Characterization of nanocrystalline nitrogen-containing titanium oxide obtained by N₂/O₂/Ar low-field helicon plasma sputtering

TiO₂ and nitrogen-containing TiO₂ thin films were deposited on glass and silicon wafer substrates using a helicon-assisted reactive plasma sputtering process in a gas mixture of Ar/O₂/N ₂. The growth mechanism, chemical composition and crystalline structure were probed by x-ray photoelectron spectroscopy, x-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy. The presence of nitrogen in the film induces the formation of some Ti³⁺ defects states, which introduces oxygen vacancies in the TiO_xN_y structure. It is also observed that nitrogen substitution selectively hinders the formation of the crystalline rutile phase and promotes the growth of a polycrystalline anatase phase film. Moreover, the film exhibits a red-shift in light absorption from UV to visible spectrum as a function of the nitrogen doping. This work shows that crystalline TiO₂ thin films can be obtained with a low temperature process and also shows that using nitrogen can control the desired crystalline structure.