several mechanisms of this superhydrophilicity have been proposed by researchers. one is the change of the surface structure to a metastable structure, and another is cleaning the surface by the photodecomposition of dirt such as organic compounds adsorbed on the surface, after either of which water molecules can adsorb to the surface. the mechanism is still controversial, and it is too soon to decide which suggestion is correct. to decide, atomic scale measurements and other studies will be necessary.