Two dimensional monolayers TetraHex-CX₂ (X = N, P, As, and Sb) with superior electronic, mechanical and optical...

The discovery of graphene in 2004 opened a new world of two dimensional (2D) materials, stimulating the broad explorations of other novel 2D carbon structures and their derivatives in many materials fields. Although many 2D materials have been proposed theoretically, the experimental fabrication of them remains a big challenge, leading to more efforts to explore novel 2D materials with excellent properties. Here, we constructed four 2D monolayers TetraHex-CX₂ (X = N, P, As, and Sb) using first-principles calculations. These thin materials composed of tetragonal and hexagonal rings exhibit good stabilities, extraordinarily flexible mechanical properties, indirect bandgaps (≤2.30 eV except TetraHex-CN₂) with a semiconducting nature and a strong optical absorption up to 10⁵ cm^-1, showing the potential nanomechanical, nanoelectronic and optoelectronic applications. On building the structure-property relationship, we found that the Pauling electronegativity of X has an important influence on the electronic and mechanical properties of CX₂, which provides a significant understanding of the fundamental origin of materials properties and is helpful to design novel 2D materials with special properties.