Controllable Synthesis And Optical Spectral Analysis Of Two-dimensional Layered TMDs Alloy

Due to the quantum confinement effect,two-dimensional（2D）semiconductor materials with atomic layer thickness have different properties from bulk materials,which arouses great interest of researchers.The regulation of the band structure of 2D semiconductor plays an important role in promoting the application of 2D semiconductor materials in the field of optoelectronic devices.Alloying has been reported as an excellent method to tune the band gap in a large range as large as hundreds of millielectronvolts or even more than 1 e V.Experimental studies and theoretical calculations have shown that the band gaps of monolayer transition metal chalcogenides（TMDs）can be regulated by tuning the ratio of component materials.Therefore,the synthesis of large-area,high-quality single-layer or few-layer 2D semiconductor alloy materials is the premise to study their optoelectronic properties and realize their wide application in optoelectronics.Here,the synthesis of 2D WS_2（1-x）Se_2xand W_xMo_（1-x）S₂alloy materials on Si O₂/Si substrate by chemical vapor deposition（CVD）method is systematically introduced,and their optical properties are studied.The details are as follows:1.A series of WS_2（1-x）Se_2xmonolayers with different x values were successfully synthesized by chemical vapor deposition of precursor of reaction source using a magnet-activated motion system.Firstly,we explored the effects of growth time,growth temperature,and the mass of halide salt on the 2D WS_2（1-x）Se_2xmaterial,and revealed its growth mechanism.Subsequently,both the Raman and the photoluminescence studies show tunable optical properties consistent with composition of the alloy nanosheets.By tuning the composition of the WS_2（1-x）Se_2x（x=0,0.11,0.32,0.46,0.56,0.78,1）alloy monolayer,we realized a very wide tunable band gap range from 1.95 e V to 1.6 e V,and the WS₂-like A_1gred-shifted from 419 cm^-1to 408 cm^-1,the WS₂-like E_2gred-shifted from 350 cm^-1to 314 cm^-1,the WSe₂-like E_2gred-shifted from 263 cm^-1to 250 cm^-1.2.A series of W_xMo_1-xS₂with different x values were successfully synthesized by salt-as sisted chemical vapor deposition.Firstly,we studied the effects of growth time,heating tempe rature of sulfur and flow rate of Ar on the 2D W_xMo_（1-x）S₂material.Subsequently,both the Ra man and the photoluminescence studies show tunable optical properties consistent with comp osition of the alloy nanosheets.We found that as the variation of composition of W（x=0,0.13,0.20,0.23,0.46,0.59,0.72,0.87,1）,the band gaps（～1.83-1.95 e V）first decrease and then increa se,and the Mo S₂-like E^′red-shifted from 382 cm^-1to 375 cm^-1,the WS₂-like E^′red-shifted fro m 357 cm^-1to 353 cm^-1,and out-of-plane vibration mode of S atom A^′blue-shifted from 408 c m^-1to 420 cm^-1.