The local atomic-bond structures in amorphous ${\mathrm{SiO}}_2$ films prepared by a nonthermal method have been investigated by electron-energy-loss spectroscopy (EELS). The method utilizes oxygen ions of energy below 600 eV impinging on Si(100) surfaces at room temperature. The results, based on an augmented-central-force model, reveal that the Si-O bond nature in the films strongly resembles a typical thermal ${\mathrm{SiO}}_2$ glass. The contribution of noncentral forces to the local Si-O bonding, in terms of the ratio of noncentral-to-central force constants β/α, is estimated by reducing the low-frequency EELS vibrational band (ħω≤80 meV). The ratio is found to be rather temperature insensitive but increases with film thickness, in the range 0.13<β/α<0.19. We also observe thermally activated migration of oxygen atoms in the films with an activation energy barrier of about 0.22 eV.

• Received 1 August 1991

DOI:https://doi.org/10.1103/PhysRevB.45.1705