Fluoride Janus MoSSe Of The Electronic Structure And Optical Properties Of The First Principles Of Research

The Janus MoSSe nanomaterial studied in this thesis is a new two-dimensional material developed on the basis of MoS2.In the thesis,based on first-principles density functional theory(DFT),a novel F atom adsorbed Janus MoSSe material has been constructed,and the changes of its electronic structure and optical properties have been calculated theoretically,which provides a theoretical reference for the design and preparation of high-efficiency optoelectronic materials.Firstly,the stability and electronic structure of fluorinated Janus MoSSe(MoSSe-Fx,x=0-16)were studied by first-principles method.In terms of energy,F atom is most inclined to adsorb on the top side of Se atom.The difference state distribution of charge density and hybridization analysis show that the fluorinated Janus MoSSe is a stable structure.As the number of F atoms adsorbed increases,the band gap of Janus MoSSeFx decreases from 1.46 eV(intrinsic,x=0)to 1.06 eV(semi-fluorine,x=16)and changes from a direct band gap semiconductor to an indirect band gap semiconductor.Charge population analysis shows that electron transfer from Se atom to F atom results in the enhancement of the built-in electric field from Mo atom to F atom,which increases the work function of fluorinated Janus MoSSe.After semi-fluorination(x=16),the work function increases from 5.22 eV in the original state to 8.30 eV.Therefore,due to its modulated work function and built-in electric field,fluorinated Janus MoSSe monolayer shows good potential application value in piezoelectric devices,optoelectronic devices and photocatalysts.Then,the effects of different fluoridation schemes on the electronic structure and dipole moment of a single layer Janus MoSSe are studied.The results show that the semifluorinated Janus MoSSe structures exhibit indirect bandgap semiconductor properties,with bandgaps of 1.077 eV and 0.313 eV,respectively.The perfluorinated Janus MoSSe exhibits the properties of a direct bandgap semiconductor with a bandgap value of 0.235 eV.The charge distribution between atoms is studied by calculating the Bader charge.For the fluorinated structure,Se/S atom is characterized by the absence of charge,and F atom is characterized by the enrichment of charge.At the same time,the dipole moment values of the system also change,which are-1.96D(Se-semi-fluorinated),1.65D(S-semifluorinated)and-0.25D(perfluorinated)respectively,where the direction of z-axis is defined as the positive direction of the dipole moment.Finally,the effect of semi/perfluorination on the optical properties of monolayer Janus MoSSe is studied.The results show that fluorination can increase the static dielectric constant of Janus MoSSe,and the peak values of the real and imaginary parts of the dielectric function appear in the low energy region.The study of optical absorption spectrum shows that the material has the greatest absorption effect on ultraviolet light.The light absorption in visible and infrared light region is also enhanced to a certain extent,which increases the absorption range of single-layer Janus MoSSe to the sunlight.In addition,the energy loss spectrum of the semi-fluorinated/perfluorinated Janus MoSSe structure decreases near the peak value of 16.65 eV,indicating that fluorination can reduce the energy loss when electrons pass through the material.These optical properties lay a foundation for the fabrication of microelectronic and optoelectronic devices,especially in the application of ultraviolet detectors,and also provide a theoretical reference for the further study of Janus MoSSe materials.