Large-sized WSe₂ Film:Its Controllable Preparation By CVD Method And Optical Properties

In recent years,with the discovery of graphene,a variety of grapheme-like two-dimensional materials have been studied,among which monolayer transition metal dichacogenides(TMDCs)has attracted the attention of researchers.Monolayer TMDCs,such as MoS2,MoSe2,WSe2 and WS2,which make up the deficiency of graphene with no band gap because this kind of material is a direct band gap semiconductor material.Monolayer WSe2 has excellent optical and electrical properties,monolayer WSe2 has excellent optical and electrical properties,particularly,monolayer WSe2 has excellent optical and electrical properties,its 1.65 eV direct band gap width can make it meet the demand of most electronic devices and optoelectronic devices,and is one of the few TMDCs material found to be characteristic of both conductivity P-type and N-type,which has significant potential application in logic circuits.The method used in large-scale preparation of the high quality monolayer WSe2 films is the essential prerequisite for large scale production devices,and chemical vapor deposition(CVD)method is one of the main methods for preparing two-dimensional materials,and the most promising in industrial production.So far,it is difficult to prepare large-scale and high-quality WSe2 films by CVD method.Therefore,it is of great significance to study the growth mechanism and the optimum growth conditions.This paper mainly focuses on the controllable preparation of large size WSe2 films with the method of atmospheric CVD.The researcher investigated the effects of temperature,the quantity of precursor source tungsten and the distance between substrate and the precursor source tungsten in atmospheric CVD-growth of WSe2 films.Through the regulation of the above parameters,the mono-layer triangular WSe2 films with the maximum side length 50 ?m,the 150 ?m hexagon mono-layer WSe2 films,and the 0.5cm*0.5cm large-sized few-layer WSe2 films on the SiO2/Si substrates were developed.In this paper,the monolayer WSe2 film was characterized by optical microscopy,Raman spectra,photo-luminescence(PL)spectra,atomic force microscopy(AFM)and scanning electron microscopy(SEM),the results show that the surface morphology of monolayer WSe2 film is intact and the size is large.The height is about 0.9 nm by AFM.In order to study the optical properties of WSe2 films,the mono-,double-,and triple-layered WSe2 films of the same sample were confirmed by optical microscope and Raman spectrum.And the optical properties of WSe2 were investigated by photoluminescence spectra of the mono-,double-,and triple-layered WSe2 films.Besides,the band structure change of WSe2 film from bulk to single layer film is theoretically analyzed.