Defect structures and dopant solution states of Hf-doped Si3N4 ceramics

Transition-metal-doped silicon nitride ceramics have attracted much attention as gate materials for semiconductors because of their electrical properties as well as chemical and thermal stability. The present study aims to clarify the defect structures of Hf-doped β-Si₃N₄ by theoretical calculations and scanning transmission electron microscopy (STEM). First-principles calculations based on a hybrid functional method were performed. It was found that Hf dopants are mainly substituted for the Si sites and can be occasionally located at interstitial sites in the lattice of β-Si₃N₄. The substitution sites of Hf dopants predicted by the first-principles calculations were also confirmed by the high-resolution STEM images.     

Carbon Nitride Loaded with an Ultrafine,Monodisperse, Metallic Platinum-Cluster Cocatalyst for the Photocatalytic Hydrogen-Evolution Reaction

For the realization of a next-generation energy society, further improvement in the activity of water-splitting photocatalysts is essential. Platinum (Pt) is predicted to be the most effective cocatalyst for hydrogen evolution from water. However, when the number of active sites is increased by decreasing the particle size, the Pt cocatalyst is easily oxidized and thereby loses its activity. In this study, a method to load ultrafine, monodisperse, metallic Pt nanoclusters (NCs) on graphitic carbon nitride is developed, which is a promising visible-light-driven photocatalyst. In this photocatalyst, a part of the surface of the Pt NCs is protected by sulfur atoms, preventing oxidation. Consequently, the hydrogen-evolution activity per loading weight of Pt cocatalyst is significantly improved, 53 times, compared with that of a Pt-cocatalyst loaded photocatalyst by the conventional method. The developed method is also effective to enhance the overall water-splitting activity of other advanced photocatalysts such as SrTiO₃ and BaLa₄Ti₄O₁₅.     

Effect of display of YOLO’s object recognition results to HMD for an operator controlling a mobile robot

Artificial Life and Robotics - An operator feels a burden when he/she controls a rescue robot remotely because he/she has to keep watching camera images to find the target object. We think that...     

Improvement of steady-state performance for discrete-valued input control with an integrator utilizing feedback control of integrated value of input

In this study, we considered the regulator problem for discrete-valued input control with an integrator. In some cases, the state does not converge to the origin in the discrete-valued input control when the plant possesses an integrator. Therefore, a method that adds minor feedback control to the integrated value of the input was proposed. However, the effect of the feedback control of the integrated value of the input was not theoretically interpreted, and the feedback gain for the state of the integrated value of the input was designed with trial and error. Herein, we clarify the effect of feedback control on the integrated value of the input. Furthermore, we reveal that the trade-off between the steady-state and transient performances is controlled by one parameter, that is, the feedback gain for the integrated value of the input.     

Single-atom microscopy in wide-bandgap nitrides

Wide bandgap III-nitrides, such as cubic boron nitride and wurtzite-type aluminum nitride, are promising systems for optoelectronics. To extend their luminescent properties, we doped single Ce atoms into III-nitride single crystals using reactive flux with a temperature gradient method at high-pressure and high-temperature conditions. To fully understand such properties in a large size-mismatch system, it is critically important to determine the point-defect structures of single dopants, their spatial distribution in three dimensions, and their atomistic dynamics at an atomic level. This review discusses point defect structures and their dynamics in III-nitrides using single-atom-sensitive scanning transmission electron microscopy, and the recent progress in the related field of electron microscopy.