Individually aligned tubular ZnO nanostructures on solid substrates

We introduce a new method for the fabrication of an ultrahigh-density (~1011/in2) array of individually aligned tubular ZnO nanostructures on solid substrates. We first prepared hybrid nanoporous templates consisting of an ultrathin anodized aluminum oxide (AAO) membrane on top and nanoporous crosslinked polystyrene (cPS) on the bottom. A nanoporous polymer template was prepared by oxygen plasma etching on a cPS thin film with the aid of AAO as an etching mask. Then, ZnO was deposited onto the nanoporous wall via atomic layer deposition, followed by the complete removal of the nanoporous polymer template at 500°C. By controlling the degree of etching of the cPS film, we were able to obtain three different nanostructures (nanocones, nanocups, and nanoflowers) of nanotubular ZnO. Because of good adhesion between the cPS nanoporous template and the AAO mask by wetting of polymer chains into AAO and direct contact of ZnO to the silicon substrate, individually and vertically aligned tubular ZnO nanostructures were successfully achieved on a silicon substrate. The hybrid nanoporous template employed in this study can be used to prepare various tubular nanomaterials with an ultrahigh density on solid substrates, which has potential for biosensors, photocatalysts, and photovoltaic devices.