Detection and analysis of 29Si hyperfine structures in ESR spectra of E′ and E′-type centers in SiO2 glasses

Four sets of ESR doublets with splittings of 9, 23, 26 or 44 mT were observed in dry a-SiO2 (Type IV, OH concentrations≾1017 cm−3) implanted with 29Si+ to a fluence of 6×1016 cm−2 at 160 keV. These doublets were attributed to the hyperfine structures due to a 29Si nucleus of E′-type centers SiSinO3−n (n=0–3). The hf doublets with the splittings of 44 and 9 mT were attributed to the centers of n=0 and 3, respectively and the doublets with 23 and 26 mT were assigned to the centers of n=1 and 2, respectively. The wave functions of the semi-occupied molecular orbitals in E′-type centers were determined through the line shape simulation against the observed spectra employing a site-to-site fluctuation of the defect structure. It was found that the wave functions of the dangling orbital on SiSinO3−n (n=0–2) are close to a sp3 hybridized orbital of Si but that on SiSi3 is Si 3p-like, indicating that the structure of E′-type centers changes from pyramidal to planar on going from n=0, 1 and 2 to 3.