The cover art is based on an annealing effect on forming Ni₃GaAs layer for Ni–P on GaAs wafer in the article entitled “Stress Analysis of the Interface Reaction Layer Between Ni–P Films and GaAs Substrate After Annealing” by Mr. Koichiro Nishizawa et al., which was selected as Editor’s Choice. The paper reports that Ni diffuses from the Ni–P film to the GaAs substrate, resulting in an epitaxial reaction layer, Ni₃GaAs, which has high stress and largely contributes to the wafer warpage.

This study used an AC impedance method to quantitatively analyze the internal resistance in a tandem cell with a gallium-nitride (GaN) based photoanode for the water splitting reaction. Impedance spectra of the whole system (two-electrode cell) and the photoanode cell (three-electrode cell) were analyzed by using an R-C equivalent circuit, and the ohmic resistance in the system and the charge transfer resistance in the photoanode cell were clarified. From the AC impedance measurement performed 1 min after light irradiation, it was found that the internal resistance of the photoanode cell was the dominant resistance in the system and the charge transfer resistance in the photoanode cell accounted for over 90 % of the internal resistance. In addition, the results indicate that the charge transfer resistance depends on the number of electron-hole pairs generated in the GaN-based photoanode.

Cyclic voltammetry of metal anode electrodeposition/dissolution often gives a linear waveform in the absence of supporting electrolyte. For a one-electron redox model system without supporting electrolyte, in which both redox species are soluble and the oxidized form is zero-valent, finite different numerical calculations on the Nernst–Plank–Poisson equation have revealed that migration effects almost entirely counteract the driving force potential to exhibit such linear waveforms in voltammetry. In the calculation the dumping Newton–Raphson method was used to avoid numerical divergence. The voltammetric response calculated on the model system was verified experimentally in a ferrocene-derivative redox system that yields a soluble zero-valent reductive product. An approximate interpretation of the linearity was also proposed.

The olivine-type Li(Fe, Mn)PO₄ positive electrode material is an alternative for LiFePO₄ because of its higher energy density. In this study, chemical fluctuations in the Li(Fe, Mn)PO₄ single particles were investigated using chemical mapping based on transmission electron microscopy. Spectral imaging based on electron energy-loss spectroscopy revealed the heterogeneous distribution of Mn and Fe in a single particle. The oxidation state of Fe fluctuated significantly in the elemental distribution compared with that of Mn, and Fe³⁺ was preferentially distributed in the Fe-rich domains of the particles. Natural air oxidation generates Fe³⁺ without batteries reactions. The spatial fluctuation of the Fe valence is affected by the local distribution of Mn and Fe.

Electroless Ni–P plating films, used as the seed layers for the backside electrodes of gallium arsenide (GaAs) semiconductor devices, cause substrate warping (wafer warpage) during annealing, leading to substrate cracking and chipping. In this study, Ni–P films with different P concentrations (6, 17, and 20 at%) were deposited on a GaAs substrate, and the wafer warpage was analyzed after annealing at 240 °C for 1 h. The wafer warpage showed a reduction in size with an increase in P concentration in the as-deposited Ni–P film. Cross-sectional observations revealed the formation of a reaction layer at the interface between Ni–P and GaAs after annealing, and its thickness decreased with increasing P concentration. X-ray photoelectron spectroscopy revealed that the reaction layer was a Ni₃GaAs alloy. The Ni atoms in the Ni–P films diffused to the GaAs substrate, and the P concentration in the Ni–P layers increased to a constant value (31–33 at%). X-ray diffraction measurements indicated that the Ni–P layers crystallized to Ni₁₂P₅ upon annealing because of the increase in P concentration owing to Ni diffusion. To evaluate the contribution of the reaction layer to the wafer warpage, the Ni–P layer was removed by ion milling, and the wafer warpage was measured. The estimated stress of the reaction layer was 580 MPa. From the calculation of the contribution of each layer to the wafer warpage, it was found that the Ni₃GaAs layer largely contributed to the wafer warpage.