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 i nvestigated. The coating sol was obtained by hydrolysis of Ti(C4H9O)(4) in ethanol solution. The films were prepared by spin-coating on glass substrat es and drying at 90 degreesC (xerogel film) or drying after immersion in a cetyltrimethylammoniumchloride (CTAC) or benzyltrimethylammoniumchloride so lution for 1-24 h (CTAC- or BTAC-modified him), followed by calcination at 500 degreesC in air. The calcined films were transparent and 30-120 nm in t hickness. 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 column s were about 30 nm in diameter. The spacing between the columns was about 1 0 nm, corresponding to the size of CTAC micelles. These results show that t he microstructure and pore size of the sol-gel films can be controlled by t he surfactant-templating. (C) 2001 Elsevier Science B.V. All rights reserve d.