Electrochemical Properties of (111)-Oriented n-Si Surfaces Derivatized with Covalently- Attached Alkyl Chains

Abstract

The electrochemical properties of alkyl-terminated, (111)-oriented, n-type Si surfaces, prepared via a two-step halogenation/alkylation procedure, were analyzed in contact with CH₃OH−1,1'-dimethylferrocene^(+/0) (Me₂Fc^(+/0)) solutions. Current density−potential and differential capacitance−potential measurements of these surfaces in contact with CH₃OH−Me₂Fc^(+/0) indicated that the electrochemical properties of the alkyl-terminated surfaces were very similar to those of the H-terminated Si surface. The alkyl overlayers did not shift the Si band edges or induce significant surface recombination, but they did provide an additional electrical series resistance to charge transfer across the Si/liquid interface. The efficacy of alkyl overlayers in preventing photooxidation and photocorrosion of n-silicon surfaces was measured in contact with CH₃OH−Me₂Fc^(+/0) solutions to which a known amount of water had been added. Under these conditions, the alkyl-terminated surfaces consistently showed excellent current density−potential characteristics and displayed lower oxidation rates than the H-terminated surface, indicating that stability toward oxidation had been achieved without any significant compromise in the electrochemical qualities of the silicon surface.

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