The soft X-ray spectromicroscopy beamline BL08U1A upgrade at SSRF.

Beamline BL08U1A is a soft X-ray spectromicroscopy beamline at Shanghai Synchrotron Radiation Facility (SSRF) that exhibits the capabilities of high spatial resolution (30 nm) and high energy resolving power (over 104). As a first-generation beamline of SSRF, owing to its continuous operation over the last ten years, an urgent upgrade of the equipment including the monochromator was deemed necessary. The upgrade work included the overall construction of the monochromator and replacement of the mirrors upstream and downstream of the monochromator. Based on its original skeleton, two elliptically cylinder mirrors were designed to focus the beam horizontally, which can increase the flux density by about three times on the exit slits. Meanwhile, the application of variable-line-space gratings in the monochromator demonstrates the dual functions of dispersing and focusing on the exit slits which can decrease abberations dramatically. After the upgrade of the main components of the beamline, the energy range is 180-2000 eV, the energy resolving power reaches 16333 @ 244 eV and 12730 @ 401 eV, and the photon flux measured in the experimental station is over 2.45 × 109 photons s-1 (E/ΔE = 6440 @ 244 eV).

Development and commissioning of a broadband online X-ray spectrometer for the SXFEL Facility.

A broadband online X-ray spectrometer has been designed and commissioned at the SUD beamline of the Shanghai Soft X-ray Free-Electron Laser Facility, which can deliver both SASE and seeded FEL pulses to user experiments, spanning the photon energy range of 50-620 eV. The resolving powers of the spectrometer calibrated via online measurement at 92 eV and 249 eV are ∼20000 and ∼15000, respectively, and the absolute photon energy is characterized by an electron time-of-flight spectrometer. The high energy resolution provided by the spectrometer can differentiate the fine structure in the FEL spectrum, to determine its pulse length.

Energy Resolution from a Silicon Detector's Interstrip Regions.

In this work, we present a novel approach for improving the energy resolution from particles impinging on the interstrip regions of silicon strip detectors. We employed three double-sided strip detectors from the GRIT array and a triple α-source under laboratory conditions. The results showed that the interstrip resolution depends not only on the impinging side but also on whether it is a P- or an N-interstrip. We obtained the interstrip energy resolution down to 0.4%, and, depending on the scenario, the resolution was enhanced by a factor of 2. We believe that this new rotation method allows for the possibility of applying particle identification methods on interstrip events, which in most cases are dismissed during data recording.

Np(V) Retention at the Illite du Puy Surface.

In this study, Np(V) retention on Illite du Puy (IdP) was investigated since it is essential for understanding the migration behavior of Np in argillaceous environments. The presence of structural Fe(III) and Fe(II) in IdP was confirmed by Fe K-edge X-ray absorption near-edge structure (XANES) and 57Fe Mössbauer spectroscopy. In batch sorption experiments, a higher Np sorption affinity to IdP was found than to Wyoming smectite or iron-free synthetic montmorillonite. An increase of the relative Np(IV) ratio sorbed onto IdP with decreasing pH was observed by solvent extraction (up to (24 ± 2)% at pH 5, c0(Np) = 10-6 mol/L). Furthermore, up to (33 ± 5)% Np(IV) could be detected in IdP diffusion samples at pH 5. Respective Np M5-edge high-energy resolution (HR-) XANES spectra suggested the presence of Np(IV/V) mixtures and weakened axial bond covalency of the NpO2+ species sorbed onto IdP. Np L3-edge extended X-ray absorption fine structure (EXAFS) analysis showed that significant fractions of Np were coordinated to Fe─O entities at pH 9. This highlights the potential role of Fe(II/III) clay edge sites as a strong Np(V) surface complex partner and points to the partial reduction of sorbed Np(V) to Np(IV) via structural Fe(II).

Radiation Damage by Heavy Ions in Silicon and Silicon Carbide Detectors.

While silicon has been a steadfast semiconductor material for the past 50 years, it is now facing competition from other materials, especially for detector design. In that respect, due to its high resistance to radiation damage, silicon carbide is one of the most promising materials. In this work, we discuss the radiation damage studies of a new, large area, p-n junction silicon carbide device developed by the SiCILIA collaboration. We have studied the general performances of several devices, as a function of fluence, irradiated in different experimental conditions with different beams. A standard p-n junction silicon detector was also irradiated for comparison. The new detectors manifest excellent performance in terms of stability of the main parameters, linearity, defect distribution, charge collection efficiency, energy resolution, leakage current, etc. Experimental results evidence a radiation resistance of SiC devices more than two order of magnitude higher than Si devices. The new construction technology applied to silicon carbide material has made it possible to create very robust devices with excellent performance. These devices will soon be available for all those scientific projects where a high resistance to radiation damage is required.

Multicolor single-analyzer high-energy-resolution XES spectrometer for simultaneous examination of different elements.

The present work demonstrates the performance of a von Hámos high-energy-resolution X-ray spectrometer based on a non-conventional conical Si single-crystal analyzer. The analyzer is tested with different primary and secondary X-ray sources as well as a hard X-ray sensitive CCD camera. The spectrometer setup is also characterized with ray-tracing simulations. Both experimental and simulated results affirm that the conical spectrometer can efficiently detect and resolve the two pairs of two elements (Ni and Cu) Kα X-ray emission spectroscopy (XES) peaks simultaneously, requiring a less than 2 cm-wide array on a single position-sensitive detector. The possible applications of this simple yet broad-energy-spectrum crystal spectrometer range from quickly adapting it as another probe for complex experiments at synchrotron beamlines to analyzing X-ray emission from plasma generated by ultrashort laser pulses at modern laser facilities.

Performance and characterization of the FinEstBeAMS beamline at the MAX IV Laboratory.

FinEstBeAMS (Finnish-Estonian Beamline for Atmospheric and Materials Sciences) is a multidisciplinary beamline constructed at the 1.5 GeV storage ring of the MAX IV synchrotron facility in Lund, Sweden. The beamline covers an extremely wide photon energy range, 4.5-1300 eV, by utilizing a single elliptically polarizing undulator as a radiation source and a single grazing-incidence plane grating monochromator to disperse the radiation. At photon energies below 70 eV the beamline operation relies on the use of optical and thin-film filters to remove higher-order components from the monochromated radiation. This paper discusses the performance of the beamline, examining such characteristics as the quality of the gratings, photon energy calibration, photon energy resolution, available photon flux, polarization quality and focal spot size.

Practical measurement of the energy resolution for meV-resolved inelastic X-ray scattering.

Several different ways of measuring the energy resolution for meV-resolved inelastic X-ray scattering (IXS) are compared: using scattering from poly(methyl methacrylate), PMMA, using scattering from borosilicate glass (Tempax), and using powder diffraction from aluminium. All of these methods provide a reasonable first approximation to the energy resolution, but, also, in all cases, inelastic contributions appear over some range of energy transfers. Over a range of ±15 meV energy transfer there is good agreement between the measurements of PMMA and Tempax at low temperature, and room-temperature powder diffraction from aluminium, so we consider this to be a good indication of the true resolution of our ∼1.3 meV spectrometer. The resolution over a wider energy range is self-consistently determined using the temperature, momentum and sample dependence of the measured response. The inelastic contributions from the PMMA and Tempax, and their dependence on momentum transfer and temperature, are then quantitatively investigated. The resulting data allow us to determine the resolution of our multi-analyzer array efficiently using a single scan. The importance of this procedure is demonstrated by showing that the results of the analysis of a spectrum from a glass are changed by using the properly deconvolved resolution function. The impact of radiation damage on the scattering from PMMA and Tempax is also discussed.

Site-Selective Real-Time Observation of Bimolecular Electron Transfer in a Photocatalytic System Using L-Edge X-Ray Absorption Spectroscopy*.

Time-resolved X-ray absorption spectroscopy has been utilized to monitor the bimolecular electron transfer in a photocatalytic water splitting system. This has been possible by uniting the local probe and element specific character of X-ray transitions with insights from high-level ab initio calculations. The specific target has been a heteroleptic [IrIII (ppy)2 (bpy)]+ photosensitizer, in combination with triethylamine as a sacrificial reductant and Fe3(CO)12 as a water reduction catalyst. The relevant molecular transitions have been characterized via high-resolution Ir L-edge X-ray absorption spectroscopy on the picosecond time scale and restricted active space self-consistent field calculations. The presented methods and results will enhance our understanding of functionally relevant bimolecular electron transfer reactions and thus will pave the road to rational optimization of photocatalytic performance.

Temperature-Dependent Broadening of the Ultraviolet Photoelectron Spectrum of Au(110).

To determine the thermodynamic temperature of a solid surface from the electron energy distribution measured by photoelectron spectroscopy, it is necessary to accurately evaluate the energy broadening of the photoelectron spectrum and investigate its temperature dependence. Broadening functions in the photoelectron spectrum of Au(110)'s surface near the Fermi level were estimated successfully using the relationship between the Fourier transform and the convolution integral. The Fourier transform could simultaneously reduce the noise of the spectrum when the broadening function was derived. The derived function was in the form of a Gaussian, whose width depended on the thermodynamic temperature of the sample and became broader at higher temperatures. The results contribute to improve accuracy of the determination of thermodynamic temperature from the photoelectron spectrum and provide useful information on the temperature dependence of electron scattering in photoelectron emission processes.

Calibration and Testing of Small High-Resolution Transition Edge Sensor Microcalorimeters with Optical Photons.

Pulses of narrow line-width optical photons can be used to calibrate and test sub-2 eV full-width at halfmaximum (FWHM) energy resolution transition-edge sensor (TES) microcalorimeters at low energies (< 1 keV), where it is very challenging to obtain X-ray calibration lines comparable to (or narrower than) the detector resolution. This scheme depends on the ability to resolve the number of 3 eV photons in each pulse, which we have recently demonstrated up to photon numbers of about 300. At LTD-18 we showed preliminary results obtained with this technique on a 0.25 eV baseline resolution TES microcalorimeter designed for the ultra-high-resolution subarray of the Lynx mission. The line-shape was well described by a simple Gaussian. However, the difficulty of delivering photons to the small 46 µm square absorbers resulted in a large thermal crosstalk signal, whose random nature is expected to rapidly degrade the observed energy resolution towards higher photon numbers/energies. We have since improved the coupling between the optical fiber and the TES absorber and report here our current results.

Performance of the BL03U beamline at SSRF.

The vacuum ultraviolet beamline BL03U with a photon energy range from 7 eV upwards has been constructed at the 3.5 GeV Shanghai Synchrotron Radiation Facility. Equipped with an APPLE-Knot undulator, this beamline is dedicated to angle-resolved photoemission spectroscopy. An energy-resolving power of higher than 4.6 × 104 has been achieved in the photon energy range 21.6-48 eV, which is almost the same as the theoretical estimation.

Performance of Optical Coupling Materials in Scintillation Detectors Post Temperature Exposure.

In this paper, the room-temperature performance of different optical coupling materials post temperature exposure was tested. The tested couplers included OC431A-LVP, OG0010 optical grease, BLUESIL V-788, and SAINT-GOBAIN BC-630. This was done by subjecting the whole detector with newly applied optical coupling materials to a 2-h temperature exposure-ranging from -20 to 50 °C and then by letting it return to room temperature before collecting a spectrum from a Cs-137 source. The energy resolution at 662 keV was computed as the metric for evaluating the performance. Three trials were run at each coupler-temperature combination. Our results reveal that the performance of all coupling agents do indeed change with temperature after the 2-h exposure. Over all the tested temperature trials, the energy resolution ranged from 11.4 to 14.3% for OC431A-LVP; 10.2 to 14.6% for OG0010; 10 to 13.4% for BLUESIL V-788; and 9.8 to 13.3% for SAINT-GOBAIN BC-630. OC431A-LVP had the lowest variance over the full range, while BC-630 was the most constant for temperatures above 20 °C. Ultraviolet-visible (UV-Vis) spectra experiments were also performed on isolated optical coupling materials to measure the light absorption coefficient. The results show that the temperature-induced variance in light absorption coefficient of each optical coupling materials is one of the reasons for the variance in energy resolution performance. Our findings suggest the need for further investigation into this effect and the recommendation that optical coupling materials need to be selected for the task at hand with greater scrutiny.

Design and Evaluation of LYSO/SiPM LIGHTENING PET Detector with DTI Sampling Method.

Positron emission tomography (PET) has a wide range of applications in the treatment and prevention of major diseases owing to its high sensitivity and excellent resolution. However, there is still much room for optimization in the readout circuit and fast pulse sampling to further improve the performance of the PET scanner. In this work, a LIGHTENING® PET detector using a 13 × 13 lutetium-yttrium oxyorthosilicate (LYSO) crystal array read out by a 6 × 6 silicon photomultiplier (SiPM) array was developed. A novel sampling method, referred to as the dual time interval (DTI) method, is therefore proposed to realize digital acquisition of fast scintillation pulse. A semi-cut light guide was designed, which greatly improves the resolution of the edge region of the crystal array. The obtained flood histogram shown that all the 13 × 13 crystal pixels can be clearly discriminated. The optimum operating conditions for the detector were obtained by comparing the flood histogram quality under different experimental conditions. An average energy resolution (FWHM) of 14.3% and coincidence timing resolution (FWHM) of 972 ps were measured. The experimental results demonstrated that the LIGHTENING® PET detector achieves extremely high resolution which is suitable for the development of a high performance time-of-flight PET scanner.

Energy calibration of high-resolution X-Ray TES microcalorimeters with 3 eV optical photons.

With the improving energy resolution of transitionedge sensor (TES) based microcalorimeters, performance verification and calibration of these detectors has become increasingly challenging, especially in the energy range below 1 keV where fluorescent atomic X-ray lines have linewidths that are wider than the detector energy resolution and require impractically high statistics to determine the gain and deconvolve the instrumental profile. Better behaved calibration sources such as grating monochromators are too cumbersome for space missions and are difficult to use in the lab. As an alternative, we are exploring the use of pulses of 3 eV optical photons delivered by an optical fiber to generate combs of known energies with known arrival times. Here, we discuss initial results of this technique obtained with 2 eV and 0.7 eV resolution X-ray microcalorimeters. With the 2 eV detector, we have achieved photon number resolution for pulses with mean photon number up to 133 (corresponding to 0.4 keV).

Tutorial on X-ray photon counting detector characterization.

BACKGROUND: Recent advances in photon counting detection technology have led to significant research interest in X-ray imaging. OBJECTIVE: As a tutorial level review, this paper covers a wide range of aspects related to X-ray photon counting detector characterization. METHODS: The tutorial begins with a detailed description of the working principle and operating modes of a pixelated X-ray photon counting detector with basic architecture and detection mechanism. Currently available methods and techniques for charactering major aspects including energy response, noise floor, energy resolution, count rate performance (detector efficiency), and charge sharing effect of photon counting detectors are comprehensively reviewed. Other characterization aspects such as point spread function (PSF), line spread function (LSF), contrast transfer function (CTF), modulation transfer function (MTF), noise power spectrum (NPS), detective quantum efficiency (DQE), bias voltage, radiation damage, and polarization effect are also remarked. RESULTS: A cadmium telluride (CdTe) pixelated photon counting detector is employed for part of the characterization demonstration and the results are presented. CONCLUSIONS: This review can serve as a tutorial for X-ray imaging researchers and investigators to understand, operate, characterize, and optimize photon counting detectors for a variety of applications.

Study on the reflectivity properties of spherically bent analyser crystals. Corrigendum.

Corrections to the paper by Honkanen et al. (2014). [J. Synchrotron Rad. 21, 104-110] are made.

High-Energy-Resolution X-ray Absorption Spectroscopy for Identification of Reactive Surface Species on Supported Single-Site Iridium Catalysts.

We report high-energy-resolution X-ray absorption spectroscopy detection of ethylene and CO ligands adsorbed on catalytically active iridium centers isolated on zeolite HY and on MgO supports. The data are supported by density functional theory and FEFF X-ray absorption near-edge modelling, together with infrared (IR) spectra. The results demonstrate that high-energy-resolution X-ray absorption spectra near the iridium LIII (2p3/2 ) edge provide clearly ascribable, distinctive signatures of the ethylene and CO ligands and illustrate effects of supports and other ligands. This X-ray absorption technique is markedly more sensitive than conventional IR spectroscopy for characterizing surface intermediates, and it is applicable to samples having low metal loadings and in reactive atmospheres and is expected to have an increasing role in catalysis research by facilitating the determination of mechanisms of solid-catalyzed reactions through identification of reaction intermediates in working catalysts.

A Low-Noise X-ray Astronomical Silicon-On-Insulator Pixel Detector Using a Pinned Depleted Diode Structure.

This paper presents a novel full-depletion Si X-ray detector based on silicon-on-insulator pixel (SOIPIX) technology using a pinned depleted diode structure, named the SOIPIX-PDD. The SOIPIX-PDD greatly reduces stray capacitance at the charge sensing node, the dark current of the detector, and capacitive coupling between the sensing node and SOI circuits. These features of the SOIPIX-PDD lead to low read noise, resulting high X-ray energy resolution and stable operation of the pixel. The back-gate surface pinning structure using neutralized p-well at the back-gate surface and depleted n-well underneath the p-well for all the pixel area other than the charge sensing node is also essential for preventing hole injection from the p-well by making the potential barrier to hole, reducing dark current from the Si-SiO2 interface and creating lateral drift field to gather signal electrons in the pixel area into the small charge sensing node. A prototype chip using 0.2 µm SOI technology shows very low readout noise of 11.0 e-rms, low dark current density of 56 pA/cm² at -35 °C and the energy resolution of 200 eV(FWHM) at 5.9 keV and 280 eV (FWHM) at 13.95 keV.

Optimization of the design for beamline with fast polarization switching elliptically polarized undulators.

Fast switching of X-ray polarization with a lock-in amplifier is a good method for acquiring weak signals from background noise for X-ray magnetic circular dichroism (XMCD) experiments. The usual way to obtain a beam with fast polarization switching is to use two series of elliptically polarized undulators (tandem twin EPUs). The two EPUs generate two individual beams. Each beam has a different polarization and is fast switched into the beamline. It is very important to ensure that the energy resolution, the flux and the spot size at the sample of the two beams are equal in XMCD experiments. However, it is difficult in beamline design because the distances from the two EPUs to the beamline optics are different and the beamline is not switchable. In this work, a beamline design without an entrance slit for fast polarization switching EPUs is discussed. The energy resolution of the two beams can be tuned to be equal by minor rotation of the optics in the monochromator. The flux of the two beams can be balanced through separation blades X, Y in the exit slit, and by adjusting the position of the X blades along the beam. The spot size of the two beams can be adjusted to be equal by shifting the sample as well.