Surface diffusion of Cu mediated by graphene coverage

Abstract

The arrangement of surface steps profoundly governs the performance of metals in catalysis, corrosion resistance, and electronic transport. While graphene (Gr) coverage is known to alter the surface morphology of copper (Cu), existing reports remain contradictory regarding whether Gr induces step dissociation or bunching. This conflict is primarily due to the neglect of kinetic effects in traditional thermodynamic analysis. Here, using molecular statics/dynamics (MS/MD) simulations, it was revealed that Gr-coverage-induced pre-compressive stress and geometric confinement fundamentally alter the corresponding atomic diffusion behavior. Specifically, this environment constrains outward-step adatom migration but promotes inward-step diffusion, resulting in a shift from hopping to exchange diffusion mechanisms along key adatom pathways. Thermodynamically, both step dissociation and bunching reduce the total energy of Gr/Cu systems, governed by the interplay between Gr bending curvature and the number of steps/bends. However, kinetic effects dictate the temperature-dependent evolution of the steps: Gr-facilitated exchange diffusion enables step dissociation at moderate temperatures (∼900 K), whereas the high activation energy for large-scale mass transport and step motion restricts step bunching to high temperatures (∼1300 K). Our work resolves contradictory experimental observations and establishes a unified thermodynamics–kinetics framework for Gr-mediated metal surface step engineering, offering strategic insights for corrosion protection and catalyst design.