Ge nanocrystals randomly dispersed in amorphous silica films were prepared by magnetron cosputtering and postannealing to investigate the polarization characteristics of Raman scattering from the Ge nanocrystals. Two acoustic vibrational modes observed in the low-frequency Raman spectra were shown by theoretical calculation based on the isotropic continuum elasticity theory to be the torsional modes activated by elastic anisotropy and the nonspherical shape of the Ge nanocrystals. Enhanced depolarized scattering was also observed from the optical phonons of the Ge nanocrystals.
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