Strain-tunable electronic properties of 2D-B9: a borophene allotrope with mechanical flexibility

In this work, we explore the structural, mechanical, and electronic properties of 2D-B9, a borophene allotrope with a unique bonding structure and promising potential for strain engineering. Through first-principles calculations, we investigate the material's stability, revealing a robust phonon spectrum and favorable mechanical flexibility, including isotropic behavior and a moderate Young's modulus. The electronic structure of 2D-B9 features key characteristics such as a van Hove singularity (vHS) and a Dirac point, which can be dynamically tuned via strain. Under tensile strain, the vHS shifts downward, while compressive strain causes it to rise, with the vHS aligning with the Fermi level at 10% compression. This strain-induced tuning of the electronic structure is further confirmed by examining changes in Fermi velocity, which is found to be similar to that of graphene at 9 × 10⁵m s^-1, indicating high electronic mobility. These results highlight the potential of 2D-B9 for applications in flexible electronics, quantum devices, and other technologies where strain-sensitive electronic properties are essential.