Structural organization of silanol and silicon hydride groups in the amorphous silicon dioxide network

We present a study on the effects of an isothermal annealing treatment on a-SiO2 having a significant content of silanol hydride groups (Si-H). We examined the properties of the IR absorption bands of silanol (Si-OH) and silicon hydride groups as a function of the duration of the thermal treatment. We showed that the Si-OH and Si-H groups contents decrease in a linearly correlated way. The annealing dynamics suggest that the two species are close to each other in the amorphous network. We showed that the profile of the silanol groups absorption band is the same as that observed in other commercial a-SiO2 materials, irrespectively of the concomitant presence of nearby Si-H groups, and, moreover, it does not change during the annealing treatment. This set of evidences supports the conclusion that silanol groups are organized in clusters in the a-SiO2 network. Finally, present data provide an unprecedented characterization of the Si-H IR absorption band. It results that the profiles of the IR and Raman activities of silicon hydride groups closely coincide