Journal articles: 'Vacancy defects'

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Melikhova, Oksana, Jakub Čížek, Ivan Procházka, Tetyana E. Konstantinova, and Igor A. Yashchishyn. "Inhibition of Positronium Formation in Yttria Stabilized Zirconia Nanopowders Modified by Addition of Chromia." Materials Science Forum 733 (November 2012): 249–53. http://dx.doi.org/10.4028/www.scientific.net/msf.733.249.

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The effect of chromia additive on defects in yttria stabilized zirconia (YSZ) nanopowders was investigated in this work. It was found that positrons are trapped at vacancy-like misfit defect at grain boundaries and at larger defects situated at triple points. Moreover, a long-lived ortho-positronium contribution was found in YSZ nanopowder without chromia. Addition of chromia prolongs the lifetime of positrons trapped at vacancy-like misfit defects which indicates segregation of Cr ions at grain interfaces and interaction of Cr with vacancy-like misfit defets. Moreover addition of chromia completely suppresses formation of positronium.

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Choudhary, Sudhanshu, and Divya Kaushik. "Understanding the effect of vacancy defects on spin transport in CrO2–graphene–CrO2 magnetic tunnel junction." Modern Physics Letters B 30, no. 09 (April 10, 2016): 1650102. http://dx.doi.org/10.1142/s0217984916501025.

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In this paper, we investigate the effect of vacancy defects on spin transport in graphene-based magnetic tunnel junction (MTJ). An increase in conductance was seen in vacancy-defected MTJ structure which is in contrast to the results reported in past where a decrease in conductance with vacancy was observed for graphene sheets. This increase in conductance may be due to the use of CrO2 half-metallic ferromagnet (HMF) electrodes instead of metallic or ferromagnet (FM) electrodes. Furthermore, high tunnel magnetoresistance (TMR) [Formula: see text]99% and perfect spin filtration was obtained for both vacancy-defected and no-defect (pristine) MTJ structures. The TMR in vacancy-defected structure is seen to decrease by 6.2% and by 13% at bias voltages of 1.2[Formula: see text]V and 1.4[Formula: see text]V, when compared to TMR in no-defect MTJ structure.

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Zhan, Si-Qi, Hui Wan, Liang Xu, Wei-Qing Huang, Gui-Fang Huang, Jin-Ping Long, and P. Peng. "Native vacancy defects in bismuth sulfide." International Journal of Modern Physics B 28, no. 23 (July 13, 2014): 1450150. http://dx.doi.org/10.1142/s0217979214501501.

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Bismuth sulfide ( Bi 2S3) exhibits excellent photocatalytic activity under visible light. We perform first-principles, density-function theory (DFT) calculations of the electronic structure for the Bi 2S3 with native vacancy to facilitate its applications by gaining insight into the role of native defects. We find that the Bi vacancies are effective p-type defects for Bi 2S3, while the S vacancies induce an intermediate level appearing in the band gap. Besides one Bi vacancy, the native vacancy defect at other four inequivalent positions in Bi 2S3 leads to a reduction of band gap. Moreover, the change of band gap depends on the position of native vacancy defect. The results indicate that the native defects are the most likely physical cause for the scattered band gaps obtained by experiments. The influence of native vacancy defects on the photocatalytic properties of Bi 2S3 is also discussed.

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Uedono, Akira, Shoji Ishibashi, Nagayasu Oshima, and Ryoichi Suzuki. "Vacancy-Type Defects in GaN for Power Devices Probed by Positron Annihilation." Defect and Diffusion Forum 373 (March 2017): 183–88. http://dx.doi.org/10.4028/www.scientific.net/ddf.373.183.

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Native defects and ion-implantation induced defects in GaN were studied by means of positron annihilation. Measurements of Doppler broadening spectra of the annihilation radiation for GaN layers grown on Si substrates showed that optically active vacancy-type defects were formed in the layers. Charge transition of the defects due to electron capture occurred when the layers were irradiated by photons with energy above 2.7 eV. It was found that Ti deposition and subsequent annealing introduced vacancy clusters. We also characterized vacancy-type defects in Mg-implanted GaN. The major defect species of vacancies introduced by Mg-implantation was a complex between Ga-vacancy (VGa) and nitrogen vacancies (VNs). After annealing above 1000C, these defects started to agglomerate, and the major defect species became (VGa)2 coupled with VNs. Through this work, we have demonstrated that positron annihilation spectroscopy is a powerful tool for characterizing vacancy-type defects in GaN for power devices applications.

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Chu, Liu, Jiajia Shi, and Shujun Ben. "Buckling Analysis of Vacancy-Defected Graphene Sheets by the Stochastic Finite Element Method." Materials 11, no. 9 (August 27, 2018): 1545. http://dx.doi.org/10.3390/ma11091545.

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Vacancy defects are unavoidable in graphene sheets, and the random distribution of vacancy defects has a significant influence on the mechanical properties of graphene. This leads to a crucial issue in the research on nanomaterials. Previous methods, including the molecular dynamics theory and the continuous medium mechanics, have limitations in solving this problem. In this study, the Monte Carlo-based finite element method, one of the stochastic finite element methods, is proposed and simulated to analyze the buckling behavior of vacancy-defected graphene. The critical buckling stress of vacancy-defected graphene sheets deviated within a certain range. The histogram and regression graphs of the probability density distribution are also presented. Strengthening effects on the mechanical properties by vacancy defects were detected. For high-order buckling modes, the regularity and geometrical symmetry in the displacement of graphene were damaged because of a large amount of randomly dispersed vacancy defects.

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PRASAD, MATUKUMILLI V. D., and BAIDURYA BHATTACHARYA. "MOLECULAR DYNAMICS SIMULATIONS OF CARBON NANOTUBE-BASED OSCILLATORS HAVING TOPOLOGICAL DEFECTS." International Journal of Nanoscience 10, no. 01n02 (February 2011): 355–59. http://dx.doi.org/10.1142/s0219581x11008009.

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Effect of vacancy and Stone–Wales defects on the oscillatory behavior of (5,5)/(10,10) carbon nanotube-based oscillator are studied using NVE molecular dynamics simulations. Results show that defects reduce stability of the oscillators. Effect of single vacancy defect on stability is very small, whereas Stone–Wales defect considerably reduces the stability thereby damping the oscillations quickly. Further increase in density of vacancy defects causes a monotonic decrease of stability of oscillator. In all cases the initial temperature (1 and 300 K) had almost no effect on the oscillation stability.

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Sozykin, Sergey Anatolevich, Valeriy Petrovich Beskachko, and G. P. Vyatkin. "Atomic Structure and Mechanical Properties of Defective Carbon Nanotube (7,7)." Materials Science Forum 843 (February 2016): 78–84. http://dx.doi.org/10.4028/www.scientific.net/msf.843.78.

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The article presents the results of first-principle modeling of a defectless (7,7) carbon nanotube and (7,7) nanotubes containing single and double vacancy defects, as well as Stone–Wales defects. These types of defects are often found in real nanotubes and affect their properties. We have established that reliable results can be obtained by using models of more than 1.5 nm in length. It turned out that a single vacancy defect has the least influence on Young modulus, and double n type vacancy defect in the most influential. The elongation at break also depends on the defect type and is 30-60% less than for perfect tubes.

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Chu, Liu, Jiajia Shi, Eduardo Souza de Cursi, Xunqian Xu, Yazhou Qin, and Hongliang Xiang. "Monte Carlo-Based Finite Element Method for the Study of Randomly Distributed Vacancy Defects in Graphene Sheets." Journal of Nanomaterials 2018 (October 10, 2018): 1–12. http://dx.doi.org/10.1155/2018/3037063.

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This paper proposed an effective stochastic finite element method for the study of randomly distributed vacancy defects in graphene sheets. The honeycomb lattice of graphene is represented by beam finite elements. The simulation results of the pristine graphene are in accordance with literatures. The randomly dispersed vacancies are propagated and performed in graphene by integrating Monte Carlo simulation (MCS) with the beam finite element model (FEM). The results present that the natural frequencies of different vibration modes decrease with the augment of the vacancy defect amount. When the vacancy defect reaches 5%, the regularity and geometrical symmetry of displacement and rotation in vibration behavior are obviously damaged. In addition, with the raise of vacancy defects, the random dispersion position of vacancy defects increases the variance in natural frequencies. The probability density distributions of natural frequencies are close to the Gaussian and Weibull distributions.

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Neupane, Hari Krishna, and Narayan Prasad Adhikari. "Tuning Structural, Electronic, and Magnetic Properties of C Sites Vacancy Defects in Graphene/MoS2 van der Waals Heterostructure Materials: A First-Principles Study." Advances in Condensed Matter Physics 2020 (November 28, 2020): 1–11. http://dx.doi.org/10.1155/2020/8850701.

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In this work, we systematically studied the structure, and electronic and magnetic properties of van der Waals (vdWs) interface Graphene/MoS2 heterostructure (HS-G/MoS2) and C sites vacancy defects in HS-G/MoS2 materials using first-principles calculations. By the structural analysis, we found that nondefects geometry is more compact than defects geometries. To investigate the electronic and magnetic properties of HS-G/MoS2 and C sites vacancy defects in HS-G/MoS2 materials, we have studied band structure, density of states (DOS), and partial density of states (PDOS). By analyzing the results, we found that HS-G/MoS2 is metallic in nature but C sites vacancy defects in HS-G/MoS2 materials have a certain energy bandgap. Also, from the band structure calculations, we found that Fermi energy level shifted towards the conduction band in vacancy defects geometries which reveals that the defected heterostructure is n-type Schottky contacts. From DOS and PDOS analysis, we obtained that the nonmagnetic HS-G/MoS2 material changes to magnetic materials due to the presence of C sites vacancy defects. Right 1C atom vacancy defects (R-1C), left 1C atom vacancy defects (L-1C), centre 1C atom vacancy defects (C-1C), and 2C (1C right and 1C centre) atom vacancy defects in HS-G/MoS2 materials have magnetic moments of −0.75 µB/cell, −0.75 µB/cell, −0.12 µB/cell, and +0.39 µB/cell, respectively. Electrons from 2s and 2p orbitals of C atoms have main contributions for the magnetism in all these materials.

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Li, Ke Jian, and Hong Xia Liu. "Electronic Structures of Vacancy Defective Chiral (6,2) SiC Nanotubes." Materials Science Forum 896 (March 2017): 3–8. http://dx.doi.org/10.4028/www.scientific.net/msf.896.3.

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Vacancy defects are common defects formed in the syntheses of silicon carbide nanotubes (SiCNTs) and seriously impact the electronic structures of the nanotubes. With first-principle calculations based on density functional theory (DFT), vacancy defective (6,2) SiCNTs are studied. Vacancies form a pair of fivefold and ninefold rings. Carbon vacancy introduces an occupied defect level near the top of the valence band and an unoccupied level in the conduction band. Three defect levels are found in the band gap of the SiCNT with a silicon vacancy. These results are helpful for investigations on SiCNT devices and sensors.

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11

Shoemaker, J. R., R. T. Lutton, D. Wesley, W. R. Wharton, M. L. Oehrli, M. S. Herte, M. J. Sabochick, and N. Q. Lam. "Point defect study of CuTi and CuTi2." Journal of Materials Research 6, no. 3 (March 1991): 473–82. http://dx.doi.org/10.1557/jmr.1991.0473.

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The energies and configurations of interstitials and vacancies in the ordered compounds CuTi and CuTi2 were determined using atomistic simulation with realistic embedded-atom potentials. The formation energy of an antisite pair was found to be 0.385 and 0.460 eV in CuTi and CuTi2, respectively. In both compounds, the creation of a vacancy by the removal of either a Cu or Ti atom resulted in a vacant Cu site, with an adjacent antisite defect in the case of the Ti vacancy. The vacant Cu site in CuTi was found to be very mobile within two adjacent (001) Cu planes, with a migration energy of 0.19 eV, giving rise to two-dimensional migration. The vacancy migration energy across (001) Ti planes, however, was 1.32 eV, which could be lowered to 0.75 or 0.60 eV if one or two Cu antisite defects were initially present in these planes. In CuTi2, the vacancy migration energy of 0.92 eV along the (001) Cu plane was significantly higher than in CuTi. The effective vacancy formation energies were calculated to be 1.09 eV and 0.90 eV in CuTi and CuTi2, respectively. Interstitials created by inserting either a Cu or Ti atom had complicated configurations in which a Cu 〈111〉 split interstitial was surrounded by two or three Ti antisite defects. The interstitial formation energy was estimated to be 1.7 eV in CuTi and 1.9 eV in CuTi2.

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12

Triantou, K., K. Mergia, and I. E. Stamatelatos. "Positron Annihilation Lifetime Spectroscopy in the study of defects in materials." HNPS Proceedings 24 (April 1, 2019): 235. http://dx.doi.org/10.12681/hnps.1872.

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The Positron Annihilation Lifetime Spectroscopy (PALS) is a valuable method for the study of the open volume defects in materials. The reduced electron density at the vacant/defect site increases the positron lifetime, and positron lifetime increases as the size of defect increases. In the current paper the experimental apparatus for the measurement of the positron lifetime in materials is described and the spectra from W and Cd specimens are analyzed. The presence of dislocations and vacancy defects is found, since the positron lifetimes of specimens are higher than the defect-free (bulk) values.

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13

Zhang, Tao, Ying Liang, Hao Guo, Tian C. Zhang, Haidong Fan, and Xiaobao Tian. "The interaction between vacancy defects in gallium sulfide monolayer and a new vacancy defect model." Physical Chemistry Chemical Physics 23, no. 24 (2021): 13623–32. http://dx.doi.org/10.1039/d1cp01194d.

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14

Cai, Lili, and Cuiju Feng. "Effect of Vacancy Defects on the Electronic Structure and Optical Properties of GaN." Journal of Nanotechnology 2017 (2017): 1–6. http://dx.doi.org/10.1155/2017/6987430.

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The effect of gallium vacancy (VGa) and nitrogen vacancy (VN) defects on the electronic structure and optical properties of GaN using the generalized gradient approximation method within the density functional theory were investigated. The results show that the band gap increases in GaN with vacancy defects. Crystal parameters decrease in GaN with nitrogen vacancy (GaN:VN) and increase in GaN with gallium vacancy (GaN:VGa). The Ga vacancy introduces defect levels at the top of the valence band, and the defect levels are contributed by N2p electron states. In addition, the energy band shifts to lower energy in GaN:VNand moves to higher energy in GaN:VGa. The level splitting is observed in the N2p states of GaN:VNand Ga3d states of GaN:VGa. New peaks appear in lower energy region of imaginary dielectric function in GaN:VNand GaN:VGa. The main peak moves to higher energy slightly and the intensity decreases.

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Zhao, Yuhong, Jinzhong Tian, Guoning Bai, Leting Zhang, and Hua Hou. "First Principles Study on the Thermodynamic and Elastic Mechanical Stability of Mg2X (X = Si,Ge) Intermetallics with (anti) Vacancy Point Defects." Crystals 10, no. 3 (March 23, 2020): 234. http://dx.doi.org/10.3390/cryst10030234.

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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.

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Ma, Bao-Long, Yi-Yuan Wu, Yan-Hui Guo, Wen Yin, Qin Zhan, Hong-Guang Yang, Sheng Wang, and Bao-Tian Wang. "Effects of Monovacancy and Divacancies on Hydrogen Solubility, Trapping and Diffusion Behaviors in fcc-Pd by First Principles." Materials 13, no. 21 (October 30, 2020): 4876. http://dx.doi.org/10.3390/ma13214876.

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The hydrogen blistering phenomenon is one of the key issues for the target station of the accelerator-based neutron source. In the present study, the effect of monovacancies and divacancies defects on the solution, clustering and diffusion behaviors of H impurity in fcc-Pd were studied through first principles calculations. Our calculations prove that vacancies behave as an effective sink for H impurities. We found that, although the H-trap efficiency of the larger vacancy defect was reduced, its H-trap ability strengthened. There is a short-ranged area around the vacancy defects in which H impurities tend to diffuse to vacancy defects, gather and form hydrogen bubbles. Therefore, the characteristic of large vacancy defects formation in materials should be considered when screening anti-blistering materials for neutron-producing targets or when designing radiation resistant composite materials.

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Sui, Yang, Zi Yu Chen, Xiao Lin Shu, and Tian Min Wang. "Point Defects in L1₀ Phase FePt Alloy: A First Principle Study." Materials Science Forum 561-565 (October 2007): 1923–26. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.1923.

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L10 phase FePt alloy is regarded as one of the most promising materials for ultra high density magnetic recording media. However, structural point defects, which would reduce the media's signal to noise ratio, are inevitable in non-stoichiometric L10 FePt alloy. Hence, possible types of point defect (vacancy and anti-site defect) in non-stoichiometric ordered FePt alloy were fully studied using density functional theory. Investigation over vacancy shows the formation energy of Fe and Pt vacancy is respectively 2.58eV and 3.20eV. Geometry relaxation implies Fe vacancy has a stronger deformation force upon the original lattice. Meanwhile, anti-site defect study shows that the formation energy of Fe anti-site (Fe occupation in Pt sublattice) and Pt anti-site (Pt occupation in Fe sublattice) is respectively 1.05eV and 0.66eV. Therefore, for Fe-rich and Pt-rich alloy, the preferred structural point defects are both anti-site substitution rather than vacancy due to the much lower formation energy.

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Li, Bao Long, Li Jun Zhou, and Jian Gao Guo. "Influence of Defects on Elastic Buckling Properties of Single-Layered Graphene Sheets." Key Engineering Materials 636 (December 2014): 11–14. http://dx.doi.org/10.4028/www.scientific.net/kem.636.11.

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Molecular structural mechanics based finite element method has been applied to study the effects of two types of Stone-Wales (SW) defects and vacancy defect on elastic buckling properties of single-layered graphene sheets (SLGSs). The defect effect factors of critical buckling stresses are calculated for the defective SLGSs with different chirality and geometrical dimensions. It is proved that defect effect factors are size-dependent and chirality-dependent. The results show that the vacancy defects will always weaken the SLGSs’ stability, and two types of SW defects have different effects on zigzag and armchair SLGSs. What’s more, the positions of defects also have remarkable influence on the critical buckling stress of SLGSs.

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Berdiyorov, G. R., F. Boltayev, G. Eshonqulov, and H. Hamoudi. "Effect of vacancy defects on the electronic transport properties of an Ag–ZnO–Pt sandwich structure." Journal of Computational Electronics 20, no. 2 (March 3, 2021): 798–804. http://dx.doi.org/10.1007/s10825-021-01663-1.

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AbstractThe effect of zinc and oxygen vacancy defects on the electronic transport properties of Ag(100)–ZnO(100)–Pt(100) sandwich structures is studied using density functional theory in combination with the nonequilibrium Green’s functional formalism. Defect-free systems show clear current rectification due to voltage dependent charge localization in the system as revealed in our transmission eigenstates analysis. Regardless of the location, oxygen vacancies result in enhanced current in the system, whereas Zn vacancy defects reduce the charge transport across the junction. The current rectification becomes less pronounced in the presence of both types of vacancy defects. Our findings can be of practical importance for developing metal-insulator-metal diodes.

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Jalili, Seifollah, Farzad Molani, and Jeremy Schofield. "First principles study on energetic, structural, and electronic properties of defective g-C3N4-zz3 nanotubes." Journal of Theoretical and Computational Chemistry 13, no. 04 (June 2014): 1450021. http://dx.doi.org/10.1142/s0219633614500217.

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The energetic, electronic and structural properties of defective g- C 3 N 4-zz3 nanotubes are considered based on spin-polarized density-functional theory calculations. Nine basic system types with vacancy defects are characterized by their stabilization energies and band gaps. It is found that the nitrogen atom denoted as N 3 is the most favorable atom for a vacancy defect. In all cases, local bond reconstruction occurs in the presence of vacancy defects. The role of C / N bond rotations on the above properties has been also investigated. The results show that N 1– C 3 bond rotation is the most favorable rotational defect. In addition, the electronic properties of the semiconducting g- C 3 N 4-zz3 nanotube with defects have been studied using band structure and density of states plots.

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Duarte Naia, Marco, Paulo M. Gordo, Orlando M. N. D. Teodoro, Adriano P. de Lima, Augusto M. C. Moutinho, and Roberto S. Brusa. "Sub-Surface Defects Induced by Low Energy Ar⁺ Sputtering of Silver." Materials Science Forum 514-516 (May 2006): 1608–12. http://dx.doi.org/10.4028/www.scientific.net/msf.514-516.1608.

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Induced defects in silver polycrystalline samples irradiated with 4 keV Ar+ were characterised with slow positron implantation spectroscopy. The implanted gas was found to interact with ion irradiation defects. The evolution of the defects and gas-defect interactions were followed through a multi-step isochronal annealing treatment. Two different defected regions were detected. A region near to the surface, due to a distribution of vacancy-like defects produced by irradiation, and a deeper one due to coalescence of Ar. The deeper defects evolve with thermal treatments and probably produce cavities which are not easily recovered.

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Johnson, R. A., and J. R. Brown. "Vacancies and antisite defects in ordered alloys." Journal of Materials Research 7, no. 12 (December 1992): 3213–18. http://dx.doi.org/10.1557/jmr.1992.3213.

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Equations for the concentrations of vacancies and antisite defects in ordered alloys in thermodynamic equilibrium at and near stoichiometry have been derived as functions of defect energies and a Lagrangian parameter. While the resulting equations cannot be solved analytically and in general require iterative calculations, an approximation is given that permits simple numerical evaluation with just a minor loss of accuracy. Using defect energies obtained from an embedded-atom method calculation for Cu3Au, it is found that the adjustment for off-stoichiometric compositions is accounted for primarily by the creation of antisite defects rather than vacancies, and the vacancy concentration on Au sites is orders of magnitude less than that on Cu sites. There is a significant increase in the Au vacancy concentration but a slight decrease in the net vacancy content with increasing Cu fraction.

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Balan, Etienne. "Theoretical infrared spectra of OH defects in corundum (α-Al2O3)." European Journal of Mineralogy 32, no. 5 (September 11, 2020): 457–67. http://dx.doi.org/10.5194/ejm-32-457-2020.

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Abstract. The atomic-scale structure, relative stability and infrared spectroscopic properties of OH defects in corundum (α-Al2O3) are theoretically investigated at the density functional theory level. Comparison with experimental data makes it possible to assign most of the narrow bands observed between 3150 and 3400 cm−1 in natural and Ti- or V-doped synthetic corundum to specific defects. These defects correspond to the association of one OH group with an Al vacancy and M4+ for Al3+ substitutions in neighboring sites. The OH group is located in the large oxygen triangle forming the base of the vacant Al site. Models of interstitial proton associated with a nearby Mg2+ for Al3+ substitution are consistent with the broad band observed at 3010 cm−1 in Mg-doped corundum. Its is also suggested that two weaker OH-stretching bands observed in nominally pure synthetic corundum at 3163 and 3209 cm−1 could be associated with intrinsic defects combining an Al and an O vacancy. These results highlight the importance of defect clustering in the high-temperature incorporation of hydrogen in nominally anhydrous minerals.

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Packard, William E., John D. Dow, Kathleen Doverspike, Ray Kaplan, and Ruth Nicolaides. "Vacancy structures on the GaN(0001) surface." Journal of Materials Research 12, no. 3 (March 1997): 646–50. http://dx.doi.org/10.1557/jmr.1997.0098.

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Scanning tunneling microscopy images are reported for the wurtzite GaN(0001) surface. Terraces are observed, with three kinds of defect structures that are assigned to ordered N-vacancies: (i) striations perpendicular to the step edges, (ii) row defects spaced about 16 Å that intersect the steps at an angle of 30°, and (iii) “oval” defects that result from intersections of lines of vacancies (oriented at 60° with respect to step edges) with the row defects.

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Sun, Linlin, Liu Chu, Jiajia Shi, and Eduardo Souza de Cursi. "The Impacts of Random Distributed Vacancy Defects in Steady-State Thermal Conduction of Graphene." Applied Sciences 9, no. 11 (June 10, 2019): 2363. http://dx.doi.org/10.3390/app9112363.

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The unavoidable vacancy defects dispersed throughout the entire pristine graphene tailor to the integrity of the lattice structure and thereby have complicated impacts on the mechanical and thermal properties of graphene. In order to analyze the influence of vacancy defects on the extraordinary thermal conductivity of graphene, three typical kinds of vacancy defects—namely center concentrated, periodic, and random distributed vacancy defects—are compared and discussed. In the steady-state thermal conduction, the finite element method (FEM) is performed to calculate the total thermal energy and temperature field. The equivalent coefficient of thermal conductivity is derived from thermal energy, amount of vacancy defects, and boundary condition. The chirality in graphene is discussed by the location of its heat source. Moreover, the Monte Carlo simulation is applied to propagate the uncertainty of random vacancy defects in the finite element model of pristine graphene. In this paper, we provide the robustness to defend the impacts of vacancy defects on thermal conduction and the fluctuation and divergence caused by a certain number of random vacancy defects.

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Mitani, Takeshi, Ryo Hattori, and Masanobu Yoshikawa. "Diffusion of Point Defects from Ion Implanted 4H-SiC: Cathodoluminescence Observation." Materials Science Forum 615-617 (March 2009): 481–84. http://dx.doi.org/10.4028/www.scientific.net/msf.615-617.481.

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Depth profiles of ion-implantation induced defect centers have been investigated by cross-sectional CL measurements in the energy range from visible to near infrared. CL observation has shown that point defects diffused out from implanted region to ~10 µm depth during activation annealing. Annealing temperature dependence of the depth distribution of CL intensity of these defects has suggested that structural transformation of point defects proceeds as “silicon vacancy (VSi) → carbon vacancy-antisite pair (VC-CSi ; UD2) → antisite pair (CSi-SiC ; DI)”.

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Parvaneh, Vali, Mahmoud Shariati, Hamid Torabi, and Amir Masood Majd Sabeti. "Influence of Boundary Conditions and Defects on the Buckling Behavior of SWCNTs via a Structural Mechanics Approach." Journal of Nanomaterials 2011 (2011): 1–6. http://dx.doi.org/10.1155/2011/297902.

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The effects of boundary conditions and defects on the buckling behavior of SWCNTs are investigated using a structural mechanics model. Due to the application of carbon nanotubes in different fields such as NEMS, where they are subjected to different loading and boundary conditions, an investigation of buckling behavior of nanotubes with different boundary conditions is necessary. Critical buckling loads and the effects of vacancy and Stone-Wales defects were studied for zigzag and armchair nanotubes with various boundary conditions and aspect ratios (length/diameter). The comparison of our results with those of the buckling of shells with cutouts indicates that vacancy defects in carbon nanotubes can most likely be modeled as cutouts of the shells. Finally, a hybrid vacancy defect and Stone-Wales defect are also developed, and their effect on the critical buckling loads is studied.

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Slugeň, Vladimir, Jana Veterníková, Jarmila Degmová, S. Kilpeläinen, F. Tuomisto, and V. Kršjak. "Vacancy Type Defects in Oxide Dispersion Strengthened Steels." Materials Science Forum 733 (November 2012): 264–69. http://dx.doi.org/10.4028/www.scientific.net/msf.733.264.

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This study was focused on commercial oxide-dispersion strengthened (ODS) steels - MA 956 (20%Cr), PM 2000 (19%Cr), ODM 751 (16%Cr) and MA 957 (14%Cr) developed for fuel cladding of GEN IV reactors. The ODS steels are described in order to comparison of their microstructure features. Vacancy defects were observed by Doppler Broadening Spectroscopy (DBS) and Positron Annihilation Lifetime Spectroscopy (PALS). Residual stress proportional to all kinds of defects was investigated by Magnetic Barkhausen Noise (MBN) measurement. The highest presence of open volume defects was found in MA 956 and the lowest defect concentration in MA 957, although this steel contains the largest defects (six-vacancies together with dislocations). Other investigated steels demonstrated probably three- or four-vacancy clusters. Further, results from positron technique indicated proportionality of chromium content to defect concentration. Magnetic Barkhausen noise results also showed that Hpeak value (describing grain size) increased with growth of chromium content. However residual stress was independent on chromium level.

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Li, Jian. "Effect of Defects on Oscillatory Behaviors of Double-Walled Carbon Nanotube Oscillators." Advanced Materials Research 308-310 (August 2011): 584–88. http://dx.doi.org/10.4028/www.scientific.net/amr.308-310.584.

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Molecular dynamics simulation is performed on the inter-tube friction force and energy dissipation of double-walled carbon nanotube oscillators with vacancy defects. It is found that there are vacancy defect-size and temperature dependences of the friction force between the inner tube and the defective outer tube. The original distance between the “hole” formed by the vacancy carbon atoms and the inserted end of the core has a significant influence on the oscillation profile.

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Brown, Joshua J., Youxiang Shao, Zhuofeng Ke, and Alister J. Page. "Anion ordering and vacancy defects in niobium perovskite oxynitrides." Materials Advances 2, no. 7 (2021): 2398–407. http://dx.doi.org/10.1039/d1ma00122a.

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Dai, Feng, Dandan Zhao, and Lin Zhang. "Atomic Simulations of Packing Structures, Local Stress and Mechanical Properties for One Silicon Lattice with Single Vacancy on Heating." Materials 14, no. 11 (June 7, 2021): 3127. http://dx.doi.org/10.3390/ma14113127.

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The effect of vacancy defects on the structure and mechanical properties of semiconductor silicon materials is of great significance to the development of novel microelectronic materials and the processes of semiconductor sensors. In this paper, molecular dynamics is used to simulate the atomic packing structure, local stress evolution and mechanical properties of a perfect lattice and silicon crystal with a single vacancy defect on heating. In addition, their influences on the change in Young’s modulus are also analyzed. The atomic simulations show that in the lower temperature range, the existence of vacancy defects reduces the Young’s modulus of the silicon lattice. With the increase in temperature, the local stress distribution of the atoms in the lattice changes due to the migration of the vacancy. At high temperatures, the Young’s modulus of the silicon lattice changes in anisotropic patterns. For the lattice with the vacancy, when the temperature is higher than 1500 K, the number and degree of distortion in the lattice increase significantly, the obvious single vacancy and its adjacent atoms contracting inward structure disappears and the defects in the lattice present complex patterns. By applying uniaxial tensile force, it can be found that the temperature has a significant effect on the elasticity–plasticity behaviors of the Si lattice with the vacancy.

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Bönisch, Matthias, Michael Zehetbauer, Maciej Krystian, Daria Setman, and Gerhard Krexner. "Stabilization of Lattice Defects in HPT-Deformed Palladium Hydride." Materials Science Forum 667-669 (December 2010): 427–32. http://dx.doi.org/10.4028/www.scientific.net/msf.667-669.427.

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Recent investigations on palladium hydride (Pd-H) showed, for the first time, evidence of formation of vacancy-hydrogen (Vac-H) clusters during Severe Plastic Deformation (SPD) effected by High Pressure Torsion (HPT). Vacancy concentrations produced in Pd-H by this method are extraordinarily high. DSC-scans show that the thermal stability range of vacancies is extended by about 150K due to trapping of hydrogen leading to the formation of vacancy-hydrogen clusters. Recent experiments give evidence that the mobility of the H atoms and/or the vacancies is conditional for the formation of Vac-H clusters during HPT. Results furthermore indicate defect stabilization by hydrogen trapping not only for vacancy-type defects but also for dislocations and grain boundaries.

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Kögler, Reinhard, Wolfgang Anwand, Asta Richter, Maik Butterling, A. Mücklich, Xin Ou, H. Reuther, Chun Liang Chen, and Andreas Wagner. "Investigation of Dual-Beam-Implanted Oxide-Dispersed-Strengthened FeCrAl Alloy by Positron Annihilation Spectroscopy." Defect and Diffusion Forum 331 (September 2012): 149–63. http://dx.doi.org/10.4028/www.scientific.net/ddf.331.149.

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Oxide-dispersion-strengthened (ODS) FeCrAl steel is a class with promising materials to be applied for future nuclear applications. However, radiation damage, especially the formation of vacancy clusters or gas-filled bubbles, may result in hardness increase and the loss of ductility. Positron annihilation spectroscopy (PAS) is demonstrated to be a very useful and non-destructive analysis method to detect and to determine open volume defects of sub-nm size in ODS alloy. Synchronized dual beam implantation of Fe and He ions is performed to simulate the radiation damage caused by (n, α) reactions and to avoid induced activation. For room temperature implantation, i.e. without significant point defect recombination, the differences in the defect formation are shown by comparison between irradiation of ODS alloy and pure Fe bulk. The open volume defects created in ODS alloy are vacancy clusters closely connected with dispersed Y oxide nanoparticles. Their profiles are in reasonable qualitative agreement with the hardness profiles, indicating a relationship between sub-nm vacancy clusters or He bubbles and the hardness of the material. In heat-treated ODS alloy, containing larger vacancy clusters, the radiation induced hardness increase is more distinctive than for as-received ODS alloy. For irradiation at a moderately enhanced temperature of 300°C open volume defects are drastically reduced. The few remaining defects are vacancy clusters of the same type as in as-received ODS alloy. Close to the surface the open volume defects completely disappear. These results are in agreement with the hardness measurements showing little hardness increase in this case. The suitability of ODS-based materials for nuclear applications was verified.

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Hou, Wenyi, and Shaoping Xiao. "Mechanical Behaviors of Carbon Nanotubes with Randomly Located Vacancy Defects." Journal of Nanoscience and Nanotechnology 7, no. 12 (December 1, 2007): 4478–85. http://dx.doi.org/10.1166/jnn.2007.862.

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In this paper, 10 0 zigzag nanotubes and (6, 6) armchair nanotubes are considered to investigate the effects of randomly distributed vacancy defects on mechanical behaviors of single-walled carbon nanotubes. A spatial Poisson point process is employed to randomly locate vacancy defects on nanotubes. Atomistic simulations indicate that the presence of vacancy defects result in reducing nanotube strength but improving nanotube bending stiffness. In addition, the studies of nanotube torsion indicate that vacancy defects prevent nanotubes from being utilized as torsion springs.

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Voronkov, Vladimir V., and Robert Falster. "Intrinsic Point Defects in Silicon Crystal Growth." Solid State Phenomena 178-179 (August 2011): 3–14. http://dx.doi.org/10.4028/www.scientific.net/ssp.178-179.3.

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In dislocation-free silicon, intrinsic point defects – either vacancies or self-interstitials, depending on the growth conditions - are incorporated into a growing crystal. Their incorporated concentration is relatively low (normally, less than 1014 cm-3 - much lower than the concentration of impurities). In spite of this, they play a crucial role in the control of the structural properties of silicon materials. Modern silicon crystals are grown mostly in the vacancy mode and contain many vacancy-based agglomerates. At typical grown-in vacancy concentrations the dominant agglomerates are voids, while at lower vacancy concentrations there are different populations of joint vacancy-oxygen agglomerates (oxide plates). Larger plates – formed in a narrow range of vacancy concentration and accordingly residing in a narrow spatial band – are responsible for the formation of stacking fault rings in oxidized wafers. Using advanced crystal growth techniques, whole crystals can be grown at such low concentrations of vacancies or self-interstitials such that they can be considered as perfect.

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Yang, Xue Ming, and Dong Ci Chen. "Molecular Dynamics Study on Formation of Carbon Nanotube X-Shaped Junction by Heat Welding." Advanced Materials Research 538-541 (June 2012): 1460–63. http://dx.doi.org/10.4028/www.scientific.net/amr.538-541.1460.

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Molecular dynamics simulations are used to investigate the junction formation of two crossed single-walled carbon nanotubes (SWCNTs) with or without preexisting structural defects by heat welding. The junction formation of the chiral SWCNTs by heat welding is discussed. Furthermore, both the single vacancy defects and double vacancy defects are introduced in SWCNTs to explore the effect on junction formation by heat welding. We found the single vacancy defects and double vacancy defects pairs distributed on both crossed SWCNTs will accelerate the heat welding process and make the junction easier, and the required temperature for junction formation will be significantly reduced.

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Liang, Yingjing, Hongfa Qin, Jianzhang Huang, Sha Huan, and David Hui. "Mechanical properties of boron nitride sheet with randomly distributed vacancy defects." Nanotechnology Reviews 8, no. 1 (November 12, 2019): 210–17. http://dx.doi.org/10.1515/ntrev-2019-0019.

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Abstract Defects and temperature effects on the mechanical properties of hexagonal boron nitride sheet (h-BN) containing randomly distributed defects are investigated by molecular dynamics simulations and the reasons of the results are discussed. Results show that defect deteriorate the mechanical performance of BNNS. The mechanical properties are reduced by increasing percentage of vacancy defects including fracture strength, fracture strain and Young’s modulus. Simulations also indicate that the mechanical properties decrease with the temperature increasing. Moreover, defects affect the stable configuration at high temperature. With the percentage of defect increases the nanostructures become more and more unstable. Positions of the defect influent the mechanical properties. The higher the temperature and the percentage of defect are, the stronger the position of the randomly distributed defect affects the mechanical properties. The study provides a theoretical basis for the preparation and performance optimization of BNNSs.

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Chen, Jun, Gyeonghee Ryu, and Jamie Warner. "Atomic Structure and Dynamics of Defects and Grain Boundaries in 2D Pd2Se3 Monolayers." Microscopy and Microanalysis 26, S2 (July 30, 2020): 1636–40. http://dx.doi.org/10.1017/s1431927620018802.

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AbstractStructural imperfections of 2D crystals such as point vacancies and grain boundaries (GBs) have considerable impacts on their chemical-physical properties. Here we study the atomic structure and dynamics of defects and GBs in monolayer Pd2Se3 using annular dark field scanning transmission electron microscopy (ADF-STEM). The Pd2Se3 monolayers are reproducibly created by thermally induced phase transformation of few-layered PdSe2 films in an in-situ heating holder in the TEM to promote Se loss. Diverse point vacancies, one-dimensional (1D) defects, GBs and defect ring complexes are directly observed in monolayer Pd2Se3, which show a series of dynamics triggered by electron beam. High mobility of vacancies leads to self-healing of point vacancies by migration to the edge and subsequent edge etching under the beam. Specific defects are stabilized by Se–Se bonds, which shift in a staggered way to buffer strain, forming a wave-like 1D defect. Bond rotations are also observed and play an important role in defect and GB dynamics in Pd2Se3 during vacancy production. The GBs form in a meandering pathway and migrate by a sequence of Se–Se bond rotations without large scale vacancy formation. In the GB corners and tilted GBs, other highly symmetric vacancy defects also occur to adapt to the orientation change. These results give atomic level insights into the defects and GBs in Pd2Se3 2D monolayers.

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Zhao, Bin, Bo Zhou, Chong Yang Li, Ning Qi, and Zhi Quan Chen. "First-Principles Calculation of Defect Formation and Positron Annihilation States in Bi₂Te₃." Defect and Diffusion Forum 373 (March 2017): 41–45. http://dx.doi.org/10.4028/www.scientific.net/ddf.373.41.

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Defect formation energy in Bi2Te3 thermoelectric material was calculated using a first principles approach based on the Density Functional Theory (DFT). For vacancy-type defect, the Te1 vacancy (VTe1) is the most stable defect with low formation energy in both Bi-rich and Te-rich conditions, which indicates that the Te1 vacancies have higher probability to be formed. For antisite defects, the formation energy of BiTe1 is much lower than that of BiTe2 in Bi-rich condition, while in Te-rich condition it is beneficial for TeBi with lower formation energy. Positron wave function distribution and positron lifetimes of different annihilation states in Bi2Te3 were also calculated using the atomic superposition (ATSUP) method. The positron bulk lifetime in Bi2Te3 is about 231 ps, and for the neutral vacancy-type defects without relaxation, the positron lifetimes of VBi, VTe1 and VTe2 are 275 ps, 295 ps and 269 ps, respectively.

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Zhang, Xin, and Shaoqing Wang. "Interfacial Strengthening of Graphene/Aluminum Composites through Point Defects: A First-Principles Study." Nanomaterials 11, no. 3 (March 15, 2021): 738. http://dx.doi.org/10.3390/nano11030738.

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The relationship between point defects and mechanical properties has not been fully understood yet from a theoretical perspective. This study systematically investigated how the Stone–Wales (SW) defect, the single vacancy (SV), and the double vacancy (DV) affect the mechanical properties of graphene/aluminum composites. The interfacial bonding energies containing the SW and DV defects were about twice that of the pristine graphene. Surprisingly, the interfacial bonding energy of the composites with single vacancy was almost four times that of without defect in graphene. These results indicate that point defects enhance the interfacial bonding strength significantly and thus improve the mechanical properties of graphene/aluminum composites, especially the SV defect. The differential charge density elucidates that the formation of strong Al–C covalent bonds at the defects is the most fundamental reason for improving the mechanical properties of graphene/aluminum composites. The theoretical research results show the defective graphene as the reinforcing phase is more promising to be used in the metal matrix composites, which will provide a novel design guideline for graphene reinforced metal matrix composites. Furthermore, the sp3-hybridized C dangling bonds increase the chemical activity of the SV graphene, making it possible for the SV graphene/aluminum composites to be used in the catalysis field.

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Neupane, Hari Krishna, and Narayan Prasad Adhikari. "Electronic and magnetic properties of defected MoS2 monolayer." BIBECHANA 18, no. 2 (April 17, 2021): 68–79. http://dx.doi.org/10.3126/bibechana.v18i2.33905.

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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

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42

Melikhova, Oksana, Jan Kuriplach, Jakub Čížek, Ivan Procházka, and Gerhard Brauer. "Structure and Positron Characteristics of Basic Open Volume Defects in Zirconia." Materials Science Forum 607 (November 2008): 125–27. http://dx.doi.org/10.4028/www.scientific.net/msf.607.125.

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In this contribution we report on the theoretical study of basic vacancy-like defects in cubic zirconia and yttria stabilized zirconia. In particular, we concentrate on oxygen vacancy, zirconium vacancy and oxygen vacancy – yttrium complex. Relaxed atomic configurations of studied defects are obtained by means of an ab initio pseudopotential method within the supercell approach. Positron characteristics, like positron lifetime and binding energy to defects, are calculated using self-consistent electron densities and potentials taken from ab initio calculations.

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43

Niwase, Keisuke. "Raman Spectroscopy for Quantitative Analysis of Point Defects and Defect Clusters in Irradiated Graphite." International Journal of Spectroscopy 2012 (February 8, 2012): 1–14. http://dx.doi.org/10.1155/2012/197609.

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We report the development of Raman spectroscopy as a powerful tool for quantitative analysis of point defect and defect clusters in irradiated graphite. Highly oriented pyrolytic graphite (HOPG) was irradiated by 25 keV He+ and 20 keV D+ ions. Raman spectroscopy and transmission electron microscopy revealed a transformation of irradiated graphite into amorphous state. Annealing experiment indicated a close relation between Raman intensity ratio and vacancy concentration. The change of Raman spectra under irradiation was empirically analyzed by “disordered-region model,” which assumes the transformation from vacancy-contained region to disordered region. The model well explains the change of Raman spectra and predicts the critical dose of amorphization, but the nature of the disordered region is unclear. Then, we advanced the model into “dislocation accumulation model,” assigning the disordered region to dislocation dipole. Dislocation accumulation model can simulate the irradiation time dependencies of Raman intensity ratio and the c-axis expansion under irradiation, giving a relation between the absolute concentration of vacancy and Raman intensity ratio, suggesting an existence of the barrier on the mutual annihilation of vacancy and interstitial.

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44

Shyichuk, A., and E. Zych. "Oxygen Vacancy, Oxygen Vacancy–Vacancy Pairs, and Frenkel Defects in Cubic Lutetium Oxide." Journal of Physical Chemistry C 124, no. 28 (June 12, 2020): 14945–62. http://dx.doi.org/10.1021/acs.jpcc.0c00974.

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45

Markevich, Vladimir P., Anthony R. Peaker, L. I. Murin, Valentin V. Emtsev, Valentin V. Litvinov, Nikolay V. Abrosimov, and L. Dobaczewski. "Electronic Properties and Thermal Stability of Defects Induced by MeV Electron/Ion Irradiations in Unstrained Germanium and SiGe Alloys." Solid State Phenomena 108-109 (December 2005): 253–60. http://dx.doi.org/10.4028/www.scientific.net/ssp.108-109.253.

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Deep states produced during γ irradiation of germanium have been compared with the defects produced by 1 and 3MeV silicon ion implantation. The deep states have been studied using DLTS and Laplace DLTS techniques. Isochronal annealing has been used to investigate the defect evolution and stability over the range 100 to 500°C. It is found that while irradiation damage can be removed with a very low thermal budget, the implantation damage is more complex and much more difficult to remove. By comparing low (1010cm-2) and high (1012cm-2) implantation doses it appears that both the complexity and stability of defects increases with increasing dose. Similar experiments have been performed on Ge rich Si1-xGex (x=0.992). The focus of this work has been on vacancy related defects. It is believed that the diffusion of both acceptors and donors is vacancy mediated in Ge and so vacancy clusters rather than interstitial clusters are expected to be the technologically significant defect in enhanced diffusion. The significance in terms of junction leakage and generation currents are discussed in the paper in the context of the observed defect reactions.

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46

Gali, Adam. "Excitation Properties of Silicon Vacancy in Silicon Carbide." Materials Science Forum 717-720 (May 2012): 255–58. http://dx.doi.org/10.4028/www.scientific.net/msf.717-720.255.

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Isolated point defects possessing high spin ground state and below-band-gap excitation may play a key role in realizing solid state quantum bits in semiconductors which are the basic building blocks of quantum computers. Silicon vacancy in silicon carbide provides these features making it a feasible candidate in this special and emerging field of science. However, it has been not clarified what is the exact nature of the luminescence of silicon vacancy detected in hexagonal polytypes. This is the first crucial step needed to understand this basic defect in silicon carbide. We report density functional theory based calculations on silicon vacancy defect. Based on the obtained results we identify the silicon vacancy related photoluminescence signals with the negatively charged defect.

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47

Murat, Altynbek, and Julia E. Medvedeva. "Native point defects in multicomponent transparent conducting oxides." MRS Proceedings 1633 (2014): 37–42. http://dx.doi.org/10.1557/opl.2014.144.

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ABSTRACTThe formation of native point defects in layered multicomponent InAMO4 oxides with A3+=Al or Ga, and M2+=Ca, Mg, or Zn, is investigated using first-principles density functional calculations. We calculated the formation energy of acceptor (cation vacancies, acceptor antisites) and donor (oxygen vacancy, donor antisites) defects within the structurally and chemically distinct layers of InAMO4 oxides. We find that the antisite donor defect, in particular, the A atom substituted on the M atom site (AM) in InAMO4 oxides, have lower formation energies, hence, higher concentrations, as compared to those of the oxygen vacancy which is know to be the major donor defect in binary constituent oxides. The major acceptor (electron “killer”) defects are cation vacancies except for InAlCaO4 where the antisite CaAl is the most abundant acceptor defect. The results of the defect formation analysis help explain the changes in the observed carrier concentrations as a function of chemical composition in InAMO4, and also why the InAlZnO4 samples are unstable under a wide range of growing conditions.

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Todorova, Mira, and Jörg Neugebauer. "Identification of bulk oxide defects in an electrochemical environment." Faraday Discussions 180 (2015): 97–112. http://dx.doi.org/10.1039/c4fd00238e.

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We discuss how electronic-structure calculations can be used to identify the dominant point defects that control the growth and dissolution of the oxide barrier layer formed if a metal comes into contact with a corrosive environment. Using the example of the Zn/ZnO/H₂O interface we develop and apply a theoretical approach that is firmly based onab initiocomputed defect formation energies and that unifies concepts of semiconductor defect chemistry with electrochemical concepts. Employing this approach we find that the commonly invoked and chemically intuitive defects such as the doubly negatively charged oxygen vacancy in electrochemically formed ZnO films may not be present. Rather, hitherto not discussed defects such as the oxygen interstitial or unexpected charge states, such as the neutral oxygen vacancy, are found. These new defect types will be shown to critically impact our understanding of fundamental corrosion mechanisms and to provide new insight into strategies to develop alloys with higher corrosion resistance.

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Zhou, Gang, Ye Tian, Shuai Xue, Guangqi Zhou, Ci Song, Lin Zhou, Guipeng Tie, Feng Shi, Yongxiang Shen, and Zhe Zhu. "Enhancement of the Load Capacity of High-Energy Laser Monocrystalline Silicon Reflector Based on the Selection of Surface Lattice Defects." Materials 13, no. 18 (September 19, 2020): 4172. http://dx.doi.org/10.3390/ma13184172.

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Various defects during the manufacture of a high-energy laser monocrystalline silicon reflector will increase the energy absorption rate of the substrate and worsen the optical properties. Micron-scale or larger manufacturing defects have been inhibited by mechanism study and improvement in technology, but the substrate performance still fails to satisfy the application demand. We focus on the changes in the optical properties affected by nanoscale and Angstrom lattice defects on the surface of monocrystalline silicon and acquire the expected high reflectivity and low absorptivity through deterministic control of its defect state. Based on the first principles, the band structures and optical properties of two typical defect models of monocrystalline silicon—namely, atomic vacancy and lattice dislocation—were analyzed by molecular dynamics simulations. The results showed that the reflectivity of the vacancy defect was higher than that of the dislocation defect, and elevating the proportion of the vacancy defect could improve the performance of the monocrystalline silicon in infrared (IR) band. To verify the results of simulations, the combined Ion Beam Figuring (IBF) and Chemical Mechanical Polishing (CMP) technologies were applied to introduce the vacancy defect and reduce the thickness of defect layer. After the process, the reflectivity of the monocrystalline silicon element increased by 5% in the visible light band and by 12% in the IR band. Finally, in the photothermal absorption test at 1064 nm, the photothermal absorption of the element was reduced by 80.5%. Intense laser usability on the monocrystalline silicon surface was achieved, and the effectiveness and feasibility of deterministic regulation of optical properties were verified. This concept will be widely applied in future high-energy laser system and X-ray reflectors.

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Luo, Qiang Hui, Wu Gui Jiang, and Qing Hua Qin. "Possibility of Improving Oscillation Performance of Double-Walled Nanotube Oscillators via Tuning Vacancy Defects." Journal of Nano Research 48 (July 2017): 148–55. http://dx.doi.org/10.4028/www.scientific.net/jnanor.48.148.

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The oscillatory behaviors of an oscillator made from double-walled carbon nanotubes (DWCNTs) with vacancy defects were systematically investigated via molecular dynamics simulation method. We found that the vacancy defects change the off-axial rocking motion and the van der Waals potential, resulting in more energy dissipation. Unlike the case in the C60–nanotube oscillators (Song, et al., Phys. Lett. A. 373 2009, 1058-1061) that one vacancy can make the oscillators more stable, our study showed that the vacancies cannot improve the performance of DWCNT-based oscillators no matter where vacancy defects are located.

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Journal articles on the topic 'Vacancy defects'

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