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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

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:100(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:1 Percentile:74.46(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:0 Percentile:100(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:4 Percentile:32.09(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:4 Percentile:32.09(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

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:1 Percentile:86.12(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:4 Percentile:70.35(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:0 Percentile:100(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:62.06(Physics, Applied)

Journal Articles

Charge-collection efficiency and long-term stability of single-crystal CVD diamond detector under different carrier-drift conditions

Sato, Yuki; Murakami, Hiroyuki*; Shimaoka, Takehiro*; Tsubota, Masakatsu*; Kaneko, Junichi*

Japanese Journal of Applied Physics, 55(4), p.046401_1 - 046401_5, 2016/04

 Times Cited Count:1 Percentile:89.8(Physics, Applied)

We investigated the performance of a charged particle detector fabricated using single-crystal diamond grown by chemical vapor deposition. The detector was able to identify four different $$^{241}$$Am $$alpha$$-particle energies (5.389, 5.443, 5.486, and 5.545 MeV) because of its superior intrinsic energy resolution of $$sim$$0.4% (full width at half maximum). The charge collection efficiency inside the diamond crystal was $$sim$$98% for both electrons and holes. The diamond detector also exhibited no significant degradation in terms of pulse height spectra and energy resolution during operation for more than 100 h in the case of mainly electron drift inside the diamond crystal. In contrast, the shapes of the pulse height spectra measured under hole drift condition deteriorated due to the polarization phenomenon.

Journal Articles

Simulation of discharge in insulating gas from initial partial discharge to growth of a stepped leader using the percolation model

Sasaki, Akira; Kato, Susumu*; Takahashi, Eiichi*; Kishimoto, Yasuaki*; Fujii, Takashi*; Kanazawa, Seiji*

Japanese Journal of Applied Physics, 55(2), p.026101_1 - 026101_10, 2016/02

 Times Cited Count:2 Percentile:79.71(Physics, Applied)

A percolation model of discharge, which can reproduce stochastic behaviors of initial partial discharge to the growth of a stepped leader, is presented. The model uses macroscopic cells, from which a network of electric circuits is defined, and the spatial and temporal evolutions of the electric field and current in the discharge medium are calculated. For each cell, one of two states, either insulator or conductor, which corresponds to neutral gas or ionized plasmas, respectively, is decided. The decision is made on the basis of probability for each calculation cell at each time step, taking the effects of local electric field and current, which enhance ionization and sustain the discharge channel, respectively, into account. The stochastic behavior of discharge is discussed, in conjunction with the characteristic feature of ionization, that is, the ionization occurs not only ahead of the streamer tip where the electric field is enhanced but randomly in the discharge medium.

Journal Articles

Effect of defocusing on laser ablation plume observed by laser-induced fluorescence imaging spectroscopy

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

Japanese Journal of Applied Physics, 55(2), p.022401_1 - 022401_4, 2016/02

 Times Cited Count:2 Percentile:79.71(Physics, Applied)

We used laser-induced fluorescence imaging with a varying beam focal point to observe ablation plumes from metal and oxide samples of gadolinium. The plumes expand vertically when the focal point is far from the sample surface. In contrast, the plume becomes hemispherical when the focal point is on the sample surface. In addition, the internal plume structure and the composition of the ablated atomic and ionic particles also vary significantly. The fluorescence intensity of a plume from a metal sample is greater than that from an oxide sample, which suggests that the number of monatomic species produced in each plume differs. For both the metal and oxide samples, the most intense fluorescence from atomic (ionic) species is observed with the beam focal point at 3-4 mm (2 mm) from the sample surface.

Journal Articles

Radiation response of silicon carbide metal-oxide-semiconductor transistors in high dose region

Oshima, Takeshi; Yokoseki, Takashi; Murata, Koichi; Matsuda, Takuma; Mitomo, Satoshi; Abe, Hiroshi; Makino, Takahiro; Onoda, Shinobu; Hijikata, Yasuto*; Tanaka, Yuki*; et al.

Japanese Journal of Applied Physics, 55(1S), p.01AD01_1 - 01AD01_4, 2016/01

 Times Cited Count:7 Percentile:43.28(Physics, Applied)

Journal Articles

High-efficiency contact grating fabricated on the basis of a Fabry-Perot type resonator for terahertz wave generation

Yoshida, Fumiko; Nagashima, Keisuke; Tsubouchi, Masaaki; Ochi, Yoshihiro; Maruyama, Momoko; Sugiyama, Akira

Japanese Journal of Applied Physics, 55(1), p.012201_1 - 012201_5, 2016/01

 Times Cited Count:5 Percentile:54.81(Physics, Applied)

Journal Articles

Local structure analysis of KNbO$$_3$$ nanocubes by solvothermal synthesis

Yoneda, Yasuhiro; Kohara, Shinji*; Nakashima, Koichi*; Nagata, Hajime*; Wada, Satoshi*

Japanese Journal of Applied Physics, 54(10S), p.10NC01_1 - 10NC01_6, 2015/10

 Times Cited Count:3 Percentile:76.7(Physics, Applied)

The atomic-scale structure of KNbO$$_3$$ nanopowder synthesized by solvothermal method has been studied using high-energy X-ray diffraction, Rietveld refinement, and the atomic pair-distribution function (PDF) technique. It was found that the local structure of KNbO$$_3$$ nanoparticles deviates from the average structure. The local structure was found to be rhombohedral structure though the average structure was tetragonal structure. The rhombohedral distortion of NbO$$_6$$ octahedra was maintained in the annealed sample.

Journal Articles

Energy loss process analysis for radiation degradation and immediate recovery of amorphous silicon alloy solar cells

Sato, Shinichiro; Beernink, K.*; Oshima, Takeshi

Japanese Journal of Applied Physics, 54(6), p.061401_1 - 061401_6, 2015/06

 Times Cited Count:2 Percentile:84.29(Physics, Applied)

Performance degradation and immediate recovery of a-Si/a-SiGe/a-SiGe triple-junction solar cells due to irradiation of silicon ions, electrons, and protons are investigated. Significant recovery is always observed independent of radiation species and temperature. It is shown that the characteristic time, which is obtained by analyzing the short-circuit current annealing behavior, is an important parameter for practical applications in space. In addition, the radiation degradation mechanism is discussed by analyzing the energy loss process of incident particles (ionizing energy loss: IEL, and non-ionizing energy loss: NIEL) and their relative damage factors. It is determined that ionizing dose is the primarily parameter for electron degradation whereas displacement damage dose is the primarily parameter for proton degradation. The impact of "radiation quality effect" has to be considered to understand the degradation due to Si ion irradiation.

Journal Articles

Line splitting by mechanical rotation in nuclear magnetic resonance

Harii, Kazuya; Chudo, Hiroyuki; Ono, Masao; Matsuo, Mamoru; Ieda, Junichi; Okayasu, Satoru; Maekawa, Sadamichi; Saito, Eiji

Japanese Journal of Applied Physics, 54(5), p.050302_1 - 050302_3, 2015/05

 Times Cited Count:6 Percentile:63.49(Physics, Applied)

Journal Articles

Diffraction of $$gamma$$-rays with energies of 1.17 and 1.33 MeV by a flat Si crystal

Matsuba, Shunya*; Hayakawa, Takehito; Shizuma, Toshiyuki; Nishimori, Nobuyuki; Nagai, Ryoji; Sawamura, Masaru; Angell, C.; Fujiwara, Mamoru; Hajima, Ryoichi

Japanese Journal of Applied Physics, 54(5), p.052203_1 - 052203_5, 2015/05

 Times Cited Count:3 Percentile:76.7(Physics, Applied)

Journal Articles

Instability of a ferrimagnetic state of a frustrated $$S$$=1/2 Heisenberg antiferromagnet in two dimensions

Nakano, Hiroki*; Sakai, Toru

Japanese Journal of Applied Physics, 54(3), p.030305_1 - 030305_4, 2015/03

To clarify the instability of the ferrimagnetism which is the fundamental magnetism of ferrite, numerical diagonalization study for the two-dimensional $$S$$=1/2 Heisenberg antiferromagnet with frustration. We find that the ferrimagnetic ground state has the spontaneous magnetization in small frustration.

490 (Records 1-20 displayed on this page)