X-ray Spectroscopy Applications Research Articles

Energy response of AlGaAs soft X-ray photon counting detectors

A variety of new types of detectors based on wide bandgap materials have been developed for soft X-ray spectroscopy applications(e.g. GaAs, SiC, diamond). In this report we describe the spectroscopicperformance of a simple p-i-n diode fabricated on AlGaAs. The energyresponse of the diode, operating in photon counting mode, at roomtemperature has been investigated using fluorescence from a number of highpurity materials. X-ray spectra over the energy range 5 keV–25 keV showthis type of diode can be used for spectroscopy with promising energyresolution ( ∼ 1.3 keV) at 30°C and excellent linearity.

Characterization and Performance of Magnetic Calorimeters for Applications in X-ray Spectroscopy

We have developed prototype arrays of metallic magnetic calorimeters for applications in X-ray astronomy. Each pixel consists of an all-gold X-ray absorber in good thermal contact to a gold-erbium paramagnetic thin film thermometer that is operated in the temperature range of 30–100 mK. The para-magnetic response is coupled to a SQUID amplifier. We have characterized pixels in an array and observed the expected temperature dependence of the magnetization and heat capacity. We have demonstrated a full width at half maximum energy resolution of 1.7 \(\pm \) 0.1 eV at 6 keV and have also read out these devices using time-division multiplexing.

VERITAS: A 128-Channel ASIC for the Readout of pnCCDs and DEPFET Arrays for X-Ray Imaging, Spectroscopy and XFEL Applications

VERITAS (VErsatile Readout based on Integrated Trapezoidal Analog Shapers) is the first 128-channel ASIC developed to read out both the pnCCDs and the DEPFET arrays produced at the MPI-Halbleiterlabor in Munich. These detectors are used in a large variety of scientific applications, ranging from high-speed optical astronomy and X-ray astronomy to the new X-ray Free Electron Laser sources. The main concept of VERITAS is to provide a flexible readout chip able to cope not only with different kinds of detectors, but also with a large set of operating conditions that may require very different noise thresholds and input dynamic ranges. These can vary by more than two orders of magnitude. Every analog channel of VERITAS provides a trapezoidal weighting function. This filtering strategy had never been applied to the pnCCD before. The very first measurements obtained coupling VERITAS with a 128 × 256 pnCCD are shown. With a readout time of 4 μs/line a noise of 3.9 electrons has been measured in the highest gain mode. The resolution obtained on the Mn-Kα peak of a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">55</sup> Fe source is 136 eV for single events. A noise of 30 electrons has been achieved in the lowest gain mode at a speed of 6.4 μs/line. In this low gain setting an input charge up to 2 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> electrons can be processed. These striking results fulfill the requirements of the main foreseen applications of large-size pnCCDs. In order to further improve the performance and the flexibility of the ASIC, a second version based on a fully differential architecture has been designed. The new topology allows one also to switch with the same ASIC between the source follower and drain current readout of the DEPFET sensors and to reach a processing time of about 2-3 μs/line with an electronics noise ≤10 el. For this reason the second version of VERITAS is very attractive for the proposed ESA X-ray astronomy mission ATHENA.

A Multichannel Integrated Readout Circuit for High Throughput X-Ray Spectroscopy With Silicon Drift Detectors

In this paper, we describe a front-end ASIC for the readout of multi-elements Silicon Drift Detectors (SDDs) specifically designed for high count-rate X-ray spectroscopy applications. In particular, the focus of this design is on the maximization of the event throughput and, at the same time, keeping a high energy resolution. The readout of a detector array by means of 8 separate channels allows increasing the maximum count-rate of the system. The use of one or more of these front-end ASICs allows the management of several readout channels required by a multi-SDD detector within a very compact detection system, as well as maintaining excellent noise performance. The use of a very-fast high-order processing filter and of an efficient pile-up rejection strategy allows minimizing the pile-up probability and maximizing the event throughput of the single channels for a given processing time. The use of a 3-phase peak-stretcher, together with a fast output multiplexer, permits to minimize the dead-time during the valid-data acquisition, practically to a value limited by the pure overlap of the shaped pulses. The ASIC is designed with the possibility of operating with the input JFET integrated on the detector itself as well as to operate in combination with an external preamplifier. The measured noise-contribution added by the front-end ASIC is only 2.9 electrons at 1.8 μs shaping time and just 4.1 electrons at the shortest 600 ns peaking time, exploiting at best the speed capability. In X-ray spectroscopy measurements, the ASIC connected to an SDD coupled to a CMOS preamplifier has allowed to achieve an energy resolution of 126 eV at 1.5 μs peaking time and 115 kcps/channel input rate, and 144 eV at 600 ns peaking time and 800 kcps/channel input rate.

Even harder X-rays

With the laser just over half a century old, another dream of the pioneers of this light source has been fulfilled. An atomic X-ray laser with unprecedentedly high photon energy has been demonstrated. See Letter p.488 Achieving lasing at increasingly shorter wavelengths is a long-standing goal. This paper demonstrates an X-ray laser operating on an inner-shell transition in singly ionized neon — the first atomic laser in the 1 kiloelectronvolt regime. It is pumped by X-ray free electron laser (XFEL) pulses from the Linac Coherent Light Source at the SLAC National Accelerator Laboratory in Menlo Park, California. The atomic laser's high-intensity, femtosecond X-ray pulse emission has significantly improved wavelength stability, monochromaticity and temporal coherence compared with XFEL radiation. Atomic X-ray lasers could have applications in high-resolution X-ray spectroscopy and nonlinear X-ray studies.

Development of high temperature AlGaAs soft X-ray photon counting detectors

New types of detectors based on the wide band gap material AlGaAs have been developed for soft X-ray spectroscopy applications. We report on the spectroscopic performance of simple p-i-n diodes and avalanche photodiodes (APDs). A number of diode types with different layer thicknesses have also been characterised. X-ray spectra from 55Fe and 109Cd radioactive sources show these diodes can be used for spectroscopy with promising energy resolution (1.0–1.25 keV) over a -30 to +90 °C temperature range. The temperature dependence of the avalanche multiplication process at soft X-ray energies in Al0.8Ga0.2As APDs was also investigated at temperatures from -20 to +80 °C. The temperature dependence of the pure electron initiated multiplication factor (Me) and the mixed carrier initiated avalanche multiplication factor (Mmix) were extracted from the X-ray spectra. The experimental results are compared with a spectroscopic Monte Carlo model for Al0.8Ga0.2As diodes from which the temperature dependence of the pure hole initiated multiplication factor (Mh) is determined.Monte Carlo simulations for the avalanche gain of absorbed X-ray photons have also been developed to study the relationship between avalanche gain and energy resolution for semiconductor X-ray avalanche photodiodes. The model showed that the distribution of gains, which directly affects the energy resolution, depends on the number of injected electron-hole pairs (and hence the photon energy), the relationship between the two ionization coefficients, and the overall mean gain. Our model showed that the conventional notion of APD gains degrading energy resolution significantly is incomplete.We compare the Monte Carlo simulations with experimental data from a number of different Al0.8Ga0.2As diodes.

Improved x-ray spectroscopy with room temperature CZT detectors

Compact, room temperature x-ray spectroscopy detectors are of interest in many areas including diagnostic x-ray imaging, radiation protection and dosimetry. Room temperature cadmium zinc telluride (CZT) semiconductor detectors are promising candidates for these applications. One of the major problems for CZT detectors is low-energy tailing of the energy spectrum due to hole trapping. Spectral post-correction methods to correct the tailing effect do not work well for a number of reasons; thus it is advisable to eliminate the hole trapping effect in CZT using physical methods rather than correcting an already deteriorated energy spectrum. One method is using a CZT detector with an electrode configuration which modifies the electric field in the CZT volume to decrease low-energy tailing. Another method is to irradiate the CZT surface at a tilted angle, which modifies depth of interaction to decrease low-energy tailing. Neither method alone, however, eliminates the tailing effect. In this work, we have investigated the combination of modified electric field and tilted angle irradiation in a single detector to further decrease spectral tailing. A planar CZT detector with 10 × 10 × 3 mm3 size and CZT detector with 5 × 5 × 5 mm3 size and cap-shaped electrode were used in this study. The cap-shaped electrode (referred to as CAPture technology) modifies the electric field distribution in the CZT volume and decreases the spectral tailing effect. The detectors were investigated at 90° (normal) and 30° (tilted angle) irradiation modes. Two isotope sources with 59.6 and 122 keV photon energies were used for gamma-ray spectroscopy experiments. X-ray spectroscopy was performed using collimated beams at 60, 80 and 120 kVp tube voltages, in both normal and tilted angle irradiation. Measured x-ray spectra were corrected for K x-ray escape fractions that were calculated using Monte Carlo methods. The x-ray spectra measured with tilted angle CAPture detector at 60, 80 and 120 kVp tube voltages were compared to corresponding theoretical spectra. The low-energy tailing was nearly completely eliminated from 59.6 and 122 keV isotope spectra, and 60, 80 and 120 kVp x-ray spectra, when CAPture detector was used with 30° tilted angle irradiation. It is concluded that using a CZT detector with modified electric field in tilted angle configuration resolves problem of the tailing effect in CZT detectors, opening promising possibilities in gamma-ray and x-ray spectroscopy applications.

Method for determining the elemental composition and distribution in semiconductor core-shell quantum dots.

In the biological sciences, the use of core-shell quantum dots (QDs) has gained wide usage but analytical challenges still exist for characterizing the QD structure. The application of energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy (XPS) to bulk materials is relatively straightforward; however, for meaningful applications of surface science techniques to multilayer nanoparticles requires novel modifications and analysis methods. To experimentally characterize the elemental composition and distribution in CdSe/CdS/ZnS QDs, we first develop a XPS signal subtraction technique capable of separating the overlapped selenium 3s (core) and sulfur 2s (shell) peaks (both peaks have binding energies near 230 eV) with higher precision than is typically reported in the nanoparticle literature. This method is valid for any nanoparticle containing selenium and sulfur. Then we apply a correction formula to the XPS data and determine that the 2 nm stoichiometric CdSe core is surrounded by 2 CdS layers and a stoichimetric ZnS monolayer. These findings and the multiapproach methodology represent a significant advancement in the detailed surface science study of multilayer nanoparticles. In agreement with recent surprising findings, the time-of-flight secondary mass spectrometry measurements suggest that the surface sites of the QDs used in this study are primarily covered with a mixture of octadecylphosphonic acid and trioctylphophine oxide.

The physics program at the Kielce EBIS-A facility

The status of the new EBIS-A irradiation facility constructed by the Dreebit GmbH company, Dresden, for the new laboratory at the Jan Kochanowski University (JKU) in Kielce designed for the studies of ion-matter interactions is presented. The facility will be used for the interdisciplinary studies involving atoms, molecules, plasmas, surfaces and cells by taking an advantage of low-energy highly charged ions (HCI) and x-ray spectroscopy techniques. The EBIS-A facility, consisting of an EBIT-type ion source, beam guiding and diagnostic system, double focusing analyzing magnet and multipurpose target chamber, offers new opportunities for performing the experiments on slow, highly charged ions colliding with matter, including such different phenomena as formation of nanostructures in ion-surface interactions, recombination processes in plasma, fragmentation of biomolecules by ion and electron impact and the radiobiological effects in living cells. In this paper a concept of the EBIT/X-ray laboratory, construction details of the EBIS-A facility, the physics program, based on our former experimental activities in the atomic and molecular collisions, and application of x-ray spectroscopy in materials science are discussed.

Microstructural Characterization and Charge Transport in Thin Films of Conjugated Polymers

The performance of semiconducting polymers has been steadily increasing in the last 20 years. Improved control over the microstructure of these materials and a deeper understanding of how the microstructure affects charge transport are partially responsible for such trend. The development and widespread use of techniques that allow to characterize the microstructure of semiconducting polymers is therefore instrumental for the advance of these materials. This article is a review of the characterization techniques that provide information used to enhance the understanding of structure/property relationships in semiconducting polymers. In particular, the applications of optical and X-ray spectroscopy, X-ray diffraction, and scanning probe techniques in this context are described.

X-ray spectroscopy of galaxy clusters: studying astrophysical processes in the largest celestial laboratories

Galaxy clusters, the largest clearly defined objects in our Universe, are ideal laboratories to study in detail the cosmic evolution of the intergalactic intracluster medium (ICM) and the cluster galaxy population. For the ICM, which is heated to X-ray radiating temperatures, X-ray spectroscopy is the most important tool to obtain insight into the structure and astrophysics of galaxy clusters. The ICM is also the hottest plasma that can be well studied under thermal equilibrium conditions. In this review we recall the basic principles of the interpretation of X-ray spectra from a hot, tenuous plasma and we illustrate the wide range of scientific applications of X-ray spectroscopy. The determination of galaxy cluster masses, the most important prerequisite for using clusters in cosmological studies, rest crucially on a precise spectroscopic determination of the ICM temperature distribution. The study of the thermal structure of the ICM provides a very interesting fossil record of the energy release during galaxy formation and evolution, giving important constraints on galaxy formation models. The temperature and pressure distribution of the ICM gives us important insight into the process of galaxy cluster merging and the dissipation of the merger energy in form of turbulent motion. Cooling cores in the centers of about half of the cluster population are interesting laboratories to investigate the interplay between gas cooling, star- and black hole formation and energy feedback, which is diagnosed by means of X-ray spectroscopy. The element abundances deduced from X-ray spectra of the ICM provide a cosmic history record of the contribution of different supernovae to the nucleosynthesis of heavy elements and their spatial distribution partly reflects important transport processes in the ICM. Some discussion of plasma diagnostics for conditions out of thermal equilibrium and an outlook on the future prospects of X-ray spectroscopic cluster studies complete our review.

Ultrasoft X-ray spectroscopy with variation of the electron excitation energy as a method for analyzing thin films and solid/solid interfaces

The application of ultrasoft X-ray spectroscopy with variation of the electron excitation energy for phase analysis of thin films and phase reactions at solid/solid interfaces is considered. CNx nanocondensatess obtained by pulsed arc sputtering of graphite in the presence of nitrogen, silicon implanted with hydrogen ions, and Fe-Co silicides fabricated by ion-beam synthesis have been studied.

The X-Ray Spectroscopic Performance of a Very Large Area Silicon Drift Detector

Silicon drift detectors (SDDs), due to their collection electrode geometry, have excellent noise performance and are well suited for low-energy X-ray spectroscopy applications. On the other hand these detectors, when dedicated to low energy X-ray spectroscopy, have a small sensitive area (from few square millimeters up to one square centimeter) to reduce the leakage current and its impact on the energy resolution. Because of this limitation they are rarely used in applications where large sensitive surfaces are required. We present the characterization of the spectroscopic performance of a very large sensitive area SDD (about 53 cm2) that has been realized in the frame of the LHC-ALICE experiment. We studied the energy resolution of the detector analyzing its dependence on both biasing conditions and temperature to evaluate the contribution of the different noise sources exploiting their relation with the shaping time. The experimental results obtained with 241 Am and 55 Fe sources show that the goal of a high energy resolution combined with large sensitive areas can be achieved.

Applications of X-ray absorption spectroscopy to biologically relevant metal-based chemistry

Recent developments in the understanding of the biosynthesis of the active site of the nitrogenase enzyme, the structure of the iron centre of [Fe]-hydrogenase and the structure and biomimetic chemistry of the [FeFe] hydrogenase H-cluster as deduced by application of X-ray spectroscopy are reviewed. The techniques central to this work include X-ray absorption spectroscopy either in the form of extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES) and nuclear resonant vibrational spectroscopy (NRVS). Examples of the advances in the understanding of the chemistry of the system through integration of a range of spectroscopic and computational techniques with X-ray spectroscopy are highlighted. The critical role played by ab initio calculation of structural and spectroscopic properties of transition-metal compounds using density functional theory (DFT) is illustrated both by the calculation of nuclear resonance vibrational spectroscopy (NRVS) spectra and the structures and spectra of intermediates through the catalytic reactions of hydrogenase model compounds.

Fast DEPFET current readout for X-ray astronomy missions

The DEPFET-based Active Pixel Sensor (APS) matrix is a new detector concept for X-ray imaging and spectroscopy applications. This type of detector can provide excellent energy resolution and high-speed readout. Both of these features, along with the advantage of random pixel accessibility, can fulfill the requirements of new imaging applications in the X-ray band. In a matrix arrangement, each pixel must be read out by a time-variant filter, so a proper multi-channel integrated filtering amplifier is needed. To operate large area matrices at very fast processing times, we have recently proposed a current readout configuration. In this paper, we explore the performance offered by this circuit when operated with a DEPFET matrix, specifically concerning its ultimate speed capabilities and the trade-off achieved between electronics noise and processing time.

Development of X-type DEPFET Macropixel detectors

The Depleted P-channel Field Effect Transistor (DEPFET) Macropixel detectors based on the combined detector/amplifier structure have been designed for X-ray spectroscopy applications at the Max-Planck Institute (MPI) Semiconductor Laboratory. Prototypes with several design variants have been fabricated. The outstanding performance of these devices has been previously demonstrated. In this paper, the development of an improved variant is presented, which applies the so-called X-type DEPFET originally designed for XEUS mission as the readout element of a silicon drift detector. The measured energy resolution for Mn-K α line at - 30 ∘ C is 122 eV with a pixel size of 1 × 1 mm 2 . The excellent peak/background ratio of the spectra is observed with a collimated 55Fe source at - 30 ∘ C . The integral nonlinearity is less than 0.2% up to 160 keV measured with laser charge injection. Homogeneity is also studied with the laser on a computer controlled X– Y stage.

VELA: The CMOS Circuit Based on Fast Current Read-Out for X-Ray Spectroscopy With DePMOS

DePMOS based active pixel sensor (APS) matrix is a new detector concept for X-ray imaging and spectroscopy applications. This type of X-ray detector can provide excellent energy resolution and high-speed readout. Both these features and the advantage of random pixel accessibility can fulfill the requirements of new space applications, like the XEUS wide field imager. In a matrix arrangement, each pixel must be read out by a time variant filter, so a new readout mechanism and a proper multi-channel integrated shaping amplifier are needed. To operate at the required fast processing time (e.g., 4 per line) DePMOS transistor cannot be operated in the classical source follower configuration, because this results in a long settling time. So a new design for multi-channel readout of the DePMOS matrix has to be considered. We propose a new fast readout concept, which is based on the DePMOS drain current readout and processing.

An 8-Channel DRAGO Readout Circuit for Silicon Detectors With Integrated Front-End JFET

We have developed a CMOS circuit to be used with Silicon Drift Detectors (SDDs) for X-ray spectroscopy and gamma-ray imaging applications. The circuit operates with the input transistor integrated directly on the detector wafer. The circuit is composed of 8 analog channels, each including a low-noise voltage preamplifier, a 6th order semi-Gaussian shaping amplifier, with four selectable peaking times from 1.8 mus up to 6 mus, and a peak stretcher. The integrated time constant used for the shaping are implemented by means of a recently proposed 'RC' cell. This cell is based on the de- magnification of the current flowing in a resistor R thanks to the use of current mirrors. The 8 analog channels of the chip are multiplexed to a single analog output. A digital section provides self-resetting of the channels, trigger output and the external programming of independent threshold on the analog channels by means of a 3 bit DAC and a programmable serial register. In this work, the main features of the circuit are described. The measurement results obtained in the characterization of the prototype are then reported and discussed. The energy resolution measured using a single channel of the chip with a Silicon Drift Detector Droplet (SDD3) is of 128 eV at 6 keV with the detector cooled at -20degC. Spectroscopy measurements using a multi-element SDD are also shown

Structure elucidation of laser-dye coumarin-540A by joint application of X-ray diffraction, X-ray fluorescence, prompt fluorescence, UV and visible spectroscopy

X-ray, ultraviolet, and visible light induced photophysical changes of coumarin-540A in ethanol has been studied by the joint applications of X-ray, ultraviolet, and visible spectroscopy. Some impurities were found by X-ray fluorescence measurements. During the high power optical pumping, coumarin showed photochemical changes. Photoproduct emission spectra characteristics showed that photoproduct molecules could also be used as a laser-dye at a different emission frequency in the ultraviolet region.

Structure elucidation of laser dye coumarin-540A by joint application of X-ray diffraction, X-ray fluorescence, prompt fluorescence, UV and visible spectroscopy

X-ray, ultraviolet, and visible light induced photophysical changes of coumarin-540A in ethanol have been studied by the joint applications of X-ray, ultraviolet, and visible spectroscopy. Some impurities were found by X-ray fluorescence measurements. During the high power optical pumping, coumarin showed photochemical changes. Photoproduct emission spectra characteristics showed that photoproduct molecules can also be used as a laser dye at a different emission frequency in the ultraviolet region.