Sturctural disorder and silanol groups content in amorphous SiO2

We present a study on the features of the Urbach edge in amorphous silicon dioxide a-SiO2 . The effects oftemperature on the absorption edge in the range from 4 to 300 K were studied in both materials havingnegligible dry, 1017 cm−3 and significant wet, 1019 cm−3 silanol groups contents. Remarkable differencesin the values and in the temperature dependence of the Urbach energy in the dry and wet samples wereobserved. These differences are interpreted as a consequence of a drastic reduction in the degree of disorder inwet materials, which turn out to be characterized by an electronic structure more similar to that of crystallinequartz. Furthermore, our results indicate that silanol groups affect the thermal component of disorder, modifyingthe vibrational modes of the network.