Graphene-driven growth of large-area ultrathin Mo2C

Abstract

Two-dimensional transition metal carbides, particularly chemical vapor deposition (CVD)-grown molybdenum carbide (Mo2C), are promising for next-generation electronic applications. However, achieving large-area, high-quality single crystals with controlled thickness remains challenging due to the non-self-limiting nature of conventional CVD. Moreover, Mo2C synthesis is often accompanied by undesired graphene coverage, necessitating additional processing steps that can degrade its electronic properties. Here, we present a graphene-driven approach that enables the direct synthesis of ultrathin Mo2C on copper without an external carbon source. Through systematic comparative experiments, we elucidate the role of graphene in Mo2C synthesis via CVD and develop a novel method marked as Process Route 3, where graphene serves as the sole carbon source, eliminating the need for CH4. We demonstrate that annealing a layered Mo/Cu/graphene film at 1100 °C enables the complete transformation of graphene into Mo2C. At this temperature, graphene tearing exposes a fresh liquid Cu surface. Mo atoms diffuse from the underlying Mo foil through molten Cu and react with carbon coming from the graphene layer via surface diffusion. This process enables preferential lateral growth, allowing Mo2C crystals to expand with minimal impingement, resulting in thin (~ 10 nm), well-faceted Mo2C domains with lateral sizes reaching up to 60 µm. X-ray diffraction and transmission electron microscopy confirm the high-quality orthorhombic structure of the synthesized Mo2C, while Raman spectroscopy verifies the complete conversion of graphene, yielding graphene-free Mo2C. This study provides a deeper understanding of metal carbide formation via CVD, overcomes key limitations of conventional approaches, and offers a viable route toward the scalable fabrication of large-area Mo2C with potential applications in high-performance electronics.