Study On Preparation And Electrical Properties Of Two-dimensional Tungsten Sulfide And Niobium Sulfide

Transition metal dichalcogenides?TMDCs?are layered materials with graphene-like structure.Due to their unique crystal structure,they have exhibited many special physical properties,and have been the focus of new materials and advanced manufacturing research recently.As a great deal of researches have shown,TMDCs have nearly ideal carrier mobility,which makes them a wide prospect of application in field effect transistor,electrophotonic detector,gas sensors,etc.This paper focuses on the controlled preparation of TMDCs.The influence of process parameters on the preparation of mono-layer crystal WS₂and two-dimensional NbS₂ by CVD,and the electrical characteristics test of FET based on WS₂ was mainly studied.The main conclusions of this thesis are as follows:To achieve controllable preparation of WS₂,We analyzed the influences of each process parameter on the shape and size of WS₂,the optimum parameters of the growth of WS₂ were determined.That is,a temperature of 750°C,a holding time of 10 min,an Ar flow rate of 100sccm,an amount of WO₃ of 30 mg,an amount of sulfur powder of 500 mg.On the basis of this,an equiaxed film about 50?m in size was successfully prepared.The prepared WS₂ film was characterized by composition and structure.The quantitative analysis results of XPS and EDS showed that the atom ratio of W and S is close to 1:2,which proved that the prepared film was WS₂.AFM results showed that the thickness of the film was about 0.8 nm.It is proved that the film is monolayer.And TEM results showed that the films had standard hexagonal stacking structure and was well-crystallized on the monolithic triangular film.Dendritic and continuous film NbS₂ were prepared by CVD using NbO₂ and NbCl₅ as niobium source,respectively.The results of the component test showed that the main component of the continuous film was Nb and S.The atomic ratio of Nb to S is 1:1.95 in continuous film.The Raman spectra showed that the continuous film contained three vibrational modes of 3R-NbS₂,which proved that the prepared films are 3R-NbS₂.The back-gate field-effect transistors based on monolayer WS₂ were fabricated by electron beam lithography.The width of the transistor was about 0.5?m and the length was about 1?m.The four-probe method was used to test the electrical performance of micro-devices.The results showed a switching ratio of 10⁵,and the FET showed characteristics of weak ambipolar behavior.