Mn Kα Research Articles

High temperature X-ray and γ-ray spectroscopy with a diamond detector

A single crystal chemical vapour deposition diamond detector was electrically characterised and then investigated as a spectroscopic photon counting X-ray and γ-ray detector across the temperature range, T, −20 °C ≤ T ≤ 100 °C. The detector was connected to a custom-built charge-sensitive preamplifier of low electronic noise and illuminated in turn by 55Fe radioisotope X-ray and 109Cd radioisotope X-ray and γ-ray sources. In combination, the radiation sources provided characteristic soft (e.g. 5.9 keV) and hard (e.g. 22.16 keV) X-rays and 88.03 keV γ-ray emissions. The Mn Kα (5.9 keV) and Kβ (6.49 keV) X-ray emissions from the 55Fe radioisotope X-ray source were detected (and separated from the zero energy noise peak) at temperatures of −20 °C ≤ T ≤ 60 °C; the Ag Kα (22.16 and 21.99 keV) and Kβ (24.94, 24.99, and 25.46 keV) X-ray emissions and 88.03 keV γ-ray emissions were detectable across the entire temperature range investigated (−20 °C ≤ T ≤ 100 °C). The detector and the preamplifier were operated without cooling across the entire temperature range. The energy resolution (full width at half maximum) at 22.16 keV (Ag Kα1) was 4.57 keV ± 0.26 keV at 100 °C and 2.70 keV ± 0.18 keV at −20 °C. Noise analysis indicated that the combination of dielectric noise and any incomplete charge collection noise present dominated the other noise components at 5.9 keV. When the detector was illuminated with the 109Cd radioisotope X-ray and γ-ray source, a high count rate introduced parasitic effects (possibly baseline shift) which reduced the optimum shaping time of the spectrometer.

A new collimated multichannel modular detection system based on Silicon Drift Detectors

After the manufacture and delivery of a state-of-the-art detection system for the XRF-XAFS beamline of the synchrotron light source SESAME, a new and improved detection system was realized. This new multichannel modular detection system based on Silicon Drift Detectors consists of 8 monolithic multipixel arrays, each comprising 8 SDD cells with a total area of 570 mm2. As the previous one, this 64 channels integrated detection system includes ultra-low-noise front-end electronics, dedicated acquisition system, digital filtering, temperature control and stabilization. With respect to the SESAME version, the new instrument implements a tungsten collimation system yielding a total collimated sensitive area of 500 mm2. Optimized to work in an energy range of 3–30 keV, the system shows an overall energy resolution (sum of its 64 cells) below 180 eV FWHM at the 5.9 Mn Kα line at room temperature. We highlight the system performance and in particular the peak to background ratio, before and after the collimation of the sensors.

Development of serial X-ray fluorescence holography for radiation-sensitive protein crystals.

X-ray fluorescence holography (XFH) is a powerful atomic resolution technique capable of directly imaging the local atomic structure around atoms of a target element within a material. Although it is theoretically possible to use XFH to study the local structures of metal clusters in large protein crystals, the experiment has proven difficult to perform, especially on radiation-sensitive proteins. Here, the development of serial X-ray fluorescence holography to allow the direct recording of hologram patterns before the onset of radiation damage is reported. By combining a 2D hybrid detector and the serial data collection used in serial protein crystallography, the X-ray fluorescence hologram can be directly recorded in a fraction of the measurement time needed for conventional XFH measurements. This approach was demonstrated by obtaining the Mn Kα hologram pattern from the protein crystal Photosystem II without any X-ray-induced reduction of the Mn clusters. Furthermore, a method to interpret the fluorescence patterns as real-space projections of the atoms surrounding the Mn emitters has been developed, where the surrounding atoms produce large dark dips along the emitter-scatterer bond directions. This new technique paves the way for future experiments on protein crystals that aim to clarify the local atomic structures of their functional metal clusters, and for other related XFH experiments such as valence-selective XFH or time-resolved XFH.

Design and fabrication of quasi-double-sided silicon drift detector for x-ray detection

Silicon drift detectors (SDDs) with excellent energy resolution are widely used in the field of x-ray detection. Normally, the higher energy resolution of a SDD is mainly due to the lower capacitance compared with other silicon radiation detectors. It is worth noting that the energy resolution is also related to imperfect charge collection and ballistic deficit, which are susceptible to the device drift voltage. However, the maximum drift voltage is limited to twice the depletion voltage because of the reach-through effect in a classical SDD. In order to address this issue, a novel quasi-double-sided silicon drift detector (QD-SDD) was designed and fabricated by the thin film deposition technology. The so-called QD-SDD consists of a symmetrical drift ring structure on both the front and bottom sides. According to the simulation results, QD-SDD can be biased at a larger drift voltage, and thus building a larger drift electrical field than the classical single-sided SDD. Furthermore, the fabricated QD-SDD sensors were characterized using a 55-Fe radioactive source. The energy resolution at the 5.9 keV Mn Kα line can be improved from 210 eV to 170 eV by increasing the bias voltage on the outermost drift ring on both sides from −80 V to −130 V.

ARDESIA-16: a 16-channel SDD-based spectrometer for energy dispersive X-ray fluorescence spectroscopy

We present ARDESIA-16, an X-ray spectrometer based on a monolithic 16-element Silicon Drift Detector (SDD) matrix specifically designed for synchrotron applications. In this work, we describe the main design guidelines which we followed concerning the signal throughput, the energy efficiency, the energy resolution and the overall solid angle covered by detector elements. The characterization of the spectrometer has been made both with radioactive sources in a laboratory environment and with synchrotron light at the P06 beamline (DESY, Hamburg). Experimental results showed an average energy resolution at the optimum peaking time equal to 125 eV (FWHM at Mn Kα), a maximum achieved Output Count Rate (OCR) equal to 17 Mcps, an increase of the energy efficiency above 10 keV thanks to the 1 mm-thick SDD and an overall solid angle equal to 0.4 sr. Finally, we report the first X-ray fluorescence microscopy (XFM) images acquired with an ARDESIA spectrometer.

Highly-sensitive Analysis of Fluorescence XANES at Europium (Eu) LIII-edge for the Determination of Oxidation State for Trace Amount of Eu in Natural Samples by Bragg-type Crystal Analyzer System

X-ray absorption near-edge structure (XANES) spectra for trace amount of Eu (<1 mg/kg) in natural samples were determined in fluorescence mode using a Bragg-type crystal analyzer system. Effective separation of Eu Lα and Mn Kα emissions by the system allowed us to measure XANES with high sensitivity. Sharpening of the XANES peak by the suppression of the inner-shell lifetime-broadening effect using high energy resolution fluorescence detection (HERFD) also contributed to determination of small amount (= 0.01) of Eu(II) relative to Eu(III) based on XANES spectra.

High temperature ([formula omitted] 160 °C) X-ray and [formula omitted] particle diamond detector

A single crystal CVD diamond detector (110μm thick) with Al contacts (11.34 mm2) was characterised as an X-ray and β− particle detector using an 55Fe radioisotope X-ray source (Mn Kα=5.9 keV, Mn Kβ=6.49 keV) and a 63Ni radioisotope β− particle source (66 keV endpoint energy). The characterisation was performed across the temperature range 160 °C to -20 °C and at applied potential differences from −400 V to +400 V (3.6 V μm−1 applied electric field strength). X-ray photocurrent and β− particle current measurements along with theoretical calculations demonstrated that the detector could detect both types of radiation with similar apparent charge collection efficiency.

Thickness measurement of low-Z films fabricated on thick substrate using EDXRF technique

The present work reports a method for thickness measurements of low-Z films deposited on a thick substrate using energy dispersive X-ray fluorescence (EDXRF) technique. For this, ZnO and single-wall carbon nanotubes (SWCNTs) films (thickness ~ 1–100 mm) were fabricated on thick Si substrates using a sol-gel spin coating technique. The fabricated films were characterized using X-ray diffraction (XRD) and atomic force microscope (AFM) measurements. The thicknesses of fabricated films were determined from the measured attenuation of Si-Kαβ characteristics X-rays emitted from the thick Si substrate in coated materials. The thick substrate was excited by Mn Kα (5.895 keV) and Kβ (6.492 keV) X-rays obtained from annular 55Fe radioactive source in reflection mode geometrical setup. The emitted characteristics X-rays were detected by a low energy Ge (LEGe) detector coupled with PC based multichannel analyzer. The obtained results show good agreement with the values obtained from well-established X-ray fluorescence (XRF) and atomic force microscopy (AFM) measurements. The experimental results recommend the use of reported methodology for thickness measurement of low-Z materials deposited on a thick substrate for material characterization in future.

Al0.6Ga0.4As x-ray avalanche photodiodes for spectroscopy

Two circular Al0.6Ga0.4As p+-i-n+ 2 µm i layer spectroscopic x-ray avalanche photodiodes (one 200 µm diameter and one 400 µm diameter) were made from a structure produced by metalorganic vapour phase epitaxy. The capacitances and currents of the detectors as functions of applied bias were measured, and 55Fe x-ray (Mn Kα = 5.9 keV; Mn Kβ = 6.49 keV) spectra were accumulated at 20 °C (293 K). Improved energy resolutions (measured as the full width at half maximum of the 5.9 keV peak) with increased applied reverse bias were observed with both detectors. In part, the improvement was attributed to avalanche multiplication. Energy resolutions of 630 eV ± 40 eV and 730 eV ± 50 eV were achieved with the 200 µm detector at an applied reverse bias of 38 V and the 400 µm detector at an applied reverse bias of 40 V, respectively. It is the first time Al0.6Ga0.4As has been demonstrated as capable of photon counting x-ray spectrometry. Measurements to determine the average electron-hole pair creation energy in Al0.6Ga0.4As were made; the results suggested a value of 4.97 eV ± 0.12 eV at 25 °C ± 1 °C (298 K ± 1 K). This value was then used to refine the apparent relationship between bandgap energy and electron-hole pair creation energy as defined by the Bertuccio–Maiocchi–Barnett relationship. AlxGa1-xAs x-ray photodiodes of this type are anticipated to be of benefit for future space missions, including those to explore the surfaces of the inner planets (e.g. Mercury and Venus) and the moons of Jupiter and Saturn.

GaAs/Al0.8Ga0.2As separate absorption and multiplication region x-ray spectroscopic avalanche photodiodes

A GaAs/Al0.8Ga0.2As separate absorption and multiplication (SAM) x-ray avalanche photodiode (APD) structure was grown by metalorganic vapor phase epitaxy. Mesa photodiodes of different diameters (200 μm and 400 μm) were fabricated from the structure. Two of the photodiodes (one of each diameter) were characterized at 20 °C for their electrical properties and response to x rays using an 55Fe radioisotope x-ray (Mn Kα = 5.9 keV; Mn Kβ = 6.49 keV) source. An energy resolution of 508 eV ± 5 eV full width at half maximum (FWHM) at 5.9 keV was achieved at an apparent avalanche gain, M, of 1.1. This is the best energy resolution so far reported for GaAs/AlxGa1−xAs x-ray SAM APDs. The noise components associated with the achievable spectroscopic energy resolutions are reported. Comparisons between the 200 μm and 400 μm diameter GaAs/AlxGa1−xAs SAM x-ray APDs and recently studied GaAs p+-i-n+ detectors were made, showing that the inclusion of the avalanche layer improves the achievable energy resolution; energy resolutions of 508 eV FWHM at 5.9 keV at M = 1.1 and 603 eV FWHM at 5.9 keV at M = 1.2 were achieved with the 200 μm and 400 μm diameter GaAs/AlxGa1−xAs SAM x-ray APDs, respectively; this is better than was previously reported for similar devices without avalanche layers: 690 eV FWHM at 5.9 keV and 730 eV FWHM at 5.9 keV for 200 μm and 400 μm diameter GaAs p+-i-n+ detectors, respectively [Lioliou et al., J. Appl. Phys. 122, 244506 (2017)].

X-ray fluorescence analysis of metal distributions in cryogenic biological samples using large-acceptance-angle SDD detection and continuous scanning at the Hard X-ray Micro/Nano-Probe beamline P06 at PETRA III.

A new Rococo 2 X-ray fluorescence detector was implemented into the cryogenic sample environment at the Hard X-ray Micro/Nano-Probe beamline P06 at PETRA III, DESY, Hamburg, Germany. A four sensor-field cloverleaf design is optimized for the investigation of planar samples and operates in a backscattering geometry resulting in a large solid angle of up to 1.1 steradian. The detector, coupled with the Xspress 3 pulse processor, enables measurements at high count rates of up to 106 counts per second per sensor. The measured energy resolution of ∼129 eV (Mn Kα at 10000 counts s-1) is only minimally impaired at the highest count rates. The resulting high detection sensitivity allows for an accurate determination of trace element distributions such as in thin frozen hydrated biological specimens. First proof-of-principle measurements using continuous-movement 2D scans of frozen hydrated HeLa cells as a model system are reported to demonstrate the potential of the new detection system.

Atomic structure stabilization in BiFeO3 thin film by Mn doping

This study experimentally investigated the atomic structure of a single-crystalline Mn-doped BiFeO3 (BFO) thin film using X-ray fluorescence holography with synchrotron radiation. Bi atoms can be reconstructed from both Fe Kβ and Mn Kα fluorescence X-ray holograms, indicating Mn doping at B sites in ABO3-type perovskite structure. The fluorescence intensity of the 1st to 4th nearest Bi atoms around target Fe atoms was lower than those around Mn atoms, confirming the selective formation of Bi vacancies around Fe atoms. In contrast, the 5th to 8th nearest Bi atoms around Fe atoms showed higher intensities than those around Mn atoms, indicating that the Mn-doped BFO thin film had a double-perovskite-like structure. These results provide important information that helps elucidate the mechanism by which Mn doping modifies the conductivity of BFO.

High temperature AlInP X-ray spectrometers

Two custom-made Al0.52In0.48P p+-i-n+ mesa photodiodes with different diameters (217 µm ± 15 µm and 409 µm ± 28 µm) and i layer thicknesses of 6 µm have been electrically characterised over the temperature range 0 °C to 100 °C. Each photodiode was then investigated as a high-temperature-tolerant photon counting X-ray detector by connecting it to a custom-made low-noise charge-sensitive preamplifier and illuminating it with an 55Fe radioisotope X-ray source (Mn Kα = 5.9 keV; Mn Kβ = 6.49 keV). At 100 °C, the best energy resolutions (full width at half maximum at 5.9 keV) achieved using the 217 µm ± 15 µm diameter photodiode and the 409 µm ± 28 µm diameter photodiode were 1.31 keV ± 0.04 keV and 1.64 keV ± 0.08 keV, respectively. Noise analysis of the system is presented. The dielectric dissipation factor of Al0.52In0.48P was estimated as a function of temperature, up to 100 °C. The results show the performance of the thickest Al0.52In0.48P X-ray detectors so far reported at high temperature. The work has relevance for the development of novel space science instrumentation for use in hot space environments and extreme terrestrial applications.

Poisson vs. Gaussian statistics for sparse X-ray data: Application to the soft X-ray spectrometer

Abstract Reliable results when fitting X-ray data require proper consideration of the statistics involved. We probe the impact of Gaussian versus Poisson statistics at low count levels using both the standard χ2 method and maximum likelihood based on Poisson (C) statistics. The difference is studied and quantified through simulated spectra with known properties. We then test the results through analysis of Mn Kα calibration data taken with the flight spare microcalorimeter for the Hitomi soft X-ray spectrometer. Through comparison with simulations, our results show that the χ2 method tends to give overly optimistic estimates of the detector energy resolution, in particular when there are few counts. Given an energy resolution of ∼5 eV and a line with about 100 photons, the line width becomes ∼10% lower in the χ2 method than in Poisson statistics. This is a consequence of the uncertainties being dominated by counting statistics, and therefore highlights the need to choose the appropriate fit statistic.

Demonstration of Athena X-IFU Compatible 40-Row Time-Division-Multiplexed Readout.

Time-division multiplexing (TDM) is the backup readout technology for the X-ray Integral Field Unit (X-IFU), a 3,168-pixel X-ray transition-edge sensor (TES) array that will provide imaging spectroscopy for ESA's Athena satellite mission. X-0IFU design studies are considering readout with a multiplexing factor of up to 40. We present data showing 40-row TDM readout (32 TES rows + 8 repeats of the last row) of TESs that are of the same type as those being planned for X-IFU, using measurement and analysis parameters within the ranges specified for X-IFU. Singlecolumn TDM measurements have best-fit energy resolution of (1.91 ± 0.01) eV for the Al Kα complex (1.5 keV), (2.10 ± 0.02) eV for Ti Kα (4.5 keV), (2.23 ± 0.02) eV for Mn Kα (5.9 keV), (2.40 ± 0.02) eV for Co Kα (6.9 keV), and (3.44 ± 0.04) eV for Br Kα (11.9 keV). Three-column measurements have best-fit resolution of (2.03 ± 0.01) eV for Ti Kα and (2.40 ± 0.01) eV for Co Kα. The degradation due to the multiplexed readout ranges from 0.1 eV at the lower end of the energy range to 0.5 eV at the higher end. The demonstrated performance meets X-IFU's energy-resolution and energy-range requirements. True 40-row TDM readout, without repeated rows, of kilopixel scale arrays of X-IFU-like TESs is now under development.

Kα X-ray Emission Spectroscopy on the Photosynthetic Oxygen-Evolving Complex Supports Manganese Oxidation and Water Binding in the S3 State.

The unique manganese-calcium catalyst in photosystem II (PSII) is the natural paragon for efficient light-driven water oxidation to yield O2. The oxygen-evolving complex (OEC) in the dark-stable state (S1) comprises a Mn4CaO4 core with five metal-bound water species. Binding and modification of the water molecules that are substrates of the water-oxidation reaction is mechanistically crucial but controversially debated. Two recent crystal structures of the OEC in its highest oxidation state (S3) show either a vacant Mn coordination site or a bound peroxide species. For purified PSII at room temperature, we collected Mn Kα X-ray emission spectra of the S0, S1, S2, and S3 intermediates in the OEC cycle, which were analyzed by comparison to synthetic Mn compounds, spectral simulations, and OEC models from density functional theory. Our results contrast both crystallographic structures. They indicate Mn oxidation in three S-transitions and suggest additional water binding at a previously open Mn coordination site. These findings exclude Mn reduction and render peroxide formation in S3 unlikely.

Al0.2Ga0.8As 2 [formula omitted] 2 square pixel X-ray photodiode array

A monolithic 2 × 2 square pixel Al0.2Ga0.8As p+–i–n+ mesa X-ray photodiode array (each photodiode area 200 μm by 200 μm, 3μm i layer) has been fabricated from material grown by MOVPE. The array was electrically characterised across the temperature range 100 °C to -20 °C. Each pixel’s response to illumination with soft X-rays from an 55Fe radioisotope X-ray source (Mn Kα=5.9 keV; Mn Kβ=6.49 keV) was investigated across the temperature range 30 °C to -20 °C. The best energy resolution (FWHM at 5.9 keV) achieved at 20 °C was 0.76 keV ± 0.06 keV (with 30 V reverse bias applied to the detector). The measured energy resolution is the best so far reported for AlGaAs X-ray photodiodes at 20 °C. It is also the first time a small AlGaAs X-ray photodiode array has been demonstrated. Due to the temperature tolerance and the radiation hardness of AlGaAs, such detectors are expected to find utility in future space science missions exposed to intense radiation environments, for example missions to study the Jovian or Saturnian aurorae and high temperature planetary surfaces.

Temperature dependence of Al0.2Ga0.8As X-ray photodiodes for X-ray spectroscopy

Two custom-made Al0.2Ga0.8As p+-i-n+ mesa X-ray photodiodes (200 μm diameter, 3 μm i layer) have been electrically characterised across the temperature range −20 °C to 60 °C. The devices were connected to a custom-made charge sensitive preamplifier to produce an AlGaAs photon-counting X-ray spectrometer. The devices' responses to illumination with soft X-rays from an 55Fe radioisotope X-ray source (Mn Kα = 5.9 keV; Mn Kβ = 6.49 keV) were investigated across the temperature range −20 °C to 20 °C. The best energy resolution (FWHM at 5.9 keV) achieved at 20 °C was 1.06 keV (with the detector at 10 V reverse bias). Improved FWHM was observed with the devices at temperatures of 0 °C (0.86 keV) and −20 °C (0.83 keV) with the photodiode reverse biased at 30 V. The average electron hole pair creation energy was experimentally measured and determined to be 4.43 eV ± 0.09 eV at 20 °C, 4.44 eV ± 0.10 eV at 0 °C, and 4.56 eV ± 0.10 eV at −20 °C.

CCD camera as feasible large-area-size x-ray detector for x-ray fluorescence spectroscopy and imaging

As X-ray fluorescence radiation isotropically spreads from the sample, one of the most important requirements for spectrometers for many years has been a large solid angle. Charge-coupled device (CCD) cameras are quite promising options because they have a fairly large area size, usually larger than 150 mm2. The present work has examined the feasibility of a commercially available camera with an ordinary CCD chip (1024 × 1024 pixels, the size of one pixel is 13 μm × 13 μm, designed for visible light) as an X-ray fluorescence detector. As X-ray photons create charges in the CCD chip, reading very quickly the amount is the key for this method. It is very simple if the charges always go into one pixel. As the charges quite often spread to several pixels, and sometimes can be lost, it is important to recover the information by filtering out the unsuccessful events. For this, a simple, versatile, and reliable scheme has been proposed. It has been demonstrated that the energy resolution of the present camera is 150 eV at Mn Kα, and also that its overall achievement in seeing minor elements is almost compatible with conventional X-ray fluorescence detectors. When the CCD camera is combined with a micro-pinhole collimator, full field X-ray fluorescence imaging with a spatial resolution of 20 μm becomes possible. Further feasibility in practical X-ray fluorescence analysis is discussed.

Al0.2Ga0.8As X-ray photodiodes for X-ray spectroscopy

Three custom-made Al0.2Ga0.8As p-i-n mesa X-ray photodiodes (200µm diameter, 3µm i layer) were electrically characterised and investigated for their response to illumination with soft X-rays from an 55Fe radioisotope X-ray source (Mn Kα = 5.9keV; Mn Kβ = 6.49keV). The AlGaAs photodiodes were shown to be suitable for photon counting X-ray spectroscopy at room temperature. When coupled to a custom-made low-noise charge-sensitive preamplifier, a mean energy resolution (as quantified by the full width at half maximum of the 5.9keV photopeak) of 1.24keV was measured at room temperature. Parameters such as the depletion width (1.92µm at 10V), charge trapping noise (61.7 e−rms ENC at 5V, negligible at 10V) and the electronic noise components (known dielectric noise (63.4 e− rms), series white noise (27.7 e−rms), parallel white noise (9.5 e−rms) and 1/f series noise (2.2 e−rms) at 10V reverse bias) affecting the achieved energy resolution were computed. The estimated charge trapping noise and mean energy resolution were compared to similar materials (e.g. Al0.8Ga0.2As) previously reported, and discussed. These results are the first demonstration of photon counting X-ray spectroscopy with Al0.2Ga0.8As reported to date.