Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session F7: Focus Session: Graphene Devices IV |
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Sponsoring Units: DMP Chair: Cory Dean, City College of New York Room: 303 |
Tuesday, March 19, 2013 8:00AM - 8:12AM |
F7.00001: Multi-state current switching by the interference between standing electronic waves in two misoriented crossed graphene nanoribbons K.M. Masum Habib, Roger Lake In semi-infinite armchair graphene nanoribbon (aGNR), the electronic wavefunctions are standing waves with energy dependent wavelengths. The wavelength of the electrons can be controlled by an external electric field. These standing electronic waves show some unique transport phenomena in crossed graphene nanoribbon (xGNR) consisting of two semi-infinite aGNRs with one placed on top of the other and a relative rotation of 90 degrees in between. At any given energy, the matrix element between a bottom aGNR state and a top aGNR state depends on the phases of the standing waves at that energy. The matrix element and hence the inter-aGNR transmission is strongly suppressed when a zero of the standing wave of either the top or the bottom aGNR falls inside the overlap region. An external bias applied between the aGNRs can control the wavelengths and hence the phases of the standing waves which in turn modulates the inter-aGNR transmission and current. Calculations show that the inter-aGNR current is an oscillatory function of the bias voltage with multiple negative differential resistance (NDR) regions and that the period of the oscillation is controlled by the length of the finite ends of the xGNR. [Preview Abstract] |
Tuesday, March 19, 2013 8:12AM - 8:24AM |
F7.00002: Vertical Transport through Twisted Graphene/h-BN Heterostructure Xingyuan Pan, Shayan Hematiyan, Jairo Sinova, Marco Polini, Allan MacDonald Graphene and its heterostructues are promising candidates for high-frequency electronics. Vertical heterostructures created by stacking graphene layers and hexagonal boron nitride layers together display orientational disorder, due to rotational stacking faults. In this work we report our theoretical study of vertical charge transport through a rotated graphene/h-BN heterostructure. Our theoretical model combines the microscopic tight-binding method with the Landauer formalism for electrical transport. Electrical conductances are calculated for a variety of system configurations and system sizes. We found that the electrical conductance has a maximum value when the rotation angle is commensurate. Away from commensurate angles transport is suppressed but cannot be completely ignored. We show that the distance dependence of the transfer integrals between two atoms is crucial in modeling the rotation-angle dependence of the vertical transport. [Preview Abstract] |
Tuesday, March 19, 2013 8:24AM - 8:36AM |
F7.00003: Vertical Transport Properties of Graphene/h-BN Hetrostructures Shayan Hemmatiyan, Xingyuan Pan, Marco Polini, Allan MacDonald, Jairo Sinova We present results of extensive first principles, studying the scaling behaviour of inter-layer tight-binding hopping parameters in vertical graphene/h-BN heterostructures. We focus, in particular, on the dependence of these parameters on orientational disorder and inter-layer distances. We will report relevant inputs for numerical studies of the vertical transport in graphene/h-BN heterostructures. [Preview Abstract] |
Tuesday, March 19, 2013 8:36AM - 8:48AM |
F7.00004: Superconducting Graphene Nanodevices in Ballistic Transport Regime Yu-An Chen, Joel I-Jan Wang, Kenji Watanabe, Takashi Taniguchi, Pablo Jarillo-Herrero Superconductivity carried by Dirac fermions can be realized through induced superconductivity in grapheme. Observation of novel phenomena anticipated by theories requires graphene devices with low disorder whereas the carrier transport is ballistic. Current fabrication procedures to make graphene devices with low disorder like suspension or ultra-flat substrates all call for certain kinds of annealing to remove organic residues derived from the fabrication process. Applying these methods to superconducting devices can be challenging since the transparency at the graphene/superconductor interface will be destroyed. Here we present a method to do dry transfer of patterned hexagonal Boron Nitride (hBN) flakes onto graphene. The ultra flatness and lack of dangling bond in the boron nitride substrate reduces the disorder in graphene, and the top layer hBN can protect the graphene from contamination in the nanofabrication procedures and yield the geometry desired for different experimental exploration. [Preview Abstract] |
Tuesday, March 19, 2013 8:48AM - 9:00AM |
F7.00005: Exploring graphene properties in a periodic electrostatic potential Nikolai N. Klimov, David B. Newell Graphene, a unique two-dimensional honeycomb lattice of carbon atoms, exhibits rich new physics and great promise for applications in electronics. It was been predicted that a slowly varying nanoscale external periodic electrostatic potential applied to a graphene modifies its lectronic structure in a very unique way and leads to novel phenomena and possible applications [1-4]. In particular, a one-dimensional electrostatic potential applied to graphene may result in strong anisotropy of the group velocity of Dirac fermions, appearance of new zero-energy states at the Fermi energy, unusual Landau levels and quantum Hall effects. Both the anisotropy of the group velocity and the number of zero-energy modes can be altered by varying parameters of the superlattice potential. Although graphene in periodic potentials has been intensively studied theoretically, a thorough experimental investigation is still missing due to difficulties of fabricating of graphene devices, in which an external periodic potential can be applied with nanoscale periodicity. In this talk we present our results on the fabrication of graphene devices with nanoscale periodic local gates. The devices will be used to investigate graphene electronic properties in a one-dimensional periodic electrostatic potential using both magnetotransport and scanning probe microscopy measurement techniques. [1] C.-H. Park et al., Nat. Phys. 4, 213 (2008); Nano Lett. 8, 2920 (2008); Physica E 43, 651 (2011). [2] M. Barbier et al., PRB 77, 115446 (2008). [3] L. Brey, H.A. Fertig, PRL 103, 046809 (2009). [4] P. Burset et al., PRB 83, 195434 (2011). [Preview Abstract] |
Tuesday, March 19, 2013 9:00AM - 9:12AM |
F7.00006: Effect of non-uniform magnetic field on Dirac fermions in graphene Fen Guan, Naomi Mizuno, Bent Nielsen, Xu Du It has been theoretically proposed that non-uniform magnetic field can trigger bound, quasi-bound and scattering states in graphene, while electrostatic barriers cannot serve this purpose due to Klein tunneling. To observe this tuning effect on the transport properties of graphene experimentally, we need high quality graphene and microscopically inhomogeneous magnetic field. Here we report building of the inhomogeneous magnetic field through magnetic vortices in type II superconductor and study the effect of this magnetic field on the transport properties of the Dirac electrons in graphene. We present the fabrication and measurements of suspended graphene over Nb thin films which generate superconducting vortices. [Preview Abstract] |
Tuesday, March 19, 2013 9:12AM - 9:24AM |
F7.00007: ABSTRACT WITHDRAWN |
Tuesday, March 19, 2013 9:24AM - 9:36AM |
F7.00008: Alternative polymer scaffolds for clean transfer of CVD-grown graphene Joshua Wood, Gregory Doidge, Basil Aruin, Hefei Dong, Justin Koepke, Enrique Carrion, Isha Datye, Kamalika Chatterjee, Jeffrey Moore, Eric Pop, Joseph Lyding We investigate and benchmark polymer scaffolds used to support large-area chemical vapor deposition (CVD) grown graphene on Cu during transfer. CVD graphene must be transferred off of Cu to be used in various applications. PMMA transfers introduce hard-to-remove residues, and thermal release tape transfers have removable residue but give holey graphene films. Films transferred by poly(bisphenol A carbonate) (PC) are atomically clean after room-temperature polymer dissolution, and we confirm this by atomic force microscopy, Raman spectroscopy, device transport, and scanning tunneling microscopy. Compared to PC-, PMMA-transferred films have fewer wrinkles but higher RMS roughness. When we use a PC/PMMA bilayer, we find lower graphene wrinkle density but higher RMS roughness from polymer co-mixing. We also transfer graphene with other industrially relevant scaffolds like polylactic acid (PLA) and chemically modified photoresists. PLA-transferred films, after polymer dissolution, have sub-nm RMS roughness, and this improves upon PLA gasification above 180 $^{\circ}$C. Graphene transfer polymers that require low thermal budgets will open possibilities for temperature-sensitive substrates or graphene encapsulation of biological specimens (e.g. viruses, bacteria). [Preview Abstract] |
Tuesday, March 19, 2013 9:36AM - 9:48AM |
F7.00009: Effect of sample preparation on charged impurities in graphene substrates K.M. Burson, C.R. Dean, K. Watanabe, T. Taniguchi, J. Hone, P. Kim, W.G. Cullen, M.S. Fuhrer The mobility of graphene as fabricated on SiO$_{2}$ has been found to vary widely depending on sample preparation conditions. Additionally, graphene mobility on SiO$_{2}$ appears to be limited to $\sim$20,000 cm$^{2}$/Vs, likely due to charged impurities in the substrate. Here we present a study of the effect of fabrication procedures on substrate charged impurity density (n$_{imp}$) utilizing ultrahigh-vacuum Kelvin probe force microscopy. We conclude that even minimal SEM exposure, as from e-beam lithography, induces an increased impurity density, while heating reduces the number of charges for sample substrates which already exhibit a higher impurity density. We measure both SiO$_{2}$ and h-BN and find that all n$_{imp}$ values observed for SiO$_{2}$ are higher than those observed for h-BN; this is consistent with the observed improvement in mobility for graphene devices fabricated on h-BN over those fabricated on SiO$_{2}$ substrates. [Preview Abstract] |
Tuesday, March 19, 2013 9:48AM - 10:24AM |
F7.00010: Graphene / Boron Nitride Heterostructures Invited Speaker: Roman Gorbachev The talk is dedicated to multilayer boron nitride/graphene heterostructures. It will review several aspects of microfabrication of such structures as well as the transport experiments. Graphene placed on boron nitride and exhibiting nanometer-scale moir\'e patterns showing strong anomalies in the density of states which can be associated with new Dirac cones formed high up in graphene's original spectrum. We describe quantum transport in specially aligned graphene-on-hBN devices such that the DoS anomalies reproducibly appear within the Fermi energy range achievable in transport measurements. We report a strongly reconstructed graphene spectrum with new sharp neutrality points and extra sets of Landau levels and quantum Hall states. Different experiments done on multilayer structures containing two interacting graphene layers will be discussed. [Preview Abstract] |
Tuesday, March 19, 2013 10:24AM - 10:36AM |
F7.00011: Characterization Of Graphene-Ferroelectric Superlattice Hybrid Devices Mohammed Yusuf, Xu Du, Matthew Dawber Ferroelectric materials possess a spontaneous electrical polarization, which can be controlled by an electric field. A good interface between ferroelectric surface and graphene sheets can introduce a new generation of multifunctional devices, in which the ferroelectric material can be used to control the properties of graphene. In our approach, problems encountered in previous efforts to combine ferroelectric/carbon systems are overcome by the use of artificially layered superlattice materials grown in the form of epitaxial thin films. In these materials the phase transition temperature and dielectric response of the material can be tailored, allowing us to avoid polarization screening by surface absorbates, whilst maintaining an atomically smooth surface and optimal charge doping properties. Using ferroelectric PbTiO$_3$/SrTiO$_3$ superlattices, we have shown ultra-low-voltage operation of graphene field effect devices within $\pm$ 1 V at room temperature. The switching of the graphene field effect transistors is characterized by pronounced resistance hysteresis, suitable for ultra-fast non-volatile electronics. Low temperature characterization confirmed that the coercive field required for the ferroelectric domain switching increases significantly with decreasing temperatures. [Preview Abstract] |
Tuesday, March 19, 2013 10:36AM - 10:48AM |
F7.00012: Transport properties of graphene devices transferred to STO substrates Raymond Sachs, Patrick Odenthal, Roland Kawakami, Jing Shi The effect of substrate on graphene transport properties can help us understand the scattering mechanisms relevant to its carrier mobility. Single-layer graphene is easily located on the surface of Silicon with 300nm SiO$_{2}$ using optical microscopy. We have developed a technique for wet-etching the SiO$_{2}$, peeling the device with metallic leads from the surface, and transferring it to any substrate. This technique eliminates the need to locate the graphene flake on the target substrate for aligning and patterning. A direct comparison can be made between the transport properties of graphene on SiO$_{2}$ and the target substrate. A device has been transferred to 500um and 200um thick Strontium Titanate (STO) substrates as well as 250nm thick layer of STO that has been grown epitaxially on Nb-doped STO via Pulsed Laser Deposition. The STO layer, with a higher dielectric constant than SiO$_{2}$, has a higher capacitance and produces a more effective graphene FET. A higher mobility is expected for a device on the surface of a material with a higher dielectric constant if charged impurity scattering is a primary limiting factor. The devices transferred to STO display a gate voltage dependent hysteresis in both the longitudinal and Hall resistances. However, the mobility obtained from these measurements remains the same as that of the device on SiO$_{2}$. Possible reasons for the absence of the high dielectric substrate effect on graphene carrier mobility and hysteretic behavior will be discussed. [Preview Abstract] |
Tuesday, March 19, 2013 10:48AM - 11:00AM |
F7.00013: Impact of atomic hydrogen on graphene on hexagonal boron nitride Masa Ishigami, Jyoti Katoch We have measured the transport property of graphene on hexagonal boron nitride as a function of density of adsorbed atomic hydrogen. Atomic hydrogen is reversibly chemisorbed and has a large carrier scattering cross section. The impact was previously found to be radically different on graphene on silicon oxide where atomic hydrogen is mostly physisorbed and the saturation coverage of hydrogen was found to correspond to the number of native scatterers. Our results can directly test the theoretical results on the resonant impurities and suggest the nature of the native scatterers in graphene on hexagonal boron nitride. These finding will be outlined in this talk. [Preview Abstract] |
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