Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session S16: 2D Devices: Mechanical metamaterialsFocus
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Sponsoring Units: DMP Chair: Charlie Johnson, University of Pennsylvania Room: 315 |
Thursday, March 17, 2016 11:15AM - 11:51AM |
S16.00001: Hard and Soft Physics with 2D Materials. Invited Speaker: Paul McEuen With their remarkable structural, thermal, mechanical, optical, chemical, and electronic properties, 2D materials are truly special. For example, a graphene sheet can be made into a high-performance transistor, but it is also the ultimate realization of a thin mechanical sheet. Such sheets, first studied in detail by August F\"{o}ppl over a hundred years ago, are notoriously complex, since they can bend, buckle, and crumple in a variety of ways. In this talk, I will discuss a number of experiments to probe these unusual materials, from the effects of ripples on the mechanical properties of a graphene sheet, to folding with atomically thin bimorphs, to the electronic properties of bilayer graphene solitons. Finally, I discuss how the Japanese paper art of kirigami (kiru $=$ `to cut', kami $=$ `paper' ) applied to 2D materials offers a route to mechanical metamaterials and the construction of nanoscale machines. [Preview Abstract] |
Thursday, March 17, 2016 11:51AM - 12:03PM |
S16.00002: Band Gap Engineering of PbI2 by Incommensurate Van der Waals Epitaxy Yiping Wang, Jian Shi Van der Waals epitaxial growth had been thought to have trivial contribution on inducing substantial epitaxial strain in thin films due to its weak nature of Van der Waals interfacial energy. Due to this, electrical and optical structure engineering via Van der Waals epitaxial strain has been rarely studied. However, by appropriate film-substrate selection, we show that significant band structure engineering could be achieved in a soft thin film material PbI2 via Van der Waals epitaxy. The thickness dependent photoluminescence of single crystal PbI2 flakes was studied and attributed to the substrate-film coupling effect via incommensurate Van der Waals epitaxy. It is proposed that the Van der Waals strain is resulted from the soft nature of PbI2 and large Van der Waals interaction due to the involvement of heavy elements. Such strain plays vital roles in modifying the band gap of PbI2. The deformation potential theory is used to quantitatively unveil the correlation between thickness, strain and band gap change. Our hypothesis is confirmed by the subsequent mechanical bending test and Raman characterization. [Preview Abstract] |
Thursday, March 17, 2016 12:03PM - 12:15PM |
S16.00003: Introducing lattice strain to graphene encapsulated in hBN Hikari Tomori, Rineka Hiraide, Youiti Ootuka, Kenji Watanabe, Takashi Taniguchi, Akinobu Kanda Due to the characteristic lattice structure, lattice strain in graphene produces an effective gauge field. Theories tell that by controlling spatial variation of lattice strain, one can tailor the electronic state and transport properties of graphene. For example, under uniaxial local strain, graphene exhibits a transport gap at low energies, which is attractive for a graphene application to field effect devices. Here, we develop a method for encapsulating a strained graphene film in hexagonal boron-nitride (hBN). It is known that the graphene carrier mobility is significantly improved by the encapsulation of graphene in hBN, which has never been applied to strained graphene. We encapsulate graphene in hBN using the van der Waals assembly method. Strain is induced by sandwiching a graphene film between patterned hBN sheets. Spatial variation of strain is confirmed with micro Raman spectroscopy. Transport measurement of encapsulated strained graphene is in progress. [Preview Abstract] |
Thursday, March 17, 2016 12:15PM - 12:27PM |
S16.00004: Probing Mechanics of Crumpled Two-Dimensional Membranes and Cantilevers Ryan Nicholl, Hiram Conley, Nickolay Lavrik, Ivan Vlassiouk, Yevgeniy Puzyrev, Vijayashree Parsi Sreenivas, Sokrates Pantelides, Kirill Bolotin Two-dimensional materials (2DMs) are inevitably crumpled in the out-of-plane direction due to both static wrinkling associated with uneven stresses and dynamic wrinkling resulting from flexural phonons. Here, we investigate the effect of this crumpling on mechanical properties of 2DMs -- in-plane stiffness and bending rigidity. To carry out these measurements, we developed techniques to fabricate graphene membranes and singly clamped graphene cantilevers that are stable in vacuum and air. The measurements are performed by actuating these devices electrostatically and monitoring their displacement via sensitive interferometric profilometry both at room and low temperatures. We find that crumpling lowers the in-plane stiffness and strongly increases the bending rigidity of 2DMs. Furthermore, we unravel the relative contribution of static and dynamic wrinkling to observed renormalization of the effective mechanical constants. [Preview Abstract] |
Thursday, March 17, 2016 12:27PM - 12:39PM |
S16.00005: Electromechanical coupling in atomically thin MoS$_{2}$ and graphene Sajedeh Manzeli, Muhammed Malik Benameur, Adrien allain, Amirhossein Ghadimi, Mahmut Tosun, Andras Kis, Fernando Gargiulo, Gabriel Autès, Oleg V. Yazyev Nanoelectromechanical systems (NEMS) based on novel materials such as graphene and MoS$_{2}$ allow studying their electromechanical characteristics. Here, we incorporate single and bilayer MoS$_{2}$ and graphene into NEMS and investigated their electromechanical behavior. We observe a Strain-induced bandgap modulation in atomically thin MoS$_{2}$ membranes with a thickness dependent modulation rate. Finite element modeling is used to extract the piezoresistive gauge factor for MoS$_{2}$. In the case of graphene, deflection of monolayer graphene nanoribbons results in a linear increase in their electrical resistance where an upper limit is estimated for the gauge factor. Surprisingly, we observe oscillations in the electromechanical response of bilayer graphene. Our numerical simulations indicate that these oscillations arise from quantum mechanical interference in the transition region induced by sliding of individual graphene layers with respect to each other. Our results reveal that atomically thin MoS$_{2}$ membranes show strong piezoresistive effect, comparable to the state-of-the-art silicon sensors. Moreover, bilayer graphene conceals unexpectedly novel physics allowing the rare observation of room temperature electronic interference phenomena. [Preview Abstract] |
Thursday, March 17, 2016 12:39PM - 12:51PM |
S16.00006: Effect of strain on the electronic transport properties of mono- and bilayer graphene Fen Guan, Xu Du It has been theoretically proposed that strain can have a significant impact on the electronic and charge transport properties of mono- and bilayer graphene. Experimental study of such "strain engineering" in field effect devices has been limited, mainly due to the challenge in creating an effective tuning knob of strain. Here we report the fabrication and characterization of suspended graphene field effect transistor (FET) on a Polyimide substrate, where uniaxial strain is applied by bending the substrate. Magnetotransport measurement of both mono- and bilayer graphene FETs are carried out with variable strain, from compressive to tensile, over wide range of temperature (4.2-300K). The impact of the strain on the conductivity of graphene will be discussed and compared to the theoretical predictions on strain-induced gauge field and flexural phonon scatterings. [Preview Abstract] |
Thursday, March 17, 2016 12:51PM - 1:03PM |
S16.00007: Simulating MEMS Chevron Actuator for Strain Engineering 2D Materials Mounika Vutukuru, Jason Christopher, David Bishop, Anna Swan 2D materials pose an exciting paradigm shift in the world of electronics. These crystalline materials have demonstrated high electric and thermal conductivities and tensile strength, showing great potential as the new building blocks of basic electronic circuits. However, strain engineering 2D materials for novel devices remains a difficult experimental feat. We propose the integration of 2D materials with MEMS devices to investigate the strain dependence on material properties such as electrical and thermal conductivity, refractive index, mechanical elasticity, and band gap. MEMS Chevron actuators, provides the most accessible framework to study strain in 2D materials due to their high output force displacements for low input power. Here, we simulate Chevron actuators on COMSOL to optimize actuator design parameters and accurately capture the behavior of~the devices while under the external force of a 2D material. Through stationary state analysis, we analyze the response of the device through IV characteristics, displacement and temperature curves. We conclude that the simulation precisely models the real-world device through experimental confirmation, proving that the integration of 2D materials with MEMS is a viable option for constructing novel strain engineered devices. [Preview Abstract] |
Thursday, March 17, 2016 1:03PM - 1:15PM |
S16.00008: Mechanically tunable strain fields in suspended graphene by micro electromechanical systems Tymofiy Khodkov, Matthias Goldsche, Jens Sonntag, Sven Reichardt, Gerard Verbiest, Stephan Trellenkamp, Christoph Stampfer The discovery of graphene triggered an enormous interest on the class of two-dimensional (2D) materials. 2D materials manifested high sensitivity of their thermal, optical or electric response to applied tensile stress. Therefore, a rigorous and systematic investigation of their mechanical properties is extremely important. On the example of graphene -- a top candidate for future flexible electronic devices and sensors -- we demonstrate fully controlled and restorable realization of various strain fields in 2D membranes by coupling them to Si-based electrostatic micro-actuators (comb-drives).~ The comb-drive actuators are capable to provide significant forces and they are made of highly-doped silicon, i.e. they can be operated down to cryogenic temperatures allowing the investigation of quantum effects in electromechanical systems. Using confocal Raman spectroscopy we characterize strain distribution in suspended mono- and bilayer graphene sheets under induced tension (up to 0.5{\%}). A detailed analysis clearly show that graphene samples reproducibly experience strain in different directions only while applying voltages to the micro-actuator. This approach empowers accurate tuning of applied tension in any isolated 2D materials independent on other crucial parameters. [Preview Abstract] |
Thursday, March 17, 2016 1:15PM - 1:27PM |
S16.00009: ABSTRACT WITHDRAWN |
Thursday, March 17, 2016 1:27PM - 1:39PM |
S16.00010: Low dissipative mechanical resonators based on WSe$_{\mathrm{2}}$ monolayers Nicolas Morell, Antoine Reserbat-Plantey, Ioannis Tsioutsios, Kevin Schadler, Francois Dubin, Frank Koppens, Adrian Bachtold Atomically thin nano-electromechanical systems (2D-NEMS) combine low mass resonators having resonant frequencies in the MHz-GHz range, wide tunability and low damping. Atomically thin 2D semi-conductors, such as transition metal dichalcogenides (TMD), have rich optical properties (direct band gap, spin valley, embedded quantum emitters\textellipsis ), which are linked to their low dimensionality. While optical and electronic properties of WSe$_{\mathrm{2}}$ have been intensively investigated, there have not been any studies on WSe$_{\mathrm{2}}$ mechanical resonators. Although TMD NEMs have been fabricated, they have not been measured at cryogenic temperature so far. I will present a new semiconductor 2D-NEMS made of a single layer of WSe$_{\mathrm{2}}$. We measured mechanical and photoluminescence spectra of WSe$_{\mathrm{2}}$ suspended drums at cryogenic temperatures. Our results demonstrate an extremely low damping at low temperature with a quality factor Q \textgreater 47000 at T$=$3K, which is higher than what can be achieved with graphene NEMs. In addition, we investigated photothermal and optoelectronic effects on the mechanical degree of freedom, revealing the high potential of semiconductor 2D-NEMS for optomechanics experiments. [Preview Abstract] |
Thursday, March 17, 2016 1:39PM - 1:51PM |
S16.00011: Folded graphene nanochannels via pulsed patterning of graphene Rodrigo G. Lacerda, Ive Silvestre, Arthur W. Barnard, Samantha P. Roberts, Paul McEuen We present a resist-free patterning technique to form electrically contacted graphene nanochannels via localized burning by a pulsed white light source. The technique uses end-point detection to stop the burning process at a fixed resistance. By this method folded graphene nanochannels down to 30 nm in width with controllable resistance ranging from 10 k$\Omega $ to 100 k$\Omega $ is achieved [1]. Folding of the graphene sheet takes place during patterning, which provides very straight edges (zigzag/armchair) as identified by AFM, SEM and TEM. Electrical transport measurements for the nanochannels show a non-linear behavior of the current vs source-drain voltage as the resistance goes above 20 k$\Omega $ indicating conduction tunneling effects. The method described can be interesting not only for fundamental studies correlating edge folded structures with electrical transport but also as a promising path for fabricating graphene devices in situ. This method might also be extended to create nanochannels in other 2D materials. [1] I. Silvestre et al., APL, 106, 153105, 2015. [Preview Abstract] |
Thursday, March 17, 2016 1:51PM - 2:03PM |
S16.00012: Shear elastic constants of thin films of the misfit layered compound [(SnSe)$_{1.05}$]$_{n}$[MoSe$_{2}$]$_{n}$ Dongyao Li, Gavin Mitchson, David Johnson, Andre Schleife, David Cahill Crystalline materials with interlayer van der Waals bonding typically have low stiffness for shear deformation that reduces the through-plane thermal conductivity and facilitates the use of layered materials as solid-state lubricants. In graphite and MoS$_{2}$, c$_{44}=$5GPa and 18GPa respectively. The shear modulus of incommensurate layered materials is expected to be strongly reduced relative to ordered crystals but the magnitude of the suppression is currently unknown. We have recently developed an approach for measuring the shear modulus of thin layers using GHz surface acoustic waves (SAW). [(SnSe)$_{1.05}$]$_{n}$[MoSe$_{2}$]$_{n}$ with n$=$1-4 were prepared as thin films (60 nm) on Si substrates using the modulated elemental reactants technique. The SAW velocity $v_{SAW} $of Al/[(SnSe)(MoSe$_{2})$]/Si structures was measured using a polydimethylsiloxane (PDMS) phase-shift optical mask in a pump-probe system. c$_{44}$ was determined by fitting the measured $v_{SAW}$ to the calculated SAW velocity using multi-layer SAW model. c$_{33\, }$was measured by picosecond acoustics. c$_{11}$, c$_{12}$ and c$_{13}$ were calculated using density functional theory (DFT) with van der Waals correction. The measured c$_{33}$ and c$_{44}$ are compared with the DFT prediction. Experimentally we obtain c$_{44}=$1.9GPa, 1.2GPa, and smaller than 0.05GPa for n$=$1, 2 and 4. [Preview Abstract] |
Thursday, March 17, 2016 2:03PM - 2:15PM |
S16.00013: Realization of Ripple Induced Pseudomagnetic Fields in Graphene. Yuhang Jiang, Jinhai Mao, Guohong Li, Daiara Faria, Andrea Latge, Ramon Carrillo-Bastos, Nancy Sandler, Eva Y. Andrei Strain induced distortions of the honeycomb lattice in graphene produce pseudo-magnetic (PM) fields which change the low energy electronic structure by introducing pseudo Landau levels (LLs), similar to real magnetic fields. The spatial distribution of the PM field is a sensitive function of the strain geometry providing new opportunities for engineering the band structure and transport properties. Here we report on scanning tunneling microscopy (STM), spectroscopy (STS), and numerical simulations on strain-induced PM field generated by quasi 1D ripples in graphene supported by flat substrates, such as hBN or SiO$_{2}$. The ripples are typically \textasciitilde 1 $\mu $m long, \textasciitilde 20 nm wide and several nm high. Their height profile, which is measured by STM, is compared to numerical simulations from which the local strain and the spatial distribution of the PM field is calculated. An independent measure of the local PM field, obtained from the LLs sequence in STS measurements, gives values comparable to those calculated from the height profile. We further show that the ripple geometry produces regions of alternating PM fields which may be associated with ballistic valley filter channels. [Preview Abstract] |
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