Nanostructuring titania by embossing with polymer molds made from anodic alumina templates.

We demonstrate a method for embossing titania sol--gel precursor with poly(methyl methacrylate) (PMMA) molds to make thin films of titania that have dense arrays of 35--65 nm diameter pores, whose features are 1 order of magnitude smaller than those previously demonstrated for sol--gel molding. We show that the high modulus of PMMA is necessary to preserve small features with high aspect ratios on the mold for nanopatterning. The molds are prepared by thermally infiltrating PMMA into anodic alumina templates, whose pore dimensions and depths are adjustable by varying anodization conditions. The difficulties associated with mold release from a master are avoided by wet etching the template. These titania films, and others made with other semiconductors, could be useful for photovoltaic, photocatalytic, and sensing applications where nanostructuring of surfaces with controlled dimensions are essential.