Explore the vast range of titles available.

This study identified the cause of the minor lifetime component and the effect of the polymer adhesive in the positron source on positron annihilation lifetime spectroscopy. Three types of positron sources with different concentrations of the polymer adhesive were compared using nickel (Ni) and adhesive specimens. The unnecessary components of the positron lifetime due to the polymer adhesive could be eliminated by a source correction of approximately 20.8%. The results showed that minimizing the amount of polymer adhesive in the positron source is recommended, or a detailed source correction is required, to analyze the positron lifetimes accurately.

Positron annihilation lifetime spectroscopy (PALS) is a valuable technique to investigate defects in solids, such as vacancy clusters and grain boundaries in metals and alloys, as well as lattice imperfections in semiconductors. Positron spectroscopy is able to reveal the size, structure and concentration of vacancies with a sensitivity of 10−7. In the field of porous and amorphous systems, PALS can probe cavities in the range from a few tenths up to several tens of nm. In the case of polymers, PALS is one of the few techniques able to give information on the holes forming the free volume. This quantity, which cannot be measured with macroscopic techniques, is correlated to important mechanical, thermal, and transport properties of polymers. It can be deduced theoretically by applying suitable equations of state derived by cell models, and PALS supplies a quantitative measure of the free volume by probing the corresponding sub-nanometric holes. The system used is positronium (Ps), an unstable atom formed by a positron and an electron, whose lifetime can be related to the typical size of the holes. When analyzed in terms of continuous lifetimes, the positron annihilation spectrum allows one to gain insight into the distribution of the free volume holes, an almost unique feature of this technique. The present paper is an overview of PALS, addressed in particular to readers not familiar with this technique, with emphasis on the experimental aspects. After a general introduction on free volume, positronium, and the experimental apparatus needed to acquire the corresponding lifetime, some of the recent results obtained by various groups will be shown, highlighting the connections between the free volume as probed by PALS and structural properties of the investigated materials.

The study investigates the effect of gamma radiation on defect formation in 20 nm titanium nitride (TiN) nanocrystals through positron annihilation lifetime (PALS) and Doppler broadening spectroscopy (DBS) studies. PALS studies were performed at atmospheric pressure, and DBS studies were performed under high vacuum conditions of 10−9 Torr. Gamma irradiation of the samples was performed in MRX-25 gamma device using 60Co isotope with 1.27 MeV energy at absorption doses of 50, 200, 900, and 3500 kGy. Two lifetime components were observed in the PALS results. Under the influence of gamma radiation, τ1 increases from 170 to 179 ps, and τ2 increases from 325 to 398 ps. As the radiation dose increases, the intensity corresponding to the short lifetime component I1 increases (from 75.6 to 81.2%), and I2 decreases (from 24.4 to 18.7%). PALS calculations were performed using the MICA package and a lifetime of 171 ps was determined for the 1Ti vacancy. With the help of Doppler broadening spectroscopy, information about the change and type of defects in the TiN nanocrystal along the volume was behavior of by studying S and W parameters. The results showed that the functionality of the material is optimal at gamma radiation doses not exceeding 3000 kGy.

We report on defects dynamics during heat treatment in plastically deformed metallic materials using positron annihilation lifetime spectroscopy carried out on the intense pulsed positron beam. The conducted experiment allowed us to observe the changes in the concentration and sizes of vacancy-like defects observed during in situ annealing. We monitored heat treatments up to 300 °C in hydrostatic extruded Ti and cavitation peened V–4Cr–4Ti alloy. We were able to track the recovery processes in Ti and redistribution of large voids at the surface of cavitation peened V–4Cr–4Ti alloy. The relaxation time during recovery was about 20 min. Performed experiments show that in cold-worked metallic materials significant changes in vacancy clusters concentrations occur at mildly elevated temperatures. The presented results give opportunity to the application of in situ observation of defects dynamic to similar problems related to thermomechanical processing of metallic materials. Graphical abstract

Positron annihilation spectroscopy using lifetime and Doppler broadening allows the characterization of the lithiation state in LiCoO2 thin film used in cathode of lithium-ion batteries. The lifetime results reflect positron spillover because of the presence of graphite in between the oxide grains in real cathode Li-ion batteries. This spillover produces an effect in the measured positron parameters which are sensitive to delocalized electrons from lithium atoms as in Compton scattering results. The first component of the positron lifetime corresponds to a bulk-like state and can be used to characterize the state of charge of the cathode while the second component represents a surface state at the grain-graphite interface.

The atomic-scale defects such as (deuterium, helium)-vacancy clusters in nuclear energy materials are one of the causes for the deterioration of the macroscopic properties of materials. Unfortunately, they cannot be observed by transmission electron microscopy (TEM) before they grow to the nanometer scale. Positron annihilation spectroscopy (PAS) has been proven to be sensitive to open-volume defects, and could characterize the evolution of the size and concentration of the vacancy-like nanoclusters. We have investigated the effects of He-D interaction on the formation of nanoscale cavities in Fe9Cr alloys by PAS and TEM. The results show that small-sized bubbles are formed in the specimen irradiated with 5 × 1016 He+/cm2, and the subsequent implanted D-ions contribute to the growth of these helium bubbles. The most likely reason is that helium bubbles previously formed in the sample captured deuterium injected later, causing bubbles to grow. In the lower dose He-irradiated samples, a large number of small dislocations and vacancies are generated and form helium-vacancy clusters with the helium atoms.

We present a materials analysis method to enable in-situ Doppler broadening spectroscopy (DBS) of the 511 keV annihilation line in matter during tensile tests. This technique allows the correlation between the formation of lattice defects on an atomic scale and the macroscopic physical materials properties stress and strain. By implanting a monoenergetic positron beam into samples of AlMg3 (3.3535) and AlMgSi (3.3206) the onset of plastic deformation was clearly observed in the recorded annihilation spectra during the measurement of the corresponding stress–strain curves. The changes of the DBS spectra are attributed to positron annihilation in (open-volume) defects—predominantly vacancies elastically bound to dislocation lines—formed during plastic deformation. The elastic strain (Hook’s region), however, does not lead to changes in DBS spectra.

A set of GaN layers prepared by metalorganic vapor phase epitaxy under different technological conditions (growth temperature carrier gas type and Ga precursor) were investigated using variable energy positron annihilation spectroscopy (VEPAS) to find a link between technological conditions, GaN layer properties, and the concentration of gallium vacancies (VGa). Different correlations between technological parameters and VGa concentration were observed for layers grown from triethyl gallium (TEGa) and trimethyl gallium (TMGa) precursors. In case of TEGa, the formation of VGa was significantly influenced by the type of reactor atmosphere (N2 or H2), while no similar behaviour was observed for growth from TMGa. VGa formation was suppressed with increasing temperature for growth from TEGa. On the contrary, enhancement of VGa concentration was observed for growth from TMGa, with cluster formation for the highest temperature of 1100 °C. From the correlation of photoluminescence results with VGa concentration determined by VEPAS, it can be concluded that yellow band luminescence in GaN is likely not connected with VGa; additionally, increased VGa concentration enhances excitonic luminescence. The probable explanation is that VGa prevent the formation of some other highly efficient nonradiative defects. Possible types of such defects are suggested.

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.

Organic pollutants in water remain a hazard to the ecosystem, emphasizing the ongoing concern. Therefore, this study focused on the nano-sized spinel ferrite as a photocatalyst for dye degradation and probing how ferrite microstructure influences the photo-degradation efficiency. The NiFe 2 O 4 and ZnFe 2 O 4 nanoparticles (NPs) were synthesized using the co-precipitation and sol–gel methods, respectively. The effects of microstructure changes of pristine and annealed (450, 600, and 800 °C) ferrites were systematically examined using the positron annihilation lifetime (PAL) and Doppler broadening (DB) techniques. Rigorous analysis, featuring X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM), confirmed the cubic spinel nanostructure for the synthesized ferrite samples as a major phase. The optical properties of the prepared ferrite NPs were studied using the UV–Vis spectroscopy. Particle size ranged from 5.0 to 34.7 nm for NiFe 2 O 4 and from 11.8 to 50.4 nm for ZnFe 2 O 4 . UV–Vis spectra unveiled bandgap energy ranges of 3.76–4.34 and 4.31–4.60 eV for Ni and Zn ferrites, respectively. The photo-degradation efficiency of methylene blue dye catalyzed by the prepared Ni and Zn ferrite NPs was investigated. Comparing PAL and DB parameters revealed notable differences, attributed to distinct crystallinity arising from varied synthesis methods. Remarkably, the highest photo-degradation efficiency was observed in the annealed NiFe 2 O 4 at 800 °C and pristine ZnFe 2 O 4 samples, surpassing others. This achievement was attributed to factors such as enhanced ordered crystallinity, increased vibrational modes, optimal particle size, fitting optical properties, and favorable defect characteristics. This study’s novelty lies in highlighting the pivotal role of microstructure in governing ferrite NPs photocatalyst performance. We underscore the significance of the defect reduction, regardless of its type, size or concentration, to substantially enhance the photo-degradation efficiency. Graphical abstract