This study investigates the interface formation between a magnesium oxide dielectric overlayer and an ultrathin SiO(2) layer (similar to 0.3 nm) grown on the atomically clean p-type Si(I I I) surface in ultra high vacuum. Both soft X-ray synchrotron radiation based photoemission and conventional X-ray photoelectron spectroscopy have been used to characterise the evolution of the interface and monitor the change in the interfacial oxide thickness. As the MgO film grows, there is an increase in the intensity of the silicon oxide features indicating the growth of the interfacial oxide which saturates at a thickness of approximately 0.7 nm. Spectra acquired at the surface sensitive 130 eV photon energy, reveal the emergence of a chemically shifted component on the low binding energy side of the substrate peak which is attributed to atomic displacement of silicon atoms from the Substrate to the interfacial oxide at room temperature. This evidence of atomic disruption at the high dielectric constant material (high-kappa) and silicon interface would be expected to contribute to charge carrier scattering mechanisms in the silicon and could account for the generally observed mobility degradation in high-kappa stacks. Thermal annealing studies of deposited MgO films show that dissociation begins to occur above 600 degrees C with desorption of Mg and the growth of a silicon oxide. (C) 2009 Elsevier B.V. All rights reserved.