Potential control characteristics of short-chain thiols of thioctic acid and mercaptohexanol self-assembled on gold

In this article we systematically investigated self-assembly of short-chain thiols of thioctic acid (TA) and mercaptohexanol (MCH) on gold under potential control, E-dc (-0.4, +0.4 and +0.7V) and compared the results obtained with open circuit potential (E-ocp). Effect of E-dc on thiol self-asembly was inspected based on the changes in electrochemical parameters including interfacial capacitance (C), phase angle (phi(1) (Hz)). current density difference (Delta i), charge transfer resistance (R-ct) through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Experimental results showed that E-cd could not obtain stable short-chain self-assembled monolayers (SAMs) (TA and MCH) in a short time. Both TA and MCH had slow self-assembly dynamics and needed a long time (> 24h) to achieve adsorption equilibrium. Furthermore, the negative potential E-dc (-0.4 V) did not facilitate the ordering of SAMs. The ordering of TA-SAMs was found to be the best when assembled under E-dc (+0.4 V), whereas that of MCH-SAMs was almost the same when assembled under either E-OCP or E-dc (+0.4, +0.7 V). We considered that permeation of ions and water molecules perhaps dominated the slow self-assembly dynamics of short-chain thiols (TA and MCH) under E-dc and mutual interaction between adjacent chains of thiols played an important role in the ordering of SAMs. (c) 2010 Elsevier Ltd. All rights reserved.