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

High-quality thin films of ZrN, ZrxAlyN and ZrxGayN have been grown by puls ed reactive crossed-beam laser ablation using Zr, Zr-Al and Zr-Ga ablation targets, respectively, and a N-2 gas pulse. The films were characterized fo r their chemical, crystallographic and tribological properties. All the fil ms had very low impurity levels and a cubic rock salt crystal structure ove r the entire investigated temperature range between room temperature and 60 0 degreesC. High-quality epitaxial films could be grown on Si (001) at 400 degreesC, though the crystallinity was disrupted at 525 degreesC by Si diff usion into the film bulk and the formation of ZrSi2 crystallites. Films gro wn 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 cont ent in the ZrxAlyN films was lower than the target value, which we attribut e to differential scattering in the ablation plume. The Ga content in the Z rxGayN films fell with increasing substrate temperature, indicative of re-e vaporation of Ga from the substrate surface. Those ZrxGayN films with the h ighest Ga content, grown at the lowest temperatures, were particularly nitr ogen-deficient, which we attribute to the low reactivity of Ga with N2. The ZrxAlyN films had an exceptionally low coefficient of friction (0.20) vers us steel and the greatest nanohardness of 28 GPa.