We have used picosecond ultrasonics to study the effects of ion irradiation on the interfacial bonding between gold films and a silicon substrate. Acoustic vibrations are excited in the metal film when a picosecond light pulse is absorbed. The rate at which these vibrations damp out via sound transmission across the interface into the substrate gives a measure of the adhesion of the film to the substrate. The films wre irradiated with 2.5 MeV helium ions with doses between 7x10~(14) and 8x10~(16) ions cm~(-2). The adhesion, as measured by the rate of acoustic damping, was found to be significantly improved by the ion irradiation.
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