Influence of the Para-Substitutent of Benzene Diazonium Salts and the Solvent on the Film Growth During Electrochemical Reduction

Abstract

Abstract In this work the nature of the substitution process in the electrochemical deposition of different 4-substituted benzene layers on Au and the influence of the solvent were studied. We monitored the deposition from the corresponding isolated salt diazonium salts and via the “in solution diazotation” process where the diazonium salt is created just before the deposition process by means of amine and nitrite. Infrared spectroscopic ellipsometry measurements proved the presence of the various substituted benzene groups on the surfaces. Quantitative studies using electrochemical quartz crystal microbalance technique showed a decrease in the deposited organic layer thickness and the faradaic efficiency of the electrochemical process with the size of the 4-substituent. As consequence nature of the substituent in the 4-position was the dominating factor for thickness of the deposited benzene layer and the faradaic efficiency. Additionally, there was also a strong increase in the thickness of the deposited benzene layer by changing the solvent from aqueous sulphuric acid to acetonitrile pointing to a stabilization of the radical intermediates during reduction of the diazonium salt by acetonitrile. This in turn led to faradaic efficiencies of about 80%–90% for the grafting process in acetonitrile and only 15% in the aqueous acidic solution.