Optical imaging of strain in two-dimensional crystals

• Published in: Nature communications Vol. 9; no. 1; pp. 516 - 6
• Main Authors: Mennel, Lukas, Furchi, Marco M., Wachter, Stefan, Paur, Matthias, Polyushkin, Dmitry K., Mueller, Thomas
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 06-02-2018; Nature Publishing Group; Nature Portfolio
• Subjects: 639/925/918/1053; 639/925/918/1054; Crystal lattices; Crystals; Deformation; Humanities and Social Sciences; Molybdenum; Molybdenum disulfide; multidisciplinary; Optics; Parameter identification; Photoluminescence; Photons; Science; Science (multidisciplinary); Second harmonic generation; Spatial discrimination; Spatial resolution; Spectroscopy; Symmetry
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-018-02830-y

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.
Strain is an effective tool to tune the optoelectronic properties of two-dimensional materials. Here, the authors demonstrate that second harmonic generation can be used to extract the full strain tensor of MoS
2
and to spatially image its two-dimensional strain field.