Characterization of Photoinduced Electron Tunneling in Gold/SAM/Q-CdSe Systems by Time-Resolved Photoelectrochemistry

Abstract

Colloidal CdSe quantum dots were chemisorbed on a gold electrode using a variety of self-assembled monolayers (SAMs) consisting of dithiols and rigid disulfides. After absorption of a photon with an energy larger than the band gap, a long-lived excited state is formed in the quantum dot; this state can decay by electron tunneling via the gold. The rate of photoinduced tunneling was measured directly by intensity-modulated photocurrent spectroscopy (IMPS), and its distance dependence was studied using rigid SAMs separating the Q-CdSe and Au. The tunneling rate was found to depend exponentially on the distance, with a decay length of 2 Å.