High-resolution and high-sensitivity X-ray ptychographic coherent diffraction imaging using the CITIUS detector.

Ptychographic coherent diffraction imaging (PCDI) is a synchrotron X-ray microscopy technique that provides high spatial resolution and a wide field of view. To improve the performance of PCDI, the performance of the synchrotron radiation source and imaging detector should be improved. In this study, ptychographic diffraction pattern measurements using the CITIUS high-speed X-ray image detector and the corresponding image reconstruction are reported. X-rays with an energy of 6.5 keV were focused by total reflection focusing mirrors, and a flux of ∼2.6 × 1010 photons s-1 was obtained at the sample plane. Diffraction intensity data were collected at up to ∼250 Mcounts s-1 pixel-1 without saturation of the detector. Measurements of tantalum test charts and silica particles and the reconstruction of phase images were performed. A resolution of ∼10 nm and a phase sensitivity of ∼0.01 rad were obtained. The CITIUS detector can be applied to the PCDI observation of various samples using low-emittance synchrotron radiation sources and to the stability evaluation of light sources.

X-ray ptychographic and fluorescence microscopy using virtual single-pixel imaging based deconvolution with accurate probe images.

Simultaneous measurement of X-ray ptychography and fluorescence microscopy allows high-resolution and high-sensitivity observations of the microstructure and trace-element distribution of a sample. In this paper, we propose a method for improving scanning fluorescence X-ray microscopy (SFXM) images, in which the SFXM image is deconvolved via virtual single-pixel imaging using different probe images for each scanning point obtained by X-ray ptychographic reconstruction. Numerical simulations confirmed that this method can increase the spatial resolution while suppressing artifacts caused by probe imprecision, e.g., probe position errors and wavefront changes. The method also worked well in synchrotron radiation experiments to increase the spatial resolution and was applied to the observation of S element maps of ZnS particles.

Nanoscale domain imaging of Li-rich disordered rocksalt-type cathode materials with X-ray spectroscopic ptychography.

Lithium-rich disordered rocksalt-type cathode materials are promising for high-capacity and high-power lithium-ion batteries. Many of them are synthesized by mechanical milling and may have heterogeneous structures and chemical states at the nanoscale. In this study, we performed X-ray spectroscopic ptychography measurements of Li-rich disordered rocksalt-type oxide particles synthesized by mechanical milling before and after delithiation reaction at the vanadium K absorption edge, and visualized their structures and chemical state with a spatial resolution of ∼100 nm. We classified multiple domains with different chemical states via clustering analysis. A comparison of the domain distribution trends of the particles before and after the delithiation reaction revealed the presence of domains, suggesting that the delithiation reaction was suppressed.

Development and application of a tender X-ray ptychographic coherent diffraction imaging system on BL27SU at SPring-8.

Ptychographic coherent diffraction imaging (CDI) allows the visualization of both the structure and chemical state of materials on the nanoscale, and has been developed for use in the soft and hard X-ray regions. In this study, a ptychographic CDI system with pinhole or Fresnel zone-plate optics for use in the tender X-ray region (2-5 keV) was developed on beamline BL27SU at SPring-8, in which high-precision pinholes optimized for the tender energy range were used to obtain diffraction intensity patterns with a low background, and a temperature stabilization system was developed to reduce the drift of the sample position. A ptychography measurement of a 200 nm thick tantalum test chart was performed at an incident X-ray energy of 2.500 keV, and the phase image of the test chart was successfully reconstructed with approximately 50 nm resolution. As an application to practical materials, a sulfur polymer material was measured in the range of 2.465 to 2.500 keV including the sulfur K absorption edge, and the phase and absorption images were successfully reconstructed and the nanoscale absorption/phase spectra were derived from images at multiple energies. In 3 GeV synchrotron radiation facilities with a low-emittance storage ring, the use of the present system will allow the visualization on the nanoscale of the chemical states of various light elements that play important roles in materials science, biology and environmental science.

Single-frame coherent diffraction imaging of extended objects using triangular aperture.

We propose a method of single-frame coherent diffraction imaging using a triangular aperture, which can not only reconstruct the projection image of extended objects from a single-frame coherent diffraction pattern, but also improve the image of the wavefield of the probe. In this method, a plane-wave illuminates a triangular aperture. An object is placed immediately after the aperture or in the image plane of the aperture through a lens. A far-field coherent diffraction pattern is collected by a two-dimensional detector. The object image is reconstructed from the single-frame diffraction pattern using a phase retrieval algorithm without support constraints. We simulate feasible experimental setups in the hard X-ray regime and show that this method can be practical use for single-frame coherent diffraction imaging. The present method has the potential exploring dynamic phenomena in materials science and biology with high spatiotemporal resolution using synchrotron radiation/free-electron lasers.

Demonstration of single-frame coherent X-ray diffraction imaging using triangular aperture: Towards dynamic nanoimaging of extended objects.

Coherent diffraction imaging (CDI) is a powerful method for visualizing the structure of an object with a high spatial resolution that exceeds the performance limits of the lens. Single-frame CDI in the X-ray region has potential use for probing dynamic phenomena with a high spatiotemporal resolution. Here, we experimentally demonstrate a general method for single-frame X-ray CDI using a triangular aperture and a Fresnel zone plate. Using 5 keV synchrotron radiation X-rays, we reconstructed the object image of the locally illuminated area with a spatial resolution of higher than 50 nm and an exposure time of more than 0.1 s without prior information about the sample. After a 10 s exposure, a resolution of 17 nm was achieved. The present method opens new frontiers in the study of dynamics at the nanoscale by using next-generation synchrotron radiation X-rays/free-electron lasers as light sources.

Nanoscale determination of interatomic distance by ptychography-EXAFS method using advanced Kirkpatrick-Baez mirror focusing optics.

This work demonstrates a combination technique of X-ray ptychography and the extended X-ray absorption fine structure (ptychography-EXAFS) method, which can determine the interatomic distances of bulk materials at the nanoscale. In the high-resolution ptychography-EXAFS method, it is necessary to use high-intense coherent X-rays with a uniform wavefront in a wide energy range, hence a ptychographic measurement system installed with advanced Kirkpatrick-Baez mirror focusing optics is developed and its performance is evaluated. Ptychographic diffraction patterns of micrometre-size MnO particles are collected by using this system at 139 energies between 6.504 keV and 7.114 keV including the Mn K absorption edge, and then the EXAFS of MnO is derived from the reconstructed images. By analyzing the EXAFS spectra obtained from a 48 nm × 48 nm region, the nanoscale bond lengths of the first and second coordination shells of MnO are determined. The present approach has great potential to elucidate the unclarified relationship among the morphology, electronic state and atomic arrangement of inhomogeneous bulk materials with high spatial resolution.

Multibeam ptychography with synchrotron hard X-rays.

We report the first demonstration of multibeam ptychography using synchrotron hard X-rays, which can enlarge the field of view of the reconstructed image of objects by efficiently using partially coherent X-rays. We measured the ptychographic diffraction patterns of a Pt test sample and MnO particles using three mutually incoherent coherent beams with a high intensity that were produced by using both the multiple slits and a pair of focusing mirrors. We successfully reconstructed the phase map of the samples at a spatial resolution of 25 nm in a field of view about twice as wide as that in the single-beam ptychography. We also computationally simulated a feasible experimental setup using random modulators to further enlarge the field of view by increasing the number of available beams. The present method has the potential to enable the high spatial resolution and large field-of-view observation of specimens in materials science and biology.

Nanoscale Visualization of Phase Transition in Melting of Sn-Bi Particles by In situ Hard X-ray Ptychographic Coherent Diffraction Imaging.

The phase transition in the melting of Sn­Bi eutectic solder alloy particles was observed by in situ hard X-ray ptychographic coherent diffraction imaging with a pin-point heating system. Ptychographic diffraction patterns of micrometer-sized Sn­Bi particles were collected at temperatures from room temperature to 540 K. The projection images of each particle were reconstructed at a spatial resolution of 25 nm, showing differences in the phase shifts due to two crystal phases in the Sn­Bi alloy system and the Sn/Bi oxides at the surface. By quantitatively evaluating the Bi content, it became clear that the nonuniformity of the composition of Sn and Bi at the single-particle level exists when the particles are synthesized by centrifugal atomization.

Three-dimensional iterative multislice reconstruction for ptychographic X-ray computed tomography.

Ptychographic X-ray computed tomography (PXCT) is a potential tool for visualizing three-dimensional (3D) structures of large-volume samples at high spatial resolution. Currently, both the requirement of a large number of views and the narrow depth of field limit the range of applications of PXCT. Here, we propose an improved 3D reconstruction algorithm for PXCT that is based on 3D iterative reconstruction and multislice phase retrieval calculation. Computer simulations showed that the proposed algorithm can reduce the number of required views without degrading the spatial resolution. In a synchrotron experiment, ptychographic diffraction data sets of a flat and thick processor specimen were collected under a limited-angle condition, and then high-resolution multislice images of the Cu multilevel interconnects were clearly reconstructed using the proposed algorithm. The proposed algorithm is expected to open up a new frontier of large-volume 3D nanoimaging in various fields.

Modulation of Electron-Phonon Coupling in One-Dimensionally Nanorippled Graphene on a Macrofacet of 6H-SiC.

Local electron-phonon coupling of a one-dimensionally nanorippled graphene is studied on a SiC(0001) vicinal substrate. We have characterized local atomic and electronic structures of a periodically nanorippled graphene (3.4 nm period) prepared on a macrofacet of the 6H-SiC crystal using scanning tunneling microscopy/spectroscopy (STM/STS) and angle-resolved photoelectron spectroscopy (ARPES). The rippled graphene on the macrofacets distributes homogeneously over the 6H-SiC substrate in a millimeter scale, and thus replica bands are detected by the macroscopic ARPES. The STM/STS results indicate the strength of electron-phonon coupling to the out-of-plane phonon at the K̅ points of graphene is periodically modified in accordance with the ripple structure. We propose an interface carbon nanostructure with graphene nanoribbons between the surface rippled graphene and the substrate SiC that periodically modifies the electron-phonon coupling in the surface graphene.

Visualization of Heterogeneous Oxygen Storage Behavior in Platinum-Supported Cerium-Zirconium Oxide Three-Way Catalyst Particles by Hard X-ray Spectro-Ptychography.

The cerium density and valence in micrometer-size platinum-supported cerium-zirconium oxide Pt/Ce2 Zr2 Ox (x=7-8) three-way catalyst particles were successfully mapped by hard X-ray spectro-ptychography (ptychographic-X-ray absorption fine structure, XAFS). The analysis of correlation between the Ce density and valence in ptychographic-XAFS images suggested the existence of several oxidation behaviors in the oxygen storage process in the Ce2 Zr2 Ox particles. Ptychographic-XAFS will open up the nanoscale chemical imaging and structural analysis of heterogeneous catalysts.

Use of Kramers-Kronig relation in phase retrieval calculation in X-ray spectro-ptychography.

Coherent diffraction imaging (CDI) is a method for reconstructing the complex-valued image of an object from diffraction intensities by using iterative phasing methods. X-ray ptychography is a scanning type of CDI using X-rays, allowing us to visualize the complex transmission function of an extended specimen. We here propose the use of the Kramers-Kronig relation (KKR) as an additional constraint in phase retrieval algorithms for multiple-energy X-ray ptychography using the absorption edge of a specific element. A numerical simulation showed that the speed of convergence was increased by using the improved algorithm with the KKR. We successfully demonstrated its usefulness in a proof-of-principle experiment at SPring-8. The present algorithm is particularly useful for imaging X-ray absorption fine structures of a specific element buried within thick samples by hard X-ray spectro-ptychography.

Human mitotic chromosomes consist predominantly of irregularly folded nucleosome fibres without a 30-nm chromatin structure.

How a long strand of genomic DNA is compacted into a mitotic chromosome remains one of the basic questions in biology. The nucleosome fibre, in which DNA is wrapped around core histones, has long been assumed to be folded into a 30-nm chromatin fibre and further hierarchical regular structures to form mitotic chromosomes, although the actual existence of these regular structures is controversial. Here, we show that human mitotic HeLa chromosomes are mainly composed of irregularly folded nucleosome fibres rather than 30-nm chromatin fibres. Our comprehensive and quantitative study using cryo-electron microscopy and synchrotron X-ray scattering resolved the long-standing contradictions regarding the existence of 30-nm chromatin structures and detected no regular structure >11 nm. Our finding suggests that the mitotic chromosome consists of irregularly arranged nucleosome fibres, with a fractal nature, which permits a more dynamic and flexible genome organization than would be allowed by static regular structures.

Grain rotation and lattice deformation during photoinduced chemical reactions revealed by in situ X-ray nanodiffraction.

In situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) have been used to investigate many physical science phenomena, ranging from phase transitions, chemical reactions and crystal growth to grain boundary dynamics. A major limitation of in situ XRD and TEM is a compromise that has to be made between spatial and temporal resolution. Here, we report the development of in situ X-ray nanodiffraction to measure high-resolution diffraction patterns from single grains with up to 5 ms temporal resolution. We observed, for the first time, grain rotation and lattice deformation in chemical reactions induced by X-ray photons: Br(-) + hv → Br + e(-) and e(-) + Ag(+) → Ag(0). The grain rotation and lattice deformation associated with the chemical reactions were quantified to be as fast as 3.25 rad s(-1) and as large as 0.5 Å, respectively. The ability to measure high-resolution diffraction patterns from individual grains with a temporal resolution of several milliseconds is expected to find broad applications in materials science, physics, chemistry and nanoscience.

Multiple defocused coherent diffraction imaging: method for simultaneously reconstructing objects and probe using X-ray free-electron lasers.

The sample size must be less than the diffraction-limited focal spot size of the incident beam in single-shot coherent X-ray diffraction imaging (CXDI) based on a diffract-before-destruction scheme using X-ray free electron lasers (XFELs). This is currently a major limitation preventing its wider applications. We here propose multiple defocused CXDI, in which isolated objects are sequentially illuminated with a divergent beam larger than the objects and the coherent diffraction pattern of each object is recorded. This method can simultaneously reconstruct both objects and a probe from the coherent X-ray diffraction patterns without any a priori knowledge. We performed a computer simulation of the prposed method and then successfully demonstrated it in a proof-of-principle experiment at SPring-8. The prposed method allows us to not only observe broad samples but also characterize focused XFEL beams.

Dark-field X-ray ptychography.

The dynamic range of X-ray detectors is a key factor limiting both the spatial resolution and sensitivity of X-ray ptychography as well as the coherent flux of incident X-rays. Here, we propose a method for high-resolution and high-sensitivity X-ray ptychography named "dark-field X-ray ptychography", which compresses the dynamic range of intensities of diffraction patterns. In this method, a small reference object is aligned upstream of the sample. The scattered X-rays from the object work as a reference beam for in-line holography. Ptychographic diffraction patterns including the in-line hologram are collected, and then the image of the sample is reconstructed by an iterative phasing method. This method allows us to obscure the low-Q region of the diffraction patterns using a beamstop since the in-line hologram complements structural information in the low-Q region, resulting in the compression of the dynamic range of intensities of diffraction patterns. A numerical study shows that the dynamic range of intensities of diffraction patterns is decreased by about three orders of magnitude.

High-resolution multislice x-ray ptychography of extended thick objects.

We report the first demonstration of hard x-ray ptychography using a multislice approach, which can solve the problem of the limited spatial resolution under the projection approximation. We measured ptychographic diffraction patterns of a two-layered object with a 105 µm gap using 7 keV focused coherent x rays. We successfully reconstructed the phase map of each layer at ∼50 nm resolution using a multislice approach, while the resolution was worse than ∼192 nm under the projection approximation. The present method has the potential to enable the three-dimensional high-resolution observation of extended thick specimens in materials science and biology.

Coherent diffraction imaging analysis of shape-controlled nanoparticles with focused hard X-ray free-electron laser pulses.

We report the first demonstration of the coherent diffraction imaging analysis of nanoparticles using focused hard X-ray free-electron laser pulses, allowing us to analyze the size distribution of particles as well as the electron density projection of individual particles. We measured 1000 single-shot coherent X-ray diffraction patterns of shape-controlled Ag nanocubes and Au/Ag nanoboxes and estimated the edge length from the speckle size of the coherent diffraction patterns. We then reconstructed the two-dimensional electron density projection with sub-10 nm resolution from selected coherent diffraction patterns. This method enables the simultaneous analysis of the size distribution of synthesized nanoparticles and the structures of particles at nanoscale resolution to address correlations between individual structures of components and the statistical properties in heterogeneous systems such as nanoparticles and cells.

Dioxin pollution disrupts reproduction in male Japanese field mice.

Dioxins cause various adverse effects in animals including teratogenesis, induction of drug metabolizing enzymes, tumor promotion, and endocrine disruption. Above all, endocrine disruption is known to disturb reproduction in adult animals and may, also seriously impact their offspring. However, most previous studies have quantified the species-specific accumulation of dioxins, whereas few studies have addressed the physiological impacts of dioxins on wildlife, such as reduced reproductive function. Here we clarify an effect of endocrine disruption caused by dioxins on the Japanese field mouse, Apodemus speciosus. Japanese field mice collected from various sites polluted with dioxins accumulated high concentrations of dioxins in their livers. Some dioxin congeners, especially, 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin, 3,3',4,4',5-pentachloro biphenyl, 1,2,3,4,6,7,8-heptachlorodibenzofuran, and octachlorodibenzo-p-dioxin, which showed high biota-soil accumulation factors, contributed to concentration of dioxins in mouse livers with an increase of accumulation of total dioxins. As for physiological effects on the Japanese field mouse, high levels of cytochrome P450 1A1 (CYP1A1) mRNA, a drug metabolizing enzyme induced by dioxins, were found in the livers of mice captured at polluted sites. Furthermore, at such sites polluted with dioxins, increased CYP1A1 expression coincided with reduced numbers of active spermatozoa in mice. Thus, disruption in gametogenesis observed in these mice suggests that dioxins not only negatively impact reproduction among Japanese field mice, but might also act as a kind of selection pressure in a chemically polluted environment.