Preparation of mesoporous TiO2 thin films by surfactant templating

Porous TiO2 thin films have potential applications in optical-, electronic- and mechanical-components, catalysts, photoelectrodes, etc. A novel method to control pore sizes of sol–gel thin films by surfactant templating was investigated. The coating sol was obtained by hydrolysis of Ti(C4H9O)4 in ethanol solution. The films were prepared by spin-coating on glass substrates and drying at 90°C (xerogel film) or drying after immersion in a cetyltrimethylammoniumchloride (CTAC) or benzyltrimethylammoniumchloride solution for 1–24 h (CTAC- or BTAC-modified film), followed by calcination at 500°C in air. The calcined films were transparent and 30–120 nm in thickness. The refractive indices of the CTAC- and BTAC-modified films were about 1.7 and 1.9, respectively. These were 10–20% lower than those of the xerogel films. A columnar structure was observed by SEM and AFM. The columns were about 30 nm in diameter. The spacing between the columns was about 10 nm, corresponding to the size of CTAC micelles. These results show that the microstructure and pore size of the sol–gel films can be controlled by the surfactant-templating.