[en] The relation between stress evolution and surface morphology during deposition of sputtered films is examined by combining kinetic Monte Carlo simulations and stress measurements. We find that the surface morphology is susceptible to an instability, which transforms from layer-by-layer growth to the formation of pillarlike columns. The gaps between these columns prevent complete densification and can lead to a network of pores in the layer. We propose that the formation of this structure changes the stress in the growing layers from compressive to tensile.

[en] We study sputtering by 100 eV deuterium irradiation on deuterated amorphous carbon layers at 300 K using molecular dynamics (MD) simulations. Two main results are reported here. First, a special mechanism for carbon release--additional to and distinct from the standard definitions for physical and chemical sputtering of carbon by hydrogen isotopes--has been identified and quantified. This process, here termed ion induced release of unsaturated hydrocarbons (IRUH's), is primarily due to a recently identified atomic collision process where momentum from an impacting particle is transferred approximately perpendicular to the C-C bond, severing it. For the prescribed conditions, the IRUH yield has been found to be comparable to that of standard physical and chemical sputtering, the former being also consistently and simultaneously calculated here. IRUH release of single C atoms does not involve any hydrogenic chemistry and is therefore properly considered to be a distinct and additive type of physical sputtering to that of standard physical sputtering. For 100 eV D⁺ the single C yields of the two physical sputtering mechanisms have been found to be approximately equal. IRUH release of carbon is directly from the surface region of the solid and is separate from, and additional to, standard chemical sputtering (not included in these MD calculations), which typically produces saturated hydrocarbons such as CD₄, from regions extending over the stopping depth of the deuteron in the solid. IRUH is evidently included in experimental measurements of total sputtering yield, e.g., by weight loss. The average energy of IRUH carbon products is about 1 eV and the angular distribution is consistent with a cosine distribution. Second, it is found that for the standard physically sputtered single C atoms the energy distribution is roughly consistent with the widely used Thompson distribution--this despite the fact that the assumptions on which the Thompson distribution is based are not satisfied for 100 eV D on C. The angular distribution of the standard physically sputtered single C atoms is also found to be consistent with the usually assumed cosine distribution

[en] We study diffusion of self-interstitial atoms (SIAs) in vanadium via molecular-dynamics simulations. The <111>-split interstitials are observed to diffuse one-dimensionally at low temperature, but rotate into other <111> directions as the temperature is increased. The SIA diffusion is highly non-Arrhenius. At T<600 K, this behavior arises from temperature-dependent correlations. At T>600 K, the Arrhenius expression for thermally activated diffusion breaks down when the migration barriers become small compared to the thermal energy. This leads to Arrhenius diffusion kinetics at low T and diffusivity proportional to temperature at high T

[en] We study the diffusion of self-interstitial atoms (SIAs) and SIA clusters in vanadium via molecular dynamics simulations with an improved Finnis-Sinclair potential (fit to first-principles results for SIA structure and energetics). The present results demonstrate that single SIAs exist in a <1 1 1>-dumbbell configuration and migrate easily along <1 1 1> directions. Changes of direction through rotations into other <1 1 1> directions are infrequent at low temperatures, but become prominent at higher temperatures, thereby changing the migration path from predominantly one-dimensional to almost isotropically three-dimensional. SIA clusters (i.e., clusters of <1 1 1>-dumbbells) can be described as perfect prismatic dislocation loops with Burgers vector and habit planes of 1/2<1 1 1>{2 2 0} that migrate only along their glide cylinder. SIA clusters also migrate along <1 1 1>-directions, but do not rotate. Both single SIAs and their clusters exhibit a highly non-Arrhenius diffusivity, which originates from a combination of a temperature dependent correlation factor and the presence of very low migration barriers. At low temperature, the diffusion is approximately Arrhenius, while above room temperature, the diffusivity is a linear function of temperature. A simple model is proposed to describe these diffusion regimes and the transition between them

[en] Direct molecular dynamics simulation of atomic deposition under realistic conditions is notoriously challenging because of the wide range of time scales that must be captured. Numerous simulation approaches have been proposed to address the problem, often requiring a compromise between model fidelity, algorithmic complexity, and computational efficiency. Coarse projective integration, an example application of the “equation-free” framework, offers an attractive balance between these constraints. Here, periodically applied, short atomistic simulations are employed to compute time derivatives of slowly evolving coarse variables that are then used to numerically integrate differential equations over relatively large time intervals. A key obstacle to the application of this technique in realistic settings is the “lifting” operation in which a valid atomistic configuration is recreated from knowledge of the coarse variables. Using Ge deposition on amorphous SiO_2 substrates as an example application, we present a scheme for lifting realistic atomistic configurations comprised of collections of Ge islands on amorphous SiO_2 using only a few measures of the island size distribution. The approach is shown to provide accurate initial configurations to restart molecular dynamics simulations at arbitrary points in time, enabling the application of coarse projective integration for this morphologically complex system