The Chemistry of thorium, plutonium and MA

Sato, Nobuaki*; Kirishima, Akira*; Watanabe, Masayuki; Sasaki, Takayuki*; Uehara, Akihiro*; Takeda, Shino*; Kitatsuji, Yoshihiro; Otobe, Haruyoshi; Kobayashi, Taishi*

The Chemistry of Thorium, Plutonium and MA, 254 Pages, 2022/03

The chemistry of nuclear materials such as Thorium (Part 1) and Plutonium (Part 2) was described in relation from the fundamentals on solid chemistry and solution chemistry to the practicals on the experiment and evaluation method in detail. Minor actinides such as Neptunium, Americium, Curium and Protoactinium, was introduced the basics on the solid and solution chemistry.

The Chemistry of uranium (II); Method and practice

Sato, Nobuaki*; Kirishima, Akira*; Watanabe, Masayuki; Sasaki, Takayuki*; Uehara, Akihiro*; Takeda, Shino*

Uran No Kagaku (II); Hoho To Jissen, 143 Pages, 2021/03

This book describes necessary facts when readers would have an opportunity to treat Uranium for experiments. In the content, the method section shows experimental facilities and equipment including method, and the practical section mentions solution and solid state experiments using Uranium and/or radioisotopes.

New isomers in Pd and Pd; Competing proton and neutron excitations in neutron-rich palladium nuclides towards the shell closure

Watanabe, Hiroshi*; Wang, H. K.*; Lorusso, G.*; Nishimura, Shunji*; Xu, Z. Y.*; Sumikama, Toshiyuki*; Orlandi, R.; 47 of others*

Physics Letters B, 792, p.263 - 268, 2019/05

https://doi.org/10.1016/j.physletb.2019.03.053

SiO/AlON stacked gate dielectrics for AlGaN/GaN MOS heterojunction field-effect transistors

Watanabe, Kenta*; Terashima, Daiki*; Nozaki, Mikito*; Yamada, Takahiro*; Nakazawa, Satoshi*; Ishida, Masahiro*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; et al.

Japanese Journal of Applied Physics, 57(6S3), p.06KA03_1 - 06KA03_6, 2018/06

https://doi.org/10.7567/JJAP.57.06KA03

The advantage of SiO/AlON stacked gate dielectrics over SiO, AlON and AlO single dielectric layers was demonstrated. Our systematic research revealed that the optimized stacked structure with 3.3-nm-thick AlON interlayer is beneficial in terms of superior interface quality, reduced gate leakage current and C-V hysteresis for next-generation high frequency and high power AlGaN/GaN MOS-HFETs.

Control of Ga-oxide interlayer growth and Ga diffusion in SiO/GaN stacks for high-quality GaN-based metal-oxide-semiconductor devices with improved gate dielectric reliability

Yamada, Takahiro*; Watanabe, Kenta*; Nozaki, Mikito*; Yamada, Hisashi*; Takahashi, Tokio*; Shimizu, Mitsuaki*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*

Applied Physics Express, 11(1), p.015701_1 - 015701_4, 2018/01

https://doi.org/10.7567/APEX.11.015701

A simple and feasible method for fabricating high-quality and highly reliable GaN-based metal-oxide-semiconductor (MOS) devices was developed on the basis of systematic physical and electrical characterizations. Chemical vapor deposition of SiO films directly onto GaN substrates forming Ga-oxide interlayers was used to fabricate SiO/GaO/GaN stacked structures. Although well-behaved hysteresis-free GaN-MOS capacitors with extremely low interface state density below 10cmeV were obtained by post-deposition annealing, Ga diffusion into overlying SiO layers severely degraded the insulating property and dielectric breakdown characteristics of the MOS devices. However, this problem was found to be solved by employing rapid thermal processing, leading to superior performance of the GaN-MOS devices in terms of interface quality, insulating property and gate dielectric reliability.

Comprehensive study on initial thermal oxidation of GaN(0001) surface and subsequent oxide growth in dry oxygen ambient

Yamada, Takahiro*; Ito, Joyo*; Asahara, Ryohei*; Watanabe, Kenta*; Nozaki, Mikito*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ishida, Masahiro*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; et al.

Journal of Applied Physics, 121(3), p.035303_1 - 035303_9, 2017/01

https://doi.org/10.1063/1.4974458

Initial oxidation of GaN(0001) epilayers and subsequent growth of thermal oxides in dry oxygen ambient were investigated by means of X-ray photoelectron spectroscopy, spectroscopic ellipsometry, atomic force microscopy and X-ray diffraction measurements. It was found that, whereas initial oxide formation tends to saturate at temperatures below 800C, selective growth of small oxide grains proceeds at dislocations in the epilayers, followed by noticeable grain growth leading to rough surface morphology at higher oxidation temperatures. This indicates that oxide growth and its morphology are crucially dependent on the defect density in the GaN epilayers. Structural characterizations also revealed that polycrystalline - and -phase GaO grains in an epitaxial relation with the GaN substrate are formed from the initial stage of the oxide growth. On the basis of these experimental findings, we also developed a comprehensive model for GaN oxidation mediated by nitrogen removal and mass transport.

Control of coordination and luminescence properties of lanthanide complexes using octadentate oligopyridine-amine ligands

Wada, Atsushi*; Watanabe, Masayuki; Yamanoi, Yoshinori*; Nankawa, Takuya; Namiki, Kosuke*; Yamasaki, Mikio*; Murata, Masaki*; Nishihara, Hiroshi*

Bulletin of the Chemical Society of Japan, 80(2), p.335 - 345, 2007/02

https://doi.org/10.1246/bcsj.80.335

Lanthanide complexes with linear and cyclic octadentate oligopyridine-amine ligands were synthesized, and their molecular structures were determined by single-crystal X-ray crystallography. All of the complexes had a distorted capped square antiprism (CSAP) geometry, and the coordination environments of lanthanide complexes were more distortedfor the complexes with the linear ligand than those with the cyclic ligand. The Eu complexes with the linear ligand showed more intense emissions, which were attributed to the D F transition, than the complex withthe cyclic ligand in acetonitrile, which can be attributed to the distortion in the coordination environments. These results indicate that the coordination environments of lanthanide complexes, and thus the luminescence properties, can be controlled by tuning the geometrical structures of polydentate ligands.

Control of molecular symmetry and luminescence properties of lanthanide complexes using octadentate oligopyridine-amine ligands

Wada, Atsushi; Watanabe, Masayuki; Yamanoi, Yoshinori*; Murata, Masaki*; Nishihara, Hiroshi*

no journal, , 

Lanthanide complexes with linear and cyclic octadentate oligopyridine-amine ligands were newly synthesized, and their molecular structures were determined by single-crystal X-ray crystallography. All of the complexes formed with the distorted CSAP geometry, the symmetry of which was higher for the complexes with the cyclic ligand than those with the linear ligand. The Eu and Tb complexes showed intense luminescence due to energy transfer from the ligand to the metal center (antenna effect). The Eu complexes with the linear ligand showed more intense emissions attributed to the 5D07F2 transition than the complex with the cyclic ligand, which can be explained by the decrease in symmetry around the lanthanide ion. The coordination of water molecules to Eu and Tb ions was strongly inhibited by surrounding the metal ions with the cyclic ligand, resulting in an appearance of intense luminescence in water. These results indicate that the symmetry and stability of lanthanide complexes, and thus the luminescence properties, can be successfully controlled by tuning the geometrical structures of multi-dentate ligands.

Separation of Am(III) by nitrogen-donor ligand

Watanabe, Masayuki; Ishimori, Kenichiro; Wada, Atsushi*; Kataoka, Yumiko*; Murata, Masaki*; Shinoda, Satoshi*; Nishihara, Hiroshi*; Tsukube, Hiroshi*; Kimura, Takaumi

no journal, , 

Soft-donor extractants containing sulfur- or nitrogen-donor are applicable to the separation of trivalent actinides (An(III)) from lanthanides (Ln(III)) by solvent extraction method. We designed two ligand systems which are expected to efficiently separate An(III) from Ln(III). The one is "Oligo-pyridine" ligand containing multiple pyridine moieties. The other is "Chirality-controlled" ligand containing chiral centers in the ligand. We synthesized more than thirty ligands and found out the ability on the separation of An(III) from Ln(III). In this presentation, we will discuss about the comprehensive results on the separation ability of An(III) from Ln(III) by means of "Oligo-pyridine" and "Chirality-controlled" ligands, and the extraction equilibrium of An(III) with selected tripodal ligands in detail.

Improved interface properties of SiO/GaN MOS capacitor by interfacial GaOx formation with post-oxidation treatment

Yamada, Takahiro*; Watanabe, Kenta*; Nozaki, Mikito*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*

no journal, , 

Interface properties of SiO/GaN structure with post-oxidation treatment were investigated by synchrotron radiation photoelectron spectroscopy and C-V measurements. High-resolution Ga 2p core-level spectra for SiO/GaN structure oxidized at 800 degrees showed asymmetric feature with a shoulder at higher binding energies compared to that for wet-cleaned GaN surface. From peak deconvolution of the Ga2p spectrum, formation of GaOx layer at the SiO/GaN interface was revealed. C-V measurements of the SiO/GaOx/GaN MOS capacitor exhibited apparently low frequency dispersion and a small hysteresis of below 50 mV. Moreover, the C-V curves well agreed with an ideal C-V curve. These results indicate that good interface properties were achieved by the interfacial GaOx formation.