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Journal Articles

Nanoscale structural analysis of Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ in high-temperature phases

Yoneda, Yasuhiro; Noguchi, Yuji*

Japanese Journal of Applied Physics, 60(SF), p.SFFA08_1 - SFFA08_10, 2021/11

 Times Cited Count:0 Percentile:0(Physics, Applied)

Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ (abbreviated as BNT) is a lead-free material but exhibits relatively large piezoelectric properties, a lot of researches have been conducted. We performed local structural analysis using high-quality BNT with a stoichiometrically correct composition, and found a chemical order structure of Bi/Na in locally. BNT undergoes a phase transition to a cubic phase at 400$$^{circ}$$C. We estimated that a new disorder structure will appear in the high-temperature phase. In the high temperature phase, pair distribution function (PDF) analysis using synchrotron radiation high-energy X-rays was performed. As a result, we found that Bi shifts from 200$$^{circ}$$C, and this shift becomes an order parameter for the phase transition.

Journal Articles

Nanoscale structural analysis of Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$

Yoneda, Yasuhiro; Noguchi, Yuji*

Japanese Journal of Applied Physics, 59(SP), p.SPPA01_1 - SPPA01_7, 2020/11

 Times Cited Count:7 Percentile:82.73(Physics, Applied)

We investigate A-site cation ordering in the ferroelectric perovskite Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ (BNT) by synchrotron X-ray total scattering. Although BNT has a problem of a low depolarization temperature, it is promising a lead-free piezoelectric material. Since the depolarization temperature is presumed to correspond to a relaxer like gradual order-disorder phase transition, local structure analysis is necessary to understand the structure of the diorder phase. Through this approach, the elusive connection between chemical heterogeneity and structural heterogeneity is revealed. Because of the large randomness, the Ti off-center shift is averaged out beyond the unit cell and the structure becomes very close to the average structure beyond the unit cell.

Journal Articles

Development of a method for positron annihilation lifetime measurement in thin polyethylene films using a Na-22 source

Yamawaki, Masato*; Uesugi, Naoya*; Oka, Toshitaka; Nagasawa, Naotsugu*; Ando, Hirokazu*; O'Rourke, B. E.*; Kobayashi, Yoshinori*

Japanese Journal of Applied Physics, 59(11), p.116504_1 - 116504_5, 2020/11

Positron annihilation lifetime measurements were performed on polyethylene films with thickness of 15$$mu$$m - 2000$$mu$$m using a Na-22 positron source enclosed in a Kapton film. For thin films, some positrons will pass through the film and annihilate behind it. Using a single film in a commercial anti-coincidence system, by placing an annealed stainless steel (SUS304) cover behind the sample, it is possible to sufficiently measure the long lifetime ortho-positronium (o-Ps) component even in thin films. Additionally, calculated intensities of the o-Ps component determined from the estimated film transmittance agreed well with the measured values. Furthermore, by applying this method to uniaxially stretched UHMWPE, we were able to observe structural changes owing to the stretching consistent with shorter measured o-Ps lifetime and increased o-Ps intensity.

Journal Articles

Degradation prediction using displacement damage dose method for AlInGaP solar cells by changing displacement threshold energy under irradiation with low-energy electrons

Okuno, Yasuki*; Ishikawa, Norito; Akiyoshi, Masafumi*; Ando, Hirokazu*; Harumoto, Masaki*; Imaizumi, Mitsuru*

Japanese Journal of Applied Physics, 59(7), p.074001_1 - 074001_7, 2020/07

 Times Cited Count:0 Percentile:0(Physics, Applied)

Performance degradation prediction for space solar cells under irradiation with low-energy electrons is greatly affected by displacement threshold energy (Ed) when a displacement damage dose (DDD) model is used. According to recent studies, the Ed of P atoms is much lower than the conventional Ed value in InP-type solar cells irradiated with low-energy electrons. This indicates that the value of Ed typically used in DDD model leads to significant error in performance degradation prediction. In this study, degradation of AlInGaP solar cells is observed after irradiation with 60 keV electrons. The results suggest that the Ed of P atoms in AlInGaP solar cells is much smaller than the conventionally used Ed value. By using the DDD model with the Ed value obtained in this study, we demonstrated that the performance degradation predicted by the DDD model agrees well with the experimental results.

Journal Articles

Development of microwave-assisted, laser-induced breakdown spectroscopy without a microwave cavity or waveguide

Oba, Masaki; Miyabe, Masabumi; Akaoka, Katsuaki; Wakaida, Ikuo

Japanese Journal of Applied Physics, 59(6), p.062001_1 - 062001_6, 2020/06

 Times Cited Count:0 Percentile:0(Physics, Applied)

Using a semiconductor microwave source and a coaxial cable for microwave transmission, a compact microwave-assisted, laser-induced breakdown spectroscopy system without a microwave cavity or waveguide was developed. Several types of electrode heads were tested, so that the emission intensity was 50 times larger than without microwave. The limit of the enhancement effect was also found.

Journal Articles

Toward technological contributions to remote operations in the decommissioning of the Fukushima Daiichi Nuclear Power Station

Kawabata, Kuniaki

Japanese Journal of Applied Physics, 59(5), p.050501_1 - 050501_9, 2020/05

 Times Cited Count:3 Percentile:31.27(Physics, Applied)

This paper describes the decommissioning work being undertaken at the Fukushima Daiichi Nuclear Power Station of the Tokyo Electric Power Company Holdings Inc.'s (FDNPS) using remote controlled robotic systems, as well as lessons learned from past remote task executions. We also summarize the issues to be considered in promoting safe, steady, and efficient decommissioning based on past experiences. In response to these issues, we are developing test methods for performance evaluation of the robots for nuclear decommissioning, robot simulator for operator proficiency training, and information generation methods to improve the operator's status awareness. The current status of technological development is also described.

Journal Articles

Strong flux pinning by columnar defects with directionally dependent morphologies in GdBCO-coated conductors irradiated with 80 MeV Xe ions

Sueyoshi, Tetsuro*; Kotaki, Tetsuya*; Furuki, Yuichi*; Fujiyoshi, Takanori*; Semboshi, Satoshi*; Ozaki, Toshinori*; Sakane, Hitoshi*; Kudo, Masaki*; Yasuda, Kazuhiro*; Ishikawa, Norito

Japanese Journal of Applied Physics, 59(2), p.023001_1 - 023001_7, 2020/02

 Times Cited Count:3 Percentile:62.13(Physics, Applied)

We show that Xe ion irradiation with 80 MeV to GdBa$$_{2}$$Cu$$_{3}$$Oy-coated conductors creates different morphologies of columnar defects (CDs) depending on the irradiation angles relative to the c-axis: continuous CDs with a larger diameter are formed for oblique irradiation at $$theta_{rm i}$$ = 45$$^{circ}$$, whereas the same ion beam at a different angle ($$theta_{rm i}$$ = 0$$^{circ}$$) induces the formation of discontinuous CDs. The direction-dependent morphologies of CDs significantly affect the angular behavior of the critical current density $$J_{rm c}$$.

Journal Articles

Short- and middle-ranges order structures of KNbO$$_3$$ nanocrystals

Yoneda, Yasuhiro; Kunisada, Ryoichi*; Chikada, Tsukasa*; Ueno, Shintaro*; Fujii, Ichiro*; Nagata, Hajime*; Ohara, Koji*; Wada, Satoshi*

Japanese Journal of Applied Physics, 58(SL), p.SLLA03_1 - SLLA03_7, 2019/11

 Times Cited Count:2 Percentile:23.94(Physics, Applied)

Journal Articles

Effect of hydrogen on chemical vapor deposition growth of graphene on Au substrates

Terasawa, Tomoo; Taira, Takanobu*; Yasuda, Satoshi; Obata, Seiji*; Saiki, Koichiro*; Asaoka, Hidehito

Japanese Journal of Applied Physics, 58(SI), p.SIIB17_1 - SIIB17_6, 2019/08

 Times Cited Count:0 Percentile:0(Physics, Applied)

Chemical vapor deposition (CVD) on substrates with low C solubility such as Cu and Au is promising to grow monolayer graphene selectively in a large scale. Hydrogen is often added to control the domain size of graphene on Cu, while Au does not require H$$_{2}$$ since Ar is inert against oxidation. The effect of H$$_{2}$$ should be revealed to improve the quality of graphene on Au. Here we report the effect of H$$_{2}$$ on the CVD growth of graphene on Au substrates using in situ radiation-mode optical microscopy. The in situ observation and ex situ Raman spectroscopy revealed that whether H$$_{2}$$ was supplied or not strongly affected the growth rate, thermal radiation contrast, and compressive strain of graphene on Au. We attributed these features to the surface reconstruction of Au(001) depending on H$$_{2}$$ supply. Our results are essential to achieve the graphene growth with high quality on Au for future applications.

Journal Articles

Local structure and phase transitions of KNbO$$_3$$

Yoneda, Yasuhiro; Ohara, Koji*; Nagata, Hajime*

Japanese Journal of Applied Physics, 57(11S), p.11UB07_1 - 11UB07_6, 2018/11

 Times Cited Count:9 Percentile:56.55(Physics, Applied)

Local structure analysis of KNbO$$_3$$, which is the parent compound for lead-free piezoelectric materials, have been performed by X-ray pair-distribution functions (PDF). The refinements of local structure in wide temperature ranges indicates that only the rhombohedral structure can describe the observed bond distributions within the unit cell. The rhombohedral distortion maintained locally in all four phases.

Journal Articles

Characterization of SiO$$_{2}$$ reduction reaction region at void periphery on Si(110)

Yano, Masahiro; Uozumi, Yuki*; Yasuda, Satoshi; Tsukada, Chie*; Yoshida, Hikaru*; Yoshigoe, Akitaka; Asaoka, Hidehito

Japanese Journal of Applied Physics, 57(8S1), p.08NB13_1 - 08NB13_4, 2018/07

 Times Cited Count:1 Percentile:7.88(Physics, Applied)

Journal Articles

Physical and electrical characterizations of AlGaN/GaN MOS gate stacks with AlGaN surface oxidation treatment

Yamada, Takahiro*; Watanabe, Kenta*; Nozaki, Mikito*; Shih, H.-A.*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.

Japanese Journal of Applied Physics, 57(6S3), p.06KA07_1 - 06KA07_6, 2018/06

 Times Cited Count:4 Percentile:25.32(Physics, Applied)

Thermal oxidation of AlGaN surface and its impact on the electrical properties of AlGaN/GaN MOS capacitors were investigated by means of synchrotron radiation photoelectron spectroscopy (SR-PES), atomic force microscopy (AFM) and C-V measurements. SR-PES analysis revealed that the AlGaN surface is oxidized even at low temperature of 400$$^{circ}$$C, in contrast to no oxide formation on GaN surface. However, since no noticeable change in the surface morphology was observed at temperatures up to 800$$^{circ}$$C, it can be concluded that an ultrathin oxide overlayer is formed on the AlGaN surface. On the other hand, for the oxidation treatments above 850$$^{circ}$$C, the formation of small oxide grains was observed over the entire area of the AlGaN surface, and the growth of oxide grains significantly degraded the surface morphology. Therefore, the AlGaN/GaN MOS capacitors were fabricated on the AlGaN surface oxidized at moderate temperatures up to 800$$^{circ}$$C. While we have confirmed that relatively good interface properties are obtained for direct AlON deposition without oxidation treatment, it was found that the oxidation treatment at 400$$^{circ}$$C leads to further improvement of interface properties and reduction of C-V hysteresis.

Journal Articles

Uniform Si nano-dot fabrication using reconstructed structure of Si(110)

Yano, Masahiro; Uozumi, Yuki*; Yasuda, Satoshi; Asaoka, Hidehito

Japanese Journal of Applied Physics, 57(6S1), p.06HD04_1 - 06HD04_4, 2018/06

 Times Cited Count:4 Percentile:33.32(Physics, Applied)

Journal Articles

SiO$$_{2}$$/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

 Times Cited Count:9 Percentile:60.66(Physics, Applied)

The advantage of SiO$$_{2}$$/AlON stacked gate dielectrics over SiO$$_{2}$$, AlON and Al$$_{2}$$O$$_{3}$$ 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.

Journal Articles

Implementation of atomic layer deposition-based AlON gate dielectrics in AlGaN/GaN MOS structure and its physical and electrical properties

Nozaki, Mikito*; Watanabe, Kenta*; Yamada, Takahiro*; Shih, H.-A.*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.

Japanese Journal of Applied Physics, 57(6S3), p.06KA02_1 - 06KA02_7, 2018/06

 Times Cited Count:12 Percentile:70.01(Physics, Applied)

We fabricated AlON dielectric films by repeating thin AlN deposition and in situ O$$_{3}$$ oxidation for AlGaN/GaN MOS-HFETs. Uniform nitrogen distribution is achievable by the proposed ALD-based process and that nitrogen concentration can be precisely controlled by changing AlN thickness (ALD cycle number) in each step. It was found that AlON films grown by ALD system offers significant advantages in terms of practical application while keeping superior Vth stability and electrical properties at the insulator/AlGaN interface in AlGaN/GaN MOS-HFETs.

Journal Articles

Effective adsorption and collection of cesium from aqueous solution using graphene oxide grown on porous alumina

Entani, Shiro*; Honda, Mitsunori; Shimoyama, Iwao; Li, S.*; Naramoto, Hiroshi*; Yaita, Tsuyoshi; Sakai, Seiji*

Japanese Journal of Applied Physics, 57(4S), p.04FP04_1 - 04FP04_4, 2018/04

 Times Cited Count:3 Percentile:25.32(Physics, Applied)

Journal Articles

Local structure analysis of (Na$$_{0.5}$$K$$_{0.45}$$Li$$_{0.05}$$)NbO$$_3$$ synthesized by malic acid complex solution method

Yoneda, Yasuhiro; Takada, Eri*; Nagai, Haruka*; Kikuchi, Takeyuki*; Morishita, Masao*; Kobune, Masafumi*

Japanese Journal of Applied Physics, 56(10S), p.10PB07_1 - 10PB07_7, 2017/10

 Times Cited Count:3 Percentile:21.75(Physics, Applied)

A monoclinic phase was discovered in (Na$$_{0.5}$$K$$_{0.45}$$Li$$_{0.05}$$)NbO$$_3$$ solid solution ceramics grown by a malic acid complex solution method. The average and local structures of this monoclinic phase were analyzed by synchrotron X-ray measurements. The local structure can be reproduced by assuming a rhombohedral model, that is the same local structure of KNbO$$_3$$. The results demonstrate that the monoclinic average structure is observed as a disordered rhombohedral structure.

Journal Articles

Local structure analysis of NaNbO$$_3$$ and AgNbO$$_{3}$$ modified by Li substitution

Yoneda, Yasuhiro; Aoyagi, Rintaro*; Fu, D.*

Japanese Journal of Applied Physics, 55(10S), p.10TC04_1 - 10TC04_5, 2016/10

 Times Cited Count:6 Percentile:37.51(Physics, Applied)

We analyzed the local structures of NaNbO$$_3$$ and Na$$_{0.94}$$Li$$_{0.06}$$NbO$$_3$$ by combining the X-ray absorption fine structure (XAFS) and atomic pair-distribution function (PDF) techniques. NaNbO$$_3$$ is known to be an antiferroelectric material at room temperature. It also undergoes a diffuse phase transition, in which an orthorhombic and a rhombohedral phases coexist over a wide temperature range. We identified a rhombohedral ground state structure of NaNbO$$_3$$ and assumed an order-disorder-type phase. We also found a disorder feature in the nearest-neighbor bond distance corresponding to the Nb-O bonds. The disordered bond distribution disappeared when Na was substituted for Li. A similar disorder feature was found in AgNbO$$_3$$.

Journal Articles

Detection of molecular oxygen adsorbate during room-temperature oxidation of Si(100)2$$times$$1 surface; In situ synchrotron radiation photoemission study

Yoshigoe, Akitaka; Yamada, Yoichi*; Taga, Ryo*; Ogawa, Shuichi*; Takakuwa, Yuji*

Japanese Journal of Applied Physics, 55(10), p.100307_1 - 100307_4, 2016/09

 Times Cited Count:1 Percentile:6.46(Physics, Applied)

Synchrotron radiation photoelectron spectroscopy during the oxidation of the Si(100)2$$times$$1 surface at room temperature revealed the existence of the molecularly adsorbed oxygen, which was considered to be absent. The O 1s spectra was found to be similar to that of the oxidation of Si(111)7$$times$$7 surfaces. Also the molecular oxygen was appeared after the initial surface oxides, indicating that this was not a precursor for dissociation oxygen adsorption onto the clean surface. We have proposed presumable structural models for atomic configurations, where the molecular oxygen was resided on the oxidized silicon with two oxygen atoms at the backbonds.

Journal Articles

Effects of growth temperature and growth rate on polytypes in gold-catalyzed GaAs nanowires studied by in situ X-ray diffraction

Takahashi, Masamitsu; Kozu, Miwa*; Sasaki, Takuo

Japanese Journal of Applied Physics, 55(4S), p.04EJ04_1 - 04EJ04_4, 2016/04

 Times Cited Count:4 Percentile:26.22(Physics, Applied)

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