Single-MoleculeInvestigation of Plasmonic Near-FieldEffects on a Dissociation Reaction

Plasmonic near-field effects have attracted more attention as a means of enhancing photoexcitation and photoresponses in materials and devices. Although chemical reactions are one of the important applications, a detailed microscopic understanding of the plasmonic near-field effect in chemical reactions is still lacking. In this study, we reveal that the degree of coupling between the plasmonic electric field and the molecular transition dipole moment governs the reactivity at the single-molecule level. This was demonstrated via single-molecule analysis of the reactivity for dimethyl disulfide weakly chemisorbed on Ag(111) by the combination of experiments using a scanning tunneling microscope (STM) and theoretical calculations. Through precise analysis of the dependence of the reactivity on the angle between the molecular axis and the local plasmonic field, the adsorption configuration dependence of dissociation can be explained by the interaction of the molecules with the plasmonic electric field anisotropically distributed at the nanogap in the STM junction.