Sumanene Monolayer of Pure Carbon: A Two‐Dimensional Kagome‐Analogy Lattice with Desirable Band Gap, Ultrahigh Carrier Mobility, and Strong Exciton Binding Energy

Abstract The design and synthesis of novel two‐dimensional (2D) materials that possess robust structural stability and unusual physical properties may open up enormous opportunities for device and engineering applications. Herein, a 2D sumanene lattice that can be regarded as a derivative of the conventional Kagome lattice is proposed. The tight‐binding analysis demonstrates sumanene lattice contains two sets of Dirac cones and two sets of flat bands near the Fermi surface, distinctively different from the Kagome lattice. Using first‐principles calculations, two possible routines for the realization of stable 2D sumanene monolayers (named α phase and β phase) are theoretically suggested, and an α‐sumanene monolayer can be experimentally synthesized with chemical vapor deposition using C₂₁H₁₂ as a precursor. Small binding energies on Au(111) surface (e.g., −37.86 eV Å⁻² for α phase) signify the possibility of their peel‐off after growing on the noble metal substrate. Importantly, the GW plus Bethe–Salpeter equation calculations demonstrate both monolayers have moderate band gaps (1.94 eV for α) and ultrahigh carrier mobilities (3.4 × 10⁴ cm² V⁻¹ s⁻¹ for α). In particular, the α‐sumanene monolayer possesses a strong exciton binding energy of 0.73 eV, suggesting potential applications in optics.