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/O-2/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 TiOxNy 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.