SYNCHROTRON-RADIATION STIMULATED EVAPORATION AND DEFECT FORMATION IN A-SIO2

The relation between synchrotron radiation stimulated evaporation and oxygen vacancy defect formation in a-SiO2 was investigated. The behavior is shown to be quite different for the following three temperature regimes. At temperatures lower than 500-degrees-C, the surface is soon covered by a thin SiO(x) (x < 2) layer upon SR irradiation. The film is etched by stimulated ejection of surface atoms from the SiO(x) layer. Between 500-700-degrees-C, film removal is rate-limited by the thermal desorption of SiO molecules. Accordingly, a thick layer of SiO(x) is accumulated over the surface. Above 700-degrees-C, the evaporation of a-SiO2 proceeds at a constant rate keeping the surface stoichiometry Of SiO2. This indicates that an SiO(x) layer, even if created, is thermally decomposed.