Characterization of nanostructured metal films by picosecond acoustics andinterferometry

Picosecond interferometry is used to study the acoustics waves created by h eating Pt films with a subpicosecond laser pulse. Both the period of the in itial oscillations in the metal film and the amplitude of the sound wave in the substrate are measured quantitatively. The platinum films are roughene d by irradiation with energetic ions. The amplitude of the sound wave is do ubled at those irradiation levels where the platinum coverage has been redu ced by about one-half. A theory for the amplitude of the launched acoustic wave predicts that the acoustic amplitude is proportional to the mean squar e film thickness. Thus changes in the morphology of a partially perforated metal film can be observed using a simple, nondestructive optical technique . (C) 2001 American Institute of Physics.