Experimental and theoretical investigation of Nb-Si-C films

Nb-Si-C films with varying silicon content were prepared using DC magnetron sputtering a target composed of elemental niobium, silicon and graphite. The films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and hardness measurements. It is shown that Nb-C films consist of metal carbide nanocrystals surrounded by amorphous carbon-oxygen phase. With addition of Si to the Nb-C films two processes occur, namely: a decrease of carbide nanocrystals size and an increase of amorphous phase amount. The results of XRD, XPS and hardness measurements allow suggestion that there is some threshold value of Si content (about 8 at.%) below which the decrease in NbC crystals size occurs thus resulting in increasing film hardness. With Si contents higher than above threshold value, the thickness of the amorphous phase that surrounds the NbC nanocrystals increases so that this soft amorphous phase lowers the strength of the films. First-principals quantum molecular dynamics calculations were carried out to interpret the structural and mechanical properties of the deposited films.