Percentage Of Vacancies Research Articles

Improved resistive switching behavior of defective fluorite structured Sm2Ce2O7 thin film prepared by RF sputtering

The Al/Sm2Ce2O7/ITO (Al/SCO/ITO) structure resistive random access memory (RRAM) was prepared using RF magnetron sputtering, and its resistive switching (RS) behaviors were systematically investigated. The memory exhibited a high switching cycle of 1031, along with set/reset voltages of −1.55/0.53 V and a Ron/Roff ratio exceeding 102. This high performance can be attributed to the presence of intrinsic oxygen vacancies in the defective fluorite structure, accounting for 34.44 % of the vacancies. This vacancy percentage can be increased to 41.97 % by simultaneously transforming Ce4+ to Ce3+ ions through annealing treatment, thereby releasing additional oxygen vacancies. Despite this increase, there remains a sufficient window (Ron/Roff > 10) to distinguish between the high-resistance state (HRS) and low-resistance state (LRS) of the SCO device. Furthermore, the device, when subjected to post-metal annealing (PMA), exhibits a high endurance of up to 1815 cycles, a set/reset voltages of −2.19/1.31 V, a Ron/Roff ratio of >10, and a retention time of over 104 s at 25 °C and 85 °C. However, it is important to note that PMA-treated device requires a higher forming voltage due to the formation of a thicker AlOx layer. This study highlights the potential of Al/SCO/ITO memory devices for RRAM applications.

EFFECT OF VACANCIES AND VOID DEFECTS ON THE STRUCTURAL AND MECHANICAL BEHAVIOR OF TUNGSTEN UNDER HARSH TEMPERATURE AND PRESSURE CONDITIONS

The body-centered cubic transition metal tungsten is frequently used as a pressure calibration material at high temperatures and pressures due to its outstanding mechanical and thermal properties. In this study, molecular dynamics simulations were performed to investigate the behavior of tungsten under harsh temperature and pressure conditions and the impact of fundamental defects, particularly vacancies, and voids, on its physical, structural, and mechanical properties through their correlation with elastic constants. The study also covers mechanical stability, elastic properties, brittleness and ductility, and hardness. The simulations utilized two different embedded atom methods and one modified embedded atom method interatomic potentials. The results show that the fundamental structural characteristics and properties of pure tungsten crystal, including lattice constant, density, cohesive and vacancy formation energies, elastic constants, and moduli in the ground state for all three potentials, are in good agreement with previous experimental and theoretical calculations and results. The calculated results demonstrate that the elastic constants-related properties for defective structures also have the same trend as the perfect crystal. The presence of defects in the crystal causes a decrease in properties at all temperatures and pressures, directly correlated to the fraction of crystal defects. As the percentage of vacancies increases, a further reduction in the elastic constants is observed. Likewise, these findings reveal that the presence of scattered vacancies in the crystal structure causes a more significant decrease in the substance's properties than a void in the center of the crystal (with the same percentage). The presence of any vacancy weakens the interatomic bonds of the atoms around the vacancy, while the existence of a void in the center has less effect on the interatomic bonds of atoms further away from the center of the crystal.

Porosity Measurements and Analysis of Sintered and Thermochemical Heat Treated P/M Compacts

The objective of this paper was to examine the porosity in fluidized-bed carburizing on sintered alloys obtained by the powder metallurgy route using an image software analysis, and to compare the results with those obtained using the conventional porosity measuring technique. A material's porosity is a measurement of its vacancy percentage. The volume of empty space divided by the material's bulk volume, given as a percentage, determines the overall porosity of the material. The advancement of digital imaging and software has resulted in a novel and appropriate technique for figuring out the porosity of materials used in powder metallurgy.

Sol-Gel-Processed Y2O3-Al2O3 Mixed Oxide-Based Resistive Random-Access-Memory Devices.

Herein, sol-gel-processed Y2O3-Al2O3 mixed oxide-based resistive random-access-memory (RRAM) devices with different proportions of the involved Y2O3 and Al2O3 precursors were fabricated on indium tin oxide/glass substrates. The corresponding structural, chemical, and electrical properties were investigated. The fabricated devices exhibited conventional bipolar RRAM characteristics without requiring a high-voltage forming process. With an increase in the percentage of Al2O3 precursor above 50 mol%, the crystallinity reduced, with the amorphous phase increasing owing to internal stress. Moreover, with increasing Al2O3 percentage, the lattice oxygen percentage increased and the oxygen vacancy percentage decreased. A 50% Y2O3-50% Al2O3 mixed oxide-based RRAM device exhibited the maximum high-resistance-state/low-resistance-state (HRS/LRS) ratio, as required for a large readout margin and array size. Additionally, this device demonstrated good endurance characteristics, maintaining stability for approximately 100 cycles with a high HRS/LRS ratio (>104). The HRS and LRS resistances were also retained up to 104 s without considerable degradation.

Insights into the atomic structure of oxygen vacancy on Bi2MoO6/MXene heterojunction and its role for boosting photocatalytic NO oxidation

Defect engineering is an effective approach to improve the gas conversion properties of photocatalysts. However, revealing the defect microstructures and performance enhancing mechanism remain challenges. In this work, the precise content and atomic-level structure of oxygen vacancy in Bi2MoO6/MXene heterojunction photocatalyst was studied by neutron scattering. Pair distribution function analysis shows that the vacancy percentage of oxygen connected with Mo in Bi2MoO6 is 16.6%, and the metal-O bond length decreases near the vacancy. The performance enhancement mechanism of oxygen vacancy in Bi2MoO6/MXene towards photocatalytic NO oxidation was investigated through experiments and density functional theory (DFT) calculations. The optical properties of the heterojunction photocatalyst can be significantly improved by the oxygen vacancies. The exposed Mo atoms at the vacancies greatly benefit the adsorption and activation of reactants, and also accelerate the generation of reactive oxygen species. The NO removal efficiency of the oxygen vacancy-containing Bi2MoO6/MXene heterojunction can reach up to 94.3% under visible light. This work provides a new approach for studying the microstructure and activity enhancement mechanism of oxygen vacancy in photocatalysts.

Numerical Simulation of Characterization of Hydraulic Jump Over an Obstacle in an Open Channel Flow

Hydraulic jumps produce so much turbulence that hydraulic energy is effectively converted to heat. The speed, form, and volume of obstructions in an open channel have a considerable impact on the characteristics of a fluid stream. To create a hydraulic leap, a numerical analysis of water flow was done for a two-dimensional open channel over three different forms of obstruction, each with three volumes. Because of the impact of the air, it is possible to think of the emulsion of air and water as a compressible fluid with a vacancy percentage (a second fluid). The volume of fluid model (VOF), linked with the turbulent model, has been used to study each type of obstruction. The second-order upwind technique incorrectly solves the two-dimensional Reynolds-averaged Navier-Stokes equations. The numerical technique is implemented using the straightforward approach that was devised using control volumes. A wide range of Reynolds numbers (Re), corresponding to various flow patterns, were calculated for. The results demonstrate that when the Reynolds number increases, the effect of the gas phases on the liquid phases increases. The boundary layer thickness in the upstream zone from the obstacle decreases with increasing Re, whereas downstream from the obstruction, the height of the recirculation zone rises. Profiles of the empty fraction reveal two zones that are consistent with a diffusion equation. This article observed an inversion of the pressure gradient in the pressure field, which caused the boundary layer to separate; this is known as the "back flow phenomenon." The results of the current work have been verified by comparison with those of related research projects, and the comparison has shown a commendable degree of agreement. Additionally, pressure in various areas of the obstacle and velocity were similar.

Tunneling FET Based on Monolayer Antimonene: The Role of Vacancy

In this work, the electrical performance of the antimonene TFET is investigated using nonequilibrium Green’s function (NEGF) through a tight-binding approach. In the following, the effect of atom vacancy on the electrical behavior of the TFET is explored. The creation of the mid-gap state due to the vacancy is shown using the local density of states (LDOS) for the TFET and the density of states (DOS) for a ribbon. Furthermore, the effects of these mid-gap states on the ON-current, OFF-current, ON– OFF ratio, and subthreshold swing (SS) are discussed. Finally, the effect of the scaling in presence of vacancy is explored. The results show that a small vacancy percentage declines the SS while the variation of the ON– OFF ratio is negligible.

Layer spacing gradient (NaLi)1−xCoO2 for electrochemical Li extraction

Layer spacing gradient (NaLi)1−xCoO2 for electrochemical Li extraction

Topological information in artificial spin ice with random vacancies

In this work, we perform a numerical study on artificial spin ice systems formed by square arrays of ferromagnetic nano-islands. Inspired by topological studies, we consider absent nano-islands at random positions throughout the array. The system is described by a Hamiltonian that includes anisotropy energy as well as dipolar interaction among the islands in the Heisenberg spin model approach. The simulations were done in the framework of the Monte-Carlo method with the Metropolis algorithm. We focus on the effect of the vacancies on the magnetic vertices configurations. In particular, we calculate the distribution of all possible magnetic configurations of the vertices as a function of the percentage of vacancies. The absent nano-islands generate a loss of geometric frustration, and the system evolves faster than the system without vacancies to a lower energy state. However, the system shows the difficulty of reaching the ground state because the vacancies generate different sub-regions that evolve towards one of the two possible orientations of the magnetic moments with the minimum energy state. Furthermore, we show this system to be stable up to room temeperature when a state with local minimal energy is initially considered. Consequently, the system retains its information in a wide range of temperatures. The introduction of vacancies breaks with any translational symmetry and allows diversifications of the number of magnetic configurations with minimum energy. Therefore, this kind of systems can be used to store information.

Effect of annealing protection atmosphere on the ferroelectric yttrium doped hafnium oxide thin films

The 10 nm thick yttrium doped hafnium oxide (Y:HfO2) thin films, prepared by chemical solution deposition which using all-inorganic aqueous salt reagents, were fabricated on Si (100) substrates. The crystalline structure, chemical composition and ferroelectric properties of thin films, annealed in protection atmosphere of Air, Ar and N2, were examined. Result showed that the crystalline structure and ferroelectric properties of films exhibited a strong annealing protection atmosphere dependence. When compared to annealing protection atmosphere of Air and Ar, the films with the N2 exhibited lowest m-phase fraction of 19.4%, and the highest oxygen vacancy percentage content of 3.06%, accompanied with the highest relative permittivity of 50.9 and the remanent polarization of 14.6 μC/cm2. These excellent ferroelectric properties were correlated with asymmetric orthorhombic phase and the concentration of oxygen vacancy introduced from the nitrogen doping concentration.

Job Vacancy Data for Dentists in Australia: Advertised vacancies as an indicator of unmet need

Objectives: The aim of this study was to determine whether job vacancy data for dentists might be used as part of a needs-based index to indicate levels of workforce supply.
 Methods: Advertised job vacancies for dentists were collected at monthly intervals between October 2011 and June 2019; compiled into a data base and geo-coded by latitude and longitude. The vacancies were mapped using QGIS software and their geographic locations were observed relative to Accessibility/Remoteness Index of Australia Plus (ARIA+ 2016) and SEIFA Index of Relative Socio-economic Disadvantage (IRSD).
 Results: There was a slight decline in the number of advertised job vacancies relative to the population of Australia in the first 18 months of the study. For the remainder of the study period the number of vacancies per million of the population rose steadily. There were differences between ARIA+ regions; but remote and very remote Australia showed very little variation in vacancies across the study period. The percentage of monthly advertised vacancies in IRSD1 (most disadvantaged) areas was much higher (>40%) at the start of the study period but by the end of the study the percentage of vacancies was relatively even across all IRSD groups.
 Conclusions: The increase in the number of vacancies per million population since 2013 implies an increase in demand for dentists. The findings do not correlate with industry and government agency reporting of an oversupply. The use of job vacancy data might form part of a needs-based index to inform dental workforce planning.

Medical schools in Brasil: population, economic and historical analysis.

To describe the current distribution and historical evolution of undergraduate courses in medicine in Brasil. Analytical cross-sectional study of secondary data. Through the Ministry of Education, the data of the medical courses were obtained, and through the Brazilian Institute of Geography and Statistics, the population and economic data of the Brazilian states were obtained. In Brasil, there were 298 medical courses (1,42 courses / million inhabitants) in January 2018, totaling 31,126 vacancies per year, with 9,217 gratuitous vacancies (29.6%) and 17,963 vacancies in the hinterland (57, 7%). In Brazilian states, there are positive and statistically significant (p <0.001) correlations of the variables: "vacancies" and "population" (R 0.92); "vacancies" and "gross domestic product" ("GDP") (R 0.83); "percentage of vacancies in the hinterland" and "population in the hinterland" (R 0.71) and "percentage of vacancies in the hinterland" and "GDP" (R 0.64). There was a negative and statistically significant correlation between "gratuitous vacancy percentage" and "GDP" (R -0.54, p = 0.003). More paid courses than gratuitous courses and more courses in the hinterland than in the capitals have been created since 1964, in proportions that have remained similar since then, but in higher numbers since 2002. The distribution of medical courses in Brasil correlates with the population and economical production of each state. The expansion of Brazilian medical education, which has been accelerated since 2002, is based mainly on paid courses in the hinterland, in the same pattern since 1964.

The magnetic and structural properties of BiFeO3-x (0&lt;x&lt;3) thin films with controllable oxygen vacancy

Abstract BiFeO3-x thin films were deposited on glass substrate by PECVD. The oxygen vacancies were produced in the thin film by introducing H2 into the PECVD process, and the oxygen vacancy percentage was regulated by H2 flow rate. The effects of oxygen vacancy percentage on the grain size, crystal structure, and magnetic properties were investigated. The surface chemical conditions of BiFeO3-x (0

The temperature and oxygen vacancy effects on the diffusion coefficient and ionic conductivity in ferroelectric BaTiO3 nanowires; A molecular dynamics study

In this work, the influence of oxygen vacancy defects on ionic conductivity and oxygen diffusion in BaTiO3 (BTO) nanowires (NWs) was investigated for different temperatures ranging from 700 K to 1000 K by molecular dynamics simulation method. The BTO NWs with cubic structure and axial directions of [001] and [110] were considered for simulation. The oxygen vacancies ranging from 0 to 4% were created by random deletion of oxygen atoms from perfect BTO NWs. The results show that ionic conductivity and diffusion constant of oxygen atoms in individual BTO NWs are at least ten times higher than those of single crystalline BTO and they enhance by increasing the oxygen vacancy percentage. The pre-exponential factor of oxygen diffusion coefficient and also oxygen activation energy of NWs were evaluated from linear least square fits to Arrhenius plots. Results also show that the activation energy of oxygen atoms reduces with increasing the oxygen vacancy percentage. The Arrhenius plots show a critical point about 850 K which at this point the slop of the fitted lines to Arrhenius plots shows a sudden change.

Buckling analysis of graphene nanosheets by the finite element method

The paper is devoted to the problems related to buckling analysis of graphene sheets without and with vacancies in the structure under different boundary conditions. The analysis was performed by the classical numerical treatment – the finite element method (FEM). The graphene sheets were modelled by beam elements. Interatomic relations between carbon atoms in the structure were represented by the beams connecting individual atoms. The behaviour of the beam as structural element was based on the properties that were established from relations of molecular mechanics. The vacancies in single layer graphene sheets (SLGSs) were created by elimination of randomly chosen atoms and corresponding beam elements connected to the atoms in question. The computations were accomplished for different percentage of atom vacancies and the results represent an obvious fact that the critical buckling force decreases for increased percentage of vacancies in the structure. The numerical results are represented in form of graphs.

Thermal transport characterization of hexagonal boron nitride nanoribbons using molecular dynamics simulation

Due to similar atomic bonding and electronic structure to graphene, hexagonal boron nitride (h-BN) has broad application prospects such as the design of next generation energy efficient nano-electronic devices. Practical design and efficient performance of these devices based on h-BN nanostructures would require proper thermal characterization of h-BN nanostructures. Hence, in this study we have performed equilibrium molecular dynamics (EMD) simulation using an optimized Tersoff-type interatomic potential to model the thermal transport of nanometer sized zigzag hexagonal boron nitride nanoribbons (h-BNNRs). We have investigated the thermal conductivity of h-BNNRs as a function of temperature, length and width. Thermal conductivity of h-BNNRs shows strong temperature dependence. With increasing width, thermal conductivity increases while an opposite pattern is observed with the increase in length. Our study on h-BNNRs shows considerably lower thermal conductivity compared to GNRs. To elucidate these aspects, we have calculated phonon density of states for both h-BNNRs and GNRs. Moreover, using EMD we have explored the impact of different vacancies, namely, point vacancy, edge vacancy and bi-vacancy on the thermal conductivity of h-BNNRs. With varying percentages of vacancies, significant reduction in thermal conductivity is observed and it is found that, edge and point vacancies are comparatively more destructive than bi-vacancies. Such study would contribute further into the growing interest for accurate thermal transport characterization of low dimensional nanostructures.

Numerical simulation study of the elastic properties of single-walled carbon nanotubes containing vacancy defects

The mechanical behaviour of non-chiral and chiral single-walled carbon nanotubes containing different percentage (up to 10%) and types of vacancy defects is studied under tensile, bending and torsional loading. A three-dimensional finite element model is used in order to evaluate the corresponding rigidities and, subsequently, Young's and shear moduli and Poisson's ratio. The three rigidities decrease with the increase of the percentage of vacancies. Also, the Young's and shear moduli and the Poisson's ratio of single-walled carbon nanotubes are sensitive to the presence of vacancy defects in nanotube: elastic moduli decrease and the Poisson's ratio increases with increasing of the percentage of vacancies. The moduli of single-walled carbon nanotubes with 10.0% of vacancy defects, when compared with the values obtained for perfect nanotubes, are of about 43% for the Young's modulus and of about 33% for the shear modulus. On the contrary, the Poisson's ratio increases of about 4 times, compared with that obtained for the perfect nanotube.

Correlation between vacancies and magnetoresistance changes in FM manganites using the Monte Carlo method

The Metropolis algorithm and the classical Heisenberg approximation were implemented by the Monte Carlo method to design a computational approach to the magnetization and resistivity of La2/3Ca1/3MnO3, which depends on the Mn ion vacancies as the external magnetic field increases. This compound is ferromagnetic, and it exhibits the colossal magnetoresistance (CMR) effect. The monolayer was built with L×L×d dimensions, and it had L=30umc (units of magnetic cells) for its dimension in the x–y plane and was d=12umc in thickness. The Hamiltonian that was used contains interactions between first neighbors, the magnetocrystalline anisotropy effect and the external applied magnetic field response. The system that was considered contains mixed-valence bonds: Mn3+eg’–O–Mn3+eg, Mn3+eg–O–Mn4+d3 and Mn3+eg’–O–Mn4+d3. The vacancies were placed randomly in the sample, replacing any type of Mn ion. The main result shows that without vacancies, the transitions TC (Curie temperature) and TMI (metal–insulator temperature) are similar, whereas with the increase in the vacancy percentage, TMI presented lower values than TC. This situation is caused by the competition between the external magnetic field, the vacancy percentage and the magnetocrystalline anisotropy, which favors the magnetoresistive effect at temperatures below TMI. Resistivity loops were also observed, which shows a direct correlation with the hysteresis loops of magnetization at temperatures below TC.

The effects of temperature and vacancies on dynamics of crack in graphene sheet

Crack propagation in a defected graphene sheet is investigated at finite temperature using molecular dynamics simulation. The effects of several initial cracks, temperature and different percentage of vacancies are considered. It is found that i) the critical load, which is a criteria for crack propagation, is larger when the load is applied on the zigzag direction, ii) the critical load decreases with increasing temperature, iii) a hole in the center of the sheet and the presence of randomly distributed vacancies reduce the critical load giving different crack propagation trajectory. Our new results would help to understand the crack propagation phenomena in defected graphene at finite temperature.

Brazil’s Health in Black and White

Brazil’s Health in Black and White