Combined near edge X-ray absorption fine structure and X-ray photoemission spectroscopies for the study of amorphous carbon thin films

Near edge X-ray absorption fine structure (NEXAFS) and X-ray photoemission (XPS) spectroscopies were used to study the chemical bonding in hard amorphous carbon (a-C) thin films. The analysis of their XPS spectra obtained at different photon energy excitations showed that the fraction of sp(3) hybridized atoms increased from the surface to the bulk. About 90% of the carbon atoms became spl hybridized over the depth probed by XPS after annealing the film at 850 degrees C. The intensity of the pi* resonance in the NEXAFS spectrum of the hard a-C film annealed at 850 degrees C was significantly smaller than the same resonance in a softer film annealed at 350 degrees C. However, the sp(2) concentration of the former film, measured by XPS, was much higher. This demonstrates that the intensity of the pi* resonance in the NEXAFS spectra of a-C films is not strictly proportional to the concentration of sp(2) hybridized atoms, but it can be strongly influenced by other effects, such as the localized character of the particular pi* bonding present in the analyzed a-C film. A sharp resonance was observed at the same photon energy as the exciton in diamond, at 289.5 eV, in the NEXAFS spectra of the a-C films. This resonance might indicate that a proportion of carbon atoms in the analyzed films occupied similar sites as the carbon atoms in crystalline diamond. (C) 1999 Elsevier Science B.V. All rights reserved.