Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P32: Mechanical Properties and Micromechanical Devices from 2D Materials |
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Sponsoring Units: DMP Chair: Paola Barbara, Georgetown University Room: 295 |
Wednesday, March 15, 2017 2:30PM - 2:42PM |
P32.00001: A multi-valued nano-electromechanical switch Dong Hoon Shin, Hakseong Kim, Kirstie McAllister, Miri Seo, Sang Wook Lee In the present work, graphene based multi-valued nano-electromechanical (NEM) switches are demonstrated. Suspended graphene can be elastically deformed without breaking owing to its extraordinarily high mechanical strength. As a result, NEM switches with multi-level contact electrodes exhibit multiple current stages without breaking as the gate voltage increases. The experimental results reveal that the numbers of current stage and contact electrode level are identical when the height differences between the levels are sufficiently small. The electrical and mechanical behavior of the multi-valued NEM switch will be discussed in detail. [Preview Abstract] |
Wednesday, March 15, 2017 2:42PM - 2:54PM |
P32.00002: Simulation of Strain Induced Pseudomagnetic Fields in Graphene Suspended on MEMS Chevron Actuators Mounika Vutukuru, Jason Christopher, David Bishop, Anna Swan Graphene has been shown to withstand remarkable levels of mechanical strain an order of magnitude larger than bulk crystalline materials. This exceptional stretchability of graphene allows for the direct tuning of fundamental material properties, as well as for the investigation of novel physics such as generation of strain induced pseudomagnetic fields. However, current methods for strain such as polymer elongation or pressurized wells do not integrate well into devices. We propose microelectromechanical (MEMS) Chevron actuators as a reliable platform for applying strain to graphene. In addition to their advantageous controllable output force, low input power and ease of integration into existing technologies, MEMS allow for different strain orientations to optimize pseudomagnetic field generation in graphene. Here, we model nonuniform strain in suspended graphene on Chevron actuators using COMSOL Multiphysics. By simulating the deformation of the graphene geometry under the device actuation, we explore the pseudomagnetic field map induced by numerically calculating the components of the strain tensor. Our models provide the theoretical framework with which experimental analysis is compared, and optimize our MEMS designs for further exploration of novel physics in graphene. [Preview Abstract] |
Wednesday, March 15, 2017 2:54PM - 3:06PM |
P32.00003: Polymer coating and stress test for carrier density stabilization in epitaxial graphene Albert Rigosi, Chieh-I Liu, Yanfei Yang, Jan Obrzut, Hsin Yen Lee, Emily Bittle, Randolph Elmquist Homogeneous monolayer epitaxial graphene (EG) is an ideal candidate for the development of a quantum Hall resistance (QHR) standard. A clean fabrication process was used to produce EG-QHR devices with a n-type doping level of order 10$^{\mathrm{11}}$ cm$^{\mathrm{-2}}$, which delivers the metrological accuracy at the $\nu =$2 plateau in a moderate magnetic field (\textless 9 T). However, the $\nu =$2 plateau deviates from h/2e$^{\mathrm{2}}$ quickly as the carrier density shifts close to the Dirac point (\textless 10$^{\mathrm{10}}$ cm$^{\mathrm{-2}})$, and this observation occurs over time as EG is exposed to air, allowing for complexation with p-type molecular dopants. Here we report experimental results on the use of parylene C as an encapsulation layer, whereby EG can maintain its carrier density level under ambient laboratory conditions for a few months. Furthermore, we varied the parylene C thicknesses and the controllable temperatures (up to 85$^{\circ}$ C) and humidities (up to 85{\%}). We monitored the electronic properties of our EG samples by low temperature magnetotransport measurements in a 9 T superconducting magnet cryostat, and room temperature surface conductance in a resonant microwave cavity. We will compare parylene C, Cytop, and PMMA and show that polymer encapsulation may offer a solution to the problem of carrier density instability from atmospheric doping. [Preview Abstract] |
Wednesday, March 15, 2017 3:06PM - 3:18PM |
P32.00004: Thermal control of tension in suspended 2D materials Dejan Davidovikj, Herre S. J. van der Zant, Peter G. Steeneken We demonstrate tuning of the resonance frequency of graphene nanodrums by more than 30~\% using current-controlled on-chip heaters. Interestingly, the tension-induced frequency change is accompanied by an increase of the mechanical quality factor by 100~\%. Our devices consist of circular metallic heaters on a substrate with cavities, on top of which we suspend graphene flakes. Depending on the difference of the thermal expansion coefficient between the metal and the 2D material, upon heating, the drum experiences a compressive or tensile strain. The negative thermal expansion coefficient of graphene further amplifies the tension tunability. The observed increase of the quality factor is in contrast to measurements involving electrostatic pulling, where the Q-factor is always observed to decrease with increasing gate voltage. The origins of the low intrinsic quality factor of two-dimensional nanodrums are still poorly understood and the reason for its drastic increase at low temperatures is still unknown. The presented on-chip heating method provides control over tension and resonance frequency in 2D nanoresonators, which is useful in applications like sensors and resonant mechanical filters and can also shed light on the origin of dissipation in suspended 2D materials. [Preview Abstract] |
(Author Not Attending)
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P32.00005: Substrate engineered graphene resonators. Rajan Singh, Ryan Nicholl, Kirill Bolotin, Saikat Ghosh With ~large Young's modulus, broad frequency tunability, high sample quality and ultra-low mass[1] , free- hanging, single layer graphene resonators have emerged as an attractive candidate for anno and opto-mechnical studies[2]. However, the quality-factor (Q) of graphene resonators have been absymally low.~Here we demonstrate the role of discrete substrate modes on the shape of graphene resonance and in particular, the quality factors. We furthermore present an alternative route to excite such resonators, through coherently driven high Q substrate mode. Such hybrid substrate modes, with low graphene mass but high substarte Q can be applied in ultra-high resolution mass sensors[3] at room temperature. References: [1]J.S.Bunch et al., Science 315, 490 (2007). [2]K.S.Novoselov et al., Science 306, 666 (2004). [3]J.Chaste et al., Nature Nanotechnology 7, 301 (2012). [Preview Abstract] |
Wednesday, March 15, 2017 3:30PM - 3:42PM |
P32.00006: Incorporating 2D Materials with Micro-electromechanical Systems to Explore Strain Physics and Devices Jason Christopher, Mounika Vutukuru, Travis Kohler, David Bishop, Anna Swan, Bennett Goldberg 2D materials can withstand an order of magnitude more strain than their bulk counterparts which can be used to dramatically change electrical, thermal and optical properties or even cause unconventional behavior such as generating pseudo-magnetic fields. Here we present micro-electromechanical systems (MEMS) as a platform for straining 2D materials to make such novel phenomena accessible. Unlike other strain techniques, MEMS are capable of precisely controlling the magnitude and orientation of the strain field and are readily integrated with current technology facilitating a path from lab bench to application. In this study, we use graphene as our prototypical 2D material, and determine strain via micro-Raman spectroscopy making extensive use of graphene’s well-characterized phonon strain response. We report on the strength of various techniques for affixing graphene to MEMS, and investigate the role of surface morphology and chemistry in creating a high friction interface capable of inducing large strain. [Preview Abstract] |
Wednesday, March 15, 2017 3:42PM - 3:54PM |
P32.00007: Abstract Withdrawn
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Wednesday, March 15, 2017 3:54PM - 4:06PM |
P32.00008: Strongly-coupled 2D membrane resonators in superconducting electromechanical circuits David Northeast, Robert Knobel Nanomechanical devices have allowed for the study of the motion of macroscopic objects near their quantum ground state for mechanical motion. Coupling these devices to resonant electrical circuits provides a method of measuring with standard laboratory electronics, and a means to interact and cool towards the ground state. We report on current work, in microwave $LC$ resonators, toward the use of graphene and niobium diselenide (NbSe$_2$) membranes as one electrode in a parallel plate capacitor with a mechanical degree of freedom. The membrane's light mass, non-linear response to an applied force and tunability potentially enable stronger electromechanical amplification and coupling. Previous work using graphene in similar systems shows that graphene's electrical resistance is a limiting factor when attempting to cool via electromechanical sideband interactions. In contrast, NbSe$_2$ is a superconductor even in single layer form, and this property has the potential to provide a system with lower loss while driving with increasing photon number, as compared to the graphene-based systems. In this talk we show fabrication, modelling and progress towards quantum-limited measurements. [Preview Abstract] |
Wednesday, March 15, 2017 4:06PM - 4:18PM |
P32.00009: Arbitrarily Shaped Graphene Nanomechanical Resonators David Miller, Benjamin Aleman The geometric shape of a mechanical resonator plays an important role in determining its frequency, mass, and dissipation. Thus, tailoring the shape can improve the system's sensitivity to physical quantities, such as mass and force, while also enabling the study of complex dynamics. Graphene nanomechanical resonators, despite many promising attributes, have rarely been shaped beyond simple drumheads or doubly clamped beams. This limitation has been driven by challenges in traditional lithographic fabrication approaches. Here we show that focused ion beam milling is a rapid, high-yield fabrication technique that can be used to shape pre-suspended graphene into devices with arbitrary geometry, with feature sizes ranging from several nanometers to several microns. We describe the specific cutting methods needed to realize such devices. We observe that by modifying the geometry, we can tune resonance frequencies, significantly increase the quality factor, and introduce mechanical non-linearities at low driving powers. [Preview Abstract] |
Wednesday, March 15, 2017 4:18PM - 4:30PM |
P32.00010: Complete cancellation of Duffing nonlinearity in atomically thin MoS$_{\mathrm{2}}$ Nanoelectromechanical Systems Chandan Samanta, Nishta Arora, V Kranthi Kumar, Srinivasan Raghavan, Akshay Naik Ultralow mass and extraordinary mechanical properties of atomically thin membrane make it an attractive alternative to conventional Nanoelctromechanical systems (NEMS) for various applications. As dimensions of these NEMS devices shrink down to atomically thin membrane, nonlinear effects dominate the linear response. Ability to control and manipulate these nonlinearities would thus be crucial for next generation of NEMS devices. Here, we present an electrostatic mechanism to completely cancel out the Duffing nonlinearity in atomically thin MoS$_{\mathrm{2}}$-NEMS at room temperature. We observe a clear crossover from hardening to softening behavior with increasing DC gate voltage. As a direct consequence we observe about 30dB improvement in dynamic range of the devices. We also present the effect of inbuilt strain of the device on the cancellation of nonlinearity. [Preview Abstract] |
Wednesday, March 15, 2017 4:30PM - 4:42PM |
P32.00011: Wireless Actuation of Micromechanical Resonators farrukh mateen, carsten maedler, shyamsunder erramilli, pritiraj mohanty Wireless transfer of power is of fundamental and technical interest with applications ranging from remote operation of electronics, biomedical implants, and device actuation where hard-wired power sources are neither desirable nor practical. In particular, biomedical implants in the body or the brain need small footprint power receiving elements for wireless charging, which can be accomplished by micromechanical resonators. In contrast for fundamental experiments, ultra low-power wireless operation of micromechanical resonators in the microwave range makes low-temperature studies of mechanical systems in the quantum regime possible, where heat carried by the electrical wires in standard actuation techniques is detrimental to maintaining the resonator in a quantum state. We demonstrate successful actuation of micron-sized silicon-based piezoelectric resonators with resonance frequencies from 36 MHz to 120 MHz, at power levels of nanowatts and distances of about 3 feet, including polarization, distance and power dependence measurements. Our demonstration of wireless actuation of micromechanical resonators via electric-field coupling down to nanowatt levels enables a multitude of applications based on micromechanical resonators, inaccessible until now. [Preview Abstract] |
Wednesday, March 15, 2017 4:42PM - 4:54PM |
P32.00012: Young${\mathb{'}}$s Modulus of bilayer Silicene Nanoribbons Lilia Meza-Montes, M. R. Ch\'avez-Castillo, M. A. Rodr\'iguez-Meza Mechanical properties of Silicene Nanoribbons (SNRs) are determined by their width and chirality, and can be also be modified by the presence of vacancy defects [1]. In the case of bilayer SNRs, interlayer interactions influence its physical properties [2]. We report results, at room temperature, on the Young$\math{'}$s Modulus (YM) of pristine and monovacancy defective bilayers of SNRs. Molecular dynamics simulations were performed using the EDIP potential [3, 4]. YM increases with SNRs length, depends on chirality, the number and location of vacancies. Distance between layers is also important. These results are discussed in terms of missing bonds. Atomic stress distributions for defective bilayer SNRs show a larger stress concentration around the vacancy defect. Besides, if only the second layer has a mono-vacancy at its center, a larger stress concentration is observed on the atom located just below the vacancy defect. Thus, the bilayer structure carries less strain and it can be easily deformed. \\ $[1]$ M. R. Ch\'avez-Castillo $et \ al.$, RSC Adv., 5, 96052 (2015). \\ $[2]$ T. Morishita $et al.$, Chem. Phys. Lett. 506, 221 (2011). \\ $[3]$ Steve Plimpton, Comput. Phys. 117, 1 (1995). \\ $[4]$ Jo\~ao F. Justo, et al., Phys. Rev. B 58, 5, 2539 (1998). [Preview Abstract] |
Wednesday, March 15, 2017 4:54PM - 5:06PM |
P32.00013: Emergent Regulation of Energy Flow in a Two-Dimensional Semiconductor Nanoscale Heat Engine Nathaniel Gabor, Trevor Arp, Yafis Barlas, Vivek Aji Simple machines, including switches, axles, and motors, have recently been demonstrated at the molecular scale, and will likely revolutionize nanotechnology. The thermodynamic heat engine, one of the most important machines, may be critical in motivating this nanoscale revolution. We propose a nanoscale quantum heat engine based on two-dimensional semiconductor heterostructures composed of molybdenum diselenide and tungsten disulphide. Based on our recent theoretical work [1], we show that such heterostructures may exhibit emergent regulation of energy flow, which results from the internal quantum electronic structure. We describe the detailed electronic structure required for emergent regulation, and present preliminary characterization of this novel quantum heat engine. [1] Arp, et al. Nano Letters DOI: 10.1021/acs.nanolett.6b03136. [Preview Abstract] |
Wednesday, March 15, 2017 5:06PM - 5:18PM |
P32.00014: Strain Dependent Direct – Indirect Band Gap Transition in Tin Monochalcogenide Heterostructures Javad Azadani, Ongun Ozcelik, Mohammad Fathi, Tony Low We present a comprehensive study of the electronic and mechanical properties of SnS-SnSe heterostructures. Based on first-principles density functional calculations, we show that SnS and SnSe layers can form hetetrostructures with diverse properties depending on the stacking and the geometrical phases of its constituent monolayers. In particular, the heterostructure created from the puckered phases of SnS and SnSe monolayers have strain dependent electronic and mechanical properties. The band gap of this material can be tuned and changed from direct to indirect by applying strain in zigzag and armchair directions. Moreover, the applied strain can also change the sliding barrier of the monolayers on top of each other giving rise to super lubricity at certain strain values. [Preview Abstract] |
Wednesday, March 15, 2017 5:18PM - 5:30PM |
P32.00015: WS2 nanopores for molecule analysis Gopinath Danda, Paul Masih Das, Yung-Chien Chou, Jerome Mlack, Carl Naylor, Nestor Perea-Lopez, Zhong Lin, Laura Beth Fulton, Mauricio Terrones, A. T. Charlie Johnson, Marija Drndic Atomically thin 2D materials like graphene and transition metal dichalcogenides (TMDs) are interesting as membranes in solid state nanopore sensors for DNA analysis as they may facilitate single base resolution sequencing. These materials also exhibit unique optical and electronic properties which may be exploited to enhance the functionality of nanopore sensors. Here, we report WS2 nanopores, fabricated using a focused TEM beam. We also report their controlled laser-induced expansion in ionic solution. This study demonstrates the possibility of dynamic control of nanopore characteristics optically. [Preview Abstract] |
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