Vacancy-type Defects Research Articles

Defects introduced by helium irradiation at different temperatures in W and W-5wt%Re alloy

W and W-5wt%Re alloy were irradiated by 50 keV helium ions at RT, 200 °C, 350 °C and 500 °C to investigate the influence of temperature on the microdefects and surface morphology in the sample. The microdefects in the subsurface region and the surface damage caused by irradiation were characterized by Doppler broadening spectroscopy (DBS) of slow positron beam, transmission electron microscope (TEM) and scanning electron microscopy (SEM), respectively. The results show that a large number of vacancy-type defects were produced after helium ions irradiation, especially at 500 °C, the vacancy-type defects of W alloy are higher than that of W-5wt%Re alloy, which indicated that Re restricted the behavior of vacancy-type defects in tungsten to some extent. The surface irradiation damage such as crystal gap enlargement, grain fell off and pores were observed at different irradiation temperatures. Compared with the coral-like structure observed in W, the circular objects and Hilly-gully structure were observed in W-5wt%Re alloy, and both of them increased and grew with the increase of irradiation temperature. It was speculated that the presence of Re led to the difference by analyzing the formation mechanism of the coral-like structure and the Hilly-gully structure.

Effect of electrochemical hydrogen charging on defect structure in titanium

The influence of hydrogen on defect structure in pure titanium was systemically investigated using X-ray diffraction (XRD) and positron annihilation spectroscopy (PAS). The results showed that hydrogen damage was related to hydrogen concentration, and PAS provided a new idea for the study in the formation of hydride and open volume defects. XRD results showed that two types of titanium hydrides were observed in hydrogen-charged samples, i.e., δ-TiHx and ε-TiH2, and the degree of lattice expansion and the content of hydride increased with hydrogen content. The variation of the S parameter and W parameter indicated that a great deal of vacancy-type defects formed during electrochemical hydrogen charging, and hydrogen atoms could combine with vacancy to form a certain amount of hydrogen-vacancy complexes (HnVm), meanwhile, the hydrogen damage varied significantly with depth. The effective open volume of vacancy-type defect increased with hydrogen charging concentration, and hydrogen-vacancy cluster transformed into HnVm (n < m) cluster, vacancy defects were gradually dominated. In addition, According to the different annihilation environment of positron in titanium hydrides and hydrogen-vacancy complexes, the existence of titanium hydrides and the existing form of hydrogen in defect could be identified in Doppler broadening spectroscopy (CDB). This provided a new way to identify the formation of hydrides and to detect the existing form of low concentration hydrogen in samples.

Vacancy-type defects in bulk GaN grown by oxide vapor phase epitaxy probed using positron annihilation

Defects in bulk GaN grown by the oxide vapor phase epitaxy (OVPE) method were probed by using positron annihilation spectroscopy. Measurements of the Doppler broadening spectra of the annihilation radiation and lifetime spectra of positrons revealed that the major defect species in OVPE-GaN was Ga vacancy-type defects coupled with oxygen atoms such as VGa(ON)n and VGaVN(ON)n. The formation of vacancy-oxygen complexes was attributed to the high concentration of oxygen incorporated in the samples during their growth process. A correlation between such defect complexes and sample transparencies was observed. An 8-μm-thick epitaxial film grown on OVPE-GaN by using metalorganic vapor phase epitaxy was also characterized. The vacancy concentration in the GaN film was found to be under or close to the detection limit of positron annihilation (1015 cm−3), suggesting that an epitaxial layer can be grown on without being influenced by vacancies in the substrates.

The investigation of distribution on size and concentration of helium bubbles in Y-bearing ODS steel using by SAXS and GIXRD

The nucleation and growth of the helium bubble in the structure material usually were subjected to temperature in a thermodynamic environment. In this study, Y-bearing oxide dispersed strengthened (ODS) ferritic/martensitic steels were used as the research material. The Y-bearing ODS steel samples with a thickness of 30 microns were irradiated successively by helium ions with three energies of 300 keV, 400 keV and 550 keV at room temperature and 450°C respectively. Firstly, the evolution of defects caused by H e + irradiation is analyzed by using slow positron beam Doppler broadening spectroscopy (DBS) in positron annihilation spectroscopy technology (PAS). The formation and growth of helium bubbles are deduced from the changes in the concentration of vacancy-type defects. The increase in the size of the helium bubbles at high temperatures leads to a certain distortion of the crystal lattice, which is also verified by analyzing the grazing incidence X-ray diffraction (GIXRD) patterns. The characterization of radius and concentration of helium bubbles in samples irradiated at room temperature and 450°C have been studied by Small Angle X-ray Scattering (SAXS) and Transmission Electron Microscopy (TEM). The results showed that the intensity (I) ~ q-vector (q) curves of samples vary with irradiation temperature over ranges of 0.13 ≤ q ≤ 4.6 nm −1 , which is attributed to the growth of helium bubbles at different irradiation temperature. It is found that the average size of helium bubbles under room temperature irradiation is about 1.78 nm, and the size distribution is narrow, while at the irradiation temperature of 450°C, the size of helium bubbles increases to 2.9 nm, and the size distribution is wider. This result is also verified from the TEM analysis. Besides, the shape of helium bubbles was assumed roughly and tends to spherical with higher temperatures.

Interpretation of optical absorption loss measurements in synthetic sapphire using positron annihilation lifetime spectroscopy

Sapphire should be highly transparent for photon energies less than the band gap, but residual, weak absorption and scattering losses in the near infrared occur as a result of extrinsic and intrinsic defects. Lattice disorder, impurities, and point defects have all been implicated as being the origin of loss phenomena but very little experimental evidence exists to quantitatively establish the relationships that might exist between these defects and optical loss. In this study, three synthetic, c-axis sapphire samples manufactured under similar conditions were characterized using UV-VIS spectroscopy, photothermal common-path interferometry, and positron annihilation lifetime spectroscopy. Model-based interpretation of optical measurements indicated that vacancy-type defects were partially responsible for absorption loss from the ultraviolet to the near-infrared and that the population densities differed among the samples. Positron annihilation lifetime spectroscopy measurements also indicated a higher concentration of cationic vacancy defects near the sample surface which correlates with a higher surface optical loss. This work establishes the use of positron annihilation techniques as a characterization tool for optical materials that could be useful for investigating the origin of weak surface absorption in the transparent region of sapphire.

The influence of rhenium addition on the distribution of vacancy-type defects in tungsten

To investigate the influence of transmutation rhenium on the irradiation-induced defects in tungsten , H + and He + irradiation of 50 keV with a fixed fluence of 1 × 10 16 atoms·cm −2 were conducted on W x Re ( x =0, 3, 5 and 25 wt.%) alloys, respectively. Doppler Broadening Spectroscopy and Coincidence Doppler Broadening Spectroscopy both based on slow positron beam were employed in the current work to characterize the depth distribution and the chemical surroundings of the irradiation-induced defects. The results showed that under 723K irradiation, Re addition suppressed the accumulation of vacancy-type defects compared with pure W. This suppression was enhanced by increasing Re content in W. An obvious Re-related peak from (7-28) × 10 −3 m 0 c was observed in CDB spectra of well-annealed W-Re alloys. The irradiation effect led to the height deviation of Re-related peak. The decrease of the Re-related peak could be attributed to the formation of irradiation-induced defects in irradiated samples, and the reduction of positron annihilation fraction with core electrons of Re.

An Insight into the Efficient Dimethoate Adsorption on Graphene-Based Materials—A Combined Experimental and DFT Study

(1) Background: The development of highly efficient methods for removing hazardous substances from the environment attracts increasing attention. Understanding the basic principles of the removal processes using graphene materials is equally essential to confirm their application efficiency and safety. (2) Methods: In this contribution, adsorption of pesticide dimethoate (DMT) on graphene-based materials has been investigated on the molecular level. (3) Results: The experimental results’ analysis revealed a cooperative binding mechanism of the DMT on the adsorption sites of investigated materials—graphene oxide (GO) and industrial graphene (IG). The adsorption data were analyzed using various adsorption isotherms to determine the thermodynamics of the adsorption process. The experimental results were correlated with Density Functional Theory (DFT) calculations of DMT adsorption on the model surfaces that appropriately describe the graphene materials’ reactive features. (4) Conclusions: Considering experimental results, calculated adsorption energies, optimized adsorption geometries, and electronic structure, it was proposed that the dispersive interactions determine the adsorption properties of DMT on plain graphene sites (physisorption). Additionally, it was shown that the existence of vacancy-type defect sites on the surfaces could induce strong and dissociative adsorption (chemisorption) of DMT.

A Slow Positron Beam Study of Helium Clustering in Oxide Dispersion Strengthened Steels

The present work provides an innovative approach to the experimental study of the radiation tolerance of oxide dispersion strengthened (ODS) steel comparing to its non-ODS variant. Inhomogeneous radiation damage, introduced by helium irradiation, was probed in a depth profile manner by a variable energy positron beam. Although numerous studies reporting the use of slow positron beam (SPB) experiments on ion-implanted materials have been published in the literature, only a few of them address the continuous distribution of microstructural damage introduced by ion beam. In this paper, we use SPB to probe a wide range of radiation damage in a single sample of each material. By evaluating positron diffusion in different parts of the Bragg peak, we were able to track the evolution of radiation-induced damage from a high density of small defects such as helium-vacancy clusters to large bubbles grown by coalescence. Combining with the transmission electron microscopy results and slow positron Doppler broadening spectroscopy, we offer new insight into different stages of microstructural bubble evolution in steels exposed to harsh radiation conditions. The obtained results show that the higher density of vacancy-type defects in the oxide dispersion strengthened steel, which act as recombination centres, suppress the formation of large defect agglomerations. While the TEM provides an indication of this effect in high displacement damage and helium production rates, positron annihilation spectroscopy elucidates the origin of this behaviour, improving the understanding of the fundamental mechanism of helium embrittlement.

Combined EXAFS and MD study to elucidate defect behaviors and stage IV recovery mechanism in heavy ion irradiated molybdenum

The microstructural behaviors of materials control material properties and the recovery mechanism is a key to understanding the microstructural changes induced by irradiation. But the recovery mechanism of many metal materials is not fully understood through traditional research methods. By using Extended X-ray absorption fine-structure (EXAFS) measurements combined with Molecular Dynamics (MD) simulations, we studied the stage IV recovery process through investigating the behaviors of irradiation induced defects (caused by 104 MeV xenon ion beam irradiation) at an elevated temperature (~350 °C) in single crystal Molybdenum (Mo). We distinctly characterized self-interstitial dumbbell defect configurations and simulated their behaviors at this elevated temperature. EXAFS measurements, together with MD simulations and TEM observations, revealed that the mechanism of IV stage recovery is the migration of interstitial type defects (including dumbbells) rather than vacancy type defects. We also discussed the possible states of dumbbells after the stage IV recovery. These results further revealed the nature of the irradiated BCC structure (Mo).

Thermal kinetics of micro-defects in He-ion implanted W and W5Re alloys

To investigate the thermal evolution of vacancy-type defects in He-ion irradiated W and W5Re alloy, different isochronal annealing treatments from 373 to 1273 K were conducted on the irradiated materials. Positron annihilation spectroscopy including positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy were mainly used to characterize the micro-defects evolution. The results showed that the thermal evolution characteristics of defects in both W and W5Re were similar. After He-ion irradiation, mono-vacancies with positron annihilation lifetime of ~ 190 ps were detected in W, together with a large amount of dislocation loops with positron annihilation lifetime of ~ 150 ps in W5Re alloys. The coarsening of vacancy clusters at the expense of small vacancy clusters was the main thermal evolution feature of vacancy-type defects in both W and W5Re when annealing temperature increased to 1073 K. In this progress, the positron annihilation lifetime increased to ~ 350 ps (clusters composed of 4 –8 mono-vacancies) in both W and W5Re. As the temperature increased to 1273 K, the positron annihilation lifetime decreased to ~ 240 ps, which was attributed to a significant population reduction of the dislocation loops, the dissociation of large HenVm complexes and the annealing of micro-voids in both W and W5Re. The vacancy-type defects in W5Re were more susceptible to the annealing temperature because of the formation of vacancy cluster-Re complexes. Re clusters in irradiated W5Re alloy could serve as the nucleation sites of He bubbles, which promoted the swelling and protrusion formation on the surface.

Recent Progress on the Positron Annihilation Experiments on Irradiated Ferritic/Martensitic Steels Containing Helium

The well-known and often acceptable radiation tolerance of ferritic/martensitic (f/m) steels can be severely diminished when neutron irradiation is accompanied by the production of helium. The presence of helium in the irradiated materials changes the kinetics of the nucleation, recombination, and clustering of the radiation-induced defects. High production rates of helium may lead to a non-negligible volumetric bubble swelling at relatively low temperatures. Extrapolation of the knowledge gained from neutron irradiation experiments to fusion or spallation environments is additionally complicated due to the unknown and comprehensive effects of dpa rate, temperature, the presence of sinks in the crystal lattice and others. To improve the understanding of the microstructure and irradiation parameters effects, close attention must be paid to the early stages of the radiation damage. It is expected that the pre-existing vacancy-type defects, attributed to lattice distortion at the grain/subgrain boundaries and oxide-matrix interfaces, are effective sinks for primary defects and helium, i.e. they control the formation and growth of helium-vacancy agglomerations. This early-stage radiation damage, however, cannot be captured by conventional transmission electron microscopy, and thus other experimental techniques are called for. One of the most perspective experimental approaches to investigate small vacancy-type defects, with a high sensitivity to confined helium, is to utilize positron annihilation spectroscopy (PAS). In particular, two spectroscopy techniques, positron annihilation lifetime spectroscopy (PALS) and Doppler broadening spectroscopy (DBS) of the annihilation line, can be beneficially used for the characterization of helium-vacancy clusters. This paper reviews the recent positron annihilation spectroscopy characterization of various irradiation experiments involving helium. Mainly two types of irradiation experiments are addressed, helium implantation and spallation neutron source irradiation experiments. Discussion is aimed at the potential of PAS in the early-stage formation of helium bubbles and the investigation of the effects of irradiation parameters in defect production and accumulation.

Comparison of Hydrogen Thermal Desorption Analysis Curves of Electron-Irradiated F82H and Creep-Ruptured Pure Fe Obtained by Experiments and Simulations

Herein, we compared thermal desorption analysis (TDA) curves obtained by conducting experiments and simulations. In addition, we discussed the validation of our simulations and trapping sites of hydrogen atoms. In as-received F82H, when the samples contained solute atoms, grain boundaries, dislocations, and precipitates, the experimental curve corresponded to the simulated curve. In positron annihilation lifetime (PAL) measurements, di-vacancies were detected in the electron-irradiated F82H. When we changed the growth and the concentration of vacancy-type defects during temperature increase using the rate theory, the simulation results agreed with experiment results. In creep-ruptured Fe, only dislocations were detected by the PAL measurements. However, the existence of a type of defect, which was related to grain boundaries, must be assumed to fit the simulation curve to the experimental one. In the next step, the diffusion of hydrogen atoms on grain boundaries should be added to simulation program.

Effect of rhenium on defects evolution behavior in tungsten under irradiation

The influence of the transmutation element rhenium (Re) on defect evolution in tungsten (W) during irradiations with heavy ions and deuterium (D) plasma was investigated. Rolled W and W–5Re alloy (Re concentration 5 wt.%) were irradiated with 500 keV iron ions to 0.06 and 0.6 dpa (displacement per atom), and deuterium plasma at 38 eV/D to a fluence of 2.2 × 1025 D m−2 at ∼373 K. The results of Doppler broadening spectroscopy by the positron annihilation technique indicate that more or larger vacancy-type defects were produced in W than in the W–5Re during Fe ion irradiation, suggesting the important role of Re on inhibiting the migration and/or clustering of vacancies. The much smaller and shallower blistering in W–5Re than in W after the same D plasma exposure points to the pinning effects on dislocations by Re. The total retained D amounts in W–5Re and W materials are comparable, but with very different concentration profile at corresponding depth. This is explained by the blister formation exerting influence on the D inward diffusion. Demonstrating the important role of Re on the defect evolution in W under irradiation, the present work provides an enhanced understanding on the possible effects of neutron irradiation on the performance of plasma-facing materials in future fusion devices.

Investigation of the interaction between hydrogen and irradiation defects in titanium by using positron annihilation spectroscopy

The formation of mono-vacancy, vacancy clusters and hydrogen-vacancy complexes with 30 keV H ion-irradiated pure titanium at different doses and temperatures was measured using by Positron annihilation spectroscopy (PAS). Results show a large number of HmVn clusters and vacancy-like defects in the samples irradiated at for room temperature, and that the formation of HmVn (m > n) at the sample irradiated at a high dose inhibits the increase of the S parameter. At increased irradiation temperature, the shrinkage of vacancy clusters and the effective open volume of defects decrease the S parameters. The high-temperature irradiation results in decreased vacancy-type defect concentration, and some hydrogen atoms diffuse from the cascade region to the track region, forming a large number of hydrogen-vacancy complexes in the track region. The coincidence Doppler broadening spectroscopy, an element analysis method, used to detect hydrogen in the ion-irradiated pure titanium sample, and results show hydrogen-related peaks in the high-momentum region, which may be due to the information of positron annihilation in the covalent bond formed by the H and the Ti elements. The increased radiation dose and temperature contribute to the formation of the hydrogen vacancy-complex, and the positron annihilation in high-momentum regions easily obtain hydrogen-related information.

The structure, vacancy characteristics, and magnetic properties of GdMn1-xCrxO3 ceramics

To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration.

Evolution of Defects in CVD-W Irradiated by H/He Neutral Beam Using Positron Annihilation Spectroscopy

One of the key problems for the application of nuclear fusion energy is to select the suitable plasma facing materials (PFMs). Among the W-based materials, CVD-W exhibits some unique advantages. In order to estimate the performance of CVD-W under the fusion environment, the vacancy-type defects and their evolution are investigated by the Doppler-broadening slow positron beam analysis (DB-SPBA) combined with SEM (scanning electron microscope). There are two kinds of neutral beam irradiation, the pure H neutral beam and the H + 6 at.% He neutral beam irradiation, which are performed at the neutral beam facility GLADIS (IPP, Germany). The surface temperatures of CVD-W irradiated by H (H + 6 at.% He) are 850 and 1000 (700 and 800 °C). By comparing the samples under different conditions, the defect evolution of CVD-W is obtained. As for the pure H neutral beam irradiated samples, the DB-SPBA results demonstrate that the CVD-W sample at the surface temperature of 1000 °C, compared to the 850 °C sample, shows a decrease in S parameters, which is due to the reduction of vacancy-type defect concentration. The defect damage layer in 1000 °C sample is narrower than that of 850 °C sample and the defect type tends to be consistent in 1000 °C sample. The SEM results suggest that the surface damage of the 1000 °C sample was recovered to some extent. As for the H + 6 at.% He neutral beam irradiated samples, compared with the CVD-W sample at the surface temperature of 700 °C, the 800 °C sample shows an increased S parameters, which can be attributed to the volume increase of vacancy-type defect. The defect damage layer in the 800 °C sample is wider than that of the 700 °C sample. Both the H + 6 at.% He irradiated samples show complex defect types. The surface of the 800 °C sample exhibits more dense pinhole damage structures compared to that of the 700 °C sample.

Influence of irradiation-induced point defects on the dissolution and diffusion properties of hydrogen in α-Al2O3: a first-principles study

Alpha-alumina (α-Al2O3) is considered to be an ideal candidate material for the tritium permeation barrier (TPB) with excellent tritium resistance properties. However, in a fusion reactor, the irradiation-induced defects could sum up on fabrication-induced defects so to reduce drastically the barrier performance. The underlying mechanism is still not settled. In this paper, the first-principles density functional theory (DFT) approach is used to explore the influence of irradiation-induced point defects on the dissolution and diffusion properties of hydrogen (H) in α-Al2O3. and defects have much lower formation energies at E G/2 in both Al-rich and O-rich growth environments that H atoms are easily captured by vacancy-type irradiation-induced point defects. As a result, higher H retention can be expected, which is consistent with the experimental results. Moreover, by calculating several different diffusion pathways of H-defect complexes and the corresponding diffusion coefficient, it can be inferred that H atoms and vacancy-type point defects can hardly diffuse as a bound entity. Therefore, isolated vacancy-type irradiation-induced point defects can trap multiple H atoms to form H-defect complexes and impede the diffusion process of H, which can enhance the efficiency of protection against H permeation through α-Al2O3 TPB. However, the minimum diffusion barrier for O i H− migration to the first nearest neighbor O interstitial site is 0.44 eV, which is so low that O i H− can migrate quickly at room temperature. This fast diffusion pathway for H could be the underlying mechanism for the low efficiency in preventing H permeation through irradiated α-Al2O3. Our results provide a sound theoretical explanation for recent experimental results of H permeation in α-Al2O3 under irradiation environment.

Defects in H/He neutral beam irradiated potassium doped tungsten alloy by positron annihilation technique

Pure tungsten (W) is a primary plasm-facing material (PFM) candidate because of its superior properties, but it still has some drawbacks. In order to solve these problems, various methods have been used to improve the performances of tungsten-based materials. Potassium (K) doping, as one of the typical dispersion-strengthening methods for W materials, improves low temperature brittleness, reduces the ductile-brittle transition temperature, and suppresses the recrystallization. Meanwhile, it also improves the thermal shock resistance and fracture toughness of the material by introducing nano-sized K bubbles. However, this method brings a large number of defects inevitably. In fact, the K bubbles and the dislocations which are pinned by these K bubbles can affect the morphology and evolution of hydrogen (H) and helium (He) atoms in the alloys. As a very sensitive method to detect vacancy-type defects in materials, positron annihilation spectroscopy is used to study the irradiation damage caused by H and He atoms in this paper. The calculation of positron lifetime shows that positrons are more sensitive to the vacancy-type defects. Bounding of H and He with vacancies reduces the positron lifetime because of the increase of valence electron density. Combining the calculated results with the positron annihilation lifetime spectrum (PLAS) results shows that the W-K alloy is easier to promote the H atoms to release. Besides, it also more likely to form larger He bubbles which can be estimated by positron lifetime values. The result is also confirmed by the measurements from the scanning electron microscope (SEM) and slow positron Doppler broadening spectroscopy (DBS). The defects in the W-K alloy such as K bubbles and their pinned dislocations can act as diffusion channels to promote the H atoms to release, which gives rise to a smoother surface under the pure H irradiation. Meanwhile, under the condition of the H+6%He irradiation, the K bubbles and their pinned dislocations in the W-K alloy become the capture center of He atoms, promote their nucleation and grow into larger He bubbles. Moreover, under the action of stress and temperature gradient, some of the He bubbles migrate to the surface and release, this process is conducive to the recovery of related defects and the reduction of radiation damage.

Исследования физико-химических свойств аблированных наночастиц диоксида церия при фотокаталитическом процессе

Purpose of the study. Investigation of the antioxidant properties of nanodispersed solutions of ablated particles of cerium dioxide under conditions of oxidative degradation of an organic dye methylene blue during a photocatalytic reaction, depending on their size characteristics and the pH-environment of solutions. Methods. The ablated cerium dioxide nanoparticles were characterized using scanning electron microscopy; a study was carried out in the visible and ultraviolet ranges of the absorption spectra of the samples using an optical spectrophotometer. The antioxidant activity of ablated nanoparticles in the oxidative photocatalytic reaction was studied using the example of the organic dye methylene blue, depending on the size composition of cerium dioxide nanoparticles and the pH environment of the systems. Cerium dioxide nanoparticles with pronounced antioxidant properties have been obtained by laser ablation. Results. Scanning electron microscopy revealed that cerium dioxide particles agglomerate in an aqueous solution. After the centrifugation process, the number of agglomerates in the upper layers of the solution with a nanometer size of the order of 10 nm increases. Dependences of the antioxidant activity of cerium dioxide nanoparticles on their size characteristics have been determined. The data obtained during the research indicate the highest antioxidant properties of solutions with cerium dioxide nanoparticles, which were centrifuged at a speed of 13400 rpm. With an increase in the pH-medium of solutions, the intensity of the process of inactivation of reactive oxygen species formed during the photocatalytic reaction increases. Conclusion. Cerium dioxide nanoparticles ablated by pulsed laser radiation are new nanomaterials that are antioxidants capable of inactivating reactive oxygen species in oxidative processes of a photocatalytic reaction. These properties of cerium dioxide nanoparticles are determined by the content of defects of the oxygen vacancy type on their surface.

Study on the interaction between He and defects induced by He-ion irradiation in W and W5Re alloy

To investigate the interaction between He atom and irradiation-induced defects in W and W5Re, multiple energetic He ions with damage dose ranging from 0.84 dpa to 1.63 dpa were selected in the present study to implant into W and W5Re samples. Doppler broadening spectroscopy (DBS) and coincidence Doppler broaden spectroscopy (CDB) based on slow positron beam and synchrotron X-ray diffraction technology were employed in the current work. Under the same dose (≤ 1 × 1021 ions m−2) irradiation at room temperature, the depth distribution of vacancy-type defects in W and W5Re is similar. With the increase of irradiation dose, the vacancy-type defects in W continue to grow through absorbing and merging. However, Re atoms are more likely to hinder this growth mechanism, leading to an accumulation of high density but small size vacancy-type defects in W5Re. The HenVm complexes in W continuously attract the mobile interstitial He atom and then induce the trap mutation in the implanted region. Micro-voids and large He bubbles (∼ μm) exceed the recognition of positron. Re atoms has strong the attraction to vacancies and positron affinity. The possible compound of Re and HenVm complexes makes it easier for positron to characterize the He-related and Re-related information around the defect sites. The lattice swelling is similar for the W and W5Re because the structure of HenVm cluster or He bubble can destroy the lattice periodicity and increase the lattice stress in the implanted region.