Mapping Adsorbates with Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy to Understand Rapid Superconformal Filling of Cu Trenches

Additive adsorbates are widely used as surfactants to guide morphological and microstructural evolution during electrochemical deposition of thin films. Even though this strategy has been employed for several decades understanding of the mechanisms at play on the interface remain limited. Modern spectroelectrochemical methods, from surface-enhanced Raman spectroscopy (SERS) to surface-enhanced infrared spectroscopy (SEIRAS) and non-linear optical methods like sum frequency generation (SFG) can provide significant insight into the composition, structure, and dynamics of the surfactant adsorbates through their vibrational signatures. on nominally static surfaces. Each strategy is limited to specimen geometry; SERS is closely linked to the use of rough, plasmonically-active surfaces while SEIRAS measurements are constrained to thin, IR-transparent, metallic films. In the last decade, a significant advance was the introduction of nanoparticle reporters, based largely on silica coated Au nanoparticles, that enable Raman spectroscopy studies on well-defined, single-crystal surfaces whereby the nanoparticle serves to channel the plasmonic energy to the nanoparticle-substrate interface. The silica or alternative coating materials are designed to be inert with respect to the chemistry of the adsorbate species under study while remaining thin enough to allow effective focusing of the optical energy. This approach has been adopted by several researchers interested in understanding molecular adsorption on well-defined, single-crystal surfaces, the electrical double layer, and numerous aspects of reactivity related to catalysis, batteries, electrodeposition, etc. The present work demonstrates the use of Au@SiO 2 (core-shell) nanoparticles, also known as SHINERS (Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy), to enable in situ vibrational spectroscopic measurements during electroplating of comparatively smooth, rapidly advancing, surfaces. In particular, the ability of the reporters to float on an advancing surface while responding to area change is used to reveal important, area-driven changes in adsorbate coverage. This study also opens a new avenue for exploring the intersection of analytical surface chemistry and composite electroplating. Figure 1