LOCAL ORDER IN CVD DIAMOND FILMS - COMPARATIVE RAMAN, X-RAY-DIFFRACTION, AND X-RAY-ABSORPTION NEAR-EDGE STUDIES

We investigated the structural changes of carbon in diamond films depo sited by microwave plasma-assisted chemical vapor deposition with vari ous methane concentrations and substrate temperatures. They were studi ed by x-ray-absorption near-edge structure (XANES) at the C K edge. Th e results on composition arid structure were compared to those given b y Raman spectra, x-ray-diffraction patterns, and scanning electron mic roscopy: Unlike Raman spectroscopy, XANES at the C K edge is nearly eq ually sensitive whatever the nature of the carbon (diamond, graphite, amorphous,...) involved in these deposits. At T < 950 degrees C and [C H4 ] < 2%, the C K edge spectra and the diffraction measurements both show that the films mainly consist of diamond, despite strong morpholo gical modifications of the films. They all display the diamond charact eristics. However a small amount of amorphous component (congruent to 10%) is incorporated, while increasing the methane concentration and/o r the substrate temperature. The presence of this amorphous carbon ind uces a drastic change in the Raman spectra with the appearance of new lines. At substrate temperatures higher than 900 degrees C and methane concentrations equal to 2%, a second characteristic modification of t he Raman spectra then stems from the presence of a disordered graphiti c phase. These amorphous and graphitic components exhibit quite charac teristic Raman and XANES spectra. The nature of these amorphous and gr aphitic phases included into the diamond films is discussed.