Theoretical Study On Electrome-Chanical Properties Of Graphene-Like Molybdenum Disulfide Nano-Structures

Molybdenum disulfide（MoS₂）,the material has excellent properties,for example,good photoelectric properties,high electron mobility,switching ratio,etc.,in particular,broke the zero band gap of the graphene to made it in the nano-level optoelectronics,advanced engineering materials and energy technologies are widely used.As a candidate material for future flexible electronic devices,obtaining products with high quality stability and good mechanical properties is a goal that experimenters have been pursuing.In practical applications,MoS₂-based flexible electronic devices are often subjected to deformation loads such as pulling,pressing,bending,and they can test the mechanical load carrying capacity of the material.Therefore,the study of the mechanical properties of MoS₂ is particularly important.In this paper,the mechanical properties of two-dimensional monolayered MoS₂ are studied.Theoretical simulation methods are used to study the influence of the variables on the mechanical properties of two-dimensional monolayer MoS₂,using size,temperature,and chirality as research variables.In terms of electronic structure,the reasons for the change in the macro structure have been sought.In addition,in view of the unavoidable existence of defects in the material,the defects of the two-dimensional monolayer MoS₂ are studied for the defects that often occur in the experimental preparation methods,and the point defects are taken as the research object,including vacancy defects and anti-sites defects.To study the impact of the above defect types and concentrations on the mechanical properties of two-dimensional monolayer MoS₂,also from the micro level to find possible causes of performance changes.In addition,based on the study and investigation of MoS₂,the new two-dimensional material MoSSe derived from it has been successfully synthesized in the experiment.The study of new two-dimensional materials is complementary to and expanded on the current two-dimensional material field.The research on the performance of the new two-dimensional material MoSSe is carried out,which has practical significance for its future application.By constructing a two-dimensional monolayer of MoSSe and its nanoribbon structure,the ground state properties including state density and energy band structure were studied,and the electronic structure was attempted to be controlled,and the energy band structure was regulated by the electric field.The specific findings are as follows:1.Size,temperature,and chirality all affected the mechanical properties of two-dimensional monolayered MoS₂.When the system temperature was 1 K,the fracture ultimate strength values of the seven structures studied in this paper all reached about16.600 Gpa,and the three structural of 10.900?×3.150?,10.900?×6.300?,and10.900?×12.600?,the fracture strain was slightly higher than about 2.500%for other structures,when the temperature rised to 300 K,the stress-strain curve of the structure was obviously oscillated,and the ultimate strength of the fracture was significantly reduced,which was about 20.500%,19.000%,24.700%,28.300%,28.500%,and28.500%,16.700%lower than 1 K,respectively.The fracture strain of the two structures,with size of 10.900?×6.300?and 10.900?×12.600?,were slightly higher than those of the other four structures by about 9%.When the size exceed 54.600?×56.700?,the fracture ultimate strength and fracture strain of the structure tend to be stable.In addition,the mechanical properties of two-dimensional monolayer MoS₂ also showed obvious chirality effects,the fracture limit and fracture strain of the armchair-type directional structure were significantly higher than that of the zigzag-type direction,and the fracture behavior of the two chiral directional structures,also showed differences.2.Point defects can significantly weaken the mechanical properties of two-dimensional monolayer MoS₂.Compared with the fracture limit of intrinsic two-dimensional monolayer of MoS₂,the fracture limit values of V_S,V_S2,V_MoS3,Mo _S,and S_Mo defects were decreased by 9.800%,29.000%,34.100%,3.700%,and 26.200%,respectively.And as the concentration of defects increased,the structural fracture limit and fracture strain decreased more significantly.In addition,in the structure containing point vacancy defects,the degradation intensity of V_MoS3 defects was significantly higher than that of V_S and V_S2 defects,in structures containing anti-sites defects,the deterioration effect of S_Mo defects was significantly greater than that of Mo _S defects.3.The preliminary study of the two-dimensional new material MoSSe showed that,the bandgap width was 1.560 eV,which was 14.700%lower than that of the two-dimensional monolayer MoS₂,and the dimension had a greater impact on its band gap,when the two-dimensional monolayer MoSSe structure became MoSSe nanoribbons,the band gap disappeared.Through the adjustment of its energy band structure by electric field,it was found that with the increase of electric field strength,the bandgap width of two-dimensional monolayer MoSSe exhibited a downward trend,and when the electric field strength increased to 5 V/nm,the threshold intensity was reached,and the band gap closed.The threshold value of the electric field was equal to the two-dimensional monolayer MoS₂.Similarly,the electric field also affected the energy band structure of the MoSSe nanoribbon.The electric field could open the band gap of the MoSSe nanoribbons.However,when the electric field intensity was in the range of 1-3 V/nm,the band gap of the MoSSe nanoribbon decreased with the electric field.When it reached 3 V/nm,the band gap almost disappeared.