mask of alumina remains. Each segment of the mask is characterized by sub-15 nm lateral width, and the segments connect to form a honeycomb pattern with a 72 nm hexagonal periodicity. With subsequent oxygen plasma treatment, the honeycomb pattern is transferred to the underlying graphene, forming an interconnected network of graphene nanoribbons. To characterize the applicability of this lithographic technique for electronics, we have fabricated field-effect transistors from the interconnected nanoribbon networks. We find that the lateral confinement in the nanoribbons induces an increased ON/OFF ratio in few-layered graphene devices presumably as a result of the opening of an electronic band gap or a mobility gap in the nanoribbon segments. We believe this could be an excellent method to define semiconducting regions in large-area “graphene sheets,” suitable for large-area transparent and flexible electronics.
10:30 AM - L7.4
Complete One-pot Conversion of Graphite Crystals to High Quality Graphene via Supercritical Fluid Exfoliation.
Dinesh Rangappa 1 , Koji Sone 1 , Mingsheng Wang 2 , Ujjal Gautam 2 , Dmitri Golberg 2 , Itaru Honma 1
1 Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan, 2 MANA, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, Japan
Show AbstractGraphene has attracted a great deal of attention in recent years due to its unusual electronic, mechanical and thermal properties. Exploiting graphene properties in variety of applications require a chemical approach for the large-scale production of high quality processable graphene sheets (GS), which has remained as an unanswered challenge. Here, we report a rapid one pot supercritical fluid (SCF) exfoliation process for high quality, large scale and processable graphene for technological applications. Direct 100 % conversion of graphite crystals to GS is possible under SCF conditions because of the high diffusivity and solvating power of SCFs. For the first time, we are reporting hundred percent yield of graphene (~98 % <8 layers, 2 % ≥ 10 layers) with ~10 % monolayer yield in one pot direct conversion method. The current and voltage plot clearly exhibits an ohmic behavior in the lower voltage range with a resistance of 2-6 kΩ, which is comparable to that of carbon nanotubes and other chemically derived graphene. This is a non-covalent, solution-phase method to produce defect free, unoxidized graphene with good conduction and electron carrier capacity and the highest yield achieved so far. The good conduction and high current-carrying capacity of GS also suggest that, our GS are potential candidates for both transistors and interconnect in future nanoelectronic circuits.
10:45 AM - L7.5
Mechanisms of Large-Scale Graphene Growth on Ruthenium.
Eli Sutter 1 , Peter Albrecht 1 , Peter Sutter 1
1 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractEpitaxy on transition metal substrates is a promising approach for the large-scale synthesis of graphene for potential applications in microelectronics and sensing. In particular, the controlled layer-by-layer growth of graphene on Ru(0001) has been shown to result in macroscopic monocrystalline graphene domains with lateral sizes greater than 200 microns, full coverage of large substrates, perfect thickness uniformity, and very low defect density [1]. Whereas the first graphene layer interacts strongly with the Ru(0001) template, the second layer is essentially decoupled from the metallic support, thus preserving the atomic structure and exotic electronic properties of isolated single-layer graphene [2]. A viable route towards large-area, free-standing graphene would be to grow on polycrystalline transition-metal thin films rather than single crystals, followed by the dissolution of the metal template to detach the graphene and transfer it to another support. Two groups have recently demonstrated the growth of few-layer graphene on polycrystalline Ni films using this method [3, 4]. Here, we discuss in-situ observations of graphene synthesis on Ru single crystals and thin films using low-energy electron microscopy and scanning tunneling microscopy. We establish the fundamental mechanisms underlying large-scale graphene growth, and discuss factors controlling graphene thickness, accommodation of substrate steps, and defect formation at domain boundaries. Using Ru thin films on SiO2, we demonstrate how these mechanisms may be modified when growing graphene on a polycrystalline substrate, focusing on the influence of grain orientation and the effect of grain boundaries on large-scale graphene growth. Our results provide a basis for the scalable synthesis of graphene on transition metal templates.[1] P. W. Sutter, J.-I. Flege, and E. A. Sutter, Nature Mater. 7, 406 (2008).[2] E. Sutter, D. P. Acharya, J. T. Sadowski, and P. Sutter, Appl. Phys. Lett. 94, 133101 (2009).[3] A. Reina et al., Nano Lett. 9, 30 (2009).[4] K. S. Kim et al., Nature 457, 706 (2009).
11:30 AM - **L7.6
Engineering Silicon and Graphene Nanosystems via Nanowire Lithography.
Alan Colli 1
1 , Nokia Research Centre, Cambridge United Kingdom
Show AbstractAs feature sizes in electronic devices approach molecular level [1], cheap, parallel and non-lithographic patterning techniques are demanded to fabricate nanowires (NWs) and other nano-architectures into materials of technological interest, such as ultra-thin silicon-on-insulator (SOI) layers or graphene. Nanowire-lithography (NWL) consists in using free-standing NWs, grown and assembled by chemical methods, as etch masks to transfer their one-dimensional morphology to an underlying thin film [2]. The final result is a heterostructure with two NWs of equivalent dimensions perfectly lying on top of each other.Here, we report that fully- or partially-oxidised silicon NWs (SiNWs) are a simple and compatible system to implement the NWL concept on silicon and graphene. SiNWs in bulk quantities are grown by chemical methods [3], and are later dispersed on thin (<100nm) SOI wafers and on graphene flakes produced on SiO2 by mechanical exfoliation [4]. The NW morphology is carved into the SOI by selective deep-reactive-ion-etching (DRIE), whereas on graphene a conformal nanoribbon (GNR) is etched by using an O2 plasma. We present field-effect devices made of a single SiNW or GNR fabricated by NWL. Further, we assess the electrical response of SOI-NW networks obtained using a mask of NWs ink-jetted from solution [2]. The resulting conformal network etched into the underlying wafer is monolithic, with single-crystalline bulk junctions, and thus does not result in any degradation of conductivity compared to a single NW directly bridging the electrodes. This opens new exciting possibilities for large-area electronics based on nanostructured thin films, irrespective of the material of choice.We finally extend the potential of the NWL concept into the third dimension. Under proper conditions, the etching process can also proceed laterally under the NW masks, resulting in a controllable undercutting effect. In case of ultra-thin films, such as graphene, this can reduce the diameter of the etched NW or nanoribbon well below that of the original NW mask. For thick films (e.g., 1-µm-thick SOIs), the undercut can be made periodic by alternating isotropic and anisotropic etching steps in the DRIE. As a result, an array of vertically-stacked NWs is formed from a single NW mask, revealing a promising line of development for future three-dimensional nano-electronics [2].[1] Barrett, C. R. MRS Bull. 2006, 31, 906[2] Colli, A.; et al. Nano Lett. 2008, 8, 1358[3] Colli, A.; et al. J. Appl. Phys. 102 034302 (2007)[4] Novoselov, K. S.; et al. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 10451
12:00 PM - L7.7
Wafer Scale Epitaxial Graphene Growth on SiC for High Frequency FETs.
Christos Dimitrakopoulos 1 , Alfred Grill 1 , Yu-ming Lin 1 , Marcus Freitag 1 , Zhihong Chen 1 , Yanning Sun 1 , Keith Jenkins 1 , Damon Farmer 1 , John Ott 1 , Robert Wisnieff 1 , Phaedon Avouris 1
1 , IBM Research, T. J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractWe report the growth of few-layer epitaxial graphene on SiC at two-inch wafer-scale and the fabrication and testing of devices using graphene as the active layer. Doped 4H(0001) and 6H(0001) polytypes of hexagonal SiC were used as substrates for the development of the graphene growth process, while high purity semi-insulating 4H(0001) wafers were used for device testing. Hall mobilities up to ~1570 cm2/Vs were measured from Hall bar devices, and field effect mobilities up to 1400 cm2/Vs were measured from field-effect transistors on the same wafer. A peak cut off frequency, fT, of 24 GHz was measured from an unoptimized top-gated graphene FET with gate length LG=500 nm, also built on the same wafer. To the best of our knowledge, this is the highest peak cut-off frequency measured from epitaxial graphene based FETs. It is expected that FETs with shorter gate lengths would produce much higher frequencies as fT is proportional to (1/LG)2 [Y.-M. Lin et al. NanoLett. 9, 422, (2009)].Acknowledgement: This work is supported by DARPA under Contract FA8650-08-C-7838 through the CERA program.
12:15 PM - L7.8
A New Mechanism for Growth of Graphene on SiC.
Weijie Lu 1 , John Boeckl 2 , Kurt Eying 2 , Larry Grazulis 2 , Roland Barsosa 1 , Tiffany Crenshaw 1 , William Mitchel 2
1 Department of Chemistry, Fisk University, Nashville, Tennessee, United States, 2 Materials and Manufacturing Directorate, Air Force Research Laboratory, NashvilleWright Patterson AFB, Ohio, United States
Show AbstractGraphene has many promising applications in the field of high speed electronics due to its very high mobility and high saturated drift velocity. One to a few layers of graphene on SiC is considered to be one of the more promising structures for fabrication of high speed electronics. The challenge is to develop techniques for growth of large area graphene with a uniform and controllable number of layers on SiC substrates. In this paper, we propose a new atomic scale mechanism for growth of graphene on SiC via partial oxidation and degradation of the SiC near surface layer, leading to more efficient decomposition. On-axis, Si-face SiC samples were annealed in a vacuum of 10-7 to 10 -8 torr. The samples were not given a hydrogen etch prior to annealing. The partial pressure of oxygen was 10-11 torr at the growth temperature. After annealing at 1200°C in vacuum, a thin surface layer (~10 nm) composed of defective SiC was revealed by cross-sectional TEM. XPS measurements showed the surface layer consisted of SiCxOy with oxygen substituting on the Si sites. Annealing the samples further to 1400°C to 1500°C resulted in the formation of a few layers of graphene on the SiC and the disappearance of the degraded SiC layer. Since it is known that SiCxOy decomposes at lower temperatures than SiC to produce C, the partial oxidation enhances the decomposition of SiC and enhances the growth of graphene. We propose that this partially oxidized defective layer is a likely intermediate phase prior to graphene formation. This growth mechanism is able to explain numerous experimental phenomena in graphene growth without in-situ hydrogen etching.
12:30 PM - L7.9
Optimizing Graphene Quality on Metals by Directly Observing Growth.
Kevin McCarty 1 , Elena Loginova 1 , Peter Feibelman 2 , Shu Nie 1 , Konrad Thurmer 1 , Norm Bartelt 1
1 , Sandia National Laboratories, Livermore, California, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractThe epitaxial growth of graphene on metal substrates is one promising route to synthesizing large-area sheets with low defect densities. We employ low-energy electron microscopy (LEEM) to directly observe graphene growth on metals. This approach enables film quality to be readily optimized and provides much information about the growth mechanisms. Using an imaging-based implementation of electron reflectivity, we measure the absolute C adatom concentration across the surface while simultaneously measuring the rate at which individual graphene islands grow [1]. We find that graphene grows on Ru(0001) and Ir(111) by the same atomic process, irrespective of whether the C comes from vapor-deposited elemental C, ethylene decomposition [2], or C segregating from the bulk of the substrate [3]. In all cases, graphene grows by adding clusters of about 5 C adatoms rather than single C atoms. The unusual “cluster-addition” kinetics can be exploited to improve film quality. The energy barrier to adding individual C adatoms causes graphene nucleation and growth to only occur at high supersaturations of C adatoms. As a consequence, extremely low nucleation densities can then be easily achieved by controlling the C adatom supersaturation. Growing the sparse nuclei until they cover the entire surface results in graphene domains 10’s of microns in size. Some growth aspects do depend on the C source. For example, ethylene only decomposes on the bare metal substrate [2]. Growth then stops once the surface is covered by one layer of graphene. However, growth from segregating C can produce graphene multilayers if sufficient C is dissolved into the substrate. Even though growth from segregating carbon occurs by cluster addition, the global growth rate is determined by the rate at which C diffuses through the substrate. Finally, we will discuss the interrelationships between graphene quality (e.g., domain size and crystallographic misorientation), growth rate, and temperature for single and multilayer films.This work was supported by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering of the US DOE under Contract No. DE-AC04-94AL85000.[1] E. Loginova, N. C. Bartelt, P. J. Feibelman and K. F. McCarty, New J. Phys. 10, 093026 (2008).[2] E. Loginova, N. C. Bartelt, P. J. Feibelman and K. F. McCarty, accepted, New J. Phys. (2009).[3] K. F. McCarty, P. J. Feibelman, E. Loginova and N. C. Bartelt, Carbon 47, 1806 (2009).
12:45 PM - L7.10
Electronic Interaction of Graphene with Transition Metals.
Peter Sutter 1 , Mark Hybertsen 1 , Jurek Sadowski 1 , Eli Sutter 1
1 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractGraphene, an atomically thin sheet of sp2-bonded carbon, has shown fascinating materials properties and holds the promise for future carbon-based device architectures. The interaction of graphene with metals may hold the key to realizing much of this potential. We have recently demonstrated epitaxy on transition metal substrates as a rational route for producing macroscopic single crystalline graphene domains [1]. For epitaxial graphene as well as the inverse configuration – metals evaporated onto graphene – theoretical calculations have predicted two distinct behaviors [2]. Transition metals that interact weakly with graphene (e.g., Al, Cu, Ir, Pt) preserve the characteristic Dirac cones, but may cause significant charge transfer doping. Metals that interact strongly (Rh, Ni, Co, Ru, and Pd) cause the complete disruption of the Dirac cones via electronic coupling of graphene π-states with metal d-states near the Fermi energy.Here we discuss measurements of the interfacial interaction and of the resulting electronic structure of graphene in close proximity with transition metals, comparing systems predicted to interact weakly (e.g., Pt) and strongly (e.g., Ru) with graphene. Graphene growth and structural measurements were performed by low-energy electron microscopy (LEEM). Experimental band maps were obtained by in-situ selected-area angle-resolved photoemission spectroscopy (micro-ARPES) in the LEEM instrument on macroscopic epitaxial graphene domains with controlled thickness [3]. The measurements combined with density-functional theory provide a detailed picture of the electronic interactions at the graphene-metal interface: the electronic coupling between first-layer graphene states and metal d-bands, charge transfer doping, screening in few-layer graphene, and the effects of interfacial registry and elastic strain. In addition, we demonstrate that the coupling between graphene and transition metals can be tuned over a wide range by judicious modifications to the graphene-metal interface. Our findings have important implications for large-scale graphene synthesis on transition metals, and demonstrate the possibility of engineering structures with reduced dimensionality in graphene by exploiting graphene-metal interactions.1. P. Sutter, J.-I. Flege, and E. Sutter, Nature Materials 7, 406 (2008).2. G. Giovannetti, et al., Phys. Rev. Lett. 101, 026803 (2008).3. P. Sutter, M.S. Hybertsen, J.T. Sadowski, and E. Sutter, Nano Letters, published online (June 8, 2009).
L8: Single-Walled Nanotube Networks I
Session Chairs
Wednesday PM, December 02, 2009
Room 310 (Hynes)
2:30 PM - **L8.1
Solution Deposited Self-sorted, Aligned Carbon Nanotube Networks for Electronic Devices.
Zhenan Bao 1
1 , Stanford University, Stanford, California, United States
Show AbstractFor single walled carbon nanotubes to find use in electronics there is a need to efficiently separate them by electronic type, and align them to ensure optimal and reproducible electronic properties. Here, we report SWNT network field effect transistors, deposited from solution, possessing controllable topology and on/off ratio as high as 900,000. The spin-assisted alignment and density of the SWNTs is tuned by different surfaces that effectively vary the degree of interaction with surface functionalities in the device channel. This leads to a self-sorted SWNT network whereby nanotube chirality separation and simultaneous control of density/alignment occurs in one step during device fabrication. Micro-Raman experiments corroborates device results as a function of surface chemistry indicating enrichment of specific SWNT electronic type absorbed onto the modified dielectric. Applications of these SNWT networks in thin film transistors, sensors and transparent electrodes will be presented.
3:00 PM - L8.2
Inkjet Printing of Carbon Nanotubes for Large Area Transparent Conducting Films.
Tianming Wang 1 , Michael Roberts 1 , Ian Kinloch 1 , Brian Derby 1
1 Materials Science, University of manchester, Manchester United Kingdom
Show AbstractCarbon Nanotubes (CNT) have excellent electrical conductivity and great potential for transparent conducting films if printed at an appropriate density. However, the applications are limited by the low concentration of their dispersion in most organic and aqueous solvent. In this work we report on the use of inkjet printing to fabricate transparent conducting networks of multiwall and single wall CNTs on glass. We have used a stable, dispersant-free, water-based CNT ink prepared by a previously reported liquid phase oxidative method. CNT films are formed by the coalescence of droplets that spread to equilibrium on the substrate after printing. The influence of printing parameters such as drop size, velocity and spacing on the substrate on film microstructure and electrical conductivity are reported. Droplet drying can lead to local segregation through “coffee staining”. We show that this effect can be minimised and more uniform films printed through careful control of the substrate temperature.
3:15 PM - L8.3
Highly Conductive and Transparent Nanotube-Filled Composite Thin Films.
Yong Tae Park 1 , Aaron Ham 1 , Jaime Grunlan 1 2 3
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Materials Science and Engineering, Texas A&M University, College Station, Texas, United States, 3 Chemical Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractLayer-by-layer (LbL) assembly was used to generate transparent, highly conductive thin films containing carbon nanotubes. Purified HiPCO single-walled carbon nanotubes (SWNT), stabilized with negatively-charged deoxycholate, were alternately deposited with poly(diallyldimethylammonium chloride) [PDDA] from water onto a heat-stabilized PET substrate. This alternating deposition of positively and negatively-charged components resulted in SWNT-based films with visible light transmission > 70% (measured at 700 nm) and electrical conductivity of ~ 100 S/cm (~ 50 nm thick with a sheet resistance of ~ 2 kΩ/sq) after 20-bilayers of deposition. With just two bilayers of SWNT/PDDA, these films have an electrical conductivity of 30 S/cm (12 nm thick with a sheet resistance of 70 kΩ/sq) and transmission greater than 95% at 700nm. Ellipsometry, a quartz crystal microbalance (QCM) and UV-Vis absorbance were used to measure the linear growth of these films as a function of bilayers deposited. TEM and AFM were used to analyze the nanostructure of these films. This study demonstrates the ability of the LbL technique to produce highly transparent and conductive nanotube-based thin films. Studies are underway to improve electrical conductivity by an order of magnitude, without reducing transparency (or increasing film thickness), by reducing the concentration of stabilizer and investigating alternative stabilizing molecules that enhance nanotube connectivity. These types of films are potentially useful for anti-static films with few bilayers or transparent electrodes with tens of bilayers. Flexible displays, smart windows and solar cells could all benefit from this technology platform.
3:30 PM - L8.4
Single Walled Carbon Nanotube Schottky Diode via Selective Electrochemical Metal Deposition.
Hyunseob Lim 1 , Hee Cheul Choi 1
1 , POSTECH, Pohang Korea (the Republic of)
Show AbstractSingle walled carbon nanotube (SWNT)-metal electrode contacts have been widely investigated to understand the fundamental properties and develop the new functional devices. One of the available functional devices that can be realized when the SWNT-metal contacts are asymmetrically modulated is Schottky diodes. In general, the formation of asymmetric metal electrode requires complex lithographic processes. Herein, we present two facile approaches to fabricate SWNT Schottky diodes from its filed effect transistor-type devices. The first method is carried out via a simple mass transport and reduction of Li ions intercalated into pyrene-methlyamine functionalized SWNT. The intercalated cationic Li ions are attracted to negatively biased electrode and reduced, resulting in selective deposition of Li on one of the electrodes. The other method is via selective electrochemical deposition of palladium under either galvanostatic or potentiostatic mode. These two approaches result in asymmetric energy barriers at the SWNT-electrode junctions, and perfectly rectified I-V curves are obtained from these devices.References1.H. Lim, H. S. Shin, H.-J. Shin, H. C. Choi, J. Am. Chem. Soc. (2008), 130, 2160. 2.H. Lim, H. J. Song, Y. Lee, H.-J. Shin, H. C. Choi, submitted.
3:45 PM - L8.5
Flexible, Spin-coated Carbon Nanotube Electrodes for High-performance n- and p-type Organic Transistors.
Sondra Hellstrom 1 , Zhenan Bao 2
1 Applied Physics, Stanford University, Stanford, California, United States, 2 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractWe show that carbon nanotube-conjugated polymer nanocomposites adhere very selectively to surfaces functionalized with different self-assembled monolayers, and we use this property to self-assemble such composites on surfaces with high density gradient and resolution down to 5 microns. The patterned nanocomposites are easily adaptable as flexible, semitransparent, spin-coated electrodes for large-area organic electronics, and towards this application we demonstrate high mobility (>0.4 cm^2/Vs) p- and n-type bottom contact transistors with pentacene and C60 as active layers respectively. The nanotube composite electrodes perform at least as well as traditional metal electrodes, with added advantages of flexibility and solution processability.
4:30 PM - **L8.6
Ink-jet Printing of Carbon Nanotubes Towards Applications -From Laboratory Experiments to a Pilot Scale.
Tero Mustonen 1 2 , Krisztian Kordas 2 , Geza Toth 2 , Heli Jantunen 2
1 Emerging Competencies / Printing Technologies, Ciba Finland Oy, part of BASF, Raisio Finland, 2 Microelectronics and Materials Physics Laboratories, Department of Electrical and Information Engineering, and EMPART Research Group of Infotech Oulu, University of Oulu, Oulu Finland
Show AbstractInk-jet printing of carboxyl functionalized single-wall carbon nanotubes (SWCNTs) and the scalability of printed electronics to industrial scale are investigated. The properties of low and high density networks of SWCNTs which have either nonlinear or linear current-voltage characteristics are utilized as transistors. The nonlinear, low-density networks are gate-controllable. The choice of having either Ohmic or nonlinear (semiconducting) films from the same material could be utilized as a versatile technique in cost-effective printable electronics, where the fabrication of all the electrodes and active semiconducting layers are printed by using the same material. In the first part of this presentation, completely inkjet printed SWCNT thin film field-effect transistors on polymers are demonstrated using only single nanotube ink. In the second part of the presentation, the issues regarding pilot processing and moving from laboratory to industrial scale of printed electronics are discussed.
5:00 PM - L8.7
Inkjet Printing of Stripe-Featured Single-Walled Carbon Nanotube Thin Film Transistors.
Jiantong Li 1 , Minni Qu 2 , Zhiying Liu 1 3 , Ana Lopez Cabezas 1 3 , Botao Shao 1 3 , Tomas Unander 4 , Zhijun Qiu 2 , Zhi-Bin Zhang 1 , Jia Zhou 2 , Yiping Huang 2 , Li-Rong Zheng 1 3 , Hans-Erik Nilsson 4 , Shi-Li Zhang 1 2 3
1 Department of Microelectronics and Applied Physics, Royal Institute of Technology, Kista, Stockholm, Sweden, 2 State Key Lab of ASIC & System, Fudan University, Shanghai China, 3 iPack Vinn Excellent Center, Royal Institute of Technology, Kista, Stockholm, Sweden, 4 Department of Information Technology and Media, Mid-Sweden University, Sundsvall Sweden
Show AbstractSingle-walled carbon nanotube (SWCNT) thin film transistors (TFTs) have already been demonstrated as promising building blocks for the newly-developed but rapidly-growing macroelectronics. However, such TFTs often suffer from the lack of high performance due to the existence of metallic SWCNTs. Specifically, the TFTs can hardly possess both high on-current and large on/off current ratio. A pioneering work of Rogers et al. has shown that trimming thin films of high-density SWCNT networks into fine stripes connecting the source and drain can effectively eliminate the metallic percolation paths and hence improve significantly its on/off current ratio at the expense of only a small reduction of its on current. In the present work, we demonstrate the realization of such stripe-featured SWCNT TFTs through an inexpensive and flexible inkjet printing technique. First, we reveal the underlying physics for the superiority of stripe-featured SWCNT networks on the basis of systematic studies of rectangle-shaped stick percolation systems. Combing with our early theoretical results of heterogeneous percolation for SWCNT networks, we find that with increasing length-to-width ratio, rectangular SWCNT networks shift their percolation threshold to higher-density region and have wider density windows within which only semiconducting SWCNTs percolate. These properties should account for the high throughput of stripe-featured SWCNT TFTs with high on-current and large on/off current ratio and suggest that trimming SWCNT thin films into fine stripes by means of lithography is not an exclusive way to make stripe-featured TFTs. Putting together independent rectangular SWCNT networks through other sophisticated methods such as inkjet printing is also a feasible alternative. Then, our theoretical results are justified by inkjet printed SWCNT TFTs on various substrates, including paperboard and plastics. These TFTs consist of multiple SWCNT stripes, ~100 μm wide and up to several mm long. Our preliminary results have already shown relatively high yield of high-performance SWCNT TFTs. In addition, inkjet printed TFTs with structures based on, but a little more complicated than, stripes are also investigated and exhibit improved performance. We believe that the present work would contribute to the development of macroelectronics and flexible electronics.
5:15 PM - L8.8
CNT-based Infrared Photovoltaic Detectors with a Near Infrared Specific Detectivity of >1011 cm-Hz½/W.
Jeramy Zimmerman 1 , Christine Austin 1 , Stephen Forrest 1 2
1 Department of Physics, University of Michigan, Ann Arbor, Michigan, United States, 2 Departments of Materials Science, and Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractOrganic photodetectors have seen limited success for applications in the near infrared (NIR), especially beyond wavelengths of 1 μm.i Carbon nanotube (CNT) hybrid devices are promising for extending sensitivity into the NIR since their E11 transitions generally absorb between 1 and 2 μm, and CNTs have carrier mobilities exceeding 105 cm2-V-1s-1.ii The deleterious effects of metallic tubes (~33% of the total CNT concentration) created by most production methods, and difficulties in processing have prevented successful demonstrations of CNT-based bulk-film photovoltaic response until recently.iii In this work, we report high-sensitivity NIR photodetectors achieved by dispersing CNTs wrapped in a solubilizing polymer.iv Devices are created by doctor blading films of MDMO-PPV wrapped CNTs onto indium tin oxide, and evaporating layers of the electron acceptor C60, and a BCP/silver cathode. The CNT-C60 interface is essential to dissociate excitons formed by absorption of NIR light by the CNTs. We have demonstrated NIR external quantum efficiency (EQE) of 2% at 1150nm and a broadband (400-1400nm) specific detectivity (D*) of >1010 cm-Hz½/W.iii While the EQE is comparatively low, we find that the internal quantum efficiency is approximately 30-50% over a wide range of wavelengths, suggesting opportunities for greatly enhancing EQE and D*. We discuss the limitations of our CNT-based photovoltaic detectors, and describe improved techniques for dispersing the CNTs, which increases the EQE in low-dark current devices. Further, we describe a light trapping scheme to increase overall EQE, resulting in D* values peaking in the mid-1011 cm-Hz½/W range. i. R. Kroon et al., Polym. Rev. 48, 531 (2008)ii. T. Durkop et al., J. Phys.-Condes. Matter 16, R553 (2004)iii. J.D. Zimmerman, et al., MRS Spring Meeting, (2009); M.S. Arnold, et al., submitted (2009) iv. A. Nish et al., Nat. Nanotechnology 2, 640, (2007)
5:30 PM - L8.9
Individually Deposited Carbon Nanotubes Films.
Jinwoo Sung 1 , Cheolmin Park 1
1 Materials Science and Engineering, Yonsei university, Seoul Korea (the Republic of)
Show AbstractThe 2 dimensional films of single-walled carbon nanotubes(SWNTs) have attracted much attention as a component of large area organic electronics because of their superior electrical, mechanical and optical properties. High density films of them have worked successfully as flexible transparent electrodes in the fields of optoelectronics with high conductivity, transparency and flexibility. Recently, some methods rendering the films semiconducting characteristics have developed. The thin films enabled field effect transistors with high on-off ratios and mobility by elaborated processes such as electrical break-down, chemical modification, and separation of semiconducting SWNTs. Actually, it is also possible that the deposition of appropriate density constructs semiconducting films without complicated processes above mentioned from general batch containing one thirds of metallic SWNTs. It happens since if SWNTs were individually deposited, junctions between metallic SWNTs and semiconducting SWNTs form Schottky barrier which is gate field modulated. But until now, thin films made by solution processes have shown low on/off ratios. In solution processes used to prepare carbon nanotubes films, the quality of dispersion was not good and, even when carbon nanotubes are individually dispersed in solution, they aggregate in the middle of film formation, producing the networks of bundles, which are weakly modulated by electric field. Here, we use conjugated block copolymer, poly(styrene-b-phenylene) for dispersing SWNTs in non-covalent way, in which conjugated block adsorbs strongly on the wall of SWNTs and styrene block gives solvation to the hybrid. We show that conjugated block copolymer has the excellent dispersing ability, so that SWNTs exist individually in solution and deposit independently on substrates when spin-cast. The fabricated films show high on-off ratios more than 105 from proper concentration of solution. Semiconducting characteristics of the films are demonstrated to be originated from their individual deposition through electrical behavior, Raman spectroscopy, UV vis spectroscopy, and NMR measurement.
5:45 PM - L8.10
Highly Flexible and Transparent Polymer Light Emitting Devices with Single-walled Carbon Nanotube Electrodes.
Zhibin Yu 1 , Zhitian Liu 1 , Qibing Pei 1
1 Materials Science and Engineering, UCLA, Los Angeles, California, United States
Show AbstractTransparent electrodes are required for a wide rang of electronic and photonic applications. The ubiquitously used indium doped tin oxide (ITO) is not suitable for highly flexible devices as ITO coatings crack at strains greater than 0.5% to 1%. Various alternative electrodes have been investigated, including conducting polymers, other metal oxides, single walled carbon nanotubes (SWNTs) and graphenes et al.SWNT thin film electrodes have been developed from solution processes onto plastic substrates with conductivity and transmittance comparable to ITO electrodes. We have shown that the SWNT electrodes are highly compliant: the electrodes remain conductive at high strains up to 700%.We report highly flexible and transparent polymer light emitting devices with SWNT electrodes. The devices have above 80% transmittance in wavelength range where the light emitting polymers are transparent. Stacking of the transparent enhances the light emitting intensities and/or tunes the emission colors. Meanwhile, the devices can be easily bended with radius less than 2mm without damaging the electroluminescence characteristics.
L9: Poster Session: Single-Walled Nanotube Networks II
Session Chairs
Thursday AM, December 03, 2009
Exhibit Hall D (Hynes)
9:00 PM - L9.1
Photocurrent of CdSe Nanocrystals on Single-walled Carbon Nanotube-field Effect Transistor.
Seung Yol Jeong 1 2 , Young Hee Lee 2
1 Nanocarbon Materials Research Group, Korea Electrotechnology Research Institute, Changwon Korea (the Republic of), 2 Physics, Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractCdSe nanocrystals (NCs) have been decorated on single-walled carbon nanotubes (SWCNTs) by combining a method of chemically modified substrate along with gate-bias control. CdSe/ZnS core/shell quantum dots were negatively charged by adding mercaptoacetic acid.. The silicon oxide substrate was decorated by octadecyltrichlorosilane and converted to hydrophobic surface. The negatively charged CdSe NCs were adsorbed on the SWCNT surface by applying a negative gate bias. The measured photocurrent clearly demonstrates that CdSe NCs decorated SWCNT can be used for photodetector and solar cell that are operable over a wide range of wavelengths.
9:00 PM - L9.10
Conformable Patch Antenna Array for Energy Harvesting.
Akshat Patel 2 , Miral Vaghela 2 , Hassan Bajwa 2 , Prabir Patra 1
2 Electrical Engineering, University of Bridgeport, Bridgeport, Connecticut, United States, 1 Mechanical Engineering, University of Bridgeport, Bridgeport, Connecticut, United States
Show AbstractCarbon nanotube (CNT) has emerged as potential candidate for replacement of conventional metal patch in antenna application. The principal objective of our research is to develop nanostructured flexible patch antenna array for multi- frequency operation in industrial, scientific and medical (ISM) band. Patch antenna design using CNT on flexible cotton sheets has been simulated with cotton as a substrate and CNT as conductive patch and ground plane. Due to high conformability and conductivity of CNT all antenna parameters like VSWR, return loss, gain and radiation pattern obtained using FEKO EMSS software meet design criteria. Our simulated antenna design shows a return loss less than -10 dB and VSWR less than 2 at 2.06 GHz, 2.38 GHz and 2.49 GHz. We have also simulated a versatile and conformable antenna design where the whole geometry is rolled up like patch array on cylindrical surface. Conformability to curved surfaces and integration with the structure brings about a unique antenna design. An inset fed square patch array is also proposed for RF energy harvesting operating in the 2.45 GHz ISM band that can harvest and store energy from the surrounding environment. Simulation result shows that dc voltage of 0.215 V can be achieved at -6 dbm received energy level at 2.45 GHz IEEE 802.11b band. This would correspond to potential working distance of 10m.
9:00 PM - L9.12
Integration of Carbon Nanotube Arrays in Lab-on-a-chip System for Blood Analyses Separation and Detection.
Ashish Mathur 1 , Susanta Sinha Roy 1 , Jim McLaughlin 1
1 NIBEC, University of Ulster, Newtownabbey United Kingdom
Show AbstractMicrofluidic lab-on-a-chip is the next generation of devices used for bio-analysis to be conducted in a miniaturized system. Miniaturized analysis not only lowers down the reagent volume but also decrease the overall size of the device. Blood-cell-free serum is required for most clinical chemistry tests. At present micro channel bends and polymeric pillars are used in polymer based microfluidic devices (such as PMMA) for the blood filtration. Also, various MEMS based experimental procedures exist to separate blood cells from whole blood. In this study, we have fabricated carbon nanotube (CNT) pillars on Si and quartz from 20-50 µm in diameter with ~10 µm spacing and placed them inside the microfluidic channels/devices with a view of using these for blood plasma filtration from whole blood. Our main objective is to design a novel sensor, comprising CNT arrays, to filter/control whole blood flow, with an integrated micro patterned gold electrode which will be sealed by bonding into microfluidics structures. The CNT microstructures were characterized by using SEM, TEM, Raman, XPS and XRD techniques. We have also characterized the microfluidic channel by measuring the meniscus movement profiles and the time (transit time) of the fluid flow across the channel with and without CNT pillars. Gold inter-digitated electrodes (IDEs) were fabricated on glass which will be immobilized with the antibody. These IDEs will further be used for as an impedimetric bio-sensor using label free antigen – antibody interaction. This method is potentially the state-of-the-art use of CNTs in microfluidic devices/ sensors.
9:00 PM - L9.2
Work Function Engineering of Transparent Conductive Films based on Graphene and Carbon Nanotube.
Seong Jun Kang 1 , Yoojin Song 1 , Yeonjin Yi 1 2 , Won Mook Choi 3 , Seon-Mi Yoon 3 , Jae-Young Choi 3
1 Center for Materials Measurement, Korea Research Institute of Standards and Science, Daejeon Korea (the Republic of), 2 Nano Surface Science, Korea University of Science and Technology, Daejeon Korea (the Republic of), 3 Display Laboratory, Samsung Advanced Insitute of Technology, Suwon Korea (the Republic of)
Show AbstractWe developed a method that allows control of the work function of graphene and carbon nanotube (CNT) transparent conductive films on a flexible sheet of plastic. The approach involves the deposition of small amount of metals, such as aluminum, on graphene and CNT transparent conductive films followed by a measure of the work function of the films using in-situ ultraviolet photoelectron spectroscopy. Core-level spectra of the films were collected in order to investigate the chemical reaction when a small amount of aluminum was deposited on their surface in a stepwise manner. The measurements revealed that deposition of less than 0.5 nm of aluminum was enough to control the work function of graphene and CNT transparent conductive films. These results could be useful for engineering the work function of flexible transparent conductive films based on graphene and CNT, and would be applied not only in electronics but also in areas such as optoelectronics, sensors, solar cells and nanomechanical systems.
9:00 PM - L9.3
Template-free Solution Growth of Highly Regular, Crystal Orientation Ordered C60 Nanorod Bundles.
Louzhen Fan 1 , Yang Zhang 1
1 Department of Chemistry, Beijing Normal University, Beijing China
Show Abstract Buckminsterfullerene (C60) has hogged the limelight ever since its discovery. Its potential utility in nanoelectronics, superconductors, optical switches and field-effect transistors has kept on attracting broad interest. Bottom-up assembly of C60 into well-defined low-dimensional structures is in many ways a prerequisite to realize the various nanodevice applications. To play an active role in photonics, it is necessary to create C60 nanostructures that are highly aligned and ordered. However, this type of nanostructures has not been realized experimentally up till now. We report on the fabrication of crystal orientation-ordered bundles of C60 nanorods by a novel strategy based on the liquid-liquid interfacial precipitation (LLIP) method. The resulting sample is dominated by a morphology consisting of “bundles” of rod-shaped 1D nanostructure of C60. Each nanorod in the bundle maintains its individual rod-shape and all of them are bundled together as a single entity. The top view of the bundle displays that all of the nanorods are vertically aligned with a high degree of size uniformity and a high density. The fractured cross-section evidently indicates that the core of bundle preserves the shape of C60 nanorods at the top. As a demonstration of the promising applications of the new C60 materials in optical devices, two-end devices were fabricated by depositing Ag gap electrodes on macroscopic C60 nanorod bundles. The C60 nanorod bundle devices exhibit high sensitivity to light. The typical current-voltage (I-V) characteristics of a C60 nanorod bundle device in the dark and under white light illumination shows that the current of the device increases with increasing light intensity, and the current increases linearly with increasing illumination power.When the bundle was irradiated, the photocurrent increased by more than 500 folds at a constant bias voltage of 20 V. Such high intensity and stability of the photocurrent demonstrate preeminent photoconductivity of the C60 nanorod bundle. It is believed that the strong photoresponse arising from the high photoconductivity of the C60 nanorod bundles is associated with the novel structures of the bundles composed of countless highly regular, crystal orientation ordered C60 nanorod arrays, which provide multiple channels of “superhighways” for shuttling the electrons.Acknowledgment. This work is financial supported by NSFC(20773015), the Major State Basic Research Development Programs (2004CB719903).
9:00 PM - L9.4
1/f Noise Behaviors with the Hysteresis of Ambi-polar CNT Field Effect Transistors.
Min Kyu Joo 1 , Un Jeong Kim 3 , Doyoung Jang 1 2 , Yonha Kim 1 , Gyu Tae Kim 1
1 School of Electrical Engineering , Korea University, Seoul Korea (the Republic of), 3 Frontier Research Laboratory, Samsung Advanced Institute of Technology, Yongin Korea (the Republic of), 2 School of Electrical Engineerging, IMEP - LAHC INP Grenoble – Minatec, Grenoble France
Show AbstractThe correlations between the low frequency noise and the hysteresis of the networked carbon nanotube (CNT) devices with ambi-polar field effects were investigated at the hole-rich or the electron-rich regimes from the gate dependence of the currents. The counter-clockwise hysteresis for the electron channel or the clockwise for the hole channel indicate the modification of the effective gate fields owing to the existence of charge traps at the interface between the gate insulator and the nanotube channels. The oxygen deficiency of the gate insulator will create the negatively charged traps with the opposite tendency for the metal deficiency. Considering the current should reflect the actual gate field applied to the channel, the noise current can be compared for the same level of the currents. The RC time of the trapping/de-trapping events can change the width or the magnitude of the hysteresis with the different sweep speed of the gate voltage. The noise amplitudes in the electron dominant regime (n channel) normalized by the current showed much larger than those in the hole dominant regime (p channel), indicating more scatterers for the electron channels. The Hooge`s parameter αH was estimated to be a few 10-3 order which was smaller than the typical value. The defects, impurities and chemical ions in the channel can modify the effective gate field inducing the change of the hysteresis or the 1/f noise characteristics. The effective gate bias and the variation of channel environments can be deduced from the noise power spectrum with the hysteresis of the gate depedence.
9:00 PM - L9.5
Bioinspired Assembly of Carbon Nanostructures for Large Scale Applications.
Zhiping Xu 1 , Markus Buehler 1
1 Civil and Environmental Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractNanostructures present novel material properties and enable insight into intriguing new physical phenomena. However, from a technological application point of view, a successful bridging between nanoscale towards large-scale applications in devices and materials must be achieved. Graphene nanoribbons – the finite width counterpart of monoatomically layered graphene materials – possess fascinating electronic properties such as width and edge shape dependent electronic properties. However, the lack of precision control at nanoscale, their structural instability at elevated temperature and their chemical activity at their open edges have thus far led to great difficulties in enabling larger-scale applications of graphene nanoribbons in devices and materials. In order to effectively utilize graphene nanoribbons we must be able to (1) assemble them into mechanically stable, macroscopic functional materials, while (2) preserving their key physical functional properties. Our paper addresses this issue by proposing a novel hierarchical graphene nanoribbon structure inspired by biological beta-sheet proteins. Here we show based on first principles calculations that hierarchical, highly functional structures of graphene nanoribbons can be fabricated through utilization of hydrogen bonds as self-assembly drivers. Our calculations show that the cooperative assembly of clustered hydrogen bonds provides a large binding energy of 1.3 eV, which provide significant mechanical stability against tension and shear. On the other hand, the relatively weak nature of hydrogen bonds preserves the intrinsic electronic properties of graphene nanoribbons at the level of the larger-scale hierarchical assembly. In our study, edge states are observed near the Fermi level and the electronic structures are controllable by changing the width of the graphene nanoribbon. Specifically for graphene nanoribbon assemblies from -C=O…H-N- hydrogen bonds, we find that the energy gap shrinks as the width of the constituting nanoribbons increases, and approaches zero (corresponding to a metallic system) at 28 Å. The controllable tuning of bulk properties through nanostructural design not only paves the way for the nanoengineering of graphene based functional materials, but also provide a test bed for hydrogen bond studies, which play a vital role in bionanoscience and technology and could enable the synthesis of a new class of biomimetic multifunctional mutable nanomaterials for electromechanical applications. This novel approach for the first time provides an effective breakthrough solution to the issues (1) and (2) mentioned above. Fabrication of the material is discussed in terms of both bottom-up (self-assembly) and top-down (mechanical manipulation) approaches.
9:00 PM - L9.6
Ultra High Density Aligned Carbon Nanotube based Field Effect Transistors and Air Stable N-type Metal Contact for Integrated Circuit Applications.
Chuan Wang 1 , Koungmin Ryu 1 , Alexander Badmaev 1 , Jialu Zhang 1 , Chongwu Zhou 1
1 Electrical Engineering, University of Southern California, Los Angeles, California, United States
Show AbstractAligned carbon naotubes are very desirable for mass production of carbon based electronic devices and integrated circuits owing to their advantages of registration-free fabrication, high device yield, and small device-to-device variation. For the aligned nanotubes, one of the most important technology components is to increase the nanotube density. High density aligned nanotubes can be extremely helpful to improve the current driving capability, transconductance, and cut-off frequency of the devices. Here in this talk, we report high-performance back-gated carbon nanotube field-effect transistors (CNTFETs) fabricated on ultra high density aligned carbon nanotubes with density up to 30 nanotubes per micrometer. Studies found that before removing the metallic nanotubes by electrical breakdown, the on-current density of the device could be as high as 92.4 μA/μm and the transconductance per unity channel width could be as high as 13.3 μS/μm. Based on the high-performance devices, a typical analog circuit, common source amplifier, was built. The -3dB frequency was measured to be 81.2 kHz and the unity gain frequency was measured to be 294.5 kHz, which agreed with the simulation results well. In addition, If the parasitic capacitance from the bonding pads was excluded from the simulation, the -3dB frequency could be as high as 88.4 MHz and the unity gain frequency could be as high as 1GHz. This study shows the potential of using high density aligned carbon nanotubes for analog and RF applications.Another important technology component for integrated circuit application is to achieve air-stable n-type transistors from carbon nanotubes. We demonstrate that by using metal contacts with small work function such as Gadolinium (Gd), the CNTFETs exhibit predominantly n-type behavior since the Fermi level of the metal is aligned with the conduction band of the carbon nanotubes. In order to achieve air stable operation, E-beam evaporated SiO2 was used for passivation and the devices exhibit clear n-type characteristics when measured in air. Further more, stepper and E-beam lithography were used to pattern both p-type (Pd contact) and n-type (Gd contact) devices on the same nanotubes and an integrated air-stable CMOS inverter with a gain of 6 was demonstrated. Rectifying diodes with Pd contact for p side and Gd contact for n side was also demonstrated and their solar-cell response was also studied.
9:00 PM - L9.7
Highly Aligned ``All-Metallic” Single-wall Carbon Nanotube Architectures for Nanoscale Interconnect.
Young-Lae Kim 1 , Swastik Kar 2 , Yung Joon Jung 3
1 Department of Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractSingle walled carbon nanotubes (SWNTs) are expected to outperform copper in terms of failure current density, power dissipation, and on-chip signal transfer delays. However, to fabricate SWNT-based interconnects in an integrated device, it is required to develop a manufacturing process that can controllably place aligned SWNTs in desired locations, orientations, and dimensions. In addition, since naturally grown SWNTs contain a mixture of metallic and semiconducting nanotubes, there is an imminent need to develop a process that will convert semiconducting nanotubes into metallic ones in such nanoscale architectures. In this talk, we will demonstrate highly aligned “All-Metallic” SWNT lateral architectures for nanoscale interconnect. For this, firstly we developed a novel fluidic assembly process to create remarkably organized lateral bundles of SWNTs in various geometries using a lithographically patterned template assisted dip coating of SWNTs-DI water solution. Then, Pt nanoclusters were decorated on the highly organized and aligned SWNT lateral nanoscale architectures to convert semiconducting SWNTs into metallic ones and further increase the conductance of existing metallic SWNTs. Electrical characterization reveals that the electrical resistivity of these Pt nanoclusters decorated SWNT interconnect structures decrease by 45% on an average by increase in the number of conductance channels near the Fermi level of the nanotube, due to charge transfer from decorated Pt nanoclusters on SWNT. Also developed SWNT interconnect structures are capable of withstanding current densities up to ~107 A/cm2. These completely CMOS-compatible and scalable processes reflect a huge step towards integration of carbon nanotubes into existing interconnect technologies.
9:00 PM - L9.8
Simulation of the One-dimensional Random Percolation Networks.
Pil Soo Kang 1 , Siegmar Roth 1 , Gyu Tae Kim 1
1 School of Electrical Engineering, Korea University, Seoul Korea (the Republic of)
Show Abstract The microscopic transport in the percolating networks of one-dimensional channels such as carbon nanotubes was simulated by Monte Carlo method and SPICE (Simulation Program with Integrated Circuit Emphasis). The percolation networks of one-dimensional channels could be generated by the randomly located channels with the different lengths or the widths following the gaussian distribution. The channels were considered as corresponding circuit models composed of resistors, diodes or field effect transistors(FETs). The nodes among the channels were extracted by calculating intersection point between two channels and the connection relations among the nodes were represented by adjacency matrix. Based on the adjacency matrix and the circuit models indicating the channels, the random percolation networks could be converted to the circuits models described by netlist for SPICE. The current-voltage characteristics of networks were simulated easily using SPICE with the netlist. By applying this method, not only the carbon nanotube network field effect transistors but also other network device could be simulated well.
9:00 PM - L9.9
A Scanning Probe Microscopy Study on the Actuation Mechanisms of Nanotube Switches.
Peter Ryan 1
1 Mechanical Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractThere is much interest in using Carbon Nanotubes (CNT’s) as the actuating element in a memory type nanoelectromechanical system (NEMS). Theoretical studies that include molecular dynamics simulations as well as continuum mechanics have demonstrated the complexity in the electrostatic effects of such switches. Current experimental studies of these devices have been predominantly limited to electronic characterization. It has been shown that Scanning Probe Microscopy (SPM) is a useful tool in the manipulation and mechanical testing of CNT’s. An experimental setup was created utilizing SPM and electronic measurement equipment with the aim of providing further information on the quasi-static and dynamic response of a CNT switch under an applied field. One such experiment utilized a continuity test during Force Distance mapping of the suspended CNT. Measured forces closely resemble our model of the structure as a self stiffening string.
Symposium Organizers
Manish Chhowalla Rutgers University
John A. Rogers University of Illinois, Urbana-Champaign
Carey M. Tanner SRI International
Pagona Papakonstantinou University of Ulster
Andrea C. Ferrari University of Cambridge
L10: Single-Walled Nanotube Networks III
Session Chairs
Thursday AM, December 03, 2009
Room 310 (Hynes)
9:00 AM - **L10.1
Electrical Transport in Carbon Nanotube Network FETs and Transparent Conductors – from Sparse Networks to Dense Films.
Michael McGehee 1 , Michael Rowell 1 , Mark Topinka 1 , Sondra Hellstrom 3 , Zhenan Bao 3 , David Goldhaber-Gordon 2 , David Hecht 4 , George Gruner 4
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 3 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Physics, Stanford University, Stanford, California, United States, 4 Physics and Astronomy, Stanford University, Los Angeles, California, United States
Show AbstractThin films of carbon nanotubes (CNT) are promising candidates for low cost transparent electrodes for solar cells and macroelectronics. We investigate the microscopic transport in both sparse networks for transistors and dense networks for transparent electrodes using electric force microscopy and simulations. We find in sparse networks for FETs that the switching is governed by different mechanisms at different densities and different semiconducting-to-metallic ratios. The effect of Schottky barriers on both conductance within semiconducting tubes and conductance between semiconducting and metallic tubes results in three possible types of FETs with fundamentally different gating mechanisms which we describe with an electronic phase diagram. We also investigate electrical transport in bundles typical of dense films used for transparent conductor (TC) applications. CNT TCs have the potential to outperform traditional transparent conducting oxides. Current performance of CNT TC films, however, is about an order of magnitude worse than their metal oxide counter parts and two orders worse than the limit predicted from single tube properties. Transport in these films is complicated by the mixed metallic-semiconducting nature and the resistive jumps between tubes in a tortuous and bundled network. We use atomic force microscope scratch lithography to isolate single CNT bundles and electric force microscopy to measure local bundle resistances.
9:30 AM - L10.2
Local Bottom Gating for High Performance Carbon Nanotube Array Transistors.
Aaron Franklin 1 , George Tulevski 1 , James Hannon 1 , Zhihong Chen 1
1 T. J. Watson Research Center, IBM Research, Yorktown Heights, New York, United States
Show AbstractCarbon nanotube (CNT) device research has taken an important turn in the past couple of years. Attention has shifted from individual device physics and demonstration, to focus more on the issues keeping CNTs from actual integration. While the potential for using these 1D structures in transparent and/or flexible electronics is a promising avenue under pursuit, many of the intrinsic properties of nanotubes still make them a promising choice for high-performance transistors. An important next step in the direction of high-performance devices is to combine the best advancements from individual CNT transistors and incorporate them into CNT array devices that are scalable, for both shrinking dimensions and ramping to production. In this work, we show how a unique local bottom gate (LBG) geometry provides a promising platform for the integration of CNT arrays into high performance transistors. Aligned CNT arrays are deposited directly onto patterned LBGs using either substrate transfer or localized deposition techniques, each having unique advantages for device fabrication and performance. The LBG structure enables aggressive scaling of the gate dielectric without the need for CNT functionalization. Thinning the dielectric has allowed for the fabrication of transistors with gate lengths down to 30 nm showing enhanced on-state conduction with no short-channel effects. Furthermore, inclusion of a metallic nanotube suppression technique enables these scaled CNT devices to be fabricated across a chip without the need for post-deposition metallic CNT removal. Overall, our presentation will illustrate how an appropriate gating geometry, combined with the implementation of other device advancements, yields a promising platform for next generation high performance CNT array transistors.
9:45 AM - L10.3
Pushing the Performance Limits of Transparent, Conducting Carbon Nanotube Films: Role of Nanotube Length and Tube-tube Bundling.
Bhupesh Chandra 1 , George Tulevski 1 , Ali Afzali-Ardakani 1 , Teresita Graham 1
1 , IBM T.J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractCarbon nanotube films are a strong candidate for use as transparent electrode in variety of applications such as solar cells, flexible electronics, displays etc.Recent advances in tube growth, purification and large scale depositions techniques have made it possible to manufacture ultrathin, conducting nanotube networks.However, the optical and electronic properties of nanotube films are still sub par to ITO-a widely used material for transparent electrodes.In order to achieve superior quality nanotube films, the current work uses ultra pure nanotubes obtained through density gradient purification technique. In addition to this, a solution based doping method is developed using metal salts that reduces the sheet resistance of nanotube films by 50%-75% depending upon the type of tubes used. Through a comprehensive study of nanotube films obtained using tubes from a variety of sources (HiPCO,Arc discharge, CVD, Laser vaporization) and processing steps it is shown that tube length and tube-tube bundling issues play a significant role in determining the resultant film properties.The presence of short nanotubes decreases the film conductance due to a higher number of resistive tube-tube junctions. Also, nanotubes present inside large tube bundles do not contribute well to electronic transport. Increasing nanotube length and minimizing tube bundling is shown to increase the performance of nanotube films significantly.
10:00 AM - **L10.4
Advanced Fiber Lasers by Carbon Nanotube Saturable Absorbers.
Aleksey Rozhin 1 , Zhipei Sun 1 , Fengqiu Wang 1 , Andrea Ferrari 1
1 Department of Engineering, University of Cambridge, Cambridge United Kingdom
Show AbstractCarbon nanotubes (CNTs) exhibit strong saturable absorption, i.e. they become transparent under sufficiently intense light. This has great potential for applications in photonics. By tuning the nanotube diameter it is easy to tune the saturable absorption in a broad optical range of interest in spectroscopy, photochemistry, biomedical research and telecommunications. The performance of CNT-based saturable absorbers strongly depends on CNT concentration, bundle size, and transparency of the matrix where CNTs are dispersed. Here, we review the fabrication and characterization of saturable absorber based on CNT-polymer composites [1,2,3]. We use ultrasonication to obtain CNT solutions. The composites are successfully used to mode-lock lasers in a broad spectral range [4-6]. We report the realisation of a mode-locked tuneable fiber laser [6]. This is achieved through the control of amplification at the transitions of an Er3+ gain medium by placing a band pass filter in the cavity. The laser generates 2.4 ps pulses continuously tuneable between 1518 and 1558 nm, the widest to date [6]. We also present a stretched-pulse fiber laser generating ~120 fs pulses. This allows us achieve high power outputs, exceeding 1 W [7], orders of magnitude higher than previous nanotube-based fiber lasers.1.V. Scardaci et al., Adv. Mat. 20, 4040 (2008)2.T. Hasan et al. J. Phys. Chem C 111, 12549 (2007)3.P. H. Tan et al. Phys. Rev. Lett. 99, 137402 (2007)4.G. Della Valle et al. Appl. Phys. Lett. 89, 231115 (2006)5.Z. Sun et al. Appl. Phys. Lett. 93, 061114 (2008)6.F. Wang et al., Nature Nano 3, 738 (2008) 7.Z. Sun et al., submitted (2009)
10:30 AM - L10.5
Conductive Transparent Single-Walled Carbon Nanotube Films: Integration with Organic Photovoltaic and CdTe Devices.
Brian Larsen 1 , Jeremy Bergeson 1 , Lynn Gedvilas 1 , Robert Tenent 1 , Teresa Barnes 1 , Jeffrey Blackburn 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractTransparent conducting (TC) films of carbon single-walled nanotubes (SWNTs) have the potential to replace conventional TC oxides in a wide variety of optoelectronic devices. TC-SWNT films are particularly attractive for solution processed photovoltaic (PV) devices due to their high transparency over much of the solar spectrum, excellent electrical conductivity, and the potential for inexpensive roll-to-roll processing. However, most SWNT film deposition methods are not scalable and are not satisfactory for PV applications. For example, SWNT films produced by membrane filtration are limited to laboratory scale applications and are susceptible to morphological inhomogeneities when transferred to a substrate, which cause short-circuited devices and poor device reproducibility. Integration of TC-SWNT films as electrodes in PV applications requires methods to produce transparent, conducting SWNT films that are smooth and homogeneous over large areas. Here, we present scalable methods to prepare TC-SWNT electrodes with high transparency, electrical conductivity, uniformity, and exceptionally low surface roughness by ultrasonic spraying and integration of TC-SWNT electrodes into specific device applications, such as organic photovoltaic (OPV) and inorganic devices such as cadmium telluride (CdTe).We have recently reported comparable performance for OPV devices fabricated on TC-SWNT and conventional indium-doped tin oxide (ITO) electrodes, with device efficiencies at 3.1% and 3.6% efficiency under AM 1.5 illumination, respectively [1]. These highly conductive films were produced by ultrasonic spraying an aqueous SWNT/surfactant dispersion and exposing the sprayed film to concentrated nitric acid, removing the residual surfactant and doping the film p-type. The device architecture int this study was amenable to TC-SWNT post-processing using nitric acid, but more benign post-processing techniques are necessary to integrate TC-SWNT electrodes into inverted OPV devices and inorganic (e.g. CdTe, CIGS) devices. To this end, we will discuss our recent progress towards TC-SWNT electrode integration with variety of different substrates. In particular, we will present a newly developed benign post-processing technique that yields TC-SWNT electrodes comparable to nitric acid processing. In addition, we will present detailed methods to prepare these TC-SWNT films and demonstrate the successful integration of TC-SWNT electrodes in OPV and CdTe devices.1. Tenent RC, Barnes TM, Bergeson JD, Ferguson AJ, To B, Gedvilas LM, Heben ML, Blackburn JL. “Ultrasmooth, Large-Area, High-Uniformity, Conductive Transparent Single-Walled-Carbon-Nanotube Films for Photovoltaics Produced by Ultrasonic Spraying”, Advanced Materials (2009), Early View.
11:15 AM - **L10.6
Alignment Controlled Growth of Single Walled Carbon Nanotubes on Quartz Substrates.
Jianliang Xiao 1 , Simon Dunham 3 , Ping Liu 4 , Yongwei Zhang 5 4 , Coskun Kocabas 7 , Yonggang Huang 1 2 , John Rogers 3 6
1 Mechanical Engineering, Northwestern University, Evanston, Illinois, United States, 3 Materials Science and Engineering, University of Illinois, Urbana, Illinois, United States, 4 , Institute of High Performance Computing, Singapore Singapore, 5 Materials Science and Engineering, National University of Singapore, Singapore Singapore, 7 Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 2 Civil & Environmental Engineering, Northwestern University, Evanston, Illinois, United States, 6 Beckman Institute and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois, United States
Show AbstractSingle walled carbon nanotubes (SWNTs) possess extraordinary electrical properties, with many possible applications in electronics. Dense, horizonally aligned arrays of linearly configured SWNTs represent perhaps the most attractive and scalable way to implement this class of nanomaterial in practical systems. Recent work shows that templated growth of tubes on certain crystalline substrates yields arrays with the necessary levels of perfection, as demonstrated by the formation of devices and full systems on quartz. This paper examines, through combined experimental and theoretical studies, the fundamental mechanisms associated with the growth of such arrays, to suggest that angle dependent van der Waals interactions dominate the process. These models account for nearly all aspects of SWNT alignment on quartz with X, Y, Z and ST cuts, as well as quartz with disordered surface layers. These findings yield important insights and development strategies for guided growth of SWNTs on crystalline substrates, in linear arrays or other arrangements that could find utility in applications in electronics, sensing, photodetection, light emission and other areas.
11:45 AM - L10.7
Silicon on Insulator Structures used to Guide the Surface Bound Growth of Carbon Nanotubes for Transistor Devices.
Arthur Blackburn 1 , Simone Pisana 2 , David Williams 1 , Stephan Hofmann 3
1 Hitachi Cambridge Laboratory, Hitachi Europe Ltd., Cambridge United Kingdom, 2 San Jose Research Center, Hitachi Global Storage Technologies, San Jose, California, United States, 3 Department of Engineering, University of Cambridge, Cambridge United Kingdom
Show AbstractA method of fabricating carbon nanotube transistor devices, using standard lithographic processes upon a silicon-on-insulator (SOI) substrate, is demonstrated to permit the pre-determined free assignment of the position and in-plane orientation of individual thermal CVD grown CNTs with a lateral positional control of better than 100 nm over the length (> 2 µm) of the nanotube. The surface-bound CNT growth is guided by the overhanging sidewalls of a thermally oxidized silicon layer, which if suitably doped can be used to gate the electron transport through the nanotube.Devices were made with the CNT growth guided through trenches of width < 100 nm, formed by dry and wet etching through the 40 nm silicon layer, followed by thermal oxidation. A patch of iron catalyst is placed adjacent to the entrance of the trenches to nucleate the CNT growth. The positioning and preparation of this catalyst patch, along with the conditions during the CVD growth process appear critical to the functioning of the process, as seen through SEM and AFM observations. Nonetheless, functioning devices with drain-source current on-off ratios of up to 1000 have been measured, using the silicon layer of the SOI substrate as the gate. The process of identifying and eliminating devices with the tube out of the channel is simple and quick. It is then possible to carry out further processing on the SOI substrate using large scale lithographic techniques, with the knowledge that CNTs are present only in certain predefined paths, and the convenience of the freely-selectable direction and path-defining channel being able to act as an electrical gate upon the CNT. This represents an advantage over many alternative large area CNT device arrangements and processing methods, aiding the possibility of integrating CMOS electronics with individual or low numbers of CNTs for new functionalities.
12:00 PM - L10.8
Single-Walled Carbon Nanotube Chemical Sensors Integrated on to CMOS Circuitry for Environmental Monitoring.
Chia-Ling Chen 1 , Niksa Valim 1 , Chih-Feng Yang 1 , Vinay Agarwal 2 , Sameer Sonkusale 2 , Ahmed Busnaina 3 , Michelle Chen 4 , Mehmet Dokmeci 1
1 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Electrical and Computer Engineering, Tufts University, Boston, Massachusetts, United States, 3 Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States, 4 Physics, Simmons College, Boston, Massachusetts, United States
Show AbstractGas sensors are needed in a wide range of applications including environmental monitoring, detection of green house gases, controlling manufacturing processes, and in domestic gas alarms. Single-walled carbon nanotubes (SWNTs) hold great promise as active materials for carrying out these sensing tasks due to their extraordinary electrical and mechanical properties and their extremely large surface area to volume ratios. Furthermore, SWNTs reportedly are very sensitive to numerous odors and could serve as the next generation of miniature gas sensors. Moreover, SWNTs functionalized with biomolecular complexes hold great promise as high sensitivity sensors. Building nanotube sensors directly on commercial CMOS circuitry allows single chip solutions eliminating the need for long parasitic lines and numerous wire bonds. In this paper, we demonstrate the successful incorporation of SWNTs on to a functional CMOS circuitry and then by decorating single-stranded (ss)-DNA on top of the SWNTs we demonstrate miniature, and ultra sensitive single chip gas sensors. The assembly process utilized Dielectrophoresis (DEP), which has been tailored to be compatible with the post-CMOS integration at the die level. The binding between ss-DNA and SWNTs is known as a spontaneous conformational change that enables the hybrid to self-assemble via the π-π stacking interactions. Three different ss-DNA sequences has been utilized to decorated SWNTs and the enhancement of gas sensitivity was observed in the ss-DNA wrapped SWNT sensors compared with the bare SWNT sensors after exposure to both methanol and IPA vapors. Furthermore, the integration of the DNA decorated gas sensors onto CMOS circuitry was demonstrated and the results show that after exposure to methanol vapor, the measured gain of the CMOS amplifier increased by about 20.71%, 55% and 31.19% for ss-DNA seq. 1, seq. 2 and seq. 3, respectively. After exposure to IPA, the measured gain of the inverting amplifier increased by 7.75%, 13.70% and 8.25% for ss-DNA seq.1, seq. 2 and seq.3, respectively. The remarkable set of attributes of the SWNTs coupled with the ss-DNA molecules provides an attractive platform for high sensitivity and low power nanotube based bio and chemical sensors.
12:15 PM - L10.9
Sorting Achiral SWCNTs Out Using Graphene Membranes Nanosieves.
Luca Ortolani 1 , Marc Monthioux 2 , Vittorio Morandi 1
1 , CNR IMM-Bologna, Bologna Italy, 2 , CNRS CEMES, Toulouse France
Show AbstractChirality dramatically affects the physical and electronic properties of single-walled carbon nanotubes (SWCNTs). Current growth methods result in SWCNTs of mixed chiral indices, and finding a simple and effective way to discriminate and sort chiral from achiral SWCNTs will be an important step toward their practical exploitation. Here we will demonstrate and discuss how graphene membranes act as effective nanoscopic tangential sieves by retaining only achiral SWCNTs, aligning them with the underlying honeycomb lattice. We have prepared ethanol solutions of graphene flakes (obtained by mechanical exfoliation of Madagascar graphite microcrystals) mixed with commercial SWCNTs (grown using the arc technique and exhibiting different chiralities). SWCNTs deposit over the graphene surface. Then, as a consequence of the subsequent mechanical agitation provided by ultrasonic vibrations and centrifugation, chiral SWNCTs were found to preferably eliminate, while achiral SWNCTs were found to still stick to the graphene surface. This sieving action is generated by the perfect match between the atomic lattices of zig-zag and armchairs tubes with that of the underlying graphene surface, thereby providing improved surface adhesion as opposed to what happens with chiral SWCNTs. We will discuss in details the HREM characterization, which provide direct evidences of SWCNT alignment and achiral feature by means of high-resolution imaging and electron diffraction analysis.
L11: Single-Walled Nanotube Networks IV
Session Chairs
Thursday PM, December 03, 2009
Room 310 (Hynes)
2:30 PM - **L11.1
Metal Nanowire Mesh Transparent Electrodes.
Peter Peumans 1
1 Electrical Engineering, Stanford University, Stanford, California, United States
Show AbstractTransparent electrodes for touch screens, displays and thin-film solar cells require a combination of the following properties: manufacturable at low cost, highly transparent, and very conductive. In the case of solar cells, the ability to scatter light may be desirable as well. We show that solution processed random meshes of silver nanowires satisfy the above requirements. Metal wires, when fused together at moderate temperatures (as low as 100°C) form ohmic contacts, ensuring good in-plane electrical-conduction. The amount of silver needed amounts to approximately $0.10 per square meter. The transparency for a mesh with subwavelength nanowire spacing can be as high as 80-95%. I will describe our recent experiments that further increase the performance of metal meshes by lowering the wire-wire contact resistance. I will also show how these silver nanowire meshes can be laminated onto devices to form a transparent electrode with low contact resistance. This leads to a method to fabricate multi-terminal multijunction solar cells with a practical efficiency potential that is much improved over that of conventional series-connected multijunction solar cells. I will conclude with an overview of our modeling work that guide us toward improved performance and new applications.
3:00 PM - L11.2
Zinc Oxide Nanowire Networks for Macroelectronic Devices.
Husnu Unalan 1 , Yan Zhang 2 , Pritesh Hiralal 2 , Sharvari Dalal 2 , Daping Chu 2 , Goki Eda 3 , Ken Teo 2 , Manish Chhowalla 3 , William Milne 2 , Gehan Amaratunga 2
1 Metallurgical and Materials Engineering, Middle East Technical University, Ankara Turkey, 2 Electrical Engineering, University of Cambridge, Cambridge United Kingdom, 3 Materials Science and Engineering, Rutgers University , Piscataway, New Jersey, United States
Show AbstractHighly transparent ZnO nanowire networks are used as the active material to fabricate basic electronic devices such as thin film transistors (TFTs) and logic inverters. High temperature grown ZnO nanowires are transferred to receiver substrates at room temperature in the form of semiconducting random networks. A systematic study on a range of networks of variable density and TFT channel length is performed. ZnO nanowire networks provide a less lithographically intense alternative to individual nanowire devices, are always semiconducting, and yield significantly higher mobilites than those achieved from currently used amorphous silicon and organic TFTs. These results suggest that ZnO nanowire networks could be ideal for inexpensive large area electronics [1].[1] H.E. Unalan et al., Appl. Phys. Lett. 94 (2009) 163501
3:15 PM - L11.3
Generic Approaches towards Large Scale Nanowire Assembly.
Zhiyong Fan 1 2 , Johnny Ho 1 2 , Toshitake Takahashi 1 2 , Zachery Jacobson 1 2 , Roie Yerushalmi 1 2 , Kuniharu Takei 1 2 , Ali Javey 1 2
1 Electrical Engineering and Computer Sciences, University of California at Berkeley, Berkeley, California, United States, 2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractSemiconductor nanowires have been extensively explored as the potential building blocks for a variety of electronic and optoelectronic applications due to the continuous increased demand for miniaturized devices and circuits. However, controlled and uniform assembly of “bottom-up” nanowire (NW) materials with high scalability is one of the major bottleneck challenges towards the integration of nanowires for circuit applications. We have achieved wafer-scale assembly of highly ordered arrays of NWs through methods utilizing van de Waals interaction between nanowires and receiving substrates. These methods include contact printing of NWs on lithographically patterned substrates using photo-resist, electron beam resist and self-assembled monolayer resist. The NW printing dynamics were investigated in order to optimize the printing result. It was found that application of liquid lubricant can significantly improve the printing results. And the assembled NW pitch is shown to be readily modulated through the surface chemical treatment of the receiver substrate, with the highest density approaching ~8 NW/µm, ~95% directional alignment and wafer-scale uniformity. We have also demonstrated a differential roll-printing method towards a large scale, low cost roll-to-roll NW printing process. With these generic approaches, a wide range of semiconductor NWs including Si NWs, Ge NWs, core/shell Ge/Si NWs, InAs NWs and CdSe NWs, etc., have been successfully assembled at large-scale on rigid and flexible substrates, configured as a variety of functional electronic and optoelectronic devices, including field-effect transistors, Schottky diodes, gas sensor and photodiodes, etc. For the first time, these functional components are integrated together to enable all-nanowire integrated photodetection circuits and image sensing circuitry.
3:30 PM - L11.4
A VLSI Technology for Vertical Nanotubes.
Shanmugamurthy Lakshmanan 1 , Alokik Kanwal 1 , Anitha Patlolla 2 , Zafar Iqbal 2 , Reginald Farrow 1
1 Department of Physics, NJIT, Newark, New Jersey, United States, 2 Department of Chemistry and Environmental Science, NJIT, Newark, New Jersey, United States
Show Abstract We have developed a controllable process protocol for depositing vertically aligned single wall carbon nanotubes (SWNT) at prescribed locations making use of the available lithographic and process technology in the semiconductor industry[1]. There is also control of the number of SWNTs deposited (down to only one per location). The process is compatible with wafer scale process integration with complementary metal oxide semiconductor (CMOS) technology. The deposition technology uses the very general methodology of electrophoresis with pre-synthesized and presorted SWNTs that are commercially available. We have used this electrophoresis deposition (EPD) technique to deposit metallic and semiconducting SWNTs in both isolated and dense arrangements. Besides the ability to rapidly deposit large numbers of SWNTs at interconnect sites, the key advantage over the traditional deposition method (i.e. chemical vapor deposition) is that it is done at room temperature and does not damage the metals that are commonly used in CMOS integrated circuits (IC). A metal interconnect structure was fabricated on a silicon wafers. A thin insulating layer of silicon nitride was deposited over the interconnects and sub-100 nm diameter windows were patterned and etched into the silicon nitride. SWNTs were deposited using EPD in the windows on the metal. During EPD electrostatic lenses that form around the windows (due to charge buildup on the insulator) guide the SWNTs. The first SWNT that deposits and makes an electrical connection with the metal modifies the electric field and affects the paths of subsequent SWNTs that approach and the number of SWNTs that make contact with the metal. Various other parameters, which influenced successful EPD, are analyzed. Controllable parameters included, the nature of the suspension, concentration of SWNTs, sonication process, surfactant, deposition time, voltage, electrode separation distance and polarity of electrodes. The success of this EPD process makes viable for a variety of noval nanoscale device applications like electronic biosensor arrays, vertical nanotransistors and nano-scale biofuel cells. We are in the process of integrating and testing such devices, which will be reported separately. The general EPD technique can be used for the deposition of any high aspect ratio nanoparticle. A stable suspension of the nanoparticle is the key criteria for successful EPD. [1] A. Goyal, S. Liu, Z. Iqbal, L. A. Fetter and R. C. Farrow, J. Vac. Sci. Technol. B 26 (2008) 2524.
3:45 PM - L11.5
Anisotropic Etching and Crystallographic Nanoribbon Formation in Single-Layer Graphene by Channeling Nickel Nanoparticles.
Javier Sanchez-Yamagishi 1 , Leonardo Campos 1 3 , Vitor Manfrinato 2 4 , Pablo Jarillo-Herrero 1 , Jing Kong 2
1 Physics, MIT, Cambridge, Massachusetts, United States, 3 Departamento de Fisica, UniVersidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil, 2 Department of Electrical Engineering and Computer Science, MIT, Cambridge, Massachusetts, United States, 4 Departamento de Engenharia de Sistemas Eletronicos, Universidade de Sao Paulo, Sao Paulo, SP, Brazil
Show AbstractThe electronic, magnetic, and chemical properties of graphene nanoribbons are strongly dependent on their edge structure and chirality. We demonstrate an anisotropic etching method of single-layer graphene(SLG) by thermally-activiated nickel nanoparticles which channel through the SLG along crystallographic directions. Using this technique, we obtain sub-10-nm nanoribbons and other graphene nanostructures with edges aligned along a single crystallographic direction. We also observe a new catalytic channeling behavior unique to SLG, whereby etched cuts do not intersect, resulting in continuously connected geometries. Raman spectroscopy and electronic measurements show that the quality of the graphene is resilient under the etching conditions, indicating that this method may serve as a powerful technique to produce graphene nanocircuits with well-defined crystallographic edges.
4:00 PM - L11:SWNN 3
BREAK
4:30 PM - **L11.6
Synthesis, Properties and Assembly of Shape- and Composition-controlled Colloidal Nanocrystals.
Liberato Manna 1
1 , Fondazione Istituto Italiano di Tecnologia, Genova Italy
Show AbstractCurrent efforts and success of nanoscale science and technology are related to the fabrication of functional materials and devices in which the individual units and their spatial arrangement are engineered down to the nanometer level. One promising way of achieving this goal is by assembling of colloidal inorganic nanocrystals as the novel building blocks of matter. This trend has been stimulated by significant advancement in the wet-chemical syntheses of robust and easily processable nanocrystals in a wide range of sizes and shapes. The increase in the degree of structural complexity of solution-grown nanostructures appears to be the natural direction toward which nanoscience will increasingly orient. Recently, several groups have indeed devised innovative syntheses of nanocrystals through which they have been able to group inorganic materials with different properties in the same particle. These approaches are paving the way to the development of nanosized objects able to perform multiple technological tasks. This talk will review the recent advances in the synthesis of colloidal nanocrystals, with emphasis on the strategies developed at IIT for the fabrication of colloidal nano-heterostructures, as well as on their properties and their assembly.
5:00 PM - L11.7
Stable, High Current Density Field Emission from Zinc Oxide Nanowires Grown on a Carbon Nanotube Array.
Mark Mann 1 , Chi Li 2 , Yan Zhang 1 , Pritesh Hiralal 1 , Husnu Unalan 3 , Wei Lei 2 , Baoping Wang 2 , William Milne 1 , Gehan Amaratunga 1
1 Department of Engineering, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom, 2 Display R&D Center, School of Electronic Science and Engineering, Southeast University, Nanjing China, 3 Department of Metallurgical and Materials Engineering, Middle East Technical University, Ankara Turkey
Show AbstractCarbon nanotubes (CNTs) have been investigated for possible applications to field emission devices such as electron sources for SEMs, microwave amplifiers and x-ray sources. However, CNTs, as is the case with all field emitting materials, are susceptible to destruction at pressures greater than 10-8 mbar due to adsorbed gaseous species being able to cause current runaway with a reduction in the local workfunction. The probability of this happening increases significantly with increase in pressure. The consequence is a poor, long-term emission stability and lifetime which has prevented field emission from being applied to an application that requires a moderate vacuum for operation, such as backlighting, room lighting and field emission displays. Zinc oxide (ZnO) is a high band gap semiconductor which, as a consequence, would not normally be considered for field emission devices which require a high current density. However, when ZnO nanowires are deposited onto vertically aligned arrays of CNTs, the extra field enhancement and a high density of emission sites results in a stable, long lifetime, high current density field emission source. Measurements have shown ZnO/CNT arrays to have a lifetime at least five times that of equivalent CNT-only arrays, a threshold macroscopic field ~30% less than CNT-only arrays whilst maintaining a current density of 1 mA/cm2 at pressures of 4×106 mbar. It is postulated that the ZnO nanowires act to self-ballast the current emitted by limiting the supply of electrons, stabilizing the emission current.
5:15 PM - L11.8
Large Yield Preparation of High Electronic Quality Graphene by a Langmuir-Schaefer Approach.
Regis Gengler 1 , Alina Veligura 1 , Dmitrios Gournis 2 1 , Bart van Wees 1 , Petra Rudolf 1
1 Zernike Institute for Advanced Materials, University of Groningen, Groningen Netherlands, 2 Departement of Materials Science and Engineering, University of Ioannina, Ioannina Greece
Show AbstractGraphene is an intriguing material with properties that are distinct from other graphitic systems. Even though this material presents outstanding electric and thermal conductivities, systematic studies and developments of potential applications have been restricted so far by the lack of a reliable and straightforward method to prepare graphene on different substrates. We present here a new approach which allows the deposition of graphene on a variety of substrates with a coverage that can be chosen as desired from isolated sheets to a densely packed 2D arrangement. In contrast to the currently most common preparation protocols which rely on micromechanical cleavage, the yield of successful deposition of our approach is 100%, qualifying it as one of today’s most trustworthy and promising methods.
5:30 PM - L11.9
Photochemical Metal to Semiconductor Conversion of Carbon Nanotubes.
Lewis Gomez De Arco 1 , Akshay Kumar 1 , Yi Zhang 1 , Koungmin Ryu 1 , Alexander Badmaev 1 , Chongwu Zhou 1
1 , University of Southern California, Los Angeles, California, United States
Show AbstractWe report inactivation of metallic nanotubes in nanotube field-effect transistor channels as a consequence of a light-assisted process that led to a scalable metal to semiconductor conversion in the nanotubes. Stronger gate bias dependence with improvements in the drain current On/Off ratio up to 10^5 was found in around 90% of the CNT-FETs. The possibility of fabricating mostly semiconducting carbon nanotube transistors by simple light irradiation in air over entire wafers constitutes an important achievement in terms of assembly, integration and large scale fabrication of nanotube-based circuits.
5:45 PM - L11.10
Role of Surfactant Molecular Structures on Nanotube Separation by Density Gradient Ultracentrifugation.
Giulia Privitera 1 , Francesco Bonaccorso 1 , Tawfique Hasan 1 , PingHeng Tan 1 3 , Pietro Gucciardi 2 , Andrea Ferrari 1
1 Department of Engineering, University of Cambridge, Cambridge United Kingdom, 3 Institute of Semiconductors, Chinese Academy of Science, Beijing China, 2 , CNR- Istituto per i Processi Chimico-Fisici (Messina), Messina Italy
Show AbstractDensity Gradient Ultracentrifugation (DGU) is one of the most successful techniques to sort Single Wall Carbon Nanotubes (SWNTs) by diameter as well as by electronic type [1,2]. Here we clarify the influence of different surfactants and polymers on the separation mechanism. We report highly selective enrichment (~94%) of (6,5) through single step DGU exploiting Sodium Cholate (SC) as surfactant. Lower enrichment (~55%) is achieved using Sodium Deoxicholate (SDC) and its taurine substitute, Sodium Taurodeoxycholate (TDC). The reduced diameter selectivity of these two dihydroxy bile salts in comparison with the trihydroxy SC is here explained in terms of hydrophobic interaction between the bile salts and the SWNTs [3]. The exploitation of polymers such us Pluronic F98 and Igepal DM-970 permits us to achieve enrichment up to ~70% of SWNTs in the diameter range (0.84-0.91nm). Other surfactants, such as Sodium Dodecylbenzene Sulfonate (SDBS), Sodium Dodecyl Sulphate (SDS) and Sodium bis(2-ethylhexyl) Sulphosuccinate, inefficiently form micelles around SWNTs, resulting in SWNT bundling, hindering their separation. Moreover, we investigate the influence of co-surfactant mixtures in the separation mechanism. In particular we show that tuning the concentration of the linear chain surfactant (SDS) respect to the tri-hydroxyl bile salt SC enhances the difference in buoyant density. This permits us to achieve (>98%) semiconducting and (>95%) metallic SWNTs (m-SWNTs) enrichment [3]. Similar results are also achieved using the tri-block co-polymer Pluronic F-98 instead of SC. We then use the sorted m-SWNTs to prepare transparent and conductive polymer-composites, which have been proposed as a viable alternative to replace the brittle and expensive transparent conductive Indium Tin Oxide (ITO) [4]. The enrichment of m-SWNTs allows us to overcome the main drawback related to the polydispersity of as-produced SWNTs. This can enhance the conductivity of polymeric films, even at low concentration.1. M. S. Arnold, et al., Nat. Nano, 1, 60-65 (2006)2. J. Crochet, et al., J. Am. Chem. Soc., 129, 8058-8059 (2007)3. F. Bonaccorso, et al., submitted (2009)4. Z. Wu, et al., Science, 305, 1273 (2004)