bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of Diamond Thin Films Having Semiconductive Properties
Authors: Okano Ken , Naruki Hidetoshi , Akiba Yukio , Kurosu Tateki , Iida Masamori , Hirose Yoichi
Published: February 2005

Semiconductive diamond films were fabricated by the thermal filament CVD method. A saturated solution of B2O3 powder in CH3OH mixed with acetone was used. The films deposited were identified as diamond by several methods including Raman spectroscopy. By the measurement of electrical properties, the obtained films were found to show p-type conduction.
Sidegating Effects in Inverted AlGaAs/GaAs HEMT
Authors: Inomata Fujishiro Hiroki , Saito Tadashi , Nishi Seiji , Sano Yoshiaki
Published: February 2005

Sidegating effects in submicron gate I-HEMTs are reported over a wide range of the drain voltage. A kink in the drain current and the disappearance of the sidegating effect at high drain voltages (3∼4 V) are attributed to the hole injection caused by the impact ionization in the channel. The observation of a new type of sidegating effect at higher drain voltages (>4 V) is also reported. The strong drain voltage dependence is explained by the enhanced electron injection into the substrate caused by the higher hole injection.
Focused Ion Beam Lithography Using Novolak-Based Resist
Authors: Kojima Yoshikatsu , Ochiai Yukinori , Matsui Shinji
Published: February 2005

A lithographic process using a novolak-based resist has been developed for the focused ion beam. It became clear that both positive and negative resist patterns can be easily achieved by choosing appropriate ion doses. The positive resist pattern with 0.4 µm linewidth could be fabricated by 260 keV Be++ FIB at a 4.0×1012 ions/cm2 dose. Moreover, the negative resist pattern with 0.3 µm linewidth could be achieved by 260 keV Be++ FIB at a 3.0×1013 ions/cm2 dose. The negative resist patterns with vertical side walls demonstrated that the image reversal method, developed here, is very useful for device fabrication processes, such as a submicron gate formation.
Reaction Mechanism of Forming the High-Tc Superconductor in the Pb-Bi-Sr-Ca-Cu-O System
Authors: Kijima Naoto , Endo Hozumi , Tsuchiya Jun , Sumiyama Akihiko , Mizuno Masaaki , Oguri Yasuo
Published: February 2005

A relationship between synthesized phases and starting compositions has been studied in the Pb-Bi-Sr-Ca-Cu-O system. The reaction step of forming the high-T
c phase (T
c∼110 K) has been presumed as follows. Firstly, the high-T
c phase and Bi2Sr2CuO
x
are obtained from the disproportionation reaction of the low-T
c phase. Bi2Sr2CuO
x
and residual Ca and Cu atoms melt into the PbO flux. The low-T
c phase is precipitated from the melt. The formed low-T
c phase causes a further disproportionation reaction. The high-T
c phase is produced in large quantities by repeating the cycle.
Formation of Superconducting Bi-Sr-Ca-Cu-O Thin Films with Controlled c-Axis Lattice Spacings by Multitarget Sputtering
Authors: Adachi Hideaki , Kohiki Shigemi , Setsune Kentaro , Mitsuyu Tsuneo , Wasa Kiyotaka
Published: February 2005

Thin films of the Bi-Sr-Ca-Cu-O system were prepared by sequential deposition of Bi, SrCu, CaCu and SrCu oxides using multitarget sputtering. It was confirmed that the c-axis spacing of lattice planes could be controlled by the variation of the CaCu oxide layer. Also, thin films of the Bi system with the insertion of four Cu-O2 planes were synthesized. The T
cs of the films were found to be 80 K, 110 K and 90 K for the Bi system with two, three and four Cu-O2 planes, respectively.
In-Situ Thermographical Temperature Measurement of Be Windows Irradiated by Synchrotron Radiation
Authors: Fujii Kiyoshi , Okada Koichi
Published: February 2005

Temperature distribution of beryllium windows irradiated by synchrotron radiation emitted from Photon Factory storage ring has been measured in situ using thermography technique. Concerning the Be window for synchrotron radiation, the temperature rise problem, related to causing compressive stress, should be examined in extreme detail to avoid window destruction in the worst case. Two-dimensional temperature distribution was explicitly obtained, which agreed well with theoretical calculation results.
a-Si1-xOx:H Films Prepared by Direct Photo-CVD Using CO2 Gas
Authors: Otsubo Shigeru , Saito Masaaki , Morimoto Akiharu , Kumeda Minoru , Shimizu Tatsuo
Published: February 2005

Hydrogenated amorphous Si-O films (a-Si1-x
O
x
:H) were prepared uisng direct photolysis of CO2 without Hg photosensitization. The films were characterized by IR absorption, ESR, electrical and optical measurements. C contamination was not detected by the IR measurement. Si dangling bonds were distributed homogeneously in the whole film, irrespective of the O-poor or O-rich region, in contrast to glow discharge-deposited a-Si1-x
O
x
:H whose dangling bonds were mainly in the O-poor region. Photosensitivity of 103 was obtained even for the film with an optical gap as large as 2.4 eV.
Thermal Annealing Effect of AlAs-GaAs Superlattice Grown at 300°C by Migration-Enhanced Epitaxy
Authors: Saku Tadashi , Horikoshi Yoshiji
Published: February 2005

AlAs-GaAs superlattices are grown at 300°C on (100) GaAs substrates by migration-enhanced epitaxy at various As4 deposition rates. They are then annealed at temperatures higher than the growth temperature. Superlattices grown at closely optimized As4 deposition rates are unaffected by thermal annealing at temperatures as high as 800°C. After annealing, no change is observed in photoluminescence linewidth, and only slight changes are observed in its efficiency and emission energy.
Measurement of Preferential Sputtering of Iron-Oxides Using Laser Fluorescence Spectroscopy
Authors: Matsuda Yoshinobu , Yamaguchi Kouji , Suenaga Kiyoyuki , Yamagata Yukihiko , Honda Chikahisa , Maeda Mitsuo , Yamamura Yasunori , Muraoka Katsunori , Akazaki Masanori
Published: February 2005

Laser fluorescence spectroscopy was used to obtain the velocity-distribution function of sputtered iron from iron oxides, and the fitting of the obtained profiles with the Thompson formula yielded the preferential sputtering of oxygen from iron oxides quantitatively.
Dynamical Detection of Ions of Metastable CO Molecules by Electron-Stimulated-Desorption Using Time-of-Flight Technique from Molybdenum Surface
Authors: Ueda Kazuyuki , Takano Akemi
Published: February 2005

In time-of-flight spectroscopic experiments of electron stimulated desorption (ESD) for a system of carbon monoxide on a molybdenum (001) surface, an ESD signal associated with a metastable ion has been observed accompanying hydrogen and oxygen ions. A simple computer simulation of the orbit of desorbed ions indicates that this peak can be attributed to the molecular ions from carbon monoxide having a kinetic energy of lass than 1 eV.
As-Deposited Superconducting Ba2YCu3O7-y Films Using ECR Ion Beam Oxidation
Authors: Moriwaki Kazuyuki , Enomoto Youichi , Kubo Shugo , Murakami Toshiaki
Published: February 2005

Superconducting Ba2YCu3O7-y
films have been grown epitaxially on (100) and (110) SrTiO3 substrates at a substrate temperature of 600°C using an evaporator combined with an ECR ion source for oxidation. Three molecular beams (BaF2, Y and Cu) were deposited simultaneously under the oxygen ion-beam (50 eV) bombardment. The as-deposited films showed zero resistance at 80–82 K with thicknesses between 200 and 700 nm on both (100) and (110) substrates. The oxygen ion beam was very useful to oxidize the metal sufficiently, to dissociate the BaF2 molecules and to lower the substrate temperature.
A New High-Tc Oxide Superconductor without a Rare Earth Element
Authors: Maeda Hiroshi , Tanaka Yoshiaki , Fukutomi Masao , Asano Toshihisa
Published: February 2005

We have discovered a new high-T
c oxide superconductor of the Bi-Sr-Ca-Cu-O system without any rare earth element. The oxide BiSrCaCu2O
x
has T
c of about 105 K, higher than that of YBa2Cu3O7 by more than 10 K. In this oxide, the coexistence of Sr and Ca is necessary to obtain high T
c.
Magnetostatic Wave Oscillator
Authors: Uehara Gen , Katakura Hisao , Naito Seiichi
Published: February 2005

This paper describes a voltage-controlled oscillator with low SSB (single side band) phase noise using an MSW (magnetostatic wave) device. There is a discussion on what is involved in eliminating the SSB phase noise. An MSW oscillator is tested and the SSB phase noise is measured to be -115 dBc/Hz at 10 kHz offset with a oscillation frequency of 2.0 GHz. A single-chip MSW delay line oscillator is also described that can sweep continuously from 2.03 to 3.18 GHz.
Study of ECR Hydrogen Plasma Treatment on Poly-Si Thin Film Transistors
Authors: Takeshita Tatsuya , Unagami Takashi , Kogure Osamu
Published: February 2005

In order to improve the characteristics of poly-Si thin film transistors (TFT's), hydrogen plasma treatment using electron cyclotron resonance plasma (ECR plasma treatment) has been studied. ECR plasma treatment has improved carrier mobility and the ON/OFF current ratio of poly-Si TFT's, which have been found to be greater than those using conventional hydrogen plasma treatment with radio frequency plasma. The improvement in the poly-Si TFT's characteristics is due to the reduction in the carrier trap density at the poly-Si grain boundary. Furthermore, the ECR plasma treatment improves leakage current.
Improvement of Written-State Retentivity by Scaling Down MNOS Memory Devices
Authors: Minami Shin-ichi , Kamigaki Yoshiaki , Uchida Ken , Furusawa Kazunori , Hagiwara Takaaki
Published: February 2005

New MNOS retention characteristic phenomena are demonstrated. Shrunk MNOS memory devices are closely evaluated. While charge retentivity of the erased state depends only slightly on silicon nitride thickness, written-state retentivity is improved by reducing silicon nitride thickness. These new phenomena are applied to memory device design. A 1 M bit MNOS EEPROM can be designed with silicon nitride thickness 20.0 nm and programming voltage 10.7 V. These results show the MNOS memory device to be a very promising candidate for Megabit EEPROM's.
Effect of Bias Sputtering on W and W-Al Schottky Contact Formation and its Application to GaAs MESFETs
Authors: Sekino Yuko , Kimura Tamotsu , Inokuchi Kazuyuki , Sano Yoshiaki , Sakuta Masaaki
Published: February 2005

The effect of DC bias on the sputter-deposition of W and W-Al on GaAs substrates was investigated. By applying a negative bias to the substrate, the concentration of impurities in the metals and at the interface, such as oxygen, was reduced, and the characteristics of the Schottky contact were improved with respect to the barrier height, the n-value and the uniformity. These results are explained by the reverse sputtering effect for the substrate. This technique was applied to the gate formation of GaAs MESFETs, and the uniformity of the threshold voltage distribution within a 2-inch wafer was much improved.
Photodetector with Embedded Semiconductor-Metal-Semiconductor Structure
Authors: Chung Ki-Woong , Kwon Young-Se
Published: February 2005

Two types of photodetectors with embedded semiconductor-metal-semiconductor (SMS) structures are proposed. One of them is the embedded metal-semiconductor-metal photodetector (MSM-PD) which has two interdigitating Schottky electrodes in the semiconductor. This has a larger light-sensitive area than the conventional MSM-PD. The other is the back-gated photoconductive detector (BPCD) which has a reduced fall time. The fall time can be reduced by dragging out the slowly moving hole through the back-gate.
Surfaces and Interfaces of High-Tc Superconductors for Contact and Junction Formation Studied with Synchrotron Radiation Photoemission Spectroscopy
Authors: Oshima Masaharu , Yamada Yasuko , Kawamura Tomoaki , Maeyama Satoshi , Hohkawa Kouji , Tazoh Yasuo , Miyahara Tsuneaki
Published: February 2005

Interface characteristics between contact metals or junction materials and oxide superconductors were analyzed by synchrotron radiation photoemission spectroscopy. A new surface processing technique consisting of O+ ion sputtering and in-situ Au deposition processes on YBa2Cu3O
y
was developed to realize very low contact resistance based on these SRPES experiments. Furthermore, a strong interface reaction in the Si/YBa2Cu3O
y
system for junction formation was observed, suggesting that amorphous Si is not a good candidate for the junction material.
Crystallization of 107 K Superconducting Phase and Partial Melting in the Bi-(Pb)-Sr-Ca-Cu-O System
Authors: Ono Akira
Published: February 2005

Formation of the superconducting phase with T
c=107 K in the Bi-(Pb)-Sr-Ca-Cu-O system was studied for specimens with various nominal compositions. Examination of sintered specimens revealed that the 107 K phases crystallized in air in the temperature range where partial melting takes place. In the strict sense, it is impossible to obtain a pure ceramic consisting of the 107 K phase because of the presence of a small quantity of a solidified liquid phase. Unlike the Pb-free 107 K phase, the Pb-containing one showed zero electrical resistivity at 105 K even if it was annealed at a low oxygen pressure.
Preparation of High-Tc Superconducting Bi-Pb-Sr-Ca-Cu-O Ceramics by the Melt Quenching Method
Authors: Komatsu Takayuki , Sato Ryuji , Hirose Chisai , Matusita Kazumasa , Yamashita Tsutomu
Published: February 2005

We prepared superconducting Bi0.8Pb0.2SrCaCu2O
y
ceramics using the melt quenching method and examined the effect of annealing conditions on the formation of high-T
c phases. It was found from the changes in inductance and X-ray powder diffraction analyses that prolonged annealing at 830°C was very effective in increasing the volume fraction of high-T
c phases. The samples annealed at 830°C for 200 h and 250 h in air exhibited superconductivity with a T
c(zero)=100 K and critical current densities (77 K, zero magnetic field) of 35∼50 A/cm2.
Effect of Ba Addition on the Properties of Bi-Pb-Sr-Ca-Cu-O Superconductors
Authors: Kawai Tomoji , Kawai Shichio , Tanaka Shigeyuki , Horiuchi Takeshi , Takagi Sadao , Ogura Kiyoshi , Kambe Shiro , Kawai Maki
Published: February 2005

The addition of Ba to Bi-Pb-Sr-Ca-Cu-O and Bi-Sr-Ca-Cu-O superconductors exhibits the effect of raising the T
czero
value to a higher temperature region, although too much Ba gives rise to semiconducting resistance-temperature behavior. The added Ba has the effect of decomposing the structure of the 80 K phase, leading to the production of BaBiO3 and BaCuO2 and enhancing the high-T
c phase formation.
Transmission Spectroscopy in the Range 3 to 500 cm-1 in a Superconductor Crystal Bi-Sr-Ca-Cu-O
Authors: Sato Masayuki , Nagasaka Keigo , Shibayama Takasi , Ishida Kohtaro
Published: February 2005

We present the transmittance in the low frequency range from 3 to 500 cm-1 for the high-T
c superconductor crystal Bi-Sr-Ca-Cu-O (T
c=80 K). The transmittance decreases with the frequency in the range 3 to 300 cm-1. The ratios of the transmittance in the superconducting state to the transmittance in the normal state (90 K) for temperatures of 8 and 50 K have been obtained. These experimental results suggest that the high-T
c superconductor crystal Bi-Sr-Ca-Cu-O behaves as a gapless superconductor.
Electron Irradiation Effects on a Ba2YCu3O7 Superconductor
Authors: Shiraishi Kensuke , Itoh Hiroshi , Yoda Osamu
Published: February 2005

A single-phased Ba2YCu3O7-y
pellet was sequentially irradiated with 3 MeV electrons up to 3×1022 m-2 at about 370 K, and the electrical resistance was measured as a function of temperature. The superconducting transition temperature of 92.5 K decreased almost linearly with electron dose at a rate of 3 K/1023 m-2 concurrently with a linear increase in electrical resistivity at 95 K from 2.9 µΩ·m with 7 µΩ·m/1023 m-2. The offset temperature measured with 105 kA ·m-2 in current density was enhanced from 88.6 to 90.4 K by electron irradiation to 1.5×1022 m-2, and then reduced upon further irradiation.
Ridge Waveguide DFB Laser Operating at λ=1.5 µm, Fabricated in a Single Step Epitaxial Growth
Authors: Binsma J. J. M. , Tiemeyer L. F. , van Zantvoort H. A. C. M. , Baele I. , van Dongen T. , van der Hofstad G. L. A.
Published: February 2005

Ridge Waveguide DFB lasers fabricated by single step liquid phase epitaxy are reported. The lasers obtained by overgrowth of a first order grating in an InP substrate and ridge waveguide fabrication show CW threshold currents of 35 mA and single facet efficiencies of 18% at 20°C. The overgrowth of more than one wafer from the same set of mother melts allows accurate matching of the Bragg wavelength to the active layer gain.
Surface-Emitting AlGaAs/GaAs DH LED with Buried-Window Cylindrical Lens
Authors: Yoo Tae-Kyung , Hahm Sung-Ho , Kwon Young-Se
Published: February 2005

Surface-emitting AlGaAs/GaAs double heterostructure (DH) LED's with buried-window cylindrical lenses have been fabricated. The selective meltback and regrowth were used for the lens and DH junctions. The far-field pattern has the full width at half maximum (FWHM) of 90°. A small protrusion with the full width of 20° was observed in the far-field pattern. The maximum power of 20 mW was obtained from the 1 µm×60 µm×300 µm active layer.
Diffusion Barrier with Reactively Sputtered TiN for Thermally Stable Contact
Authors: Mitsuhashi Katsunori , Yamazaki Osamu , Ohtake Koui , Koba Masayoshi
Published: February 2005

The barrier capability of reactively sputtered TiN thin films was investigated in W/TiN/Si structures. During high-temperature annealing, a thin layer was formed at the interface between TiN and Si. This phenomenon is due to the oxygen combining with Ti in the TiN film and slight diffusion of Ti and Si atoms. The film properties of this TiN, especially film resistivity, were greatly affected by the oxygen impurities which combined with the Ti. This seems to be one of the reasons why a high-temperature annealing barrier capability was obtained. The ohmic contacts to n
+ and p
+ Si in this structure were maintained even after annealing at 900°C for 6 hours by performing an additional 31P+ and 11B+ implantation into W.
Picosecond Response of A Planar GaAs/Al0.3Ga0.7As Schottky Barrier Photodiode
Authors: Lee D. H. , Li S. S. , Paulter N. G.
Published: February 2005

A high-speed, high-sensitivity planar GaAs/Al0.3Ga0.7As heterostructure Schottky barrier photodiode has been designed, fabricated, and characterized. A highly doped Al0.3Ga0.7As buffer layer is deposited on semi-insulating GaAs substrate to reduce the series resistance and the undesired diffusion tailing of the photodetector. Furthermore, surface passivation and antireflection coatings using various dielectric films are studied to reduce the reverse-bias dark current and the reflection loss of the incident light, thereby significantly improves the sensitivity of the photodiode. The external quantum efficiency of 60% to 70% and responsivity of 0.47 A/W to 0.6 A/W were measured for the wavelength range of 0.5 µm to 0.84 µm. A risetime of 8.5 ps and a 3-dB cutoff frequency of 50 GHz have been obtained for this detector.
Orthorhombic-to-Tetragonal Phase Transition in the Y-Ba-(Cu, Co)-O System
Authors: Sankawa Izumi , Sato Makoto , Konaka Tsuneo
Published: February 2005

X-ray powder diffraction, thermal analysis and resistivity measurements have been carried out for the YBa2(Cu1-x
, Co
x
)3O7-δ system with 0<x<0.333. With increasing Co content, weight loss in the thermogravimetric (T
G) curve steadily decreases and the structure transforms from orthorhombic to tetragonal. Around this phase transition at x=0.02, T
c starts to decrease. This phenomenon is considered to be ascribed to the disordering of oxygen sandwiched between Ba planes.
New Amorphous Alloys with Good Ductility in Al-Y-M and Al-La-M (M=Fe, Co, Ni or Cu) Systems
Authors: Inoue Akihisa , Ohtera Katsumasa , Tsai An-Pang , Masumoto Tsuyoshi
Published: February 2005

New aluminum-based amorphous alloys were found to be formed in Al-Y-M and Al-La-M (M=Fe, Co, Ni or Cu) ternary systems by melt spinning. Their compositional ranges are 3 to 33 at%M and 3 to 22 at%Y or 2 to 18 at%La. The alloys containing more than about 80 at%Al have good bend ductility. The crystallization temperature T

x
increases from 414 to 831 K with an increase of M and yttrium or lanthanum contents. The effect of the solute elements on T

x
is interpreted to be dominated by the attractive interaction between aluminum and M, yttrium or lanthanum atoms.
Initial Growth Conditions of GaAs on (100) Si Grown by Migration-Enhanced Epitaxy
Authors: Stolz Wolfgang , Naganuma Mitsuru , Horikoshi Yoshiji
Published: February 2005

This paper investigates the effect of initial growth conditions on the structural and optical properties of GaAs and (AlGa)As/GaAs quantum well heterostructures (QWH) on (100)Si. Samples are grown by migration-enhanced epitaxy (MEE) at 300°C. Only the growth conditions of the first GaAs monolayer on Si substrates are varied. Optimization requires: 1) no exposure of the hot Si surface to As, and 2) Ga-dominated initial growth conditions. Sharp low-temperature excitonic luminescence (8.0 meV (FWHM) for L
z=2 nm) confirms the smooth heterointerfaces of the MEE-grown layers. Samples grown by conventional MBE at 300°C show a clearly poorer crystal quality.
Interface Study on GaAs-on-Si by Transmission Electron Microscopy
Authors: Nozaki Chiharu , Naritsuka Shigeya , Kokubun Yoshihiro , Yasuami Shigeru
Published: February 2005

A correlation between the surface and interface defects in GaAs-on-Si structures was examined by KOH etching and transmission electron microscopy. Line-shaped etch pits revealed on the GaAs-on-Si (100) were attributed to twins produced at the interface. This twin generation was avoided by off-setting the substrate orientation. An alternative for this is the application of an additional heat treatment after the GaAs buffer layer is grown. In this case, the twin propagation ends on the buffer layer.
Improvement of the Electrical Properties of the AlN/GaAs MIS System and Their Thermal Stability by GaAs Surface Stoichiometry Control
Authors: Fujieda Shinji , Mizuta Masashi , Matsumoto Yoshishige
Published: February 2005

The GaAs surface pre-treatment conditions for the MOCVD-AlN/GaAs MIS diodes are investigated. An AsH3 pre-treatment just prior to the AlN deposition degraded the C-V characteristics of AlN/n-GaAs MIS diodes in the accumulation side. The characteristics and their stability were drastically improved by a pure H2 pre-treatment at 500°C. It was confirmed that the free As at the interface generates surface states near the conduction band edge and that control of the surface stoichiometry and atomic structure is necessary to improve the MIS characteristics.
1/f Fluctuations in the Dielectric Response of Triglycine Sulfate
Authors: Musha Toshimitsu , Nakajima Akira , Akabane Hideo
Published: February 2005

1/f fluctuations have been observed in the imaginary part of the complex dielectric constant of ferroelectric triglycine sulfate crystals near the Curie temperature T
c. The observed 1/f power spectral density S

ε
i
(f) of the imaginary dielectric constant, when normalized to the square of the real part of the dielectric constant ε
r, is given by S

ε
i
(f)/ε
r
2=3.2×10-15/f(Δ
T) where Δ
T=T-47.73(°C) in the paraelectric phase and Δ
T=47.82-T(°C) in the ferroelectric phase.
Effects of Preparation Conditions and Mechanical Polishing on the Superconducting Behavior of High-Tc Oxide Y1Ba2Cu3O7-y
Authors: Kishida Satoru , Tokutaka Heizo , Nishimori Katsumi , Ishihara Naganori , Watanabe Yoshihide , Noishiki Yoshio
Published: February 2005

We investigated the effects of preparation conditions and mechanical polishing on the resistance-temperature characteristics of superconducting oxides, Y1Ba2Cu3O7-y
which were prepared from different starting materials of (1) Y2O3, Ba(NO3)2 and Cu(NO3)2 (A-series) and (2) Y2O3, BaCO3 and CuO (B-series). The A-series samples were ten times more closely packed than the B-series samples. It was found that mechanical polishing of the specimen surface was necessary to obtain stable and reproducible resistance-temperature characteristics. In addition, the specimen, which was prepared from the A-series starting material, gave the best zero-resistance result at 95.5 K.
Examination of Sorption-Desorption of Oxygen on YBa2Cu3O7-x Superconducting Oxide by TPD Technique
Authors: Miura Norio , Suzuta Hiroki , Teraoka Yasutake , Yamazoe Noboru
Published: February 2005

Temperature programed desorption (TPD) spectra of oxygen from YBa2Cu3O7-x
compounds with different oxygen contents are reported in connection with their superconductivities. Superconducting orthorhombic samples (x<ca. 0.5) with a T
c,end of ca. 90 K were found to have two desorption peaks (Peak I centered at 550°C and Peak II centered at ca. 660°C), while tetragonal samples (x>ca. 0.5) showing semiconductive behavior in the temperature range above 77 K had only Peak II. This implies that the oxygen desorbed as Peak I from orthorhombic samples is deeply correlated with the superconductivity.
Crystal Structures of YBa2Cu3-δAδO9-γ (A=Ni, Zn and Co)
Authors: Kajitani Tsuyoshi , Kusaba Keiji , Kikuchi Masae , Syono Yasuhiko , Hirabayashi Makoto
Published: February 2005

A structural study of orthorhombic YBa2Cu3O6.94, YBa2Cu2.8Ni0.2O6.85 and YBa2Cu2.7Zn0.3O6.75, and tetragonal YBa2Cu2CoO7.16 by means of X-ray and time-of-flight type (TOF) neutron diffractometers was carried out to determine the locations of the dopant atoms, Ni, Zn and Co, in the 1-2-3 (Y/Ba/Cu) oxide. The nickel atoms occupy only the Cu2 site 2q(00z) with z=0.36. The zinc atoms occupy the Cu1 site 1a(000) and the Cu2 site with occupancies of 0.20(5) and 0.05(2). In the tetragonal YBa2Cu2CoO7.16, cobalt atoms were found at both the Cu1 and Cu2 sites with occupancies of 0.83(2) and 0.08(1).
Identification of a High-Tc Superconducting Phase in the Bi-Ca-Sr-Cu-O System
Authors: Kijima Tsuyoshi , Tanaka Junzo , Bando Yoshio , Onoda Mitsuko , Izumi Fujio
Published: February 2005

Bismuth-based copper oxides with varying nominal compositions in the Bi-Ca-Sr-Cu-O system were prepared and identified by the methods of X-ray and electron diffraction, spectroscopic microanalysis and electrical resistivity measurement. It yielded a pseudo single phase with an offset superconducting transition temperature of 70 K and a width of 10 K. The major phase concerned with the superconducting transition near 75 K has a composition of Bi2CaSr1.5Cu2O
y
and is orthorhombic with unit cell dimensions of a=5.40, b=27.0 and c=30.6 Å. The X-ray diffraction pattern for the pseudo single phase was in good agreement with that simulated on the basis of proposed structure models which are fairly different from the structure of the layered bismuth titanate.
Magnetron Sputtering of Bi-Ca-Sr-Cu-O Thin Films with Superconductivity above 80 K
Authors: Nakao Masao , Kuwahara Hideki , Yuasa Ryohkan , Mukaida Hiromi , Mizukami Atsuo
Published: February 2005

Superconducting Bi-Ca-Sr-Cu-O thin films on (100) MgO were prepared by rf magnetron sputtering from a sintered Bi1Ca1Sr1Cu2O
x
target. Post-annealing after sputtering resulted in superconducting films with a resistance anomaly around 110 K and zero resistance at 80 K. X-ray diffraction patterns indicated a preferential orientation, where the c axis of a fourfold stacked perovskite, with a lattice constant c=15.38 Å, is perpendicular to the substrate plane.
Magnetic Anisotropy in A High-Tc Superconductor YBa2Cu3O7-δ Single Crystal below Tc
Authors: Isikawa Yosikazu , Mori Katsunori , Kobayashi Koichi , Sato Kiyoo
Published: February 2005

We have measured the magnetic field dependence of magnetization of single-crystal YBa2Cu3O7-δ in detail in fields up to 5 kOe in the temperature range below T
c, i.e., 93 K. Lower critical fields, H
c1's, at which the magnetization deviates from linearity, are very anisotropic; H
c1
⊥(0) (perpendicular to the a
b-plane) is 305 Oe and H
c1
//(0) (parallel to the a
b-plane) is 104 Oe. Both H
c1
⊥ and H
c1
// decrease linearly with increasing temperature up to about T
c. It is suggested that random oxygen defects in the Cu-O planes and chains are important for the high-J
c type II superconductor YBa2Cu3O7-δ.
Growth of High-Mobility 3C-SiC Epilayers by Chemical Vapor Deposition
Authors: Shinohara Mikiya , Yamanaka Mitsugu , Daimon Hiroshi , Sakuma Eiichiro , Okumura Hajime , Misawa Shunji , Endo Kazuhiro , Yoshida Sadafumi
Published: February 2005

Non-doped 3C-SiC epilayers having mobility higher than 750 cm2/(V ·s) at room temperature and 3000 cm2/(V ·s) around 66 K were obtained for the first time, using large size (60×70 mm2) Si substrates. The conditions for obtaining such high-mobility epilayers are discussed in terms of the distribution of the electrical properties over the epilayers and their substrate size dependence.
Very-Low-Temperature Silicon Epitaxy by Plasma-CVD Using SiH4-PH3-H2 Reactants for Bipolar Devices
Authors: Uematsu Tsuyoshi , Matsubara Sunao , Kondo Masao , Tamura Masao , Saitoh Tadashi
Published: February 2005

A novel plasma-CVD process has been developed for growing specular silicon epitaxial layers at very low temperatures of approximately 200°C. The epitaxial layers were deposited from SiH4-PH3 gases diluted with H2 on single-crystal substrates just after being etched in a HF dip. The highest electron mobility and lowest resistivity of the n+-layers were 30 cm2/V ·s and 4×10-4 Ω·cm, respectively. This technology has been successfully applied to fabricate bipolar transistors with a high current gain of 370.
A New Icosahedral Al-Fe-Ta Alloy Prepared by Rapid Solidification
Authors: Tsai An-Pang , Inoue Akihisa , Masumoto Tsuyoshi
Published: February 2005

A new icosahedral phase in the Al-Fe-Ta system has been produced by rapid solidification. The formation of the icosahedral phase is limited in the vicinity of 20%Fe and 10%Ta. The icosahedral phase consists of grains with a size of about 200 nm and each grain includes a high density of internal defects showing a contrast of radiating branches. Heating at 10 K/min gives rise to the decomposition of the icosahedral phase into Al3Fe and Al3Ta at about 900 K. It is thus concluded that the icosahedral phase has considerably higher thermal stability than Al-Mn and Al-Cr binary icosahedral alloys.
Ab initio MO Studies of the Hole Delocalization in Copper Oxides and Related Species: Necessity of the Extended Hubbard Model
Authors: Yamaguchi Kizashi , Takahara Yoichi , Fueno Takayuki , Nasu Keiichiro
Published: February 2005

The positive holes for copper oxides and isoelectronic species were investigated by the ab initio molecular orbital (MO) method. It is found that the hole is delocalized over the oxide clusters because of the strong 3d σ-2p σ hybridization, and that the spin polarization of the closed-shell pairs is remarkable, indicating an important role of the spin fluctuation for high-T
c superconductivity. The extended Hubbard model is necessary for theoretical studies of the hole delocalizations in copper oxides.
Nonstoichiometry of Superconducting Ba2YCu3O7-y at Temperatures between 870 and 1180 K
Authors: Iwase Masanori , Iritani Hideki , Ichise Eiji , Osamura Kozo
Published: February 2005

A thermogravimetric technique was employed for the determination of the nonstoichiometry of Ba2YCu3O7-y
at temperatures between 870 and 1180 K and the oxygen partial pressure of 0.005 to 1 atm. The oxygen deficiency, y, varied from 0.8 to 1.3, corresponding to the presence of Cu2+ and Cu+ at the temperatures investigated.
New Oxygen-Deficient Perovskite Phase, La1-xSrxCuO3-y (0.20≦x≦0.25)
Authors: Murayama Norimitsu , Sakaguchi Shuji , Wakai Fumihiro , Sudo Eiichi , Tsuzuki Akihiro , Torii Yasuyoshi
Published: February 2005

In a given system, a new nonstoichiometric perovskite solid solution was found to exist in a narrow range of 0.20≦x≦0.25. This perovskite phase has a tetragonal distortion based on a Jahn-Teller effect of the Cu ion. The lattice parameters are closely related to those of the simple cubic perovskite: a=10.834(1) Å, c=3.8638(4) Å for La0.75Sr0.25CuO2.44 and a=10.851(1) Å, c=3.8623(6) Å for La0.80Sr0.20CuO2.47, where a≃2√2c. These perovskites are metallic conductors and no superconducting transition has been observed in a measured temperature range of 77–300 K.
Phase Transition in YBa2Cu3O7-x through Hydrogen Ion Implantation
Authors: Kato Takahiko , Aihara Katsuzo , Kuniya Jiro , Kamo Tomoichi , Matsuda Shin-Pei
Published: February 2005

Phase transition in YBa2Cu3O7-x
through hydrogen ion implantation was investigated by means of X-ray diffraction. It was found that the orthorhombic-to-tetragonal phase transition was induced by the implantations in the ion fluences of 7.6×1016 H+/cm2 and above. At the 2.3×1017 H+/cm2 implantation, the extra phases Y2BaCuO5 and CuO were also formed. These phenomena suggested that the implanted hydrogen atoms deoxidized the YBa2Cu3O7-x
to produce H2O which reacted with YBa2Cu3O7-x
.
High-Jc Superconducting Single Crystalline HoBaCuO Thin Films by Sputtering
Authors: Tanaka Saburo , Itozaki Hideo
Published: February 2005

HoBaCuO high-J
c superconducting single crystalline thin films were first grown on MgO (001) substrates by magnetron sputtering. The films showed sharp resistive transition with T
c(R=0)=84 K. The critical current density J
c was 2.54×106 A/cm2 at 77.3 K. Even under the influence of a magnetic field of 1.0 T, J
c was sustained at more than 1.5×106 A/cm2 at 77.3 K. X-ray and electron diffraction analyses showed that the basal planes of the films are parallel to the substrates and that these films are epitaxially grown single crystals.
Sputter Synthesis of Ba2YCu3Oy As-Deposited Superconducting Thin Films from Stoichiometric Target–A Mechanism of Compositional Deviation and Its Control
Authors: Terada Norio , Ihara Hideo , Jo Masatoshi , Hirabayashi Masayuki , Kimura Yoichi , Matsutani Katsuhiro , Hirata Kazuo , Ohno Eizo , Sugise Ryoji , Kawashima Fumiyuki
Published: February 2005

A mechanism of compositional deviation of Ba-Y-Cu-O films during sputtering has been investigated, and a process for obtaining as-deposited superconducting films from a stoichiometric target has been developed. The main factor of the deviation is the radiation of high-energy electrons emitted from the oxide target with a low work function onto the growing surface. By eliminating the electron bombardment, films with the same composition were obtained reproducibly. As-grown films 4000 Å thick deposited at 580°C showed T
c ( ρ=0) of 82.5 K and an excellent surface smoothness.
Reversible Resistivity Control of Ba2YCu3O7-δ Thin Films by Laser Annealing
Authors: Koinuma Hideomi , Takemura Yasuhiko , Hishimoto Takuya , Takeuchi Kou , Fueki Kazuo
Published: February 2005

Laser annealing of superconducting Ba2YCu3O7-δ (BYCO) thin films has been investigated by using a Nd:YAG cw laser. By laser irradiation at power densities higher than 1.4×105 W/cm2, superconducting polycrystalline films became amorphous and showed semiconductor-like temperature dependence on resistivity. The amorphization is apparently caused by a rapid quenching of molten BYCO after laser irradiation. The superconductivity of the film could be recovered by annealing the laser-irradiated film in a furnace. With this mask-free laser irradiation process, patterning of superconducting films can be achieved.
A Simple Method for Attaching Electrical Leads to Small Samples of High-Tc Oxides
Authors: Iye Yasuhiro , Tamegai Tsuyoshi , Takeya Hiroyuki , Takei Humihiko
Published: February 2005

A simple technique for attaching a number of electrical leads to a small sample of YBa2Cu3O7-x
has been devised. Thin gold wires are spark-bonded onto a crystal by using a capacitor discharge. As-bonded contacts are highly resistive suggesting a local oxygen deficiency caused by the bonding process. Contact resistance (for a contact area ∼10-2 mm2) can be lowered to ∼1 Ω by annealing at 800°C in an oxygen atmosphere. Some results of electrical measurements on single crystal samples of YBa2Cu3O7-x
using this technique are presented.
Nonaqueous Suspension Spinning of High-Tc Ba-Y-Cu-O Superconductor
Authors: Goto Tomoko
Published: February 2005

The preparation of a high-T
c Ba2Y1Cu3O
x
superconducting filament was studied by nonaqueous suspension spinning. The fine powder of the oxide was suspended in PVA dimethyl sulfoxide solution containing a dispersant. The viscous suspension was extruded as a filament into a precipitating medium of methyl alcohol and coiled on a winding drum. The obtained filament, 200 µm in diameter, was heated to remove volatile components and to generate the layered perovskite phase. The heated filament with tensile strength of 37 MPa was a superconductor at 84 K and had a J
c value of 680 A/cm2 at 77 K.
High-Tc Superconductors Prepared by Oxidation of Vapor-Quenched Amorphous Alloy Films in Ba-Y-Cu and Ba-Yb-Cu Systems
Authors: Kataoka Noriyuki , Furukawa Shinji , Matsuzaki Kunio , Inoue Akihisa , Masumoto Tsuyosi
Published: February 2005

Amorphous Ba1Y2Cu5 and Ba2Yb1Cu6 alloy films were obtained by rf sputtering. The oxidization treatment by annealing of the alloy films in the range of 1173 to 1223 K in an oxygen flowing atmosphere gave rise to the formation of Ba1Y2Cu5O
y
and Ba2Yb1Cu6O
y
oxide films. The Ba1Y2Cu5O
y
and Ba2Yb1Cu6O
y
films consisted mainly of an orthorhombic phase and exhibited high-T
c superconductivity with onset at 91 and 86 K and zero resistance at 75 and 82 K, respectively.
Effect of Insulator Gap on the Performance of a Reversed-Field Pinch Produced in a Thick Metal Chamber
Authors: Masamune Sadao , Oshiyama Hiroshi
Published: February 2005

A reversed-field pinch (RFP) plasma which has characteristics typical of that produced in a conventional thin metal liner has been obtained in the STE-1(M) device. It uses a 3.4 mm-thick stainless-steel chamber with four insulators for the application of the toroidal voltage, along with the aided self-reversal mode for setting up the RFP configuration. Displacement of the center-of-current channel at the insulator gap was twice as large as that far from the gap. This local displacement could be reduced by the vertical field. Optimization of the vertical field resulted in a 20% decrease of the sustaining voltage.
Crystal Growth of Superconducting Bi-Sr-Ca-Cu-O Compounds from KCl Solution
Authors: Katsui Akinori
Published: February 2005

A flux method using KCl as a solvent is proposed for single-crystal growth of Bi-Sr-Ca-Cu-O compounds. Bi-Sr-Ca-Cu-O thin plates are grown by slowly cooling a KCl solution maintained at 850∼950°C. Four-probe electrical resistance measurement indicates that the as-grown crystals act as a superconductor with a transition temperature of about 80 K.
Diamagnetic Properties of High-Tc Bi-Sr-Ca-Cu-O Superconducting Thin Films
Authors: Hatta Shin-ichiro , Ichikawa Yo , Hirochi Kumiko , Setsune Kentaro , Adachi Hideaki , Wasa Kiyotaka
Published: February 2005

The diamagnetic properties of superconductive Bi-Sr-Ca-Cu oxide thin films were studied, by using an rf SQUID susceptometer. The specimen showing diamagnetization up to about 100 K has also indicated the zero-resistance temperature of 102 K. The critical current density is estimated from the diamagnetization shielding effect to be 3.3×106 A/cm2 at 4.2 K and 7×104 A/cm2 at 77 K.
Magnetic Properties and Upper Critical Fields of Sintered Tl-Ca-Ba-Cu-O Superconductors
Authors: Kumakura Hiroaki , Togano Kazumasa , Takahashi Kazuhiko , Shimizu Hitoshi , Uehara Mitsuru , Maeda Hiroshi , Nakao Masao
Published: February 2005

Magnetic properties and upper critical field H
c2 near T
c (zero field) were measured for sintered Tl-Ca-Ba-Cu-O compound whose zero resistance temperature was 105 K. The magnetic susceptibility curve indicated that the sample contained only one superconducting phase. Hysteresis of magnetization at 77 K was larger than that of Bi-Sr-Ca-Cu-O. H
c2 values at 77 K and 0 K, estimated by extrapolation, were 50 T and 130 T, respectively. These values were slightly higher than those of high-T
c phase in Bi-Sr-Ca-Cu-O compound.
Superconducting Y1Ba2Cu3O7-δ Films Prepared by the Dip-Coating Technique on MgO Substrates
Authors: Nakada Tokio , Kazusawa Michiya , Kunioka Akio , Fujimori Takashi
Published: February 2005

The preparation of high-T
c superconducting films of Y1Ba2Cu3O7-δ on MgO(001) substrates by a simple dip-coating technique is described. The superconducting properties, adhesion, and microstructure of these films depend strongly on the heat treatment conditions. The critical current and the adhesion of the films can be increased by the extremely short exposure to high temperature at 1100°C followed by a proper thermal annealing process in oxygen. The best film with T
c(onset)=84 K, T
c(R=0)=80 K, and zero-field critical current density of roughly 70 A/cm2 at 77 K is obtained.
Low Voltage Driven MOCVD-Grown ZnS:Mn Thin-Film Electroluminescent Devices Using Insulating BaTiO3 Ceramic Sheets
Authors: Minami Tadatsugu , Miyata Toshihiro , Kitamura Kentarou , Nanto Hidehito , Takata Shinzo
Published: February 2005

A thin-film electroluminescent (EL) device with a ZnS:Mn emitting layer grown by a metalorganic chemical vapor deposition method using carbon disulfide as a sulfur source has been prepared on a BaTiO3 ceramic sheet used as an insulating layer. The luminance of 1 nt under the applied voltage (sinusoidal wave of 5 kHz) of 7 V is attained for the EL devices with a ZnS:Mn emitting layer 170 nm thick, and 20 V with a 400 nm thick layer. The maximum luminance and luminous efficiency obtained are 6300 nt and about 11 lm/W, respectively. A device driven with an applied voltage of 100 V at 60 Hz exhibits a luminance of 200 nt.
Analysis of Thermionic Emission Current over the AlxGa1-xAs Barrier in a GaAs/AlxGa1-xAs/GaAs (x>0.45) Structure
Authors: Zohta Yasuhito
Published: February 2005

Thermionic emission (TE) current over the Al
x
Ga1-x
As barrier in a GaAs/Al
x
Ga1-x
As/GaAs (x>0.45) structure has been analyzed taking into account the conduction band structures of GaAs and Al
x
Ga1-x
As. Assumption of a noninteracting electron model leads to the conclusion that the L valley governs the TE current. This is true for x∼0.45, but contradicts recent experiments when x approaches 1. The model has been modified to include the \varGamma→X→\varGamma current which arises from the mixing between \varGamma and X wave functions at heterojunction interfaces. On the basis of the modified model, the competition between the L current and the \varGamma→X→\varGamma current is discussed.
STM Study of the Effects of Etching on the Surface of Kish-Graphite
Authors: Koga Yasunori , Miyazaki Yasumichi , Nakagiri Nobuyuki
Published: February 2005

We used a scanning tunneling microscope to study how the surface of Kish-Graphite roughens with etching. We present STM images of the etched surfaces for different etch times. The roughness (rms) and the peak-to-valley height were calculated from the digitized STM signals. The roughness vs sputtering time graph shows that the roughness increases with sputtering time up to about a roughness of 1 nm, then does not change with increased etching. The peak-to-valley height is proportional to the roughness with a coefficient of 8.7.
Simulation Study on the Behavior of X-Rays and Gamma Rays in an Inhomogeneous Medium Using the Monte Carlo Technique
Authors: Murase Kenya , Kataoka Masaaki , Kawamura Masashi , Tanada Shuji , Hamamoto Ken
Published: February 2005

A computer program based on the Monte Carlo technique was developed for the analysis of the behavior of X-rays and gamma rays in an inhomogeneous medium. The statistical weight of a photon was introduced and the survival biasing method was used for reducing the statistical error. This computer program has the mass energy absorption and attenuation coefficients for 69 tissues and organs as a database file, and can be applied to various cases of inhomogeneity. The simulation and experimental results of the central axis percent-depth dose in an inhomogeneous phantom were in good agreement. This computer program will be useful for analysis on the behavior of X-rays and gamma rays in an inhomogeneous medium consisting of various tissues and organs, not only in radiotherapy treatment planning but also in diagnostic radiology and in the field treating radiation protection.
Hydrogen Release and Retention Dynamics of Amorphous Carbon Layers Exposed to a Hydrogen/Helium Plasma
Authors: Yoshida Shinji , Sugai Hideo , Toyoda Hirotaka
Published: February 2005

H2 and DH release was measured in a pulsed deuterium discharge over a carbon-thin-film deposited wall. The 300 eV D2
+ irradiation induced a large quantity of hydrogen release from carbon layers deposited by a H2+CH4 discharge. On the other hand, a strong pumping effect was observed for carbon layers deposited by a He+CH4 discharge. The pumping effect was attributed to interstitial vacancies in the films. Experimental evidence suggesting molecular formation by direct hydrogen abstraction was found. A dynamic model of hydrogen recycling on carbon layers is proposed. Corresponding calculations yield satisfactory agreement with observations. The pumping effect was always observed after conditioning of the wall with a helium glow discharge. The helium ion bombardment creates many interstitial vacancies after the hydrogen release.
Measuring Method for Ion Temperature by Asymmetric Probes in Magnetic Fields
Authors: Amemiya Hiroshi
Published: February 2005

A method for measuring the positive ion temperature by asymmetric probes in a strongly magnetized plasma, where the ion temperature is comparable to or higher than the electron temperature, is presented. The probe system consists of cylindrical and planar electrodes, the axis of the former being aligned parallel to and the surface of the latter perpendicular to the magnetic field. The ion temperature can be determined from the ratio of positive ion saturation currents.
Characterization of Multilayer GaAs/AlGaAs Transistor Structures by Variable Angle Spectroscopic Ellipsometry
Authors: Merkel Kenneth G. , Snyder Paul G. , Woollam John A. , Alterovitz Samuel A. , Rai A. K.
Published: February 2005

Variable angle of incidence spectroscopic ellipsometry (VASE) has been implemented as a means of determining layer thickness, alloy composition, and growth quality of GaAs/AlGaAs samples composed of relatively thick layers as well as superlattices. The structures studied in this work contained GaAs/AlGaAs multilayers with a superlattice “barrier” and were grown for later formation of modulation-doped field effect transistors (MODFETs). Sample modeling was performed by treating the superlattice as a bulk AlGaAs layer of unknown composition. Extremely good data fits were realized when five layer thicknesses and two alloy ratios were allowed to vary in a regression analysis. Room temperature excitonic effects associated with the e-hh(1), e-lh(1) and e-hh(2) transitions were observed in the VASE data.
Eddy Current Measurement on a Noncircular Model Shell
Authors: Sometani Taro , Toi Kazuo , Tanahashi Shugo , Shimomura Haruyuki , Midzuno Yukio
Published: February 2005

Toroidal eddy current density is measured on a 1/7 model of the aluminum shell (vacuum vessel) of the R-tokamak in order to confirm experimentally the computation done by eddy current analysis computer code EDDYTOR 6. Parallel and perpendicular components of magnetic induction measured with four sets of magnetic probes near the internal and external surfaces of the model shell are expanded in Fourier series of the poloidal angle of the shell. The eddy current density is determined from the measured components based on Ampère's law. Acceptable agreement is found between measurement and computation.
Wave Field Structures in a Toroidal Plasma at the Frequency Range of Alfvén Resonance
Authors: Takamura Shuichi , Mori Takashi , Okuda Takayoshi , Amagishi Yoshimitsu
Published: February 2005

Wave field structures at the frequency range of Alfvén resonance are studied in a toroidal plasma, laying stress on discrete Alfvén waves and local Alfvén resonances.