Diamanes from novel graphene allotropes: Computational study on structures, stabilities and properties

We have computationally studied eight carbon monolayer materials, including the recently synthesized biphenylene, graphyne, and DHQ-graphene, as precursors of the bilayer C₂H-diamanes. The interlayer C-C bonds of about 1.6 Å confirmed the strong covalent bonding between the monolayers. Density functional theory calculations revealed that the considered diamanes have a wide range of band gaps ranging from 1.5 to 4.2 eV. Diamanes, which are based on graphene allotropes, significantly expand the range of electronic and optical properties of conventional graphene derivatives and other traditional carbon materials. Tight-binding molecular dynamics simulations showed that diamanes are less stable than monolayers due to tendency of interlayer bonds tend to break. Out of the eight considered structures, only three diamonds were identified as certain stable systems suitable for processing at elevated temperatures of about 500 K. The nudged elastic band approach provided an understanding of the rate-defined thermal decomposition steps and corresponding energy barriers, which are equal to 2.79, 4.86, and 5.41 eV for the three stable diamanes. The elastic constants of the considered diamanes are comparable to those of graphene. The absorbance spectra of diamanes are calculated using linear response time-dependent density functional theory.