Vibrational modes in amorphous silicon dioxide

The optical properties of the broad absorption region due to asymmetric stretching vibration of bridging oxygen in the: amorphous structure of bulk SiO2 were studied. The complex refractive index of thick densified chemical-vapour deposited silicon oxide film was calculated and used further to obtain the dielectric response function of the sample. Vibrational modes were analysed by energy-loss functions for transverse and longitudinal optical phonons. In the 900-1300 cm(-1) spectral region: three vibrational modes with well-resolved TO-LO phonon splitting were obtained. The phonon spectra appears as the smeared-out version of the crystalline counterpart, i.e. the alpha-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 lines 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.