Microstructure and hardness of reactively r.f. magnetron sputtered Cr-V-O thin films in dependence on composition and substrate bias

Cr-V-O thin films were deposited by reactive r.f. magnetron sputtering of a segmented Cr-V target in an Ar/O-2 atmosphere at 0.4 Pa. During deposition the substrate temperature was set to 350 C and the substrate bias voltage was systematically varied from 0 to -100 V. Cr-rich thin films were nanoaystalline and exhibited a single-phase solid solution corundum structure, (Cr,V)(2)O-3, with only small deviation from the perfect corundum stoichiometry. This corundum structure was revealed for films with low vanadium content (up to a maximum vanadium concentration of 11 at.%) and confirmed by transmission electron microscopy analyses. All films of higher vanadium content were X-ray amorphous. In case of the Cr-V-O thin films with corundum structure, two effects on hardness were observed: First, the hardness of the films increased moderately with increasing vanadium concentration (in case of films deposited at zero volt substrate bias). Second, by applying a moderate substrate bias of -100 V during deposition, the hardness values increased up to 38 GPa. These results indicate that proper chemical modification of Cr2O3 thin films, shown here for a modification with vanadium, can be a tool to design new protective coatings. (C) 2014 Elsevier B.V. All rights reserved.