Combined near edge X-ray absorption fine structure and X-ray photoemissionspectroscopies 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 amorph ous carbon (a-C) thin films. The analysis of their XPS spectra obtained at different photon energy excitations showed that the fraction of sp(3) hybri dized 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 t he 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 s maller 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 m uch higher. This demonstrates that the intensity of the pi* resonance in th e NEXAFS spectra of a-C films is not strictly proportional to the concentra tion of sp(2) hybridized atoms, but it can be strongly influenced by other effects, such as the localized character of the particular pi* bonding pres ent in the analyzed a-C film. A sharp resonance was observed at the same ph oton energy as the exciton in diamond, at 289.5 eV, in the NEXAFS spectra o f 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 c rystalline diamond. (C) 1999 Elsevier Science B.V. All rights reserved.