Upgrade of beamline BL08B at Taiwan Light Source from a photon‐BPM to a double‐grating SGM beamline

During the last 20 years, beamline BL08B has been upgraded step by step from a photon beam‐position monitor (BPM) to a testing beamline and a single‐grating beamline that enables experiments to record X‐ray photo‐emission spectra (XPS) and X‐ray absorption spectra (XAS) for research in solar physics, organic semiconductor materials and spinel oxides, with soft X‐ray photon energies in the range 300–1000 eV. Demands for photon energy to extend to the extreme ultraviolet region for applications in nano‐fabrication and topological thin films are increasing. The basic spherical‐grating monochromator beamline was again upgraded by adding a second grating that delivers photons of energy from 80 to 420 eV. Four end‐stations were designed for experiments with XPS, XAS, interstellar photoprocess systems (IPS) and extreme‐ultraviolet lithography (EUVL) in the scheduled beam time. The data from these experiments show a large count rate in core levels probed and excellent statistics on background normalization in the L‐edge adsorption spectrum.     

Zr and Ba edge phenomena in the scintillation intensity of fluorozirconate‐based glass‐ceramic X‐ray detectors

The energy‐dependent scintillation intensity of Eu‐doped fluorozirconate glass‐ceramic X‐ray detectors has been investigated in the energy range from 10 to 40 keV. The experiments were performed at the Advanced Photon Source, Argonne National Laboratory, USA. The glass ceramics are based on Eu‐doped fluorozirconate glasses, which were additionally doped with chlorine to initiate the nucleation of BaCl₂ nanocrystals therein. The X‐ray excited scintillation is mainly due to the 5d–4f transition of Eu²⁺ embedded in the BaCl₂ nanocrystals; Eu²⁺ in the glass does not luminesce. Upon appropriate annealing the nanocrystals grow and undergo a phase transition from a hexagonal to an orthorhombic phase of BaCl₂. The scintillation intensity is investigated as a function of the X‐ray energy, particle size and structure of the embedded nanocrystals. The scintillation intensity versus X‐ray energy dependence shows that the intensity is inversely proportional to the photoelectric absorption of the material, i.e. the more photoelectric absorption the less scintillation. At 18 and 37.4 keV a significant decrease in the scintillation intensity can be observed; this energy corresponds to the K‐edge of Zr and Ba, respectively. The glass matrix as well as the structure and size of the embedded nanocrystals have an influence on the scintillation properties of the glass ceramics.     

Fabrication of superconducting tunnel junctions for soft X‐ray spectroscopy

Superconducting tunnel junction (STJ) array detectors with a new design, which has a minimum junction edge coverage of an SiO₂ insulation, passivation layer and an asymmetric tunnel junction layer structure, have been fabricated for a soft X‐ray region between 100 eV and 1 keV. The sensitive area was patterned by removing the SiO₂ deposition layer by a lift‐off technique that ensured no contamination layer on the top Nb electrode surface. The width of the passivation rim was as narrow as 0.5 µm at the junction edge. The clean Nb surface and the narrow SiO₂ rim resulted in almost no artifact photon events in a low‐energy region. The asymmetric layer design is effective in solving a problem of double peak response to monochromatic X‐rays, which is commonly observed in STJ detectors. The performance of a 100 pixel array detector was investigated by the fluorescent X‐ray analysis of oxides and nitrides: an energy resolution of about 30 eV for the total absorption of the Kα lines of oxygen and nitrogen. We plan to realize an energy resolution of better than 20 eV and a counting rate of over 1 Mcps for fluorescence‐yield X‐ray absorption spectroscopy for light trace elements. Copyright © 2011 John Wiley & Sons, Ltd.     

Soft X‐ray absorption spectroscopy and resonant inelastic X‐ray scattering spectroscopy below 100 eV: probing first‐row transition‐metal M‐edges in chemical complexes

X‐ray absorption and scattering spectroscopies involving the 3d transition‐metal K‐ and L‐edges have a long history in studying inorganic and bioinorganic molecules. However, there have been very few studies using the M‐edges, which are below 100 eV. Synchrotron‐based X‐ray sources can have higher energy resolution at M‐edges. M‐edge X‐ray absorption spectroscopy (XAS) and resonant inelastic X‐ray scattering (RIXS) could therefore provide complementary information to K‐ and L‐edge spectroscopies. In this study, M_2,3‐edge XAS on several Co, Ni and Cu complexes are measured and their spectral information, such as chemical shifts and covalency effects, are analyzed and discussed. In addition, M_2,3‐edge RIXS on NiO, NiF₂ and two other covalent complexes have been performed and different d–d transition patterns have been observed. Although still preliminary, this work on 3d metal complexes demonstrates the potential to use M‐edge XAS and RIXS on more complicated 3d metal complexes in the future. The potential for using high‐sensitivity and high‐resolution superconducting tunnel junction X‐ray detectors below 100 eV is also illustrated and discussed.     

Early commissioning results for spectroscopic X‐ray Nano‐Imaging Beamline BL 7C sXNI at PLS‐II

For spectral imaging of chemical distributions using X‐ray absorption near‐edge structure (XANES) spectra, a modified double‐crystal monochromator, a focusing plane mirrors system and a newly developed fluorescence‐type X‐ray beam‐position monitoring and feedback system have been implemented. This major hardware upgrade provides a sufficiently stable X‐ray source during energy scanning of more than hundreds of eV for acquisition of reliable XANES spectra in two‐dimensional and three‐dimensional images. In recent pilot studies discussed in this paper, heavy‐metal uptake by plant roots in vivo and iron's phase distribution in the lithium–iron–phosphate cathode of a lithium‐ion battery have been imaged. Also, the spatial resolution of computed tomography has been improved from 70 nm to 55 nm by means of run‐out correction and application of a reconstruction algorithm.     

A three‐crystal spectrometer for high‐energy resolution fluorescence‐detected X‐ray absorption spectroscopy and X‐ray emission spectroscopy at SSRF

A Johann‐type spectrometer for the study of high‐energy resolution fluorescence‐detected X‐ray absorption spectroscopy, X‐ray emission spectroscopy and resonant inelastic X‐ray scattering has been developed at BL14W1 X‐ray absorption fine structure spectroscopy beamline of Shanghai Synchrotron Radiation Facility. The spectrometer consists of three crystal analyzers mounted on a vertical motion stage. The instrument is scanned vertically and covers the Bragg angle range of 71.5–88°. The energy resolution of the spectrometer ranges from sub‐eV to a few eV. The spectrometer has a solid angle of about 1.87 × 0^?3 of 4π sr, and the overall photons acquired by the detector could be 10⁵ counts per second for the standard sample. The performances of the spectrometer are illustrated by the three experiments that are difficult to perform with the conventional absorption or emission spectroscopy. Copyright © 2016 John Wiley & Sons, Ltd.     

A fast energy‐dispersive multi‐element detector for X‐ray absorption spectroscopy

In this paper results are presented from fluorescence‐yield X‐ray absorption fine‐structure spectroscopy measurements with a new seven‐cell silicon drift detector (SDD) module. The complete module, including an integrated circuit for the detector readout, was developed and realised at DESY utilizing a monolithic seven‐cell SDD. The new detector module is optimized for applications like XAFS which require an energy resolution of ～250–300 eV (FWHM Mn Kα) at high count rates. Measurements during the commissioning phase proved the excellent performance for this type of application.     

Cesium doped and undoped ZnO nanocrystalline thin films: a comparative study of structural and micro‐Raman investigation of optical phonons

Undoped and cesium‐doped zinc oxide (ZnO) thin films have been deposited on sapphire substrate (0001) using the sol–gel method. Films were preheated at 300 °C for 10 min and annealed at 600 and 800 °C for 1 h. The grown thin films were confirmed to be of wurtzite structure using X‐ray diffraction. Surface morphology of the films was analyzed using scanning electron microscopy. The photoluminescence (PL) spectra of ZnO showed a strong ultraviolet (UV) emission band located at 3.263 eV and a very weak visible emission associated with deep‐level defects. Cesium incorporation induced a blue shift of the optical band gap and quenching of the near‐band‐edge PL for nanocrystalline thin film at room temperatures because of the band‐filling effect of free carriers. A shift of about 10–15 cm⁻¹ is observed for the first‐order longitudinal‐optical (LO) phonon Raman peak of the nanocrystals when compared to the LO phonon peak of bulk ZnO. The UV resonant Raman excitation at RT shows multiphonon LO modes up to fifth order. Copyright © 2010 John Wiley & Sons, Ltd.     

Suppression of Bragg reflection glitches of a single‐crystal diamond anvil cell by a polycapillary half‐lens in high‐pressure XAFS spectroscopy

In combination with a single‐crystal diamond anvil cell (DAC), a polycapillary half‐lens (PHL) re‐focusing optics has been used to perform high‐pressure extended X‐ray absorption fine‐structure measurements. It is found that a large divergent X‐ray beam induced by the PHL leads the Bragg glitches from single‐crystal diamond to be broadened significantly and the intensity of the glitches to be reduced strongly so that most of the DAC glitches are efficiently suppressed. The remaining glitches can be easily removed by rotating the DAC by a few degrees with respect to the X‐ray beam. Accurate X‐ray absorption fine‐structure (XAFS) spectra of polycrystalline Ge powder with a glitch‐free energy range from ?200 to 800 eV relative to the Ge absorption edge are obtained using this method at high pressures up to 23.7 GPa, demonstrating the capability of PHL optics in eliminating the DAC glitches for high‐pressure XAFS experiments. This approach brings new possibilities to perform XAFS measurements using a DAC up to ultrahigh pressures.     

Measurement of the X‐ray mass attenuation coefficients of silver in the 5–20 keV range

The X‐ray mass attenuation coefficients of silver were measured in the energy range 5–20 keV with an accuracy of 0.01–0.2% on a relative scale down to 5.3 keV, and of 0.09–1.22% on an absolute scale to 5.0 keV. This analysis confirms that with careful choice of foil thickness and careful correction for systematics, especially including harmonic contents at lower energies, the X‐ray attenuation of high‐Z elements can be measured with high accuracy even at low X‐ray energies (<6 keV). This is the first high‐accuracy measurement of X‐ray mass attenuation coefficients of silver in the low energy range, indicating the possibility of obtaining high‐accuracy X‐ray absorption fine structure down to the L₁ edge (3.8 keV) of silver. Comparison of results reported here with an earlier data set optimized for higher energies confirms accuracy to within one standard error of each data set collected and analysed using the principles of the X‐ray extended‐range technique (XERT). Comparison with theory shows a slow divergence towards lower energies in this region away from absorption edges. The methodology developed can be used for the XAFS analysis of compounds and solutions to investigate structural features, bonding and coordination chemistry.     

Carbon K‐edge spectra of carbonate minerals

Carbon K‐edge X‐ray spectroscopy has been applied to the study of a wide range of organic samples, from polymers and coals to interstellar dust particles. Identification of carbonaceous materials within these samples is accomplished by the pattern of resonances in the 280–320 eV energy region. Carbonate minerals are often encountered in the study of natural samples, and have been identified by a distinctive resonance at 290.3 eV. Here C K‐edge and Ca L‐edge spectra from a range of carbonate minerals are presented. Although all carbonates exhibit a sharp 290 eV resonance, both the precise position of this resonance and the positions of other resonances vary among minerals. The relative strengths of the different carbonate resonances also vary with crystal orientation to the linearly polarized X‐ray beam. Intriguingly, several carbonate minerals also exhibit a strong 288.6 eV resonance, consistent with the position of a carbonyl resonance rather than carbonate. Calcite and aragonite, although indistinguishable spectrally at the C K‐edge, exhibited significantly different spectra at the Ca L‐edge. The distinctive spectral fingerprints of carbonates provide an identification tool, allowing for the examination of such processes as carbon sequestration in minerals, Mn substitution in marine calcium carbonates (dolomitization) and serpentinization of basalts.     

A method to stabilize the incident X‐ray energy for anomalous diffraction measurements

A method to calibrate and stabilize the incident X‐ray energy for anomalous diffraction data collection is provided and has been successfully used at the single‐crystal diffraction beamline 1W2B at the Beijing Synchrotron Radiation Facilities. Employing a feedback loop to control the movement of the double‐crystal monochromator, this new method enables the incident X‐ray energy to be kept within a 0.2 eV range at the inflection point of the absorption edge.     

A high‐resolution X‐ray fluorescence spectrometer and its application at SSRF

A high‐resolution X‐ray fluorescence spectrometer based on Rowland circle geometry was developed and installed at BL14W1 XAFS beamline of Shanghai Synchrotron Radiation Facility. The spectrometer mainly consists of three parts: a sample holder, a spherically curved Si crystal, and an avalanche photodiode detector. The simplicity of the spectrometer makes it easily assembled on the general purpose X‐ray absorption beamline. X‐ray emission spectroscopy and high‐resolution X‐ray absorption near edge spectroscopy can be carried out by using this spectrometer. X‐ray emission preliminary results with high‐resolution about 3 eV of Mn compounds were obtained, which confirmed the feasibility of the spectrometer. The application about Eu (III) retention on manganese dioxide was also studied using this spectrometer. Compared with conventional X‐ray absorption fine structure spectroscopy technique, the fluorescence peak of probed element [Eu (III) Lα] and matrix constituents (Mn Kα) were discriminated using this technique, indicating its superiority in fluorescence detection. Copyright © 2013 John Wiley & Sons, Ltd.     

A scanning transmission X‐ray microscope at the Pohang Light Source

A scanning transmission X‐ray microscope is operational at the 10A beamline at the Pohang Light Source. The 10A beamline provides soft X‐rays in the photon energy range 100–2000 eV using an elliptically polarized undulator. The practically usable photon energy range of the scanning transmission X‐ray microscopy (STXM) setup is from ～150 to ～1600 eV. With a zone plate of 25 nm outermost zone width, the diffraction‐limited space resolution, ～30 nm, is achieved in the photon energy range up to ～850 eV. In transmission mode for thin samples, STXM provides the element, chemical state and magnetic moment specific distributions, based on absorption spectroscopy. A soft X‐ray fluorescence measurement setup has been implemented in order to provide the elemental distribution of thicker samples as well as chemical state information with a space resolution of ～50 nm. A ptychography setup has been implemented in order to improve the space resolution down to 10 nm. Hardware setups and application activities of the STXM are presented.     

Study of radiation damage induced by 12 keV X‐rays in MOS structures built on high‐resistivity n‐type silicon

Imaging experiments at the European X‐ray Free Electron Laser (XFEL) require silicon pixel sensors with extraordinary performance specifications: doses of up to 1 GGy of 12 keV photons, up to 10⁵ 12 keV photons per 200 µm × 200 µm pixel arriving within less than 100 fs, and a time interval between XFEL pulses of 220 ns. To address these challenges, in particular the question of radiation damage, the properties of the SiO₂ layer and of the Si–SiO₂ interface, using MOS (metal‐oxide‐semiconductor) capacitors manufactured on high‐resistivity n‐type silicon irradiated to X‐ray doses between 10 kGy and 1 GGy, have been studied. Measurements of capacitance/conductance–voltage (C/G–V) at different frequencies, as well as of thermal dielectric relaxation current (TDRC), have been performed. The data can be described by a dose‐dependent oxide charge density and three dominant radiation‐induced interface states with Gaussian‐like energy distributions in the silicon band gap. It is found that the densities of the fixed oxide charges and of the three interface states increase up to dose values of approximately 10 MGy and then saturate or even decrease. The shapes and the frequency dependences of the C/G–V measurements can be quantitatively described by a simple model using the parameters extracted from the TDRC measurements.     

Time‐resolved XAFS measurement using quick‐scanning techniques at BSRF

A new quick‐scanning X‐ray absorption fine‐structure (QXAFS) system has been established on beamline 1W1B at the Beijing Synchrotron Radiation Facility. As an independent device, the QXAFS system can be employed by other beamlines equipped with a double‐crystal monochromator to carry out quick energy scans and data acquisition. Both continuous‐scan and trapezoidal‐scan modes are available in this system to satisfy the time scale from subsecond (in the X‐ray absorption near‐edge structure region) to 1 min. Here, the trapezoidal‐scan method is presented as being complementary to the continuous‐scan method, in order to maintain high energy resolution and good signal‐to‐noise ratio. The system is demonstrated to be very reliable and has been combined with in situ cells to carry out time‐resolved XAFS studies.     

Fabrication of polycrystalline silicon films by Al‐induced crystallization of silicon‐rich oxide films

Polycrystalline silicon (poly‐Si) films were fabricated by aluminum (Al)‐induced crystallization of Si‐rich oxide (SiO_x) films. The fabrication was achieved by thermal annealing of SiO_x /Al bilayers below the eutectic temperature of the Al–Si alloy. The poly‐Si film resulting from SiO_1.45 exhibited good crystallinity with highly preferential (111) orientation, as deduced from Raman scattering, X‐ray diffraction, and transmission electron microscopy measurements. The poly‐Si film is probably formed by the Al‐induced layer exchange mechanism, which is mediated by Al oxide.     

Fluorescence imaging of reactive oxygen species by confocal laser scanning microscopy for track analysis of synchrotron X‐ray photoelectric nanoradiator dose: X‐ray pump–optical probe

Bursts of emissions of low‐energy electrons, including interatomic Coulomb decay electrons and Auger electrons (0–1000 eV), as well as X‐ray fluorescence produced by irradiation of large‐Z element nanoparticles by either X‐ray photons or high‐energy ion beams, is referred to as the nanoradiator effect. In therapeutic applications, this effect can damage pathological tissues that selectively take up the nanoparticles. Herein, a new nanoradiator dosimetry method is presented that uses probes for reactive oxygen species (ROS) incorporated into three‐dimensional gels, on which macrophages containing iron oxide nanoparticles (IONs) are attached. This method, together with site‐specific irradiation of the intracellular nanoparticles from a microbeam of polychromatic synchrotron X‐rays (5–14 keV), measures the range and distribution of OH radicals produced by X‐ray emission or superoxide anions () produced by low‐energy electrons. The measurements are based on confocal laser scanning of the fluorescence of the hydroxyl radical probe 2‐[6‐(4′‐amino)phenoxy‐3H‐xanthen‐3‐on‐9‐yl] benzoic acid (APF) or the superoxide probe hydroethidine‐dihydroethidium (DHE) that was oxidized by each ROS, enabling tracking of the radiation dose emitted by the nanoradiator. In the range 70 µm below the irradiated cell, radicals derived mostly from either incident X‐ray or X‐ray fluorescence of ION nanoradiators are distributed along the line of depth direction in ROS gel. In contrast, derived from secondary electron or low‐energy electron emission by ION nanoradiators are scattered over the ROS gel. ROS fluorescence due to the ION nanoradiators was observed continuously to a depth of 1.5 mm for both oxidized APF and oxidized DHE with relatively large intensity compared with the fluorescence caused by the ROS produced solely by incident primary X‐rays, which was limited to a depth of 600 µm, suggesting dose enhancement as well as more penetration by nanoradiators. In conclusion, the combined use of a synchrotron X‐ray microbeam‐irradiated three‐dimensional ROS gel and confocal laser scanning fluorescence microscopy provides a simple dosimetry method for track analysis of X‐ray photoelectric nanoradiator radiation, suggesting extensive cellular damage with dose‐enhancement beyond a single cell containing IONs.     

Investigation of nanoparticulate silicon as printed layers using scanning electron microscopy,transmission electron microscopy,X‐ray absorption spectroscopy and X‐ray photoelectron spectroscopy

The presence of native oxide on the surface of silicon nanoparticles is known to inhibit charge transport on the surfaces. Scanning electron microscopy (SEM) studies reveal that the particles in the printed silicon network have a wide range of sizes and shapes. High‐resolution transmission electron microscopy reveals that the particle surfaces have mainly the (111)‐ and (100)‐oriented planes which stabilizes against further oxidation of the particles. X‐ray absorption spectroscopy (XANES) and X‐ray photoelectron spectroscopy (XPS) measurements at the O 1s‐edge have been utilized to study the oxidation and local atomic structure of printed layers of silicon nanoparticles which were milled for different times. XANES results reveal the presence of the +4 (SiO₂) oxidation state which tends towards the +2 (SiO) state for higher milling times. Si 2p XPS results indicate that the surfaces of the silicon nanoparticles in the printed layers are only partially oxidized and that all three sub‐oxide, +1 (Si₂O), +2 (SiO) and +3 (Si₂O₃), states are present. The analysis of the change in the sub‐oxide peaks of the silicon nanoparticles shows the dominance of the +4 state only for lower milling times.