Liu, L; Xie, C; Tudi, A; Butler, K; Yang, Z; (2025) Two-dimensional graphene-like BeO sheet: a promising deep-ultraviolet nonlinear optical material with strong and highly tunable second harmonic generation. Science China Materials , 68 (12) pp. 4566-4574. 10.1007/s40843-025-3680-8.

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Abstract

Two-dimensional (2D) materials with large band gaps and strong and tunable second-harmonic generation (SHG) coefficients play an important role in the miniaturization of deep-ultraviolet (DUV) nonlinear optical (NLO) devices. Despite the existence of numerous experimentally synthesized 2D materials, none of them have been reported to meet DUV NLO requirements. Herein, an experimentally available graphene-like BeO monolayer created only by NLO-active [BeO<inf>3</inf>] units is suggested as an excellent 2D DUV NLO material because of its ultrawideband gap (6.86 eV) and a strong SHG effect (χ<inf>22</inf>⁽²⁾(2D) = 6.81 Å pm/V) based on first-principles calculations. By applying stacking, strain, and twist engineering methods, numerous 2D BeO sheets have been predicted, and their flexible structural characteristics provide them with tunable NLO propertie s. Remarkably, the extremely stress-sensitive out-of-plane χ<inf>15</inf>⁽²⁾(2D) and χ<inf>33</inf>⁽²⁾(2D) (with an exceptional 30% change) and robust in-plane χ<inf>22</inf>⁽²⁾(2D) against large strains can be achieved together in AC- and ACE-stacked BeO sheets under in-plane biaxial strain, exhibiting emergent phenomena uniquely not observed in other known 2D NLO materials. Our results reveal that 2D BeO systems should be a new option for 2D DUV NLO materials. (Figure presented.).

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