Design And Simulation Of Low-dimensional Nanodevices Based On Non-equilibrium Green's Function Method

Compared with bulk materials,low-dimensional nanomaterials exhibit many novel characteristics because of their significant quantum confinement effect.After years of development,the research of nanomaterials has made great progress and nanomaterials have been widely used in many fields.However,there are still some urgent problems in the research and exploration of nanomaterials,and the properties of many nanomaterials are difficult to meet people's needs for high-performance materials.On the one hand,researchers continue to modify the existing material system,on the other hand,they also explore and discover new materials and further study the properties of materials.With the continuous advancement of experimental technology,theoretical simulation has gradually become an important means of nanomaterial research.With the continuous improvement of theoretical simulation methods,theoretical calculations can reveal the properties of nanomaterials and design novel nanomaterials on the atomic scale.In this thesis,the electronic structure and transport properties of several new low-dimensional nanomaterials are systematically studied by density functional theory(DFT)combined with the non-equilibrium Green's function(NEGF)method.By exploring the use of strain,doping,construction of heterojunctions and other ways to control the properties of materials,understanding the influence of external factors on the properties of materials,we can rationally analyze the reasons for changes caused by external conditions,and expand the application range of materials on this basis.The main content of this article is as follows:(1)The sensing performance of two-dimensional borophene containing line defects as a gas sensor was explored.Our studies have shown that nitrogen-containing gas molecules can be strongly adsorbed at the line defects of borophene and produce obvious electron transfer with the line-defective borophene.The I-V characteristics of line-defective borophene adsorbed gas were further studied,and the sensitivity was shown by the current change.Under the small bias,the adsorption of NO,NO₂,and NH₃ showed dramatic current changes.The corresponding current changes indicate excellent sensitivity and selectivity.The analysis of the transmission spectrum and the local density of states reveal the reason for the current change,and the change of the density of states after adsorbing gas molecules leads to the change of transmission.This research reveals the application prospects of line-defective borophene in the field of gas sensor in the future.(2)The spin transport properties of VBr₃ nanowires with half-metallic characteristics were studied.Firstly,explore the spin filter efficiency(SFE)of VBr₃ nanowires with different lengths.Under the certain bias voltage,the fixed-length VBr₃ has a spin filter efficiency of 100%.We further explore the changes in the nature of material transportation through external control methods.By applying strain and transition metal doping to VBr₃,the bias window of the perfect SFE of VBr₃ will expand under tensile strain,and become narrower under compressive strain.For VBr₃ nanowires doped with specific transition metals,the ideal SFE bias range will be significantly expanded at low doping concentrations.Under tensile strain or through a certain number of doping,the half-metallicity of VBr₃ can be improved.This research provides a promising method for adjusting the half-metallic behavior of one-dimensional magnetic nanowires and designing high-performance spintronic devices.