  Liquid metal catalysts (LMCats), primarily molten copper, have demonstrated
their efficiency in the chemical vapour deposition (CVD) approach for
synthesising high-quality, 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).
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.
Additionally, we detected a systematic increase in adsorption height on the
alloys' surface, suggesting a weaker graphene adhesion on gallium. These
findings propose a trade-off between layer quality and production cost
reduction is feasible. Our results offer 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 high melting
temperatures of conventional LMCats.
