Monochromatized Synchrotron Radiation Research Articles

Experimental study and modeling of extreme ultraviolet 4000 lines/mm diffraction gratings coated with periodic and aperiodic Al/Mo/SiC multilayers.

Multilayer coated diffraction gratings are crucial components for extreme ultraviolet (EUV) applications such as spectroscopy or spectro-imaging. However, for high groove density, the smoothening of the grating surface profile with multilayer deposition remains a limitation that requires further investigation. In this paper, we report on the design, characterization, and modeling of 4000 lines/mm diffraction gratings coated with periodic and aperiodic Al/Mo/SiC multilayers for EUV radiation. Two types of gratings with different groove depths are compared. Multilayer coatings were designed using a genetic algorithm to maximize the first-order diffraction efficiency in the 17-21 and 19-23nm wavelength ranges at normal incidence. Periodic and aperiodic multilayers with different numbers of layers were deposited by magnetron sputtering on the two types of fused silica gratings, and the grating groove profile evolution was measured by atomic force microscopy and cross-section transmission electron microscopy. The first-order diffraction efficiency was measured in the EUV at 5° incidence using monochromatic synchrotron radiation and modeled using the rigorous coupled-wave analysis method. The simulation models refined by using the Debye-Waller factor to account for the multilayer interfacial roughness show good agreement with experimental data. The results reported in this study will allow for designing efficient EUV multilayer gratings for high-resolution spectro-imaging instruments.

Large-view x-ray imaging for medical applications using the world’s only vertically polarized synchrotron radiation beam and a single asymmetric Si crystal

Objective. X-ray microangiography provides detailed information on the internal structure and function of a biological subject. Its ability to evaluate the microvasculature of small animals is useful for acquiring basic and clinical medical knowledge. The following three conditions are necessary to attain detailed knowledge of biological functions: (1) high temporal resolution with sufficient x-ray intensity, (2) high spatial resolution, and (3) a wide field of view. Because synchrotron radiation microangiography systems provide high sapatial resolution and high temporal resolution as a result of their high x-ray intensity, such systems have been developed at various synchrotron radiation facilities, starting with the photon factory, leading to numerous medical discoveries. However, the three aforementioned functions are incompatible with the use of synchrotron radiation because the x-ray intensity decreases when a wide field of view is obtained. To overcome these problems, we developed a new x-ray optical system for microangiography in rats using synchrotron radiation x-rays. Approach. Instead of using monochromatic synchrotron radiation x-rays with a conventional double-crystal monochromator, we used white synchrotron radiation x-rays and an asymmetric Si crystal to simultaneously monochromatize the beam and widen the field of view. Main results. The intensity profile and spatial resolution of the x-ray images were then evaluated. The proposed x-ray optics increased the x-ray intensity and beam width by factors of 1.3 and 2.7, respectively, compared with those of conventional monochromatic x-rays. In addition, in vivo studies on microangiography in rats were performed to confirm that the images had sufficient intensity, spatial resolution, and field of view. One of a series of images taken at 50 ms frame−1 was shown as an example. Significance. This x-ray optics provides sufficient x-ray intensity, high spatial resolution, and a wide field of view. This technique is expected providing new insights into the evaluation of the vascular system.

An electron–ion coincidence spectrometer for commissioning of a synchrotron radiation beamline: Absolute photon intensity and content of higher harmonic radiation

We describe the commissioning of a new electron-ion coincidence spectrometer used to diagnose the photon beam from a plane grating monochromator beamline at the ASTRID2 synchrotron radiation facility. The spectrometer allows determination of the absolute photon intensity by calibration to the photoabsorption cross sections of known gases, such as the rare gases Ar, Kr, and Xe presented here. The spectrometer operates at very low pressure (∼10-8-10-9 mbar) and-due to the coincidence electron-ion detection scheme-the detector efficiencies can be determined routinely; hence, the spectrometer can be recalibrated swiftly. By variation of a single potential of the spectrometer, the content of higher order radiation in the monochromatized synchrotron radiation can be analyzed. The layout and operation of the synchrotron radiation beamline at ASTRID2 and its additional photon diagnostic units are additionally described.

Characterization of a CdTe single-photon-counting detector for biomedical imaging applications

PurposeThe Eiger 2X CdTe 1 M−W (Dectris ltd, Baden, Switzerland) single photon counting detector was characterized for imaging applications at the biomedical beamline ID17 of the European Synchrotron Radiation Facility. MethodsLinearity, Modulation Transfer Function, Noise Power Spectrum and Detective Quantum Efficiency were measured as a function of photon energy and flux in the range 26–80 keV. ResultsThe linearity was confirmed in the flux range specified by Dectris and a detection efficiency higher than 60 % was measured for energies up to 80 keV. The spatial resolution was inferred from the Modulation Transfer Function and was found to be compatible with the pixel size of the detector (75 μm), except at energies just above the K-edge of Cd and Te where it reached 150 μm. The study of the Noise Power Spectrum showed a time-dependency in the response of the sensor, which is mitigated at low photon fluxes (<2⨯108 ph mm−2 s−1). ConclusionsThis work was the first characterization of the Eiger 2X CdTe 1 M−W for imaging applications with monochromatic synchrotron radiation. The spatial resolution and the quantum efficiency are compatible with low-dose imaging applications.

Nanocrystalline CaWO4 and ZnWO4 Tungstates for Hybrid Organic-Inorganic X-ray Detectors.

Hybrid materials combining an organic matrix and high-Z nanomaterials show potential for applications in radiation detection, allowing unprecedented device architectures and functionality. Herein, novel hybrid organic-inorganic systems were produced using a mixture of tungstate (CaWO4 or ZnWO4) nanoparticles with a P3HT:PCBM blend. The nano-tungstates with a crystallite size of 43 nm for CaWO4 and 30 nm for ZnWO4 were synthesized by the hydrothermal method. Their structure and morphology were characterized by X-ray diffraction and scanning electron microscopy. The hybrid systems were used to fabricate direct conversion X-ray detectors able to operate with zero bias voltage. The detector performance was tested in a wide energy range using monochromatic synchrotron radiation. The addition of nanoparticles with high-Z elements improved the detector response to X-ray radiation compared with that of a pure organic P3HT:PCBM bulk heterojunction cell. The high dynamic range of our detector allows for recording X-ray absorption spectra, including the fine X-ray absorption structure located beyond the absorption edge. The obtained results suggest that nanocrystalline tungstates are promising candidates for application in direct organic-inorganic X-ray detectors.

On the optical constants of cobalt in the M-absorption edge region

Using monochromatized synchrotron radiation, the optical constants of cobalt are determined in the spectral range 8.0–25.0 nm. The optical constants are determined from Angle-Dependent Reflectometry (ADR) measurements of a multilayer sample. Since cobalt is prone to strong oxidation, carbon capping was used to stabilize the probed sample. The fine-structure of the optical constants in the M-absorption edge region is resolved with unprecedented resolution for the element. The determination of the optical constants from reflectivity data was conducted using Markov Chain Monte Carlo (MCMC) based Bayesian inferences, supported with X-ray Reflectivity (XRR) data. This work further demonstrates establishing MCMC-based Bayesian inferences for determining optical constants. Time-Frequency Analysis (TFA) methods are also used to solve the corresponding inverse problem by supporting initializing a model of the sample. The results here are highly relevant for developing Co-based Multilayer Mirrors (MLMs) targeting the Extreme Ultraviolet (EUV) range, particularly those MLMs dedicated for EUV astronomy.

Tunability of the optical constants of tantalum-cobalt alloy thin films in the extreme ultraviolet

The optical constants of two Ta-Co binary alloys are determined in the spectral range 8.0 nm–22.0 nm using angle-dependent reflectometry (ADR). The extreme-ultraviolet reflectivity (EUVR) profiles of the alloys were measured using highly monochromatized synchrotron radiation from sputtered thin films, each with a nominal thickness of 30.0 nm. Concerning the alloys, the inability to predict the variability of the optical constants' profiles in the vicinity of cobalt’s M-absorption edge region gives unique proof for the need to derive a more complete theory for predicting the optical constants. Markov chain Monte Carlo (MCMC) based Bayesian inferences, and frequency analysis of X-ray reflectivity (XRR) data were utilized to treat the relevant inverse-problem needed for determining the optical constants. An approach is presented here where both the optical constants of the alloys and their surface layers are simultaneously sampled. The results of this report are apropos to strengthen customizing multilayer mirrors (MLMs) and similar ad hoc optical components intended for the extreme-ultraviolet (EUV) spectral range.

Highly Charged Ions for High-Resolution Soft X-ray Grating Monochromator Optimisation

The energy-resolving performance of a synchrotron radiation monochromator can be characterised by measuring the fluorescence response of a gas in scans across characteristic absorption lines. Here, we describe a method using exceptionally narrow absorption features in the soft x-ray range. The features belong to helium-like ions and examples of the transition 1s → 2p in O6+ and Ne8+ are shown. We describe the instrument PolarX-EBIT and show typical data. A performance with ten times sharper effective feature width, when compared to neutral-gas absorption features, is demonstrated.

Nested Sampling aided determination of tantalum optical constants in the EUV spectral range.

We report on determining the optical constants of Ta in the sub-extreme ultraviolet (EUV) spectral range 5.0-24.0 nm from the angle-dependent reflectance (ADR) measured using monochromatized synchrotron radiation. Two sputtered samples with differing thicknesses were investigated. Complementarily x-ray reflectance was measured at shorter wavelengths and evaluated by Fourier transform to facilitate an unambiguous selection of a model for the data evaluation based on an inverse solution of the Fresnel's equations for a layered system. Bayesian inferences coupled with a Nested Sampling (NS) algorithm were utilized to derive the optical constants with their corresponding uncertainties. This report further emphasizes the applicability of an acclaimed NS algorithm on a high-dimensional inverse problem. We explore the possibility of addressing the correlations between the optical constants of thin films and their structural parameters based on other established studies.

Phase transition and twinning in polycrystals probed by in situ high temperature 3D reciprocal space mapping

Polycrystalline materials exhibit physical properties that are driven by both the interatomic crystallographic structure as well as the nature and density of structural defects. Crystallographic evolutions driven by phase transitions and associated twinning process can be observed in situ in three-dimensional (3D) using monochromatic synchrotron radiation at very high temperatures (over 1000 °C). This paper focuses on continuous measurements of the 3D-reciprocal space maps by high-resolution x-ray diffraction as a function of temperature along a phase transition process occurring between 1200 °C and room temperature. These high precision measurements allow observing the reciprocal space node splitting and the evolution of the diffuse scattering signal around that node as a function of temperature. The capability of this experimental method is illustrated by direct in situ high temperature measurements of the 3D splitting of a reciprocal space node due to phase transition recorded on dense pure zirconia polycrystals.

Al/Mo/SiC multilayer diffraction gratings with broadband efficiency in the extreme ultraviolet.

Al/Mo/SiC periodic and aperiodic multilayers were optimized and deposited on high groove density gratings to achieve broadband efficiency in the extreme ultraviolet (EUV). Grating efficiencies were measured by monochromatic synchrotron radiation under 5° and 45° incident angles in the wavelength ranges 17-25 nm and 22-31 nm, respectively. We study the influence of the number of deposited periods on the initial trapezoidal profile and the EUV diffraction efficiency. We propose models of periodic and aperiodic coatings based on a combination of characterizations and compare rigorous coupled-wave analysis (RCWA) simulations with experimental data. We demonstrate the possibility to select the optimal balance between peak efficiency and bandwidth by adjusting the number of periods in the case of periodic multilayer grating. We also report unprecedented broadband diffraction efficiency with an Al/Mo/SiC aperiodic multilayer grating.

Complementarity of neutron, XFEL and synchrotron crystallography for defining the structures of metalloenzymes at room temperature.

Room-temperature macromolecular crystallography allows protein structures tobe determined under close-to-physiological conditions, permits dynamic freedom in protein motions and enables time-resolved studies. In the case of metalloenzymes that are highly sensitive to radiation damage, such room-temperature experiments can present challenges, including increased rates of X-ray reduction of metal centres and site-specific radiation-damage artefacts, as well as in devising appropriate sample-delivery and data-collection methods. It can also be problematic to compare structures measured using different crystal sizes and light sources. In this study, structures of a multifunctional globin, dehaloperoxidase B (DHP-B), obtained using several methods of room-temperature crystallographic structure determination are described and compared. Here, data were measured from large single crystals and multiple microcrystals using neutrons, X-ray free-electron laser pulses, monochromatic synchrotron radiation and polychromatic (Laue) radiation light sources. These approaches span a range of 18 orders of magnitude in measurement time per diffraction pattern and four orders of magnitude in crystal volume. The first room-temperature neutron structures of DHP-B are also presented, allowing the explicit identification of the hydrogen positions. The neutron data proved to be complementary to the serial femtosecond crystallography data, with both methods providing structures free of the effects of X-ray radiation damage when compared with standard cryo-crystallography. Comparison of these room-temperature methods demonstrated the large differences in sample requirements, data-collection time and the potential for radiation damage between them. With regard to the structure and function of DHP-B, despite the results being partly limited by differences in the underlying structures, new information was gained on the protonation states of active-site residues which may guide future studies of DHP-B.

Revealing dynamic processes in laser powder bed fusion with in situ X-ray diffraction at PETRA III.

The high flux combined with the high energy of the monochromatic synchrotron radiation available at modern synchrotron facilities offers vast possibilities for fundamental research on metal processing technologies. Especially in the case of laser powder bed fusion (LPBF), an additive manufacturing technology for the manufacturing of complex-shaped metallic parts, in situ methods are necessary to understand the highly dynamic thermal, mechanical, and metallurgical processes involved in the creation of the parts. At PETRA III, Deutsches Elektronen-Synchrotron, a customized LPBF system featuring all essential functions of an industrial LPBF system, is used for in situ x-ray diffraction research. Three use cases with different experimental setups and research questions are presented to demonstrate research opportunities. First, the influence of substrate pre-heating and a complex scan pattern on the strain and internal stress progression during the manufacturing of Inconel 625 parts is investigated. Second, a study on the nickel-base superalloy CMSX-4 reveals the formation and dissolution of γ' precipitates depending on the scan pattern in different part locations. Third, phase transitions during melting and solidification of an intermetallic γ-TiAl based alloy are examined, and the advantages of using thin platelet-shaped specimens to resolve the phase components are discussed. The presented cases give an overview of in situ x-ray diffraction experiments at PETRA III for research on the LPBF technology and provide information on specific experimental procedures.

Resonant Auger decay induced by the symmetry-forbidden 1a1g → 6a1g transition of the SF6 molecule

Resonant Auger electron spectroscopic study at the symmetry-forbidden 1a1g→6a1g excitation below the S K-shell threshold of SF6 is reported. Partial electron yield and resonant KLL Auger spectra have been measured by using monochromatized undulator synchrotron radiation. By changing the photon energy in small steps, a so-called 2D map is produced. In this map, the dipole-forbidden transition exhibits spectral features (e.g., an S-shaped dispersion relation), which are well known and understood for dipole-allowed transitions. We validate by a theory that for the case of dipole-forbidden transitions, these spectral features can be analyzed in the same way as previously established for the dipole-allowed ones. This approach grants information on the nuclear dynamics in the K-shell core-excited states of SF6 on the femtosecond (fs) timescale. In particular, for the potential-energy curves of the states S 1s−16a1g and S 2p−26a1g, the slopes at the equilibrium distance of the ground state are derived. Symmetry breaking as a result of ultrafast vibronic coupling is revealed by the population of the electronically forbidden excited state.

Design of a high-resolution VLS monochromator for synchrotron radiation

A high-resolution monochromator with a broad spectral range of 125-4200 Angstrem is designed for a measuring beamline of the projected synchrotron radiation source "SKIF" (Novosibirsk). The optical configuration of the monochromator comprises a grazing-incidence concave mirror, a plane VLS grating, and an exit slit. It is planned to use two replaceable VLS gratings with central groove frequencies of 600 and 150 mm-1 intended for subranges of 125-1000 Angstrem and 900-4200 Angstrem, respectively. Wavelength tuning in each of the two subranges is carried out by solely the rotation of the VLS-gratings. Due to the proper choice of p1 VLS-grating coefficients, the focal distance varies only slightly over the entire spectral range, and the p2 VLS-grating coefficients are used to suppress the aberrations of the mirror and the gratings. The resolving power of the configuration obtained by numerical ray tracing exceeds 1000 in the 125-1000 Angstrem range and 2000 in the 900-4200 Angstrem range. Keywords: VUV, spectroscopy, VLS-grating, synchrotron radiation.

Time-frequency analysis assisted determination of ruthenium optical constants in the sub-EUV spectral range 8 nm – 23.75 nm

The optical constants of ruthenium in the spectral range 8 nm – 23.75 nm are determined with their corresponding uncertainties from the reflectance of a sputtered ruthenium thin film, measured using monochromatized synchrotron radiation. This work emphasizes the correlation between structure modelling and the determined optical parameters in a robust inverse-problem solving strategy. Complementary X-ray Reflectivity (XRR) measurements are coupled with Markov chain Monte Carlo (MCMC) based Bayesian inferences and a quasi-model-independent method to create a model factoring the sample’s oxidation, contamination, and interfacial imperfections. The robustness of the modelling scheme against contamination and oxidation is tested and verified by measurements after hydrogen-radical cleaning of the sample’s surface.

Advanced X-ray imaging at beamline 07 of the SAGA Light Source.

The SAGA Light Source provides X-ray imaging resources based on high-intensity synchrotron radiation (SR) emitted from the superconducting wiggler at beamline 07 (BL07). By combining quasi-monochromatic SR obtained by the newly installed water-cooled metal filter and monochromatic SR selected by a Ge double-crystal monochromator (DCM) with high-resolution lens-coupled X-ray imagers, fast and low-dose micro-computed tomography (CT), fast phase-contrast CT using grating-based X-ray interferometry, and 2D micro-X-ray absorption fine structure analysis can be performed. In addition, by combining monochromatic SR obtained by a Si DCM with large-area fiber-coupled X-ray imagers, high-sensitivity phase-contrast CT using crystal-based X-ray interferometry can be performed. Low-temperature CT can be performed using the newly installed cryogenic system, and time-resolved analysis of the crystallinity of semiconductor devices in operation can be performed using a time-resolved topography system. The details of each instrument and imaging method, together with exemplary measurements, are presented.

Rocking Curve Imaging Investigation of the Long-Range Distortion Field between Parallel Dislocations with Opposite Burgers Vectors

We observe a long-range distortion field between parallel dislocations with opposite Burgers vectors in a platelet-shaped single crystal of 4H-SiC with a low dislocation density (~103 cm/cm3). This distortion field is in the µradian range when the distance D between dislocations is in the ~50–250 µm range. We were able to characterise this weak distortion field through Rocking Curve Imaging (RCI), a highly sensitive Bragg diffraction imaging technique using monochromatic synchrotron radiation. From the experimental images, we generate maps of the angle of maximum reflectance (“peak position”) that provide a measurement of the local lattice orientation. Deviations from the crystal matrix orientation are associated with the long-range distortion field around dislocations. Between parallel dislocations with opposite Burgers vectors, this distortion does not decay to zero but towards a constant value α. We propose a simple model considering the angular parameter α characterising the distortion. This model indicates that α should roughly vary as 1/D. This appears to be in fair agreement with our experimental data.

X-ray induced luminescence spectroscopy for DNA damaging intermediates aided by a monochromatic synchrotron radiation

Purpose To identify the bonding sites of initial radiation interaction with DNA and to trace the following chemical reaction sequences on the pathway of damage induction, we carry out a spectroscopy XIL (X-ray induced luminescence) using soft X-ray synchrotron radiation. This is a nondestructive analysis of the excited intermediate species produced in a molecular mechanism on the damage induction pathway. Materials and Methods We introduce aqueous samples of UMP (uridine-5’-monophosphate) in the vacuum by the use of a liquid micro-jet technique. The luminescence in the region of UV-VIS (from visible to ultraviolet) radiation induced after the absorption of monochromatic soft X-ray by aqueous UMP is measured with sweeping the soft X-ray energy in the region of 370–560 eV. Results The enhanced XIL intensities for aqueous UMP in the region of soft X-ray of 410–530 eV (in “water window” region) are obtained. The enhancement of XIL intensities in the UV-VIS region, relative to the water control, is explained by the excitation and ionization of a K-shell electron of nitrogen atoms in the uracil moiety. The enhanced XIL intensities do not match the structure of XANES (X-ray absorption near-edge structure) of the aqueous UMP. This suggests that the XIL intensities reflect the quantum yields of luminescence, or the quantum yields for conversion by UMP of an absorbed X-ray into UV-VIS radiation. In this paper, spectra of luminescence are shown to be resolved by combining low pass filters. The filtered luminescence spectra are obtained at the center of gravity (λc) of the band pass wavelength regions at λc = 270nm, 295 nm, 340 nm, 385 nm, 450 nm, and 525 nm., which show a trend similar to the fluorescence of nucleobases induced by ultraviolet radiation. Conclusion It is concluded that the origin of the observed XIL is the hydrated uracil moiety in aqueous UMP, decomposition of which is suppressed by the migration of excess charge and internal energy after the double ionization due to Auger decay.

Photoionization of methanol: a molecular source for the prebiotic chemistry

Methanol is one of the most abundant and ubiquitous molecules in the space. Its chemistry is fundamental to understand the molecular growing from prebiotic molecules, ions and radicals. In this work the reaction of labelled methanol CD3OH•+ radical cation, produced with different internal energies by monochromatic synchrotron radiation, with neutral CD3OH was studied. The dynamics of the main reaction channels were investigated by theoretical calculations. The results show how these processes can be considered suitable pathways for the formation of fundamental species as CH3O(H)H+, CH3O•, •CH2OH, CH2O which are potential precursors to prebiotic molecules.