Theoretical Design And Properties’Regulation Of Two-dimensional Materials

The nanomaterials are those geometry size between lnm and100nm, and those nanomaterials own some novel characteristics because of the size effect and large surface effect, which have made great progress in physics, chemistry and material science. The applications of nanomaterials across various fields, including magnetic nano-materials, nano-semiconductor materials, nano-catalytic materials, medical applications, environmental Protection and machinery Industry and so on. Today’s world economic development and social progress of nano-materials-based nanotechnology is bound to have an important impact. Therefore, the scientific research of nanomaterials has a very important significance.Two-dimensional (2D) monolayer materials with one-atom thickness, such as graphene, boron-nitride, and ZnO, have aroused great interests due to their unique properties not seen in their bulk counterparts. Tushce et al. were the first to successfully synthesize two-monolayer-thick ZnO(0001) films deposited on a Ag(111) surface, where Zn and O atoms are arranged in planar sheet like in the hexagonal BN monolayer, may become the latest popular nanomaterial. Recently, another class of2D materials with three-atom thickness, that is, the transitionmetal dichalcogenides (TMDCs) such as MoS2and WS2, has received intensive attention not only because of their novel electronic and catalytic properties but also owing to their widerange tunability via strain or vertical electric field engineering.For the reseach of nano-materials, calculations based on first-principles density functional thory have become an indispensable tool. In this paper, we mainly study and calculation of the electronic structure and magnetic properties of new two-dimentional nanomaterials by using the first-principles method.In the first chapter, we introduce the development of density functional theory. Firstly, we give a brief introduction about the quantum chemical approximation method:Born-Oppenheimer approximation. And then describes the Hatree-Fock equation, Hohenberg-Kohn theorems, Kohn-Sham equation and the core content of density functional theory:the exchange-correlation energy functional. Finally, we describe several common computing software packages based on density functional theory.In the second chapter, we first introduce the ZnO monolayer, including the characteristic of structure, its properties and main applications. Then we dope non-metallic elements (B, C, N) in ZnO monolayer and investigate the doping system’s electronic structure and magnetic properties systematically using the first-principle calculation. Then, we study the effect of chemical modification on the geometry and electronic structure of ZnO nanofilms. We also consider the effect of the stacking between neighboring layers on the electronic structure of ZnO nanofilms, including AB and AA stackings, respectively.In the third chapter, using the first-principle calculation, we mainly investigate the electronic structure and magnetic properties systematically of the transitionmetal dichalcogenides and corresponding van der Waals heterostructure, and the band gap engineering via electric field and mechanical strain, which the research objects include early transitionmetal dichalcogenides monolayer, van der Waals hetero-bilayer, trilayer and superlattice based M0S2monlayer.In the fourth chapter, we perform a comprehensive first-principles study of the electronic properties of phosphorene nanoribbons, phosphorus nanotubes, multilayer phosphorene sheets, and heterobilayers of phosphorene and two-dimensional transition-metal dichalcogenide monolayer. The tensile strain and electric-field effects on electronic properties of low-dimensional phosphorene nanostructures are also investigated. We also show that the combined phosphorene/MoS2heterolayers can be an effective solar cell material. Our estimated power conversion efficiency for the phosphorene/MoS2heterobilayer has a theoretical maximum value of17.5%. These novel electronic properties of low-dimensional (1D and2D) phosphorene nanostructures, in conjuction with their remarkable strain enegineering and electric field effects in tuning the bandgaps, suggest that phosphorene is a promising candidate for future nanoelectronic and optoelectronic applications.