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.

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.

A THEORETICAL STUDY OF POINT DEFECTS IN ZIRCONIA – SILICON INTERFACES

2006 ◽  
Vol 16 (01) ◽  
pp. 389-396
Author(s):  
Masashi Nakatomi ◽  
Koichi Yamashita
Keyword(s):  
Point Defects ◽  
Density Functional ◽  
Theoretical Study ◽  
Gate Dielectrics ◽  
Cell Model ◽  
Interstitial Oxygen ◽  
Super Cell ◽  
Defect Levels ◽  
Silicon Interface ◽  
Oxygen Atoms

We present a theoretical study on the point defects in ZrO 2–silicon interfaces using molecular dynamics (MD) calculations. A super-cell model that contains 9 atomic layers of silicon and 9 atomic layers of ZrO 2 was used for the simulation. Three atomic layers containing 17 oxygen atoms, eight silicon atoms, and nine Zr atoms were used to simulate the ZrO 2–silicon interface. We then performed density functional theory (DFT) with plane-wave basis to calculate the interface band structure. Results demonstrate that the stretched Zr – O bonds at the interface would produce some defect levels in the band gap. Particularly, the defect levels originated from the interstitial oxygen atoms are located close to the bottom of the ZrO 2 conduction band and hence it will affect the electrical properties of the gate dielectrics.

scholarly journals DFT Study of Cs/Sr/Ag Adsorption on Defective Matrix Graphite

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Zengtong Jiao ◽  
Xiaotong Chen ◽  
Chao Fang ◽  
Gang Xu ◽  
Chi Zhang ◽  
...  
Keyword(s):  
Point Defects ◽  
Electronic Structures ◽  
Density Functional ◽  
Fission Products ◽  
Generalized Gradient ◽  
Single Vacancy ◽  
Vacancy Defects ◽  
Adsorption Behaviors ◽  
Matrix Graphite ◽  
Adsorption Energies

The geometries, adsorption energies, and electronic structures of Cs, Sr, and Ag atoms on matrix graphite surface with point defects were calculated and analyzed using the density functional theory (DFT) and the Perdew–Burke–Ernzerhof (PBE) formulation of the generalized gradient approximation (GGA). Three different types of point defects, i.e., single vacancy and “bridge” and “spiro” interstitials are considered using approximate van der Waals (vdW) correction methods. The results of adsorption energies show that the metal fission products of Cs, Sr, and Ag are more stable on single vacancy defects than “bridge” or “spiro” interstitial defects. This is further confirmed by the analysis of electronic structures, such as charge density difference (CDD) and density of state (DOS). All these results indicate that dangling bonds play an important role in the adsorption behaviors of metallic fission products on matrix graphite.

Furnace and Rta Injection of Point Defects into CVD-Grown B Doped Si and SiGe

2000 ◽  
Vol 610 ◽  
Author(s):  
Janet M. Bonar ◽  
Barry M. Mcgregor ◽  
Nick E. B. Cowern ◽  
Aihua Dan ◽  
Graham A. Cooke ◽  
...  
Keyword(s):  
Point Defect ◽  
Point Defects ◽  
Enhancement Factor ◽  
Rapid Thermal Anneal ◽  
Furnace Annealing ◽  
Vacancy Defects ◽  
Conventional Furnace ◽  
Interstitial Defects ◽  
Defect Injection ◽  
Sims Analysis

AbstractThe diffusion of B in Si and SiGe under the influence of point defect injection by Rapid Thermal Anneal (RTA) and conventional furnace anneal is studied in this work. B-doped regions in SiGe and Si were grown by LPCVD, and point defects were injected by RTA or furnace annealing bare, Si3N4 or SiO2 + Si3N4 covered samples in an oxygen atmosphere. Self-interstitial defects will be injected into bare Si while vacancy defects will be injected into Si3N4 covered samples, and inert annealing will occur in SiO2 + Si3N4 covered samples. The annealed and asgrown profiles were determined using SIMS analysis, and the diffusivities extracted by direct comparison of the profiles. Both interstitials and vacancies were injected during furnace annealing of SiGe, as demonstrated by the respective enhancement and retardation of the B diffusion. Enhanced B diffusion in SiGe was observed even for 5 s RTA at 1000°C, with an enhancement factor of ∼2.5. The B in Si diffusivity enhancement for interstitial injection by RTA oxidation was found to be a factor of ∼3 compared to inert anneals, close to the factor for SiGe.

scholarly journals Identification of lead vacancy defects in lead halide perovskites

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
David J. Keeble ◽  
Julia Wiktor ◽  
Sandeep K. Pathak ◽  
Laurie J. Phillips ◽  
Marcel Dickmann ◽  
...  
Keyword(s):  
Point Defects ◽  
Density Functional ◽  
Defect Density ◽  
Direct Detection ◽  
Deep Level ◽  
Vacancy Defects ◽  
Positron Annihilation Lifetime ◽  
Hole Trapping ◽  
Detection And Identification ◽  
Lead Vacancy

AbstractPerovskite photovoltaics advance rapidly, but questions remain regarding point defects: while experiments have detected the presence of electrically active defects no experimentally confirmed microscopic identifications have been reported. Here we identify lead monovacancy (VPb) defects in MAPbI3 (MA = CH3NH3+) using positron annihilation lifetime spectroscopy with the aid of density functional theory. Experiments on thin film and single crystal samples all exhibited dominant positron trapping to lead vacancy defects, and a minimum defect density of ~3 × 1015 cm−3 was determined. There was also evidence of trapping at the vacancy complex $$({{{{{\rm{V}}}}}}_{{{{{\rm{Pb}}}}}}{{{{{\rm{V}}}}}}_{{{{{\rm{I}}}}}})^{-}$$ ( V Pb V I ) − in a minority of samples, but no trapping to MA-ion vacancies was observed. Our experimental results support the predictions of other first-principles studies that deep level, hole trapping, $${{{{{{\rm{V}}}}}}}_{{{{{{\rm{Pb}}}}}}}^{2-}$$ V Pb 2 − , point defects are one of the most stable defects in MAPbI3. This direct detection and identification of a deep level native defect in a halide perovskite, at technologically relevant concentrations, will enable further investigation of defect driven mechanisms.

Antimony and Boron Diffusion in Silicon and Silicon Germanium under the Influence of Point Defects Injection by Rapid Thermal Anneal

2001 ◽  
Vol 669 ◽  
Author(s):  
Aihua Dan ◽  
Arthur F. W. Willoughby ◽  
Janet M. Bonar ◽  
Barry M. McGregor ◽  
Mark G. Dowsett ◽  
...  
Keyword(s):  
Point Defect ◽  
Point Defects ◽  
Silicon Germanium ◽  
Secondary Ion Mass Spectrometry ◽  
Diffusion Time ◽  
Injection Technique ◽  
Boron Diffusion ◽  
Rapid Thermal Anneal ◽  
Vacancy Defects ◽  
Defect Injection

ABSTRACTThe effect of point defect injection on the diffusion of antimony and boron in silicon and silicon-germanium alloys has been studied by comparison of inert with injection diffusions. In this work, Sb and B in Si were used as control wafers to investigate Sb and B diffusion behavior in Si0.9Ge0.1. The point defect injection technique was carried out by rapid thermal annealing (RTA) Sb and B in Si and Si0.9Ge0.1 samples with the various surface coatings in either oxygen or ammonia atmospheres to inject either interstitial or vacancy defects. The diffusion profiles for as-grown and RTA annealed samples were measured by Secondary Ion Mass Spectrometry (SIMS). Diffusivities for B in Si and Si0.9Ge0.1 were obtained using computer simulations of the measured boron profiles for their annealed samples. Sb diffusion in Si and Si0.9Ge0.1 was found enhanced by vacancy injection and retarded by interstitial injection. The enhanced B diffusion in Si and Si0.9Ge0.1 was found by interstitial injection. These results confirm that Sb diffusion in Si0.9Ge0.1 is primarily dominated by vacancy-mediated mechanism, while B diffuses in Si0.9Ge0.1 by an interstitially mediated mechanism. The effect of the RTA diffusion time on the B diffusion in Si and Si0.9Ge0.1 has also been investigated. The diffusivity versus diffusion time of B in Si and Si0.9Ge0.1 for inert and injection samples is presented. It was found that the shorter annealing time had the faster diffusion. This suggested that it caused by transient diffusion effect arising from point defects.

Detection of a point defect in a silicon single crystal by high-resolution TEM

1995 ◽  
Vol 53 ◽  
pp. 466-467
Author(s):  
M. Awaji
Keyword(s):  
High Resolution ◽  
Single Crystal ◽  
Point Defect ◽  
Point Defects ◽  
Noise Level ◽  
Dark Field ◽  
Silicon Single Crystal ◽  
High Resolution Image ◽  
Dark Field Imaging ◽  
Field Imaging

It is necessary to improve the resolution, brightness and signal-to-noise ratio(s/n) for the detection and identification of point defects in crystals. In order to observe point defects, multi-beam dark-field imaging is one of the useful methods. Though this method can improve resolution and brightness compared with dark-field imaging by diffuse scattering, the problem of s/n still exists. In order to improve the exposure time due to the low intensity of the dark-field image and the low resolution, we discuss in this paper the bright-field high-resolution image and the corresponding subtracted image with reference to a changing noise level, and examine the possibility for in-situ observation, identification and detection of the movement of a point defect produced in the early stage of damage process by high energy electron bombardment.The high-resolution image contrast of a silicon single crystal in the [10] orientation containing a triple divacancy cluster is calculated using the Cowley-Moodie dynamical theory and for a changing gaussian noise level. This divacancy model was deduced from experimental results obtained by electron spin resonance. The calculation condition was for the lMeV Berkeley ARM operated at 800KeV.

scholarly journals Mechanical Stability of Hybrid Corrugated Sandwich Plates under Fluid-Structure-Thermal Coupling for Novel Thermal Protection Systems

2020 ◽  
Vol 10 (8) ◽  
pp. 2790
Author(s):  
Wenzheng Zhuang ◽  
Chao Yang ◽  
Zhigang Wu
Keyword(s):  
Mechanical Stability ◽  
Thermal Protection ◽  
Element Model ◽  
Parameter Study ◽  
The Novel ◽  
Thermal Coupling ◽  
Mechanical Instability ◽  
Fluid Structure ◽  
Thermal Protection Systems ◽  
Protection Systems

Hybrid corrugated sandwich (HCS) plates have become a promising candidate for novel thermal protection systems (TPS) due to their multi-functionality of load bearing and thermal protection. For hypersonic vehicles, the novel TPS that performs some structural functions is a potential method of saving weight, which is significant in reducing expensive design/manufacture cost. Considering the novel TPS exposed to severe thermal and aerodynamic environments, the mechanical stability of the HCS plates under fluid-structure-thermal coupling is crucial for preliminary design of the TPS. In this paper, an innovative layerwise finite element model of the HCS plates is presented, and coupled fluid-structure-thermal analysis is performed with a parameter study. The proposed method is validated to be accurate and efficient against commercial software simulation. Results have shown that the mechanical instability of the HCS plates can be induced by fluid-structure coupling and further accelerated by thermal effect. The influences of geometric parameters on thermal buckling and dynamic stability present opposite tendencies, indicating a tradeoff is required for the TPS design. The present analytical model and numerical results provide design guidance in the practical application of the novel TPS.

scholarly journals Imaging and identification of point defects in PtTe2

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Kuanysh Zhussupbekov ◽  
Lida Ansari ◽  
John B. McManus ◽  
Ainur Zhussupbekova ◽  
Igor V. Shvets ◽  
...  
Keyword(s):  
Point Defects ◽  
Density Functional ◽  
Transition Metal Dichalcogenides ◽  
Density Functional Theory Calculations ◽  
Charge Carrier Mobility ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Recombination Rates ◽  
And Performance

AbstractThe properties and performance of two-dimensional (2D) materials can be greatly affected by point defects. PtTe2, a 2D material that belongs to the group 10 transition metal dichalcogenides, is a type-II Dirac semimetal, which has gained a lot of attention recently due to its potential for applications in catalysis, photonics, and spintronics. Here, we provide an experimental and theoretical investigation of point defects on and near the surface of PtTe2. Using scanning tunneling microscopy and scanning tunneling spectroscopy (STS) measurements, in combination with first-principle calculations, we identify and characterize five common surface and subsurface point defects. The influence of these defects on the electronic structure of PtTe2 is explored in detail through grid STS measurements and complementary density functional theory calculations. We believe these findings will be of significance to future efforts to engineer point defects in PtTe2, which is an interesting and enticing approach to tune the charge-carrier mobility and electron–hole recombination rates, as well as the site reactivity for catalysis.

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