First-Principles Observation of Bonded 2D BC Bilayers.

Two-dimensional (2D) B-C compounds possess rich allotropic structures with many applications. Obtaining new 2D BC structures is highly desirable due to the novel applications of three-dimensional (3D) BC in protections. In this work, we proposed a new family of 2D BC from the first-principles calculations. Distinct from previous observations, this family of 2D BC consists of bonded 2D BC bilayers. Six different types of bilayers with distinct bonded structures are found. The phonon spectrum calculations and ab initio molecular dynamics simulations at room temperature demonstrate their dynamic and thermal stabilities. Low formation energies suggest the high possibility of realizing such structures in experiments. Rich electronic structures are found, and the predicted Young's moduli are even higher than those of the previous ones. It is revealed that the unique electronic and mechanical properties are rooted in the bonding structures, indicating the prompting applications of this family of 2D BC materials in photovoltaics, nanoelectronics, and nanomechanics.