High-resolution Soft X-ray Research Articles

Structures of Liquid-Liquid Interfaces in Partially Miscible Systems Revealed by Soft X-ray Imaging.

The properties of liquid-liquid interfaces are intricately linked to its structure, with a particular focus on the concentration distribution within the interface. To obtain precise information regarding the concentration distribution, we have developed a high-resolution soft X-ray imaging method for liquid-liquid interfaces. This work focused on representative partially miscible systems, analyzing the interfacial concentration distribution profiles of water-alkanols under both steady-state and dynamic processes, and obtaining the diffusion coefficients of different water concentrations in alkanols. Significant disparities in concentration distributions and the concentration-related diffusion coefficients were observed despite comparable diffusion distances within the same system across different states. Meanwhile, it was found that alkanols exhibit adsorption phenomena at the interface. This newfound knowledge serves as a crucial stepping stone toward a deeper understanding of partially miscible systems. Our study opens a way to explore liquid-liquid interface information with high-resolution.

Correlative light and X-ray tomography jointly unveil the critical role of connexin43 channels on inflammation-induced cellular ultrastructural alterations

Non-junctional connexin43 (Cx43) plasma membrane hemichannels have been implicated in several inflammatory diseases, particularly playing a role in ATP release that triggers activation of the inflammasome. Therapies targeting the blocking of the hemichannels to prevent the pathological release or uptake of ions and signalling molecules through its pores are of therapeutic interest. To date, there is no close-to-native, high-definition documentation of the impact of Cx43 hemichannel-mediated inflammation on cellular ultrastructure, neither is there a robust account of the ultrastructural changes that occur following treatment with selective Cx43 hemichannel blockers such as Xentry-Gap19 (XG19).A combination of same-sample correlative high-resolution three-dimensional fluorescence microscopy and soft X-ray tomography at cryogenic temperatures, enabled in the identification of novel 3D molecular interactions within the cellular milieu when comparing behaviour in healthy states and during the early onset or late stages under inflammatory conditions. Notably, our findings suggest that XG19 blockage of connexin hemichannels under pro-inflammatory conditions may be crucial in preventing the direct degradation of connexosomes by lysosomes, without affecting connexin protein translation and trafficking. We also delineated fine and gross cellular phenotypes, characteristic of inflammatory insult or road-to-recovery from inflammation, where XG19 could indirectly prevent and reverse inflammatory cytokine-induced mitochondrial swelling and cellular hypertrophy through its action on Cx43 hemichannels. Our findings suggest that XG19 might have prophylactic and therapeutic effects on the inflammatory response, in line with functional studies.

Direct Observation of Room-Temperature Magnetic Skyrmion Motion Driven by Ultra-Low Current Density in Van Der Waals Ferromagnets.

The recent discovery of room-temperature ferromagnetism in 2D van der Waals (vdW) materials, such as Fe3GaTe2 (FGaT), has garnered significant interest in offering a robust platform for 2D spintronic applications. Various fundamental operations essential for the realization of 2D spintronics devices are experimentally confirmed using these materials at room temperature, such as current-induced magnetization switching or tunneling magnetoresistance. Nevertheless, the potential applications of magnetic skyrmions in FGaT systems at room temperature remain unexplored. In this work, the current-induced generation of magnetic skyrmions in FGaT flakes employing high-resolution magnetic transmission soft X-ray microscopy is introduced, supported by a feasible mechanism based on thermal effects. Furthermore, direct observation of the current-induced magnetic skyrmion motion at room temperature in FGaT flakes is presented with ultra-low threshold current density. This work highlights the potential of FGaT as a foundation for room-temperature-operating 2D skyrmion device applications.

Free light-shape focusing in extreme-ultraviolet radiation with self-evolutionary photon sieves

Extreme-ultraviolet (EUV) radiation is a promising tool, not only for probing microscopic activities but also for processing nanoscale structures and performing high-resolution imaging. In this study, we demonstrate an innovative method to generate free light-shape focusing with self-evolutionary photon sieves under a single-shot coherent EUV laser; this includes vortex focus shaping, array focusing, and structured-light shaping. The results demonstrate that self-evolutionary photon sieves, consisting of a large number of specific pinholes fabricated on a piece of Si3N4 membrane, are capable of freely regulating an EUV light field, for which high-performance focusing elements are extremely lacking, let alone free light-shape focusing. Our proposed versatile photon sieves are a key breakthrough in focusing technology in the EUV region and pave the way for high-resolution soft X-ray microscopy, spectroscopy in materials science, shorter lithography, and attosecond metrology in next-generation synchrotron radiation and free-electron lasers.

Hydrogen-Bonded Structures of Water Molecules in Hydroxy-Functionalized Nanochannels of Columnar Liquid Crystalline Nanostructured Membranes Studied by Soft X-ray Emission Spectroscopy.

Here, we report a synchrotron-based high-resolution soft X-ray emission spectroscopy study on hydrogen-bonded structures of water molecules in the self-organized, hydroxy-group-functionalized one-dimensional nanochannels of liquid crystalline nanostructured membranes. The water molecules confined in the uncharged hydroxy-functionalized nanochannels (which have a diameter of about 1.5 nm) exhibit hydrogen-bonded structures close to those of bulk liquid water, even directly interacting with diol groups. These hydrogen-bonded structures contrast with the more distorted hydrogen bonding of water molecules confined in self-organized channels with a diameter of 0.6 nm formed by an analogous nanostructured membrane with a cationic moiety, which was explained by the ability of the channel functional groups to donate and accept hydrogen bonds in a confined space and the nanochannel diameter.

Soft X-Ray Operando Characterization of Electrochemical Interfaces

HIPPIE is a high-flux, high-resolution soft x-ray beamline at MAX IV Laboratory (Sweden) with a new dedicated experimental setup for operando studies of electrochemical interfaces.[1] Such experiments utilize the dip-and-pull method to form a thin liquid meniscus on the surface of the working electrode in a three-electrode cell with a liquid electrolyte solution. Both the liquid film itself and the electrode-electrolyte interface can then be probed using X-ray photoelectron spectroscopy (PES) whilst maintaining full electrochemical control. The technique can be used to probe oxidation state changes, chemical shifts, electronic structure and electrochemical potentials in-situ.In this talk we will discuss status of spectroelectrochemical PES using soft X-rays, discussing the merits of the various different approaches to cell design. We will present three case studies on the topics of molecular redox reactions, battery interfaces and metal corrosion, all of which can be studied using dip-and-pull.[2-4] We will primarily aim to provide an introduction to the dip-and-pull method for those interested in this genre of advanced operando characterization. We will additionally outline the experimental realities and challenges that any potential new user of the dip-and-pull method should be aware of before applying for beamtime to conduct an experiment.The three case studies were all measured at HIPPIE, where the beamline operates in the 250-2000 eV range, providing access to the L absorption edges of many transition metals and the K edges of light elements. The dip-and-pull PES experiments are realized with an ambient-pressure hemispherical electron analyzer allowing measurements in vapor pressures up to 25 mbar. Electrochemical cells can therefore use aqueous electrolyte solutions as well as some organic solvents, including many of those common in batteries. An argon/nitrogen atmosphere glove box can be attached to the measurement chamber such that air sensitive materials can be studied. Typically foils or thin films are used for the working electrode. This apparatus therefore provides one of the most flexible platforms for electrochemical studies using soft-X-ray spectroscopy.

Interface Energy Alignment between Lead Halide Perovskite Single Crystals and TIPS-Pentacene.

At present, there is a huge development in optoelectronic applications using lead halide perovskites. Considering that device performance is largely governed by the transport of charges across interfaces and, therefore, the interfacial electronic structure, fundamental investigations of perovskite interfaces are highly necessary. In this study, we use high-resolution soft X-ray photoelectron spectroscopy based on synchrotron radiation to explore the interfacial energetics for the molecular layer of TIPS-pentacene and lead halide perovskite single crystals. We perform ultrahigh vacuum studies on multiple thicknesses of an in situ formed interface of TIPS-pentacene with four different in situ cleaved perovskite single crystals (MAPbI3, MAPbBr3, FAPbBr3, and CsxFA1-xPbBryI3-y). Our findings reveal a substantial shift of the TIPS-pentacene energy levels toward higher binding energies with increasing thickness, while the perovskite energy levels remain largely unaffected regardless of their composition. These shifts can be interpreted as band bending in the TIPS-pentacene, and such effects should be considered when assessing the energy alignment at perovskite/organic transport material interfaces. Furthermore, we were able to follow a reorganization on the MAPbI3 surface with the transformation of the surface C 1s into bulk C 1s.

The High-resolution Soft X-Ray Spectrum of Nova Delphini 2013

We present the high-resolution soft X-ray spectrum of Nova Delphini 2013. Two spectra were taken with the Low Energy Transmission Grating Spectrometer on the Chandra X-ray Observatory, on 2013 November 9 and 2013 December 6, 87 and 114 days after the nova eruption, respectively. The spectra are of very high statistical quality, and reveal clear spectral evolution between the two observations. The source is bright enough on the two occasions that the third spectral order, with resolving power up to ∼3000, can easily be seen. We observe the photospheric emission spectrum of the hot white dwarf, which exhibits a rich absorption line spectrum from an atmosphere of effective temperature likely near T eff ∼ 640,000 K, and complex chemical abundances. Superimposed on this photospheric spectrum, we detect the absorption spectrum of a shell of highly ionized gas, comprising absorption by the K-shell ions of C and N, blueshifted (outflowing) by ∼1400 km s−1, and with a velocity width of ∼1000 km s−1. The abundance ratio C/N is clearly very nonsolar, and indicative of thermonuclear fusion by the CNO cycle. We discuss the physical properties (kinematics, ionization balance, radiative transfer, mechanical energy balance, chemical abundances) of this hot shell, in the context of the physics of nova eruptions.

Valence fluctuation in Yb3Si5 probed by synchrotron X-ray photoemission spectroscopy

We report the direct evidence of valence fluctuation in the thermoelectric material Yb3Si5 by using synchrotron X-ray photoemission spectroscopy. The Yb 3d core level photoemission spectrum of a Yb3Si5 single crystal shows clear separation of the Yb2+ peak and Yb3+ multiplet peaks. From the spectral weight of each component, the mean valence of Yb ions is estimated to be +2.67 at 20 K. Furthermore, a Kondo resonance peak just below the Fermi energy is also observed by high-resolution soft X-ray photoemission spectroscopy, suggesting the valence fluctuating state in Yb3Si5.

Ultra high precision in-vacuum long trace profiler for real time slope determination of optical surface

The development of an in-vacuum long trace profiler (IVLTP) which can provide ultra high precision real time measurements on the surface slope of optical elements is reported. The unique features of this instrument include a specifically designed ultra high repeatability linear slide, a pentamirror composed of two plane mirrors of ultra low slope error, and an ultra high vacuum (UHV) compatible complementary metal oxide semiconductor (CMOS) image sensor. The mechanical system is made of Invar 36 alloy to reduce the room temperature drift effect during data acquisitions. Each IVLTP scan completes in 120 seconds, covering a 168 mm of surface length and generating more than 5000 slope data points. The root mean square (RMS) of the difference between two consecutive scans was found to be 0.0081 μrad on average and 0.0045 μrad RMS at its best. The main application of this IVLTP is to provide the real time feedback signals needed for controlling the 25-actuator surface benders of the active mirrors and active gratings installed in the ultra high resolution soft X-ray beamlines at the Taiwan Photon Source (TPS).

Highly Charged Ions for High-Resolution Soft X-ray Grating Monochromator Optimisation

The energy-resolving performance of a synchrotron radiation monochromator can be characterised by measuring the fluorescence response of a gas in scans across characteristic absorption lines. Here, we describe a method using exceptionally narrow absorption features in the soft x-ray range. The features belong to helium-like ions and examples of the transition 1s → 2p in O6+ and Ne8+ are shown. We describe the instrument PolarX-EBIT and show typical data. A performance with ten times sharper effective feature width, when compared to neutral-gas absorption features, is demonstrated.

The Long Stare at Hercules X-1. I. Emission Lines from the Outer Disk, the Magnetosphere Boundary, and the Accretion Curtain

Hercules X-1 is a nearly edge-on accreting X-ray pulsar with a warped accretion disk, precessing with a period of about 35 days. The disk precession allows for unique and changing sightlines toward the X-ray source. To investigate the accretion flow at a variety of sightlines, we obtained a large observational campaign on Her X-1 with XMM-Newton (380 ks exposure) and Chandra (50 ks exposure) for a significant fraction of a single disk precession cycle, resulting in one of the best data sets taken to date on a neutron star X-ray binary. Here we present the spectral analysis of the high state high-resolution grating and CCD data sets, including the extensive archival data available for this famous system. The observations reveal a complex Fe K region structure, with three emission line components of different velocity widths. Similarly, the high-resolution soft X-ray spectra reveal a number of emission lines of various widths. We correct for the uncertain gain of the European Photon Imaging Camera pn Timing mode spectra, and track the evolution of these spectral components with Her X-1 precession phase and observed luminosity. We find evidence for three groups of emission lines, the first of which originates in the outer accretion disk (105 R G from the neutron star). The second line group plausibly originates at the boundary between the inner disk and the pulsar magnetosphere (103 R G). The last group is too broad to arise in the magnetically truncated disk and instead must originate very close to the neutron star surface, likely from X-ray reflection from the accretion curtain (∼102 R G).

Lifetime effects and satellites in the photoelectron spectrum of tungsten metal

Tungsten is an important and versatile transition metal and has a firm place at the heart of many technologies. A popular experimental technique for the characterisation of tungsten and tungsten-based compounds is X-ray photoelectron spectroscopy (XPS), which enables the assessment of chemical states and electronic structure through the collection of core level and valence band spectra. However, in the case of metallic tungsten, open questions remain regarding the origin, nature, and position of satellite features that are prominent in the photoelectron spectrum. These satellites are a fingerprint of the electronic structure of the material and have not been thoroughly investigated, at times leading to their misinterpretation. The present work combines high-resolution soft and hard X-ray photoelectron spectroscopy (SXPS and HAXPES) with reflection electron energy loss spectroscopy (REELS) and a multi-tiered ab-initio theoretical approach, including density functional theory (DFT) and many-body perturbation theory (G0W0 and GW+C), to disentangle the complex set of experimentally observed satellite features attributed to the generation of plasmons and interband transitions. This combined experiment-theory strategy is able to uncover previously undocumented satellite features, improving our understanding of their direct relationship to tungsten's electronic structure. Furthermore, it lays the groundwork for future studies into tungsten based mixed-metal systems and holds promise for the re-assessment of the photoelectron spectra of other transition and post-transition metals, where similar questions regarding satellite features remain.

Metal halide perovskite layers studied by scanning transmission X-ray microscopy.

We describe the investigation of metal halide perovskite layers, particularly CH3NH3PbI3 used in photovoltaic applications, by soft X-ray scanning transmission X-ray microscopy (STXM). Relevant reference spectra were used to fit the experimental data using singular value decomposition. The distribution of key elements Pb, I, and O was determined throughout the layer stack of two samples prepared by wet process. One sample was chosen to undergo electrical biasing. Spectral data shows the ability of STXM to provide relevant chemical information for these samples. We found the results to be in good agreement with the sample history, both regarding the deposition sequence and the degradation of the perovskite material.

Soft X-Ray Imaging of Polymer Electrolyte Fuel Cells Using Different Support Materials for Catalyst Layers

The polymer electrolyte fuel cell (PEFC) is a highly efficient and environmentally friendly energy device that has been developed for fuel cell vehicles and other applications due to its low operating temperature and compact size. The PEFC is assembled by putting a membrane electrode assembly (MEA), which consists of the polymer electrolyte membrane with the catalyst layers and the gas diffusion layers on both sides, between separators. Pt nanoparticle catalysts supported on carbon black (Pt/C) are usually used for catalyst layers because of their large surface area and high electrical conductivity. However, carbon supports are oxidized and corroded during operation, resulting in performance degradation. Therefore, research has been conducted using Pt supported on tin oxide (Pt/Nb-SnO2), which has high durability and a porous structure similar to that of carbon supports, as an alternative material for the catalyst layers [1]. Tin oxide supports have material properties such as wettability that differ greatly from carbon supports, and the effect of these material properties on liquid water behavior during power generation has not been clarified. It is essential to understand the liquid water transport in PEFCs for the improvement of performance, because excessive liquid water accumulation (flooding) at the cathode hinders the transport of the reaction gas and causes concentration overvoltage.In this study, in order to clarify the effect of the catalyst layer support material on the liquid water transport, we made catalyst layers using carbon and tin oxide supports respectively, and investigated the liquid water behavior in the MEAs under fuel cell operation using high-resolution soft X-ray radiography.PEFCs with a reaction area of 5×8 mm2 were constructed using carbon support catalyst layers and tin oxide support catalyst layers, respectively. The same components were used except for the catalyst layer. The PEFCs were set in a soft X-ray imaging system (TUX-9000D, Mars-Tohken X-ray Inspection). This system can observe PEFCs and take images at a spatial resolution of about 1.0 µm. Hydrogen was supplied to the anode and air to the cathode, and the power generation tests were conducted in the high current density region where flooding is likely to occur. The voltage drop during power generation of the PEFC with Pt/SnO2 catalyst layer was larger than that of the PEFC with Pt/C catalyst layer. In-situ observation of the liquid water behavior in the PEFC was performed by taking images in the MEA cross-sectional direction at the same time as power generation. The images were taken at the position where both the area under the rib and the area under the channel could be observed. The soft X-ray radiograph of the MEA before power generation is shown in Figure 1 (a). The generated water during the power generation was identified by image processing that subtracted the image taken after operation from the image taken under open-circuit voltage conditions. Figure 1 (b) and (c) show the soft X-ray radiographs of liquid water after 20 minutes of power generation under the current density of 0.8 A/cm2. After the cell startup, the amount of water retention increases on the cathode side of the PEFC and the difference in the amount of water retention under the rib and under the channel was observed. It was also shown that the distribution of liquid water in the porous material was different between the carbon support and tin oxide support catalyst layers attributed to support materials and structures of the catalyst layers properties.AcknowledgmentsThe catalyst with Tin oxide support material used in this study was provided by NEDO ECCEED'30. The authors would like to acknowledge their assistance in assembling PEFCs for visualization study.[1] Y. Chino et al, J Electrochem Soc., 162-7 (2015), F736. Figure 1

Annealing Temperature Dependence of Various Properties of ZnO Nanoparticles Investigated with Soft XAS

In this paper, structural, optical and electronic properties of ZnO nanoparticles were investigated with the variation in the annealing temperature. X-ray diffraction, High-Resolution Transmission Electron Spectroscopy, Absorption spectroscopy, Raman Spectroscopy and Soft X-ray spectroscopy techniques were invoked to investigate and gauge the effect of annealing temperature on these properties. Intact Hexagonal Wurtzite phase of the nanoparticles with increasing crystallinity and spherical shape with particle size between 20[Formula: see text]nm and 23[Formula: see text]nm [using both X-ray Diffractometer (XRD) and High-resolution Transmission of electron microscopy (HRTEM)], blue shift of absorption peak from 372[Formula: see text]nm to 366[Formula: see text]nm and Optical Band Gap from 3.24[Formula: see text]eV to 3.17[Formula: see text]eV (UV-Vis-NIR), narrowing of [Formula: see text] mode in Raman Spectra; all indicated enhanced crystallinity with increased annealing temperature. Effects produced by the sole variable such as annealing temperature on the indicative parameters in a definite order catapult the annealing conditions as a significant candidate for customized properties. To have a deeper insight at the electronic levels, Synchrotron-based X-ray absorption spectroscopic studies of ZnO nanoparticles were undertaken. The analysis of Soft XAS spectra showed the change in number of O 2[Formula: see text] and Zn 4[Formula: see text] unoccupied states with increasing particle size and crystallinity of ZnO nanoparticles for varying annealing temperature.

Double-filter high-resolution soft x-ray tomographic diagnostic for investigating electron acceleration in TS-6 reconnection merging experiments.

An innovative tangential-view soft x-ray (SXR) tomographic imaging measurement was developed on the TS-6 spherical tokamak merging device as a key diagnostic for investigating the mechanism of electron acceleration. In order to measure SXR with different energy ranges, two micro-channel plates (MCPs) are, respectively, installed in two vacuum chambers, which are equipped with different filters. Especially designed lenses and fiber bundles serve as an optical system to transfer images from phosphor plates of MCPs to a high speed imaging system. This design also enables us to simultaneously measure two images appearing on phosphor plates of MCPs by just one high speed imaging system. The temporal and spatial resolution of this diagnostic can be up to 5 µs and 4mm, respectively, at present. The tomographic method based on the Phillips-Tikhonov regularization is employed to reconstruct line-integrated images into the local emissivity of SXR, which reflects the spatial distribution of high-energy electrons. Owing to this diagnostic, we successfully measured SXR emitted from the downstream region of magnetic reconnection in TS-6 merging experiments for the first time. The energy range of SXR turned out to be higher than 100eV but lower than 400eV.

PEAXIS: A RIXS and XPS Endstation for Solid-State Quantum and Energy Materials at BESSY II

PEAXIS (Photo Electron Analysis and resonant X-ray Inelastic Spectroscopy) is a dedicated endstation installed at the beamline U41-PEAXIS that offers high resolution soft X-ray spectroscopy measurements with incident photon energies ranging from 180 – 1600 eV. The endstation combines two X-ray spectroscopic techniques, X-ray photoelectron spectroscopy (XPS) and resonant inelastic soft X-ray scattering (RIXS), which are important for probing the electronic structure and local and collective excitations of solid-state materials. It features a continuous variation of scattering angle under UHV conditions for wave vector-resolved studies and a modular sample environment that allows investigation in the temperature range between 10 K and 1000 K.

Band alignment of wide bandgap NiO/MoO3 and NiO/WO3p-n heterojunctions studied by high-resolution X-ray photoelectron spectroscopy

NiO is one of the few transition metal oxides exhibiting p-type conductivity and visible light transparency. On the other hand, MoO3 and WO3 are high work function, wide gap metal oxides which show predominantly n-type character and have been widely applied in carrier selective contacts, heterojunction diodes, electrochromic and sensing applications. Hence, detailed understandings of the optical properties and electronic band offsets of the NiO/MoO3 and NiO/WO3p-n heterojunctions are crucial for the design and application of transparent oxide-based optoelectronic devices utilizing these heterojunctions. In this work, we synthesized thin films of the three oxides and characterized their structural and optical properties. In particular, the band alignment of NiO/MoO3 and NiO/WO3p-n heterojunctions were studied by high-resolution soft x-ray photoelectron spectroscopy (XPS). We found that both heterojunctions have a type-II band offset with the NiO/MoO3 exhibiting a larger valence band offset of 2.02 eV compared to 1.71 eV for NiO/WO3. The band positions of the three oxides with respect to the vacuum level obtained by Ultraviolet-Ambient Photoemission spectroscopy suggest that MoO3 and WO3 have a propensity to be n-type due to the easy formation of native donor defects. In contrast, NiO has a p-type character due to the high position of its VBM which favors the formation of native acceptor defects.

High Resolution Soft X-ray Spectroscopy and the Quest for the Hot (5–10 MK) Plasma in Solar Active Regions

We discuss the diagnostics available to study the 5–10 MK plasma in the solar corona, which is key to understanding the heating in the cores of solar active regions. We present several simulated spectra, and show that excellent diagnostics are available in the soft X-rays, around 100 Å, as six ionization stages of Fe can simultaneously be observed, and electron densities derived, within a narrow spectral region. As this spectral range is almost unexplored, we present an analysis of available and simulated spectra, to compare the hot emission with the cooler component. We adopt recently designed multilayers to present estimates of count rates in the hot lines, with a baseline spectrometer design. Excellent count rates are found, opening up the exciting opportunity to obtain high-resolution spectroscopy of hot plasma.