Visible light-mediated photocatalysis, which relies on the ability to absorb low-energy visible light, is a greener approach for degrading organic pollutants in water. Among the photocatalysts, titanium dioxide (TiO₂) nanoparticles (NPs) are widely utilized because of their affordability, nontoxicity, large surface area, and strong photocatalytic properties. However, their effectiveness is restricted to the ultraviolet range, and recovery can be difficult when they are in NP form. Nanofibers, on the other hand, provide a similar high surface area and are simpler to recover. Additionally, coupling metal cations such as silver (Ag) to TiO₂ extends the sensitivity to the visible light region, enhancing photocatalytic efficiency. In this work, electrospun TiO₂ nanofiber mats (NFMs) were fabricated and decorated with Ag NPs. The TiO₂ NFMs were designed for extended use and improved reusability in wastewater treatment, reducing the environmental risks associated with NP catalysts. Ag was introduced via wet impregnation with Ag nitrate and reduced to metallic Ag using plasma treatment. The plasma-treated Ag-TiO₂ NFMs achieved 85% methylene blue removal from water under simulated solar irradiation, showing an 8% improvement in efficiency over TiO₂. These results demonstrate the potential of Ag-TiO₂ NFMs as an efficient and cost-effective solution to remove organic pollutants from wastewater under visible light irradiation.

Formation of a glassy state of two-dimensional simple monatomic system with a pentagonal structure is studied by cooling from the melt via molecular dynamics simulations. We use the so-called Lennard-Jones-Gauss interatomic potential proposed by Engel and Trebin [Phys. Rev. Lett. 98, 225505 (2007)] with the pentagonal structure forming ability. We find that although a relatively low cooling rate is used, crystallization does not occur in the system. Instead, glass-like phase transition occurs in the system while temperature dependence of total energy per atom in the system is rather smooth (i.e., glassy-like transition) and fivefold rings dominate in the system during the whole cooling process. At around the glass transition temperature fraction of pentagons steeply increases toward the stable high value of solid glassy state. Moreover, diffraction pattern of the final state at low temperature exhibits a glassy-like behavior of the atomic configuration which contains diffusive rings. Glass formation is analyzed based on the occurrence/growth of solid-like atoms.

Synchrotron radiation photoemission electron microscopy (SR-PEEM) combining with hard X-ray photoelectron spectroscopy (HAXPES) was utilized to obtain detailed structural and chemical insights into radioactive cesium-bearing microparticles (CsMPs) smaller than 10 µm, collected from a location 25 km northwest of the Fukushima Daiichi Nuclear Power Plant (FDNPP). X-ray absorption spectromicroscopy with a spatial resolution of approximately 50 nm was employed to investigate the presence of five elements (Cs, Fe, U, Zn, Si) on the microparticle surface. HAXPES data revealed the presence of several elements such as C, O, Mg, Al, Si, Sr, and Cs, while the chemical mapping images obtained by SR-PEEM clearly demonstrated that Cs atoms almost exclusively cover the particle surface. Owing to the surface-sensitive nature of SR-PEEM compared to HAXPES, the results notably indicate inhomogeneous distributions of elements, suggesting an eggshell-like structure with a Cs shell, with a thickness greater than the escape depth of the photoelectrons (a few nanometers) as a most presumable structural model of CsMPs. These novel findings strongly suggest that the aggregation of Cs atoms likely occurs at the microparticle surface and are expected to have applications in the remediation of nuclear power plant accidents.

Quantum oscillation effects of electrons in metal nanostructures on localized plasmons are investigated using the random phase approximation at high frequency condition. The scalar potentials for electrons can be calculated by the integral equations with the local electron densities in metal nanostructures. The scalar potentials and light emission intensities are calculated in the quasi-static approximation using local electron densities in Na nanospheres showing quantum oscillations. The integral equations for the scalar potentials are transformed into simultaneous linear equations and the resonant frequencies of localized plasmons are obtained by the eigenvalues of the matrices derived from the linear equations. The quantum oscillations produce multiple resonant frequencies, which is different from the case for the local electron density with step function shape that gives only the surface plasmon frequency. The quantum oscillations at inside areas of Na nanospheres contribute to producing higher resonant frequencies than the classical surface plasmon frequency, while those at surface areas contribute to producing lower resonant frequencies.

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.

Partial fluorescence yield X-ray absorption fine structure (PFY-XAFS) spectroscopy in the soft X-ray region is important for obtaining information about the bulk region of a sample. However, the self-absorption effect is a serious problem that causes distortions to the fine structure of PFY-XAFS spectra. This self-absorption can be analytically corrected for flat surfaces but not for arbitrary shapes such as those of particles in powders. In this study, we propose a voxel method where we divide the sample with arbitrary shapes into small boxes (called voxel) to calculate the self-absorption effect. By comparing the O K-edge PFY-XAFS spectra of a CoO single crystal, a thin layer Li₂CO₃ on a NiO substrate, and a CoO powder sample, we investigate the validity of the voxel method, along with its merits and limitations.

Electronic states formed at the interfaces of molecular semiconductor materials in organic optoelectronic devices are essential for their functionality. However, resolving these states at the complex and disordered interfaces of practical devices is challenging. In this study, the electronic states at well-defined molecular semiconductor p–n heterojunctions formed by epitaxial growth of C₆₀ on single-crystals of dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) were characterized by X-ray photoelectron spectroscopy and photoelectron yield spectroscopy. Our observations revealed the formation of interfacial electronic states and band bending on both sides of the heterojunction, suggesting electron transfer from DNTT to C₆₀. Notably, these features were not revolved for conventional disordered interfaces formed on vacuum-deposited thin-films of DNTT.

Titanium and its alloys are ideal for applications with high levels of reliable performance due to its high strength, low weight ratio, and outstanding corrosion resistance. However, titanium’s corrosion resistance depends on the thin oxide layer naturally forming on the surface, which can easily be damaged and subsequently reduce its corrosion resistance. Plasma electrolytic oxidation is an electrochemical technique that can create protective coatings on metals. The synthesized coatings can provide high hardness, excellent corrosion resistance, and wear resistance. Voltage and electrolyte parameters are some of the factors that can affect coating properties. In this study, the voltage and electrolyte concentration of a mixed electrolyte (aluminate, phosphate, and silicate) were varied in the plasma electrolyte oxidation of commercially pure titanium. The morphology, thickness, composition, and corrosion resistance of the synthesized coatings were characterized by scanning electron microscope, energy dispersive X-ray spectroscopy, X-ray diffractometer, potentiodynamic polarization, and electrochemical impedance spectroscopy. The electrolyte concentration and voltage affect the coating composition, morphology, and thickness. These properties affect the corrosion resistance. Lower electrolyte concentration increased the effect of aluminate and silicate on the coating morphology and composition. Low concentration settings produced looser and more porous coatings with high Al₂TiO₅ content. Increasing the voltage increases the rutile-to-anatase ratio and the coating thickness. Overall, the thicker and denser coating, and high rutile to anatase ratio exhibited the best corrosion resistance. The high electrolyte concentration and high voltage settings produced the most corrosion-resistant coating.

Mixing solutions and evaluating their concentrations are common and often critical tasks in laboratory experiments. Traditionally, these tasks have been conducted though manual optimization and by sampling across all conditions. Here, we present an alternative approach adopting a robotic system integrated with Bayesian optimization whereby solvents are automatically and autonomously mixed to the desired concentration. The solution control system has a robot-controlled pipette and an optical transmission setup that makes both the liquid injections and measurement evaluations. A demonstration achieved the target solvent concentration after several iterations. The methodology can be applied to various research scenarios, and the presented system can be extended to sophisticated applications. In this technical note, we provide details of the system for installation in other laboratories.

In the present study, low-temperature heating of the dry residue of a 10 µL droplet of an HAuCl₄ solution on a substrate and a metallic foil facing the dry residue was performed for 20 min in air in order to produce gold nanostructures on the metallic foil. When a titanium foil and a stainless steel (SUS316L) foil were used as metallic foils, dispersed gold nanoparticles were produced on these foils. On the other hand, in the case that a silver foil was used, microscopic objects having nanostructures, which would contain metallic gold, were densely formed on the silver foil.

The so-called C exciton resonance enhancement peak for heterostructures (HSs) of transition-metal dichalcogenides is indicative of a change in the band structure due to interlayer coupling. However, the superposition of the broad C exciton peaks from the two layers presents a significant challenge to the analysis of the alteration. The aim of this study was to gain insight into the electronic states of the C exciton region in each layer of a MoS₂/WSe₂ HS. To this end, we obtained second-harmonic generation (SHG) spectra of the HS by fixing the incident polarization angle to sequentially minimize the second-harmonic signals from the WSe₂ and MoS₂ layers. The resulting SHG spectra comprised signals from the MoS₂ (former case) and WSe₂ layers (latter case), demonstrating that the C exciton peak from each layer of the HS could be observed individually.

Three dimensional atomic structures of a zinc ferrite Franklinite ZnFe₂O₄ crystal were investigated by X-ray fluorescence holography with an atom-resolved and element-selected functions at room temperature. The obtained holograms were analyzed using a sparse modeling approach of a L₁-regression. From the present experiment and analysis, it was found that Zn atoms are located at tetrahedral A sites, which is in good agreement with the existing X-ray diffraction data. On the other hand, well-damped atomic images are observed around the central Fe atom. The present results are discussed by comparing with existing neutron diffraction and X-ray absorption fine structure experiments, where cation exchange occurs between Zn and Fe atoms for fine particles by about 10–15%, but the existence of cation exchanges is not clarified by considering the positional fluctuations of the Fe atoms at the B sites.

Known for its exceptional mechanical properties, diamond-like carbon (DLC) serves as an effective coating capable of improving a material’s performance in a variety of applications. While difficult to produce and analyze experimentally, molecular dynamics simulations serve as a sufficient method by which a material such as DLC can be studied at an atomistic level with respect to its microstructural properties. Large-scale atomic/molecular massively parallel simulator was used for the simulation while open visualization tool was used for visualization. In this study, C atoms were deposited onto Si trenches of multiple aspect ratios (0, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5) at varying deposition angles (0°, 15°, 30°, and 45°). Tersoff potential was used to define the interactions between Si–Si, Si–C, and C–C atoms. The effectiveness of the coating was assessed by inspecting the thickness conformity along the sidewall and bottom surfaces along with the sticking coefficients and radial distribution functions (RDF) of the deposited carbon films. At low deposition angles, the trench bottom was better coated whereas at higher deposition angles rougher films were obtained and thicker sidewall films were observed. RDF graphs showed similar results to DLC as observed in the literature. At higher aspect ratios of 2.0 and greater, deposition at low angles did not sufficiently coat the sidewalls whereas the shadowing effect prevented deposition at higher angles onto the lower portion of trench structures. The findings of this study contribute to the discussion regarding three-dimensional coating techniques for DLC which has applications in medical implants. Simulation of more C deposition onto trenches of higher aspect ratio is recommended to determine the extent of the shadowing effect and identify if sufficient coating is indeed possible.