Coherent X-ray Research Articles

High-resolution imaging of organic and inorganic nanoparticles at nanometre-scale resolution by X-ray ensemble diffraction microscopy.

Coherent diffraction microscopy (CDM) is a robust direct imaging method due to its unique 2D/3D phase retrieval capacity. Nonetheless, its resolution faces limitations due to a diminished signal-to-noise ratio (SNR) in high-frequency regions. Addressing this challenge, X-ray ensemble diffraction microscopy (XEDM) emerges as a viable solution, ensuring an adequate SNR in high-frequency regions and effectively surmounting resolution constraints. In this article, two experiments were conducted to underscore XEDM's superior spatial resolution capabilities. These experiments employed 55 nm-sized silicon-gold nanoparticles (NPs) and 19 nm-sized nodavirus-like particles (NV-LPs) on the coherent X-ray scattering beamline of the Taiwan Photon Source. The core-shell density distribution of the silicon-gold NPs was successfully obtained with a radial resolution of 3.4 nm per pixel, while NV-LPs in solution were reconstructed at a radial resolution of 1.3 nm per pixel. The structural information was directly retrieved from the diffraction intensities without prior knowledge and was subsequently confirmed through transmission electron microscopy.

Comparative Study on Phase Imaging of X-Ray and Neutron Sources

After the discovery of X-ray in 1895 the vast majority of radiographs have been taken and interpreted on the basis of absorption contrast of the object. In recent years the possibility of utilizing phase-contrast effect has received considerable attention. This new technique is capable of providing improved information from weakly absorbing samples, together with improved edge enhancement. The method requires use of coherent X-rays to allow wave interferences to occur and manifest itself as contrast formation in the intensity distribution recorded at the detector plane. This paper presents study of phase contrast imaging technique using X-rays & neutron sources.

Giant deformation potential induced small polaron effect in Dion–Jacobson two-dimensional lead halide perovskites

Abstract Halide perovskites have attracted much attention recently. However, the strong lattice distortion effects in these materials have led to debates regarding the nature of charge carriers. While the behavior of carriers in bulk three-dimensional materials is well-documented, the characteristics of carriers in two-dimensional perovskites remain less understood. In this study, we provide direct and clear evidence of small polaron formation through transient spectroscopic analysis of deformation potential and dynamic lattice screening. Coherent acoustic phonon wave signals reveal a strong coupling between carriers and lattice degrees of freedom, leading to small polaron formation and a spin lifetime enhancement of up to tenfold. Utilizing optical Kerr spectroscopy and theoretical modeling, we observed a notably long polarization response time at room temperature, attributed to lattice distortion and small polarons approximately two-unit cells in size. Temperature-dependent coherent phonon dynamics and X-ray diffraction further confirmed the presence of small polarons. This discovery underscores the significance of the cooperative interplay between exciton dynamics and the small polaron field, particularly in influencing the Coulomb exchange interaction of excitons.

Spatial coherence of synchrotron radiation degraded by grating monochromators

Fourth-generation synchrotron sources promise an enormous increase in the spatial coherence of X-ray radiation. In the EUV to soft X-ray range, the spatial coherence could reach almost 100% in both the horizontal and vertical directions. Identifying and understanding potential sources of degradation in the spatial coherence of X-rays transported along the beamline is critical to enable optimal performance for the experiments at the beamlines. Grating monochromators are an essential optical component of most EUV and soft X-ray beamlines. Recently, we have found that the spatial coherence is strongly degraded by the gratings used in these monochromators. In this work, we present a detailed physical and theoretical description of the origin and underlying effects that cause this degradation and describe the influence of the grating parameters and the exit slit of the monochromator. The theoretical analysis is presented in the framework of statistical optics. It is important to note that the described effects in the paper are distinct from the decoherence effects based on optics vibrations and the resulting virtual source broadening or wavefront degradation caused by surface irregularities and optical roughness.

Spatial filtering and optimal generation of high-flux soft x-ray high harmonics using a Bessel–Gauss beam

In recent years, significant advancements in high-repetition-rate, high-average-power mid-infrared laser pulses have enabled the generation of tabletop high-flux coherent soft x-ray harmonics for photon-hungry experiments. However, for practical applications, it is crucial to effectively filter out the driving beam from the high harmonics. In this study, we leverage the distinctive properties of a Bessel–Gauss (BG) beam to introduce a novel approach for spatial filtering, specifically targeting soft x-ray harmonics, releasing with a high-photon flux simultaneously. Our simulations reveal that by finely adjusting the focus geometry and gas pressure, the BG beam naturally adopts an annular shape, emitting high harmonics with minimal divergence in the far field. To achieve complete spatial separation of the driving beam and harmonic emissions, we pinpoint the optimal gas pressure and focusing geometry, particularly under overdriven laser intensities, for achieving good phase matching of harmonic emissions from short-trajectory electrons within the gas medium when the exact ionization level is higher than the “critical” value. Additionally, we establish scaling relations for sustaining optimal phase-matching conditions crucial for spatially separating the driving laser and the high-harmonic field, especially as the wavelength of the driving laser increases. Furthermore, our analysis demonstrates a substantial enhancement of harmonic yields by at least one order of magnitude compared to a truncated Gaussian annular beam. We also show that under accessible experimental conditions, soft x-ray photon flux up to 1010 photons/s at 250 eV can be achieved. The utilization of the BG beam opens up a promising pathway for the development of high-flux attosecond soft x-ray light sources, poised to serve a wide range of applications.

(Invited) Coherent X-ray Studies of Electrode Nanoparticles and Surfaces

Coherent X-rays provide a unique structural and dynamical viewpoint of electrode surfaces and nanoparticles. Using the coherent X-ray techniques, we have been studying several electrochemical phenomena such as electrochemical dissolution reactions of silver surfaces and nanoparticles, oxygen reduction/evolution reactions of platinum and platinum alloy nanoparticles, and the surface reconstruction dynamics of gold surfaces and nanoparticles. The coherent X-ray techniques are typically developed for real-space images and real-time dynamics. For imaging techniques, X-ray imaging such as Bragg Coherent Diffraction Imaging (BCDI) is used to image nanoparticles, and X-ray Ptychography is used to image electrode surfaces, and X-ray photon correlation spectroscopy (XPCS) is used to monitor the electrode surface dynamics.In this talk, we will present a broad overview of the examples based on our previous studies and provide each example with an emphasis on the uniqueness of the coherent X-ray techniques and the structural and dynamical aspects of the electrodes, unavailable in traditional X-ray techniques. We will also provide a perspective of the coherent X-ray techniques using the more powerful and brilliant coherent X-rays becoming available in the newest generation X-ray photon sources such as upgraded Advanced Photon Source (APS-U).

Nanoscopic Strain-Associated Lithium Diffusion in Single-Crystalline NMC Battery Particles

Understanding the dynamics of lithium diffusion within solid-state electrodes is pivotal for advancing high-performance batteries. Conventionally, lithium diffusion within solid-solution battery particles has been assumed to be solely driven in the direction of minimizing the concentration gradient, resulting in a monotonous lithium distribution. However, employing operando scanning transmission X-ray microscopy, this study has revealed the presence of non-monotonous dense and dilute concentration domains of lithium within individual single-crystalline LiNi1/3Mn1/3Co1/3O2 particles at the nanoscale during charging and discharging processes. Our findings advocate that the formation of Li-dense and -dilute domains is associated with nanoscopic non-uniform strain fields, challenging conventional solid-solution lithium diffusion models that rely solely on the concentration gradient as the driving force. Bragg coherent X-ray diffraction imaging verified such non-uniform nanoscopic intraparticle strain fields, which may cause the direction of lithium diffusion to deviate from the direction of the concentration gradient. Moreover, we have identified that Li-dilute domains near the surface could be manipulated in situ to enhance rate-capability. This study paves a new avenue for understanding solid-state diffusion at the nanoscale, enabling the fabrication of high-performance batteries. Figure 1

Origin of Structural Degradation in Li-Rich Layered Oxide Cathode

Li and Mn-rich cathode materials (LMR) that utilize both cation and anion redox can yield substantial increases in battery energy density.1-3 However, even though voltage decay issues cause continuous energy loss and impedes its commercialization, prerequisite driving force for this phenomena are a mystery3-6 Here, with in-situ nanoscale sensitive coherent X-ray diffraction imaging (BCDI) techniques, we reveal that nanostrain and lattice displacement accumulate continuously during cell operation. Evidence unequivocally shows that this effect is the driving force for both structure degradations and oxygen loss that triggers the well-known rapid voltage decay in LMR. By further leveraging micro to macro length characterizations that span atomic structure, primary particle, multi-particle and electrode level, we demonstrate that the heterogeneous nature of LMR cathodes inevitably causes pernicious phase displacement/strain which cannot be eliminated by conventional doping or coating methods. These results affirm that lattice displacement and nano-strain, which represent commonly occurred but less detectable dynamic structure evolutions, play an undeniable role in structure decomposition and voltage fade. With these fundamental discoveries, we propose mesostructural design as a strategy to mitigate lattice displacement and inhomogeneous electrochemical/structural evolutions, thereby achieving stable voltage and capacity profiles. These findings highlight the significance of lattice strain/displacement in causing voltage decay and will inspire a wave of efforts to unlock the potential of the broad-scale commercialization of LMR cathode material.

Spectral analysis of ultraluminous X-ray pulsars with models of X-ray pulsars

ABSTRACT A fraction of the ultraluminous X-ray (ULX) sources are known to be accreting neutron stars as they show coherent X-ray pulsations with pulse periods ranging from ${\sim} 1{\!-\!}30$ s. While initially thought to host intermediate-mass black holes, ULXs have since been recognized as a diverse class of objects, including ULX pulsars. These pulsars require models specifically tailored to account for their unique accretion physics, distinct from those used for Galactic black hole binaries. The X-ray spectra of all Galactic accreting X-ray pulsars (including sources in the Magellanic Clouds) are dominated by a high-energy cut-off power law and some of the sources show a soft excess, some emission lines, cyclotron absorption features, etc. In this work, we undertake a comprehensive analysis of the broad-band X-ray spectra of five ULX pulsars using simultaneous XMM–Newton and NuSTAR observations and show that their X-ray spectra can be effectively described by spectral models, similar to those used for the local accretion-powered X-ray pulsars. A soft excess is detected in all the sources which is also consistent with the local X-ray pulsars that have low absorption column density. We have marginal detection or low upper limit on the presence of the iron K-alpha emission line from these sources, which is a key difference of the ULX pulsars with the local accreting X-ray pulsars. We discuss the implication of this on the nature of the binary companion and the accretion mechanism in the ULX pulsars.

In situ visualisation of zeolite anisotropic framework flexibility during catalysis

Zeolites exhibit framework flexibility driving their chemical and catalytic properties. Since the zeolitic pores are extremely small, a slight strain generated in the crystal induces compelling changes in shape, connectivity, accessibility, and the framework chemical properties. These modifications affected the adsorption and desorption of reactants/products and the diffusion within the channels during reaction. Using in situ 3D Bragg coherent X-ray diffraction imaging, we unveil the dynamics of the zeolite structure during catalysis, contraction and/or expansion of its framework also known as zeolite framework flexibility. We imaged three-dimensionally a single faujasite zeolite crystal during the ethanol dehydration reaction revealing anisotropic lattice dynamics simultaneously to guest molecules formation. Understanding zeolite flexibility could permit to tune zeolites properties towards potentially higher adsorption and selectivity.

Imaging in-operando LiCoO2 nanocrystallites with Bragg coherent X-ray diffraction

Although the LiCoO2 (LCO) cathode material has been widely used in commercial lithium ion batteries (LIB) and shows high stability, LIB’s improvements have several challenges that still need to be overcome. In this paper, we have studied the in-operando structural properties of LCO within battery cells using Bragg Coherent X-ray Diffraction Imaging to identify ways to optimise the LCO batteries’ cycling. We have successfully reconstructed the X-ray scattering phase variation (a fingerprint of atomic displacement) within a ≈ (1.6 × 1.4 × 1.3) μm3 LCO nanocrystal across a charge/discharge cycle. Reconstructions indicate strained domains forming, expanding, and fragmenting near the surface of the nanocrystal during charging, with a determined maximum relative lattice displacements of 0.467 Å. While discharging, all domains replicate in reverse the effects observed from the charging states, but with a lower maximum relative lattice displacements of 0.226 Å. These findings show the inefficiency-increasing domain dynamics within LCO lattices during cycling.

Computer simulation of x-ray section topography of gas pores in a silicon carbide crystal

The results of computer simulation of images of gas pores in a silicon carbide crystal in sectional topograms, that is, during diffraction of a narrow beam of X-rays in the crystal, are presented for the first time. For this purpose, a special module of the universal computer program XRWP was used. This program is developing by the author to calculate the effects of coherent X-ray optics. The calculation method combines two methods, previously known, namely, Fourier transform methods (Kato method), and the method of solving the Takagi-Taupin equations. It is shown that gas pores can produce a wide variety of images, depending on the experimental conditions and the position of the gas pore inside the crystal.

Dynamic X-ray Coherent Diffraction Analysis: Bridging the Time Scales between Imaging and Photon Correlation Spectroscopy.

The advent of diffraction limited sources and developments in detector technology opens up new possibilities for the study of materials in situ and operando. Coherent X-ray diffraction techniques such as coherent X-ray diffractive imaging (CXDI) and X-ray photon correlation spectroscopy (XPCS) are capable for this purpose and provide complementary information, although due to signal-to-noise requirements, their simultaneous demonstration has been limited. Here, we demonstrate a strategy for the simultaneous use of CXDI and XPCS to study in situ the Brownian motion of colloidal gold nanoparticles of 200 nm diameter suspended in a glycerol-water mixture. We visualize the process of agglomeration, examine the spatiotemporal space accessible with the combination of techniques, and demonstrate CXDI with 22 ms temporal resolution.

Synchrotron X-ray imaging of soft biological tissues - principles, applications and future prospects.

Synchrotron-based tomographic phase-contrast X-ray imaging (SRµCT or SRnCT) is a versatile isotropic three-dimensional imaging technique that can be used to study biological samples spanning from single cells to human-sized specimens. SRµCT and SRnCT take advantage of the highly brilliant and coherent X-rays produced by a synchrotron light source. This enables fast data acquisition and enhanced image contrast for soft biological samples owing to the exploitation of phase contrast. In this Review, we provide an overview of the basics behind the technique, discuss its applications for biologists and provide an outlook on the future of this emerging technique for biology. We introduce the latest advances in the field, such as whole human organs imaged with micron resolution, using X-rays as a tool for virtual histology and resolving neuronal connections in the brain.

Octave-spanning supercontinuum coherent soft x-ray for producing a single-cycle soft x-ray pulse.

This study demonstrates the potential to generate a soft x-ray single-cycle attosecond pulse using a single-cycle mid-infrared pulse from advanced dual-chirped optical parametric amplification (DC-OPA). A super continuum high harmonic (HH) spectrum was generated in argon (80-160 eV) and neon (150-270 eV). The experimental spectra reasonably agree with those calculated by the strong-field approximation model and Maxwell's equations. In addition, simulation results indicate that the dispersion of HHs in argon can be compensated using a 207-nm Zr filter to obtain 40 as (Fourier transform limited (FTL)) pulses (1.1 cycles at 118 eV). For neon, a 278-nm Sn filter can compensate for the dispersion of HH and create 23 as FTL pulses (1.1 cycles at 206 eV). This soft x-ray single-cycle attosecond pulse is expected to be highly valuable for ultrafast science and applications in quantum information science.

3D Laser Lithography Technique in the Fabrication of a Coherent 2D Kinoform X-ray Lens

3D Laser Lithography Technique in the Fabrication of a Coherent 2D Kinoform X-ray Lens

Computer simulation of the effect of focusing X rays by means of refractive-diffractive lens

The features of focusing X rays using a refractive-diffractive lens (RDL), which is a system of two asymmetrically reflecting crystals with asymmetry factors, the product of which is equal to unity, and a refractive lens with a large focal length, are theoretically studied. Crystals make it possible to shorten the focal length of the lens by b2 times, where b is the asymmetry factor of the second crystal. A detailed numerical simulation of the effect of radiation focusing using the RDL has been performed. The universal computer program XRWP was used which is created to calculate the effects of coherent X-ray optics. Analytical formulas are obtained for the optimal aperture and radius of curvature of the lens, as well as for the width of the radiation spectrum that can be focused.

X-ray nano-holotomography reconstruction with simultaneous probe retrieval.

In conventional tomographic reconstruction, the pre-processing step includes flat-field correction, where each sample projection on the detector is divided by a reference image taken without the sample. When using coherent X-rays as a probe, this approach overlooks the phase component of the illumination field (probe), leading to artifacts in phase-retrieved projection images, which are then propagated to the reconstructed 3D sample representation. The problem intensifies in nano-holotomography with focusing optics, which, due to various imperfections creates high-frequency components in the probe function. Here, we present a new iterative reconstruction scheme for holotomography, simultaneously retrieving the complex-valued probe function. Implemented on GPUs, this algorithm results in 3D reconstruction resolving twice thinner layers in a 3D ALD standard sample measured using nano-holotomography.

Data-driven discovery of dynamics from time-resolved coherent scattering

Coherent X-ray scattering (CXS) techniques are capable of interrogating dynamics of nano- to mesoscale materials systems at time scales spanning several orders of magnitude. However, obtaining accurate theoretical descriptions of complex dynamics is often limited by one or more factors—the ability to visualize dynamics in real space, computational cost of high-fidelity simulations, and effectiveness of approximate or phenomenological models. In this work, we develop a data-driven framework to uncover mechanistic models of dynamics directly from time-resolved CXS measurements without solving the phase reconstruction problem for the entire time series of diffraction patterns. Our approach uses neural differential equations to parameterize unknown real-space dynamics and implements a computational scattering forward model to relate real-space predictions to reciprocal-space observations. This method is shown to recover the dynamics of several computational model systems under various simulated conditions of measurement resolution and noise. Moreover, the trained model enables estimation of long-term dynamics well beyond the maximum observation time, which can be used to inform and refine experimental parameters in practice. Finally, we demonstrate an experimental proof-of-concept by applying our framework to recover the probe trajectory from a ptychographic scan. Our proposed framework bridges the wide existing gap between approximate models and complex data.

Transverse recoil imprinted on free-electron radiation

Phenomena of free-electron X-ray radiation are treated almost exclusively with classical electrodynamics, despite the intrinsic interaction being that of quantum electrodynamics. The lack of quantumness arises from the vast disparity between the electron energy and the much smaller photon energy, resulting in a small cross-section that makes quantum effects negligible. Here we identify a fundamentally distinct phenomenon of electron radiation that bypasses this energy disparity, and thus displays extremely strong quantum features. This phenomenon arises when free-electron transverse scattering occurs during the radiation process, creating entanglement between each transversely recoiled electron and the photons it emitted. This phenomenon profoundly modifies the characteristics of free-electron radiation mediated by crystals, compared to conventional classical analysis and even previous quantum analysis. We also analyze conditions to detect this phenomenon using low-emittance electron beams and high-resolution X-ray spectrometers. These quantum radiation features could guide the development of compact coherent X-ray sources facilitated by nanophotonics and quantum optics.