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Based on two-component density functional theory integrated with the projector augmented-wave basis and incorporating both calculated and experimental data from Positron Annihilation Spectroscopy (PAS), this study introduces a novel method for identifying and analyzing specific types of vacancies when multiple types of vacancies are coexisting. This method was then tested on 4H-SiC irradiated by 300 keV C4+ ion beams. By calculating charge density to analyze positron annihilation lifetime spectroscopy and calculating wave functions to analyze slow positron-beam Doppler broadening spectroscopy, for the first time, silicon monovacancies (VSi) and carbon monovacancies (VC) in irradiated 4H-SiC were quantitatively detected separately, allowing them to be distinguished with high accuracy. In addition, a decreasing trend in the relative percentage of VC with increasing irradiation dose, consistent with that expected when irradiating with carbon ions, was also observed, illustrating both the effectiveness and potential of this method for broader applications in material defect analysis. This study not only addresses the challenges of identifying multiple coexisting vacancy types using PAS but also extends the applicability and depth of PAS in fields such as nuclear energy, aerospace, and semiconductors. [ABSTRACT FROM AUTHOR]

We have applied positron annihilation spectroscopy to study the vacancy-type defects in β-Ga2O3 single crystals. The three different types of crystals were prepared by Czochralski and edge-defined film-fed growth and doped with Fe, Mg, and Sn for semi-insulating and n-type characteristics. The crystals were also subjected to 6-MeV proton irradiation for controlled introduction of mono-vacancy defects. Positron lifetime and the details of the anisotropy of the Doppler broadening signals were measured as a function of temperature, and the results were compared with the annihilation signals predicted by theoretical calculations. We find Ga vacancies in all three basic split Ga vacancy configurations to dominate the positron data in the as-grown crystals. In contrast, unrelaxed Ga vacancies are found as the main defect introduced by the irradiation. [ABSTRACT FROM AUTHOR]

We have applied positron annihilation spectroscopy to study the vacancy-type defects in β-Ga2O3 single crystals. The three different types of crystals were prepared by Czochralski and edge-defined film-fed growth and doped with Fe, Mg, and Sn for semi-insulating and n-type characteristics. The crystals were also subjected to 6-MeV proton irradiation for controlled introduction of mono-vacancy defects. Positron lifetime and the details of the anisotropy of the Doppler broadening signals were measured as a function of temperature, and the results were compared with the annihilation signals predicted by theoretical calculations. We find Ga vacancies in all three basic split Ga vacancy configurations to dominate the positron data in the as-grown crystals. In contrast, unrelaxed Ga vacancies are found as the main defect introduced by the irradiation. [ABSTRACT FROM AUTHOR]

The outstanding radiation damage stability of an NiCoCrFePd high entropy alloy (HEA) as compared to conventional alloys poses the question for the mechanism of an ion–matter interaction. The positron annihilation lifetime spectroscopic and TEM (transmission electron microscopic) measurements are implemented to trace different kinds of defects produced by 120 MeV Au+9 ion irradiation and their evolution as a function of ion fluence. The variation of lifetimes and corresponding intensities with the ion fluence indicates the formation of dislocation-type defects at a lower ion fluence and vacancy clusters at a higher ion fluence caused by coalescence or agglomeration of dislocation defects. Formation of different types of defects in turn modulates the strain development inside the crystal. Additionally, the HR-TEM investigation of NiCoCrFePd HEA also exhibits the formation of dislocation and vacancy clusters with the average size of vacancy clusters increases from ∼2.9 ± 0.1 to ∼3.8 ± 0.1 nm with the increases in the ion fluence. Surprisingly, the average defect cluster size in NiCoCrFePd HEA is suppressed compared to NiCoCrFe MEA, thereby showing the enhanced radiation stability on Pd incorporation due to the high defect recombination caused by reduced thermal conductivity and high lattice distortion. Nano-indentation measurement shows that the radiation hardening behavior of the NiCoCrFePd HEA responded slowly owing to its damage suppression property as compared to the NiCoCrFe MEA. Additionally, softening behavior also appeared at an early fluence in NiCoCrFe MEA compared to the NiCoCrFePd HEA signifying its excellent resistance to defect accumulation. [ABSTRACT FROM AUTHOR]

The effects of hydrogen absorption on the local lattice structure in palladium (Pd) were investigated by means of positron annihilation lifetime spectroscopy (PALS) and time-differential perturbed angular correlation (TDPAC) spectroscopy. The PALS measurements demonstrated that dislocations and vacancies formed in the preparation process of a pristine Pd plate can be clearly removed by vacuum annealing at 1073 K and the subsequent absorption of a large quantity of hydrogen, resulting in the production of the β-phase hydride PdH0.62, induces the formation of the open-volume defects again. It was also found that the absorbed hydrogen atoms remain in the Pd sample at 323 K but they are completely evacuated during 5 h heating at 383 K. In addition to the overall thermal behavior, an atomic scale observation of the hydrogen dynamics was carried out by means of TDPAC spectroscopy, indicating the nuclear quadrupole relaxation of the present (111m,111Pd → 111Ag→)111Cd probe, which evidently suggests that the hydrogen atoms show fast dynamic motion around the probe. From the temperature-dependent nuclear quadrupole relaxation rate, we obtained an activation energy of 41(4) meV for the motion. [ABSTRACT FROM AUTHOR]

For rooting the development of GaN-based optoelectronic devices, understanding the roles of midgap recombination centers (MGRCs), namely, nonradiative recombination centers and deep-state radiative recombination centers, on the carrier recombination dynamics is an essential task. By using the combination of time-resolved photoluminescence and positron annihilation spectroscopy (PAS) measurements, the origins of major MGRCs in the state-of-the-art GaN epilayers, bulk crystals, and Mg-implanted layers were identified, and their concentrations were quantified for deriving the capture coefficients of minority carriers. In this article, potential standardization of the room-temperature photoluminescence lifetime for the near-band-edge emission (τ PL RT ) as the concentration of major MGRCs well below the detection limit of PAS is proposed. For n-GaN substrates and epilayers grown from the vapor phase, τ PL RT was limited by the concentration of carbon on N sites or divacancies comprising a Ga vacancy (VGa) and a N vacancy (VN), [VGaVN], when carbon concentration was higher or lower, respectively, than approximately 1016 cm−3. Here, carbon and VGaVN act as major deep-state radiative and nonradiative recombination centers, respectively, while major MGRCs in bulk GaN crystals were identified as VGa(VN)3 vacancy clusters in Na-flux GaN and VGa or VGaVN buried by a hydrogen and/or VGa decorated with oxygen on N sites, VGa(ON)3–4, in ammonothermal GaN. The values of τ PL RT in n-GaN samples are compared with those of p-GaN, in which τ PL RT was limited by the concentration of VGa(VN)2 in Mg-doped epilayers and by the concentrations of VGaVN and (VGaVN)3 in Mg-implanted GaN right after the implantation and after appropriate activation annealing, respectively. [ABSTRACT FROM AUTHOR]

The concentration of vacancies and impurities in semiconductors plays a crucial role in determining their electrical, optical, and thermal properties. This study aims to clarify the nature of the interaction between positrons and ionized p-type impurities, emphasizing the similarities they share with the interaction between holes and this type of impurity. An overall strategy for investigating defects in semiconductor crystals that exhibit a combination of vacancies and p-type impurities is presented. By using positron annihilation spectroscopy, in particular, Doppler broadening of the annihilation radiation, we quantify the concentration of vacancies in epitaxial Si crystals grown by low-energy plasma-enhanced chemical vapor deposition. The vacancy number densities that we find are (1.2 ± 1.0) × 1017 cm−3 and (3.2 ± 1.5) × 1020 cm−3 for growth rates of 0.27 and 4.9 nm/s, respectively. Subsequent extended annealing of the Si samples effectively reduces the vacancy density below the sensitivity threshold of the positron technique. Secondary ion mass spectrometry indicates that the boron doping remains unaffected during the annealing treatment intended for vacancy removal. This study provides valuable insights into the intricate interplay between vacancies and ionized impurities with positrons in semiconductor crystals. The obtained results contribute to advance the control and understanding of material properties in heterostructures by emphasizing the significance of managing vacancy and dopant concentrations. [ABSTRACT FROM AUTHOR]

This Perspective focuses on experimental and theoretical aspects of positron annihilation spectroscopy. This set of methods is highly suitable for identifying and quantifying vacancy-type defects in semiconductors and also allows for analyzing their physics characteristics. We present selected examples from the past decade, where the methods have been used for obtaining timely and useful insights into the defect-controlled phenomenon in narrow-gap (Ge, GaSb) and wide-gap (III-nitride, oxide) semiconductors. We also discuss possible future developments that may allow more detailed studies in novel semiconductor materials and devices with ever more complex lattice structures. [ABSTRACT FROM AUTHOR]

Vacancies are generated in semiconductor devices while operating in the space radiation environment, impacting semiconductor carrier concentrations and dynamics. Positron annihilation lifetime spectroscopy (PALS) is used to probe these defect concentrations in bulk grown GaN, GaP, InAs, InP, Si, MgO, and ZnO both as-grown and as a function of 2–4 MeV proton irradiation. All samples were irradiated to yield a common initial damage production and characterized identically. In as-grown samples, PALS reveals vacancy concentrations above the saturation limit in the oxides, disabling further analysis. As a function of dose, of the materials in which defect accumulation could be probed, it is observed that GaN is the most resistant to the accumulation of defects (attributed to the Ga vacancies) and Si is the least. GaP (attributed to the Ga vacancy) and InAs exhibit slightly higher rates of vacancy accumulation than GaN. InP exhibits high defect accumulation rates approaching that of Si. This information is key to understanding the operation of a diverse set of semiconductors in the space radiation environment. [ABSTRACT FROM AUTHOR]

Positron annihilation was used to probe vacancy-type defects in electrodeposited Cu films after nanosecond pulse laser annealing. For the as-deposited Cu film, we identified the coexistence of two different vacancy-type defects, vacancy clusters (such as V16) and monovacancy-type defects, coupled with impurities. An enlargement in the vacancy size was observed after the laser annealing process. The size of these defects was estimated to be close to V30, and such defects could not be formed by conventional furnace annealing. After furnace annealing at 400 °C, the size of the larger vacancy clusters decreased, but that of the smaller vacancies increased. The observed change in the sizes of vacancies is considered to be related to interactions between vacancies and impurities. The depth profile of the defects varied by changing the laser energy density and the number of laser shots. The impact of laser annealing on the vacancy-type defects was observed even after furnace annealing at 800 °C. Because the presence of point defects in electroplated Cu directly correlates with electromigration and grain growth, the ability of laser annealing to introduce large vacancy clusters in the localized region shows the potential of nanosecond laser annealing as a low-thermal budget process tool for back-end-of-line materials. [ABSTRACT FROM AUTHOR]

Electron and positron chemical potentials, positron affinity and bulk lifetime, positronium work function and positron effective mass have been computed for ZnxCd1−xS using a pseudo-potential approach within the virtual crystal approximation (VCA) and the independent particle model. A correction to VCA is included taking into consideration the disorder effect. This has permitted the computation of the positron affinity to separate materials of interest. The performances indicated that the positron annihilates differently in CdS than in ZnS. The bulk lifetime of positron has been obtained as 241.17 ps for CdS and 215.47 ps for ZnS. Hence, it decreases when going from CdS to ZnS. The positronium work function increases from 2.245 to 3.08 eV when augmenting the composition x from 0 to 1, indicating that only fewer positronium atoms are figured in a specimen surface and ejected for the vacuum. The positron effective mass augments from 0.96 to 1.34 m0 when going from CdS to ZnS materials. The details collected from the assisted investigation are of a former significance for an ameliorate accordance of positron annihilation in ZnxCd1−xS. [ABSTRACT FROM AUTHOR]

Palladium plays an important role in modern industry, agriculture and medicine. The direct discharge of palladium results in serious environmental pollution and loses of precious palladium metal. Herein, kaolin/chitosan hybrid nanofibers were successfully prepared to recover Pd2+ cations from aqueous solution. Chitosan and kaolin mixture was first electrospun into nanofibers with citric acid as the in situ crosslinking agent and poly(ethylene oxide) as the co-spinning polymer. Then, the chitosan molecules in these hybrid nanofibers were in situ crosslinked by critic acid at elevated temperatures to endow these nanofibers with excellent solvent resistance. Their structure characterization was conducted by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and positron annihilation lifetime spectroscopy (PLAS). The adsorption performances of these fibrous adsorbents were carefully investigated and optimized (e.g. kaolin content, temperature, pH of solution and initial Pd2+ concentration). The adsorption results demonstrated that incorporation of kaolin powders into the nanofibers could enhance the adsorption capacity from 31 mg/g to 64 mg/g. Thermodynamic parameters studies revealed the endothermic and spontaneous natures of the adsorption process of Pd2+ cations on these hybrid nanofibers. The Pd2+ adsorption behavior of this fibrous adsorbent fitted well with the second-order kinetic model, suggesting the chemical adsorption behavior of Pd2+ cations on this fibrous adsorbent. Moreover, this fibrous adsorbent can be easily regenerated and reused at least three times without significant loss of initial adsorption capacities. These results clearly indicate that this fibrous chitosan/kaolin hybrid absorbent holds great potential in the recovery of precious palladium cations from aqueous solution. [ABSTRACT FROM AUTHOR]

Positron annihilation spectroscopy is applied to high‐quality β‐Ga2O3 [010] oriented 5 μm thick epilayer before and after electron irradiation to calculate absolute vacancy concentrations. Room temperature irradiated is carried out with 2.5 MeV electrons to a dose of 1.9 × 1019 cm−2 to generate high concentrations of vacancies. Both oxygen and gallium vacancies are generated. The vacancy‐sensitive depth‐dependent S‐parameter and the positron diffusion length were measured to determine vacancy concentrations. The positron diffusion length dropped from 101 ± 2 nm to 47 ± 2 nm while the S‐value in the epilayer rose 2.1 ± 0.3%. The positron annihilation spectroscopies (PAS) results on the irradiated film, in comparison with unirradiated as‐grown high‐quality bulk single crystals, are used to obtain for the first time a quantitative estimate of the defect concentration from the S‐parameter for various samples. The −3 charge state of gallium vacancies is taken into account. PAS results on irradiated silicon are shown for contrast, to illustrate the complications in β‐Ga2O3 introduced by a significant orientation dependence and, likely, the presence of hydrogen. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) is widely used in bottle production by stretch blow molding processes (SBM processes) due to its cost-effectiveness and low environmental impact. The presented literature review focuses on microcavitation and solid-state post-condensation effects that occur during the deformation of PET in the SBM process. The literature review describes cavitation and microcavitation effects in PET material and solid-state post-condensation of PET on the basis of a three-phase model of the PET microstructure. A three-phase model of PET microstructure (representing the amorphous phase in two ways, depending on the ratio of the trans-to-gauche conformation of the PET macromolecule and the amount of free volume) with a nucleation process, a crystallization process, and the use of positron annihilation lifetime spectroscopy (PALS) to analyze PET microstructure are discussed in detail. The conceptual model developed based on the literature combines solid-state post-condensation with microcavitation via the diffusion of the post-condensation product. This review identifies the shortcomings of the developed conceptual model and presents them with five hypotheses, which will be the basis for further research. [ABSTRACT FROM AUTHOR]

The investigation focused on nanovoids (free-volume defects) in spinel MgAl2O4 ceramics, synthesized at various temperatures, both before and after saturation (water-immersion), utilizing the positron annihilation spectroscopy method. The findings were analyzed within the framework of a multi-channel model. It was demonstrated that this model integrates channels capturing positrons by volumetric defects and the decay of ortho-positronium atoms. Within this refined approach, the first component reflects the microstructural characteristics of the spinel structure, the second component corresponds to volumetric defects near grain boundaries, while the third pertains to the "pick-off" process of ortho-positronium annihilation within water-filled nanopores of the ceramics. [ABSTRACT FROM AUTHOR]

The European Union is studying the possibility of prohibiting the use of fluorinated-based materials which could limit the use of the most studied and used Nafion and Nafion-like membranes for any applications. Therefore, this study focuses on the preparation and performance evaluation of green, non-fluorinated proton exchange membranes in a chlor-alkali-based reversible electrochemical cell system for renewable energy storage applications. The membranes were prepared by casting and cross-linking of polyvinyl alcohol (PVA) with varying chitosan (CS) concentrations (5–20 wt%), followed by sulfonation using diluted sulfuric acid at room temperature. CS concentrations significantly influenced membrane's physicochemical properties, including ion exchange capacity, ionic conductivity, mechanical strength, and water uptake. Positron annihilation lifetime spectroscopy revealed a correlation between free volume properties and other membrane characteristics. A custom-designed 3D-printed electrochemical cell was developed, capable of operating in reversible mode (both electrolysis and fuel cell modes) with a zero-gap configuration. The PVA/CS (20 wt%) membrane outperformed Nafion, exhibiting a lower voltage (4 V vs. 6 V) in electrolysis mode at 50 mA cm⁻2 and a higher specific power density (2.7 vs. 1.9 mW cm⁻2 mgPt) in fuel cell mode. The obtained results demonstrate that crosslinked PVA/CS non-fluorinated based membranes can be sulfonated using diluted sulfuric acid and work effectively in reversible chlor-alkali electrochemical cells. • Cross-linked PVA/CS membranes were successfully sulphonated with dilute H₂SO₄. • High CS content improves ion exchange capacity, water absorption, and conductivity. • High Chitosan (CS) concentrations weaken the mechanical properties. • A strong correlation between PALS analysis results and the key membrane properties. • PVA membrane/20 wt % CS is the best for reversible chlor-alkali electrochemical cell. [ABSTRACT FROM AUTHOR]

PVDF polymer dielectrics, renowned for their ultra-high-power density, ultra-fast response times, remarkable toughness, and lightweight properties, constitute the essential material foundation for the development of dielectric capacitors. Nevertheless, the low-energy density of these dielectrics presents a challenge to the advancement of dielectric capacitors. In this paper, in the process of preparing monolayer pure PVDF dielectric films by the solution casting method, a fixed-direction magnetic field and a rotating magnetic field were introduced in the horizontal direction, respectively, and this investigation explores the impact of magnetic field modulation on the polymer films' free-volume pore size, grain size, phase structure, dielectric properties, and energy storage capabilities by altering the duration and orientation of the magnetic field's influence. This study also discusses how microscopic alterations, particularly in the free-volume pore size, affect the macroscopic dielectric properties. Polymer films treated with a magnetic field of constant orientation for 3 min were obtained with the smallest free-volume hole size of 2.91 Å, the highest γ-phase contents of 54.8%, the smallest grain size of 68 Å, the largest electrical displacement of 10.64 and a very high discharge energy density of 12.68 J/cm3 (a 200% enhancement over pure PVDF). [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) is widely used in bottle production due to its cost-effectiveness and low environmental impact. The first part of this article describes the research and statistical analysis methodology of the influence of the virgin PET (vPET) and recycled PET (rPET) content in the vPET-rPET blend, as well as the preform heating/cooling conditions in the stretch blow molding (SBM) process on the microscopic bottle properties. Microscopic properties such as crystallinity, density, viscosity, relaxation degree of the amorphous phase, and microcavitation in PET were examined. This study reveals that microcavity and solid-state post-condensation effects occur during PET deformation in the SBM process. The increase in free volume, indicating microcavitation, was confirmed by measuring positron annihilation lifetime spectroscopy (PALS). PALS and density of the amorphous phase studies prove a reduction in the dimensions of the free volumes, with a simultaneous significant increase in their number and ellipsoidization. It can be associated with crystallite rotation in a temperature-dependent non-crystalline matrix. The occurrence of solid-state post-condensation effects was confirmed by measuring the intrinsic viscosity. The conclusions resulting from the analysis of the microstructure affecting the mechanical strength of the material were validated by pressure resistance tests of the bottles. [ABSTRACT FROM AUTHOR]

Based on the generalized results of experimental methods for studying the viscosity of oligomers—DSC, electron microscopy, NMR spin echo, x‐ray diffraction analysis, edge wetting angles, laser microinterference, atomic force microscopy, dynamic light scattering, plastic flow—an analysis of the features of the supramolecular organization of melts and solutions of epoxy oligomers was carried out. In terms of thermofluctuation approach, a qualitative assessment of the structural elements forming a macroscopic polymer body is given, and direct morphological evidence of their structure, thermodynamic stability, size evolution with temperature changes and elastic‐strain effects is presented. A mathematical apparatus has been developed to describe the destruction of domains in solutions and melts of oligomers. Analytical equations have been proposed for calculating the time of thermofluctuation relaxation of domains. Based on the analysis of the supramolecular structure of dian epoxy oligomers by transmission electron microscopy and translational mobility of oligomer macromolecules in the high temperature region (Tg + 150°C), it has been suggested that a structure such as "flickering clusters" of free volume elements is formed in the oligomer melts. Highlights: Phase diagrams of aromatic and aliphatic epoxy oligomers have been constructed.The influence of molecular weight on the activation energy of diffusion of viscous flow is estimated.It has been shown that the supramolecular structure of epoxy oligomers in the melt contains "flickering clusters."The lifetime of density fluctuations of epoxy oligomers domains in melts has been calculated. [ABSTRACT FROM AUTHOR]

Serrated flow effects are visible on a metal surface even after coating. Thus, they are undesirable to manufacturers and product users. To meet the expectations of the industry, research on the conditions for serrated flow occurrence in 5019 aluminum alloy was carried out and the results were collected in the current paper. Thus, the influence of the alloy initial microstructure due to different tempers as well as plastic deformation conditions, i.e., strain rate and temperature, on the alloy stress–strain behavior was determined. Two tempers were considered: the as-fabricated F-temper and the W-temper (i.e., quenched in water after annealing at 500 °C). The synergic influence of these tempers and their tensile test conditions on the serration behavior of the stress–strain curves, i.e., the stress drop and reloading time, were also determined and categorized. Structural and X-ray diffraction studies rationalized the stress–strain characteristics according to dynamic strain aging models with positron annihilation lifetime spectroscopy providing insight into the role of lattice defects (i.e., dislocations and vacancies). The map of the serrated flow domain allowed us to obtain the activation energy of the onset of the Portevin–Le Chatelier effect equal to 56 kJ/mol. It is close to the activation energy for the pipe diffusion mechanism, obtained by applying the model formulated originally for Type B stress serration. [ABSTRACT FROM AUTHOR]

Here we show a novel approach to characterize the gas transfer behavior of silicon-oxide (SiO x) coatings and explain the underlying dynamics. For this, we investigate the coating on a nm-scale both by measurement and simulation. Positron annihilation spectroscopy (PAS) and quantum mechanical electronic structure-based molecular dynamics simulations are combined to characterize the porous landscape of SiO x coatings. This approach analyses the influence of micropores smaller than 2 nm in diameter on gas permeation which are difficult to study with conventional methods. We lay out the main pore diameter ranges and their associated porosity estimates. An influence of layer growth on pore size and porosity was found, with an increased energy input during layer deposition leading to smaller pore sizes and a reduced porosity. The molecular dynamics simulations quantify the self-diffusion of oxygen and water vapor through those PAS deducted micropore ranges for hydrophilic and hydrophobic systems. The theoretical pore size ranges are fitting to our PAS results and complete them by giving diffusion coefficients. This approach enables detailed analysis of pore morphology on mass transport through thin film coatings and characterization of their barrier or membrane performance. This is a crucial prerequisite for the development of an exhaustive model of pore dominated mass transports in PECVD coatings. [ABSTRACT FROM AUTHOR]

A key challenge in efficient molecular separation is fabricating large‐scale, highly selective polymeric membranes with precise pore control at the molecular scale. Herein, a new contorted monomer 6,6′‐dihydroxy‐2,2′‐biphenyldiamine (DHBIPDA) is introduced as a building block to generate cross‐linked, ultra‐thin microporous nanofilms (sub‐10 nm) via interfacial polymerization, enabling rapid, and precise molecular nanofiltration. Using diacyl chloride (TPC) as the cross‐linker instead of trimesoyl chloride (TMC) significantly reduces the pore sizes within the membranes and achieves a narrower pore distribution due to a semi‐crystalline structure. The film structures are confirmed using comprehensive characterization techniques including wide‐angle X‐ray scattering (WAXS), X‐ray diffraction (XRD), positron annihilation lifetime spectroscopy (PALS), CO2 adsorption analysis, and molecular‐scale simulation. The DHBIPDA/TPC and DHBIPDA/TMC membranes achieve methanol permeance values of up to 16.4 and 15.1 LMH bar−1 coupled with molecular weight cutoffs (MWCOs) as low as 283 and 306 Da, respectively. The DHBIPDA/TPC membrane demonstrates both higher permeance and higher selectivity compared to its relatively disordered counterpart DHBIPDA/TMC, consistent with characterization data. The DHBIPDA‐derived membrane efficiently separates dye mixtures with similar molecular weights and enables effective recycling of organometallic homogeneous catalysts, suggesting its potential for industrial applications. [ABSTRACT FROM AUTHOR]

In this study, we reported a defect‐rich porous carbon (SAC) derived from sodium alginate (SA) via combined processes of high‐temperature carbonization at N2 atmosphere, NaCl hard template, and HCl etching for high‐performance absorbents. Besides the meso/macro‐porous structure characterization performed with usual morphological and structural analysis methods, sub‐nanolevel atomic microdefects of the derived SAC were investigated by positron annihilation lifetime spectroscopy (PALS) for the first time. All the samples displayed hierarchical pore structure, including numerous 3D‐interconnected macroporous (0.5‐2 µm), abundant mesopores (3‐5 nm), and rich intrinsic microdefects (mean size of 0.304 nm). The specific surface area and pore volume of the optimized SAC sample were 1191.3 m2·g−1 and 0.69 cm3·g−1, respectively. It was confirmed that the adsorption process of the derived SAC to the dye molecules mainly occurred through a chemical and monolayer adsorption mechanism. The SAC sample showed high efficiency in dye removal, with superior removal capacitance of 230.5 mg·g−1 for anionic dye of methyl orange (MO) and 1655.1 mg·g−1 for cationic dye of Rhodamine B (RhB) at pH = 7, respectively, which were about two times of that of commercial AC for the presence of more active sites of the derived SAC. This study also exhibited that the derived defect‐rich porous carbons from natural‐polymers of SA can be considered as an effective adsorbent to remove MO and RhB dyes from industrially polluted water at neutral pH conditions. [ABSTRACT FROM AUTHOR]

We present a newly developed instrument for 22Na-based positron-annihilation lifetime spectroscopy, designed to facilitate the simultaneous control of temperature, gas atmosphere, and humidity in a single experimental system. The spectrometer operates within a temperature range of 50–480 K and pressures from 10−6 mbar to 1.5 bars. It features a novel gas dosing chamber that allows in situ adsorption studies with gases such as but not limited to CO2, N2, Ar, O2, and their mixtures, with precise control over mixing ratios. Additionally, the device supports in situ humidity exposure, allowing for comprehensive studies of sample interactions with both humidity and humid gases. Fully automated, the system provides seamless data acquisition and environmental control, including pressure and temperature regulation. We demonstrate the instrument's capability to elucidate alterations in the free volume of maltodextrin under humidity exposure. Additionally, we illustrate the instrument's efficacy through case studies on CPO-27 metal-organic frameworks (MOFs), highlighting its versatility in analyzing adsorption phenomena across diverse gas adsorbates and temperatures. This state-of-the-art spectrometer stands as an indispensable tool for probing the physicochemical attributes of materials under varying conditions, providing pivotal insights into gas adsorption mechanisms and material dynamics. [ABSTRACT FROM AUTHOR]

Enhancing the corona resistance of epoxy resin (EP) is crucial for ensuring the reliable operation of electrical equipment and power systems, and the incorporation of inorganic nanofillers into epoxy resin has shown significant potential in achieving this. In this study, functionalized graphene oxide (KHGO) was synthesized via a sol-gel method to enhance the corona resistance of EP with electrochemical impedance spectroscopy (EIS) used to assess the properties of KHGO/EP composites. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) verified the successful grafting of epoxy groups onto the GO surface. The thermal conductivity and stability of the KHGO/EP composite initially increased with KHGO content but declined when the content exceeded 1.2 wt.%. Positron annihilation lifetime spectroscopy (PALS) indicated that KHGO improved interfacial compatibility with EP compared to GO, with agglomeration occurring when KHGO content exceeded a threshold value (1.2 wt.%). EIS analysis revealed that the corona resistance of the KHGO/EP composite was optimal at a filler content of 0.9 wt.%. After corona treatment, the saturation water uptake of the 0.9 wt.% KHGO/EP composite decreased by 15% compared to pure EP with its porosity reduced to just 1/40th of that of pure EP. This study underscores that well-dispersed KHGO/EP composite exhibits excellent corona resistance property suggesting the potential for industrial applications in high-voltage equipment insulation. [ABSTRACT FROM AUTHOR]

Ternary halo‐sulfur bismuth compound Bi19X3S27 (X = Cl, Br, I) with distinct electronic structure and full‐spectrum light‐harvesting properties show great application potential in the CO2 photoreduction field. However, the relationship between photocatalytic CO2 reduction performance and the function of halogens in Bi19X3S27 is still poorly understood. Herein, a series of Bi19X3S27 nanorod photocatalysts with intrinsic X and S dual vacancies were developed, which showed significant near‐infrared (NIR) light responses. The types and concentrations of intrinsic vacancies were confirmed and quantified by positron annihilation spectrometry and electron spin resonance spectroscopy. Experimental results showed that Br atoms and intrinsic vacancies (dual Br‐S) in Bi19Br3S27 could greatly enhance the internal polarized electric field and improve the transfer and separation of photogenerated carriers compared with Bi19Cl3S27 and Bi19I3S27. Theoretical calculations revealed that Br atoms in Bi19Br3S27 could facilitate CO2 adsorption and activation and decrease the formation energy of reactive hydrogen. Among Bi19X3S27 nanorods, Bi19Br3S27 nanorods revealed the highest CO2 photoreduction activity with CO yield rate of 28.68 and 2.28 μmol gcatalyst−1 h−1 with full‐spectrum and NIR lights, respectively. This work presents an atomic understanding of the intrinsic vacancies and halogen‐mediated CO2 photoreduction mechanism. [ABSTRACT FROM AUTHOR]

Treatment of cancer patients requires high-sensitivity diagnostic techniques. Recently, the Society of Positron Annihilation Spectroscopy (PAS) has been working on hypoxia detection using positron lifetime and hopes to diagnose cancer at its initial phases. The accepted hypothesis for the use of positron as a biomarker of tumor hypoxia is that due to the distance between the blood vessels and the cancerous tissues, the oxygen concentration strongly decreases in cancerous tissues. The point that can put the PAS technique in the category of cancer diagnosis tools is its potential capability for oxygen-sensing in tissues. So, the partial pressure of oxygen in the patients tissues can be measured from the Positron Annihilation Lifetime Spectroscopy (PALS). However, before the positron lifetime imaging technique can be established, it is essential to verify the oxygen-sensing capability of the PALS in various chemical environments. In this paper, the mechanisms of positron annihilation in the deionized water and air-bubbled water samples were investigated via systematic experiments by our homemade Doppler Broadening Spectroscopy (DBS) and PALS spectrometer. Three mechanisms for positron annihilation in the investigated liquid samples including oxidation, Positronium conversion, and Positronium inhibition were described. The outcome of this investigation could advance the development of the PALS method for detecting tumors before metastasis, using the J-PET machine, which is still under development at Jagiellonian University. [ABSTRACT FROM AUTHOR]

The medium-entropy alloy (NbTa) 0.67 (HfZr) 0.33 and the high-entropy alloy (NbTa) 0.67 (HfZrTi) 0.33 were prepared by mechanical alloying using high-energy planetary ball mill. The results of X-ray diffraction, scanning electron microscopy, and positron annihilation lifetime spectroscopy measurements suggest that both as-prepared powders are multicomponent alloys in amorphous (or highly disordered) state. The magnetic and thermodynamic results obtained for these powders undoubtedly prove that bulk superconductivity is not observed at temperatures exceeding 2 K. Thermal treatment of both studied materials leads to decomposition of the amorphous phase and precipitation of several crystalline phases. In both annealed samples, the structure of the main crystalline phase was identified as body-centered cubic (bcc), and in this phase, bulk superconductivity was observed below 6.5 K. [ABSTRACT FROM AUTHOR]

The paper presents the application of the multi-layer perceptron regressor model for predicting the parameters of positron annihilation lifetime spectra using the example of alkanes in the solid phase. Good agreement of calculation results was found when the approach is compared with the commonly used methods, e.g., LT. The presented method can be used as an alternative quick and accurate tool for the decomposition of positron annihilation lifetime spectroscopy (PALS) spectra in general. The advantages and disadvantages of this new method are discussed. We show the preliminary results where the trained network can give better outcomes than the results yielded by programs based on an analysis of a single PALS spectrum. [ABSTRACT FROM AUTHOR]

N-type doping in GaAs is a self-limited process, rarely exceeding a carrier concentration level of 1019 cm−3. Here, we investigated the effect of intense pulsed light melting on defect distribution and activation efficiency in chalcogenide-implanted GaAs by means of positron annihilation spectroscopy and electrochemical capacitance–voltage techniques. In chalcogenide-doped GaAs, donor–vacancy clusters are mainly responsible for donor deactivation. Using positrons as a probe of atomic scale open volumes and DFT calculations, we have shown that after nanosecond pulsed light melting the main defects in heavily doped GaAs are gallium vacancies decorated with chalcogenide atoms substituting As, like VGa–nTeAs or VGa–nSAs. The distribution of defects and carriers in annealed GaAs follows the depth distribution of implanted elements before annealing and depends on the change in the solidification velocity during recrystallization. [ABSTRACT FROM AUTHOR]

Positron annihilation lifetime spectroscopy (PALS) enables the nondestructive measurement of nanoscale cavities in materials. In this study, a strategy was proposed for mapping PALS measurement data of isotactic polypropylene to classical molecular dynamics (CMD) simulations. The discrepancy between simulated and experimental glass transition temperatures was resolved by shortening the polymer chains, rather than adjusting for the temperature, using the Williams–Landel–Ferry (WLF) equation. The effective probe radii of ortho-positronium (o-Ps), determined by comparing PALS data with CMD simulations, were ∼0.8 nm, which was consistent with the o-Ps size given by the solution of the Schrödinger equation. The free-volume fraction corresponding to the effective probe radius was 12.3% at the glass transition temperature, close to the value estimated using Simha–Boyer theory. The cavity number density was proportional to the effective probe radius and decreased with temperature. The o-Ps effective probe radius was proportional to both the critical probe radius and the −1/3 power of the monomer number density, and increased with increasing temperature. These findings suggest that combining PALS measurements with CMD simulations may provide insight into cavities in polymeric materials without relying on the WLF equation. [ABSTRACT FROM AUTHOR]

Mixed valence manganites are potential functional materials due to their unique electromagnetic properties. In this work, half-doped ceramics with the perovskite structure Sm 0.5 Ca 0.5 MnO 3 polycrystalline samples are synthesized by the solid-state reaction method in open air at different final sintering temperatures. Structures and particle sizes are studied by x-ray diffraction and scanning electron microscopy, respectively. Positron annihilation spectroscopy and density-functional theory calculations are used to characterize the intrinsic vacancies in the bulk. Thereafter, the effect of vacancies on the magnetic and magnetoresistance (MR) properties is investigated. We find that Mn monovacancies (V Mn ) exist in the bulk among all the samples, and the concentration of V Mn is different. We suggest a possible defect model that can be well applied to explain the phenomena of their electromagnetic properties. The transition temperature of the charge-order state (T CO ) and ferromagnetic and anti-ferromagnetic (T N ) are most likely related to the concentration of V Mn and the particle sizes or pore sizes, respectively. The glass spin state transition temperature seems to be independent of the defect concentration and type. The metal conductive behavior does not appear in a high magnetic field and at low temperatures, which may be caused by the presence of a high concentration of V Mn in the bulk and oxygen-related defects in the boundary, and the double exchange interaction is suppressed. At temperatures below T N and under a weak magnetic field, the MR is related to the total defect concentration. In addition, the high concentration of V Mn is unfavorable for obtaining a high MR value. [ABSTRACT FROM AUTHOR]

Vacancy-type defects in AlInN(10 nm)/AlN(1–2 nm)/GaN were probed by using a positron annihilation technique. The crystal quality of the AlInN layer and atomic diffusion near heterointerfaces were also studied by x-ray diffraction reciprocal space mapping, transmission electron microscopy, and energy-dispersive x-ray spectroscopy. For an as-deposited sample without an AlN spacer layer (AlInN/GaN), Ga atoms diffused into the AlInN layer, and as a result, the concentration of Ga-vacancy-type defects in the GaN layer increased. The vacancy concentration was decreased by inserting the AlN layer, which was attributed to the suppression of out-diffusion of Ga from the GaN layer. The effect of the thickness of the AlN layer on the mobility of two-dimensional electron gas is discussed in terms of the introduction of vacancies into the channel region. The annealing behaviors of vacancies in the GaN layer and atomic exchange near heterointerfaces are also discussed. [ABSTRACT FROM AUTHOR]

TaAs single crystals were grown by a standard chemical vapor transport method. The single-crystallinity and homogeneous distribution of elements were confirmed by transmission electron microscope and x-ray diffraction observations. Positron annihilation measurements revealed that the atomic vacancy concentration was kept below 10 − 5 at. %. However, inductively coupled plasma analysis showed an As-deficient (7–9 at. %) off-stoichiometry. First-principles calculations implied that the off-stoichiometry could be compensated for with excess Ta antisite defects, thereby inducing metallic states. Nevertheless, excellent semimetallic transport properties of a well-suppressed carrier density (≲ 10 18 cm − 3 ), ultrahigh carrier mobility (≳ 10 6 cm 2 /V/s), and large transverse magnetoresistance (> --> 200 000 % at 9 T) with the quantum oscillation were obtained at 1.7 K. This indicated the robustness of semimetallic transport properties against the off-stoichiometric disorder and the quenching of metallic conduction associated with excess Ta atoms. The negative longitudinal magnetoresistance, which is considered evidence of a Weyl semimetal (chiral anomaly), was not observed. These data were discussed with theoretical calculations. [ABSTRACT FROM AUTHOR]

Radiation-induced property changes in materials originate from the energy transfer from an incoming particle to the existing lattice, displacing atoms. The displaced atoms can cause the formation of extended defects including dislocation loops, voids, or precipitates. The non-equilibrium defects created during damage events determine the extent of these larger defects and are a function of dose rate, material, and temperature. However, these defects are transient and can only be probed indirectly. This work presents direct experimental measurements and evidence of irradiated non-equilibrium vacancy formation, where in situ positron annihilation spectroscopy was used to prove the generation of non-equilibrium defects in silicon. [ABSTRACT FROM AUTHOR]

Abstract Two-dimensional transition metal dichalcogenides, particularly MoS2, are interesting materials for many applications in aerospace research, radiation therapy and bioscience more in general. Since in many of these applications MoS2-based nanomaterials can be placed in an aqueous environment while exposed to ionizing radiation, both experimental and theoretical studies of their behaviour under these conditions is particularly interesting. Here, we study the effects of tiny imparted doses of 511 keV photons to MoS2 nanoflakes in water solution. To the best of our knowledge, this is the first study in which ionizing radiation on 2D-MoS2 occurs in water. Interestingly, we find that, in addition to the direct interaction between high-energy photons and nanoflakes, reactive chemical species, generated by γ-photons induced radiolysis of water, come into play a relevant role. A radiation transport Monte Carlo simulation allowed determining the elements driving the morphological and spectroscopical changes of 2D-MoS2, experimentally monitored by SEM microscopy, DLS, Raman and UV–vis spectroscopy, AFM, and X-ray photoelectron techniques. Our study demonstrates that radiolysis products affect the Molybdenum oxidation state, which is massively changed from the stable + 4 and + 6 states into the rarer and more unstable + 5. These findings will be relevant for radiation-based therapies and diagnostics in patients that are assuming drugs or contrast agents containing 2D-MoS2 and for aerospace biomedical applications of 2DMs investigating their actions into living organisms on space station or satellites.

Two-dimensional transition metal dichalcogenides, particularly MoS2, are interesting materials for many applications in aerospace research, radiation therapy and bioscience more in general. Since in many of these applications MoS2-based nanomaterials can be placed in an aqueous environment while exposed to ionizing radiation, both experimental and theoretical studies of their behaviour under these conditions is particularly interesting. Here, we study the effects of tiny imparted doses of 511 keV photons to MoS2 nanoflakes in water solution. To the best of our knowledge, this is the first study in which ionizing radiation on 2D-MoS2 occurs in water. Interestingly, we find that, in addition to the direct interaction between high-energy photons and nanoflakes, reactive chemical species, generated by γ-photons induced radiolysis of water, come into play a relevant role. A radiation transport Monte Carlo simulation allowed determining the elements driving the morphological and spectroscopical changes of 2D-MoS2, experimentally monitored by SEM microscopy, DLS, Raman and UV–vis spectroscopy, AFM, and X-ray photoelectron techniques. Our study demonstrates that radiolysis products affect the Molybdenum oxidation state, which is massively changed from the stable + 4 and + 6 states into the rarer and more unstable + 5. These findings will be relevant for radiation-based therapies and diagnostics in patients that are assuming drugs or contrast agents containing 2D-MoS2 and for aerospace biomedical applications of 2DMs investigating their actions into living organisms on space station or satellites. [ABSTRACT FROM AUTHOR]

Porous liquids (PLs) represent a new frontier in material design combining the merits of solid porous host and liquid phase in gas separation and catalysis. Herein, the PL construction approach is harnessed to tailor the gating effect of organic cages toward enhanced gas separation. A type‐II fluorinated PL (F‐PL) is developed via liquifying a fluorinated organic cage (F‐cage) by a fluorinated ionic liquid (F‐IL). The F‐cage is featured by a small window size (≈5.1 Å), high surface area, good stability under highly ionic conditions, and abundant fluorine moieties. The F‐IL possesses high steric hindrance (bulky cation) and structure similarity with the F‐cage (fluorinated alkyl chain in the anion). The existing status structure integrity of F‐cage in F‐IL upon F‐PL formation is illustrated via spectroscopy and X‐ray‐based techniques. The existence of rigid voids in F‐PL is illustrated by positron annihilation lifetime spectroscopy (PALS) and the improved gas uptake capacity than F‐IL via pressure‐swing CO2 uptake isotherms (0−40) bar. The comparison of the gas uptake behavior (CO2, N2, CH4, and Xe) of F‐PL and F‐cage, combining the computational simulation, highlights that the PL construction can be leveraged to tune the window size of porous scaffolds, leading to enhanced gas selectivity. [ABSTRACT FROM AUTHOR]

The objective of this work is to showcase the ortho-positronium lifetime as a probe for soft-tissue characterization. We employed positron annihilation lifetime spectroscopy to experimentally measure the three components of the positron annihilation lifetime—para-positronium (p-Ps), positron, and ortho-positronium (o-Ps)—for three types of porcine, non-fixated soft tissues ex vivo: adipose, hepatic, and muscle. Then, we benchmarked our measurements with X-ray phase-contrast imaging, which is the current state-of-the-art for soft-tissue analysis. We found that the o-Ps lifetime in adipose tissues (2.54 ± 0.12 ns) was approximately 20% longer than in hepatic (2.04 ± 0.09 ns) and muscle (2.03 ± 0.12 ns) tissues. In addition, the separation between the measurements for adipose tissue and the other tissues was better from o-Ps lifetime measurement than from X-ray phase-contrast imaging. This experimental study proved that the o-Ps lifetime is a viable non-invasive probe for characterizing and classifying the different soft tissues. Specifically, o-Ps lifetime as a soft-tissue characterization probe had a strong sensitivity to the lipid content that can be potentially implemented in commercial positron emission tomography scanners that feature list-mode data acquisition. [ABSTRACT FROM AUTHOR]

\nHIGHLIGHTSPolymer nanocomposites are increasingly used in insulation applications for enhanced electrical properties. However, there are intricate parameters that control the properties of the polymer, and hence investigations are required. This paper attempts to correlate the electrical properties of Epoxy/Organically modified montmorillonite clay composites with the free volume resulting from the incorporation of the Organically modified montmorillonite clay filler of 2, 5, and 7 weight per cent (wt.%). Positron annihilation spectroscopy has been used to compute the fractional free volume and free volume. The free volume percentage is observed to increase with the incorporation of 2 and 5 wt.% and reduces at 7 wt.%. A similar trend is observed in the average size of free volume. The filler increases the AC electric breakdown strength by 20%, arc resistance by 5%, and comparative tracking index by 10% at 5 wt.%. Thermal conductivity is seen to increase marginally with the filler. The surfaces of the composites are hydrophilic at 2 and 7 wt.%, and at 5 wt.%, it is hydrophobic. Longer durations of water diffusion render the surfaces of the nanocomposites hydrophobic. Fourier transform infrared spectroscopy investigations reveal broadening of peak, increase in peak intensity and stretching of Si–O–Si bonds at 5 wt.% of filler due to exfoliation. An attempt has been made to understand the results of electrical parameters based on the results of positron annihilation lifetime spectroscopy and thermal conductivity. Water diffusion is minimal at 5 wt.% of OMMT.Highest CTI of 588 is achieved at 5 wt.%.Arc resistance of 400 s is achieved at 5 wt.%. OMMT.Proof tracking is higher at 5 wt.% of OMMT.Surface is hydrophobic at 5 wt.% OMMT.Water diffusion is minimal at 5 wt.% of OMMT.Highest CTI of 588 is achieved at 5 wt.%.Arc resistance of 400 s is achieved at 5 wt.%. OMMT.Proof tracking is higher at 5 wt.% of OMMT.Surface is hydrophobic at 5 wt.% OMMT. [ABSTRACT FROM AUTHOR]

Background: The distance traveled by the positron before annihilation with an electron, the so‐called positron range, negatively effects the positron emission tomography (PET) image quality for radionuclides emitting high‐energy positrons such as Gallium‐68 (68Ga). Purpose: In this study, the effect of a tissue‐independent positron range correction for Gallium‐68 (68Ga‐PRC) was investigated based on phantom measurements. The effect of the 68Ga‐PRC was also explored in four patients. Methods: The positron range distribution profile of 68Ga in water was generated via Monte Carlo simulation. That profile was mapped to a spatially invariant 3D convolution kernel which was incorporated in the OSEM and Q.Clear reconstruction algorithms to perform the 68Ga‐PRC. In addition, each reconstruction method included point spread function (PSF) modeling and time‐of‐flight information. For both Fluorine‐18 (18F) and 68Ga, the NEMA IQ phantom was filled with a sphere‐to‐background ratio of 10:1 and scanned with the GE Discovery MI 5R PET/CT system. Standard non‐positron range correction (PRC) reconstructions were performed for both radionuclides, while also PRC reconstructions were performed for 68Ga. Reconstructions parameters (OSEM: number of updates, Q.Clear: beta value) were adapted to achieve similar noise levels between the corresponding reconstructions. The effect of 68Ga‐PRC was assessed for both OSEM and Q.Clear reconstructions and compared to non‐PRC reconstructions for 68Ga and 18F in terms of image contrast, noise, recovery coefficient (RC), and spatial resolution. For the clinical validation, 68Ga‐labeled prostate‐specific membrane antigen (68Ga‐PSMA) and 68Ga‐DOTATOC PET scans were included of two patients each. For each PET scan, patients were injected with 1.5 MBq/kg of 68Ga‐PSMA or 68Ga‐DOTATOC and the contrast‐to‐noise ratio (CNR) was calculated and compared to the non‐PRC reconstructions. Results: For OSEM reconstructions, including the 68Ga‐PRC improved the RC by 9.4% (3.7%–19.3%) and spatial resolution by 21.7% (4.6 mm vs. 3.6 mm) for similar noise levels. For Q.Clear reconstructions, 68Ga‐PRC modeling improved the RC by 6.7% (2.8%–10.5%) and spatial resolution by 15.3% (5.9 mm vs. 5.0 mm) while obtaining similar noise levels. In the patient data, the use of 68Ga‐PRC enhanced the CNR by 13.2%. Conclusions: Including 68Ga‐PRC in the PET reconstruction enhanced the image quality of 68Ga PET data compared to the standard non‐PRC reconstructions for similar noise levels. Limited patient results also supported this improvement. [ABSTRACT FROM AUTHOR]

The microstructure and chemical properties of the corona discharge process could provide an effective method for predicting the performance of high-voltage cable insulation materials. In this work, the depth profile of the microstructure and chemical characteristics of corona discharge-treated PE were extensively investigated using Doppler broadening of position annihilation spectroscopy accompanied with positron annihilation lifetime spectroscopy, attenuated total reflectance Fourier transform infrared spectra, Raman spectra and contact angle measurement. By increasing corona discharge duration, the oxygen-containing polar groups, including hydroxyl, carbonyl and ester groups, strongly contribute to the deterioration of hydrophobicity and the enhancement of hydrophilicity. And the mean free volume size, with a broadening distribution, decreases slightly. The line shape S parameter decreases because of the decrease in free volume elements and the appearance of oxygen-containing groups. Also, the thickness of the degradation layer, determined from the S parameter with positron injection depth, increases and diffuses into the PE matrix. A linear S-W plot within the degradation layer of different corona treatment duration samples indicates the defect type does not change. The S parameter decreases and the W parameter increases with an increasing corona duration. Using a slow positron beam, the nondestructive probe can be used to profile the microstructure and chemical environment across the corona discharge damage depth, which is beneficial for investigating the surface and interfacial insulation materials. [ABSTRACT FROM AUTHOR]

In the present work, the doping effect of Zn2+ ion (varying doping concentrations in the range of 0 %–30 %) on PbO nanoparticles (NPs) has been investigated proficiently. This study aims at in-depth analysis of the structure-property relationships of the sol-gel derived Zn doped PbO (Pb 1- x Zn x O) NPs, especially the vacancy evolved properties and the luminescence properties. The X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), field emission scanning electron microscopy (FESEM) and Fourier-transform infrared (FT-IR) spectroscopic characterization analyses justified the nanocrystallinity of the Pb 1- x Zn x O powdered NPs while the mean crystallite sizes were located in between 12 and 36 nm range. Williamson – Hall (W – H) method revealed a monotonous increase of the lattice strain which is compatible with the decrease of NPs' crystallite size by increase in the Zn2+ doping level. The replacement of Pb2+ ions with the Zn2+ ions caused the reduction of crystallite size by the higher Zn2+ doping level. Prominent peaks of Zn, Pb and O elements are noticed in energy dispersive X-ray spectroscopic (EDS) characterization. The elemental distributions of the chemicals present in the NPs were explored by the elemental mapping analysis. The optical absorption (OA) analysis indicated that the energy band gap (E g) can be estimated to be 2.21, 2.36, 2.55 and 2.70 eV for 0, 10, 20 & 30 % Zn doped PbO NPs, respectively. The positron annihilation lifetime (PAL) spectroscopic studies evidenced the presence of vacancy type defects within the NPs and an increase in defect concentrations has been observed by the increase in Zn concentrations. The photo-induced fluorescence (FL) emission spectra exhibited three luminescence peaks around the wavelengths 430 nm, 490 nm and 522 nm for all the NPs. The observations suggested the possibility of tailoring the characteristics of the synthesized NPs for practical applications in the field of optoelectronics. [ABSTRACT FROM AUTHOR]

Silicon nanowalls atop the (100) – oriented boron doped P-type (1–10 Ω-cm) single crystalline silicon wafers were prepared using a metal assisted chemical etching route for different durations 1, 5, 15, and 30 min. The scanning electron microscopy results revealed that the structure evolved up on etching is in the form of vertical silicon nanowalls with mean wall thickness of 70 nm. It can be observed that as the etching time increases, the height of the SiNWs increases linearly at an etching rate of ~ 301 nm per minute. The transmission electron microscopy results combined with FTIR spectroscopy results indicate that about one nanometer thick Si–O-Si- bonded amorphous layer formed at the surface of the grown silicon nanowalls. A defect sensitive Variable energy positron beam Doppler broadening technique used to study the etched silicon wafers confirms that the defect structures that are evolved in the silicon nanowalls with etching are different from that of planar Silicon. Analysis of the Doppler broadened line-shape profiles shows that the effective positron diffusion length and height of the silicon nanowalls are related logarithmically with a scaling exponent of—1/2, indicating that the implanted positrons that are thermalized in the silicon nanowalls diffuse back to the wall surfaces and are annihilated at the defects linked (Si–O-Si)/Si interface region. The present positron experimental results abound with literature reports suggest that understanding the microstructure of the surface layer in SiNWs is significantly important in determining their performance for producing efficient solar cells. [ABSTRACT FROM AUTHOR]

Background: Positron emission tomography (PET) traditionally uses coincident annihilation photons emitted from a positron interacting with an electron to localize cancer within the body. The formation of positronium (Ps), a bonded electron-positron pair, has not been utilized in clinical applications of PET due to the need to detect either the emission of a prompt gamma ray or the decay of higher-order coincident events. Assessment of the lifetime of the formed Ps, however, can potentially yield additional diagnostic information of the surrounding tissue because Ps properties vary due to void size and molecular composition. To assess the feasibility of measuring Ps lifetimes with a PET scanner, experiments were performed in a Biograph Vision Quadra (Siemens Healthineers). Quadra is a long-axial field-of-view (LA-FOV) PET scanner capable of producing list-mode data from single interaction events. Results: Ortho-Ps (o-Ps) lifetimes were measured for quartz-glass and polycarbonate samples using a 22 Na positron source. Results produced o-Ps lifetimes of 1.538 ± 0.036 ns for the quartz glass and 1.927 ± 0.042 ns for the polycarbonate. Both o-Ps lifetimes were determined using a double-exponential fit to the time-difference distribution between the emission of a prompt gamma ray and the annihilation of the correlated positron. The measured values match within a single standard deviation of previously published results. The quartz-glass samples were additional measured with 82 Rb , 68 Ga and 124 I to validate the lifetime using clinically available sources. A double-exponential fit was initially chosen as a similar methodology to previously published works, however, an exponentially-modified Gaussian distribution fit to each lifetime more-accurately models the data. A Bayesian method was used to estimate the variables of the fit and o-Ps lifetime results are reported using this methodology for the three clinical isotopes: 1.59 ± 0.03 ns for 82 Rb , 1.58 ± 0.07 ns for 68 Ga and 1.62 ± 0.01 ns for 124 I . The impact of scatter and attenuation on the o-Ps lifetime was also assessed by analyzing a water-filled uniform cylinder (20 ϕ × 30 cm 3 ) with an added 82 Rb solution. Lifetimes were extracted for various regions of the cylinder and while there is a shape difference in the lifetime due to scatter, the extracted o-Ps lifetime of the water, 1.815 ± 0.013 ns, agrees with previously published results. Conclusion: Overall, the methodology presented in this manuscript demonstrates the repeatability of Ps lifetime measurements with clinically available isotopes in a commercially-available LA-FOV PET scanner. This validation work lays the foundation for future in-vivo patient scans with Quadra. [ABSTRACT FROM AUTHOR]

Binary AsxSe100−x alloys from the border of a glass-forming region (65 < x < 70) subjected to nanomilling in dry and dry–wet modes are characterized by the XRPD, micro-Raman scattering (micro-RS) and revised positron annihilation lifetime (PAL) methods complemented by a disproportionality analysis using the quantum–chemical cluster modeling approach. These alloys are examined with respect to tetra-arsenic biselenide As4Se2 stoichiometry, realized in glassy g-As65Se35, glassy–crystalline g/c-As67Se33 and glassy–crystalline g/c-As70Se30. From the XRPD results, the number of rhombohedral As and cubic arsenolite As2O3 phases in As-Se alloys increases after nanomilling, especially in the wet mode realized in a PVP water solution. Nanomilling-driven amorphization and reamorphization transformations in these alloys are identified by an analysis of diffuse peak halos in their XRPD patterning, showing the interplay between the levels of a medium-range structure (disruption of the intermediate-range ordering at the cost of an extended-range one). From the micro-RS spectroscopy results, these alloys are stabilized by molecular thioarsenides As4Sen (n = 3, 4), regardless of their phase composition, remnants of thioarsenide molecules destructed under nanomilling being reincorporated into a glass network undergoing a polyamorphic transition. From the PAL spectroscopy results, volumetric changes in the wet-milled alloys with respect to the dry-milled ones are identified as resulting from a direct conversion of the bound positron–electron (Ps, positronium) states in the positron traps. Ps-hosting holes in the PVP medium appear instead of positron traps, with ~0.36–0.38 ns lifetimes ascribed to multivacancies in the As-Se matrix. The superposition of PAL spectrum peaks and tails for pelletized PVP, unmilled, dry-milled, and dry–wet-milled As-Se samples shows a spectacular smoothly decaying trend. The microstructure scenarios of the spontaneous (under quenching) and activated (under nanomilling) decomposition of principal network clusters in As4Se2-bearing arsenoselenides are recognized. Over-constrained As6·(2/3) ring-like network clusters acting as pre-cursors of the rhombohedral As phase are the main products of this decomposition. Two spontaneous processes for creating thioarsenides with crystalline counterparts explain the location of the glass-forming border in an As-Se system near the As4Se2 composition, while an activated decomposition process for creating layered As2Se3 structures is responsible for the nanomilling-driven molecular-to-network transition. [ABSTRACT FROM AUTHOR]

This study systematically analyzed the effects of Fe3+ ion doping and annealing treatment on the properties of ammonium dihydrogen phosphate (ADP) crystals. X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS), and energy-dispersive X-ray (EDX) spectroscopy confirmed the concentrations of Fe3+ ions in the pyramid (PY) and prism (PR) face, with doping levels ranging from 10 ppm to 30 ppm. Raman spectroscopy analysis indicated that the ADP crystal's fingerprint peak at 924 cm−1 shifted to a lower wavenumber as the Fe3+ doping concentration increased from 10 ppm to 30 ppm, illustrating lattice distortions caused by doping. Fourier-transform infrared (FTIR) spectroscopy further confirmed these changes, with the crystal fingerprint peak at 967 cm−1 shifting in two opposite directions due to doping with Fe3+ and annealing. The results from positron annihilation lifetime spectroscopy (PALS) indicated that the τ1 values for the annealed samples decreased from 0.135–0.153 ns to 0.123–0.147 ns, suggesting that annealing reduced the concentration of small-sized defects. Meanwhile, τ2 values for the untreated samples decreased from 0.635–0.671 ns to 0.589–0.696 ns, indicating that annealing reduced the number of large-sized defects. Ultraviolet-visible–near-infrared spectroscopy analysis showed that in the wavelength range of 240–800 nm, the average reflectance of the untreated samples was 15–30% higher than that of the annealed ADP crystals, with the reflectance of the latter converging and the variation reducing to below 5% after annealing. These findings suggest that by controlling the growth concentration of Fe3+ ions and optimizing the annealing process, the internal defects within the crystals can be effectively controlled, thereby improving their optical uniformity and mechanical properties, which in turn enhances the performance in nonlinear optical applications. [ABSTRACT FROM AUTHOR]

PLA and PBAT blending is of great significance as biodegradable polymers with good properties. However, they are immiscible and form phase separation morphology in their blend; toughening is critical for the blend to obtain better mechanical properties. Copolymer of malic acid and l-lactide (PMLA) with long-chain branched topology is blended with PLA and PBAT, as to enhance the interfacial interactions for a toughened biodegradable polymer blend. The mechanical and thermal properties are investigated of the resultant blend. Together with SEM and positron annihilation lifetime spectroscopy analysis, the results show that PMLA is an efficient toughening agent for PLA and PBAT blend. The elongation at break increases more than sixfold and the impact strength increases 87.5% than neat PLA and PBAT blend with 8-to-2 weight fraction ratio. At the same time, the resultant blend still keeps fully biodegradable and shows promoted potential for broader application. [ABSTRACT FROM AUTHOR]

In this work, 2,2‐bis(3‐amino‐4‐hydroxyphenyl) hexafluoropropane (APAF) was used as the fixed diamine monomer, and 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 4,4′‐oxydiphthalic anhydride (ODPA), 3,3′,4,4′‐biphenyltetracarboxylic diandhydride (BPDA) and pyromellitic dianhydride (PMDA) were selected as four different dianhydride monomers, respectively, to prepare the thermally rearranged polybenzoxazole (TR‐PBO) gas separation membranes with different structures via a thermal rearrangement reaction at 450°C. The microstructure of TR‐PBO membranes was investigated using X‐ray diffraction and positron annihilation spectroscopy. All the TR‐PBO membranes exhibit bimodal free volume structure, containing ultramicropores (<0.7 nm) and micropores (<2 nm) with size of 3.6–4.6 and 7.6–8.4 Å, respectively. As the steric hindrance of the bridging groups in the dianhydride monomers increases, the radius and number of pores in the membranes increases, leading to an increase in fractional free volume (FFV). The pure gas permeation test shows a positive correlation between gas permeability and FFV in the TR‐PBO membranes, indicating that an increase in FFV is favorable for the diffusion of gas molecules. Particularly, the ultramicropores play a decisive role on the gas selectivity. All the TR‐PBO membranes exhibit excellent gas permeaselectivity. Among them, the H2/CH4 separation performance of APAF‐6FDA and APAF‐ODPA membranes approaches the 2008 Robeson upper bound, which is due to the high number of both micropores and ultramicropores. Our results demonstrate that the free volume structure of polymer membranes can be designed by selecting monomers with different structures and utilizing thermal rearrangement reactions, allowing for the preparation of gas separation membranes with high permeability and selectivity. [ABSTRACT FROM AUTHOR]

The nature and type of defects formed due to heavy-ion irradiation in tungsten foils are analyzed using transmission electron microscopy. The recrystallized tungsten foils were irradiated by 80 MeV gold ions at room temperature for a fluence of 1.3 × 10 14 ions/cm 2 that amounts to a net displacement per atom (dpa) of 0.22. The defect structures were analyzed using bright-field and weak-beam dark field imaging at two different depths to understand the depth profile of the defects. It is found that the defect clusters formed during the irradiation, both at the near-surface and at 2 μ m depth are of vacancy type that is confirmed by the local strain analysis and supports the findings of vacancy clusters in positron lifetime measurements. The analysis also shows that the dislocation-lines were of pure edge, pure screw and mixed. The fraction of mixed dislocation is found to increase during irradiation at the expense of pure edge and screw dislocations. [ABSTRACT FROM AUTHOR]