Mechanisms and resolution of photocatalytic lithography

Remote oxidation via the gas phase by the TiO2 photocatalyst was exploited for a novel technique for solid surface patterning, photocatalytic lithography. A TiO2-coated photomask was placed on an organic or inorganic substrate to be patterned with a small gap (12.5-100 mum), and irradiated with UV light. Heptadecafluoro-decyltrimethoxysilane-, octadecyltriethoxysilane-, and methyltriethoxysilane-coated glass plates, a silicon plate, and a copper plate could be patterned in greater than or equal to 10 min with resolution of 10 mum or better. Such resolution could be obtained even when the intervening gap between the TiO2 film and the substrate was 100 mum. This may be explained in terms of a double excitation scheme, in which not only TiO2 but also a chemical species diffusing from the TiO2 surface or the substrate to be oxidized is excited by the incident light.