Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session J37: Focus Session: Graphene Growth on Cu Substrates |
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Sponsoring Units: DMP Chair: Zachary Robinson, U.S. Naval Research Laboratory Room: 705/707 |
Tuesday, March 4, 2014 2:30PM - 2:42PM |
J37.00001: Novel Growth Mechanism of Low-Temperature-Grown Graphene by Plasma-Enhanced Chemical Vapor Deposition (PECVD) Chen-Chih Hsu, David Boyd, Wei-Hisang Lin, Nai-Chang Yeh We show a one-step method that employs PECVD for rapidly producing superior quality, large-area ($\sim$ 1 cm$^{2})$, monolayer graphene on Cu at low temperature (LT). The key to our approach is that deposition of high-quality graphene on Cu can be achieved through balancing carbon deposition by methyl radicals with etching of amorphous carbon by atomic hydrogen, while concurrently preparing the Cu surface for growth by cyano radicals. We find that removal of Cu always accompanies graphene growth, as evidenced by the presence of Cu deposits on the quartz tube and sample holder for each successful growth. We are also able to fabricate monolayer graphene by PECVD growth in 3 minutes. Even if the growth time is increased to 20 minutes, we still observe monolayer instead of multilayer graphene, suggesting that the growth mechanism differs from high-temperature CVD grown graphene. Electrical mobility determined by the field-effect-transistor configuration exhibits consistently high values, up to 60,000 cm$^{2}$/V-s on BN at 300K, exceeding the best values reported for thermal-CVD graphene on BN. Our findings suggest a promising pathway to large-scale, superior-quality and one-step inexpensive graphene fabrication for scientific research and technological applications. [Preview Abstract] |
Tuesday, March 4, 2014 2:42PM - 2:54PM |
J37.00002: Electronic and Atomic-Scale Properties of Ultraflat CVD Graphene Christopher Gutierrez, Ethan Rosenthal, Ali Dadgar, Lola Brown, Edward Lochocki, Kyle Shen, Jiwoong Park, Abhay Pasupathy Chemical vapor deposition (CVD) growth on copper foils has proven to be a reliable and cost-effective method for the production of graphene. However, most films grown by this method suffer from misoriented graphene grains as well as topographic roughness due to the polycrystallinity of the underlying copper foil substrate. Recent methods of copper foil treatment have allowed for the growth of graphene predominantly on large single crystal Cu(111) facets. In this talk we discuss scanning tunneling microscope (STM) measurements on such samples that reveal large terraces and atomically-resolved images that allow us to analyze the graphene-copper interaction during the growth. Scanning tunneling spectroscopy (STS) measurements and mapping are further employed to probe the electronic interaction between the graphene and copper substrate. [Preview Abstract] |
Tuesday, March 4, 2014 2:54PM - 3:06PM |
J37.00003: Influence of Substrate Orientation on the Growth of Graphene on Cu Single Crystals Tyler R. Mowll, Zachary R. Robinson, Parul Tyagi, Eng Wen Ong, Carl A. Ventrice, Jr. A systematic study of graphene growth on on-axis Cu(100) and Cu(111) single crystals oriented within 0.1$^{\circ}$ from the surface normal and a vicinal Cu(111) crystal oriented 5$^{\circ}$ off-axis has been performed. Initial attempts to grow graphene by heating each crystal to 900 $^{\circ}$C in UHV, followed by backfilling the chamber with C$_{2}$H$_{4}$ at pressures up to 5 x 10$^{-3}$ Torr did not result in graphene formation on either the on-axis Cu(100) or on-axis Cu(111) surfaces. For the vicinal Cu(111) surface, epitaxial graphene was formed under the same growth conditions. By backfilling the chamber with C$_{2}$H$_{4}$ before heating to the growth temperature, epitaxial graphene was formed on both the on-axis Cu(100) and off-axis Cu(111) surfaces, but not the on-axis Cu(111) surface. By using an argon overpressure, epitaxial overlayers could be achieved on all three Cu substrates. These results indicate that the most catalytically active sites for the dissociation of ethylene are the step edges, followed by the Cu(100) terraces sites and the Cu(111) terrace sites. The need for an argon overpressure to form graphene the on-axis Cu(111) surface indicates that the Cu sublimation rate is higher than the graphene growth rate for this surface. [Preview Abstract] |
Tuesday, March 4, 2014 3:06PM - 3:18PM |
J37.00004: Chemical vapor deposition growth of large grapheme single crystal from ethanol Xiao Chen, Pei Zhao, Shohei Chiashi, Shigeo Maruyama Ethanol as a precursor has proven effective in the chemical vapor deposition (CVD) synthesis of graphene on both Ni foils and Cu capsule substrates. For applications of graphene in field effect transistors or as transparent conducting electrodes, larger singe-crystal graphene without any grain boundaries shows superior electrical performance and has attracted enormous interests. Here we report a protocol to synthesize large graphene single crystals (up to 600 $\mu $m) using ethanol as precursor on commercially-available polycrystalline Cu foils. We explored the mechanism by studying the influences of different growth parameters such as pressure, flow rate and temperature. Low partial pressure and low flow rate of ethanol is essential in achieving low nucleation density over the metal surface and therefore large graphene grains can be obtained. We found that growth temperature dramatically affects the crystallinity and the growth rate of graphene grains. Moreover, this CVD growth of large graphene single crystals involves no electro-polishing or annealing treatments to the metal surface, presenting a significant simplification to the current graphene synthesis process. [Preview Abstract] |
Tuesday, March 4, 2014 3:18PM - 3:30PM |
J37.00005: Large Single-Crystal Graphene Growth on Copper: The Role of Oxygen Yufeng Hao, M.S. Bharathi, Lei Wang, Yuanyue Liu, Hua Chen, Shu Nie, Xiaohan Wang, Harry Chou, Cheng Tan, Babak Fallahazad, Hariharaputran Ramanarayan, Emanuel Tutuc, Boris I. Yakobson, Kevin F. McCarty, Yong-Wei Zhang, Philip Kim, James Hone, Luigi Colombo, Rodney S. Ruoff Graphene grown by CVD on Cu is enabling fundamental studies and applications. However, growth of high quality single crystals with controlled domain size and morphology has not been achieved, implying unknown or uncontrolled growth parameters. We discovered that oxygen on the Cu surface not only decreases the graphene nucleation density but also accelerate graphene domain growth and affect the domain shapes. SEM, EBSD, Raman, and LEED were used to characterize and analyze the graphene domains under the effects of oxygen. First-principles calculations and phase-field simulations provide deeper insight into the proposed growth mechanisms. Finally, electric- and magneto-transport measurements show that the graphene quality is comparable to mechanically exfoliated graphene, in spite of being grown in the presence of oxygen. [Preview Abstract] |
Tuesday, March 4, 2014 3:30PM - 3:42PM |
J37.00006: Influence of Chemisorbed Oxygen on the Growth of Graphene on Cu(100) by Chemical Vapor Deposition Eng Wen Ong, Tyler R. Mowll, Parul Tyagi, Carl A. Ventrice, Jr., Zachary R. Robinson, D. Kurt Gaskill, Heike Geisler The growth of graphene by catalytic decomposition of ethylene in a UHV chamber on both a clean Cu(100) surface and a Cu(100) surface predosed with a layer of chemisorbed oxygen has been studied. The crystal structure of the graphene films was characterized with in-situ LEED. By heating the clean Cu(100) substrate from room temperature to the growth temperature in ethylene, epitaxial graphene films were formed. The crystal quality was found to depend strongly on the growth temperature. At 900 $^{\circ}$C, well-ordered two-domain graphene films were formed. Predosing the Cu(100) surface with a chemisorbed layer of oxygen before graphene growth was found to adversely affect the crystal quality of the graphene overlayer by inducing a much higher degree of rotational disorder of the graphene grains with respect to the Cu(100) substrate. The growth morphology of the graphene islands during the initial stages of nucleation was monitored with ex-situ SEM. The nucleation rate of the graphene islands was observed to drop by an order of magnitude by predosing the Cu(100) surface with a chemisorbed oxygen layer before growth. Therefore, the presence of oxygen during graphene growth affects both the relative orientation and average size of grains within the films grown on Cu(100) substrates. [Preview Abstract] |
Tuesday, March 4, 2014 3:42PM - 4:18PM |
J37.00007: Physics and applications of novel structures with CVD graphene: edges, grain boundaries, twisted bilayers, and hybrids Invited Speaker: Yong P. Chen In this talk, I will discuss experimental studies (including electronic transport, optical/Raman, and STM) of physical properties of various novel synthetic graphene structures formed in CVD graphene grown on Cu, including edges of graphene single crystals, grain boundaries between such single crystals, and twisted bilayer graphene. Such synthetic graphene structures could be used as playground to explore novel physics and engineer new functionalities in graphene based electronic devices. Furthermore, I will discuss graphene based ``hybrid'' materials combining CVD graphene with semiconductor and metallic nanostructures for potential optoelectronic and plasmonics applications. [Preview Abstract] |
Tuesday, March 4, 2014 4:18PM - 4:30PM |
J37.00008: Steps in Cu(111) thin films affect graphene growth kinetics David L. Miller, Will Gannett, Mark W. Keller The kinetics of chemical vapor deposition of graphene on Cu substrates depend on the relative rates of C diffusion on the surface, C attachment to graphene islands, and removal of C from the surface or from graphene islands by etching processes involving H atoms. Using Cu(111) thin films with centimeter-sized grains [1], we have grown graphene under a variety of conditions and examined the edges of graphene islands with SEM and AFM. The Cu surface shows a series of regular steps, roughly 2~nm in height, and the graphene islands are diamond-shaped with faster growth along the edges of Cu steps. In contrast, growth on polycrystalline Cu foils under the same conditions shows hexagonal graphene islands with smooth edges. \\[4pt] [1] D. L. Miller, M. W. Keller, J. M. Shaw, K. P. Rice, R. R. Keller, and K. M. Diederichsen, ``Giant secondary grain growth in Cu films on sapphire,'' AIP Advances, vol. 3, p. 082105, 2013. [Preview Abstract] |
Tuesday, March 4, 2014 4:30PM - 4:42PM |
J37.00009: Synthesis of Bilayer and Trilayer Graphene with Different Stacking Orders Luyao Zhang, Anyi Zhang, Bilu Liu, Han-Wen Cheng, Chongwu Zhou We report the growth of bilayer and few layer graphene with different multilayer morphologies and stacking orders. The synthesis was performed by ambient pressure chemical vapor deposition at low methane concentrations. The shape of the monolayer graphene region was hexagon. The few layer graphene regions had different shapes either in the center or at the edge of the monolayer. The grain size of the hexagonal graphene was enlarged with Cu foil pretreatment and annealing. Raman spectra and selected area electron diffraction at the few layer graphene regions revealed the stacking order. Under different growth conditions, both Bernal and twisted stacking order were observed, and different growth mechanism was proposed. [Preview Abstract] |
Tuesday, March 4, 2014 4:42PM - 4:54PM |
J37.00010: A Comparative Study of Graphene and h-BN Growth on Cu(100) based on DFT Calculations Wei Chen, Lei Liu, Gong Gu, Zhenyu Zhang Using density functional theory (DFT) calculations, we carry out a comparative study of the epitaxial growth of graphene and hexagonal boron nitride (h-BN) on Cu(100) foils. We first show that van der Waals interactions play an important role in stabilizing the h-BN islands as they are nucleated on the metal substrate, similar to the physical picture from our previous study of graphene nucleation on Cu(111). By exploring the atomic structures of characteristic graphene and h-BN islands, we reveal the contrasting behavior between the orientations of graphene and h-BN clusters on the Cu(100) substrate, and correlate the differences with the differences in bond strength. We further advance the understanding on the spatial orientation at the nucleation stage to grain boundary (GB) formation, and provide insights in explaining the characteristic angle distribution of the GBs in graphene growth on Cu foils. The present theoretical study clearly explains our experimental observations, and may prove to be instrumental in modifying growth methods for large-scale fabrication of high-quality graphene and h-BN without GBs. [Preview Abstract] |
Tuesday, March 4, 2014 4:54PM - 5:06PM |
J37.00011: ABSTRACT WITHDRAWN |
Tuesday, March 4, 2014 5:06PM - 5:18PM |
J37.00012: Low Temperature Synthesis of Graphene on Cu(111) from CH4 via Chemical Vapor Deposition Robert Jacobberger, Feng Xu, Meng-Yin Wu, Michael Arnold We report the low temperature CVD synthesis of high-quality, monolayer graphene on epitaxial Cu(111) thin films. The growth temperature of 750 $^{\circ}$ C used in this work is around 150 $^{\circ}$C lower than previous reports of continuous graphene growth using CH4 as the carbon precursor. Conditions that yield continuous films on Cu(111) result in sub-monolayer coverage on Cu(110) and Cu(100). This demonstrates that Cu(111) is a more effective graphene catalyst than Cu(100), which is predominately used in literature. The single crystal orientation of the Cu(111) thin films allows us to control the graphene orientation over large areas. Field effect measurements show ambipolar carrier behavior and electron and hole mobilities of 2500 cm$^{2}$/Vs. The Dirac point is near 0 V and the sheet resistance is 2 k$\Omega $/$\Box$. Raman imaging reveals a negligible D:G ratio, indicating a low level of defects in these samples. We find that the graphene becomes more defective on all Cu facets with increasing growth rate. Optical transmittance of 97{\%} over the visible spectrum confirms that the graphene is monolayer. This low temperature synthesis will help enable industrial scale fabrication of high-quality, continuous graphene films. [Preview Abstract] |
Tuesday, March 4, 2014 5:18PM - 5:30PM |
J37.00013: Atomistic Processes in Self-Assembly of Millimeter-Sized Conducting Graphenne on Cu(111) Ping Cui, Hongbin Zhu, Jin-ho Choi, Qiang Zhang, Xiaoxia Li, Fangfei Ming, Zhenyu Li, Jinlong Yang, Changgan Zeng, Zhenyu Zhang In a latest study, we have fabricated a new two-dimensional material which we call graphenne, consisting of perfectly ordered N dopants in a graphene matrix. Due to the doped electrons and the ordered nature of the N dopants, the newly discovered graphenne is a highly conducting crystal possessing superb electronic properties. Using density functional theory calculations, here we investigate the atomistic processes in the fabrication of graphenne on Cu(111) using molecular precursors, and reveal the elegant concerted roles played by the London dispersion, chemical, and screened Coulomb repulsive forces in enhancing molecule-substrate binding, facilitating easy detachment of the terminating atoms, and dictating the overall orientation of the remaining radicals, respectively. Furthermore, in contrast to graphene growth, the ordered N atoms anchor the selection of a single orientation relative to the substrate, effectively suppressing the creation of orientational disorders such as grain boundaries as the islands coalesce to form graphenne samples as large as the millimeter-sized Cu(111) substrate. These findings are directly compared with experimental observations. [Preview Abstract] |
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