Early stages of the Schottky barrier formation in submonolayer Pt on SrTi O3 (001)

We investigate the early stages of Pt nanocluster formation on SrTiO3 (001) and the emergence of the Schottky barrier at the interface as a function of submonolayer Pt coverage using density functional theory. We find that there is a critical coverage of a 3/8 monolayer (ML), below which the Pt-oxygen interaction is dominant, leading to an ordered reconstructed surface with local Pt(II)-oxide structures. Beyond the critical coverage of 3/8 ML, the system undergoes a crossover at which the Pt-Pt interaction becomes dominant, leading to the formation of closed-packed hexagonal Pt nanoclusters. We show that cluster-induced gap states that pin the Fermi level at 1.3 eV above the valence band edge emerge at the same time as this crossover, thus showing the critical role it plays in determining the Schottky barrier height of the Pt/SrTiO3 (001) interface.