ZrN, ZrxAlyN and ZrxGayN thin films – novel materials for hard coatings grown using pulsed laser deposition

Abstract

High-quality thin films of ZrN, ZrxAlyN and ZrxGayN have been grown by pulsed reactive crossed-beam laser ablation using Zr, Zr-Al and Zr-Ga ablation targets, respectively, and a N2 gas pulse. The films were characterized for their chemical, crystallographic and tribological properties. All the films had very low impurity levels and a cubic rock salt crystal structure over the entire investigated temperature range between room temperature and 600 °C. High-quality epitaxial films could be grown on Si (001) at 400 °C, though the crystallinity was disrupted at 525 °C by Si diffusion into the film bulk and the formation of ZrSi2 crystallites. Films grown on stainless steel were polycrystalline. The ratios of the metals in the alloy targets were in general not equal to those in the films: the Al content in the ZrxAlyN films was lower than the target value, which we attribute to differential scattering in the ablation plume. The Ga content in the ZrxGayN films fell with increasing substrate temperature, indicative of re-evaporation of Ga from the substrate surface. Those ZrxGayN films with the highest Ga content, grown at the lowest temperatures, were particularly nitrogen-deficient, which we attribute to the low reactivity of Ga with N2. The ZrxAlyN films had an exceptionally low coefficient of friction (0.20) versus steel and the greatest nanohardness of 28 GPa.