Structures And Electronic Properties Of The Nitrogen And Boron Doped Graphene Under Strain

Because of its distinct two-dimensional structure, graphene exhibits unique mechanical, electrical and thermodynamic properties. Graphene is expected to be widely used in the areas of nanoscale electronic devices, sensors, composites and energy storage. Especially because its excellent electronic properties, it is possible that graphene, instead of semiconductor silicon materials, becomes a new material for nanoscale electronic devices. However,because graphene is a zero-band-gap metal, its application to nanoscale electronic devices is very limited. So how to effectively control its electronic structure is one of the most important part of the application. Studies have found that, doping nitrogen(N) and boron(B), n(p)-graphene-semiconductor can be obtained, and can regulate the property by changing doping concentration. And in the actual application, the interaction with the substrate or other circumstance will bring the graphene deformation. Moreover, the deformation can also impact on its physical nature. Therefore, the research of structures and electronic properties of the nitrogen(N) and boron(B) doped graphene under different strain is very important. In this thesis, we adopt the first principles method(Ab initio) based on the Density Functional Theory(DFT), to study electronic properties and structures of the nitrogen(N) and boron(B) doped graphene under different strain. The main results of the research are as follows:1. Through optimizing the structure of pure graphene, N doped graphene and B doped graphene, we obtained the lattice constants under equilibrium state. The lattice constant of pure graphene is 1.4683 nm, the lattice constant of N doped graphene is 1.4663 nm and the lattice constant of B doped graphene is 1.4713 nm. Compared with the intrinsic graphene, the lattice constant of N doped graphene decreases, and the lattice constant of B doped graphene increases.2. Through examining the change trend of the total energy of systems with strain, we found that, for pure graphene, there is a sudden change in the gross energy of system under 30% strain. That means, system under more than 30% strain is no longer in elastic strain range, namely the critical strain of pure graphene is 30%. For nitrogen and boron doped graphene, the critical strain were 17.6% and 17.4% respectively. The result shows that, after doping nitrogen(N) and boron(B), the elastic strain field of system is reduced greatly.3. Through analysing the Electron Localization Function, we found that, for the graphene, in the elastic strain field, there is an attractor between each carbon atom and its three adjacent carbon atoms. That shows that carbon atoms interact with strong covalent bonds. While in the inelastic strain field, attractors between the carbon atoms display obvious separation phenomenon with the high electronic localization area moving close to each carbon atom. For nitrogen and boron doped system, we found that in less than or equal to the critical strain, system can remain the original hexagonal lattice structure. When entering the inelastic strain range, system no longer remains the original bonding characteristics, where C-N(B) bond become ruptured and atomic bonds form atomic links or clusters.4.For the electronic properties of intrinsic graphene and doped graphene, we found that intrinsic graphene under the symmetry strain remains its zero band gap, the N/B doped graphene changes from a semimetal to a metal with finite density of states at the Fermi level. In addition, the result shows that the strain can adjust the Fermi level of the doped graphene but cannot open a gap at the Dirac cone.