Study of formation, stabilization and properties of porous silicon and porous silica

The large specific surface area of porous silicon (PS) gives it a high degree of chemical surface reactivity. Formation of silicon oxide (silica, SiO2), via different oxidation methods (thermal or electrochemical) within the porous matrix turns out to be an additional factor of PS stability and an improvement of its chemical, structural, morphological, crystalline and optical properties. In this work, PS reactivity is justified by the presence of siloxane (SiOSi) and silanol (SiOH) free and bound sites. Oxidation and densification effects on mesoporous silicon layers properties were investigated. The influence of operating parameters (current density, electrolyte concentration, treatment time, temperature, and oxidizing gas) on PS morphology and oxide quality were assessed. Sample characterization was performed using FTIR, SEM, EDS, XRD and UV-Visible spectrophotometry. Our results showed that oxidation provides stabilization and chemical modification of PS specific surface by creation of SiOH and SiOSi active sites. The optical and crystalline properties are dependent on oxidation temperature. Wet thermal oxidation, preceded by a short dry oxidation under O2, followed by densification under N2, with an oxidation rate of greater than 62%, improves PS properties for a functionalization via silanization.