Electrodeposition of Cu from cyanoalkaline solutions in the presence of CPC and PEG. An electrochemical and in-situ SERS investigation

The behavior of a cyanoalkaline copper plating system was studied with a special focus on the role of two organic additives, cetylpyridinium chloride (CPC) and poly(ethylene glycol) Mw 1500 (PEG). The influence of these additives on the adsorption behavior of the CN¯ ligands released during the Cu(I) complex reduction process has been investigated. Spectroelectrochemical results obtained by in situ Raman spectroscopy were complemented with cyclic voltammetric measurements. The potential-dependent surface-enhanced Raman spectroscopy spectra showed two prominent features at ca. 2090 and 2040 cm−1, within the Raman shift range typical of C≡N stretching v(CN¯). Using a double-Gaussian model, a numerical elaboration of the two v(CN) bands was done, estimating the potential-dependent values of the (i) peak position, (ii) peak intensity, and (iii) full-width at half-maximum. Our results show (i) a chemical interaction of CPC with adsorbed CN¯, weakening the Cu-CN¯ adsorption bond, (ii) an interaction of PEG with the Cu surface giving rise to cathode-blocking and alteration of the Cu growth mode.