Symposium Organizers
AlexanderA. Balandin University of California-Riverside
Andre Geim University of Manchester
Jiaxing Huang Northwestern University
Dan Li Monash University
Symposium Support
Cambridge NanoTech Inc
Elsevier Ltd.
Y1: Synthesis and Processing of Graphene I
Session Chairs
Jiaxing Huang
Rodney Ruoff
Tuesday PM, April 26, 2011
Room 3009 (Moscone West)
9:30 AM - **Y1.1
History and Prospects for Graphene-based Materials.
Rodney Ruoff 1
1 Mechanical Engineering, The University of Texas at Austin, Austin, Texas, United States
Show AbstractAn update on progress by our research group on graphene-based materials. Two main thrusts are on chemically modified graphenes (synthesis, characterization, uses) and on large area graphene made on Cu and other metal foils. Useful information is on our website http://bucky-central.me.utexas.edu/ . We acknowledge funding support from NSF, DOE, DARPA (CERA, iMINT), ONR, ARO, SWAN-NRI, Graphene Energy, Inc.
10:00 AM - **Y1.2
Synthesis and Applications of Graphene, Graphene Nanoribbons and Other Carbon Nanomaterials.
James Tour 1
1 Smalley Institute, Rice University, Houston, Texas, United States
Show AbstractWith its extraordinary electronic and mechanical properties, graphene is showing promise in a plethora of applications. Recent developments in our laboratories concerning the synthesis and use of graphene, graphene nanoribbons and other carbon nanomaterials will be discussed. This will include the synthesis of pristine and doped graphene from solid carbon sources, the synthesis and analysis of high quality CVD graphene and single-layer atomic resolution lithography of graphene and graphite oxide. The use of these materials in diverse applications from the oil field to photovoltaics, transparent conductors and medicine will be detailed.
10:30 AM - Y1.3
Properties of Fluorinated Graphene Films.
Jeremy Robinson 1 , James Burgess 1 , Chad Junkermeier 1 , Stefan Badescu 1 , Thomas Reinecke 1 , Keith Perkins 1 , Maxim Zalalutdinov 1 , Jeffrey Baldwin 1 , James Culbertson 1 , Paul Sheehan 1 , Eric Snow 1
1 , Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractThe functionalization of graphene is a scalable and inexpensive route to modify its transport, optical, and chemical properties. Here we describe a route to stoichiometrically add fluorine atoms to graphene using room temperature exposure to XeF2 gas. Graphene films were grown on Cu foils and have been fluorinated on one or both sides[1]. When exposed on one side the F coverage saturates at C4F, which is significantly more resistive than graphene and can be readily patterned. Density functional calculations for varying coverages indicate that a C4F configuration is lowest in energy and the calculated band gap increases with increasing coverage, becoming 2.93 eV for one C4F configuration. During defluorination, we find hydrazine treatment effectively removes fluorine while retaining graphene’s carbon skeleton. The same films may be fluorinated on both sides by transferring graphene to a silicon-on-insulator substrate enabling XeF2 gas to etch the Si underlayer and fluorinate the backside of the graphene film to form perfluorographane (CF) for which the calculated band gap is 3.07 eV. Our results indicate single-side fluorination should be sufficient to considerably modify both the electronic and optical properties of graphene devices.[1] JT Robinson et al., Nano Letters 10, 3001 (2010)
10:45 AM - Y1.4
High Quality Bilayered Graphene Sheets from One-Step Electrochemical Exfoliation.
Ching-Yuan Su 1 , Ang-Yu Lu 1 , Lain-Jong Li 1
1 Research Center for applied science, Academia Sinica, Taipei Taiwan
Show AbstractFlexible and ultra-transparent conductors based on graphene sheets have been considered as one promising candidate for replacing currently used indium tin oxide films that are unlikely to satisfy future needs due to losses in conductivity on bending and their increasing cost. Here we demonstrate a simple and fast electrochemical method to efficiently exfoliate graphite into thin graphene sheets, mainly AB-stacked bilayered graphene with a large lateral size (several to several tens microns). The electrical properties of these exfoliated sheets are readily superior to the reported reduced graphene oxide, where their preparation typically requires many steps including oxidation of graphite and high temperature or aggressive reduction. These graphene sheets dissolve in dimethyl foramide (DMF) and due to their strong surface hydrophobicity they can self-aggregate on air-DMF surface after adding water as a poor solvent. Interestingly the continuous films obtained at air-DMF surface are highly continuous and with ultra-transparency (~96% transmittance), and the sheets resistance is ~1kOhm/sq after a simple acid treatment, readily superior to those based on reduced graphene oxide or other exfoliated graphite. Raman and STM characterizations corroborate that the graphene exfoliated by our electrochemical method preserve graphene structures inherited from graphite.
11:30 AM - **Y1.5
Advances in Graphene Chemistry.
Robert Haddon 1
1 Center for Nanoscale Science and Engineering, University of California, Riverside, California, United States
Show AbstractWe have recently demonstrated the high density functionalization of epitaxial graphene wafers with nitrophenyl groups (NP).[Bekyarova, E.; Itkis, M. E.; Ramesh, P.; Berger, C.; Sprinkle, M.; de Heer, W. A.; Haddon, R. C., Chemical Modification of Epitaxial Graphene: Spontaneous Grafting of Aryl Groups. J. Am. Chem. Soc. 2009, 131, 1336-1337; Niyogi, S.; Bekyarova, E.; Itkis, M. E.; Zhang, H.; Shepperd, K.; Hick, J.; Sprinkle, M.; Berger, C.; Lau, C. N.; de Heer, W. A.; Conrad, E. H.; Haddon, R. C., Spectroscopy of Covalently Functionalized Graphene. Nano Lett. 2010, 10, 4061] The chemical formation of covalent carbon-carbon bonds involving the basal plane carbon atoms offers an alternative approach to the control of the electronic properties of graphene; the transformation of the carbon centers from sp2 to sp3 introduces a barrier to electron flow by saturating the carbon atoms and opening a band gap which potentially allows the generation of insulating and semiconducting regions in graphene wafers.In this talk I will discuss our recent results on the electronic and magnetic properties of chemically modified graphene.
12:00 PM - Y1.6
Chemical Vapour Deposition (CVD) Growth of Graphene and Few-layered Graphene on Different Crystallographic Orientations of the Copper Grains.
Cecilia Mattevi 1 , Hokwon Kim 1 , Manish Chhowalla 2
1 Materials Department, Imperial College London, London United Kingdom, 2 Department of Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States
Show AbstractIntegration of graphene into practical electronic devices necessitates large-scale fabrication of high quality thin films. Chemical vapour deposition (CVD) of graphene on copper is a potential scalable route for high quality graphene deposition because is easy to etch, facilitating transfer onto insulating substrates [1]. It has been also demonstrated that atmospheric pressure (AP)CVD, with high partial pressure of CH4, can deposit few- layered graphene films over a large fraction copper surface [2]. To fully understand the growth of graphene with variable thickness, it is necessary to understand the nature of nucleation sites on the copper surface. Moreover, the activation mechanism of the graphene nucleation and density of such sites as a function of the copper morphology, size and crystallographic orientation of grains, are not yet fully understood. Here we demonstrate the thickness dependence of graphene on CH4 (carbon precursor source) flow rate, growth pressure, different polycrystalline microstructures and morphologies of copper foils. We used CH4/H2 mixture to grow graphene by low pressure (LP)CVD (0.1-0.5 Torr) and copper foils which underwent different manufacturing processes. Graphene over ~ 95% of the surface was obtained at low CH4 flow rate (0.5 sccm) on copper foils with uniform crystallographic orientations of the grains. While applying the same growth conditions on copper foils with random crystallographic orientation of the grains, the resulting graphene was bilayer over >60% of the surface and the left over surface was covered by either monolayer or 3 layered graphene film. Higher CH4 flow rate and growth pressure extended the bilayer graphene up to >90 % of the copper surface. Interestingly the higher pressure growth employed on the copper foils with random crystallographic orientation of the grains, lead to homogeneous films of higher quality with respect to the low growth pressure and CH4 flow. Our results reveal that the graphene nucleation sites can be activated differently depending on the CH4 partial pressure, copper crystallinity and morphology. Hence, varying the copper texture should allow the control over the graphene thickness. Optoelectronic properties of the transferred graphene films onto SiO2 are also presented.[1] X. Li, W. Cai, J. An, S. Kim, J. Nah, D. Yang, R. Piner, A. Velamakanni, I. Jung, E. Tutuc, S. K. Banerjee, L. Colombo, and R. S. Ruoff, Science 324, 1312 (2009).[2]S. Bhaviripudi, X. Jia, M.S. Dresselhaus, J. Kong, Nano Lett., 10, 4128 (2010).
12:15 PM - Y1.7
Synthesis of a Pillared Graphene Nanostructure: A Counterpart of Three-dimensional Carbon Architectures.
Maziar Ghazinejad 1 2 , Rajat Kanti Paul 1 , Miroslav Penchev 2 , Jian Lin 1 , Shirui Gue 3 , Mihrimah Ozkan 2 , Cengiz Sinan Ozkan 1
1 Mechanical Engineering, University of California, Riverside, Riverside, California, United States, 2 Electrical Engineering, University of California, Riverside, Riverside, California, United States, 3 Chemistry, University of California, Riverside, Riverside, California, United States
Show AbstractUsing chemical vapor deposition technique a novel 3D carbon nano-architecture called a pillared graphene nanostructure (PGN) is synthesized in situ. The fabricated novel carbon nanostructure consists of CNT pillars of variable length grown vertically from large-area graphene planes. A one-step CVD process for large-area PGN fabrication through combination of surface catalysis and in situ vapor–liquid– solid mechanisms is described. The dependence of the morphology of the large-area PGN on the synthesis process conditions was investigated by optical microscopy, SEM, TEM, and HRTEM techniques. The highly crystalline interface between the CNT pillar and graphene floor confirmed the seamless contact between the two carbon allotropes. Moreover, to tune the PGN architecture, arrays of catalyst particles with controlled size and separation distance are fabricated using block copolymer films as template. This strategy yields tunable diameter and separation distance of pillar carbon nanotubes, and provides control over the amount of final carbon structure surface area. Our methodology provides a pathway for fabricating novel 3D nanostructures which are envisioned for future ultra large and tunable surface area applications in hydrogen storage and supercapacitors, as well as potential applications in photovoltaics, and nanoelectronics.
12:30 PM - Y1.8
Facile Synthesis of Large-area Monolayer Graphene Films on Cobalt and Nickel.
Carlo Orofeo 1 , Hiroki Ago 1 2 , Yoshito Ito 1 , Masaharu Tsuji 1 2
1 Graduate School of Engineering Sciences, Kyushu University, Fukuoka Japan, 2 Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka Japan
Show AbstractGraphene, a quasi 2-dimensional (2D) material, has attracted much attention due to its great potential as a new material for future technologies [1]. Catalytic chemical vapor deposition (CVD) on poly-crystalline Ni metal film deposited on SiO2/Si is a popular means to produce large-area graphene films due to the simplicity of the process and scalability. One setback, however, is that the grown graphene is inhomogeneous, which varies from single to multi-layers [2]. Here, we show that we can produce homogenous graphene films on either Co or Ni metal.Recently, we have found a way to improve the crystallinity of sputtered Co and Ni on single crystal sapphire (α-Al2O3) [3]. The method involves sputtering of the metal film at elevated temperature. We have synthesized graphene films by annealing the substrate with sputtered amorphous carbon (a-C/metal/sapphire) under vacuum conditions. After annealing and transfer to SiO2/Si substrate, our produced films are optically homogenous (>95%). From analyses using Raman spectroscopy, AFM, TEM, and transmittance measurements, we confirmed that our film is single layer. Using our method, we can produce monolayer graphene in centimeter (cm) sizes and is only limited to the substrate size and our vacuum chamber size. Further experiments suggested that the uniformity of the films produced is independent of the cool-down rate, in contrast with the previously reported result [4]. We believe that our facile method (without the use of CVD gases) is practical enough for large-scale application. References :[1] A. K. Geim et al., Nat. Mater. 2007, 6, 183. [2] A. Reina et al., Nano Lett. 2009, 9, 30. [3] H. Ago et al., Small 2010, 6, 1226. [4] Q. Yu, et al., Appl. Phys. Lett. 2008, 93, 113103.
12:45 PM - Y1.9
Second-layer Graphene Growth from Below on Metal Substrates.
Shu Nie 1 , Elena Starodub 1 , Kevin McCarty 1 , Norman Bartelt 1
1 , Sandia National Laboratories, Livermore, California, United States
Show AbstractSome proposed applications of graphene require Bernal-stacked bilayers. Thus, an interesting question is how the second graphene layer grows on transition-metal substrates. Once the metal is covered by the first graphene layer, the rate of hydrocarbon decomposition in CVD processes slows greatly, nearly stopping second-layer growth [1]. However, carbon dissolved in the metal bulk can still segregate to the substrate surface under the first graphene layer. A basic question is whether these carbon atoms nucleate a new layer below the first layer (i.e., next to the substrate) or on top of the first layer. We explore this question by examining growth on Ir(111), a system where one-layer graphene has five discrete in-plane orientations relative to substrate directions [2]. Low-energy electron diffraction (LEED) reveals that the first and second graphene layers are not always rotationally aligned in plane. This misalignment allows us to determine without ambiguity which sheet is on the top and which is on the bottom by varying the electron energy to change the escape depth of diffracting electrons. We first use low-energy electron microscopy (LEEM) to determine the spatial distribution of rotational domains in a single-layer film. We then cool the substrate and observe growth of the second layer. We find that the top sheet of the bilayer has the exact same domain structure as the initially grown single layer. Thus, additional layers are added from below. This mechanism has significant consequences. For example, we propose that nucleation and growth of the second layer strongly depends upon how difficult it is to debond the first layer from the substrate.This work was supported by the Office of Basic Energy Sciences 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. 11, 063046 (2009).[2] E. Loginova, S. Nie, K. Thürmer, K., N. C. Bartelt and K. F. McCarty, Phys. Rev. B 80, 085430 (2009).
Y2: Synthesis and Processing of Graphene II
Session Chairs
Dan Li
Lain-Jong (Lance) Li
Tuesday PM, April 26, 2011
Room 3009 (Moscone West)
2:30 PM - **Y2.1
Functionalized Graphene Oxide and Graphene: Chemistry and Materials Properties.
Owen Compton 1 , Zhi An 1 , SonBinh Nguyen 1
1 Department of Chemistry, Northwstern University, Evanston, Illinois, United States
Show AbstractIn spite of its humble appearance, graphite is a very attractive precursor to graphene oxide and graphene due to its high abundance and low cost. It can also be easily exfoliated into bulk quantities of graphene oxide—oxygenated graphene sheets covered with epoxy, hydroxyl, and carboxyl groups—via chemical oxidation and mechanical exfoliation. The resulting graphene oxide can be reduced back to graphene, chemically modified graphene, or functionalizable reduced graphene oxide. This presentation will focus on the syntheses of these graphene oxide and graphene derivatives, including chemical modifications that make them compatible in both aqueous and organic solvents as well as in polymer matrices. These materials can then be used in the bottom-up fabrication of new graphene-based macroscopic structures and composites.
3:00 PM - **Y2.2
Graphene-based Nanomaterials and Nanostructures: Synthesis, Characterization and Applications.
Hua Zhang 1
1 School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore
Show AbstractIn this talk, I will summarize the research on synthesis, characterization and applications of graphene-based nanomaterials and nanostructures, which my group has done recently. I will introduce the synthesis and characterization of novel grapheme-based materials [1] and patterned graphene structures [2]. Then I will demonstrate the applications of graphene-based materials in chemical and bio-sensors [3], solar cells [4], electric devices [5], memory devices [6], conductive electrodes [7], cell cultures [8], matrix of MALDI-TOF-MS [9], etc. Reference:[1] (a) X. Y. Qi, K.-Y. Pu, H. Li, X. Z. Zhou, S. X. Wu, Q.-L. Fan, B. Liu, F. Boey, W. Huang, H. Zhang, Angew. Chem. Int. Ed., 2010, DOI: 10.1002/anie.201004497. (b) X. Y. Qi, K.-Y. Pu, X. Z. Zhou, H. Li, B. Liu, F. Boey, W. Huang, H. Zhang, Small, 2010, 6, 663-669. (c) X. Huang, X. Z. Zhou, S. X. Wu, Y. Y. Wei, X. Y. Qi, J. Zhang, F. Boey, H. Zhang, Small, 2010, 6, 513-516. (d) X. Z. Zhou, X. Huang, X. Y. Qi, S. X. Wu, C. Xue, F. Y. C. Boey, Q. Y. Yan, P. Chen, H. Zhang, J. Phys. Chem. C, 2009, 113, 10842–10846.[2] (a) B. Li, G. Lu, X. Z. Zhou, X. Cao, F. Boey, H. Zhang, Langmuir, 2009, 25, 10455-10458. (b) H. Li, J. Zhang, X. Z. Zhou, G. Lu, Z. Y. Yin, G. Li, T. Wu, F. Boey, S. S. Venkatraman, H. Zhang, Langmuir, 2010, 26, 5603–5609. (c) X. Z. Zhou; G. Lu; X. Y. Qi; S. X. Wu; H. Li; F. Boey; H. Zhang, J. Phys. Chem. C, 2009, 113, 19119–19122.[3] (a) Q. Y. He, H. G. Sudibya, Z. Y. Yin, S. X. Wu, H. Li, F. Boey, W. Huang, P. Chen, H. Zhang, ACS Nano, 2010, 4, 3201-3208. (b) Z. J. Wang, X. Z. Zhou, J. Zhang, F. Y. C. Boey, H. Zhang, J. Phys. Chem. C, 2009, 113, 14071–14075.[4] (a) Z. Y. Yin, S. Sun, T. Salim, S. X. Wu, X. Huang, Q. Y. He, Y. M. Lam, H. Zhang, ACS Nano, 2010, 4, 5263–5268. (b) Z. Y. Yin, S. X. Wu, X. Z. Zhou, X. Huang, Q. C. Zhang, F. Boey, H. Zhang, Small, 2010, 6, 307-312.[5] B. Li, X. H. Cao, H. G. Ong, J. W. Cheah, X. Z. Zhou, Z. Y. Yin, H. Li, J. L. Wang, F. Boey, W. Huang, H. Zhang, Adv. Mater., 2010, 22, 3058–3061.[6] (a) J. Q. Liu, Z. Y. Yin, X. H. Cao; F. Zhao; A. Ling; L. H. Xie, Q. L. Fan; F. Boey, H. Zhang, W. Huang, ACS Nano, 2010, 4, 3987–3992. (b) J. Q. Liu, Z. Lin, T. Liu, Z. Y. Yin, X. Z. Zhou, S. Chen, L. H. Xie, F. Boey, H. Zhang, W. Huang, Small, 2010, 6, 1536–1542.[7] S. X. Wu, Z. Y. Yin, Q. Y. He, X. Huang, X. Z. Zhou, H. Zhang, J. Phys. Chem. C, 2010, 114, 11816–11821.[8] S. Agarwal, X. Zhou, F. Ye, Q. He, G. C. K. Chen, J. Soo, F. Boey, H. Zhang, P. Chen, Langmuir, 2010, 26, 2244-2247.[9] X. Z. Zhou, Y. Y. Wei, Q. Y. He, F. Boey, Q. C. Zhang, H. Zhang, Chem. Commun., 2010, 46, 6974–6976.
3:30 PM - Y2.3
Synthesis of High Surface Area Graphene Macroassemblies.
Marcus Worsley 1 , Tammy Olson 1 , Jonathan Lee 1 , Carlos Valdez 1 , Brian Mayer 1 , James Lewicki 1 , Peter Pauzauskie 2 , Juergen Biener 1 , Joe Satcher 1 , Theodore Baumann 1
1 Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Department of Materials Science and Engineering, Unversity of Washington, Seattle, Washington, United States
Show AbstractWe report a simple method for the synthesis of three-dimensional macroassemblies of graphene sheets that exhibit high conductivity, large surface area, and mesopore volume. The macroassemblies are formed using sol-gel chemistry to cross-link suspensions of single layer graphene oxide (GO). GO gels are formed under both acidic and basic conditions with or without organic precursors (e.g. resorcinol, formaldehyde). The cross-linked GO gels are then supercritically dried and thermally reduced to produce the graphene aerogels. These graphene macroassemblies possess electrical conductivities (~1 x 102 S/m) orders of magnitude higher than those formed using physical cross-linking. The surface areas of these aerogels (>1000 m2/g) approach the theoretical values expected for a single graphene sheet. In addition, pore size is tunable and mesopore volumes in excess of 7 cm3/g have been achieved. These extraordinary properties make these aerogels desirable for various catalytic, sensing, and energy storage applications. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the DOE Office of Energy Efficiency and Renewable Energy.
4:00 PM - **Y2.4
Two-dimensional Layered Chalcogenide Nanoribbons: Energy and Topological Insulators.
Yi Cui 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractIII-VI (III= In, Ga, VI= S, Se, Te) and V-VI (V= Sb, Bi) chalcogenides possess highly anisotropic chemical bonding and show two-dimensional layers in their crystal structure, similar as graphene in graphite. There are very rich chemical and physical properties in this family of materials. In this talk I will present our studies in the past five years on synthesis, chemical transformation, electrical transport property of nanostructures of these 2D chalcogenides. I will also present our exciting results on developing these materials towards topological insulators and energy conversion.
4:30 PM - **Y2.5
Carbon Materials Nanofabrication via Graphene Self-assembly.
Sang Ouk Kim 1
1 , KAIST, Daejeon Korea (the Republic of)
Show AbstractThe organization of carbon materials, especially planar and mechanically flexible graphene, into complex three-dimensional geometries is a major challenge for their ultimate utilization in various applications. In this presentation, our recent research achievements of graphene assembly into three-dimensional functional architectures will be introduced [1]. In the first approach, reduced graphene films with nanoscale thickness assembled from graphene oxide aqueous solution, has been utilized for the substrate material for vertical carbon nanotubes growth [2-4]. The resultant mechanically flexible and electro-conductive carbon nanotubes-graphene hybrid architecture is potentially useful for electrodes of flexible display or energy storage. In the second approach, Polymer-grafted graphene oxide was assembled into macroporous films by self-organized aqueous droplets [5]. Subsequent pyrolysis yielded mechanically flexible carbon films that exhibited highly ordered morphologies. Incorporation of a nitrogen-doping into the aforementioned protocols enhanced the electrical properties and supercapacitor performances of the carbon-based assemblies, and provided chemical functionality for further chemical derivatization.------------------------------1. S. H. Lee, D. H. Lee, W. J. Lee, S. O. Kim ‘Tailored Assembly of Carbon Nanotubes and Graphene’ Adv. Funct. Mater. (invited feature article).2. D. H. Lee, J. E. Kim, T. H. Han, J. W. Hwang, S. W. Jeon, S.-Y. Choi, S. H. Hong, W. J. Lee, R. S. Ruoff, S. O. Kim ‘Versatile Carbon Hybrid Films Composed of Vertical Carbon Nanotubes Grown on Mechanically Compliant Graphene Films’ Adv. Mater. 22, 1247 (2010).3. B. H. Kim, J. Y. Kim, S. -J. Jeong, J. O. Hwang, D. H. Lee, D. O. Shin, S. Y. Choi, S. O. Kim ‘Surface Energy Modification by Spin Cast, Large Area Graphene Film for Block Copolymer Lithography’ ACS Nano 4, 5464 (2010).4. D. H. Lee, J. A. Lee, W. J. Lee, S. O. Kim ‘Flexible Field Emission of Nitrogen-Doped Carbon Nanotubes/Reduced Graphene Hybrid Films’ Small inpress.5. S. H. Lee, H. W. Kim, J. O. Hwang, W. J. Lee, J. Kwon, C. W. Bielawski, R. S. Ruoff, S. O. Kim ‘Three-Dimensional Self-Assembly of Graphene Oxide Platelets into Mechanically Flexible Macroporous Carbon Films’ Angew. Chem. Int. Ed. inpress.
5:00 PM - Y2.6
Self-aligned Graphene Sheets-polyurethane Nanocomposites.
Mohsen Moazzami Gudarzi 1 , Seyed Hamed Aboutalebi 1 , Qing Bin Zheng 1 , Jang-Kyo Kim 1
1 Mechanical Engineering, Hong Kong University of Science & Technology, Clear Water Bay, Kowloon Hong Kong
Show AbstractGraphene reinforced polyurethane composites are produced through an environmentally benign process. The process involves the chemical reduction of aqueous dispersion of graphene oxide in water-borne polyurethane latex, resulting in fine dispersion and high degree of orientation of graphene sheets. Adsorption of polyurethane particles on the surface of graphene is the mechanism behind the high stability of the resulting hybrid dispersion. Self-alignment of graphene sheets occurs during the film formation and the degree of alignment rapidly increases as the graphene content increases, reaching almost full alignment at 2 wt% of graphene content. The alignment is confirmed by the examination of cross-sectional morphology as well as Raman spectroscopy. The steric hindrance due to the overlapping of graphene sheets is mainly responsible for the self-organization, and the excluded volume model explains the behavior. The resulting composites show excellent electrical conductivity with an exceptionally low percolation threshold of 0.076 vol%, which is one of the lowest values reported in the literature. The mechanical properties are greatly enhanced: a remarkable 21-fold increase in the Young’s modulus is achieved due to 3wt% of graphene while the indentation hardness is improved by 300% with 5wt% of graphene. The consistency of the experimental results with the theoretical prediction for the mechanical properties proves that the graphene sheets are indeed dispersed in the polymer matrix at the molecular level in almost perfect 2D alignment. The composite also shows much improved moisture barrier resistance. The implications and the potential applications of the remarkable properties are discussed.
5:15 PM - Y2.7
Solution-processed Graphene/MnO2 Composite Nanostructures for Electrochemical Capacitors.
Guihua Yu 1 , Liangbing Hu 2 , Michael Vosgueritchian 1 , Yi Cui 2 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractCarbon based materials have been the subject of extensive research for use in energy storage devices such as supercapacitors and Li-ion batteries because of their excellent electrical conductivity, mechanical stability, chemical resistance in aqueous electrolytes and long cycle life. To realize practical applications of these energy storage devices, key issues remain to be developing low-cost, lightweight and high-performance materials which are compatible with low-temperature and large-scale processing. In this report, we demonstrated that solution-exfoliated graphene materials can be conformally coated on 3D porous textiles which allow high loading of active electrode materials and facilitate the easy access of electrolyte ions to those materials, through facile solution process to form conductive energy textiles. With further controlled loading of pseudocapacitive MnO2 nanomaterials, these energy textiles yield much improved supercapacitor performance with over 6 times increase in specific capacitance compared with that using graphene-only materials. Specific capacitance of ~ 400 F/g and areal capacitance ~ 0.45F/cm2 have been achieved in our studies. The low-cost, lightweight conductive energy textiles based on solution-processed graphene/MnO2 composite films offer great promise in grid-scale energy storage device applications.
5:30 PM - Y2.8
Tailoring the Atomic and Electronic Structure of Two-dimensional Carbon and Boron-nitride Systems with Electron and Ion Beams.
Arkady Krasheninnikov 1 2
1 Department of Physics, University of Helsinki, Helsinki Finland, 2 Department of Applied Physics, Aalto University, Espoo Finland
Show AbstractRecent experiments (see Refs. [1,2] for an overview) on ion and electron bombardment of nanostructures demonstrate that irradiation can have beneficial effects on such targets and that electron or ion beams can serve as tools to change the morphology and tailor mechanical, electronic and even magnetic properties of various nanostructured materials. We systematically study irradiation effects in nanomaterilas, including two-dimensional (2D) systems like graphene and hexagonal boron-nitride (h-BN) sheets. By employing various atomistic models ranging from empirical potentials to time-dependent density functional theory we simulate collisions of energetic particles with 2D nanostructures and calculate the properties of the irradiated systems. In this talk, our latest theoretical results on the response of graphene and h-BN to irradiation will be presented, combined with the experimental results obtained in collaboration with several groups [3]. The electronic structure of defected graphene sheets with adsorbed transition metal atoms will be discussed, and possible avenues for tailoring the electronic and magnetic structure of graphene by irradiation-induced defects and impurities will be introduced [4]. The effects of ion and electron irradiation on boron-nitride sheets and nanotubes will also be touched upon. Finally, we will discuss how electron irradiation and electron beam-assisted deposition can be used for engineering hybrid BN-C nanosystems by substituting B and N atoms with carbon with high spatial resolution.[1]Krasheninnikov A. V. and Banhart F., Nature Materials, 6, 723 (2007).[2]Krasheninnikov A. V. and Nordlund K., J. Appl. Phys. (Appl. Phys. Reviews), 107, 071301 (2010).[3] J. Kotakoski, C. H. Jin, O. Lehtinen, K. Suenaga, and A. V. Krasheninnikov, Phys. Rev. B 82 (2010) 113404. [4] O. Cretu, A.V. Krasheninnikov, J. A. Rodriguez-Manzo, L.Sun, R.M. Nieminen, and F.Banhart. Phys. Rev. Lett. 105 (2010) in press.
Symposium Organizers
AlexanderA. Balandin University of California-Riverside
Andre Geim University of Manchester
Jiaxing Huang Northwestern University
Dan Li Monash University
Symposium Support
Cambridge NanoTech Inc
Elsevier Ltd.
Y5: Characterization and Properties of Graphene I
Session Chairs
Alexander Balandin
Vincent Tung
Wednesday AM, April 27, 2011
Room 3009 (Moscone West)
11:30 AM - **Y5.1
Atomically Controlled Graphene and Hexa Boron Nitride Layer Sstack for Advanced Electronics.
Philip Kim 1
1 Physics, Columbia University, New York, New York, United States
Show AbstractGraphene devices on a typical silicon oxide substrates are highly disordered, exhibiting characteristics that are far inferior to the expected intrinsic properties of graphene. Although suspending the graphene above the substrate leads to a substantial improvement in device quality, this geometry imposes severe limitations on device architecture and functionality. There is a growing need, therefore, to identify dielectrics that allow a substrate-supported geometry while retaining the quality achieved with a suspended sample. Hexagonal boron nitride (h-BN) is an appealing substrate, because it has an atomically smooth surface that is relatively free of dangling bonds and charge traps. It also has a lattice constant similar to that of graphite, and has large optical phonon modes and a large electrical bandgap. Here we report the fabrication and characterization of high-quality exfoliated mono- and bilayer graphene devices on single-crystal h-BN substrates, by using a mechanical transfer process. Graphene devices on h-BN substrates have mobilitiesand carrier inhomogeneities that are almost an order of magnitude better than devices on SiO2. These devices also show reduced roughness, intrinsic doping and chemical reactivity. The ability to assemble crystalline layered materials in a controlled way permits the fabrication of graphene devices on other promising dielectrics and allows for the realization of more complex graphene heterostructures.
12:00 PM - **Y5.2
Making Nanographene.
Kian Loh 1 , Jiong Lu 1
1 Department of Chemistry, National University of Singapore, Singapore Singapore
Show AbstractConfining the size and geometry of graphene is one way of engineering its band gap. The bottom up synthesis of nanographene from chemical precursors is an attractive option. The fragmentation of fullerenes using ions, surface collisions or thermal effects is a complex process that typically leads to the formation of small carbon clusters of variable size. Here, we show that single crystalline graphene as well as geometrically well-defined graphene quantum dots can be synthesized on a ruthenium surface using C60 molecules as a precursor. Scanning tunnelling microscopy imaging, supported by density functional theory calculations, suggests that the structures are formed through the ruthenium-catalysed cage-opening of C60. In this process, the strong C60–Ru interaction induces the formation of surface vacancies in the Ru single crystal and a subsequent embedding of C60 molecules in the surface. The equilibrium shape of the graphene can be tailored by optimizing the annealing temperature and the density of the carbon clusters. The fragmentation of the embedded molecules at elevated temperatures then produces carbon clusters that undergo diffusion and aggregation to form graphene quantum dots. Coronene clusters are observed to be the central building block in the assembly process to form graphene nanoislands, as well as the residual clusters remaining behind after the fragmentation of graphene nanoislands. Insights into how graphene nanoislands merge to form graphene sheets and how defects develop can be obtained by studying the dynamics of the aggregation processes.ReferenceTransforming C60 molecules into graphene quantum dots, Jiong Lu, Pei Shan Emmeline Yeo, Chee Kwan Gan, Ping Wu and Kian Ping Loh*, Nature Nanotechnology, 6, 247–252, (2011) doi:10.1038/nnano.2011.30
12:30 PM - Y5.3
Transport Properties of Graphene on SiO2 with Gpecific Surface Structures.
Kosuke Nagashio 1 , Takaaki Yamashita 1 , Tomonori Nishimura 1 , Koji Kita 1 , Akira Toriumi 1
1 Materials Engineering, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
Show Abstract Mobility of graphene transferred on the SiO2/Si substrate is limited to ~10,000 cm2/Vs. Without understanding the interaction between graphene and SiO2, it is difficult to improve transport properties. Although several surface structures for SiO2 such as OH-termination and O-termination are recognized, the relation between the surface treatment of SiO2 and graphene characteristics has not been elucidated yet in spite of its importance. This paper discusses the electrical transport properties of graphene on specific surface structures of SiO2 prepared by plasma treatments and reoxidization. OH-terminated and O-terminated SiO2 surfaces were prepared by O2-plasma treatment and reoxidization at 1000 °C for 5 min. in 100%-oxygen gas flow, respectively. The hydrophilic properties of these SiO2 surfaces were studied by the contact angle measurement. The contact angles of droplets on plasma-treated SiO2 decreases from ~6° for untreated SiO2 (HF-last) to nearly zero, indicating that the hydrophilic nature is enhanced due to the increase in OH groups with the strong polarization by removing hydrocarbon contaminants on untreated SiO2. On the other hand, the reoxidized SiO2 was hydrophobic (42.6°) because of O-termination with the weak polarization. Graphene was transferred on surface-treated SiO2 by the mechanical exfoliation of Kish graphite and, then, typical 4-probe FET devices were fabricated by the conventional EB lithographic technique. The mobility of graphene on OH-terminated SiO2 was much lower than those on untreated SiO2 and Dirac point considerably deviated positively from VG=0. The polarized OH group of 4~5×1014 cm-2 on the SiO2 surface might interact strongly with graphene and work as scattering centers. Therefore, it is reasonable that the Coulomb interaction results in the considerable mobility degradation and large Dirac point shift. For untreated SiO2, on the other hand, the hydrocarbon does exist, which separates graphene from OH groups, that is, the weak interaction. Therefore, Dirac point stayed at VG=~0. Moreover, the mobility and Dirac point shift of graphene on O-terminated SiO2 were very similar to untreated SiO2, while the hysteresis was considerably reduced because of hydrophobic nature. Finally, it should be pointed out that “ideal” SiO2 surface structure is defined as O-termination only at high temperature since the surface is constructed only by constituent atoms of Si and O. The surface structure of untreated SiO2 (HF-last) is not intrinsic due to the existence of hydrocarbons. Although full OH-termination by O2-plasma treatment seems to be intrinsic in terms of uniformity, it is very active to the environment and attracts water, hydrocarbons and so on. In terms of the stability to the environment, O-terminated SiO2 seems to be best due to hydrophobic nature.
12:45 PM - Y5.4
Influence of Chemical Functionalization on the Electron Transport in Graphene.
Fabian Koehler 1 , Arnhild Jacobsen 2 , Klaus Ensslin 2 , Wendelin Stark 1
1 Institute for Chemical and Bioengeneering, ETH Zurich, Zurich Switzerland, 2 Solid State Physics Laboratory, ETH Zurich, Zurich Switzerland
Show AbstractChemical functionalization of graphene with organic molecules extends the available derivatization methods, namely oxidation of graphene to graphite oxide and hydrogenation of graphene to graphane. Instead of oxygen or hydrogen a carbon atom is attached to the graphene lattice. Previous studies(1,2) showed the potential for the modification of single and bilayer graphene by reaction with diazonium reagents. A combination of Atomic force microscopy and confocal Raman spectroscopy are used to characterize the chemically introduced changes (sp2 to sp3) of the graphene carbon atoms. A clear difference is seen in the reactivities on single and double layer graphene. Surprisingly, the reaction rate is enhanced at the graphene edge regions due to a lower steric hindrance and activation energy. These edge regions grow into the bulk graphene areas, like a domino effect. In a second aspect(3) the influence of water and solvents, used in the reaction step, are investigated. These show a dramatic effect on the Dirac point and mobility of graphene, which is probably due to the removal of residues or dopants. Furthermore, we have performed a transport study of chemically modified graphene and found that the influence of isopropanol treatment is comparable to the influence of functionalization itself. It is shown that isopropanol leads to p-doping similar to that observed after functionalization. In addition, it is observed that isopropanol treatment followed by heating significantly improves the electronic quality of graphene beyond the improvement due to heating alone. In conclusion, this may lead to a better understanding of how organic molecules interact with graphene and influence its electron transport. [1] F.M. Koehler, N.A. Luechinger, D. Ziegler, E.K. Athanassiou, R.N. Grass, A. Rossi, C. Hierold, A. Stemmer, W.J. Stark, Angew. Chem. Int. Ed., 2009, 48, 224[2] F.M.Koehler, A. Jacobsen, K. Ensslin, C. Stampfer, W.J. Stark, Small, 2010, 6(10), 1125[3] A. Jacobsen, F.M. Koehler, W.J. Stark, K. Ensslin, NJP, 2010, accepted
Y6: Characterization and Properties of Graphene II
Session Chairs
Andrea Ferrari
Lain-Jong (Lance) Li
Wednesday PM, April 27, 2011
Room 3009 (Moscone West)
2:30 PM - **Y6.1
Exploiting Graphene Optoelectrionic Properties in Photonic Devices and Novel Characterisation Tools.
Andrea Ferrari 1
1 , University of Cambridge, Cambridge United Kingdom
Show AbstractThe richness of optical and electronic properties of graphene attracts enormous interest. So far, the main focus has been on fundamental physics and electronic devices. However, we believe its true potential to be in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited, even in the absence of a bandgap, and the linear dispersion of the Dirac electrons enables ultra-wide-band tunability[1]. The rise of graphene in photonics and optoelectronics is shown by several recent results, ranging from solar cells and light emitting devices, to touch screens, photodetectors and ultrafast lasers. Despite being a single atom thick, graphene can be optically visualized [2]. Its transmittance can be expressed in terms of the fine structure constant [3]. The linear dispersion of the Dirac electrons enables broadband applications[1]. Saturable absorption is observed as a consequence of Pauli blocking [4,5]. Chemical and physical treatments enable luminescence [6]. Graphene-polymer composites prepared using wet chemistry [4-6] can be integrated in a fiber laser cavity, to generate ultrafast pulses, down to 200fs, and enable broadband tunability [4,5]. Plasmonic interaction with metal nanoparticles enhance light absorption, and allow a significant enhancement of the Raman signal [7]. Manipulation and characterisation of individual flakes in solution is possible using an optical Raman tweezers [8]1. F. Bonaccorso et al. Nature Photonics 4, 611 (2010)2. C. Casiraghi et al. Nano Lett. 7, 2711 (2007).3. R. R. Nair et al. Science 320, 1308 (2008).4. T. Hasan, et al. Adv. Mat. 21,3874 (2009)5. Z. Sun et al. ACS Nano 4, 803 (2010); Nano research 3, 404 (2010)6. T. Gokus et al. ACS Nano 3, 3963 (2009)7. F. Schedin et al. ACS Nano 4, 5617 (2010)8. O. M. Marago et al. ACS Nano in press (2010)
3:00 PM - Y6.2
Rapid Large-Scale Characterization of CVD Graphene Layers on Glass Using Fluorescence Quenching Microscopy.
Jennifer Reiber Kyle 1 , Ali Guvenc 1 , Maziar Ghazinejad 2 , Jian Lin 2 , Cengiz Ozkan 2 , Mihrimah Ozkan 1
1 Electrical Engineering, University of California Riverside, Riverside, California, United States, 2 Mechanical Engineering, University of California Riverside, Riverside, California, United States
Show AbstractGraphene is a two-dimensional sheet of carbon atoms arranged in hexagonal lattices. Graphene exhibits exceptional electrical, optical, and mechanical properties which has generated a great interest in the material. At first, graphene was fabricated by mechanical exfoliation of highly ordered graphite. However, due to the small size limitation of exfoliated graphene, a new method for fabricating graphene, known as chemical vapor deposition (CVD), was developed. CVD-grown graphene is not limited in size but is subject to quality concerns due to growing conditions that have yet to be optimized. Two important parameters in the performance and properties of graphene are the number of layers and uniformity throughout the sample. In this research project we measure the thickness and uniformity of large CVD-grown graphene samples on microscope glass slides using fluorescence quenching microscopy (FQM). FQM is a novel technique for visualizing graphene that is based on the discovery that graphene quenches fluorescence via resonant energy transfer. FQM offers improvements over alternative graphene imaging techniques such as atomic force microscopy, Raman spectroscopy, transmission electron microscopy, and optical reflection and transmission techniques because it can be performed on arbitrary substrates, imaging time is short, large areas can be measured, and the imaging equipment (a fluorescent microscope) is widely available. Currently, FQM has only been used to visualize graphene-oxide and exfoliated graphene samples and has been unable to achieve quantitative characterization of the graphene samples, specifically, counting graphene layers. FQM is achieved by spin-coating a solution of polymer mixed with a fluorescent dye onto the graphene layer. In this work, we calibrate the fluorescent quenching by the graphene layers, measuring the contrast between the graphene and background for dye layers of different thickness. As the dye layer thickness decreases, the contrast between graphene and the substrate increases, but the contrast between graphene layers decreases. Using the results from our fluorescence quenching calibration, we quantify the thickness and uniformity of an entire CVD-grown sample. This is achieved by creating a large-scale, high-resolution fluorescence montage image of the entire graphene sample using a microscope with a motorized stage. We segment the image based on graphene layer thickness using histogram-based segmentation and calculate the mean thickness and RMS roughness of the graphene sample. This work introduces a new method for graphene quantification that can quickly and easily identify graphene layers in a large area on arbitrary substrates.
3:15 PM - Y6.3
Nanoscale Mapping of Bulk and Interface Elastic and Related Physical Properties of Layered Materials Using Scanning Force Microscopy at Ultrasonic Frequencies.
Oleg Kolosov 1 , Manuel Pumarol 1 , Peter Tovee 1 , Vladimir Falko 1 , Franco Dinelli 2
1 Physics, Lancaster University, Lancaster United Kingdom, 2 , CNR-INO, Pisa Italy
Show AbstractWe report new scanning probe microscopy approach for the investigation of nanoscale physical properties of two-dimensional materials. It is hard to overestimate the importance of such properties as local elastic moduli, interface adhesion, thermal expansion coefficient, and in-plane, out-of-plane and layer-to-substrate thermal conductivity for the exploration of physical nature of 2D materials as well influence of these properties on the performance of related devices.In order to realise such measurements, we combined atomic force microscope (AFM) that is known to have required nanometre scale resolution, with the ultrasonic excitation of the sample or force sensitive cantilever at high frequencies (HF) ranging from few MHz to hundreds MHz. A first combination, known as Ultrasonic Force Microscope (UFM), uses an excitation of only the sample or the cantilever and was shown to be directly sensing nanoscale mechanical properties of materials including ones of stiff ceramics and ceramic based composites. The Heterodyne Force Microscopy (HFM), where two HF vibrations at adjacent frequencies are detected by the nonlinearity of tip-surface contact, is shown in addition to be sensitive to the time dynamics of these interactions. In addition, both UFM and HFM were shown to reveal the mechanical properties of the interfaces and subsurface delaminations.In this paper, we report novel experimental results of imaging of thin graphene layers ranging from a single graphene sheet to few tens of graphene layers. UFM revealed variability of adhesion of graphene layers to the substrate on the lateral scale of few tens of nanometres (in the flat sheet), and few nm (near the edge of the sheet). The contact elasticity of layer-on-substrate was shown to consistently decrease with the increase of layer thickness between one to four graphene layers, as well as to change a character of delaminations between layer and substrate. In addition, UFM and HFM studies of folded layers showed variability of the intimate elastic contact between layers revealing the nanomechanics of such folding. We also observed a correlation between mechanical and thermal transport properties in two-dimensional structures by using a scanning thermal microscopy of such layered materials as graphene and mica with the thermal resolution on the scale of few tens of nm. Finally, we compare these data with the finite elements simulation of heat conductance of two dimensional materials on the substrate.A. Briggs and O. Kolosov, Acoustic Microscopy, ch. 13, 2nd edition, Oxford University Press, 2010.
3:30 PM - Y6.4
Sub-100 nm Spatial Resolution Imaging of Conductance Inhomogeneities in CVD Graphene.
Alexander Tselev 1 , Nikolay Lavrik 1 , Ivan Vlassiouk 1 , Sergei Kalinin 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractContinued interest in graphene is due to its unique atomic structure as well as remarkable mechanical, optical, thermal, and electronic properties. In particular, graphene has attracted substantial attention due to its potential applications in photovoltaics and in energy storage systems. Among many properties of graphene, high electrical conductivity is of primary importance for these applications. From this standpoint, there is a trade-off between more challenging technological approaches that yield in a nearly perfect graphene and those that are more suitable for large-scale fabrication. Growth of large-area graphene on polycrystalline catalytic surfaces using chemical vapor deposition (CVD) is compatible with wafer level fabrication and can readily be scaled up. However, CVD-grown graphene is not always characterized by the high degree of structural perfection and tends to exhibit lower electron mobility and electrical conductivity. This points to an ultimate importance of characterization and mapping of local conductivity of various graphene samples with nanoscale lateral resolution. In this work, we demonstrate that local conductivity in continuous large-area graphene layers can be imaged with a spatial resolution of better than 100 nm using near-field scanning microwave microscopy (SMM). The important feature of the SMM technique is that it does not require deposition of metal contacts to access the local conductivity in contrast to conducting AFM. Due to a relatively high frequency used—about 2 GHz—the electric current path is complete by displacement currents due to capacitive coupling between the sample, probe tip, and the probe shield electrode. To make the system sensitive to local properties of the graphene film, rather than to its overall capacitance in respect to the conducting substrate and the microwave circuit ground, we cover the whole sample with a layer of alumina of about 4 nm thickness using Atomic Layer Deposition. These thickness provides a pinhole-free film insuring a strong enough capacitive coupling between the probe tip and the graphene film. Alumina can be readily removed by a mild chemical etching using a standard recipe. Research at ORNL's CNMS was sponsored by the Scientific User Facilities Division, BES, U.S. DOE. I.V. acknowledges a Eugene P. Wigner fellowship from the ORNL.
3:45 PM - Y6.5
Direct Atomic-Scale Structural Characterization of Epitaxial Graphene on 6H-SiC(0001) by Cross-sectional Scanning Transmission Electron Microscopy.
Xiaojun Weng 1 , Joshua Robinson 2 3 , Kathleen Trumbull 2 , Randall Cavalero 2 , Mark Fanton 2 , David Snyder 2 4
1 Materials Research Institute, Penn State University, University Park, Pennsylvania, United States, 2 Electro-Optics Center, Penn State University, University Park, Pennsylvania, United States, 3 Materials Science and Engineering, Penn State University, University Park, Pennsylvania, United States, 4 Chemical Engineering, Penn State University, University Park, Pennsylvania, United States
Show AbstractThe interface layer between the epitaxial graphene (EG) and the SiC substrate significantly affects the epitaxial growth and the electronic properties of the EG [1]. It is thus critical to obtain an explicit understanding of the structure and chemistry of the interface layer in order to understand the EG growth mechanism and eventually produce EG layers with desired thickness uniformity and electronic properties. However, the nature of the interface layer is still elusive to date. Other structural properties of EG, e.g. layer spacings and the atomic structure of surface steps, also remain to be ambiguous.Most of the current knowledge of the structure of the interface layer, interlayer spacings, and the thickness and the surface steps of graphene layers in EG/SiC(0001) was either from theoretical studies, or derived from experimental measurements such as plan-view scanning tunneling microscopy, low-energy electron diffraction/microscopy, angle-resolved photoelectron spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy (TEM). These experimental methods require complicated data analysis or image simulation in order to obtain accurate structural information of EG/SiC. Here, we report the atomic-scale structural properties of EG with 1 to 4 layers on SiC(0001) obtained from directly interpretable cross-sectional high-angle annular-dark-field (HAADF) scanning TEM (STEM).We find that the interface layer between the EG and the SiC substrate possesses a relatively weaker contrast than the other EG layers in STEM images, indicating that it possesses a lower areal density of C atoms than a graphene monolayer. This is in contradiction with the assertion from several recent reports that the interface layer was a graphene-like sheet with the 6√3×6√3R30° structure. Direct measurements of the layer spacings revealed that the EG interlayer spacing was considerably larger than that of bulk graphite. Interestingly, the spacing between the interface layer and the top bilayer of the SiC substrate apparently increased with the EG layer thickness. The surface of the SiC(0001) substrate, often treated as relaxed, was found to be strained. The strain may be due to the point defects induced by the partial decomposition of the surface layers. We find that the top two layers of a 4-layer EG terminated at the step instead of growing continuously. This observation contradicts the commonly believed carpet-like growth mode for the EG layers as determined by other experimental techniques, in which the top EG layers grow continuously over the surface steps of the SiC substrates. We believe that these results provide fundamental structural information for the better understanding of the relationship between the structure and electronic properties, as well as for the theoretical predictions of the electronic properties of EG layers on SiC(0001). [1] J. Hass, W.A. de Heer, and E.H. Conrad, J. Phys.: Condens. Matter 20 (2008) 323202.
4:30 PM - **Y6.6
Nearly Free Electron States in Graphene Nanoribbon Superlattices.
Jinlong Yang 1
1 Dept. of Chem. Phys., Univ. of Sci. & Tech. of China, Hefei, Anhui, China
Show AbstractNearly free electron (NFE) state is an important kind of unoccupied state in low dimensional systems. Although it is intensively studied, a clear picture on its physical origin and its response behavior to external perturbations is still not available. Our systematic first-principles study based on graphene nanoribbon superlattices suggests that there are actually two kinds of NFE states. It is understood by a simple Kronig-Penney potential model. An atom-scattering-free NFE transport channel can be obtained via electron doping, which may be used as a conceptually new field effect transistor.
5:00 PM - Y6.7
Low-frequency Noise of Graphene Nanostructures for Device and Material Characterizations.
Guangyu Xu 1 , Carlos Torres Jr. 1 , Jingwei Bai 2 , Emil Song 1 , Xiangfeng Duan 3 , Yuegang Zhang 4 , Kang Wang 1
1 Electrical Engineering, University of California, Los Angeles, Los Angeles, California, United States, 2 Material Science and Engineering, University of California, Los Angeles, Los Angeles, California, United States, 3 Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California, United States, 4 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractGraphene is a two-dimensional atomically-thin film with great potential in diverse applications. However, most non-suspended graphene sheets can be degraded by external perturbations from the environment. For example, the charged impurity lowers the carrier mobility of graphene devices and creates an inhomogeneous charge distribution along the graphene sheet; the trap-induced carrier switching process near the graphene-substrate interface leads to device variability, which has been broadly characterized using low-frequency (1/f) noise. Study on the 1/f noise behavior of substrated graphene would help to understand and realize high-speed graphene electronics with high signal-to-noise-ratios. It would be also of fundamental interest to investigate how the presence of spatial charge inhomogeneity influences the 1/f noise behavior in graphene. We conduct the low frequency noise measurement of SiO2-substrated single-layer and bi-layer graphene (SLG/BLG)1, whose gate dependence of graphene, M-shape for SLG and V-shape for BLG, exhibits strong correlation with the spatial charge inhomogeneity. A new noise model has been set for understanding these noise behaviors in graphene. Taking a step further, we also analyzed the noise behavior in nanowire-patterned graphene nanoribbons (GNRs)2, which is advantageous over the wide graphene sheets for switching on/off the devices in the presence of an energy gap. We observe a strong correlation between the enhanced conductance fluctuations (noise) of GNR and its quasi-one-dimensional electronic band structure at 77K. This correlation provides a robust mechanism to directly probe the band structure of GNRs, especially when the subband feature is smeared out in conductance measurement. Our result can further extend to a broad range of low-dimensional nano-materials and promote the noise-based metrology for the electronic band structure of quantum transport systems. The low-frequency noise thus proves its great potential in both the device and material characterization for graphene electronics. 1. G. Xu et. al. Nano Lett. 10, 3312-3317 (2010);2. G. Xu et. al. Nano Lett. 10.1021/nl1025979, ASAP (2010)
5:15 PM - Y6.8
Force Field Spectroscopy of the h-BN Nanomesh on Rh(111).
Thilo Glatzel 1 , Sascha Koch 1 , Markus Langer 1 , Shigeki Kawai 1 , Jorge Lobo-Checa 3 , Thomas Brugger 2 , Thomas Greber 2 , Ernst Meyer 1
1 Department of Physics, University of Basel, Basel Switzerland, 3 Centre d'Investigaciò en Nanociència i Nanotecnologia (CIN2), Campus Universitat Autònoma de Barcelona, Barcelona Spain, 2 Department of Physics, University of Zürich, Zürich Switzerland
Show AbstractBy high temperature exposure of Borazine [(HBNH)3] on Rh(111) at 520°C under UHV conditions a hexagonal graphene like monolayer structure is formed. Due to a lattice mismatch between the layer and the rhodium surface a superstructure with a periodicity of about 3.2nm and a hole size of 2nm is build, the so called h-BN nanomesh. High temperature stability of up to more than 900°C and its insulating character are making the “white graphene” suitable as a template for molecules.Former scanning tunnelling microscopy (STM) measurements showed various imaging contrasts arising from the complicated surface geometry and electronic properties. In our noncontact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM) experiments the complexity of the nanomesh is also frequently observed in the topography as well as in the local contact potential difference.Here, we thoroughgoing investigate the tip-sample interaction by 2D and 3D dynamic force spectroscopy at room temperature. The unique periodic surface of the superstructure causes a relatively large magnitude of long-range interaction. Therefore, the detection ratio of short- and long-range forces can be changed drastically by accidental tip changes. Such a feature disturbs measurements of the surface geometry by nc-AFM as well as the local contact potential difference by KPFM. With a bimodal dynamic force microscopy setup, using the first and second resonance frequency or the second and the torsion resonance mode, further investigations are persued. The use of this high-sensitive detection scheme directly allows to achieve insight information about the interplay of short- as well as long-range interaction between tip and sample.
5:30 PM - Y6.9
Imaging and Spectroscopy of Chemical and Structural Defects in Single-layer Materials.
Matthew Chisholm 1 , Veena Krishnan 2 , Gerd Duscher 2 1 , Wolfgang Windl 3
1 Materials Science and Technology, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials Science and Engineering Department, University of Tennessee, Knoxville, Tennessee, United States, 3 Materials Science and Engineering Department, The Ohio State University, Columbus, Ohio, United States
Show AbstractAberration correction has lead to remarkable improvements in scanning transmission electron microscopy. With a new fifth order corrector, probe sizes close to 0.1 nm at 60 keV are now possible enabling imaging of single-layer materials consisting of light atoms such as B, C, N and O without knock-on damage.1 We present annular dark-field images and electron energy-loss spectra from graphene and BN with and without structural and chemical defects. Atom-by-atom structural and chemical analysis of these two-dimensional materials reveals defects, which have not been predicted. First-principles calculations provide insight into the origins and impact of the defects on the electronic structure of the layers.This research was sponsored in part by the Materials Sciences and Engineering Division of the US Department of Energy, and by NSF Award number DMR-0925529 and the Center for Emergent Materials at The Ohio State University, an NSF MRSEC.1 O.L. Krivanek et al., Nature 464 571 (2010).
Symposium Organizers
AlexanderA. Balandin University of California-Riverside
Andre Geim University of Manchester
Jiaxing Huang Northwestern University
Dan Li Monash University
Symposium Support
Cambridge NanoTech Inc
Elsevier Ltd.
Y10: Poster Session II
Session Chairs
Alexander Balandin
Jiaxing Huang
Dan Li
Thursday PM, April 28, 2011
Salons 7-9 (Marriott)
Y7: Characterization and Properties of Graphene III
Session Chairs
Thursday PM, April 28, 2011
Room 3009 (Moscone West)
9:15 AM - **Y7.1
New Developments in Synthesis and Characterization of Graphene and Layered Boron Nitride.
Alex Zettl 1
1 , University of California at Berkeley, Berkeley, California, United States
Show AbstractBoth carbon and boron-nitride form planar sp2 bonds, allowing for sheet and tubular structures. I will discuss some of our explorations of low-dimensional BN-containing materials, including pure BN nanotubes, doped BN nanotubes, and thin few-layer sheets of hexagonal BN. Of interest is also the mating of BN and carbon structures, and novel geometrical configurations containing folds. The primary experimental tools are high resolution transmission electron microscopy, and related microscopies such as STM and AFM.
9:45 AM - Y7.2
Anomalous Strength Characteristics of Tilt Grain Boundaries in Graphene.
Vivek Shenoy 1
1 , Brown University, Providence, Rhode Island, United States
Show AbstractGraphene in its pristine form is one of the strongest materials tested, but defects influence its strength. Using atomistic calculations, we find that, counter to standard reasoning, graphene sheets with large-angle tilt boundaries that have a high density of defects are as strong as the pristine material and, surprisingly, are much stronger than those with low-angle boundaries having fewer defects. We show [1] that this trend is not explained by continuum fracture models, but can be understood by considering the critical bonds in the strained 7-member carbon rings that lead to failure; the large-angle boundaries are stronger as they are able to better accommodate these strained rings. Our results provide guidelines for designing growth methods to obtain sheets with strengths close to that of pristine graphene. [1] R. Grantab, V. B. Shenoy and R. S. Ruoff, Science (in press, 2010).
10:00 AM - Y7.3
In situ High-temperature Scanning Tunneling Microscopy Studies of Epitaxial Graphene Growth on SiC(0001).
Yuya Murata 1 , Vania Petrova 2 , Ivan Petrov 2 , Suneel Kodambaka 1
1 Materials Science and Engineering, University of California Los Angeles, Los Angeles, California, United States, 2 Frederick-Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois, United States
Show AbstractGraphene, a one-atom-thick sheet of sp2-bonded carbon atoms arranged in a honeycomb lattice, has attracted a lot of attention for transparent conductor and high-speed electronic applications owing to its ultra-thin geometry, transparency, high carrier mobility, and tunable band gap. Recent efforts focused on, and succeeded in, the fabrication of large-area graphene on SiC, an encouraging step toward realization of graphene electronics. Here, we focus on understanding the mechanisms of graphene growth on SiC(0001). Using in situ ultra-high vacuum, high-temperature (∼ 1400 K), scanning tunneling microscopy (UHV HT-STM), we investigated graphene formation on Si-rich SiC(0001). We observe the nucleation and growth of bilayer graphene during annealing in UHV. Time-lapsed STM images show that the second layer nucleates at the step edges of SiC terraces, and grows inward into the terrace, i.e. at the expense of SiC. In case of monolayer graphene, previous studies indicate that the growth occurred at the free step edges of SiC [1]. For the observed growth of bilayer graphene at the graphene-SiC interface, we suggest that the inward growth is energetically favorable compared to the growth at the outer edges. [1] T. Ohta, N. C. Bartelt, S. Nie, K. Thürmer, and G. L. Kellogg, Phys. Rev. B 81 (2010) 121411.
10:15 AM - Y7.4
In-situ Analysis of Graphene Growth Process on Magnetic Metal Thin Films.
Shiro Entani 1 , Yoshihiro Matsumoto 1 , Pavel Avramov 1 , Hiroshi Naramoto 1 , Seiji Sakai 1
1 , Japan Atomic Energy Agency, Tokai Japan
Show AbstractRecently, graphene has proved interesting for nanoelectronics and spintronics. There have been plenty of attempts to fabricate graphene devices. The most conventional method to fabricate graphene sheets is micromechanical cleavage of graphite. However, the graphene sheet obtained by this method is difficult to satisfy the following requests: to control the number of graphene layers, the size of the graphene sheets and the degree of crystallinity, and to reduce contamination and impurities, which are essential for device application. Ultra high vacuum chemical vapor deposition (UHV-CVD) is a promising method to solve these problems, since the homogeneous monolayer film of graphene is known to be formed on the catalytic metal surfaces. In UHV-CVD, it is considered that graphene grows due to the dissociation and polymerization of the precursor hydrocarbon molecules on the metal surfaces. This allows us to control the crystallinity depending on the growth condition and to keep samples free from contamination.In the present study, the growth process of graphene on Ni(111) films by UHV-CVD was investigated using in-situ reflection high energy electron diffraction (RHEED) and Auger electron spectroscopy (AES). It was observed significant changes in the RHEED patterns after the exposure to 100 L (1L = 10-6 torr sec) of benzene (precursor). Taking into account of the surface composition analyses by AES, it was elucidated that the Ni(111) surface is completely covered with single-layer graphene after 100 L exposure. It was also clarified that the negligible growth of the second graphene layer occurs during the growth of the first layer, and the exposure of more than several 1000 times is required for the formation of bi-layer graphene. The present results indicate the controlled growth of single- and bi-layer graphene by the dosage of precursors.
10:30 AM - Y7.5
Wrinkles and Overlaps: Structure-property Relationships of Graphene Oxide Monolayers.
Laura Cote 1 , Jaemyung Kim 1 , Zhen Zhang 2 , Cheng Sun 2 , Jiaxing Huang 1
1 Materials Science, Northwestern University, Evanston, Illinois, United States, 2 Mechanical Engineering , Northwestern University, Evanston, Illinois, United States
Show AbstractGraphene oxide sheets have recently gained immense interest as a building block for graphene based materials and devices. Rapid developments have been made in the chemistry and applications of GO. However, assembly, too, plays a critical role in the final properties of bulk graphene based materials as it determines the microstructures of the 2D sheets. There is thus a pressing need for controllable assembly strategies. Based on the recent identification of the pH dependent surfactant-like behavior of GO sheets, we are now able to control the tiling morphologies of such sheets to produce thin films with either wrinkled or overlapped types of microstructures. This allows for the deconvolution of the effects of these two basic morphological features in the electrical and optical properties of the resulting thin films, providing a well-defined example of the processing-microstructure-properties relationship for this unique soft material building block.
10:45 AM - Y7: Charact
BREAK
Y8: Applications of Graphene I
Session Chairs
Thursday PM, April 28, 2011
Room 3009 (Moscone West)
11:15 AM - **Y8.1
Large Scale Production of 2D Atomic Crystals by Liquid Phase Exfoliation of Layered Materials.
Jonathan Coleman 1 , Valeria Nicolosi 2 , Mustafa Lotya 1 , Arlene O'Neill 1 , Shane Bergin 1 , Paul King 1 , Umar Khan 1 , Karen Young 1 , Sukanta De 1 , Ronan Smith 1 , Gregory Moriarty 3 , Jaime Grunlan 3
1 , Trinity College Dublin, Dublin Ireland, 2 , University of Oxford, Oxford United Kingdom, 3 , Texas A&M University, College Station, Texas, United States
Show AbstractLayered materials represent a diverse and largely untapped source of 2-dimensional systems with exotic electronic properties and high specific surface areas that are crucially important for applications including sensing, catalysis and energy storage. While graphene is the most well-known layered material, transition metal dichalcogenides (TMDs), transition metal oxides (TMOs) and other 2-dimensional (2D) compounds such as BN, FeTe, Bi2Te3 and Bi2Se3 are also important. If they could be easily exfoliated in large quantities, such layered materials would become an important source of 2-dimensional crystals. Here we show that layered compounds such as MoS2, WS2, MoSe2, MoTe2, TaSe2, NbSe2, NiTe2, BN, MnO2 and Bi2Te3, can be efficiently dispersed and exfoliated in both in common solvents and in aqueous surfactant solutions. Electron microscopy shows these materials may be exfoliated down to individual layers. These dispersions can be deposited as individual flakes or formed into films. By blending with suspensions of other nano-materials or polymer solutions, we can prepare hybrid dispersions or composites which can be cast into films. Such materials demonstrate huge potential for a range of applications. For example, we show that WS2 and MoS2 effectively reinforce polymers, WS2/carbon nanotube hybrid films display promising thermoelectric properties while NbSe2 films are viable candidates for transparent conductor applications.
11:45 AM - Y8.2
Material Choices For Haptic Interfaces.
Paul Beecher 1 , Piers Andrew 1 , Zoran Radivojevic 1 , Chris Bower 1 , Samiul Haque 1 , Andrea Ferrari 2 , Tawfique Hasan 2 , Francesco Bonaccorso 2
1 , Nokia Research Center, Cambridge United Kingdom, 2 Engineering, University of Cambridge, Cambridge United Kingdom
Show AbstractWe present a robust, thin and optically transparent interface structure that can be overlaid unobtrusively on top of a display screen. This structure acts as an electrotactile system that directly delivers localized and visually correlated tactile information to the user’s skin, enabling graphic tactile feedback. The device structure operates at very low current level (< 10µA) and with potentials in the range of tens of volts, which is a significant improvement on current electrotactile paradigms. The proposed structure doubles as an input and output device in assisting the user interaction with a touch screen display.The technology is based on electrovibration, in which touch receptors in the skin can be deceived into perceiving texture when a fingertip is swiped across an insulating layer above a metal surface carrying an alternating potential. This effect is due to the varying electrostatic attraction between the conductor and the deeper, liquid-rich conducting layers of the skin – an effect which changes the perceived dynamic friction. Complex stimulation patterns, involving the mixing of multiple AC frequency components (10Hz – 500Hz) and the actuation of several electrodes simultaneously, may allow for the generation of an unprecedented range of “haptic illusions”. These may range from the emulation of real touch sensations, to completely new patterns of tactile feedback, and new ways of interacting with electronic devices. This solution also overcomes the need for the physical displacement of mechanical parts and is therefore several orders-of-magnitude more energetically efficient in providing real time feedback to the user.Our work tackles the expected evolution of mobile devices and displays towards flexible and compliant form factors. Our concept implementation is based on the use of novel nanomaterials and structures that are compatible with the requirements for these new technologies. Conductors that are simultaneously flexible, conductive and transparent have been investigated, ranging from wide-bandgap oxide materials to carbon nanostructures, e.g., carbon nanotube networks and graphene, and also include silver nanowire networks and thin metal grids. These conductors can all be deposited on flexible substrates, and uniformly coated with appropriate dielectric materials. Much focus has been on high-k amorphous oxide materials such as hafnia, but, barium titanate and parylene have also been used. The exploration of an extensive materials library necessitates use of a number different fabrication techniques including sputtering, vacuum deposition, and various solution methods and printing techniques. In addition, the inclusion of scratch resistant, hydrophobic and oleophobic materials on the top surface to combine electrical insulation, scratch resistance and stain/water/fingerprint repellence in a single finishing layer helps maintain and protect a pristine display surface.
12:00 PM - Y8.3
Graphene-based Platforms for Bioanalysis of Enzyme Activities.
Dal-Hee Min 1
1 , KAIST, Daejeon Korea (the Republic of)
Show AbstractVarious nanomaterials are being harnessed as important components of bioanalytical platforms such as gold nanoparticles for sensing DNA-related biochemical changes. To design “good” bioanalytical systems using new nanomaterials, one should be able to understand and fully utilize chemical/physical properties to measure changes in certain biochemical status in a biological system. Moreover, a new system should overcome limitations of conventional assay methods—detection limits, cost issues, labors, efficiencies, quantitativeness, reproducibility, etc. In this talk, I will introduce recent efforts to utilize “graphene oxide” for bioanalytical platforms, especially in enzyme activity assays. Graphene oxide is readily soluble in aqueous solvent, strongly binds to nucleobases of single stranded nucleic acids via pi-pi stacking and has a good fluorescence quenching capability. We collectively harnessed those properties of graphene oxide to develop a platform for an activity assay of helicase, an enzyme which unwinds double stranded nucleic acids into single stranded ones. We demonstrated that the present helicase activity assay platform allows quantitative, robust, real-time measurement and high-throughput assay for chemical screening with low cost.
12:15 PM - Y8.4
Nanoscale Friction and Adhesion Behavior of Atomically-thin Two-dimensional Materials.
Robert Carpick 1 , Xin-Zhou Liu 1 , Qunyang Li 1 , Baolei Zhang 1 , Zhengtang Luo 1 , Luke Somers 1 , Andrew Konicek 2 , Changgu Lee 3 , Ji Feng 1 , J. Li 1 , A. T. (Charlie) Johnson 1 , James Hone 4
1 Mechanical Engineering & Applied Mechanics Department, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 , Columbia University, New York, New York, United States, 3 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 4 , Sungkyunkwan University, Gyeonggi Korea (the Republic of)
Show AbstractThe remarkable characteristics of two-dimensional (2D) materials not only include physical, chemical, electronic, and optical properties but also extends to their mechanical and frictional (tribological) behavior. We have used friction force microcopy (FFM) to study atomic-scale friction between FFM tips and several 2D materials, down to the level of single atomic sheets1. For mechanically exfoliated samples of graphene, MoS2, NbSe2, and hexagonal BN weakly bound to supporting substrates, we observe atomic scale stick-slip friction that diverges from bulk behavior as the limit of single atomic sheets is approached. Specifically, while frictional energy dissipation is low compared to bare Si and many other common materials, friction increases substantially for fewer layers, with single layers exhibiting roughly 50% higher friction than their thick counterparts. Moreover, the friction force required to slip increases with sliding distance for the first few nanometers of scanning, but then saturates. This unusual layer-dependence of friction is suppressed by exfoliating on to highly adherent substrates. The details revealed by the atomic-scale friction measurements coupled with finite element modeling (FEM) and molecular dynamics simulations indicate that the trend arises from the thinner sheets’ increased susceptibility to out-of-plane elastic deformation. However, measurements of adhesion between nanoscale tips and few-layered graphene reveal that the adhesion does not change appreciably for different layer numbers, consistent with the weak dependence of adhesion on thickness predicted by the FEM simulations. We will discuss the mechanism accounting for this behavior, which, based on preliminary measurements, is rooted in the need to develop deformations of the sheets that is dependent on the scanning history. We have also investigated the mechanical and chemical properties of chemically exfoliated graphene oxide (GO). FFM was used to determine the friction between Si tips and GO samples. Unlike the other 2-D materials, no strong dependence of friction on thickness was observed. We will discuss the distinct behavior of GO with reference to the enhanced chemical interaction of GO with the silicon oxide substrate. An enhancement of friction and adhesion with respect to graphene is observed, suggesting that oxidation of graphene is an effective route for tailoring nanoscale friction and adhesion. The chemical properties of GO are further examined by near edge x-ray absorption fine structure spectroscopy experiments. 1. C. Lee, Q. Li, W. Kalb, X.-Z. Liu, H. Berger, R.W. Carpick & J. Hone, Frictional characteristics of atomically-thin sheets. Science 328, 76-80 (2010).
12:30 PM - Y8.5
Gas Phase Electronic Sensing Using DNA-coated Graphene Field Effect Transistors.
Ye Lu 1 , Brett Goldsmith 1 , Nicholas Kybert 1 , A.T.Charlie Johnson 1
1 Physics, University of Pennsylvania, Phl, Pennsylvania, United States
Show AbstractGraphene is a true two dimensional material with exceptional electronic properties and enormous potential for practical applications. Graphene’s promise as a chemical sensor material has been noted but there has been relatively little work on practical chemical sensing using graphene, and in particular how chemical functionalization may be used to sensitize graphene to chemical vapors. Here we show one route towards improving the ability of graphene to work as a chemical sensor by using single stranded DNA as a sensitizing agent. The resulting broad response devices show fast response times, complete and rapid recovery to baseline at room temperature, and discrimination between several similar vapor analytes.
12:45 PM - Y8.6
Study of Plasmon Excitation in Graphene.
Long Ju 1 , Baisong Geng 1 , Jason Horng 1 , Caglar Girit 1 , Micahel Martin 1 , Zhao Hao 2 3 , Hans Bechtel 2 , Xiaogan Liang 4 , Alex Zettl 1 5 , Y. Ron Shen 1 5 , Feng Wang 1 5
1 Department of Physics, University of California at Berkeley, Berkeley, California, United States, 2 Advanced Light Source Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 5 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractPlasmon is the basic form of collective excitation in graphene which plays an important role in the massless electron dynamics. It also forms the basis of graphene’s potential application as optical meta materials. In this talk I’ll show our recent study of plasmon excitation in engineered graphene structure. The exotic dispersion behavior of graphene plasmon will be discussed. Also, the strong and tunable plasmon excitation can enable graphene-based THz meta materials.
Y10: Poster Session II
Session Chairs
Alexander Balandin
Jiaxing Huang
Dan Li
Friday AM, April 29, 2011
Salons 7-9 (Marriott)
9:00 PM - Y10.1
Hydrothermally Grown ZnO Nanostructures on Few-layer-graphene Sheets.
Yong-Jin Kim 1 2 , Hadi Tukiman 3 , Aram Yoon 4 , Miyoung Kim 4 , Gyu-Chul Yi 1 5 , Chunli Liu 3
1 , Creative Research Initiative Center for Semiconductor Nanorods, Seoul Korea (the Republic of), 2 Department of Materials Science and Engineering, POSTECH, Pohang Korea (the Republic of), 3 Department of Physics, Hankuk University of Foreign Studies, YongIn Korea (the Republic of), 4 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 5 Department of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of)
Show AbstractThe growth of one-dimensional (1-D) semiconductor nanocrystals on graphene layers has attracted much attention because the hybrid nanostructures on graphene layer can be a candidate material system for integrated devices of solid-state electronics and optoelectronics. Graphene has shown a great potential for replacing conventional Si-based electronics due to its high carrier mobility exceeding 10000 cm2/Vs and a high thermal conductivity of 10 kW/m-K. Combined with the excellent electrical and thermal characteristics of graphene layers, graphene-based hybrid 1-D semiconducting nanostructures will provide the diverse and sophisticated device applications. More importantly, recent advances in the large-scale growth of single-layer and few-layer-graphene (FLG) and the transfer of FLG sheets to flexible plastic substrates are promising for stretchable, foldable, and transparent electronics and optoelectronics. However, the growth of 1-D nanostructures has been mostly achieved at high temperature, which is incompatible with flexible and transparent plastic substrates.[1] Compared with high-temperature growth methods, the hydrothermal method is a good candidate for fabricating nanostructures on plastic substrates with FLG sheets. In addition, to fabricate functional components on graphene layers, a facile growth method should be developed to control the dimensions, density, and morphology, as well as to synthesize the nanostructures directly on the FLG sheets without degrading the electrical properties of the graphene.Here, we report on the hydrothermal growth of ZnO nanostructures on FLG sheets with controlled dimensions, density, and morphology. The ZnO nanostructures were directly grown on FLG sheets without seed layer. By changing the hydrothermal growth parameters, including temperature, reagent concentration, and the pH value of the solution, we readily controlled the dimensions, density, and morphology of the ZnO nanostructures. As determined by transmission electron microscopy, single crystalline ZnO nanostructures with c-axis orientation grew vertically on the FLG sheets. Furthermore, high optical quality of ZnO nanostructures on FLG sheets was observed by both photoluminescence and cathodoluminescence spectroscopy. The ability to grow high-quality ZnO nanostructures on FLG sheets at low temperature should greatly increase the versatility and power of these building blocks for stretchable, foldable, and transparent electronics and optoelectronics.References[1] Y.-J. Kim et al., Appl. Phys. Lett. 95, 213101 (2009).
9:00 PM - Y10.10
Pt Deposited Functionalized Graphene Nanosheets/Polypyrrole Composites as a Fuel Cell Catalyst Support.
Burcu Saner 1 , Neylan Gorgulu 1 , Selmiye Alkan-Guersel 1 , Yuda Yueruem 1
1 Materials Science and Engineering, Sabanci University, Istanbul Turkey
Show AbstractThe incorporation of metal particles into the graphene layers can be a bright opportunity to enhance thermal and electronic conductivities of the membrane electrolyte to be utilized as catalyst support in polymer electrolyte membrane fuel cells. Recently, conducting polymer matrices reinforced with nanofillers have been studied for energy storage applications. The filler’s type, size, shape, content, distribution and synthesis methods affect the electrical, mechanical, and thermal properties of conducting polymer composites. Herein, functionalized graphene nanosheets (FGNS) can be used as a cheap filler in polymer matrices since it has a huge specific surface area, large aspect ratio, and excellent electrical conductivity. A rapid thermal expansion step can efficiently separate oxidized graphite oxide stacks to graphene nanosheets. In this work, FGNS was fabricated in large quantities by the oxidation of graphite flakes with chromic acid and then rapid thermal expansion at 1000 oC about 1 min. FGNS as a conductive filler was coated with pyrrole monomers in situ polymerization with different feed mass ratios of pyrrole to FGNS. Composites were sytnhesized by applying both direct and sonicated polymerization techniques. Sonication process provided the best exfoliation and dispersion of graphite nanosheets. Pt/ FGNS/polypyrrole composites with different Pt content were produced by manipulating the relative ratio of Pt nanoparticles and FGNS based composites. The characteristics of composites were analyzed by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Thermal Gravimetric Analyzer (TGA), Atomic Force Microscope (AFM), Raman spectroscopy and surface area analyzer. The electrical conductivities of composites in pellet forms were measured by a conventional four-probe method at room temperature.
9:00 PM - Y10.11
Rapid Self-propagating Domino Reactions in Graphite Oxide.
Franklin Kim 1 , Rodolfo Cruz-Silva 3 , Jiayan Luo 2 , Jiaxing Huang 2
1 Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto University, Kyoto Japan, 3 Research Center for Exotic Nano Carbon Project, Shinshu University, Nagano Japan, 2 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractGraphite oxide (GO) has gained much interest as a precursor for graphene based materials, especially for large-scale productions. Generally, GO is reduced using a variety of approaches, including thermal, chemical, electrochemical, and photochemical methods. This deoxygenating reaction is highly exothermic, and therefore when the heat released from the reaction is fed back to the material, it can further drive the reduction of neighboring sites. Indeed, we observe such a self-propagating reaction using solid GO films, where a locally triggered reduction rapidly propagated throughout the entire area. This shows that caution should be taken when storing large amounts of GO in solid state. Moreover, heat released during the reduction of GO can trigger additional domino reactions. For example, in cases where residual potassium salts are present in the GO sample, we observe a violent self-propagating carbon combustion following the deoxygenating reaction, posing a serious fire hazard. As potassium salts are often used for graphite oxidation, our results signify the importance of well-purifying the GO product. To address this issue, we developed a two-step acid/acetone filtration procedure, which significantly improved the speed of GO purification compared to conventional methods.The released energy during GO reduction can also be harnessed for more useful reactions. As a proof of concept, we prepared GO films blended with various metal precursors. The self-propagating reduction of these films triggered thermal decomposition of the salts, resulting in graphene sheets decorated with corresponding metal or metal oxide nanoparticles. The simplicity and energy-efficiency of this method opens a promising synthetic procedure for creating a wide range of functional carbon based composites.
9:00 PM - Y10.12
The Dynamics of Formation of Graphane-like Fluorinated Graphene Membranes (Fluorographene): A Reactive Molecular Dynamics Study.
Ricardo dos Santos 1 , Pedro Autreto 2 , Marcelo FLores 2 , Sergio Legoas 3 , Douglas Galvao 2
1 Applied Physics, State University of Campinas, Campinas, Sao Paulo, Brazil, 2 , Universidade Estadual de Maringa, Maringa, Parana, Brazil, 3 Physics, Federal University of Roraima, Boa Vista, Roraima, Brazil
Show AbstractGraphane is a two-dimensional system consisting of a single layer of fully saturated (sp3 hybridization) carbon atoms [1]. Recently, Elias et al. [2] performed a series of experiments which resulted on the formation of graphane from the graphene membranes under cold plasma exposure. More recently, the experimental realization of fluorographene (graphane-like fluorinated graphene membranes or graphene fluoride) have been reported by different groups [3,4]. In this work we have investigated, using reactive molecular dynamics simulations [5], the dynamics of fluorination of graphene membranes leading to the formation of fluorographene structures. Our results show that the dynamics of formation of flurographene is very similar to the observed to graphane [6], with the main differences being the result of stronger and faster chemical reactivity processes. Fluorographene exhibits the presence of frustrated domains. A frustration is a breaking in the up and down (with relation to the plane defined by carbon atoms) alternating pattern of F atoms. Our results show that a significant percentage of uncorrelated F frustrated domains are formed in the early stages of the fluorination processes leading to membrane shrinkage and extensive corrugations. We have observed that fluorination tends to produce significant defective areas, sometimes with the presence of large holes due to carbon losses. These results suggest that, as in the case of graphanes, large domains of perfect flurographene structures are unlikely to be formed. [1]. J. O. Sofo, A. S. Chaudhari, and G. D. Baker, Phys. Rev. B v75, 153401 (2007).[2] D. C. Elias, R. R. Nair, T. M. G. Mohiuddin, S. V. Morozov, P. Blake, M. P. Halsall, A. C. Ferrari, D. W. Boukhvalov, M. I. Katsnelson, A. K. Geim, K. S. Novoselov., Science v323, 610 (2009).[3] S.-H Cheng et al, Phys. Rev. B v81, 205435 (2010).[4] R. R. Nair et al, arXiv:condmat/1006.3016.[5] A. C. T. van Duin, S. Dasgupta, F. Lorant, and W. A. Goddard III, J. Phys. Chem. A v105, 9396 (2001).[6] M. Z. S. Flores, P. A. S. Autreto, S. B. Legoas and D. S. Galvao, Nanotechnology v20, 465704 (2009); arXiv:condmat/ 0903.0278v1.
9:00 PM - Y10.13
``Graphene-like” Exfoliation of Quasi-2D Crystals of Titanium Ditelluride: A New Route to Charge Density Wave Materials.
Javed Khan 1 , Criag Nolen 1 , Desalehne Teweldebrhan 1 , Roger Lake 1 , Alexander Balandin 1
1 , UC Riverside, Riverside, California, United States
Show AbstractThe discovery of graphene and its unique properties stimulated an interest in atomically thin materials which can be obtained by the “graphene-like” mechanical exfoliation. This interest is driven by a possibility of obtaining new properties and functionality in the quasi-2D crystals of different materials. We have recently demonstrated that quasi-2D crystals can be produced from bismuth telluride (Bi2Te3) family of materials [1-2]. The bismuth telluride crystal has a layered structure with the five strongly bound atomic planes – quintuples – separated by the van der Waals gaps. The presence of van der Waals gaps allows one to obtain individual quintuples or few-quintuple films of these materials, important for topological insulator and thermoelectric applications [3]. In this talk, we report on the first exfoliation of quasi-2D crystals of another important material – titanium ditelluride (TiTe2). It is interesting to note that unlike Bi2Te3 family, TiTe2 consists of strongly bound tri-layers separated by the van der Waals gaps. Thus, one can obtain another interesting quasi-2D crystal consisting of just three atomic planes. Moreover, TiTe2 tri-layers are even thinner than graphene’s atomic layers [4]. Due to the extremely small thickness of such atomic crystals, one can achieve the regime of the strong quantum confinement of charges and very strong spatial confinement of phonons. We have characterized the resulting films using the atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and micro-Raman spectroscopy. The Raman spectroscopy was used as a nanometrology tool to identify the crystals with proper thickness and quality. The back-gated field-effect transistors with the TiTe2 channels reveal interesting current-voltage characteristics. We argue that such devices can be used for inducing the charge density wave (CDW) transport regime at higher temperature. The CDWs can also be controlled with the fabricated gates [5]. [1] D. Teweldebrhan, V. Goyal and A.A. Balandin, Nano Letters, 10, 1209 (2010); D. Teweldebrhan, V. Goyal, M. Rahman and A.A. Balandin, Applied Physics Letters, 96, 053107 (2010). [2] K.M.F. Shahil, M.Z. Hossain, D. Teweldebrhan and A.A. Balandin, Applied Physics Letters, 96, 153103 (2010).[3] J. Khan, C. Nolen, D. Teweldebrhan, A. Balandin, ECS Trans, 33 (2010).[4] V. Goyal, D. Teweldebrhan and A.A. Balandin, Applied Physics Letters, 97, 133117 (2010).
9:00 PM - Y10.17
Surface Energy Modification by Spin-cast, Large-area Graphene Film for Block Copolymer Lithography.
Juyoung Kim 1 , Bong Hoon Kim 1 , Seong-Jun Jeong 1 , Jin Ok Hwang 1 , Duck Hyun Lee 1 , Dong Ok Shin 1 , Sang Ouk Kim 1
1 , KAIST, Yuseong-gu, Daejeon Korea (the Republic of)
Show AbstractGraphene is a monolayer of carbon atoms tightly packed into a twodimensional honeycomb lattice.Since its unexpected isolation from natural graphite, the extraordinary properties of graphene have immediately fascinated the scientific community. While a considerable body of research has been devoted to investigating these novel properties, the surface energy of graphene has rarely been investigated yet. Given thatgraphene is one of the thinnest materials ever known, it can serve as a highly effectivesurface energy modifier.We demonstrate a surface energy modification method exploiting graphene film. Spin-cast, atomic layer thick, large-area reduced graphene film successfully played the role of surface energy modifier for arbitrary surfaces. The degree of reduction enabled the tuning of the surface energy. Sufficiently reduced graphene served as a neutral surface modifier to induce surface perpendicular lamellae or cylinders in a block copolymernanotemplate. Our approach integrating large-area graphene film preparation with block copolymer lithography is potentially advantageous in creating semiconducting graphene nanoribbons and nanoporous graphene.
9:00 PM - Y10.18
Reduced Graphene Oxide-nylon 6,6 Nanocomposites by In Situ Thermal Reduction Method.
Rodolfo Cruz-Silva 1 , Loyda Albanil-Sanchez 2 , Selene Sepulveda 2
1 Shinshu University, Research Center for Exotic Nanocarbons, Nagano Japan, 2 , Universidad Autonoma de Nuev Leon, Monterrey Mexico
Show AbstractGraphene and graphene oxide are two dimensional materials that have attracted scientist interest due to their outstanding physicochemical properties. Some of them potential applications are in the polymer nanocomposites field, where it is expected to take advantage of the good mechanical properties, light weight, and electrical conductivity of graphene to reinforce electrically insulating polymers. In this work, nanocomposites of graphene/nylon 6,6 were prepared by thermal reduction of the graphite oxide/nylon 6,6 nanocomposite. First, a nanocomposite of graphite oxide and nylon 6,6 was prepared by mixing a dispersion of graphite oxide and a solution of the polymer in formic acid. After mechanic mixing and ultrasound treatment, the nanocomposite was obtained by precipitation of the abovementioned mixture in water, followed by washing and drying. The reduced graphene oxide/ nylon 6,6 nanocomposite was obtained by compression molding at high temperature of the graphite oxide/nylon 6,6 nanocomposite in the form of samples of about 1.0 mm thick. The change in electrical conductivity of the graphene rich domains of the nanocomposite was studied by low-voltage scanning electron microscopy (LV-SEM) of the samples. The reduction of the graphite oxide within the polymer matrix was studied by differential scanning electron microscopy, fourier transformed infrared spectroscopy, electrical conductivity measurements and x-ray diffraction. Additional characterization of the graphene/nylon 6,6 nanocomposite includes high resolution transmission electron microscopy and mechanical properties characterization by nanoindentation. Infrared spectroscopy shows that graphene is This works reports a new in situ reduction technique for graphite-oxide polymer nanocomposites that can be extended to other high melting point engineering polymers. This method is environmentally friendly and free from chemical reducing reagents such as hydrazine or hydroquinone.
9:00 PM - Y10.2
Flexible, Transparent Carbon Nanotube Transistors with Graphene Electrodes.
Sukjae Jang 1 2 , Jong-Hyun Ahn 1 2 3
1 SKKU Advanced Institute of Nano Technology, Sungkyunkwan University, Suwon, Gyeonggi-do, Korea (the Republic of), 2 Center for Human Interface Nano Technology, Sungkyunkwan University, Suwon, Gyeonggi-do, Korea (the Republic of), 3 School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do, Korea (the Republic of)
Show AbstractThis work reports a mechanically flexible, transparent thin film transistor that uses graphene as a conducting electrode and single-walled carbon nanotubes (SWNTs) as a semiconducting channel. These SWNTs and graphene films were printed on flexible plastic substrate using a printing method. The SWNTs are dispersed entirely with a density of ~ 3 tubes per μm2 and the S/D graphene electrodes cover the SWNTs perfectly. The average transmittance through the source/drain region (graphene/SWNT/epoxy/SiO2/graphene) at 550 nm was 81.4 % except from the bare PET effect. The representative unipolar p-type SWNT device with a 200 μm channel width and 25 μm channel length showed an effective mobility of ~ 2 cm2/Vs, on/off ratio of ~ 102 and threshold voltage of ~ -7 V. The ~ 90 % devices exhibited the stable operation without failure. This device showed the stable operation in the range of strains up to ~ 2.2 %. The characteristics of all carbon-based devices observed in this study are very promising for future flexible electronic applications.
9:00 PM - Y10.20
Simultaneous Exfoliation of Graphite-magadiite into Colloidal Silicate-nanosheets Graphene composites.
Pasquale Fulvio 1 , Xiqing Wang 1 , Shannon Mahurin 1 , Gary Baker 1 , Raymond Unocic 2 , Sheng Dai 1
1 Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials Science and Technology, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractAtomically-ordered two-dimensional carbon and silica nanomaterials exhibit interesting catalytic, adsorptive, electronic and mechanical properties. Silicate nanosheets and graphene have been prepared by solution methods using polymers or other organic groups for dispersion and surface stabilization. Colloidal few layer graphene (FLG) suspensions have also been prepared by the exfoliation of graphene oxide (GO) and most recently by the direct exfoliation of graphite using homoaromatic and aliphatic ionic liquids. Composites however, have been prepared by silica polymerization in the presence of GO and a reduction step was required to partially restore the graphene structure. In this work, we demonstrate that graphite and crystalline layered sodium silicates (Magadiite) can be simultaneously exfoliated in various ratios using pyrrolidinium-based ionic liquids (ILs) in ultrasonic conditions. Stable and concentrated ethanol suspensions of FLG with crystalline silicate nanosheets attached to the FLG surfaces were successfully synthesized in large yields as shown by Raman spectroscopy, high resolution transmission electron microscopy (TEM), selected area electron diffraction (SAED). Thermogravimetric analysis (TG) showed that ethanol-free slurries further exhibited 10-15wt% silicate residues and higher oxidation temperatures than those found for FLG. Results suggest that silicate nanosheets and graphene composites were stabilized by charge interactions between their surfaces and the ILs.Acknowledgements: Work supported as part of Fluid Interface Reactions, Structures and Transport (FIRST) Center, Energy Frontier Research Center, U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.
9:00 PM - Y10.21
Graphene Oxide Nano Colloids.
Jiayan Luo 1 , Jiaxing Huang 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractGraphene oxide (GO) is typically made by chemical exfoliation of graphite powders using strong oxidants. During reaction, the graphene sheets are not only derivatized with oxygen containing groups, but also torn up into smaller pieces. As a result, the lateral sizes of GO sheets are usually very polydispersed, ranging from a few nanometers to tens of micrometers. Although prolonged oxidation and sonication can break the sheets smaller, such top-down, size reduction approaches are unlikely to result in uniform size distribution. Here we report a size controlled synthesis of nano GO sheets using graphite nanofibers as the precursor. Uniform nano GO colloids can be directly synthesized, with size tunable by the nanofiber diameter and oxidation time. GO nano sheets were more hydrophilic than their regular counterparts, resulting in different thin film processability. The small size of GO nano sheets also enhances their colloidal stability. Even r-GO nano sheets are stable in a wide pH range. The enhanced stability of GO nano colloids makes them very promising as dispersing agents for single wall carbon nanotubes.
9:00 PM - Y10.22
Kevlar-based Layer-by-layer Nanocomposite.
Keqin Cao 1 , Ming Yang 2 , Michael Thouless 1 , Ellen Arruda 1
1 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Chemical Engineering, Unversity of Michigan, Ann Arbor, Michigan, United States
Show Abstract Layer-by-layer (LBL), or bottom-up, assembly has been shown to be an effective method for assembling molecules in a highly ordered fashion to synthesize nanocomposites with enhanced mechanical properties. Previous research in this field has focused on using water-soluble polymers to fabricate nanocomposites. However, the use of high-performance polymers requires that this technique be extended to non-water-soluble materials. This talk will describe a successful demonstration of this using p-phenylene terephtalamides (PPTA), better known as Kevlar. This is the first example of a Kevlar-based nanocomposite fabricated by a LBL process. LBL assembly is a process by which oppositely charged macromolecules are deposited on a substrate in a layer-by-layer fashion. Owing to the interaction between the polyelectrolyte chains, spontaneous ordering of the macromolecules in the solution can be achieved through the alignment of molecules to maximize the attractive energy with the surface. This results in a highly ordered structure through a self-organizing mechanism during the fabrication. Owing to its relative simplicity and effectiveness, the LBL technique has wide applicability in different fields and has attracted much interest. Kevlar belongs to the class of high-performance polymers used as the reinforcing fibers in structural components of aircrafts and high-functionality boats. Since its invention, the application of Kevlar has been basically limited to fiber reinforcement in a polymer matrix, and the great mechanical properties of Kevlar are realized only along the fiber axes. In this work, we demonstrate that an isotropic, nanoscale, planar structure of Kevlar can be fabricated via LBL. This form of Kevlar, uniform high-aspect-ratio nanoplates, was used as building blocks to assemble transparent composites. In order to achieve stronger interactions between the Kevlar nanoplates, functionalization of the Kevlar macromolecules and crosslinking agent were used. The treatment brought in crosslinks between the polymer chains which modified microstructure of the nanocomposite and resulted in the improvement of mechanical properties. The properties of the treated and cross-linked films are comparable to the properties of plain-weaved Kevlar Mat along its strongest direction. This high strength and stiffness Kevlar nanoplates were further used as building blocks binding with thin layers of ductile polymers (Polyurethane and Poly (acrylic acid)) to create a hierarchically structured nanocomposite. By tuning the amount of the ductile polymers in the system, the ductility of nanocomposites could be adjusted and a maximized toughness could be potentially obtained. The thin layers between the stiff Kevlar blocks also serve as crack deflection pathways to prevent catastrophic failure of the relatively brittle Kevlar blocks due to crack propagation.
9:00 PM - Y10.24
Transformation of Polyacrylonitrile Based Solid Precursors into Graphene-like Layers.
Nickolay Lavrik 1 , Ivan Vlassiouk 2 , Ilia Ivanov 1
1 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Measurement Science and Systems Engineering Division, Oak Ridge National Laboratory, Oak Rdige , Tennessee, United States
Show AbstractSynthesis of graphene and graphene-like layers using various modifications of the chemical vapor deposition (CVD) approach has become an extremely active research area in the last several years. While the vast majority of the effort in this area focuses on synthesis of single layer graphene and few layer graphene (FLG) using metal catalyst substrates and gaseous organic precursors, such as methane and acetylene, alternative approaches to graphene based on solid precursors have also been explored. In particular, the use of solid carbon-containing precursors is attractive as a way to avoid hazardous gases and, more importantly, as a way to control the amount of carbon in the system more precisely. The continued search of alternatives to the well established protocols of CVD growth of graphene from gaseous precursors is also related to the fact that graphene transfer from the catalyst surface onto a suitable dielectric substrate represents a significant practical challenge for many potential applications as well as for more extensive fundamental studies. The ultimate goal of the present study is to identity a viable technological pathway to large-area graphene and FLG materials that would not involve the etch-and-transfer step. To this point, we explore thin polyacrylonitrile (PAN) films formed in a glow discharge plasma and study their transformation into graphene like layers as a result of annealing in presence of Cu and Ni catalysts. In contrast to the more conventional CVD growth of graphene on metal catalysts, our approach consists in depositing Ni and Cu films on top of the PAN precursor so that the metal catalyst could be removed subsequently by wet chemical etching. In our preliminary experiments, we prepared a series of plasma polymerized PAN films of various thicknesses on SiO2 coated Si substrates using acrylonitrile as a precursor monomer. The PAN films were subsequently annealed at temperatures in the range of 350-800 C in the atmosphere of pure Ar or an Ar:H2 mixture. Chemical and structural changes in the films caused by annealing were studied by Raman and IR spectroscopy combined with complementary electrical measurements and SEM analysis. As expected, the most immediate consequence of the PAN films anneal is formation of disordered carbonaceous layers. Our comparative characterization of the PAN films annealed with and without metal catalyst overlayers, however, indicate that noticeable ordering and formation of FLG-like layers takes place in presence of Ni catalyst at temperatures compatible with typical wafer level processes.This research is sponsored by the U. S. Department of Energy, under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory, managed and operated by UT - Battelle, LLC. A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, U.S. Department of Energy.
9:00 PM - Y10.25
Transparent and High Gas Barrier Films Based on Poly(vinyl alcohol)/Graphene Oxide Composites.
Hye Min Kim 1 , Heon Sang Lee 1
1 Chemical Engineering, Dong-A University, Busan Korea (the Republic of)
Show AbstractGraphene has attracted attention especially in materials science due to exceptional electrical and mechanical properties. Another benefit from graphene is gas impermeable atomic membrane. And also PVA is the best gas barrier but the poorest water barrier due to its hydroxyl group. Here, we show that graphene oxide(GO) is an excellent gas barrier itself. We also demonstrated that gas barrier property of PVA/GO composite film is drastically improved compared to those of PVA, holding high light transmittance. Poly(vinyl alcohol)(PVA)/GO nanocomposites were prepared with various GO concentrations with solvent mixing method and PVA/GO composite films were obtained by bar coating method. GO is fully exfoliated in PVA/GO nanocomposites. The size of PVA crystalline is not changed by mixing GO with PVA. GO acts as a crystallization agent for PVA during non-isothermal crystallization, but do not affect on the crystallization of PVA during solvent evaporation. Glass transition temperatures of PVA are not changed by adding GO into PVA, indicating the H-bonding interaction is not so large. We demonstrate that oxygen transmission rate (O2TR) of GO/PVA film containing 0.1wt.% GO reduces to 86% of that of PVA with 97% light transmittance at 550 nm. We furthermore demonstrate that O2TR of GO/PVA film containing 0.3 wt.% GO reduces to 17% of that of PVA with 92% light transmittance at 550 nm.
9:00 PM - Y10.26
Layered Double Hydroxide Nanosheets Modified with Anthraquinone Sulfonate for Dye-sensitized Solar Cells.
Jong Hyeon Lee 1 , Juyeon Chang 2 , Ji-Hyun Cha 2 , Yeji Lee 2 , Duk-Young Jung 2
1 chemistry, The Catholic University of Korea, Bucheon Korea (the Republic of), 2 Chemistry, Sungkyunkwan University, suwon Korea (the Republic of)
Show AbstractA new functional nanomaterial consisting of layered double hydroxide (LDH) nanosheets with AQS dyes chemically immobilized on the nanosheets was investigated. In this nanomaterial, the LDHs induce a strong photochromic function of the dyes. Considering their strong light-absorption ability in the visible range, we also report a photovoltaic function of the hybrid nanosheets as a new hybrid light-sensitizer, where the AQS dyes act as a light-sensitizer and the LDH nanosheets as an inorganic host. To the best of our knowledge, this is the first example using hybrid LDH-organic nanosheets as a light sensitizer in photovoltaic devices. The photovoltaic cells were fabricated with this hybrid sensitizer on a nanoporous TiO2 electrode using a self-organization process. The J−V characteristic of the hybrid sensitized cell demonstrates a higher solar-to-electric conversion efficiency than the single-dye cell, despite a smaller amount of adsorbed dye molecules in the hybrid sensitized-cell. The efficiency of the hybrid cell is of particular importance because it gradually increased up to 60 % of its initial value as the irradiation time increased. This result clearly indicates that the cell performance is strongly governed by the photochromic function of the hybrid nanosheets. Apparently, the remarkable photovoltaic functions of the hybrid sensitizers are ascribed to the “hybridization effect” of the LDH nanosheets acting as an inorganic stabilizer for the photo-excited organic dyes. Therefore, this LDH-based sensitizer provides a new platform for the development of hybrid light-sensitizers due to the variable composition of the LDHs and their stabilizing ability on organic dyes.
9:00 PM - Y10.27
Template Assisted Self Assembly of Block Copolymer via Direct Imprint Lithography.
Sarah Kim 1 , Dong-Ok Shin 2 , Dae-Geun Choi 1 , Jong-Ryul Jeong 3 , Ki-don Kim 1 , Yosep Shin 1 3 , Sang-Ouk Kim 2 , Jun-Ho Jeong 1
1 Nanomechanical System Research Center, Korea Institute of Machinery and Materials, Daejeon Korea (the Republic of), 2 Department of Materials Science and Engineering, KAIST, Daejeon Korea (the Republic of), 3 Department of Materials Science and Engineering, Chungnam National University, Daejeon Korea (the Republic of)
Show AbstractUp to now, 2D block copolymer (BCP) structure has been studied extensively because of their potential applications as alternative pathway to conventional lithography for transistor, optical memories, and high density magnetic storage. The key to the use of block copolymer in such applications is the control of the orientation and lateral order of the domains in the confined geometry. Here, we report on multiring structure with a various type controlled cylindrical morphology polystyrene-block-poly (methylmethacrylate) (PS-b-PMMA) using metal oxide template imprinted by flexible mold. As a template for a BCP alignment, ZnO, TiO2 or SiO2 prepattern was fabricated in a range of shape using UV imprint method. Then, A block copolymer thin film was successfully assembled within the sub-microscale confinement imposed by a initially patterned ceramic substrate that can endure the high temperature annealing required to accomplish directed blockcopolymer assembly.This technique can be useful method for pattern transfer into functional materials with 30 nm line width features in a large area, cost-effectively.
9:00 PM - Y10.28
Bio-inspired Layer-by-layer Assembled Hydrogel.
Kim Taek Gyoung 1
1 Severance Integrative Research Institute for Cerebral & Cardiovascular Diseases, Severance Hospital, Seoul Korea (the Republic of)
Show AbstractSurface engineering of materials can introduce the preferable functionality by physical, chemical, or biological decoration into the elaborated architecture having inert exterior, which can boost the end role of the consequent product in a wide range of areas. Due to processing limitation of functional materials in production, bulk material manufacturing with subsequent surface modification of interesting species is often desirable. In particular, surface modification with hydrogels has unique advantages of a high degree of hydrophilicity and biocompatibility in the context of biomedical applications. In this study, we devised the novel layer-by-layer assembly using mussel adhesive-inspired driving force, which led to spontaneous formation of surface-bound hydrogel on virtually all types of substrates including plastics, metals, and ceramics. First, we synthesized many types of catechol-polymer conjugates through simple EDC chemistry. The catechol-polymer conjugates was sequentially adsorbed on the substrate by layer-by-layer fashion with each subsequent oxidation of catechol groups. The resulting hydrogel on the substrate exhibited anisotropic swelling and tenacious adherence to various substrates. This surface-bound hydrogel has promising potential for biomedical applications such as local drug reservoir, biocompatible coating, and protective lubricious surface layer.
9:00 PM - Y10.3
Synthesis of Pt Nanoparticles Laden Graphene Nanosheets via Aerosol Assisted Self-assembly.
HeeDong Jang 1 , Franklin Kim 2 , Jiayan Luo 2 , Kwonnam Sohn 2 , Jiaxing Huang 2
1 Industrial Materials Research, Korea Institute of Geoscience & Mineral Resources, Daejeon Korea (the Republic of), 2 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractPlatinum/graphene (Pt/GR) nanocomposite was directly synthesized from a colloidal mixture of aqueous chloroplatinic acid (H2PtCl6) and grapheme oxide (GO) nanosheets via an aerosol assisted self-assembly (AASA). Effects of Pt content of Pt/GR nanocomposite and temperature of heating zone on the particle morphology and specific surface area were investigated. As Pt content of the nanocomposite increased from 2 to 20 wt %, number of Pt nanoparticles less than 5 nm in diameter increased on the surface of GR. As temperature increased from 800 to 1000 oC, the average particle size of Pt increased from 5 to 10 nm due to sintering. The specific surface area of the as-prepared Pt/GR ranged 117 to 162 m2/g. Electrocatalytic application of the Pt/GR nanocomposites was examined through methanol oxidation reaction. The 20 wt % Pt/GR synthesized at 1000 oC showed higher performance on methanol oxidation than a commercial 20 wt% Pt/carbon black catalyst.
9:00 PM - Y10.30
Preparation of Graphene with Few Defects in a One-step Exfoliation.
Gyeong Sook Bang 1 , Hye-Mi So 1 , Chi Won Ahn 1
1 , National Nanofab Center, Daejon Korea (the Republic of)
Show AbstractGraphene, a two-dimensional sheet of sp2-hybridization carbon, has been attracting great attention due to its excellent electronic and mechanical properties and potential applications in nanocomposites and microelectrical devices. Graphene-based applications involve mostly use of strong acids and oxidants. Then, the obtained graphene oxide (GO) is disrupted the sp2-hybridization carbon network by forming covalently bonded hydroxyl, carboxyl and epoxide groups. Raman studies reported that GO (or reduced GO) is extremely defective compared to the graphene cleaved directly from graphite. Therefore, simple method for production of high quality graphene from graphite is important. Some researchers suggested methods for high quality graphene, their methods, different re-intercalation and dispersion methods, are quite complicated and involves a long processing time consist of 6-8 steps. We report that graphene sheets with few defects were produced by microwave-assisted heating. This method produce strong expansion of graphite worm in a short time with little energy cost and has the advantage of being able to produce graphene sheet in one-step exfoliation. The graphene sheets obtained in this method were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy.Keywords: graphene, microwave-assisted heating, nanostructure
9:00 PM - Y10.31
Electrodeposited Metal Nanoparticles in Reduced Graphene Oxides.
Hye-Mi So 1 , Gyeong Sook Bang 1 , Il-Suk Kang 1 , Chi Won Ahn 1
1 , NNFC, Daejon Korea (the Republic of)
Show AbstractWe report the electrodeposition of metal nanoparticles on graphene oxide (GO) or reduced graphene oxide (r-GO) and the electrical transport properties of devices. GO was synthesized from graphite by a modified Hymmers method and r-GO is achieved by thermal reducing the GO substrate. Electrodes were formed with photolithography and metal-lift off. To decorate metal (Au, Sn etc) nanoparticles on GO, we used inert gas condensation and electrochemical deposition. By cyclic voltammetry or linear sweep voltammetry, we controlled both metal nanoparticle size and packing density. A droplet of HAuCl4 in 100 mM KCl (supporting electrolyte) was placed on the device, electrode was used as working electrodes, and a reduction potential was applied with respect to the Ag/AgCl reference electrode with current monitoring using a Pt counter-electrode. In particular, for Au electrodeposition, it is possible for Au+ in an aqueous solution to be reduced spontaneously on the r-GO surface since the reduction potential of the Au+ is higher than that of r-GO.Keywords: metal nanoparticle, electrodeposition, graphene oxide
9:00 PM - Y10.32
Porous Graphene Oxide Sheets via Steaming.
Tae Hee Han 1 , Alvin Tan 1 , Laura Cote 1 , Yi-Kai Huang 1 , Franklin Kim 1 , Jiaxing Huang 1
1 Materials Science and Enginnering, Northwestern University, Evanston, Illinois, United States
Show AbstractGraphene oxide (GO) is produced by chemical exfoliation of graphite, and its surfaces are functionalized with oxygen-containing groups such as phenol hydroxyl and epoxide groups mainly on the basal plane, and ionizable carboxylic acid groups at the edges. As the presence of defects causes GO to be electronically insulating, considerable research have been done on the preparation of electrically and optically active materials from GO. However, the defect control of GO, which is critical for diverse applications, has not been explored in great detail. In this study, we demonstrate that the GO sheets can be made porous by etching with water vapor. Pore size can be tuned from approximately 2 nm to 40 nm by etching time. Further etching breaks GO sheets into nano-sized reduced GO (rGO). We hypothesize that the etching starts at the sp3 defects. Potential applications of porous GO and rGO will be discussed.
9:00 PM - Y10.33
Flexible Transparent Conducting Films Based on Self-assembled Metal Nanowires Using Langmuir-Blodgett Method.
Dong Jun Lee 1 , Hyun Suk Jung 1
1 School of Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of)
Show AbstractWe fabricated flexible transparent conducting films containing self-assembled gold nanowires. The gold nanowires with 30~50 nm in diameter and 800~1000 nm in length are synthesized in aqueous solution and transferred into toluene solution by surfactant change. The Langmuir-Blodgett technique was employed to assemble the gold nanowires on substrate. The resultant films showed a good optical transparency and electrical conductivity which are appropriate to utilize them as flexible transparent conducting films with high performance.
9:00 PM - Y10.34
Local Structures around Al and B Heteroatoms in Layered Alumino- and Borosilicates.
Mounesha Garaga Nagendrachar 1 , Sylvian Cadars 1 , Ramzy Shayib 2 , Ming-Feng Hsieh 2 , Michael Deschamps 1 , Bradley Chmelka 2 , Dominique Massiot 1
1 CEMHTI UPR3079, CNRS, Universite d'Orleans, Orleans France, 2 Department of Chemical Engineering, University of California, Santa Barbara, California, United States
Show AbstractMuch attention has been paid to the studies of porous alumino- and (to less extent) borosilicate materials because of their paramount importance in catalysis, ion exchange and gas separation. Unfortunately, there still lacks fundamental understanding of the molecular origins of the catalytic activity of these materials. This is primarily because the incorporation of Al or B heteroatoms into the silicate frameworks deteriorates the molecular ordering by generating compositional (Al/Si or B/Si substitutions) and geometric (bond lengths, angles… etc.) local disorder, to extents that are particularly difficult to establish. Since diffraction methods are often limited to powder analyses in these systems due to generally small crystal sizes, solid-state nuclear magnetic resonance (NMR) can play a key complimentary role to solve this long-standing issue.Surfactant-templated layered silicate materials with short-range molecular order[1,2] are particularly interesting model systems to study the local structures around incorporated heteroatoms, because their synthesis and local molecular structures in pure-silicate are well understood[3] and because they have simple and well-resolved 29Si NMR signatures. Amounts of Al and B atoms small enough to yield well-isolated defects have been incorporated into the framework of such layered silicates. This is demonstrated by state-of-the-art multidimensional NMR measurements that unambiguously establish spatial proximities (via dipolar couplings) between 29Si and 11B or 27Al nuclei, and hence make it possible to distinguish incorporated heteroatoms from extra-framework sites or side products. These and additional 1D or 2D NMR experiments probing spatial proximities or through-bond connectivities (via scalar couplings) set the bases of the understanding, to a level of detail never before attained, of the local structures around hetero-atom environments.[1] Christiansen, S. C.; Zhao, D. Y.; Janicke, M. T.; Landry, C. C.; Stucky, G. D.; Chmelka, B. F. J. Am. Chem. Soc. 2001, 123, 4519-4529.[2] Hedin, N.; Graf, R.; Christiansen, S. C.; Gervais, C.; Hayward, R. C.; Eckert, J.; Chmelka, B. F. J. Am. Chem. Soc. 2004, 126, 9425-9432.[3] Cadars, S.; Mifsud, N.; Lesage, A.; Epping, J. D.; Hedin, N.; Chmelka, B. F.; Emsley, L. J. Phys. Chem. C 2008, 112, 9145–9154.
9:00 PM - Y10.35
Hybridization of Graphene Sheets with Carbon Nanotubes for Tough Nanocomposite Fibers.
Min Kyoon Shin 1 , Bommy Lee 1 , Shi Hyeong Kim 1 , Hyun-U Cho 1 , Jea Ah Lee 1 , Seon Jeong Kim 1
1 Center for Bio-Artificial Muscle, Dept. of Biomedical Engineering, Hanyang University, Seoul Korea (the Republic of)
Show AbstractHighly strong and ductile materials such as spider silk are very promising for practical applications (for example: parachutes, medical sutures, and tissue regeneration) and commercialization. Carbon nanomaterials have been used as reinforcing fillers to achieve high performance nanocomposites due to their outstanding mechanical properties and large surface to volume ratios. Many researches have shown that additions of carbon nanotubes (CNTs) and graphene sheets (GSs) enhance mechanical properties of polymer matrices. However, most nanocomposites reinforced by single nanomaterials have limitations in maximizing mechanical strength and toughness because of difficulties in dispersion, orientation, and effective load transfer between nanofillers and matrices at high loading of carbon nanomaterials. Thereby, the development of composites with high strength and extensibility is still challenging despite recent progress in tough composites. Here, we report that nanomaterials hybridized by functionalized GSs with CNTs dramatically enhance toughness of composites compared to CNT or GS based composites. The hybrid composite fibers formed by wet-spinning were weavable and shaped as a spring with larger spring constants than CNT yarns which are directly formed from CNT forests.
9:00 PM - Y10.36
Surfactant-free Water-processable Photoconductive All-carbon Composite.
VIncent Tung 1 , Franklin Kim 1 , Jiaxing Huang 1
1 MSE, Northwestern University, Evanston, Illinois, United States
Show AbstractHeterojunctions between different graphitic nanostructures including fullerenes, carbon nanotubes and graphene-based sheets have attracted immense research interests for light to electrical energy conversion.Due to their insolubility, fabrication of such all-carbon nanocomposites typically involves covalently linking of the individual constituents or extensive surface functionalization to impart solvent processibility. However, such strategy often deteriorates or contaminates the functional carbon surfaces. Here we co-assembled fullerenes, pristine carbon nanotubes and graphene oxide sheets to form a hybrid, which upon thermal reduction of graphene oxide, forms a solvent-resistant, photoconductive all-carbon hybrid of fullerene-nanotube-graphene. The all-carbon composite shows on-off ratios of nearly six orders of magnitude and unprecedented photovoltaic responses among all known carbon-based materials. Such surfactant-free, water-processed, all-carbon thin films should lead to their wide applications in organic optoelectronic devices.
9:00 PM - Y10.5
Materials Issues for Fabrication of the Triple-mode Ambipolar Graphene Amplifiers for the Analog Circuit Application.
Guanxiong Liu 1 , Xuebei Yang 2 , Kartik Mohanram 2 , Alexander Balandin 1
1 Electrical Engineering, University of California Riverside, Riverside, California, United States, 2 Electrical and Computer Engineering, Rice University, Houston, Texas, United States
Show AbstractGraphene, owing to its high carrier mobility, saturation velocity, mechanical strength and high thermal conductivity, is a promising material for high-frequency, analog and communication applications. The ambipolar properties of graphene provide opportunities for increased functionality in unconventional circuit architectures. We designed, built, and experimentally demonstrated the communication circuit for the common-source, common-drain, and frequency multiplication modes using the graphene transistor amplifier [1]. The different operational modes of the graphene amplifier can be achieved by switching the gate bias in the field, where Vgs larger than VDirac, Vgs smaller than VDirac and Vgs equal to VDirac correspond to the mentioned modes. As we add a sinusoid carrier wave and a data square wave together as input signal, where the square wave is used to switch the bias between the three modes, we implemented the functionality necessary for phase shift keying and frequency shift keying, which are widely used in wireless and audio applications. Compared with the conventional designs for such applications, which use complex designs based on multiple unipolar transistors, the proposed graphene amplifier has the advantages of a simplified structure with lower parasitics, larger bandwidth, and lower power consumption. In this presentation we address the materials and device fabrication issues, which are required to be solved in order to increase the gain of graphene amplifiers while preserving their enhanced functionality. The gain in our back-gated graphene devices was low due to the thick SiO2 gate oxide. We succeeded in achieving higher gain by using a thinner (~20 nm) high-k dielectric as the top gate oxide [2]. In this work we apply a similar approach to the graphene amplifier fabrication. As progress continues in graphene-based thin films for transparent and printable electronics, we believe that our circuits will deliver both the enhanced functionality and in-field configuration capability necessary for large-scale integration and commercialization.The work at UCR was supported, in part, by SRC – DARPA through the FCRP Functional Engineered Nano Architectonics (FENA) center. The work at Rice University was supported by NSF grant CCF-0916636. [1] X. Yang, G. Liu, A.A. Balandin and K. Mohanram, "Triple-mode single-transistor graphene amplifier and its applications," ACS Nano, DOI: 10.1021/nn1021583 (2010).[2] G. Liu, W. Stillman, S. Rumyantsev, Q. Shao, M. Shur and A.A. Balandin, "Low-frequency electronic noise in the double-gate single-layer graphene transistors," Appl. Phys. Lett., 95, 033103 (2009).
9:00 PM - Y10.6
Effect of Substrate on the Quality of Graphene Layers Growing from a Molten Phase.
Shaahin Amini 1 , Haamun Kalaantari 1 , Alexander Balandin 2 , Reza Abbaschian 1
1 Mechanical Engineering , University of California Riverside, Riverside, California, United States, 2 Electrical Engineering , University of California Riverside, Riverside , California, United States
Show AbstractWe report on the development of a new technique for the growth of large-area graphene films from a metal-carbon melt. The process involves dissolving carbon inside a molten metal initially at a specified temperature and then allowing the dissolved carbon to nucleate and grow on top of the melt at a lower temperature. The chosen metal system should not possess any forming carbide since there would then be a competition between the growth of carbide and graphene films. Accordingly, the transition metals of nickel, copper and cobalt opted for the growing process. The consequential graphene layers were then examined carefully by optical microscopy, Raman spectroscopy, scanning and cross-sectional transmission electron microscopy. The deconvolution of the Raman 2D band and G-peak to 2D-peak ratio were deployed to accurately determine the number of atomic planes in grown graphene layers. In addition, the intensity of D band was examined to show the quality of the layers. The results indicate the graphene layers contain a wrinkled structure due to thermal expansion coefficient mismatch between the grown layer and metal substrate. The graphene layers, however, preserve their continuity over these wrinkles. Although the formation of wrinkles was found not to be dependent on the type of metal substrate, it was observed that the substrate have strong effect on the quality of grown layers. Adversely, the graphene films precipitated on copper possess quite a few amounts of defects including cracks and entrapped vacancies from high temperatures. Contrastingly, the graphene films grown on nickel substrate hold highly ordered crystal structure free of defects. The pristine single layer graphene was successfully grown on nickel substrate and proved the nickel as a suitable metal for growth process. It is conceivable that the presence of defects is due to the different thermal diffusivity of various metals which will lead to different amount of cooling rates and the consequential defect formation.
9:00 PM - Y10.7
The Effect of Hydrogen in Chemical Vapor Deposition Synthesis of Graphene.
Zhihong Liu 1 , Wei Wu 1 , Zhihua Su 1 , Qingkai Yu 1 , Jiming Bao 1
1 Electrical & Computer Engineering, University of Houston, Houston, Texas, United States
Show AbstractGraphene has drawn significant attention with its unusual physical properties. Chemical vapor deposition ( CVD ) using Cu as catalyst and Methane as Carbon source has been developed to synthesize lager area graphene, but the synthesis mechanism is still not clearly. In this article, the role of Hydrogen in CVD process is presented. The concentration of Hydrogen not only can dramatically change the growth velocity but also can change the morphology of the graphene islands. The coverage of the copper surface decreases from 100% to 18% when the percentage of H2 in gas increases from 3.3% to 6.3%. The Graphene islands change from starlike to irregular, then Hexagonal shape when the concentration of Hydrogen in the gas flow increased gradually. The non-Hexagonal Graphene islands can be etched to hexagonal shape by post annealing in high Hydrogen concentration. So we believe that Hydrogen has two effects in the growth process. First, it will change the equivalent concentration of C atom on the surface of copper foil. Second, the Hydrogen will etch the edge of graphene islands. It is a competition between growth and etching in the synthesis process. TEM, STM and Raman analysis show that the hexagonal graphene islands have zigzag edges. The high quality hexagonal graphene single crystal can be used for fabricating electronic device.
9:00 PM - Y10.8
Strain Engineering in Ultra-thin III-V on Insulator (XOI).
Hui Fang 1 , Kuniharu Takei 1 , Carlo Carraro 2 , Morten Madsen 1 , Alexandra Ford 1 , Elena Plis 3 , Nutan Gautam 3 , Sanjay Krishna 3 , Roya Maboudian 2 , Ali Javey 1
1 Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California, United States, 2 Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California, United States, 3 Center for High Technology Materials, University of New Mexico, Albuquerque, New Mexico, United States
Show Abstract It has been shown that epitaxial transfer of crystalline structures to various substrates is promising for applications ranging from optoelectronics to large area electronics. Recently, single crystalline ultrathin (below the Bohr Radius) compound semiconductor has been transferred onto Si/SiO2 substrates for MOSFETs application (Ref. 1). This XOI technique easily combines the high mobility III-V semiconductors and the well established, low cost processing of the Si technology, while it has lower defect densities and junction leakage compared to conventional heteroepitaxial growth of complex multilayers on Si. To further boost the performance of XOI device, it is important to know the strain status of the III-Vs in XOI and control it, since strain plays a critical role in materials properties and provides a mechanism to control both the carrier mobility and band offsets. Here, we use several characterization tools including HRXRD and Micro-Raman to study the strain status in X, which is InAs in this work, both in the source wafers and XOI. While XRD shows us there is ~ 0.6% tensile strain inside InAs in the source wafer, Raman spectra indicates that this strain will be released if we use our previous transfer apporach. We later demonstrated a versatile method based on XOI processing to preserve the strain inside XOI InAs by simply using a deposited cap layer, and hence we propose to engineer the strain in the X of XOI by choosing different cap layers (with different Young’s modulus), changing the cap thickness and initial stress inside the cap, etc.Reference:1. H. Ko, K. Takei, R. Kapadia, S. Chuang, H. Fang, P. W. Leu, K. Ganapathi, E. Plis, H. Kim, S.-Y. Chen, M. Madsen, A. C. Ford, Y.-L. Chueh, S. Krishna, S. Salahuddin, A. Javey. “Ultrathin compound semiconductor on insulator layers for high performance nanoscale transistors”, Nature, in press, 2010.
9:00 PM - Y10.9
Field Emission from Atomically Thin Edges of Reduced Graphene Oxide.
Hisato Yamaguchi 1 , Katsuhisa Murakami 2 , Goki Eda 3 , Takeshi Fujita 4 , Julien Boisse 1 , Pengfei Guan 4 , Fujio Wakaya 2 , Kyeongjae Cho 5 , Yves Chabal 5 , Mingwei Chen 4 , Mikio Takai 2 , Manish Chhowalla 1
1 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States, 2 Center for Quantum Science and Technology under Extreme Conditions, Osaka University, Osaka Japan, 3 Materials, Imperial College London, London United Kingdom, 4 WPI-AIMR, Tohoku University, Sendai Japan, 5 Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas, United States
Show AbstractPoint sources show the best electron emission properties due to local field enhancement at the tip. A drawback of tip emitters is that they must be positioned sufficiently apart to achieve field enhancement, limiting the number of emission sites and therefore the overall current. In contrast, we report ultra-low threshold voltage emission of multiple electron beams from atomically thin edges of individual reduced graphene oxide (rGO) sheets. The emission sites observed by field emission (FEM) and field ion (FIM) microscopies are atomically spaced along the edge. FEM measurements indicate evidence for interference, suggesting that the emitted electron beams are coherent. Based on our spectroscopy, high-resolution transmission electron microscopy and theory results, field emission is attributed to the aggregation of oxygen groups in the form of cyclic edge ethers. Such closely spaced electron beams from rGO offer prospects for novel applications and understanding the physics of linear electron sources.
Symposium Organizers
AlexanderA. Balandin University of California-Riverside
Andre Geim University of Manchester
Jiaxing Huang Northwestern University
Dan Li Monash University
Symposium Support
Cambridge NanoTech Inc
Elsevier Ltd.
Y12: Other 2D Materials
Session Chairs
Friday PM, April 29, 2011
Room 3009 (Moscone West)
2:30 PM - **Y12.1
Creation of Hybrid Layered Materials with Carbon and Boron Nitride.
Pulickel Ajayan 1
1 Mechanical Engineering and Materials Science, Rice University, Houston, Texas, United States
Show AbstractPlanar graphitic carbon (C) and hexagonal boron nitride (BN) are quintessential layered materials with similar lattice structure but very different electronic properties. This talk will describe the various approaches we have used to create hybrid layered structures made from C and BN. Stable layered structures that could be from C and BN extends over large composition ranges of these components and the ability to stabilize some of these phases will be described. In addition to the alloyed phases we will also look at the segregation of domains of C and BN within layers and the possibility of introducing each of these compositions as dopants in the other. By controlling growth and fabrication we will look at possibilities of engineering these mixed phases into atomic layers and engineering the shapes and morphologies of these domains. The implications of creating such hybrid atomically layered structures will be discussed.
3:00 PM - Y12.2
White Graphene: Atomically Thin BN Nanoribbons.
Haibo Zeng 1
1 , National Institute for Materials Science (NIMS), Japan, Tsukuba Japan
Show AbstractHexagonal BN has similar structure to graphite, so called white graphite, but has completely different properties, such as insulating, higher thermal and chemical stability, band gap, and high thermal conductivity. Therefore, inspired by graphene, many groups have been attracted to fabricate two dimensional crystals of BN and to explore their novel properties. Currently, the fabrication of atomically thin sheets and ribbons is still a challenge. But, mass of theoretical calculations have been published, promising very exciting potentials in optoelectronics and spintronics devices although the experimental evidences are still missing.Herein for the first time, we report fabrication of atomically thin BN nanoribbons, analogues of graphene nanoribbons, and their electronics properties. The fabrication method involves the nanotube unzipping through plasma etching, wherein the layer number of BN nanoribbons can approach to single-layer through the modulation of plasma power and etching time. The microstructure characterizations demonstrated that the BN nanoribbons by this method prefer to be of zigzagged edges. Usually, BN is an insulator. This greatly depresses the application of BN nanostructures, such as previous BN nanotubes. Here, through electron transport investigation, the electronic conductivity of nanoribbons was found to be greatly improved through the formation of atomically thin ribbons. Through atomic imaging on the microstructure and theoretical calculation, we suggested that such conductivity improvement is induced by the zigzag edge states and vacancy defects. They act as shallow acceptor-like dopants. This study could pave the way for BN nanoribbon production and usage as functional semiconductors with a wide range of applications in optoelectronics and spintronics.Referees: H. B. Zeng, C. Y. Zhi, Z. H. Zhang, X. L. Wei, X. B. Wang, W. L. Guo, Y. Bando, D. Golberg, “White Graphenes”: Boron Nitride Nanoribbons via Boron Nitride Nanotube Unwrapping, Nano. Lett. 2010, Articles ASAP, DOI: 10.1021/nl103251m.
3:15 PM - Y12.3
Synthesis and Molecular Characterization of a New Molecularly-ordered Layered Silicate Material.
Sylvian Cadars 1 , Ramzy Shayib 2 , Mathieu Allix 1 , Mounesha Garaga Nagendrachar 1 , Allen Burton 3 , Stacey Zones 3 , Lyndon Emsley 4 , Bradley Chmelka 2
1 CEMHTI UPR3079, CNRS, Universite d'Orleans, Orleans France, 2 Department of Chemical Engineering, University of California, Santa Barbara, California, United States, 3 , ChevronTexaco Energy Research and Technology Center, Richmond, California, United States, 4 Centre de RMN a Tres Hauts Champs, Universite de Lyon, (CNRS/ENS-Lyon/UCB Lyon 1), Lyon France
Show AbstractLayered silicates have several important applications as host materials, supports for catalysis, and precursors for the synthesis of zeolites, but their local structures, though generally ordered at the molecular level, are often particularly difficult to establish. A new layered silicate material with a high degree of molecular order named CLS-1 was synthesized using a fluorine-based protocol[1] and cationic alkylamino-pyridinium as a structure-directing agent (SDA). The molecular structure of this novel tectosilicate was investigated using a combination of electron microscopy, X-ray diffraction (XRD) using conventional and synchrotron sources, and solid-state nuclear magnetic resonance (NMR) in one and two dimensions. Despite the complications due to the presence of stacking disorder inherent to such complicated layered structures, this unique combination of spectroscopic approaches made it possible to clearly determine the unit cell parameters, composition (number, type, and multiplicity of silicon sites) and topology (complete set of Si-O-Si connectivities) of the silicate framework.NMR 29Si chemical shifts are, furthermore, particularly sensitive to organic-inorganic interactions between the SDA and the silicate framework and represent a powerful probe of the dynamics and disorder that they may induce at the proximity of interfaces.[2] Variable-temperature XRD diffraction and 29Si 1D and 2D NMR measurements collected on samples prepared with different relative amounts of reactants established that the CLS-1 material presents complicated extents of slight structural disorder that primarily result from variations in these organic-organic interactions.A new protocol was finally introduced for the synthesis of a CLS-1 layered silicate material enriched in 29Si, from which 29Si-O-29Si scalar (J) couplings, an interaction characteristic of Si-O-Si chemical bonds with a high sensitivity to the local structures of silicate frameworks,[3] could be accurately measured. Analyses of these scalar couplings indicate for example the presence in the framework of a four-member silicate ring with a remarkable shape strongly deviating from a square. This opens new possibilities for the development of structure determination protocols integrating ab initio calculations of NMR parameters.[4][1] Zones, S. I.; Hwang, S. J.; Elomari, S.; Ogino, I.; Davis, M. E.; Burton, A. W. C. R. Chim. 2005, 8, 267-282.[2] Cadars, S.; Mifsud, N.; Lesage, A.; Epping, J. D.; Hedin, N.; Chmelka, B. F.; Emsley, L. J. Phys. Chem. C 2008, 112, 9145–9154.[3] Cadars, S.; Brouwer, D. H.; Chmelka, B. F. Phys. Chem. Chem. Phys. 2009, 11, 1825-1837.[4] Brouwer, D. H. J. Am. Chem. Soc. 2008, 130, 6306-6307.
3:30 PM - Y12.4
Nanosheet Lighting: Rare-earth Photoactivated Perovskite-type Nanosheets for Lighting Applications.
Tadashi Ozawa 1 , Katsutoshi Fukuda 2 , Kosho Akatsuka 1 , Yasuo Ebina 1 , Takayoshi Sasaki 1
1 International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Ibaraki-pref., Japan, 2 , Shinshu University, Ueda, Nagano-pref., Japan
Show Abstract
Some of the layered oxides can be delaminated into individual layers by soft-chemical reactions. Such 2D crystalline materials, known as "oxide nanosheets," have a few nanometer thickness and several micrometer lateral size. Because of this unique morphology, they exhibit variety of new and enhanced properties, which are not observed in bulk materials. We have successfully prepared several perovskite-type nanosheets that are photoactivated using rare-earth ions by exfoliating layered compounds such as Li2La2/3-xEuxTa2O7. Photoluminescence characterization results of several newly synthesized perovskite-type nanosheet phosphors indicate that these nanosheet phosphors have enhanced photoluminescence emission via host excitation with respect to that in there bulk precursors. In addition, host structure dependence of emission colors has been observed.
These nanosheet phosphors are obtained as a colloidal suspension, and they can be used as phosphor paint. Because of its sheet-like morphology, when such nanosheet phosphor paint is applied onto a flat substrate, all the nanosheets in the paint align perfectly parallel to the substrate. This ordered alignment of the phosphor component yields good transparency in visible light. Such transparency is quite important for their utilization in wavelength conversion applications such as a color conversion filter for LED where minimization of the attenuation of the excitation and emission light is important. This kind of utilization of nanosheets in the form of paint is quite useful when the desired physical properties for the applications require more than nano-scale quantity of the materials. In addition, device fabrication methods such as bubble jet and screen printing are expected to become available for the paint form of the materials.
Furthermore, we have succeeded in fabricating a densely packed monolayer film of these nanosheet phosphors using Langmuir-Blodgett and layer-by-layer deposition methods. Utilizing these techniques, fabrication of a nano-device can be realized by combining such a nano-phosphor film with films of previously reported many kinds of oxide nanosheets with various practical properties, such as high-k, photochromism, photocatalicity, metallic electrical conductivity and ferroelectricity.
The concept of new nanosheet-based phosphor design, so called "nanosheet lighting" is presented along with preparation and characterization of the new perovskite-type nanosheet phosphors.
3:45 PM - Y12.5
Stable Superconducting Niobium Ultrathin Films.
Cecile Delacour 1 , Luc Ortega 1 , Marc Faucher 2 , Thierry Crozes 1 , Thierry Fournier 1 , Bernard Pannetier 1 , Vincent Bouchiat 1
1 , Institut Néel, CNRS-Université Joseph Fourier-Grenoble INP, Grenoble, 38042, France, 2 , IEMN-CNRS UMR 8520, Villeneuve d’Ascq , 59652, France
Show AbstractSuperconductivity has been recently shown to survive down to extremely confined nanostructures such as metal monolayers (1) or clusters made of few organic molecules (2). While these structures are extremely interesting to probe the ultimate limits of superconductivity, their studies are limited to in-situ measurements. Preserving a superconducting state in ultrathin films that can be processed by state-of-the-art nanofabrication techniques and withstand multiple cooling cycles remains technologically challenging and is timely for quantum devices applications.Elaborating ultrathin time and air stable superconducting films is valuable for quantum device fabrication. An ultrathin film improves the sensitivity of single particle detectors (either based on bolometric, kinetic inductance, or hot spot diffusion effects). These quantum detectors are highly demanded for astrophysics or quantum cryptography applications (3). Here we report on a combined structural and electronic analysis performed on sub-10 nm thick niobium films evaporated in ultra-high vacuum on atomically flat R-plane sapphire wafers. By reducing the thickness from 10nm down to 2nm, we demonstrate a structural transition from single crystal to a mosaic poly-crystal, which precede the onset of a superconducting to metallic transition. The transition is discussed with the framework of the Finkelstein theory for weak disorder in homogeneous superconductors (4). We investigate inverse proximity effects (5) induced by the interfaces that could be involved in the depression of superconductivity.3nm-thick films provide a reliable material to make air and time stable superconducting nanostructures. To illustrate the possibility to obtain stable nanostructures using our technique, the 3-nm-thick (9 ML) Nb-thick superconducting film has been patterned using conventional Deep-UV photolithography followed and AFM nanolithography leading to nanometer scaled superconducting quantum interferometer devices.(1) Zhang, T. et al. Superconductivity in one-atomic-layer metal films grown on Si(111). Nature Phys. 6, 104-108 (2010).(2) Clark, K. et al. Superconductivity in just four pairs of (BETS)2GaCl4 molecules. Nature Nanotech. 5, 261–265 (2010).(3) Annunziata, A.J. et al. Niobium superconducting nanowire single-photon detectors. IEEE Trans. Appl. Superconductivity 19, 327-331 (2009).(4) A.M. Finkel'stein. Suppression of superconductivity in homogeneously disordered systems. Physica B 197, 636-648 (1994).(5) McMillan, W.L. Tunnelling Model of the Superconducting Proximity Effect. Phys. Rev. 175, 537-542 (1968).
4:30 PM - Y12.6
Surface States of Three-Dimensional Topological Insulators: How Robust are They?
Bhagawan Sahu 1 , Jiwon Chang 1 , Priyamvada Jadaun 1 , Leonard Register 1 , Sanjay Banerjee 1 , Allan MacDonald 2
1 Microelectronics Research Center, University of Texas, Austin, Texas, United States, 2 Department of Physics, University of Texas, Austin, Texas, United States
Show AbstractThis talk will focus on theoretical studies of surface state properties of Bi-based binary, its ternary counterpart and the Thallium (Tl)-based ternary topological insulators and their sensitivity in presence of different chemical environments and the film size. We consider oxide dielectrics and ‘white graphene’ are two representative chemical systems for interfacial properties and predict the interface asymmetry driven breaking of topological features of the surface states. The role of point defects in the bulk as well as on the surface in affecting the topological features will be discussed.
4:45 PM - Y12.7
Colloidal Synthesis of Chalcogenide Nanosheets of Controlled Dimensions.
Benoit Mahler 1 , Sandrine Ithurria 1 , Benoit Dubertret 1
1 , ESPCI Paristech, Paris France
Show AbstractConfined nanostructures exhibit new properties compared to their bulk counterparts. As the size decrease, we can assist to a modification of their magnetic, electronic or optical characteristics. For almost thirty years, the field of semiconductor colloidal synthesis has attracted a lot of attention. Following the synthesis of spherical quantum dots, we are able today to grow a multiplicity of shapes ranging from rods to platelets through tetrapods and octopods.Here we report a new class of nanostructures that appears as colloidal nanosheets. Such nanostructures can be synthesized in CdSe, CdS and CdTe. Surprisingly, we are able to perfectly control the thickness which is atomically defined up to 10 monolayers thick. Modifying the synthetic parameters allow us to control the thickness and the shape of the sheets. We are furthermore able to laterally extent these nanosheets from 10nm to more than 1µm using a slow injection pathway. These objects are stabilized with fatty carboxylic acid such as myristic acid or oleic acid preventing aggregation.These structures in between molecules and bulk semi-conductors present a one dimensional confinement only, due to their thinness compared to their lateral dimensions. These new type of confinement induces a very sharp fluorescence emission, with a full width half maximum of the order of kT at room temperature. Furthermore, their emission lifetime is very short, on the order of the nanosecond. Finally, the fluorescence quantum yield of these nanosheets can be more than 30%.For the first time, we are able to synthesize semiconductor nanosheets using a colloidal chemistry pathway. The materials currently obtainable are CdS, CdSe and CdTe. The lateral dimensions of these objects as well as their thickness can be controlled using different synthetic schemes. The surface chemistry can also be modified to some extent. We believe that such objects are very promising for applications ranging from solar-cells to lasers. Electronic characterizations of a single nanosheet are currently under investigation.
5:00 PM - Y12.8
``Pseudo-Superlattices” of Bi2Te3 Topological Insulator Films with Enhanced Thermoelectric Performance.
Vivek Goyal 1 , Desalegne Teweldebrhan 1 , Alexander Balandin 1
1 Nano-Device Laboratory, Department of Electrical Engineering and Materials Science and Engineering Program, Bourns College of Engineering, University of California, Riverside, Riverside, California, United States
Show AbstractIt was recently suggested theoretically that atomically thin films of Bi2Te3 topological insulators (TIs) have strongly enhanced thermoelectric figure of merit ZT [1]. We used the “graphene-like” process to exfoliate Bi2Te3 thin films [2]. Since any practical application of thermoelectric nanostructures requires a sufficient volume of the material, we fabricated “pseudo-superlattices” (non-periodic) structures by mechanical stacking of the exfoliated single-crystal Bi2Te3 films followed by the thermal treatment [3]. We experimentally measured the thermal conductivity of these “pseudo-superlattices” using two techniques: “hot disk” and “laser flash”. The room-temperature in-plane and cross-plane thermal conductivity of the stacks decreased by a factor of ~2.4 and 3.5 respectively as compared to that of bulk. The strong decrease of the thermal conductivity with preserved electrical properties translated to ~140-250% increase in ZT at RT. We attributed the thermal conductivity reduction to the strong phonon scattering at the interfaces between the individual Bi2Te3 layers. It is expected that the film thinning to few-quintuples and tuning of the Fermi level can help in achieving the topological-insulator surface transport regime with an extraordinary thermoelectric efficiency predicted theoretically [1]. In this presentation, we will also report the results of our experiments with tuning the carrier concentrations in such stacked structures with an external gate [4]. The role of the interface quality on the value of the thermal conductivity and ZT will be discussed in details. The work at UCR was supported, in part, by SRC – DARPA through FCRP Center on Functional Engineered Nano Architectonics (FENA). [1] F. Zahid and R. Lake, arXiv: 1009.4512[2] D. Teweldebrhan, V. Goyal and A.A. Balandin, Exfoliation and characterization of bismuth telluride atomic quintuples and quasi-two-dimensional crystals, Nano Lett., 10, 1209 (2010); D. Teweldebrhan, V. Goyal, M. Rahman and A.A. Balandin, Atomically-thin crystalline films and ribbons of bismuth telluride, Appl. Phys. Lett., 96, 053107 (2010). [3] V. Goyal, D. Teweldebrhan and A.A. Balandin, "Mechanically-exfoliated stacks of thin films of Bi2Te3 topological insulators with enhanced thermoelectric performance," Appl. Phys. Lett., 97, 133117 (2010).[4] For details, visit Balandin group web-site: http://ndl.ee.ucr.edu
5:15 PM - Y12.9
Crystal Symmetry Breaking in Bi2Te3, Bi2Se3 and Related Thin Films: Applications in Raman Nanometrology of Topological Insulators.
Khan Shahil 1 , Md. Zahid Hossain 1 , Desalegne Teweldebrhan 1 , Alexander Balandin 1 2
1 Electrical Engineering, University of California, Riverside (UCR), Riverside, California, United States, 2 Materials Science and Engineering, University of California, , Riverside, California, United States
Show AbstractTopological insulators (TI) are materials with an insulating gap exhibiting quantum-Hall-like behavior in the absence of a magnetic field. It was suggested that TIs can be used for realization of the quantum computing because TIs contain surface states that are topologically protected against scattering by time-reversal symmetry. TI thin films were also proposed for applications in thermoelectrics [1]. We have recently demonstrated a “graphene-like” mechanical exfoliation of the atomically-thin single-crystal films [2] of bismuth telluride (Bi2Te3). It was shown that a bulk Bi2Te3 and Bi2Se3 crystals can be cleaved into films with the thickness down to ~1 nm, which corresponds to a single quintuple (five atomic planes). We have also took the graphene analogy further and proposed the use of micro-Raman spectroscopy as a robust nanometrology tool for identification of few-quintuple layer (FQL) films of Bi2Te3 and other TI materials [3]. Here we show that the technique, originally proposed by us [3], can be readily extended to other quasi-2D TI films. It also allows for the film quality control. The detail micro-Raman investigation was carried out for Bi2Te3 and Bi2Se3 films with the thickness ranging from a few-nm to bulk limit. It was found that the optical phonon mode A1u, which is not-Raman active in bulk Bi2Te3, appears in the atomically-thin films due to the crystal-symmetry breaking at the film-substrate interface. The intensity ratios of the out-of-plane A1u and A1g modes to the in-plane Eg mode grow with the decreasing film thickness. The calibrated evolution of the Raman peaks with the changing film thickness can be used for identification of FQL important for TI and thermoelectric applications. We extended the method to other materials of the bismuth telluride family, e.g. Bi2Se3, Sb2Te3 [4]. This work was supported, in part, by SRC – DARPA through FCRP Functional Engineered Nano Architectonics (FENA) center. [1] V. Goyal, D. Teweldebrhan and A.A. Balandin, "Mechanically-exfoliated stacks of thin films of Bi2Te3 topological insulators with enhanced thermoelectric performance," Appl. Phys. Lett., 97, 133117 (2010).[2] D. Teweldebrhan, V. Goyal and A.A. Balandin, "Exfoliation and characterization of bismuth telluride atomic quintuples and quasi-two-dimensional crystals," Nano Lett., 10, 1209 (2010).[3] K.M.F. Shahil, M.Z. Hossain, D. Teweldebrhan and A.A. Balandin, "Crystal symmetry breaking in few-quintuple Bi2Te3 films: Nanometrology of topological insulators," Appl. Phys. Lett., 96, 153103 (2010). [4] For details visit Balandin group web-site: http://ndl.ee.ucr.edu
5:30 PM - Y12.10
Thermoelectric Figure of Merit of Quintuple Layer Bi2Te3.
Ferdows Zahid 1 , Roger Lake 1
1 Electrical Engineering, University of California Riverside, Riverside, California, United States
Show AbstractMotivated by recent experimental results [1], we derive the thermoelectric parameters of a Bi2Te3 film of one quintuple layer thickness. Our results show approximately ten times increase in the figure of merit (ZT) for the thin film (ZT = 7.2) compared to that for the bulk (ZT = 0.68). The large enhancement in ZT results from the change in the distribution of the valence band density of modes brought about by the quantum confinement in the thin film. Our theoretical model uses ab initio electronic structure calculations as implemented in the VASP software package combined with a Landauer approach for calculating the linear-response transport coefficients. We employ two fitting parameters: a rigid shift of the conduction and valence bands to match the known bulk bandgap (i.e. a ‘scissors operator’), and an energy independent electron mean free path for the phonon scattering inside the device. With these two fitting parameters, our results show excellent agreement with the known experimental values for bulk Bi2Te3. [1] D. Teweldebrhan, V. Goyal and A. A. Balandin, Nano Lett. v.10, 1209 (2010); D. Teweldebrhan, V. Goyal, M. Rahman, and A. A. Balandin, Appl. Phys. Lett. v.96, 053107 (2010); Y. Zhang et al., Nat. Phys. v.6, 584 (2010).