Atomistic nitriding processes of titanium thin films due to nitrogen-implantation

Nitrogen ions (N2+) with 62 keV were implanted into the as-deposited Ti film composed of mainly (1 1 0)-oriented TiHx and (0 3 · 5)-oriented hcp-Ti at room temperature, which results in the epitaxial formation of (1 1 0)-oriented and (0 0 1)-oriented TiNy, respectively. The electron energy loss spectroscopy experiments elucidate that in the early N-implanting stage the release of hydrogen constituting TiHx gives rise to the shift of the loss peak due to plasmon excitation to lower loss energy side. On the other hand, the energy loss peaks due to plasmon excitation for nitriding of hcp-Ti gradually shifted to higher energy side with increasing dose. Through the N-invasion into the octahedral sites of hcp-Ti with larger space and lower electron density, the hcp-fcc transformation of Ti sublattices is induced by the shift of the (0 0 · 1)-plane in the 01⋅0 direction of hcp-Ti promoted by the forming of the strong Ti-N bonds including the π-type covalent bonds, and by the weakening of the Ti-Ti bonds. Furthermore, the inheritance of square atomic arrangement and the movement of the N atom to other neighboring O-site in the transformed fcc-Ti sublattice are responsible for the epitaxial growth of TiNy. The atomistic processes of the epitaxial growth of TiNy are discussed with the aid of the molecular orbital calculations.