Third-generation Synchrotron Sources Research Articles

Advances in hard X-ray RIXS toward meV resolution in the study of 5d transition metal materials

Resonant inelastic X-ray scattering (RIXS) has played a pivotal role in advancing our understanding of spin-orbit physics in 5d transition metal materials. The progress in RIXS techniques has closely paralleled improvements in energy resolution, which have enabled the study of very low-lying excitations and led to the discovery of numerous new phenomena with significant scientific and technological implications. The multi-bend achromat (MBA) lattice upgrade of third-generation synchrotron sources, such as the Advanced Photon Source (APS), heralds a transformative era by introducing enhancements in brilliance and emittance. These advancements provide an opportunity to push the boundaries of RIXS techniques, meeting the challenges at the research frontiers of material science. This article aims to highlight key instrumental and technical advancements that enable the achievement of meV resolution in RIXS and discuss the impact of such high-resolution RIXS on exploring spin-orbit physics in 5d transition metal materials.

GaAs-chip-based mid-infrared supercontinuum generation

The mid-infrared spectral region opens up new possibilities for applications such as molecular spectroscopy with high spatial and frequency resolution. For example, the mid-infrared light provided by synchrotron sources has helped for early diagnosis of several pathologies. However, alternative light sources at the table-top scale would enable better access to these state-of-the-art characterizations, eventually speeding up research in biology and medicine. Mid-infrared supercontinuum generation in highly nonlinear waveguides pumped by compact fiber lasers represents an appealing alternative to synchrotrons. Here, we introduce orientation-patterned gallium arsenide waveguides as a new versatile platform for mid-infrared supercontinuum generation. Waveguides and fiber-based pump lasers are optimized in tandem to allow for the group velocities of the signal and the idler waves to match near the degeneracy point. This configuration exacerbates supercontinuum generation from 4 to 9 µm when waveguides are pumped at 2750 nm with few-nanojoule energy pulses. The brightness of the novel mid-infrared source exceeds that of the third-generation synchrotron source by a factor of 20. We also show that the nonlinear dynamics is strongly influenced by the choice of waveguide and laser parameters, thus offering an additional degree of freedom in tailoring the spectral profile of the generated light. Such an approach then opens new paths for high-brightness mid-infrared laser sources development for high-resolution spectroscopy and imaging. Furthermore, thanks to the excellent mechanical and thermal properties of the waveguide material, further power scaling seems feasible, allowing for the generation of watt-level ultra-broad frequency combs in the mid-infrared.

X-ray Emission Spectroscopy of Single Protein Crystals Yields Insights into Heme Enzyme Intermediates.

Enzyme reactivity is often enhanced by changes in oxidation state, spin state, and metal-ligand covalency of associated metallocofactors. The development of spectroscopic methods for studying these processes coincidentally with structural rearrangements is essential for elucidating metalloenzyme mechanisms. Herein, we demonstrate the feasibility of collecting X-ray emission spectra of metalloenzyme crystals at a third-generation synchrotron source. In particular, we report the development of a von Hamos spectrometer for the collection of Fe Kβ emission optimized for analysis of dilute biological samples. We further showcase its application in crystals of the immunosuppressive heme-dependent enzyme indoleamine 2,3-dioxygenase. Spectra from protein crystals in different states were compared with relevant reference compounds. Complementary density functional calculations assessing covalency support our spectroscopic analysis and identify active site conformations that correlate to high- and low-spin states. These experiments validate the suitability of an X-ray emission approach for determining spin states of previously uncharacterized metalloenzyme reaction intermediates.

High-efficiency coherence-preserving harmonic rejection with crystal optics.

This work reports a harmonic-rejection scheme based on the combination of Si(111) monochromator and Si(220) harmonic-rejection crystal optics. This approach is of importance to a wide range of X-ray applications in all three major branches of modern X-ray science (scattering, spectroscopy, imaging) based at major facilities, and especially relevant to the capabilities offered by the new diffraction-limited storage rings. It was demonstrated both theoretically and experimentally that, when used with a synchrotron undulator source over a broad range of X-ray energies of interest, the harmonic-rejection crystals transmit the incident harmonic X-rays on the order of 10-6. Considering the flux ratio of fundamental and harmonic X-rays in the incident beam, this scheme achieves a total flux ratio of harmonic radiation to fundamental radiation on the order of 10-10. The spatial coherence of the undulator beam is preserved in the transmitted fundamental radiation while the harmonic radiation is suppressed, making this scheme suitable not only for current third-generation synchrotron sources but also for the new diffraction-limited storage rings where coherence preservation is an even higher priority. Compared with conventional harmonic-rejection mirrors, where coherence is poorly preserved and harmonic rejection is less effective, this scheme has the added advantage of lower cost and footprint. This approach has been successfully utilized at the ultra-small-angle X-ray scattering instrument at the Advanced Photon Source for scattering, imaging and coherent X-ray photon correlation spectroscopy experiments. With minor modification, the harmonic rejection can be improved by a further five orders of magnitude, enabling even more performance capabilities.

Hard X-Ray Photon Correlation Spectroscopy Methods for Materials Studies

Understanding and designing sophisticated new materials require measurements of not only their average structural properties but also their dynamic behavior. X-ray photon correlation spectroscopy (XPCS) provides this information by characterizing fluctuations in condensed matter across a broad range of length scales and timescales. Over the past two decades, XPCS has provided a wide variety of results in the study of materials properties. In this review, we provide an overview of coherence, photon correlation spectroscopy, and the dynamic structure factor as well as information on the mechanics of XPCS experiments. We highlight the impact that this infrastructure has had on materials research and the bright future that is forthcoming with the anticipated upgrade of many third-generation synchrotron sources to fourth-generation multibend achromat sources.

The Influence of Photoelectron Escape in Radiation Damage Simulations of Protein Micro-Crystallography

Radiation damage represents a fundamental limit in the determination of protein structures via macromolecular crystallography (MX) at third-generation synchrotron sources. Over the past decade, improvements in both source and detector technology have led to MX experiments being performed with smaller and smaller crystals (on the order of a few microns), often using microfocus beams. Under these conditions, photoelectrons (PEs), the primary agents of radiation-damage in MX, may escape the diffraction volume prior to depositing all of their energy. The impact of PE escape is more significant at higher beam energies (>20 keV) as the electron inelastic mean free path (IMFP) is longer, allowing the electrons to deposit their energy over a larger area, extending further from their point of origin. Software such as RADDOSE-3D has been used extensively to predict the dose (energy absorbed per unit mass) that a crystal will absorb under a given set of experimental parameters and is an important component in planning a successful MX experiment. At the time this study was undertaken, dose predictions made using RADDOSE-3D were spatially-resolved, but did not yet account for the propagation of PEs through the diffraction volume. Hence, in the case of microfocus crystallography, it is anticipated that deviations may occur between the predicted and actual dose absorbed due to the influence of PEs. To explore this effect, we conducted a series of simulations of the dose absorbed by micron-sized crystals during microfocus MX experiments. Our simulations spanned beam and crystal sizes ranging from 1μm to 5μm for beam energies between 9 keV and 30 keV. Our simulations were spatially and temporarily resolved and accounted for the escape of PEs from the diffraction volume. The spatially-resolved dose maps produced by these simulations were used to predict the rate of intensity loss in a Bragg spot, a key metric for tracking global radiation damage. Our results were compared to predictions obtained using a recent version of RADDOSE-3D that did not account for PE escape; the predicted crystal lifetimes are shown to differ significantly for the smallest crystals and for high-energy beams, when PE escape is included in the simulations.

Quick X-ray reflectivity using monochromatic synchrotron radiation for time-resolved applications.

A new technique for the parallel collection of X-ray reflectivity (XRR) data, compatible with monochromatic synchrotron radiation and flat substrates, is described and applied to the in situ observation of thin-film growth. The method employs a polycapillary X-ray optic to produce a converging fan of radiation, incident onto a sample surface, and an area detector to simultaneously collect the XRR signal over an angular range matching that of the incident fan. Factors determining the range and instrumental resolution of the technique in reciprocal space, in addition to the signal-to-background ratio, are described in detail. This particular implementation records ∼5° in 2θ and resolves Kiessig fringes from samples with layer thicknesses ranging from 3 to 76 nm. The value of this approach is illustrated by showing in situ XRR data obtained with 100 ms time resolution during the growth of epitaxial La0.7Sr0.3MnO3 on SrTiO3 by pulsed laser deposition at the Cornell High Energy Synchrotron Source (CHESS). Compared with prior methods for parallel XRR data collection, this is the first method that is both sample-independent and compatible with the highly collimated, monochromatic radiation typical of third-generation synchrotron sources. Further, this technique can be readily adapted for use with laboratory-based sources.

Towards on-the-fly data post-processing for real-time tomographic imaging at TOMCAT

Sub-second full-field tomographic microscopy at third-generation synchrotron sources is a reality, opening up new possibilities for the study of dynamic systems in different fields. Sustained elevated data rates of multiple GB/s in tomographic experiments will become even more common at diffraction-limited storage rings, coming in operation soon. The computational tools necessary for the post-processing of raw tomographic projections have generally not experienced the same efficiency increase as the experimental facilities, hindering optimal exploitation of this new potential. We present here a fast, flexible, and user-friendly post-processing pipeline overcoming this efficiency mismatch and delivering reconstructed tomographic datasets just few seconds after the data have been acquired, enabling fast parameter and image quality evaluation as well as efficient post-processing of TBs of tomographic data. With this new tool, also able to accept a stream of data directly from a detector, few selected tomographic slices are available in less than half a second, providing advanced previewing capabilities paving the way to new concepts for on-the-fly control of dynamic experiments.

Fast X-ray microfluorescence imaging with submicrometer-resolution integrating a Maia detector at beamline P06 at PETRA III.

The high brilliance of third-generation synchrotron sources increases the demand for faster detectors to utilize the available flux. The Maia detector is an advanced imaging scheme for energy-dispersive detection realising dwell times per image-pixel as low as 50 µs and count rates higher than 10 × 106 s-1. In this article the integration of such a Maia detector in the Microprobe setup of beamline P06 at the storage ring PETRA III at the Deutsches Elektronen-Synchrotron (DESY) in Hamburg, Germany, is described. The analytical performance of the complete system in terms of rate-dependent energy resolution, scanning-speed-dependent spatial resolution and lower limits of detection is characterized. The potential of the Maia-based setup is demonstrated by key applications from materials science and chemistry, as well as environmental science with geological applications and biological questions that have been investigated at the P06 beamline.

WavePropaGator: interactive framework for X-ray free-electron laser optics design and simulations.

This article describes the WavePropaGator (WPG) package, a new interactive software framework for coherent and partially coherent X-ray wavefront propagation simulations. The package has been developed at European XFEL for users at the existing and emerging free-electron laser (FEL) facilities, as well as at the third-generation synchrotron sources and future diffraction-limited storage rings. The WPG addresses the needs of beamline scientists and user groups to facilitate the design, optimization and improvement of X-ray optics to meet their experimental requirements. The package uses the Synchrotron Radiation Workshop (SRW) C/C++ library and its Python binding for numerical wavefront propagation simulations. The framework runs reliably under Linux, Microsoft Windows 7 and Apple Mac OS X and is distributed under an open-source license. The available tools allow for varying source parameters and optics layouts and visualizing the results interactively. The wavefront history structure can be used for tracking changes in every particular wavefront during propagation. The batch propagation mode enables processing of multiple wavefronts in workflow mode. The paper presents a general description of the package and gives some recent application examples, including modeling of full X-ray FEL beamlines and start-to-end simulation of experiments.

Advanced Crystallographic Data Collection Protocols for Experimental Phasing.

Experimental phasing by single- or multi-wavelength anomalous dispersion (SAD or MAD) has become the most popular method of de novo macromolecular structure determination. Continuous advances at third-generation synchrotron sources have enabled the deployment of rapid data collection protocols that are capable of recording SAD or MAD data sets. However, procedural simplifications driven by the pursuit of high throughput have led to a loss of sophistication in data collection strategies, adversely affecting measurement accuracy from the viewpoint of anomalous phasing. In this chapter, we detail optimized strategies for collecting high-quality data for experimental phasing, with particular emphasis on minimizing errors from radiation damage as well as from the instrument. This chapter also emphasizes data processing for "on-the-fly" decision-making during data collection, a critical process when data quality depends directly on information gathered while at the synchrotron.

Synchrotron X-ray Scattering Measurements of Disordered Materials

Abstract With the advent of third-generation synchrotron sources and the development of light source techniques, X-ray scattering techniques have become feasible, leading to new approaches for studying the structures of disordered materials in a quantitative manner. We introduce a dedicated diffractometer for high-energy total X-ray scattering measurement and a newly developed anomalous X-ray spectrometer at SPring-8. As advanced methodologies for the measurement of liquids, we now offer three state-of-art levitation instruments for aerodynamic levitation, electrostatic levitation, and acoustic levitation at the SPring-8 beamlines, covering a wide temperature range of −40–3000 ℃. Furthermore, scientific investigations of glasses, liquids, and amorphous materials reported in the last five years at SPring-8 are reviewed.

Accurate Measurements of Dielectric and Optical Functions of Liquid Water and Liquid Benzene in the VUV Region (1-100 eV) Using Small-Angle Inelastic X-ray Scattering.

Using a third-generation synchrotron source (the BL12XU beamline at SPring-8), inelastic X-ray scattering (IXS) spectra of liquid water and liquid benzene were measured at energy losses of 1-100 eV with 0.24 eV resolution for small momentum transfers (q) of 0.23 and 0.32 au with ±0.06 au uncertainty for q. For both liquids, the IXS profiles at these values of q converged well after we corrected for multiple scattering, and these results confirmed the dipole approximation for q ≤ ∼0.3 au. Several dielectric and optical functions [including the optical oscillator strength distribution (OOS), the optical energy-loss function (OLF), the complex dielectric function, the complex index of refraction, and the reflectance] in the vacuum ultraviolet region were derived and tabulated from these small-angle (small q) IXS spectra. These new data were compared with previously obtained results, and this comparison demonstrated the strong reproducibility and accuracy of IXS spectroscopy. For both water and benzene, there was a notable similarity between the OOSs of the liquids and amorphous solids, and there was no evidence of plasmon excitation in the OLF. The static structure factor [S(q)] for q ≤ ∼0.3 au was also deduced and suggests that molecular models that include electron correlation effects can serve as a good approximation for the liquid S(q) values over the full range of q.

Application of in situ diffraction in high-throughput structure determination platforms.

Macromolecular crystallography (MX) is the most powerful technique available to structural biologists to visualize in atomic detail the macromolecular machinery of the cell. Since the emergence of structural genomics initiatives, significant advances have been made in all key steps of the structure determination process. In particular, third-generation synchrotron sources and the application of highly automated approaches to data acquisition and analysis at these facilities have been the major factors in the rate of increase of macromolecular structures determined annually. A plethora of tools are now available to users of synchrotron beamlines to enable rapid and efficient evaluation of samples, collection of the best data, and in favorable cases structure solution in near real time. Here, we provide a short overview of the emerging use of collecting X-ray diffraction data directly from the crystallization experiment. These in situ experiments are now routinely available to users at a number of synchrotron MX beamlines. A practical guide to the use of the method on the MX suite of beamlines at Diamond Light Source is given.

Nanoscale structure of Si/SiO2/organics interfaces.

X-ray reflectivity measurements of increasingly more complex interfaces involving silicon (001) substrates reveal the existence of a thin low-density layer intruding between the single-crystalline silicon and the amorphous native SiO2 terminating it. The importance of accounting for this layer in modeling silicon/liquid interfaces and silicon-supported monolayers is demonstrated by comparing fits of the measured reflectivity curves by models including and excluding this layer. The inclusion of this layer, with 6-8 missing electrons per silicon unit cell area, consistent with one missing oxygen atom whose bonds remain hydrogen passivated, is found to be particularly important for an accurate and high-resolution determination of the surface normal density profile from reflectivities spanning extended momentum transfer ranges, now measurable at modern third-generation synchrotron sources.

High-pressure X-ray science on the ultimate storage ring.

The advent of the ESRF, APS and SPring-8 third-generation synchrotron sources in the mid-1990s heralded a golden age of high-pressure X-ray science. The high-energy monochromatic micro-focused X-ray beams from these storage rings, combined with the new high-pressure diffraction and spectroscopy techniques developed in the late 1980s, meant that researchers were immediately able to make detailed structural studies at pressures comparable with those at the centre of the Earth, studies that were simply not possible only five years previously. And new techniques, such as X-ray inelastic scattering and X-ray nuclear scattering, became possible at high pressure for the first time, providing wholly-new insight into the behaviour of materials at high densities. The arrival of new diffraction-limited storage rings, with their much greater brightness, and ability to achieve focal-spot diameters for high-energy X-ray beams of below 1 µm, offers the possibility of a new generation of high-pressure science, both extending the scope of what is already possible, and also opening ways to wholly-new areas of investigation.

X-ray micro-diffraction studies on biological samples at the BioCAT Beamline 18-ID at the Advanced Photon Source.

The small source sizes of third-generation synchrotron sources are ideal for the production of microbeams for diffraction studies of crystalline and non-crystalline materials. While several such facilities have been available around the world for some time now, few have been optimized for the handling of delicate soft-tissue specimens under cryogenic conditions. Here the development of a new X-ray micro-diffraction instrument at the Biophysics Collaborative Access Team beamline 18-ID at the Advanced Photon Source, and its use with newly developed cryo-diffraction techniques for soft-tissue studies, are described. The combination of the small beam sizes delivered by this instrument, the high delivered flux and successful cryo-freezing of rat-tail tendon has enabled us to record data to better than 4 Å resolution. The ability to quickly raster scan samples in the beam allows selection of ordered regions in fibrous samples for markedly improved data quality. Examples of results of experiments obtainable using this instrument are presented.

A fast white-beam shutter for hard x-ray topography at beamline 1-BM of the Advanced Photon Source

Beamline 1-BM at the Advanced Photon Source (APS) delivers a white beam from a bending magnet with very intense x-ray photon flux. One important application of this beamline is white-beam x-ray topography imaging for crystal-based x-ray optics development and for industrial characterization of single crystals and epitaxial materials. Due to the intense photon flux from the third-generation synchrotron source of the APS, the exposure time of the imaging process should be accurately controlled down to the millisecond level. For this purpose we have designed and implemented a fast shutter that is vacuum compatible to 10−8 torr. The aperture is a copper block with a 70 mm horizontal and 5 mm vertical opening and is water cooled. The aperture is moved vertically up and down by means of a linear voice-coil actuator. The aperture's position is controlled using encoder feedback in a servo loop running on an industrial motion controller. A shutter opening response time of 32 milliseconds was measured. In this paper, we describe the shutter mechanics and its associated electronics installed at the 1-BM, and we report example white-beam topographs of diamond type IIa crystals.

X-ray harmonics rejection on third-generation synchrotron sources using compound refractive lenses.

A new method of harmonics rejection based on X-ray refractive optics has been proposed. Taking into account the fact that the focal distance of the refractive lens is energy-dependent, the use of an off-axis illumination of the lens immediately leads to spatial separation of the energy spectrum by focusing the fundamental harmonic at the focal point and suppressing the unfocused high-energy radiation with a screen absorber or slit. The experiment was performed at the ESRF ID06 beamline in the in-line geometry using an X-ray transfocator with compound refractive lenses. Using this technique the presence of the third harmonic has been reduced to 10(-3). In total, our method enabled suppression of all higher-order harmonics to five orders of magnitude using monochromator detuning. The method is well suited to third-generation synchrotron radiation sources and is very promising for the future ultimate storage rings.

Fast synchrotron X-ray tomography study of the packing structures of rods with different aspect ratios

We present a fast synchrotron X-ray tomography study of the packing structures of rods with different aspect ratios. Utilizing the high flux of the X-rays generated from the third-generation synchrotron source, we can complete a high-resolution tomography scan within a short period of time, after which the three-dimensional (3D) packing structure can be obtained for the subsequent structural analysis. The image phase-retrieval procedure has been implemented to enhance the image contrast. We systematically investigated the effects of particle shape and aspect ratio on the structural properties including packing density and contact number. It turns out that large aspect ratio rod packings will have wider distributions of free volume fraction and larger mean contact numbers.