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À propos de : Surfactant Removal and Silica Condensation during the Photochemical Calcination of ThinFilm Silica Mesophases        

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  • Surfactant Removal and Silica Condensation during the Photochemical Calcination of ThinFilm Silica Mesophases
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  • The evolution of photochemical surfactant removal and silica condensation from organically templated thinfilm silica nanocomposites with mesoscopic ordering has been probed using a combined application of Fouriertransform infrared (FT-IR) spectroscopy and single wavelength ellipsometry. Thin films of silica nanocomposites were prepared by a previously reported evaporation-induced self-assembly process. Specifically, oxidizedsilicon and gold substrates were withdrawn at 25 mm/min from a subcritical micelle concentration solutioncontaining an ethylene oxide surfactant as a structure-directing agent and tetraethyl orthosilicate as a silicaprecursor. Real-time grazing incidence difference FT-IR spectra of the nanocomposite films on gold takenduring exposure to short-wavelength ultraviolet light (184−257 nm) show that surfactant removal and silicacondensation occur gradually and concomitantly. Surfactant removal and silica reconstructions were found tobe nearly complete after 90 min of exposure. Further, a transient feature was observed in the FT-IR spectraaround 1713 cm-1 during the UV exposure process and was assigned to a carbonyl (CO) stretching modeabsorption, reflecting the transient formation of a partially oxidized surfactant intermediate. From these datawe propose a stepwise model for surfactant removal from the nanocomposite films. Ellipsometrically determinedindex of refraction values collected as a function of UV exposure are also shown to support such a stepwisemechanism of surfactant removal from the ordered nanocomposite silica thin film mesophases studied here.
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