Raman study of carbon clusters in W-C thin films

A dispersion of nanocrystalline tungsten carbides in an amorphous carbon (a-C) matrix blends the hardness and thermal stability of carbides with the low-friction coefficient of a-C to form a superior coating. A dc-reactive (Ar + C6H6) magnetron sputtering of tungsten was used to produce tungsten-carbon films with variable fraction of incorporated unreacted carbon. Raman spectroscopy was used to study the carbon phase in these films, and the nanoindentation measurements were employed for their mechanical characterization. All Raman spectra indicate occurrence of the graphitic carbon, characterized by two peaks, one related to graphite mode (G-line), and another which is due to disorder (D-line). It is concluded that the enhancement of graphitic carbon fraction phase in the films is effected through the increase in concentration of the presumably uniformly distributed carbon clusters less than 1 nm in size.