Resonant localization, enhancement, and polarization of optical fields in nano-scale interface regions for photo-catalytic applications.

We report results of theoretical simulations of optical field enhancement in a system consisting of spherical and hemispherical noble metal nanoparticles on a smooth titania surface, which is a model system relevant to applications in photo-catalysis and solar energy harvesting. Simulations conducted using Finite-Difference Time-Domain (FDTD) technique reveal presence of resonant optical extinction bands at visible wavelengths, whose optical scattering is weak, but the associated localization and intensity enhancement of optical near-field are significant. For hemispheres, the field is strongly localized at the metal-substrate interface, where intensity enhancement of up to 10(4) times is reached. Moreover, the field is predominantly polarized along the normal to the substrate. These findings indicate potential of the hemisphere-substrate system for applications relying on optically promoted charge transport through the metal-substrate interface, such as photochemical reactions and light-to-current conversion. The results of theoretical analysis are compared with reported experimental data on photo-catalytic reactions.