bluuebunny/crossref_metadata_2025 huggingface dataset:
Damping of Diocotron Oscillation in A Nonneutral Electron Plasma by Excited Axisymmetric Electrostatic Wave
Authors: Yohei Yamazawa Yohei Yamazawa , Toshinori Michishita Toshinori Michishita , Akihiro Mohri Akihiro Mohri
Published: October 2002

The diocotron oscillation of the ℓ=1 mode, which was excited in a nonneutral electron plasma column, was damped by the continuous excitation of an axisymmetric electrostatic wave. The observed time evolution of the two-dimensional line-density profile showed that the density bump of the diocotron oscillation was flattened by the azimuthal diffusion enhanced by the axisymmetric wave field. The damping rate was nearly proportional to A
s
2/B (A
s: wave field amplitude, B: magnetic field). This dependence can be explained using a simplified quasilinear model.
Near-Field Scanning Optical Microscope Using a Gold Particle
Authors: Takayuki Okamoto Takayuki Okamoto , Ichirou Yamaguchi Ichirou Yamaguchi
Published: October 2002

A new near-field scanning optical microscope using a small metallic particle attached onto the tip of the silicon-nitride cantilever of an atomic force microscope is presented. In this near-field scanning optical microscope the metallic particle converts the evanescent waves generated on the sample surface to propagating waves, which are detected through the microscope objective. Feedback control of the probe height is performed using an atomic force microscope combined with the near-field scanning optical microscope. Near-field optical images of a magnetooptical disk were obtained using a gold particle of 1.0-µm diameter attached to the cantilever and were compared with atomic force images obtained in parallel.
Low Threshold Self-Starting Operation of an Additive-Pulse Mode-Locked, Diode-Pumped Nd:YLF Laser
Authors: Kang Eung Cheol , Jeong Tae Moon , Lee Jong Moo , Kim Jai Ki , Nam Chang Hee
Published: October 2002

The birefringence effect of a single mode fiber on the self-starting threshold in a diode-pumped, additive-pulse mode-locked Nd:YLF laser is investigated. By controlling the polarization state of pulses in the external cavity containing a single-mode fiber, the mode locking could be self-started with CW power (as low as 10 mW) coupled to the fiber and stably maintained over several hours.
Site-Specific Extinction Rule for Kikuchi Bands in X-ray Photoelectron Diffraction
Authors: Omori Shinji , Hideshi Ishii Hideshi Ishii , Yoshimasa Nihei Yoshimasa Nihei
Published: October 2002

The anomalous extinction of specific Kikuchi bands has been recently observed in the X-ray photoelectron diffraction (XPED) pattern for F1s emission from a CaF2(111) surface, even though the corresponding structure factors are not zero. To explain this phenomenon, we have derived a novel extinction rule and have shown that the extinction of Kikuchi bands in XPED depends not only on the structure factors but also on the lattice sites of source atoms. This rule can be used to locate the lattice sites of impurities in single-crystal substrates.
Exterior Corona Effect on Sphere-Plane Discharge in SF6 Gas Utilizing Optical Measurement
Authors: Kamatani Humihiro , Watabe Katsunori , Masuoka Hiroaki , Mitsuyoshi Onoda Mitsuyoshi Onoda , Hiroshi Nakayama Hiroshi Nakayama
Published: October 2002

The discharge characteristics of composite electrodes having a needle as the secondary electrode in SF6 gas under µs rectangular pulsing were examined. The discharge voltage in the composite electrodes was dependent on the resistance between the needle and high-voltage terminal. With a sharply rising pulse, the discharge voltage-resistance characteristics showed unexpected features. The corona behavior of the composite electrodes was investigated utilizing an ultrahigh-speed digital framing camera (IMACON 468). The relationship between the corona initiated from the needle and the breakdown voltage of the gap between the sphere and plane electrodes was examined on the basisof the optical measurement.
Precise Line-and-Space Monitoring Results by Ellipsometry
Authors: Hiroshi Arimoto Hiroshi Arimoto
Published: October 2002

I have demonstrated rapid and nondestructive line-and-space monitoring by ellipsometry. With this method, subquartermicron line-and-space chloromethylated poly-α-methylstyrene (CMS) negative electron beam resist patterns with linewidths varying in 10 nm increments are clearly distinguishable with good repeatability. I also showed that ellipsometry is an effective tool for monitoring polysilicon line-and-space patterns and their cross-sectional line shape variation. These capabilities are essential for future in-line monitoring of relative linewidth fluctuations.
Bulk Superconductivity in Single Crystals of PrBa 2Cu 3Ox
Authors: Zou Zhigang , Oka Kunihiko , Ito Toshimitsu , Nishihara Yoshikazu
Published: October 2002

We report the observation of bulk superconductivity in PrBa2Cu3O

x

single crystals for the first time. These samples were grown by the travelling-solvent floating-zone (TSFZ) method in oxygen-reduced atmosphere. The as-grown crystal has a longer c-axis lattice constant an than any values previously reported for oxygen-reduced PrBa2Cu3O

x

. After oxygen annealing, resistivity becomes zero below T=80 K, and zero-field-cooled magnetization shows diamagnetism with full volume fraction. X-ray energy dispersion spectrum and X-ray diffraction analyses show that this superconducting phase is orthorhombic PrBa2Cu3O

x

.
ESR Studies on the Linewidth Temperature Variation of CO2
- Radicals in Carbonated Apatite and Calcium Carbonates
Authors: Delson U. Schramm Delson U. Schramm , Alexandre M. Rossi Alexandre M. Rossi
Published: October 2002

The isotropic ESR dating species at g=2.0007, produced by ionizing radiation in synthetic and biological carbonated apatites and calcium carbonates, is attributed to rapidly tumbling CO2
- radicals. In this paper experiments on ESR linewidth variation with temperature were caried out in order to study the rotational properties of these radicals in B type carbonated apatite and calcium carbonates. The experimental data were fitted with Dattagupta and Blume and Ayant et al.. analytical models developed for radicals rotating in crystal lattice sites and in viscous media, respectively. It was verified that the viscous medium formalism gives a better description of the rotational dynamics of the radicals. Exchange interactions were found to play an important role on the CO2
- motional relaxation, besides the contributions from spin-rotational and motional g-tensor modulation relaxations. These results also reinforce the hypothesis that the radicals are surrounded by water molecules.
Far-Infrared Optically Detected Cyclotron Resonance in GaAs Layer Grown by Molecular Beam Epitaxy
Authors: Nakata Hiroyasu , Tatsuki Iwao Tatsuki Iwao , Tyuzi Ohyama Tyuzi Ohyama
Published: October 2002

Optically detected cyclotron and impurity resonances in molecular beam epitaxy (MBE)-grown GaAs are investigated in the far-infrared region in order to study their mechanisms. An increase in electron temperature due to the resonant absorption is responsible for the optically detected cyclotron resonance. A photothermal effect is a dominant mechanism for the optically detected impurity resonance of 1s-2p+ in the case of the energy of the 2p+state lying below the lowest Landau level.
On the Field-induced Refractive Index Change Considering Valence Band Nonparabolicity in Quantum Well Structures
Authors: Takayuki Yamanaka Takayuki Yamanaka , Naoto Yoshimoto Naoto Yoshimoto , Koichi Wakita Koichi Wakita , Kiyoyuki Yokoyama Kiyoyuki Yokoyama
Published: October 2002

We investigate the effect of valence subband dispersion on predicting the field-induced change in the refractive index in a lattice-matched InAlGaAs/InAlAs quantum well (QW). Emphasis is on the second-lowest valence subband dispersion having heavy-hole nature at the Brillouin zone center, which displays negative hole effective masses due to the presense of the valence subband nonparabolicity. Realistic electroabsorption (EA) spectra calculated taking the nonparabolicity, are compared with approximated EA spectra assuming parabolic valence subbands. It is shown that the nonparabolicity makes the transition from the second heavy-hole subband contribute more to the EA change than the transition from the first light-hole subband. Only the nonparabolic EA spectra is found to be essential to the nearly quadratic dependence of the increase in the refractive index change with electric field strength, which we expect in the electro-optic modulation due to the quantum-confined Stark effect.
Formation of Cubic Phase Carbon Nitride Solid by Low Energy Nitrogen Implantation into Graphite
Authors: Yamamoto Kazuhiro , Koga Yoshinori , Yase Kiyoshi , Shuzo Fujiwara Shuzo Fujiwara , Masaaki Kubota Masaaki Kubota
Published: October 2002

The formation of carbon nitrogen solid by the low energy nitrogen implantation is investigated. Room temperature implantation of nitrogen into the graphite was performed, and small precipitates with a diameter of 50 nm were observed in the graphite. The precipitates consist of carbon and nitrogen based upon the analysis of electron spectroscopic imaging. The carbon nitride solid has a zinc-blende structure with a lattice parameter of 0.34 nm. The results suggest that the cubic phase C3N4, which has a defect zinc-blende structure with the lattice parameter of 0.343 nm, is formed in the graphite by the nitrogen implantation.
Color-Sensitive Si-Photodiode Using Porous Silicon Interference Filters
Authors: Krüger Michael , Berger Michael Goetz , Marso Michel , Reetz Winfried , Eickhoff Thomas , Loo Roger , Vescan Lili , Thönissen Markus , Lüth Hans , Arens-Fischer Rüdiger , Hilbrich Stefan , Theiss Wolfgang
Published: October 2002

A new method for the fabrication of color-sensitive Si-photodiodes is presented. Color sensitivity was achieved by using porous silicon multilayer stacks which act as interference filters if the formation parameters are controlled carefully. These filters were integrated in the upper, p+-type part of a p+n-junction. As expected, the spectral response of the photodiodes was determined by the transmission spectra of the filters, while the porous silicon had no significant influence on the electrical characteristics. The great advantage of this method over conventional ones is that it makes very cheap, fast filter fabrication requiring no expensive deposition process possible.
Anomalous Electrical Characteristics of Epitaxial InN Films Having a High Electron Concentration at Very Low Temperature
Authors: Miura Naruhisa , Ishii Hideaki , Yamada Akira , Konagai Makoto , Yamauchi Yasuyuki , Yamamoto Akio
Published: October 2002

Epitaxial indium nitride films were grown by metalorganic chemical vapor deposition (MOCVD) using trimethylindium (TMI) and ammonia ( NH3). High electron concentrations of the order of 1020 to 1021 cm-3 were obtained, which are considered to be due to nitrogen vacancies. The temperature dependence of the electrical properties of the epitaxial films were investigated. A sharp decrease of resistivity and an increase of mobility were observed below 4.2 K, and it was found that films with a lower electron concentration showed a sharper thermal slope of resistivity in the electron concentration range from 1×1020 to 2×1021 cm-3. Moreover, a large magnetic field dependence of the differential resistance of the InN film was also seen at 1.4 K. X-ray rocking curves and atomic force microscopy (AFM) images were measured for evaluation of the origin of these unusual electrical characteristics.
Influences of Superficial Si Layer Thickness on Band-to-Band Tunneling Current Characteristics in Ultra-Thin n-Channel Metal-Oxide-Semiconductor Field-Effect-Transistor by Separation by IMplanted OXygen (nMOSFET/SIMOX)
Authors: Omura Toshihiko Ishiyama
Published: October 2002

The band-to-band tunneling current characteristics of buried-channel nMOSFETs/SIMOX are investigated. It is shown that the drain current due to band-to-band tunneling current increases with decreasing superficial Si layer thickness. Two-dimensional device simulation results indicate that the decrease in superficial Si layer thickness leads to an increase in surface electric field in the gate-overlapped drain region. The device simulation results also suggest that the doping profile in the diffusion region affects the surface electric field moderately. The expression of surface electric field is improved to include the terms that depend on Si layer thickness and diffusion profile. This improved expression results in a quantitative coincidence between calculation and experimental results.
A Model Analysis for Current-Voltage Characteristics of Superconducting Weak Links
Authors: Saitoh Kazuo , Ishimaru Yoshihiro , Hiroyuki Fuke Hiroyuki Fuke , Youichi Enomoto Youichi Enomoto
Published: October 2002

A new phenomenological model for realizing the current-voltage ( I-V ) characteristics of superconducting weak links has been proposed and studied. In this model, the total bias current to the weak link is decomposed in two parts. One part obeys the usual resistively shunted junction (RSJ) type current-voltage relation, and the other obeys the flux-flow (FF) one. It has been shown that the fitting results of the I-V characteristics agree quite well to experimental data. The model and analysis method presented here is quite general, thus the model can be applied to other types of superconducting weak links for both high- and low-T
c material.
New Technique for Fabrication of Two-Dimensional Photonic Bandgap Crystals by Selective Epitaxy
Authors: Tetsuko Hamano Tetsuko Hamano , Hideki Hirayama Hideki Hirayama , Yoshinobu Aoyagi Yoshinobu Aoyagi
Published: October 2002

A two-dimensional (2D) photonic bandgap (PBG) crystal is formed from an array of either rods (pillars) or holes arranged in a periodic lattice. Use of selective epitaxy to fabricate a 2D PBG crystal provides the possibility of obtaining pillars with a high aspect ratio and facets free from surface damage. We have fabricated semiconductor 2D PBG crystals using selective metalorganic vapor phase epitaxy on (111)B GaAs for the first time. The fabricated crystals consist of hexagonal GaAs micropillars arranged in a triangular lattice of 490 nm pitch. Each micropillar has a high aspect ratio (>10) and six smooth, steep sidewalls consisting of {\overline110} facets.
Characteristics of Poly( p-pyridyl vinylene)/Poly(3-alkylthiophene) Heterojunction Photocell
Authors: Kazuya Tada Kazuya Tada , Mitsuyoshi Onoda Mitsuyoshi Onoda , Anvar A. Zakhidov Anvar A. Zakhidov , Katsumi Yoshino Katsumi Yoshino
Published: October 2002

Photoirradiation effects of a poly( p-pyridyl vinylene) (PPyV)/poly(3-hexylthiophene) (PAT6) heterojunction photocell have been investigated. The photovoltaic characteristics of the heterojunction photocell are considerably improved from those in a single-PAT6-layer photocell. Quenching of photoluminescence both in the PAT6 layer and in the PPyV layer has also been observed in the PPyV/PAT6 double layer. The observed photoirradiation effects of the heterojunction have been discussed in terms of interfacial photoinduced charge transfer between PAT6 and PPyV.
Photoluminescence and Raman Spectral Study of Porous Si during F 2 Exposure
Authors: Toshimasa Wadayama Toshimasa Wadayama , Tsuyoshi Arigane Tsuyoshi Arigane , Katsuhiko Hujine Katsuhiko Hujine , Aritada Hatta Aritada Hatta
Published: October 2002

Visible luminescence and Raman spectral changes of porous Si (PS) during F2 exposure were recorded. F2 exposure of the PS under Ar+ laser light (488 nm) irradiation at 373 K leads to a significant spectral change of photoluminescence (PL). During an early stage of the exposure, the PL band of the 750 nm peak decreased in intensity and a new band emerged at 600 nm. After 30 min, the new band dominated the spectrum while the band at 750 nm almost disappeared. On the contrary, the phonon band due to nanosize Si crystals of the PS remained unchanged. These results suggest that the PL spectral change arises due to a change in the chemical structure of the sample surface.
A New Superconducting Cuprate Prepared by Low-Temperature Thin-Film Synthesis in a Ba–Cu–O System
Authors: Yamamoto Hideki , Michio Naito Michio Naito , Hisashi Sato Hisashi Sato
Published: October 2002

A new high-T
c superconducting cuprate composed of Ba, Cu and O was prepared on SrTiO3(001) substrate by reactive coevaporation. The superconducting phase is formed only in the limited temperature range between 575 and 625° C and in a narrow compositional range. Observations of the X-ray diffraction and transmission electron microscopy suggests that the superconducting phase is the 214-based structure. Superconductivity is obtained only after strong oxidation after film growth. The resistivity measurement shows T
c
onset≈60 to 70 K and T
c
end≤38 K and the magnetic measurement shows T
c
onset≈85 to 90 K.
Effect of Nd422 Addition on Jc in Nd123 Melt-Textured Bulk Superconductor
Authors: Ikeda Shunichi , Oka Tetsuo , Yamada Yuh , Yoshikawa Masaaki , Yanagi Yousuke , Itoh Yoshitaka , Uichiro Mizutani Uichiro Mizutani
Published: October 2002

Nd4Ba2Cu2O10(Nd422) fine powder was intentionally added to NdBa2Cu3O7-δ(Nd123) powder and heat treated in melt-textured growth processing under reduced oxygen atmosphere. We found that fine Nd422 particles are dispersed uniformly in the Nd123 matrix. The J
c values derived from the M-H curves increase with increasing amount of Nd422 addition in the low magnetic field region, but decrease in the high field region as the peak effect gradually weakens. The enhancement of J
c in low fields is attributed to the increase in the number of pinning centers introduced due to the addition of Nd422 particles.
Bistable Diffractive Electro-Optical Effect in Cholesteric Gels*
Authors: Heinz-Siegfried Kitzerow Heinz-Siegfried Kitzerow
Published: October 2002

The present study shows that a cholesteric gel consisting of a low molar mass liquid crystal and a highly crosslinked anisotropic network can be switched between a transparent and a colored scattering state. The latter state can be induced in an initially non-aligned cholesteric liquid crystal by an electric field, as described recently by Chilaya and coworkers. A short pulse of an electric field can be used to select between the two states which are stable at zero field. The angular dependence of the wavelength of the diffracted light is studied in detail and explained by the known properties of the spatially periodic cholesteric structure.
Self-Phase Modulation Induced by a He–Ne Laser in Host-Guest Liquid Crystals with Different Nematic-Isotropic Transition Temperatures
Authors: Kawatsuki Hiroshi Ono
Published: October 2002

We observed diffraction rings and a He-Ne laser induced self-phase modulation due to photothermal effects in host-guest liquid crystals with different nematic-isotropic transition temperature (T
NI). A far-field pattern of the laser beam passed through the host-guest liquid crystals depended on the polarization of the incident laser beam and the results were explained by sign of the refractive index change and spatial self-phase modulation. Higher photosensitivity in low T
NI of host-guest liquid crystals was obtained than that in high T
NI of those. The multiple diffraction ring pattern of the laser beam passed through the low T
NI of host-guest liquid crystals was observed since the maximum phase increment was much larger than 2π.
Scanning Tunneling Spectroscopy of Dangling-Bond Wires Fabricated on the Si(100)–2×1–H Surface
Authors: Taro Hitosugi Taro Hitosugi , Tomihiro Hashizume Tomihiro Hashizume , Seiji Heike Seiji Heike , Satoshi Watanabe Satoshi Watanabe , Yasuo Wada Yasuo Wada , Tetsuya Hasegawa Tetsuya Hasegawa , Koichi Kitazawa Koichi Kitazawa
Published: October 2002

Tunneling spectroscopy of atomic-scale dangling-bond wires on a hydrogen-terminated Si(100)–2×1–H surface is studied using ultrahigh-vacuum scanning tunneling microscopy. Individual dangling bonds are fabricated by extracting hydrogen atoms one by one from the hydrogen terminated surface to form atomic-scale dangling-bond wires. These wires show a finite density of states at the Fermi level and do not show semiconductive band gaps. The results are compared with first-principles theoretical calculations.
Optical Properties and EL Characteristics of Poly[(disilanylene)oligophenylenes]
Authors: Katsumi Yoshino Katsumi Yoshino , Kazuhisa Hosoda Kazuhisa Hosoda , Akihiko Fujii Akihiko Fujii , Mitsuo Ishikawa Mitsuo Ishikawa
Published: October 2002

Band-gap energies of poly[(disilanylene)terphenylene] (PDSiTP) and poly[(disilanylene)quaterphenylene] (PDSiQP) films have been evaluated as 3.5 eV and 3.3 eV, respectively, which are similar to those of p-terphenyl and p-quaterphenyl films. Contrary to poly(methylpropylsilane), large Stokes shift of photoluminescence (PL) is observed in these polymers, which is similar to the cases of p-terphenyl and p-quaterphenyl. Blue electroluminescence (EL) has been observed in diodes of MgAg/PDSiTP/ITO and MgAg/PDSiQP/ITO structures with peaks at 440 nm and 443 nm, respectively. These polymers are much more stable than poly(methylpropylsilane) under ultraviolet light irradiation.
P-Type Doping Limits in ZnMgSSe and ZnSSe Compound Semiconductors
Authors: Kenkichi Hirano Kenkichi Hirano , Ikuo Suemune Ikuo Suemune , Go Sato Go Sato
Published: October 2002

The p-type doping limit in ZnMgSSe was examined using an amphoteric native defect model. The results of measurements on p-type doping in ZnMgSSe were well reproduced with the band offset localized to the valence band in ZnSe/ZnMgSSe considering the growth temperature. This result is close to the one reported recently by Shahzad et al. [Appl. Phys. Lett.  67 (1995) 659], i.e., ΔE
v≈0.9ΔE
g. The results of measurements on p-type doping in ZnSSe were also well reproduced with the known band offset in ZnSe/ZnSSe. Although the doping efficiency is reduced for a larger energy gap in both material systems, the improvement of doping efficiency by increase of the growth temperature was predicted from the model.
Suppression of Surface Roughening on Strained Si/SiGe Layers by Lowering Surface Stress
Authors: Nobuyuki Ikarashi Nobuyuki Ikarashi , Toru Tatsumi Toru Tatsumi
Published: October 2002

Stress-induced surface roughening usually occurs in strained semiconductor layers, such as SiGe layers on Si substrates, which is technologically undesirable. We demonstrate that the roughening of a strained Si0.34Ge0.66 layer is suppressed by depositing a thin Si layer (≤1.5 nm). This thin Si layer is not stressed on the SiGe layer, which is lattice-matched to the Si substrate. The thin Si layer lowers the surface stress of the strained heterostructure, thereby preventing the surface roughening. The main advantage of this method is that the surface roughening can be suppressed by making only a minor change in crystal growth procedure.
Measurement of Azimuthal Anchoring Energy at Liquid Crystal/Photopolymer Interface
Authors: Li Xiang Tong , Pei Dong He , Kobayashi Shunsuke , Yasufumi Iimura Yasufumi Iimura
Published: October 2002

The photopolymer material of poly(vinyl cinnamate) (PVCi) has been used to investigate the contribution of the anisotropic van der Waals force to the azimuthal anchoring energy in a pentyl cyanobiphenyl (5CB)/PVCi system. The optical anisotropy of a PVCi film is precisely controlled by varying the exposure time of linearly polarized UV light, and the azimuthal anchoring energy in the film is estimated by measuring the width of the Néel wall. The result shows that the azimuthal anchoring energy in the 5CB/PVCi system increases exponentially with increasing optical anisotropy, indicating the existence of additional contributions to the LC alignment.
Laser-Beam Induced Remote Thermoluminescence (R-TL) Image for Future Planetary Material Survey
Authors: Motoji Ikeya Shunji Takaki Motoji Ikeya Shunji Takaki , Chihiro Yamanaka Chihiro Yamanaka
Published: October 2002

Thermoluminescence (TL) of calcite (CaCO3) irradiated by γ-rays has been measured from a distance by heating with a CO2 infrared laser beam. The diameter of a TL spot at the exposure site increased due to thermal diffusion and became dark. The surrounding area showed TL in the form of a broad ring. TL images obtained after the exposure were compared with those simulated by numerically solving the equation of three-dimensional heat diffusion using the parameters of the TL peaks, i.e., frequency factors ν0 I = ν0 II = 5×1011 s-1 and activation energies E
I = 1.28 and E
II = 1.58 eV, the thermal conductivity and the specific heat. The remote TL (R-TL) may be used in the future for planetary survey by heating or exciting a ground object from a rover or from a spacecraft.
Growth of Self-Organized GaN Nanostructures on Al2O3(0001) by RF-Radical Source Molecular Beam Epitaxy
Authors: Yoshizawa Masaki , Kikuchi Akihiko , Mori Masashi , Nobuhiko Fujita Nobuhiko Fujita , Katsumi Kishino Katsumi Kishino
Published: October 2002

Columnar GaN nanostructures (GaN nanocolumns) were grown on Al2O3(0001) by RF-radical source molecular beam epitaxy (RF-MBE) through a self-organization process. The nanocolumns were grown at high density, with the c-axis maintained perpendicular to the substrate surface. The dependence of column diameter and density on growth conditions was systematically investigated. The average diameter was minimized to 53 nm and the density of the GaN nanocolumns was 130×1012 columns per square meter.
Tc of Overdoped YLa0.2Ba1.8Cu3O7.06+y and La1.2Ba1.8Cu3O7.2+y
Authors: Kato Bin Okai
Published: October 2002

Heat treatment of YLa0.2Ba1.8Cu3O7.06 at high oxygen pressure produces overdoped YLa0.2Ba1.8Cu3O7.06+
y

(y ≦0.7). Likewise, such treatment of La1.2Ba1.8Cu3O7.2 produces overdoped La1.2Ba1.8Cu3O7.2+
y

(y ≦0.8). With increasing y, T
c of the former rises from 50 K (y=0) to 90 K (y=0.3), then fluctuates somewhat between 87 and 90 K up to y=0.7. In the case of the latter, although T
c remains unchanged at 27 K with increase in y up to ∼0.2, the volume fraction of superconductivity is reduced to zero at y=0.2.
New Intermetallic Compound Found in Sm–Fe System
Authors: Samata Hiroaki , Satoh Yasuo , Nagata Yujiro , Uchida Takayuki , Kai Masahiro , Lan Ming Der
Published: October 2002

A new intermetallic compound, SmFe7, has been found in the Sm–Fe system. We grew SmFe7 single crystals via a self-flux method. Precise X-ray analysis revealed that SmFe7 has a tetragonal structure with a space group of P42/m
n
m and lattice constants of a=0.8765 and c=1.2133 nm. The structure is very similar to that of R2Fe14B (R=rare earth) except that the boron sites of R2Fe14B are vacant. Magnetization measurement results suggest that SmFe7 is a ferrimagnet with a significantly large spontaneous magnetization (136 emu/g at 293 K) and a huge anisotropy constant (K
1+K
2∼-6.9×107 erg/cc at 293 K).
Nonlinear Optical Response in Higher Fullerenes
Authors: Kikuo Harigaya Kikuo Harigaya
Published: October 2002

Nonlinear optical properties of extracted higher fullerenes – C70, C76, C78, and C84 – are theoretically investigated. Magnitudes of off-resonant third-harmonic generation are calculated using the intermediate exciton theory. We find that optical nonlinearities of higher fullerenes are a few times larger than those of C60. The magnitudes of nonlinearity tend to increase as the optical gap decreases in higher fullerenes.
Temperature Dependence of Free-Exciton Luminescence from High-Quality ZnS Epitaxial Layers
Authors: Nakamura Seiji , Sakashita Takashi , Yoshimura Kazumasa , Yoichi Yamada Yoichi Yamada , Tsunemasa Taguchi Tsunemasa Taguchi
Published: October 2002

High-quality ZnS epitaxial layers were grown by low-pressure metalorganic chemical vapor deposition using all gaseous sources. The photoluminescence spectrum of high-quality ZnS epitaxial layers at 4.2 K was dominated by the radiative recombination of free excitons. The free-exciton luminescence was observed even at room temperature (300 K). The linewidth broadening of the free-exciton luminescence with increase in temperature was analyzed in terms of exciton–LO-phonon and exciton–acoustic-phonon scattering processes.
Deep-Level Luminescence in Czochralski-Grown Silicon Crystals after Long-Term Annealing at 450°C
Authors: Shigeo Ibuka Shigeo Ibuka , Michio Tajima Michio Tajima , Hiroshi Takeno Hiroshi Takeno , Masatoshi Warashina Masatoshi Warashina , Takao Abe Takao Abe , Keigo Nagasaka Keigo Nagasaka
Published: October 2002

Isothermal annealing at 450°C for more than 100 h was performed for Czochralski-grown silicon crystals. We detected a photoluminescence (PL) band at around 0.86 eV at room temperature. Temperature dependence of PL spectra indicates that the 0.86 eV band has an origin distinct from that of the 0.885 eV line observed at liquid helium temperature. Spectral shape analysis using the curve-fitting technique indicates that at least two different electronic levels are formed by oxygen precipitation during annealing. The peak energy position and half-width of the 0.86 eV band were different from those of a similar 0.86 eV band resulting from two-step annealing at 450°C and subsequently at 650°C. The difference in the spectral shape is ascribed to the structural change of oxygen aggregates. We believe that PL at room temperature is sensitive to the morphology of these aggregates.
Coating of Carbon Nanotube with Nickel by Electroless Plating Method
Authors: Qunqing Li Qunqing Li , Shoushan Fan Shoushan Fan , Weiqiang Han Weiqiang Han , Chenhang Sun Chenhang Sun , Wenjie Liang Wenjie Liang
Published: October 2002

A method to fabricate one dimensional nanoscale composite based on coating of carbon nanotube with metal is proposed and demonstrated in this letter. Carbon nanotubes have been coated with a layer of nickel by electroless plating. It was found that the nickel coating had a tendency to form as nanoparticles on the surface of carbon nanotube and on the net of carbon nanotubes. High density active sites and low deposition rate were found to be critical for getting better coating.
Initial Stage of Bias-Enhanced Diamond Nucleation Induced by Microwave Plasma
Authors: Hiromasa Yagi Hiromasa Yagi , Kimihiko Hoshina Kimihiko Hoshina , Akimitsu Hatta Akimitsu Hatta , Toshimichi Ito Toshimichi Ito , Takatomo Sasaki Takatomo Sasaki , Akio Hiraki Akio Hiraki
Published: October 2002

Ion channeling and X-ray photoelectron spectroscopy (XPS) measurements were performed for characterization of the early stage of diamond nucleation on Si substrates. The diamond nucleation was induced by CH4/H2 microwave-enhanced plasma with negative dc bias. Areal densities of C atoms N
C (atoms/cm2) and displaced Si atoms N
Si (atoms/cm2) near the surface were determined by ion channeling. At bias voltages V
b of ≤80 V, N
Si is approximately constant and at V
b ≥80 V, N
Si increases monotonously with V
b, while N
C increases monotonously with V
b in the entire range of bias voltage. XPS measurements revealed that an increase in V
b enhances a reaction between C and Si atoms. The results are discussed in terms of reactions on the substrate and in the plasma.
Growth of RuO2 Thin Films on a MgO Substrate by Pulsed Laser Deposition Method
Authors: Fang Xiaodong , Minoru Tachiki Minoru Tachiki , Takeshi Kobayashi Takeshi Kobayashi
Published: October 2002

RuO2 thin films have been grown on (100)MgO substrates by the pulsed laser deposition (PLD) method. X-ray diffraction (XRD) and Reflection high-energy electron diffraction (RHEED) measurements showed that the RuO2 thin film were (110) oriented and in-plane ordered (epitaxially grown). The electrical and optical properties of the RuO2 have been studied. Temperatures above 600° C were required for growth of high quality films. When grown at 700° C, the films exhibited resistivities as low as 39 µ Ω· cm at room temperature. The real and imaginary parts of the dielectric constant and complex refractive index for RuO2 thin films were estimated in the photon energy range from 1.5 to 4.5 eV by spectroscopic ellipsometry measurements. A transition from the valence band to the conduction band was observed for RuO2 thin films near 2.7 eV and the dependence of the refractive index on the deposition temperature was also observed.
Simultaneous and Accurate Formation of Variously Shaped Holes in Silicon Substrate
Authors: Lee Hi-Deok , Kim Jae-Kwan , Han Chul-Hi
Published: October 2002

An electrochemical etching method for forming high-precision holes in silicon substrates is presented. An n-type layer is formed in the periphery of the hole pattern in order to define accurately current flow and a solution (1:2 HF:H2O) which does not chemically attack silicon is used. The silicon substrate is etched from the back side of the silicon wafer by means of a novel electrochemical etching method. Circular and square holes spaced 400 µ m apart are formed simultaneously and accurately in a boron doped (100) silicon substrate. The circular and square holes are 400 µ m in diameter and 400 µ m on side, respectively. The combination of an n-type layer and electrochemical etching enables variously shaped holes which can be widely applied in silicon micromachining to be formed concurrently with high precision.
Defect Creation in a-Si:H Thin Film Transistors by Bias-Stress
Authors: Ryeong Wi Bo , Hyoung Lee Wook , Choochon Lee Choochon Lee , Sung-Chul Shin Sung-Chul Shin
Published: October 2002

We have studied defect creation in hydrogenated amorphous silicon thin film transistors by measuring the I-V characteristic curves with the bias condition varied. It is found that there is a distortion in the I-V curves after a spatially asymmetric bias-stress. In order to explain the unusual behavior in the I-V characteristic curves, we employed increased defects at the lower part of the gap which have an asymmetric distribution along the channel due to the spatially asymmetric positive gate bias. Compared with the experiments, good agreement is obtained.
Optical Confinement Effect for below 5 µm Thin Film Poly-Si Solar Cell on Glass Substrate
Authors: Yamamoto Kenji , Suzuki Takayuki , Masashi Yoshimi Masashi Yoshimi , Akihiko Nakajima Akihiko Nakajima
Published: October 2002

The optical confinement effect of a thin film poly-Si solar cell on a glass substrate fabricated by plasma chemical vapor deposition (CVD) at low temperature has been investigated for a cell thickness of less than 5 µ m. The structure of the cell is glass/back reflector/ n-i-p poly-Si/ITO/Ag grid. The cell with a thickness of 3.5 µ m demonstrated an intrinsic efficiency of 9.8%, as independently confirmed by Japan Quality Assurance. The cell is well characterized by the structure of naturally surface texture and enhanced absorption with a back reflector (STAR). The optical confinement effect of the cell with STAR structure explains both the excellent high short circuit current density of above 27 mA/cm2 for the 4.7 µ m thick cell and the markedly high quantum efficiency at long wavelength as determined through PC1D analysis.
Current-Voltage Characteristics of Field Electron Emission through Phthalocyanine Molecules on a Tungsten Field Emitter
Authors: Morikawa Hiroshi , Okamoto Ken-ichi , Yoshino Yasuhiro , Fumio Iwatsu Fumio Iwatsu , Terumi Terao Terumi Terao
Published: October 2002

The current-voltage characteristics on field emission through a four-leaf pattern, a two-leaf pattern and a single large bright spot of adsorbed Cu- and Co-phthalocyanines on a tungsten tip have been measured, and Fowler-Nordheim (FN) plots of field emission were obtained. The slopes of the FN plots for the four-leaf patterns were almost equal to or even a little higher than those for the substrate surface. In contrast, the slopes of the two-leaf patterns were about 10–15% lower than those of the substrate surface and the slopes of the single bright spots were about 20–25% lower.
Epitaxial Growth of InN by Plasma-Assisted Metalorganic Chemical Vapor Deposition
Authors: Michio Sato Michio Sato
Published: October 2002

InN epitaxial films were grown on (0001) sapphire substrates by plasma-assisted metalorganic chemical vapor deposition, by which large amounts of radicals can be supplied to a surface with less ion damages, using triethylindium and nitrogen radicals as the precursors. When argon was used as a carrier gas, InN having a rough surface with a lot of indium droplets was grown. When hydrogen was used, the InN surface was specular and few droplets were found. InN was grown in hydrogen at a low temperature of 400° C where no growth occurred in argon. These results suggest that the carrier gas influences the InN growth and that hydrogen enhances both the decomposition of organometallics and the removal of excess metal atoms at the growing surface.
Growth of MnSb Thin Films on CdTe Substrates by Hot-Wall Epitaxy
Authors: Jaime Gordon Jaime Gordon , Hiroshi Ikekame Hiroshi Ikekame , Tomohiro Nakamura Tomohiro Nakamura , Jun-ichi Itabashi Jun-ichi Itabashi , Hiroshi Nagayoshi Hiroshi Nagayoshi , Katsuaki Sato Katsuaki Sato
Published: October 2002

Ferromagnetic MnSb thin films were grown on CdTe (110) substrates for the first time by hot-wall epitaxy (HWE) technique using polycrystalline powders of MnSb as an evaporation source. The crystal orientation of these thin films was determined by X-ray diffractometry (XRD). The chemical composition of the films was determined by means of electron-probe microanalysis (EPMA) and by electron spectroscopy for chemical analysis (ESCA) depth profiling. Polar magnetooptical Kerr rotation spectra were measured in the 1.2 eV to 4 eV photon energy range.
Robust Quantum Levels in n-AlxGa1-xAs/u-GaAs/u-AlxGa1-xAs Modulation-Doped Corrugated Double Heterojunctions
Authors: Karel Vacek Karel Vacek , Toshiyuki Usagawa Toshiyuki Usagawa
Published: October 2002

Extremely robust quasi-one-dimensional quantum states are formed in the modulation-doped n-Al

x

Ga1-
x

As/ u-GaAs/ u-Al

x

Ga1-
x

As double-heterostructure with interfaces corrugated by periodical bending. Electrons accumulate strongly in a very narrow channel at the convex corner of GaAs region at the u-GaAs/ n-Al

x

Ga1-
x

As interface. Wave functions for holes are limited to a very narrow channel near the convex corner of the same GaAs region at the opposite interface, u-GaAs/ u-Al

x

Ga1-
x

As. The energy levels of the quasi-one-dimensional states are found to be insensitive to the variation of the well width d of u-GaAs at least wider than 90 Å. Furthermore, the energy level spacing is large, and electrons and holes wave functions are spatially separated from each other.
Giant Magnetoresistance of Multilayers Prepared on Replicas of V-Groove Substrates
Authors: Ono Teruo , Shigeto Kunji , Shinjo Teruya , Shintaku Kazuhiko , Moriya Hisao
Published: October 2002

Co/Au/NiFe/Au multilayers were fabricated on replicas of Si surfaces with V-groove microstructures, and the giant magnetoresistance of these multilayers was measured. The multilayers on the replicas exhibited MR values similar to those of the samples on the master substrates.
Observation of Hydrogen-Coverage- and Temperature-Dependent Adsorption Kinetics of Disilane on Si(100) during Si Gas-Source Molecular Beam Epitaxy
Authors: Suemitsu Maki , Nakazawa Hideki , Morita Tomoyuki , Miyamoto Nobuo
Published: October 2002

Precise measurements of the growth rate, R
g, and the surface hydrogen coverage, θ H, of the gas-source-molecular-beam-epitaxy-grown Si(100) surface using disilane have been conducted to obtain the reaction order m of the adsorption process. The data points separated into three regions: region (I) for 1-θ H<0.5 monolayer (ML) with m=0.5, region (II) for 0.5<1-θ H<0.75 ML with m=2, and region (III) for 1-θ H>0.75 ML with m=4, which was successfully interpreted by a hydrogen-coverage- and temperature-dependent adsorption kinetics model.
Chaotic Fluctuations and a Plasma Density Change at the Beginning of Microwave Discharges
Authors: Junichi Kaga Junichi Kaga , Sumio Kogoshi Sumio Kogoshi
Published: October 2002

Nonmonotonic behavior of plasma density was observed as the output power of a magnetron increased. The behavior was classified into four steps: The electron density increased; became nearly constant; increased again; and finally saturated. In the first two steps, ion saturation current showed chaotic fluctuations. The amplitude of these fluctuations decreased as the output power of the magnetron increased, and disappeared at the final step.
Nonradiative Investigation of Hole Photoionization Spectrum of EL2 in Carbon Concentration Controlled Semi-Insulating GaAs
Authors: Atsuhiko Fukuyama Atsuhiko Fukuyama , Yukihiro Morooka Yukihiro Morooka , Yoshito Akashi Yoshito Akashi , Kenji Yoshino Kenji Yoshino , Kouji Maeda Kouji Maeda , Tetsuo Ikari Tetsuo Ikari
Published: October 2002

Piezoelectric photoacoustic (PPA) measurements were carried out before and after secondary light illumination to investigate EL2 in carbon concentration controlled semi-insulating (SI) GaAs. The PPA spectra before secondary light illumination show a broad peak around 0.95 eV and a hump up to the band gap energy and are attributed to hole and electron photoionizations of EL2, respectively. The photoionization spectra of EL2 were obtained from PPA measurements. We also found that the hole photoionization of EL2 is not influenced by secondary light illumination even after a long period of illumination.
Gas Source Molecular Beam Epitaxy Growth of GaN on C-, A-, R- and M-Plane Sapphire and Silica Glass Substrates
Authors: Iwata Kakuya , Asami Hajime Asahi , Reiko Kuroiwa Reiko Kuroiwa , Shun-ichi Gonda Shun-ichi Gonda
Published: October 2002

GaN layers are grown on C-, A-, R- and M-plane sapphire substrates by gas source molecular beam epitaxy (MBE). The c-axis of GaN is perpendicular to the surface plane and photoluminescence spectra exhibit strong and sharp (full width at half maximum≤39 meV at 77 K) excitonic emission without deep level emission for all cases. GaN layers grown on silica glass substrates also have the c-axis perpendicular to the surface, although they are poly-crystalline. They exhibit an n-type conduction with an electron concentration of 7×10-16 cm-3 and a mobility of 23 cm2/V·s. They also exhibit strong photoluminescence comparable to that of GaN grown on sapphire substrates, although showing a wide spectral half width (245 meV at 77 K). GaN layers grown on glass substrate is considered promising for fabrication of large area and low cost light emitting devices and solar cells.
A Comparative Study Of D-C Electrochemiluminescence from Poly(2-methoxy-5-dodecyloxy-p-pheynylenevinylene) in Solution and in Solid Polymer Electrolyte Media
Authors: Nambu Maki Hamaguchi , Ohsawa Toshiyuki , Katsumi Yoshino Katsumi Yoshino
Published: October 2002

D-C electrochemiluminescence (ECL) of poly(2-methoxy-5-dodecyloxy- p-pheynylenevinylene) was observed for the film immersed in an electrolytic solution and for its dry composite film with a solid polymer electrolyte using interdigitated gold electrodes spaced 5 µ m apart. The coincidence of the onset voltages and spectra of the ECL suggests that both ECLs can be interpreted by the same mechanism: negatively and positively charged excited species of the polymer are formed at the cathode and anode, respectively, and recombine between the electrodes to form singlet excitons which radiatively relax to the ground state.
Characterization of a Sol-Gel Derived Pb(Zr, Ti)O3 Thin-Film Capacitor with Polycrystalline SrRuO3 Electrodes
Authors: Aoki Katsuhiro , Murayama Ikuko , Nishimura Yukio Fukuda
Published: October 2002

The characteristics of a sol-gel derived Pb(Zr, TiO)3 thin-film capacitor with polycrystalline SrRuO3 electrodes deposited by reactive sputtering were evaluated. A single perovskite phase Pb(Zr, Ti)O3 film with columnar grain structure was formed on SrRuO3 substrates since nucleation of Pb(Zr, Ti)O3 took place at the interface with SrRuO3. A Pb(Zr, Ti)O3 capacitor with top and bottom SrRuO3 electrodes showed excellent electrical properties. Leakage current densities were around 1×10-7 A/cm2 at ±5.0 V. The capacitor exhibited good reversibility at an applied voltage of 3.0 V. Remanent polarization density for 3.0 V was 14.3 µc/cm2. Degradation of remanent polarization density was not observed up to switching cycles of 1×1010. Polycrystalline SrRuO3 thin film is expected to be a good candidate for the electrode material of Pb(Zr, Ti)O3 capacitors.
Si–H Bonds on the 6H–SiC(0001) Surface after H2 Annealing
Authors: Tsuchida Hidekazu , Isaho Kamata Isaho Kamata , Kunikazu Izumi Kunikazu Izumi
Published: October 2002

The Si–H bonds on the 6H–SiC(0001) on-axis surface were investigated using Fourier-transformed infrared attenuated total reflection (FTIR-ATR). The clear absorption bands of the Si–H stretching vibrations were observed from the 6H–SiC(0001) on-axis surface after H2 annealing. The configuration of the Si–H bonds on the surface was discussed from the polarized spectra, the chemical characteristics and the electronegativities of the atoms bonded to the Si. The FTIR-ATR spectra suggested that the 6H–SiC(0001) on-axis surface after H2 annealing at 1000° C was primarily terminated by silicon monohydride with high regularity.
Cobalt Thin Films Prepared by Chemical Vapor Deposition from Cobalt Acetylacetonates
Authors: Toshiro Maruyama Toshiro Maruyama
Published: October 2002

Cobalt thin films were prepared by low-temperature atmospheric-pressure chemical vapor deposition from cobalt(II) acetylacetonate and cobalt(III) acetylacetonate. The resistivity was low ( 10–30 µ Ω·cm) and independent of film thickness, when the film thickness ranged from 150 to 700 nm. The thin films deposited from cobalt(III) acetylacetonate consisted of particles of uniform diameter, and consequently an island structure of high resistivity was formed on the substrate when the film thickness was less than 150 nm. A similar island structure of high resistivity but one order of magnitude larger than that for the thin films was formed for the thick films deposited from cobalt(II) acetylacetonate.
Atomic Force Microscopy Study of the Initial Growth of Copper Films by Chemical Vapor Deposition from Hexafluoroacetylacetonate-copper(I)-trimethylvinylsilane: An Indication of a Surface Electron Transfer Reaction
Authors: Lu-Sheng Hong Lu-Sheng Hong , Mei-Zu Lin Mei-Zu Lin
Published: October 2002

Atomic force microscopy was employed to study the initial growth of copper films on various substrates in a metal-organic chemical vapor deposition (MOCVD) system using copper (I)-hexafluoroacetylacetonate trimethylvinylsilane as the precursor. Three-dimensional nuclei growth was observed. The nuclei-number density differs on various substrate surfaces, from 2×108 cm-2 on SiO2 surface to 2×1010 cm-2 on Pt surface at a substrate temperature of 498 K. Kinetic analysis about the nuclei number density on various substrate surfaces shows that the activation energy of the surface nucleation of the precursor is reversely proportional to the electric conductivity of the surface. The results indicate an electron transfer reaction between Cu+1(hfac), an intermediate product of the surface decomposition of the precursor, and substrate surface plays a key role in the formation of initial Cu nucleus.
The Optical Properties of Porous Opal Crystals Infiltrated with Organic Molecules
Authors: Ozaki Katsumi Yoshino , Zakhidov Anvar A. , H. Baughman Ray
Published: October 2002

A fluorescent dye and a photochromic dye were infiltrated into polycrystalline samples of porous opal in order to determine the effects of opal repeat dimension on the optical properties of the dyes. These opals consist of faulted face-centered-cubic arrays of monodispersed, nanoscale SiO2 spheres. The observed absorption and fluorescence of tris(8-hydroxyquinoline) aluminum (Alq3) depended on the lattice constant of the opal. The Alq3 exhibited a blue shift of the absorption edge and a decrease of fluorescence intensity with decreasing lattice constant. Also, the stability of the photochromic behavior of cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl) ethene (CMTE) increased remarkably inside the opal matrix. These characteristics are possibly due to the interaction between the nano-structure-confined dyes and the surfaces of the SiO2 spheres.