Characterization of photoinduced electron tunneling in gold/SAM/Q-CdSe systems by time-resolved photoelectrochemistry

Colloidal CdSe quantum dots were chemisorbed on a gold electrode using a va riety of self-assembled monolayers (SAMs) consisting of dithiols and rigid disulfides. After absorption of a photon with an energy larger than the ban d 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 tunn eling was measured directly by intensity-modulated photocurrent spectroscop y (IMPS), and its distance dependence was studied using rigid SAMs separati ng the Q-CdSe and Au. The tunneling rate was found to depend exponentially on the distance, with a decay length of 2 Angstrom.