SIZE EFFECT IN OPTICAL-SPECTRA OF MICROCRYSTALLINE DIAMOND POWDERS AND CVD FILMS

In this work, we present the results of study of diamond polycrystalli ne films, synthetic powders, and single crystal. Using a method of pho toacoustic spectroscopy, we have found that in light absorption spectr a of all three types of diamond material there is a band corresponding to the fundamental absorption for quantum energies more than 5.5 eV. For diamond single crystal, we found an absorption band that is due to nitrogen impurity, and for polycrystalline films and powders, a broad band that relates to structural defects. A characteristic feature of the spectra of the films and powders has been strong light scattering in the UV range (of 4 to 5 eV). The efficiency of such scattering incr eased as the crystallite size was reduced from similar to 100 mu m dow n to 1 mu m. Further diamond particles size decrease (less than 1/4 mu m) led to a diminishing of scattered light, due in part to changes in grain facets and particle coalescence.