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RESEARCH PRODUCT

Structural disorder and silanol groups content in amorphousSiO2

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We present a study on the features of the Urbach edge in amorphous silicon dioxide $(a{\text{-SiO}}_{2})$. The effects of temperature on the absorption edge in the range from 4 to 300 K were studied in both materials having negligible (dry, $l{10}^{17}\text{ }{\text{cm}}^{\ensuremath{-}3}$) and significant (wet, $g{10}^{19}\text{ }{\text{cm}}^{\ensuremath{-}3}$) 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 groups affect the thermal component of disorder, modifying the vibrational modes of the network.