The development of Van der Waals heterostructures has enabled the fabrication of diverse layered materials by stacking different 2D materials with precise control over composition and twist angle. This flexibility optimizes material properties and allows unique characteristics, advancing applications in electronics and photonics [ 1]. Novel properties in heterostructures emerge from complex architectures, where layers with differing crystallographic symmetries and lattice constants form moiré superlattices with alternating high-symmetry regions in which the top and bottom layers align locally with varied metal-chalcogen positioning. While Transmission Electron Microscopy (TEM) has been crucial for directly observing structural changes within moiré patterns [ 2, 3], comprehensive studies on hetero-growth via interlayer interactions—where one layer grows on a differently structured layer—remain limited.
In this study, we analyzed MoS 2 patches in a MoS 2/WSe 2 vertical heterostructure synthesized via two-step growth, where the upper MoS 2 layer was directly grown on a monolayer WSe 2. The focus is to elucidate the structural changes that arise when dissimilar layers align in Van der Waals heterostructures, where greater deviation in lattice mismatch leads to strain and localized effects. To examine growth behavior in aligned heterostructures having significant lattice mismatch, patch sizes were controlled by varying annealing times. An overall assessment of the patches was conducted using Raman spectroscopy and Selected Area Diffraction Pattern (SADP) techniques.
Notably, unlike mechanically assembled heterostructures, over 90% of the MoS 2 patches aligned with the crystal symmetry of the underlying WSe 2, either parallel or anti-parallel. The lower frequencies and higher FWHM in the E 2g mode of MoS 2 grown on WSe 2, compared to freestanding MoS 2, indicate a coupled heterostructure where MoS 2 layer experiences deformation in the heterostructure due to its alignment with the underlying WSe 2 layer ( Fig. 1a) [ 4].
Fig. 1
a, Comparison of Raman spectroscopy results for the intralayer modes of MoS 2 and WSe 2 mono-layers with those of the MoS 2/WSe 2 heterostructure, showing E 2g and A 1g modes near 250 cm -1 for WSe 2 and near 400 cm -1 for MoS 2. b, Lattice Mismatch calculated by Selected Area Diffraction Pattern for aligned stacked (Parallel & Anti-Parallel stacked) and Twisted samples.
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