This report describes a study of the formation of TiN thin films produced by laser irradiation of titanium targets immersed in liquid nitrogen. Three fluence thresholds have been determined, corresponding to: (i) surface melting in gaseous nitrogen (0.7 J/cm2) (ii) surface melting under liquid nitrogen with TiN formation (1.2 J/cm2) and (iii) gross melting accompanied by the generation of periodic surface structures ( >2.0 J/cm2). Data obtained from transmission electron microscopy, Auger spectroscopy, and XPS studies show that the rapid solid-statecooling rates ( l010deg/sec ) result in a supersaturated, twinned hcp structure with solute contents up to 40 at% nitrogen.

Theoretical estimates suggest that the majority of the incident excimer laser radiation is absorbed by the target with subsequent thermal transfer to the liquid producing a highpressure shock wave originating at the liquid-solid interface. Pressures up to 4.3 GPa are predicted with the expanding vapor layer reaching a terminal velocity after 5 μs and a total lifetime of 28 μs. Such a lifetime is considerably longer than the thermal pulse in the substrate (from a I-dimensional heat flow analysis). The results are discussed with reference to such estimates. Because the thermal diffusivity far exceeds that of the solute, the extent of nitridation is determined predominantly by the first 200 ns of the thermal pulse experienced by the target.