Computer simulation studies of interface growth of 1+1 dimensional thin films and of bulk silicon germanium.

摘要

Using computer simulations, we have performed extensive studies of the interface growth of two systems: 1+1 dimensional thin films and bulk Silicon-Germanium mixtures. In the 1+1 dimensional thin film study, several models of thin films were investigated, including molecular beam epitaxy, “zero flux” diffusion, absorption and evaporation, the Edwards-Wilkinson and Restricted Edwards-Wilkinson models. In examining bulk Silicon-Germanium, we performed the first computational studies of phase unmixing in an elastic three dimensional model. We investigated the phase separation of the binary alloy in both the spinodal decomposition and nucleation regimes by investigating two points in temperature and concentration space.; For 1+1 dimensional thin film study, we used a solid-on-solid model with periodic boundary conditions. The interfacial width and structure factor were measured for the thin films for various lattice sizes. From those results, we extracted dynamic finite size scaling exponents for the respective models. For the molecular beam epitaxy model, we obtained α = 1.63 ± 0.07, β = 0.36 ± 0.02, and z = 4.2 ± 0.1, which self-consistently agreed with the estimate z = α/β = 4.53 ± 0.32. Comparing our results to other models examined here and to other works, we concluded that the molecular beam epitaxy model fell into the Das Sarma Tamborenea/Wolf-Villain universality class, and not the Kardar-Parisi-Zhang or Edwards-Wilkinson classes.; For the bulk Silicon-Germanium binary alloy study, we used a deformable diamond lattice with periodic boundary conditions with 4096 unit cells and 32,768 atoms. The Stillinger-Weber potential was used to describe the interactions. Thus, elastic interactions, allowing the atoms to vibrate off-lattice, were included, as well as homogeneous volume fluctuations to keep the system at constant pressure. For comparison, we investigated the effect of turning the elastic interactions off. By measuring the structure factor and spatial correlation function, we examined the process by which the system phase separated in two different growth regimes: spinodal decomposition and nucleation. From these measurements, we further extracted various scaling exponents, which further describe the growth processes in the respective regimes. Our results are compared to the results of other binary alloy rigid lattice simulations.