Stability, electronic and optical properties of group IV graphenylene-like materials. An ab initio investigation

Abstract

Graphenylene is a 2D porous carbon layer with a semiconducting character. In recent years, it has been gaining attention due its interesting applicability, such as a energy storage medium. Aiming to explore and elucidate the main properties of graphenylene and graphenylene-like structures, we consider the first three elements of the group IV: C, Si and Ge and its binary alloys in 1:1 stoichiometry. First principles calculations, within the density functional theory (DFT), are addressed to investigate the energetic and mechanical stability as well as the electronic and optical properties of these 2D porous materials. The calculated stiffness constants and phonon spectrum show that these structures are thermodynamically stable, and ab initio molecular dynamic simulations at 300 and 600 K confirm the stability at environment conditions. Our results using DFT and the PBE functional shows that non carbon porous structures: Si, Ge and SiGe are metallic, while the C is a narrow band gap semiconductor (70 meV) and SiC and GeC are large band gap semiconductors (band gap greater than 2 eV). The use of the hybrid functional, HSE06, leads Ge and SiGe to exhibit a very small band gap (45 and 27 meV, respectively) while Si is a metallic system. The metallic and narrow band gap semiconductors systems present optical absorption in the infrared and visible region, while the carbides (SiC and GeC) start to adsorb photons with energies in the visible region (approximately 2 eV).