Fabrication of Well-Ordered High-Aspect-Ratio Nanopore Arrays in TiO2 Single Crystals

In this work a successful method for producing high-aspect-ratio nanopatterned single-crystal TiO2 is presented. The method used is based on nanolithography involving swift heavy ion bombardment through a porous anodic alumina mask. Nanopatterning of large areas allows for fabrication of new devices, for example, photonic crystals and electrodes for energy storage and conversion. Crystalline TiO2 also presents optimal characteristics for optical and catalysis applications. Samples were irradiated by MeV Br7+ ions with fluencies ranging from 7.9 × 1013 to 1.2 × 1015 cm-2. The high-energy Br7+ ions induce latent tracks of amorphous material into the TiO2 crystal suitable for selective etching by hydrofluoric acid. High-aspect-ratio (16) nanopatterned areas, up to 4 mm2, were obtained in a single radiation spot onto single-crystalline TiO2.