Two-Dimensional Aluminum Boride AlB₄ Nanosheets as a Platform to Architecture Very Rare Semiconducting Phase and Superconductor

Abstract

Semiconducting phase is extremely rare and difficult to be realized in two-dimensional (2D) aluminum borides. Here, we for the first time report the discovery of a rarely semiconducting allotrope (labeled as AlB₄-1) in 2D AlB₄ nanosheets. This semiconductor is the global minimum structure in 2D space with two layers stacked together connected by strong Al-B bonds. Systematic studies demonstrate the high thermodynamic, lattice dynamic, thermal, and mechanical stabilities of AlB₄-1. More importantly, this semiconducting AlB₄-1 shows fascinating properties and promising applications, such as, the optimal band gap (1.156 eV at HSE06 level), high carrier mobility (up to 3.14 × 10³ cm²V⁻¹s⁻¹), substantially high solar energy conversion efficiency (21.9 %) and large optical response (10⁶ cm⁻¹) in the visible region. Extensive studies indiate that h-BN can serve as an effective substrate to support and encapsulate AlB₄-1 with minimal impact on the electronic properties of AlB₄-1, laying the foundation for the real application of AlB₄-1 in electronic devices. Besides this semiconducting phase, other low-lying allotropes (AlB₄-2 to -11) also display high stabilities, exotic properties and diverse applications. For example, the metallic AlB₄-4 shows Dirac cone near Fermi level and superconductivity with T_C as high as 23.4K, which can be substantially enhanced to 34.1K at tensile strain of 11%. These allotropes with different shapes show diverse hypercoordinate motifs with unusual bonding patterns. Comprehensive studies demonstrate that 2D AlB₄ nanosheets is a class of highly stable, multifunctional nanomaterials for diverse applications in electronics, optics, optoelectronics, nanodevices, solar energy conversion, superconductivity, nanomechanics, and so on. The present study will provide useful guidance in fabricating these interesting nanostructures and stimulate both experimental and computational efforts in this direction.

Keywords

carrier mobility / electronic structure / solar energy conversion efficiency / superconductivity / 2D aluminum boride nanosheets

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2025 The Author(s). SusMat published by Sichuan University and John Wiley & Sons Australia, Ltd.