Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session D37: Focus Session: Graphene Structure, Dopants, and Defects: Strain Engineering I |
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Sponsoring Units: DMP Chair: Jeanie Lau, University of California, Riverside Room: C146 |
Monday, March 21, 2011 2:30PM - 3:06PM |
D37.00001: Strain Engineering in Graphene Invited Speaker: Graphene is a unique example of a one atom thick metallic membrane. Hence, graphene brings together properties of soft and hard condensed matter systems. The elementary electronic excitations in graphene, the Dirac quasiparticles, couple in a singular way to structural distortions in the form of scalar and vector potentials. Therefore, graphene has an effective electrodynamics where structural deformations couple to the Dirac particles at equal footing to electric and magnetic fields. This so-called strain engineering of the electronic properties of graphene opens doors for a new paradigm in terms of electronic devices, where electronic properties can be manipulated at will using its membrane-like properties. [Preview Abstract] |
Monday, March 21, 2011 3:06PM - 3:18PM |
D37.00002: Optical absorption and giant Faraday rotation in strained graphene Vitor Pereira, Nuno M.R. Peres, Ricardo M. Ribeiro, Antonio Castro Neto Slightly doped or undoped graphene is characterized by an universal optical absorption coefficient of $\pi\alpha$ (nearly 2\%), which is constant in a frequency band spanning the near UV, down to the far IR. Strain-induced anisotropy breaks this universality, while keeping the optical response constant up to energies close to the van-Hove singularity of the spectrum. This allows for the possibility of exploring the photoelasticity of graphene towards the development of atomically thin, broadband optical elements. We show, and analytically quantify, the amount of polarization rotation and dichroism expected for uniaxially strained graphene. The effect can be used to tailor the optical response of graphene or, conversely, to use light to measure the amount and direction of uniaxial strain in graphene for sensing applications. Exposure to an external magnetic field brings about the Faraday effect, which is shown to be extremely large in comparison with conventional materials. Moreover, the sharp enhancement of Faraday rotation and absorption at the field and stain tunable cyclotron frequency opens the possibility of tunable broadband optics in atomically thin transparent membranes. [Preview Abstract] |
Monday, March 21, 2011 3:18PM - 3:30PM |
D37.00003: Electron-electron interactions in strained graphene Anand Sharma, Valeri Kotov We present a theoretical study on the effects of electron-electron interactions under an applied weak uni-axial strain in graphene, described as anisotropic Dirac liquid. We calculate the electron self-energy using perturbation theory in both the Coulomb interactions and strain, and find that near the Dirac point the self-energy exhibits logarithmic singularity structure, similarly to an un-deformed graphene. We present results for the renormalization of the electronic anisotropy by using first the bare Coulomb interaction, as well as the random-phase approximation, which takes into account the anisotropic nature of the vacuum polarization. The mutual interplay of interactions and strain can provide a route towards understanding the role of correlations in graphene, which so far have been quite elusive in the un-deformed case. [Preview Abstract] |
Monday, March 21, 2011 3:30PM - 3:42PM |
D37.00004: Scattering from localized strain profiles in graphene: effects on conductance Matthew Barr, Eric Heller Graphene has attracted significant attention for, amongst other properties, its Dirac-like quasiparticles and long coherence length. In the ballistic regime, we theoretically investigate the scattering properties of localized strain profiles. Manipulating strain in graphene has been proposed as a novel method of shaping graphene devices; modulated hopping parameters effectively introduce vector potentials equivalent to pseudomagnetic fields up to 300T [1]. We determine the localized potential and scattering parameters of several such ``bubbles''; with this information we calculate the effects on conductance in both valleys of introducing one or many such impurities.\\[4pt] [1] N. Levy, S. A. Burke, K. L. Meaker, M. Panlasigui, A. Zettl, F. Guinea, A. H. Castro Neto and M. F. Crommie, Science 30, July 2010 [Preview Abstract] |
Monday, March 21, 2011 3:42PM - 3:54PM |
D37.00005: Ab-initio study of the Kohn anomalies in strained graphene M.E. Cifuentes-Quintal, R. de Coss, O. de la Pe\~na-Seaman, R. Heid, K.-P. Bohnen Recent experimental studies have show that the electronic and vibrational properties of graphene can be modulated by means of strain. However, there are not studies on strain effects on the Kohn anomalies, which is a principal key to understand the electron phonon coupling in graphene. In this work we have studied the phonon band structure of graphene under biaxial and uniaxial strain using the mixed basis pseudopotential method, within the framework of the density functional perturbation theory. For tensile/compressive biaxial strain, we found an increasing/decreasing behavior on the slop of the phonon frequencies close to Kohn anomalies. Under uniaxial strain, the two highest optical branches show a discontinuity in the frequency derivative at gamma point, instead of only one branch like in the biaxial and unstrained case. The present results suggest that the electron-phonon coupling in graphene can be modulated via strain. [Preview Abstract] |
Monday, March 21, 2011 3:54PM - 4:06PM |
D37.00006: Graphene rubber band: suspended graphene sheets with controlled uniaxial strain Zenghui Wang, David Hutchison, Carlos Ruiz-Vargas, Pinshane Huang, Sunil Bhave, David Muller, Jiwoong Park The recent advances in growth and transfer techniques of CVD graphene have made it an excellent candidate for making electrical and mechanical devices, especially at larger scale than with exfoliated graphene flakes. Nevertheless, the electrical, electromechanical and optomechanical properties of CVD graphene need to be further characterized before one can make full use of this 2D material. Here, we study the properties of CVD graphene under well controlled uniaxial strain. We fabricate devices with adjustable-width gaps actuated by comb drives, and transfer CVD graphene sheets onto these gaps. We study the slipping, straining, and breaking of CVD graphene in real time under TEM, with identification of individual single crystal domains and domain boundaries. [Preview Abstract] |
Monday, March 21, 2011 4:06PM - 4:18PM |
D37.00007: Suspension of Graphene and Bi2Se3 Atomic Membrane Zeng Zhao, Jairo Velasco, Hang Zhang, Fenglin Wang, Zhiyong Wang, Philip Kratz, Lei Jing, Wenzhong Bao, Jing Shi, Jeanie Lau Coupling high quality, suspended atomic membranes to specialized electrodes enables investigation of many novel phenomena, such as spin or Cooper pair transport in these two dimensional systems. However, many electrode materials are not stable in acids that are used to dissolve underlying substrates. Here we present a versatile and powerful multi-level lithographical technique to suspend atomic membranes, which can be applied to the vast majority of substrate, membrane and electrode materials. We also demonstrate, for the first time, fabrication and measurement of a free-standing thin Bi$_{2}$Se$_{3}$ membrane, which has low contact resistance to electrodes and a mobility of $\ga$500 cm$^{2}$/Vs. [Preview Abstract] |
Monday, March 21, 2011 4:18PM - 4:30PM |
D37.00008: In-situ Investigation of Electrical-Mechanical Coupling in graphene-based devices Mingyuan Huang, Tod Pascal, Hyungjun Kim, William Goddard III, Julia Greer Graphene, a truly two-dimensional gapless semiconducting material, recently deemed strongest ever measured, can sustain very high (up to 25{\%}) in-plane tensile elastic strains. Several recent theoretical-only studies on strained graphene predict that strain can shift the Dirac cones, reduce the Fermi velocity, introduce a pseudo-magnetic field, and be used to engineer the electronic structure. However, no direct experiments on electrical measurements of highly strained graphene have yet been reported. Here, we present the results of \textit{in-situ} investigation of electrical-mechanical coupling in graphene-based devices. In our experiment, \textit{in-situ} nanoindentation was performed on suspended graphene transistors to introduce homogeneous tensile strain up to 3{\%}, while electrical measurements were carried out simultaneously. We find that the electrical resistance shows only a marginal change under strain, and the electronic transport measurement confirms that there is no opening of the band gap for graphene under moderate uniform strain. We also report first-principles informed molecular dynamics simulation that lead to Young modulus consistent with our experiments and show no opening of a band gap. [Preview Abstract] |
Monday, March 21, 2011 4:30PM - 4:42PM |
D37.00009: Radio Frequency Electrical Transduction of Graphene Mechanical Resonators Changyao Chen, Vikram Deshpande, Yuehang Xu, Frank DiRenno, Alexander Gondarenko, David Heinz, Shuaimin Liu, Philip Kim, James Hone We report radio frequency (RF) electrical readout of graphene mechanical resonators. The mechanical motion is actuated and detected directly by using a vector network analyzer (VNA), employing a local gate to minimize parasitic capacitance. Resist-free doubly-clamped samples with resonant frequency in MHz range, Q factor $\sim $10,000 at 77 K and signal-to-background ratio of over 20 dB, are demonstrated. In addition to being over two orders of magnitude faster than the electrical RF mixing method, this technique paves the way for use of graphene in RF devices such as filters and oscillators. [Preview Abstract] |
Monday, March 21, 2011 4:42PM - 4:54PM |
D37.00010: Measurement of the shear modulus of single-layer graphene Thomas Metcalf, Xiao Liu, Jeremy Robinson, Keith Perkins, Brian Houston We have measured the shear modulus of large area (2mm $\times$ 5mm), single-layer (90--95\%) polycrystalline graphene sheets and found values consistent with theoretical predictions of $G$=200 GPa. The graphene was grown by chemical vapor deposition onto a copper foil and subsequently transferred onto a mechanical resonator known as a double-paddle oscillator (DPO). DPOs are fabricated from single-crystal, 0.3mm thick silicon wafers, and have a torsional vibratory mode at 5500 Hz which has a very large quality factor, $Q=5\times10^7$, at low ($<10$ K) temperatures, giving the DPO a high sensitivity to a film deposited on its torsional element. Such a film increases the (lumped-element) spring constant of the resonator, and the film's shear modulus can be deduced from the subsequent resonant frequency shift. [Preview Abstract] |
Monday, March 21, 2011 4:54PM - 5:06PM |
D37.00011: Tearing of Graphene Maria Moura, Michael Marder Experiments on free standing graphene can expose the graphene sheets to out-of-plane forces. An example of that is the back-gate voltage experimental setup. Here we show that out-of-plane forces can cause free standing graphene to fracture. This fracture mode is known as tearing mode and is common in materials like paper. We present a numerical study of the propagation of cracks in clamped, free standing graphene as a function of the out-of-plane force. We report a threshold for the graphene fracture energy. [Preview Abstract] |
Monday, March 21, 2011 5:06PM - 5:18PM |
D37.00012: Variable strain in graphene sealed microchambers studied with Raman spectroscopy A.L. Kitt, J.W. Suk, S. Remi, S. Ahmed, R. Piner, K.M. Liechti, R.S. Ruoff, A.K. Swan, B.B. Goldberg Raman measurements are a sensitive tool for evaluating strain in graphene. Graphene sealed cylindrical microchambers provide a unique way of generating strain. Suspended graphene avoids substrate interactions which make it difficult to evaluate the graphene response, e.g., combined graphene-substrate Poisson ratio, or slippage. Additionally, the system provides a wide range of strain states with different lattice symmetries. At a fixed external pressure, the strain state varies radially. The strain is biaxial in the center and changes gradually to only radial strain at the edges. The continuum model is evaluated to find~the radial strain states. Combined with Raman Spectroscopy, several fundamental parameters can be measured. We will discuss the strain and polarization dependent splitting of the G and 2D bands and compare to previous works [1,2]. Furthermore, preliminary measurements of the strain dependence of thermal properties will be discussed. \\[4pt] [1] T. Mohiuddin et al, Phys Rev B 79, 1-8 (2009) \\[0pt] [2] M. Huang, et al, Nano Letters 10, 4074-9 (2010) [Preview Abstract] |
Monday, March 21, 2011 5:18PM - 5:30PM |
D37.00013: An Effective Tensional Strain View on the Bandgap Tunability of Helical Graphene Nanoribbons with Open and Closed Edges Dong-Bo Zhang, Traian Dumitrica Despite the scientific importance of graphene nanoribbons, little is known about their electronic structure other than in the flat-form presupposition. To quantify the strain stored in helical graphene nanoribbons and fractional carbon nanotubes, we supplement the standard elasticity concepts with an effective tensional strain. Using $\pi$-orbital tight binding and objective molecular dynamics coupled with density functional theory, we develop a unified theory for the electromechanical response in which the consequences of the torsional deformation are taken into account via the effective tensional strain. In spite of the open and closed edges as well as the inverse Poynting effect exhibited by these nanostructures, from the effective strain perspective the twist-induced bandgap modulations appear strikingly similar with those exhibited by carbon nanotubes in tension. Our theory may be useful for designing new electromechanical devices and experiments using carbon nanocomponents, and for establishing edge-chemistry driven nanofabrication principles for helical graphene nanoribbons with tunable bandgaps. [Preview Abstract] |
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