Probing the mechanism of electroless gold plating using an electrochemical quartz crystal microbalance. I. Elucidating the nature of reactive intermediates in dimethylamine borane

This work shows that the coupling of voltammetry with an electrochemical quartz crystal microbalance furnishes firm evidence of the formation and reduction of a surface gold oxide layer which is accompanied by the adsorption of a reactive intermediate from dimethylamine borane (DMAB) solutions. The purpose of this study is to provide further insights into the identity and role of the reactive intermediate assumed in the mechanism of electroless gold in the DMAB bath. It was found that alkaline DMAB solutions exhibit a rapid mass increase at 0.2 V vs. Ag/AgCl, which is accompanied by the reduction of the gold oxide in hydroxide media. The anodic current and mass increase associated with gold oxide reduction is attributed to reactivation of DMAB oxidation. On the contrary, a frequency increase is observed at this potential in the absence of DMAB. X-ray photoelectron spectroscopy measurements further indicate that the adsorption/desorption of a borane-containing reactive intermediate onto the gold surface is short-lived. The intermediate is consequently eliminated from the surface after interaction with the gold oxide layer.