In situ characterisation of graphene growth on liquid copper-gallium alloys: Paving the path for cost-effective synthesis

[Display omitted] •Effect of alloying liquid copper with gallium on graphene growth studied in situ.•Use of radiation-mode optical microscopy and synchrotron X-ray reflectivity.•Single-layer graphene on alloys with up to 60 wt% of gallium.•Transformation of growth mechanism with increasing gallium content in CuGa alloys.•Increasing interfacial distance, thus decreasing bonding, with Ga content. Liquid metal catalysts (LMCats), primarily molten copper, have demonstrated their efficiency in the chemical vapour deposition (CVD) approach for synthesising highquality, large-area graphene. However, their high melting temperatures limit broader applications. Reducing the temperature of graphene production on LMCats would lead to a more efficient and cost-effective process. Here, we investigated the effects of alloying copper with a low-melting temperature metal on graphene growth in real-time. We examined a set of liquid copper-gallium alloy systems using two complementary in situ techniques: radiation-mode optical microscopy and synchrotron X-ray reflectivity (XRR). The microscopy observations revealed reduced catalytic activity and graphene quality degradation in compositions with gallium domination. The XRR confirmed the formation of single-layer graphene on alloys with up to 60 wt% of gallium. Furthermore, we detected a systematic increase in adsorption height on the alloys' surface, indicating weaker adhesion of graphene on gallium. These findings suggest that a trade-off between layer quality and cost reduction in production is feasible. Our results provide insights into the CVD synthesis of graphene on bimetallic liquid surfaces and underscore the potential of gallium-copper alloys for enabling the direct transfer of graphene from a liquid substrate, thereby addressing the limitations imposed by the high melting temperatures of conventional LMCats.