Effects Of Stacking Fault,Dislocation And Stone-Wales Defects On The Electronic And Optical Properties Of MoS₂ Nanoribbons From First-Principles Calculations

Transition metal dichalcogenides?TMDCs?have been widely applied in flexible devices,electronics,photocatalysis and photodetects due to excellent mechanical flexibilities,thermostabilities,distinct catalytic,electronic and optical properties.However,defects can be generated during the growth and using.The physical properties of materials can be influenced because of the existence of defects so that the performance of materials can be effected further.Therefore,defects have attracted great attentions in the properties of two dimensional materials.In present thesis,effects of stacking faults,SW defects and dislocations on the electronic and optical properties of armchair MoS₂ nanoribbons have been investigated using first-principles calculations.The results provide the theoretical calculation references in the application of optoelectronics.The main contents in this paper are as follows:The effect of stacking faults on the electronic properties of MoS₂ monolayer and nanoribbons have been investigated based on the first-principles calculations.The results indicate that the band gap of MoS₂ monolayer with periodically arranged stacking faults increase with the decreasing of stacking faults densities and the gaps converge to 0.27 eV,which is much smaller than that of perfect MoS₂ monolayer?1.76eV?.For nanoribbons with stacking faults,the band gaps increase for ribbon width?18 and decrease slightly for?18.The band gaps of nanoribbons with stacking faults are smaller than that of perfect nanoribbon.To explain the decrease of band gap which are originated from the stacking faults,the partial charge densities have been calculated.The results indicate that there are defective levels in the forbidden gap,and they are originated from the defect.Hence,the decrease of gaps is resulted from the introduction of stacking faults.First-principles calculations have been performed to investigate the effects of multiple stacking faults on the electronic and optical properties.The results show that the band gaps approach to zero for armchair MoS₂ nanoribbons with two and four stacking faults.Apparently,analogous Dirac point is emerged for nanoribbons with two stacking faults,which is similar with band structure of graphene.The gaps are about0.46 eV and 0.36 eV for armchair MoS₂ nanoribbons with one and three stacking faults,respectively.The band gaps are decreased due to the stacking faults.The defective levels are originated from the stacking faults according to the partial charge densities.Simultaneously,the optical response,such as dielectric function,adsorption,reflectance and electron energy loss spectra is presented.The optical results of monolayer MoS₂ are in agreement with other previous literatures.The peaks in the imaginary part of perfect armchair MoS₂ nanoribbon are around 2.8,4.0 and 5.4 eV and the peaks of armchair MoS₂ nanoribbons with stacking faults are 2.8 eV and 5.4 eV.They are independent of ribbon width.The peaks in electron energy loss spectra move toward larger wavelengths?redshift?due to the existence of stacking faults.The effect of Stone-Wales on the electronic and optical properties of armchair MoS₂ nanoribbons have been calculated.The structures of OH-passivated armchair MoS₂ nanoribbons with SW-2 at the edge is unstable,and can be relaxed to perfect nanoribbon.The others are stable.The band gaps of nanoribbons are decreased due to the introduction of SW defect.The gaps of armchair MoS₂ nanoribbons with SW-1 at the center is greater than that of SW-1 at the edge,while the gaps of armchair MoS₂nanoribbons with SW-2 defect at the center is smaller than that of SW-2 at the edge.Besides,the gaps of armchair MoS₂ nanoribbons with OH passivation is greater than that of nanoribbons with H passivation.The partial charge densities indicate that the defective levels are originated from the SW defect.The dielectric function,adsorption,reflectance,and electron energy loss spectra are calculated.The optical results show that₁^??0?and₁^??0?of armchair MoS₂ nanoribbons wih SW defect are greater that that of perfect MoS₂ nanoribbon.Besides,armchair MoS₂ nanoribbon with SW defect can be regarded as a promising donor material for solar cells due to its high power conversion efficiency?PCE?The effects of dislocation dipole on the adsorption of zigzag MoS₂ nanoribbons have been investigated based on first-principles methods.The magnetic moment increases from⁵to¹0.In addition,the adsorption of gas molecules is enhanced due to the existence of dislocation.It's physical adsorption.Therefore,this work provides a reference for the application of gas molecules on the sensors.