Understanding the light induced hydrophilicity of metal-oxide thin films

The transition metal oxides (MOx), titanium dioxide (TiO₂), and zinc oxide (ZnO), belong to a class of wide-bandgap natively doped n-type semiconductors^1,2 with several remarkable and widely studied properties^3,4,5,6. The reported applications of TiO₂ and ZnO surfaces date back several decades and comprise solar energy conversion by single-crystal electrodes for water splitting^7,8,9, photocatalytic reduction of carbon dioxide to fuels using solar energy¹⁰, photocatalytic decomposition of organic compounds^2,11,12, photo-electrodes for dye-synthesized solar cells^13,14, and photo-induced…