In-Situ Transmission Electron Microscopy and Electron Energy Loss Spectroscopy Observation of TiN Grown by N-Implantation

Abstract

Nitrogen ions (N2+) with 62 keV were implanted into evaporated-Ti films in the 400 kV analytical and high resolution transmission electron microscopy (TEM) combined with ion accelerators at JAERI-Takasaki. Observations by in-situ TEM equipped with electron energy loss spectroscopy, along with the discrete variational Xα molecular orbital calculations, revealed changes in the crystallographic and electronic structures of evaporated-Ti films due to N-implantation. A (001)-oriented NaCl-type TiNy is epitaxially formed by the transformation of (03·5)-oriented hcp-Ti to (001)-oriented fcc-Ti and by the occupation of N in the octahedral (O-) sites, whereas a (110)-oriented TiNy is formed by nitriding a (110)-oriented TiHx. The release of H from the TiHx occurs preferentially rather than the occupation of N in the O-sites of fcc-Ti sublattice. The loss peak due to volume plasmon of areas where TiHx has grown in the as-grown Ti film shifts to lower loss energy in the early N-implanting stage, while that of areas, where hcp-Ti has grown, gradually shifts to higher loss energies with increasing N dose. Analysis of Mulliken bond overlap populations determines that occupation of N in the O-sites gives rise to weakening Ti-Ti bonds and formation of Ti-N covalent bonds. The growth process of TiNy accompanied by changes of the crystallographic and electronic structures of Ti films due to N-implantation is discussed.