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

Previous studies have shown that electron transfer rate constants for a bimolecular reaction between conduction band electrons and solution acceptors 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–potential curves) and band edge positions (derived from interfacial capacitance measurements) are shown to depend on the length of exposure to solutions containing either ferricenium cations or cyclopentadienide anions. Surprisingly, the effects of these pretreatments are reversed when the electrodes are removed from solution. Catalyzed binary reaction sequence chemistry was used to fabricate n-Si electrodes with silicon dioxide overlayers with thicknesses ranging from 13 to 49 Å. Initiation of the growth process by a water plasma resulted in changes to the n-Si surface region producing highly non-ideal electrochemical behavior, which prevented the measurement of electron transfer rate constants at the oxide covered electrodes. Electrodeposition of silver on these electrodes demonstrated that the oxide contained pinholes that accommodated Faradaic current flow.