Electrochemical transfer at p-type silicon(1 1 1)-alkyl monolayer hybrid electrodes in acetonitrile medium

In this work we study the chain length dependence of charge transfer at p-type Si(1 1 1) electrodes modified with n-alkyl monolayers (Si(1 1 1)–CnH2n+1) in contact with a redox electrolyte. Cyclic voltammetry in acetonitrile containing the ferrocenium/ferrocene reversible system shows a clear diode-like behaviour with a nearly linear log(j) vs V relationship in the oxidation regime. Electrochemical impedance spectroscopy data give a flatband potential Efb = 0.04 ± 0.10 V vs SCE that is nearly independent of the chain length. Using this parameter we estimated the attenuation tunneling length β at ∼0.37 per methylene unit by plotting log(j) vs the chain length d, with j measured at a fixed band bending. This value, which is found to be independent of the applied bias, is discussed in relation with the measured dielectric constant εeff ∼ 2.9 a value larger than expected (theoretical value ∼2.1).