Magnetron sputtered W-C films with C60 as carbon source

Thin films in the W-C system were prepared by magnetron sputtering of W with coevaporated C60 as carbon source. Epitaxial deposition of different W-C phases is demonstrated. In addition, nanocrystalline tungsten carbide film growth is also observed. At low C60/W ratios, epitaxial growth of α-W with a solid solution of carbon was obtained on MgO(001) and Al2O3(001) at 400 deg. C. The carbon content in these films (10-20 at.%) was at least an order of magnitude higher than the maximum equilibrium solubility and gives rise to an extreme hardening effect. Nanoindentation measurements showed that the hardness of these films increased with the carbon content and values as high as 35 GPa were observed. At high C60/W ratios, films of the cubic β-WC1-x (x=0-0.6) phase were deposited with a nanocrystalline microstructure. Films with a grain size <30 A were obtained and the hardness of these films varied from 14 to 24 GPa. At intermediate C60/W ratios, epitaxial films of hexagonal W2C were deposited on MgO(111) at 400 deg. C. Polycrystalline phase mixtures were obtained on other substrates and hexagonal WC could be deposited as minority phase at 800 deg. C