Rippling-induced stabilization and property modulation in freestanding two-dimensional B2O3

Abstract

Two-dimensional (2D) boroxol-based B2O3 has recently been experimentally realized on metal substrates [Zio et al., Science 390, 95–99 (2025)], providing the first crystalline polymorph of B2O3 composed exclusively of boroxol units. However, the intrinsic structural stability and equilibrium geometry of freestanding 2D B2O3 remain unresolved. In this work, we investigate the intrinsic structural stability and physical properties of freestanding 2D boroxol-based B2O3 using first-principles calculations. While a perfectly planar monolayer is dynamically unstable, allowing spontaneous out-of-plane rippling stabilizes the lattice. The most stable rippled configuration lowers the total energy by ∼8 meV per B2O3 unit and satisfies both dynamical and elastic stability criteria. Rippling significantly modulates the electronic and mechanical properties: the indirect bandgap increases slightly, and the in-plane mechanical response becomes strongly anisotropic. Our results establish intrinsic rippling as a key stabilization mechanism in freestanding 2D B2O3 and provide guidance for its transfer, strain engineering, and mechanical tuning in boroxol-based 2D oxides.