A nanoscale template (for making materials and devices) can be created by coating an array of closely packed particles, but it often is difficult to handle such a film without tearing it, because it is, in essence, a thin ceramic sheet. Wang et al. report on the formation of transferable and reusable TiO2 "nanobowl" templates. They coated a silicon substrate with a 300-nm-thick film of poly(methyl methacrylate) (PMMA) and then applied a 100-nm-thick film of polystyrene (PS). Next, a monolayer of 500-nm-diameter PS spheres was loaded onto the composite film from a water surface, and topped off with a 25-nm-thick coating of TiO2 via atomic layer deposition. Ion milling removed the top half of the spheres, and the PMMA was dissolved with acetone to free the film from the silicon substrate. Finally, the nanobowl film could be freed completely by removing the PS with toluene. These films (as large as 10 mm2) were lifted with a copper mesh support and examined in a transmission electron microscope, which revealed that the bottoms of the TiO2 bowls have a 100-nm opening. The films could then be used as templates to create a regular array of 100-nm gold dots, spaced 500 nm apart. -- PDS
Nano. Lett. 10.1021/nl051389x (2005).
