Toyohiko Kinoshita

Laboratory‐source angle‐resolved hard X‐ray photoelectron spectroscopy (AR‐HAXPES) is photon‐starved at the spatial resolution required for mapping, where the frame averaging needed to recover a clean depth profile at every position drives total acquisition time into a prohibitive regime. Self‐supervised deep‐neural‐network (DNN) denoising offers an alternative to acquisition‐time scaling, and a recent companion study has systematically benchmarked its performance against alternative strategies; however, its operational envelope across exposures, its cross‐exposure transferability, and its failure modes in the photon‐starved regime remain uncharacterized. Here, we evaluate self‐supervised denoising at the smallest possible target window across three exposures spanning a 25‐fold range of per‐frame photon flux on a model C/Al ₂ O ₃ /TiO ₂ /Si multilayer. We find cross‐exposure denoiser deployment to agree with an empirical directional rule—train signal‐to‐noise ratio ( S / N ) ≥ inference S / N —characterize the failure boundary in the photon‐starved regime where upstream denoiser collapse propagates into constraint‐saturated inversion solutions, and locate the asymptotic reach of all tested denoising strategies (frame averaging, Self‐DNN, Cross‐DNN) relative to a methodological floor set by the reproducibility of the reference. Within the success region of this rule, cross‐exposure transfer enables up to a 48‐fold equivalent acquisition‐time reduction on the depth root‐mean‐square error (RMSE) axis (14‐fold on the Wasserstein‐1 interface‐localization axis) at the most photon‐starved 4.8 s/frame condition. These results frame self‐supervised AR‐HAXPES denoising as a characterizable engineering operation with quantifiable failure boundaries and recovery routes, rather than as an empirical post‐processing recipe.

Nondestructive three-dimensional visualization of buried interfaces in multilayer thin films is central to semiconductor device characterization. Angle-resolved hard x-ray photoelectron spectroscopy (AR-HAXPES) enables such depth-resolved analysis, but short-exposure measurements suffer from photon shot noise that degrades the reconstructed depth profiles—a problem that becomes acute as the technique is pushed toward spatiotemporal “4D-XPS” (spatially and temporally resolved XPS) at focused-beam instruments. Here, we benchmark two denoising strategies—statistical bin-pool (BP) resampling and self-supervised deep neural network (DNN) denoising—applied to AR-HAXPES data from a C/Al2O3/TiO2/Si multilayer film acquired with a laboratory Ga Kα source (9.25 keV) under two per-frame noise levels (24 s/frame × 2500 frames; 120 s/frame × 400 frames). Depth profiles are reconstructed per pixel via L1-regularized inversion and scored against a pseudoground truth using the depth-profile root mean square error (Depth RMSE), film-thickness fidelity Δthk, and the first-order Wasserstein distance W1. The two strategies turn out to be complementary rather than competing: under high-noise conditions, the self-supervised DNN dominates with up to a 27-fold equivalent-exposure gain, whereas under low-noise conditions, BP matches or slightly surpasses the DNN at roughly a six- to eightfold gain and retains a clear advantage in reconstructed layer-thickness fidelity. BP—training-free and computationally trivial—is, therefore, the preferred choice whenever the per-frame statistics are sufficient for the inversion to resolve interfaces, while the self-supervised DNN remains justified specifically when photon starvation is severe.

To tackle disorder in crystals and short- and intermediate-range order in amorphous materials, such as glass, we developed a carry-in diffractometer to utilise X-ray fluorescence holography (XFH) and anomalous X-ray scattering (AXS), facilitating element-specific analyses with atomic resolution using the wavelength tunability of a synchrotron X-ray source. Our diffractometer unifies XFH and AXS configurations to determine the crystal orientation via diffractometry. In particular, XFH was realised even for a crystal with blurred emission lines by a standing wave in a hologram, and high-throughput AXS with sufficient count statistics and energy resolution was achieved using three multi-array detectors with crystal analysers. These features increase tractable targets by XFH and AXS, which have novel functionalities.

The silicon cage nanoclusters encapsulating a tantalum atom, termed Ta@Si₁₆, exhibit characteristics of alkali metal "superatoms (SAs)". Despite this conceptual framework, the precise structures of Ta@Si₁₆ and Ta@Si₁₆⁺ remain unclear in quantum calculations due to three energetically close structural isomers: C_3v, T_d, and D_4d structures. To identify the geometrical structure of Ta@Si₁₆ SAs, structural analysis was conducted using extended X-ray absorption fine structure (EXAFS) with a high-intensity monochromatic X-ray source, keeping anaerobic conditions. Focusing on "superordered" films, which constitute amorphous thin films composed solely of Ta@Si₁₆ SAs, this analysis preserved locally ordered structures. Spectral comparisons between experimental and simulated Ta L₃-edge EXAFS unveil that Ta@Si₁₆ SAs on a substrate adopt a C_3v-derived structure, while Si K-edge EXAFS introduces spectral ambiguity in structural identifications, attributed to both intracluster and intercluster scatterings. These findings underscore the significance of locally ordered structure analyses in understanding and characterizing novel nanoscale materials.

Progress of surface and interface science using synchrotron radiation in Japan is reviewed. Investigations for electronic structure, and atomic structures including magnetic, catalytic, and other functional origins with dynamical information have been done. Historical milestones and future prospects are discussed.

Progress of surface and interface science using synchrotron radiation in Japan is reviewed. Investigations for electronic structures, and atomic structures including magnetic, catalytic, and other functional origins with dynamical information have been done. Historical milestones and future prospects are discussed.

An endstation dedicated to angle-resolved photoemission spectroscopy (ARPES) using a soft X-ray microbeam has been developed at the beamline BL25SU of SPring-8. To obtain a high photoemission intensity, this endstation is optimized for measurements under the condition of grazing beam incidence to a sample surface, where the glancing angle is 5° or smaller. A Wolter mirror is used for focusing the soft X-rays. Even at the glancing angle of 5°, the smallest beam spot still having a sufficient photon flux for ARPES is almost round on the sample surface and the FWHM diameter is ∼5 µm. There is no need to change the sample orientation for performing k _x − k _y mapping by virtue of the electron lens with a deflector of the photoelectron analyzer, which makes it possible to keep the irradiation area unchanged. A partially cleaved surface area as small as ∼20 µm was made on an Si(111) wafer and ARPES measurements were performed. The results are presented.

The angular distributions of photoelectrons and Auger electrons from single crystal surfaces show characteristic diffraction patterns, which contain information on the local atomic structures surrounding the emitter atoms. Using computational reconstruction processes on the diffraction patterns enables us to determine the local atomic structures of, for example, dopants, catalytic active sites, and surface/interface structures. This method has become known as “photoelectron holography (PEH)”. Several advanced photoelectron analyzers for PEH are now available at beamlines at SPring-8, the world’s largest synchrotron radiation facility. Recently, the use of micron-sized photon beams, as well as pump-and-probe time-resolved techniques has become possible with relatively high energy resolution. Here, the experimental apparatus and some representative applications are introduced.

Diamond has two crystallographically inequivalent sites in the unit cell. In doped diamond, dopant occupation in the two sites is expected to be equal. Nevertheless, preferential dopant occupation during growth under nonequilibrium conditions is of fundamental importance, for example, to enhance the properties of nitrogen-vacancy (N-V) centers; therefore, this is a promising candidate for a qubit. However, the lack of suitable experimental techniques has made it difficult to study the crystal- and chemical-site-resolved local structures of dopants. Here, we confirm the identity of two chemical sites with asymmetric dopant incorporation in the diamond structure, via the photoelectron holography (PEH) of heavily phosphorus (P)-doped diamond prepared by chemical vapor deposition. One is substitutionally incorporated P with preferential site occupations and the other can be attributed to a PV split vacancy complex with preferential orientation. The present study shows that PEH is a valuable technique to study the local structures around dopants with a resolution of crystallographically inequivalent but energetically equivalent sites/orientations. Such information provides strategies to improve the properties of dopant related-complexes in which alignment is crucial for sensing of magnetic field or quantum spin register using N-V centers in diamond.