PNNL

Abstract

We report an atomic force microscopy (AFM) and confocal Raman microscopy study on the interfacial electron transfer of a dye-sensitization system, alizarin adsorbed upon TiO2 nanoparticles. Resonance Raman and absorption spectral analyses revealed the distribution of the mode-specific vibrational reorganization energies encompassing different local sites (~250 nm spatial resolution), suggesting spatially inhomogeneous vibrational reorganization energy and different Franck-Condon coupling factors of the interfacial electron transfer. We found that the total vibrational reorganization energy was inhomogeneous from site to site, and specifically, the mode-specific analyses indicated that the energy distributions were inhomogeneous for bridging normal modes and homogeneous for nonbridging normal modes, especially for modes far away from the alizarin- TiO2 coupling hydroxyl modes. Our results demonstrate a significant step forward in characterizing site-specific inhomogeneous interfacial charge transfer dynamics.