document: There have been suggestions that electrons can be trapped in the bulk and at surfaces of silica [15] but new models of electron trapping centres started to appear only recently. It has been suggested by Bersuker et al., who used molecular models, that electrons can be trapped by Si–O bonds in a-SiO2 leading to their weakening and thus facilitating Si–O bond dissociation [16]. Further calculations by Camellone et al. have shown that electrons can spontaneously trap in non-defective continuum random network model of a-SiO2 [17]. Recent calculations have also demonstrated that the two dominant neutral paramagnetic defects at surfaces of a-SiO2, the non-bridging oxygen centre and the silicon dangling bond, are deep electron traps and can form the corresponding negatively charged defects [18]. However, these theoretical predictions have not yet been confirmed experimentally, emphasising the challenges for identifying defect centres.
doc_bio_tags: O O O O O B O O B O O B O O O O B O O O O O B I I O O O O O O O O O O O O O O O B I O B O O B O B I O O O O O B O O O B I O O O O O O O O O O O B O B I O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O B I I O B I I O O O O O B I I O O O O O O O O O O O O O O O B I I