Susumu Imashuku

Although the identification of solidified liquid (12CaO·7Al ₂ O ₃ , 3CaO·Al ₂ O ₃ ) and CaO·Al ₂ O ₃ phases is critical for detecting stopper rod degradation, it is hindered by complex morphologies and the analytical effort required. We propose a rapid method for identifying mineral phases on alumina stopper rods used in continuous casting of Ca‐treated Al‐killed steels using cathodoluminescence and scanning electron microscopy (SEM) analyses. Experiments using model stopper rods demonstrated that CaO·Al ₂ O ₃ , CaO·2Al ₂ O ₃ , CaO·6Al ₂ O ₃ , and 3CaO·5Al ₂ O ₃ could be distinguished by their cathodoluminescence colors and peak wavelengths. The CaO·Al ₂ O ₃ phase was identified by green luminescence with a 547 nm peak, distinct from CaO·6Al ₂ O ₃ (517 nm) and MgO·Al ₂ O ₃ (524 nm). The non‐luminescent 12CaO·7Al ₂ O ₃ and 3CaO·Al ₂ O ₃ phases were identified by their dendritic microstructures via SEM. This integrated approach enables the identification of mineral phases leading to stopper rod degradation within tens of seconds on unpolished samples, providing an efficient diagnostic tool for optimizing Ca treatment and ensuring stable continuous casting.

Lithium phosphate (Li₃PO₄) is a key solid electrolyte for all-solid-state thin-film batteries. Although sputtering enables high-throughput film deposition, precise compositional control is essential because ionic conductivity is highly sensitive to stoichiometry. In this study, optical emission spectroscopy was employed for real-time compositional monitoring of Li₃PO₄ films during sputtering. Emission spectra acquired under various powers (20-40 W) and chamber pressures (1-5 Pa) were analyzed, and the intensities of Li I, P I, and O I lines were correlated with the atomic ratios determined by inductively coupled plasma mass spectrometry and field-emission electron probe microanalysis. Strong correlations were observed between P I 253.5 nm and O I 777.3 nm (R² = 0.977, 1-5 Pa), Li I 670.8 nm and P I 253.5 nm (R² = 0.837, 1-5 Pa), and Li I 391.5 nm and O I 777.3 nm (R² = 0.940, 3-5 Pa), demonstrating that these emission lines are suitable for in situ compositional analysis. The emission lines composing these pairs exhibited identical input power dependence, providing a useful criterion for selecting appropriate diagnostic lines. This study represents the first demonstration of real-time compositional monitoring for Li- and P-containing films, offering a promising approach for process control during sputtering.

Unlike bulk analysis, thin film compositional analysis necessitates considering substrate effects, such as secondary fluorescence induced by x‐rays generated in the substrate and backscattered electrons. Several methods have been proposed to address these challenges. This study examines the influence of secondary fluorescence induced by characteristic x‐rays from the substrate on the film composition as determined by the method employed in JEOL's EPMA system. A CuAlO ₂ film deposited on a Si substrate was selected as the representative specimen, given that the effect of secondary fluorescence induced by characteristic x‐rays of the Si substrate is substantial, due to the absorption edge energy of Al being slightly lower than that of the Si K α line. The findings reveal that the Si K α line generated from the Si substrate affected the generation of secondary Al K α fluorescence in the CuAlO ₂ film when the film thickness was 200 nm or less. This interference can be mitigated through either depositing a 500 nm‐thick Au layer on the Si substrate or by depositing a CuAlO ₂ film with a thickness exceeding 500 nm.

X‐ray reflectometry is a powerful technique for investigating layered films. Conventional angular‐dispersive X‐ray reflectometers require a high‐intensity, monochromatic X‐ray source and a complex angular scanning system, resulting in a large and complicated setup. In contrast, the energy‐dispersive technique enables a more compact and simplified reflectometer configuration. We then realized a portable X‐ray reflectometer primarily composed of a polychromatic 4 W X‐ray tube, a planar waveguide‐resonator, and an energy‐dispersive X‐ray detector. Using the reflectometer, the thickness and density of a Cu film could be determined. In the present study, we demonstrated that the portable X‐ray reflectometer can determine the thickness and density of a Mo monolayer thin film, as well as those of each layer in a Cu/Mo double‐layer thin film, by comparing the measured reflectivity profiles with simulated ones. These results indicate that the portable X‐ray reflectometer is applicable for determining the thickness and density of various monolayer and multilayer films.

Titanium carbide (TiC) films are used as wear- and corrosion-resistant coatings, thermal barriers, and diffusion barriers owing to their superior properties. Among the various deposition techniques, magnetron sputtering is a standard method for producing these films. However, sputtering conditions can influence film composition and properties, making real-time compositional analysis crucial for improving film productivity and quality. This study used optical emission spectroscopy for the real-time compositional analysis of TiC films and established a method for efficiently selecting Ti emission lines for composition determination. To develop this method, the correlation between the emission intensity ratio of Ti I lines to C I 247.9 nm line and the Ti/C atomic ratio in deposited films was examined under various conditions. At chamber pressures of 5 and 10 Pa, three Ti I line combinations (226.8, 230.0, and 416.4 nm) with C I 247.9 nm line demonstrated R2 values above 0.900. These Ti I lines were single emission lines that did not overlap with Ar I or II lines and followed a similar input power dependence as the C I 247.9 nm line at chamber pressures of 5 and 10 Pa. Thus, TiC film composition can be monitored in real time during sputtering using the emission intensities of C I 247.9 nm and Ti I lines that (i) are single emission lines without overlap with Ar I or Ar II lines and (ii) follow a similar input power dependence as the C I 247.9 nm line.

In situ elemental analysis is required to improve the yield and quality of sputter-deposited metal oxide films by detecting the films whose compositions are deviated from the required compositions. In this study, the author proposed a method to determine the MgO film composition by measuring the intensities of the Mg emission lines and O I 777.3 nm line during sputter deposition. Linearity (R2 value) between the emission intensity ratios of the Mg lines to the O I 777.3 nm line and Mg/O atomic ratio in the films was investigated. The Mg I 518.4 and 517.3 nm lines exhibited R2 values higher than 0.80, and showed the properties that (1) they did not overlap with other emission lines and (2) their intensities exhibited a dependence on the input power to the MgO target and chamber pressure, similar to that of the O I 777.3 nm line, which were consistent with the properties of the Zn emission lines that can accurately determine the ZnO films compositions. Therefore, searching emission lines that satisfy the two properties is a powerful approach for the in situ elemental analysis of sputter-deposited metal oxide films.

The identification of internal α-alumina (α-Al2O3) scales is crucial because α-Al2O3 determines the performance of heat-resistant alloys. A non-destructive method was recently developed to rapidly identify internal α-Al2O3 scales on the Ni–Cr–Al and Ni–Al alloys by obtaining their surface cathodoluminescence (CL) spectra. However, the peak intensities at 695 nm originating from α-Al2O3 considerably deviated from those estimated from the attenuation rates of overlaid scales (Cr2O3, NiO, and NiAl2O4) and the CL peak intensity at 695 nm for the α-Al2O3 scale on the Fe–Cr–Al alloy surface. In this study, factors causing the deviations in the CL peak intensity at 695 nm for the internal α-Al2O3 scales were investigated by obtaining images of the scales and their CL spectra. The surface Cr2O3 scale on the Ni–25Cr–5Al alloy exhibited a surface the roughness of ~1 μm, causing the CL peak intensity at 695 nm to be one order of magnitude higher than the estimated value. The CL spectrum and scanning transmission electron microscopy observation revealed that θ-Al2O3 overlaid on α-Al2O3 in the internal Al2O3 scale on the Ni–14Al alloy reduced the CL peak intensity at 695 nm by two orders of magnitude.

This article describes results of the residual stress measurements in different iron alloys using a few non-destructive techniques based on X-ray diffraction. It was shown that the results provide useful information for understanding the microstructural phenomenon in each alloy, although these techniques are not universally applicable to various cases. In this paper, the residual stresses formed during stress-induced martensitic transformation and its reverse transformation in shape memory alloys, the residual stresses balancing between two phases in duplex stainless steels and the residual stresses formed by inhomogeneous plastic strains in polycrystalline twin-induced plasticity steels are shown. It is important to select an adequate method according to the phenomena and properties of interest in iron alloys. The residual stresses formed in a high-entropy alloy containing iron are also presented, taking into account into the inhomogeneity in bulk. The residual stresses and related microstructural data in materials in structures and device components are considered to be effective parameters for evaluating their mechanical properties. While modern diffraction measurement methods are relatively easy to be operated, it is noted that the results include issues related to the microstructure of the materials. These issues should also be discussed in the residual stress measurements at different scales, and reliable fundamental data related to residual stress considering the microstructure would be necessary for discussion.