SEIRAS Study of Chloride-Mediated Polyether Adsorption on Cu.

Surface-enhanced infrared absorption spectroscopy is used to examine the co-adsorption of a selection of polyethers with Cl under conditions relevant to superconformal Cu electrodeposition in CuSO-HSO electrolytes. In 0.1 mol/L HSO, a potential-dependent mixed SO -HO/HO layer forms on weakly textured (111) Cu thin-film surfaces. With the addition of 1 mmol/L NaCl, the SO -HO/HO adlayer is displaced and rapidly replaced by an ordered halide layer that disrupts the adjacent solvent network, leading to an increase in non-hydrogen-bonded water that makes the interface more hydrophobic. The altered wetting behavior facilitates co-adsorption of polyethers, such as poly(ethylene glycols), polyoxamers, or polyoxamines. Interfacial water is displaced by co-adsorption of the hydrophobic polymer segments on the Cl-terminated surface, while the hydrophilic ether oxygens are available for hydrogen bond formation with the solvent. The combined polyether-Cl layer serves as an effective suppressor of the Cu electrodeposition reaction by limiting access of Cu to the underlying metal surface. This insight differs from previous work which suggested that polymer adsorption is mediated by Cu-ether binding.