Copper-Assisted Etching of Gold through Electrochemical Deposition and Dissolution of Copper in Ionic Liquids

Abstract

A novel green-chemistry process for etching polycrystalline gold has been successfully developed by tuning electrochemical deposition and dissolution of metallic copper onto and away from gold in an ionic liquid bath based on a copper assisted etching mechanism. During the cathodic reduction of Cu from CuCl2 dissolved in the ionic liquid, the interaction of the electrodeposited Cu layer and the gold substrate leads to not only the formation of interfacial Cu-Au alloy intermediates but also the diffusion of Au into the Cu layer. During the subsequent anodic oxidation of Cu, the Au components in both the intermediates and the Cu layer are removed from the Au substrate, resulting in its etching. Cyclic voltammograms of CuCl2 on the Au electrode in 1-ethyl-3-methylimidazolium chloride in the potential range of approximately −1.50 to 0.60 V vs a silver pseudo reference electrode, exhibit the reduction and oxidation peaks associated with the redox couples of copper species. Scanning-electron-microscope studies of the samples treated in the CuCl2-containing ionic liquid by potential cycles clearly demonstrate the etching of the Au substrate. Elemental X-ray diffraction analyses of the etched Au substrate reveal that there is no detectable Cu residue in the etched substrate. Furthermore, our calculation suggests that the Cu assisting method can obtain an etching rate of approximately 105 nm/min, favorably comparable to those of several dry and wet etching methods.