Unraveling the Superior Stability of 3–5-Layer α7-Borophene

The discovery of bilayer borophene has highlighted the importance of interlayer covalent B−B bonds in addressing the stability challenges of air-sensitive monolayer borophene, which showcases promising attributes for diverse electronic and energy applications. Yet, investigations into multilayer borophene structures, particularly beyond the bilayer, are sparse. In this study, we conducted a systematic investigation of the geometries, stabilities, electronic structures, and work functions of 2- to 5-layer α7- and α8-borophene using density functional theory calculations, based on different stacking modes. Remarkably, we identified metallic 3- to 5-layer configurations of α7-borophene (α7ABA, α7ABAbB, and α7ABABA), each demonstrating the highest thermodynamic stability reported to date for their respective layer numbers. Additionally, the 3- to 5-layer α8-borophene variants, including α8AAB, α8AABbA, and α8AABAB, also exhibited significant thermodynamic stability, ranking second highest among the borophene configurations examined. With increasing layer number from 2 to 5, the influence of in-plane orbitals (s, px, and py) on in-plane bonding became more pronounced, while their effect on interlayer interactions diminished. This evolution led to greater geometric distortion within the layers and enhanced in-plane binding, resulting in higher overall binding energies in both the α7- and α8-borophene series. Importantly, the calculated work functions for the 3- to 5-layer α7- and α8-borophene were found to be comparable to that of graphene (4.37–4.60 eV), suggesting that these multilayer borophene materials could potentially serve as viable alternatives to graphene. Overall, these findings offer valuable insights into the structural and electronic properties of multilayer borophene, paving the way for its integration into future nanotechnology applications.