Visualizing Van der Waals Epitaxial Growth of Two-Dimensional Heterostructures

TL;DR

This study employs in situ optical and spectroscopic techniques to reveal a new growth mode in 2D van der Waals heterostructures, providing insights into their formation mechanisms and potential for controlled synthesis.

Contribution

The paper introduces a novel in situ method to observe and model a new growth mode in 2D vdW heterostructures, expanding understanding of their synthesis.

Findings

Identification of a new growth mode with distinct morphology

Development of a model explaining growth rate differences

Systematic investigation of multiple material combinations

Abstract

Understanding the growth mechanisms of two-dimensional (2D) van der Waals (vdW) heterostructures is of great importance in exploring their functionalities and device applications. A custom-built system integrating physical vapor deposition and optical microscopy/Raman spectroscopy was employed to study the dynamic growth processes of 2D vdW heterostructures in situ. This allows us to identify a new growth mode with a distinctly different growth rate and morphology from those of the conventional linear growth mode. We propose a model that explains the difference in morphologies and quantifies the growth rates of the two modes by taking the role of surface diffusion into account. We have systematically investigated a range of material combinations including CdI2/WS2, CdI2/MoS2, CdI2/WSe2, PbI2/WS2, PbI2/MoS2, PbI2/WSe2 and Bi2Se3/WS2. These findings may be generalized to the synthesis of many other 2D heterostructures with controlled morphologies and physical properties, benefiting future device applications.