Graphene Growth Dynamics on Epitaxial Copper Thin Films

Abstract

Graphene chemical vapor deposition on copper is phenomenologically complex, yielding diverse crystal morphologies, including lobes, dendrites, stars, and hexagons, of various orientations depending on conditions. We present a comprehensive study of the evolution of these morphologies as a function of the copper surface orientation, absolute pressure, hydrogen-to-methane ratio (H2:CH4), and nucleation density. Growth was studied on ultrasmooth, epitaxial copper films inside copper enclosures to minimize copper polycrystallinity and roughness and decrease the graphene nucleation density. At low pressure and low H2:CH4, circular graphene islands initially form. After exceeding ∼1.0 μm, Mullins-Sekerka instabilities evolve into dendrites extending hundreds of micrometers in the ⟨100⟩, ⟨111⟩, and ⟨110⟩ directions on Cu(100), Cu(110), and Cu(111), respectively, indicating mass transport limited growth. Twin boundaries perturb the preferential growth direction on Cu(111) and alter graphene morphology. Increasing H2:CH4 results in compact islands that reflect the copper symmetry. At atmospheric pressure and low H2:CH4, Mullins-Sekerka instabilities develop but with multiple preferred orientations. Increasing H2:CH4 results in more hexagonal islands. Every growth regime can be tuned to yield continuous monolayers with a D:G Raman ratio <0.1. The understanding gained from this study provides a roadmap to rationally tailor the structure, morphology, and orientation of graphene crystals.