NONDESTRUCTIVE EVALUATION OF DIAMOND AND DIAMOND-LIKE CARBON-FILMS BYLASER-INDUCED SURFACE ACOUSTIC-WAVES

Young's modulus of diamond-like carbon films varies in a wide range wh ich suggests the use of this material parameter to characterize the fi lm quality. It can be obtained non-destructively by means of surface a coustic waves. A reliable and quick photoacoustic technique has been d eveloped which enables the film modulus to be determined for rather sm all samples such as cutting tools. The technique is based on the measu rement of the surface wave velocity vs. frequency. This spectrum is de rived from laser induced surface wave impulses by Fourier transformati on. Comparison with the theoretical results may provide Young's modulu s, density, and film thickness simultaneously. Less information is obt ained for very thin films so that less than three parameters can be de rived. By taking into account an empirical relation between Young's mo dulus and density which has been found for diamond-like carbon films, two parameters can be obtained even for films about 100 nm thick. The informational content of the measurement depends on the bandwidth of t he equipment and on the substrate material. Diamond and diamond-like c arbon films were studied. They were deposited using different technolo gies onto silicon single crystals, steel, and WC-Co cemented carbide. The film thickness was in the range 60 nm < d < 6 mu m. (C) 1997 Elsev ier Science S.A.