Transforming Graphene into High-Quality Large-Area 2D Mo₂C

Transition metal carbides (TMCs) exhibit an exceptional combination of mechanical strength, electrical conductivity, chemical stability, and superior optical characteristics, rendering them highly appropriate for a wide range of applications. Molybdenum carbide (Mo₂C) holds significant promise for advanced electronics and quantum technologies due to its thickness-dependent superconductivity and excellent electrical properties, as well as its remarkable catalytic performance and chemical and thermal stability for other applications.<br/>One of the most versatile methods for synthesizing high-quality 2D Mo₂C is chemical vapor deposition (CVD), which allows precise control over the morphology of the crystals. However, the use of hydrocarbon precursor in CVD results in the simultaneous formation of graphene, which affects the growth kinetics of Mo₂C, leading to the formation of graphene/Mo₂C heterostructures. While this one-step formation of heterostructures may be advantageous for certain applications, it may be undesirable for others where the presence of graphene is not desired. Therefore, post-synthesis removal of graphene using techniques such as reactive ion etching is necessary; this is also crucial for properly investigating the potential of Mo₂C.<br/>In this study, we systematically explore the impact of graphene on the formation of 2D Mo₂C crystals through CVD by designing experiments with three different routes. Two of these processing routes, established in the literature, served as benchmarks for comparison with our novel approach. In our innovative method, we synthesized graphene prior to Mo₂C formation and halted methane flow at high temperatures. This strategy aimed to transform graphene into Mo₂C without needing an additional carbon source like CH₄, thereby preventing the formation of graphene/Mo₂C heterostructures. Raman spectroscopy was employed to characterize the presence of graphene, while atomic force microscopy and scanning electron microscopy were used to examine changes in crystal morphologies, highlighting the effectiveness of our approach. (This study is supported by Air Force Office of Scientific Research, grant numbers: FA9550-22-1-0358 and FA9550-18-1-7048.)