The effects of acid pretreatment and surface stresses on the evolution of impurity clusters and graphene formation on Cu foil

In this study, the effects of acid pretreatment together with the surface stresses are studied systematically to control the densities of Si and Ca based impurities on the surface and to understand their effects on the final graphene morphology formed on Cu foil via CVD. In order to investigate the surface coverage and morphology of graphene, in addition to scanning electron microscope (SEM) studies, graphene grown on Cu foils are oxidized in air to reveal the graphene domains under the optical microscope (OM). Graphene formation is also confirmed using Raman spectroscopy directly on the Cu foil. Our studies show that the coverage and the morphology of the final graphene are strongly affected by the acid pretreatment because it removes the surface oxide layer and surface Ca impurities inherently present on the copper foil. Furthermore, it is found that the surface elastic stresses have also direct influence on the sizes and distribution of the surface impurities which affect the final morphology of graphene.