Optical imaging of strain in two-dimensional crystals

Lukas Mennel,Dmitry K Polyushkin,Matthias Paur,Thomas Mueller,Stefan Wachter,Marco M Furchi

doi:10.1038/s41467-018-02830-y

Lukas Mennel, Dmitry K Polyushkin + Show 4 more

Open Access

https://doi.org/10.1038/s41467-018-02830-y

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Journal: Nature Communications	Publication Date: Feb 6, 2018
Citations: 195	License type: open-access

Affiliation: TU Wien

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 extraction of 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.

Highlights

Strain engineering is widely used in material science to tune theelectronic properties of materials and enhance the performance of devices
Xray diffraction (XRD) is employed, but submicron spatial resolution can in most cases only be achieved by the use of coherent radiation, e.g., from a synchrotron[16]
In a more thorough theoretical investigation, Lyubchanskii et al demonstrated that strain and nonlinear susceptibility are connected via a photoelastic tensor[36,37]

Summary

Introduction

Strain engineering is widely used in material science to tune the (opto-)electronic properties of materials and enhance the performance of devices. 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. While silicon typically breaks at strain levels of ~1.5%, two-dimensional (2D) atomic crystals[6] can withstand strain of >10%7,8, making them promising candidates for stretchable and flexible electronics[9] Their high flexibility further allows for folding or wrapping them around (lithographically defined) nanostructures to induce spatially inhomogeneous atom displacements. We adapt this theory and determine, to our knowledge for the first time, all photoelastic tensor elements of a material from SHG Once identified, these parameters allow us to spatially map the full strain tensor in a mechanically deformed 2D material with a spatial resolution below the diffraction limit of the excitation light. It establishes a novel optical strain probing technique that provides an unprecedented depth of information

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