Investigation of diffuse interfaces using time-resolved acoustic spectroscopy

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Abstract
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 transfer-matrix representation of the extended diffusional interface. Experimental results are obtained with time-resolved thermal and acoustic spectroscopy applied to a sputter-deposited two-layer thin film sample of aluminum and gold on a glass substrate. For the first time, variations in the spectral character of reflected acoustic waves, as measured with time-resolved spectroscopy, are quantified using the transfer function between successive arrivals at the free surface. This transfer function is used as a basis for quantitatively determining the nanometer sized extent of a diffuse interface.