Electronic property of intrinsic point defect system on β–Si3N4 (0001) surface

2021 ◽  
pp. 2150359
Author(s):  
Lingxia Li ◽  
Xuefeng Lu ◽  
Jianhua Luo ◽  
Xin Guo ◽  
Junqiang Ren ◽  
...  
Keyword(s):  
Surface Layer ◽  
Energy Level ◽  
Absorption Coefficient ◽  
Fermi Level ◽  
Point Defect ◽  
Density Functional ◽  
Intrinsic Point Defect ◽  
Energy Bands ◽  
Additional Energy ◽  
Vacancy Defects

The intrinsic point defect influence data for [Formula: see text]–Si3N4 by far are incomplete and experimental clarification is not easy. In this contribution, the effects of vacancy ([Formula: see text], [Formula: see text] and [Formula: see text]) and interstitial ([Formula: see text] and [Formula: see text]) defects on the electronic properties of H-passivated [Formula: see text]–Si3N4 (0001) surface are explored based on density functional theory (DFT) calculation. The results show that it is easier to form [Formula: see text] vacancy defects in the surface layer under Si-rich conditions. The existence of N vacancies makes the bottom of conduction bands shift downwards, and the top of valance band is away from Fermi level. The presence of [Formula: see text] makes the system have the characteristics of p-type semiconductor, and the closer to the inner layer, the narrower the range of additional energy bands and the greater the degree of localization of electrons. The closer the Si atom vacancy is to the surface, the smaller the photon energy corresponding to the maximum absorption coefficient is. Compared with the N vacancy system, the Si vacancy system has higher reflection ability in the low energy region. For the interstitial defect systems, [Formula: see text] is easy to form on the surface layer, and [Formula: see text] is easy to produce in the inner layer. The [Formula: see text] system has a new additional energy level at the Fermi level, and as the [Formula: see text] is closer to the inner layer, the energy range of the additional energy level is also narrower. In the [Formula: see text] system, the new additional energy levels appear at the Fermi level and the intermediate band. The results have positive significance for the design of this advanced structural and functional integrated ceramics. The absorption coefficient and reflection coefficient of [Formula: see text] system are much higher than those of other systems when the energy is greater than 2.5 eV.

scholarly journals First-Principles Study of Vacancy and Impurities Defects in Graphene

2021 ◽  
Vol 2 (01) ◽  
pp. 93-102
Author(s):  
Hari Krishna Neupane ◽  
Narayan Prasad Adhikari
Keyword(s):  
Magnetic Properties ◽  
Energy Level ◽  
Density Of States ◽  
Fermi Energy ◽  
First Principles ◽  
Density Functional ◽  
Partial Density ◽  
Fermi Energy Level ◽  
Vacancy Defects ◽  
Impurity Defects

In this work, we have studied the electronic and magnetic properties of 1C atom vacancy defects in graphene (1Cv-d-G), 1N atom impurity defects in graphene (1NI-d-G) and 1O atom impurity defects in graphene (1OI-d-G) materials through first principles calculations based on spin-polarized density functional theory (DFT) method, using computational tool Quantum ESPRESSO (QE) code. From band structure and density of states (DOS) calculations, we found that supercell structure of monolayer graphene is a zero bandgap material. But, electronic bands of 1Cv-d-G, 1NI-d-G and 1OI-d-G materials split around the Fermi energy level and DOS of up & down spins states appear in the Fermi energy level. Thus, 1Cv-d-G, 1NI-d-G and 1OI-d-G materials have metallic properties. We have studied the magnetic properties of pure and defected materials by analyzing density of states (DOS) and partial density of states (PDOS) calculations. We found that graphene and 1OI-d-G materials have non-magnetic properties. On the other hand, 1C vacancy atom and 1N impurity atom induced magnetization in 1Cv-d-G & 1NI-d-G materials by the rebonding of dangling bonds and acquiring significant magnetic moments of values -0.75μB/cell & 0.05μB/cell respectively through remaining unsaturated dangling bond. Therefore, non-magnetic graphene changes to magnetic 1Cv-d-G and 1NI-d-G materials due to 1C atom vacancy defects and 1N atom impurity defects. The 2p orbital of carbon atoms has main contribution of magnetic moment in these defected structures.

scholarly journals First Principles Study on the Thermodynamic and Elastic Mechanical Stability of Mg2X (X = Si,Ge) Intermetallics with (anti) Vacancy Point Defects

Crystals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 234 ◽  
Author(s):  
Yuhong Zhao ◽  
Jinzhong Tian ◽  
Guoning Bai ◽  
Leting Zhang ◽  
Hua Hou
Keyword(s):  
Point Defect ◽  
Elastic Deformation ◽  
Point Defects ◽  
Density Functional ◽  
Lattice Site ◽  
Mechanical Stability ◽  
Cell Model ◽  
Mechanical Instability ◽  
Volume Deformation ◽  
Vacancy Defects

In this paper, based on the density functional theory, through thermodynamic and mechanical stability criteria, the crystal cell model of intermetallic compounds with vacancy and anti-site point defects is constructed and the lattice constant, formation heat, binding energy, elastic constant, and elastic modulus of Mg2X (X = Si, Ge) intermetallics with or without point defects are calculated. The results show that the difference in the atomic radius leads to the instability and distortion of crystal cells with point defects; Mg2X are easier to form vacancy defects than anti-site defects on the X (X = Si, Ge) lattice site, and form anti-site defects on the Mg lattice site. Generally, the point defect is more likely to appear at the Mg position than at the Si or Ge position. Among the four kinds of point defects, the anti-site defect x M g is the easiest to form. The structure of intermetallics without defects is more stable than that with defects, and the structure of the intermetallics with point defects at the Mg position is more stable than that at the Si/Ge position. The anti-site and vacancy defects will reduce the material’s resistance to volume deformation shear strain, and positive elastic deformation, and increase the mechanical instability of the elastic deformation of the material. Compared with the anti-site point defect, the void point defect can lead to the mechanical instability of the transverse deformation of the material and improve the plasticity of the material. The research in this paper is helpful for the analysis of the mechanical stability of the elastic deformation of Mg2X (X = Si, Ge) intermetallics under the service condition that it is easy to produce vacancy and anti-site defects.

scholarly journals Ti3O5 and Al2TiO5 Crystals Flotation Characteristics from Ti-bearing Blast Furnace Slag: A Density Functional Theory and Experimental Study

Crystals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 838
Author(s):  
Shan Ren ◽  
Zenghui Su ◽  
Weizao Liu ◽  
Yali Sun ◽  
Xiaoming Li ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Blast Furnace ◽  
Energy Level ◽  
Fermi Energy ◽  
Density Functional ◽  
Dft Calculation ◽  
Fermi Energy Level ◽  
Energy Bands ◽  
Functional Theory ◽  
Bond Population

Anosovite crystalline is an ideal mineral for flotation from the Ti-bearing blast furnace (TBBF) slag. Ti3O5 crystal and Al2TiO5 crystal are two kinds of anosovites, and the Al element significantly affects the electronic structure and flotation performance of anosovite. The floatability of Ti3O5 and Al2TiO5 crystals were studied by Mulliken populations, energy bands, and density of states (DOS). In addition, the flotation experiment of the two kinds of anosovite crystals (Ti3O5 and Al2TiO5) was conducted and proved that the density functional theory (DFT) calculation results were accurate. Compared with Ti3O5 crystal, the Fermi energy level of Al2TiO5 crystal shifts around 2 eV in a negative direction by DOS analysis, which is beneficial to flotation. And Al2TiO5 crystal possesses a larger value of bond population, which is 0.41, for Ti-O bonds than Ti3O5 crystal and the bond length of Ti-O in Al2TiO5 crystal is shorter, therefore Al2TiO5 crystal shows a stronger covalency. The changes of the Fermi energy level and the covalency bonds in Al2TiO5 crystal both demonstrated that doping the Al component into the Ti3O5 crystal was beneficial to improve the flotation effect. Moreover, the Al2TiO5 crystal had a higher flotation efficiency compared to the Ti3O5 crystal when the dosages of salicylhydroxamic acid (SHA) and sodium oleate were the same. Therefore, both DFT calculation and experiment show that the flotation effect of the Al2TiO5 crystal is better than that of the Ti3O5 crystal.

scholarly journals Effect of Intrinsic Point Defect on the Magnetic Properties of ZnO Nanowire

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Jiangni Yun ◽  
Zhiyong Zhang ◽  
Tieen Yin
Keyword(s):  
Magnetic Properties ◽  
Point Defect ◽  
Density Functional ◽  
Population Analysis ◽  
First Principles Calculation ◽  
Spin Splitting ◽  
Partial Density ◽  
Intrinsic Point Defect ◽  
Zno Nanowire ◽  
Mulliken Population

The effect of intrinsic point defect on the magnetic properties of ZnO nanowire is investigated by the first-principles calculation based on the density functional theory (DFT). The calculated results reveal that the pure ZnO nanowire without intrinsic point defect is nonmagnetic and ZnO nanowire withVO,Zni,Oi,OZn, or ZnOpoint defect also is nonmagnetic. However, a strong spin splitting phenomenon is observed in ZnO nanowire withVZndefect sitting on the surface site. The Mulliken population analysis reveals that the oxygen atoms which are close to theVZndefect do major contribution to the magnetic moment. Partial density states calculation further suggests that the appearance of the half-metallic ferromagnetism in ZnO nanorod withVZnoriginates from the hybridization of the O2p states with Zn 3d states.

Electronic and magnetic properties of defected MoS2 monolayer

BIBECHANA ◽  
2021 ◽  
Vol 18 (2) ◽  
pp. 68-79
Author(s):  
Hari Krishna Neupane ◽  
Narayan Prasad Adhikari
Keyword(s):  
Magnetic Properties ◽  
Magnetic Moment ◽  
Density Functional ◽  
2D Materials ◽  
Dft Method ◽  
Vacancy Defect ◽  
Energy Bands ◽  
Band Structures ◽  
Vacancy Defects ◽  
Electronic And Magnetic Properties

It is interesting to understand the effect of defects in 2D materials because vacancy defects in 2D materials have novel electronic and magnetic properties. In this work, we studied electronic and magnetic properties of 1S vacancy defect (1Sv-MoS2), 2S vacancy defects (2Sv-MoS2), 1Mo vacancy defect (Mov-MoS2), and (1Mo & 1S) vacancy defects ((Mo-S)v-MoS2) in 2D MoS2 material by first-principles calculations within spin-polarized density functional theory (DFT) method. To understand the electronic properties of materials, we have analyzed band structures and DOS calculations and found that 1Sv-MoS2 & 2Sv-MoS2 materials have semiconducting nature. This is because, 1Sv-MoS2 & 2Sv-MoS2 materials open a small energy band gap of values 0.68 eV & 0.54 eV respectively in band structures. But, in Mov-MoS2 & (Mo-S)v-MoS2 materials, energy bands around the Fermi level mix with the orbital’s of Mo and S atoms. As a result, bands are split and raised around and above the Fermi energy level. Therefore, Mov-MoS2 & (Mo-S)v-MoS2 materials have metallic nature. We found that MoS2, 1Sv-MoS2 & 2Sv-MoS2 materials have non-magnetic properties, and Mov-MoS2 & (Mo-S)v-MoS2 materials have magnetic properties because magnetic moment of MoS2, 1Sv-MoS2 & 2Sv-MoS2 materials have 0.00 µB/cell value and Mov-MoS2 & (Mo-S)v-MoS2 materials have 2.72 µB/cell & 0.99 µB/cell  respectively. Therefore, non-magnetic MoS2 changes to magnetic Mov-MoS2 & (Mo-S)v-MoS2 materials due to Mo and (1Mo & 1S) vacancy defects.  The magnetic moment obtained in Mov-MoS2 & (Mo-S)v-MoS2 materials due to the distribution of up and down spins in 4p, 4d & 5s orbitals of  Mo atoms and 3s & 3p orbitals of S atoms in structures. The significant values of the magnetic moment are given by distributed spins in 4d orbital of Mo atoms and 3p orbital of S atoms. BIBECHANA 18 (2) (2021) 68-79  

scholarly journals Structural, Electronic and Magnetic Properties of Defected Water Adsorbed Single-Layer MoS2

2021 ◽  
Vol 26 (1) ◽  
pp. 43-50
Author(s):  
Hari Krishna Neupane ◽  
Narayan Prasad Adhikari
Keyword(s):  
Magnetic Properties ◽  
Band Structure ◽  
Density Of States ◽  
Density Functional ◽  
Single Layer ◽  
Vacancy Defect ◽  
Partial Density ◽  
Energy Bands ◽  
Vacancy Defects ◽  
Electronic And Magnetic Properties

Water adsorbed in MoS2 (wad-MoS2), 1S atom vacancy defect in wad-MoS2 (1S-wad-MoS2), 2S atoms vacancy defects in wad-MoS2 (2S-wad-MoS2), and 1Mo atom vacancy defect in wad-MoS2 (Mo-wad-MoS2) materials were constructed, and their structural, electronic, and magnetic properties were studied by spin-polarized density functional theory (DFT) based first-principles calculations. The wad-MoS2, 1S-wad-MoS2, 2S-wad-MoS2, and Mo-wad-MoS2 materials were found stable. From band structure calculations, wad-MoS2, 1S-wad-MoS2 and 2S-wad-MoS2 materials open energy bandgap of values 1.19 eV, 0.65 eV and 0.38 eV respectively. Also, it was found that the conductivity strength of the material increases with an increase in the concentration of S atom vacancy defects in the structure. On the other hand, the Mo-wad-MoS2 material has metallic properties because energy bands of electrons crossed the Fermi energy level in the band structure. For the investigation of magnetic properties, the density of states (DoS) and partial density of states (PDoS) calculations were used and found that wad-MoS2, 1S-wad-MoS2, and 2S-wad-MoS2 are non-magnetic materials, while Mo-wad-MoS2 is a magnetic material. The total magnetic moment of Mo-wad-MoS2 has a value of 2.66 µB/cell, due to the arrangement of unpaired up-spin and down-spin of electrons in 3s & 3p orbitals of S atoms; and 4p, 4d & 5s orbitals of Mo atoms in the material.

scholarly journals Theory of the Thermal Stability of Silicon Vacancies and Interstitials in 4H–SiC

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 167
Author(s):  
José Coutinho
Keyword(s):  
Thermal Stability ◽  
Fermi Level ◽  
Density Functional ◽  
Dynamic Properties ◽  
Type Material ◽  
Temperature Threshold ◽  
Effect Analysis ◽  
Mobile Species ◽  
Two Stages ◽  
Thermal Stability Of

This paper presents a theoretical study of the electronic and dynamic properties of silicon vacancies and self-interstitials in 4H–SiC using hybrid density functional methods. Several pending issues, mostly related to the thermal stability of this defect, are addressed. The silicon site vacancy and the carbon-related antisite-vacancy (CAV) pair are interpreted as a unique and bistable defect. It possesses a metastable negative-U neutral state, which “disproportionates” into VSi+ or VSi−, depending on the location of the Fermi level. The vacancy introduces a (−/+) transition, calculated at Ec−1.25 eV, which determines a temperature threshold for the annealing of VSi into CAV in n-type material due to a Fermi level crossing effect. Analysis of a configuration coordinate diagram allows us to conclude that VSi anneals out in two stages—at low temperatures (T≲600 °C) via capture of a mobile species (e.g., self-interstitials) and at higher temperatures (T≳1200 °C) via dissociation into VC and CSi defects. The Si interstitial (Sii) is also a negative-U defect, with metastable q=+1 and q=+3 states. These are the only paramagnetic states of the defect, and maybe that explains why it escaped detection, even in p-type material where the migration barriers are at least 2.7 eV high.

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