X-ray Spectroscopy Applications Research Articles

Gaining More Insights from Synchrotron-Based X-ray Spectroscopy for Alkali Ion Rechargeable Batteries.

Alkali ion rechargeable batteries play a significant part in portable electronic devices and electronic vehicles. The rapid development of renewable energy technology nowadays demands batteries with even higher energy density for grid storage. To fulfill such demand, extensive research efforts have been devoted to optimizing electrochemical properties as well as developing novel energy storage schemes and designing new systems. In the investigation process, synchrotron-based X-ray spectroscopy plays a vital role in investigating the detailed degradation mechanism and developing novel energy storage schemes. Herein, we critically review the applications of synchrotron-based X-ray spectroscopy in battery research in recent years. This review begins with a discussion of the different scientific issues in alkali ion rechargeable batteries within various time and space scales. Subsequently, the principle of synchrotron-based X-ray spectroscopy is introduced, and the characteristics of various characterization techniques are summarized and compared. Typical application cases of synchrotron-based X-ray spectroscopy are then introduced into battery investigations. The final part presents perspectives in the development direction of both alkali ion rechargeable battery systems and synchrotron-based X-ray spectroscopy in the future.

Efficient prediction of attosecond two-colour pulses from an X-ray free-electron laser with machine learning

X-ray free-electron lasers are sources of coherent, high-intensity X-rays with numerous applications in ultra-fast measurements and dynamic structural imaging. Due to the stochastic nature of the self-amplified spontaneous emission process and the difficulty in controlling injection of electrons, output pulses exhibit significant noise and limited temporal coherence. Standard measurement techniques used for characterizing two-coloured X-ray pulses are challenging, as they are either invasive or diagnostically expensive. In this work, we employ machine learning methods such as neural networks and decision trees to predict the central photon energies of pairs of attosecond fundamental and second harmonic pulses using parameters that are easily recorded at the high-repetition rate of a single shot. Using real experimental data, we apply a detailed feature analysis on the input parameters while optimizing the training time of the machine learning methods. Our predictive models are able to make predictions of central photon energy for one of the pulses without measuring the other pulse, thereby leveraging the use of the spectrometer without having to extend its detection window. We anticipate applications in X-ray spectroscopy using XFELs, such as in time-resolved X-ray absorption and photoemission spectroscopy, where improved measurement of input spectra will lead to better experimental outcomes.

Multicolor x-rays from free electron-driven van der Waals heterostructures.

The emergence of van der Waals (vdW) heterostructures has led to precise and versatile methods of fabricating devices with atomic-scale accuracies. Hence, vdW heterostructures have shown much promise for technologies including photodetectors, photocatalysis, photovoltaic devices, ultrafast photonic devices, and field-effect transistors. These applications, however, remain confined to optical and suboptical regimes. Here, we theoretically show and experimentally demonstrate the use of vdW heterostructures as platforms for multicolor x-ray generation. By driving the vdW heterostructures with free electrons in a table-top setup, we generate x-ray photons whose output spectral profile can be user-customized via the heterostructure design and even controlled in real time. We show that the multicolor photon energies and their corresponding intensities can be tailored by varying the electron energy, the electron beam position, as well as the geometry and composition of the vdW heterostructure. Our results reveal the promise of vdW heterostructures in realizing highly versatile x-ray sources for emerging applications in advanced x-ray imaging and spectroscopy.

Impact of Flexible Circuit Bonding and System Integration on Energy Resolution of Cross-Strip CZT Detectors.

Cadmium zinc telluride (CZT) detectors enable high spatial resolution and high detection efficiency and are utilized for many gamma-ray and X-ray spectroscopy applications. In this article, we describe a stable bonding process and report on the characterization of cross-strip CZT detectors before and after bonding to flexible circuit. The bonding process utilizes gold stud bonding and polymer epoxy technique to bond the flexible circuits to two CZT crystals and form a detector module in an anode-cathode-cathode-anode (ACCA) configuration. The readout electronics is optimized in terms of shaper setting and steering electrode voltage. The average full-width half maximum (FWHM) energy resolution at 662 keV of 110 CZT crystals tested individually was 3.5% ± 0.59% and 4.75% ± 0.48% prebonded and post-bonded, respectively. No depth correction was performed in this study. The average FWHM energy resolution at 662 keV of the scaled-up system with 80 CZT crystals was 4.40% ± 0.53%, indicating the scaled-up readout electronics and stacking of the modules does not deteriorate performance. The proper shielding and grounding of the scaled-up system slightly improved the system-wide performance. The FWHM energy resolution at 511 keV of the scaled-up system was 5.85% ± 0.73%.

Free-electron interactions with van der Waals heterostructures: a source of focused X-ray radiation

The science and technology of X-ray optics have come far, enabling the focusing of X-rays for applications in high-resolution X-ray spectroscopy, imaging, and irradiation. In spite of this, many forms of tailoring waves that had substantial impact on applications in the optical regime have remained out of reach in the X-ray regime. This disparity fundamentally arises from the tendency of refractive indices of all materials to approach unity at high frequencies, making X-ray-optical components such as lenses and mirrors much harder to create and often less efficient. Here, we propose a new concept for X-ray focusing based on inducing a curved wavefront into the X-ray generation process, resulting in the intrinsic focusing of X-ray waves. This concept can be seen as effectively integrating the optics to be part of the emission mechanism, thus bypassing the efficiency limits imposed by X-ray optical components, enabling the creation of nanobeams with nanoscale focal spot sizes and micrometer-scale focal lengths. Specifically, we implement this concept by designing aperiodic vdW heterostructures that shape X-rays when driven by free electrons. The parameters of the focused hotspot, such as lateral size and focal depth, are tunable as a function of an interlayer spacing chirp and electron energy. Looking forward, ongoing advances in the creation of many-layer vdW heterostructures open unprecedented horizons of focusing and arbitrary shaping of X-ray nanobeams.

Free-electron-driven X-ray caustics from strained van der Waals materials

Tunable control of X-ray waves remains an open challenge of critical importance for applications in high-resolution X-ray spectroscopy, medical imaging, and radiation therapy. Unlike in the X-ray regime, control over light waves in the visible and IR regimes is ubiquitous in a vast range of applications, and typically relies on widely available optical components. However, analogous optical elements for X-rays are usually inefficient and challenging to fabricate. Here, we propose a method for shaping X-ray waves directly at the source, using the interaction of free electrons with crystalline materials. Specifically, by inducing strain on van der Waals materials, we control their interaction with free electrons in a manner that tunes the emissions of the X-rays and forms caustic X-ray beams. The development of wave-shaping concepts like caustics generation in the X-ray spectral range could benefit from achievements in this field in the optical range and may help bypass the noted limits of current X-ray optics technology. Looking forward, shaping the interference of X-rays at the atomic scale could enable further developments in high-resolution X-ray science.

Kramers–Kronig relation in attosecond transient absorption spectroscopy

The Kramers–Kronig relation (KKR) has a wide range of applications in extreme ultraviolet (XUV) and x-ray spectroscopy. However, the validity of KKR for many of these applications has not been systematically studied, while it is known to require careful attention in nonlinear and pump–probe experiments in optical domain spectroscopy. Here, we study the validity of KKR in XUV attosecond transient absorption spectroscopy pump–probe measurements both experimentally and theoretically using argon Fano resonances as a case study. Experiments are enabled by a phase-resolved method dubbed Complex Attosecond Transient-absorption Spectroscopy (CATS). Although the estimations based on the rotating-wave approximation suggest that KKR violation could be expected in the studied case, our results validate KKR and provide a solid basis for its application in a broad range of attosecond spectroscopy experiments.

X-ray performance of a small pixel size sCMOS sensor and the effect of depletion depth

In recent years, scientific Complementary Metal Oxide Semiconductor (sCMOS) devices have been increasingly applied in X-ray detection, thanks to their attributes such as high frame rate, low dark current, high radiation tolerance and low readout noise. We tested the basic performance of a backside-illuminated (BSI) sCMOS sensor, which has a small pixel size of 6.5 μm × 6.5 μm. At a temperature of -20°C, The readout noise is 1.6 e-, the dark current is 0.5 e-/pixel/s, and the energy resolution reaches 204.6 eV for single-pixel events. The effect of depletion depth on the sensor's performance was also examined, using three versions of the sensors with different deletion depths. We found that the sensor with a deeper depletion region can achieve a better energy resolution for events of all types of pixel splitting patterns, and has a higher efficiency in collecting photoelectrons produced by X-ray photons. We further study the effect of depletion depth on charge diffusion with a center-of-gravity (CG) model. Based on this work, a highly depleted sCMOS is recommended for applications of soft X-ray spectroscopy.

Compact high-flux X-ray source based on irradiation of solid targets by gigahertz and megahertz bursts of femtosecond laser pulses

In this study, we demonstrate the significant increase in the hard X-ray yield (more than 1011 photons/s in 4π solid angle in 6 - 40 keV range) that can be achieved in an ambient air environment when solid targets are irradiated by sequences of high average power (90 W) bursts of femtosecond laser pulses, generated in GHz burst laser amplifier operated at high repetition rate (100 kHz). The combination of the prepulse and ∼ 10 times greater driving pulse not only enhances X-ray generation efficiency (∼ 10−6) by more than two orders of magnitude compared to the single pulse regime but also protects a target allowing continuous operation for 3 hours with only 30% predictable and gradual drop of X-ray yield. In addition, we show that X-ray yield enhancement becomes around 6 times more pronounced at higher repetition rates (100 kHz compared to < 5 kHz). The simplicity and relative cost-effectiveness of the presented X-ray source makes it an attractive solution for future applications in ultrafast X-ray imaging and spectroscopy.

Large area silicon drift detectors system for high precision timed x-ray spectroscopy

The current work presents the optimization of large area silicon drift detectors developed by the SIDDHARTA-2 collaboration for high precision x-ray measurements of light exotic atom transitions. Two different radiation sources were employed in the study: an x-ray tube, for investigating the energy resolution and the charge collection efficiency of the device in the range 4000 eV–13 000 eV, and a β − 90Sr radioactive source for measuring the timing response, thus qualifying the charge drift parameters inside the semiconductor. The study reports the spectroscopic response optimization, together with the tuning of the electron dynamics for the given Silicon technology, by adjusting the applied electric field and the working temperature, which allow a good control of the device’s performances for high precision, timed x-ray spectroscopy applications.

Design and characterization of Kerberos: a 48-channel analog pulse processing and data acquisition platform

A multi-channel data processing and acquisition system based on an analog ASIC (SFERA) has been designed and realized. The platform, called Kerberos, is suitable for the readout of large arrays of Silicon Drift Detector (SDD) for X-ray, γ-ray and electron spectroscopy applications. Each one of its 48 inputs is equipped with a 9th order semi-Gaussian shaping amplifier with programmable peaking time (0.5, 1, 2, 3, 4 and 6 ). The pulse amplitudes are multiplexed into three 16-bit high linearity SAR ADCs and digitized into an Artix-7 FPGA module. Kerberos will be used for the characterization of monolithic SDD matrices for the TRISTAN project. Many different readout strategies can be selected on Kerberos Graphic User Interface: for TRISTAN it has been decided to use a full detector readout strategy, with maximum input throughput of about 166 kcount/s. This work presents a full characterization of this scalable platform and its use with several detectors types (SDD, micro-strips) in X-ray, gamma and beta spectroscopy.

A review of synchrotron X-ray radiation spectroscopy and imaging ‎ ‎

Synchrotron radiation is an advanced polarized and collimated light source with high brilliance and intensity. whereas This radiation has a wavelength range of infrared to the highest-energy x-rays. In this article, we provide a summary of application of x-ray spectroscopy with synchrotron radiation to x-ray spectroscopy. Here we discuss ten types of x-ray techniques include X-ray Powder Diffraction(XRPD), Wide Angle X-ray Scattering (WAXS), Small-Angle X-ray Scattering (SAXS), X-ray fluorescence(XRF), X-ray reflectometry (XRR), Near Edge X-ray Absorption Fine Structure (NEXAFS), X-ray Absorption Near Edge Structure (XANES), Photo Electron Spectroscopy (XPS), X-ray Emission Spectroscopy (XES), and x-ray imaging spectroscopy. These techniques have good potential for characterization of various micro- and nano-materials. Furthermore, some advantages of the use of these techniques are as follows: improving signal to noise ratio, better spatial resolution, and improving data acquisition.

In situ compositional mapping of combinatorial materials libraries by scanning low-angle x-ray spectroscopy

A novel in situ diagnostic, scanning low-angle x-ray spectroscopy, has been introduced for compositional mapping of combinatorial thin film libraries. The technique uses high-energy electron beam-generated characteristic x rays from the films as they are deposited. The x-ray intensities are acquired dynamically, layer by layer at different film thicknesses, processed, and analyzed by Neocera-developed software using a unique algorithm. A fully automated four-axis mechanical stage facilitates data acquisition from a 2-in. diameter wafer providing a comprehensive compositional map across the wafer. A ternary materials library of Zn-Ti-Cr oxide has been deposited by continuous composition spread pulsed laser deposition to demonstrate the novel application of scanning low-angle x-ray spectroscopy for compositional mapping in situ. This in situ feedback on composition across the wafer significantly enhances the capability of any physical vapor deposition technique used for depositing combinatorial libraries, by providing compositional feedback during growth as well as the ability to monitor and control deposition processes for composition optimizations.

Laser-driven photoelectron induced pulsed X-ray source for energy dispersive X-ray spectroscopy and radiography applications

We present the details of a nanosecond pulsed X-ray source developed for energy dispersive X-ray spectroscopy (EDX) and low-dose fast radiography. The source is based on the illumination of a metal photocathode, placed in a Pierce-type electron gun geometry, with a low energy Nd:YAG laser, delivering 266 nm wavelength pulses with a time duration of 5 ns and energy in the range of 12–100 mJ. The emitted nanosecond pulsed photoelectrons are accelerated up to 30 keV energy and impinge on the cathode. The influence of laser energy and electron accelerating potential on the X-ray flux is investigated. The X-ray flux is found to follow power law as I x ∝ ( E l ) α , where E l is the laser energy and α depends on the accelerating potentials. The preliminary experiments confirm that this source can be used for increased sensitivity EDX analysis as compared to the commercial secondary electron microscope. Our radiography results indicate that the use of alkali-based photocathodes can facilitate capturing a radiograph in a single laser pulse of a nanosecond time duration.

X-ray spectrometer simulation code with a detailed support of mosaic crystals

We present a newly developed ray tracing code called mmpxrt, dedicated to study and design X-ray crystal optics, with a special focus on mosaic crystal spectrometers. Its main advantage over other currently available ray tracing codes is that it includes a detailed and benchmarked algorithm to treat mosaic crystals, especially HOPG and HAPG (Highly Oriented/Annealed Pyrolitic Graphite). The code is primarily designed to study crystal spectrometers, therefore their implementation is very straightforward and includes the automated evaluation of their performance. It can, however, be used universally to study other Bragg crystal based instruments, such as monochromators, mirrors, and analyzers. The code is publicly available, written in Python3 and is distributed as a Python library with test cases and user manual included. Program summaryProgram title: mmpxrtCPC Library link to program files:https://dx.doi.org/10.17632/dkpbzvtz3b.1Developer’s repository link:https://gitlab.hzdr.de/smid55/mmpxrtLicensing provisions: MITProgramming language: Python 3Nature of problem: Mosaic crystals are commonly used for X-ray spectroscopy and similar applications. However, the complicated structure of such crystals makes their function non-trivial and often counter-intuitive, therefore a proper simulation tool is needed to design and understand such instruments.Solution method: We have developed a Monte-Carlo X-ray ray tracing code which simulates the setup of given spectrometer, analyzes the results and provides the performance of the spectrometer.

Resonant inelastic x-ray spectroscopy on UO2 as a test case for actinide materials

Resonant inelastic x-ray spectroscopy at the uranium N4 absorption edge at 778 eV has been used to reveal the excitations in UO2 up to 1 eV. The earlier (1989) studies by neutron inelastic scattering of the crystal-field states within the 3H4 multiplet are confirmed. In addition, the first excited state of the 3F2 multiplet at ∼520 meV has been established, and there is a weak signal corresponding to the next excited state at ∼920 meV. This represents a successful application of soft x-ray spectroscopy to an actinide sample, and resolves an open question in UO2 that has been discussed for 50 years. The technique is described and important caveats are drawn about possible future applications.

Application of Synchrotron Radiation X-ray Scattering and Spectroscopy to Soft Matter

Light produced by synchrotron radiation (SR) is much brighter than that produced by conventional laboratory X-ray sources. The photon energy of SR X-ray ranges from soft and tender X-rays to hard X-rays. Moreover, X-rays become element sensitive with decreasing photon energy. By using a wide energy range and high-quality light of SR, different scattering and spectroscopic methods were applied to various soft matters. We present five of our recent studies performed using specific light properties of a synchrotron facility, which are as follows: (1) In situ USAXS study to understand the deformation behavior of colloidal crystals during uniaxial stretching; (2) structure characterization of semiconducting polymer thin films along the film thickness direction by grazing-incidence wide-angle X-ray scattering using tender X-rays; (3) X-ray absorption fine structure (XAFS) analysis of the formation mechanism of poly(3-hexylthiophene) (P3HT); (4) soft X-ray absorption and emission spectroscopic analysis of water structure in polyelectrolyte brushes; and (5) X-ray photon correlation spectroscopic analysis of the diffusion behavior of polystyrene-grafted nanoparticles dispersed in a polystyrene matrix.

Gaussian process tomography based on Bayesian data analysis for soft x-ray and AXUV diagnostics on EAST**Project supported by the National Magnetic Confinement Fusion Science Program of China (Grant No. 11505226) and the National Natural Science Foundationof China (Grant No. 11975273).

This work presents the Gaussian process tomography (GPT) based on Bayesian data analysis and its applications in soft x-ray (SXR) and absolute extreme ultraviolet spectroscopy (AXUV) diagnostics on experimental advanced superconducting tokamak (EAST). This is the first application of the GPT method in the AXUV diagnostic system in fusion devices. It is found that even if only horizontal detector arrays are used to reconstruct the two-dimensional (2D) distribution of SXR and AXUV emissivity fields, the GPT method performs robustly and extremely fast, which enables the GPT method to provide real-time feedback on impurity transport and fast magnetohydrodynamics (MHD) events. By reconstructing SXR emissivity in the poloidal cross section on EAST, an m/n = 1/1 internal kink mode has been observed, and the plasma redistribution due to the kink mode is clearly visible in the reconstructions, where m is the poloidal mode number and n is the toroidal mode number. Sawtooth-like internal disruptions extended throughout the entire plasma core and mainly driven by the m/n = 2/1 mode have been acquired. During the sawtooth-like internal disruption crash phase, the conversion from an m = 2 mode to an m = 1 mode is observed. Using the reconstructed AXUV emissivity field we were able to observe the process of impurity accumulated in the plasma core and the mitigation of core impurity due to neon injection in the plasma edge. The data from all other diagnostics involved in the analysis shows that the reconstructions from AXUV measurements are reliable.

Towards Understanding the Temperature and Current Sensitivities of Transition-Edge Sensors

The transition-edge sensor (TES) technology is widely applied to X-ray spectroscopy or imaging applications at wavelengths ranging from infrared to sub-mm, with the aim of potentially achieving unprecedented spectral resolution and detection sensitivity. As a critical component of the X-ray microcalorimeter, the TES affects the energy resolution via two main parameters: temperature sensitivity and current sensitivity. Tremendous efforts have been made to fabricate TESs with high temperature sensitivity and low current sensitivity, in order to enhance the energy resolution of the microcalorimeters. However, since the resistance of TESs is a complex function of temperature, current, and magnetic field, it is difficult to optimize the operational point of the detector from the first principle. We conducted an experiment to map the parameter space of a sample of MoAu TESs in the transition phase. The results show that the current sensitivity depends only on the resistance of the TESs, which is in line with the two-fluid model. The figure of merit of energy resolution dependence on the quasiparticle diffusion length has been compared with the prediction of the two-fluid model, which indicates that the time-averaging critical current of phase-slip centers is not a constant throughout the superconducting transition. The magnetic field could potentially enhance the energy resolution by reducing the charge imbalance relaxation time.

Binary sinusoidal single-order multilayer gratings for tender x-ray region.

We propose and theoretically analyze a single-order diffractive optical element, termed binary sinusoidal multilayer grating (BSMG), to effectively suppress high-order diffractions while retaining high diffraction efficiency in the first order. The key idea is to integrate sinusoidal-shaped microstructures with high-reflectivity multilayer coatings. The dependence of the high-order diffraction property on the microstructure shape and multilayer coatings is investigated. Theoretical calculation reveals that the second-, third-, fourth-, and fifth-order diffraction efficiencies are as low as 0.01%. Strikingly, we show that first-order relative diffraction efficiency (the ratio between the intensity of the first diffraction order versus that of the reflected light) as high as 97.7% can be achieved. Thus, the proposed BSMG should be highly advantageous in future development and application of tender x-ray spectroscopy.