Characterization of amorphous and nanocomposite Nb-Si-C thin films deposited by DC magnetron sputtering

Two series of Nb-Si-C thin films of different composition have been deposited using DC magnetron sputtering. In the first series the carbon content was kept at about 55 at.% while the Si/Nb ratio was varied and in the second series the C/Nb ratio was varied instead while the Si content was kept at about 45 at.%. The microstructure is strongly dependent on Si content and Nb-Si-C films containing more than 25 at.% Si exhibit an amorphous structure as determined by X-ray diffraction. Transmission electron microscopy, however, induces crystallisation during analysis, thus obstructing a more detailed analysis of the amorphous structure. X-ray photo-electron spectroscopy suggests that the amorphous films consist of a mixture of chemical bonds such as Nb-Si, Nb-C, and Si-C. The addition of Si results in a hardness decrease from 22 GPa for the binary Nb-C film to 18 - 19 GPa for the Si-containing films, while film resistivity increases from 211 μΩcm to 3215 μΩcm. Comparison with recently published results on DC magnetron sputtered Zr-Si-C films, deposited in the same system using the same Ar-plasma pressure, bias, and a slightly lower substrate temperature (300 °C instead of 350 °C), shows that hardness is primarily dependent on the amount of Si-C bonds rather than type of transition metal. The reduced elastic modulus on the other hand shows a dependency on the type of transition metal for the films. These trends for the mechanical properties suggest that high wear resistant (high H/E and H3/E2 ratio) Me-Si-C films can be achieved by appropriate choice of film composition and transition metal.