EPR and IR spectral properties of hydrogen-associated bulk and surface defects inSiO2:Ab initiocalculations

Abstract

Electron paramagnetic resonance and IR spectral properties of hydrogen-associated centers in silica have been studied by means of first-principles Hartree-Fock and density-functional-theory calculations. The geometric and electronic structure of the paramagnetic centers ͑wSi-O͒ 3 Si • , ͑wSi-O͒ 2 Si • ͑OH͒ and ͑wSi-O͒ 2 Si • ͑H͒, and of the corresponding diamagnetic centers formally derived from the addition of one H atom, ͑wSi-O͒ 3 Si͑H͒, ͑wSi-O͒ 2 Si͑OH͒͑H͒, and ͑wSi-O͒ 2 Si͑H͒͑H͒, have been determined using cluster models. A substantial agreement is found between the computed hyperfine splittings and those measured for bulk paramagnetic centers in high-purity amorphous silica. The different experimental hyperfine splittings obtained for ͑wSi-O͒ 3 Si • centers at the surface of mechanically or thermally activated silica are explained in terms of small structural differences from the bulk counterparts. An almost quantitative agreement with the experiment is found also for the vibrational properties of the Si-H groups of the silylhydride centers. The calculations allow a firm assignment of the spectral features to specific point defects in silica. ͓S0163-1829͑98͒08136-3͔

An increased F2-laser damage in ‘wet’ silica glass due to atomic hydrogen: A new hydrogen-related E′-center

“…Ab initio calculations of hfs in E 0 (OH)-center predict significantly smaller 1 H hfs (%0.1 mT) and ca. 1 mT decrease of the 'strong' 29 Si hfs as compared to the E 0 -center without neighboring OH group [22]. These values are in accord with those observed in the present work.…”

Optical absorption and electron paramagnetic resonance of theEα′center in amorphous silicon dioxide

“…In particular, the O-Si-O angle should be larger for the E' γ than for the E' s [25]. It is worth to note that the EPR and OA properties of the E' α center does not follow an analogous trend.…”

“…• moieties involved in the two defects [25]. In particular, the O-Si-O angle should be larger for the E' γ than for the E' s [25].…”

“…The fundamental microscopic structure of the E' s center is similar to that of the E' γ center but for the fact that in the former the positive + Si≡O group is absent and the unpaired electron projects toward the outside of the material surface [8,11,[24][25][26]. The E' s center is known to possess a 29 Si hyperfine doublet split by ~48 mT [11,24] and an OA band peaked at ~6.3 eV [11].…”

First principles study of oxygen vacancy defects in amorphous SiO2

“…Based on the electron paramagnetic resonance (EPR) experiments, four kinds of paramagnetic point defects, such as E α , E β , E γ and E δ , have been distinguished in bulk materials. [4][5][6][7] The E γ center is one of the most extensively studied defects in irradiated a-SiO 2 , [8][9][10] which is analogous to the E 1 center in α-quartz. 11,12 It is believed to be related with the model that consists of a puckered positively charged oxygen vacancy: O ≡ Si…”