Properties of vacancies and N-doping in monolayer g-ZnO: First-principles calculation and molecular orbital theory analysis

Abstract

The geometric structure, electronic structure, magnetic properties and absorption spectrum of graphene-like ZnO (g-ZnO) monolayer supercell with defects are systemically studied by the first-principles calculation based on density functional theory in this work. The defect supercell model includes zinc atom vacancy (V<sub>Zn_</sub>g-ZnO), oxygen atom vacancy (V<sub>O_</sub>g-ZnO), nitrogen atom substituted for oxygen atom (N<sub>O_</sub>g-ZnO) and nitrogen adsorbed on the g-ZnO monolayer (N@g-ZnO). The results indicate that the geometric deformation induced by N-doping in N<sub>O_</sub>g-ZnO and N@g-ZnO structure is negligible, while that of supercell with vacancy is relatively large. The O atoms neighboring a Zn vacancy center in V<sub>Zn_</sub>g-ZnO model move away from each other as a result of symmetry breaking. As a contrast, three N atoms around V<sub>O</sub> center move into V<sub>Zn_</sub>g-ZnO supercell. The pristine g-ZnO is non-magnetic. But the magnetic moment of V<sub>Zn</sub>_g-ZnO is 2.00 μ<sub>B</sub> in total as a result of symmetry breaking. The partial magnetic moment mainly results from the p-orbitals of the three neighboring O atoms. V<sub>O_</sub>g-ZnO has no magnetic moment, but possesses the electronic structure with identical spin-up and spin-down. The total magnetic moment of the N-doped N<sub>O_</sub>g-ZnO is 1.00 μ<sub>B</sub>, and the total magnetic moment of N@g-ZnO is 3.00 μ<sub>B</sub>. Their local magnetic moments are mainly contributed by the p-orbitals of N atom. The density of states and the spin density are given to analyze the magnetic properties. Based on the supercell local symmetry and molecular orbital theory, the origin of magnetic moment is well explained. The magnetic V<sub>Zn_</sub>g-ZnO, N<sub>O_</sub>g-ZnO and N@g-ZnO supercell are found to have a <i>D</i><sub>3<i>h</i></sub>, <i>D</i><sub>3<i>h</i></sub> and <i>C</i><sub>3<i>v</i></sub> local symmetry, respectively, which well explains that their total magnetic moments are 2.00 μ<sub>B</sub>, 1.00 μ<sub>B</sub> and 3.00 μ<sub>B</sub>, respectively. The optical absorption characteristics are also discussed. An enhancement of light absorption can be observed for the defective supercells, due to the introduction of defect states into the band gap. The optical transition between gap state and valance band leads to the below band gap absorption. These results are of insightful guidance for understanding properties of graphene-like ZnO monolayer as well as g-ZnO with vacancy and N dopant, and can be theoretically adopted for investigating the nano-electronic devices and catalytic applications based on g-ZnO monolayer.

Effects of Vacancy Defects and the Adsorption of Toxic Gas Molecules on Electronic, Magnetic, and Adsorptive Properties of g−ZnO: A First-Principles Study

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High-precision and high-efficiency measurement method of accelerator tunnel control network based on total station angle observation

“…The angle intersection method of a total station is a technique that utilizes angle observations from a total station. Each point is observed at least twice, and selected known distances are used as length constraints to solve for the overall control network [33]. As shown in figure 2, the bold line represents the observed distance as the length constraint and the fine lines represent the observed directions of devices.…”

Effects of intrinsic point defects (Tii-Vo) on the photocatalytic performance of bilayer rutile/anatase TiO2

“…In contrast to pure bilayer TiO 2 , the B-M effect in all systems is greater than the influence of the multibody effect, which widens the band gap of the system. Also, given that twodimensional TiO 2 was mainly prepared by annealing and DC magnetron sputtering in the experiments, the coexistence of O vacancies and Ti impurities during the preparation led to the formation of unavoidable composite defects, and the O vacancies caused the surrounding Ti atoms to form dangling bonds, which acted as electron capture centers [51]. The energy band diagrams in figures 3(b), (c), (e), and (f) show that the oxygen vacancies and Ti interstitials created impurity energy levels, and the photoexcitation leap, transition from the VBM, through the impurity level, and finally to the CBM, thus grading the photoexcitation leap.…”