A new two-dimensional semiconducting carbon allotrope: A first-principles study

Abstract

A new two-dimensional carbon allotrope, which consists of 18 atoms in a hexagonal cell, is theoretically investigated by performing first-principle method. The allotrope displays a P6/mmm symmetry (termed as hP-C18 carbon). The new 2D carbon phase has an sp2-sp3 network, consisting of hexagons and octagons formed by near-by atoms. The calculations demonstrate that hP-C18 carbon is a metastable 2D carbon phase compared to graphene, but it is more energetically stable than penta-graphene. The dynamical, thermal and mechanical stabilities are demonstrated by phonon dispersion, ab inito MD simulations and elastic constants, respectively. The analysis of electronic band structure shows that hP-C18 is an indirect semiconductor with a band gap of 2.93 eV (HSE06). Besides, its buckled 3D structure, hP-C18-3D carbon, is also predicted. The stability of the new 3D phase is discussed by phonon dispersion and elastic constants. It is found that hP-C18-3D carbon is a super-hard indirect semiconductor with an indirect band gap of 2.24 eV (HSE06). Thus, hP-C18 carbon and its buckled 3D structure may possess not only potential electronic applications but also mechanical applications.