▎ 摘　　要

Due to its semi-metallic characteristics, graphene may allow electron transfer to take place between itself and electrically-contacted metals. Here, we discover a two-component (graphene and copper) and two-process (ion migration and electron transfer) cycle, in which (a) electrons travel from the copper substrate to graphene based on Fermi-level variations through the interface, and (b) ions migrate vice versa due to Coulomb force via the intercalated electrolyte. To validate this proposed cycle, we scrutinize the copper-oxide formation, graphene-lattice phonon-frequency variations, and the morphological evolution of copper oxides, primarily via Raman measurements. Our study may provide the guidance for fundamental research on other graphene-metal assemblies as well as may enhance the versatility of graphenebased applications. (C) 2017 Elsevier Ltd. All rights reserved.