著者

Fukata N. Sato S. Morihiro H. Murakami K. Ishioka K. Kitajima M. Hishita S.

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.101, no.4, pp.046107, 2007-02

被引用文献数

12 3

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The formation of hydrogen (H)-related complexes and H effects on boron (B) and phosphorus (P) dopants was investigated in B- or P-doped silicon (Si) crystal treated with high concentration of H. The reactivation process of dopant carriers by annealing after hydrogenation was significantly different between the p-type and n-type specimens. The difference is likely to be attributable to the formation of H-related defects based on the stable sites of the H atoms, i.e., complicated H multiple trapping centers are formed by bond breaking due to H atoms in only p-type B-doped Si.

著者

Uedono A. Shaoqiang C. Jongwon S. Ito K. Nakamori H. Honda N. Tomita S. Akimoto K. Kudo H. Ishibashi S.

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.103, no.10, pp.104505, 2008-08

被引用文献数

22 27

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A relationship between intra-4f transitions of Er and vacancy-type defects in Er-doped GaN was studied by using a monoenergetic positron beam. Doppler broadening spectra of the annihilation radiation were measured for Er-doped GaN grown by molecular beam epitaxy. A clear correlation between the defect concentration and the photoluminescence (PL) intensity was observed. The major defect species detected by positrons was identified as a Ga vacancy VGa, and its concentration increased with increasing Er concentration [Er]. For the sample with [Er]=3.3 at. %, the maximum integrated intensity of PL was observed. The VGa concentration was above 1018 cm−3 and additional vacancies such as divacancies started to be introduced at this Er concentration. For the sample with higher [Er], the PL intensity decreased, and the mean size of vacancies decreased due to an introduction of precipitates and/or metastable phases.

著者

Yokomaku Hiroomi Satoh Wataru Fukuda Junji Suzuki Hiroaki

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.104, no.6, pp.064910, 2008-09

被引用文献数

13 6

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To improve the performance of electrowetting-based microfluidic devices, we used micropillar structures to enhance the changes in the wettability of gold electrodes. The changes in the contact angle of a sessile drop were influenced by the diameter of the micropillars and interpillar distances. For a potential change between 0 V and −1.0 V, the change of the contact angle of the KCl sessile drop was 41° on a smooth electrode, but 88° on an electrode with micropillars with a 10 µm diameter. Furthermore, the existence of the micropillars accelerated the change of the contact angle. The gold electrodes with the micropillars were used to generate the capillary force to mobilize a liquid column in a microflow channel. Compared to a device with a smooth electrode, this device showed a fourfold increase in the flow velocity at −0.9 V. The electrodes were also used as a valve. The ability to stop an intruding solution and the switching speed was improved with the micropillar structure.

著者

Ko Jae-Hyeon Lushnikov S. G. Kim Do Han Kojima Seiji Jun Byeong-Eog Hwang Yoon Hwae

出版者

American Institute of Physics

雑誌

Journal of applied physic (ISSN:00218979)

巻号頁・発行日

vol.104, no.10, pp.104105, 2008-11

被引用文献数

9 5

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Acoustic properties were investigated for four tungsten bronze (TB) uniaxial ferroelectric crystals, i.e., (Sr0.61Ba0.39)5Nb10O30 (SBN61), Cu-doped (K0.5Na0.5)1.0(Sr0.75Ba0.25)4.5Nb10O30 (KNSBN:Cu), K5.80Li3.82Nb10.12O30, and K4.74Li3.07Nb10.44O30 of which the spontaneous polarization is directed along the polar c axis. Large acoustic anisotropy between the two elastic constants C11 and C33 have been observed from all samples. C33 exhibits a significant softening on approaching the diffuse phase transition temperature from high-temperature side while C11 does not show any substantial change in the same temperature range. This softening is accompanied by substantial growth of hypersonic damping, appearance and growth of central peak (CP), and slowing down of the relevant dynamics of CP represented by the reducing half width. All these results indicate that the lattice motions along the c axis couple strongly to the one-component order parameter of the polar nanoregions (PNRs) or precursor polar clusters which form and grow below a certain temperature in the paraelectric phase. The inverse dielectric constant measured along the c axis of SBN61 and KNSBN:Cu can be described by two linear regions divided by a crossover temperature at which the change in the magnitude of dipole moments and the strength of the dipole couplings are expected due to the formation of PNRs. C33 of SBN61 becomes continuously softened upon cooling even when the temperature crosses the Burns temperature TB at which PNRs begin to appear. It may suggest that additional relaxation process other than that of PNRs may exist at high temperatures above TB and couple to the longitudinal acoustic waves propagating along the polar axis. Recent observation of a single-particle relaxation at high temperatures and its transformation into a collective relaxation of PNRs by dielectric spectroscopy [Belous et al., J. Appl. Phys. 102, 014111 (2007)] might be related to the anomalous acoustic behavior of SBN61 observed above TB.

著者

Shabbir Ghulam Kojima Seiji

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.105, no.3, pp.034106, 2009

被引用文献数

7 5

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Lanthanum-doped lead zirconate titanate, PLZT-x/65/35 (x=8.0, 9.0, and 9.4), relaxor ferroelectric ceramics were investigated by the high resolution Brillouin light scattering spectroscopy in the temperature range from ~870 down to ~170 K. Broad anomalies were observed in the acoustic phonon mode velocity and related elastic stiffness coefficient showing minimum between ~320–~240 K. The deviation in the acoustic mode velocity from the high temperature linearity at the Burns temperature (TB~720 K) and presence of a broad central peak in the temperature range 200T540 K were attributed to the dynamics of polar nanoregions with randomly oriented local polarization appearing due to site and/or charge disorder at both A- and B-sites of the ABO3 perovskite lattice. The presence of a new temperature point Td (~575 K) was conclusively established in PLZT-x/65/35 relaxor ceramics.

著者

Sivasubramanian V. Tsukada S. Kojima S.

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.105, no.1, pp.014108, 2009

被引用文献数

9 4

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The temperature dependences of acoustic phonon mode and the central peak have been investigated in Pb[(In1/2Nb1/2)0.65Ti0.35]O3 single crystal by Brillouin scattering. Longitudinal acoustic phonon begins to show marked softening below the Burns temperature TB~700 K. The longitudinal acoustic phonon mode exhibits clear anomalies at the cubic-tetragonal phase transition temperature of 540 K and at the tetragonal-rhombohedral one of 460 K. Below 600 K, the relaxation time calculated from the phonon mode agrees well with that of the broad central peak, suggesting a coupling between the local polarization and strain fluctuations of polar nanoregions. This temperature has been identified as another characteristic temperature T* besides TB, where the formation of long-lived polar nanoregions accompanied by the local strain fields governs the relaxation dynamics.

著者

Murakami Kouichi Shirakawa Ryota Tsujimura Masatoshi Uchida Noriyuki Fukata Naoki Hishita Shun-ichi

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.105, no.5, pp.054307, 2009-03

被引用文献数

23 11

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We have investigated phosphorus ion (P+) implantation in Si nanocrystals (SiNCs) embedded in SiO2, in order to clarify the P donor doping effects for photoluminescence (PL) of SiNCs in wide P concentrations ranging in three orders. Some types of defects such as Pb centers were found to remain significantly at the interfaces between SiNCs and the surrounding SiO2 even by high-temperature (1000 °C) annealing of all the samples. Hydrogen atom treatment (HAT) method can efficiently passivate remaining interface defects, leading to significant increase in the intensity of PL arising from the recombination of electron-hole pairs confined in SiNCs, in addition to significant decrease in interface defects with dangling bonds detected by electron spin resonance. From both the results of the P dose dependence before and after HAT, it is found that the amount of remaining defects is higher for samples with SiNCs damaged by implantation with relatively lower P+ doses and then annealed, and that through HAT the observed PL intensity increases surely as the P concentration increases up to a critical concentration. Then it begins to decrease due to Auger nonradiative recombination above the critical concentration which depends on the size of SiNCs. These results suggest an effect of relatively low concentration of P atoms for the enhancement of PL intensity of SiNCs and we present an unconventional idea for explaining it.

著者

Morimoto Katsuya Yamaguchi Shigeki Fukuda Junji Suzuki Hiroaki

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.105, no.10, pp.102013, 2009-05

被引用文献数

2 3

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The possibility to develop a microanalysis system for the acquisition of gastrointestinal information is presented here. The system consists of four assay sites for trypsin, pepsin, and other biochemical compounds. The major components in each assay site were a pH-responsive valve, a pH-stat used to maintain the pH of the solution to be analyzed and used for electrochemical pH-titration, and a freeze-dried enzyme substrate stored in the pH-stat. The operation of the valve is based on electrowetting, and the valve is made pH-responsive by means of a nonstandard three-electrode system. The sample solution was automatically injected into the compartment and rapidly dissolved into the substrate layer. The automatic pH-stat, based on another nonstandard use of the electrochemical three-electrode system, maintained the solution pH and, at the same time, conducted pH-titration. The determination of the activity of the proteases was conducted at their optimum pHs. The output current showed a clear dependence on the activity of the enzymes. Integrating the functions provides significant advantages for the use of this system as an isolated telemetric microsystem that may operate with wireless signal transmission using a small power supply.

著者

Aoki M. Toyoshima S. Kamada T. Sogo M. Masuda S. Sakurai T. Akimoto K.

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.106, no.4, pp.043715, 2009-08

被引用文献数

11 7

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Electron emission spectra resulting from thermal collision of He*(23S) atoms with 2,9-demethyl-4,7-diphenyl-1,10-phenanthroline (BCP) films deposited on metal substrates were measured to characterize gap states emerged at the organic-metal interface. For BCP on Au, the gap state is originated from weak chemisorption and serves as a mediator of metal wave functions to the first layer. For BCP on K, organic-metal complex is formed by spontaneous diffusion, yielding the gap states delocalized over the film. In the interfacial region, all the gap state reveals an incommensurate shift with the valence band top of the film, indicating the breakdown of the Schottky–Mott model as evaluating the transport characteristics in organic-metal system.

著者

Kamioka Hayato Hirano Masahiro Hosono Hideo

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.106, no.5, pp.053105, 2009-09

被引用文献数

12

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Eu2+ doped sorosilicate Ca2ZnSi2O7 (melilite) exhibits a broad band emission peaking at ~600 nm (~2 eV) due to the electric dipole allowed transition of 4f65d1 to 4f7 of Eu2+ by an excitation with blue light (460 nm). Strong O2− ligand field with low symmetry due to the layered tetragonal crystallographic structure of the melilite may play a dominant role in lowering the emission band energy to ~2 eV. In addition, line emissions attributable to the transitions from 5D0 to 7FJ of Eu3+ ions are detected by an excitation with deep UV light with sub-360 nm wavelengths. This is due to the formation of transient Eu3+ ions via charge transfer from Eu2+ to the matrix. The lifetime of the transient Eu3+ ion is found to be 58 ms by a pump-probe measurement, in which UV pulse laser and green continuous wave laser are employed as pump and probe lights, respectively. Based on these results, the energy diagram of Eu2+ in Ca2ZnSi2O7 is proposed.

著者

Kim Young-ho Zhao Jianwei Uosaki Kohei

出版者

American Institute of Physics

雑誌

Journal of Applied Physics (ISSN:00218979)

巻号頁・発行日

vol.94, no.12, pp.7733-7738, 2003-12-15

被引用文献数

8

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Nanosized patterns of tantalum oxide were fabricated on a tantalum substrate by applying a potential pulse utilizing current sensing atomic force microscopy (CSAFM). The dimensions of the dots were strongly dependent on the bias applied, scan rate, and potential pulse duration. By controlling these variables, the minimum size nanodots with full width at half maximum of 35 nm was achieved. Immediately after pattern formation, the electrical properties of the Ta oxide nanodots were measured using CSAFM. The charge transport at the CSAFM tip and the nanosized Ta oxide dot can be described by Poole–Frenkel type conduction. The relative dielectric constant of the nanosized Ta2O5 dots was calculated to be 17.8–24.3, showing that the quality of the oxide was high. In addition, by controlling the substrate bias applied, pulse duration, and tip scan speed, nanosized Ta oxide lines with the desired dimensions were prepared.