Study On The First Principle Of New Type Two - Dimensional Monolayer

Since the breakthrough in the fabrication of monolayered graphene from bulk graphite, atomic thick two-dimensional (2D) materials have triggered an extensive investigation because of their exceptional physical and chemical properties. Among them, monolayer MoS2 and phosphorene possess exotic properties similar to or even surpassing those of gapless of graphene, and become promising materials in assisting or even replace graphene. Their excellent physical and chemistry properties make them favorable for catalyst, field-effect transistors, photoelecronic devices, spintronic and valley electronics. Given these excellent properties and multitude of applications, it is no surprise that these two new 2D materials have become one of the hotpots in the physics, chemistry, materials, electronics, and so on. In the process of studying new materials, researchers often modify the properties of materials to optimize device functionality and facilitate wider applications of them. Theoretical calculations based on density functional theory (DFT) can help us predict the structure and properties of new material very well. At the same time, it can provide a theoretical basis for the success of experiments. Hence first-principle calculations have become a strong background of experiments and industry. In the present paper, based on the first-principle calculations within the framework of DFT, we carried out systematic investigations on the geometric, electronic and optical properties of monolayer MoS2 and phosphorene with different dopants by using reasonable theoretical methods. The main contents of this article include two aspects:(1) First of all, the O-doping effects for monolayer molybdenum disulfide (MoS2) are systematically investigated by first-principle calculations. For the models design, the influence of O doping concentration (2.08%,3.70%and 8.33%) on the physical properties of 2D monolayer materials has been taken into consideration. It is shown that the geometrical, electronic and optical properties are affected distinctively by the oxygen dopant. Structural analysis reveals a local contraction along c axis in the substituted cases. The substitution of oxygen for a sulfur atom in monolayer MoS2 leads to a transition from a direct K-K band gap to an indirect Γ-K band gap. And, the value of band gap decreases with increasing doping concentration. In addition, for the pure MoS2, strong covalent chemical bonds are formed on the Mo-S bonds, which is ascribed to the strong hybridization between Mo-4d and S-3p orbitals. After oxygen doping, the covalent bonding of Mo-S is distinctively weakened. More electrons are transferred from Mo to O because of the larger electronegativity of O, and the atomic populations of O atoms become larger than that of S atoms. Optical properties are also found to be affected distinctively by the oxygen dopant. An interesting blue-shift of the absorption threshold is observed in the O-doped systems.(2) Subsequently, with a 4×3×1 supercell, the electronic and optical properties of phosphorene co-doped by vanadium and nonmetallic atoms (B, C, N and O) are investigated by employing first-principle calculations based on density functional theory. It is found that the geometrical, electronic and optical properties are affected distinctly by these dopants. Both single V-doping and V-B (C, N, O) co-doping induce significant local lattice distortions. All the substituted systems remain semiconducting characters, but their band gaps become smaller than that of the primitive phosphorene. It indicates that the impurity doping is an effective way to modulate the band gap of phosphorene for different applications in electronic devices. There exist obvious covalent interactions between the impurity and their adjacent phosphorus atoms. In these doped systems, an interesting redshift phenomenon and a significant anisotropy are observed in their optical properties.Our theoretical results imply that substitutional doping is an effective way to modulate the electronic and optical properties of new 2D monolayer materials for various potential applications. We hope that our findings may facilitate wider applications of these new materials.