Few-Layer WS₂-WSe₂Lateral Heterostructures: Influence of the Gas Precursor Selenium/Tungsten Ratio on the Number of Layers

Two-dimensional (2D) lateral heterostructures based on transition metal dichalcogenides (TMDCs) attract great interest due to their properties and potential applications in electronics and optoelectronics, such as p-n rectifying diodes, light-emitting diodes, photovoltaic devices, and bipolar junction transistors. However, the studies of 2D lateral heterostructures have mainly focused on monolayer nanosheets despite bilayer heterostructures exhibiting higher performance in many electronic and optoelectronic devices. It remains a great challenge to synthesize lateral heterostructures with few layers. Here, we report the growth of bilayer-bilayer (bl-bl), bilayer-bilayer-monolayer (bl-bl-mo), bilayer-monolayer (bl-mo), monolayer-bilayer (mo-bl), and monolayer-monolayer (mo-mo) tungsten disulfide (WS2) and tungsten diselenide (WSe2) lateral heterostructures. The selenium/tungsten (Se/W) ratio of WSe2 precursor powders and the growth atmosphere can be changed with the extension of annealing time, which influences the layer number of the heterostructures. More bilayer WSe2 epitaxially grows at the WS2 edge with short annealing time (high Se/W ratio), and more monolayer WSe2 grows at the WS2 edge with long annealing time (low Se/W ratio). The density functional theory (DFT) calculations provide an in-depth understanding of the growth mechanism. This report expands the 2D material lateral heterostructure family, which gives impetus to their applications in electronics and optoelectronics.