Theoretical Study On The Manipulation Of Structural And Electronic Properties Of Graphene And Low Dimensional Ferroelectric Material

Low dimensional material has drawn great interests in comunities of condensed matter physics and material science, which shows unique quantum pheonomena due to the quantum confinement, surface and interface e?ect. With the rapid development of the high integration and miniaturization of the electronic devices, low dimensional material will play a significant role in the application of the next generation electronic devices.Using first-principles calculations, we have systematically studied the structure and the electronic properties of graphene and low dimensional ferroelectric material and corresponding modification methods.It is a significant issue for the application of graphene in next-generation electronic device to open gap by patterning graphene into graphene nanoribbons(GNRs). We have proposed a method to obtain the electronic structure of GNRs by controlled hydrogenation of carbon nanotubes(H-CNT). The essential di?erence between CNT and GNR lies on the di?erent boundary condition of π-electrons of carbon sp2 carbon networks.By breaking the circumference periodic boundary condition, H-CNT showed dramatically similarity to GNRs in spin polarized edge states and symmetry dependent transport properties.Chemically functionalized graphene(CFG) has been a key method for large scale growth and commercial application of graphene. We have demonstrated that the di?erent adsorption coverage and geometry of functionalized group determined the electronic structure of the CFG. It can be either semiconducting or metallic due to the adsorption induced the boundary condition transition. Our results well explained the experimental controversy on the conductance of CFG.Epitaxial growth graphene on silicon carbide is one of the synthesis method of high quality graphene. The interfacial magnetism is of significant contribution to the graphene spintronics by hydrogenated epitaxial graphene on silicon carbide(HG-SiC). We have investigated the origin of the interfacial magnetism in HG-SiC and proposed a method to tune the magnetism by changing the polytypes of the silicon carbide substrate. The insight physics is general and applicable to other semiconductor heterostructures.It is of great significance to high density magnetic storage that, represented by Barium Titanite, low dimensional ferroelectric material has been widely used in multiferroics heterostructures. The structure and electronic properties of ferroelectric surface play an important role in the interfacial properties of the heterostructures. We have investigated the e?ect of the ferroelectric polarization switching on the surface phase diagram of the ferroelectric surface and proposed an approach to tune the surface structure and resulting surface electronic properties of ferroelectric materials.