Photoinduced hydrophilicity of epitaxially grown TiO2 films by RF magnetron sputtering

Titanium dioxide (TiO2) films were deposited by r.f. reactive magnetron sputtering on the following four different substrates, (a) nonalkali glass (Corning #7059), (b) MgO (100), (c) SrTiO3 (100) and (d) rutile (110), (001), (100), where (b)-(d) were single crystals. X-ray diffraction and pole figure analyses revealed that TiO2 films on a) were anatase polycrystals with (101) preferred orientation, whereas hetero- or homoepitaxial growth of anatase or rutile TiO2 was observed on the (b)-(d) substrates. The epitaxial relationships were as follows: (b) anatase, (100)[001]//MgO(100)[001], (c) anatase (001)[100]//SrTiO3(100)[001] and (d) rutile homoepitaxy. The heteroepitaxl anatase films with the thickness greater than 100 nm showed UV-induced super-hydrophilicity, where the water contact angle decreased to less than 1degrees.