Kentaro Kawai

Sn-6.4Sb-3.9Ag (mass%)系はんだの高耐熱化を目指して高温疲労特性に対するNiまたはCu添加の影響を調査した。Sn-6.4Sb-3.9AgにNiおよびCuを添加することで，大傾角粒界を有する結晶粒が生成し，結晶粒の数が増加した。微量元素の添加による引張特性の劣化は見られなかった。疲労試験より，Ni添加材においては175°Cにおいて優れた疲労特性が確認され，特に0.4%Ni添加材が最も優れた特性を持つことが確認された。一方，Cu添加材については，2.0%Cu添加で175°Cにおける疲労特性が劣化した。EBSD解析結果から疲労特性の違いは疲労損傷挙動の違いによるものと考えられ，Ni添加および1.0%Cu添加材は連続動的再結晶を伴うのに対し，2.0%Cu添加材は動的回復による応力緩和に起因すると推察された。

Multi‐shell InP/ZnSe/ZnS quantum dots (QDs) are expected to be applied to next‐generation displays. While the effect of the thickness of the ZnSe intermediate shell on the properties of InP/ZnSe/ZnS QDs has been reported for red‐emission, there are few reports on green‐emitting ones. Here we show the effects of ZnSe thickness on full width at half maximum (FWHM) and photoluminescence quantum yield (PLQY) of the emission spectra of green‐emitting InP/ZnSe/ZnS QDs. The results revealed that the ZnSe intermediate shell of green‐emitting InP/ZnSe/ZnS QDs has an optimum thickness (1.2 nm in this study). Excessive or insufficient ZnSe intermediate shell broadened FWHM and decreased PLQY. This means that difference in the thickness of the ZnSe intermediate shell changes the band structure and the electron behavior. The ZnSe thickness is one of the dominant factors that determine the optical properties in green‐emitting InP/ZnSe/ZnS QDs.

In the field of fuel cells, the microscopic understanding of the catalytic activity of nanocarbons or graphene-based materials for oxygen reduction reaction (ORR) is highly demanded. In the current study, a novel concept is presented to achieve it, which is a different approach from familiar electrochemical measurements. To prove this concept, we prepared two nanocarbon materials, whose ORR activities were tested and compared via macroscale cyclic and linear sweep voltammetry. Next, considering the electrochemical potential of ORR and the band-edge position of semiconductors, we chose single-crystalline Ge as the substrate on which the single-sheet nanocarbons were dispersed. We found that etched hollows formed under the loaded nanocarbons after immersing the nanocarbon/Ge sample into O ₂ -containing water. The histogram analysis of the hollows represented the difference in catalytic activities to promote Ge etching between the used nanocarbons, and the corresponding trends agreed qualitatively with the electrochemical measurements.

A Si-face 4H-SiC surface was modified by plasma oxidation followed by HF etching. The resulting surface was covered with a carbon overlayer composed of C–C bonded clusters and Si–O–C bonding from Si₄C₄O₄ and Si₄C_4−xO₂ (x < 2), as evidenced by photoemission spectroscopy measurements and wetting properties. A trend was observed in which the thickness of the carbon overlayer was proportional to the SiO₂ thickness after plasma oxidation, indicating that the former could be controlled on the subnanometer scale by adjusting plasma conditions. After a subsequent annealing under ultrahigh vacuum, we found that graphene grew on the modified SiC surface without the formation of a pitting morphology, which is in contrast to the case using an untreated SiC substrate. Raman spectroscopy revealed that the former graphene includes fewer defects than the latter graphene. We discuss the microscopic mechanism by which reaction products composed of C–C and Si–O–C bonds form in the SiO₂ film near the SiO₂/SiC interface via plasma oxidation as well as their influence on the subsequent growth of graphene.

Structures with pores several nanometers in diameter can be used for distinguishing nucleotides in DNA. A 2D material such as a thin membrane is expected to enhance precise molecule recognition. Here, we present the nanopore fabrication to thin 2D membranes using HIM (He ion microscopy). We transferred three 2D materials of CVD (chemical vapor deposition) graphene, CVD BN, and peel-off MoS$_{2}$, to the sub-micrometer pore of freestanding SiO$_{2}$ membranes on a silicon substrate. The number of atomic layers of the 2D materials was confirmed via Raman spectroscopy and XPS (X-ray Photoelectron Spectroscopy). We examined the reproducibility and accuracy of nanopore fabrication as a function of the focal position and beam irradiation intensity of the HIM system. Reproducible nanopores having diameters of less than 10 nm were realized by optimizing the intensity and focal position. We achieved 1.5-nm-diameter nanopores in a single layer of graphene using this HIM technique.

Toward large scale 2D-array of DNA origami which can be widely applicable to various applications, a dimer formation of triangular DNA origami connected by linker ssDNA was investigated. From the results of analysis and experiments, it was concluded that the dimerization is strongly influenced by the deformation of a side of a triangle.