Effect of Electrode Surface Roughness on Copper Oxide Nanoparticle Synthesis via Atmospheric-Pressure Plasma in Liquid

Atmospheric-pressure plasma–liquid interactions provide a non-equilibrium environment for surface modification and nanostructure formation under ambient conditions. In this work, the effect of copper surface roughness on copper oxide nanostructure formation is investigated using an atmospheric-pressure plasma-in-liquid configuration in a strongly alkaline electrolyte (3 M NaOH). Copper electrodes with three controlled roughness levels were exposed to stable argon microplasma under identical operating conditions. X- ray diffraction indicates the formation of crystalline copper oxide on the copper surface without the use of metal salt precursors. UV–Vis spectroscopy reveals optical features characteristic of copper oxide nanostructures. Electron microscopy shows a clear roughness-dependent morphological evolution, where coarse surfaces promote localized growth and agglomeration, while smoother surfaces lead to higher nucleation density and finer, more uniform nanostructures. Elemental analysis indicates copper and oxygen as the dominant constituents of the formed layers. The results demonstrate that surface roughness governs local electric field distribution and microdischarge interaction at the plasma–liquid interface, thereby controlling the balance between nucleation and growth. These findings highlight surface roughness as an effective parameter for tuning plasma–liquid-driven oxidation processes and contribute to a deeper understanding of plasma–liquid interaction mechanisms.