Construction and electrochemical characteristics of multilayer assemblies of Au nanoclusters protected by mixed self-assembled monolayers on tin-doped indium oxide

Abstract

The electrochemical characteristics of multilayers of gold nanoclusters (GNCs) on a tin-doped indium oxide (ITO) electrode were investigated and were compared with those of GNC multilayers on an Au (111) surface. Two types of GNC, one covered by self-assembled monolayers (SAMs) of mercaptoundecanoic acid (MUA), hexanethiol (C₆SH), and ferrocenylhexanethiol (FcC₆SH), MHF-GNC, and the other covered by MUA and C₆SH, MH-GNC, were consecutively deposited with an ionic polymer (poly(allylamine hydrochloride) (PAH)) binding layer based on an electrostatic principle. At the ITO electrode modified with multilayers composed only with MHF-GNC, a reversible wave corresponding to the redox of the ferrocene group was observed at +350 mV. The full width at half maximum (fwhm) of the redox peak was much narrower than that expected for a simple Langmuir-type redox process, which was observed on the MHF-GNC-modified Au (111) surface, suggesting a strong interaction between the ferrocene groups on the GNC within the multilayer on the ITO electrode. The transfers of both electrons and perchlorate ions through these GNC multilayers were found to be rather facile. The amount of deposited GNC of the multilayers on the ITO substrate was 5-times greater than that on Au (111). This discrepancy was attributed to the different GNC arrangements in the multilayers on the two substrates. The substrate effect on GNC multilayer formation is also discussed.