Towards the perfect graphene membrane

We investigated the limiting factors affecting the crystal quality of graphene grown on polycrystalline Cu foils, a promising new system for applications in large-scale graphene production. The first important result of this study is that a high temperature hydrogen pretreatment of the Cu foil lowers considerably the nucleation density of graphene crystals, favouring the growth of large single crystalline graphene flakes. Second, a characterization of the morphology and structure of the Cu support was performed. The faceting of the substrate involves ordered sequences of (100)- and (410)-facets, interrupted by further highly inclined planes, consisting of (n11) - type facets. The alignment of the graphene layer has no influence on the restructuring of the Cu foil. Despite the fact that the interaction of graphene on the Cu substrate is weak, the graphene layer was found to be a replica of the former morphology of the faceted Cu substrate.

This structure even persists if suspended graphene membranes are formed when carefully removing locally the Cu support underneath the monolayer graphene. As a result, graphene based membranes or transferred graphene layers, which have been grown on Cu foils, are intrinsically corrugated.

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