Optical imaging of strain in two-dimensional crystals

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Strain engineering is crucial for tuning optoelectronic properties and device performance in materials.
• Two-dimensional (2D) atomic crystals are ideal for studying strain effects due to their high deformability.
• Existing optical methods like Raman and photoluminescence spectroscopy have limitations in strain analysis.

Purpose of the Study:

• To demonstrate optical second harmonic generation (SHG) as a superior technique for strain analysis in 2D materials.
• To achieve full strain tensor extraction with sub-diffraction limit spatial resolution.
• To investigate the photoelastic effect in molybdenum disulfide (MoS2) under strain.

Main Methods:

• Utilized optical second harmonic generation (SHG) to probe strain-induced modifications of the nonlinear susceptibility tensor.
• Employed a two-point bending technique to apply controlled strain to molybdenum disulfide (MoS2) samples.
• Determined the photoelastic tensor elements of MoS2 based on SHG response.

Main Results:

• Optical SHG allows for the extraction of the complete strain tensor in 2D materials.
• The technique achieves a spatial resolution below the optical diffraction limit.
• Successfully mapped the 2D strain field in an inhomogeneously strained MoS2 sample using determined photoelastic parameters.

Conclusions:

• Optical second harmonic generation is a powerful, high-resolution technique for characterizing strain in 2D materials.
• The photoelastic effect in MoS2 was quantified, enabling precise strain mapping.
• This method offers significant advantages over conventional optical spectroscopy for strain analysis in nanostructured materials.