A two-component model for the 2260 cm− 1 infrared absorption band in electron irradiated amorphous SiO2

We report an experimental study by infrared absorption (IR) measurements focused on the effects of electron irradiation in the dose range from 1.2 × 103 kGy to 5 × 106 kGy on the intrinsic band peaked at 2260 cm− 1 in amorphous silicon dioxide (a-SiO2) materials. This IR band is particularly relevant as it is assigned to an overtone of the strong asymmetric stretching vibration of Si–O–Si bridges and consequently it is intimately related to the Si–O–Si bond angle distribution. In a recent work we have shown that structural modifications induced by irradiation take place through the nucleation of confined high-defective and densified regions statistically dispersed into the whole volume of the material [G. Buscarino et al., Phys. Rev. B 80 (2009) 094202]. Based on these results here we propose a two-component model to describe the IR band around 2260 cm− 1 in irradiated materials: the former component is due to the Si–O–Si groups located in the portion of volume of the material with pristine structure, whereas the latter to those located into the portion of the material densified by irradiation. Our results indicate that this scheme actually allows a reliable quantitative description of the effects of electron irradiation on the IR spectra of a-SiO2 and gives further support to the equivalence previously proposed between pressure- and radiation-induced compaction processes.