Atomistic modelling of titania grown using PVD methods

Results are presented for the atomistic modelling of titania growth, specifically the rutile {110} surface. Long time scale dynamics techniques are used to model the growth of thin films at realistic growth rates. Between deposition events, the system is evolved through an on-the-fly Kinetic Monte Carlo (otf-KMC) method, finding diffusion pathways and barrier heights without any prior knowledge of transitions. Otf-KMC allows thorough investigation of transitions and barriers observed during the film growth, giving a deeper understanding of growth mechanisms. An important rutile growth mechanism observed during all simulations, involves the upward diffusion of Ti interstitials below an O rich surface, with a barrier of 0.61 eV. The energy required for a single O ad-atom to diffuse on the surface is higher (between 0.65 eV - 0.85 eV). Methods used also allow examination of the effects of varying the experimental parameters, such as substrate bias, plasma density and stoichiometry of the deposited material. Conclusions drawn from the film growth suggest that the evaporation process produces an incomplete structure with voids, which is interesting for dye cell use. The inclusion of a low energy ion-beam assist does however add enough kinetic energy to the substrate to enable the completion and densification of layers, producing a film with greater crystallinity. The sputtering process produces highly crystalline growth, which is useful for anti-reflection coatings.