Epitaxial transformation of hcp–fcc Ti sublattices during nitriding processes of evaporated-Ti thin films due to nitrogen-implantation

Abstract

Abstract Atomistic transformation processes of Ti films due to N-implantation have been clarified through in-situ observations by using transmission electron microscope (TEM) along with molecular orbital calculations. The N 2 + ions with 62 keV are implanted into as-deposited Ti films which consist of hcp-Ti and TiH x with preferred orientations, in the 400 kV analytic high resolution TEM combined with ion accelerators. Thus, titanium nitride (TiN y ) films with preferred orientations are epitaxially formed by the inheritance of partial atomic arrangement of hcp-Ti or TiH x in as-deposited Ti films and by the occupation of octahedral sites by N atoms, which elucidates that epitaxial transformation of hcp–fcc Ti sublattices occurs. The analysis of electronic structure of Ti films during the implantation clarifies that octahedral sites of hcp-Ti with larger space have lower electron density, which leads to the invasion of N ions into octahedral sites. Thus, the hcp–fcc transformation is induced by the shear in the direction on the (0 0 · 1) plane, promoted by the forming of covalent bonds mainly composed of hybridized orbitals due to combination of Ti3d and N2p orbitals, and by the weakening of Ti–Ti bonds.