To prepare photocatalysts promoting water splitting under visible light irradiation, GaOOH was nitrided by the calcination at a temperature ranging from 773 to 1273 K under a NH₃ flow to produce nitrogen doped Ga₂O₃. X-ray diffraction measurements suggested that even under NH₃ atmosphere dehydration of GaOOH to α-Ga₂O₃ occurred by calcining below 873 K. In the samples nitrided above 973 K, gallium nitride (GaN) phase started to appear and the crystallinity became better with increasing the nitriding temperature. In diffuse reflectance ultraviolet-visible measurements, absorption bands appeared in the visible light region after the nitrization, and the shift of the absorption edge with nitriding temperature suggested the formation of a new phase like gallium oxy-nitride. X-ray photoelectron spectroscopy and scanning transmission electron microscopy-electron energy-loss spectroscopy analyses revealed that oxygen atoms were distributed homogeneously and mixed with nitrogen atoms in the sample nitrided at 1173 K [referred as S(1173 K)] while oxygen atoms were mainly distributed at the surface of the sample nitrided at 1273 K [S(1273 K)]. The differences in the composition and chemical state near the sample surface closely related to the activity and stability during water splitting reaction under visible light irradiation between S(1173 K) and S(1273 K), i.e., the former sample provided stable H₂ and O₂ evolution while the latter sample was inactive and unstable.

For the development and maintenance of materials and infrastructures that enable the realization of “hydrogen society”, an analytical technique capable of determining hydrogen distribution is highly desirable. Recently, we have developed a method using laser-induced breakdown spectroscopy (LIBS) for the quantitative determination of the three-dimensional hydrogen distribution; however, the validity of the method was not completely confirmed. Herein, we demonstrate the validity of the hydrogen mapping method using LIBS by comparing the hydrogen mapping and a surface photographic image of an electrodeposited Ni(OH)₂ cathode that was subjected to charge-discharge reaction cycles. The hydrogen mapping was obtained by measuring the hydrogen emission line intensities at 656.28 nm under a 3000-Pa helium atmosphere for the cathode after the third charge, and a pristine Ni(OH)₂ cathode and a nickel plate as reference samples for 2.15 and 0 mass% of hydrogen, respectively. The photographs of the pristine Ni(OH)₂ cathode and a cathode once charged fully, which primarily comprised NiOOH, showed black and gray, respectively. In the hydrogen mapping of the cathode after the third charge, dark gray areas showed the hydrogen concentrations above 2.15 mass%, corresponding to the hydrogen concentration of Ni(OH)₂, whereas gray areas showed the hydrogen concentrations between 1.09 mass% (corresponding to the hydrogen concentration of NiOOH) and 2.15 mass%. The experimental results demonstrate that the hydrogen distribution measured using LIBS corresponded to the distribution of Ni(OH)₂ and NiOOH estimated according to their photographic colors, indicating the validity of the LIBS-based method for hydrogen mapping.

In this study, we report for the first time the use of colloidal fluorescent submicrometer-sized particles as tracers for microliter liquid transport through multilayered biomass. We showed that the in-plane spread and the trans-planar penetration of the liquid can be visualized by mapping the fluorescent particle distribution in each biomass layer using image analysis. The temperature and inter-layer connectivity were found to be vital factors determining the fate of the liquid transport. Inter-layer connectivity is influenced by both the physical connections among the layers and the property of the fluid filling the inter-layer pores. Utilizing this characteristic, we could use our visualization method to detect trace amounts of nano- to sub-micrometer impurities in one of the layers.

We proposed an automatic procedure of identification of crystalline orientation of W tips observed by field ion microscopy by means of machine-learning-based objective detection and classification. The identification is performed with the geometrical position of {110} and {112} planes detected by YOLOv3, and the correct crystalline orientation was output for 85% of the total data by k-nearest neighbor algorithm, indicating the effectiveness of this method.

Using scanning tunneling microscopy (STM), we study the adsorption of copper-phthalocyanine (CuPc) on the anisotropic Au(110)-(1 × 2) surface as a function of coverage. For the initial adsorption at room temperature, we observe CuPc monomers as well as a molecular chain that forms along the step edge. By STM manipulation, we reveal that the CuPc adsorption is accompanied by surface reconstruction from the initial adsorption stage; the periodicity beneath the monomer and the chain changes locally from (1 × 2) to (1 × 1) and (1 × 3), respectively. This finding highlights that the Au atom mobility of the surface plays an essential role in CuPc adsorption. At higher coverage, we observe the development of CuPc chains along the [110] direction on the terrace with periodicities of (7 × 5) and (5 × 5), and compare the obtained results with those from the previous studies by diffraction methods.

Second harmonic generation (SHG) is a unique non-linear optical effect that can be used to investigate chemical states of molecules at surfaces/interfaces. By the use of soft X-rays, SHG gains element selectivity through the inner-core excitation resonance. However, it is challenging to observe SHG signals separately from the second-order light generated from the undulator. Here, we report a new ellipsometry method for soft X-ray SHG to suppress the contribution of second-harmonic radiation from the light source. Through measurements of a GaAs(100) crystal, we demonstrate that pure SHG signals can be obtained for the horizontally polarized component. The present method is generally applicable regardless of the incident photon energy and hence the absorption edge of the targeted materials. If combined with optical filters blocking the second-harmonic radiation and equipped with soft X-ray phase shifters, the method allows one to obtain further information from SHG signals such as tensor components of second-order non-linear susceptibility.

The 13th International Symposium “Atomic Level Characterizations for New Materials and Devices '21 (ALC'21 Online)” was held virtually from October 19 to 20, 2021, under the organization of the Division of Microbeam Analysis, the Japan Society of Vacuum and Surface Science (JVSS). ALC'21 was initially planned to be held in Okinawa, Japan, but the on-site meeting was postponed to 2022 as ALC'22 due to the COVID-19 pandemic. ALC'21 Online was held as a pre-meeting for ALC'22. In this symposium, there were 276 participants from 17 countries, and 86 papers, consisting of two Plenaries, three Tutorials, and 81 posters, were presented in a wide range of research fields related to atomic level characterization. Twelve papers out of them are collected in this special issue.

Fe Kα X-ray fluorescence holography measurements were carried out at room temperature on an FeSe high-temperature superconductor to clarify the relationship between the local structures around the Fe atoms and the superconducting nature. The obtained three-dimensional atomic arrangements strongly reveal a formation of strong FeSe₄ clusters. On the other hand, the Se—Fe—Se bond angle largely spreads, causing a large ambiguity in the chalcogen height and large displacements of the Fe sublattice. Thus, it is reasonable that the tetragonal-to-orthorhombic structural (nematic) transition does not affect the magnetic ordering in the Fe layer.

We fabricated a SiO₂ embedded-TiO₂ slanted nanograting sample using reactive ion etching and electron beam lithography techniques and investigated their optical responses. Surface morphology for the fabricated gratings was monitored by a scanning electron microscope (SEM). According to the SEM observation, the cross-section shape of gratings was like saw-tooth with a slanted angle of 55°, and their periodicity was determined to be ∼704 nm. In the measurement, high order diffraction with intensity of 4.63% at 0th and 14.8% at +1st at the interface between SiO₂ and TiO₂ were obtained by irradiating a transverse electric polarized beam with wavelength 532 nm at the incident angle 17.5° from the rear side of TiO₂. The 0th order diffraction beam was passed through the SiO₂ substrate sample and, then, directly emitted into the atmosphere. The emitted beam can create a virtual reality (VR) image to project on a board. On the other hand, the +1st order diffraction beam is guided by a zigzag into the SiO₂ substrate. During waveguide, the beam duplicated using optical property either a forbidden system or an accepted system permits partial penetration to a permeable display mounted on a surface of the SiO₂ substrate. Penetrated duplication beams are waveguided with total internal reflection in a display, resulting in emission from the side face of the permeable display. The emitted beam can provide the duplicated VR images in the atmosphere. In future, this integrated devise will play an important role for a head mounted display creating a projection VR and duplicated VR simultaneously.

Y and Zr Kα X-ray fluorescence holography measurements were carried out on a single crystal of yttria-stabilized zirconia with 13 mol% of yttria at room temperature to investigate the local structures around the impurity Y and host Zr atoms. Around the central Y atom, the images of the surrounding Zr/Y atoms are seen as a face-centered-cubic (fcc) sub-lattice. Thus, the impurity Y atoms are sure to be replaced with the Zr atoms as expected earlier. In addition, strong images are also observed, by which some of the Y atoms are located at the interstitial positions at the center of the fcc lattice. The atomic images around the central Zr atom are very weak, indicating large lattice distortions around the Zr atom. Some images outside of the ideal fcc lattice indicate that the local structures around the Zr atoms are similar to the original pure monoclinic ZrO₂, and some of them would be rotated due probably to the interstitial doping of the impurity Y atoms.

The affiliation of the first author (T. F.) was wrong in the original article. The correct affiliation is as follows: Department of Physical Electronics and Informatics, Graduate School of Engineering, Osaka City University, Osaka 558-8585, Japan