PHOTOACOUSTIC-SPECTROSCOPY OF DIAMOND POWDERS AND POLYCRYSTALLINE FILMS

Photoacoustic spectroscopy is used to study optical absorption in diam ond powders and polycrystalline films. The photoacoustic spectra of di amond powders with crystallite sizes in the range from similar to 100 mu m to 4 nm and diamond films grown by chemical vapor deposition (CVD ) had a number of general characteristic features corresponding to the fundamental absorption edge for light with photon energies exceeding the width of the diamond band gap (similar to 5.4 eV) and to absorptio n in the visible and infrared by crystal-structure defects and the pre sence of non-diamond carbon. For samples of thin (similar to 10 mu m) diamond films on silicon, the photoacoustic spectra revealed peculiari ties associated with absorption in the silicon substrate of light tran smitted by the diamond film. The shape of the spectral dependence of t he amplitude of the photoacoustic signal in the ultraviolet indicates considerable scattering of light specularly reflected from the randoml y distributed faces of the diamond crystallites both in the polycrysta lline films and in the powders. The dependence of the shape of the pho toacoustic spectra on the light modulation frequency allows one to est imate the thermal conductivity of the diamond films, which turns out t o be significantly lower than the thermal conductivity of single-cryst al diamond. (C) 1997 American Institute of Physics.