Microscale Controlled Electrogeneration of Patterned Mesoporous Silica Thin Films

Mesoporous and mesostructured thin films typically prepared through the combination of low cost sol–gel processing and supramolecular chemistry are important in a wide range of applications including micro-optics and photonic devices, microelectronics, sensors, energy, environment, coatings, biomaterials, and biomicrofluidics, among others. For many of them, the full practical exploitation of these high-tech materials requires the development of micro- and nanofabrication technologies. Even if some patterning techniques have been proposed for mesostructured films (often based on extension of established procedures to mesoporous materials), controlling the important features of the local deposits (e.g., pore orientation) is still challenging. Here, we describe a novel concept to locally generate surfactant-templated silica nanostructures using a scanning electrochemical microscope. The method is based on a fine nonelectrochemical positioning of an ultramicroelectrode close to a solid support immersed in a surfactant-containing hydrolyzed sol solution, the tip electrode being then used as a micrometric “pen” inducing self-assembly polycondensation of the precursors by local pH change under potential control. Tuning the characteristics of the deposits (size, thickness, structure) can be easily achieved by adjusting some key parameters (potential, distance to the surface, size of the electrode). It was notably shown that using the tip as the counter-electrode and the underlying support as the working electrode enabled to get vertically oriented mesopores in honeycomb-structured microdots (i.e., the most suitable configuration for diffusion-controlled applications), which cannot be obtained by other patterning techniques. The proof-of-concept of electrochemically driven nanolithography demonstrated here for silica should be applicable to other patterned mesostructures (other oxides or functionalized materials).