Growth of Single-Crystalline Cadmium Iodide Nanoplates, CdI₂/MoS₂ (WS₂, WSe₂) van der Waals Heterostructures, and Patterned Arrays.

Abstract

Two-dimensional layered materials (2DLMs) have attracted considerable recent interest for their layer-number-dependent physical and chemical properties, as well as potential technological opportunities. Here we report the synthesis of two-dimensional layered cadmium iodide (CdI₂) nanoplates using a vapor transport and deposition approach. Optical microscopy and scanning electron microscopy studies show that the resulting CdI₂ nanoplates predominantly adopt hexagonal and triangular morphologies with a lateral dimension of ∼2-10 μm. Atomic force microscopy studies show that the resulting nanoplates exhibit a thickness in the range of 5-220 nm with a relatively smooth surface. X-ray diffraction studies reveal highly crystalline CdI₂ in hexagonal phase, which is also confirmed by the characteristic Raman A_g mode at 110 cm^-1. High-resolution transmission electron microscopy and selected area electron diffraction reveal that the resulting CdI₂ nanoplates are single crystals. Taking a step further, we show the CdI₂ nanoplates were readily grown on other 2DLMs (e.g., WS₂, WSe₂, MoS₂), forming diverse van der Waals heterostructures. Using prepatterned WS₂ monolayer square arrays as the nucleation and growth templates, we also show that regular arrays of CdI₂/WS₂ vertical heterostructures can be prepared. The synthesis of the CdI₂ nanoplates, heterostructures, and heterostructure arrays offers a valuable material system for 2D materials science and technology.