Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session M37: Focus Session: Graphene on Cu and Other Metal Substrates |
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Sponsoring Units: DMP Chair: Paul Thibado, University of Arkansas Room: 705/707 |
Wednesday, March 5, 2014 11:15AM - 11:27AM |
M37.00001: Role of catalytic metals on formation process of carbon nanotube and graphene: ab initio molecular dynamics study Yasushi Shibuta, Kohei Shimamura, Tomoya Oguri, Rizal Arifin, Wataru Hashizume, Fuyuki Shimojo, Shu Yamaguchi The growth mechanism of carbon nanotubes and graphene has been widely discussed from both the experimental and computational points of view. At the present, most of numerical studies focuses on the aggregation of isolate carbon atoms on the catalytic metal surface, whereas the initial dissociation of carbon source molecules should affect the yield and quality of the products [1]. Under such circumstance, we have investigated the dissociation of carbon source molecules on the metal surface using the ab initio molecular dynamics simulation in order to discuss the initial stage of graphene growth via a chemical vapor deposition (CVD) technique [2,3]. In the presentation, we performed the ab initio MD simulations of the dissociation process of methane on Ni(111) surface to discuss initial dissociation process of the graphene formation, and the dissociation process of ethanol on Ni32 cluster to discuss that for the carbon nanotube formation. [1] Y. Shibuta, Diamond and Related Materials, 20 (2011) 334-338. [2] Y. Shibuta, R. Arfin, K. Shimamura, T. Oguri, F. Shimojo, S. Yamaguchi , Chem. Phys. Lett. 565 (2013) 92. [3] T. Oguri, K. Shimamura, Y. Shibuta*, F. Shimojo, S. Yamaguchi, J. Phys. Chem. C 117 (2013) 9983. [Preview Abstract] |
Wednesday, March 5, 2014 11:27AM - 11:39AM |
M37.00002: CVD Growth Studies of Graphene on Cu(111) Heike Geisler, Seamus Murray, Eng Wen Ong, Zachary R. Robinson, Tyler R. Mowll, Parul Tyagi, Carl A. Ventrice, Jr. Because of its unique chemical and physical properties, graphene shows great promise for use in a wide variety of technological applications. However, Industry has not been able to widely implement the use of graphene because of the difficulty in growing low-cost, defect-free, large-area graphene films. One method of producing graphene films with a low defect density is to grow epitaxial films on single crystal substrates. A study of the growth of graphene on the Cu(111) surface in UHV was performed with methane and ethylene. With ethylene, no graphene was formed at 900 $^{\circ}$C with pressures as high as 5 mTorr. By using an Ar overpressure of 50 mTorr, single-domain epitaxial graphene films could be formed. With methane, no graphene could be formed even with an Ar overpressure. This result indicates that methane has a much lower dissociation probability on the Cu(111) surface than ethylene. In addition, the effect of predosing the surface with a chemisorbed oxygen layer was measured. The oxygen predosing was determined to adversely affect the order of the graphene grains with respect to the Cu(111) substrate. [Preview Abstract] |
Wednesday, March 5, 2014 11:39AM - 11:51AM |
M37.00003: Influence of Subsurface Hydrogen on the Structural Properties of Graphene Templates Grown on Ru(0001) Maxwell Grady, Bogdan Diaconescu, Darren Valovcin, Frank Hagelberg, Karsten Pohl Graphene has aroused tremendous interest due to its remarkable electronic and mechanical properties. Graphene's optical properties and conductance make it an ideal candidate for use in nanoelectronic devices and organic photoelectric devices. We will present a STM/LEED/DFT study of the single layer graphene on Ru(0001) system grown via a novel growth mechanism that co-adsorbs atomic hydrogen and carbon vapor to the ruthenium surface while simultaneously segregating carbon from the crystal bulk to the surface. Structural studies show a wide array of moire superlattices sizes ranging from 0.9 to 3.0 nm. DFT calculations help explain the appearance of these graphene reconstructions driven by the H presence at the Ru interface. A LEED I(V) study guided by DFT calculations will accompany the STM investigation to provide insight into the graphene layer thickness. The structural polymorphism displayed by this system is of interest for the study of directed self-assembly. Control over moire superstructure size can aid in future work using graphene as a nanotemplate for self-assembled growth of nanoelectronic and organic photovoltaic devices based on pentacenes and fullerenes. Finally the impact of the structural changes on the electronic properties of the system will be studied. [Preview Abstract] |
Wednesday, March 5, 2014 11:51AM - 12:03PM |
M37.00004: Momentum-Space Imaging of the Dirac Band Structure in Molecular Graphene via Quasiparticle Interference Anna Stephenson, Kenjiro K. Gomes, Wonhee Ko, Warren Mar, Hari C. Manoharan Molecular graphene is a nanoscale artificial lattice composed of carbon monoxide molecules arranged one by one, realizing a dream of exploring exotic quantum materials by design. This assembly is done by atomic manipulation with a scanning tunneling microscope (STM) on a Cu(111) surface. To directly probe the transformation of normal surface state electrons into massless Dirac fermions, we map the momentum space dispersion through the Fourier analysis of quasiparticle scattering maps acquired at different energies with the STM. The Fourier analysis not only bridges the real-space and momentum-space data but also reveals the chiral nature of those quasiparticles, through a set of selection rules of allowed scattering involving the pseudospin and valley degrees of freedom. The graphene-like band structure can be reshaped with simple alterations to the lattice, such as the addition of a strain. We analyze the effect on the momentum space band structure of multiple types of strain on our system. [Preview Abstract] |
Wednesday, March 5, 2014 12:03PM - 12:15PM |
M37.00005: Metal Oxide Growth, Characterization and Spin Precession Measurements in CVD Graphene Akitomo Matsubayashi, Westly Nolting, Dhiraj Prasad Sinha, Avyaya Jayanthinarasimham, Ji Ung Lee, Vincent LaBella Thin metal oxide layers deposited on graphene can be utilized as dielectric barriers between metals and graphene to help isolate a metal contact from the graphene channel. This is important for graphene based spintronic devices as dielectric layers between the ferromagnetic electrode and graphene have been shown to increase the spin relaxation time measured utilizing non-local detection and spin precession measurements by avoiding the conductivity mismatch problem. However, simply depositing metal oxide layers such as aluminum oxide on graphene results in non-uniform film lowering the quality of the interface barrier. We will present a systematic study of aluminum oxide layers grown on CVD (chemical vapor deposition) graphene under ultra-high vacuum conditions with and without titanium seed layers. The aluminum oxide layers with the 0.2 nm titanium seed layers showed reduced surface roughness. The chemical and structural composition determined by XPS (X-ray photoelectron spectroscopy) will be also presented that shows full oxidation of the aluminum and partial oxidation of the titanium. The results on the I-V and spin precession measurements in CVD graphene will be also presented. [Preview Abstract] |
Wednesday, March 5, 2014 12:15PM - 12:27PM |
M37.00006: Laser induced nanoparticles and crystals and their characterization Mohammadreza Rezaee, Robert Compton Intense nanosecond lasers are used to fabricate nanoparticles by direct laser solid interactions as well as laser produced shock wave induced crystallization in saturated solutions. In particular, laser graphite interactions under liquid nitrogen results in variety of interesting new carbon nanoclusters. In particular, exfoliation of graphite to produce graphene is considered. Laser produced shock wave in unsaturated salt (e.g. NaCl, NaClO$_{3})$ solution immediately produces thousands of tiny crystals. These nonmaterials are examined using Raman spectroscopy under liquid nitrogen, RUN), laser induced fluorescence, plasma spectroscopy, UV-Vis spectroscopy as well as conventional characterization methods such as SEM and HRTEM imaging. [Preview Abstract] |
Wednesday, March 5, 2014 12:27PM - 12:39PM |
M37.00007: Metal-catalyzed etching of graphene Guangjun Cheng, Irene Calizo, Angela Hight Walker We present a comparative investigation on the etching of graphene catalyzed by Fe and Cu. With combined evidence from scanning electron microscopy and Raman spectroscopy, we demonstrate that the strikingly different etching behaviors between Fe and Cu are governed by their distinct interactions with carbon. Due to the strong Fe-C interactions, graphene is severely damaged through not only catalytic carbon hydrogenation but also carbon dissolution into Fe alone. In contrast, due to the weak Cu-C interactions and non-wetting behavior of Cu on graphene, Cu particles etch channels in graphene through carbon hydrogenation and the width of the channel width is much narrower than the diameter of catalytic particle. This work provides unprecedented insights into the metal-catalyzed carbon hydrogenation. [Preview Abstract] |
Wednesday, March 5, 2014 12:39PM - 12:51PM |
M37.00008: Fabrication of contamination-free CVD Graphene devices using soak and peel method Abhilash Sebastian, Aniket Kakatkar, Roberto De Alba, Nikolay Zhelev, Paul McEuen, Harold Craighead, Jeevak Parpia Large area graphene-based devices are commonly fabricated by transferring the CVD grown graphene from metal foils to semiconductor substrates. However, during device fabrication, the transfer process involves chemical etching of metal that leads to the degradation of electrical properties of graphene. Recently, a clean transfer of graphene to devices with improved electrical properties, by delamination of graphene from metal substrates by soak and peel using DI-water has been demonstrated [1]. We employed the soak and peel scheme to fabricate graphene transistor arrays on a SiO$_{2}$/Si substrate with a back gate configuration. The source-drain contacts are patterned using Ti/Pt with graphene channel length varying from 2-50um. The graphene is transferred subsequently to the substrate and yields a high quality junction between metal electrodes and graphene. The contact resistance is low and the Dirac peak is observed across the array. The suitability of the graphene transistors for chemical functionalization will be presented. Possible application of this transfer technique for fabricating large area suspended nano-electro mechanical systems will be discussed. \\[4pt] [1] Priti Gupta, et al., arXiv: 1308.1587 [cond-mat.mtrl-sci] [Preview Abstract] |
Wednesday, March 5, 2014 12:51PM - 1:03PM |
M37.00009: Direct transfer of graphene onto flexible substrates Luiz Gustavo Pimenta, Yi Song, Tingying Zeng, Mildred Dresselhaus, Jing Kong, Paulo Araujo We explore the direct transfer via lamination of chemical vapor deposition graphene onto different flexible substrates. The transfer method investigated here is fast, simple, and does not require an intermediate transfer membrane, such as polymethylmethacrylate. Various substrates of general interest in research and industry were studied including polytetrafluoroethylene filter membranes, PVC, cellulose nitrate/cellulose acetate filter membranes, polycarbonate, paraffin, polyethylene terephthalate, paper, and cloth. By comparing the properties of these substrates, two critical factors to ensure a successful transfer on bare substrates were identified: the substrate's hydrophobicity and good contact between the substrate and graphene. For substrates that do not satisfy those requirements, polymethylmethacrylate can be used as a surface modifier or glue to ensure successful transfer. Our results can be applied to facilitate present processes and open up directions for applications of chemical vapor deposition (CVD) graphene on flexible substrates. A broad range of applications of CVD graphene can be envisioned, including fabrication of graphene devices for opto/organic electronics, graphene membranes for gas/liquid separation, and ubiquitous electronics with graphene. [Preview Abstract] |
Wednesday, March 5, 2014 1:03PM - 1:15PM |
M37.00010: A novel polymer-free transfer technique for high mobility graphene field effect transistors (FET) Wei-Hsiang Lin, Shang-Yi Liu, Chen-Chi Hsu, Jieh-I Taur, David A. Boyd, Chih-I Wu, Nai-Chang Yeh We demonstrate a novel polymer-free method that can routinely transfer large-area graphene to any substrates and preserve the optimal properties of as-grown samples as compared to the graphene transferred with conventional polymer-assisted methods. We have also developed a one-step method that employs plasma-enhanced chemical vapor deposition for rapidly producing superior quality, large-area, monolayer graphene on Cu at low temperature (LT). Combining these two techniques, we find excellent properties of the LT-CVD grown graphene based on studies of Raman spectroscopy, XPS, UPS and STM. We have also investigated the effect of various substrates and PMMA residuals on the performance of the LT-CVD grown graphene FETs by constructing four types of devices (graphene/SiO$_{2}$ FETs, graphene/BN FETs, PMMA residuals/ graphene/SiO$_{2}$ FETs, and PMMA residuals/graphene/BN FETs). The LT-CVD grown graphene combined with the polymer-free transfer technique has achieved an electrical mobility $\sim$ 60,000 cm$^{2}$ V$^{-1}$ s$^{-1}$, which may be further improved to approaching the ideal value of pristine graphene. [Preview Abstract] |
Wednesday, March 5, 2014 1:15PM - 1:27PM |
M37.00011: Transfer-free growth of atomically thin hexagonal boron nitride Sushant Sonde, Ning Lu, Moon Kim, Luigi Colombo, Sanjay K. Banerjee Recent interest in and hence the opportunities presented by two-dimensional materials and their stacked assemblies have necessitated growth of high quality sheets of hexagonal boron nitride (h-BN). Chemical vapor deposition on transition metals is perhaps the most promising technique for large-scale growth of single or few-layer h-BN films with relatively controllable means to produce predetermined number of layers. In most of the studies till date, it is not very clear as to why the growth is not self-limiting to a monolayer and how multilayer h-BN is grown. In this study we present growth of high quality h-BN on Nil and Co films deposited on oxidized silicon. h-BN films thus produced show excellent optical (E$_{g} =$ 5.85 eV) and electrical insulating properties (breakdown strength $=$ 7.94 MV/cm). We deliberate on the growth mechanism driven by diffusion vs. segregation of B and N, with evidence that the growth occurs via segregation of B and N from the metal films. We discuss solubility of N and B in Ni and Co films. By controlling the growth parameters we show that h-BN segregation can be achieved on both sides of the metal film, thus allowing deposition of such atomic films by a transfer free method on arbitrary substrates. [Preview Abstract] |
Wednesday, March 5, 2014 1:27PM - 1:39PM |
M37.00012: Improved synthesis of chemically derived graphene using a thermal processing step Priyank Kumar, Neelkanth Bardhan, Angela Belcher, Jeffrey Grossman The excellent physical and electronic properties of graphene have fueled the exploration of novel methods for its large-scale production and solution-processability. To this end, thermal or chemical reduction of graphene oxide (GO) represents a promising step. However, the problem of incomplete reduction and the presence of residual oxygen in reduced GO (rGO) sheets continue to persist in current reduction protocols. Here, we present a thermal processing step that improves the reduction efficiency of GO sheets, and results in superior sheet properties of chemically derived graphene. For instance, upon using the additional thermal processing step, the electronic conductivity increased by a factor of 6-8 in the reduced GO samples. Using atomistic calculations, we provide detailed insights into the physical mechanisms resulting in improved reduction. Overall, we show that our processing step can be easily integrated into current thermal and chemical reduction protocols, and could be crucial toward producing large-scale, high quality graphene. [Preview Abstract] |
Wednesday, March 5, 2014 1:39PM - 1:51PM |
M37.00013: Synthesis of Graphene Nanoribbons by Covalent Assembly of Monomers Sumit Beniwal, Mikhail Shekhirev, Timothy Vo, Donna Kunkel, Alexander Sinitskii, Axel Enders We present bottom up approach for synthesis of graphene nanoribbons on Ag (111) from monomers using scanning tunneling microscopy, photoemission, ultraviolet and Raman spectroscopy. In this study we used N-modified precursor molecules to form graphene nanoribbons by thermal evaporation on Ag (111) under UHV conditions. Of particular interest is the role of substrate temperature, which catalyses the polymerization and de-hydrogenation of the precursor molecules. The catalytic nature of the surface is demonstrated by the fact the polymerization happens only in the first layer monomers while the second layer monomers remain as individuals. The orientation of these ribbons with respect to substrate can be controlled by the structure of the monomers. Instead of lying flat on Ag (111) surface, nanoribbons form $\pi $-stacked networks and they stand up tilted with respect to substrate surface. This type of arrangement is attributed to the replacement of two carbon atoms in the precursor molecules with nitrogen atoms. Our approach not only bolsters previously demonstrated bottom up fabrication of graphene nanoribbons but also provides additional insight into manipulation of their orientation on substrate surface by modifying the edge of precursor monomers. [Preview Abstract] |
Wednesday, March 5, 2014 1:51PM - 2:03PM |
M37.00014: Graphene Superlattice Construction by Intercalation of Fullerenes at the Metal-Graphene Interface Petra Reinke, Ehsan Monazami, Gopalakrishnan Ramalingam The electronic properties of graphene can be modified through the formation of a charge or topographic superlattice, in our study this is achieved by intercalation of fullerene molecules at the interface between copper and graphene. Amorphous and crystalline superlattices can be synthesized and are controlled by annealing T (650 K to 850 K) and time. The crystalline superlattices present a square geometry defined by the Cu(001) facet and the period can be controlled by deposition conditions. The geometric and electronic structure of the superlattice is measured with STM (scanning tunneling microscopy), ST spectroscopy and differential conductivity maps. The intercalation of C60 is confirmed by (i) atomic resolution of graphene on top of molecule, (ii) spectral signature of graphene is modulated with shoulder at 250 meV, (iii) bias voltage dependence of apparent height, and (iv) depth between molecules correlates with intermolecule distance due to mechanical deformation of graphene. The crystalline layer imprints a charge superlattice with 1.5 holes/molecule donated to graphene - while the graphene is nearly neutral in between. The intercalation is a versatile method to control superlattice formation with potential for tuning charge carrier transport. [Preview Abstract] |
Wednesday, March 5, 2014 2:03PM - 2:15PM |
M37.00015: Graphene/Ni Nanocomposite Materials from First Principles Dalal K. Kanan, Chris A. Marianetti Nanocomposite materials made by alternating layers of graphene and nickel offer exciting new possibilities for light-weight, high-strength materials. To better understand these systems, we used density functional theory with dispersion to first study graphene adsorbed onto Ni(111). The results indicate strong binding at the interface and a substantial perturbation of the graphene electronic structure, consistent with previous work. We mapped out the potential energy for sliding graphene on Ni(111) along the C-C bond and find a maximum binding energy that is substantially stronger than the interlayer binding in graphite. Ni 3$d$ to graphene $\pi $* charge transfer causes the strong chemisorption; although occupation of graphene's antibonding states likely affects the C-C bond strength. Next, we studied the bulk composite material with varying Ni layer thickness. Charge density analysis shows graphene sandwiched between Ni layers accepts charge from both layers, which should enhance the binding. The computed elastic coefficients will be presented. [Preview Abstract] |
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