Regulation Of WS₂/MoS₂ Heterostructure Thin Films And Study On Their Photoluminescence Properties

As an important component of two-dimensional(2D)materials,2D transition metal dichalcogenides(TMDs)have become a research hotspot in the applications of electronics,physics,materials science and other fields in recent years due to their unique physical properties when their thickness is within atomic-level.Moreover,this kind of material has attracted much attention in the fields of electricity,optics,quantum,energy,etc.Also,different kinds of TMDs are assembled into various heterostructures by vertical stacking or in-plane bonding,which have the characteristic of 2D,band gap adjustable,heterostructure interface and other characteristics,showing a series of novel properties.It has opened the way for the research and application of a new generation of high-performance optoelectronic devices.WS₂/MoS₂ heterostructure was prepared by the Na Cl-assisted one-step chemical vapor deposition(CVD)method with WO₃,MoO₃ and S powder as the reaction sources.To achieve the controllable preparation of WS₂/MoS₂ heterostructure films with few atomic layers and further study its photoluminescence(PL)properties,the following six experimental factors were optimized:the amount of S source,growth temperature,growth time,mass ratio of tungsten source to molybdenum source,the distance between S source and metal source,and the flow rate of carrier gas.Firstly,the most appropriate S powder dosage in this experimental work was 160 mg which is obtained through six-factor and five-level orthogonal experiment and the single-factor experiment of the dosage of S powder.Then,based on this amount of S powder,the influence degree of each factor on the vertical heterostructure area was clear through five-factor and four-level orthogonal experiment,which is:growth temperature>WO₃:MoO₃ mass ratio>source spacing>Ar flow>growth time.Next,the single-factor experiment of growth temperature and WO₃:MoO₃ mass ratio were used to further optimize the process parameters,and the optimal preparation conditions of WS₂/MoS₂ vertical heterostructure in atmospheric pressure CVD system were obtained.Finally,the optimized process parameters were used for low-pressure CVD single-factor experiment.The results show that as the pressure of the reaction system gradually decreases,the type of WS₂/MoS₂ heterostructure changes from vertical to hybrid and then to in-plane.The different types of WS₂/MoS₂ heterostructures were obtained after process optimization,which are all based on the single material of double-layer WS₂ and double-layer MoS₂.The study of PL performance of the prepared WS₂/MoS₂ heterostructure includes the comparison of PL test results of heterostructure and single material,the PL test characterization of vertical heterostructure prepared by different processes,and the PL test characterization of different regions of three typical heterostructures(vertical,hybrid and in-plane).The results show that the formation of the three heterostructures all contribute to the space separation of photogenerated carriers,which leads to the obvious quenching of the PL intensity in the heterogeneous region,and a new exciton transition is produced at the interface which is different from the intrinsic exciton transition of the single material.In addition,the PL performance of WS₂ and MoS₂ exhibit layer-dependent characteristics in both single material and heterostructure.Moreover,the area and stress factors will also affect the PL performance of the heterogeneous region.