Showing papers by "David J. Srolovitz published in 1998"
TL;DR: In this article, the authors analyzed the low-temperature growth and relaxation of misfitting films using two-dimensional molecular dynamics simulations using Lennard-Jones potentials, and the temporal evolution of the surface morphology and the mechanisms for misfit dislocation nucleation and stress relaxation were monitored.
Abstract: The low-temperature growth and relaxation of misfitting films are analyzed on the basis of two-dimensional molecular dynamics simulations using Lennard–Jones potentials. The temporal evolution of the surface morphology and the mechanisms for misfit dislocation nucleation and stress relaxation are monitored. Pseudomorphic film growth is observed up to a critical thickness. In some cases, the formation of voids within the film relaxes some of the stress. At the critical thickness, dislocations nucleate and relax most of the misfit. The critical thickness increases with decreasing lattice mismatch and depends on the sign of the misfit. The critical thickness of compressively strained films is smaller than that of films with the same magnitude of misfit, but in tension. The mechanism of dislocation nucleation is different in tension and compression and, in all cases, is associated with the roughness of the film surface. In the compressive misfit case, dislocations nucleate by squeezing-out an atom at the base...
112 citations
TL;DR: In this article, the authors examined the dependence of steady-state grain boundary migration rate on grain boundary curvature by varying the half-loop width at constant temperature and found that grain boundary velocity is proportional to the curvature.
Abstract: We present two dimensional molecular dynamics simulations of grain boundary migration using the half-loop bicrystal geometry in the experiments of Shvindlerman et al. We examine the dependence of steady-state grain boundary migration rate on grain boundary curvature by varying the half-loop width at constant temperature. The results confirm the classical result derived by absolute reaction rate theory that grain boundary velocity is proportional to the curvature. We then measure the grain boundary migration rate for fixed half-loop width at varying temperatures. Analysis of this data establishes an Arrhenius relation between the grain boundary mobility and temperature, allowing us to extract the activation energy for grain boundary migration. Since grain boundaries have an excess volume, curvature driven grain boundary migration increases the density of the system during the simulations. In simulations performed at constant pressure, this leads to vacancy generation during the boundary migration, making the whole migration process jerky.
104 citations
TL;DR: In this article, three-dimensional molecular dynamics simulations of ion beam assisted deposition (IBAD) are performed to determine the mechanisms of crystallographic texture selection during the IBAD of polycrystalline films.
Abstract: Three-dimensional molecular dynamics simulations of ion beam assisted deposition (IBAD) are performed to determine the mechanisms of crystallographic texture selection during the IBAD of polycrystalline films A face centered cubic bicrystal consisting of [111] and [110] oriented grains is grown while an ion beam bombards the growing film at normal incidence As the film grows, the grain boundaries delimiting the [111] and [110] grains move towards each other, eventually pinching off the [111] grain such that the film texture changes from equal densities of [111] and [110] to purely [110] Examination of single crystals grown in the presence of ion beams shows two important effects: ion beam induced atomic sputtering from the surface and ion beam induced damage are significantly reduced when the ion beam is oriented along channeling directions of the crystals The first observation suggests that grains with channeling directions aligned parallel to the ion beam grow more quickly than those where they are
101 citations
TL;DR: In this paper, the growth of diamond by chemical vapor deposition was simulated on nine substrates corresponding to flat and slightly miscut (1, 0, 0), (1, 1, 0), and (1 1, 1, 1) surfaces.
47 citations
TL;DR: The work of adhesion of bimaterial interfaces is commonly computed using quantum mechanical methods in which the two materials are strained into coherency, contrary to what is commonly observed for essentially all systems other than very thin films as discussed by the authors.
Abstract: The work of adhesion of bimaterial interfaces is commonly computed using quantum mechanical methods in which the two materials are strained into coherency. There is no relaxation of the coherency by the formation of an array of interfacial misfit dislocations, contrary to what is commonly observed for essentially all systems other than very thin films. In this paper, we investigate the errors introduced into the work of adhesion associated with the assumption of coherency. Series of atomistic simulations in two and three dimensions are performed using a simple Lennard-Jones-type model potential. We demonstrate that the assumption of coherency introduces errors that increase rapidly with misfit (for small misfit) and can easily be of the order of several tens of percent. We trace the source of these errors to the neglect of the elastic fields of misfit dislocations and to the variation in the number of bonds per unit interfacial area with misfit when coherency is assumed. Suggestions are made to minimize and/or correct for this error.
42 citations
TL;DR: In this article, a simulation of grain growth in which boundary mobility varies in time and/or space has been performed, showing that grain growth is equiaxed and normal at low and high profile velocities.
41 citations
TL;DR: In this article, an analytical approach for determining the elastic fields in problems containing bimaterial interfaces of arbitrary stiffness is presented, which is useful for the common situation in which the classical “welded” and “slipping” interface elastic boundary conditions do not adequately describe the interface.
39 citations
TL;DR: In this paper, a molecular dynamics simulation study of vacancy generation and emission from grain boundaries during curvature-driven grain boundary migration is presented, where the U-shaped half-loop bicrystal geometry is employed in order to maintain a constant driving force during boundary migration.
Abstract: We present a molecular dynamics simulation study of vacancy generation and emission from grain boundaries during curvature-driven grain boundary migration. The U-shaped half-loop bicrystal geometry is employed in order to maintain a constant driving force during boundary migration. Nonlinearities in plots of half-loop grain area versus time indicate the onset of non-steady-state behavior and vacancy formation. Such events appear much more frequently at elevated temperature than at low temperature. Detailed observation of the atomic configurations in the vicinity of the grain boundary before and after these events clearly demonstrate that these non-linearities are associated with the generation and subsequent emission of vacancies. The excess volume associated with the grain boundaries in conjunction with the loss in grain boundary area during curvature-driven migration accounts for the generation of these vacancies. This description is used to predict the rate of vacancy emission, which represents an upper bound on the observed emission rates.
32 citations
01 Mar 1998
TL;DR: In this article, molecular dynamics simulations of the glass transition through isobaric and isochoric cooling of a model polymeric material were performed, and it was shown that the transition is primarily associated with freezing of the torsional degrees of the polymer chains which is strongly coupled to the degree of freedom associated with the nonbonded Lennard-Jones potential.
Abstract: We perform molecular dynamics simulations of the glass transition through isobaric and isochoric cooling of a model polymeric material. In general, excellent agreement between the simulation results and the existing experimental trends is observed. The glass transition temperature (Tg) is found to be a function of pressure under isobaric conditions and specific volume under isochoric conditions. Under both isobaric and isochoric conditions, the trans-state fraction and the torsional contributions to the energy undergo abrupt changes at the glass transition temperature. We analyze these data to show that the glass transition is primarily associated with the freezing of the torsional degrees of the polymer chains which is strongly coupled to the degree of freedom associated with the nonbonded Lennard-Jones potential. We attribute the greater strength of the glass transition under constant pressure conditions to the fact that the nonbonded Lennard-Jones potential is sensitive to the specific volume, which do...
31 citations
12 citations
TL;DR: In this paper, the β-scission growth mechanism at the diamond (100) (2×1) surface was studied by a combination of nanoscale ab-initio LDA/GGA and semiempirical tight-binding techniques to provide the necessary input into the mesoscale variable time step Kinetic Monte-Carlo (KMC) simulations of CVD diamond growth.
Abstract: The β-scission growth mechanism at the diamond (100) (2×1) surface is studied by a combination of nanoscale ab-initio LDA/GGA and semiempirical tight-binding techniques to provide the necessary input into the mesoscale variable time step Kinetic Monte-Carlo (KMC) simulations of CVD diamond growth. The reaction path of the beta-scission reaction is critically examined and the activation barrier of the reverse etching of the methylene adsorbate is deduced. Our quantum mechanical calculations support a previous semiempirical PM3 study confirming that the molecular mechanics values for the entalphy of the reaction are a factor of 2 wrong. This conclusion provides strong support for the preferential etching mechanism introduced into KMC to predict experimentally measured growth rates.