The dynamics of acoustic and optical phonons is studied in amorphous silicon at 2 K employing pulsed anti-Stokes Raman spectroscopy and transport of 29-cm −1 phonons using the ruby spectrometer. The tens-of-nanosecond phonon lifetimes and the surprising frequency dependence found at very high frequencies are explained by phonon localization. The elastic scattering and absorption observed for 29-cm −1 phonon transport are discussed in terms of soft oscillators.
