Concentration Of Structural Defects Research Articles

Time-Dependent Growth of ZnO Nanowires: Unveiling Antibacterial and Photocatalytic Properties.

This study investigates the synthesis, characterization, and functional properties of well-aligned zinc oxide (ZnO) nanowires (NWs) obtained by a two-step hydrothermal method. ZnO NWs were grown on silicon substrates precoated with a ZnO seed layer. The growth process was conducted at 90 °C for different durations (2, 3, and 4 h) to examine the time-dependent evolution of the nanowire properties. A comprehensive characterization of the ZnO NWs was performed using several analytical techniques. Scanning electron microscopy (SEM) revealed the morphological progression, specifically tracking changes in length and diameter as a function of the growth time. Ultraviolet (UV)-visible spectroscopy was employed to determine the optical band gap, while photoluminescence (PL) analysis provided insight into the concentration of structural defects and its evolution as a function of nanowire growth. The photocatalytic efficiency of the ZnO NWs was evaluated through the degradation of the organic dye methylene blue (MB) under UV light irradiation (365 nm). The kinetic of MB degradation was monitored for each growth time, with non-purgeable organic carbon (NPOC) analysis providing a detailed perspective on the photocatalytic activity over time. The antibacterial properties were tested against Pseudomonas putida, a Gram-negative bacterium, to determine the efficiency of the synthesized ZnO NWs as antimicrobial agents. The release of zinc ions (Zn2+), a key factor in the antibacterial mechanism, was quantified using inductively coupled plasma (ICP) analysis for each sample. By exploration of the relationship between the growth time, nanostructure morphology, and functional properties, this study provides insights into optimizing the synthesis of ZnO NWs for enhanced photocatalytic and antibacterial applications. These findings contribute to the development of advanced materials for environmental and biomedical applications.

The effect of oxygen vacancies on the optical and thermophysical properties of (1-x)Si3N4 – xAl2O3 ceramics

Interest in composite ceramics based on silicon nitride (Si3N4) and aluminum oxide (Al2O3) is due to the possibility of using them as semiconductor applications associated with their operation under conditions of external influences, including heating. The paper presents the results of assessing the influence of variations in the phase composition of (1-x)Si3N4 – xAl2O3 ceramics on alterations in optical and thermophysical parameters, as well as their relationships. Analysis of the optical characteristics of the ceramics under study showed that changes in the phase composition associated with the dominance of the Al2O3 phase in the composition of the ceramics lead to a change in covalent bonds and an increase in the number of ionic bonds, which also affects the change in the semiconductor nature of the ceramics, and therefore, a change in the thermophysical properties. According to the assessment of changes in the thermal conductivity coefficient of the studied ceramics, with the dominance of the Al2O3 phase in the composition, the observed growth in the concentration of structural defects, as well as oxygen vacancies, results in the thermal conductivity coefficient decrease, as well as an elevation in the thermal expansion of ceramics during thermal heating. It has been determined that the presence of a combination of Al2(SiO4)O and Si3N4 phases in the ceramic composition leads to an increase in the thermal conductivity coefficient, as well as maintaining its stability over a wide temperature range.

Surface quality and microstructure evolution in fused silica under SF6/Ar reactive ion beam etching

The SF6/Ar reactive ion beam etching (RIBE) was proposed to explore the evolution of surface quality, subsurface defects, surface molecular structure, and chemical composition of fused silica. Also, the mechanism of reactive ion beam etching of fused silica surfaces was discussed. The results show that RIBE can maintain the original surface roughness by choosing suitable process parameters. this etching process can suppress the replication and expansion of subsurface defects and the deposition of reactants without bringing obvious contamination. The concentration of structural defects reaches a minimum at an etching depth of about 2 μm. However, further etching may lead to an increase in the chemical structure defects on the surface. The evolution of the intrinsic ring structure demonstrates that most intrinsic defects tend to reorganize into short (Si-O) ring structures. The etching mechanisms of Ar ions were discussed by simulating the stopping power and energy deposition. Phonon dissipation through atomic displacements and atomic vibrations is an important way of energy loss. Phonon vibrations and atomic dislocations induced by nuclear collisions are not only important factors causing the enhancement of electron-phonon coupling but also important causes of surface structural defects. The researches provide a theoretical basis for in-depth understanding of fused silica surface defect repair.

Impact of microwave sintering and NiO additive on the densification and conductivity of BaCe0.2Zr0.7Y0.1O3-δ electrolyte for protonic ceramic fuel cell

This work investigated the influence of microwave sintering on the BaCe0.2Zr0.7Y0.1O3-δ phase, incorporating 2 mol% or 4 mol% NiO as sintering aid. X-ray diffraction analysis of perovskite phase detected a rhombohedral structure under both sintering heating rates (280 and 500 °C/min), also exhibiting the presence of a second phase deficient in Ba with Ni incorporated into the structure, replacing part of the Zr. Raman analysis indicated no distortions in the perovskite structure, independent of the rates and NiO concentrations. The efficacy of NiO addition as a sintering aid was demonstrated by high densification of the samples, exceeding 97 % relative density. Detailed analysis of structural, microstructural, and conductivity properties revealed that microwave sintering, particularly using a heating rate of 500 °C/min, yielded superior results compared to conventional sintering. The enhanced electrical response was attributed to a higher concentration of structural defects, oxygen vacancies, in the microwave-sintered samples, evidenced by the band at 630 cm−1 in the Raman spectrum. Among these, the BCZY sample with 2 mol% NiO, sintered under these conditions, stood out as the most promising, showcasing not only high density but also a uniform microstructure and appreciable electrical conductivity.

Раціональні технологічні засади отримання коксу із заданими показниками питомого електричного опору

DOI: 10.31081/1681-309X-2024-0-1-8-15 Specialty 161. U.D.C. 661.66.2:537.311/.312 RATIONAL TECHNOLOGICAL BASES OF PRODUCTION OF COKE WITH SPECIFIED ELECTRICAL RESISTIVITY © I.V. Shulga, Ph.D. in Technical Sciences, O.V. Sytnyk, Ph.D. in Technical Sciences (State Enterprise “Ukrainian State Research Institute for Carbochemistry (UKHIN)”, 7 Vesnina str., Kharkiv, 61023, Ukraine), O.I. Zelenskii, Ph.D. in Technical Sciences, V.V. Vladymirenko (National Technical University "Kharkiv Polytechnic Institute", 2, Kyrpychova str., Kharkiv, 61002, Ukraine) The article is devoted to the practically important issue of obtaining coke with a specific electrical resistance of no more than 0.1 Ohm∙cm for the needs of blast furnace production. Achievement of this indicator should occur simultaneously with the improvement of the entire range of properties of blast furnace coke. It is noted that the concept of production of blast furnace coke of improved quality consists of the formation of a rational raw material base, ensuring proper coking technology and post-furnace coke treatment. It has been shown that the production of high-quality blast furnace coke with low resistivity requires: high sinterability and coking capacity of the charge based on highly sinterable coals; coking pressure of the coal charge not exceeding 7 kPa; coking speed not exceeding 24 mm/hour; final coking temperature of 1050-1100 °C; maximum temperature level in the heating system not exceeding 1410 °C. It is confirmed that in order to obtain a low electrical resistivity, it is necessary to produce coke with the most ordered anisotropic structure. It is shown that the resistivity of coke naturally changes when used in blast furnace production: the destruction of lumps leads to the formation of fragments of different sizes. At the same time, coarser fragments have lower resistivity values, and smaller ones, characterized by an increased concentration of structural defects that are the centers of crack formation, have a higher resistivity. After gasification with carbon dioxide, the number of structural defects increases in grains of any size due to the weakening of the surface due to chemical interaction, so the resistivity of coke increases and becomes almost equal for both coarser and finer grains. Keywords: hard coal coke, blast furnace production, resistivity, vertical temperature, final coking temperature, coke gasification. Corresponding author I.V. Shulga, e-mail: ko@ukhin.org.ua

Effect of the Presence of Structural Defects on the Superconducting Properties of (NbTa)0.67(MoHfW)0.33 and Nb-47wt%Ti

A comparison of the results of studies on the influence of structural defects on the critical parameters of superconductivity has been made for the high-entropy alloy (NbTa)0.67(MoHfW)0.33 and for the conventional superconducting magnet material Nb-47wt%Ti. Positron annihilation lifetime spectroscopy (PALS), electrical resistivity, magnetization and magnetic susceptibility measurements were used. In addition, X-ray powder diffraction studies were performed on the high-entropy alloy (NbTa)0.67(MoHfW)0.33. Due to the rapid cooling of the materials after melting in the arc furnace, they contain a higher concentration of structural defects compared to the heat-treated materials. Magnetic property measurements showed that both the critical temperatures Tc and the upper critical fields μ0Hc2 of bulk superconductivity-related materials are improved in the presence of structural defects.

Change in the gas sensing mechanism and improved sensing response on ion-irradiated palladium-graphene oxide nanocomposite

In this study, we synthesized Pd-graphene oxide (Pd-GO) nanocomposite layers on SiO2/Si substrates using chemical method. Pd-GO layers were treated with swift heavy ion irradiation (100 MeV Ag ions, 1013 ions/cm2). The structural properties of the pristine as well as the ion irradiated samples were investigated using synchrotron grazing incidence x-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. XRD shows peaks corresponding to Pd (FCC, space group-Fd-3m), GO and synthetic graphite. The relative graphite peak intensities increased after ion irradiation, indicating reduction of GO. The sensor responses of nanocomposite layers towards exposure of 35 ppm H2 at 100 °C, were measured for several cycles. Ion-irradiated Pd-GO samples show enhancement in the sensing response of H2 gas by about 24% and with lower recovery times (25%), as compared to pristine Pd-GO nanocomposite samples. The change in type of conductivity from p-type gas sensing layer in pristine nanocomposite to n-type conductivity, along with an increase in conductivity (about 500 times) in ion irradiated samples were observed. The change in type of conductivity on ion-irradiation is attributed to the reduction of GO layer and the changes in conductivity on hydrogen exposure is explained due to hydrogen spill-over effect in the two-component system. The improvement in sensitivity upon ion-irradiation was due to the increase in concentration of structural defects due to electronic energy loss, as studied by SRIM simulation. This study points towards using ion induced electronic energy loss as a new tool for varying the gas sensing properties of GO based sensors.

Features of Light-Matter Coupling in Non-Ideal Lattice of Coupled Microcavities Containing Quantum Dots

In this paper, within the framework of virtual crystal approximation, the mathematical modeling of the dependence of the density of states of polariton excitations in a 1D photonic crystal—a system of pores (tunnel-coupled microresonators) containing quantum dots—on the concentration of structural defects is performed.

Эластопроводимость германеновых нанолент с изоморфными дефектами замещения

The results of the theoretical study of the impurity germanium nanoribbons piezoresistance are demonstrated in this article. The nanomaterial contains point isomorphic substitution defects of different concentrations of two types of isomorphic atoms of group IV: silicon (Si) and tin (Sn). The functions of the dependence of the longitudinal component of the elastic conductivity tensor on the magnitude of the strain of tension (compression), types and concentrations of defects are presented to study the characteristics of the piezoresistance effect. The results of the calculations show a qualitative agreement of the behavior of the piezoresistance constant of germanene nanoribbons for two types of isomorphic defects and with the literature data. Quantitative analysis allows us to conclude that the longitudinal component is higher in modulus in nanofilms with tin impurities, which indicates a more pronounced piezoresistance of the material. Conclusions are showed, that the impurity germanene with the tin atoms manifested more pronounced piezoresistance properties. It was be explained by high the electron mobility of the valence shell of this element compared to the germanium atom. This shell of the atom turns out to be more sensitive to deformations of the structure. Such material can be more effectively integrated as a basic element of semiconductor electronics devices due to the high susceptibility of its properties to the effects of deformations and the concentration of structural defects in accordance with this factor.

Controllable synthesis for carbon self-doping and structural defect co-modified g-C3N4: Enhanced photocatalytic oxidation performance and the mechanism insight

For the purpose of improving the photocatalytic performance of graphitic carbon nitride (g-C3N4) in the field of contaminant elimination, an in-situ malonamide-assisted strategy is provided to prepare carbon self-doping and structural defect co-modified g-C3N4 (CDCN) via preprocessing of the mixture of urea and malonamide followed by thermal copolymerization. Changing the initial malonamide dosage can precisely adjust the carbon doping level and structural defect concentration of CDCN. The characteristic results confirm that the doped C derived from malonamide was successfully implanted into the g-C3N4 framework by replacing sp2 hybrid N atoms (C−N=C) in the heptazine units, simultaneously forming some structural defects. Additionally, the preprocessing endows CDCN with good textural properties. So, the optimal CDCN20 shows remarkably enhanced visible-light photocatalytic activity in eliminating acetaminophen (APAP) and methylparaben (MPB) in water than pristine g-C3N4. By combining experimental and theoretical calculating results, the synergistic effect of C self-doping and structural defect promoting the photocatalytic performance of g-C3N4 is revealed thoroughly. This work provides a controllable strategy for synthesizing effective C self-doped g-C3N4 and a new insight into electronic structure and band structure-regulated photocatalytic oxidation mechanisms.

Polarization Rotation Control Domain Dynamic Response Modulates Piezoelectric Properties of Lead‐Free Thin Films

AbstractDomain orientation engineering regulates the polarization direction of thin film and facilitates the enhancement of piezoelectric properties. A change in polarization direction implies a structural change in the piezoelectric thin film. In this work, some unexpected results are obtained by preparing three orientations of Bi0.5Na0.5TiO3‐based lead‐free piezoelectric thin films to amplify this structural change. In distinction to the conventional perception, the piezoelectric properties decrease with increasing polarization direction. This anomaly is influenced by the concentration of structural defects, and rotation of the polarization direction may induce a change in the electronic structure of the material and hence in the concentration of structural defects. Ultimately, the suppression of the domain dynamics response by increasing structural defects leads to the worst piezoelectric properties for thin films with the traditionally perceived optimal (100) orientation. The revelation of this anomaly has implications for the design of the next generation of high‐performance piezoelectric thin films.

Anion doping enabling SnO2 superior electrocatalytic performances for vanadium redox reactions

ABSTRACT SnO2 has been applied in various fields due to its high activity, low cost, variety, and tunable structure. However, the low electrical conductivity of SnO2 hinders its application in electrochemical catalysis. Both cationic and anionic doping can improve the electrical conductivity of SnO2. In this work, doping F was used to optimize the catalysis of SnO2 on the redox reactions for VO2+/VO2 + and V3+/V2+. O2- is replaced by F- with the production of a free electron in SnO2 structure, which increases the electronic conductivity of SnO2. Furthermore, F doping increases the concentration of structural defects in SnO2, such as oxygen vacancies. F doping increases the structural defect of SnO2, such as oxygen vacancy. Therefore, F doping can increase the electrochemical activity of SnO2 by increasing active sites, promoting vanadium ion adsorption and accelerating electron transport. The activity of the VO2+/VO2 + and V3+/V2+ reactions of F doped SnO2 is higher than that of undoped SnO2. The SnO2 at doping mass ratio of 10% (SnO2/F-10) exhibits the best electrochemical performance over 5% and 20%. After SnO2/F-10 modification, the reversibility and electrochemical kinetics of the graphite felt are improved. Cell adopting SnO2/F-10 has larger discharge capacity, higher utilization rate of electrolyte and lower polarization than blank cell. At 150 mA cm−2, the energy efficiency of cell is increased from 52.3% to 68.7% by using SnO2/F-10. At 50 mA cm−2, the modified cell also shows good stability during 50 cycles. Overall, this work promotes the application of metal oxides in vanadium redox flow battery.

Dielectric dispersion impedance spectroscopy and polaron tunneling phenomenon in Au2O3 mixed PbO-B2O3-SeO2:Er2O3 glass ceramics

The glass ceramics of the composition PbO-B2O3-SeO2:Er2O3 (PBSE) doped with small concentrations of Au2O3 were synthesized. The results of detailed studies on various characterization techniques and also different spectroscopic investigations suggested that these glass ceramics are entrenched with Au2(SeO3)3 crystal phases and Au0 metallic particles (MPs). These studies further revealed increasing concentration of [SeO3]2- groups and Au0 metallic particles with the increase of Au2O3 content upto 0.075 mol%. Such [SeO3]2- groups are predicted to induce structural imperfections in the glass ceramic. Optical absorption (OA) and photoluminescence (PL) spectral studies also indicated increasing concentration of imperfections with increase of Au2O3 content. The dielectric viz, dielectric permittivity (ε′), electrical modulus (M), electrical impedance (Z) and a.c. conductivity (σac) spectra in the frequency (ω) region 4 Hz to 8 MHz and in the temperature (T) region 303–633 K of these glass ceramic samples were measured as functions of Au2O3 concentration. The dielectric permittivity (ε′) exhibited an increasing trend with Au2O3 concentration and it is ascribed to the increase in the magnitude of the space charge polarization (scp) due to the increase in the concentration of structural defects induced by [SeO3]2- units and Au0 metallic particles. The plots of electric modulus (M) with frequency and temperature exhibited dipolar relaxation phenomena. Such effects were analyzed further using Cole-Cole diagrams and the possible dipoles responsible for these effects were identified. A.C. conductivity (σac) exhibited increasing trend with the concentration of Au2O3 (up to 0.075 mol%) and such increase is attributed to the polaronic exchange between different structural groups of selenium oxide. The conduction mechanism is analyzed using polaronic tunneling effect in the middle frequency and high temperature regions, whereas in the lower temperature region QMT model seems to be applicable. Conclusions drawn from dielectric properties were found to be well in accordance with the results of spectroscopic properties.

Hydrothermal synthesis and characterization of transition metal (Mn/Fe/Cu) co-doped cerium oxide-based nano-additives for potential use in the reduction of exhaust emission from spark ignition engines.

The goal of this work was to synthesize new cerium oxide-based nano-additives to minimise emissions from spark ignition (SI) engines fueled with gasoline blends, such as carbon monoxide (CO), unburned hydrocarbons (HC) and oxides of nitrogen (NOx). To investigate the effect of transition metal dopants on their respective catalytic oxidation activity, nano-sized CeO2 catalysts co-doped with Mn, Fe, Cu and Ag ions were successfully produced by a simple hydrothermal technique. The synthesis of nano-catalysts with cubic fluorite geometry was confirmed by XRD data. The addition of transition metal ions to the CeO2 lattice increased the concentration of structural defects like oxygen vacancies and Ce3+ ions, which are advantageous for the catalytic oxidation reaction, as also supported by XAFS and RAMAN analysis. Further, nano-gasoline fuel emission parameters are measured and compared to straight gasoline fuel. The results demonstrated that harmful exhaust pollutants such as CO, HC and NOx were significantly reduced. The high surface area, better redox characteristics and presence of additional oxygen vacancy sites or Ce3+ ions have been linked to the improved catalytic performance of the synthesized catalyst.

Effect of growth parameters on defect structure and optical properties of ultrathin SnO2 films

Tin oxide films with thicknesses in the range from 5 to 110 nm have been deposited by reactive dc magnetron sputtering of Sn in Ar + O plasma at a low working pressure of 1.0× 10 −3 Torr on glass substrates at different temperatures (150–400 °C). The effect of deposition time, substrate temperature, and oxygen partial pressure on surface morphology , crystallographic structure, optical properties, and photoluminescence characteristics of SnO 2 films has been studied and correlated with their defect structure . The structural transformation from nanocrystalline to polycrystalline of thicker films >40 nm and films were grown at higher temperature is explained based on adatom mobility and uniform substrate coverage. Based on photoluminescence characteristics and transmittance spectra, the 20 nm thick film exhibits the least defect structure and best electronic and optical behaviors. • Ultrathin SnO 2 films (5–20 nm) are successfully grown by DC reactive sputtering. • Effect of scaling down film thickness (down to 5 nm) on physical properties. • Correlation between defect structure and optical properties. • Thinner films are much smoother than the thicker films. • Low structural defect concentration found in 10–40 nm films.

Flexible Impedimetric Electronic Nose for High-Accurate Determination of Individual Volatile Organic Compounds by Tuning the Graphene Sensitive Properties

We investigated functionalized graphene materials to create highly sensitive sensors for volatile organic compounds (VOCs) such as formaldehyde, methanol, ethanol, acetone, and isopropanol. First, we prepared VOC-sensitive films consisting of mechanically exfoliated graphene (eG) and chemical graphene oxide (GO), which have different concentrations of structural defects. We deposited the films on silver interdigitated electrodes on Kapton substrate and submitted them to thermal treatment. Next, we measured the sensitive properties of the resulting sensors towards specific VOCs by impedance spectroscopy. We obtained the eG- and GO-based electronic nose composed of two eG films- and four GO film-based sensors with variable sensitivity to individual VOCs. The smallest relative change in impedance was 5% for the sensor based on eG film annealed at 180 °C toward 10 ppm formaldehyde, whereas the highest relative change was 257% for the sensor based on two-layers deposited GO film annealed at 200 °C toward 80 ppm ethanol. At 10 ppm VOC, the GO film-based sensors were sensitive enough to distinguish between individual VOCs, which implied excellent selectivity, as confirmed by Principle Component Analysis (PCA). According to a PCA-Support Vector Machine-based signal processing method, the electronic nose provided identification accuracy of 100% for individual VOCs. The proposed electronic nose can be used to detect multiple VOCs selectively because each sensor is sensitive to VOCs and has significant cross-selectivity to others.

Laves Phase Formation in High Entropy Alloys

One of the intriguing recent results in the field of high-entropy alloys is the discovery of single-phase equiatomic multi-component Laves intermetallics. However, there is no clear understanding that a combination of chemical elements will form such high-entropy compounds. Here we contribute to understanding this issue by modifying the composition of duodenary TiZrHfNbVCrMoMnFeCoNiAl (12x) alloy in which we recently reported the fabrication of hexagonal C14 Laves phase. We consider three alloys based on 12x: 7x = 12x-VCrMoMnFe, 12x + Sc, 12x + Be and observe that all of them crystalize with the formation of C14 Laves phase as a dominant structure. We report that 12x + Be alloy reveals a single-phase C14 structure with a very high concentration of structural defects and ultra-fine dendritic microstructure with an almost homogenous distribution of the constituted elements over the alloy matrix. The analysis of electrical and magnetic properties reveals that the Laves phases are Curie-Weiss paramagnets, which demonstrate metallic conduction; 7x and 12x alloys also reveal a pronounced Kondo-like anomaly. Analysis of experimental data as well as ab initio calculations suggest that chemical complexity and compositional disorder cause strong s-d band scattering and thus the rather high density of d-states in the conduction band.

Polaritonic crystal formed of a tunnel-coupled microcavity array and an ensemble of quantum dots

Propagation of polariton excitations in a defect-containing one-dimensional lattice of microcavities with embedded ultracold atomic nanoclusters (quantum dots) is being considered. The virtual crystal approximation is used to study the properties of electromagnetic excitation spectrum resulting from random variations of the atomic subsystem composition and positions of micropores, as well as from a homogeneous elastic deformation of the considered one-dimensional structure. The group velocity dependence of polariton excitations on structural defect concentration and on deformation parameter is being numerically modeled.

High electrical conductivity and breakdown current density of individual monolayer Ti3C2Tx MXene flakes

High electrical conductivity and breakdown current density of individual monolayer Ti3C2Tx MXene flakes

Propagation of Crystal Defects during Directional Solidification of Silicon via Induction of Functional Defects

The introduction of directional solidified cast mono silicon promised a combination of the cheaper production via a casting process with monocrystalline material quality, but has been struggling with high concentration of structural defects. The SMART approach uses functional defects to maintain the monocrystalline structure with low dislocation densities. In this work, the feasibility of the SMART approach is shown for larger ingots. A G2 sized crystal with SMART and cast mono silicon parts has been analyzed regarding the structural defects via optical analysis, crystal orientation, and etch pit measurements. Photoluminescence measurements on passivated and processed samples were used for characterization of the electrical material quality. The SMART approach has successfully resulted in a crystal with mono area share over 90% and a confinement of dislocation structures in the functional defect region over the whole ingot height compared to a mono area share of down to 50% and extending dislocation tangles in the standard cast mono Si. Cellular structures in photoluminescence measurements could be attributed to cellular dislocation patterns. The SMART Si material showed very high and most homogeneous lifetime values enabling solar cell efficiencies up to 23.3%.