Direct Measurement of Folding Angle and Strain Vector in Atomically Thin WS₂ Using Second-Harmonic Generation

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Strain engineering and folding in 2D materials modulate optoelectronic properties.
• Accurate measurement of nanoscale strain and folding is crucial for device optimization.
• Conventional methods for strain/folding analysis are time-consuming and costly.

Purpose of the Study:

• To demonstrate a single-tool method for accurate and efficient determination of folding angle and strain vector in ultrathin WS2.
• To utilize polarization-dependent second-harmonic generation (SHG) for nanoscale structural analysis.
• To establish SHG as a powerful probe for optoelectronic device optimization.

Main Methods:

• Employing polarization-dependent second-harmonic generation (SHG) on ultrathin WS2.
• Analyzing SHG enhancement factor, phase difference, and linear dichroism to probe folding angles.
• Utilizing strain-dependent SHG quenching/enhancement and a photoelastic approach to determine strain vectors.

Main Results:

• SHG accurately determines folding angles in trilayer WS2 folds, showing 1-9 times enhancement.
• Compressive strain vectors are precisely mapped using SHG response parallel and perpendicular to the strain.
• SHG sensitivity to band-nesting-induced transitions (C-peak) is confirmed, showing strain modulation.

Conclusions:

• Polarization-dependent SHG is a powerful, single-tool method for analyzing nanoscale structural parameters in 2D materials.
• This technique offers accurate and efficient measurement of folding angles and strain vectors.
• SHG provides a pathway for optimizing the performance of 2D material-based optoelectronic devices.