Ruggedised high-temperature neutron detectors have been identified as important in many industrial applications, such as the monitoring of nuclear reactors. This study focuses on optimising the thermal neutron detection efficiency of silicon carbide (SiC) neutron detectors. Such detectors employ neutron conversion materials deployed in various geometries either as a planar layer on top of a SiC detector or infilling trenches cut into the detector itself. The converter materials investigated in the present work include boron (10B), boron carbide (B4C), boron nitride (BN), boric acid (H3BO3), and lithium fluoride (6LiF). The option of natural boron-containing or 10B-enriched materials was explored. Simulations using GEANT4 were performed to optimise different configurations to identify the key geometrical features that would maximise detection efficiency. A single-trench detector, filled with 10B, achieved a peak efficiency of 40.9% with an optimal trench depth of 25 mu m, while a double trench configuration filled alternately with 10B and 6LiF at the same depth exhibited a lower efficiency of 14.9%. Planar configurations using optimal thickness layers of conversion materials were also explored. Simulation results indicated that single and double-layer planar designs exhibited neutron absorption efficiencies of 5% and 7%, respectively. Comparisons between planar and trench-type designs show a trade-off between efficiency and structural complexity, with trench designs outperforming planar ones in neutron absorption and showing significant improvements in energy deposition. This work provides insights into the optimal design of high-efficiency, rugged SiC-based neutron detectors.

Fe/GaAs is a prototype system of spin injection at room temperature. The interfacial strain and oriented bonds are both considered the origin of the Fe in-plane uniaxial magnetic anisotropy (UMA), which remains decisive. Here, by the x-ray magnetic circular dichroism (XMCD) and the vibrating sample magnetometer measurements, this study shows that in the Fe/Cr(t)/GaAs structure, the in-plane UMA of Fe originates from the chemical bonding between the Fe and the GaAs substrate by varying Cr thickness, t. The UMA drops as the Cr coverage increases, characterized by a decrease in the saturation field from 2400 to 57 Oe. The XMCD studies reveal that the Fe orbital moment, a signature of chemical bonds, decreases from 0.216 μB at Cr = 0 ML to 0.138 μB at Cr = 5 ML. The reduction of the Fe orbital moment and the UMA are qualitatively consistent, establishing a link between the UMA and the interfacial chemical bonds. The decreased UMA remains unchanged at t > 5 ML, above which Fe and GaAs are fully separated by a continuous Cr layer. Our findings provide clear experimental evidence that the UMA in the Fe/GaAs system originates from the oriented interface bonds, clarifying the UMA origin in this prototype system.

The antiferromagnetic Co 0.6 Fe 0.4 O core couples via exchange interaction with the ferrimagnetic Co 1.4 Fe 1.6 O 4 shell at their interface, inducing a giant exchange bias.

Efficient spin injection is essential for the development of ferromagnet-semiconductor spintronic devices with high performances, including spin transistors. Although the Co2Fe(Al-0.5,Si-0.5) (CFAS)/Ge hybrid structure has been identified as an outstanding platform for such devices, there is a lack of systematic analyses on the effects of the interface atomic structure on the spin-electronic properties. In this study, we investigate electronic and magnetic properties of CFAS/Ge (001) interfaces by density functional theory calculations under two possible scenarios, with atomically abrupt bulk-like interfaces and with intermixing at the interfaces. For two possible terminations in the case of abrupt interfaces, we show considerable reductions in spin polarization (SP), which is emphasized in the case of the -Fe-Si,Al/Ge interface, where the SP has reversed sign. Further, we show that Fe-Ge interdiffusion is most likely to occur at the interface, and that this intermixing does not largely affect the spin-electronic properties. In contrast, the model of interdiffusion affecting the Co sublattice in the CFAS film exhibits a reversed SP at the interface layers, but this is less likely to occur owing to the higher energy for such atomic swaps. Band alignment analyses show that interfaces with a small degree of Fe/Ge intermixing could be beneficial for the spin injection efficiency. This study demonstrates that the spin injection efficiency is strongly dependent on the ferromagnet-semiconductor interface atomic structure, and thus can guide further theoretical and experimental studies for development of spintronic devices with improved properties.

Utilizing state of the art diffraction, imaging and spectroscopic techniques in conjunction with two-dimensional correlation analysis, we provide novel in-depth insights into the physics and chemistry behind the different tendencies towards self-assembling in NiO nanoparticles as function of their surface facets. We demonstrate substantially different temperature dependence of the spectroscopic behavior of the two types of NiO NPs, polar versus non-polar faceted. Temperature-dependent spectroscopy data for NiO NPs obtained by the ammonia route are consistent with the process in which high amount of water molecules that take part in hydrogen-bonding interaction with the surface-adsorbed non-dissociated water molecules on the neutral (100) planes are lost during the thermal treatment and attached back upon cooling. Interactions between water molecules adsorbed on two vicinal NiO NPs are responsible for keeping the self-assembly of the Ni(OH)2 NPs upon heat treatment. In carbamide-based NiO NPs, the self-assembly of initially formed Ni3(OH)4(NO3)2 NPs is not preserved. These NPs are terminated with polar (111) atomic planes, on which water molecules dissociatively adsorb, giving surface hydroxyl groups. As the hydrogen bonding proton - donating and accepting abilities are negligible at OH-polar terminated NiO NPs, only unfavorable inter-NP interactions are possible which leads to disruption of the NP assembly.

The miniaturization of transistors is approaching its limits owing to challenges in heat management and information transfer speed1. To overcome these obstacles, emerging technologies such as spintronics2 are being developed, which make use of the electron's spin as well as its charge. Local phenomena at interfaces or structural defects will greatly influence the efficiency of spin-based devices, making the ability to study spin-wave propagation at the nanoscale and atomic scale a key challenge3,4. The development of high-spatial-resolution tools to investigate spin waves, also called magnons, at relevant length scales is thus essential to understand how their properties are affected by local features. Here we detect bulk THz magnons at the nanoscale using scanning transmission electron microscopy (STEM). By using high-resolution electron energy-loss spectroscopy with hybrid-pixel electron detectors, we overcome the challenges posed by weak signals to map THz magnon excitations in a thin NiO nanocrystal. Advanced inelastic electron scattering simulations corroborate our findings. These results open new avenues for detecting magnons and exploring their dispersions and their modifications arising from nanoscale structural or chemical defects. This marks a milestone in magnonics and presents exciting opportunities for the development of spintronic devices.

In this work, we demonstrate the colloidal bottom-up synthesis of spinel AgIn5S8 quantum dots (QDs) with tunable optical properties. The QD size, and consequently their band gap energy (Eg), is effectively controlled by reaction temperature and ultrasound (US) irradiation. Under combined conditions of 75 °C and US irradiation, ultrasmall QDs with an average size of 2.6 nm are obtained, exhibiting a wide band gap of 3.77 eV. In the absence of US, reactions conducted at 55 °C and 75 °C yield larger QDs (∼5 nm and 31 nm, respectively), with reduced band gaps of 3.09 eV and 2.18 eV. The elevated temperature (75 °C) suppresses sulfur-chain formation that otherwise limits growth at 55 °C, while acoustic cavitation induced by US enables narrowest size distribution. Annealing of as prepared QDs, at 200 °C for 2 h, promotes coalescence resulting in QDs with increased size of ∼34 nm, with a bulk like band gap of 1.73 eV for QDs prepared without US. In contrast, annealing of the QDs, prepared with US, results in polycrystalline QDs with average size of ∼21 nm. High-resolution transmission electron microscopy reveals a strong correlation between QD size, structural ordering and optical behavior. The as-prepared 2.6 nm QDs exhibit lower Urbach energy, attributed to their single-crystalline nature, unlike the less ordered QDs synthesized without US. Annealing improves structural ordering and reduces Urbach energy in QDs prepared at 75 °C, while stacking faults and grain boundaries in other QDs hinder such improvements. Photoluminescence measurements further confirm a strong relationship between QD structure, size, and emission characteristics. The synthesized AgIn5S8 QDs exhibit remarkable band gap tunability of up to 2 eV across the visible spectrum and sharp band-edge emission, underscoring their potential for applications in optoelectronic and biomedical devices. This work provides a robust and sustainable pathway to high-performance, non-toxic QDs, addressing a key bottleneck for their use in biocompatible and consumer electronics.

Magnetron sputtering offers a scalable route to magnetic topological insulators (MTIs) based on Cr-doped Sb2Te3. We combine a range of X-ray diffraction (XRD), reciprocal-space mapping (RSM), scanning transmission electron microscopy (STEM), scanning TEM-energy-dispersive X-ray spectroscopy (STEM-EDS), and X-ray absorption spectroscopy, and X-ray magnetic circular dichroism (XAS/XMCD) techniques to study the structure and magnetism of Cr-doped Sb2Te3 films. Symmetric θ-2θ XRD and RSM establish a solubility window. Layered tetradymite order persists up to ∼10 at.-% Cr, while higher doping yields CrTe/Cr2Te3 secondary phases. STEM reveals nanocrystalline layered stacking at low Cr and loss of long-range layering at higher Cr concentrations, consistent with XRD/RSM. Magnetometry on a 6% film shows soft ferromagnetism at 5 K. XAS and XMCD at the Cr L2,3 edges exhibits a depth dependence: total electron yield (TE; surface sensitive) shows both nominal Cr2+ and Cr3+, whereas fluorescence yield (FY; bulk sensitive) shows a much higher Cr2+ weight. Sum rules applied to TEY give mL=(0.20±0.04) μB/Cr, and mS=(1.6±0.2) μB/Cr, whereby we note that the applied maximum field (3 T) likely underestimates mS. These results define a practical growth window and outline key parameters for MTI films.

This article embarks on an analytical exploration of the degradation mechanisms affecting the proton exchange membrane (PEM) fuel cell with 3.2 kW capacity, pivotal in hybrid systems of Toyota vehicles and electric scooters. Through rigorous experimentation, we quantitatively dissect the impact of varying operational conditions-humidity (25%-100% RH), temperature (45 degrees C-75 degrees C), and load (half-load to over-load)-on fuel cell efficiency and longevity. Notably, our findings reveal that humidity levels above 75% RH precipitate a stark efficiency decline at higher current densities due to exacerbated internal resistance, with a degradation rate peaking at -0.019%/day under optimal conditions and escalating significantly under adverse conditions. Temperature variations further illuminate the critical balance between performance and durability, with the highest stability observed at 55 degrees C, manifesting in a moderated degradation rate of -0.024%/day, contrasting sharply with the -0.124%/day observed under over-load scenarios. Structural integrity analysis, facilitated by scanning electron microscope (SEM) imaging, identified two distinct defect types, directly correlating to degradation rates of -0.0384%/day and -0.0552%/day, respectively. This comprehensive study provides pivotal insights into fuel cell operational efficiency, unveiling specific degradation rates and operational thresholds that demarcate resilience from rapid decline, thereby guiding the future of sustainable fuel cell technology in transportation.

We present a methodology based on the calculation of the inelastic scattering from magnons via the spin scattering function in confined geometries such as thin films using a second quantization formalism, for both ferromagnetic and antiferromagnetic materials. The case studies are chosen with an aim to demonstrate the effects of film thickness and crystal orientation on magnon modes, using bcc Fe(100) and NiO with (100) and (111) crystallographic orientations as prototypical systems. Due to the quantization of the quasi-momentum we observe a granularity in the inelastic spectra in the reciprocal space path reflecting the orientation of the thin film. This approach also allows to capture softer modes that appear due to the partial interaction of magnetic moments close to the surface in a thin film geometry, in addition to bulk modes. The softer modes are also affected by crystallographic orientations as illustrated by the different surface-related peaks of NiO magnon density of states at approximately 65 meV for (100) and 42 meV for (111). Additionally, we explore the role of anisotropy on magnon modes, revealing that introducing anisotropy to both Fe and NiO films increases the overall hardness of the magnon modes. The introduction of a surface anisotropy produces a shift of the surface-related magnon DOS peak to higher energies with increased surface anisotropy, and in some cases leading to surface confined mode.

Using first-principles techniques, we study the structural, magnetic and electronic properties of (111)-oriented (LaMnO$_3$)$_{2n}$$\vert$(SrMnO$_3$)$_{n}$ superlattices of varying thickness ($n=2,4,6$). We find that the properties of the thinnest superlattice ($n=2$) are similar to the celebrated half-metallic ferromagnetic alloy La$_{2/3}$Sr$_{1/3}$MnO$_3$, with quenched Jahn-Teller distortions. At intermediate thickness ($n=4$), the $a^{-}a^{-}a^{-}$ tilting pattern transitions to the $a^{-}a^{-}c^{+}$ tilting pattern, driven by the lattice degrees of freedom in the LaMnO$_3$ region. The emergence of the Jahn-Teller modes and the spatial extent needed for their development play a key role in this structural transition. For the largest thickness considered ($n=6$), we unveil an emergent separation of Jahn-Teller and volume-breathing orders in the ground-state structure with the $a^{-}a^{-}c^{+}$ tilting pattern, whereas it vanishes in the antiferromagnetic configurations. The ground state of all superlattices is half-metallic ferromagnetic, not affected by the underlying series of structural transitions. Overall, these results outline a thickness-induced crossover between the physical properties of bulk La$_{2/3}$Sr$_{1/3}$MnO$_3$ and bulk LaMnO$_3$.

We explore the inelastic spectra of electrons impinging in a magnetic system. The methodology here presented is intended to highlight the charge-dependent interaction of the electron beam in a STEM-EELS experiment, and the local vector potential generated by the magnetic lattice. This interaction shows an intensity $10^{-2}$ smaller than the purely spin interaction, which is taken to be functionally the same as in the inelastic neutron experiment. On the other hand, it shows a strong scattering vector dependence ($\kappa^{-4}$) and a dependence with the relative orientation between the probe wavevector and the local magnetic moments of the solid. We present YIG as a case study due to its high interest by the community.

Conduction of spin currents in disordered insulating antiferromagnets has recently been at the center of scientific debate with both long-range spin transport or no spin transport at all observed experimentally. In this study, ferromagnetic resonance has been used to probe the transmission of ac spin current through thin amorphous yttrium iron garnet (YIG) layers. The spin current is found to be mediated by evanescent spin waves with a penetration length four times larger than that of previous studies of amorphous YIG, even exceeding the spin penetration length of crystalline NiO.

We explore epitaxial growth of Co2MnSi/Ge/Co2MnSi vertical spin-valve structures on Si, where the Co2MnSi (CMS) is expected to be a half-metallic material for spintronics. By combining solid phase epitaxy, low-temperature molecular beam epitaxy, and atomic layer termination techniques, we can grow an epitaxial Ge layer on CMS at 250 °C, where the atomic interdiffusion between Ge and CMS is suppressed. After further optimization of the growth condition of the Ge intermediate layer, all-epitaxial CMS/Ge/CMS vertically stacked structures with spin-valve like magnetization reversal processes are demonstrated. This vertically stacked structures can be utilized for vertical spin-valve devices with a Ge channel on Si.

In this study, the effect of Mg composition on structural and optical properties of MgxNi1-xO alloy thin film single crystal semiconductors as well as their implementation into Metal-Semiconductor-Metal (MSM) photodetector are studied. An 850 meV blue-shift of the bandgap is observed from 3.65 eV to 4.50 eV with increasing Mg composition from 0% to 67%. The deep ultraviolet/visible rejection ratio, which is the ratio of photosensitivity at a peak wavelength of 360 nm to that at 450 nm is found to be similar to 58 for Mg composition of 67%. Mg rich (%67 Mg) alloy-based photodetector is found to have two orders smaller dark current and have higher spectral response compared to NiO-based one. Spectral responsivities for MgxNi1-xO photodetectors are determined as 415 mA W-1, 80 mA W-1, and 5.6 mA W-1 for Mg compositions of 67%, 21%, and 0% (reference-NiO), respectively. Furthermore, the detectivity of the photodetectors enhances as Mg composition increases and the highest detectivity of a magnitude of similar to 1011 Jones is found for the photodetector with Mg composition of 67%.