Local Defects Introducing And Phase Modulation Of 2D Materials Using High-resolution Focused Ion Beam

Defects are the deviation of the actual crystal from the ideal structure,and are of great significance to the study of the basic properties and physical phenomena of materials.However,in three-dimensional systems,the introduction of higher defect densities is required to change the material properties,and the effects of different defect states on the properties cannot be distinguished.Two-dimensional layered materials have the characteristics of atomic-level thickness,no chemical dangling bonds on the surface,and large specific surface area.They are a good platform to study the relationship between defects and material properties.In this project,the focused ion beam technology was used to introduce controllable local defects in the two-dimensional materials molybdenum ditelluride and boron nitride.Through a series of material characterization methods,the optical and electrical properties of the two-dimensional materials before and after ion irradiation were compared.Analyze the effect of defects on material properties.The main research contents are as follows:First,the effect of focused ion beam on the introduction of MoTe₂ defects and the change of material structure were explored.We characterize the material composition of MoTe₂,and qualitatively determine the generation of defects.Under the characterization of Raman spectroscopy,the original MoTe₂ is transformed from the unirradiated semiconductor 2H phase to the metallic 1T’phase driven by the defect.Electrical tests were carried out on the localized samples with irradiation dose of1×10¹⁵ion/cm²,and it was found that the electrical properties of the 1T’phase irradiated at variable temperature had obvious metallic properties.At the same time,a field effect transistor with a 1T’buffer layer was fabricated on the MoTe₂ sample to realize a device with a device switching ratio of 10⁴ and an ohmic contact.At the same time,a 1T’phase MoTe₂ region was also fabricated at a scale of 100 nm,which proved that the focused ion This approach is a reliable means of localized phase transition.Second,in order to study the application of focused ion beam defect engineering in other two-dimensional materials.We introduced defects in h-BN,a graphene-like two-dimensional material,to change its conductivity,and used the mechanism of defects to form conductive filaments to fabricate a vertical resistive memory with an on-off ratio of 10⁶.The Raman peak position of h-BN gradually shifts and disappears under Raman spectroscopy,and it transforms into a polycrystalline phase.This focused ion beam treatment of two-dimensional materials provides a new engineering method for changing material properties.