Research On Controlled Growth And Optoelectronic Properties Of Dendritic TMDs

As one of the most important members of the two-dimensional materials family,transitional metal dichalcogenides（TMDs）are perfectly suited for optoelectronic devices because of their excellent properties such as modifiable band gap,graphene-like structure and high electron mobility.TMDs have a wide range of prospects in optoelectronic devices.In addition,TMDs have a wide range of applications in the fields of heat,force,magnetism,and electricity.However,the research on TMDs is not comprehensive yet,and most of the TMDs grown by chemical vapor deposition（CVD）are triangular in shape due to the structural symmetry,and the research on dendritic TMDs is rare.Dendritic TMDs are able to combine the inherent symmetry of crystals and at the same time,give surface lattice defects to triangular TMDs through dendritic morphology to achieve the purpose of material modification.Therefore,the controllable preparation of dendritic TMDs is the key to enhance their development space.After the completion of the controllable preparation in the field of optoelectronics,it is found that it has a large application prospect,and the specific work is as follows:（1）Controlled preparation and structural characterization of dendritic WS₂:The optimal parameters for the growth of dendritic WS₂(dendritic WS₂/monolayer WS₂were determined by comparing the effects of four conditions,including growth temperature,growth time,precursor mass ratio,and carrier gas flux,on the growth of dendritic WS₂.Next,the morphological evolution of dendritic WS₂in CVD was investigated,and the samples were divided into four regions-superimposed growth region,dendritic growth region,hexagonal growth region,and no specific morphological growth region-according to their different morphologies in the substrate.The reason for the morphology evolution was explained using the sulfur-tungsten vapor ratio.The dendritic WS₂was confirmed to be an atomic-level thickness film by characterization means of scanning electron microscopy and transmission electron microscopy.（2）Controlled preparation and structural characterization of dendritic MoS₂:To expand the variety of dendritic TMDs,the effects of various parameters on the nucleation and morphology of dendritic MoS₂were investigated based on the growth of dendritic WS₂,and dendritic MoS₂with high crystal quality was prepared,further demonstrating that the high temperature,sulfur-rich,and high airflow CVD environment is favorable for the controlled growth of dendritic TMDs and providing a reference for the preparation of other dendritic TMDs.Various characterizations of dendritic TMDs reveal that they are different from TMDs in terms of band gap,defect density of states,specific surface,etc.,which are helpful for the application of TMDs in optoelectronic,catalytic,gas-sensitive and other fields.（3）Study of the photovoltaic properties of dendritic WS₂:The dendritic WS₂/monolayer WS₂FET was constructed by photolithography,and the electrical characteristics of the device were tested,obtaining an optical responsivity of 0.49m A/W and response and recovery times of 121 and 135μs.On this basis,dendritic WS₂/monolayer WS₂/Pb S heterostructured devices were constructed to test the device performance and it was found that the dendritic WS₂/monolayer WS₂enhanced the Pb S photocurrent.In addition,the dendrite WS₂/monolayer WS₂/Pb S heterostructure was optimised by preparing Si/dendrite WS₂/monolayer WS₂/Pb S trilayer heterostructure devices.The optical responsiveness and specific detectivity of the device were tested to be 2.7×10^-2m A/W,3.2×10⁸Jones,0.45 m A/W and 3.9×10⁷Jones for the near infrared and visible wavelengths respectively.The better performance parameters were obtained to achieve the design purpose of wide band detection.The dendritic WS₂and dendritic MoS₂were successfully prepared by tuning the CVD parameters,providing a reference for the preparation of other dendritic TMDs.In addition,the dendritic WS₂exhibits good optoelectronic properties which are expected to be further investigated in the field of photodetectors.