Two-dimensional kagome semiconductor Sc₆S₅X₆ (X = Cl, Br, I) with trilayer kagome lattice

Two-dimensional (2D) multilayer kagome materials hold significant research value for regulating kagome-related physical properties and exploring quantum effects. However, their development is hindered by the scarcity of available material systems, making the identification of novel 2D multilayer kagome candidates particularly important. In this work, three types of 2D materials with trilayer kagome lattices, namely Sc₆S₅X₆ (X = Cl, Br, I), are predicted based on first-principles calculations. These 2D materials feature two kagome lattices composed of Sc atoms and one kagome lattice composed of S atoms. Stability analysis indicates that these materials can exist as free-standing 2D materials. Electronic structure calculations reveal that Sc₆S₅X₆ are narrow-bandgap semiconductors (0.76–0.95 eV), with their band structures exhibiting flat bands contributed by Sc-based kagome lattices and Dirac band gaps resulting from symmetry breaking. The sulfur-based kagome lattice in the central layer contributes an independent flat band below the Fermi level. Additionally, Sc₆S₅X₆ exhibit high carrier mobility, with hole and electron mobilities reaching up to 10³ cm²⋅V⁻¹⋅s⁻¹, indicating potential applications in low-dimensional electronic devices. This work provides an excellent example for the development of novel multilayer 2D kagome materials.