Ultraviolet Light-Induced Surface Changes of Tungsten Oxide in Air: Combined Scanning Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy Analysis.

Scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy analyses were combined to clarify the ultraviolet light-induced surface changes of WO in air. Identical-location STEM (IL-STEM) analysis showed that the WO particle surface was covered with an amorphous thin film after ultraviolet irradiation in air. X-ray photoelectron spectroscopy analysis showed that hydrocarbon decomposition and the formation of carboxyl/hydroxyl species occurred. These results suggested that the amorphous thin films consisted of photocatalytic oxidative species of hydrocarbon. The IL-STEM analysis could detect small light-induced changes. This technique will be useful for the microscopic characterization of photocatalysis or photoinduced hydrophilic conversion.