Abstract
We carried out near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) measurements of water-adsorbed ultrathin GeO2 films on Ge substrates, and the results were compared with those for SiO2 films on Si. We obtained NAP-XPS spectra at relative humidity (RH) values of up to ∼15% and showed that the GeO2/Ge structures attract more water molecules than the SiO2/Si structures at RH above ∼10−4%. This is probably because water molecules infiltrate the GeO2 films to form hydroxyls. Then we revealed positive charging of the water-adsorbed SiO2 films by their interaction with X-rays. For the water-adsorbed GeO2 films, we observed greater positive charging of the films, of which origin is discussed.
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