Abstract
The synthesis of large, defect-free two-dimensional materials (2DMs) such as graphene is a major challenge toward industrial applications. Chemical vapor deposition (CVD) on liquid metal catalysts (LMCats) is a recently developed process for the fast synthesis of high-quality single crystals of 2DMs. However, up to now, the lack of in situ techniques enabling direct feedback on the growth has limited our understanding of the process dynamics and primarily led to empirical growth recipes. Thus, an in situ multiscale monitoring of the 2DMs structure, coupled with a real-time control of the growth parameters, is necessary for efficient synthesis. Here we report real-time monitoring of graphene growth on liquid copper (at 1370 K under atmospheric pressure CVD conditions) via four complementary in situ methods: synchrotron X-ray diffraction and reflectivity, Raman spectroscopy, and radiation-mode optical microscopy. This has allowed us to control graphene growth parameters such as shape, dispersion, and the hexagonal supra-organization with very high accuracy. Furthermore, the switch from continuous polycrystalline film to the growth of millimeter-sized defect-free single crystals could also be accomplished. The presented results have far-reaching consequences for studying and tailoring 2D material formation processes on LMCats under CVD growth conditions. Finally, the experimental observations are supported by multiscale modeling that has thrown light into the underlying mechanisms of graphene growth.
Highlights
Reproducible mass production of large, defect-free twodimensional materials (2DMs) such as graphene is a major challenge toward their industrial applications
We demonstrated in situ multiscale monitoring of graphene growth on liquid copper via optical microscopy, Raman spectroscopy, grazing incidence X-ray diffraction (GIXD), and X-ray reflectivity (XRR), and tailoring of the graphene growth thanks to direct feedback on growth parameters according to the observed changes in morphology, structure, or defects
The experimental observations are supported by multiscale modeling of short- and long-range interactions between graphene flakes, explaining their movement and assembly into a 2D hexagonal network of singlecrystal graphene on liquid copper
Summary
Reproducible mass production of large, defect-free twodimensional materials (2DMs) such as graphene is a major challenge toward their industrial applications. Chemical vapor deposition (CVD) is to date the most promising method to produce large, high-quality graphene sheets.[1,2] CVD involves decomposing a gas precursor on a hot catalyst and its subsequent diffusion, followed by flake nucleation, growth, and coalescence into a continuous 2D layer. High nucleation rate and growth at random substrate positions result in a polycrystalline layer, whose properties are affected by the purity, roughness, crystallographic structure, and domain boundaries of the substrate.[3,4] Notable achievements for graphene growth on solid copper have been reported, such as the stitching of aligned graphene domains into a single-crystal film[5] or the growth of inch-size single crystals from one nucleus.[6,7] these results were obtained using conditions that are hard to implement at an industrial scale. After cooling to room temperature, special chemical methods (e.g., etching the catalyst away using an acid) are applied to separate and transfer the graphene due to the presence of considerable van der Waals forces between the graphene and Received: December 11, 2020 Accepted: May 27, 2021 Published: June 1, 2021
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