Strain-dependent anisotropic nonlinear optical response in two-dimensional functionalized MXene Sc2CT2 (T = O and OH)

Abstract

Tunable optical properties play an important role in the high performance of optoelectronic applications based on two-dimensional (2D) transition metal carbide and nitride (MXene) materials. Herein, the optical properties of functionalized MXene monolayers Sc₂CT₂ (T = O and OH) are investigated by strain engineering. The strain-dependent linear optical properties of Sc₂CT₂ possess broadband optical response due to the geometry and orbital overlap effect. The peaks from the second-order nonlinear coefficient elements d (d₁₅, d₁₆, and d₃₁) at around half the band-gap exhibit a redshift for Sc₂CO₂ (blueshift for Sc₂C(OH)₂) with the increase of strain. The strain-dependent d reveals that Sc₂CO₂ with −1268 pm V⁻¹ %⁻¹ has a larger photoelastic coefficient than that of Sc₂C(OH)₂ with −574 pm V⁻¹ %⁻¹ at 1% strain. Meanwhile, the photoelastic tensors can not only be increased but also reduced with the increase of strain due to the dispersion relation. Moreover, the azimuthal angle-dependent second harmonic generation (SHG) from strained Sc₂CT₂ monolayers depends highly on the strained states and the pumping photon energy. The results pave the way for the tunable, broadband, and anisotropic applications of nonlinear optoelectronic devices based on MXenes based on strain engineering.