Stability, electronic and optical properties of group IV-carbide semiconductors: Graphenyldiene, and naphthylene-based monolayers

The discovery of graphene has driven a paradigm shift in 2D materials research, leading to the prediction of various new 2D carbon allotropes using approaches like density functional theory (DFT) and machine learning. One significant advancement was the introduction of naphthylenes in 2020, followed by the proposal of graphenyldiene monolayer in 2023. This work introduces news classes of 2D semiconductors based on these frameworks — termed inorganic naphthylenes (INP) and graphenyldiene (IGPD) — incorporating group IV compounds (SiC, GeC, and SnC) into the lattices. DFT simulations were employed to analyze the stability and electronic properties, including band structures, electron localization functions (ELF), carrier effective masses, Fermi velocities, charge distribution, and mechanical properties. IGPD-SiC and IGPD-GeC exhibit hexagonal symmetry with direct band gaps of 3.83 eV and 1.93 eV at the Γ point, while INP-SiC, GeC, and SnC, with rectangular symmetry, show band gaps of 3.75 eV (indirect), 2.49 eV (direct), and 1.17 eV (direct), respectively. The ELF analysis revealed that Si–C bonds in INP- and IGPD-SiC show pronounced ionic character, while Ge–C and Sn–C bonds exhibit more delocalized electron distribution. IGPD monolayers show lower mechanical rigidity and flexibility compared to INP monolayers, with IGPD-SiC having Young’s modulus (Y) of 75.28 N/m and Shear modulus (G) of 27.85 N/m. At the same time, IGPD-SnC is significantly lower (Y = 21.37 N/m, G = 8.57 N/m). In contrast, INP monolayers, especially INP-SiC, exhibit much higher values ( Y m a x / Y m i n = 157.41/109.98 N/m, G m a x / G m i n = 53.89/40.04 N/m), reflecting greater mechanical strength and stiffness. The Poisson’s ratio values are also higher in INP materials, indicating better isotropic behavior, with INP-SiC showing the highest ν m a x at 0.40. Notably, the IGPD monolayers exhibit a systematic redshift in their optical responses compared to those of their INP counterparts. The results underscore the influence of structural modifications on the electronic and optical properties of these materials.