Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Z16: Focus Session: Graphene - Growth |
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Sponsoring Units: DMP Chair: Anthony Boyd, Naval Research Laboratory Room: 101AB |
Friday, March 6, 2015 11:15AM - 11:27AM |
Z16.00001: First-Principles Simulations for the Initial Stage of Graphene Growth Induced by Si Sublimation from Stepped SiC Surface Youky Ono, Takahiro Yamasaki, Takahisa Ohno An epitaxial graphene sheet can be obtained by heat sublimation of Si atoms from the stepped SiC surface. Although this method is expected as one of the most encouraging procedure to make clean sheets, its atomic scale growth mechanism is yet not understood in detail. In this study, the initial stage of the graphene growth processes on a stepped SiC(0001) surface are analyzed by first-principles molecular dynamics (FPMD) simulations. A first-principles calculation code ``PHASE'' [1] which is appropriate for efficient large scale parallel calculations is used. Our FPMD simulations proceed as follows. Before the start, some of the Si atoms on the top layer are intentionally removed from the initial SiC substrate to emulate the Si heat sublimation. MD is executed for 1 psec. under the condition of high temperature and then relaxed. Next, additional Si atoms are removed from the 2nd top layer, and then the same MD is repeated again. We tracked the behaver of the redundant C atoms during the series of these procedures. Where, when and how do those C atoms start to re-create the new C-C networks will be discussed in detail by comparing the results from several different patterns of the SiC substrates. \\[4pt] [1] http://www.ciss.iis.u-tokyo.ac.jp/english/project/device/. [Preview Abstract] |
Friday, March 6, 2015 11:27AM - 11:39AM |
Z16.00002: Energy Efficient Growth of Epitaxial Graphene on Hexagonal SiC Surface with Molybdenum Plate Capping during UHV Annealing Kibog Park, Han Byul Jin, Youngeun Jeon, Sungchul Jung, Vijayakumar Modepalli, Hyung-Joon Shin, Jung-Woo Yoo, Sung Youb Kim, Soon-Yong Kwon, Hyun Suk Kang, Byung Cheol Lee, Jae-Hyeon Ko, Daejin Eom The quality of epitaxial graphene (EG) grown on a hexagonal SiC substrate is found to be improved greatly by capping the surface with a molybdenum plate (Mo-plate) during UHV annealing. The significant reduction of D-peak and increase of 2D-peak in the measured Raman spectra, compared with the spectra for no capping, confirm the crystallinity enhancement of EG film grown with Mo-plate capping. Mo-plate capping is considered to induce heat accumulation on SiC surface by thermal radiation mirroring and raise Si partial pressure near surface by confining the sublimated Si atoms between SiC substrate and Mo-plate. These two phenomena can cooperatively facilitate an environment favorable for growing high-quality EG films. A top-gated field effect transistor is fabricated on EG film grown on Si-face 6H-SiC surface at $\sim$ 950 degree C, showing the field effect mobility of $\sim$ 1800 cm$^{2}$/Vs. With no need to heat the entire SiC substrate to high temperature over 1300 degree C as in the conventional annealing under UHV or Ar atmosphere, the Mo-plate capping can be an efficient method to reduce energy consumption significantly in growing high quality EG films. [Preview Abstract] |
Friday, March 6, 2015 11:39AM - 11:51AM |
Z16.00003: Atomic Scale Studies of Graphene on Germanium Brian Kiraly, Robert Jacobberger, Andrew Mannix, Mark Hersam, Mike Arnold, Nathan Guisinger The successful growth of single crystal wafer-scale graphene directly on semiconducting Ge(110) substrates drastically shifted the graphene growth paradigm set in 2009. To further understand the interface between graphene and germanium, we performed ultra-high vacuum scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) experiments of graphene grown on Ge(001), Ge(110) and Ge(111) wafers. The STM studies confirm that graphene grown on the Ge(111) contains rotational disorder resulting in strongly scattering grain boundaries; conversely graphene on the Ge(110) surface demonstrates strong epitaxy. STS shows that the graphene on Ge(111) retains a nearly free-standing character. Upon \textit{in-situ} annealing, reconstructed surface domains appear underneath the graphene covering up to 90{\%} of the Ge(110) and Ge(111) surfaces. Raman spectroscopy reveals band shifts in graphene G/2D band of up to 12 cm$^{\mathrm{-1}}$/50 cm$^{\mathrm{-1}}$, attributed to substantial increase in doping from the underlying substrate. This work shows the electronic interaction between graphene and germanium is both tunable and closely related to the atomic reconfiguration of the underlying germanium surfaces. [Preview Abstract] |
Friday, March 6, 2015 11:51AM - 12:27PM |
Z16.00004: CVD growth of single-crystal monolayer graphene on H-terminated germanium surface Invited Speaker: Dongmok Whang Large-area graphene has been grown by catalytic chemical vapor deposition (CVD) on various metal substrates. However, the uniform growth of single-crystal graphene over wafer-scale areas remains a challenge toward the commercial realization of various electronic, photonic, mechanical, and other devices based upon the outstanding properties of graphene. In this talk, we present the growth of single-crystal monolayer graphene on hydrogen-terminated germanium (Ge) surface. A single-crystal Ge substrate is a promising candidate for the growth of single-crystal graphene, because of (i) its catalytic activity for the catalytic decomposition of the formation of graphitic carbon on the surface; (ii) the extremely low solubility of carbon in Ge even at its melting temperature, enabling growth of complete monolayer graphene; (iii) the anisotropic atomic arrangement of single crystal Ge surface, enabling aligned growth of multiple seeds; (iv) the availability of a large area single-crystal surface via epitaxial Ge growth on Si wafers. We observed that well-defined atomic arrangement on the single crystal Ge surface enabled aligned growth of multiple seeds which can merge to single crystal graphene. Furthermore very weak van der Waals interaction between graphene and underlying Ge surface enabled facile dry transfer of graphene and recycling the Ge/Si wafer for continuing growth. [Preview Abstract] |
Friday, March 6, 2015 12:27PM - 12:39PM |
Z16.00005: Atomistic mechanisms for bilayer growth of graphene on metal substrates Wei Chen, Ping Cui, Wenguang Zhu, Efthimios Kaxiras, Yanfei Gao, Zhenyu Zhang Epitaxial growth on metal substrates has been shown to be the most powerful approach in producing large-scale high-quality monolayer graphene, yet it remains a major challenge to realize uniform bilayer graphene growth. Here we carry out a comparative study of the atomistic mechanisms for bilayer graphene growth on the (111) surfaces of Cu and Ni, using multi-scale approaches combining first-principles calculations and rate equation analysis. We first show that the relatively weak graphene-Cu interaction enhances the lateral diffusion and effective nucleation of C atoms underneath the graphene island, thereby making it more feasible to grow bilayer graphene on Cu. In contrast, the stronger graphene-Ni interaction suppresses the lateral mobility and dimerization of C atoms underneath the graphene, making it unlikely to achieve controlled growth of bilayer graphene on Ni. We then determine the critical graphene island size beyond which nucleation of the second layer will take place. Intriguingly, the critical size exhibits an effective inverse ``Ehrlich-Schwoebel barrier'' effect. These findings allow us to propose a novel alternating growth scheme to realize mass production of bilayer graphene. [Preview Abstract] |
Friday, March 6, 2015 12:39PM - 12:51PM |
Z16.00006: Grain size control for CVD-grown single crystal mono- and bi-layer graphene Zhengtang Luo By suppressing the nucleation density during Chemical Vapor Deposition (CVD) growth, we demonstrate that the large-size single crystal monolayer and bilayer graphene can be synthesized by this method. For single layer, single crystals with diameter up to 5.9 mm, have been successfully obtained by adjusting degree of oxidation during surface treatment step and hydrogen annealing duration during growth, thereby allow us to control nucleation density and consequently to control graphene grains sizes. For bilayer growth, our main strategy is to maximize the duration that is controlled by the absorption-diffusion mechanism. With this method, sub-millimeter size single crystal bilayer graphene is also obtained. Electron transport measurement on those produced graphene has shown carrier mobility that is comparable with that of mechanical exfoliated graphene, indicating the high quality of our graphene sample. [Preview Abstract] |
Friday, March 6, 2015 12:51PM - 1:03PM |
Z16.00007: Breaking of symmetry in graphene growth on metal surfaces Vasilii I. Artyukhov, Yufeng Hao, Rodney S. Ruoff, Boris I. Yakobson Understanding and controlling the factors that define the morphology of graphene crystals is crucial for improving CVD-produced graphene quality. First-principles atomistic calculations linked to crystal growth theory have successfully explained\footnote{V. I. Artyukhov, Y. Liu, and B. I. Yakobson, \emph{Proc. Natl. Acad. Sci. U.S.A.} 109, 15136 (2012).} the striking polygonal (hexagons, dodecagons) graphene island shapes. However, more recently, islands with broken symmetry that is lower than the intrinsic symmetries of both graphene and the substrate were observed in our experiments as well as by other groups. Here we examine the effect of metal surface symmetry on graphene crystal shapes via first-principles calculations and Monte Carlo modeling, focusing primarily on Ni and Cu substrates. For equilibrium shape, edge energy variations $\delta E$ manifest in distorted hexagons with different ground-state edge structures. In growth or nucleation, energy variation enters exponentially as $\sim e^{\delta E/k_{\textrm{B}}T}$, strongly amplifying the symmetry breaking, up to completely changing the shapes to triangular, ribbon-like, or rhombic.\footnote{V. I. Artyukhov, Y. Hao, R. S. Ruoff, and B. I. Yakobson, \emph{arXiv}:1405.5799 (2014)} [Preview Abstract] |
Friday, March 6, 2015 1:03PM - 1:15PM |
Z16.00008: The effects of silicon and aluminum content in copper on the growth of CVD graphene Richard Piner, Alvin Lee, Xiaohan Wang, C. Grant Willson, Carl Magnuson, Harry Chou All commercially available copper foils suitable for CVD graphene growth contain trace impurities, with silicon and aluminum being among the most prominent. Here, the presence of these trace elements near the copper surface from a large number of suppliers was quantified via EDS. The differing amounts of silicon and aluminum are shown to have a quantifiable effect on the quality of graphene grown on the foils based on graphene domain size, ad-layer density, and structural defects density. Results of these studies will be presented along with strategies to counteract the deleterious effects of copper foils' trace element content on graphene growth. [Preview Abstract] |
Friday, March 6, 2015 1:15PM - 1:27PM |
Z16.00009: Role of Surface Termination on the Growth of Graphene on Cu Tyler R. Mowll, Eng Wen Ong, Parul Tyagi, Zachary R. Robinson, Carl A. Ventrice, Jr. Graphene growth on on-axis Cu(100) and Cu(111) substrates and a Cu(111) substrate intentionally miscut by 5$^{\circ}$ was performed to determine the effect that the substrate termination has on both the rate of carbon deposition and the crystal quality of the graphene. A CVD process using C$_{2}$H$_{4}$ was used to grow the graphene. All experiments were performed in a UHV chamber, and the surfaces were cleaned using multiple Ar sputtering and annealing cycles until the LEED demonstrated a clean surface. By heating the substrates to 900 $^{\circ}$C in UHV and then backfilling with 5 mTorr of C$_{2}$H$_{4}$, graphene could only be grown on the off-axis Cu(111) surface. This is attributed to the high vapor pressure of Cu and the low reactivity of the on-axis surfaces. By first backfilling with 5 mTorr of C$_{2}$H$_{4}$ and heating the substrate to 900 $^{\circ}$C, graphene could be grown on both the on-axis Cu(100) and off-axis Cu(111) substrates. To achieve growth on the on-axis Cu(111) substrate, an argon overpressure was used to suppress Cu sublimation. Growth of graphene at 900 $^{\circ}$C using a mixture of 5 mTorr C$_{2}$H$_{4}$ and 45 mTorr of argon produced single domain epitaxial films on the Cu(111) substrates and two domain epitaxial films on the Cu(100) substrate. [Preview Abstract] |
Friday, March 6, 2015 1:27PM - 1:39PM |
Z16.00010: Growth of Graphene by Catalytic Dissociation of Ethylene on CuNi(111) Carl A. Ventrice, Jr., Parul Tyagi, Max Golden, Tyler Mowll The growth of graphene by the catalytic decomposition of ethylene on a 90:10 CuNi(111) substrate was performed. The growths were done in a UHV system by either heating the substrate to the growth temperature followed by introducing the ethylene precursor or by introducing the ethylene precursor and subsequently heating it to the growth temperature. The growth using the former method results in a two-domain epitaxial graphene overlayer at temperatues as low as 550 $^{\circ}$C. However, introducing the ethylene before heating the substrate resulted in considerable rotational disorder within the graphene film. This has been attributed to the formation of a carbide phase below 550 $^{\circ}$C. [Preview Abstract] |
Friday, March 6, 2015 1:39PM - 1:51PM |
Z16.00011: ABSTRACT WITHDRAWN |
Friday, March 6, 2015 1:51PM - 2:03PM |
Z16.00012: 3D Epitaxy of Graphene nanostructures in the Matrix of Ag, Al and Cu Lourdes Salamanca-Riba, Romaine Isaacs, Manfred Wuttig, Melburne LeMieux, Liangbing Hu, Jaim Iftekhar, Sergey Rashkeev, Maija Kukla, Oded Rabin, Azzam Mansour Graphene nanostructures in the form ribbons were embedded in the lattice of metals such as Ag, Cu, and Al in concentrations up to 36.4 at.{\%}, 21.8 at{\%} and 10.5 at.{\%}, respectively. These materials are called covetics. Raman scattering from Ag and Al covetics indicate variations in the intensity of peaks at $\sim$ 1,300 cm$^{-1}$ and 1,600 cm$^{-1}$ with position on the sample. These peaks are associated with the D (defects) and G (graphite E$_{\mathrm{2g}}$ mode) peaks of graphitic carbon with \textit{sp2} bonding and reveal various degrees of imperfections in the graphene layers. First principles calculations of the dynamic matrix of Ag and Al covetics show bonding between C and the metal. EELS mapping of the C-K edge and high resolution lattice images show that the graphene-like regions form ribbons with epitaxial orientation with the metal lattice of Ag and Al. The temperature dependences of the resistivites of Ag and Cu covetics are similar to those of the pure metals with only slight increase in resistivity. Films of Cu covetic deposited by e-beam evaporation and PLD show higher transmittance and resistance to oxidation than pure metal films of the same thickness indicating that copper covetic films can be used for transparent electrodes. [Preview Abstract] |
Friday, March 6, 2015 2:03PM - 2:15PM |
Z16.00013: Controlled growth of large area multilayer graphene on copper by chemical vapour deposition Ismet I. Kaya, Sibel Kasap, Hadi Khaksaran, Suleyman Celik, Hasan Ozkaya, Cenk Yanik The growth of multilayer graphene on the surface of a copper foil is studied experimentally. It has been shown that the average film thickness can be controlled by the growth time with a linear trend and the growth can be extended until nearly full coverage of multilayer graphene over the copper surface. It is observed that the impurity particles on the copper surface mediate the multilayer growth. The formation of large multilayer islands is explained by a qualitative model which takes into account the interplay between the length scales governed by the molecular mean free path of gas molecules and the distribution of the impurities. [Preview Abstract] |
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