Dual-Polarization SHG Interferometry for Imaging Antiparallel Domains and Stacking Angles of 2D Heterocrystals

TL;DR

This paper introduces dual-polarization spectral phase interferometry (DP-SPI) for imaging and analyzing antiparallel domains and stacking angles in 2D heterocrystals, overcoming limitations of traditional intensity-based SHG methods.

Contribution

The work develops a generalized SHG superposition model and demonstrates DP-SPI for layer-resolved imaging and design of TMD heterostructures, advancing crystallographic analysis of 2D materials.

Findings

Successfully imaged antiparallel domains in monolayer TMDs.

Determined layer orientations in TMD heterobilayers.

Enabled design of ternary TMD heterostructures for circular SHG.

Abstract

Optical second-harmonic generation (SHG) enables orientational polarimetry for crystallographic analysis and domain imaging of various materials. However, conventional intensity polarimetry, which neglects phase information, fails to resolve antiparallel domains and to describe two-dimensional heterostructures, which represent a new class of van der Waals-bound composite crystals. In this work, we report dual-polarization spectral phase interferometry (DP-SPI) and establish a generalized SHG superposition model that incorporates the observables of DP-SPI. Antiparallel domains of monolayer transition metal dichalcogenides (TMDs) were successfully imaged with distinction, validating the interferometric polarimetry. From DP interferograms of TMD heterobilayers, the orientation of each layer could be determined, enabling layer-resolved probing. By employing the superposition model, we also demonstrate the photonic design and fabrication of ternary TMD heterostructures for circularly polarized SHG. These methods, providing comprehensive SHG measurements and theoretical description, can be extended to heterostructures consisting of more than two constituent layers and are not limited to TMDs or 2D materials.