Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session H37: Focus Session: Graphene Structure, Dopants, and Defects: Transport I |
Hide Abstracts |
Sponsoring Units: DMP Chair: Caio Lewenkopf, Universidade Federal Fluminense, Brazil Room: C146 |
Tuesday, March 22, 2011 8:00AM - 8:36AM |
H37.00001: Probing the nature of impurity scattering in graphene Invited Speaker: Since the very first investigations of the electronic properties of graphene the nature of defects has been shown to play an essential role in determining the carrier density dependence of the conductance. Impurity scattering is characterized by two different times the transport and elastic scattering times which are sensitive to the mass less energy dispersion of graphene. The analysis of the ratio between these two times gives insight on the nature (neutral or charged) and range of the scatterers. We will discuss how to extract these two times from magneto-transport measurements in macroscopic samples and analyze their differences in monolayer and bilayer Graphene in relation with the different symmetry properties of their band structure and wave functions. \\[4pt] \textit{``Transport and Elastic Scattering Times as Probes of the Nature of Impurity Scattering in Single-Layer and Bilayer Graphene}'' M.~Monteverde, C. Ojeda-Aristizabal, R. Weil, K. Bennaceur, M.~Ferrier, S. Gu\'{e}ron, C. Glattli, H. Bouchiat, J. N. Fuchs, and D. L. Maslov Phys. Rev. Lett. \textbf{104}, 126801 (2010). [Preview Abstract] |
Tuesday, March 22, 2011 8:36AM - 8:48AM |
H37.00002: ABSTRACT WITHDRAWN |
Tuesday, March 22, 2011 8:48AM - 9:00AM |
H37.00003: Transport and optical measurements on Graphene - hBN heterostructures Lei Wang, Cory Dean, Andrea Young, Zheyuan Chen, Inanc Meric, Ken Shepard, Louis Brus, Philip Kim, James Hone Placing graphene on hexagonal BN (hBN) substrates has recently been shown to lead to improved device quality.~ In addition, the planar nature of the h-BN allows for the realization of novel device architectures with high mobility graphene, including dual-gated devices.~ I will discuss recent transport and optical measurements on such graphene-hBN heterostructures, focusing on high mobility dual gated bilayer graphene, in which the carrier density and the band-gap can be tuned independently. [Preview Abstract] |
Tuesday, March 22, 2011 9:00AM - 9:12AM |
H37.00004: Fabrication and transport characterization of Graphene/Hexagonal Boron Nitride sandwich structures Jian-Hao Chen, Kwanpyo Kim, Will Regan, William Gannett, Kris Erickson, Michael Rousseas, Alex Zettl High quality, large size hexagonal Boron Nitride (h-BN) thin films and single layer graphene were grown on metal substrates via the chemical vapor deposition method (CVD) and transferred to form Graphene/h-BN sandwich structures. High resolution transmission microscopy (TEM) was performed on Graphene and h-BN, confirming highly-ordered crystalline structures of both. The electronic transport properties of various sandwich configurations were investigated at low temperature and high magnetic field. [Preview Abstract] |
Tuesday, March 22, 2011 9:12AM - 9:24AM |
H37.00005: Tunable band gaps in bilayer graphene-BN heterostructures Ashwin Ramasubramaniam, Doron Naveh, Elias Towe We investigate band-gap tuning of bilayer graphene between hexagonal boron nitride sheets, by external electric fields. Using density functional theory, we show that the gap is continuously tunable from 0 to 0.2 eV, and is robust to stacking disorder. Moreover, boron nitride sheets do not alter the fundamental response from that of free-standing bilayer graphene, apart from additional screening. Our calculations suggest that graphene-boron nitride heterostructures could provide a viable route to graphene-based electronic devices. [Preview Abstract] |
Tuesday, March 22, 2011 9:24AM - 9:36AM |
H37.00006: Dielectric thickness dependence of carrier mobility in graphene with Al$_{2}$O$_{3}$ and HfO$_{2}$ top dielectrics Babak Fallahazad, Seyoung Kim, Luigi Colombo, Emanuel Tutuc We study the carrier mobility in graphene with high-$k$ top dielectrics, as a function of the dielectric thickness and temperature. Metal-oxide high-$k$ films, Al$_{2}$O$_{3}$ ($k\sim $8.4) and HfO$_{2}$ ($k\sim $16), are deposited on graphene by atomic layer deposition (ALD), at deposition temperatures of 200-250 \r{ }C. A considerable ($\sim $50{\%}) mobility drop is observed after the deposition of the first 2-4 nm of dielectric. For thicker dielectrics the mobility is relatively insensitive to thickness. The carrier mobility has a weak temperature dependence, which indicates that phonon scattering is not the primary mobility limiting factor in these devices. Our results suggest that Coulomb scattering caused by fixed charged impurities located in the high-$k$ dielectric, and in proximity to the graphene layer plays a significant role in mobility degredation. The ALD grown high-$k$ films are inherently oxygen deficient, and oxygen vacancies form donor levels which become positively charged in the proximity of the graphene layer. We speculate that Coulomb scattering due to charged point defects is the mobility limiting mechanism in graphene devices with Al$_{2}$O$_{3}$ or HfO$_{2}$ high-$k$ dielectrics. [Preview Abstract] |
Tuesday, March 22, 2011 9:36AM - 9:48AM |
H37.00007: Coulomb Drag in Independently Contacted Graphene Bilayers Seyoung Kim, Insun Jo, Junghyo Nah, Yao Zhen, Sanjay Banerjee, Emanuel Tutuc Two graphene layers placed in close proximity, and electrically isolated, offer a unique system to investigate interacting electron physics. In such graphene bilayer, the interlayer spacing can be reduced to values much smaller than otherwise achievable in semiconductor heterostructures. Moreover, the zero energy band-gap allows the realization of coupled hole-hole, electron-hole, and electron-electron two-dimensional systems in the same sample. Here we demonstrate the realization of independently contacted graphene bilayers. We probe the resistance and density of each layer, and quantitatively explain their dependence on the back-gate bias. We experimentally measure the Coulomb drag between the two graphene layers, by flowing current in one layer and measuring the voltage drop in the opposite layer. The drag resistivity gauges the momentum transfer between the two layers, which in turn probes the interlayer coupling. The temperature dependence of the Coulomb drag above temperatures of 77K reveals that the ground state in each layer is a Fermi liquid. Below 77K we observe mesoscopic fluctuations of the drag resistivity, as a result of the interplay between coherent transport in the graphene layer and interlayer interaction. [Preview Abstract] |
Tuesday, March 22, 2011 9:48AM - 10:00AM |
H37.00008: Probing charge scattering mechanisms in suspended and supported graphene by varying dielectric environment A.K.M. Newaz, Kirill I. Bolotin The electronic properties of graphene are drastically affected by its environment, such as the substrate underneath it and the impurities near it. To elucidate the effect of scattering due to the environment, we used the Hall probe technique to study the electronic transport properties and the quantum capacitance of single layer graphene devices in environments with different dielectric susceptibility $\kappa$. We have varied the susceptibility by i) using solvents of different dielectric constants, ii) mixing two miscible solvents of different dielectric strengths and iii) varying the temperature of the solvent. To eliminate the effects due to a substrate, we have also studied suspended graphene devices. We have observed enhancement in the Hall mobility and reduction in the minimal conductivity in both supported and suspended devices as the static dielectric constant is increased from $\kappa\sim2$ to $\kappa\sim30$. This suggests stronger screening of charge scattering in higher $\kappa$ dielectric environment. Our results support the conjecture that the dominant scattering mechanism in graphene is the long range Coulomb interaction due to the charge impurities. [Preview Abstract] |
Tuesday, March 22, 2011 10:00AM - 10:12AM |
H37.00009: Charge transport studies in graphene devices: a focus on mobility behavior Archana Venugopal, Wiley Kirk, Luigi Colombo, Eric Vogel Graphene has been the subject of extensive electrical characterization since 2004. As in semiconductor based FETs, mobility ($\mu )$ is used as the parameter to gauge and compare the device performance. Typically reported is the effective mobility, $\mu _{eff}$, extracted from I$_{d}$ -- V$_{g}$ characteristics or the channel mobility ($\mu _{H})$ extracted from Hall measurements, which can be especially illuminating when more than one carrier type is participating in the charge transport process. The dependence of the mobility on parameters such as applied field, dielectric type, underlying oxide thickness, channel dimensions and temperature is not well understood. A study of $\mu _{H}$ and the accompanying magnetoresistance as a function of the above mentioned parameters in low to moderate magnetic fields was performed, as well as $\mu _{eff}$ on the same devices, the results of which will be compared and presented. The dependence on graphene type (grown vs. exfoliated) will also be discussed. [Preview Abstract] |
Tuesday, March 22, 2011 10:12AM - 10:24AM |
H37.00010: Graphene nanoelectronics from ab initio theory Jesse Maassen, Wei Ji, Hong Guo We employ atomic first principles theory to study the properties of realistic graphene nanoelectronic systems. We focus on the role of different contact materials and their effect on the transport properties at the graphene/metal junction. The current-voltage characteristics were calculated using density functional theory (DFT) combined with non-equilibrium Green's functions (NEGF). [Preview Abstract] |
Tuesday, March 22, 2011 10:24AM - 10:36AM |
H37.00011: Charge transport in two-terminal graphene junctions with bonding metal contacts Barraza-Lopez Salvador, M. Y. Chou One has to attach graphene to metal leads to measure charge transport characteristics. In a number of experiments a thin Ti film is grown on top of graphene and additional metal leads (e.g., Au or Al) are created on top of this film. Ti forms covalent bonds with graphene, destroying the linear dispersion at the Ti/graphene contact. For practical reasons (i.e., the use of Hamiltonians with a linear dispersion) most theoretical approaches either consider only the effects of the inhomogeneities caused by the insulating substrate, or, when two-terminal calculations exist, use assumptions that preclude quantitative modeling. These assumptions include: (i) extremely large bias steps separating the leads and the central region of the device, or (ii) unusually large imaginary contributions to the self-energies representing metal leads. We depart from these models and follow an atomistic approach to compute transmission characteristics of Ti/graphene/Ti junctions. From these calculations we identify the key physical ingredients determining the transport features, and extract parameters to be used in a quantitative effective model that describes accurately the electronic structure and the transmission probabilities of charge carriers. This work complements our previous results in metal/graphene/metal junctions where the metal does not bond covalently to graphene (PRL {\bf 104}, 076807 (2010)). [Preview Abstract] |
Tuesday, March 22, 2011 10:36AM - 10:48AM |
H37.00012: Transport in Metal/Graphene Tunnel Junctions Chris Malec, Dragomir Davidovic We present a technique to fabricate thin oxide barriers between graphene and Al and Cu to create tunnel junctions and directly probe graphene in close proximity to a metal. We map the differential conductance of our junctions versus probe and back gate voltage, and observe fluctuations in the conductance that are directly related to the graphene density of states. We develop a simple theory of tunneling into graphene to extract experimental numbers, and take into account the electrostatic gating of graphene by the tunneling probe. Results of measurements in magnetic fields will also be discussed, including evidence for incompressible states in the Quantum Hall regime. [Preview Abstract] |
Tuesday, March 22, 2011 10:48AM - 11:00AM |
H37.00013: Quantum transport in high-quality Bilayer Graphene pnp Junctions Yongjin Lee, Lei Jing, Jairo Velasco Jr., Philip Kratz, Gang Liu, Wenzhong Bao, Marc Bockrath, Chun Ning Lau Using high-quality bilayer grapheme pnp junctions with suspended top gates, we perform transport measurements. At a magnetic field B=0, by an applied perpendicular electric field, band gap opens at 260mK. Within the band gap, we demonstrate the conductance decreases exponentially by 3 orders of magnitude with increasing electric field and this can be explained by variable range hopping with a gate-tunable density of states, effective mass, and localization length. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700