Growth kinetics of nanometric dendrites in metal-carbon thin films

Tungsten-carbon films deposited by pulsed-DC reactive magnetron sputtering show the formation of a dendritic structure at nanometric scale. The structure is formed by a combination of a polycrystalline beta-W phase together with a non-stoichiometric phase. The nanodendrites coincide with W-rich zones, whereas C-rich regions are located at the interstices. The characteristics of nanostructure have been modulated by varying the metal concentration of the films. The composition, structure and morphology characterized by X-ray photoelectron spectroscopy, electron probe microanalysis, transmission electron microscopy, X-ray diffraction and atomic force microscopy, and the mechanical and tribological properties were evaluated by profilometry, nanoindentation and microscratch. The observed growth pattern is interpreted as the result of nucleation and growth of a W phase into a W-C amorphous matrix, whose growth is controlled by diffusion of carbon. A simulation model based on phase field modelling and presenting similar morphologies is formulated. This special structure combines properties of W and diamond-like carbon films, which enlarges the of applications towards self-lubricating hard and low-friction coatings with improved stability. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.