Irradiation-induced reactions at the CeO2/SiO2/Si interface

Abstract

The influence of high-energy (1.6 MeV) Ar²⁺ irradiation on the interfacial interaction between cerium oxide thin films (∼15 nm) with a SiO₂/Si substrate is investigated using transmission electron microscopy, ultrahigh vacuum x-ray photoelectron spectroscopy (XPS), and a carbon monoxide (CO) oxidation catalytic reaction using ambient pressure XPS. The combination of these methods allows probing the dynamics of vacancy generation and its relation to chemical interactions at the CeO₂/SiO₂/Si interface. The results suggest that irradiation causes amorphization of some portion of CeO₂ at the CeO₂/SiO₂/Si interface and creates oxygen vacancies due to the formation of Ce₂O₃ at room temperature. The subsequent ultra-high-vacuum annealing of irradiated films increases the concentration of Ce₂O₃ with the simultaneous growth of the SiO₂ layer. Interactions with CO molecules result in an additional reduction of cerium and promote the transition of Ce₂O₃ to a silicate compound. Thermal annealing of thin films exposed to oxygen or carbon monoxide shows that the silicate phase is highly stabile even at 450 °C.