Copper electrodeposition is a central process in the metallization of microelectronics and more recently has found use as an important electrocatalyst in the conversion of CO­₂ to hydrocarbons. Gaining mechanistic insight into the nature of the respective reactions requires in situ and better still in operando measurements. Herein the utility of shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) and electrochemical mass spectrometry (EC-MS) to study the potential dependent anion adsorption and hydride formation on low index Cu single crystals surface will be detailed. SHINERs enables monitoring of competitive adsorption between Cl^- and SO₄^2- on Cu(100) and Cu(111) surfaces (Figure 1a). Saturated ordered halide adlayers are formed at potentials slightly below the open circuit potential while moving to more negative values halide is disrupted resulting with the emergence of a sulfate mode near 970 cm^-1. In the case of Cu(111) the desorption of the halide adlayer is coupled to the formation of a hydride phase (Figure 1b) as evident in both SHINERS and EC-MS measurements. SHINERS was also employed to examine the adsorbate dynamics associated with superconformal electrodeposition of Cu. Specifically, competitive adsorption between Cl^- and sulfonate terminated thiol/disulfide accelerators molecules was examined during Cu deposition on planar and patterned surfaces (Figure 1c). The ability of the nanoparticle reporters to float on the advancing surface is demonstrated and used to probe the additive evolution on the growth front associated with superconformal electrodeposition. This work demonstrates the capabilities of operando electrochemical measurements and their importance in achieving future technological breakthroughs.

Figure 1. Capturing Cu interfacial chemistry with operando SHINERS (a) on a c(2x2)-Cl covered Cu(100) surface, (b) coupling to EC-MS to reveal the existence of hydride on Cu(111) in Cl containing electrolyte and (c) to track accelerator coverage on electrodeposited pattern surfaces.