Exploration Of Point Defects Induced Anomalous Mechanical Properties In 1H-MoS₂ With Molecular Dynamics Simulation

The outstanding physical and chemical properties of single layer molybdenum disulfide(1H-MoS2),especially its direct semiconductor band gap of 1.8eV,make it a popular material in the field of nano-optoelectronic.Therefore,it is necessary and significant to have a deep insight into the characters of 1H-MoS2 for its practical application.At present,the amount of relative research on mechanical properties of 1H-MoS2,notably those films with solid defects which are unavoidable in the preparation process,is limited.According to the phenomenon of anomalous stiffness enhancement which were found in the defective graphene,the further study for graphene-like 1H-MoS2are conducted via molecular dynamics simulation,to explore whether the various frictions,types,as well as the distributions of defects,will also boost its mechanical properties.The research mainly includes aspects as following:So as to acquire the 1H-MoS2 configuration with all point defects conveniently,we developed the programming modeling method first.Subsequently the bending simulation to 1H-MoS2 are carried out using MD methods and it is found that the different boundary types and interatomic potential functions have a negligible effect on the bending stiffness of thin films.The simple supported boundary and REBO potential function are more suitable than others,which can be used for fitting the bending stiffness of the thin film in the larger load range.In addition,we also find that the disordered Vs defect and the ordered Vmos3 defect located on the bottom S layer exhibit promising characteristic on anomalous stiffness enhancement.The nonlocal elasticity theory is also used to character the bending response of 1H-MoS2.The corresponding result shows that the existence of nonlocal parameters plays an unusual role in strengthening the bending stiffness of 1H-MoS2,which is contrary to graphene.In the process of resonance simulation,the increase of beam length can eliminate the influence of different boundary conditions and potential functions on the resonance characteristics.In addition,Both the ordered and disordered Vs defects located on the bottom S layer will affect the basic frequency of the film,but the disordered Vs defects are more easily induced to produce the high order mode.In some cases of concentration,Vmo defect and Vs2 defect can slightly enhance the bending stiffness of 1H-MoS2,while the other defect models show the obvious weakening effect as the defects concentration increases.The result from the nano indentation simulation indicates that various ratios of indenter size to model size will effects the elastic modulus in some degree.Through loading and unloading tests,we find a pit occurring on the film center after unloading at the plastic stage.It is noted that,the existence of a new phase in the pit waist of 1H-MoS2 is observed during the unloading process.Those atoms on the pit waist contribute main deformation to the phase transformation.Subsequently,the phase transition mechanism changed immediately as the point defects introduced,because the maximum deformation moves to those atoms near the vacancy S.Finally,the study focusing on the effect of Vs defect with various concentrations on the elastic modulus of 1H-MoS2 is conducted,and the result reflects that the slight abnormal enhancement of the elastic modulus is observed when the Vs defect located on the bottom S layer with ratio of 0.45%is introduced into 1H-MoS2.