Tender X-ray Research Articles

Chemical speciation using high energy resolution PIXE spectroscopy in the tender X-ray range

High energy resolution X-ray emission spectroscopy employing wavelength dispersive (WDS) crystal spectrometers can provide energy resolution on the level of core-hole lifetime broadening of the characteristic emission lines. While crystal spectrometers have been traditionally used in combination with electron excitation for major and minor element analysis, they have been rarely considered in proton induced X-ray emission (PIXE) trace element analysis mainly due to low detection efficiency. Compared to the simplest flat crystal WDS spectrometer the efficiency can be improved by employing cylindrically or even spherically curved crystals in combination with position sensitive X-ray detectors. When such spectrometer is coupled to MeV proton excitation, chemical bonding effects are revealed in the high energy resolution spectra yielding opportunity to extend the analytical capabilities of PIXE technique also towards chemical state analysis. In this contribution we will focus on the high energy resolution PIXE (HR-PIXE) spectroscopy in the tender X-ray range performed in our laboratory with our home-built tender X-ray emission spectrometer. Some general properties of high energy resolution PIXE spectroscopy in the tender X-ray range are presented followed by an example of sulfur speciation in biological tissue illustrating the capabilities as well as limitations of HR-PIXE method used for chemical speciation in the tender X-ray range.

Evolution of the Uranium Chemical State in Mixed-Valence Oxides.

A fundamental question concerning the chemical state of uranium in the binary oxides UO2, U4O9, U3O7, U3O8, and UO3 is addressed. By utilizing high energy resolution fluorescence detection X-ray absorption near edge spectroscopy (HERFD-XANES) at the uranium M4 edge, a novel technique in the tender X-ray region, we obtain the distribution of formal oxidation states in the mixed-valence oxides U4O9, U3O7, and U3O8. Moreover, we clearly identify a pivot from U(IV)-U(V) to U(V)-U(VI) charge compensation, corresponding with transition from a fluorite-type structure (U3O7) to a layered structure (U3O8). Such physicochemical properties are of interest to a broad audience of researchers and engineers active in domains ranging from fundamental physics to nuclear industry and environmental science.

Operando Spectromicroscopy of Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are a “beyond Li-ion” technology that provides high capacity (1675 mAh g-1) while also being low cost, earth-abundant, and lightweight. Li-S batteries have a unique chemistry that achieves high capacity via chemical transformation rather than Li intercalation as in Li-ion. Elemental sulfur S8 is reduced through a series of soluble Li polysulfides (Li2Sx, 2 ≤ x ≤ 8) to a final solid discharge product Li2S, and the process is reversed upon charging. However, Li-S suffers from unrealized theoretical capacity and rapid capacity fade due to loss processes that are not well-understood. Batteries are spatially and chemically heterogeneous. Deciphering the chemical states of sulfur and the distribution of dissolved polysulfides in the anode, cathode, and especially the electrolyte during cycling is critical for realizing the potential of Li-S. We present operando characterization using sulfur K-edge X-ray absorption spectromicroscopy performed at the Stanford Synchrotron Radiation Lightsource (SSRL, BL 14-3). Synchrotron radiation provides the high energy resolution and micron-scale beam size needed to distinguish complicated polysulfide spectral features in the tender X-ray regime. From this information, we can observe a spatially and chemically varied system to gain insight into how sulfur speciation and spatial distribution contribute to capacity fade. Typically, operando X-ray characterization is conducted perpendicular to battery electrodes, providing an average of the chemistry throughout the entire stack. The cross-sectional pouch cell geometry presented here provides a spatially resolved picture of sulfur diffusion between the cathode and anode, which cannot be achieved by typical characterization methods. Cells consisting of a sulfur/carbon cathode, Li anode, and 1 M LiClO4 + 0.5 LiNO3 in 1,3-dioxolane/1,2-dimethoxyethane (DOL/DME) were discharged, and maps were collected at energies sensitive to the sulfur and Li polysulfide species. Tuning the incident X-ray energy allows for targeted observations of species such as polysulfides, sulfates, elemental sulfur, and lithium sulfide during cycling. A novel electrochemical cell with well-defined electrode geometry, electrolyte volume, and current collection has been designed at SSRL to map the battery cross-section in fluorescence mode. This cell will mitigate the challenges of using pouch cells for X-ray experiments such as water and oxygen contamination and sample-to-sample variation. It will also provide more robust, longer-term cycling that better replicates the offline electrochemistry of a typical coin or pouch cell. Because the new cell will increase reproducibility, we can alter electrode architecture and electrolyte composition to directly compare polysulfide and sulfur distributions, illuminating the direct influence that these parameters have on battery chemistry. Using this new design, changes in sulfur and polysulfide chemistry are systematically correlated to structure and performance.

(Invited) Concepts of the Solid-Electrolyte Phase Boundary: Experimental Evidence and Resulting Devices

The original fundamental concepts at solid-electrolyte interfaces are reviewed including the traditional microcapacitor model of the Helmholtz layer1. Theoretical approaches that expand beyond the classical dielectric model for water and solvation shells are accounted for and recent advanced experiments will be presented that enable a direct profiling of the energetics at this junction by tender x-ray synchrotron radiation photoelectron spectroscopy (TSRPES) 2,3. Combined (photo)electrochemical and surface analytical investigations are presented. For the rectifying semiconductor - solution junction, the space charge behavior of semiconductors in concentrated electrolytes is examined and in dilute solutions, the Galvani potential profiles at metal - electrolyte junctions are followed by TSRPES. The role of truncated profiles for thinner water layers and dilute electrolytes on charge equilibration and build-up of contact potential differences is analyzed. Fig.1 shows an example of the resulting photoelectron spectroscopy tomography. Fig.1: (left): scheme for tomographic peak sampling; (right): influence of electrostaic potential on peak width Implications regarding charge transfer and the development of efficient devices for light - induced fuel generation are outlined and optimized structures which show unassisted water splitting are presented, obtained upon modifying the surfaces of III-V tandem absorbers. Application of (photo)electrochemically induced surface transformations 4,5 and of re-directed (photo)corrosion reactions allows passivation of surface and interface states and increased robustness. Details of these procedures will be given. The achieved efficiencies are compared to theoretically achievable limits of solar hydrogen evolution for the respective material combinations6. The influence of the optical properties of the combined catalyst - electrode - solution composite structures is described and routes to more advanced multi-electron and proton transfer reactions are outlined.

Photoelectron recoil in CO in the x-ray region up to 7 keV

Carbon $1s$ photoelectron spectra of CO molecules in gas phase were recorded in the tender x-ray energy range, from 2.3 to 6.9 keV. The intensity ratios of individual peaks from $\ensuremath{\nu}=0$ to 3 within the vibrational progression of the C $1s$ photoelectron spectrum were determined at the various photon energies and are shown to be strongly affected by the photoelectron recoil effect. The experimental vibrational intensity ratios are compared with theoretical predictions at different levels of accuracy. Developments of the recoil model, using generalized Franck-Condon factors, rovibrational coupling, Morse potential energy curves, and accurate angular averaging are presented and applied to the analysis of the experimental results.

Comparison of Iron Oxide-Related MRI Artifacts in Healthy and Neuropathological Human Brain Tissue

The paper describes an original technique for non-contact in situ monitoring of the temperature developed for experiments in a vacuum environment at the tender X-ray beamline I23 of the Diamond Light Source. The sample temperature is established by determining the luminescence decay constant of a Bi4Ge3O12 (BGO) scintillation sensor. BGO is ideally suited for a temperature range of 30 K to 130 K, in which its decay constant shows a strong temperature dependence. The principle of the method, system design and application examples are discussed and the performance and potential of the technique is assessed.

In situ X-ray photoelectron spectroscopy of electrochemically active solid-gas and solid-liquid interfaces

In this account the application of synchrotron radiation based X-ray photoelectron spectroscopy (XPS) for the investigation of electrochemically active gas-solid and liquid-solid interfaces will be discussed. The potential of Near Ambient Pressure XPS (NAP-XPS) for the estimation of the surface electronic structure of electrochemically active interfaces will be described by two examples. Thereto the oxygen evolution reaction (OER) over Pt and IrOx anodes will be introduced. In particular the analysis of XP core level spectra of IrOx requires the development of an appropriate fit model. Furthermore the design of reaction cells based on proton exchange membranes (PEM) and on electron transparent graphene membranes, which enables the investigation of liquid-gas and liquid-solid interfaces under electrochemical relevant conditions will be discussed. In the last part of this article a perspective to the EMIL project at the synchrotron radiation facility BESSY will be given. The purpose of this project is the implementation of two new beamlines enabling X-ray photoelectron spectroscopy in the X-ray regime from 80eV–8keV under reaction conditions. The extension to the so called tender X-ray regime will allow the release of higher kinetic energy photoelectrons which have a higher inelastic mean free path compared to photoelectrons excited by soft X-ray radiation and therefore will enable the investigation of solid-liquid interfaces under electrochemical reaction conditions.

Operando X-ray photoelectron spectroscopic investigations of the electrochemical double layer at Ir/KOH(aq) interfaces

Tender X-ray operando photoemission spectroscopy has been used to directly analyze the energetics of the double layer at a metal-water interface in a dilute electrolyte having a Debye length of several nanometers. The data are compared to a theoretical evaluation of the potential of the solution near the electrode. Due to its noble nature, Ir was chosen as a working electrode material, and KOH(aq) at varied concentrations and thicknesses constituted the electrolyte. Shifts in peak width and binding energy of the water O 1s core level were analyzed by modeling based on Debye-Hückel approximations. The data are consistent with electrochemical formulations of the double layer that provide a foundation to electrochemistry.

Design of a multilayer-based collimated plane-grating monochromator for tender X-ray range.

Collimated plane-grating monochromators (cPGMs), consisting of a plane mirror and plane diffraction grating, are essential optics in synchrotron radiation sources for their remarkable flexibility and good optical characteristics in the soft X-ray region. However, the poor energy transport efficiency of a conventional cPGM (single-layer-coated) degrades the source intensity and leaves reduced flux at the sample, especially for the tender X-ray range (1-4 keV) that covers a large number of K- and L-edges of medium-Z elements, and M-edges of high-Z elements. To overcome this limitation, the use of a multilayer-based cPGM is proposed, combining a multilayer-coated plane mirror with blazed multilayer gratings. With this combination, the effective efficiency of cPGMs can be increased by an order of magnitude compared with the conventional single-layer cPGMs. In addition, higher resolving power can be achieved with improved efficiency by increasing the blaze angle and working at higher diffraction order.

Structural analysis of polymer thin films using GISAXS in the tender X-ray region: Concept and design of GISAXS experiments using the tender X-ray energy at BL-15A2 at the Photon Factory

If small angle X-ray scattering (SAXS) utilizing the soft X-ray region is available, advanced and unique experiments, which differ from traditional SAXS methods, can be realized. For example, grazing-incidence small angle X-ray scattering (GISAXS) using hard X-ray is a powerful tool for understanding the nanostructure in both vertical and lateral directions of thin films, while GISAXS utilizing the tender X-ray region (SX-GISAXS) enables depth-resolved analysis as well as a standard GISAXS analysis in thin films. Thus, at BL-15A2 at the Photon Factory, a dedicated diffractometer for SX-GISAXS (above 2.1 keV) was constructed. This diffractometer is composed of four vacuum chambers and can be converted into the vacuum state from the sample chamber in front of the detector surface. Diffractions are clearly observed until 12th peak when measuring collagen by SAXS with an X-ray energy of 2.40 keV and a camera length of 825 mm. Additionally, we conducted the model experiment using SX-GISAXS with an X-ray energy of 2.40 keV to confirm that a poly(methyl methacrylate)-poly(n-butyl acrylate) block copolymer thin film has a microphase-separated structure in the thin film, which is composed of lamellae aligned both parallel and perpendicular to the substrate surface. Similarly, in a polystyrene-poly(methyl methacrylate) block copolymer thin film, SX-GISAXS with 3.60 keV and 5.73 keV revealed that hexagonally packed cylinders are aligned parallel to the substrate surface. The incident angle dependence of the first order peak position of the qz direction obtained from experiments at various incident X-ray energies agrees very well with the theoretical one calculated from the distorted wave Born approximation.

Electrochemical Characterization of the Titanium/Pbs Interface By Ambient Pressure X-Ray Photoelectron Spectroscopy

A novel operando Ambient Pressure Tender X-Ray Photoelectron Spectroscopy (T-APXPS) technique, developed by beamline 9.3.1 at the Advanced Light Source (ALS) [1], allows for the first time to study in detail the corrosion phenomena at the metallic biomaterial/body fluid electrified interface under operando electrochemical conditions. “Dip and Pull” method was used in order to create a stable nanometer-thick aqueous layer on the metallic biomaterial surface (Figure 1(a)). The ionically sustained electrical contact between the liquid layer on the sample surface and the bulk electrolyte is ensured by keeping the bottom part of each electrode immersed in the electrolyte. By using synchrotron radiation in the range of tender X-rays (at an energy of 4keV), it is possible to detect photoelectrons ejected from the solid/liquid interface, directly probing complex (electro-)chemical phenomena occurring at such important spatial region. Titanium is one of the most commonly used metal biomaterials (such as dental implants or restoration) because of its biocompatibility and chemical stability in biological environments [2]. This metal is characterized by the spontaneous formation of an oxide film (mainly composed of amorphous TiO2) on the surface, which protects the bulk material for further oxidation (passive metal). Thus, the formation of the surface oxide is responsible for both biocompatibility and corrosion resistance (related to the long-term durability of the biomaterial implanted into the body and metal ion release) [3]. Changes in the chemical composition of the Ti/TiO2/electrolyte junction during cathodic/anodic polarization in simulated body fluids were characterized using operando T-APXPS technique. Experimental. An electrochemical characterization of pure polycrystalline titanium in phosphate buffer solution (PBS) was carried out. Polarization curves were used in order to determine the different potential domains (cathodic, cathodic-anodic transition and passive domain). Potentiostatic tests were conducted between potentials comprised in the range -1VAg/AgCl and 1VAg/AgCl to determine the effect of the applied potential (belonging to the different potential domains) in the electrochemical reactions occurring at the biomaterial/electrolyte interface. During the potentiostatic tests, XPS spectra of Ti2p, O1s, C1s, P2s, and Cl2p were acquired under ultra high vacuum (UHV) and hydrated conditions (i.e., T-APXPS measurements were performed exposing the sample to a water gas pressure of about 16Torr prior any electrochemical treatment). Results Figure 1(b) shows the Ti2p spectra obtained at different conditions: (i) UHV, (ii) hydrated conditions, and (iii) during operando electrochemical conditions when potentials of -1.0VAg/AgCl (cathodic domain) and 1.0VAg/AgCl (passive domain) were applied to the working electrode (WE). In those spectra, attenuation in the Ti2p intensities upon water vapor exposure and subjected to polarization conditions were both measured. This observation reveals the formation of a thin electrolyte film (of about ~15 nm) on the titanium (WE). In this talk, our findings related to the titanium polarization at different applied potentials will be shown. New features on the higher binding energy (BE) side of the Ti2p spectra were observed after increasing the applied potential towards more anodic values. The change in the Ti2p photoelectron peak points to a change of the oxidation state of titanium, with the consequent increase of the Ti+4 concentration. In addition, a demonstration of the functionality and electrochemical activity of the formed thin electrolyte film on the titanium surface will be discussed. O1s photoelectron spectra are reported in Figure 1(c). It is possible to observe that the core level peaks from the electrolyte elements (EE) undergo a rigid shift in BE (with respect to the Fermi level of the grounded WE) that follows the variation of the applied potential (U) accordingly to the relation BEEE = BE0 EE - eU. This effect demonstrates that the electrolyte layer on the WE is conductive and connected to the bulk electrolyte, allowing potential control at the solid/liquid electrified interface. The O1s spectra shows two main components, centered at 533.6eV and 536.4eV, attributed to the liquid phase water from the thin film and the gas phase water filling the chamber, respectively. A shift of 2.0eV was observed between the liquid phase peaks obtained at 1.0VAg/AgCl and -1.0VAg/AgCl, which match perfectly with the applied potential difference. In summary, the newly developed T-APXPS technique at ALS allows the operando investigation of corrosion phenomena occurring at the metallic biomaterials/electrolyte interface. The advantage of using such technique relies on the simultaneous acquisition of electrochemical and spectroscopy data which allows a direct probing of the electrochemical process occurring at the biomaterial/liquid interface, including changes in the electrolyte species and evaluation of the metal degradation under simulated biological conditions.

High pressure XANES and XMCD in the tender X-ray energy range

ABSTRACTWe have developed an experimental setup at the ESRF beamline ID12 dedicated to X-ray absorption and magnetic circular dichroism measurements at high pressure adapted for the tender X-ray energy range and compatible with low temperatures and with high magnetic field. The focused incoming X-ray beam passes through a thin diamond disk attached to a fully perforated diamond anvil and X-ray fluorescence photons from the sample are collected in back-scattering geometry through the same diamond disk. The pressure in the cell is measured using the ruby luminescence through a full diamond anvil. The highest pressure attainable with this diamond anvil cell (DAC) depends on the thickness of the diamond disk and it is above 16 GPa for a 80-μm thick plate and exceeds 4.5 GPa in the case of 30-μm diamond disk. Excellent performances of this setup in the tender X-ray range are illustrated with X-ray absorption near-edge structure studies of the phase transitions in KCl at the potassium and chlorine K-edges (3.61 and 2.82 keV, respectively) as well as in CdS at the sulfur K-edge (2.47 keV). This DAC together with a dedicated total fluorescence yield (TFY) detector could be mounted in the main heat exchanger of a cryostat and inserted in a bore of a superconducting magnet, this makes possible to perform X-ray magnetic circular dichroism (XMCD) experiments at low temperature, high magnetic field and high pressure. Feasibility of this approach is shown with the XMCD results obtained at the U M-edges in ferromagnetic superconductor UGe.

Understanding the Good Kinetics of Mo6S8 As Cathode in Mg Ion Batteries By Key Electronic States

Mg rechargeable batteries are being considered as one of the most prospective alternatives for Li rechargeable batteries because of their merits including Mg abundance, absence of Mg dendrite and high theoretical specific capacity attributed to two-electron charge transfer reaction process. [1] However，the achievable performance of Mg rechargeable batteries is still limited regarding their practical application. The key limitation to this lies in cathode. To date, Chevrel phase Mo6(SxSe1-x)8 is the only cathode material in which Mg2+ can be efficiently intercalated/deintercalated. Extensive theoretical and experimental studies have been done to screen out promising cathode materials by constructing the crystal structure similar to Chevrel phase. However, successful research has been rarely reported. It indicates that only taking into account of the crystal structure is not sufficient enough to explore the Mg storage/transport behavior in the electrode. Given the facts that the two-electron charge transfer process was involved in Mg batteries while the great success has been made in the studies on lithium ion batteries through the key electronic states [2-5], the evolution of electronic structure in Chevrel phase might provide more important information to elucidate the physical nature of Mg storage/transport in the electrode. However, the experimental study on the evolution of electronic structure in Chevrel phase cathode is rare. In this report, the study on the unoccupied states of a typical Chevrel phase Mo6S8 including Mo L-edge and S K-edge were conducted by tender X-ray absorption spectroscopy. In contrast with the conventional understanding that only Mo cation is involved in the charge transfer process, the key electronic states at the pre-edge of S spectra were also found to be evolved regularly with different states of charge/discharge. It is assigned to the hybridization between Mo 4d states and S 3p states. The evolution of this state opens a gate to reveal the nature of good kinetics in Chevrel phase. 1. Aurbach, D., et al., Prototype systems for rechargeable magnesium batteries. Nature, 2000. 407(6805): p.724-727.2. Liu, G., et al., Polymers with Tailored Electronic Structure for High Capacity Lithium Battery Electrodes. Advanced Materials, 2011. 23(40): p. 4679-4683.3. Liu, X., et al., Phase Transformation and Lithiation Effect on Electronic Structure of LixFePO4: An In-Depth Study by Soft X-ray and Simulations. Journal of the American Chemical Society, 2012. 134(33): p. 13708-13715.4. Yang, W., et al., Key electronic states in lithium battery materials probed by soft X-ray spectroscopy. Journal of Electron Spectroscopy and Related Phenomena, 2013. 190, Part A(0): p. 64-74.5. Liu, X., W. Yang, and Z. Liu, Recent Progress on Synchrotron-Based In Situ Soft X-ray Spectroscopy for Energy Materials. Advanced Materials, 2014: 7710-7729.

Highly efficient blazed grating with multilayer coating for tender X-ray energies.

For photon energies of 1 - 5 keV, blazed gratings with multilayer coating are ideally suited for the suppression of stray and higher orders light in grating monochromators. We developed and characterized a blazed 2000 lines/mm grating coated with a 20 period Cr/C- multilayer. The multilayer d-spacing of 7.3 nm has been adapted to the line distance of 500 nm and the blaze angle of 0.84° in order to provide highest efficiency in the photon energy range between 1.5 keV and 3 keV. Efficiency of the multilayer grating as well as the reflectance of a witness multilayer which were coated simultaneously have been measured. An efficiency of 35% was measured at 2 keV while a maximum efficiency of 55% was achieved at 4 keV. In addition, a strong suppression of higher orders was observed which makes blazed multilayer gratings a favorable dispersing element also for the low X-ray energy range.

Operando Analyses of Solar Fuels Light Absorbers and Catalysts

Operando synchrotron radiation photoelectron spectroscopy in the tender X-ray energy range has been used to obtain information on the energy-band relations of semiconductor and metal-covered semiconductor surfaces while in direct contact with aqueous electrolytes under potentiostatic control. The system that was investigated consists of highly doped Si substrates that were conformally coated with ∼70nm titania films produced by atomic-layer deposition. TiO2/electrolyte and Si/TiO2/Ni/electrolyte interfaces were then analyzed by synchrotron radiation photoelectron spectroscopy. The PES data allows for determination of the flat-band position and identification of potential regions in which Fermi level pinning, depletion, or accumulation occurred. Operando X-ray absorption spectroscopy (XAS) techniques were additionally used to investigate the properties of heterogeneous electrocatalysts for the oxygen-evolution reaction. Operando XAS including the pre-edge, edge and EXAFS regions allowed the development of a detailed picture of the catalysts under operating conditions, and elucidated the changes in the physical and electronic structure of the catalyst that accompanied increases in the applied potential. Specifically, XAS data, combined with DFT studies, indicated that the activity of the electrocatalyst correlated with the formation of Fe dopant sites in γ-NiOOH.

Electronic Structure of Third-Row Elements in Different Local Symmetries Studied by Valence-to-Core X-ray Emission Spectroscopy.

The electronic structure of phosphorus, sulfur, and chlorine in compounds with Td and C3v local symmetries was studied with high-resolution Kβ X-ray emission spectroscopy (XES) in the tender X-ray range. Measured spectra are compared to the results of ab initio quantum chemical calculations based on density functional theory (DFT). The spectral structure is reproduced by the model spectra of isolated XO4n– and XO3n– (X = P, S, or Cl) anions incorporating only the first coordination sphere around the central atom. The main spectral components can be explained by the molecular orbital theory. Finally, the potential of XES spectroscopy combined with DFT calculations to study the electronic structure of third-row elements in a slightly larger molecule is investigated.

Orientation and relaxation behaviors of lamellar microdomains of poly(methyl methacrylate)-b-poly(n-butyl acrylate) thin films as revealed by grazing-incidence small-angle X-ray scattering

The orientation behavior and domain spacing relaxation of the phase-separated structure of poly(methyl methacrylate-b-n-butyl acrylate) (PMMA-PnBA) thin films were investigated by grazing-incidence small-angle X-ray scattering (GISAXS). Moreover, low-energy GISAXS (tender X-ray) was performed for the in-depth profiling of the microphase-separated structure. PMMA-PnBA forms a lamellar structure. Parallel orientation of the lamellae was induced by thermal annealing. XPS measurements indicated that surface segregation of the PnBA component occurred rapidly, within 1 min after annealing at 160 °C. GISAXS measurements revealed that the apparent degree of orientation and the domain spacing D|| of the parallel-oriented lamellae increased with annealing time, and the final D|| was close to the domain spacing of the bulk material. The domain spacing relaxation took longer than the orientation of the lamellae of the block copolymers. Furthermore, it was found that D|| in the vicinity of the surface was greater than inside the film, which indicates that the domain spacing near the surface relaxed faster than inside due to the higher mobility of the polymer chain. The orientation behavior and domain spacing relaxation of the phase-separated structure of poly(methyl methacrylate-b-n-butyl acrylate) thin films were investigated by grazing-incidence small-angle X-ray scattering (GISAXS). Moreover, low-energy GISAXS was performed for the in-depth profiling of the lamellar structure. The domain spacing (D||) relaxation took longer than the orientation of the lamellae. Furthermore, the D|| in the vicinity of the surface was greater than inside the film, which indicates that the D|| near the surface relaxed faster than inside due to the higher mobility of the polymer chain.

The Environmental Photochemistry of Oxide Surfaces and the Nature of Frozen Salt Solutions: A New in Situ XPS Approach

Recent years have witnessed fast advancements in near ambient pressure X-ray photoelectron (NAPP) spectroscopy, which is emerging as a powerful tool for the investigation of surfaces in presence of vapors and liquids. In this paper we present a new chamber for the investigation of solid/vapor interfaces relevant to environmental and atmospheric chemistry that fits to the NAPP endstation at the Swiss Light Source. The new chamber allows for performing X-ray photoelectron spectroscopy (XPS) and electron yield near-edge X-ray absorption fine structure spectroscopy (NEXAFS) using soft, tender and hard X-ray in vacuum and in near-ambient pressures up to 20 mbar at environmentally relevant conditions of temperature and relative humidity. In addition, the flow tube design of the chamber enables the dosing of sticky reactive gases with short pressure equilibration time. The accessible photoelectron kinetic energy ranges from 2 to 7000 eV. This range allows the determination of surface and bulk electronic properties of ice and other environmental materials, such as metal oxides and frozen solutions, which are relevant to understanding atmospheric chemistry. The design of this instrument and first results on systems of great interest to the environmental and atmospheric chemistry community are presented. In particular, near-ambient pressure XPS and NEXAFS, coupled to a UV-laser setup, were used to study the adsorption of water on a TiO2 powder sample. The results are in line with previously proposed adsorption models of water on TiO2, and, furthermore, indicate that the concentration of water molecules tends to increase upon UV irradiation. In a second example we illustrate how NEXAFS spectroscopy measurements at the chlorine K-edge can provide new insight on the structures of eutectic and sub-eutectic frozen NaCl solutions at high and low relative humidity, respectively, indicating the formation of solution and solid NaCl phases, respectively. Finally, we demonstrate the assets of this new chamber for the dosing of sticky acidic gases and, in particular, for the investigation of formic acid uptake on ice surfaces.

Detective quantum efficiency for photon-counting hybrid pixel detectors in the tender X-ray domain: application to Medipix3RX.

Synchrotron-radiation-based X-ray imaging techniques using tender X-rays are facing a growing demand, in particular to probe the K absorption edges of low-Z elements. Here, a mathematical model has been developed for estimating the detective quantum efficiency (DQE) at zero spatial frequency in the tender X-ray energy range for photon-counting detectors by taking into account the influence of electronic noise. The experiments were carried out with a Medipix3RX ASIC bump-bonded to a 300 µm silicon sensor at the Soft X-ray Spectroscopy beamline (D04A-SXS) of the Brazilian Synchrotron Light Laboratory (LNLS, Campinas, Brazil). The results show that Medipix3RX can be used to develop new imaging modalities in the tender X-ray range for energies down to 2 keV. The efficiency and optimal DQE depend on the energy and flux of the photons. The optimal DQE values were found in the 7.9-8.6 keV photon energy range. The DQE deterioration for higher energies due to the lower absorption efficiency of the sensor and for lower energies due to the electronic noise has been quantified. The DQE for 3 keV photons and 1 × 10(4) photons pixel(-1) s(-1) is similar to that obtained with 19 keV photons. Based on our model, the use of Medipix3RX could be extended down to 2 keV which is crucial for coming applications in imaging techniques at modern synchrotron sources.

低エネルギーX線を用いた斜入射小角X線散乱法によるブロック共重合体薄膜のミクロ相分離構造の深さ依存性と配向挙動の解析

In this review, we demonstrated grazing-incidence small-angle X-ray scattering (GISAXS) measurement with tender X-ray to achieve depth-resolved structure analysis of block copolymer systems, polystyrene-b-poly (2-vinylpyridine)(S2VP) and poly (methyl methacrylate)-b-poly (n-butyl acrylate) thin films (approximately 300 - 400 nm in thick). In the case of using tender X-rays, the penetration depth of X-rays in the vicinity of critical angle of total reflection becomes gentle as compared to the case of using hard X-rays. Herein, X-ray energies of 2.40 keV and 4.36 keV were employed to conduct depth-resolved structure analysis. The experimental full width at half maximum (FWHM) magnitudes of a diffraction spot was investigated to estimate the penetration depth. The incident angle dependence of experimental FWHM magnitudes indicated the same tendency as the FWHM values calculated with Laue function considering attenuation decay, meaning that the penetration depth was controlled by varying incident angles. Depth-resolved structure analysis revealed that in the case of the completely oriented thin film, micro-phase separated structures slightly deformed along the depth direction in the inside of the thin film and the deformation gradually relaxed near the surface.