Supported mesostructured thin films are of major importance for applications in optical, electrochemical and sensing devices. However, good performance is restricted to mesostructured phases ensuring good accessibility from the film surface, which would be straightforward with cylindrical pores oriented normal to the underlying support, but this remains challenging. Here, we demonstrate that electrochemistry is likely to induce self-assembly of surfactant-templated (organo)silica thin films on various conducting supports, homogeneously over wide areas. The method involves the application of a suitable cathodic potential to an electrode immersed in a surfactant-containing hydrolysed sol solution to generate the hydroxyl ions that are necessary to catalyse polycondensation of the precursors and self-assembly of hexagonally packed one-dimensional channels that grow perpendicularly to the electrode surface. The method is compatible with controlled and localized deposition on heterogeneous supports, opening the way to electrochemically driven nanolithography for designing complex patterns of widely accessible mesostructured materials.

We have recently reported the possible fabrication of highly ordered mesoporous silica thin films with mesopore channels oriented perpendicularly to the underlying substrate, by means of novel electroassisted self-assembly (EASA) method (Nature Mater. 6, 602 (2007)). Such films deposited on an electrode surface can be of great interest in sensing applications if one could introduce organo-functional groups likely to interact with target analytes in a regular environment ensuring great accessibility and fast mass transfer rates. We demonstrate here that aminopropyl-functionalized mesoporous silica films can be electrogenerated in one step by the sol-gel co-condensation route using cetyltrimethylammonium bromide as template. The orientation of the pore is maintained up to 10% aminopropyltriethoxysilane precursor in the starting sol. The presence of amine functions into the film affects its permeability to external reagents, as studied using various redox probes (Ru(bpy)3(2+), FcEtOH, I(-), Fe(CN)6(3-)), and the lack of mesostructuration was found to hinder dramatically mass transport processes. When applied to the voltammetric detection of copper(II) subsequent to open-circuit accumulation, the response of the electrode was greatly affected by the functionalization level, the optimal sensor sensitivity being defined from the best compromise between an amount of amine groups high enough while maintaining mesostructural order.

Well-adherent sol-gel-derived silica films functionalized with amine or thiol groups have been electrogenerated on gold electrodes and both the deposition process and the film properties have been studied by various physicochemical techniques. Electrodeposition was achieved by combining the formation of a self-assembled "nanoglue" on the electrode surface, the sol-gel process, and the electrochemical manipulation of pH to catalyze polycondensation of the precursors. Gold electrodes pretreated with mercaptopropyltrimethoxysilane (MPTMS) were immersed in sol solutions containing the selected precursors (tetraethoxysilane, TEOS, in mixture with (3-aminopropyl)triethoxysilane, APTES, or MPTMS) where they underwent a cathodic electrolysis to generate the hydroxyl ions that are necessary to catalyze the formation of the organosilica films on the electrode surface. Special attention was given to analyze the effects of deposition time and applied potential and to compare APTES and MPTMS films. Characterization was made using quartz crystal microbalance, scanning electron microscopy, cyclic voltammetry, and atomic force microscopy (including in situ monitoring). The electrodeposition process was found to occur at two growing rates: a first slow stage giving rise to rather homogeneous, yet rough, films with thickness in the sub-mum range (increasing continuously when increasing the deposition time), which was followed by a faster gelification step resulting in much thicker (>1 microm) and rougher macroporous deposits. These two successive situations were observed independently on the applied potential except that more cathodic values led to narrower sub-microm ranges (as expected from the larger amounts of the electrogenerated hydroxyl catalyst). Thiol-functionalized silica films were deposited more rapidly than the amine ones and, for both of them, permeability to redox probe was found to decrease when increasing the film thickness because of higher resistance to mass transport.