First-Principles Investigation of Irida-Graphane: A Wide-Band-Gap Semiconductor Derived from Irida-Graphene

Abstract

Opening a band gap in metallic two-dimensional carbon allotropes is an important step toward their use in electronic and optoelectronic devices, and full hydrogenation has proven to be an effective route to achieve it. Here, we propose irida-graphane, the fully hydrogenated derivative of the irida-graphene, a monolayer composed of three-, six-, and eight-membered rings, and investigate its structural, mechanical, electronic, and optical properties using density functional theory (DFT) at the PBE and HSE06 levels combined with phonon and \textit{ab initio} molecular dynamics (AIMD) simulations. All carbon atoms adopt $sp^3$ hybridization, with the hydrogen atoms of the three- and six-membered rings bonded to opposite sides of a buckled carbon framework, and the lattice parameter contracts by 4.3% with respect to irida-graphene. The hydrogenation energy of $-0.53$ eV/H indicates that the hydrogenation of irida-graphene from molecular hydrogen is exothermic. The absence of imaginary phonon frequencies confirms the dynamical stability of irida-graphane, and AIMD simulations show that its structure remains intact at temperatures up to 2000 K. Irida-graphane is mechanically isotropic, with an in-plane stiffness of approximately 156 N/m, a Poisson's ratio of approximately 0.1, and critical strains of approximately 20%. Hydrogenation transforms the metallic parent structure into a semiconductor with an indirect band gap of 4.68 eV (PBE) and 6.0 eV (HSE06). Irida-graphane is transparent in the visible range, with reflectivity below 0.3%, and absorbs strongly in the deep ultraviolet, with absorption coefficients of the order of $10^{5} - 10^{6}$ cm$^{-1}$. These results suggest irida-graphane as a candidate wide-gap material for ultraviolet optoelectronics and transparent coatings.