(Invited) Reactivity of Water Vapor with Ultrathin GeO2/Ge and SiO2/Si Structures Investigated by Near-Ambient-Pressure X-ray Photoelectron Spectroscopy

The purpose of this study is to investigate the reactivity of water vapor with a thin GeO2 film on Ge. We conducted near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) measurements of this system, and the results were compared with those for a SiO2 film on Si. We obtained NAP-XPS spectra at relative humidity (RH) values of up to ~15% and found that a thicker water film is formed on a GeO2/Ge structure than on a SiO2/Si structure at RH above ~10-4%. This is probably caused by infiltrated water molecules in the GeO2 film. Then we detected positive charging of both the water-adsorbed GeO2 and SiO2 films under X-ray irradiation, the extent of which was greater on the GeO2 films. We propose that this is due to the emission of electrons from adsorbed water species in the GeO2 films to the Ge bulk, resulting in the creation of immobile cations in GeO2.