Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L6: Focus Session: Phononic And Mechanical Phenomena In Nanostructures |
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Sponsoring Units: DMP Chair: Michael Scheibner, University of California, Merced Room: 006A |
Wednesday, March 4, 2015 8:00AM - 8:12AM |
L6.00001: Coherent phonon modulation by nanoscale acoustically mismatched interface Shangjie Yu, Min Ouyang Precise engineering of phonon spectrum by material design is essential for in-depth understanding of fundamental physical phenomena as well as new technology breakthrough. When phonons propagate through two different constituents, their mismatched interface can coherently modulate phonon spectrum. In this talk, we will demonstrate the phonon characteristics can be precisely tailored through nanoscale interfacial coupling by investigating acoustically mismatched core-shell hetero-nanostructures with ultrafast pump-probe technique. Coherent phonon coupling between core and shell through their interface has been experimentally revealed, which agrees well with theoretical simulation. This interfacial phonon coupling also represents a unique fingerprint of complex nanostructures. [Preview Abstract] |
Wednesday, March 4, 2015 8:12AM - 8:24AM |
L6.00002: Acoustic vibrations of complex metal nanostructures Aftab Ahmed, Anna Klinkova, Eugenia Kumacheva, Jeffrey Guest Coherent acoustic vibrations of plasmonic nanoparticles modulate light at ultrahigh frequencies. Plasmonic nanoparticles are of particular interest because of their high absorption cross sections, and offer wide range of applications including sensing and nano-mechanical devices. Here we show acoustic vibrations of complex metal nanostructure using a femtosecond pump-probe technique. The studied nanostructure is composed of an octahedral core (Au) and cube shell (Ag). Unique elastic properties and complex geometries of the two metals provide a richer transient absorption spectrum as compared to that of a simple nanocube of similar dimensions. Further, two different vibrational modes are detected at different probe wavelengths. Numerical simulations were carried out to explain our experimental findings and to study the dynamics of the complex structure. Dependence of the excited modes on the pump wavelength is also investigated. These oscillations provide insights into the mechanical properties of the material at nanoscale. [Preview Abstract] |
Wednesday, March 4, 2015 8:24AM - 8:36AM |
L6.00003: Slow light using crystal lattice vibrations in coupled quantum dots Andrew Jacobs, Joshua Casara, Cameron Jennings, Mark Kerfoot, Michael Scheibner Phonons can induce an optical transparency in crystal structures, as was recently shown in an experimental study of asymmetric coupled quantum dots [1]. This transparency occurs due to Fano-type quantum interference between the discrete interdot exciton and continuum single dot-like polaron states. Here, we study this phonon-induced optical transparency as an avenue for slowing light. We find that slowdown factors up to 80,000 are possible, corresponding to a time delay of order 1 ps for a photon passing through a single coupled quantum dot pair. The optical slowdown is sensitive to both the Fano asymmetry factor and the homogeneous linewidth of the interdot exciton--we discuss the tunability of the slowdown factor using either parameter. Lastly, we investigate the effect of charge fluctuations, which are found to decrease the amount of optical slowdown. The experimentally measured interdot exciton linewidth is then used to theoretically infer the maximum possible optical transparency and slowdown factor without fluctuations present. [1] M. L. Kerfoot et al., Nat. Commun. 5, 3299 (2014). [Preview Abstract] |
Wednesday, March 4, 2015 8:36AM - 8:48AM |
L6.00004: Phononic frequency combs through nonlinear resonances Ru-Wen Peng, Lu-Shuai Cao, Dong-Xiang Qi, Mu Wang, Peter Schmelcher It is well known that optical frequency combs have become important coherent optical sources with diverging applications, ranging from optical frequency metrology to ultracold gases. In this work, we explore an analogue of optical frequency combs in driven nonlinear phononic systems, and present a mechanism for generating phononic frequency combs through nonlinear resonances. In the underlying process, a set of phonon modes is simultaneously excited by the external driving which yields frequency combs with an array of discrete and equidistant spectral lines of each nonlinearly excited phonon mode. Frequency combs through nonlinear resonance of different orders are investigated, and in particular the possibility of correlation tailoring in higher-order cases is revealed. We suggest that our results can be applied in various nonlinear acoustic processes, such as phonon harvesting, and can also be generalized to other nonlinear systems. Reference: L. S. Cao, D. X. Qi, R. W. Peng, Mu Wang and P. Schmelcher, Phys. Rev. Lett. 112, 075505 (2014). [Preview Abstract] |
Wednesday, March 4, 2015 8:48AM - 9:00AM |
L6.00005: Low Frequency Thermal Conductivity in Micro Phononic Crystals Virgilio Anjos, Alison Arantes We study theoretically the cumulative thermal conductivity of a micro phononic crystal at low temperature regime. The phononic crystal considered presents carbon microtubes inclusions arranged periodically in a two-dimensional square lattice embebed in soft elastic matrix. Moderate and high impedance mismatch are considered concerning the material composition. The low frequency phonon spectra (up to tens of GHz) are obtained solving the generalized wave equation for inhomogeneous media within the Plane Wave Expansion method. We consider low temperatures in order to increase the participation of GHz thermal phonons. We observed suppression in the cumulative thermal conductivity at the band gap region and thus a reduction of thermal conductivity of the phononic crystal when compared with the bulk matrix. [Preview Abstract] |
Wednesday, March 4, 2015 9:00AM - 9:12AM |
L6.00006: ABSTRACT WITHDRAWN |
Wednesday, March 4, 2015 9:12AM - 9:24AM |
L6.00007: How intermixing and anharmonicity enhances interfacial thermal conductance? Carlos Polanco, Jingjie Zhang, Nam Le, Rouzbeh Rastgarkafshgarkolaei, Pamela Norris, Avik Ghosh The thermal conductance at an interface, whether ballistic or diffusive, can be expressed as a product of the number of conducting channels (M) and their average transmission (T). The common expectation is that interfacial defects reduce T and thus hurt the conductance. This is however at odds with recent simulations showing that a thin intermixing layer can in fact enhance the conductance. We argue that such an enhancement occurs when the increase in number of modes outweighs the reduction in their average transmission. The new channels open as a result of (a) the random interfacial structure that relaxes the conservation rules for the transverse momentum and promotes transitions between formerly symmetry disallowed channels; and (b) inelastic scattering through phonon-phonon interactions that allow modes beyond the contact cut-off frequency to contribute to transport. We use these results to build a back of the envelope model for interfacial conductance that depends on the mixing distribution, the anharmonic strength, the phonon polarization and wavelength. Non-Equilibrium Green's Function (NEGF) as well as Molecular Dynamics (MD) simulations on Si/mixed layer/Ge, as well as simpler FCC crystals support our results. [Preview Abstract] |
(Author Not Attending)
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L6.00008: Interfacial thermal transport and phonon-phonon conversion at the graphene-boron nitride lateral interface Zhun-Yong Ong, Gang Zhang, Yong-Wei Zhang Using the nonequilibrium Green's function method, we compute the the thermal boundary conductance of a monolayer graphene-boron-nitride (Gr-BN) lateral heterostructure with an armchair interface. At 300 K, the thermal conductance of the Gr-BN interface is computed to be 3.5 nW/nm$^2$ or equivalent to approximately 200 nm of BN. The application of a strain, parallel or normal to the interface, also reduces the interfacial thermal resistance by improving the transmission of acoustic phonons. We do a modal decomposition of the phonon transmission spectrum and identify the phonon scattering channels responsible for heat transfer at the interface. We show that at low frequencies, interfacial heat transfer is dominated by the longitudinal, transverse and flexural acoustic phonons while at higher frequencies, it is mostly by longitudinal acoustic and optical phonons. Our work sheds light on the mechanism of phonon-phonon conversion at the interface of 2D lateral heterostructures and how it can be modified via the application of strain. \\[4pt] [1] Levendorf et al., Nature 488, 627 (2012); Liu et al., Nature Nanotechnology 8, 119 (2013) [Preview Abstract] |
Wednesday, March 4, 2015 9:36AM - 9:48AM |
L6.00009: Thermoelectric transport through a quantum nanoelectromechanical system and its backaction Hangbo Zhou, Juzar Thingna, Jian-Sheng Wang, Baowen Li In recent years, nanoelectromechanical systems (NEMS) have been in the limelight of intense experimental and theoretical investigation due to their potential applications in quantum-controlled devices. In this work we study the theromoelectric transport through a single electron transistor (SET) coupled to a quantum nano mechanical resonator (NR). The effects of the quantum NR on the thermoelectric current are investigated with special emphasis on how the SET-NR coupling strength plays a role in such a NEMS. We find that the SET-NR coupling is not only able to suppress or enhance the thermoelectric current but can also switch its direction. The effect of the NR on the thermoelectric coefficients of the SET are studied and we find that even a small SET-NR coupling could dramatically suppress the figure of merits $ZT$. Lastly, we investigate the backaction of electronic current on the NR and possible routes of heating or cooling the NR are discussed. We find that by appropriately tuning the gate voltage the backaction can be eliminated, which could find possible applications to enhance the sensitivity of detection devices. [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:00AM |
L6.00010: Emergence of Chaos in nano-electromechanical shuttles with hard-wall collision: Nonanalytic charge transport Hee Chul Park, Kang-Hun Ahn We develop a theory for charge transport in nano-electromechanical shuttles in the presence of hard-wall collision. We show that, in certain regimes, the time-averaged charge current is not predictable and is not an analytic function of applied voltage. The rectified electric current and its non-analyticity emerge from a non-Markovian process in the presence of the hard-wall collision, which causes chaotic motion of the shuttle. [Preview Abstract] |
Wednesday, March 4, 2015 10:00AM - 10:12AM |
L6.00011: Nonlinearity-induced synchronization enhancement in micromechanical oscillators Jeffrey R. Guest, Dario Antonio, David A. Czaplewski, Daniel L\'opez, Sebasti\'an I. Arroyo, Dami\'an H. Zanette An autonomous oscillator synchronizes to an external harmonic force only when the forcing frequency lies within a certain interval around the oscillator's natural frequency. Under ordinary conditions, the width of this ``synchronization range'' decreases when the oscillator's self-sustained amplitude grows, constraining synchronized motion of micro- and nanomechanical resonators to narrow frequency and amplitude bounds. In this talk, we will show that {\it nonlinearity} in the oscillator can be exploited to manifest a regime where the synchronization range {\it increases} with increasing oscillation amplitude. We demonstrate this regime experimentally with a self-sustained micromechanical oscillator, revealing an increase in the synchronization range by orders of magnitude over that expected for a linear oscillator. We provide analytical results which show that nonlinearities are the key determinants of this enhancement. Our results suggest a new strategy to enhance synchronization of micromechanical oscillators by capitalizing on their intrinsic nonlinear dynamics. [Preview Abstract] |
Wednesday, March 4, 2015 10:12AM - 10:24AM |
L6.00012: Fluctuation Reduction in a Si Micromechanical Resonator Tuned to Nonlinear Internal Resonance B. Scott Strachan, David Czaplewski, Changyao Chen, Mark Dykman, Daniel Lopez, Steven Shaw We describe experimental and theoretical results on an unusual behavior of fluctuations when the system exhibits internal resonance. We study the fundamental flexural mode (FFM) of a Si microbeam. The FFM is electrically actuated and detected. It is resonantly nonlinearly coupled to another mode, which is not directly accessible and has a frequency nearly three times the FFM frequency. Both the FFM and the passive mode have long lifetimes. We find that the passive mode can be a ``sink'' for fluctuations of the FFM. This explains the recently observed dramatic decrease of these fluctuations at nonlinear resonance [1]. The re-distribution of the vibration amplitudes and the fluctuations is reminiscent of what happens at level anti-crossing in quantum mechanics.~However, here it is different because of interplay of the dependence of the vibration frequency of the FFM on its amplitude due to internal nonlinearity and the nonlinear resonance with the passive mode. We study both the response of the system to external resonant driving and also the behavior of the system in the presence of a feedback loop. The experimental and theoretical results are in good agreement. [1] D. Antonio, \textit{Nat. Comm}., \textbraceleft \textbf{3}\textbraceright , 806 (2012). [Preview Abstract] |
Wednesday, March 4, 2015 10:24AM - 10:36AM |
L6.00013: Dynamical properties of single crystalline 4H-SiC micro-cantilevers and determination of Poisson's ratio and density of 4H-SiC thin film Feng Zhao, Allen Lim, Quan Tran As a wide bandgap semiconductor, single crystalline 4H-polytype silicon carbide (4H-SiC) is a very attractive material for microelectromechanical systems (MEMS) with operation in harsh environments such as high temperature, radiation, chemical/biomedical, etc. Fabrication and performance prediction of 4H-SiC MEMS require releasing of thin films as well as an accurate value of its important material properties including density and Poisson's ratio. However, releasing single crystal 4H-SiC microstructures is extremely challenging due to the very inert chemical resistance of 4H-SiC (practically only etched by molten KOH above 600 $^{\circ}$C). Although density and Poisson's ratio in bulk 4H-SiC form have been known, they may not be the same in thin film with the thickness in the order of micrometers for MEMS systems. In this paper, we successfully released single crystal 4H-SiC to fabricate suspended micro-cantilever structures using a recently developed surface micromachining technique. The dynamical properties of these cantilevers including resonant frequency and force-distance were characterized, from which the density and Poisson's ratio of 4H-SiC thin film were determined. [Preview Abstract] |
Wednesday, March 4, 2015 10:36AM - 10:48AM |
L6.00014: Structural and Mechanical Properties of (Co/Cu) Co-doped Nano ZnO Ozgur Ozturk, Elif Asikuzun, Dogan Akcay, Lutfi Arda, Ahmet Tolga Tasci, Abdulkadir Senol, Sevim Senol, Cabir Terzioglu Zn$_{\mathrm{1-x}}$Co$_{\mathrm{x}}$O (x$=$0.01, 0.02, 0.03, 0.04, 0.05 and 0.10) and Zn$_{\mathrm{0.95-x}}$Co$_{\mathrm{0.05}}$Cu$_{\mathrm{x}}$O (x$=$0.0, 0.01, 0.02, 0.03, 0.04 and 0.05) solutions were prepared by sol-gel synthesis using zinc acetate dihydrate, cobalt acetate tetrahydrate and copper acetate tetrahydrate which were dissolved into solvent and chelating agent. Zn$_{\mathrm{1-x}}$Co$_{\mathrm{x}}$O and Zn$_{\mathrm{0.95-x}}$Co$_{0.05}$Cu$_{\mathrm{x}}$O nanoparticles were annealed at 600$^{\circ}$C for 30 min to observe the doping effect on structural and mechanical properties. The particle size, crystal structure, particle morphology and elemental composition were characterized by XRD, SEM and EDS. Vickers microhardness measurements have been done on the sample surfaces using a digital Vickers microhardness tester in the load range of 0.245--2.940 N. In this work, the crystal structure, morphology, and mechanical properties of nanoparticles were presented. [Preview Abstract] |
Wednesday, March 4, 2015 10:48AM - 11:00AM |
L6.00015: The structural and mechanical behaviours of Boron-doped ZnO nanostructures Abdulkadir Senol, Sevim Demirozu Senol, Ozgur Ozturk, Elif Asikuzun, Ahmet Tolga Tasci, Cabir Terzioglu Undoped and Boron (B)-doped Zinc Oxide (ZnO) nanopowders were synthesized by Hydrothermal method. The structural and mechanical behaviours of B doped ZnO (Zn$_{\mathrm{1-x}}$B$_{\mathrm{x}}$ O, x$=$0, 0.05, 0.07, 0.11) were systematically examined. The crystal structure, phases, sizes and microstructure of Zn1-xBx O powder samples characterized by using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Microhardness values of all B doped ZnO powders were measured with different loads (0.245, 0.490, 0.980, 1.960 ve 2.940 N) using a digital Vickers microhardness tester. The experimental microhardness data were used to determine elastic modules, yield strength, and fracture toughness value of the samples. Additionally, the experimental results were analyzed using the various theoretical models namely, Kick's Law, Elastic/Plastic Deformation (EPD) models, Proportional Specimen Resistance (PSR), and Hays-Kendall (HK) approach. The Vickers microhardness measurements revealed that hardness of Zn$_{\mathrm{1-x}}$B$_{\mathrm{x}}$ O powder samples increased with B doping. [Preview Abstract] |
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