# Optical imaging of strain in two-dimensional crystals

## TL;DR

This paper introduces a novel optical second harmonic generation technique capable of mapping the full strain tensor in two-dimensional crystals with sub-diffraction spatial resolution, advancing strain imaging methods.

## Contribution

It demonstrates the use of SHG to extract the full strain tensor in 2D materials, surpassing traditional optical methods in resolution and detail.

## Key findings

- SHG allows full strain tensor extraction in 2D crystals.
- The method achieves spatial resolution below the diffraction limit.
- Photoelastic tensor elements of MoS2 were determined.

## Abstract

Strain engineering is widely used in material science to tune the (opto-)electronic properties of materials and enhance the performance of devices. Two-dimensional atomic crystals are a versatile playground to study the influence of strain, as they can sustain very large deformations without breaking. Various optical techniques have been employed to probe strain in two-dimensional materials, including micro-Raman and photoluminescence spectroscopy. Here we demonstrate that optical second harmonic generation constitutes an even more powerful technique, as it allows to extract the full strain tensor with a spatial resolution below the optical diffraction limit. Our method is based on the strain-induced modification of the nonlinear susceptibility tensor due to a photoelastic effect. Using a two-point bending technique, we determine the photoelastic tensor elements of molybdenum disulfide. Once identified, these parameters allow us to spatially image the two-dimensional strain field in an inhomogeneously strained sample.

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Source: https://tomesphere.com/paper/1903.02970