Structure And Photoelectric Properties Based On Janus Two Layers Of Transition Metal Disulfide

Janus transition metal chalcogenide(TMD)is a kind of two-dimensional material that has recently received widespread attention.Its unique tunable photoelectric characteristics are the biggest feature,and it is also the reason that attracts researchers' attention.Especially after the representative Janus MoSSe was successfully prepared,people's enthusiasm for the research of this material is increasing day by day.In this paper,we use the first-principles based on spin polarization theory and the calculation method of density functional theory(DFT)to study the structural characteristics and single-layer and double-layer,different stacking methods,and different phase MXY structure Electronic characteristics.We first calculated the non-Janus MX2 structure and compared it with the existing research results,and further calculated the single-layer Janus MXY(M=Mo,W;X,Y=S,Se,Te)structure,Comparing the results with MX2,it is found that when the symmetry is broken,the structural parameters such as the bond length,bond angle,height,and lattice constant of the system will change.At the same time,the energy band structure of the MXY system will also change,with a band gap between MX2 and MY2.The article also focuses on the five most likely stacking methods of the 2H phase Janus MXY double-layer structure.By comparing the specific binding energies of the systems with different configurations and different spacings,the stack type with the most favorable energy and the corresponding interlayer gap are determined.The article also attempts to change the arrangement order of the MXY atoms,flip the arrangement of XMY-XMY into YMX-XMY form,and compare the specific binding energy of the two to find that the former is more stable.The calculation results for the energy band show that the Janus MXY bilayer with the most favorable energy stacking method is an indirect semiconductor with a band gap ranging from 0.01 eV to 0.91 eV.Band gap,and the amplitude of the band gap varies greatly.The minimum values of the conduction bands of the MoSeTe,WSSe,and WSeTe bilayer films move to the highly symmetric K point,while the maximum values of the valence bands of all bilayer films except MoSSe move between the K point and the ? point.The article also uses MoSSe as the representative,and compares the electron density distribution under the five configurations.In addition,a total of 30 possible electronic energy band structures of Janus TMD double-layer membranes are shown in the article.The crystal structure of different phases will also affect the structure and photoelectric properties of the material.The transition metal sulfides represented by molybdenum disulfide generally have three phases of 1T phase,2H phase and 3R phase,of which 3R phase exists in the bulk material.Among them,for two-dimensional TMD materials,materials with a 2H phase are naturally occurring and also the most stable and common.The 1T phase is generally non-naturally occurring and requires artificial processing to obtain it.It is a tetrahedral phase.Not long ago,the MoS2 material with stable 1T phase has been successfully prepared,and its preparation method can be extended to other 2D TMD materials.Therefore,we further took MoSSe as an example to calculate and analyze the 1T phase Janus MXY structure.The results show that compared with the same structure of the 2H phase,the 1T phase MXY structure has a larger amplitude than the MX2,and it also has a completely different characteristic from the 2H phase.Whether it is a single-layer 1T MoSSe or a double-layer structure,they all show the characteristics of overlapping bands,that is,they have metallic properties,and their conductivity is very good,not the semiconductor characteristics of the 2H phase.In addition,through the analysis of electron density,it is also found that the relationship between the layer spacing and configuration of the 1T phase and the 2H phase also show different rules.In summary,this article makes a series of comparisons on the structure and electronic properties of different conditions such as the presence or absence of Janus,different elemental compositions,single and double layer changes,different phases,etc.,which provides a foundation and a basis for the research of nanoelectronics and optoelectronic devices Value reference.