Twist Bilayer And Electronic Properties Of Two-dimensional Carbon Materials

In the past decade,two-dimensional(2D)materials have been the focus of research,but in recent years,experimental and theoretical studies have found that the composition and arrangement of atoms in layered materials and the stacking configuration of layered materials play a crucial role in the basic electronic properties of materials.This leads to a great deal of interest in the twisted and stacked of 2D materials.In terms of twisted,many properties that are different from monolayer materials have been discovered successively,such as the superconducting mechanism found in twisted bilayer graphene(TBG).In terms of three-dimensional(3D)stacked,various complex topological phases are found in different materials,such as nodal chains and nexus points.At present,a lot of 2D materials have been synthesized experimentally.However,their applications are not rich because the monotonicity of their properties and the limitation of their dimensions.In order to have better application of these 2D materials,we need to continuously study these materials by twisted and stacked.In this paper,the effects of 2D twisted and 3D stacked on the electronic properties of biphenylene carbon were studied.The paper is divided into five chapters:In the first part,2D film materials,including carbon thin film materials and other thin film materials,are introduced.At the same time,some recent studies on twisted and stacked of 2D materials are introduced.Finally,the significance and content of this paper are introduced.The second chapter mainly introduces the calculation methods and principles used in the research process,including first-principles calculation and tight-binding approximation theory.In third chapter,we conducted twisted on 2D biphenylene carbon,and found some properties different from monolayer by calculating twisted models with different angles.The transformation from semiconductor to metal could be realized by rotation,and semiconductors with different bandgap could be adjusted by changing twist angles.It is found that apart from the flat bands generated by rotating small angles,the twisted bilayer biphenylene carbon also produces flat bands at several large angles.These flat bands have small bandwidths and are almost dispersion-free,and some of them are near degenerate and some of them are energy separated.These flat bands have local charge densities,which means they have different properties.In addition,the band gap of the flat band can also be changed by twisted angle.In Chapter 4,we carried out 3D stacked operation for biphenylene carbon and found some interesting topological phases,such as nodal spot and nodal tube,through calculation.In addition,the energy bands of monolayer and 3D layered materials are fitted by the tight-binding model to further explain the generation and evolution of their topological phases.Our results show that 2D materials can be stacked in 3D to realize and find some new topological phases.Our research work provides a reference for the stacking research of 2D materials.In the fifth chapter,we summarize the work of this paper and look forward to the future research.