Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Y27: Mechanical Properties of Nanomaterials |
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Sponsoring Units: DCMP Chair: John Sullivan, Sandia National Laboratories Room: 329 |
Friday, March 20, 2009 8:00AM - 8:12AM |
Y27.00001: Carbon nanotube dispersed liquid crystal: A nano electromechanical system Rajratan Basu, Germano Iannacchione Electric field induced director orientation of a nematic liquid crystal (LC) + carbon nanotube (CNT) system reveals insights on switching behavior for this anisotropic composite. Once the field goes off, the LC+CNT system relaxes back to the original orientation through a mechanical rotation, revealing the intrinsic dynamics. LC molecules and CNTs cooperatively form local \textit{pseudonematic }domains in the isotropic phase due to strong LC-CNT interactions. These field-responsive anisotropic domains do not relax back to the original orientation on switching of the field off, which could find potential applications in memory devices. [Preview Abstract] |
Friday, March 20, 2009 8:12AM - 8:24AM |
Y27.00002: Strong ``position squared'' optical readout of a micromechanical oscillator Jack Sankey, Andrew Jayich, Benjamin Zwickl, Cheng Yang, Jack Harris Optomechanical devices with a flexible SiN membrane inside an optical cavity allow for very high optical finesse and high mechanical quality factor in a single device. They also provide fundamentally new functionality: the cavity detuning can have a quadratic dependence on the membrane position. This enables a measurement of ``position squared'' ($x^2$) and in principle a QND phonon number readout of the membrane. However, the readout achieved using a single cavity mode is not sensitive enough to observe quantum jumps between phonon Fock states. Here we demonstrate an $x^2$-sensitivity that is orders of magnitude stronger using two nearly-degenerate transverse cavity modes, and that we can tune this sensitivity somewhat by tilting the membrane. We derive a perturbatve treatment that describes the interactions between the transverse optical modes and achieve good agreement with observation using realistic parameters. We also show that the $x^2$-coupling should be easily tunable over a wide range via mm-scale membrane displacements along the cavity axis. [Preview Abstract] |
Friday, March 20, 2009 8:24AM - 8:36AM |
Y27.00003: \textit{In-situ} Transduction of the In-Plane and Out-of-Plane Modes of Nanowire-based Very-High Frequency Electromechanical Resonators Wayne Fung, Wei Lu Recent advances in nanoelectromechanical systems (NEMS) promise important applications such as mass and force sensing, rf signal generation and timing, and quantum measurement studies. Chemically synthesized nanowires appear especially attractive for NEMS because of their atomically smooth surfaces and large aspect ratios. Here we report the measurements of doubly-clamped beam mechanical resonators using SnO$_{2}$ nanowires with widths ranging from 30 to 80 nm. The devices are electrostatically actuated and detected on-chip using a dual-gate setup and an all-electronic transduction scheme. This setup also allows us to independently actuate and tune the resonant frequencies of both the in-plane and out-of-plane modes of vibration \textit{in situ}, potentially leading to NEMS-based practical applications. Our devices exhibit resonant frequencies ranging from 30 to 100 MHz, quality factors up to 2000, force sensitivities down to 10$^{-14}$ N/Hz$^{1/2}$, and mass sensitivities down to 5 x 10$^{-17}$ g. The frequency of the in-plane and out-of-plane modes can be tuned within $\pm $1 MHz of their nominal values at gate voltages of $\pm $5 V. [Preview Abstract] |
Friday, March 20, 2009 8:36AM - 8:48AM |
Y27.00004: ABSTRACT WITHDRAWN |
Friday, March 20, 2009 8:48AM - 9:00AM |
Y27.00005: Mechanical properties of metal-repaired defective carbon nanotubes Guangping Zheng Carbon nanotubes (CNs) are promising in the producing of strong and light structural materials because of their unique mechanical properties such as ultrahigh mechanical strength and large ultimate tensile strain. However, CNs are not defect free. Instead, several types of intrinsic defects exist, hence the mechanical strength and ductility of CN can be significantly lower than those of an ideal one. In this study, 3d transition-metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) or clusters are filled into the defective sites of single-walled (SW) CN containing vacancy defects, resulting in stable repaired SWCN. The mechanical and electronic properties of the repaired SWCNs are investigated by spin-polarized density functional theory. The results indicate that the 3d transition-metal atoms acting as substitutional defects can substantially modify the electronic structure and magnetization of an un-deformed CN. Compared with defective SWCN, the metal-repaired CN shows significant enhancements in mechanical strength and ductility that are close to or even better than those of pristine CNs. The underlying physics of these behaviors are analyzed by the structural transformation, electronic structures and spin and charge distributions during the tensile tests. Strong magneto-mechanical coupling effect is found to be responsible for the enhanced mechanical behaviors of metal-CN hybrid structures. [Preview Abstract] |
Friday, March 20, 2009 9:00AM - 9:12AM |
Y27.00006: Mechanics of Nanometric Water Wire Manhee Lee, Baekman Sung, Bongsu Kim, Jongwoo Kim, Wonho Jhe Water has been one of the perfect newtonian viscous liquids, which are exactly described by navier-stokes equation. However, it has been found that the effective shear viscosity of water confined between mica crystals at few nanometer thickness is very different from the one of 3-dimensional bulk water. While some researchers have measured very high viscoelasticity of the confined liquid [1], the other researchers reported the fluidic nature of water confined between mica surfaces at $<$3.5 nm interfacial separation like bulk-water viscosity [2]. These conflicting results concerning the mechanical properties of nanometric water have been continually reported for the past several years. None of them clearly clarified the mechanical properties of nanometric water, and the detailed behavior of the viscoelasticity within a tip-sample separation less than 1 nm has not been measured. Here, we investigate a nanometric water cluster formed between AFM tip and sample surface and present the nano-mechanical properties of it including viscoelasticity, dissipation energy, and phase transitions. [1] Y. Zhu and S. Granick, Phys. Rev. Lett. \textbf{87}, 096104 (2001). [2] U. Raviv, P. Laurat, and J. Klein, Nature (London) \textbf{413}, 51 (2001). [Preview Abstract] |
Friday, March 20, 2009 9:12AM - 9:24AM |
Y27.00007: Torsional Stick-Slip Behavior in WS$_{2}$ Nanotubes K.S. Nagapriya, Ohad Goldbart, Ifat Kaplan-Ashiri, Gotthard Seifert, Reshef Tenne, Ernesto Joselevich We experimentally observed atomic-scale torsional stick-slip behavior in individual nanotubes of tungsten disulfide (WS$_{2})$. When an external torque is applied to a WS$_{2}$ nanotube, all its walls initially stick and twist together, until a critical torsion angle, at which the outer wall slips and twists around the inner walls, further undergoing a series of stick-slip torque oscillations. This is contrary to what happens in a multi-wall carbon nanotube, where an external torque causes the outer wall to slip and twist smoothly around the inner walls. We present a theoretical model based on DFTB calculations, which explains the torsional stick-slip behavior of WS$_{2}$ nanotubes in terms of a competition between the effects of the in-plane shear stiffness of the WS$_{2}$ walls and the inter-wall friction arising from the atomic corrugation of the interaction between adjacent WS$_{2}$ walls. K. S. Nagapriya, Ohad Goldbart, Ifat Kaplan-Ashiri, Gotthard Seifert, Reshef Tenne, and Ernesto Joselevich, Phys. Rev. Lett. \textbf{101}, 195501 (2008). [Preview Abstract] |
Friday, March 20, 2009 9:24AM - 9:36AM |
Y27.00008: Optical Requirements for Quantum Mechanics with Micromechanical Systems Dustin Kleckner, Brian Pepper, Evan Jeffrey, Petro Sonin, Dirk Bouwmeester Interest in micro-optomechanical systems is motivated by the desire to test quantum mechanics on relatively massive scales. Proposals for realizing these effects have extremely challenging technical requirements, particularly with regards to optical quality. We present the results of simulations designed to determine the effects of imperfections in real systems on the maximum achievable optical finesse. Additionally, we will discuss recent progress in our efforts to fabricate novel devices with the required properties. [Preview Abstract] |
Friday, March 20, 2009 9:36AM - 9:48AM |
Y27.00009: A Servo-Controlled Atomic Break Junction: Closing the Gap between Experiment and Modeling Douglas Smith, Jon Pratt, Francesca Tavazza Measurement of force and displacement in atomic-scale deformation experiments enables direct measurement of atomic bond strength and stiffness, promises insight into phenomena like adhesion and friction, and promises to provide reliable experimental data for atomistic models. Such experiments require displacement accuracy well below atomic dimensions and force accuracy below predicted atomic-bond rupture forces of 1.5 nN. A break junction instrument has been realized that uses a fiber-optic laser interferometer to hold the position of a gold contact stable to better than 5 pm for tens of minutes in vacuum at 4 K. This has allowed a careful study of quantized electron transport through a gold junction as it is drawn down to a single Au-Au bond and broken. Density functional calculations show that the junction necks down to a single bond that breaks with a reproducible rupture force that is independent of the crystallographic orientation of the original junction. The work represents one of the first direct deformation studies of an experimental system small enough to be modeled in its entirety using density functional methods. [Preview Abstract] |
Friday, March 20, 2009 9:48AM - 10:00AM |
Y27.00010: High-performance supercapacitors, actuators and elastomeric composites based on CNT assemblies Mikhail Kozlov, Jiyoung Oh, MinKyoon Shin, Raquel Robles, M\'arcio Lima, Ray Baughman A number of materials ranging from carbon nanotube (CNT) yarns, sheets and CNT-based composites to shape memory alloys (SMA) have been explored for the application in the area of energy conversion and storage. Highly porous sheets comprised of Single Walled Carbon Nanotubes and doped polypyrrole (SWNT-PPy) were found to possess remarkably high specific capacitance of about 131 F/g; CNT-elastomeric polymer composites exhibited electrical conductivity of about 0.5 S/cm and can be stretched by 1400{\%}. We found that if powered electrically, the isometric stress generated by the CNT-based actuators could be as large as 12 MPa. This approaches the stress generation capability of commercial ferroelectrics and is significantly larger than that of natural muscles. We also report several types of artificial muscles that convert the chemical energy of high--energy-density fuels to mechanical energy. Because of more than 30 times higher energy density obtainable for fuels like methanol, compared to that for the most advanced batteries, the major expected benefits are dramatic increase in energy conversion efficiency, work capacity, power performance. [Preview Abstract] |
Friday, March 20, 2009 10:00AM - 10:12AM |
Y27.00011: Determination of Intrinsic Damping in a MWNT using the Harmonic Detection of Resonance Method Doyl Dickel, Gayatri Keskar, Malcolm Skove, Apparao Rao Harmonic Detection of Resonance (HDR) method has been shown to be an effective method of electrically determining the resonant frequency of cantilevered structures at both the micro- and nanometer scale. Previously, HDR has been used effectively to study nonlinear behavior in highly anharmonic systems, as a gas sensor, and to determine the resonant frequency of nanoscale structures such as a Multi-wall Carbon Nanotube (MWNT). In addition, HDR method has been used for determining material properties such as the Young's Modulus. Here, we provide a simple model describing the theory underlying the HDR method and a demonstration of its use to determine the resonant behavior of a MWNT. Finally, we report the effects of varying pressures on both the resonant frequency and quality factor of the MWNT. We also estimate the intrinsic damping inherent in the MWNT from these effects and show its correlation with defect density. The MWNT examined was found to have a resonant frequency for its primary mode of oscillation of 2.79 MHz with a quality factor of 10.15 at a pressure less than 1 Pa. [Preview Abstract] |
Friday, March 20, 2009 10:12AM - 10:24AM |
Y27.00012: Eigenmodes and Vibration Spectra of Ag$_2$Ga Nanoneedles Measured Using Laser Doppler Vibrometry R. Reifenberger, L. Biedermann, R. Tung, A. Raman, M. Yazdanpanah, R. Cohn Applications for selectively grown Ag$_2$Ga nanoneedles include high-aspect ratio conductive AFM tips, mass sensors, force sensors, and high resonant frequency nano-cantilevers. To help enable these applications, reliable estimates for the elastic modulus of these nanoneedles and the quality factors of their oscillations are of interest. We have used Laser Doppler Vibrometry (LDV) to measure the vibration spectra and eigenmodes of individual Ag$_2$Ga nanoneedles. An advantage of this technique is that the vibration spectra between 0 and 20~MHz can be measured with high frequency resolution, allowing the eigenfrequencies and quality factors of each resonance to be accurately determined. Using Euler-Bernoulli beam theory, the elastic modulus and spring constant can be calculated from the nanoneedles' eigenfrequencies and the dimensions of the nanoneedles. The techniques developed can be used to measure the vibrational spectra of any suspended nanowire with high frequency resolution. [Preview Abstract] |
Friday, March 20, 2009 10:24AM - 10:36AM |
Y27.00013: Digital Batteries Alfred Hubler The energy density in conventional capacitors is limited by sparking. We present nano-capacitor arrays, where - like in laser diodes and quantum wells [1] - quantization prevents dielectric breakthrough. We show that the energy density and the power/weight ratio are very high, possibly larger than in hydrogen [2]. Digital batteries are a potential clean energy source for cars, laptops, and mobile devices. The technology is related to flash drives. However, because of the high energy density, safety is a concern. Digital batteries can be easily and safely charged and discharged. In the discharged state they pose no danger. Even if a charged digital battery were to explode, it would produce no radioactive waste, no long-term radiation, and probably could be designed to produce no noxious chemicals. We discuss methodologies to prevent shorts and other measures to make digital batteries safe. [1] H. Higuraskh, A. Toriumi, F. Yamaguchi, K. Kawamura, A. Hubler, Correlation Tunnel Device, U. S. Patent No. 5,679,961 (1997) [2] Alfred Hubler, http://server10.how-why.com/blog/ [Preview Abstract] |
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