Morphology and bonding structure of fullerene-like nanocomposite C:Ni (~30 at%.) thin films grown by ion beam sputtering

The morphology and bonding structure of nanocomposite C:Ni (~30 at.%) thin films grown by ion beam sputtering at different temperatures (RT-500°C) is investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray absorption near edge structure (XANES). XRD and XANES of the LII–LIII absorption edges of Ni reveal that at lower temperatures nickel is in the carbidic state whose signatures become more pronounced when the growth temperature increases up to ~300°C. Further increase in the growth temperature results in XRD and XANES features resembling to those of metallic nickel. According to the TEM observations, nickel or nickel carbide nanoparticles embedded in a carbon matrix have a columnar structure with the diameter of ~2-5 nm, which is typical for the films grown under surface diffusion dominated conditions for the structuring processes. At lower temperatures carbon is mainly in an amorphous state, while the transition into a fullerene-like structure, which consists of nickel nanoparticles wrapped in curved graphite sheets, can be clearly identified at ~200°C. The present results show that the nickel nanoparticles act as nucleation centres for the formation of the fullerene-like structures in both carbidic and metallic states, provided that the temperature for surface diffusion during the deposition process is sufficiently high.