Flat Graphene Growth on Ru-Ni Bimetallic Catalysts via Carbide-Suppressed Solid-State Graphitization.

Understanding solid-state graphitization is critical for the low-temperature synthesis of ultrathin graphene with controlled thickness and morphology. Here, we directly reveal the graphitization mechanism of a Ru-Ni bimetallic thin-film catalyst using in situ transmission electron microscopy, complemented by theoretical calculations. Unlike conventional Ni catalysts, in which graphene growth is mediated by Ni3C formation and decomposition, Ru alloying suppresses detectable carbide formation across all investigated alloy compositions under the present conditions and promotes a surface-diffusion-dominated graphitization pathway distinct from that of pure Ni. The Ru-Ni 1:1 ratio catalyst exhibits enhanced thermal stability at ∼650°C, enabling graphene formation prior to catalyst diffusion and yielding an ultraflat nanocrystalline graphene film from an ultrathin catalyst/precursor stack. In situ electron diffraction and electron energy loss spectroscopy precisely identify the onset of graphene formation, while compositional tuning reveals growth behavior that fundamentally differed with pure Ni, even in Ni-rich alloys. Density functional theory calculations confirm that carbide phases are thermodynamically unfavorable in Ru-Ni alloys, supporting a surface-diffusion-dominated growth mechanism analogous to that of Cu. These findings establish a new catalyst design rule for low-temperature synthesis of ultrathin and flat graphene.