Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session P13: Mechanical Properties of 2D materialsFocus
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Sponsoring Units: DMP Room: 309 |
Wednesday, March 16, 2016 2:30PM - 3:06PM |
P13.00001: IUPAP Award: Ion transport in 2D materials Invited Speaker: Wenzhong Bao Intercalation in 2D materials drastically influences both physical and chemical properties, which leads to a new degree of freedom for fundamental studies and expands the potential applications of 2D materials. In this talk, I will discuss our work in the past two years related to ion intercalation of 2D materials, including insertion of Li and Na ions in graphene and MoS2. We focused on both fundamental mechanism and potential application, e.g. we measured in-situ optical transmittance spectra and electrical transport properties of few-layer graphene (FLG) nanostructures upon electrochemical lithiation/delithiation. By observing a simultaneous increase of both optical transmittance and DC conductivity, strikingly different from other materials, we proposed its application as a next generation transparent electrode. [Preview Abstract] |
Wednesday, March 16, 2016 3:06PM - 3:18PM |
P13.00002: Tuning frictions between graphene layers via Li ion intercalation Aijiang Lu, Jiayu Wan, Teng Li, Liangbing Hu Graphite intercalated with Li ions are widely studied and applied in Li ion batteries. It was revealed in experiments that, the Li ion intercalation leads to a phase transition of the graphite with about 10{\%} volume expansion. The increased interlayer distance should contribute to decrease the frictions between the grahene layers, but the Li ion intercalation would take an opposite effect. In order to show the total effect of the Li ion interalation, we studied the frictions between graphene layers with and without lithiation, based on density functional theory (DFT). In a sandwich-like model, slipping of the middle sheet of the graphene was simulated. Displacements between layers were fixed and the other parts were relaxed, thus the energies were record to estimate the energy barriers accordingly. We found that the frictions between the graphene layers with the Li ion intercalation are higher than those without intercalation. The energy barrier appears correlated with the concentration of the intercalated ions. As the atomic ratio between lithium and carbon increases from 0 (no intercalation) to 1:6, the energy barriers increase from 0.01 eV/atom to 0.05 eV/atom or so. Such an interesting result indicates that, just via ion intercalation, we can effectively tune the friction between graphene layers. [Preview Abstract] |
Wednesday, March 16, 2016 3:18PM - 3:30PM |
P13.00003: Lithium Intercalation of Single-Layer Graphene / Boron Nitride Heterostructures Shu Yang Frank Zhao, Giselle A. Elbaz, Cyndia Yu, D. Kwabena Bediako, Yinsheng Guo, Kenji Watanabe, Takashi Taniguchi, Louis Brus, Xavier Roy, Philip Kim Graphene intercalate compounds form a new generation of graphene derivative systems where novel physical phenomena such as superconductivity and magnetism may emerge. Experimental realization of intercalated few-layer graphenes have been limited by harsh intercalation processes, often incompatible with mesoscopic device fabrication techniques. Using electrochemical methods, we demonstrate lithium intercalation of single and few-layer graphene encapsulated in hexagonal boron nitride (BN), where the BN simultaneously serves as a scaffold for the lithium atoms as well as protects the graphene from parasitic chemical reactions in the electrolyte. In addition, we developed techniques to monitor intercalation electronically. By performing in-situ Raman spectroscopy, we confirmed that the intercalated single layer graphene/BN heterostructure reached a Fermi energy in excess of $1.16eV$, and corresponding Hall measurements showed a density in excess of $7E13 cm^{-2}$. [Preview Abstract] |
Wednesday, March 16, 2016 3:30PM - 3:42PM |
P13.00004: Slipping and friction at the interface between two-dimensional materials Vijayashree Parsi Sreenivas, Ryan Nicholl, Kirill Bolotin Friction at the macroscopic scale is primarily due to the surface roughness while at the atomic scale it is governed by commensurability and environmental conditions. Here, we investigate slipping and friction at the interface between two dissimilar two-dimensional materials, such as graphene and monolayer molybdenum disulfide. Such a system provides a powerful platform to study frictional forces at the atomic scale as chemical nature of the interface and commensurability between the layers can be varied with ease. To carry out such a study, a monolayer of e.g. graphene is exfoliated onto a flexible substrate material -- polypropylene - and clamped down by evaporating titanium to avoid slippage. A monolayer of e.g. MoS$_{\mathrm{2}}$ is then transferred on top of graphene and the entire stack is strained using a four point bending apparatus. By measuring strain vs. bending via Raman spectroscopy, we detect slippage at graphene/MoS2 interface and characterize frictional forces as a function of interface parameters. [Preview Abstract] |
Wednesday, March 16, 2016 3:42PM - 3:54PM |
P13.00005: ABSTRACT WITHDRAWN |
Wednesday, March 16, 2016 3:54PM - 4:06PM |
P13.00006: Bilayer Graphene Electromechanical Systems Alexandre Champagne, Matthew Storms, Serap Yigen, Bertrand Reulet Bilayer graphene is an outstanding electromechanical system, and its electronic and mechanical properties, as well as their coupling, are widely tunable. To the best of our knowledge, simultaneous charge transport and mechanical spectroscopy (via RF mixing) has not been realized in bilayer graphene. We present data showing clear electromechanical resonances in three suspended bilayer devices whose length range from 1 to 2 microns. We first describe the low-temperature current annealing of the devices which is crucial to achieve the transconductance, $I-V_{G}$, necessary to implement a RF mixing detection method. We describe our RF mixing circuit and data. We measure clear mechanical resonances ranging in frequency from 50 to 140 MHz. We show that we can smoothly tune the resonance frequencies of our bilayer resonators with mechanical strain applied via a backgate voltage. We measure quality factors up to 4000. We briefly discuss the effects of the RF driving power on the dispersion of the mechanical resonance. We aim to use these high quality mechanical resonance as a mechanical sensor of the bilayer quantum Hall phase transitions. We show initial data of a bilayer mechanical resonance as a function of magnetic field and quantum Hall phase transitions. [Preview Abstract] |
Wednesday, March 16, 2016 4:06PM - 4:18PM |
P13.00007: Electro-vibronic Coupling Effects on "Intrinsic Friction" in Transition Metal Dichalcogenides Antonio Cammarata, Tomas Polcar One of the main difficulties in understanding and predicting frictional response is the intrinsic complexity of highly non-equilibrium processes in any tribological contact, which include breaking and formation of multiple interatomic bonds between surfaces in relative motion. To understand the physical nature of the microscopic mechanism of friction and design new tribologic materials, we conducted a systematic quantum mechanic investigation at the atomic scale on prototipical Van der Waals MX$_2$ (M=Mo, W; X=S, Se, Te) Transition Metal Dichalcogenides under variable load. We combined the structural and dynamic information from group theoretical analysis and phonon band structure calculations with the characterisation of the electronic features using non-standard methods like orbital polarization and the recently formulated bond covalency and cophonicity analyses. We formulated guidelines on how to engineer macroscopic friction at nanoscale, and finally applied them to design a new Ti-doped MoS$_2$ phase. The formulated protocol can be promptly used for the design of new materials with diverse applications beyond tribology. [Preview Abstract] |
Wednesday, March 16, 2016 4:18PM - 4:30PM |
P13.00008: The positive piezoconductive effect in graphene Kang Xu, Ke Wang, Wei Zhao, Erfu Liu, Wenzhong Bao, Michael S. Fuhrer, Yafei Ren, Zhenhua Qiao, Baigeng Wang, Dingyu Xing, Feng Miao As the thinnest conductive and elastic material, graphene is expected to play a crucial role in post-Moore era. Besides applications on electronic devices, graphene has shown great potential for nano-electromechanical systems. While interlayer interactions play a key role in modifying the electronic structures of layered materials, no attention has been given to their impact on electromechanical properties. Here we report the positive piezoconductive effect observed in suspended bi- and multi-layer graphene. The effect is highly layer number dependent and shows the most pronounced response for tri-layer graphene. The effect, and its dependence on the layer number, can be understood as resulting from the strain-induced competition between interlayer coupling and intralayer transport, as con?rmed by the numerical calculations based on the non-equilibrium Green's function method. Our results enrich the understanding of graphene and point to layer number as a powerful tool for tuning the electromechanical properties of graphene for future applications. [Preview Abstract] |
Wednesday, March 16, 2016 4:30PM - 4:42PM |
P13.00009: ABSTRACT WITHDRAWN |
Wednesday, March 16, 2016 4:42PM - 4:54PM |
P13.00010: Mechanical Properties and Failure Mechanisms in Polycrystalline Graphene Joseph Gonzalez, Romain Perriot, Ivan Oleynik Large-scale growth of graphene using chemical vapor deposition produces polycrystalline material containing grain boundaries. Recent experiments demonstrate that polycrystalline graphene is nearly as strong as pristine. In this work, the mechanical properties of bi-crystal and polycrystalline graphene samples are investigated by simulating nano-indentation of a circular membrane using classical molecular dynamics and a novel Screened Environment Dependent Reactive Bond Order (SED-REBO) potential. The failure mechanisms and crack propagation in graphene samples containing grain boundaries are also discussed. [Preview Abstract] |
Wednesday, March 16, 2016 4:54PM - 5:06PM |
P13.00011: Highly Stretchable MoS2 and Phosphorene Kirigami David Campbell, Paul Hanakata, Harold Park Several recent works have shown how nanomesh and kirigami patterning can be used to increase the ductility of monolayer graphene and thin film electrodes, suggesting that this approach should be useful for other 2D materials. We have studied the effects of kirigami patterning on the mechanical properties of MoS2 and phosphorene ``monolayers,'' using classical molecular dynamics simulations. We have explored several different kirigami structures, focusing on two simple non-dimensional parameters found to be relevant in our previous study of graphene [1]. These parameters are related to the density of cuts and to the ratio of the overlapping cut length to the nanoribbon length. We found that these membranes, despite not having the single atomic layer planar structure of graphene, show a significantly enhanced ductility that can be understood in terms of the two geometric parameters. For instance, fracture strains of MoS2 kirigami can be enhanced by a factor of six relative to pristine MoS$_{\mathrm{2\thinspace }}$nanoribbons. Our findings suggest that the kirigami cuts are the key to changing the morphology of 2D membranes to allow out of plane deflection and to prevent early failure. [1] Zenan Qi, David K. Campbell, and Harold S. Park, Phys. Rev. B 90, 245437 (2014). . [Preview Abstract] |
Wednesday, March 16, 2016 5:06PM - 5:18PM |
P13.00012: Modulated Nanoindentation (MoNI) -- a novel characterization tool of two-dimensional materials and nanotubes Yang Gao, Suenne Kim, Si Zhou, Hsiang-Chih Chiu, Daniel Nelias, Claire Berger, Walt de Heer, Laura Polloni, Roman Sordan, Christian Klinke, Angelo Bongiorno, Elisa Riedo We report~on~a novel Atomic Force Microscopy (AFM) based technique with sub-angstrom vertical resolution -- Modulated~Nanoindentation~(MoNI).~MoNI~has been applied to measure the radial elasticity of multi-walled nanotubes.~Recently~the~interlayer~coupling of~two-dimensional materials (such~as~graphene and~MoS$_{2})$ characterized by~strong in-plane bonds and weak interlayer interactions has been studied by~MoNI~combined with semi-analytical methods (SAM) and DFT calculations.~The out-of-plane stiffness of varied 2D materials and its dependence on number of layers~and intercalated water~has been investigated in different environmental conditions.~This~non-destructive~technique~provides~a new path to study the interlayer elastic coupling and the Van der Waals forces in~few-layer-thick~2D materials,~offering the possibility to understand how interlayer coupling is related to the electronic, phononic, and thermal properties of 2D materials. [Preview Abstract] |
Wednesday, March 16, 2016 5:18PM - 5:30PM |
P13.00013: Coherent Generation of Photo-Thermo-Acoustic Wave from Graphene Sheets Yichao Tian, He Tian, Yanling Wu, Leilei Zhu, Luqi Tao, Wei Zhang, Yi Shu, Dan Xie, Yi Yang, Zhiyi Wei, Xinghua Lu, Tian-Ling Ren, Chih-Kang Shih, Jimin Zhao Many remarkable properties of graphene are derived from its large energy window for Dirac-like electronic states and have been explored for applications in electronics and photonics. In addition, strong electron-phonon interaction in graphene has led to efficient photo-thermo energy conversions, which has been harnessed for energy applications. By combining the wavelength independent absorption property and the efficient photo-thermo energy conversion, here we report a new type of applications in sound wave generation underlined by a photo-thermo-acoustic energy conversion mechanism. Most significantly, by utilizing ultrafast optical pulses, we demonstrate the ability to control the phase of sound waves generated by the photo-thermal-acoustic process. Our finding paves the way for new types of applications for graphene, such as remote non-contact speakers, optical-switching acoustic devices, etc. [Preview Abstract] |
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