Laser Raman Studies of Polycrystalline and Amorphic Diamond Films

This report describes the results of a number of different, but related, laser Raman studies on various CVD diamond samples. It attcmpts to show the versatility of Raman spectroscopy as a diagnostic tool for the quality of diamond films, by demonstrating its use in a few novel applications. The studies of the laser Raman spectra of amorphic diamond and CVD diamond films are performed using lasers of different excitation wavelength (632.8, 514.5, and 780 nm). For CVD diamond films, a significant reduction in unwanted laser induced fluorescence is observed when using the near-IR diode laser (780 nm) compared to excitation using the shorter (visible) wavelengths. The luminescence peak at a Raman shift of 2260 cm-' coinciding with the graphite G band, can be used as a reliable indicator of poor quality diamond. Additional information about the stress of the diamond films on hard substrates can be obtained from the intensity of the luminescence peak at a Raman shift of 2600 cm-'. Laser Raman spectra of CVD diamond films that have previously been used in electron emission tests show that graphitisation had occurred around emission sites. Direct Raman imaging was used to investigate the cut, exposed surface of a diamond fibre reinforced metal matrix composite. Amorphic diamond films prepared by laser ablation are examined by both Raman and transmission electron diffraction, and the presence of nanocrystalline diamond clusters embedded within the amorphic diamond matrix is verified.