Fast Electron Transfer Across Semiconductor−Molecule Interfaces: GaAs/Co(Cp)2+/0

Abstract

The kinetics of majority electron transfer in the dark from n-GaAs electrodes to cobaltocenium (Co(Cp)2+) acceptors in acetonitrile has been studied in detail, both experimentally and theoretically. The experimental results were obtained from electrochemical impedance spectroscopy, quartz crystal microbalance (QCM and EQCM) studies, and current−potential characteristics. The theoretical work involved calculating the adsorption energy and molecular configuration of the cobaltocenium acceptors at the GaAs surface using high level density functional theory (B3LYP and variations thereof) as well as semiempirical methods. The QCM experiments showed that both Co(Cp)2+ and Co(Cp)20 are physisorbed at GaAs surfaces, with adsorption energies of about 0.2 and 0.4 eV, respectively. The theoretical results are consistent with these experimental results. They indicate that adsorption of the Co(Cp)2+/0 redox system occurs on GaAs, with Co(Cp)20 somewhat more strongly adsorbed than Co(Cp)2+; the Co(Cp)2+/0 molecules wer...