Electron transfer at n-silicon vertical bar methanol interfaces: effects of ferricenium pretreatment and silicon dioxide overlayers

Previous studies have shown that electron transfer rate constants for a bim olecular reaction between conduction band electrons and solution accepters can be obtained at the n-Si / methanol interface [A.M. Fajardo, N.S. Lewis, Science 274 (1996) 969]. These rate constants (derived from current-potent ial curves) and band edge positions (derived from interfacial capacitance m easurements) are shown to depend on the length of exposure to solutions con taining either ferricenium cations or cyclopentadienide anions. Surprisingl y, the effects of these pretreatments are reversed when the electrodes are removed from solution. Catalyzed binary reaction Sequence chemistry was use d to fabricate n-Si electrodes with silicon dioxide overlayers with thickne sses ranging from 13 to 49 Angstrom. Initiation of the growth process by a water plasma resulted in changes to the n-Si surface region producing highl y non-ideal electrochemical behavior, which prevented the measurement of el ectron transfer rate constants at the oxide covered electrodes. Electrodepo sition of silver on these electrodes demonstrated that the oxide contained pinholes that accommodated Faradaic current flow. (C) 2001 Elsevier Science B.V. All rights reserved.