In Situ Characterisation of Graphene Growth on Liquid Copper-Gallium Alloys: Paving the Path for Cost-Effective Synthesis

TL;DR

This study explores how alloying copper with gallium lowers the melting point and affects graphene growth, aiming to develop a more cost-effective, real-time method for synthesizing high-quality graphene on liquid metal catalysts.

Contribution

It provides the first in situ analysis of graphene growth on liquid copper-gallium alloys, revealing the effects of alloy composition on graphene quality and adhesion, and suggests a trade-off between cost and quality.

Findings

Graphene forms on alloys with up to 60 wt% gallium.

Gallium reduces catalytic activity and graphene quality.

Weaker graphene adhesion observed on gallium-rich alloys.

Abstract

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.