Investigation of diffuse interfaces using time-resolved acoustic spectroscopy

A theoretical and experimental investigation is conducted on the frequency- dependent reflectivity of ultrashort acoustic elastic waves from a diffuse interface. One-dimensional theoretical predictions are obtained from a tran sfer-matrix representation of the extended diffusional interface. Experimen tal results are obtained with time-resolved thermal and acoustic spectrosco py applied to a sputter-deposited two-layer thin film sample of aluminum an d gold on a glass substrate. For the first time, variations in the spectral character of reflected acoustic waves, as measured with time-resolved spec troscopy, are quantified using the transfer function between successive arr ivals at the free surface. This transfer function is used as a basis for qu antitatively determining the nanometer sized extent of a diffuse interface. (C) 1999 American Institute of Physics. [S0021-8979(99)01602-3].