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

Abstract

Thin film oxide–oxide interfaces with associated lattice misfits ranging from –20 to +27%, have been ‘grown’ by depositing ions onto a surface in conjunction with dynamics simulation and energy minimisation. Inspection of the resulting interfaces revealed significant structural features within the thin film. These included, for the CaO/MgO(100) system (+13% misfit), the exposure of various CaO surfaces at the interface; grain-boundary formation; the evolution of periodic arrays of misfit induced dislocations; lattice slip, and rotations of the thin film with respect to the support. In each case the driving force to such behaviour was attributed to the reduction in the strain energy generated within the interface which arises from the lattice misfit between the two materials. The implications of employing periodic boundary conditions within interface calculations are also addressed. For those interfaces with high associated lattice misfits: BaO/MgO (+27%), SrO/MgO (+20%) and MgO/SrO (–20%), the deposition procedure yielded thin films with amorphous type structures. In the second part of this study we have explored briefly how one may exercise a degree of control over the influence of the lattice misfit and its implications for the structure and consequently the chemical and physical properties of the thin film. For example, for the SrO/MgO system, by including a CaO buffer layer between the SrO thin film and the MgO support material, it was possible to generate a more coherent and crystalline thin film, contrasting to the amorphous type structures observed without the inclusion of a buffer layer. An alternative approach, in which dopant ions were introduced into the thin film, resulted in pseudomorphic growth. In particular, the dopant ions modified the lattice parameter of the thin film to be commensurate with that of the support.