Research on the Coherent Interface Design and Surface Microstructure Tailoring of Cu Matrix Materials

Surface microstructures, including surface orientation and step structures, play a critical role in determining the electrical conductivity and stability of copper (Cu)-based materials, owing to their electron scattering effect and anisotropic surface energy levels. Previous works have demonstrated that achieving close-packed surface orientation and atomic flat surface can greatly enhance the surface properties of Cu. However, the intrinsic surface kinetics and thermodynamics of face centered cubic metals always result in non-close packed surfaces with large surface steps during heat treatment, raising challenges in the optimization of surface microstructures. In this work, we propose to tailor the surface microstructures of Cu by changing the intrinsic surface thermodynamic and kinetic conditions through the construction of coherent interfaces. Using cobalt (Co) and single layer graphene (SLG) as model materials, we constructed Cu/Co and Cu/SLG interfaces on Cu and found that the atomic flat {111} Cu surface can be achieved in Cu/SLG interfaces. Further microstructure characterizations and molecular dynamic simulations revealed that the formation of {111} reconstructed Cu surface was dominated by melting and re-solidification of Cu surface under the assisted from Cu/SLG interface energy. Meanwhile, the formation of atomic flat surface can be ascribed to the minimization of Gr strain energy and high-temperature assisted surface diffusion. Based on these mechanisms, two important criteria that can achieve atomic flat {111} Cu surface are proposed: (i) an appropriate processing temperature that can trigger the surface melting/surface diffusion and (ii) a crystalline surface coated layer with high modulus that can modify the Cu surface energy. The present results not only elucidate our designing concept but also provide a feasible strategy for tailoring the surface properties of Cu-based materials.