Investigation of metal distribution and carbide crystallite formation in metal-doped carbon films (a-C:Me, Me = Ti, V, Zr, W) with low metal content

Metal-doped amorphous carbon films (a-C:Me) were deposited at room temperature by magnetron sputtering using a metal (Me = Ti, V, Zr, W) and a graphite target. The metal distribution and the temperature-induced carbide crystallite formation were analyzed by X-ray diffraction (XRD), electron microscopy (TEM, STEM) and X-ray absorption spectroscopy (EXAFS, XANES), focusing on low metal concentrations between 6.5 and 9.5%. In as-deposited samples, the metal atoms are atomically distributed in the carbon matrix without significant formation of carbide particles. With annealing to 900 K the local atomic environment around the metal atoms becomes similar to the carbide. The carbide crystallites grow with annealing up to 1300 K, their size is dependent on the metal type: V > Ti > Zr≈W. W2C and WC1 − x crystallites were identified for W-doped films, whereas the monocarbides are formed for the other metals. It is demonstrated, that EXAFS and high resolution electron microscopy are required to get a correct picture of the structure of the analyzed a-C:W films.