Work Function on Dye-Adsorbed TiO2 Surfaces Measured by Using a Kelvin Probe Force Microscope

Abstract

Work function measurements were conducted on Ru(4,4‘-dicarboxy-2,2‘-bipyridine)2(NCS)2 (N3 dye)-adsorbed titanium dioxide (TiO2) surfaces by using a Kelvin probe force microscope. A rutile TiO2(110)-(1 × 1) surface covered by a pivalate anion monolayer was immersed in acetonitrile containing N3 dye. In topographic images, the N3 molecules which replaced the pivalate anions were observed as bright particles embedded in the pivalate monolayer. Work function maps obtained in the dark showed that work function on the N3 molecules was larger by 0.07 eV than that on the surrounding pivalate monolayer. When measured under visible light irradiation, the work function on 44% of the N3 molecules reduced by 0.14 eV. We assume that the adsorbed molecules provide electric dipole moments to perturb the work function. The reduced work function indicates that the dipole moment directed from the surface to the vacuum is enhanced by the irradiation. Electron injection from N3 molecules to the surface is proposed to origina...