Prediction of C7N6 and C9N4: stable and strong porous carbon-nitride nanosheets with attractive electronic and optical properties

Abstract

In this work, three novel porous carbon-nitride nanosheets with C₇N₆, C₉N₄ and C₁₀N₃ stoichiometries are predicted. First-principles simulations were accordingly employed to evaluate stability and explore the mechanical, electronic and optical properties. Phonon dispersions confirm the dynamical stability of all predicted nanosheets. Nonetheless, ab initio molecular dynamics results indicate that only C₇N₆ and C₉N₄ are thermally stable. C₇N₆, C₉N₄ and C₁₀N₃ nanosheets were predicted to exhibit high elastic moduli of 212, 202 and 208 N m⁻¹ and maximum tensile strengths of 14.1, 22.4 and 15.8 N m⁻¹, respectively. The C₇N₆ monolayer was confirmed to be a direct band-gap semiconductor, with a 2.25 eV gap according to the HSE06 method estimation. Interestingly, C₉N₄ and C₁₀N₃ monolayers show metallic character. The first absorption peaks of the optical spectra reveal that the C₇N₆ nanosheet can absorb visible light, whereas C₉N₄ and C₁₀N₃ monolayers can absorb in the infrared range of light. Moreover, the absorption coefficient and optical conductivity of the predicted nanosheets in the visible range of light are larger than those of graphene. The results provided by this study confirm the stability and highlight the very promising properties of C₇N₆ and C₉N₄ nanosheets, which may serve as promising candidates for numerous advanced technologies.