EVIDENCE FOR STRUCTURAL SIMILARITIES BETWEEN CHEMICAL-VAPOR-DEPOSITED AND NEUTRON-IRRADIATED SIO2

Raman spectroscopy, infrared absorption, and refractive index measurements have been carried out on films of amorphous SiO2 deposited by plasma enhanced chemical vapor deposition from SiH4 and N2O gases. It is demonstrated that the films have physical characteristics different from those of thermally grown or bulk oxide. Comparison with the data obtained from neutron irradiated, bulk SiO2 leads to the conclusion that deposited oxides and heavily neutron irradiated oxides have a similar and unusual network structure. In this network the Si-O-Si bond angles are substantially reduced (approximately 10-degrees) with respect to bulk and relaxed silica. The three membered ring density is significantly enhanced and there is a considerably larger fraction of free volume. These structures coincide with materials having a fictive temperature in excess of 2400-degrees-C and it is argued that they are analogous to the porosil structure known in crystalline forms of SiO2.