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

---

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

---

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

---

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

22 11

---

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

---

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

---

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

---

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

Yoshida Katsuhisa Okada Yoshitaka Sano Nobuyuki

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.97, no.13, pp.133503, 2010-09

被引用文献数

57 30

---

In order to design optimum structures for intermediate band solar cells, simulations based on self-consistent drift-diffusion model with a suitable treatment of the intermediate band in device domain are necessary. In this work, we have included the dependence of occupation rate of intermediate band at each position on optical generation rate via the intermediate band. Typical material parameters of GaAs were used except for the absorption coefficient of each corresponding band-to-band transition. Simulation results using our model indicate that the dependence of occupation rate on device position strongly affect short-circuit currents and also electrostatic potentials of the cell.

著者

Umeda T. Isoya J. Ohshima T. Onoda S. Morishita N. Okonogi K. Shiratake S.

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.97, no.4, pp.041911, 2010-07

被引用文献数

5

---

An electron paramagnetic resonance (EPR) study on fluorine-vacancy defects (FnVm) in fluorine-implanted silicon is demonstrated. Fluorine implantation is an important technology for Si microdevices and EPR measurements showed that this process created a variety of FnVm defects of different sizes (V2, V4, and V5). In FnVm, a Si–F bond exhibited a different chemical nature compared to a Si–H bond in hydrogen-vacancy complexes. The most primitive defect was FV2 (F0 center) and the final types were FnV5 (F1 center) and FnV2 (F2 center) which increased in annealing processes as low temperature as 200 °C.

著者

Chen Shaoqiang Dierre Benjamin Lee Woong Sekiguchi Takashi Tomita Shigeo Kudo Hiroshi Akimoto Katsuhiro

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.96, no.18, pp.181901, 2010

被引用文献数

29 12

---

Erbium-doped GaN with different doping concentrations were grown by ammonia-source molecular beam epitaxy. The intra-4f-shell transitions related green luminescence were observed by both photoluminescence (PL) and cathodoluminescence (CL) measurements. It was found that concentration quenching of Er-related luminescence was observed in PL measurements while not in CL measurements. The different excitation and relaxation processes are suggested as the cause of the concentration quenching characteristics between PL and CL. The strong Er-related CL intensity in highly doped GaN demonstrates that high energy excitation is a promising approach to suppress the concentration quenching in Er-doped GaN.

著者

Leiner Johannes Saleem Sajid Fenton J. C. Yamamoto Takashi Kadowaki Kazuo Warburton P. A.

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.95, no.25, pp.252505, 2009-12

被引用文献数

2 2

---

We have measured the response of an array of Bi2Sr2CaCu2O8+delta intrinsic Josephson junctions to irradiation at 3 GHz. By measuring the dependence of the switching current upon the radio-frequency current for five of the junctions in the array we show quantitatively that the junctions have identical impedances at 3 GHz, this impedance being given by the inverse of the slope of the current-voltage characteristics.

著者

Siribunbandal Papaorn Yamaguchi Shigeki Kojima Kenichi Fukuda Junji Suzuki Hiroaki

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.95, no.20, pp.204105, 2009-11

被引用文献数

10 9

---

Autonomous control of the transport of solutions in microfabricated flow channels using electrowetting-based valves and integrated electrochemical cells is proposed. An electrowetting-based valve formed with a gold electrode was opened when an electrolyte solution reached a zinc electrode in a controlling flow channel and a potential was applied to the gold electrode, causing the transport of the solution in the flow channel. Independent composite electrodes consisting of gold and zinc could function in the same manner without requiring additional electrodes. Controlled autonomous transport of solutions in a network of flow channels could also be carried out using the integrated valves.

著者

Narahara A. Ito K. Suemasu T. Takahashi Y. K. Ranajikanth A. Hono K.

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.94, no.20, pp.202502, 2009-05

被引用文献数

62 29

---

The spin polarization of (100)-oriented gamma[prime]-Fe4N layers grown on MgO(001) substrates by molecular beam epitaxy was deduced from point contact Andreev reflection measurements, and the value was compared with that of alpha-Fe. The spin polarization (P) for gamma[prime]-Fe4N is approximately 0.59 at 7.8 K. This value is distinctly larger than that for alpha-Fe (P=0.49 at 7.8 K) measured with an identical setting. The mechanism of enhanced spin polarization in gamma[prime]-Fe4N is discussed.

著者

Ahart Muhtar Hushur Anwar Bing Yonghong Ye Zuo-Guang Hemley Russell J. Kojima Seiji

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.94, no.14, pp.142906, 2009-04

被引用文献数

27

---

Brillouin spectroscopy of Pb(Sc0.5Nb0.5)O3 single crystals reveals an order-disorder ferroelectric phase transition occurs at 110 °C upon cooling. A softening of the longitudinal acoustic (LA) mode is observed that can be attributed to the coupling between polar nanoregions and acoustic modes. A critical slowing down of the central peak, a feature of order-disorder ferroelectric phase transitions, is observed near Tc. The similarity in temperature dependences of the two kinds of relaxation times determined from the central peak and LA mode suggests that the changes in the central peak arise from local polarization fluctuations in the polar nanoregions.

著者

Tanaka Hisaaki Watanabe Shun-ichiro Ito Hiroshi Marumoto Kazuhiro Kuroda Shin-ichi

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.94, no.10, pp.103308, 2009-03

被引用文献数

33 17

---

Charge carrier concentration in operating field-effect transistor (FET) of regioregular poly(3-hexylthiophene) has been directly determined by electron spin resonance (ESR). ESR signals of field-induced polarons are observed around g=2.003 under the application of negative gate-source voltage (Vgs). Upon applying drain-source voltage (Vds), ESR intensity decreases linearly in the low Vds region, reaching to about 50% of the initial intensity at the pinch-off point (Vds~=Vgs). For larger absolute values of Vds, it becomes nearly Vds independent. These behaviors are well explained by the change in the carrier concentration obtained by the FET theory using gradual channel approximation.

著者

Kita Yuki Yoshida Shinichi Hosoi Takuji Shimura Takayoshi Shiraishi Kenji Nara Yasuo Yamada Keisaku Watanabe Heiji

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.94, no.12, pp.122905, 2009-03

被引用文献数

8 8

---

Change in the work function (WF) of the gate electrode material caused by the contact with Hf-based high-k gate dielectrics was investigated by means of the flat-band voltage (Vfb) shift in capacitance-voltage curves, and the interface dipole, which modifies the WF, was characterized by x-ray photoelectron spectroscopy. We observed a negative Vfb shift and corresponding interface dipole, which suggest the formation of oxygen vacancy (VO) in the Hf-based oxides. In contrast, we observed an opposite (positive) Vfb shift and interface dipole when Au electrodes were formed on cleaned Hf-based dielectrics. This indicates that Au–Hf bond hybridization at the Au/HfSiON interface also causes effective WF modulation, as theoretically predicted by Shiraishi et al. (Tech. - Dig. Int. Electron Devices Meet. 2005, 43).

著者

Moritomo Y. Nakada F. Kurihara Y.

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.94, no.11, pp.111914, 2009-03

被引用文献数

5 4

---

Electrochromism is extensively investigated for practical application of display and memory devices. To develop the material, reliable information on the optical and electronic properties of the solid film is indispensable. Here, we propose valence-differential spectroscopy that can selectively extract the spectral components related to the oxidized/reduced metal site. We applied the spectroscopy to Co2+–Fe2+delta and Co2+delta–Fe2+ cyanide films with finely control of averaged valence (delta) of the transition metal by external electric pulses. The spectroscopy revealed transition energy E, width Gamma, and oscillator strength f of the spectral components related to the transition metal.

著者

Hase Muneaki

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.94, no.11, pp.112111, 2009-03

被引用文献数

18 6

---

Ultrafast dephasing of the plasmonlike longitudinal optical phonon-plasmon coupled (LOPC) mode in highly doped n-GaAs has been investigated by using a femtosecond optical pump-probe technique with 40 THz bandwidth as a function of photodoping levels. The direct measurement of plasmon damping with the help of a wavelet analysis enables us to extract carrier (electron) mobility, which decreases with increasing the photodoping levels. It is found that the mobility is suppressed at high photodoping levels due to electron-hole scattering, while it is enhanced near a critical density, being plausibly attributed to the strong coherent coupling of the LO phonon with the plasmon.

著者

Xu Maojie Okada Arifumi Yoshida Shoji Shigekawa Hidemi

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.94, no.7, pp.073109, 2009

被引用文献数

5 7

---

Methods of forming various In nanostructures on Si surfaces are demonstrated. Using a high-index Si(311) surface, isolated nanotriangles and wires were grown by optimizing the deposition rate and substrate temperature. In contrast, nanodots were formed by the deposition of In on a Si(111)-In-31×31 surface at room temperature (RT) deposition. On a Si(111)-In-4×1/31×31 coexisting surface, nanowires were selectively grown in the Si(111)-In 4×1 area by RT deposition through the nucleation promoted by the boundary barrier produced by the surrounding 31×31 area. Details were studied using scanning tunneling microscopy.

著者

Fukata N. Mitome M. Bando Y. Seoka M. Matsushita S. Murakami K. Chen J. Sekiguchi T.

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.93, no.20, pp.203106, 2008-11

被引用文献数

33 20

---

Codoping of boron (B) and phosphorus (P) atoms was performed during the synthesis of silicon nanowires (SiNWs) by laser ablation. The observation of a local vibrational mode of B clearly showed B doping in codoped SiNWs, while Fano broadening due to heavy B doping disappeared, indicating compensation by P donors. The electrospin resonance signal of conduction electrons also disappeared due to compensation by B acceptors. These results indicate that codoping of B and P atoms was achieved in SiNWs during laser ablation.