Control of magnetism through electric-field-driven migration of ions, referred to as magneto-ionics (MI), holds promise for the development of non-volatile energy-efficient memory storage, as well as spintronic, neuromorphic and magnetoelectric devices. Here, we study the MI phenomena in 350 nm thick Ni55Co45 oxide films with varying degrees of porosity, obtained by electrodeposition of the parent Ni-Co metallic alloy on metallized Si substrate and subsequent annealing in air. Annealing at 450 °C of the film electrodeposited from a P-123-containing electrolyte with Ni and Co sulfate salts yields a Ni-Co oxide that partially retains its mesoporosity. This sample exhibits a higher MI response compared to a low-porosity (nearly dense) Ni-Co oxide film, indicating that an increased surface-to-volume ratio enhances MI. Comprehensive characterization of the mesoporous Ni-Co oxide-coated Si/Ti/Au sample reveals that annealing not only oxidizes the top ≈100 nm of the Ni-Co film but also induces silicon diffusion. MI phenomena occur via O2- migration out of and into the top Ni-Co oxide layer under negative and positive biasing, respectively. While the system shows some irreversibility, endurance improves significantly as cycling frequency increases, evidencing the potential of this material for voltage-tunable memory applications.

Magneto-ionics-as the voltage-driven control of magnetic properties through ionic motion and redox processes-offers a promising route toward energy-efficient spintronic devices. Exchange bias, being the unidirectional anisotropy arising from interfacial coupling between antiferromagnets and ferromagnets, plays a central role in spintronics. Here, we demonstrate reversible, room-temperature magneto-ionic generation, suppression, and modulation of exchange bias within a 50 nm-thick antiferromagnetic, magneto-ionically active NiCoO layer. Instead of relying on field cooling to set exchange bias, an applied magnetic field during the growth promotes alignment of the antiferromagnetic spin sublattices, producing a preferential unidirectional orientation. Gating drives oxygen-ion migration along columnar grain boundaries, partially reducing NiCoO and forming ferromagnetic NiCo clusters that couple to the antiferromagnetic matrix. The exchange bias can be controlled by tuning the Ni/Co ratio, which adjusts the Néel temperature, and by varying the actuation time and voltage amplitude which control ferromagnetic cluster size. Micromagnetic simulations reveal that the exchange bias originates from the interfacial uncompensated spins exhibiting partial ferromagnetic-like behavior. This single-layer approach, together with the voltage-controlled formation and tuning of exchange bias without heat treatments, simplifies fabrication and offers a framework for low-power antiferromagnetic spintronic devices.

The stability and transport of native point defects at the interface between ammonothermally grown GaN substrates and MOVPE-grown GaN epilayers remain insufficiently understood, despite their relevance for highperformance GaN electronics. In this work, we investigate the long-standing question of whether native vacancies can diffuse from low-dislocation-density ammonothermal GaN into subsequently grown epitaxial layers. A combination of complementary techniques-including Secondary Ion Mass Spectroscopy (SIMS), C-V profiling, photoluminescence, Raman spectroscopy, and detailed modelling of variable-energy positron annihilation spectroscopy (VEPAS)-is employed to resolve vacancy distributions with high depth sensitivity. Our results consistently show that vacancy-related defects do not propagate from the substrate into the MOVPE epilayer. Instead, we identify a highly compensated interfacial region extending several hundred nanometres into the ammonothermal GaN. This region electrically decouples the epilayer from the substrate and generates builtin electric fields that may influence carrier transport and device behavior. These findings provide new insight into defect behaviour at GaN heterointerfaces and have direct implications for the optimization of ammonothermal GaN substrates for power and optoelectronic devices.

Soda lime silicate glass produced by the float process is among the materials with the largest use worldwide. The manufacturing process introduces an asymmetry in the glass sheets that causes well-known modifications in terms of properties between the so-called “air side” and “tin side”. Nevertheless, not much is known about the structural changes induced by the diffusing tin ions in the network. In the present work, we show that surprisingly, the short range of the tin side is akin to that of the bulk, while the network connectivity in the air side vicinity is enhanced with a larger concentration of bridging oxygens. This correlates with a partial depletion of modifiers from the air side as detected by secondary ion mass spectrometry. On the other hand, the incorporation of tin markedly changes the medium range. In fact, the tin side is characterized by: (i) longer correlation distances, (ii) a more homogeneous structure depicted by a more reduced splitting of the medium frequency Raman features into R and R c bands, (iii) a substantially lower amount of free volume, and (iv) a slight reduction in the average free volume size. Furthermore, the spontaneous hydration layer on the two surfaces is studied, and its effect on the free volume is discussed. These results provide new insight into the soda lime silicate glass structure and have various technological implications for processes like chemical tempering or phenomena like surface defects nucleation.

We investigated the structural evolution and optical properties of β-Ga_2O_3 crystals implanted with different rare-earth (RE) ions using channeling Rutherford Backscattering Spectrometry, Positron Annihilation, Photoluminescence, and Photoluminescence Excitation spectroscopies. The studies reveal that implantation-induced disorder, accompanying phase transitions, and post-annealing structural recovery are largely insensitive to the implanted RE species. The defect microstructure is also found to be similar for all implanted RE ions. Thermal annealing does not completely remove radiation-induced defects but instead drives their rearrangement into larger defect complexes. Unimplanted (virgin) β-Ga_2O_3 exhibits strong UV-visible emission attributed to oxygen vacancies, whereas the introduction of RE ions produces additional emission lines originating from electronic transitions within RE3+ ions. The results indicate that RE3+ ions are excited through the host conduction band, followed by non-radiative relaxation to the 4f excited states and radiative decay to the respective ground states. Fluence-dependent studies of Yb3+ reveal the onset of concentration quenching, while RE-related emission remains efficient even in the presence of substantial lattice disorder. These findings provide new insight into defect evolution in ion-implanted beta-Ga2O3 and clarify the excitation mechanisms of RE3+ ions, offering guidance for optimizing the optical performance of β-Ga_2O_3:RE materials.

Electrophoretic deposition (EPD) is valued for its simplicity, cost-effectiveness, and ability to assemble nanoparticles (NPs) into micrometer-thick functional coatings, membranes, or interconnects at room temperature. In this work, we present a surfactant-free strategy to optimize the colloidal stability and electrophoretic mobility of CuO NPs in nonaqueous solutions by tuning their surface defectiveness and resulting space-charge region in the dry state. To this end, various commercial and in-house synthesized CuO nanopowders (with unknown synthesis, storage, and atmospheric aging histories) are subjected to mild, organic-free surface treatments, such as washing and subsequent annealing in O2 or O3. These optimized treatments yield "pristine" CuO surfaces with reduced defect densities─primarily monovacancies and vacancy clusters, as confirmed by combining X-ray photoelectron and positron annihilation lifetime spectroscopies─which in turn produce narrower and sharper surface space-charge regions, corresponding to higher effective surface potentials. The resulting ζ-potential of treated CuO NPs dispersed in ethanol exceeds > |±100| mV, enabling excellent colloidal stability and high electrophoretic mobility, even for very high NP loadings. A relatively high and stable steady-state EPD current is observed during EPD, which is postulated to originate from capacitive discharging of the electrophoretically deposited CuO NPs at the electrode surface. As such, coherent, uniform, porous CuO coatings with micrometer-scale thickness are obtained, entirely free of organic contaminants often detrimental for surface reactivity and material performance. These findings enable the development of efficient, up-scalable, and environmental-friendly EPD manufacturing routes of organic-free NP-based oxide coatings and membranes, independent of the nanopowder type and aging history.

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 (Pb centers). The positron data also suggest that the charge state of the Pb centers likely varies with the operation mode of the MOS, which affects their positron trapping behavior.

Pnictogen-based solar absorbers have gained prominence as promising nontoxic and stable alternatives to lead-halide perovskites (LHPs), but are severely limited by carrier localization, preventing their performance from approaching those of LHPs. Recent efforts have uncovered routes to overcome carrier localization, but these early efforts only considered intrinsic factors. Herein, we push beyond these limited early efforts, examining the role of defects, not only on cold carriers but also hot carriers. Focusing on the structurally one-dimensional pnictogen chalcohalide BiSBr, we find that whilst this material intrinsically does not exhibit carrier localization, vacancies introduced during synthesis or post-treatment lead to pronounced extrinsic self-trapping via the formation of defect-bound hot polarons-excited charge-carriers strongly coupled to local defect-induced vibrational modes. These above-gap defect states divert hot carriers from cooling to the band edge, thus depleting the mobile carrier population. Our findings establish the key role of defect-bound hot polarons in mediating extrinsic localization and offer new mechanistic insights into the interplay between defects, lattice coupling, and excited-state charge-carrier transport, which are critical to designing efficient perovskite-inspired solar absorbers.

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 (VZn) and zinc–oxygen vacancy complexes (VZn+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.

This study provides a comprehensive analysis of the radiation response and structural evolution of differently orientedβ-Ga_2O_3 single crystals subjected to Yb ion implantation over a wide fluence range from 5 × 10^12 to 1 × 10^16 cm^-2 (0.04–74 dpa). A multi-technique approach (RBS/c, PAS, HRTEM, and HRXRD) was employed to investigate the mechanisms of damage accumulation. The results reveal a multi-stage process of defect evolution. At a critical threshold of around 0.4 dpa, the accumulation of lattice strain triggers a phase transformation from monoclinic β-Ga_2O_3 to a defective spinel structure of γ-Ga_2O_3. Notably, the formation of this new phase is accompanied by strain relaxation. With further irradiation, defects develop within the crystal structure of γ-Ga_2O_3. The associated atomic reorganization at this stage is reflected by a distinct dip in the damage accumulation curve and the appearance of stacking faults in the subsurface region of the implanted layer. In contrast to previous reports suggesting high radiation stability of this phase, the present study clearly demonstrates that continuous defect accumulation results in a significant increase in both displaced atoms and vacancy-type defects, with a strong depth dependence in their type and density. Ultimately, at an irradiation level of approximately 7 dpa, the surface layer amorphizes. With further irradiation, the amorphous layer expands, gradually replacing the transient γ-Ga_2O_3 phase. These findings reveal that the radiation tolerance of gallium oxide is highly sensitive to ion-specific interactions and strain-induced instabilities, thereby challenging the previously assumed robustness of this material under high-fluence ion irradiation.

CoFe 2 O 4 (CFO) nanoparticles were synthesized via controlled co‐precipitation with subsequent calcination at 400 °C, 500 °C, and 600 °C to systematically investigate the influence of thermal treatment on mesostructure, catalytic performance, and especially defect landscape. Structural characterization revealed enhanced crystallinity, sintering, and reduced defect concentration with increasing calcination temperature. Mössbauer spectroscopy and magnetometry indicated increased inversion parameters, improved magnetic alignment, and reduced spin canting, which is consistent with enhanced atomic diffusion during calcination and structural ordering. Positron annihilation lifetime spectroscopy confirmed a calcination‐dependent decrease in vacancy‐type defects. Catalytic testing showed diverging trends: chemical water oxidation (CAN test) activity increased with calcination temperature, but electrochemical oxygen evolution (OER) activity decreased. The opposing behavior is attributed to distinct differences in mechanism: CAN test reactivity is dominated by surface site availability, whereas OER benefits from defect mediated conductivity and charge‐transfer. These results underline the pivotal role of defect engineering while tailing spinel catalysts and highlight that optimal mesostructures depend strongly on the target reaction.

Upconversion in GdVO 4 :Yb 3+ /Er 3+ was tuned by co-doping with Sc 3+ , Cd 2+ , and Zn 2+ . Enhanced PLQY was achieved through Zn 2+ -induced suppression of large vacancy clusters, while Cd 2+ introduced extended defects that quenched luminescence.

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.

Corrosion of stainless steels often produces a duplex structure of an outer iron oxide and inner chromium oxide. The effect of irradiation on multilayer oxides and, in particular, the role of the interface on defect transport are not well understood. In this work, model thin film stacks of epitaxial Fe2O3/Cr2O3/Al2O3(0001) and Cr2O3/Fe2O3/buffer Cr2O3/Al2O3(0001) were synthesized by molecular beam epitaxy and irradiated with 100 keV Fe+ in stages to 5.0 dpa. Irradiation conditions were chosen to limit atomic displacements and Fe+ implantation to the top film only. Structural characterization by X-ray diffraction showed that the d-spacing of the top film was expanded by the irradiation. Cation vacancy defect characterization by Doppler broadening and lifetime positron annihilation spectroscopy revealed that cation defects were present in Cr2O3 after irradiation of the top Fe2O3 film. Based on defect mobility and stability, it is suggested that oxygen interstitials cross from Fe2O3 to Cr2O3 and react with the lattice to generate cation vacancies. This transport is found to be asymmetric: no defects are observed in Fe2O3 when the top Cr2O3 film is irradiated. This asymmetry is attributed to the lower defect mobility in Cr2O3 than Fe2O3.

Abstract Electrochemical CO2 reduction (eCO2R) represents an important strategy to mitigate CO2 emissions while yielding value-added multicarbon (C2+) products, such as ethylene and ethanol. Copper nitride (Cu3N) nanoparticles (NPs) have emerged as attractive catalysts for eCO2R; however, their synthesis remains challenging and is typically limited to multistep liquid phase methods. This work demonstrates an efficient gas-phase approach for the compositional and structural tuning of Cu3N-based NPs by using cylindrical magnetron reactive sputtering with controlled N2/Ar gas mixtures. By varying nitrogen incorporation, the NPs exhibit a controlled transition from metallic Cu to biphasic Cu/Cu3N and ultimately to stoichiometric Cu3N, while maintaining a nearly constant NP size (20–27 nm). Structural characterization combining HR-TEM, Doppler broadening variable-energy positron annihilation spectroscopy (DB-VEPAS), and variable-energy positron annihilation lifetime spectroscopy (VEPALS) reveals a progressive increase in structural defects with nitrogen incorporation, including vacancy clusters, subnanometer voids, mesopores, and nanometer-sized internal voids. The defect-rich Cu3N NPs exhibit the highest concentration of vacancy-type defects and the most pronounced internal porosities. Electrochemical measurements demonstrate that these NPs are active eCO2R catalysts for C2+ product formation, with Cu3N outperforming both metallic Cu and biphasic Cu/Cu3N in terms of the Faradaic efficiency (FE), achieving 50% for C2H4 and 20% for C2H5OH. Cu3N NPs also yield a narrower C2+ product distribution with an overall FE of 79%. These results establish reactively sputtered Cu3N-based NPs as a tunable catalyst platform in which composition, structure, and morphology govern eCO2R selectivity and efficiency.

We investigate the thermal evolution of implantation-induced defects in single-crystal CVD diamond using depth-resolved positron annihilation lifetime spectroscopy (PALS). Samples were implanted with 0.5 MeV N+ ions at a fluence of 1 x 1014 cm-2 and annealed between 600 degrees C and 1200 degrees C. We probe defect populations as a function of depth and quantify their types and concentrations. In the pristine material, small vacancies, predominantly divacancies, are detected at similar to ppm levels together with a low concentration of larger vacancy clusters. Nitrogen implantation increases the abundance of mono-/divacancies. In nitrogen-rich regions, fewer isolated vacancies are observed despite higher displacement damage. Upon annealing, small vacancies become mobile. In nitrogen-poor regions, they agglomerate and grow pre-existing clusters. In contrast, in nitrogen-rich zones, they are efficiently captured by substitutional nitrogen to form NV centers, which limits the formation of new vacancy clusters. At annealing above 1000 degrees C, positron annihilation occurs predominantly in perfect bulk or small open-volume defects consistent with NV center-related positron lifetimes. These results reveal a nitrogen content-and temperature-dependent competition between vacancy clustering and NV center formation.

Chemical strengthening based on ion exchange, IE, is a crucial process for improving the mechanical properties of glass through the formation of a surface residual compression layer. Herein, we investigate the IE of float soda lime silicate glass at temperatures from 380°C to 490°C, with a focus on how the medium-range structure evolves and its relation to stress-relaxation phenomena. Using positron annihilation lifetime and Raman spectroscopy, it is shown that the free volume is substantially reduced by potassium incorporation starting at the lowest IE temperature (380°C), while no changes are observed in the silicate ring structure or bonding angles. When the maximum compressive stress is achieved (430°C), the free volume and the positron lifetime reach a minimum. Moreover, the Raman bands shift, indicating a narrowing of the Si-O-Si bond angle in the vicinity of the alkali cations. The transition between the squeezed and relaxed configuration is sharp, suggesting the existence of two well-defined configurations of the silicate backbone. As the IE temperature further increases, the residual stresses relax. This is coupled with an increase in the free volume and a relaxation of the Si-O-Si bonding angles toward the original configuration. These results clarify that (i) the free volume shrinkage can partially account for the residual stress relaxation through a mechanism not involving a re-construction of the network; (ii) potassium can fill different types of sites accessible at different temperatures, with higher temperatures activating sites straining the silicate framework; (iii) stress relaxation at “high temperature” mirrors a relaxation of the medium-range structure.

We have prepared a set of samples comprising 40 InGaN/GaN quantum wells (QWs), all of which were grown by using the same technological procedure. However, the samples differ in terms of their surface morphology, as they were grown on four different types of buffer layers. Although the MQW region was prepared in the same way, the properties and characteristics of the samples differ significantly. We demonstrate that growing the MQW region on a surface fully covered by V-pits with semipolar facets improves the photoluminescence (PL) properties, particularly for samples with high dislocation densities. Our results suggest that 3D buffer layer morphology can be advantageous for growing GaN-based LEDs on Si substrates, where a high dislocation density cannot be avoided. This is due to the formation of different defects on a flat surface compared with a surface covered with semipolar facets. To elucidate the correlation between PL properties and defect formation, the samples were characterized using various techniques, including SEM, photoluminescence spectroscopy, time-resolved photoluminescence, spectrally and spatially resolved cathodoluminescence, thermally stimulated luminescence, and, for selected samples, cross-sectional STEM. Vacancy-related defect formation was studied for the first time for thick InGaN/GaN MQW structures by variable-energy positron annihilation spectroscopy.

Plasma polymer nanoparticles (pp-NPs) have emerged as linker-free nanocarriers for bioactive cargo and as nanofuels for laser-driven nuclear fusion, yet the structural factors governing their functionality remain poorly understood. Here, pp-NPs were synthesized via plasma polymerization of hexane, cyclohexane, and benzene to determine how monomer structure and specific energy input control radical concentration, hydrogen content, and hierarchical topology. Electron spin resonance and variable-energy positron annihilation lifetime spectroscopy establish that unquenched radical concentrations (1014-1016 spins mg-1) and free-volume size (0.5-0.6 nm) increase from aliphatic to aromatic monomers, whereas free-volume concentration decreases inversely. These trends arise from biradical formation in benzene plasma, steric constraints of aromatic rings, and denser packing caused by reduced hydrogen content, as confirmed by elastic recoil detection analysis. Higher discharge power unexpectedly reduces cross-link density in pp-NPs; statistical network reconstruction reveals that unsaturated carbon bonds reduce the concentration of elastically active network chains more strongly than dehydrogenation increases it. Atomic force microscopy demonstrates that aliphatic monomers yield smoother overall NP surfaces but with a more locally roughened profile (roughness exponent alpha = 0.68), whereas pp-benzene NPs exhibit higher global roughness yet smoother local morphology (alpha = 0.75). Upon deposition, pp-NPs assemble into porous coatings with interparticle voids tunable via NP size (65-560 nm). Together, these findings elucidate how plasma chemistry governs the hierarchical architecture of pp-NPs from subnanometer free volumes to nanoscale surface morphology and mesoscopic interparticle voids, establishing design principles for tailoring radical concentration, hydrogen content, and multiscale porosity for advanced applications.

Copper nitride nanoparticles (Cu3N NPs) are emerging as promising catalysts for the electrochemical conversion of waste CO₂ into valuable multicarbon (C2+) chemicals, with efficiencies approaching industrially relevant figures of merit. However, currently available synthetic routes to Cu3N NPs are largely unsustainable. This work introduces a solvent-free, gas-phase synthesis of Cu3N NPs via reactive sputtering of Cu in N₂, thereby avoiding hazardous solvents and chemicals, high processing temperatures, and excessive waste generation, and providing a fundamentally greener alternative to conventional wet-chemical methods. X-ray diffraction analyses confirm the formation of the Cu3N phase, while electron microscopies reveal cubic NPs with sizes tunable from 10 to 50 nm by adjusting the N2 pressure. Positron annihilation spectroscopy, supported by density functional theory calculations, identifies vacancy clusters containing 7–10 missing atoms as the dominant defects, while sub-nanometer voids, mesopores (1.5–5.5 nm), and larger pores are also observed. X-ray photoelectron spectroscopy indicates that nitrogen vacancies contribute to vacancy clustering and reveals partial surface oxidation of the Cu3N NPs. This unique combination of structural and chemical features enables remarkable electrocatalytic performance toward CO2 reduction. When operated in a flow cell at an industrially relevant current density of 150 mA cm−2, the Cu3N NPs achieve Faradaic efficiencies of 50% for ethylene and 20% for ethanol, with a total C2+ selectivity of 78%, rivaling the best values reported to date. More broadly, this work demonstrates how solvent-free, surfactant-free materials synthesis coupled with defect and porosity engineering can accelerate the development of high-performance, earth-abundant catalysts for carbon utilization.