Visible-light-induced patterning of Au- and Ag-TiO2 nanocomposite film surfaces on the basis of plasmon photoelectrochemistry.

A novel technique for patterning based on visible light at Au-TiO2 and Ag-TiO2 nanocomposite film surfaces has been developed for the first time. TiO2 films loaded with Au and Ag nanoparticles were modified with hydrophobic thiols to obtain hydrophobic surfaces. The surfaces were converted to hydrophilic by visible light irradiation. Hydrophobic/hydrophilic patterning was also possible by visible light irradiation through a photomask. The patterning was due to removal of the thiol based on plasmon photoelectrochemistry. Visible-light-induced plasmon resonance at the Au and Ag nanoparticles gives rise to charge separation and redox reactions. The thiol is removed from the Au-TiO2 film probably by oxidative desorption, and from the Ag-TiO2 film owing chiefly to oxidation of Ag nanoparticles to Ag+.