Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session M51: Focus Session: Beyond Graphene: Synthesis, Defects, Structure, and Properties VI |
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Sponsoring Units: DMP Chair: Fan Zhang, University of Pennsylvania Room: Mile High Ballroom 1E |
Wednesday, March 5, 2014 11:15AM - 11:27AM |
M51.00001: Edge contact to BN encapsulated graphene -- towards contamination-free 2D system Lei Wang, Cory Dean, Inanc Meric, Philip Kim, Ken Shepard, James Hone Since the first discovery in 2004, graphene has been electrically contacted by metal layers deposited on its surface. In the process, this single atomic layer sheet experiences polymers and solvents contaminations and thermal annealing. Our recent progress shows that we can metalize only the one-dimensional (1D) edge of a graphene layer in a BN/G/BN structure. In addition to outperforming conventional surface contacts, the edge contact geometry allows a complete separation of the layer assembly and contact metallization processes. For the first time, the graphene surface has never contacted any polymer or solvent contaminations, and thermal annealing is found to be unnecessary. Over 1000 um$^{\mathrm{2}}$ bubble free BN/G/BN stack is achieved and carrier mean free path on these devices are found to be over 20 um. 1 000 000 cm$^{\mathrm{2}}$/Vs carrier mobility is for the first time observed at carrier density as high as 3 X 10$^{\mathrm{12}}$/cm$^{\mathrm{2}}$. [Preview Abstract] |
Wednesday, March 5, 2014 11:27AM - 11:39AM |
M51.00002: Thermal Interface Conductance across a Graphene-BN Heterojunction Chun Chung Chen, Zhen Li, Shi Li, Stephen Cronin We deposit graphene on h-BN flakes and measure the thermal interface conductance of a graphene/h-BN interface by passing current through the graphene sheet to create Joule heating while monitoring the temperatures of the graphene and h-BN using Raman spectroscopy. During the electrical heating, the Raman G band, 2D band, and h-BN frequency downshift with the increasing of the applied power, indicating the heating in graphene and h-BN. The Raman temperature coefficient of the G band, 2D band, and h-BN frequency are calibrated by heating the device from 300K to 400K in a temperature-controlled stage, yielding values of 0.0102 and 0.0215 cm$^{-1}$/K for graphene, and 0.0246 cm$^{-1}$/K for h-BN. These electrical heating and the temperature calibration results suggest a maximum temperature gradient of 60K at the graphene/h-BN interface during the electrical heating. Multiple electrical heating experiments are conducted, showing consistent results, validating the reliability of the acquired data. From the power dependence of the temperature difference between the graphene and h-BN, we are able to establish the interface thermal conductance across the graphene/h-BN interface to be 7.41 $\pm$ 0.43 MW/m2K. [Preview Abstract] |
Wednesday, March 5, 2014 11:39AM - 11:51AM |
M51.00003: Transport Properties of Crystallographically Aligned Heterostructures of Graphene and Hexagonal Boron Nitride Peng Wang, Bin Cheng, Tengfei Miao, Oleg Martynov, Marc Bockrath Graphene and hexagonal boron nitride (hBN) heterostructures have been heavily studied due to graphene's high electronic mobility in this system. Hexagonal BN also shows possibilities to alter graphene's electronic properties. Recently several research groups have demonstrated accurate placement of graphene on hBN with crystallographic alignment[1][2][3]. Due to the resulting superlattice formed in the graphene/hBN heterostructures, an energy gap, secondary Dirac Points, and Hofstadter quantization in a magnetic field have been observed. However, many aspects of the electronic properties of graphene/hBN heterostructures remain unexplored. Using aligned layer transfer we are able to produce graphene/hBN heterostructures with ~1 degree alignment accuracy, and measure the transport properties of the resulting systems. We will discuss our latest transport data, which contribute towards a greater understanding the electron motion in the graphene/hBN interface. [1] P. A. Ponomarenko et al., Nature 497, 594-597 (2013). [2] C. R. Dean, et al., Nature 497, 598-602(2013). [3] B. Hunt, et al., Science 340, 1427(2013). [Preview Abstract] |
Wednesday, March 5, 2014 11:51AM - 12:03PM |
M51.00004: Wafer-scale integration of graphene heterojunction transistors for low-power electronics Jinseong Heo, Kyung-Eun Byun, Jaeho Lee, Hyun-Jong Chung, Sanghun Jeon, Seongjun Park, Sungwoo Hwang Recently, vertical graphene field effect transistors (VGFETs) in which graphene is combined with semiconductors including layered two-dimensional materials have attracted much attention for application in digital electronics. Work-function tunability of graphene was employed in VGFETs to modulate energy barrier between graphene and semiconductors, and therefore Ion/Ioff was dramatically increased. Here, we demonstrate wafer-scale VGFETs based on graphene-thin semiconductor-metal asymmetric junctions on a transparent 150 $\times$ 150 mm2 glass. In this system, a triangular energy barrier between the graphene and metal is designed by selecting a metal with a proper work function. We obtain a maximum Ion/Ioff up to 1,000,000 with an average of 3,010 over 2,000 devices at ambient conditions. Furthermore, an inverter that combines complementary n-type and p-type devices was demonstrated to operate at a bias of only 0.5 V. [Preview Abstract] |
Wednesday, March 5, 2014 12:03PM - 12:15PM |
M51.00005: Edge Contact to 2D materials Bo Wen, Matthew Koci, Cory Dean Electrically interfacing 3D metal electrodes to atomically thin 2D materials presents a fundamental technical challenge.~ Recently we demonstrated that metalizing along the 1D edge of graphene enables a new device topology with remarkably low contact resistance.~ Here we expand the capability of this edge-contact technique by integrating leads with complex properties, such as ferromagnetic and superconducting metals.~ Implications for realizing novel electronic behavior in 2D layered materials will be discussed. ~ ~[1] L. Wang, \textit{et al.,} One-Dimensional Electrical Contact to a Two-Dimensional Material, \textit{Science}, \textbf{342} (6158), 614-617. (2013) [Preview Abstract] |
Wednesday, March 5, 2014 12:15PM - 12:27PM |
M51.00006: First-principles Simulations of a Graphene-Based Field Effect Transistor Yun-Peng Wang, Hai-Ping Cheng We propose a first-principles method to simulate the effect of a gate voltage on a two-dimensional channel. Because of the aperiodic structure of field effect devices, we adopt the effective screening medium (ESM) method, which enables us to solve the Poisson equation with free boundary conditions, to simulate nanoscale field effect devices. With this approach, we investigated a graphene-based vertical field effect tunneling transistor with a graphene$|h$-BN$|$graphene multilayer structure. The calculated carrier density on the graphene away from the gate electrode is sublinear with respect to the gate voltage, and decreases as the thickness of the $h$-BN barrier increases. The band structure of graphene layers near the Fermi energy exhibit a $\sim 0.05 \,\mathrm{eV}$ gap opening due to interactions with $h$-BN, as well as the chemical potential difference between the two graphene monolayers. This work paves the road to first-principles simulations of nanoscale field effect transistors and opens a new avenue towards computational guided device design. [Preview Abstract] |
Wednesday, March 5, 2014 12:27PM - 12:39PM |
M51.00007: Investigation of Charge Transfer in Graphene-Based Heterostructure by Raman Spectroscopy Hui-Chun Chien, Matt Bellus, Jatinder Kumar, Hsin-Ying Chiu, T.B. Hoffman, Y. Zhang, J.H. Edgar Van der Waals heterostructures are an emerging research area in novel electronics and optoelectronics. They can be assembled layer by layer with any stacking order via precise micromechanical manipulation. Moreover, their material properties can be theoretically tailored on demand. Two interesting properties, the interfacial interaction between dissimilar layer materials and the accordingly modified bandstructure, are important; however, they are rarely studied. Herein, we take graphene-MoS$_{2}$ as an example, and we utilize the well-studied Raman fingerprint of graphene to inspect charge transfer between graphene and an adjacent material. The layer dependence of charge transfer is observed as well as the edge effect. Further fundamental understanding of this heterostructure will be presented. Our work will serve as a platform to study the band alignment of graphene-based heterostructures. [Preview Abstract] |
Wednesday, March 5, 2014 12:39PM - 12:51PM |
M51.00008: Synthesis of white graphene (h-BN) from polymeric precursors and its physical properties Myung Jong Kim, Sungchan Park, Hyunjin Cho, Byung Soo Lee Large area and high quality white graphene (h-BN, hexagonal boron nitride) has been effectively synthesized from borazine oligomer on Ni catalysts. Synthetic methods for white graphene only included spin coating and subsequent annealing steps, and the thickness of white graphene was controlled with variation of spin coating speed. Characterization methods such as TEM, SAED, XPS, Raman, and EELS revealed highly crystalline boron nitride structures with stoichiometric B/N ratio close to 1. Catalytic activity of Ni catalyst for the phase conversion reaction through crosslinking and BN crystallization was clearly demonstrated and proper mechanism was suggested. Considering thermal conductivity and capacitance measured from this white graphene, it has potential applications such as gate dielectric layers for graphene, and thermal management coatings. [Preview Abstract] |
Wednesday, March 5, 2014 12:51PM - 1:03PM |
M51.00009: Nanoscale Capacitors Composed of Graphene and Boron Nitride Layers: Size Effects at Small Separation V. Ongun Ozcelik, Salim Ciraci A nanoscale dielectric capacitor model consisting of two-dimensional, hexagonal h-BN layers placed between two commensurate and metallic graphene layers is investigated using self-consistent field density functional theory. The separation of equal amounts of electric charge of different sign in different graphene layers is achieved by applying electric field perpendicular to the layers. The stored charge, energy, and the electric potential difference generated between the metallic layers are calculated from the first-principles for the relaxed structures. Predicted high-capacitance values exhibit the characteristics of supercapacitors. The capacitive behavior of the present nanoscale model is compared with that of the classical Helmholtz model, which reveals crucial quantum size effects at small separations, which in turn recede as the separation between metallic planes increases. [Preview Abstract] |
Wednesday, March 5, 2014 1:03PM - 1:15PM |
M51.00010: SPM Study and Growth Mechanism of Graphene Directly CVD-Grown on h-BN Film Young Jae Song, Minwoo Kim, Qinke Wu, Joohyun Lee, Sungjoo Lee, Min Wang We present our Scanning Tunneling Microscopy (STM)/Spectroscopy (STS) and Kelvin Probe Force Microscope (KPFM) study for graphene directly CVD-grown on h-BN film. High resolution STM image shows perfect honeycomb lattice structure of graphene on top surface and Moir\'{e} pattern indicating the structural interference patter with the underlying h-BN crystal. Non-disturbed electronic structure of graphene on h-BN film is also confirmed by spatially-resolved STS measurements, which show very sharp and symmetric V shape with a Dirac point at Fermi level. To confirm the graphene growth mechanism on h-BN film/Cu foil, careful Atomic Force Microscopy (AFM) and Kelvin Probe Force Microscopy (KPFM) measurements were performed on different thickness of h-BN film on a SiO$_{2}$ substrate to unveil the catalytic origin of graphene growth on h-BN/Cu. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Korean government (MSIP) (Grant Numbers: 2009-0083540, 2011-0030046, 2012R1A1A2020089 and 2012R1A1A1041416). [Preview Abstract] |
Wednesday, March 5, 2014 1:15PM - 1:27PM |
M51.00011: Synthesis of Large Scale MoS2-Graphene Heterostructures Kathleen McCreary, Aubrey Hanbicki, Adam Friedman, Jeremy Robinson, Berend Jonker A rapidly progressing field involves the stacking of multiple two dimensional materials to form heterostructures. These heterosctructures have exhibited unique and interesting properties. For the most part, heterostructure devices are produced via mechanical exfoliation followed by careful aligning and stacking of the various components, limiting dimensions to micron-scale devices. Chemical vapor deposition (CVD) has proven to be a useful tool in the production of graphene and has very recently been investigated as a means for the growth of other 2D materials such as MoS2, hexagonal boron nitride and WS2. Using a two-step CVD process we are able to synthesize MoS2 on CVD grown graphene. AFM and Raman microscopy of the MoS2-graphene heterostructure show a uniform and continuous film on the cm scale. [Preview Abstract] |
Wednesday, March 5, 2014 1:27PM - 1:39PM |
M51.00012: A stable path to ferromagnetic hydrogenated-graphene growth Shayan Hemmatiyan, Marco Polini, Allan H. MacDonald, Jairo Sinova Based upon first principle calculations, we present results that indicate the presence of a preferential site on one sublattice for hydrogen adsorption due to the screening effect of hexagonal boron nitride (h-BN). Our results show the effect of h-BN increases the hydrogen migration barrier on top of graphene. We propose a functional heterostructure as a TMR device, which is exploiting the screening effect caused by h-BN and the insulating properties of this exotic 2-D material. The density of states (DOS) calculations, with 1, 2 and 3 h-BN layers sandwiched in between two layers of graphone, show a half metallic state for these new heterostructures. [Preview Abstract] |
Wednesday, March 5, 2014 1:39PM - 1:51PM |
M51.00013: Toward disorder-free graphene Jesse Balgley, Lei Wang, Yuanda Gao, Bo Wen, Jim Hone, Cory Dean Integration of monolayer graphene with BN dielectrics has enabled substantial reduction in disorder with recent graphene devices exhibiting ballistic transport over tens of microns. However, low density response and magneto transport in the quantum Hall effect regime indicate a remnant disorder temperature above a few Kelvin. In my talk I will show how low field Shubnikov-de Haas oscillations measured from encapsulated BN/G/BN devices are consistent with a remote-impurity scattering model, suggesting that the residual source of disorder may lie outside the heterostack. Using our recently developed fabrication techniques together with the edge contact geometry, we will present new strategies to eliminate this residual scattering. [Preview Abstract] |
Wednesday, March 5, 2014 1:51PM - 2:03PM |
M51.00014: Atomic-scale study of lateral graphene/h-BN hybrid structure Jaekwang Lee, Jewook Park, An-Ping Li, Mina Yoon Recently, atomically sharp 1D interfaces have been successfully implemented in lateral graphene/hexagonal boron nitride (h-BN) hybrid structures. Graphene/h-BN interfaces are of particular interest, because their bandgap and magnetic properties can be engineered by controlling the arrangement of nonmagnetic B, C and N atoms. Despite the enormous interest in graphene/h-BN, there has been very limited experimental success in determining the local atomic structure of the graphene/h-BN interface. Here, using state-of-the-art scanning tunneling microscopy, we report the direct and precise observation of a graphene/h-BN interface bonding structure at the atomic scale. Based on the detailed atomic structure, first-principles density-functional calculations show that graphene zigzag edge states and the h-BN polarity are strongly coupled to each other near the interface and induce spatial modulation of physical properties along the lateral direction. In addition, we investigate how the d-orbitals of metal surfaces (Cu (111), Cu (001)) and the pi-orbital of graphene/h-BN hybridize and predict resulting modification of the electronic properties of graphene/h-BN. [Preview Abstract] |
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