LASER-INDUCED CHEMICAL-VAPOR-DEPOSITION OF TITANIUM DIBORIDE

The CO2 laser-induced chemical vapor deposition process of titanium diboride (TiB2) is described. The TiB2 was deposited on mullite, alumina, and thermally oxidized silicon by a hydrogen reduction of titanium tetrachloride (TiCl4) and boron trichloride (BCl3). The process resulted in a reaction-limited regime, a heat-diffusion limited regime, and a mass-diffusion limited regime. The hydrogen concentration has a large influence on the growth rate, nucleation rate, and morphology of the coatings. The photothermal deposition process is photolytically enhanced by the 193 nm beam of an ArF excimer laser which dissociates TiCl4. However, the 193 nm beam enhances the nucleation rate and crystal-growth rate to a different extent. The nucleation rate increases with increasing atomic hydrogen concentration, as is illustrated by experiments performed with a separate atomic hydrogen source (i.e., hot filament-enhanced chemical vapor deposition).