Some dielectric solvation effects on the energetics of electrified metal interfaces and related molecular systems

Abstract

The sensitivity of the surface potential of metal-vacuum interfaces to the presence of molecular dielectric (solvating) species both with or without free ionic/electronic charge is discussed with the objective of comparing the behavior of such “electrified dielectric” interfaces with analogous metal-solution (i.e. electrochemical) systems. The close connection between “surface-potential” scales based on work function (Φ) and electrode-potential ( E) measurements is outlined. The chief factors determining the surface potential are illustrated by means of composition-dependent Φ data for single-crystal metal surfaces modified by thin (1–3 monolayer) films of dipolar molecules along with ionizable species in relation to E values for corresponding in-situ electrochemical interfaces. The former Φ-composition measurements, for vacuum-based electrified dielectric interfaces, demonstrate how even primary solvation (i.e. a single molecular layer) is sufficient to engender substantial and electrochemical-like stabilization of interfacial ionic species. The essential nature of dielectric-induced modifications to electron-transfer energetics at metal-vacuum interfaces are considered, and also related to the observed marked solvation effects on the charging of metalliclike clusters, such as fullerenes. The potential value of such unified treatments of surface potential-charge relationships in vacuum and electrochemical systems is also sketched in more general terms.