Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session A7: Focus Session: Graphene Devices I |
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Sponsoring Units: DMP Chair: K.C. Fong, Caltech Room: 303 |
Monday, March 18, 2013 8:00AM - 8:12AM |
A7.00001: Graphene-based Hall Sensors for direct magnetic imaging by using Scanning Hall Probe Microscope Selda Sonusen, Seda Aksoy, Munir Dede, Ahmet Oral Graphene has been attracting great interest due to its unique electronic and mechanical properties for both fundamental and experimental studies since 2004. Graphene is a promising material for many applications in high speed electronic and spintronic devices as well as sensors. Its high mobility makes graphene a good candidate for magnetic imaging in Scanning Hall Probe Microscope (SHPM). Hall probes are used to scan the magnetic samples to image magnetic domains in SHPM. In this work, single layer graphene produced by chemical vapor deposition technique is used to fabricate Hall sensors by optical and the e-beam lithography with sizes from 500 nm to a few micrometers. The Hall crosses are characterized by Raman mapping to make sure that they are made of a single layer graphene. The Graphene Hall Sensors noise spectra is measured as a function of different bias currents and carrier concentrations at 300 K, 77 K and 4.24K. The imaging performance of the Hall sensor will be demonstrated at different temperatures by imaging a garnet crystal using a Low Temperature Scanning Hall Probe Microscope (LT-SHPM). [Preview Abstract] |
Monday, March 18, 2013 8:12AM - 8:24AM |
A7.00002: Molecular Dynamics Studies of Graphene Nanobubbles Zenan Qi, Harold Park, Vitor M. Pereira, Antonio H. Castro-Neto, David K. Campbell We apply classical molecular dynamics to study pressure-induced deformations and the resulting pseudomagnetic (PSM) fields for monolayer graphene nanobubbles (NBs) of various geometries. We obtain the PSM field distributions for triangular, square, rectangular, hexagonal, and circular graphene NBs and find that in most cases the PSM fields near the tops of the NBs are smaller than around the NB edges. For circular NBs of diameter smaller than about 2nm, we find that the PSM field contribution from bending and curvature becomes comparable to from the traditional in-plane component of the gauge field. [Preview Abstract] |
Monday, March 18, 2013 8:24AM - 8:36AM |
A7.00003: Spatial manipulation of massless Dirac fermions in ballistic graphene devices Piranavan Kumaravadivel, Xu Du Pseudo-spin conservation of the chiral quasi-particles in graphene, governed by the Dirac-Weyl equation, has resulted in interesting study of transport phenomena such as their selective transmission across potential barriers. Utilizing these properties to spatially manipulate the electrons in graphene devices require ballistic samples with well-defined, sharp junctions. We report our current work on the fabrication and characterization of such ballistic devices that will enable us to guide and control electron flow in 2D. [Preview Abstract] |
Monday, March 18, 2013 8:36AM - 8:48AM |
A7.00004: Graphene as an etch mask for silicon Aniruddh Rangarajan, Joshua Wood, Justin Koepke, Joseph Lyding We are using graphene as a hard etch mask for silicon. The error introduced by its edges is hypothesized to be far less compared to innate issues of photolithography (e.g. undercut, sidewall hardening). This presents the possibility of making a highly precise etch mask. We lithographically pattern a graphene layer transferred to a Si(100) surface and fluorinate the sample to demonstrate the selective etching on exposed regions. The graphene layer becomes fluorinated, but shields the silicon underneath. The Si(100) with selective graphene coating was subjected to isotropic etching by xenon difluoride (at 1.0 Torr, and N$_{2}$ at 35.0 Torr) for 180 s to remove approximately 190 nm of silicon. Raman spectroscopy confirms the onset of sp$^{3}$ hybridization of carbon atoms in the hexagonal lattice, brought on by covalent C--F bonding. Along with the possibility of producing highly precise silicon structures, the monolayer mask has added advantages, such as not requiring as many processing steps as the conventional method involving photoresist. [Preview Abstract] |
Monday, March 18, 2013 8:48AM - 9:00AM |
A7.00005: Low-Damage Sputter Deposition on Graphene Ching-Tzu Chen, Emanuele Casu, Marcin Gajek, Simone Raoux Despite its versatility and prevalence in the microelectronics industry, sputter deposition has seen very limited applications for graphene-based electronics. We have systematically investigated the sputtering induced graphene defects and identified the reflected high-energy neutrals of the sputtering gas as the primary cause of damage. In this talk, we introduce a novel sputtering technique that is shown to dramatically reduce bombardment of the fast neutrals and improve the structural integrity of the underlying graphene layer. We also demonstrate that sputter deposition and in-situ oxidation of 1 nm Al film at elevated temperatures yields homogeneous, fully covered oxide films with r.m.s. roughness much less than 1 monolayer, which shows the potential of using such technique for gate oxides, tunnel barriers, and multilayer fabrication in a wide range of graphene devices. [Preview Abstract] |
Monday, March 18, 2013 9:00AM - 9:12AM |
A7.00006: Enhanced Breakdown Reliability and Spatial Uniformity of Atomic Layer Deposited High-k Gate Dielectrics on Graphene via Organic Seeding Layers Vinod Sangwan, Deep Jariwala, Stephen Filippone, Hunter Karmel, James Johns, Justice Alaboson, Tobin Marks, Lincoln Lauhon, Mark Hersam Ultra-thin high-$\kappa $ top-gate dielectrics are essential for high-speed graphene-based nanoelectronic circuits. Motivated by the need for high reliability and spatial uniformity, we report here the first statistical analysis of the breakdown characteristics of dielectrics grown on graphene. Based on these measurements, a rational approach is devised that simultaneously optimizes the gate capacitance and the key parameters of large-area uniformity and dielectric strength. In particular, vertically heterogeneous oxide stacks grown \textit{via} atomic-layer deposition (ALD) seeded by a molecularly thin perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) organic monolayer result in improved reliability (Weibull shape parameter $\beta $ \textgreater\ 25) compared to the control dielectric directly grown on graphene without PTCDA ($\beta $ \textless\ 1). The optimized sample also showed a large breakdown strength (Weibull scale parameter, E$_{\mathrm{BD}}$ \textgreater\ 7 MV/cm) that is comparable to that of the control dielectric grown on Si substrates. [Preview Abstract] |
Monday, March 18, 2013 9:12AM - 9:48AM |
A7.00007: Gate-defined Quantum Confinement in Suspended Bilayer Graphene Invited Speaker: Monica Allen Quantum confined devices in carbon-based materials offer unique possibilities for applications ranging from quantum computation to sensing. In particular, nanostructured carbon is a promising candidate for spin-based quantum computation due to the ability to suppress hyperfine coupling to nuclear spins, a dominant source of spin decoherence. Yet graphene lacks an intrinsic bandgap, which poses a serious challenge for the creation of such devices. We present a novel approach to quantum confinement utilizing tunnel barriers defined by local electric fields that break sublattice symmetry in suspended bilayer graphene. This technique electrostatically confines charges via band structure control, thereby eliminating the edge and substrate disorder that hinders on-chip etched nanostructures to date. We report clean single electron tunneling through gate-defined quantum dots in two regimes: at zero magnetic field using the energy gap induced by a perpendicular electric field and at finite magnetic fields using Landau level confinement. The observed Coulomb blockade periodicity agrees with electrostatic simulations based on local top-gate geometry, a direct demonstration of local control over the band structure of graphene. This technology integrates quantum confinement with pristine device quality and access to vibrational modes, enabling wide applications from electromechanical sensors to quantum bits. More broadly, the ability to externally tailor the graphene bandgap over nanometer scales opens a new unexplored avenue for creating quantum devices. [Preview Abstract] |
Monday, March 18, 2013 9:48AM - 10:00AM |
A7.00008: Band gap estimation in bilayer graphene through quantum capacitance measurement Kosuke Nagashio, Tomonori Nishimura, Akira Toriumi The estimation of the quantum capacitance ($C_{Q})$ through the capacitance measurement provides the direct information on Density of states (\textit{DOS}) in graphene since the energy cost to induce carriers is introduced as $C_{Q}=e^{2}$\textit{DOS} in series with the geometrical capacitance ($C_{ox})$ in the equivalent circuit (1/$C \quad =$ 1/$C_{ox} \quad +$ 1/$C_{Q})$. For bilayer graphene with Y$_{\mathrm{2}}$O$_{\mathrm{3}}$ topgate structure, the band gap opening was qualitatively observed in DOS - energy relation estimated from $C_{Q}$ under the large displacement. The band gap determined by C$_{\mathrm{Q}}$ was larger than the transport gap determined by variable-range hopping in gap states on IV measurement since carriers which respond to the alternating voltage are not required to transport throughout the device. [Preview Abstract] |
Monday, March 18, 2013 10:00AM - 10:12AM |
A7.00009: Local Spectroscopy of the Electrically Tunable Band Gap in Trilayer Graphene Matthew Yankowitz, Fenglin Wang, Chun Ning Lau, Brian LeRoy Trilayer graphene exhibits two natural stacking orders (Bernal and rhombohedral), and the electronic properties differ substantially between the two. While Bernal-stacked trilayer graphene is a semimetal with an electrically tunable band overlap, rhombohedrally stacked trilayer graphene has an electrically tunable band gap. We have performed low-temperature ultra-high vacuum STM measurements of both stacking orders. In Bernal-stacked trilayer graphene, we observe metallic behavior for all energies and electric fields probed. In rhombohedrally stacked trilayer graphene, we measure an electric field tunable band gap whose magnitude is well described by theoretical predictions. Furthermore, we explore the microscopic nature of the band gap by probing spatial variations throughout the sample. [Preview Abstract] |
Monday, March 18, 2013 10:12AM - 10:24AM |
A7.00010: Dual-dated suspended double-layer graphene devices Fenglin Wang, Jhao-Wun Huang, Yongjin Lee, Lei Jing, Kevin Myhro, Jairo Velasco Jr., Hang Zhang, Chunning Lau Using a transfer technique, we are able to align two graphene sheets together and fabricate a dual-gated suspended double-layer system via a delicate multi-step fabrication process. This experimental system includes variety of parameters, which provides potential for the discovery of new physics, such as the coupling and decoupling between two graphene sheets. We will present and discuss latest experimental results. [Preview Abstract] |
Monday, March 18, 2013 10:24AM - 10:36AM |
A7.00011: Electron-state engineering of bilayer graphene by sandwiching ionic molecules Nguyen Thanh Cuong, Minoru Otani, Susumu Okada Graphene has stimulated intense interest not only in the field of the low-dimensional sciences but also in the electronic device engineering because of its unique structural and electronic properties. In particular, they are regarded as a candidate material for the next-generation semiconductor devices. However, graphene is a metal with a pair of liner dispersion bands at the Fermi level, so that they are not utilized for the logic circuit. Therefore, it is important to tune the electronic structure and to get a semiconducting graphene. In this work, we demonstrate the possibility of controlling the band-gap and carrier type of bilayer graphene by using ionic molecules based on the first-principles total-energy calculations. Our calculations suggest that bilayer graphene sandwiched by a pair of cation and anion molecules is a semiconductor with a moderate energy gap of 0.26 eV that is attributable to the strong local dipole field induced by the ionic molecules. Furthermore, we also show that the carrier type of semiconducting bilayer graphene is controllable,i.e. intrinsic, p-type, or n-type semiconductors, by tuning anion-cation pair. [1]. \\[4pt] [1] N. T. Cuong, M. Otani, and S. Okada, Appl. Phys. Lett. (2012), in press. [Preview Abstract] |
Monday, March 18, 2013 10:36AM - 10:48AM |
A7.00012: Towards \emph{in situ} correlation of atomic structure and device functionality in graphene-based devices S. M. Hollen, Nancy Santagata, Justin Young, Jay Gupta, Ezekiel Johnston-Halperin The use of scanned probe microscopy to study atomic-scale phenomena is well established; however, there is a gap in our understanding of how atomistic studies connect to macroscopic measurements such as electron and spin transport. This gap is of particular importance to 2D materials such as graphene, germanane and MoS$_2$ due to the extreme sensitivity to defects, adatoms, and local electronic inhomogeneities. We present work towards the integration of low temperature scanning tunneling microscopy (STM) with \emph{in situ} transport measurements on nanoscale graphene devices in ultrahigh vacuum. Challenges we are addressing include (i) fabricating devices small enough that a sufficient fraction of the surface can be modified within the small scan range typical of STM, (ii) design of alignment electrodes for locating the devices with STM, and (iii) modification of the STM hardware to integrate electron transport measurements. We anticipate that being able to correlate device transport measurements with atomic scale characterization and modification of the graphene surface will allow us to address the importance of the local environment to device functionality. [Preview Abstract] |
Monday, March 18, 2013 10:48AM - 11:00AM |
A7.00013: In-situ Fabrication and Electronic Characterization of Junction-confined Single Layer Graphene Nanoribbons Zhengqing John Qi, Julio Rodriguez-Manzo, Sung Ju Hong, Marija Drndic, A.T. Charlie Johnson We report electronic measurements on high quality single layer junction-confined graphene nanoribbons fabricated in a transmission electron microscope (TEM). In this work, a process is demonstrated for the fabrication and confirmation of pristine single layer graphene nanoribbons using high vacuum current annealing and precision nano-sculpting, both conducted within the vacuum chamber of a TEM. Briefly, CVD-grown graphene is patterned into a freely-suspended nanoribbon connected to large area contacts. The sample is then mounted on a TEM holder with electrical feedthroughs to allow for simultaneous imaging and in-situ electrical transport measurements within the TEM. A focused electron beam is used to progressively narrow the ribbon, providing a platform to controllably sculpt and define the device geometry while characterizing its electrical properties. In-situ electrical measurements and TEM imaging with sub-nm resolution revealed the dependence of the nanoribbon resistance as a function of width in the range 17 -- 280 nm. Monolayer graphene were found to sustain current densities in excess of 5 x 10$^9$ A/cm$^2$, orders of magnitude higher than copper while the conductance varied approximately as w$^{0.75}$, where w is the ribbon width in nanometers. These results demonstrates graphene's potential as a next generation, high performance interconnects material with the ability to reach single-digit technology nodes at the level of a single atomic layer. [Preview Abstract] |
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