Bonding duality and optoelectronic properties of bilayer carbon structures based on the T12 phase and penta-graphene

Bilayer compounds of two-dimensional T12 phase carbon allotrope and penta-graphene have been studied using the electron density functional theory. The stability of the considered two-dimensional structures with different types of stacking order at different temperatures has been estimated from the calculated phonon spectra and molecular dynamics simulation. The stability of the two-dimensional planar structure up to 1350 K has been demonstrated. It has been shown that bilayer penta-graphene compounds with the AA' and AB' stacking orders have energy minima both in the state with the van der Waals interaction and in the form of covalently bonded layers in the AA-T12 and T12 phases. The barrier for the transition between covalently and van der Waals bonded AA' and AB' stacking orders has been analyzed. The calculated electronic and optical characteristics show that the band gap in the case of covalent bonding is much narrower than that in the case of van der Waals bonding.