Direct experimental evidence was presented for the presence, and X-ray dose-dependence, of radiolytically displaced O in high-purity O-deficient amorphous material. Anneal-interrupted X-irradiation, and electron spin resonance measurements, were used to investigate the dose-dependence of the radiation response of 2 types of low-OH amorphous oxide: O-excess and O-deficit. The production and annealing of paramagnetic defects in these 2 materials were compared in order to deduce the role that was played by dissolved and radiolytically displaced O. It was found that the multiple reversible inter-conversions of E’ centers and peroxy radicals were very sensitive to the presence of free O in the amorphous network. Such inter-conversions were very probable in the O-excess material, due to the presence of dissolved O. Such inter-conversions were not expected in O-deficient material, at least at low doses, in agreement with experimental data. However, the results showed that such inter-conversions took place above a certain threshold dose in O-deficient material. Peroxy radicals were observed in O-deficient material, and their production was attributed to the presence of radiolytically displaced O. A simple physical model for this behavior was presented which involved the random creation of displaced O atoms which underwent elastically driven recombination into O molecules. These molecules then participated in inter-conversions in the O-deficient material. A threshold was observed because the recombination did not occur unless the distance between the O atoms was less than some characteristic length. This was the correlation radius of an elastically coherent nano-region in the amorphous network. The experimental results and the above model implied the operation of a universal radiation response at high doses, when the density of radiolytically displaced O exceeded that of any precursors.

L.Zhang, V.A.Mashkov, R.G.Leisure: Physical Review B, 1996, 53[11], 7182-9