Imaging the crystal orientation of 2D transition metal dichalcogenides using polarization-resolved second-harmonic generation

Abstract

We use laser-scanning nonlinear imaging microscopy in atomically thin transition metal dichalcogenides (TMDs) to reveal information on the crystalline orientation distribution, within the 2D lattice. In particular, we perform polarization-resolved second-harmonic generation (PSHG) imaging in a stationary, raster-scanned chemical vapor deposition (CVD)-grown WS 2 flake, in order to obtain with high precision a spatially resolved map of the orientation of its main crystallographic axis (armchair orientation). By fitting the experimental PSHG images of sub-micron resolution into a generalized nonlinear model, we are able to determine the armchair orientation for every pixel of the image of the 2D material, with further improved resolution. This pixel-wise mapping of the armchair orientation of 2D WS 2 allows us to distinguish between different domains, reveal fine structure, and estimate the crystal orientation variability, which can be used as a unique crystal quality marker over large areas. The necessity and superiority of a polarization-resolved analysis over intensity-only measurements is experimentally demonstrated, while the advantages of PSHG over other techniques are analysed and discussed.

Nonlinear Optical Characterization of 2D Materials

“…For 2D materials with inversion symmetry broken, such as MoS 2 and WS 2 [ 56 ], it is found that the SHG signal can only be observed in odd-numbered layers, but it disappears in even-numbered layers. In the early research, the strong SHG response of the odd layer was used to effectively determine the crystal axis orientation of the crystal through the polarized SHG method.…”

Helicity-dependent THz emission induced by ultrafast spin photocurrent in nodal-line semimetal candidate Mg3Bi2

“…L 2 represents the photon drag effect (PDE), which is linked by the linear momentum transfer between incident photons and electrons. Optical rectification (OR), as a second-order nonlinear optical process, is the major process to coefficient D, which is following the well-known second-harmonic generation in noncentrosymmetric materials 7,19,30,35,38,39 .…”

Realization of noncontact confocal optical microsphere imaging microscope

“…Microsphere nano‐imaging encounters the similar challenge (Chen, Zhou, Zhou, & Hong, 2020). To enhance the contrast, one can improve the microscope illumination condition (e.g., polarization) and via image processing (Maragkakis et al, 2019; Westphal & Hell, 2005). The contrast of a conventional microscope can be enhanced by decreasing the background noise of the image obtained.…”