(113f) Atomic Scale Electric Field Control of the Structure and Morphology of a Growing Ultra-Thin Oxide Film
In several catalytic applications of surface oxides, controlled manipulation of oxygen related defects in the growing oxide microstructure is critical to achieve desired chemical activity. Controlling oxide microstructure and surface oxide coverage in the case of discontinuous oxide growth on metal substrates exhibiting slow oxidation kinetics remains a major challenge. The kinetics of surface oxide growth is very strongly correlated to the microstructure of the developing oxide film i.e. structure, morphology and chemical composition. We show through molecular dynamics simulations that take into account dynamic charge transfer between atoms that it is possible to exercise control over the structure and morphology of ultra-thin oxide films at atomic scale by electric fields, using NiO as a representative example. Precise understanding of the microscopic processes involved in electric field assisted oxidation is provided by the atomistic models employing dynamic charge transfer between atoms. Electric field assisted control of surface oxygen dynamics is shown to dictate the formation and evolution of the oxide domains. Atomistic simulations also indicate that the surface diffusion of adsorbed oxygen can be controlled by the applied electric field and utilized to tune the growing oxide structure and morphology. A critical factor of importance here is that this allows an athermal and oxygen pressure independent route for oxygen point defect control, which is of universal importance in the field of complex oxides. This opens up an unprecedented route for synthesis of ultra-thin oxides that are of paramount importance to catalysis, electronics, emerging energy technologies and variety of environmental coatings.