Hydrophilicity variation of WO3 thin films with annealing temperature

The influence of annealing temperature on the hydrophilic property of WO3 thin films deposited by thermal evaporation and sol-gel dip-coating methods was studied and compared for the first time. The thermal evaporated WO3 thin films annealed at 400 degrees C showed a nearly super-hydrophilic property without UV and visible illumination. By analysing the O( 1s) core level peak of XPS spectra, the amount of oxygen contributed at various bonds ( including O2-, OH- and (HO)-O-2) on the surface of the annealed samples at different temperatures were measured. In addition, a correlation between the hydrophilicity and the concentration of chemisorbed water on the film surface was suggested, independent of the thin film deposition method.