Soft X-ray Absorption and Emission Spectroscopic Investigation of Carbon and Carbon: Transition Metal Composite Films

Carbon and C:V, C:Co, C:Cu nanocomposite films grown by ion beam cosputtering in the temperature range from room temperature (RT) to 500 degrees C are investigated. Soft X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) have been used to determine electronic structure of the occupied and unoccupied electronic states of the coexisting carbon and transition metal (TM) constituents. The results from the spectroscopy are. supplemented by the film composition data and TM inclusion phase structural information obtained by elastic recoil detection analysis and X-ray diffraction, respectively. The TM(2p) XAS shows that V (Cu) is in carbidic (metallic) state over the whole temperature range, while Co shows a transition from a carbidic toward a metallic state when the growth temperature increases from RT to 500 degrees C. The C(1s) XAS demonstrates that the increase in the growth temperature favors the formation of graphite-like structures in carbon films. On the other hand, the TM metal incorporation strongly promotes the sp(3) admixture in the surrounding carbon phase which manifests itself through a significant increase in the intensity of a feature in the C(1s) XAS spectra positioned at similar to 291 eV resulting from 1s ->sigma* transitions. In addition, the codeposition of TM atoms with carbon enhances the formation of carbon structures with the prominent peak between pi* and sigma* regions in the C(1s) XAS spectra positioned at similar to 288.5 eV. The effect is independent of the TM tendency to form carbides or TM state (carbidic metallic) while its magnitude increases concomitantly with the TM content and decreases when the crystallinity degree of the inclusion phase increases. The results are discussed on the basis of the nanoparticle imposed curvature on the surrounding carbon network and interactions at the atomic level at the C-TM interfaces.