title: Surfactant removal and silica condensation during the photochemical calcination of thin film silica mesophases.
abstract: The evolution of photochemical surfactant removal and silica condensation from organically templated thin film silica nanocomposites with mesoscopic ordering has been probed using a combined application of Fourier transform 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 Specifically, oxidized silicon and gold substrates were withdrawn at 25 mm/min from a subcritical micelle concentration solution containing an ethylene oxide surfactant as a structure-directing agent and tetraethyl orthosilicate as a silica precursor. Real-time grazing incidence difference FT-IR spectra of the nanocomposite films on gold taken during exposure to short-wavelength ultraviolet light (184-257 nm) show that surfactant removal and silica condensation occur gradually and concomitantly. Surfactant removal and silica reconstructions were found to be nearly complete after 90 min of exposure. Further, a transient feature was observed in the FT-IR spectra around 1713 cm(-1) during the UV exposure process and was assigned to a carbonyl (C=O) stretching mode absorption, reflecting the transient formation of a partially oxidized surfactant intermediate. From these data we propose a stepwise model for surfactant removal from the nanocomposite films. Ellipsometrically determined index of refraction values collected as a function of UV exposure are also shown to support such a stepwise mechanism of surfactant removal from the ordered nanocomposite silica thin film mesophases studied here.
authors.affiliation: Bioscience Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Dattelbaum
authors.forename: Meri L
authors.initials: ML
authors.lastname: Amweg
authors.forename: Julia D
authors.initials: JD
authors.lastname: Ruiz
authors.forename: Laurel E
authors.initials: LE
authors.lastname: Ecke
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Shreve
authors.forename: Atul N
authors.initials: AN
authors.lastname: Parikh
mesh_terms: D002244:Carbon / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D010777:Photochemistry; D012822:Silicon Dioxide / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D013501:Surface-Active Agents; D002244:Carbon; D012822:Silicon Dioxide; D006859:Hydrogen