Structural Changes of Ultrathin Cub-PrO2(111)/Si(111) Films Due to Thermally Induced Oxygen Desorption

Abstract

The structural changes of ultrathin PrO2(111) films grown on Si(111) due to thermal reduction in ultra high vacuum are investigated. Therefore, praseodymia films are treated with oxygen plasma to obtain completely oxidized PrO2 films. The reduction of these films is studied with thermal desorption spectroscopy combined with ex situ X-ray diffraction measurements. It is shown that the distinct desorption peaks of molecular oxygen are correlated with stabilization of several intermediate phases of praseodymia. The most intense signal of desorbing oxygen is observed at similar to 650 K. It is coupled to the strongest impact on the crystalline structure since we observe the transition PrO2 -> Pr5O9. Further oxygen desorption leads to additional phase transitions with laterally coexisting phases. Grazing incidence X-ray diffraction measurements reveal that the initial pinning to the lateral lattice constant of hexagonal Pr2O3(0001) is not breached due to the plasma treatment. This hexagonal pinning is released during the oxygen desorption so that the crystalline structure of the praseodymia films does not only expand vertically but also laterally.