Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session V30: Nanowires and Nanotubes: Thermal and Mechanical Properties |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Traian Dumitrica, University of Minnesota Room: C147/154 |
Thursday, March 24, 2011 8:00AM - 8:12AM |
V30.00001: Thermal boundary resistance between carbon nanotubes in nanocomposites with Monte Carlo simulations Khoa Bui, Brian Grady, Dimitrios Papavassiliou Enhancing the thermal conductivity of composites by incorporating carbon nanotubes (CNTs) has been an area of vigorous research recently. Measurements of the effective thermal conductivity (keff) for CNT-polystyrene composites at high CNT \%wt found that the ratio (keff/kpolymer) at high concentration of CNTs is not as good as that at low CNT concentration [1]. It appears that the CNT dispersion pattern becomes worse, resulting in the formation of CNT bundles. In this work, we apply Monte Carlo simulations to investigate the keff at different weight fractions taking into account the bundle size and orientation, as well as the thermal boundary resistance. By validating with the experiment data, we found that the phonon transmission probability at the interface decreases by temperature. In addition, the poor enhancement of keff at high CNT concentration is because of the CNT-CNT contact resistance and because of the bundle geometry itself, which is equivalent to the presence of one low aspect ratio nanotube. References [1] Peters J. E.; Papavassiliou D.V; Grady B. P., Macromolecules 2008, 41, 7274-7277. [Preview Abstract] |
Thursday, March 24, 2011 8:12AM - 8:24AM |
V30.00002: Strain Engineering of the thermal conductance in Si nanowires A. Paul, K. Miao, M. Luisier, G. Klimeck Silicon nanowires (SiNWs) are promising semiconductor structures spanning a wide range of applications from CMOS devices to thermoelectric modules. Recently, SiNWs have shown tremendous potential as good thermoelectric materials with ZT coefficients larger than 1 [1]. This figure of merit can be further improved by tuning the thermal conductivity of the SiNWs. Here, we show that strain provides a natural way of tuning the thermal conductance of ultra-scaled SiNWs. We utilize a modified Valence Force Field (MVFF) model [2] to calculate the phonon dispersion in these SiNWs under strain and extract their thermal conductance using Landauer's approach. Our investigation shows that uniaxial tensile and hydrostatic compressive help reduce the thermal conductance of SiNWs. For example, a 3nm X 3nm, $<$100$>$ oriented nanowire undergoing a 2{\%} uniaxial tensile strain exhibits a thermal conductance reduced up to 2.6{\%}, whereas a compressive hydrostatic strain of 2{\%} gives a reduction of around 8{\%}. Thus, strain engineering can prove beneficial in tuning the thermal conductance in Si nanowires and offers an efficient way to further improve the ZT figure of merit. Finanacial support from MSD, SRC, MIND and NSF, computational support from nanoHUB.org under NCN. Refs: [1] A. I. Hochbaum et al., 'Enhanced thermoelectric performance of rough silicon nanowires', Nature 451, no. 7175, pp. 163, 2008. [2] A Paul, M Luisier and G Klimeck, 'Modified valence force field approach for phonon dispersion: from zinc-blende bulk to nanowires.', arXiv:1009.6188v2[cond-mat.mes-hall]. [Preview Abstract] |
Thursday, March 24, 2011 8:24AM - 8:36AM |
V30.00003: Thermal Conductivity of Metallic Nanowires near Room Temperature N. Stojanovic, J. Berg, D.H.S. Maithripala, M. Holtz In metallic structures with nanoscale dimension both electrical and thermal conductivities are significantly different from their bulk counterparts. The total thermal conductivity is generally the sum of the electronic and phonon contributions. We examine electron and phonon heat transport in metals, in the temperature range near to or above the Debye temperature, where it is generally assumed that phonon component is negligible for metals, an assumption that has not been subjected to rigorous experimental verification, particularly at the nanoscale, due to difficulties in direct measurement of thermal conductivity. Experimental evidence suggests that the Wiedemann-Franz (W-F) law breaks down at the nanoscale. The neglected phonon component is one factor that has been cited as contributing to the apparent discrepancy in W-F. Another factor is inelastic electron-phonon scattering that influences transport due to a temperature gradient, but not due to an electric field. We report experimental results for Al nanowires and develop a model based on the Boltzmann transport equation for size dependence of electrical and thermal conductivity in nanowires. The model is validated with available data reporting direct measurements of thermal conductivity of nanowires, ribbons, and thin films. The W-F law and Lorenz factor are examined and a modified version of W-F is presented, corrected for these two factors and valid from macro- to nanoscale provided characteristic sizes exceed the phonon mean free path. [Preview Abstract] |
Thursday, March 24, 2011 8:36AM - 8:48AM |
V30.00004: Diffusion-induced dephasing and bistability of nanoresonators Juan Atalaya, Mark I. Dykman, Andreas Isacsson We study dephasing of an underdamped harmonic oscillator due to frequency fluctuations. The spectrum of the response to an external field is sensitive to the nature of the fluctuations. For nanomechanical resonators, if the dephasing is due to diffusion of adsorbed particles along the resonator, the spectrum varies from a single Lorentzian peak to two closely spaced peaks depending on the parameters. If the dephasing depends on the oscillator state, the oscillator can exhibit bistability of forced vibrations. We study this bistability for a nanomechanical resonator with diffusing adsorbed particles. The vibrations affect the particles by driving them toward the antinodes of the vibrational mode. Unexpectedly, even though diffusion is a random process, the bistability arises if it is sufficiently strong, i.e., fast compared to the vibrations decay time. For fast diffusion, we find the bistable response in the mean-field approximation. We also study, analytically and numerically, the rate of fluctuation-induced switching between the coexisting stable states. [Preview Abstract] |
Thursday, March 24, 2011 8:48AM - 9:00AM |
V30.00005: Electrical Detection of Resonance of ZnO nanowires using Harmonic Detection of Radiation Deepika Saini, Ramakrishna Podila, Malcolm Skove, Apparao Rao ZnO nanowires exhibit semiconducting and piezoelectric properties making them a technologically promising material. We have measured the mechanical resonance of cantilevered ZnO nanowires using the Harmonic Detection of Resonance (HDR) method.\footnote{J. Gaillard, M.J. Skove, R. Ciocan and A.M. Rao, Rev. Sci. Instrum. 77, 073907(2006)} The resonance is induced by an oscillating electric field and detected by second harmonic electric response of the ZnO nanocantilever. The diameter of the nanowires used was about 200 nm and length varied from 60 to 300 $\mu $m. Other mechanical properties of the cantilever, such as Young's modulus, are calculated from the observed resonance frequency. [Preview Abstract] |
Thursday, March 24, 2011 9:00AM - 9:12AM |
V30.00006: Semiconducting nanowire electromechanics in the Coulomb blockade regime Hari Solanki, Sajal Dhara, Arnab Bhattacharya, Mandar Deshmukh We fabricate and study Indium Arsenide (InAs) nanowire electromechanical resonators, in field effect transistor (FET) geometry, which allows us to tune the carrier density and tension in the wire at electromechanical resonance by tuning the dc gate voltage. At temperatures below 5K, quality factor (Q) of these resonators is $\sim$10000, two orders of magnitude larger than at room temperature, and the dynamic range reduces by an order of magnitude at low temperatures. Further in Coulomb blockade regime (charging energy $\sim$10 meV), using rectification technique, we have observed the modification in Coulomb diamond structure at the resonance frequency of the wire. Near the electromechanical resonance frequency, Coulomb peaks become broader symmetrically (independent of dc gate voltage and frequency sweep direction) and right at the resonance frequency their intensity is significantly reduced. This indicates a strong coupling between electron transport and mechanical vibration of the nanowire. [Preview Abstract] |
Thursday, March 24, 2011 9:12AM - 9:24AM |
V30.00007: Capacitive Spring Softening in Single-Walled Carbon Nanotube Nanoelectromechanical Resonators Chung Chiang Wu Due to their low mass density and high Young's modulus, single-walled carbon nanotubes (SWNTs) offer great promise as nanoelectromechanical (NEM) resonators with applications in ultrasmall mass and force sensing. Nanotube resonators can be actuated and detected simultaneously through electrostatic gate coupling. This gate induced frequency tuning of NEM resonators is known to be governed by two mechanisms: the elastic hardening effect and the capacitive softening effect. Although elastic hardening effect has been widely reported in SWNT resonators, the field-induced capacitive spring softening has rarely been observed. Here we report the capacitive spring softening effect observed in SWNT resonators. The nanotube resonators adopt dual-gate configuration with both bottom-gate and side-gate capable of tuning the resonance frequency through capacitive coupling. Interestingly, downward resonance frequency shifting is observed with increasing side-gate voltage, which can be attributed to the capacitive softening of spring constant. Furthermore, in-plane vibrational modes exhibit much stronger spring softening effect than out-of-plan modes. Our dual-gate design should enable the differentiation between these two types of vibrational modes, and open up new possibility for nonlinear operation of nanotube resonators. Other nonlinear effects in SWNT resonators will also be discussed. [Preview Abstract] |
Thursday, March 24, 2011 9:24AM - 9:36AM |
V30.00008: Vibrational Behaviour of Metal Nanowires under Tensile stress Yasemin Sengun, Sondan Durukanoglu We present results of calculations on vibrational density of states (VDOS) of a thin Cu nanowire with $<$100$>$ axial orientation and discuss on the effect of axial strain. The calculations are performed using real space Green's function method with the force constant matrix extracted from the interaction potentials based on the embedded atom method. It is shown that the characteristics of the VDOS of a strain-free nanowire are quite distinctive compared to that of a bulk atom. Among the striking features of this type nanowire is the existence of high frequency modes above the top of the bulk spectrum. From an examination of VDOS of local atoms it is seen that the corner and core atoms are the primary moderators for the anomalous increase in low frequency and high frequency modes, respectively. We, additionally, find that while the high frequency band above the top of the bulk phonon shifts to even higher frequencies, the characteristics at low frequencies remains almost the same upon stretching the nanowire along the axial direction. [Preview Abstract] |
Thursday, March 24, 2011 9:36AM - 9:48AM |
V30.00009: Understanding and Controlling Intrinsic Dissipation in Driven Single Walled Carbon Nanotube Resonators Rajamani Raghunathan, P. Alex Greaney, Jeffrey C. Grossman A ``Phonostat'' algorithm that can regulate total energy in a given internal degree of freedom within a molecular dynamics (MD) simulation is presented. The algorithm computes modal energies at every MD timestep, controls energy in a chosen vibrational mode with an external driving force and an internal damping. Using a test case of driven damped anharmonic oscillator, two different approaches of force correction are presented and various parameters that control the phonostat algorithm are analyzed. This algorithm is then employed to drive a chosen vibrational mode in carbon nanotube resonator to understand intrinsic dissipation under continuous driving, simultaneously computing its quality factor to mimic experimental conditions. The \textit{gateway} modes that couple the driven mode to the thermal background are identified. Regulating these gateway modes hold the key to control intrinsic dissipation and improve quality factor for mass sensing application. [Preview Abstract] |
Thursday, March 24, 2011 9:48AM - 10:00AM |
V30.00010: Anomalous Electromechanical Resonance Behavior of Single-walled Carbon Nanotubes under High Bias Voltages Mehmet Aykol, William Branham, Zuwei Liu, Moh Amer, I-Kai Hsu, Rohan Dhall, Shun-Wen Chang, Stephen Cronin By monitoring the nanoelectromechanical response of suspended individual carbon nanotubes (CNT), we observe the onset of optical phonon (OP) emission in these CNTs under high bias voltages. An abrupt upshift in the mechanical resonance frequency is observed at high voltage biases. The underlying cause of this behavior is the sudden increase in the lattice temperature of the CNT that causes contraction of the lattice due to the negative thermal expansion coefficient. This, in turn, results in increased tension in the suspended nanotube and an upshift in the mechanical resonance frequency. The sudden increase in temperature is explained by the OP emission in CNT. This effect is also observed in the Raman spectra of CNTs as a sudden downshift in the G band OP frequencies at high bias voltages. [Preview Abstract] |
Thursday, March 24, 2011 10:00AM - 10:12AM |
V30.00011: Transport in partially equilibrated inhomogeneous quantum wires Alex Levchenko, Tobias Micklitz, Jerome Rech, Konstantin Matveev We study transport properties of weakly interacting one-dimensional electron systems including on an equal footing thermal equilibration due to three-particle collisions and the effects of large-scale inhomogeneities. We show that equilibration in an inhomogeneous quantum wire is characterized by the competition of interaction processes which reduce the electrons total momentum and such which change the number of right- and left-moving electrons. We find that the combined effect of interactions and inhomogeneities can dramatically increase the resistance of the wire. In addition, we find that the interactions strongly affect the thermoelectric properties of inhomogeneous wires and calculate their thermal conductance, thermopower, and Peltier coefficient. [Preview Abstract] |
Thursday, March 24, 2011 10:12AM - 10:24AM |
V30.00012: Energy loss of the electron system in individual single-walled carbon nanotubes Daniel Santavicca, Joel Chudow, Daniel Prober, Meninder Purewal, Philip Kim We characterize the energy loss of the non-equilibrium electron system in individual metallic single-walled carbon nanotubes at low temperature. Using Johnson noise thermometry, we demonstrate that, for a nanotube with ohmic contacts, the dc resistance at finite bias current directly reflects the average electron temperature. This enables a straightforward determination of the thermal conductance associated with cooling of the nanotube electron system. In analyzing the temperature- and length-dependence of the thermal conductance, we consider contributions from acoustic phonon emission, optical phonon emission, and hot electron outdiffusion [1]. In the same sample, we also characterize the radio frequency heterodyne response. Distinct responses are seen from bolometric detection and from the electrical nonlinearity due to non-ohmic contacts. \\[4pt] [1] D.F. Santavicca, J.D. Chudow, D.E. Prober, M.S. Purewal, and P. Kim, Nano Lett. 10, 4538 (2010). [Preview Abstract] |
Thursday, March 24, 2011 10:24AM - 10:36AM |
V30.00013: Heat pumping in nanomechanical systems Liliana Arrachea, Claudio Chamon, Eduardo Mucciolo, Rodrigo Capaz We propose using phonon pumping mechanism to transfer heat from a cold to a hot body. The mechanism is based on inducing a traveling modulation of the acoustic phonon velocity along the medium connecting the two bodies. This phonon pumping can cool nanomechanical systems without the need for active feedback. We have derived an estimate of the lowest achievable temperature. We have also analyzed this mechanism in the framework of simple one-dimensional microscopic models, which can be exactly solved with non-equilibrium Green function techniques. [Preview Abstract] |
Thursday, March 24, 2011 10:36AM - 10:48AM |
V30.00014: Phonon spectrum in a CdSe nanowire Chris Barrett, Lin-Wang Wang It is important to calculate the phonon spectrum of realistic nanowires, e.g. to understand its thermo conductivity or to calculate the electron-phonon interaction. In this talk, we will present results of phonon spectrum calculation using valence force field (VFF) method. An important issue is to construct the VFF to describe the surface atomic displacement. We have developed a general VFF formalism to fit our VFF result with the density functional theory (DFT) calculated surface atom displacement energies. In particular, the (10-10) CdSe surface is modelled with Cd-Se dimerization. We will discuss the quality of such VFF model. The phonon spectrum of the nanowire will be presented, and its implication on the phonon transport and electron-phonon coupling will also be discussed. [Preview Abstract] |
Thursday, March 24, 2011 10:48AM - 11:00AM |
V30.00015: Curvature-induced Effects on the Phonon Modes in Sub-nanometer Diameter Single-walled Carbon Nanotubes Ramakrishna Podila, Rahul Rao, Codruta Loebick, Nan Li, Jason Reppert, Lisa Pfefferle, Apparao M. Rao Sub-nanometer diameter single-walled carbon nanotubes (sub-nm SWNTs) are of great interest for fundamental studies due to the effect of large curvature on their properties. We have recently synthesized high quality, narrow diameter distribution sub-SWNTs using CoMn catalysts supported on MCM-41 silica templates in a thermal chemical vapor deposition process [1]. The high curvature in the sub-nm SWNTs leads an unusual S-like dispersion of the G-band frequency due to the strong electron--phonon coupling. In addition, we observe diameter-selective intermediate frequency modes (IFMs) that are as intense as the low frequency radial breathing modes (RBMs). The effect of large curvature in the sub-nm SWNTs is also evident in the lower phonon dispersion of the double resonant Raman features compared to SWNTs with larger diameters. The origin of previously unidentified IFM features (600-1100 cm$^{-1})$ and the dispersion of high frequency phonons (1650 -- 2300 cm$^{-1})$ will be discussed.\\[0pt] [1] C. Z. Loebick \textit{etal.}, \textit{J. Am. Chem. Soc.},132, 11125 (2010) [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700