Insight and control of the chemical vapor deposition growth parameters and morphological characteristics of graphene/Mo2C heterostructures over liquid catalyst

Transition metal carbides is a family of materials with many fascinating properties, especially when studied close to the 2D limit. Molybdenum carbide (Mo2C) is a member of this group which has attracted interest especially thanks to its potential application as electrode in energy storage as well as in catalysis. The latest methods development has demonstrated the potential to grow ultrathin Mo2C domains of high quality through chemical vapor deposition (CVD) over melted substrates, together with graphene. This progress provides new routes towards the preparation of vertical Van der Waals (VdW) heterostructures. In the present work we provide a detailed study of the dominant growth mechanisms of pure Mo2C crystals as well as graphene/Mo2C heterostructures. The findings reveal that the methane flow controls the growth of graphene/Mo2C heterostructures or pure Mo2C domains, while the high growth temperature and presence of hydrogen significantly increase the growth rate. Additionally, the presence of graphene serves as a blocking diffusion layer, permitting the growth of ultrathin crystals and increasing their nucleation density. Atomic Force Microscopy (AFM) characterization demonstrates the growth of stacks of crystals which consist of individual crystals with thickness as low as similar to 2 nm.