Controllable Preparation And Performance Study Of 2D TMDs

The wide variety of two-dimensional transition group metal-sulfide compounds（TMDs）with tunable band gaps and rich optical and electrical properties make them promising for a wide range of applications in electronics and optoelectronic devices.MoS₂ and WS₂ are the most representative two-dimensional semiconductor TMDs,with direct band gaps in monolayer MoS₂ and WS₂ and indirect band gaps in MoS₂/WS₂heterojunctions,which facilitate the effective separation of electron-hole pairs,making them ideal for optoelectronic devices.NbS₂ materials have great potential for the design and development of sensor devices.However,the large-scale preparation of NbS₂materials is still a major impediment to their development,and further optimisation of their preparation methods is required.This project focuses on the preparation of TMDs by Chemical Vapor Deposition（CVD）and further investigates the application of TMDs in the fields of photoelectric detection,hydrogen precipitation catalysis and moisture-sensitive sensing.The details are as follows:（1）MoS₂,WS₂ and MoS₂/WS₂ heterojunctions can be prepared in a controlled manner by CVD,and the grown materials were characterised by Raman,AFM and XPS to demonstrate their high crystallinity.The photodetectors were prepared based on MoS₂/WS₂ heterojunctions and their photodetective properties at 488,532 and 633 nm were investigated.The best performance at 633 nm was obtained with a response value of 431.9 m A/W,a detection rate D*of 418.1×10¹¹ Jones,an external quantum efficiency of 100.64%and a photoresponse time of 37.1μs.（2）A method for the growth of NbS₂ single crystals and nanosheets by CVD using copper foil and carbon cloth as substrates is proposed.A method for the growth of NbS₂single crystals and nanosheets by CVD using copper foil and carbon cloth as substrates is proposed.The controlled preparation of NbS₂ single crystals and nanosheets is achieved by regulating the growth conditions such as growth temperature,growth time and gas flow rate,and the grown materials are verified to be highly crystalline,homogeneous and up to tens of microns in size using Raman spectroscopy,atomic force microscopy（AFM）,X-ray photoelectron spectroscopy（XPS）,X-ray diffraction（XRD）and scanning electron microscopy（SEM）.（3）The hydrogen precipitation and moisture-sensitive properties of NbS₂nanosheets grown on copper foil and carbon cloth substrates were investigated.The effects of growth temperature,growth time and gas flow rate on the hydrogen precipitation catalytic performance were investigated,and the best hydrogen precipitation performance was obtained:the overpotential was 274 m V and the Tafel slope was 144 m V/dec,which was found to be due to the increased hydrophilicity and specific surface area of the material.The best humidity sensing performance was obtained with a response time and recovery time of about 4 s.