| Summary: | We quantitatively study interfacial adhesion in a two-layer membrane system consisting of Al and Si with femtosecond time-resolved laser spectroscopy. High-frequency acoustic pulses in the sub-THz regime are utilized to characterize the membrane system. In order to explain the distinct features of the measured data, a spring model for the Al/Si interface is employed. We show that acoustic dissipation in this system needs to be included for accurate modeling of the interface adhesion over a broad frequency range. This modeling approach yields a spring constant of ${\eta }_{\mathrm{Al}-\mathrm{Si}}=17$ $\mathrm{kg}\,{\mathrm{nm}}^{-2}\,{{\rm{s}}}^{-2}$ , an acoustic phonon lifetime of ${\tau }_{\mathrm{Al}}=68$ ps at 240 GHz in polycrystalline Al and a frequency dependence of the lifetime in Si $\propto \,{\omega }^{-1}$ in the frequency range from 50–800 GHz.
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