Morphology Engineering Of Two-Dimensional MoS₂-WS₂ Lateral Heterostructures

In recent years,two-dimensional（2D）lateral heterojunctions have received extensive attention from researchers due to their novel physical properties above that of single component material.2D transition metal chalcogenides with different compositions,phase structures,and properties can offer great opportunities to construct novel 2D lateral heterostructures.At present,chemical vapor deposition（CVD）method has been considered as the most effective method to synthesize 2D lateral heterojunctions.Various lateral heterojunctions based on transition metal sulfides such as MoS₂-WS₂,MoS₂-MoSe₂,MoS₂-WSe₂,WSe₂-WS₂have been synthesized by CVD method.However,precisely controlling the morphology of lateral heterojunctions by one-step chemical vapor deposition remains a great challenge.Here,high-quality monolayer MoS₂-WS₂lateral heterojunctions were synthesized by one-step CVD method using molten salts such as Na₂Mo O₄and Na₂WO₄as precursor in this experiment.By adjusting growth parameters,such as growth temperature,the ratio of Mo source and W source in the precursor,growth time,gas flow,we realized morphology engineering of MoS₂-WS₂lateral heterojunction.A series of characterizations were performed on the prepared samples,which prove that monolayer MoS₂-WS₂lateral heterojunction synthesized in this experiment has good crystallinity.The main research contents are as follows:（1）We introduced a molten-liquid-intermediated chemical vapor deposition for the growth of MoS₂and WS₂.The effects of growth time,growth temperature and gas flow on the the WS₂samples were explored,and the controllable preparation of the WS₂samples was realized.High-quality monolayer MoS₂and WS₂with a grain size of hundreds of microns were successfully prepared.The morphology,thickness,optical properties and crystalline quality of the MoS₂and WS₂samples were characterized by Raman Spectroscopy,Photoluminescence Spectroscopy,Optical Microscope,Atomic Force Microscope,Scanning Electron Microscope and Transmission Electron Microscope,which prove that the monolayer MoS₂and WS₂prepared in this experiment have uniform thickness,clean surface and good crystallinity.（2）MoS₂-WS₂lateral heterojunctions were controllably synthesized by one-step chemical vapor deposition using molten-liquid-phase Na₂Mo O₄and Na₂WO₄as precursors.Morphology engineering of MoS₂-WS₂lateral heterojunction was realized by controlling gas flow,growth time,growth temperature and the ratio of Mo source and W source.The size of the heterojunction can be adjusted from～20μm to～200μm;the proportion of WS₂in the heterojunction can be adjusted from 0%to～60%.The morphology,thickness,optical properties and crystalline quality of the samples were characterized by Raman Spectroscopy,Photoluminescence Spectroscopy,Optical Microscope,Atomic Force Microscope,Scanning Electron Microscope and Transmission Electron Microscope,which prove that the monolayer MoS₂-WS₂lateral heterojunction prepared in this experiment has uniform thickness,clean surface,sharp interface and good crystallinity.