Growth And Characterization Of Monolayer WSe₂ And W_xMo_1-xSe₂ Alloys By CVD In A Single Temperature Zone

The zero band gap characteristics of graphene materials limits its development in semiconductor devices,while transition metal chalcogenides(TMDs)have a similar two-dimensional layered structure,and when TMDs transition from multiple layers to single layers,the indirect band The gap is transformed into a direct band gap,and its unique properties make it of high research value in the semiconductor field.However,the band gap of binary TMDs is limited.In order to promote the application of TMDs,researchers have set their sights on TMDs alloys.By changing the composition of TMDs alloys,the band gaps of the materials are adjusted to achieve the purpose of enriching the band gaps of TMDs materials.In this paper,based on the chemical vapor deposition method,two-dimensional WSe₂ and molybdenum tungsten selenide(W_xMo_1-xSe₂)were grown with the aid of NaCl and H₂,and the growth conditions of two-dimensional WSe₂were explored and its growth mechanism was analyzed.Based on this,the preparation of W_xMo_1-xSe₂ alloy is realized,and the composition of the alloy is adjusted by changing the ratio of precursors.The specific research content is as follows:(1)Through the simulation calculation of the castep module in the materials studio software,the structural stability and basic electronic properties of WSe₂ are studied,and the band gap of the WSe₂ single layer is calculated to be 1.547 eV,and the double layer The band gap is 1.513 eV,the three-layer band gap is 1.511 eV,and the bulk material band gap is 1.436 eV.The single-layer WSe₂ is a direct band gap semiconductor material.As the number of layers increases,the direct band gap gradually changes to an indirect band gap,and the band gap gradually narrows.By exploring the factors that affect the growth of two-dimensional WSe2 crystals:the type of carrier gas,the distance between the precursors,the amount of precursors and the growth time on the reaction,we can find out how to prepare single-layer WSe₂ crystals by the CVD method assisted by H₂and NaCl.Suitable window.The WSe₂ monolayer crystal was prepared at a growth temperature of 850?,using Ar/H₂ mixed gas as a carrier gas,a precursor distance of 24 cm,and a reaction time of 4 min.The sample size was about 20?m under an optical microscope,and the thickness measured by AFM was 0.69 nm,which is consistent with the literature data,which proves that the WSe₂monolayer is prepared.The single-layer sample has extremely strong photoluminescence at 776 nm,while the photoluminescence peaks of the double-layer and three-layer samples are at 786 nm and 789 nm respectively.As the layer thickness increases,the WSe₂ photoluminescence phenomenon is obvious Attenuation,and the peak position is red-shifted(excitation wavelength is 532nm).The characteristic peaks of Raman spectroscopy appear at 249.5 cm^-1 and 260 cm^-1,and the active peak appears at 310 cm^-1 for multilayer materials.This peak disappears when the material is a single layer(excitation wavelength is 532 nm).(2)The band gaps of W_xMo_1-xSe₂ alloy monolayers with different compositions are simulated and calculated by the castep module.The band gaps of W₃Mo Se₈,W₂Mo₂Se₈,W₁Mo₃Se₈,and Mo₄Se₈ are 1.473 eV,1.437 eV,1.429 eV,and 1.420 eV,respectively.The feasibility of alloy band gap adjustment is verified.Under the reaction conditions for preparing WSe2,the precursor was changed,and MoO₃ was used as the molybdenum source to be placed in the middle of the substrate and the selenium powder to complete the preparation of Mo Se₂,and Mo Se₂ crystals with a size of about 10?m were prepared.Based on this,the preparation of W_xMo_1-xSe₂ alloy is realized.The alloy samples were characterized by Raman spectroscopy.The characteristic peaks of Mo Se₂appeared near 230 cm^-1,and the characteristic peaks of WSe₂ appeared near 250 cm^-1,260 cm^-1,and 305 cm^-1.The wavelength is 532 nm).The samples were characterized by EDS mapping,and three elements of W,Mo,and Se appeared in the samples,which verified the successful preparation of W_xMo_1-xSe₂ alloy,and the alloy size was about 6?m.By changing the ratio of precursors,the composition of the alloy was successfully controlled.According to the test data,the values of x under different precursor ratios were 0.44,0.76,and 0.83,respectively.54 pictures,4 tables,63 references.