Visualizing Van der Waals Epitaxial Growth of 2D Heterostructures.

Understanding the growth mechanisms of 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 is employed to study the dynamic growth processes of 2D vdW heterostructures in situ. This allows the identification of a new growth mode with a distinctly different growth rate and morphology from those of the conventional linear growth mode. 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 is proposed. A range of material combinations including CdI2 /WS2 , CdI2 /MoS2 , CdI2 /WSe2 , PbI2 /WS2 , PbI2 /MoS2 , PbI2 /WSe2 , and Bi2 Se3 /WS2 is systematically investigated. These findings may be generalized to the synthesis of many other 2D heterostructures with controlled morphologies and physical properties, benefiting future device applications.