Structural, magnetic and optical properties of Ni-doped TiO_2 thin films deposited on silicon(l 00) substrates by sol-gel process

摘要

Ni-doped TiO_2 films were deposited on Si(l 00) substrates by sol-gel technique. X-ray photoelectron spectroscopy analysis suggests that the valence of Ni ion is in +2 and oxygen vacancies increase with increasing Ni content. X-ray diffraction measurements indicate that Ni doping catalyzes the anatase-to-rutile transformation (ART) of TiO_2 films, which is due to the decrease of the ART activation energy. The reversible ferromagnetism of the samples with Ni fraction is found, which is due to an anatase-to-rutile junction destroying an F-center bound magnetic polaron. Optical properties of Ni-doped TiO_2 films were studied by the ellipsometric spectra. With increasing Ni content, the optical band gap of TiO_2 films is decreased from 3.56 to 3.34 eV, which may be related to phase composition and impurity band.