Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session T21: Semiconductors: Mechanical and Dynamic Properties |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Ben Larson, Oak Ridge National Laboratory Room: 323 |
Wednesday, March 18, 2009 2:30PM - 2:42PM |
T21.00001: 3D X-Ray Microscopy and Dislocation Dynamics Simulation Investigation of Deformation in Copper B. C. Larson, Jie Deng, Anter El-Azab, J. Z. Tischler We have combined submicron resolution 3D x-ray microscopy measurements at the Advanced Photon Source and discrete dislocation dynamics (DD) simulations to initiate fundamental investigations of deformation in metals. Half-micron resolution 3D x-ray microscopy measurements of local plastic rotation deformation were performed on initially dislocation free Cu single crystals that were compression deformed axially along [100] to strains varying from 1{\%} to 7.6{\%}. Accordingly, dislocation dynamics simulations of axial [100] deformation in fcc Cu were performed for strains ranging up to 1.6{\%}. The overlapping range of the measured and simulated strain magnitudes provides the first direct and quantitative link on mesoscopic length scales between first principles simulations of deformation and submicron resolution deformation measurements. Quantitative comparisons between the measured and simulated local lattice curvatures will be presented in graphical and statistical form. [Preview Abstract] |
Wednesday, March 18, 2009 2:42PM - 2:54PM |
T21.00002: Low speed fracture instabilities in a brittle crystal Noam Bernstein, James R. Kermode, Tristan Albaret, Dov Sherman, Peter Gumbsch, Michael C. Payne, G\'abor Cs\'anyi, Alessandro De Vita Brittle materials under mechanical load fail by nucleation and propagation of cracks, and these cracks show well known instabilities at high crack speeds. In this work we show that new instabilities caused by the atomic structure of the crack tip can occur at low crack speeds as well [1]. Using state of the art computer simulations, we find atomic rearrangements at a silicon crack tip on the (111) cleavage plane that occur preferentially on one side of the crack, but only at low crack speeds. Experiments using a novel technique for applying low tensile loads show that real silicon cracks form distinctive features on one side of the exposed crack surface. A mesoscopic model explains how the microscopic atomic rearrangements lead to the observed macroscopic features. We present extensive results on silicon and preliminary results on other brittle materials including sapphire, diamond, and silicon carbide. We conclude that even very brittle single-crystal materials can have a complex crack tip atomic structure, and that atomic scale rearrangements can lead to macropscopic changes in crack morphology. [1] J. R. Kermode {\it et al.}, Nature {\bf 455}, 1224 (2008). [Preview Abstract] |
Wednesday, March 18, 2009 2:54PM - 3:06PM |
T21.00003: Thermoelastic damping in micromechanical resonators Thomas Metcalf, Bradford Pate, Douglas Photiadis, Brian Houston The performance of micro- and nano-mechanical resonators as sensors, filters, and in other devices is determined by the quality factor, $Q$, which measures the fractional energy loss per oscillation cycle of the resonator. In any given resonator, several energy loss mechanisms are likely to be simultaneously present. However, for micro- and nano-scale resonators, the relative strengths and identity of these mechanisms is largely unknown. We measure the temperature dependence of $Q^{-1}$ of two resonant modes (460 kHz and 510 kHz) of a 1.5 $\mu$m thick silicon micromechanical plate resonator. In-situ ultra-high vacuum annealing lowers the background energy loss at 120 K to $Q^{-1}\leq5\times10^{-7}$. The $Q^{-1}$ increases with increasing temperature by different rates for the two modes, quantitatively agreeing with a modification of Zener's theory of thermoelastic damping. This provides strong evidence that thermoelasticity is the dominant energy loss mechanism in one resonant mode. [Preview Abstract] |
Wednesday, March 18, 2009 3:06PM - 3:18PM |
T21.00004: Ab initio guided design of bcc Mg-Li alloys for ultra light-weight applications Martin Fri{\' a}k, William Art Counts, Dierk Raabe, J{\" o}rg Neugebauer Ab initio calculations are becoming increasingly useful to engineers interested in designing new alloys because these calculations are able to accurately predict basic material properties only knowing the atomic composition of the material. In this paper, fundamental physical properties (like formation energies and elastic constants) of 11 bcc Mg-Li compounds are calculated using density-functional theory (DFT) and compared with available experimental data. These DFT-determined properties are in turn used to calculate engineering parameters like (i) specific Young's modulus (Y/$\rho )$ or (ii) bulk over shear modulus ratio (B/G) differentiating between brittle and ductile behavior. The engineering parameters are then used to identify alloys that have optimal mechanical properties needed for a light weight structural material. It was found that the stiffest bcc magnesium-lithium alloys contain about 70 at.{\%} Mg while the most ductile alloys have 0-20 at.{\%} Mg. The specific modulus for alloys with 70 at.{\%} Mg is equal to that of Al-Mg alloys. An Ashby map containing Y/$\rho $ vs. B/G shows that it is not possible to increase both Y/$\rho $ and B/G by changing only the composition or local order of a binary alloy (W. A. Counts, M. Fri\'{a}k, D. Raabe and J. Neugebauer, Acta Mater 57 (2009) 69-76). [Preview Abstract] |
Wednesday, March 18, 2009 3:18PM - 3:30PM |
T21.00005: Thermal Stability of Shape Transition in Strained Nano-Islands Cristiano Nisoli, Douglas Abrahams, Turab Lookman, Avadh Saxena Two dimensional Stranski-Krastanow strained islands are known to undergo a shape anisotropy transition as they grow in size, finally evolving toward nanowires. We investigate thermal stability of this process and find a phase transition both in temperature and, in simple cases, in growth. While our results are general, they can explain recent data on Erbium Silicide growth on vicinal Si surface. [Preview Abstract] |
Wednesday, March 18, 2009 3:30PM - 3:42PM |
T21.00006: Neutron Time of Flight phonon spectra of Cu$_{2}$O and Ag$_{2}$O powders Barry Winn, Mark Hagen, Steve Shapiro Negative thermal expansion materials cuprite (Cu$_{2}$O) and Ag$_{2}$O share the same structure (space group \textit{Pn3m}). Here, we report inelastic neutron time of flight measurements of room temperature powder samples of each system, using the Pharos chopper spectrometer at LANSCE, at up to 100 meV energy transfer. For Cu$_{2}$O, high energy optical phonons are observed between 60 and 80 meV, while for Ag$_{2}$O, these phonons are observed between 50 and 70 meV. Results are compared to previous work, and to recent neutron triple axis spectrometer results for Cu$_{2}$O, and their relevance to negative thermal expansion is discussed. [Preview Abstract] |
Wednesday, March 18, 2009 3:42PM - 3:54PM |
T21.00007: Large-Amplitude Anharmonic Decay of Coherent A1g phonon motion in Bismuth Stephen Fahy, Aaron Hurley, Donal O Donoghue, Eamonn Murray, David Prendergast, Tadashi Ogitsu, David Reis, David Fritz Large amplitude coherent motion of the A1g phonon in bismuth can be generated by ultrafast optical excitation. At low amplitude, the decay rate agrees with that observed in Raman scattering. At high levels of photoexcitation, the observed phonon damping is substantially increased, compared to low-amplitude motion. We present a classical simulation of the anharmonic decay of the phonon, including third-order anharmonic terms in the energy, calculated using density functional perturbation theory, coupling the A1g motion to modes throughout the Brillouin Zone. At low amplitude, the classical decay can be shown in perturbation theory to be almost identical in classical and quantum dynamics at room temperature, demonstrating the validity of a classical simulation of the dynamics. For very large A1g amplitude, the amplitude of motion in the final state modes is substantially increased over their thermal average values, leading to an increase in the decay rate of the A1g mode. [Preview Abstract] |
Wednesday, March 18, 2009 3:54PM - 4:06PM |
T21.00008: Phonon dispersion relations for unstrained Si$_{1-x}$Ge$_{x}$ via density functional theory Md Hossain, Jonathan Freund, Harley Johnson Phonon dispersions for the Si$_{1-x}$Ge$_{x}$ alloy system are computed using localized basis density functional theory. Including interactions up to third-nearest-neighbors and the effect of atomic randomness, phonon dispersion for the full Brillouin zone of a supercell containing 8 atoms is computed for 8 different compositions. Frequencies are found to be in excellent agreement with available experimental results for both crystalline Si and Ge. Results are compared with a 64-atom supercell calculation for optical frequencies to show any possible effect of supercell size on the phonon calculation. The atoms in the calculation are relaxed to a force tolerance of 0.0001eV/{\AA}, which is found to be important to correctly determine the dispersion near the $\Gamma $- and X-points of the Brillouin zone where q-convergence is harder to achieve. The highest optical phonon frequencies are observed to vary nonlinearly with composition, a fact not investigated before using computational methods. [Preview Abstract] |
Wednesday, March 18, 2009 4:06PM - 4:18PM |
T21.00009: Grating-Enhanced Response for current-driven coupled quantum wells Antonios Balassis, Godfrey Gumbs We have investigated the conditions necessary to achieve stronger plasmon instability leading to emission in the terahertz (THz) regime for semiconductor quantum wells (QWs). The surface response function is calculated for a bilayer two-dimensional electron gas (2DEG) system in the presence of a metal grating placed on the surface and which modulates the electron density. The 2DEG layers are coupled to surface plasmons arising from excitations of free carriers in the bulk region between the layers. A current is passed through one of the layers and is characterized by a drift velocity $v_D$. With the use of the surface response function, the plasmon dispersion equation is obtained as a function of frequency $\omega$, the in-plane wave vector ${\bf q}_{\parallel}=(q_x,q_y)$ and reciprocal lattice vector $nG$ where $n=0,\pm1,\pm2,\cdots$ and $G=2\pi/d$ with $d$ denoting the period of the grating. The dispersion equation, which yields the resonant frequencies, is solved in the complex $\omega$-plane for real wave vector ${\bf q}_{\parallel}$. It is ascertained that the imaginary part of $\omega$ is enhanced with decreasing $d$, and with increasing the doping density of the free carriers in the bulk medium for fixed grating period. [Preview Abstract] |
Wednesday, March 18, 2009 4:18PM - 4:30PM |
T21.00010: Where the reactive sites are in anatase nanoparticles? --Theoretical Investigation on (001) and (101) surfaces in anatase nanoparticles Hong Wang, James Lewis Recently, with the development of nanotechnology, the devices' size shrinks to nano-scale size where the surface properties play a role. Thus, it is required scientists to provide fundamental level understanding of anatase surfaces in nano-size anatase materials to improve its applications. In this work, applying DFT ab initio method, we investigate the fundamental properties of anatase (001) and (101) surfaces in anatase nanoparticles. By adopting different portions of (001) and (101) surfaces along with the size of nanoparticles, we analyze the geometric properties and energetic stabilities of nanoparticles. The electronic properties of these nanoparticles are also calculated in this work. The frontier orbitals located mostly in the (001) surfaces indicate these sizes are possibly reactive sizes in the external molecule adsorption reactions. To verify their activity, we add water molecules in different sits and different concentration on these nanoparticles. The results show that the sites where the frontier orbitals are localizing are very reactive for water adsorption. [Preview Abstract] |
Wednesday, March 18, 2009 4:30PM - 4:42PM |
T21.00011: Collective Excitations in Cylindrical Quantum Dots Chains Jimena Vergara, Angela Camacho We are interested in the study of collective excitations in quantum dot chains because these can be used to effectively transmit information at nano scale and to control spontaneous and stimulate electromagnetic emission in the quantum dots. [1] This work is centered in the study of semiconductor one-dimensional quantum dot arrays. Based on a tight-binding bandstructure calculation combined with a self consistent field approximation we obtain the dispersion relations and we analyze how the geometry of the dot affects the collective oscillation of charge and its propagation. We focus our study first on Coulomb interaction between charges as the main cause of the 1D plasmons neglecting tunneling to finally compare with the case where tunneling is allowed. We find out that Coulomb interaction plays an important role in these systems and that tunneling opens the energy spectrum permitting new excitations, which are good candidates to be used in nanometric devices. [1] A.V.Akimov, A.Mukherjee, C.L. Yu, D.E Chang, A.S.Zybrov, P.R. Hemmer, H Park and M.D Lukin, \textit{Generation of Single optical plasmons in metallic nanowires coupled to quantum dots}, Nature 450, 402 (2007). [Preview Abstract] |
Wednesday, March 18, 2009 4:42PM - 4:54PM |
T21.00012: Electrical characterization of MOVPE-grown InSb nanowires Henrik Nilsson, Philippe Caroff, Claes Thelander, Marcus Larsson, Lars-Erik Wernersson, Lars Samuelson, Hongqi Xu In bulk, InSb is a narrow band gap (E$_{g}$ = 170 meV) semiconductor with high electron mobility ($\mu _{n}$ = 77~000 cm$^{2}$/Vs) and is therefore of relevance for low power and high speed transistor applications. It also has a low electron effective mass (0.015m$_{e})$ and a very high electron g-factor $\vert $g$\vert $=51 which is of interest for studies of quantum and spin physics. InSb nanowires were grown by MOVPE from 40 nm Au aerosol seed particles deposited on a $<$111$>$B InAs substrate, where the growth was initiated by a 100 nm InAs segment. The InSb nanowires are untapered and free from stacking faults. The grown InSb nanowires were transferred to degenerately doped, SiO$_{2}$ capped, Si substrates. After locating the wires, Ti/Au contacts were made by electron beam lithography. Electrical measurements of the fabricated InSb nanowire devices were performed in the high bias, field-effect transistor (FET) regime at temperatures ranging from 300 K to 4.2 K as well as in the low bias, single-electron transistor (SET) regime at temperatures ranging from 4.2 K to 300 mK. In particular, effective electron g-factors and Kondo physics have been studied at low temperatures with the nanowire devices. [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