Inelastic light scattering was shown to be a valuable tool for probing elastic properties of thin free-standing membranes (See for instance Ref. [1]). We report on a low frequency Raman scattering study of silicon-based membranes. Thin silicon membrane spectra display a series of peaks assigned to standing acoustic modes. It was shown that both acoustical and optical cavity effects have to be considered in order to account for their scattering efficiencies. [2] Here we focus on the optical cavity effects by modifying the environment of the thin silicon layer. We present low frequency Raman spectra from three different free-standing membrane structures : a silicon single layer  membrane (32 nm), a Si/SiO₂ double layer membrane (32 nm/200 nm) and a Si₃N₄/Si/SiO₂ triple layer membrane (100 nm/32 nm/200 nm). These membranes were fabricated using a silicon nitride coated silicon on insulator wafer.

The three different membranes present specific spectral signatures (peak positions and intensities) which point out the specific role of the optical cavity effects. The membrane spectra are systematically compared to those recorded on the equivalent (multi)layer supported on a thick silicon substrate. Experimental data are compared to spectra calculated within the frame of the photoelastic model. It is shown that such comparisons are required in order to perform a quantitative analysis of the experimental data.

[1] R. S. Bandhu, X. Zhang, R. Sooryakumar, and K. Bussmann, Phys. Rev. B 70, 075409 (2004).

[2] J. Groenen, F. Poinsotte, A. Zwick, C.M. Sotomayor Torres, M. Prunnila and J. Ahopelto. Phys. Rev. B 77, 045420 (2008).

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