C2 LASER PICOSECOND ACOUSTICS IN VARIOUS TYPES OF THIN FILM

We report on the excitation and detection of picosecond stress pulses in thin films using a laser pump-probe technique. An opaque thin film of diamond-like carbon of known thickness is first investigated and the longitudinal sound velocity derived. Two methods of testing transparent films on opaque substrates are then described, one a conventional technique in which an opaque transducer layer is deposited on the transparent film, and one a new technique in which the transparent film is uncoated. The latter technique is applied to films of silica and silicon oxide on metallic and semiconductor substrates, and it is shown how both the sound velocity and the film thickness can be determined.