Probing Noncentrosymmetric 2D Materials by Fourier Space Second Harmonic Imaging

TL;DR

This paper introduces a rapid Fourier space SHG imaging method to determine the crystal orientation of 2D materials like TMDs and hBN, improving efficiency over traditional polarization rotation techniques.

Contribution

The authors develop a Fourier space SHG imaging technique using azimuthally polarized laser beams for quick, accurate crystal orientation determination in 2D materials.

Findings

SHG images reflect crystal lattice structure clearly

Method provides faster orientation measurement

Applicable to various 2D materials

Abstract

The controlled assembly of twisted 2D structures requires precise determination of the crystal orientation of their component layers. In the established procedure, the second-harmonic generation (SHG) intensity of a noncentrosymmetric layer is recorded while rotating the polarization of both the incident laser field and detected SHG, which can be time-consuming and tedious. Here, we demonstrate that the crystal orientation of transition metal dichalcogenides and hexagonal boron nitride can be directly determined by recording SHG images generated by tightly focused laser beams in Fourier space. Using an azimuthally polarized laser beam, the SHG image distinctly reflects the hexagonal structure of the crystal lattice, revealing its orientation quickly and accurately. This technique could significantly impact the field of twistronics, which studies the effects of the relative angle between the layers of a stacked 2D structure, as well as advances the nanofabrication of 2D materials.