Search results for " amorphous silicon dioxide"

Structural relaxation of E_gamma centers in amorphous silica

2002

We report experimental evidence of the existence of two variants of the E' gamma centers induced in silica by gamma rays at room temperature. The two variants are distinguishable by the fine features of their line shapes in paramagnetic resonance spectra. These features suggest that the two E' gamma differ for their topology. We find a thermally induced interconversion between the centers with an activation energy of about 34 meV. Hints are also found for the existence of a structural configuration of minimum energy and of a metastable state.

Sturctural disorder and silanol groups content in amorphous SiO2

2009

We present a study on the features of the Urbach edge in amorphous silicon dioxide a-SiO2 . The effects of temperature on the absorption edge in the range from 4 to 300 K were studied in both materials having negligible dry, 1017 cm−3 and significant wet, 1019 cm−3 silanol groups contents. Remarkable differences in the values and in the temperature dependence of the Urbach energy in the dry and wet samples were observed. These differences are interpreted as a consequence of a drastic reduction in the degree of disorder in wet materials, which turn out to be characterized by an electronic structure more similar to that of crystalline quartz. Furthermore, our results indicate that silanol gro…

Vacuum-ultraviolet absorption of amorphous SiO2: intrinsic disorder and role of silanol groups

2008

We present a study on the vacuum-ultraviolet VUV absorption properties of amorphous SiO2 a-SiO2 with high concentrations of silanol groups Si-OH . We found that the absorption spectra are made up of a couple of exponential profiles. The first, in the range from 7.5 to 8.1 eV, was attributed to Si-OH group absorption, while the second, in the range from 8.1 to 8.25 eV, was ascribed to the intrinsic absorption. The VUV absorption cross section of Si-OH groups in a-SiO2 was determined as well. The intrinsic absorption was found to be affected by the Si-OH concentration: high silanol group contents allow lower values of the Urbach energy. This result is interpreted in terms of a reduction in th…

EPR investigation on the polyamorphic transformation induced by electron irradiation in SiO2 glass

2013