Highly Ordered Titanium Dioxide Nanostructures via a Simple One-Step Vapor-Inclusion Method in Block Copolymer Films

Nanostructured crystalline titanium dioxide (TiO 2 ) finds applications in numerous fields such as photocatalysis or photovoltaics, where its physical and chemical properties depend on its shape and crystallinity. We report a simple method of fabricating TiO 2 nanowires by selective area deposition of titanium tetraisopropoxide (TTIP) and water in a chemical vapor deposition-based approach at low temperature by utilizing a polystyrene-block-poly(ethylene oxide) self-assembled block copolymer thin film as a template. Parameters such as exposure time to TTIP (minutes to hours), working temperature (∼18 to 40 °C), and relative humidity (20 to 70%) were systemically investigated through grazing incidence small-angle scattering, scanning electron microscopy, and X-ray photoelectron spectroscopy and optimized for fabrication of TiO 2 nanostructures. The resulting processing conditions yielded titanium dioxide nanowires with a diameter of 24 nm. An extra calcination step (500 °C) was introduced to burn off the remaining organic matrix and introduce phase change from amorphous to anatase in TiO 2 nanowires without any loss in order.