XRD and XPS studies of room temperature spontaneous interfacial reaction of CeO2 thin films on Si and Si3N4 substrates

Abstract

X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) investigations of interfacial reactions between Ce and Si have been carried out on the same set of as-deposited and 15 month aged films. XRD patterns demonstrate the presence of several peaks associated with CeO₂ planes in aged CeO₂/Si₃N₄ thin film in comparison with as-deposited nanocrystalline film, whereas the peak is broadened in the CeO₂/Si film after aging. XPS studies show that interfacial reaction occurs spontaneously in CeO₂/Si thin film at room temperature. Ce is present as both Ce⁴⁺ and Ce³⁺ oxidation states in as-deposited CeO₂/Si thin film, whereas Ce⁴⁺ is the main species in CeO₂ thin film deposited on the Si₃N₄ substrate. When XPS is recorded after 15 months, the concentration of Ce³⁺ species is observed to increase drastically in the CeO₂/Si thin film. In contrast, interfacial reaction between the CeO₂ and the Si₃N₄ substrate is not significant in the film even after 15 months of deposition. This shows that the initial room temperature spontaneous interfacial reaction observed in the CeO₂/Si film continues at a much higher rate, whereas the nature of the CeO₂/Si₃N₄ interface remains the same after 15 months, proving its stability.