ESR studies of damage processes in X-irradiated high purity a-SiO2:OH and characterization of the formyl radical defect

Abstract

A range of high purity type III synthetic silicas (Suprasil 1, Spectrosil, Dynasil 1000) has been subjected to 100 keV X irradiation at 77 K and the induced ESR spectra have been recorded at 100 K before and after successive pulse anneals to higher temperatures. Absolute spin concentrations are determined as functions of radiation dose, anneal temperature and time, prior irradiation history, and sample supplier. Defects monitored comprise E′ centers, oxygen‐associated hole centers (OHCs), atomic hydrogen, and a previously unidentified defect in a‐SiO₂ characterized by a 13.3 mT doublet centered on g=2.0. The 13.3. mT doublet is ascribed here to formyl radicals HCO produced by the reaction of radiolytic hydrogen atoms with minute amounts (≲0.1 ppm) of dissolved carbon monoxide present in Suprasil 1 and Dynasil 1000 but not Spectrosil. This identification is based on production kinetics and the similarity of the spin Hamiltonian parameters measured at 30 K to those previously reported for the formyl radical in solid carbon monoxide. Motional effects apparent in the HCO spectra at ≳100 K are interpreted with the aid of computer line shape simulations, and inferences are drawn concerning the interaction of the HCO molecule with the glass network. The isochronal anneal data are discussed in some detail and an influence of radiolytic molecular hydrogen on the color‐center bleaching kinetics is postulated.