No abstract

There have been many studies applying atomistic simulation techniques to investigate the structure and energetics of surfaces and interfaces. Almost all start by de®ning the basic structure of the interface, which is then simulated by static or dynamical methods. A different approach is adopted here, where we allow interfacial structures to evolve during the course of the simulation. In particular, three atomistic simulation methodologies for constructing models for thin ®lm interfaces have been developed, including `atom deposition', where the thin ®lm 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 ®nally, `cube-on-cube' whereby the whole of the thin ®lm is placed directly on top of the substrate, before dynamical simulation and energy minimisation. The methodologies developed in this study provide a basis for simulating the nucleation, growth and structure of interface systems ranging from small supported clusters to monolayer and multilayer thin ®lm interfaces. In addition, the layer-by-layer methodology is ideally suited to explore the critical thickness of thin ®lms. We illustrate these techniques with studies on systems with large negative mis®ts. The calculations suggest that the thin ®lms (initially constrained under tension due to the mis®t) relax back to their natural lattice parameter resulting in 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 (z20%) positive mis®t. For this system, the SrO thin ®lm underwent an amorphous transition which, under prolonged dynamical simulation, recrystallised revealing mis®t-induced structural modi®cations, including screw-edge dislocations and low angle lattice rotations.

The applicability of ionic liquids within the nuclear industry has been investigated. The radiation stability of ionic liquids containing dialkylimidazolium cations has been tested through with alpha, beta and gamma irradiation. The results of these tests suggest that imidazolium salts have stabilities similar to alkylbenzenes and greater than tetrabutylphosphate / odorless kerosene (TBP/OK) mixtures. The oxidative dissolution of uranium dioxide and the anodic dissolution of uranium metal and plutonium metal have been carried out in various ionic liquid media 162