State-of-the-art manufacturing of semiconductor devices involves electrodeposition of copper interconnects The process depends on additives that affect the local deposition rate to yield void-free superconformal, or bottom–up filling of trenches and vias. Chemical process models describing the filling of high aspect ratio features, from nanometers (on-chip wiring) to micrometers (through-silicon-vias) to millimeters (printed circuit boards) are available. Nevertheless, much remains to be known about the molecular nature and competitive, co-adsorption dynamics of the additives and their impact on metal deposition. This lecture will detail experiments that reveal important aspects in the operation of additives used for superconformal film growth.