Strain relaxation in different shapes of single crystal graphene grown by chemical vapor deposition on copper

Abstract

The chemical vapor deposition (CVD) growth of single-crystal graphene on polycrystalline copper foils is a complex process affected by thermodynamics, kinetics, and growth conditions. These factors lead to the diversity of island shapes of single crystal graphene. Here, we present an experimental atomic force microscopy (AFM) study of the different shapes of single-crystal graphene grown on the inner surface of copper enclosures using the low pressure CVD technique. Most remarkably, this study indicates that graphene single crystal appears to form below the adjacent copper foil surface. This feature is revealed in cross sectional AFM scans of the height, which indicate that the graphene surface lies below the neighboring foil surface by ∼15–30 nm. Our results also show that an impurity assisted growth mechanism governs the growth of single crystal graphene via isotropic diffusion, producing two-fold, four-fold, and six-fold symmetries in the resulting flakes. In addition, single crystal graphene produced via anisotropic diffusion is also present here, but they do not exhibit signs of an impurity assisted growth mechanism. Finally, we find that strain relaxation in two-fold and four-fold symmetric graphene structures via isotropic diffusion is more complicated than the six-fold structures via isotropic diffusion, which results in multiple steps orientations in low symmetry structures.