Three-dimensional mesoporous structures fabricated by independent stacking of self-assembled films on suspended membranes.

We report an original iterative method for fabricating three-dimensional mesoporous structures by independently stacking multiple self-assembled block copolymer films supported by Si membranes. A first layer is formed on the substrate by a self-assembled PS-b-PMMA (polystyrene-block-poly(methyl methacrylate)) film. A porous, permeable Si membrane deposited on top of the first block copolymer film provides mechanical support, preventing pattern collapse during the wet developing used to selectively remove the PMMA component of the PS-b-PMMA film. A second, dense Si membrane is deposited to seal the porous membrane, resulting in an impermeable coating suspended atop the self-assembled mesoporous polystyrene structures. The process can then be iterated using the sealed membrane as the new substrate to support a subsequent self-assembled block copolymer film. This multilayer approach provides a flexible three-dimensional fabrication technique where, in each layer, pattern morphology, domain orientation and degree of ordering can be designed independently. Furthermore, the process is compatible with electron-beam directed assembly, used to achieve regular patterns with feature density multiplication at any level in the stack.

Wetting of nanopatterned grooved surfaces.

The wetting by perfluoromethylcyclohexane of a well-defined silicon grating with a channel width of 16 nm has been studied using transmission small angle x-ray scattering. Prefilling, capillary filling, and postfilling wetting regimes have been identified. A detailed comparison of the data with theory reveals the importance of long-ranged substrate-fluid and fluid-fluid interactions for determining the wetting behavior on these length scales, especially at the onset of capillary condensation and in the prefilling regime.