Influence of transition metal doping on the structural, optical, and magnetic properties of TiO(2) films deposited on Si substrates by a sol–gel process

Transition metal (TM)-doped TiO(2) films (TM = Co, Ni, and Fe) were deposited on Si(100) substrates by a sol–gel method. With the same dopant content, Co dopants catalyze the anatase-to-rutile transformation (ART) more obviously than Ni and Fe doping. This is attributed to the different strain energy induced by the different dopants. The optical properties of TM-doped TiO(2) films were studied with spectroscopic ellipsometry data. With increasing dopant content, the optical band gap (E(OBG)) shifts to lower energy. With the same dopant content, the E(OBG) of Co-doped TiO(2) film is the smallest and that of Fe-doped TiO(2) film is the largest. The results are related to electric disorder due to the ART. Ferromagnetic behaviors were clearly observed for TM-doped TiO(2) films except the undoped TiO(2) film which is weakly magnetic. Additionally, it is found that the magnetizations of the TM-doped TiO(2) films decrease with increasing dopant content.