Jaemyung Kim

The high-energy X-ray beamline BL15XU is designed to drive advancements in materials science and high-pressure research by leveraging the photon source characteristics of SPring-8. The beamline provides an intense 100 keV pink beam, extracted from undulator radiation using a double-multilayer monochromator, and delivers a high flux of 6.0 × 10 ¹³ photons s ⁻¹ to the sample position. Experimental hutch 1 is dedicated to materials engineering, employing non-destructive methods based on scanning 3D X-ray diffraction and computed laminographic imaging. Experimental hutch 2 focuses on high-pressure science, and is equipped with a rotational slit system capable of switching between radiography and diffraction modes at speeds up to 144 Hz, with a minimum exposure time of approximately 2.7 ms. Installed high-pressure apparatuses include: the 1500 ton MADONNA multi-anvil press for generating pressures up to 120 GPa, the mobile 200 ton Hyaku-shiki press for in situ deformation experiments up to 20 GPa, and a dedicated Paris–Edinburgh press setup for pair distribution function analysis of liquids and amorphous materials over a wide momentum transfer range up to 27.8 Å ⁻¹ . These diverse capabilities establish BL15XU as a versatile platform for in situ investigations of materials science and high-pressure research, well prepared for future high-brilliance operations at SPring-8-II.

Recently developed inclined scanning three-dimensional X-ray diffraction ( i -S3DXRD) microscopy enables the non-destructive mapping of crystal orientations in planar-shaped specimens. However, its inherently slow raster-scanning procedure limits its practical applicability. In this work, we achieve a 21-fold reduction in the number of scans, from 51 × 37 to 51 + 37, by introducing a dual line–beam X-point (DLX) scanning mode in i -S3DXRD. Here, 51 and 37 correspond to the numbers of scan steps along the z and x directions under horizontally and vertically elongated X-ray beam illumination, respectively. The DLX approach selectively enhances diffraction peaks corresponding to the intersection point (X-point) through pixel-wise multiplication of two diffraction images acquired under horizontally and vertically elongated incident beams. Using the reorganized data, we performed multigrain indexing and found that the resulting orientation map agrees with that obtained from conventional point–beam raster scanning, demonstrating the validity and time efficiency of the DLX scanning mode.

Understanding the failure mechanisms of Pb-free solder joints during thermal cycling is a critical issue in electronic packaging, where solder joints strongly influence device reliability and lifetime. While electron backscatter diffraction (EBSD) has been widely used for this purpose, its destructive nature prevents tracking the microstructural evolution of solder joints from their pristine state. Non-destructive X-ray-based orientation microscopy techniques can address this limitation but typically require cylindrical, pillar-shaped specimens, which are incompatible with the planar geometry of practical solder joints. To overcome this constraint, we apply inclined scanning three-dimensional X-ray diffraction microscopy ( i -S3DXRD), which is specifically designed for plate-like specimens. Using i -S3DXRD, we found that thermal cycling induces preferential reorientation of β-Sn grains toward specific crystallographic directions relative to the Cu substrate. This reorientation is associated with recrystallization-assisted grain boundary migration and grain coalescence, and is closely related to the thermal fatigue behavior of Pb-free solder joints.

The spatial resolution in scanning-based two-dimensional microscopy is normally limited by the size of the probe, thereby a smaller probe is a prerequisite for enhancing the spatial resolution. For three-dimensional microscopy that combines translation and rotation motions of a specimen, however, complex trajectories of the probe highly overlap in the specimen, which could change the postulate above. Here, the spatial resolution achieved in scanning three-dimensional X-ray diffraction (s3DXRD) microscopy is investigated. In this method, the most appropriate orientation of the pixel in the specimen coordinate is selected by comparing the completeness of diffraction peaks with theory. Therefore, the superposed area of the beam trajectory has a strong effect on the spatial resolution, in terms of the completeness of diffraction peaks. It was found that the highly superposed area by the incident X-rays, which has the highest completeness factor in the pixel of the specimen, is much smaller than the X-ray probe size, and that sub-pixel analysis by dividing a pixel into small pieces leads to drastic improvement of the spatial resolution in s3DXRD.

The microstructure of a material plays a crucial role in determining its mechanical and chemical properties, as well as in predicting potential malfunctions. In polycrystalline materials, the orientation of each grain has a significant impact on the material's properties. It is thus imperative to conduct non-destructive 3D observations of the grain orientation with high resolution. This study presents a novel method to enhance the spatial resolution of 3D grain orientation maps in scanning 3D X-ray diffraction (S3DXRD) microscopy beyond the size of the probe beam. The new method, inclined scanning 3D X-ray diffraction (iS3DXRD) microscopy, combines an inclined geometry for the rotation axis of the object with the concept of `sub-voxel' analysis, where the voxel is subdivided into smaller pieces. The validity of the method was verified for a polycrystalline α-Fe wire using a 37 keV X-ray beam with a size of 10 × 20 µm (horizontal × vertical), and it successfully produced a high-resolution 3D grain orientation map with a spatial resolution of about 2.5 µm. The method can provide complex details on the microstructure of a polycrystalline material, which will pave the way for precise prediction of the material's properties.

The compositional space of high-entropy-alloy nanoparticles (HEA NPs) significantly expands the diversity of the materials library. Every atom in HEA NPs has a different elemental coordination environment, which requires knowledge of the local electronic structure at an atomic level. However, such structure has not been disclosed experimentally or theoretically. We synthesized HEA NPs composed of all eight noble-metal-group elements (NM-HEA) for the first time. Their electronic structure was revealed by hard X-ray photoelectron spectroscopy and density function theory calculations with NP models. The NM-HEA NPs have a lower degeneracy in energy level compared with the monometallic NPs, which is a common feature of HEA NPs. The local density of states (LDOS) of every surface atom was first revealed. Some atoms of the same constituent element in HEA NPs have different LDOS profiles, whereas atoms of other elements have similar LDOS profiles. In other words, one atom in HEA loses its elemental identity and it may be possible to create an ideal LDOS by adjusting the neighboring atoms. The tendency of the electronic structure change was shown by supervised learning. The NM-HEA NPs showed 10.8-times higher intrinsic activity for hydrogen evolution reaction than commercial Pt/C, which is one of the best catalysts.

A hydrothermal method was used to epitaxially grow 70-nm-thick tetragonal (Bi,K)TiO₃ films with stoichiometric compositions at 240 °C on (001)_cSrRuO₃//(001)SrTiO₃ substrates. Crystal structure analysis revealed that the obtained (Bi,K)TiO₃ films had a polar-axis orientation attributable to the matching of the in-plane lattice with the SrRuO₃ underlayer. Large coherent displacement of A-site ions along the polar direction observed by transmission electron microscopy may have induced the large tetragonal distortion of c/a = 1.046. The dielectric constant was about 100 and was almost frequency independent in the range of 10³–10⁵ Hz, while the dielectric loss, tan δ, was below 5%. Well-saturated ferroelectric polarization−electric field (P−E) hysteresis loops were observed, and the remanent polarization (P_r) was 84 μC/cm². In addition, the effective piezoelectric constant, d_33,eff., was estimated to be 85 pm/V by time-resolved x-ray diffraction measured under an applied electric field. The P_r and d_33,eff. values were larger than those reported for polar-axis-oriented epitaxial tetragonal Pb(Zr_0.35Ti_0.65)O₃ films, indicating that the polar-axis-oriented tetragonal (Bi,K)TiO₃ film has high potential as a lead-free material for various applications. Specifically, the small ε_r and large d_33,eff. led to an improvement in the figures of merit [d_33,eff./ε_r and (d_33,eff.)²/ε_r], the most important index in sensor and energy-harvester applications.

We report a total x-ray scattering (TXS) system for structural analysis of crystalline particle materials at the BL15XU NIMS beamline of SPring-8 in Japan. To achieve a high angular resolution over a high Q region up to 25 Å⁻¹, the TXS system was capable of measuring to 120° at an x-ray energy of 29.02 keV with five CdTe pin detectors. The sample alignment and measuring system were controlled by LabView software. The x-ray pair distribution function (PDF) results for Ni bulk powder and Pt and AgRh nanoparticles were successfully simulated by the PDFgui program. In addition, Rietveld refinement results were also obtained from x-ray diffraction patterns, reflecting long-range order in the Pt nanoparticles. We expect that this TXS system may be useful for understanding structural information of crystalline nanoparticles, including amorphous features at their surface region.