SrTaO x N y (STON) is a well-known visible light-responsive semiconductor with ideally located band edges that allow the operability of overall water splitting. Like many oxynitrides, STON shows evidence of detrimental physicochemical changes under oxygen evolution reaction (OER) conditions involving strong caustic electrolytes. We investigate the development of STON instability with detailed electron microscopy and neutron reflectometry (NR) techniques using epitaxial thin films. Different crystallographic orientations are compared with ex situ analysis before and after OER in photoelectrochemical testing. A remarkable difference in stability of the STON surface is observed depending on the crystalline facets, with the [011] lattice planes being the more favorable orientation as compared to [001]. In addition, we show that the electrochemical stability of the photoelectrode surface can be dramatically improved by a homogeneous coating of NiO x , which significantly improves OER kinetics and surface stability in the alkaline environment. NR is realized in this work as a novel route to monitor this photoelectrochemical environment, and it lies in agreement with its microscopy counterpart to monitor the physicochemical changes. This demonstrates potential of NR as an alternative and complementary tool that also has the feasibility for future in situ experimental design.

The reversible incorporation of lithium into electrodes is a key process in energy storage in Li-ion batteries. A detailed understanding of lithiation and delithiation mechanisms acting in electrodes is therefore essential for both fundamental and application-oriented research. We introduce an approach that combines isotope multilayer electrodes with neutron reflectometry to directly probe the lithiation mechanism in operando during electrochemical cycling. The core idea is that the isotope multilayer transforms complex reflectivity patterns into simpler patterns characterized by a single, well-defined Bragg peak. The evolution of the peak (scattering vector position and intensity) as a function of state-of-charge provides a signature of the underlying mechanism. This drastically simplifies data analysis and, in some cases, makes it possible at all. Proof-of-concept experiments on 73Ge/Ge multilayer electrodes demonstrate the effectiveness of the method. A direct and easy comparison between experimental results and simulations indicates a homogeneous lithiation and delithiation mechanism, independent of cycle number and cycling rate.

Operando neutron reflectometry was used to investigate the redistribution of Li during electrochemical insertion into and extraction from stratified amorphous silicon/carbon (Si/C) multilayer electrodes for lithium-ion batteries (lithiation mechanism). Constant-current cycling from low to high rates (4-160 mu A cm(-2), C/40-2C) was applied during reflectometry measurements. Due to the multilayer structure, Bragg peaks are detected in the reflectivity pattern. By analyzing changes in both the intensity and the scattering vector positions of these peaks during electrochemical cycling, specific lithiation and delithiation mechanisms were identified. During initial lithiation, a heterogeneous, moving phase-front mechanism dominates, followed by a superimposed homogeneous mechanism. In contrast, delithiation and subsequent cycles are primarily governed by a homogeneous mechanism. Additionally, the lithium content of the lithiated phase is influenced by both the silicon-layer thickness and the lithiation rate.

The interdiffusion between Fe and Ni is sluggish, and in order to synthesize the technologically important L10-ordered FeNi phase, it needs to be boosted. Cu doping is expected to create a disorder, leading to an enhancement in interdiffusion. Therefore, during the growth of Fe/Ni multilayers (MLs) by the sputtering process, Cu is cosputtered, and its amount is varied nominally at 5, 10, and 15 at% by tuning the sputtering power of Cu source. The interdiffusion is studied using polarized neutron reflectivity (PNR) of annealed Fe/Ni ML samples. Resulting FeNi phases are analyzed using X-ray diffraction. Both PNR and a magnetometer are used to study the magnetization, and the surface morphology is studied using atomic force microscopy. It is found that the lowest amount of doping at 5 at% is the most effective in accelerating the interdiffusion, but as the amount of Cu doping is further increased, the interdiffusion again becomes sluggish due to excessive grain boundary segregation and clustering of Cu. These findings highlight the importance of controlling the Cu doping concentration to promote the interdiffusion, leading to the realization of the formidable L10 FeNi phase.

This study reports on advancements in operando characterization of volume changes in lithium-ion battery (LIB) electrode materials during electrochemical cycling. Volume changes are crucial for LIB operation because they are related to the amount of stored energy as well as LIB integrity, performance, and safety. The study introduces a method based on isotope multilayers as active material to track the intrinsic modification of electrode volume in real time under operating conditions with operando neutron reflectometry. A natGe/73Ge multilayer film is used as a model system to measure the volume change of amorphous germanium electrodes during charging and discharging. Isotope modulation produces a Bragg peak in the neutron reflectivity pattern, sensitive only to the modification of volume within the active material of the electrode. Battery side reactions, such as the growth and reduction of the solid-electrolyte interphase, are excluded. Using this method, the volume modification as a function of Li content x in Li x Ge can easily be derived from the scattering vector position of the Bragg peak without fitting numerous complex reflectivity patterns. The experiments show a reversible volume change of amorphous germanium of up to 250% for x approximate to 3, which appears to be largely independent of current density, cycle number, and the thickness of the individual Ge layers. Also, there are tentative indications that the crystallization and reamorphization of Li x Ge do not influence the volume change.

Organic photovoltaics (OPVs) offer a promising solution for indoor energy harvesting. However, fundamental investigations to understand and optimize industrial processes such as roll‐to‐roll lamination for upscaling remain limited. This study investigates a critical failure mode in the upscaling of OPVs. One major challenge for thick semitransparent laminated OPV devices is current–voltage ( J–V ) asymmetry, where performance under cathode‐side illumination exceeds that under anode‐side illumination. X‐ray reflectivity, neutron reflectivity, and drift‐diffusion simulations reveal that a vertically stratified polymer‐rich region within the bulk of photoactive layers is the main cause of asymmetric J–V characteristics. Based on this fundamental understanding, a model is proposed to explain the mechanism, wherein electron extraction is hindered by the polymer‐rich region during anode illumination. By exploring upscaling‐compatible blends, cathode/anode‐balanced, high‐performing, and air‐stable semitransparent laminated OPVs are developed for indoor applications using commercially available PV‐X‐plus material. These findings provide valuable guidance for designing OPVs with balanced performance, facilitating roll‐to‐roll adoption and commercialization.

Neutron reflectivity is a powerful technique for probing density profiles in films, with applications across physics, chemistry and biology. However, challenges arise when dealing with samples characterized by high roughness, unknown scattering length density (SLD) with low contrast, very thin layers or complex multi-layered structures that cannot be uniquely resolved due to the phase problem. Incorporating a magnetic reference layer (MRL) and using polarized neutron reflectivity improves the sensitivity and modelling accuracy by providing complementary information. In this study, we introduce a quantitative means of comparing MRL systems in a model-free way. We apply this approach to demonstrate that CoTi alloys offer a superior solution as MRLs compared with the commonly used Fe or Ni MRLs. The low nuclear and magnetic scattering length densities of CoTi significantly enhance sensitivity, making it particularly advantageous for soft-matter research. Furthermore, the tunable Co versus Ti ratio allows for optimization of the SLD to achieve maximum sensitivity, establishing CoTi as a highly effective choice for MRL applications. The applied simulation framework for optimizing MRL sensitivity to a specific materials system and research question is a generic approach that can be used prior to growing the MRL for a given experiment.

Neutron reflectivity is a powerful technique for probing density profiles in films, with applications across Physics, Chemistry, and Biology. However, challenges arise when dealing with samples characterized by high roughness, unknown scattering length density (SLD) with low contrast, very thin layers, or complex multi-layered structures, that cannot be uniquely resolved due to the phase problem. Incorporating a magnetic reference layer (MRL) and using polarized neutron reflectivity improves sensitivity and modeling accuracy by providing complementary information. In this study, we introduce a quantitative way to compare MRL systems in a model-free way. We apply this approach to demonstrate that CoTi alloys offer a superior solution as an MRL compared to the commonly used Fe or Ni-based MRLs. The low nuclear and magnetic scattering length densities of CoTi significantly enhance sensitivity, making it particularly advantageous for soft matter research. Furthermore, the tunable Co vs Ti ratio allows for optimization of the SLDs to achieve maximum sensitivity, establishing CoTi as a highly effective choice for MRL applications. The applied simulation framework for optimizing MRL sensitivity to a specific materials system and research question is a generic approach that can be used prior to growing the MRL for a given experiment.

This study further investigates the effects of 11B4C co-sputtering on the structural and optical properties of Fe/Si stacked multilayers, with a focus on neutron supermirror applications. X-ray and neutron reflectivity techniques confirm with greater clarity that 11B4C incorporation improves interface sharpness, reduces roughness, and enhances reflectivity for various multilayer periods, compared to earlier studies on a single period thickness. Neutron reflectivity measurements show reduced spin-flip intensities, while wafer-curvature measurements indicate a 50 % reduction in internal stress, allowing for higher mechanical stability of the multilayers. These improvements are attributed to the amorphization of Fe layers, which also suppress the formation of structural and magnetic domains responsible for stress and spin-flip scattering. In contrast, the pure Fe/Si sample exhibits a persistent half-order Bragg peak, indicating residual antiferromagnetic coupling. The results demonstrate that 11B4C enhances neutron optics by reducing spin-flip effects, increasing reflectivity and polarization, and alleviating stress, enabling the use of polarizers at reduced external fields compared to pure Fe/Si multilayers. These findings establish 11B4C as a transformative material for advancing neutron supermirror technology, paving the way for more efficient, stable, and high-performance polarizers in next-generation neutron optics.

This study investigates the effects of incorporating 11B4C interlayers into Fe/Si multilayers, with a focus on interface quality, reflectivity, polarization, and magnetic properties for polarizing neutron optics. It is found that the introduction of 1-2 & Aring; 11B4C interlayers significantly improves the interface sharpness, reducing interface width and preventing excessive Si diffusion into the Fe layers. X-ray reflectivity and polarized neutron reflectivity measurements show enhanced reflectivity and polarization, with a notable increase in polarization for 30 & Aring; period multilayers. The inclusion of interlayers also helps prevent the formation of iron-silicides, improving both the magnetic properties and neutron optical performance. However, the impact of interlayers is less pronounced in thicker-period multilayers (100 & Aring;), primarily due to the ratio between layer and interface widths. These results suggest that 11B4C interlayers offer a promising route for optimizing Fe/Si multilayer performance in polarizing neutron mirrors.

Transparent polymers are low-cost, light, and flexible, making them prospective for a plethora of applications. Still, their usage in photonics is impeded by a low refractive index, usually less than 1.7. In this work, an alternative strategy is proposed for improving optical characteristics by developing poly(ionic liquids) (PILs) with a gradient refractive index (GRIN) in thin films. The obtained PILs are transparent, environmentally friendly, and possess the GRIN effect in thin films. Inspired by the architecture of the animal's eye, PILs are employed for inkjet fabrication of microlenses with a giant GRIN value of 0.8, which is up to several times higher than that in previous studies on nanolayered polymeric and 3D printed GRIN lenses. Furthermore, in terms of focusing power, lens transparency, and depth of field, these microlenses outperform the result of high refractive index polymers. Hence, the findings open a novel platform for compact optical components based on new types of ionic polymers.

Magnetic hysteresis properties in Fe/Si multilayers have been studied as a function of the B4C content to control magnetization amplitude, coercivity, and hysteresis tilt, properties that are beneficial to tune for advancing applications in e.g. data storage, spintronics, and sensors. With an ion-assisted magnetron sputtering technique, 35 distinct thin film multilayer samples were prepared and their magnetic and structural properties were characterized by vibrating sample magnetometry, X-ray photoelectron spectroscopy, near edge X-ray absorption fine structure spectroscopy, and X-ray and neutron scattering methods. Key findings indicate that adding B4C lowers the coercivity and can decrease the saturation magnetization, demonstrating the tunability of magnetic responses based on composition. For samples with Lambda=30 & Aring; periodicity, 10-15 % of B4C addition produces antiferromagnetically (AF) coupled multilayers, and such AF coupling strength increases with the B4C content. Our findings reveal that B atoms do not chemically bind within the Fe atoms but instead occupy interstitial positions, disrupting medium- to long-range crystallinity thereby inducing the amorphization. Thereon, the observed effects on magnetic properties are directly attributed to this amorphization process caused by the presence of B4C. The demonstrated ability to finely adjust magnetic properties by varying the B4C content offers a promising approach to overcome challenges in magnetic device performance and efficiency.

High-temperature and high-magnetic-field-induced re-entrant superconductivity has been discovered in the infinite-layer nickelate Sm_1-x-y Eu_x Ca_y Ni O_2 (SECNO). Infinite-layer nickelates are the closest known analogues of high-T_c cuprate superconductors, yet they host distinct magnetic ground states. Using low-energy muon spin relaxation and polarized neutron reflectometry, we reveal the magnetic order in SECNO. We find that magnetic freezing occurs at a higher-temperature than in other nickelate compounds, and that a substantial net magnetization of 55 kA m^-1 ±10 kA m^-1 emerges and remains largely unchanged across the superconducting transition. The magnetism in SECNO is disordered and nonuniform.

The Multi-Blade (MB) Boron-10-based neutron detector is the chosen technology for three instruments at the European Spallation Source (ESS): the two ESS reflectometers, ESTIA and FREIA, and the Test Beam Line. A fourth MB detector has been built, installed and commissioned for the user operation of the reflectometer Amor at PSI (Switzerland). Amor can be considered a downscaled version of the ESS reflectometer ESTIA. They are based on the same Selene guide concept, optimized for performing focusing reflectometry on small samples. The experience gained at Amor is invaluable for the future deployment of the MB detector at the ESS. This manuscript describes the MB detector construction and installation at Amor along with the readout electronics chain based on the VMM3a ASIC. The readout chain deployed at Amor is equivalent of that of the ESS, including the readout master module (RMM), event-formation-units (EFUs), Kafka, FileWriter and live visualisation tools.

GexSi1-x alloys are gaining renewed interest for many applications in electronics and optics, especially for miniaturized devices showing quantum size effects. Point defects and atomic diffusion play a crucial role in miniaturized and metastable systems. In the present work, Ge self-diffusion in sputter deposited amorphous GexSi1-x alloys is studied in situ as a function of Ge content x = 0.13, 0.43, 0.8, and 1.0 by neutron reflectometry. The determined Ge self-diffusivities obey the Arrhenius law in the investigated temperature ranges. The higher the Ge content x, the higher the Ge self-diffusivity at the same temperature. The activation enthalpy decreases with x from 4.4 eV for self-diffusion in pure silicon films to about 2 eV self-diffusion in Ge0.8Si0.2 and Ge. The decrease of the activation enthalpy for amorphous GexSi1-x is similar to the case of crystalline GexSi1-x. Possible explanations are discussed.

The concept of scattering length density tuning for improved polarization is investigated for Fe/B411CTi multilayers and compared to the commonly used Fe/Si system in polarizing multilayer neutron optics. X-ray and neutron reflectivity, magnetization, and neutron polarization were measured on such multilayers, highlighting differences from conventional Fe/Si multilayers. The multilayer systems were deposited with 25 Å period thickness, a layer thickness ratio of 0.35, and 20 periods using ion-assisted dc magnetron sputtering. Replacing Si with B411CTi for these multilayers showed an increase in reflectivity due to a reduction in interface width. Tuning the ratio between B411C and Ti in the nonmagnetic layers enabled a wide range of scattering length density contrasting and matching for spin-down neutrons, which in turn led to an improved polarization. These findings demonstrate the potential of Fe/B411CTi multilayers as a promising option for polarizing neutron optics and highlight the concept of scattering length density tuning in a large range using B411CTi. Published by the American Physical Society 2024

Abstract Harvesting indoor light to power electronic devices for the Internet of Things has become an application scenario for emerging photovoltaics, especially utilizing organic photovoltaics (OPVs). Combined liquid‐ and solid‐state processing, such as printing and lamination used in industry for developing indoor OPVs, also provides a new opportunity to investigate the device structure, which is otherwise hardly possible based on the conventional approach due to solvent orthogonality. This study investigates the impact of fullerene‐based acceptor interlayer on the performance of conjugated polymer–fullerene‐based laminated OPVs for indoor applications. We observe open‐circuit voltage (VOC) loss across the interface despite this arrangement being presumed to be ideal for optimal device performance. Incorporating insulating organic components such as polyethyleneimine (PEI) or polystyrene (PS) into fullerene interlayers decreases the work function of the cathode, leading to better energy level alignment with the active layer (AL) and reducing the VOC loss across the interface. Neutron reflectivity studies further uncover two different mechanisms behind the VOC increase upon the incorporation of these insulating organic components. The self‐organized PEI layer could hinder the transfer of holes from the AL to the acceptor interlayer, while the gradient distribution of the PS‐incorporated fullerene interlayer eliminates the thermalization losses. This work highlights the importance of structural dynamics near the extraction interfaces in OPVs and provides experimental demonstrations of interface investigation between solution‐processed cathodic fullerene layer and bulk heterojunction AL.