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Polymer‐coated nanoparticles are widely studied in the context of nanomedicine and it is therefore of utmost importance to understand not only how their structure but also how their colloidal dynamics are affected by physiologically relevant conditions. A characteristic feature of the cytosol of cells is the very high concentration of proteins among other matrix components, often termed macromolecular crowding. Here, the structure and colloidal dynamics of poly(ethylene glycol) (PEG)‐coated gold nanoparticles in the presence of bovine serum albumin (BSA) concentrations ranging from 0 to 265 mg/mL are studied with X‐ray photon correlation spectroscopy. For protein–nanoparticle mixtures with high BSA concentrations, comparable to intracellular levels, a significant deviation of the apparent viscosity from expectations for pure BSA solutions is found. The findings strongly indicate that the nanoscopic viscous properties of the dense protein solutions are significantly affected by the nanoparticles. At these high concentrations, the colloidal stability of the samples depends on the molecular weight of the coating PEG–ligand, whereas at lower concentrations no differences are observed. [ABSTRACT FROM AUTHOR]

Abstract Polymer‐coated nanoparticles are widely studied in the context of nanomedicine and it is therefore of utmost importance to understand not only how their structure but also how their colloidal dynamics are affected by physiologically relevant conditions. A characteristic feature of the cytosol of cells is the very high concentration of proteins among other matrix components, often termed macromolecular crowding. Here, the structure and colloidal dynamics of poly(ethylene glycol) (PEG)‐coated gold nanoparticles in the presence of bovine serum albumin (BSA) concentrations ranging from 0 to 265 mg/mL are studied with X‐ray photon correlation spectroscopy. For protein–nanoparticle mixtures with high BSA concentrations, comparable to intracellular levels, a significant deviation of the apparent viscosity from expectations for pure BSA solutions is found. The findings strongly indicate that the nanoscopic viscous properties of the dense protein solutions are significantly affected by the nanoparticles. At these high concentrations, the colloidal stability of the samples depends on the molecular weight of the coating PEG–ligand, whereas at lower concentrations no differences are observed.

Recent technical developments and the performance of the X-ray photon correlation spectroscopy (XPCS) method over the ultra-small-angle range with the Extremely Brilliant Source (EBS) at the ESRF are described. With higher monochromatic coherent photon flux (∼1012 photons s−1) provided by the EBS and the availability of a fast pixel array detector (EIGER 500K detector operating at 23000 frames s−1), XPCS has become more competitive for probing faster dynamics in relatively dilute suspensions. One of the goals of the present development is to increase the user-friendliness of the method. This is achieved by means of a Python-based graphical user interface that enables online visualization and analysis of the processed data. The improved performance of XPCS on the Time-Resolved Ultra-Small-Angle X-ray Scattering instrument (ID02 beamline) is demonstrated using dilute model colloidal suspensions in several different applications.

Recent technical developments and the performance of the X-ray photon correlation spectroscopy (XPCS) method over the ultra-small-angle range with the Extremely Brilliant Source (EBS) at the ESRF are described. With higher monochromatic coherent photon flux (~1012 photons s-1) provided by the EBS and the availability of a fast pixel array detector (EIGER 500K detector operating at 23000 frames s-1), XPCS has become more competitive for probing faster dynamics in relatively dilute suspensions. One of the goals of the present development is to increase the user-friendliness of the method. This is achieved by means of a Python-based graphical user interface that enables online visualization and analysis of the processed data. The improved performance of XPCS on the Time-Resolved Ultra-Small-Angle X-ray Scattering instrument (ID02 beamline) is demonstrated using dilute model colloidal suspensions in several different applications. [ABSTRACT FROM AUTHOR]

The occurrence of non-equilibrium transitions between arrested states has recently emerged as an intriguing issue in the field of soft glassy materials. The existence of one such transition has been suggested for aging colloidal clays (Laponite® suspensions) at a weight concentration of 3.0%, although further experimental evidences are necessary to validate this scenario. Here, we test the occurrence of this transition for spontaneously aged (non-rejuvenated) samples by exploiting the rheological tools of dynamical mechanical analysis. On imposing consecutive compression cycles to differently aged clay suspensions, we find that quite an abrupt change of rheological parameters occurs for ages around three days. For Young's and elastic moduli, the change with the waiting time is essentially independent from the deformation rate, whereas other "fluid-like" properties, such as the loss modulus, do clearly display some rate dependence. We also show that the crossover identified by rheology coincides with deviations of the relaxation time (obtained through x-ray photon correlation spectroscopy) from its expected monotonic increase with aging. Thus, our results robustly support the existence of a glass-glass transition in aging colloidal clays, highlighting characteristic features of their viscoelastic behavior. [ABSTRACT FROM AUTHOR]

With the development of X-ray free-electron lasers (XFELs), producing pulses of femtosecond durations comparable with the coherence times of X-ray fluorescence, it has become possible to observe intensity–intensity correlations due to the interference of emission from independent atoms. This has been used to compare durations of X-ray pulses and to measure the size of a focusedX-ray beam, for example. Here it is shown that it is also possible to observe the interference of fluorescence photons through the measurement of the speckle contrast of angle-resolved fluorescence patterns. Speckle contrast is often used as a measure of the degree of coherence of the incident beam or the fluctuations of the illuminated sample as determined from X-ray diffraction patterns formed by elastic scattering, rather than from fluorescence patterns as addressed here. Commonly used approaches to estimate speckle contrast were found to suffer when applied to XFEL-generated fluorescence patterns due to low photon counts and a significant variation of the excitation pulse energy from shot to shot. A new method to reliably estimate speckle contrast under such conditions, using a weighting scheme, is introduced. The method is demonstrated by comparing the speckle contrast of fluorescence observed with pulses of 3 fs to 15 fs duration.

The PERCIVAL detector is a CMOS imager designed for the soft X-ray regime at photon sources. Although still in its final development phase, it has recently seen its first user experiments: ptychography at a free-electron laser, holographic imaging at a storage ring and preliminary tests on X-ray photon correlation spectroscopy. The detector performed remarkably well in terms of spatial resolution achievable in the sample plane, owing to its small pixel size, large active area and very large dynamic range; but also in terms of its frame rate, which is significantly faster than traditional CCDs. In particular, it is the combination of these features which makes PERCIVAL an attractive option for soft X-ray science.

Brownian motion of Cowpea mosaic virus (CPMV) in water was measured using small-angle X-ray photon correlation spectroscopy (SA-XPCS) at 19.2 µs time resolution. It was found that the decorrelation time τ(Q) = 1/DQ2 up to Q = 0.091 nm−1. The hydrodynamic radius RH determined from XPCS using Stokes–Einstein diffusion D = kT/(6πηRH) is 43% larger than the geometric radius R0 determined from SAXS in the 0.007 M K3PO4 buffer solution, whereas it is 80% larger for CPMV in 0.5 M NaCl and 104% larger in 0.5 M (NH4)2SO4, a possible effect of aggregation as well as slight variation of the structures of the capsid resulting from the salt–protein interactions.

The X-ray-induced, nonthermal fluidization of the prototypical SiO2 glass is investigated by X-ray photon correlation spectroscopy in the small-angle scattering range. This process is initiated by the absorption of X-rays and leads to overall atomic displacements which reach at least few nanometers at temperatures well below the glass transition. At absorbed doses of ∼5 GGy typical of many modern X-ray-based experiments, the atomic displacements display a hyperdiffusive behavior and are distributed according to a heavy-tailed, Lévy stable distribution. This is attributed to the stochastic generation of X-ray-induced point defects which give rise to a dynamically fluctuating potential landscape, thus providing a microscopic picture of the fluidization process. [ABSTRACT FROM AUTHOR]

The PERCIVAL detector is a CMOS imager designed for the soft X-ray regime at photon sources. Although still in its final development phase, it has recently seen its first user experiments: ptychography at a free-electron laser, holographic imaging at a storage ring and preliminary tests on X-ray photon correlation spectroscopy. The detector performed remarkably well in terms of spatial resolution achievable in the sample plane, owing to its small pixel size, large active area and very large dynamic range; but also in terms of its frame rate, which is significantly faster than traditional CCDs. In particular, it is the combination of these features which makes PERCIVAL an attractive option for soft X-ray science. [ABSTRACT FROM AUTHOR]

With the development of X-ray free-electron lasers (XFELs), producing pulses of femtosecond durations comparable with the coherence times of X-ray fluorescence, it has become possible to observe intensity-intensity correlations due to the interference of emission from independent atoms. This has been used to compare durations of X-ray pulses and to measure the size of a focused X-ray beam, for example. Here it is shown that it is also possible to observe the interference of fluorescence photons through the measurement of the speckle contrast of angle-resolved fluorescence patterns. Speckle contrast is often used as a measure of the degree of coherence of the incident beam or the fluctuations of the illuminated sample as determined from X-ray diffraction patterns formed by elastic scattering, rather than from fluorescence patterns as addressed here. Commonly used approaches to estimate speckle contrast were found to suffer when applied to XFEL-generated fluorescence patterns due to low photon counts and a significant variation of the excitation pulse energy from shot to shot. A new method to reliably estimate speckle contrast under such conditions, using a weighting scheme, is introduced. The method is demonstrated by comparing the speckle contrast of fluorescence observed with pulses of 3 fs to 15 fs duration. [ABSTRACT FROM AUTHOR]

Linking the physics of the relaxation behavior of viscoelastic fluids as they form arrested gel states to the underlying chemical changes is essential for developing predictive controls on the properties of the suspensions. In this study, 3 wt.% laponite suspensions are studied as model systems to probe the influence of salt-induced relaxation behavior arising from the assembly of laponite nanodisks. X-ray Photon Correlation Spectroscopy (XPCS) measurements show that laponite suspensions prepared in the presence of 5 mM concentrations of CaCl2, MgCl2 and CsCl salts accelerate the formation of arrested gel states, with CaCl2 having a significant impact followed by CsCl and MgCl2 salts. The competing effects of ion size and charge on relaxation behavior are noted. For example, the relaxation times of laponite suspensions in the presence of Mg2+ ions are slower compared to Cs+ ions despite the higher charge, suggesting that cation size dominates in this scenario. The faster relaxation behavior of laponite suspensions in the presence of Ca2+ ions compared to Cs+ ions shows that a higher charge dominates the size of the ion. The trends in relaxation behavior are consistent with the cluster formation behavior of laponite suspensions and the electrostatic interactions predicted from MD simulations. Charge balance is achieved by the intercalation of the cations at the negatively charged surfaces of laponite suspensions. These studies show that the arrested gel state of laponite suspensions is accelerated in the presence of salts, with ion sizes and charges having a competing effect on relaxation behavior. [ABSTRACT FROM AUTHOR]

Brownian motion of Cowpea mosaic virus (CPMV) in water was measured using small-angle X-ray photon correlation spectroscopy (SA-XPCS) at 19.2 ms time resolution. It was found that the decorrelation time (Q) = 1/DQ2 up to Q = 0.091 nm-1. The hydrodynamic radius RH determined from XPCS using Stokes-Einstein diffusion D = kT/(6RH) is 43% larger than the geometric radius R0 determined from SAXS in the 0.007 M K3PO4 buffer solution, whereas it is 80% larger for CPMV in 0.5 M NaCl and 104% larger in 0.5 M (NH4)2SO4, a possible effect of aggregation as well as slight variation of the structures of the capsid resulting from the salt-protein interactions. [ABSTRACT FROM AUTHOR]

[Display omitted] Stimuli-responsive self-assembly of (an) isotropic colloids has resulted in a plethora of self-assembled structures with potential applications in fabricating smart materials. A lack of detailed understanding of the interplay between these self-assembled structures and the resulting dynamics has often impeded the exploitation of their full potential. Herein, we have unveiled the relationship between the field-driven self-assembled structures and the corresponding collective dynamics at the nearest neighbor length scale using X-ray photon correlation spectroscopy and magnetic colloidal ellipsoids. We demonstrate that the effective long-time collective diffusion coefficient, D eff (q) , scales with the inverse of the scattered intensity for various stimuli-responsive self-assembled phases. At high-volume fraction, the system approaches a kinetically arrested state. The anisotropic slowdown of D eff (q) hints towards the formation of an oriented glass. Our approach opens new avenues for exploring the stimuli-responsive dynamics of strongly interacting colloidal systems with diverse shapes and properties. [ABSTRACT FROM AUTHOR]

Self-propelled particulate systems manifest certain collective behavior of living matter, which have been the subject of intense research over the past decades. One of the elegant methods for realizing such active motions is by means of custom synthesized Janus particles suspended in a catalytic medium that can be triggered upon illumination by ultraviolet light. In this work, the evolution of the particle dynamics from passive diffusive to active ballistic behavior upon light illumination was probed by multispeckle x-ray photon correlation spectroscopy (XPCS). This technique enables not only studying the emergence of active motions in three dimensions (3D) but also deciphering different contributions to the overall dynamics. Using a combination of homodyne and heterodyne analysis, the ensemble averaged mean velocity, velocity fluctuations and diffusion coefficient of particles were determined in the thermodynamic limit. Results revealed a gradual transition from diffusive to ballistic dynamics with systematic increase of the catalytic activity. At the intermediate region, the dynamics is dominated by Gaussian velocity fluctuations and an enhanced relaxation rate with a weaker wave vector dependence similar to superdiffusive behavior. For the highest activity, the dynamics became purely ballistic with Lorentzian-like distribution of velocity fluctuations. Presented results demonstrate that different aspects of active dynamics can be investigated in 3D over a broad range of PĂ©clet numbers and other control parameters by means of multispeckle XPCS. [ABSTRACT FROM AUTHOR]

Machine learning methods are used for an automated classification of experimental two-time X-ray photon correlation maps from an arrested liquid--liquid phase separation of a protein solution. The correlation maps are matched with correlation maps generated with Cahn--Hilliard-type simulations of liquid--liquid phase separations according to two simulation parameters and in the last step interpreted in the framework of the simulation. The matching routine employs an auto-encoder network and a differential evolution based algorithm. The method presented here is a first step towards handling large amounts of dynamic data measured at high-brilliance synchrotron and X-ray free-electron laser sources, facilitating fast comparison with phase field models of phase separation. [ABSTRACT FROM AUTHOR]

Many soft-matter systems are composed of macromolecules or nanoparticles suspended in water. The characteristic times at intrinsic length scales of a few nanometres fall therefore in the microsecond and sub-microsecond time regimes. With the development of free-electron lasers (FELs) and fourth-generation synchrotron light-sources, time-resolved experiments in such time and length ranges will become routinely accessible in the near future. In the present work we report our findings on prototypical soft-matter systems, composed of charge-stabilized silica nanoparticles dispersed in water, with radii between 12 and 15 nm and volume fractions between 0.005 and 0.2. The sample dynamics were probed by means of X-ray photon correlation spectroscopy, employing the megahertz pulse repetition rate of the European XFEL and the Adaptive Gain Integrating Pixel Detector. We show that it is possible to correctly identify the dynamical properties that determine the diffusion constant, both for stationary samples and for systems driven by XFEL pulses. Remarkably, despite the high photon density the only observable induced effect is the heating of the scattering volume, meaning that all other X-ray induced effects do not influence the structure and the dynamics on the probed timescales. This work also illustrates the potential to control such induced heating and it can be predicted with thermodynamic models.

An improved understanding of fundamental chemistry, electronic structure, morphology, and dynamics in polymers and soft materials requires advanced characterization techniques that are amenable to in situ and operando studies. Soft X-ray methods are especially useful in their ability to non-destructively provide information on specific materials or chemical moieties. Analysis of these experiments, which can be very dependent on X-ray energy and polarization, can quickly become complex. Complementary modeling and predictive capabilities are required to properly probe these critical features. Here, we present relevant background on this emerging suite of techniques. We focus on how the combination of theory and experiment has been applied and can be further developed to drive our understanding of how these methods probe relevant chemistry, structure, and dynamics in soft materials.

An improved understanding of fundamental chemistry, electronic structure, morphology, and dynamics in polymers and soft materials requires advanced characterization techniques that are amenable to in situ and operando studies. Soft X-ray methods are especially useful in their ability to non-destructively provide information on specific materials or chemical moieties. Analysis of these experiments, which can be very dependent on X-ray energy and polarization, can quickly become complex. Complementary modeling and predictive capabilities are required to properly probe these critical features. Here, we present relevant background on this emerging suite of techniques. We focus on how the combination of theory and experiment has been applied and can be further developed to drive our understanding of how these methods probe relevant chemistry, structure, and dynamics in soft materials.

High repetition-rate X-ray free-electron lasers (XFELs) enable the study of fast dynamics on microsecond time scales. Split-delay lines (SDLs) further bring the time scale down to femtoseconds by splitting and delaying the XFEL pulses. Crystals and multilayers are two common types of optical elements in SDLs, offering either long delay ranges or high temporal accuracy. In this work, we introduce the design of a hybrid SDL for the coherent diffraction endstation of Shanghai High Repetition Rate XFEL and Extreme Light Facility (SHINE). It uses crystals for the first branch and multilayers for the second one, thus simultaneously offering a relatively long delay range and high temporal accuracy. Moreover, a third branch can be installed to switch the SDL to the all-crystal configuration for longer delay ranges. [ABSTRACT FROM AUTHOR]

The new technical features and enhanced performance of the ID02 beamline with the Extremely Brilliant Source (EBS) at the ESRF are described. The beamline enables static and kinetic investigations of a broad range of systems from ångström to micrometre size scales and down to the sub‐millisecond time range by combining different small‐angle X‐ray scattering techniques in a single instrument. In addition, a nearly coherent beam obtained in the high‐resolution mode allows multispeckle X‐ray photon correlation spectroscopy measurements down to the microsecond range over the ultra‐small‐ and small‐angle regions. While the scattering vector (of magnitude q) range covered is the same as before, 0.001 ≤ q ≤ 50 nm−1 for an X‐ray wavelength of 1 Å, the EBS permits relaxation of the collimation conditions, thereby obtaining a higher flux throughput and lower background. In particular, a coherent photon flux in excess of 1012 photons s−1 can be routinely obtained, allowing dynamic studies of relatively dilute samples. The enhanced beam properties are complemented by advanced pixel‐array detectors and high‐throughput data reduction pipelines. All these developments together open new opportunities for structural, dynamic and kinetic investigations of out‐of‐equilibrium soft matter and biophysical systems. [ABSTRACT FROM AUTHOR]

An improved understanding of fundamental chemistry, electronic structure, morphology, and dynamics in polymers and soft materials requires advanced characterization techniques that are amenable to in situ and operando studies. Soft X-ray methods are especially useful in their ability to non-destructively provide information on specific materials or chemical moieties. Analysis of these experiments, which can be very dependent on X-ray energy and polarization, can quickly become complex. Complementary modeling and predictive capabilities are required to properly probe these critical features. Here, we present relevant background on this emerging suite of techniques. We focus on how the combination of theory and experiment has been applied and can be further developed to drive our understanding of how these methods probe relevant chemistry, structure, and dynamics in soft materials.

An improved understanding of fundamental chemistry, electronic structure, morphology, and dynamics in polymers and soft materials requires advanced characterization techniques that are amenable to in situ and operando studies. Soft X-ray methods are especially useful in their ability to non-destructively provide information on specific materials or chemical moieties. Analysis of these experiments, which can be very dependent on X-ray energy and polarization, can quickly become complex. Complementary modeling and predictive capabilities are required to properly probe these critical features. Here, we present relevant background on this emerging suite of techniques. We focus on how the combination of theory and experiment has been applied and can be further developed to drive our understanding of how these methods probe relevant chemistry, structure, and dynamics in soft materials.

The CoSAXS beamline at the MAX IV Laboratory is a modern multi‐purpose (coherent) small‐angle X‐ray scattering (CoSAXS) instrument, designed to provide intense and optionally coherent illumination at the sample position, enabling coherent imaging and speckle contrast techniques. X‐ray tracing simulations used to design the beamline optics have predicted a total photon flux of 1012–1013 photons s−1 and a degree of coherence of up to 10% at 7.1 keV. The normalized degree of coherence and the coherent flux of this instrument were experimentally determined using the separability of a ptychographic reconstruction into multiple mutually incoherent modes and thus the Coherence in the name CoSAXS was verified. How the beamline can be used both for coherent imaging and XPCS measurements, which both heavily rely on the degree of coherence of the beam, was demonstrated. These results are the first experimental quantification of coherence properties in a SAXS instrument at a fourth‐generation synchrotron light source. [ABSTRACT FROM AUTHOR]

Linking the physics of the relaxation behavior of viscoelastic fluids as they form arrested gel states to the underlying chemical changes is essential for developing predictive controls on the properties of the suspensions. In this study, 3 wt.% laponite suspensions are studied as model systems to probe the influence of salt-induced relaxation behavior arising from the assembly of laponite nanodisks. X-ray Photon Correlation Spectroscopy (XPCS) measurements show that laponite suspensions prepared in the presence of 5 mM concentrations of CaCl2, MgCl2 and CsCl salts accelerate the formation of arrested gel states, with CaCl2 having a significant impact followed by CsCl and MgCl2 salts. The competing effects of ion size and charge on relaxation behavior are noted. For example, the relaxation times of laponite suspensions in the presence of Mg2+ ions are slower compared to Cs+ ions despite the higher charge, suggesting that cation size dominates in this scenario. The faster relaxation behavior of laponite suspensions in the presence of Ca2+ ions compared to Cs+ ions shows that a higher charge dominates the size of the ion. The trends in relaxation behavior are consistent with the cluster formation behavior of laponite suspensions and the electrostatic interactions predicted from MD simulations. Charge balance is achieved by the intercalation of the cations at the negatively charged surfaces of laponite suspensions. These studies show that the arrested gel state of laponite suspensions is accelerated in the presence of salts, with ion sizes and charges having a competing effect on relaxation behavior.

The nanometer length-scale holds precious information on several dynamical processes that develop from picoseconds to seconds. In the past decades, X-ray scattering techniques have been developed to probe the dynamics at such length-scales on either ultrafast (sub-nanosecond) or slow ((milli-)second) time scales. With the start of operation of the European XFEL, thanks to the MHz repetition rate of its X-ray pulses, even the intermediate μ s range have become accessible. Measuring dynamics on such fast timescales requires the development of new technologies such as the Adaptive Gain Integrating Pixel Detector (AGIPD). μ s-XPCS is a promising technique to answer many scientific questions regarding microscopic structural dynamics, especially for soft condensed matter systems. However, obtaining reliable results with complex detectors at free-electron laser facilities is challenging and requires more sophisticated analysis methods compared to experiments at storage rings. Here, we discuss challenges and possible solutions to perform XPCS experiments with the AGIPD at European XFEL; in particular, at the Materials Imaging and Dynamics (MID) instrument. We present our data analysis pipeline and benchmark the results obtained at the MID instrument with a well-known sample composed by silica nanoparticles dispersed in water. [ABSTRACT FROM AUTHOR]

In the past two decades, numerous relaxation or physical aging experiments of metallic glasses have revealed signatures of intermittent atomic-scale processes. Revealed via intensity cross-correlations from coherent scattering using X-ray photon correlation spectroscopy (XPCS), the observed abrupt changes in the time-domain of atomic motion does not fit the picture of gradual slowing down of relaxation times and their origin continues to remain unclear. Using a binary Lennard-Jones model glass subjected to microsecond-long isotherms, we show here that temporally and spatially heterogeneous atomic-cluster activity at different length-scales drive the emergence of highly non-monotonous intensity cross-correlations. The simulated XPCS experiments reveal a variety of time-dependent intensity-cross correlations that, depending on both the structural evolution and the q -space sampling, give detailed insights into the possible structural origins of intermittent aging measured with XPCS. [Display omitted] [ABSTRACT FROM AUTHOR]

The application of X-ray photon correlation spectroscopy (XPCS) at free-electron laser (FEL) facilities enables, for the first time, the study of dynamics on a (sub-)nanometre scale in an unreached time range between femtoseconds and seconds. For soft-matter materials, radiation damage is a major limitation when going beyond single-shot applications. Here, an XPCS study is presented at a hard X-ray FEL on radiation-sensitive polymeric poly(N-isopropylacrylamide) (PNIPAM) nanoparticles. The dynamics of aqueous suspensions of densely packed silica-PNIPAM core-shell particles and a PNIPAM nanogel below the radiation-damage threshold are determined. The XPCS data indicate non-diffusive behaviour, suggesting ballistic and stress-dominated heterogeneous particle motions. These results demonstrate the feasibility of XPCS experiments on radiation-sensitive soft-matter materials at FEL sources and pave the way for future applications at MHz repetition rates as well as ultrafast modes using split-pulse devices.

An experimental setup to measure X‐ray photon correlation spectroscopy during continuous sample translation is presented and its effectiveness as a means to avoid sample damage in dynamics studies of protein diffusion is evaluated. X‐ray damage from focused coherent synchrotron radiation remains below tolerable levels as long as the sample is translated through the beam sufficiently quickly. Here it is shown that it is possible to separate sample dynamics from the effects associated with the transit of the sample through the beam. By varying the sample translation rate, the damage threshold level, Dthresh = 1.8 kGy, for when beam damage begins to modify the dynamics under the conditions used, is also determined. Signal‐to‐noise ratios, Rsn ≥ 20, are obtained down to the shortest delay times of 20 µs. The applicability of this method of data collection to the next generation of multi‐bend achromat synchrotron sources is discussed and it is shown that sub‐microsecond dynamics should be obtainable on protein samples. [ABSTRACT FROM AUTHOR]

High repetition-rate X-ray free-electron lasers (XFELs) enable the study of fast dynamics on microsecond time scales. Split-delay lines (SDLs) further bring the time scale down to femtoseconds by splitting and delaying the XFEL pulses. Crystals and multilayers are two common types of optical elements in SDLs, offering either long delay ranges or high temporal accuracy. In this work, we introduce the design of a hybrid SDL for the coherent diffraction endstation of Shanghai High Repetition Rate XFEL and Extreme Light Facility (SHINE). It uses crystals for the first branch and multilayers for the second one, thus simultaneously offering a relatively long delay range and high temporal accuracy. Moreover, a third branch can be installed to switch the SDL to the all-crystal configuration for longer delay ranges.

Self-propelled particulate systems manifest certain collective behavior of living matter, which have been the subject of intense research over the past decades. One of the elegant methods for realizing such active motions is by means of custom synthesized Janus particles suspended in a catalytic medium that can be triggered upon illumination by ultraviolet light. In this work, the evolution of the particle dynamics from passive diffusive to active ballistic behavior upon light illumination was probed by multispeckle x-ray photon correlation spectroscopy (XPCS). This technique enables not only studying the emergence of active motions in three dimensions (3D) but also deciphering different contributions to the overall dynamics. Using a combination of homodyne and heterodyne analysis, the ensemble averaged mean velocity, velocity fluctuations and diffusion coefficient of particles were determined in the thermodynamic limit. Results revealed a gradual transition from diffusive to ballistic dynamics with systematic increase of the catalytic activity. At the intermediate region, the dynamics is dominated by Gaussian velocity fluctuations and an enhanced relaxation rate with a weaker wave vector dependence similar to superdiffusive behavior. For the highest activity, the dynamics became purely ballistic with Lorentzian-like distribution of velocity fluctuations. Presented results demonstrate that different aspects of active dynamics can be investigated in 3D over a broad range of Péclet numbers and other control parameters by means of multispeckle XPCS.

We reveal a slow-to-fast dynamics transition in the as-cast Cu 46 Zr 46 Al 8 (at.%) metallic glass (MG) at a temperature below the glass transition upon heating, which depends on the competition between free volume annihilation and thermally-activated atomic mobility, well consistent with the bond-length change of Cu-Cu pairs. The activation of α -relaxation at high temperatures could be related to the bond-length extension of Cu-Cu and Zr-Zr like-atom pairs together with the shortening of Cu-Zr unlike-atom pairs. Our results provide new insights into the correlation of dynamics with atomic structure in MGs and will be helpful to the understanding of ageing behaviors in MGs. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Probing the microscopic slow structural relaxation in oxide glasses by X‐ray photon correlation spectroscopy (XPCS) revealed faster than expected dynamics induced by the X‐ray illumination. The fast beam‐induced dynamics mask true slow structural relaxation in glasses and challenges application of XPCS to probe the atomic dynamics in oxide glasses. Here an approach that allows estimation of the true relaxation time of the sample in the presence of beam‐induced dynamics is presented. The method requires two measurements either with different X‐ray beam intensities or at different temperatures. Using numerical simulations it is shown that the slowest estimated true relaxation time is limited by the accuracy of the measured relaxation times of the sample. By analyzing the reported microscopic dynamics in SiO2, GeO2 and B2O3 glasses, it is concluded that the beam‐induced dynamics show rich behavior depending on the sample. [ABSTRACT FROM AUTHOR]

X‐ray speckle visibility spectroscopy using X‐ray free‐electron lasers has long been proposed as a probe of fast dynamics in noncrystalline materials. In this paper, numerical modeling is presented to show how the data interpretation of visibility spectroscopy can be impacted by the nonidealities of real‐life X‐ray detectors. Using simulated detector data, this work provides a detailed analysis of the systematic errors of several contrast extraction algorithms in the context of low‐count‐rate X‐ray speckle visibility spectroscopy and their origins are discussed. Here, it was found that the finite detector charge cloud and pixel size lead to an unavoidable 'degeneracy' in photon position determination, and that the contrasts extracted using different algorithms can all be corrected by a simple linear model. The results suggest that experimental calibration of the correction coefficient at the count rate of interest is possible and essential. This allows computationally lightweight algorithms to be implemented for on‐the‐fly analysis. [ABSTRACT FROM AUTHOR]

The nanometer length-scale holds precious information on several dynamical processes that develop from picoseconds to seconds. In the past decades, X-ray scattering techniques have been developed to probe the dynamics at such length-scales on either ultrafast (sub-nanosecond) or slow ((milli-)second) time scales. With the start of operation of the European XFEL, thanks to the MHz repetition rate of its X-ray pulses, even the intermediate μs range have become accessible. Measuring dynamics on such fast timescales requires the development of new technologies such as the Adaptive Gain Integrating Pixel Detector (AGIPD). μs-XPCS is a promising technique to answer many scientific questions regarding microscopic structural dynamics, especially for soft condensed matter systems. However, obtaining reliable results with complex detectors at free-electron laser facilities is challenging and requires more sophisticated analysis methods compared to experiments at storage rings. Here, we discuss challenges and possible solutions to perform XPCS experiments with the AGIPD at European XFEL; in particular, at the Materials Imaging and Dynamics (MID) instrument. We present our data analysis pipeline and benchmark the results obtained at the MID instrument with a well-known sample composed by silica nanoparticles dispersed in water.

A compact hard X‐ray split‐and‐delay line for studying ultrafast dynamics at free‐electron laser sources is presented. The device is capable of splitting a single X‐ray pulse into two fractions to introduce time delays from −5 to 815 ps with femtosecond resolution. The split‐and‐delay line can operate in a wide and continuous energy range between 7 and 16 keV. Compact dimensions of 60 × 60 × 30 cm with a total weight of about 60 kg make it portable and suitable for direct installation in an experimental hutch. The concept of the device is based on crystal diffraction. The piezo‐driven stages utilized in the device give nanometre positioning accuracy. On‐line monitoring systems based on X‐ray cameras and intensity monitors are implemented to provide active alignment feedback. Performance estimates of the system are also presented. [ABSTRACT FROM AUTHOR]

This article presents the main technical features and performance of the upgraded beamline ID02 at the ESRF. The beamline combines different small‐angle X‐ray scattering techniques in one unique instrument, enabling static and kinetic investigations from ångström to micrometre size scales and time resolution down to the sub‐millisecond range. The main component of the instrument is an evacuated detector tube of length 34 m and diameter 2 m. Several different detectors are housed inside a motorized wagon that travels along a rail system, allowing an automated change of the sample–detector distance from about 1 to 31 m as well as selection of the desired detector. For optional combined wide‐angle scattering measurements, a wide‐angle detector is installed at the entrance cone of the tube. A scattering vector (of magnitude q) range of 0.002 ≤ q ≤ 50 nm−1 is covered with two sample–detector distances and a single‐beam setting for an X‐ray wavelength of 1 Å. In the high‐resolution mode, two‐dimensional ultra‐small‐angle X‐ray scattering patterns down to q < 0.001 nm−1 can be recorded, and the resulting one‐dimensional profiles have superior quality as compared to those measured with an optimized Bonse–Hart instrument. In the highest‐resolution mode, the beam is nearly coherent, thereby permitting multispeckle ultra‐small‐angle X‐ray photon correlation spectroscopy measurements. The main applications of the instrument include the elucidation of static and transient hierarchical structures, and nonequilibrium dynamics in soft matter and biophysical systems. The technical features and performance of a new instrument for time‐resolved ultra‐small‐angle and coherent X‐ray scattering are presented. The instrument enables static and kinetic investigations from ångström to micrometre size scales and time resolution down to the sub‐millisecond range. Applications include elucidation of static and transient hierarchical structures in soft matter and biophysical systems. [ABSTRACT FROM AUTHOR]

Successful implementation of the single‐photon‐counting Eiger 500k pixel array detector for sub‐millisecond X‐ray photon correlation spectroscopy (XPCS) measurements in the ultra‐small‐angle scattering region is reported. The performance is demonstrated by measuring the dynamics of dilute silica colloids in aqueous solvents when the detector is operated at different counter depths, 4, 8 and 12 bit. In the fastest mode involving 4 bit parallel readout, a stable frame rate of 22 kHz is obtained that enabled measurement of intensity–intensity autocorrelation functions with good statistics down to the 50 µs range for a sample with sufficient scattering power. The high frame rate and spatial resolution together with large number of pixels of the detector facilitate the investigation of sub‐millisecond dynamics over a broad length scale by multispeckle XPCS. This is illustrated by an example involving phoretic motion of colloids during the phase separation of the solvent. The performance of the high‐resolution fast‐photon‐counting Eiger 500k detector for sub‐millisecond X‐ray photon correlation spectroscopy measurement is demonstrated. [ABSTRACT FROM AUTHOR]

X-ray photon correlation spectroscopy accesses a wide variety of dynamic phenomena at the nanoscale by studying the temporal correlations among photons that are scattered by a material in dynamical equilibrium when it is illuminated with a coherent X-ray beam. The information that is obtained is averaged over the illuminated area, which is generally of the order of several square microns. We propose here that more local information can be obtained by using nanobeams with great potential for the study of heterogeneous systems and show the feasibility of this approach with the support of numerical simulations.