Structural phase transition of ultra thin PrO2 films on Si(111)

Abstract

Ultra thin heteroepitaxial PrO2 films on Si(111) were annealed under UHV conditions and investigated by x-ray diffraction (XRD), x-ray reflectometry (XRR) and spot profile analysis low energy electron diffraction (SPALEED) with regard to structural stability and phase transitions due to the high oxygen mobility of the oxide. This gives information about the manageability of the material and its application as a model catalyst system in surface science. While the samples are stable in UHV at room temperature, annealing at 300 degrees C exhibits a terminated phase transition from PrO2 and PrO2-Delta to cub-Pr2O3 with an increase in the silicate at the interface and a decrease in the crystalline praseodymia layer mainly due to atomic diffusion of silicon into the oxide film. Strain effects during the phase transition also cause mosaic formation at the surface. Further annealing up to 600 degrees C shows only little change in the film structure. This will finally lead to a model of the film structure during the annealing process.