Atomistic simulation methodologies for modelling the nucleation, growth and structure of interfaces

Most of the atomistic simulation techniques for studying the structure and energetics of surfaces and interfaces start by defining the basic structure of the interface, which is then simulated by static or dynamical methods. A different approach, in which interfacial structures are allowed to evolve during the course of the simulation is presented. In particular, three atomistic simulation methodologies for constructing models for thin film interfaces were developed, including "atom deposition", where the thin film is "grown" by sequentially depositing atoms onto a support material to obtain information on nucleation and growth mechanisms; "layer-by-layer" growth, where monatomic layers of a material are successively deposited on top of a substrate surface; and finally, "cube-on-cube" whereby the whole of the thin film is placed directly on top of the substrate, before dynamical simulation and energy minimisation. The methodologies provide a basis for simulating the nucleation, growth and structure of interface systems ranging from small supported clusters to monolayer and multilayer thin film interfaces. The layer-by-layer methodology is also ideally suited to explore the critical thickness of thin films. These technqiues are illustrated for systems with large negative misfits. The calculations suggest that the thin films (initially constrained under tension due to the misfit) relax back to their natural lattice parameter leading to the formation of surface cracks and island formation. The cube-on- cube methodology was then applied to the SrO/MgO system, which has a large (+20%) positive misfit. For this system, the SrO thin film underwent an amorphous transition which, under prolonged dynamical simulation, recrystallised revealing misfit-induced structural modifications, including screw-edge dislocations and low angle lattice rotations. Future work will use the developed methods to explore supported catalysts such as CeO2 supported on YSZ. 41 refs.