Exercising control over the influence of the lattice misfit on the structure of oxide-oxide thin film interfaces

Thin film oxide-oxide interfaces with associated lattice misfits ranging fr om -20 to +27%, have been 'grown' by depositing ions onto a surface in conj unction with dynamics simulation and energy minimisation. Inspection of the resulting interfaces revealed significant structural features within the t hin film. These included, for the CaO/MgO(100) system (+13% misfit), the ex posure of various CaO surfaces at the interface; grain-boundary formation; the evolution of periodic arrays of misfit induced dislocations; lattice sl ip, and rotations of the thin film with respect to the support. In each cas e the driving force to such behaviour was attributed to the reduction in th e strain energy generated within the interface which arises from the lattic e misfit between the two materials. The implications of employing periodic boundary conditions within interface calculations are also addressed. For t hose interfaces with high associated lattice misfits: BaO/MgO (+27%), SrO/M gO (+20%) and MgO/SrO (-20%), the deposition procedure yielded thin films w ith amorphous type structures. In the second part of this study we have exp lored briefly how one may exercise a degree of control over the influence o f the lattice misfit and its implications for the structure and consequentl y the chemical and physical properties of the thin film. For example, for t he SrO/MgO system, by including a CaO buffer layer between the SrO thin fil m and the MgO support material, it was possible to generate a more coherent and crystalline thin film, contrasting to the amorphous type structures ob served without the inclusion of a buffer layer. An alternative approach, in which dopant ions were introduced into the thin film, resulted in pseudomo rphic growth. In particular, the dopant ions modified the lattice parameter of the thin film to be commensurate with that of the support.