Although graphene can be grown on solid copper surfaces, higher precursor pressures that lead to faster growth can be used on molten metals, and smoother graphene films can be made on liquid surfaces. However, investigating chemical vapor deposition growth on a liquid surface can be challenging. Jankowski et al. used a combination of x-ray diffraction and reflectivity, Raman spectroscopy, and optical microscopy methods to characterize and control graphene growth on molten copper. By changing the ratios of methane to hydrogen, the authors were able to produce highly ordered flake assemblies, and by using a single nucleation seed, they could grow millimeter-scale, single-crystalline graphene sheets.
ACS Nano 10.1021/acsnano.0c10377 (2021).