Tailoring linear and nonlinear optical properties of 2D Sc₂C MXenes via surface termination modulation

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Surface termination engineering is crucial for tuning the optoelectronic properties of two-dimensional (2D) MXenes.
• Scandium-based MXenes (Sc₂CT_x) are promising candidates for optoelectronic applications.
• Understanding the relationship between surface termination and nonlinear optical (NLO) responses is essential.

Purpose of the Study:

• To systematically investigate the stability and second-order NLO responses of Sc-based MXenes with varying surface terminations (O, F, OH).
• To identify stable Sc-MXene phases with tunable electronic and optical properties.
• To explore the potential of these materials for frequency conversion applications.

Main Methods:

• Theoretical investigation of twelve termination configurations for Sc₂CT_x.
• Calculation of dynamical stability and electronic band structures.
• Computation of second-order nonlinear optical (NLO) responses, including static second-harmonic generation (SHG) coefficients.
• Band and atomic-resolved susceptibility decomposition analysis.

Main Results:

• Identified six dynamically stable Sc-MXene phases, including mixed-termination configurations, with band gaps tunable from 0.56 to 1.82 eV.
• Sc₂C(OH)₂ demonstrated a giant static SHG coefficient of 191.4 pm V^-1, surpassing benchmark NLO crystals.
• Sc₄C₂F(OH)₃ exhibits a significant SHG response (d₁₂ = 185.0 pm V^-1) and mid-infrared transparency.

Conclusions:

• Sc-based MXenes are highly efficient platforms for frequency conversion due to their tunable NLO properties.
• The Sc-3d orbital covalency, modulated by termination electronegativity, dictates the SHG response.
• Surface engineering provides a general strategy for optimizing NLO performance in 2D materials.