Preparation And Characterization Of Two-Dimensional Material MoS_2?1-x?Se_2x

Two-dimensional semiconductor materials with atomic layer thickness are of great interest to researchers due to their unique low-dimensional effects.In order to be applied to a wide range of optoelectronic devices,it is particularly important to control the band structure of two-dimensional semiconductors,such as bandgap,valence band/conduction band position.The alloy method is the most versatile method of controlling the semiconductor band gap.Experimental and theoretical studies have shown that changing the ratio of the end component materials can control the band gap value of the single-layer transition metal chalcogenide.Finding a suitable preparation method and preparing a single-layer or a small-layer two-dimensional semiconductor alloy with a large area and a high crystal quality is a prerequisite for researching and applying it to practical production and life.In this paper,MoS2(1-x)Se2x alloys with a gradient of Se concentration were synthesized on a Si/SiO2 substrate by chemical vapor deposition.When preparing MoS2(1-x)Se2x by chemical vapor deposition,we found that the system pressure,the concentration gradient of the deposition zone and the evaporation temperature of the precursor source affect the size,thickness and morphology of the film deposition.In the MoS2(1-x)Se2x sample prepared by chemical vapor deposition,the morphology and size of the prepared MoS2(1-x)Se2x samples were characterized by optical microscopy and scanning electron microscopy,the thickness of the sample was characterized by atomic force microscopy,and the band gap value was analyzed by photoluminence spectroscopy.We not only studied the variation of the band gap value of the bilayer MoS2(1-x)Se2x alloy with the Se concentration,but also analyzed the effect of Se concentration gradient on Raman spectrumthe.Both the regulation of the bilayer MoS2 band gap has been realized,and the introduction of Se leads to the change of the structural properties of the material,with the position and intensity of the Raman characteristic peak changing.In addition,during the process of growth of material,a new morphology-the stacked stepped MoS2(1-x)Se2x alloy could be obtained.Material with a thickness from 2.2 nm(about 3 layers)to 5.6 nm(about 7 layers)shows a strong luminescence characteristic.Even at 100 nm,the spectral line of the sample still presents two luminescence peaks,and the exciton luminescence energy has nonlinear variety.Unlike the Raman peak of the bilayer MoS2(1-x)Se2x alloy,which moves with the change of Se concentration,at the same Se concentration,the Raman spectrum has almost no peak shift as the thickness of the sample increases,but the corresponding Mo-S-related and Mo-Se-related vibration modes are enhanced.Further analysis illustrate that the the effect of change in the number of layers on the electronic structure of the stacked stepped MoS2(1-x)Se2x alloy.