Zinc oxide (ZnO) is a wide-bandgap semiconductor with excellent optical and electrical properties, making it a promising material for a wide range of applications in optoelectronics and sensors. The properties of ZnO can be easily modified through doping and defect engineering, which determines its long-term stability and ultimate application. One of the most well-known dopants for ZnO is aluminum (Al), which is used to produce the transparent conductive oxide AZO. In this study, using positron annihilation spectroscopy (PAS) and photoluminescence (PL), we demonstrate defect engineering in AZO through millisecond flash-lamp annealing. We show that the nature of the defects strongly depends on the Al-concentration. The highest electrical conductivity of AZO is obtained at an Al:Zn layer ratio of 1:20, i.e., 2.64 at. % Al. Samples with higher Al content are more resistant to annealing and contain more defects. PAS results reveal the presence of zinc vacancies (V_Zn) and zinc–oxygen vacancy complexes (V_Zn+O) in the delta-AZO thin films, and although the PAS and PL results are generally consistent, slight differences suggest the possible existence of non-optically active defects that are not revealed by the PL measurements. Additionally, an appropriate amount of aluminum doping contributes to improving the crystallinity of ZnO.

The enhancement of microporosity in HMDSO-derived plasma polymer films through sequential cycles of plasma polymerization and etching has been demonstrated using positron spectroscopy techniques. These thin films exhibit a labyrinthine nanoporous architecture, characterized by an interconnected pore network with bottlenecks. The configuration of the plasma reactor significantly influences the final nanoporous structure, governed by the balance between ion-induced densification and chemical oxidation of residual hydrocarbons. By fine-tuning the plasma parameters and reactor design, small nanopores within the Si-O-Si cage structure are optimized to approximately 0.3 nm. These structural units are acting as interconnections of larger nanopores around 0.65 nm, functionalized with Si-OH groups along the pore walls. The high precision of positron annihilation spectroscopy enables clear differentiation between samples, with complementary insights provided by ellipsometry and Rutherford backscattering spectroscopy. Further optimization of the intrinsic microporosity was achieved through near-plasma chemical surface engineering, effectively mitigating ion-induced densification. Given the application potential of superhydrophilic SiOx-like thin films, the thermal stability of the nanoporous network was evaluated at moderate temperatures, revealing excellent structural integrity. These findings support the use of plasma polymer films fabricated via polymerization of hexamethyldisiloxane followed by etching as advanced membrane materials, where well-defined, defect-free microporous structures are essential.

Upconversion (UC) luminescence enhancement in trivalent lanthanide-doped materials – particularly the ytterbium (Yb³⁺)/erbium (Yb³⁺) ion pair – remains challenging due to complex, interdependent mechanisms involving structural modifications and defect formation. Here, we present a systematic investigation of UC enhancement in relation to defect formation in GdVO₄:Yb³⁺/Er³⁺ microcrystals through strategic co-doping with optically inactive ions (Sc³⁺, Cd²⁺, Zn²⁺). We employ a novel multi-technique approach combining positron annihilation lifetime spectroscopy (PALS) – to quantify vacancy-type defects in UC materials – with X-ray diffraction and photoluminescence quantum yield (PLQY) measurements to establish direct structure–defect–property relationships. Our results reveal that dopant valence and ionic radius dictate distinct defect formation patterns: isovalent Sc³⁺ substitution primarily induces lattice contraction with minimal point defect generation, while aliovalent Cd²⁺ and Zn²⁺ doping creates extensive Gd vacancy networks through charge compensation mechanisms. Critically, we demonstrate that defect cluster size and spatial distribution, rather than total defect concentration, govern UC efficiency. Zn³⁺ co-doping achieves a remarkable PLQY enhancement through progressive suppression of large vacancy clusters at grain boundaries, coupled with favorable redistribution of oxygen vacancies within crystallite interiors. In contrast, Cd²⁺ doping, despite similar charge compensation requirements, produces extended defect clusters that act as efficient non-radiative quenching centers, limiting PLQY improvement. These findings establish defect engineering as a powerful strategy for UC optimization and provide a quantitative framework for rational design of high-efficiency lanthanide-based photonic materials.

This study demonstrates drift-assisted positron annihilation lifetime spectroscopy on a p-type (100) silicon substrate in a MOS capacitor, using an applied electric field to control the spatial positron distribution prior to annihilation. The device was operated under accumulation, depletion, and inversion conditions, revealing that the internal electric field can drift-transport positrons either toward or away from the SiO₂/Si interface, acting as a diffusion barrier or support, respectively. Key positron drift-transport parameters were derived from lifetime data, and the influence of the non-linear electric field on positron trapping was analyzed. The comparison of the presented results to our previous oxide-side drift experiment on the same metal-oxide–silicon capacitor indicates that the interface exhibits two distinct sides, with different types of defects: void-like and vacancy-like ((Formula presented.) centers). The positron data also suggest that the charge state of the (Formula presented.) centers likely varies with the operation mode of the MOS, which affects their positron trapping behavior.

Porous glasses produced through melt-quenching of some selective metal organic frameworks like Zeolitic Imidazolate Framework-62 (ZIF-62) and ZIF-4 belong to the advanced functional materials because of their inherent porosity, ease of processing, high gas adsorption capacity and gas separation selectivity. We have delineated thermal induced modifications in the porosity features (pore size, size-distribution and pore density) of crystalline ZIF-62 from room temperature (RT) to its melt-state (> melting point, T_m) followed by its quenching, back to RT, carrying out the depth sensitive positron annihilation lifetime spectroscopy (PALS) measurements in-situ at varying temperatures (RT−T_m). On heating under vacuum, the pores' size as well as size-distribution of crystalline ZIF-62 increases up to ∼473 K as a consequence of removal of entrapped solvent molecules and nonuniform thermal expansion. At higher temperatures (∼473 −573 K), a reduction in pores’ size and size-distribution is observed due to the loss of long range ordering and volume collapse. On melting, ZIF-62 turns into a porous liquid having ∼1.4 times larger pores compared to its crystalline form. The quenching of this porous melt is fully irreversible, and results in the formation of a porous glass having the pores larger than its crystalline counterpart. The in-situ PALS investigation provides the first experimental evidence of inherent porosity in ZIF-62 melt existing at high temperature that has been predicted before through molecular dynamics simulation of the ZIFs-based melts.

The drive to expand the implementation of membrane separation technology towards harsher environments prompted the development of chemically robust epoxide-based TFC membranes. This work seeks to better understand the influence of the support on epoxide-based TFC membrane performance and properties. More specifically, it investigates the impact of porous PAN support layers of different porosities and pore sizes on the formation of poly(epoxyether) (PEE) thin films via interfacial initiation of polymerization (IIP), and their more cross-linked and more charged PEE counterparts (XL-PEE) arising from a subsequent post-treatment step. A systematic study was conducted using a series of supports with pore sizes varying from 20 nm to 90 nm and porosities in the range of 4% to 10%, while maintaining identical synthesis conditions for the selective layer. The physicochemical properties of the selective layer were characterized in-depth with X-ray photoelectron spectroscopy (XPS), elastic recoil detection (ERD), transmission electron microscopy (TEM), positron annihilation lifetime spectroscopy (PALS), and atomic force microscopy (AFM) to elucidate the synthesis-structure-performance relationship. PEE TFC membranes comprising these supports had a broad range in water permeances of 5 – 30 L m⁻² h⁻¹ bar⁻¹ with consistent methyl orange (327.33 g mol⁻¹) rejections of ca. 90%. The densified XL-PEE TFC membranes all achieved ca. 65% NaCl rejections, again independent of the support properties. In contrast, more porous supports resulted in more permeable TFC membranes, which can be attributed to the so-called funnel effect. Additionally, the solvent used to prepare the support layers through non-solvent induced phase separation also impacted the selective layer by affecting the interfacial properties during IIP. This work thus demonstrates that the support can serve as an easy tool to fine-tune the performance of the next-generation of high-performance epoxide-based TFC membranes.

The layered structure of MAX phases is associated with a number of functional properties and is the subject of extensive research. While the unit-cell layers of these structures have been well studied, much less is known about the distribution and manipulation of point defects within them. Here, we selected the prototype Cr₂AlC system and, using variable energy positron beams, observed Doppler broadening and positron annihilation lifetimes to track the evolution of defects caused by the penetration of energetic transition metal ions (Co⁺ and Mn⁺) and noble gas ions (Ar⁺ and Ne⁺). In all cases an overall reduction of the open-volume defect concentration is observed post-irradiation. Atomic displacements induced by the penetrating ions drastically modify the defect distribution: the concentration of agglomerates of 9–15 vacancies (corresponding to positron lifetimes of 335–450 ps) in the precursor [Cr₂C/Al]n layers is suppressed, whereas Al mono- and Al-Cr di-vacancy (lifetimes 217–231 ps) concentrations are enhanced. This breakdown of large defects into point defects scales with atomic displacements and is largely independent of the penetrating ion species, providing insights into the manipulation of point defects in nano-layered systems.

Positron annihilation lifetime spectroscopy (PALS) was employed to study the water-dependent free volume characteristics of wood cell walls in earlywood and latewood of loblolly pine (Pinus taeda). Measurements were conducted across relative humidity levels (1–80% RH) at room temperature, demonstrating good reproducibility and consistency with polymer science principles. The Tao-Eldrup model was applied to the measured ortho-positronium lifetimes to estimate the mean sizes of free volume elements in wood cell walls. At low relative humidity (below ~ 11%), water absorption resulted in antiplasticization, evidenced by a decrease in mean free volume element sizes. As relative humidity increased, water started acting as a plasticizer, causing the free volume elements to expand. While dry cell walls showed no significant differences in free volume element sizes between earlywood and latewood, earlywood exhibited larger mean free volume element sizes at all higher relative humidity levels. At higher relative humidity levels (above ~ 70% RH), the ortho-positronium lifetimes of cell wall free volume elements overlapped with those of liquid water, indicating PALS cannot provide reliable free volume information at higher cell wall moisture contents. Interpreting the intensity of ortho-positronium annihilation was complicated by the possibility of water inhibiting ortho-positronium formation in wood cell walls.

Radiation-induced helium (He) bubble formation poses a major challenge to the structural integrity of materials in nuclear energy systems. In this study, we investigate defect evolution and He behavior in Zr/Nb nanoscale metallic multilayers (NMMs) with immiscible BCC/HCP interfaces, irradiated with 80 keV He ions at fluences ranging from 1 × 10¹⁶ to 1 × 10¹⁷ He/cm². For comparison, single-crystal Nb and polycrystalline Zr were also irradiated under identical conditions to serve as reference materials. Using cross-sectional TEM, SIMS, STEM-EELS, nanoindentation, Doppler Broadening Positron Annihilation Spectroscopy (DBPAS), Positron Annihilation Lifetime Spectroscopy (PALS), and atomistic simulations (DFT and MD), we reveal a highly asymmetric damage response across the multilayer interfaces. Zr layers exhibit larger He bubbles (1.5–2.8 nm), higher swelling (∼1.2%), and greater helium retention, while Nb layers develop bubble-denuded zones (BDZs) exclusively around the interfaces, where bubble nucleation is strongly suppressed and swelling is limited to ∼0.4%. This asymmetry arises from differences in atomic transport properties: DFT calculations show lower migration barriers for vacancies and He atoms in Nb (0.4 and 0.19 eV, respectively), enabling efficient defect migration and recombination at interfaces, whereas Zr retains defects due to higher migration barriers. EELS and DBS-PALS measurements confirm bubble densities of 63–96 He/nm³ and the presence of sub-nanometer open volumes. Compared to monolithic samples, the Zr/Nb multilayers exhibit ∼50% lower irradiation-induced hardening and reduced He retention (11% vs. 17.5% in single-crystal Nb and 16% in polycrystalline Zr). These findings highlight the role of interfaces in driving asymmetric radiation damage and demonstrate the effectiveness of BCC Nb layers in mitigating defect growth. Overall, Zr/Nb multilayers are established as a superior alternative to conventional single- and polycrystalline materials for extreme irradiation environments.

The microstructure of Mo was significantly refined by high pressure torsion to verify its irradiation tolerance in comparison with its micrograined counterpart. After deformation microhardness increased from 231 Hv0.2 for a microgarined sample to 542 and 558 Hv0.2, respectively after one and five rotations. Concurrently, the grain refinement was observed, as the grain size decreased with the increase of the deformation degree down to 480 and 110 nm, respectively for one and five rotations. Subsequently, deformed Mo and a micrograined one were irradiated by He ions to the dose of 8 × 10¹⁶/cm ² to verify their potential application as fusion mirrors. Irradiations were followed by reflectivity measurements in the 300–2400 nm range with a dual beam spectrometer. The measurements revealed that the applied dose causes a decrease in total reflectivity of the micrograined sample, whereas the total reflectivity of deformed samples decreases by additional 2.5%. Nanohardness measurements, detailed microscopy observations using focused ion beam and scanning transmission electron microscope as well as positron annihilation spectroscopy investigations were performed to elucidate changes in the microstructure and understand the different mechanisms of bubble creation after irradiation in micrograined and high pressure torsion processed samples.