EVALUATION OF DIAMOND FILMS BY NUCLEAR-MAGNETIC-RESONANCE AND RAMAN-SPECTROSCOPY

The quality of chemically vapor deposited diamond films was assessed in terms of sp2/sp3 content as determined by solid-state nuclear magnetic resonance (NMR) and Raman spectroscopy. While the results of the two techniques are in qualitative agreement, only the NMR spectra yield quantitative values for the sp2/sp3 ratio. Only sp3 carbon was observed in the NMR spectra of very high quality hot-filament, microwave plasma, and d.c. arc-jet chemically vapor deposited films. As expected, Raman spectroscopy is extremely sensitive to sp2 bonded carbon, identifying small amounts below the detection limit of the NMR spectrometer. Comparison of the two techniques, however, indicates that Raman spectroscopy may be so sensitive to sp2 bonded carbon that sp3 bonded carbon in films containing as much as 90% sp3 bonded material may remain undetected. NMR linewidths indicate that the sp3 carbon in such material shows more disorder than that found in high-quality polycrystalline films.