This thesis is an investigation of thin oxides formed on Si(100) in a device manufacturing environment. Chemical analysis was performed on SiC>2 and SiON films comprising a sample set with thicknesses spanning 5 to 20 nm. Chemical characterisation, using XPS confirmed film quality through the consistency in stoichiometry, thickness, elemental composition and peak parameters for the asreceived wafers. ARXPS measurements provided a qualitative interpretation of the interface and suggest suboxides are localised near the interface. In synchrotron studies using soft X- rays, both tunable photon energy and high resolution revealed precise information on the chemical and spatial distribution of interfacial suboxides and nitrides in the Si02 and SiON film respectively. It was possible to identify the presence of hydrides at both interfaces. For the oxynitrides the presence of a nitrogen rich region at the surface and interface is supported by the XPS and synchrotron studies. X-ray Absorption Spectroscopy XAS and X-ray emission Spectroscopy XES measurements were performed using synchrotron radiation in order to profile the partial density of states of the nitrogen and the oxygen in the valence band and conduction respectively. While the 8.5 eV energy bandgap between the PDOS associated with the oxygen in the valence band and conduction band agrees with the Si0 2 bandgap, the equivalent energy gap for the nitrogen related states is approximately 5.5 eV. The surface reconstruction of sulphur passivated Si(100) and Ge(100) surfaces were investigated by LEED and synchrotron soft X- ray photoemission spectroscopy. These studies were an attempt to ideally terminate these group IV (100) surfaces by a monolayer of divalent group VI element. Sulphur was deposited onto the atomically clean Si(100) (2x1) from an electrochemical cell. While the resulting surface displayed a (lx l) LEED pattern indicating ideal termination, the core level photoemission spectra reveled the presence both +1 and +2 oxidation states. Analysis of these spectra concluded that the sulphur coverage approximated to % of a monolayer meaning that the surface termination was non-ideal. LEED results from the study of sulphur deposition on the clean Ge(100) surface again revealed the presence of a (lx l) surface reconstruction. The photoemission results from the Ge3d displayed the presence of all four Ge oxidation states again indicating the non-ideal termination of the surface. The samples examined in this thesis were realised in an industrial fabrication process. Precise knowledge of the nature of the sample history is limited to that which is expressed in the thesis.