Thin films of Me-Si-C (Me = early transition metal) have interesting multifunctional properties, see, e.g., [1]. We have in the present study investigated thin films in the Nb-Si-C system deposited by dc-magnetron sputtering using elemental targets. The microstructure and composition of the films have been characterized with x-ray diffraction, x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy. Nanoindentation and atomic force microscopy were used to investigate the mechanical properties of the thin films while the electrical contact resistance was measured using a four wire set-up with an Au-coated probe pressed against the film surface.

 

Our results show that films with a silicon content less than 20 at.% exhibit a nanocomposite (nc-NbC/a-SiC) structure with nanocrystalline NbC grains embedded in an amorphous matrix phase. The size of the carbide grains decrease with the carbon content increase. A transition to a completely amorphous structure occurs with a Si content above 20 at.%. The transition in microstructure is reflected in the properties of the films with an abrupt increase in contact resistance (from 30 mΩ to 200 mΩ at 1 N) and a change in the mechanical behavior of the thin films. The XPS spectra show a change of chemical bonding from mainly C-Nb to a significant amount C-Si bonds as the Si and C content increase in the films. This results in harder films and an increase in the electrical resistivity. The amorphous films can be described as a metal carbide-based glass and the formation of this type of structures in sputtered Me-Si-C films will be discussed.

 

[1] J. Lauridsen et al., Surf. Coat. Technol., 205, 299-305, 2010