Optical and structural characterization of CVD diamond

Infrared and Raman spectroscopy as well as X-ray diffraction have been used to investigate polycrystalline diamond films prepared by hot filament assisted CVD or by filament assisted microwave plasma deposition. The absorption spectrum of a 400 m um thick CVD diamond wafer clearly shows the two-phonon absorption band of diamond together with C-H str cetching bands. An average hydrogen concentration below 1 at. per cent is inferred. The applicability of fine-grained CVD diamond films as dielectric layers in interference optics in the infrared is demonstrated. Resonant Raman spectroscopy has been applied to study the 1550 cm(exp -1) Raman band present in the spectrum of many diamond films. It was found, that the relative intensity of this band as compared to the 1332 cm(exp -1) diamond line decreases significantly with increasing exciting photon energy. In addition, a high frequency shift of about 60 cm(exp -1) was observed. These findings are explained by extended (several 10 nm) absorb ing regions consisting of amorphous carbon with sp2 and sp3 bonded carbon atoms. X-ray diffraction measurements revealed, that part of the investigated diamond samples exhibit pronounced fibre textures, i.e. a preferential alignment of the (110) planes perpendicular to the growth direction. Furthermore, twinning on (111) planes due to stacking faults is shown to exist in the films.