Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session T35: Metals: Defects and Surfaces |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Don Nicholson, Oak Ridge National Laboratory Room: C140 |
Wednesday, March 23, 2011 2:30PM - 2:42PM |
T35.00001: Orientation effect on dislocation nucleation and related interaction during void growth simulations in Aluminum Amitava Moitra, Mehul Bhatia, Kiran N. Solanki Molecular dynamics simulations are performed to understand the void growth for fcc Aluminum. Dislocation nucleation at the void surface and growth of those dislocations in matrix, are studied for seven different crystallographic orientations: [100], [110], [111], [210], [211], [221], and [321]. A significant effect of the loading orientation on dislocation loop nucleation and configuration, and consequently the shape change of voids are found. Calculations related to the interaction of burgers vectors of the nearby leading and trailing dislocations are performed to find the reason why dislocation extremities are attached to the void surface. It has been also shown for a particular orientation that the extremities leave the void surface in order to reduce the interaction energy. Cross slip and triplanar loops are also found during the study of void growth simulations. [Preview Abstract] |
Wednesday, March 23, 2011 2:42PM - 2:54PM |
T35.00002: MD Study of the Nucleation and Growth of Deformation Twins in Polycrystalline Tantalum Luis Sandoval, David Richards Recovered samples from high strain rate experiments clearly show that twin formation serves as an important plasticity mechanism in Tantalum. Despite years of study however, the nucleation and growth mechanisms of twining are still poorly understood, especially in bcc metals. Twins are typically thought to nucleate at grain boundaries via a cooperative emission of partials after a critical value of shear stress. We have used molecular dynamics (MD) simulation to observe the nucleation and growth of twin domains from grain boundaries and grain boundary junctions in polycrystalline cells, which have been prepared as arrangements of hexagon-columnar grains. Using a Finnis-Sinclair potential, we have examined the role of strain rate, temperature and hydrostatic pressure on the kinetic phenomena, in particular the twinning threshold and twin growth rates. We discuss how kinetic parameters extracted from MD simulations help inform a multiscale strength model for Tantalum that includes both twinning and slip as deformation mechanisms in the regime of high strain rates. [Preview Abstract] |
Wednesday, March 23, 2011 2:54PM - 3:06PM |
T35.00003: Large Scale Dislocation Dyniamics Simulation of Precipitation Hardening in Ni-based Superalloys Renge Li, Zhiqiang Wang The precipitation hardening in Ni-based superalloys, which contain up to 73{\%} volume fraction of $\gamma '$, has been investigated by large scale 3D dislocation dynamics simulations. Dislocations glide under external stress across a {\{}111{\}} plane of $\gamma $/ $\gamma '$ phase, intersected by cubic $\gamma '$precipitates. The critical resolved shear stress (CRSS) has been investigated for different microstructureal parameters: $\gamma '$volume fraction, anti-phase boundary (APB) energy and channel width. It is shown that the CRSS depends on the square root of the volume fraction of $\gamma '$. The CRSS is linearly proportional to the APB energy. Stuctures with a non-uniform distribution of $\gamma '_{ }$have CRSS that is 20{\%}-30{\%} smaller than a stucture with unique $\gamma '$ size corresponding to the average size of the non-uniform disribution of $\gamma '$. The fact is that the channel width is not uniform and some channel width is larger than the average channel width of a stucture with a non-uniform distribution of $\gamma '$, which makes the dislocation line easier to bend. This reveals that the channel width plays more important role than the $\gamma '$ size. When channel width decreases to about 20nm, CRSS weakly depends on the $\gamma '$size and increases dramatically. [Preview Abstract] |
Wednesday, March 23, 2011 3:06PM - 3:18PM |
T35.00004: Thermodynamics of point defects in deformable lattices Roman Groger, Libor Smejkal, Turab Lookman We develop a mean-field model that can be used to study the evolution of microstructure and the density of point defects in irradiated materials. Within this model, the lattice is viewed as an elastic template that is distorted by point defects. The stresses that each defect exerts on its immediate neighborhood in the lattice are represented by its elastic dipole tensor. The lattice responds to these stresses by developing long-range strains that mediate interactions between spatially separated defects. Nonlocal (gradient) elasticity is used to describe the elastic strain energy of the distorted lattice. This gives rise to the gradients of strain in the free energy and ensures an accurate representation of the phonon dispersion curves. In order to demonstrate this model, we consider a cubic lattice with a given density of randomly distributed vacancies and $\langle 100 \rangle$ split interstitials (dumbbells). The occupation of each cell is described by a ``spin'' with the states \{ideal lattice, vacancy, and the three orientations of the $\langle 100 \rangle$ dumbbell\}. The evolution of this spin field is obtained by the Monte Carlo (Metropolis) method, with the free energy calculated for each state of the system as described above. Double spin-flip mechanism is adopted to conserve the total mass of the system. [Preview Abstract] |
Wednesday, March 23, 2011 3:18PM - 3:30PM |
T35.00005: Continuum dislocation dynamics: comparison between models Woosong Choi, Yong Chen, Stefanos Papanikolaou, James Sethna Many continuum theories of dislocation dynamics have been proposed to bridge the gap in between discrete microscopic simulations and macroscale phenomenology. As of yet, however, these theories had limited success in explaining or predicting the physics of microstructure formation and evolution. Recently, we have shown that a simple isotropic continuum model dynamically form walls\footnote{S. Limkumnerd and J. P. Sethna, Phys. Rev. Lett. \textbf{96}, 095503 (2006)} and exhibit complicated microstructure formation and evolution\footnote{Y. S. Chen, W. Choi, S. Papanikolaou, and J. P. Sethna, Phys. Rev. Lett. \textbf{105}, 105501 (2010)} similar to experiments. Most other continuum theories have not seen such structures emerging, and to what extent this theory explains the physics remains to be answered. We explore several variants of the current theories which have different microscopic physics as to how slip systems, cross-slip, statistically stored dislocations, explicit or effective short range interactions, etc. are treated. Comparisons among simulation results of these models will be presented, and we will discuss the relevant mechanisms and their consequences in the dynamics of microstructures. [Preview Abstract] |
Wednesday, March 23, 2011 3:30PM - 3:42PM |
T35.00006: Quantum Monte Carlo calculations of defects in aluminum Randolph Q. Hood, Paul R.C. Kent, Fernando A. Reboredo We use first-principles fixed-node diffusion quantum Monte Carlo to calculate the energetics of point defects in bulk FCC aluminum demonstrating a very high accuracy when compared to experiment. Aluminum has been well studied experimentally as a ``simple'' metal prototype for investigating the effects of radiation damage such as void formation and helium embrittlement. Often accuracies at the level of milli-electronvolts are required, which is not achieved even for the simple case of pairs of vacancies in aluminum, using common density functionals. Perhaps surprisingly, even single vacancy energies are not reliable in many simple structural materials. Also presented are results for the bulk properties of aluminum - the equilibrium lattice constant, the cohesive energy, and the bulk modulus. These calculations bring a new level of rigor to the study of defects in metals. [Preview Abstract] |
Wednesday, March 23, 2011 3:42PM - 3:54PM |
T35.00007: Molecular dynamics simulation of ablation and spallation in nickel films irradiated by ultra-short laser pulses Brian Demaske, Vasily Zhakhovsky, Nail Inogamov, Carter White, Ivan Oleynik Ablation and spallation of micron-sized Ni films irradiated by ultra-short laser pulses were investigated via large-scale molecular dynamics simulations. The interatomic interactions are described by a new embedded atom method potential that was specifically developed to accurately simulate response of Ni to strong compression and tensile waves as well as to high temperatures. It was shown that ablation results from cavitation within strongly stretched molten layer beneath the surface of the Ni film. Owing to a superposition of tensile waves, ablation threshold fluence is an increasing function of film thickness, which asymptotically approaches the experimental value for micron-sized films. Processes of wave-breaking and formation of ultra-short shock waves were also investigated in detail. Fluence threshold for onset of spallation at the rear of the film and spall strength of solid Ni subjected to ultrahigh strain rates were predicted. [Preview Abstract] |
Wednesday, March 23, 2011 3:54PM - 4:06PM |
T35.00008: The thresholds of twinning in \textit{bcc} tantalum Kyle Caspersen, Robert Rudd, Mike Surh, Luis Sandoval, David Richards The dominate stress relaxation mechanism for most crystalline materials under most conditions is dislocation motion, or slip. However, materials subjected to extreme conditions (for example, conditions that arise in laser based dynamic compression experiments) can exhibit more complex stress relaxation mechanisms. Specifically, for large stress and large strain rates there is a competition between slip and phase transformations and twinning. The conditions at which phase transformations and twinning become important are not known. Therefore, here we present a molecular dynamics study of thresholds of twinning in \textit{bcc} tantalum under various temperatures, pressures, and strain rates. [Preview Abstract] |
Wednesday, March 23, 2011 4:06PM - 4:18PM |
T35.00009: Development of Phase-Field Crystal model free energy functionals based on molecular dynamics D.M. Nicholson, J.A. Dantzig, Sarma Gorti, Bala Ranhakrishnan, D.D. Johnson The Phase-Field Crystal (PFC) model represents the density as a continuous function, whose spatial distribution evolves in time at diffusional, rather than vibrational time scales. PFC provides a tool to study defect interactions at the atomistic level but over longer time scales than those achievable with MD. We examine the behavior of the PFC model with the goal of relating the PFC parameters to physical parameters for Fe and Mo, derived from molecular dynamics (MD) simulations (using either classical force fields or on density-functioanl-theory-based Hellmann-Feynman forces). MD and PFC results for diffusion rates, energy and volumes of fusion, and melting points as a function ofvacancy concentration are used to validate free energy functionals used in the PFC model. Acknowledgments: This work was supported by the Center for Defect Physics, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences. [Preview Abstract] |
Wednesday, March 23, 2011 4:18PM - 4:30PM |
T35.00010: Terminating Surface Electromigration at the Source Kirk Bevan, Wenguang Zhu, Hong Guo, Zhenyu Zhang Through an extensive search across the periodic table utilizing first-principles density functional theory, we have established a general elemental trend for determining electromigration inhibiting impurities on the technologically important Cu(111) surface -- the dominant diffusion pathway in modern nanoelectronics interconnects. Unrecognized thus far, such inhibitors are characterized by energetically favoring (and binding strongly at) the kink sites of step edges. These properties are determined to generally reside in elements that form strong covalent bonds with substrate metal atoms. This finding sheds new light on the possibility of halting surface electromigration via kink blocking impurities. [Preview Abstract] |
Wednesday, March 23, 2011 4:30PM - 4:42PM |
T35.00011: Coverage Dependent Collective Diffusivity of Dense Pb Wetting Layer on Si(111) Li Huang, Cai-Zhuang Wang, Maozhi Li, Kai-Ming Ho The anomalous mass transport in the Pb wetting layer on Si(111) surface observed in recent experiments is studied using dynamical calculations of a generalized Frankel-Kontorova model. Instead of typical random-type diffusion, a novel collective liquid-like motion of the Pb atoms within the dense wetting layers is revealed to give rise to the ultrafast kinetics of the wetting layers even at low temperatures. With this collective spreading mechanism of the dense wetting layer, a simple kinetic Monte-Carlo simulation quantitatively reproduces the experimental observations. [Preview Abstract] |
Wednesday, March 23, 2011 4:42PM - 4:54PM |
T35.00012: Atomic layer deposition of metallic cobalt Jinhee Kwon, Mark Saly, Ravi Kanjolia, Yves Chabal Metallic cobalt has rich catalytic, electronic and magnetic properties, which makes it critical to have a better control of Co thin film deposition for various applications. This work focuses on the atomic layer deposition (ALD) of cobalt using (tertiarybutylallyl)cobalttricarbonyl ($^{t}$BuAllyl)Co(CO)$_{3}$ and dimethylhydrazine (DMHy) on H-terminated Si to uncover the growth mechanisms. The first pulse of ($^{t}$BuAllyl)Co(CO)$_{3}$ reacts with surface H--Si bonds completely, forming one monolayer of metallic silicide. In situ infrared absorption spectra show that further deposition of Co is made possible only after linear carbonyl groups which remain after the first ($^{t}$BuAllyl)Co(CO)$_{3}$ pulse as the surface ligand are removed by subsequent ALD cycles. Further ALD cycles give rise to metallic Co growth through ligand exchange after a nucleation period of 8--10 cycles. The derived growth rate of cobalt is 0.6 $\pm $ 0.1 {\AA}/cycle. The resultant Co film shows low concentration of carbon and nitrogen impurities in the bulk according to X-ray photoemission spectroscopy. [Preview Abstract] |
Wednesday, March 23, 2011 4:54PM - 5:06PM |
T35.00013: Periodic Stacking Faults in Ag Films Grown on Si(111) Decorated by Atomic Chains Aaron Gray, Manami Ogawa, Hawoong Hong, Iwao Matsuda, Tai Chaing Thin films grown on a substrate decorated by a periodic array of atomic wires can exhibit unusual properties such as stacking faults and electronic topological phase transitions due to the interfacial modulation. We report a study of Ag films grown on an array of atomic In chains on Si(111). Prior STM studies have suggested an array of stacking faults in the Ag films that allow the film lattice structure to match the interfacial modulations. STM however can only probe the surface. Our work uses x-ray diffraction to elucidate the internal 3-dimensional structure of this system. The measurements are found to be best explained by a model in which the unit cell contains a single stacking fault. [Preview Abstract] |
Wednesday, March 23, 2011 5:06PM - 5:18PM |
T35.00014: Measurement of the Spectral Distribution of Low Energy Electrons emitted as a result of NVV Auger Transitions in Ag (100) S. Kalaskar, S.L. Hulbert, Q. Dong, B.R. Bartynski, A.H. Weiss Auger Photoelectron Coincidence Spectroscopy (APECS) was used to investigate the physics of the Low Energy Tail (LET) of the Auger spectrum of Ag (100) at the National Synchrotron Light Source, Brookhaven National Lab, NY. The incident photon energy was set at 180eV. The APECS spectrum contains the contributions from electrons excited by the NVV Auger transition plus a background due to true coincidences between photoemitted valence band electrons that undergo inelastic~scattering and transfer part of their energy with other valence electrons which exit the sample. A series of coincidence measurements were made with the fixed~analyzer set at energies 150,160,171.5 and 175eV. These measurements were used to obtain an estimate of the background due to the inelastically scattered valance band electrons. The estimated background was then subtracted from the NVV APECS data to obtain the spectrum of electrons emitted solely as a result of the NVV Auger transitions, which contains implications for quantitative interpretation of the Auger spectrum. [Preview Abstract] |
Wednesday, March 23, 2011 5:18PM - 5:30PM |
T35.00015: First measurements of the Low Energy Tail (LET) down to 0 eV using Auger Photoelectron Coincidence Spectroscopy (APECS) in Ag (100) and Cu (100) K. Shastry, S. Kalaskar, S.L. Hulbert, B.R. Bartynski, A.H. Weiss We present the Auger Photoelectron Coincidence Spectroscopy (APECS) measurements of Ag (100) and Cu (100) over a full range of emitted energies from 0 eV to 81eV. The measurements were successful in separating the low energy Auger lines from a large background, due to loss processes unrelated to the Auger transition. The measurements reveal a well formed Auger peak at 60 eV for Cu and an Auger peak at 40 eV for Ag accompanied by a low energy tail (LET). The LET extends to 0 eV with a broad maximum at 6eV and 10 eV in the case of Cu and Ag respectively. The integrated intensity of the LET in Cu (100) and Ag (100) were 6 and 2 times larger than that of the Auger peak itself. The origin of this LET is discussed in terms of extrinsic mechanisms in which electrons from the peak lose energy as they propagate to the sample surface, as well as intrinsic mechanisms in which multi-electron Auger processes distribute the energy gained by the filling of the core-hole to multiple valence electrons.~ [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