EPR on Radiation-Induced Defects in SiO2

Mineralogy and mineral chemistry of quartz: A review

“…Le Page et al (1980) noted that the two Si–O bond distances are 1.611(1) Å and 1.606(1) Å at 94 K, and they do not change in the temperature range from 94 K to 298 K, however the Si–O–Si angle increases from 142.69(4)° to 143.65(5)°. In the EPR literature, the SiO 4 tetrahedron in the quartz structure is typically represented by the notation [SiO 4 ] 0 to emphasise its overall neutrality, whereas substitutional groups such as [GeO 4 ] 0 and [AlO 4 ] – , together with their associated paramagnetic centres [GeO 4 ] – and [AlO 4 ] 0 are denoted accordingly (Weil, 1984; Mashkovtsev and Pan, 2013; Alessi et al , 2014).

Fig.

…”

The Relevance of Point Defects in Studying Silica-Based Materials from Bulk to Nanosystems

“…Such a defect is constituted by a threefold coordinated Si atom with an unpaired electron, and so it is paramagnetic [6,12,32,[98][99][100][101][102][103][104][105][106][107][108]. After decades of investigations, many properties of this defect, its generation, and relation with the network are known [6,12,32,[98][99][100][101][102][103][104][105][106]. The presence and formation under irradiation of the Si-Eí n the SiO 2 layers and in the Si/SiO 2 interface of components has been recognized as crucial in microelectronics [1][2][3][4]106].…”

“…Beyond this, the present section is more focused on how much this defect was and can be used to improve the understanding of various aspects of silica and radiation-induced processes. For the clarity of the following, it is also important to remind that the 29 Si has a natural abundance of about 4.67% and that, differing from the 28 Si, it has a nuclear magnetic momentum of quantum number 1 2 [6,12,[101][102][103][104][105]. Consequently, the Si-E´γ presents a hyperfine doublet of lines in the EPR spectra with separation of about 420 Gauss (42 mT) [101][102][103][104][105].…”

“…For the clarity of the following, it is also important to remind that the 29 Si has a natural abundance of about 4.67% and that, differing from the 28 Si, it has a nuclear magnetic momentum of quantum number 1 2 [6,12,[101][102][103][104][105]. Consequently, the Si-E´γ presents a hyperfine doublet of lines in the EPR spectra with separation of about 420 Gauss (42 mT) [101][102][103][104][105]. This feature is particularly relevant, and Devine et al [6,103,104] have demonstrated that the separation between the two lines depends on the density of the silica, even under irradiation, where a maximum of about 4% of densification is observed.…”

“…In the context of the E'-like defects family, it is interesting to note that several widely used dopants give rise to defects with E'-like structures [6,9,[100][101][102]108], so in principle, their EPR hyperfine lines should have a dependence on the density. This feature could be mapped and used to investigate the density and the radiation effects in different parts of an optical fiber with quite high precision.…”