Carbonizing processes of titanium thin films by carbon-implantation

Observations of the crystallographic structural changes of deposited Ti films (100 nm thick) during C-implantation were made by using transmission electron microscope (TEM) for the purpose to elucidate the carbonizing processes of Ti films. The Ti films were deposited by an electron beam heating method onto thermally cleaned NaCl (001) surfaces held at room temperature (RT). Both the 200 kV conventional TEM and the 400 kV analytical high resolution TEM combined with ion accelerators were used. The deposited Ti films consisted of mainly (03 · 5)-oriented hcp-Ti and (110)-oriented CaF₂2 type TiH_x, (x ∼ 1.5). Carbon ions (C⁺) with 26 keV were implanted into the Ti films held at RT in the 400 kV TEM. The H atoms which constituted TiH_x were released from the as-deposited Ti films during the early stage of C-implantation. In the C-implanted Ti film (C/Ti=0.54), there coexisted (001)- and (110)- oriented NaCl-type TiC_y and a small amount of hcp-Ti. The results of TEM observation indicated that (001)- and (110)-oriented TiC_y were epitaxially formed by the transformation of (03 · 5)-oriented hcp-Ti and (110)-oriented TiH_x, respectively. In the cases, the hcp-Ti sublattice is transformed into fcc-Ti sublattice of TiC_y with inheritance of square atomic arrangement of hcp-Ti. The hcp-fcc transformation was discussed with the results of a self-consistent charge discrete variational (DV)-Xa molecular orbital (MO) calculation.