Coverage and bonding of thin, buried epitaxial SrTiO$_{3}$ on Si(100)

SrTiO$_{3}$ can be used as a buffer layer for the growth of perovskite oxide heterostructures, opening up possibilities for the incorporation of novel materials into existing Si-based technology. While these layers have been studied during growth, a serious question for such thin layers is if their structure remains unaltered after they have been overgrown. Here, we present results of thin SrTiO$_{3}$ films grown on Si(100). Scanning transmission electron microscopy (STEM) of the buried structures shows the formation of islands and a non-uniform coverage of the first few monolayers after capping with a-Si. The island size increases if the SrTiO$_{3}$ film is grown on a SrSi$_{x}$ seed. An important question that arises is the existence of oxygen vacancies at the interface between the oxide and the substrate. Oxygen deficiency leads to a doping of the empty Ti 3d band in bulk SrTiO$_{3}$ with electrons, thereby inducing a metallic phase as the Ti formal valence changes from 4+ to 3+. Using electron energy loss spectroscopy in a STEM the Ti valence across the interface is probed on the atomic scale.