Measurement of Phonon Densities of States for Pure and Hydrogenated Amorphous Silicon

Vibrational spectra for $a$-Si and $a$-Si${\mathrm{H}}_{0.12}$ have been measured by inelastic neutron scattering, directly yielding the phonon density of states for the former material, and the partial phonon density of states for H vibrations for the latter. The relevance of these results to the interpretation of infrared and Raman spectra is discussed.