Magnetron sputtered W-C films with C-60 as carbon source

Thin films in the W-C system were prepared by magnetron sputtering of W with coevaporated C-60 as carbon source. Epitaxial deposition of different W-C phases is demonstrated. In addition, nanocrystalline tungsten carbide film growth is also observed. At low C-60/W ratios, epitaxial growth of alpha-W with a solid solution of carbon was obtained on MgO(001) and Al2O3(001) at 400 degreesC. 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 C-60/W ratios, films of the cubic beta-WC1-x (x = 0-0.6) phase were deposited with a nanocrystalline microstructure. Films with a grain size < 30 Angstrom were obtained and the hardness of these films varied from 14 to 24 GPa. At intermediate C-60/W ratios, epitaxial films of hexagonal W2C were deposited on MgO(111) at 400 degreesC. Polycrystalline phase mixtures were obtained on other substrates and hexagonal WC could be deposited as minority phase at 800 degreesC. (C) 2003 EIsevier B.V. All rights reserved.