Reactive magnetron sputtering deposition and characterization of niobium carbide films

Niobium carbide thin films have been deposited on Si(100) substrates by direct current reactive magnetron sputtering using CH4 as a carbon source. With increasing F-CH4 from 4 to 22 sccm, the carbon content for the film increases from 32.7 to 68.7 at.% gradually, accompanying with a phase transition from hexagonal-Nb2C to cubic-NbC, and at the highest carbon content, the film exhibits a typical nanocomposite structure consisting of NbC nanocrystallites embedded in an amorphous hydrocarbon (a-C:H) matrix. The morphology, mechanical properties and tribological behavior for the films exhibit a significant dependency on the amount of the amorphous carbon in the nanocomposite structure. The film surface becomes smooth with increasing the carbon content, corresponding to a transition from columnar crystallites to free of columnar features. In addition, the increase in carbon content for the films leads to an increase in the compressive stress for the well-crystallized film, but the excessive amorphous phase partially relaxes the stress. The NbCx film with 53.9 at.% carbon content shows the maximum hardness 25.0 GPa. Both friction coefficient and wear resistance are improved by increasing the content of the surplus amorphous carbon. (c) 2013 Elsevier Ltd. All rights reserved.