Study Of Electronic Properties And Optical Properties Of Several Two-dimensional Materials

Since the advent of graphene,a two-dimensional materials of various studies have mushroomed,become one of hotspots in the field of scientific research,experiments on the preparation of the various performance of chalcogenide,inspired by the experimental study,to explore the excellent properties of chalcogenide,we used the first principles calculation,the two-dimensional binary compounds ReX₂,ReSX chalcogenide?X=S,Se and Te?and two dimensional chalcogenide ternary compound X₃C₆S₆?X=zinc,Cd,Sb,Bi?were studied.Firstly,we studied the structure,electronic properties and optical properties of the two-dimensional ReS₂ monolayer and bilayer.The results show that ReS₂ is a direct bandgap semiconductor.Compared with indirect bandgap semiconductor,direct bandgap semiconductor has higher carrier mobility and easier electron transition.First,we calculated the band structure of the material,and the results showed that the band gap of ReS₂ monolayer and bilayer was1.43eV and 1.38eV respectively,indicating that the band gap would decrease with the increase of the number of layers.Then we applied strain to the material.After stress regulation,we found that when the compression strain reached 10%,ReS₂ changed from semiconductor material to metal material.Moreover,when the strain is applied,not only the size of the band gap changes,but also the direct band gap and the indirect band gap change.Next,through electric field regulation,we found that ReS₂ double layer is more sensitive to electric field regulation than single layer.Finally,we also studied its optical properties,and the results showed that both monolayer and bilayer ReS₂ had strong absorption in the ultraviolet band,but not in the infrared band.Therefore,the study of optical properties is of great significance in the application of short wavelength leds.All the above results indicate that ReS₂ has a great prospect in future research and application.Secondly,we constructed three structures containing transition metal Re:ReS₂,Janus-ReSSe and ReSe₂,respectively,to study their structure and electronic properties,and to study the influence of biaxial strain on the three structures.Through calculation,we found that the two-dimensional ReS₂,Janus-Resse and ReSe₂ films remained stable under the control of biaxial strain.It should be noted that when the strain changes,not only the band gap changes,but also the band gap types?direct and indirect?convert to each other.Bond angles and bond lengths also vary with strain.These findings will provide a theoretical basis for future research and experiments.Nextly,ReX₂ and ReXS?X=S,Se,Te?monolayer structures were constructed to study the electronic properties and optical properties of electroluminescent materials under strain regulation.Biaxial strain can effectively adjust the band gap of single-layer ReSSe,and the band gap is converted between direct and indirect band gap.It is worth noting that ReSSe and ReSe₂ not only retain the characteristics of direct band gap,but also have larger band gap and better optical characteristics compared with ReS₂.ReSe₂ and ReSSe have strong absorption in the ultraviolet band and zero absorption in the infrared band.Therefore,the adjustable band gap and excellent optical properties make it have a broad application prospect in the field of infrared detector and strain sensor.Finally,on the basis of the study of two dimensional sulfur group binary compounds,we studied the topological properties of two dimensional sulfur group ternary compound X₃C₆S₆?X=Zn,Cd,Sb,Bi?.Firstly,we studied the band structure of the material,and the results showed that the intrinsic band gaps of the structure were all direct band gaps.More importantly,under the control of biaxial strain,we found that two-dimensional Zn₃C₆S₆ and Cd₃C₆S₆ thin films would become Nodal-line semimetal under certain strain conditions,and the nodal ring would not disappear with the increase of compression strain.We also prove the existence of nodal ring by using some point drawing method and partial charge density diagram in three dimensional band band.Nextly,we study the influence of spin orbit coupling effect on energy band structure,and find that nodal ring is stable under spin orbit coupling,indicating that the structure has strong robustness to spin orbit coupling effect.For Sb₃C₆S₆ and Bi₃C₆S₆,the energy band structure forms the Dirac cone near the Fermi energy level.We also calculate the three dimensional energy band structure of the two structures,which further proves the existence of the Dirac cone.This study provides an excellent candidate for the fabrication of low-power electronic devices.