On the Interpretation of Multiple Waves in Cyclic Voltammograms of Self-Assembled Monolayers of n-Alkane Thiols on Gold

Abstract

A homologue series of n-alkane thiols (CH3(CH2) m SH, MCm, m between 8 and 22) adsorbed on Au/mica substrates was studied in an alkaline environment using cyclic voltammetry (CV) and second harmonic generation (SHG). The known split of the reductive desorption signal in the cyclic voltammogram for thiols with chain length of m > 12 disappears again for m = 22. Simultaneous recording of SHG and CV data allowed correlation of thiol coverage with charge which was found to be linear, irrespective of the shape of the desorption signal. This evidences that the double peak structure of the desorption signal does not arise from the separation of faradaic and capacitive processes. The same is found for the double wave of the readsorption signal. The transient appearance of a split desorption signal for the one electron process of thiol desorption in the range of 12 < m < 22 is suggested to originate from intermolecular interactions.