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

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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

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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.

著者

Tanimoto H. Yamada K. Mizubayashi H. Matsumoto Y. Naramaoto H. Sakai S.

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.93, no.15, pp.151919, 2008-10

被引用文献数

7

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C60 films with thicknesses of 100–480 nm were deposited on Si reed substrates under in situ photoirradiation. In anelasticity measurements, no internal friction peaks associated with rotational motions of the C60 molecules were observed, and Young's modulus was 1.5 times larger than that of a pristine C60 material. X-ray diffraction patterns suggested that the face-centered cubic lattice was contracted by about 3% and locally distorted from the pristine C60 material. Raman spectra very similar to those reported for dimerized C60 were also obtained. These characteristics recovered to those of the pristine C60 materials after annealing the C60 films at 523 K. These results indicate uniform dimerization in C60 films deposited under in situ photoirradiation.

著者

Ko J.-H. Kojima S. Koo T.-Y. Jung J. H. Won C. J. Hur N. J.

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.93, no.10, pp.102905, 2008-09

被引用文献数

69 45

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A strong relaxation mode was observed in the paraelectric phase of barium titanate (BaTiO3) single crystals by Brillouin scattering study and was found to correlate with the softening of the longitudinal acoustic mode and the increase in the hypersonic damping. These observations support the existence of polar percursors and their electrostrictive coupling with the strain caused by the acoustic waves, consistent with former studies evidencing off-centered Ti ions in the high-symmetry cubic phase. A critical slowing down has been clearly observed in the vicinity of the cubic-tetragonal phase transition, indicating order-disorder component contributes to the phase transition of BaTiO3.

著者

Chong S. V. Kadowaki K. Xia J. Idriss H.

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.92, no.23, pp.232502, 2008-06

被引用文献数

34

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The magnetic behavior of titanium dioxide nanobelts has been investigated with and without Codoping. Room temperature ferromagnetism was observed when the Co-doped anatase TiO2nanobelts were prepared via vacuum annealing of 2.5 at. % Co-doped titanate nanobelts, whileannealing them in air resulted in paramagnetic ordering. Interestingly, by vacuum annealing theundoped titanate nanobelts under the same conditions, superparamagnetic ordering was observed inthe resulting anatase TiO2 nanobelts. The electron paramagnetic resonance of this latter sampleshows a strong symmetrical signal at g=2.003 suggesting some sort of exchange interactions amongthe localized electrons’ spin moments from single electron trapped in oxygen vacancies.

著者

Ootsuka Teruhisa Suemasu Takashi Chen Jun Sekiguchi Takashi Hara Yoshiaki

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.92, no.19, pp.192114, 2008-05

被引用文献数

14

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We have evaluated the lifetime and diffusion length of photogenerated minority carriers (holes) in single-crystalline n-type beta-FeSi2 bulk grown by chemical vapor transport. The diffusion length measured by optical-beam-induced current agreed well with that measured by electron-beam-induced current, that is, 51 and 38 µm, respectively, for samples annealed at 800 °C for 8 h. The decay curve of photoconductivity obtained by 1.31 and 1.55 µm light pulses was well fitted by assuming a carrier lifetime of approximately a few microseconds. The mobility of photogenerated minority carriers was estimated to be approximately 200–360 cm2/V s from the measured lifetime and diffusion length.

著者

Uchida Noriyuki Mikami Youhei Kintoh Hiroshi Murakami Kouichi Fukata Naoki Mitome Masanori Hase Muneaki Kitajima Masahiro

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.92, no.15, pp.153112, 2008-04

被引用文献数

5

---

We have developed a robust method for fabricating Si nanoregions in silica glass using femtosecond laser processing. We attained a vivid formation of silicon-rich nanoregions site-selectively generated in SiO2 by irradiation of femtosecond laser pulses to the interface of a SiO2 substrate and deposited aluminum (Al) thin film, where the Al element acts as a gettering site for O atoms. Growth of high-density Si nanocrystals and amorphous Si was observed by transmission electron microscopy in the region that was multiply irradiated with the femtosecond laser. Furthermore, local annealing with a cw laser enhances the Si nanocrystal growth, which was determined by micro-Raman measurements.

著者

Moritomo Y. Nakada F. Kamioka H. Kim J. E. Takata M.

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.92, no.14, pp.141907, 2008-04

被引用文献数

4 4

---

The guest-host interaction is one of the promising tools to control the material state. Here, we found that a cyano-bridged compound Na0.50Co[Fe(CN)6]0.723.8H2O shows a first-order structural phase transition below a critical pressure Pc (150 Pa) at 300 K. Judging from suppression of the OH stretching mode in the infrared spectra, we ascribed the phase transition to desorption of the ligand waters. The phase transition accompanies a significant change of the visible absorption spectra, reflecting the strong hybridization between the Co eg state and the CNσ states.

著者

Ootsuka Teruhisa Suemasu Takashi Chen Jun Sekiguchi Takashi

出版者

American Institute of Physics

雑誌

APPLIED PHYSICS LETTERS (ISSN:00036951)

巻号頁・発行日

vol.92, no.4, pp.042117, 2008-01

被引用文献数

13 15

---

We have evaluated the diffusion length of minority carriers (holes) in single-crystalline n-type beta-FeSi2 bulk grown by chemical vapor transport by means of electron-beam-induced current (EBIC) technique in the edge-scan configuration. The EBIC line-scan data showed a clear exponential dependence of distance from the Al electrode. The diffusion length was estimated to be 20 µm at room temperature, and increased upon high-temperature annealing, reaching approximately 30 µm after annealing at 800 °C for 8 h. This result explained the improvement of photoresponsivity in the Al/n-beta-FeSi2 Schottky diodes by high-temperature annealing.

著者

Ko Jae-Hyeon Kojima Seiji Bokov Alexei A. Ye Zuo-Guang

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.91, no.25, pp.252909, 2007-12

被引用文献数

36 25

---

The dynamic polar nanoregions (PNRs) which form below the Burns temperature and determine the unique properties of relaxor ferroelectrics were predicted [Tinte et al., Phys. Rev. Lett. 97, 137601 (2006)] to be pinned to the quenched chemically ordered regions (CORs) usually observed in lead-containing relaxors. In Pb[(Mg1/3Nb2/3)0.45Ti0.55]O3 crystal where CORs are known to be absent, we have found the phenomena typically related to the relaxation of dynamic PNRs, namely, the significant Brillouin quasielastic scattering, the softening of the longitudinal acoustic mode, and the deviation from the Curie-Weiss law above the Curie point. This implies that PNRs may appear in crystals without CORs.

著者

Yamaguchi Ryo-taro Hirano-Iwata Ayumi Kimura Yasuo Niwano Michio Miyamoto Ko-ichiro Isoda Hiroko Miyazaki Hitoshi

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.91, no.20, pp.203902, 2007-11

被引用文献数

13

---

We have developed a method for real-time monitoring of the cell responses to cytotoxicants using Fourier transform infrared spectroscopy with the multiple internal reflection (MIR-FTIR) geometry. To prevent cell damages induced by measurement environments, we have constructed specialized chambers, in which temperature was maintained at (37±0.5) °C and humidified air containing 5% CO2 was supplied. We monitored cell death induced by cytotoxic surfactant Tween20 using MIR-FTIR spectroscopy. It was found that cell death can be monitored by the absorption intensity of amide II band. This result suggests that our method has a potential to be applied for real-time cytotoxicity assay.

著者

Ootsuka Teruhisa Fudamoto Yasunori Osamura Masato Suemasu Takashi Makita Yunosuke Fukuzawa Yasuhiro Nakayama Yasuhiko

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.91, no.14, pp.142114, 2007-10

被引用文献数

23 25

---

We have clearly observed photoresponse properties in an Al/n-beta-FeSi2 structure using beta-FeSi2 single crystals grown by chemical vapor transport. A photocurrent is observed for photons with energies greater than 0.68 eV. It increases sharply with increasing photon energy and attains a maximum at approximately 0.95 eV (1.31 µm). The photocurrent originated from the photoexcited electrons in the Al and the band-to-band photoexcited carriers in the beta-FeSi2 located under the Al contact. The photoresponsivity increased upon high-temperature annealing, reaching 58 mA/W at 0.95 eV after annealing at 800 °C for 8 h.

著者

Fujiwara Seiji Bando Kazuki Masumoto Yasuaki Sasaki Fumio Kobayashi Shunsuke Haraichi Satoshi Hotta Shu

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.91, no.2, pp.021104, 2007-07

被引用文献数

30 27

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Laser oscillation of whispering gallery modes was observed in microring structures of semiconducting thiophene/phenylene co-oligomer (TPCO) crystals at room temperature. Microring structures were formed by dry etching from thin film crystals of TPCO. The thresholds for the laser oscillation of a microring and a thin film crystal are 200 and 1400 µJ/cm2 for picosecond excitation, respectively. Therefore, the threshold for the microring was reduced to 1/7 of that for the thin film crystal. The dramatic reduction of threshold clearly demonstrates the importance of microcavity in making efficient organic semiconductor lasers.

著者

Hattori Toshiaki Sakamoto Masaya

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.90, no.26, pp.261106, 2007-06-25

被引用文献数

16

---

The authors have developed a method of real-time terahertz imaging in which image deformation due to nonuniformity of residual birefringence in the electro-optic (EO) sampling crystal is corrected. Real-time terahertz imaging using intense terahertz pulses and two-dimensional EO sampling can suffer from birefringence nonuniformity of the EO crystal since the birefringence is explicitly used for the linear detection of the terahertz field. In the proposed method, the distribution of the residual birefringence of the EO crystal is measured and used for image correction. Deformation-free images of the spatial profile of a focused terahertz pulse were obtained.

著者

Fukata N. Chen J. Sekiguchi T. Matsushita S. Oshima T. Uchida N. Murakami K. Tsurui T. Ito S.

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.90, no.15, pp.153117, 2007-04

被引用文献数

40 32

---

Phosphorus (P) doping was performed during the synthesis of silicon nanowires (SiNWs) by laser ablation. At least three types of signals were observed by electron spin resonance (ESR) at 4.2 K. Phosphorus doping into substitutional sites of crystalline Si in SiNWs was demonstrated by the detection of an ESR signal with a g value of 1.998, which corresponds to conduction electrons in crystalline Si, and by an energy-dispersive x-ray spectroscopy spectrum of the P Kalpha line. The ESR results also revealed the presence of defects. These defects were partially passivated by hydrogen and oxygen atoms.

著者

Nakamura Yoshiaki Ichikawa Masakazu Watanabe Kentaro Hatsugai Yasuhiro

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.90, no.15, pp.153104, 2007-04

被引用文献数

40 33

---

A scanning tunneling microscopic study revealed quantum fluctuation of tunneling currents in individual Ge quantum dots (QDs) on SiO2/Si. This was due to the charging energy change in the QDs caused by single-electron transfer from or into the QDs. The observed electron discharging time of approximately milliseconds agreed with the propagation model of the electron wave packets from the QDs to the Si substrates by a tunneling effect rather than by passing through voids in the SiO2 smaller than electron de Broglie wavelength.

著者

Maczka Miroslaw Hanuza Jerzy Majchrowski Andrzej Kojima Seiji

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.90, no.12, pp.122903, 2007-03

被引用文献数

5

---

K2MgWO2(PO4)2 single crystal, related to famous optical nonlinear material KTiOPO4, was investigated by micro-Brillouin scattering with a focus on the central components of the relaxation modes. A critical slowing down has been clearly observed in the vicinity of T1=436 K while suppressed by the coupling with the order parameter. The temperature dependence of the relaxation time indicates that the former transition is the second order, while the latter is strongly first order. The obtained results show that disorder processes in the sublattice of potassium ions play a major role in the mechanism of these phase transitions.

著者

Kato K. Takata M. Moritomo Y. Nakamoto A. Kojima N.

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.90, no.20, pp.201902, 2007

被引用文献数

25

---

A photoexcitation is one of the promising external fields to control the material phases. Here, the authors have demonstrated that the magnetic and structural properties of a spin-crossover complex, Fe(phen)2(NCS)2 (phen=1,10-phenanthroline), can be reversibly switched by the on-off action of the continuous photoexcitation at the same temperature. The structural data suggest that the density of the high-spin Fe2+ in the photoinduced phase is about 0.88. Suppressed atomic vibrations of the photoinduced phase exclude the conventional heating effect as the origin for the observed optical switching.

著者

Fukata N. Chen J. Sekiguchi T. Okada N. Murakami K. Tsurui T. Ito S.

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.89, no.20, pp.203109, 2006-11

被引用文献数

54 38

---

Local vibrational modes of boron (B) in silicon nanowires (SiNWs) synthesized by laser ablation were observed at about 618 and 640 cm−1 by Raman scattering measurements. Boron doping was performed during the growth of SiNWs. Fano [Phys. Rev. 124, 1866 (1961)] broadening was also observed in the Si optical phonon peak. These results prove that B atoms were doped in the SiNWs. Hydrogen (H) passivation of B acceptors in the SiNWs was also investigated. A broad peak was observed at around 650–680 cm−1 after hydrogenation, demonstrating that B dopants were passivated by the formation of the well-known H–B passivation centers.

著者

Tsukada Shinya Ike Yuji Kano Jun Sekiya Tadashi Shimojo Yoshihito Wang Ruiping Kojima Seiji

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.89, no.21, pp.212903, 2006-11

被引用文献数

40 28

---

Brillouin and Raman scatterings of a 0.71Pb(Ni1/3Nb2/3)O3-0.29PbTiO3 single crystal have been measured to investigate broadband inelastic spectra. The two different central peaks related to fast and slow relaxation processes have been observed separately. These two processes are attributed to the thermally activated switching of polarization in polar nanoregions. By the analysis of modified superparaelectric model, the activation energies of fast and slow relaxation processes are determined to be 3.66×103 and 4.31×102 K, respectively. The fast process with the lower activation energy probably originated from 180° switching, whereas the slow one with the higher energy from non-180° switching.