Comparative study of optical absorption in diamond powders and polycrystalline CVD films

Optical absorptivity of powders and polycrystalline films is difficult to measure by common methods because of the strong diffuse light scattering. In this report we present the results of studies of diamond powders and polycrystalline CVD films by photoacoustic (PA) spectroscopy which allows us to measure the light absorption in the light scattering substances due to the photothermal effect. Diamond powders and polycrystalline CVD films with a crystallite size ranging from hundreds of microns to a few nanometers were investigated. The optical absorption in the spectral range 200 to 1500 nm was estimated from PA spectra registered at the various light modulation frequencies (of 20 to 1500 Hz). The efficiency of PA spectroscopy for investigating diamond-related materials was shown. The spectral features corresponding to the different kinds of defects in the diamond crystal lattice, and to non-diamond carbon inclusions, were detected. The dependence of the PA spectrum shape on the modulation frequency exhibited a correlation of the light scattering and the crystallite size in samples studied. (C) 1997 Elsevier Science S.A.