The Experts below are selected from a list of 237 Experts worldwide ranked by ideXlab platform
David J. Srolovitz - One of the best experts on this subject based on the ideXlab platform.
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Grain growth stagnation in thin films due to shear-coupled grain Boundary Migration
Scripta Materialia, 2020Co-Authors: Eugen Rabkin, David J. SrolovitzAbstract:Abstract Normal grain growth in thin films attached to a substrate has been considered. It has been shown that shear-coupled grain Boundary Migration results in the build-up of elastic stresses in the film. A semi-quantitative model of grain growth combining the elements of disclinations theory with the Burke-Turnbull model of normal grain growth has been proposed. It has been shown that shear-coupled grain Boundary Migration may lead to stagnation of normal grain growth, whereas for high coupling factor values, the grains in the film do not grow at all. Finally, the mechanisms of stress relaxation enabling some grain growth are discussed.
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characterization of atomic motion governing grain Boundary Migration
Physical Review B, 2006Co-Authors: Hao Zhang, David J. Srolovitz, Jack F Douglas, James A. WarrenAbstract:Molecular dynamics simulations were employed to study atomic motion within stationary and migrating asymmetric tilt grain boundaries. We employ several measures of the ``complexity'' of the atomic trajectories, including the van Hove correlation function, the non-Gaussian parameter, and dynamic entropy. There are two key types of dynamical events within the grain boundaries (i) a stringlike cooperative motions parallel to the tilt axis and occurring on a characteristic time scale of $\ensuremath{\approx}25\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ and (ii) atomic motion across the grain Boundary plane occurring on a characteristic time scale of $\ensuremath{\approx}150\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$. The characteristic times associated with each type of event decreases with increasing driving force for Boundary Migration. We present evidence as to how the driving force biases these types of events, leading to Boundary Migration. While the stringlike atomic motion is an intrinsic feature of grain Boundary dynamics and is important for grain Boundary Migration, it is the second type of event that controls grain Boundary Migration rates.
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Simultaneous grain Boundary Migration and grain rotation
Acta Materialia, 2006Co-Authors: Moneesh Upmanyu, David J. Srolovitz, Alexander E. Lobkovsky, James A. Warren, W. C. CarterAbstract:The energy of a polycrystalline network can be reduced by both grain Boundary Migration and grain rotation. We perform a series of molecular dynamics (MD) simulations of a circular grain embedded in an otherwise single-crystal matrix and monitor both the grain size and the misorientation of the two grains as a function of time. The MD simulations show that grain Boundary Migration and grain rotation occur simultaneously. The grains rotate toward local minima or cusps in the grain Boundary energy versus misorientation plots. The rate of rotation decreases with increasing grain size. The Boundary Migration rate is a maximum at the orientations corresponding to cusps in the Boundary energy. We use the MD results to fit parameters in a sharp interface limit of a phase field model of simultaneous grain Boundary Migration and grain rotation. With this parameterization, the phase field model is able to reproduce simultaneously the time dependence of the grain size and misorientation of the initially circular grain. The MD simulations are consistent with the phase field prediction of the grain size dependence of the rotation rate. The implications of the results for grain growth are discussed.
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A size effect in grain Boundary Migration: A molecular dynamics study of bicrystal thin films
Acta Materialia, 2005Co-Authors: Lang Zhou, Hao Zhang, David J. SrolovitzAbstract:Molecular dynamics simulations of stress-driven grain Boundary Migration in bicrystal thin films demonstrate that the grain Boundary mobility decreases as the films are made thinner. Examination of the surface morphology proves that this effect is not associated with grain Boundary grooving. The simulation data demonstrate that the grain Boundary mobility is a linear function of the inverse thickness. We present a simple model to explain this effect based upon the fundamental mechanism of grain Boundary Migration: the collective rearrangement of a large group of atoms. Decreasing system size implies that more of the Boundary is near the surface. The presence of the free surface interferes with the collective rearrangement of the atoms during Boundary motion and hence slows the Migration. A simple heuristic analysis, based on this effect, is consistent with the observed functional dependence of Boundary mobility on bicrystal thickness.
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impurity effects on grain Boundary Migration
Modelling and Simulation in Materials Science and Engineering, 2002Co-Authors: Mikhail I Mendelev, David J. SrolovitzAbstract:Experiments show that the impurities can drastically change grain Boundary mobilities in a non-trivial manner. The most widely used type of theoretical model for impurity effects on Boundary Migration is a one-dimensional, continuum model, based upon several simplifying assumptions. Although several of these assumptions can be relaxed, these models cannot adequately describe realistic situations and are not quantitative. Since grain Boundary mobility depends on several atomic-scale properties that are difficult to reliably extract from experiments (or calculate from a first principles method), it is not currently possible to make a quantitative comparison between theoretical models and experiment. Dynamic atomistic (MD) simulations do not provide a practical alternative because of the need to include such slow processes as long range diffusion and Boundary Migration. An alternative approach is based upon simple spin (extended Ising) models and kinetic Monte Carlo. This provides a concrete model against which the prediction of the continuum theory can be compared in a situation where all microscopic physical properties are known. Such simulations show that the key deficiencies of the continuum models are the assumption that intrinsic and impurity drag effects can be superimposed and not considering the mechanism of grain Boundary Migration. Analytical theories that address these two deficiencies are capable of reproducing the effects of impurities on Boundary mobility seen in the simulations. Simple simulations provide rigorous tests against which new theories should be compared.
George H. Gilmer - One of the best experts on this subject based on the ideXlab platform.
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Texture competition during thin film deposition – effects of grain Boundary Migration
Computational Materials Science, 2002Co-Authors: Hanchen Huang, George H. GilmerAbstract:In this paper, we describe an implementation of grain Boundary Migration in the atomistic simulator of thin film deposition (ADEPT), and apply the simulator to study effects of the grain Boundary Migration on texture evolution. In the implementation, atoms are classified into two categories: those belong to a single grain and those at grain boundaries. An atom is defined as one at a grain Boundary if it has more than half of its neighbors occupied and not all of the neighboring atoms are in the same grain. The grain Boundary atom is attempted to re-align with neighboring grains to represent the grain Boundary Migration; the attempt probability is defined by the grain Boundary Migration coefficient. Our studies show that grain Boundary Migration does not always assist formation of texture with a top surface of the lowest energy. At the nucleation stage of thin film deposition, high Migration coefficient of grain boundaries may enhance the formation of grain nuclei with top surfaces of higher energy, and therefore effectively may suppress formation of textures with a top surface of the lowest energy. This effect may provide an extra dimension to engineer textures of thin films.
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Texture competition during thin film deposition – effects of grain Boundary Migration
Computational Materials Science, 2002Co-Authors: Hanchen Huang, George H. GilmerAbstract:In this paper, we describe an implementation of grain Boundary Migration in the atomistic simulator of thin film deposition (ADEPT), and apply the simulator to study effects of the grain Boundary Migration on texture evolution. In the implementation, atoms are classified into two categories: those belong to a single grain and those at grain boundaries. An atom is defined as one at a grain Boundary if it has more than half of its neighbors occupied and not all of the neighboring atoms are in the same grain. The grain Boundary atom is attempted to re-align with neighboring grains to represent the grain Boundary Migration; the attempt probability is defined by the grain Boundary Migration coefficient. Our studies show that grain Boundary Migration does not always assist formation of texture with a top surface of the lowest energy. At the nucleation stage of thin film deposition, high Migration coefficient of grain boundaries may enhance the formation of grain nuclei with top surfaces of higher energy, and therefore effectively may suppress formation of textures with a top surface of the lowest energy. This effect may provide an extra dimension to engineer textures of thin films.Department of Mechanical Engineerin
Suk-joong L. Kang - One of the best experts on this subject based on the ideXlab platform.
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Grain-Boundary Migration and Dielectric Properties of Semiconducting SrTiO3 in the SrTiO3-BaTiO3-CaTiO3 System
Journal of the American Ceramic Society, 2004Co-Authors: Joo-seon Kim, Suk-joong L. KangAbstract:Chemically induced grain-Boundary Migration and its effects on the interface and dielectric properties of semiconducting SrTiO3 have been investigated. Strontium titanate specimens that had been doped with 0.2 mol% of Nb2O5 were sintered in 5H2/95N2. The sintered specimens were diffusion annealed at 1400°C in 5H2/95N2 with BaTiO3 or 0.5BaTiO3-0.5CaTiO3 (mole fraction) packing powder. The grain boundaries of the annealed specimens were oxidized in air. In the case of BaTiO3 packing, grain-Boundary Migration occurred with the diffusion of BaTiO3 along the grain Boundary. The effective dielectric constant of the specimen decreased gradually as the temperature increased but showed two peaks, possibly because of barium enrichment at the grain Boundary and an oxidized Sr(Ba)TiO3 layer. In the case of 0.5BaTiO3-0.5CaTiO3 packing, although barium and calcium were present at the grain Boundary of the specimen, no Boundary Migration occurred, as in a previous investigation. With the diffusion of barium and calcium, the resistivity of the specimen increased and the variation of the effective dielectric constant with temperature was much reduced, in comparison to those without solute diffusion. These enhanced properties were attributed to the solute enrichment and the formation of a thin diffusional Sr(Ba,Ca)TiO3 layer at the grain Boundary.
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Chemical Control of the Grain‐Boundary Migration of SrTiO3 in the SrTiO3─BaTiO3─CaTiO3 System
Journal of the American Ceramic Society, 1993Co-Authors: Kyung J. Yoon, Suk-joong L. KangAbstract:The grain-Boundary Migration induced by chemical instability has been studied in SrTiO3. Sintered SrTiO3 has been packed with various BaTiO3/CaTiO3 powder mixtures and annealed at 1400°C for various times. At the surface region of most SrTiO3 specimens, the grain Boundary has migrated with the diffusion of Ba and Ca ions. The ratio of Ba and Ca ions present in the migrated region varies with the depth from the surface and the packing-powder composition, and is not equal to the cation ratio of packing powder. When the Ba/Ca ratio of packing powder is 1, cessation of Migration has been observed. The composition of the area without Migration is estimated to be approximately equal to the composition for the matching of crystal lattices between the original grain (SrTiO3) and the layer formed by diffusion of Ba and Ca ions. The coherency strain energy induced by diffusion of solute atoms is believed to be the major driving force for the grain-Boundary Migration of SrTO3 under the chemical instability. The grain-Boundary Migration can be accordingly controlled by lattice parameter change and matching.
Hanchen Huang - One of the best experts on this subject based on the ideXlab platform.
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Texture competition during thin film deposition – effects of grain Boundary Migration
Computational Materials Science, 2002Co-Authors: Hanchen Huang, George H. GilmerAbstract:In this paper, we describe an implementation of grain Boundary Migration in the atomistic simulator of thin film deposition (ADEPT), and apply the simulator to study effects of the grain Boundary Migration on texture evolution. In the implementation, atoms are classified into two categories: those belong to a single grain and those at grain boundaries. An atom is defined as one at a grain Boundary if it has more than half of its neighbors occupied and not all of the neighboring atoms are in the same grain. The grain Boundary atom is attempted to re-align with neighboring grains to represent the grain Boundary Migration; the attempt probability is defined by the grain Boundary Migration coefficient. Our studies show that grain Boundary Migration does not always assist formation of texture with a top surface of the lowest energy. At the nucleation stage of thin film deposition, high Migration coefficient of grain boundaries may enhance the formation of grain nuclei with top surfaces of higher energy, and therefore effectively may suppress formation of textures with a top surface of the lowest energy. This effect may provide an extra dimension to engineer textures of thin films.
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Texture competition during thin film deposition – effects of grain Boundary Migration
Computational Materials Science, 2002Co-Authors: Hanchen Huang, George H. GilmerAbstract:In this paper, we describe an implementation of grain Boundary Migration in the atomistic simulator of thin film deposition (ADEPT), and apply the simulator to study effects of the grain Boundary Migration on texture evolution. In the implementation, atoms are classified into two categories: those belong to a single grain and those at grain boundaries. An atom is defined as one at a grain Boundary if it has more than half of its neighbors occupied and not all of the neighboring atoms are in the same grain. The grain Boundary atom is attempted to re-align with neighboring grains to represent the grain Boundary Migration; the attempt probability is defined by the grain Boundary Migration coefficient. Our studies show that grain Boundary Migration does not always assist formation of texture with a top surface of the lowest energy. At the nucleation stage of thin film deposition, high Migration coefficient of grain boundaries may enhance the formation of grain nuclei with top surfaces of higher energy, and therefore effectively may suppress formation of textures with a top surface of the lowest energy. This effect may provide an extra dimension to engineer textures of thin films.Department of Mechanical Engineerin
Ze Zhang - One of the best experts on this subject based on the ideXlab platform.
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in situ observation of stress induced grain Boundary Migration in nanocrystalline gold
Scripta Materialia, 2017Co-Authors: Lihua Wang, Deli Kong, Yanhui Chen, Hao Zhou, Jiao Teng, Ze ZhangAbstract:In this study, the plastic behaviors of nanocrystalline Au with an average grain size of 18 nm were investigated in situ using a home-made tensile device in a transmission electron microscope. We provide the direct experimental results revealed the process of grain Boundary Migration. The results show that dislocation behaviors are prevalent for large grains. However, for grain sizes below similar to 15 nm, grain Boundary Migration occurs frequently. The results of our statistical analyses show that grain Boundary Migration occurs more frequently than grain Boundary sliding and rotation in nanocrystalline Au. (c) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.