Peak‐in‐Valley Metal Nano‐Architectures via E‐Beam‐Guided Metal Oxide Redox

Abstract Focused electron beams enable nanoscale material modification via localized etching or deposition. In liquid‐phase electron‐beam‐mediated processing, radiolysis‐driven redox reactions present an opportunity to control both etching and deposition simultaneously. Here, this duality using a water‐ammonia solvent as a tunable redox mediator on copper surfaces is demonstrated. At lower ammonia concentrations, the oxidation process dominates, etching copper to sub‐50‐nm depths. The copper ions and ion‐complexes released during this initial oxidation step are reduced by solvated electrons resulting in metal deposition into the etched sites, over longer e‐beam exposures, producing characteristic peak‐in‐valley nanostructures. Conversely, at higher ammonia concentrations copper‐ammine ion complexation and radiolytic oxidizing species scavenging by ammonia occur at higher rates, creating a reducing environment conducive to rapid beam‐guided copper deposition. Reaction‐transport simulations and experiments are performed to show the effects of ammonia‐mediated radiolysis chemistry, describing the direct influence of solvent concentration on redox balance and the outcome of e‐beam guided processing. By uniting both etching and deposition within a single framework, this work provides a versatile route for controlled surface nanostructuring.