Towards the selective growth of two-dimensional ordered C_xN_y compounds via epitaxial substrate mediation

Two-dimensional (2D) ordered carbon-nitrogen binary compounds (C_xN_y) show great potential in many fields owing to their diverse structures and outstanding properties. However, the scalable and selective synthesis of 2D C_xN_y compounds remain a challenge due to the variable C/N stoichiometry induced coexistence of graphitic, pyridinic, and pyrrolic N species and the competitive growth of graphene. Here, this work systematically explored the mechanism of selective growth of a series of 2D ordered C_xN_y compounds, namely, the g-C₃N₄, C₂N, C₃N, and C₅N, on various epitaxial substrates via first-principles calculations. By establishing the thermodynamic phase diagram, it is revealed that the individualized surface interaction and symmetry match between 2D C_xN_y compounds and substrates together enable the selective epitaxial growth of single crystal 2D C_xN_y compounds within distinct chemical potential windows of feedstock. The kinetics behaviors of the diffusion and attachment of the decomposed feedstock C/N atoms to the growing C_xN_y clusters further confirmed the feasibility of the substrate mediated selective growth of 2D C_xN_y compounds. Moreover, the optimal experimental conditions, including the temperature and partial pressure of feedstock, are suggested for the selective growth of targeted 2D C_xN_y compound on individual epitaxial substrates by carefully considering the chemical potential of carbon/nitrogen as the functional of experimental parameters based on the standard thermochemical tables. This work provides an insightful understanding on the mechanism of selective epitaxial growth of 2D ordered C_xN_y compounds for guiding the future experimental design.