Study And Application Of Electronic Properties Of Graphyne Nanotubes And Carbon Nitride Nanotubes

The continuous miniaturization of electronic devices is the trend of today’s times,and this requires the continuous progress and development of conductor materials and chip technology.According to the prediction of Moore’s law,the current silicon-based chip is close to its performance limit,so there is an urgent need to find new semiconductor materials to replace silicon-based materials to generate electronic chips with smaller gate length.Carbon materials,which are in the same main family as silicon and are as abundant,cheap and stable as silicon,have attracted attention.Among many carbon materials,graphene and carbon nanotubes have many outstanding properties that are particularly attractive to researchers.Semiconductor single-walled carbon nanotubes,which are used to make field-effect transistors,are considered candidates for producing chips with lower gate lengths because of their nanoscale size,high carrier mobility and excellent stability.However,the conductivity of single-walled carbon nanotubes depends on its chirality（n,m）,and this behavior leads to the coexistence of metallic and semiconducting carbon nanotubes.The presence of metallic carbon nanotubes greatly degrades the performance of electronic devices,while the cost of purifying semiconductor carbon nanotubes is high.Therefore,new semiconductor carbon-based materials need to be found to make its band gap less correlated with chirality.In contrast,graphyne nanotubes and carbon nitride nanotubes,which are also carbon-based materials,have attracted our attention due to their wide variety and excellent properties.In this thesis the electronic properties of eight graphyne nanotubes ofγ-GDy NTs,β-GDy NTs,δ-Gy NTs,T_4,4,4-Gy NTs,β4-Gy NTs,4,12,2-Gy NTs,4,12,4-Gy NTs,cp-Gy NTs and five carbon nitride nanotubes of C₃N₄NTs,C₆N₈NTs,C₆N₂NTs,C₆N₆NTs,C₁₂N₆NTs are systematically investigated using density functional tight binding method.The band gap and chirality patterns of these nanotubes were obtained,which can provide a theoretical basis for the experimentalists to develop new carbon-based semiconductor materials.The main research and conclusions of the thesis are as follows:The first chapter mainly outlines the background and significance of this thesis,including the origin development and application of carbon-based materials,carbon nitride materials and their nanotubes,graphyne materials and their nanotubes.In addition,the purpose,significance and problems to be solved in this study are pointed out.The second chapter provides a detailed introduction to density functional theory and describes the main computational software and computational parameters used in this thesis.The third chapter introduces the mathematical methods for constructing various chiral nanotubes and details the programming methods for implementing modeling using Python programs.The fourth chapter focuses on the electronic properties of the eight graphyne nanotubes,γ-GDy NTs,β-GDy NTs,δ-Gy NTs,T_4,4,4-Gy NTs,β4-Gy NTs,4,12,2-Gy NTs,4,12,4-Gy NTs and cp-Gy NTs,were mainly investigated.The calculations show that all the semiconductingγ-GDy NTs,β-Gdy NTs andδ-Gy NTs have moderate band gap values with different dependence on the handedness.In contrast,allβ4-Gy NTs,T_4,4,4-Gy NTs,4,12,2-Gy NTs,4,12,4-Gy NTs,and cp-Gy NTs are quasimetals with very small band gaps.Further studies show thatγ-GDy NTs exhibit chiral and diameter-dependent bandgap behavior,and we can produceγ-GDy NTs with fixed bandgap values by tuning the precise control of chirality and tube diameter.β-GDy NTs possess almost the same bandgap value（～1.12 e V）when n-m≠0,which provides a new strategy for bandgap manipulation.The quasimetallicβ4-Gy NTs,T_4,4,4-Gy NTs,4,12,2-Gy NTs,4,12,4-Gy NTs,and cp-Gy NTs provide a new approach for the production of Gy-/GDy-based conducting devices.The fifth chapter focuses on the electronic properties of five nitrided carbon nanotubes,C₃N₄NTs,C₆N₈NTs,C₆N₂NTs,C₆N₆NTs,and C₁₂N₆NTs,were mainly investigated.The calculations showed that all five nitrided carbon nanotubes are semiconducting nanotubes.Further studies show that（n,n）-C₆N₂NTs possess almost the same band gap value（about 1.77e V）and the chiral C₆N₂NTs possess almost the same band gap value（about 1.15 e V）,which provides a new strategy for band gap manipulation.We believe that C₆N₂NTs are good candidates for fabricating next-generation electronic devices.C₁₂N₆NTs exhibit a diameter-dependent band gap behavior,and we can produce C₁₂N₆NTs with fixed band gap values by tuning precisely controlled chirality and tube diameter.All C₃N₄NTs,C₆N₈NTs and C₆N₆NTs are semiconductors with very high bandgap values above 2.35 e V,and the effect of chirality on the bandgap almost disappears when the tube diameter is larger than 15（?）.This provides a new idea for the production of wide band gap semiconductor devices.In conclusion,in this thesis,the electronic properties of eight graphyne nanotubes and five carbon nitride nanotubes were systematically investigated using density functional tight binding method.We found that the stability of all chirally identical nanotubes is diameter dependent.We summarize the band gap laws of various nanotubes;we propose the mechanism of band gap regulation by chirality and tube diameter of different nanotubes.The research work in this thesis is meaningful for experimentalists to develop semiconductor materials and conductive materials in a targeted manner,and provides new ideas for producing conductive devices and semiconductor devices with certain practical values.