Copper deposition in the presence of surface-confined additives

The galvanostatic deposition of Cu from sulfuric acid solutions onto evaporated (111) Au electrodes bearing alkanethiol monolayers (SAMs) was studied with a combination of cyclic voltammetry, in situ atomic force microscopy, and x-ray photoelectron spectroscopy. The morphology of the electrodeposit was found to depend on the chain length of the alkanethiol used to form the SAM and the applied current density. It was found that short chain length (n = 4) thiols and high current densities (j ≥ 1.67 mA/cm²) promote the formation of smooth deposits. We attribute this effect to the over-potential-driven activation of numerous monolayer defects that play the role of nucleation centers. The passage of the current was found to cause a change in the monolayer defect density. X-ray photoelectron spectroscopic analysis showed that deposition occurred on top of the monolayer in a completely reversible manner and that the deposition and subsequent stripping did not affect the S-Au bond of most thiolate moieties contained in the SAM. The implications of these results for additive-based electrodeposition are discussed.