Vibrational modes in amorphous silicon dioxide

The optical properties of the broad absorption region due to asymmetric str etching vibration of bridging oxygen in the: amorphous structure of bulk Si O2 were studied. The complex refractive index of thick densified chemical-v apour deposited silicon oxide film was calculated and used further to obtai n the dielectric response function of the sample. Vibrational modes were an alysed by energy-loss functions for transverse and longitudinal optical pho nons. In the 900-1300 cm(-1) spectral region: three vibrational modes with well-resolved TO-LO phonon splitting were obtained. The phonon spectra appe ars as the smeared-out version of the crystalline counterpart, i.e. the alp ha-quartz. The most intense phonon couple at 1064 (TO), and 1248 cm(-1) (LO ) has the smallest damping and appears to be more crystalline-like than the remaining two. The broad frequency distribution of lattice-like phonon lin es gives rise to frequency-dependent damping where the phonons only purely feel each other and have different phonon decays. (C) 2000 Elsevier Science B.V. All rights reserved.