Modulation Of Stress And Photoelectric Properties Of Suspended Two-dimensional Materials By Focused Helium-ion Irradiation

In recent years,MoS₂ has been widely studied in the field of catalysis due to its adjustable energy band structure,stable chemical properties and abundant active sites.People adjust the energy band by changing the lattice structure by introducing defects in the doping of various elements and the coincidence of various materials.However,these methods cannot introduce defects quantitatively,nor can they characterize the relationship between the defect concentration and the change of lattice structure.For this reason,a new technology is proposed in this paper.Focused helium ion technology is used to irradiate MoS₂,and the introduction of defects is changed quantitatively by changing the irradiation dose.In addition,the micro stress regulation caused by the introduction of defects in the irradiated area and the macro stress regulation in the non-irradiated area are realized through nanoscale patterned irradiation.Furthermore,the crystal structure and energy band of MoS₂ can be regulated.The experimental data are analyzed,and a set of theory on how the defect stress regulates the crystal structure and energy band structure of MoS₂ is summarized.First,in order to obtain high quality,smooth surface,without a suspension of prestressed large single MoS₂ material,according to the mechanical stripping process and experiments have been carried out to explore the preparation of suspended substrate,through a large number of experiments,summarized the gold auxiliary stripping technology,as well as control fingers press the condition such as pressure in the large area is flat prestressed suspended MoS₂ materials,The different layers of the material were characterized,and the layers of the material could be distinguished,which provided an experimental basis for the subsequent investigation of radiation damage and stress regulation.Secondly,the effects of focused helium ions on the radiation damage of suspended MoS₂ under different irradiation dose,acceleration voltage,irradiation beam and residence time were studied.Combined with the subsequent fluorescence and Raman test results,it is shown that helium ions can effectively introduce topological defects and introduce the equivalent doped S-vacancy defects in a fine and controllable manner.After the introduction of defects,the neutral exciton,triexciton and defect-bound exciton show some typical characteristics with the increase of dose.For this phenomenon,Landau phase transition theory and mass action theory are proposed for the first time to explain.The mechanism of formation and movement of irradiation introduced defects is explained.Then,the regulation of MoS₂ stress in the non-irradiated region and the band structure changes associated with the patterned radiation on the micro and nano scale of focused helium ion are studied.Irradiation by suspended MoS₂ micro/nano graphics area,induced defects,the irradiation area material strain,make the nature of the material itself has changed,through further irradiation region boundary stress,achieve the irradiation stress regulation of regional material,combined with fluorescence,Raman,atomic force microscope,such as test results,found that due to the introduction of irradiation defects,The mechanical properties and energy band structure of the material in the irradiated area are directly changed,and the local effect of the long-wave thermal fluctuation wave,which is the main effect of stress conduction in two-dimensional material due to defects,is given at low dose,making the Young’s modulus increase.In addition,with the accumulation of dose,the S-Mo bond begins to weaken,leading to the Young’s modulus decrease.According to the above theory,the theoretical explanation of strain change reflected in the Raman fluorescence spectrum in the unirradiated region is successfully given.Finally,the generality of the above work in other catalytic materials is summarized and prospected.