bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulated Single Electron to Single Photon Conversion in a Constant-Current-Driven pn Microjunction
Authors: Yoshihisa Yamamoto Yoshihisa Yamamoto , Seigo Tarucha Seigo Tarucha
Published: February 2005

The single electron-hole pair injection followed by the emission of a single photon is regulated with time separation τ=e/I in a constant-current-driven semiconductor pn microjunction. Oscillation of the junction voltage with a frequency f=I/e results from the coexistence of continuous uniform charging into a depletion layer via a high-impedance constant-current source and discrete thermionic emission of an electron into the active p-region. The principle is similar to the Coulomb blockade in an ultrasmall-capacitance tunnel junction. The proposed scheme is expected to open up an interesting new field of combined single electronics and single photonics.
Helium Liquefaction by a Two-Stage Gifford-McMahon-Cycle Refrigerator Using New Regenerator Material of Er3Ni
Authors: Kuriyama Toru , Takahashi Masahiko , Nakagome Hideki , Eda Tatsuji , Seshake Hikaru , Hashimoto Takasu
Published: February 2005

This paper describes the experimental results of the two-stage Gifford-McMahon (GM)-cycle refrigerator using a rare-earth compound as a regenerator material. The purpose of this study was to obtain a practical refrigeration capacity at 4.2 K, where the lowest temperature for a typical two-stage GM-cycle refrigerator is limited to 8 K. The technical point was to adopt erbium 3 nickel (Er3Ni) as a regenerator material. A refrigeration capacity of 0.28 W at 4.2 K was obtained, and the lowest temperature of 3.22 K was achieved. Helium liquefaction by the two-stage GM-cycle refrigerator was also confirmed for the first time.
Switching of Photon Helicities in the Hard X-Ray Region with a Perfect Crystal Phase Retarder
Authors: Hirano Keiichi , Ishikawa Tetsuya , Koreeda Satoshi , Fuchigami Katsuhiro , Kiyoshi Kanzaki Kiyoshi Kanzaki , Seishi Kikuta Seishi Kikuta
Published: February 2005

Alternate production of right- and left-handed circular polarizations was performed with a X-ray phase retarder of the transmission type in Bragg geometry. A piezo-driven oscillation stage was constructed for flipping the X-ray phase retarder around the Bragg angle by 10∼80 arcseconds in the bistable mode. Switching of photon helicities up to 100 Hz was achieved at λ=0.1463 nm
Characterization of HF-Treated Si Surfaces by Photoluminescence Spectroscopy
Authors: Konishi Tomohiro , Yao Takafumi , Tajima Michio , Ohshima Hisayoshi , Ito Hiroyasu , Hattori Tadashi
Published: February 2005

The properties of Si surfaces treated in HF solution of various concentrations are characterized by photoluminescence (PL). The Si surfaces treated in 4.5%-HF solution show higher PL intensity than thermally oxidized Si, indicating low surface recombination velocity of the HF-treated Si surface. The effect of ambient gases on HF-treated Si surfaces is studied. The temporal variation of PL intensity is such that it shows an abrupt rise in nitrogen followed by saturation, and the saturated intensity shows only a slight change with time. In air or in oxygen, HF-treated Si shows a gradual or fast rise in PL intensity followed by saturation for a short period and the PL intensity eventually decreases with time presumably due to generation of recombination centers. It is suggested that the oxidation of HF-treated Si induces the formation of recombination centers at the surface.
Magnetization and Anisotropy in Single Crystals of Tl-(1223) Phase of Tl-Sr-Ca-Cu-O System
Authors: Matsuda Shin-Pei , Soeta Atsuko , Doi Toshiya , Katsuzo Aihara Katsuzo Aihara , Tomoichi Kamo Tomoichi Kamo
Published: February 2005

The magnetization and intra-grain critical current density of Tl-(1223) phase of Tl-Sr-Ca-Cu-O system were investigated using single crystals. The intragrain J
c deduced from the magnetization was found to be 2-8×104 A/cm2 at 77 K and 1 T. The irreversibility field H
* was estimated to be ∼2 T for H//c-axis and >5 T for H⊥c-axis at 77 K.
Property and Structure of YBa2Cu3O7-x-Nb2O5 Composite
Authors: Hikichi Yasuo , Maruta Takashi , Suzuki Suguru , Miyamoto Masaaki , Okada Shigeru , Kudou Kunio
Published: February 2005

Nb2O5-doped YBa2Cu3O7-x
superconductors were prepared by heating at 950°C for 24 h in air and cooling to room temperature at a rate of 5°C/min in air. The bulk density and critical current density (J
c, 77 K and H=0 T) increased with increasing amount of Nb2O5≦0.5 wt%; up to 5.80 g/cm3 and 437 A/cm2 (sample thickness 1 mm), respectively. The critical temperature (T
c (zero)) was about 92 K. Experimentally we have succeeded in improving the superconducting properties, microstructure and degradation in moisture with addition of Nb2O5≦0.5 wt%.
Generation of Multifrequency Laser Emission by Injection of Two-Color Beam into Dye/Raman Composite Resonator
Authors: Imasaka Totaro , Yamanishi Seiichi , Shuichi Kawasaki Shuichi Kawasaki , Nobuhiko Ishibashi Nobuhiko Ishibashi
Published: February 2005

A two-color laser beam separated by 587 cm-1 is injected into a composite resonator consisting of a dye amplifier and two Raman cells pressurized with hydrogen. The efficiency of the two-color stimulated Raman effect is improved by increasing intracavity intensity. More than 10 rotational lines are generated simultaneously in the fundamental region as are many additional lines in the vibrationally shifted regions.
Reactive Ion Etching of Sputtered PbZr1-xTixO3 Thin Films
Authors: Saito Katsuaki , Choi Jai Ho , Takuya Fukuda Takuya Fukuda , Michio Ohue Michio Ohue
Published: February 2005

Reactive ion etching (RIE) by CCl4 plasma of sputtered PbZr1-x
Ti
x
O3 (PZT) thin film has been investigated. The etching rate of the as-deposited pyrochlore phase PZT is comparable to that of perovskite which was crystallized by 600°C annealing. Etching rate increased with increasing RF power and reached a plateau at 1.0 W/cm2. Highly anisotropic etching of PZT with little resist damage could be realized by reducing RF power.
One-Dimensional Conduction on the Cleaved Edge of InAs Quantum Wells
Authors: Haug R. J. , H. Munekata H. Munekata , L. L. Chang L. L. Chang
Published: February 2005

The cleaved edge of a GaAlSb/InAs/GaAlSb heterostructure contains a surface channel of accumulated electrons with the channel width given by the thickness of the InAs well. We achieved such structures and studied the temperature and magnetic-field dependence of the resistance along this edge. A strong negative magnetoresistance and well defined conductance fluctuations were observed, which were interpreted consistently by one-dimensional electron conduction.
Highly Preferred [111] Texture in Al Films Deposited on Ultrathin Metal Underlayers
Authors: Tsutomu Mitsuzuka Tsutomu Mitsuzuka
Published: February 2005

Al films on ultrathin metal underiayers 1-100 Å thick were fabricated on quartz and thermally oxidized Si substrates by the ion beam sputtering (IBS) technique. These Al films showed a highly preferred [111] texture and flat surfaces, as compared with the Al films deposited directly on the substrates. The texture in these Al films was related to the buffer layer structure and Al structure at the beginning of deposition. The metal underlayer textured into a double-rotated symmetry prevented the [111] texture of Al. The highly textured Al films had an amorphouslike structure at the beginning of Al deposition.
Shadowing Pattern Imaging with High-Energy Secondary Electrons Induced by Fast Ions
Authors: Kudo Hiroshi , Yoshida Eiji , Shima Kunihiro , Nagashima Yasuo , Ishihara Toyoyuki
Published: February 2005

High-quality images of the ion-beam shadowing effect in single crystals have been constructed with keV secondary electrons induced by 60-MeV oxygen ions. Under a high count rate (∼104 counts/s) of the electron yield, the time needed to measure the electron yield for about 3000 tilt angles, from which the shadowlng pattern for a 1°×1° angular space (for two independent tilts) was obtained, was 40-60 min when accumulating the electron yield up to 5000-10000 counts per tilt angle. This practical method for visualizing the crystal lattice is suitable for characterization of crystalline materials.
Phase Transitions in DC Discharges in SiH4
Authors: Makabe Yukio Yamaguchi
Published: February 2005

The entire V-I characteristics of a dc discharge in SiH4 were numerically obtained for the first time by solving a one-dimensional self-consistent fluid model with the computer-aided method based on the bifurcation theory. The glow discharge was found to exhibit a phase transition in non-equilibrium.
Two-Dimensional Measurement of Strain Distribution by Speckle Correlation
Authors: Noh Seokho , Ichirou Yamaguchi Ichirou Yamaguchi
Published: February 2005

Electronic speckle pattern correlation is applied to two-dimensional measurement of in-plane displacement and strain distributions. Speckle displacement distribution is determined by the peak of the 2-D cross-correlation of each block of images before and after surface deformation. From the distribution, we can derive the biaxial strain distributions with the sensitivity of millistrains.
Reproducible Fabrication Technique of Nanometric Tip Diameter Fiber Probe for Photon Scanning Tunneling Microscope
Authors: Pangaribuan Togar , Yamada Kazunobu , Jiang Shudong , Ohsawa Hisao , Motoichi Ohtsu Motoichi Ohtsu
Published: February 2005

Nanometric tip diameter fiber probes for photon scanning tunneling microscopes (PSTM) were fabricated by selective chemical etching of GeO2-doped optical fibers. The cone angle θ of the fiber probe tip was controlled by varying the doping ratio of the fiber core and the composition of the etching solution, and the standard deviation of the cone angle Δθ was within 0.5°. A fiber probe with θ=20° and tip diameter of less than 10 nm was fabricated. This is, to the authors' knowledge, the sharpest PSTM probe which has ever been reported.
Application of the Focused-Ion-Beam Technique for Preparing the Cross-Sectional Sample of Chemical Vapor Deposition Diamond Thin Film for High-Resolution Transmission Electron Microscope Observation
Authors: Tarutani Masayoshi , Yoshizo Takai Yoshizo Takai , Ryuichi Shimizu Ryuichi Shimizu
Published: February 2005

Atomic-scale observation of chemical vapor deposition (CVD)-diamond/silicon interface structures was successfully performed by applying a focused-ion-beam (FIB) technique for preparing the cross-sectional samples. Several severe conditions such as weak adhesion and extreme difference in sputtering yield have virtually prevented the proper processing of the interface cross sections by only the conventional method. A sample preparation procedure is proposed with some specific devices for extreme thinning, sufficient for high-resolution transmission electron microscope (HRTEM) observation, emphasizing the good potential for wider practical use.
Plasma Doping of Nitrogen in ZnSe Using Electron Cyclotron Resonance
Authors: Ito Satoshi , Masao Ikeda Masao Ikeda , Katsuhiro Akimoto Katsuhiro Akimoto
Published: February 2005

Nitrogen-doped p-type ZnSe films have been grown by molecular beam epitaxy using electron cyclotron resonance (ECR) plasma of N2. The nitrogen concentration in the film from 1×1017 to 6×1018 cm-3 has been controlled by adjusting both the aperture area of the ECR cell and the input microwave power. A net acceptor concentration as high as 4.5×1017 cm-3 was obtained by C-V measurements, and up to this level, the ratio of the net acceptor concentration to the incorporated nitrogen impurity concentration was almost unity. Donor-to-acceptor (DA) emission dominated the photoluminescence spectra at 4.2 K, and the emission intensity ratio of deep to DA emissions was less than 1/1000 for the ZnSe films with nitrogen concentrations less than 2×1018 cm-3.
Quantum Size Effect of Excitonic Band-Edge Luminescence in Strained Si1-xGex/Si Single Quantum Well Structures Grown by Gas-Source Si Molecular Beam Epitaxy
Authors: Fukatsu Susumu , Yoshida Hironobu , Usami Noritaka , Fujiwara Akira , Takahashi Yutaka , Ito Yasuhiro Shiraki
Published: February 2005

Strained SiGe/Si single quantum well structures were successfully grown by gas-source molecular beam epitaxy using disilane and germane. Quantum confined excitonic transitions of band-edge states dominated low-temperature photoluminescence (PL) spectra. The temperature dependence of PL intensity was in agreement with type-I quantum well formation. The quantum size effect was evidenced in these structures by the fact that the transition energy increased with decreasing well width.
Transport Critical Current Densities in Cation-Deficient Bi2(Sr, Ca)3Cu2O8+δ
Authors: Nomura Shunji , Hisashi Yoshino Hisashi Yoshino , Ken Ando Ken Ando
Published: February 2005

We demonstrate the effect of cation vacancy on flux pinning, or the critical current density in an applied field, by the transport method. The critical current density for a Bi-deficient composition is found to be 2-6 times greater than that for a stoichiometric one at 20 K in 5 T, while both samples have the same J
c values without a magnetic field and approximately the same H
c2 values. The data provide convincing evidence that the cation vacancies and/or their clusters function as effective pinning centers in the Bi2(Sr, Ca)3Cu2O8+δ system.
New Fabrication Method of Channel Optical Waveguides of Organic Crystal Using an Inorganic Photoresist
Authors: Tsuda Keiji , Kondo Takashi , Saito Fumiyo , Kudo Tetsuichi , Ryoichi Ito Ryoichi Ito
Published: February 2005

A microlithographic technique applicable to optical waveguides made of organic crystals is described. The new technique consists in the use of a water-soluble inorganic photoresist followed by wet or dry etching. Since the process is organic-solvent free and does not require high-temperature baking, it should be applicable to a wide range of organic crystals.
Strained-Layer Multi-Quantum Barriers for Reducing Hot Electron Leakage in Long-Wavelength Semiconductor Lasers
Authors: Irikawa Michinori , Sasaki Yoshitaka , Iga Masayuki Iwase
Published: February 2005

Multi-quantum barriers with a 1%-tensile-strained AlInAs/GaInAsP system are proposed for the purpose of suppressing the overflow leakage of hot electrons generated by the Auger effect. It is theoretically demonstrated for the first time that an effective barrier height of 1.2 eV, which is sufficient to confine hot electrons, can be obtained for 1.3 µm GaInAsP lasers. This implies that the overflow is almost suppressed, and dramatic improvement of high-temperature operation is expected.
Pigtailed Compact Tunable Wavelength-Selective Filter Using a Liquid Crystal for Wavelength-Division-Multiplexing Systems
Authors: Hirabayashi Katsuhiko , Kurokawa Takashi , Hanafusa Hiroaki , Ando Yasuhiro
Published: February 2005

A very compact, pigtailed, low-voltage-driven, electrically tunable wavelength-selective filter for wavelength-division-multiplexing systems is described. It consists of a fiber-coupled open resonator Fabry-Perot interferometer with a liquid crystal in the intracavity. To minimize the loss, a thermally diffused expanded core fiber is used. The filter has a wide tuning range of 50 nm, a bandwidth of 1.4 nm, a finesse of 40, and a loss of 3 dB at the mirror reflectivity of 95%.
External Electro-Optic Sampling Using Poled Polymers
Authors: Nagatsuma Tadao , Makoto Yaita Makoto Yaita , Mitsuru Shinagawa Mitsuru Shinagawa
Published: February 2005

External electro-optic sampling using poled polymers is discussed both theoretically and experimentally. Voltage sensitivity is calculated based on static electric-field analysis. A semiconductor laser diode is incorporated in the sampling system which has a temporal resolution of 20 ps and a voltage sensitivity of less than 20 mV/√Hz.
Thermal Annealing Effects on P-Type Mg-Doped GaN Films
Authors: Nakamura Shuji , Mukai Takashi , Masayuki Senoh Masayuki Senoh , Naruhito Iwasa Naruhito Iwasa
Published: February 2005

Low-resistivity p-type GaN films were obtained by N2-ambient thermal annealing at temperatures above 700°C for the first time. Before thermal annealing, the resistivity of Mg-doped GaN films was approximately 1×106 Ω·cm. After thermal annealing at temperatures above 700°C, the resistivity, hole carrier concentration and hole mobility became 2 Ω·cm, 3×1017/cm3 and 10 cm2/V·s, respectively. In photoluminescence measurements, the intensity of 750-nm deep-level emissions (DL emissions) sharply decreased upon thermal annealing at temperatures above 700°C, as did the change in resistivity, and 450-nm blue emissions showed maximum intensity at approximately 700°C of thermal annealing.
Highly Reliable Operation of InGaP/InGaAlP Multi-Quantum-Well Visible Laser Diodes
Authors: Watanabe Minoru , Okajima Masaki , Itaya Kazuhiko , Nitta Koichi , Yukie Nishikawa Yukie Nishikawa , Gen-ichi Hatakoshi Gen-ichi Hatakoshi
Published: February 2005

Highly reliable operation has been achieved for transverse-mode stabilized InGaP/InGaAlP multi-quantum-well (MQW) laser diodes with a selectively buried ridge waveguide structure emitting at 663 nm. These MQW laser diodes have been operating for more than 9,000 hours at an output power of 3 mW at 40°C. This achievement is attributed to the low threshold current and the excellent temperature characteristics (the maximum temperature for CW oscillation is 95°C) for such a short wavelength.
Device Quality SiO2 Deposited by Distributed Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition without Substrate Heating
Authors: Jiang Nan , Hugon Marie-Christine , Agius Bernard , Kretz Thierry , Plais Fran\ccois , Pribat Didier , Carriere Thierry , Puech Michel
Published: February 2005

The deposition of high electrical quality SiO2 films on Si wafers has been achieved without substrate heating, (T<∼100°C), using distributed electron cyclotron resonance (DECR) microwave plasmas. We have studied the effects of the reactant gas mixture composition (O2/SiH4) on the dielectric behavior of DECR SiO2. The electrical performances of both Si-SiO2 interfaces and SiO2 films in metal-oxide-semiconductor (MOS) structures were assessed by several characterization methods including critical field (E
c) evaluation, fixed charge densities (Q
ox) and interface traps densities (D
it) determinations. We report typical values of E
c around 6 MV·cm-1, and Q
ox and D
it densities around 2×1010 cm-2 and 3×1010 cm-2·eV-1 respectively. Thin film SOI-MOSFETs have also been fabricated to prove the DECR oxide quality.
Electric Field Effect in Al/SrTiO3/YBa2Cu3Oy Structure in the Normal State
Authors: Sakuta Ken , Awaji Takahiro , Matsui Ken-ichi , Hirano Takashi , Tatsuhiko Fujii Tatsuhiko Fujii , Takeshi Kobayashi Takeshi Kobayashi
Published: February 2005

The electric field effect in YBa2Cu3O
y
(YBCO) thin film was investigated by means of drain-current modulation measurements on Al/(100)SrTiO3/(001)YBCO metal-insulator-superconductor field-effect transistors (MISFETs) in the normal state. Sufficient current modulation was obtained in every specimen without exception. Moreover, even an YBCO channel with a semi-insulating phase could be changed to a conductive state by the field effect. The semiconductor band model explained the observed electric field effect semi-quantitatively.
Oscillation of Preferred Orientation with Thickness of Cu Layer in Ni-Fe/Cu Multilayers
Authors: Nakatani Ryoichi , Toshiyuki Dei Toshiyuki Dei , Yutaka Sugita Yutaka Sugita
Published: February 2005

In Ni-Fe/Cu multilayers with oscillatory magnetoresistance changes, oscillation of preferred orientation depending on Cu thickness has been observed. The preferred orientation oscillates between <100> and <111>. The period of the oscillation agrees with that for the oscillation of magnetoresistance ratio. When the multilayers have <100> preferred orientations, they show high magnetoresistance ratios.
Characterization of Ion Implantation Dose by Raman Scattering and Photothermal Wave Techniques
Authors: Nakashima Shin-ichi , Mizoguchi Kohji , Inoue Morio , Yoshida Masakatsu , Ishikawa Katsuya
Published: February 2005

Damage in silicon crystals implanted with various doses at different acceleration energies has been characterized by Raman scattering and photothermal wave techniques. Depth profiles of the damage in the implanted silicon crystals have been estimated from the Raman scattering measurements. The Raman scattering and photothermal wave measurements were compared. The results show that the quantities measured by the two techniques are strongly correlated at low dose levels and that they can be used to characterize damage induced by ion implantation.
Competition between Ferroelectric and Antiferroelectric Interactions Stabilizing Varieties of Phases in Binary Mixtures of Smectic Liquid Crystals
Authors: Isozaki Tadaaki , Fujikawa Takayuki , Takezoe Hideo , Fukuda Atsuo , Hagiwara Takashi , Suzuki Yoshiichi , Kawamura Ichiro
Published: February 2005

An electric field-temperature (E-T) phase diagram has been drawn for several binary mixtures of antiferroelectric liquid crystals using conoscopic observation. All the possible phases are SmA-SmCα
*-SmC*-new antiferroelectric phase-new ferrielectric phase-SmCγ
*-new ferrielectric phase-SmCA
*, some of which appear in the above regular order. Two Devil's staircases are necessary to elucidate systematic understanding of successive phase transitions among ferroelectric, ferrielectric and antiferroelectric phases: one is a staircase of SmCα
*(q
T) already discussed by Takanishi et al. and the other is a staircase of SmCA
*(q
T). Competition between an antiferroelectric interaction responsible for SmCA
* and a ferroelectric one for SmC* is considered to stabilize a variety of phases, SmCA
*(q
T).
Role of Hydrogen Radical Treatment in Nucleation of Nanocrystalline Silicon
Authors: Masanori Otobe Masanori Otobe , Shunri Oda Shunri Oda
Published: February 2005

We have investigated the nucleation process and crystallization process in the fabrication of nanocrystalline silicon (nc-Si). The nanocrystallization process consists of deposition of hydrogenated amorphous Si (a-Si:H) and treatment of hydrogen radicals. Nuclei of nanocrystallization are formed on the a-Si:H surface only if the atmosphere is hydrogen rich. Nuclei are not formed under the normal growth conditions of a-Si:H, not to be found either on the surface or inside as-grown a-Si:H. Growth of nc-Si is caused by hydrogen radicals diffusing through the a-Si:H layer to the nuclei.
Hydrogenating Effect of Single-Crystal Diamond Surface
Authors: Maki Tetsuro , Shikama Syozo , Komori Masaaki , Sakaguchi Yoshiyuki , Ken Sakuta Ken Sakuta , Takeshi Kobayashi Takeshi Kobayashi
Published: February 2005

Hydrogenation of diamond has been carried out using the electron-cyclotron-resonance microwave plasma chemical-vapor deposition apparatus. According to reflection high-energy and low-energy electron diffraction and X-ray photoelectron spectroscopy measurements, the natural- and synthetic-diamond surfaces maintained their crystallinity even after the hydrogenation. Seebeck effect measurement and the temperature dependence of the resistance revealed an appearance of deep acceptor levels in the hydrogenated diamond layer. The diffusion depth of the hydrogen by the plasma treatment (2 h, 830°C) was roughly estimated to be ∼0.6 µm from the drain current-voltage characteristics of a rudimentary MISFET using the hydrogenated diamond.
Effect of Phosphorus Doping and Deposition Temperature on the Deep-Level Transient Spectra in a-Si:H
Authors: Nakata Jun-ichi , Tsuchida Kazuhito , Inuishi Shozo Imao
Published: February 2005

Both voltage- and photoinjected deep-level transient spectroscopy measurements were performed on phosphorus-doped a-Si:H films to clarify the nature of a hole trap state located at E
v+0.6 eV, which was extinguished by light soaking. The density of trapped holes at the state in as-deposited films was weakly dependent on the phosphorus doping concentration. However, it decreased with increasing deposition temperature of the films. These results suggest that the hole trap state is related to weak silicon bonds which act as a precursor to optical degradation.
Geometric Phase in a System of Two Quarter-Turn Optical Fibers
Authors: Lee Y. S. , Kong H. J. , Kwon J. K. Kim
Published: February 2005

The value of the geometric phase observed with two disconnected uniformly wound quarter-turn optical fibers and a linear polarizer between them is quite different from that measured with a uniformly wound half-turn optical fiber, although evolution curves in the propagation vector sphere for the above-mentioned cases are the same. We try to analyze the experimental data by applying the geodesic rule separately to each evolution curve for the two quarter-turn fibers, and the theoretically obtained values are in good agreement with the experimental data.
Measurement of Minority-Carrier Drift Velocity in Quantum Well Structures by Photoluminescence Intensity Correlation Method
Authors: Okuno Eiichi , Hori Tetuya , Sawaki Nobuhiko , Höpfel Isamu Akasaki
Published: February 2005

A new time-of-flight (ToF) method is proposed for the study of transport properties in low-dimensional systems. By analyzing the photoluminescence intensity correlation curves under external fields, the drift velocity of excess carriers in quasi-1-dimensional (1D) quantum wells is determined. The drift velocity in a p-type doped GaAs/AlGaAs quasi-1D structure is determined in various electric fields, and the electron mobility is estimated as 4800 cm2/V·s at 300 K, which is in agreement with that in a conventional two-dimensional electron gas (2DEG) structure.
Infrared to Visible Upconversion of Er3+ Doped in a Chloride Matrix
Authors: Wang Junichi Ohwaki
Published: February 2005

Efficient infrared-to-visible upconversion is achieved in the YCl3-ErCl3-PbCl2-KCl phosphor system. Under 1.52 µm laser diode (LD) excitation, a specimen containing 20 mol% Er3+ dopant emitted bright green luminescence, and the fluorescence lines at 410 nm, 550 nm and 660 nm reached the respective intensities of 48, 20 and 9 times those of conventional Er3+-doped fluoride. A strong upconversion fluorescence at 496 nm due to the 4F7/2-4I15/2 transition is observed in the chloride phosphor under 0.972 µm LD excitation. This is ascribed to the direct two-step excitation process which occurs when multiphonon relaxation is suppressed in the chlorides.
Relaxation of Two-Dimensional Visco-Elasticity in a Long Chain Fatty Acid Monolayer Expanded at the Air/Water Interface
Authors: Keiji Sakai Keiji Sakai , Kenshiro Takagi Kenshiro Takagi
Published: February 2005

Two light scattering techniques developed for surface wave spectroscopy by the authors were used to study the two-dimensional visco-elastic properties in a mono-molecular film of tetradecanoic acid spread on a water surface. The spectra of the surface viscosity and elasticity obtained in the 10 kHz-1 MHz range revealed, as the first instance of such an observation, a relaxation which is widely distributed around 100 kHz. Moore and Eyring's theory of surface viscosity is useful for describing the present results, and its prediction for the relaxation frequency was consistent with the above value.
In Situ Observation of Gold Adsorption onto Si(111)7×7 Surface by Scanning Tunneling Microscopy
Authors: Hasegawa Tsuyoshi , Sumio Hosaka Sumio Hosaka , Shigeyuki Hosoki Shigeyuki Hosoki
Published: February 2005

Gold adsorption onto a Si(111)7×7 surface is studied in situ by Scanning Tunneling Microscopy (STM). Gold is deposited onto the Si(111)7×7 surface, kept at 500°C during the STM observation. The 5×2 structure grows at a step edge and expands towards both the higher and lower terraces. Si islands are also formed during the gold deposition. These phenomena are explained by the production and migration of excess Si atoms during the phase transition from the 7×7 to the 5×2 structure.
Fibrous Textured Surface of an Ultrafiltration Membrane Delineated by Atomic Force Microscope
Authors: Miwa Tetsuya , Yamaki Mariko , Yoshimura Hideyuki , Satoshi Ebina Satoshi Ebina , Kuniaki Nagayama Kuniaki Nagayama
Published: February 2005

The resolution of atomic force microscopy (AFM) is limited by the aspect ratio and bluntness of the currently available probe tips. With the use of electron beam deposition, the apex of an existing tip was modified, resulting in a sharp probe tip with a high aspect ratio. Application of AFM to an ultrafiltration membrane, using the modified tip, revealed numerous pores in a randomly aligned fibrous matrix. Such features were not depicted either by AFM with a commercial cantilever or by scanning electron microscopy.
Glancing Angle Dependence of the X-Ray Emission Measured under Total Reflection Angle X-Ray Spectroscopy (TRAXS) Condition during Reflection High Energy Electron Diffraction Observation
Authors: Yamanaka Toshiro , Hanada Takashi , Daimon Shozo Ino
Published: February 2005

We measured the glancing angle (θg) dependence of the X-ray emission from Si(111)-√3×√3-Ag and α-√3×√3-Au surfaces during Reflection High Energy Electron Diffraction observation under the Total Reflection Angle X-ray Spectroscopy condition. The characteristic X-rays AgL and AuM decreased according to 1/sin θg. The function 1/sin θg is easily understood in terms of Ag and Au atoms located at the top layer of the surface. The SiK and the bremsstrahlung showed broad peaks around 8°. These trends of the curves are explained by an analysis using Monte Carlo electron trajectory simulation. By measuring the glancing angle dependence we can easily distinguish whether or not a specific kind of atom is confined at the top layer of the surface.
Photoexcitation Effects on Scanning Tunneling Microscope Images of Surface Oxide Layer of Titanium
Authors: Sugimura Hiroyuki , Noboru Kitamura Noboru Kitamura , Hiroshi Masuhara Hiroshi Masuhara
Published: February 2005

Scanning tunneling microscopy (STM) was applied to observe a surface oxide layer of titanium in air. When a sample bias voltage was set at -0.2 V, the STM tip penetrated into the surface oxide damaged the sample, while clear and stable images of the surface TiO2 layer were obtained under photoexcitation. The results were discussed in terms of enhanced electric conductivity of the oxide layer under photoexcitation.
The Relationship of the Silicon Surface Roughness and Gate Oxide Integrity in NH4OH/H2O2 Mixtures
Authors: Meuris M. , Verhaverbeke S. , Mertens P. W. , Heyns M. M. , Hellemans L. , Bruynseraede Y. , Philipossian A.
Published: February 2005

In this study some recent findings on the cleaning action of the NH4OH/H2O2 (SC1) step in a pre-gate oxidation cleaning (RCA cleaning) are given. An important parameter in this mixture is the NH4OH/H2O2 ratio. The Fe contamination on the silicon surface after this cleaning step is found to increase upon decreasing the NH4OH/H2O2 ratio. This can be attributed to the incorporation of Fe in the chemical oxide, grown by the hydrogen peroxide. The particle removal efficiency of the cleaning step is found to decrease upon decreasing the NH4OH/H2O2 ratio. On the other hand, using a lower NH4OH concentration results in a less severe silicon surface roughening. It is demonstrated in this study that the NH4OH/H2O2 ratio during the SC1 step of the cleaning is the determining parameter for the breakdown properties of a gate oxide. A (0.25/1/5) NH4OH/H2O2/H2O mixture at 75°C in our experimental conditions is suggested to be the best compromise between particle removal and surface roughness during the SC1 step.
Direct Observation of Self-Limiting Gallium Deposition on GaAs during Laser-Atomic Layer Epitaxial Processing
Authors: Simko Jeffry P. , Meguro Takashi , Iwai Sohachi , Ozasa Kazunari , Hirata Akira , Aoyagi Yoshinobu , Sugano Takuo
Published: February 2005

The first real-time observation of the gallium arsenide surface during laser-assisted atomic layer epitaxy (LALE) is presented. Self-limiting decomposition of trimethylgallium (TMG) to gallium on (001) GaAs at temperatures between 340°C-390°C during LALE processing was observed by surface photo-absorption (SPA) measurements. The self-limiting deposition is due to an equilibrium between alkylgallium species arriving at the surface and those desorbing from the surface during simultaneous TMG and laser exposure. When the TMG flow is stopped, the remaining alkyl species desorb from the surface leaving a self-limited deposition of gallium behind.
Controllable Superconducting Nb Long Microbridge by Low Frequency, and Its Resonant Characteristics
Authors: Keiji Tsukada Keiji Tsukada , Toshimitsu Morooka Toshimitsu Morooka
Published: February 2005

A Nb superconducting microbridge is fabricated, 40-µm long, less than 0.25-µm wide and 0.1-µm thick. Four-terminal measurement of the I-V characteristics reveals hysterisis in the I-V curve. The microbridge has an excess current over its current in its normal state. Frequency resonance appears over the range of a few hundred kiloherz by electromagnetic wave radiation. The I-V characteristics show that critical current I
c is depressed, and as radiation power increases I
c decreases. This phenomenon is thought to be due to resonance of quasiparticles in the microbridge, and to resonance restricting the supercurrent.
Spin-Spin Relaxation Time of E' Centers in Neutron-Irradiated Quartz (SiO2) and in Fault Gouge
Authors: Ikeya Motoji , Kohno Hideo , Mizuta Shin Toyoda
Published: February 2005

Microwave power dependence of electron spin resonance (ESR) and spin-spin relaxation times (T
2) of E′ centers (an electron in an oxygen vacancy) in quartz (SiO2) were studied for (1) grains annealed at 600°C and irradiated by neutrons, (2) grains mechanically crushed and gamma-ray irradiated, and (3) the natural fault gouge. Spin-spin relaxation times of 29.6 µs, 10.5 µs and 17.4 µs were obtained for the above samples with the tendency of saturation behavior. E′ centers in the fault gouge will be localized around dislocations introduced by faulting.
Highly Sensitive Measurement of Doppler-Shift with a Microchip Solid-State Laser
Authors: Kenju Otsuka Kenju Otsuka
Published: February 2005

Intensity modulation of a LiNdP4O12 microchip solid-state laser by reflected scattered light from a moving object is investigated experimentally and numerically. Ultra-high sensitivity detection of Doppler-shift and application to a laser velocity meter are demonstrated.
Narrow Linewidth Characteristics in Tunable Twin-Guide Distributed Feedback Laser Diodes
Authors: Hamada Madoka , Yamamoto Eiji , Suda Kazuya , Seiji Nogiwa Seiji Nogiwa , Tokukoh Oki Tokukoh Oki
Published: February 2005

A sub-MHz (467 kHz) spectral linewidth for a tunable twin-guide distributed feedback laser is achieved for the first time. The linewidth is kept to less than 9 MHz during a continuous tuning range of 2 nm. The measured linewidth can be expressed separately by a power-dependent term and a power-independent term. The linewidth during tuning is separated into two terms experimentally for the first time. The power-dependent term conforms to the estimated linewidth during tuning. The experimental results indicate that linewidth broadening during tuning is mainly caused by the power-independent factor.
Preparation of YBaCuO Film on a MgO Substrate by Chemical Vapor Deposition at 650°C
Authors: Lee Hee-Gyoun , Park Soon-Dong , Yang Suk-Woo , Shin Hyung-Shik , Dong-Yeon Won Dong-Yeon Won
Published: February 2005

YBaCuO films were prepared on a MgO(100) single-crystal substate at 650°C by a chemical vapor deposition method. The films were fabricated at various oxygen partial pressures of 0.516 Torr, 0.121 Torr, 0.0126 Torr and 0.009 Torr. Superconductivity above liquid nitrogen temperature (T
c,0=87 K and T
c,onset=91 K) was obtained for the film prepared at 0.0126 Torr. J
c(77 K, 0 T) was measured as 3×104 A/cm2. A two-dimensionally well-aligned microstructure was observed for the film prepared at 0.0126 Torr.
Atomic Layer Epitaxy of ZnSe-(CdSe)m(ZnSe)n Short-Period Superlattice Multiple Quantum Wells
Authors: Peng Zhongling , Li Jie , Yao Wenhua , He Li , Xingyu Cheng Xingyu Cheng , Shinxi Yuan Shinxi Yuan
Published: February 2005

Atomic-layer epitaxy growth of ZnSe-(CdSe)
m
(ZnSe)
n
short-period superlattice multiple quantum wells (SPSQWs) has been investigated. High crystalline quality has been achieved in this system by the introduction of an ultra-short-period (CdSe)
m
(ZnSe)
n
superlattice in the well to replace a ZnCdSe alloy, due to the success in solving problems associated with mismatch dislocations and alloying. Material characterizations have been performed by X-ray diffraction and photoluminescence. The critical thickness of CdSe on ZnSe has been determined to be less than four monolayers.
Two-Domain 80°-Twisted Nematic Liquid Crystal Display for Grayscale Applications
Authors: K. H. Yang K. H. Yang
Published: February 2005

Iso-contrast curves as a function of viewing angle between eight gray levels in sequence have been investigated for two-domain twisted nematic liquid crystal displays. The optimal twist angle has been found to be approximately 80°. The two-domain 80°-twisted nematic LCD shows a large viewing zone of ±45° in the vertical and ±60° in the horizontal directions without grayscale reversals. We have demonstrated a simple fabrication method which requires only one photo-lithographic exposure and a total of three independent rubbing directions on two polyimide-coated substrates.
DC Green Electroluminescence of Al-CuGaS2 Diode
Authors: Kobayashi Satoshi , Youichi Momiyama Youichi Momiyama , Futao Kaneko Futao Kaneko
Published: February 2005

The dc green electroluminescence (EL) spectra observed at the Al-CuGaS2 diode are described over the temperature range of 100-220 K. The EL is just correspondent with the main EL of the Al-ZnS-CuGaS2 heterojunction diode. This confirms our previous proposal for the green EL from the Al-ZnS-CuGaS2 heterojunction diode that it originates from the CuGaS2 crystal, not from the ZnS film. Some possibilities for the electron injection from the Al electrode are also discussed in association with the current-voltage characteristics.
Enhanced Photochromism in the Hybrid Film of Tungstic Acid and Polyethylene Glycol
Authors: Kuboyama Keiichi , Kazuhiro Hara Kazuhiro Hara , Kazumi Matsushige Kazumi Matsushige
Published: February 2005

The mixing of polyethylene glycol (PEG) with tungstic acid induced drastic enhancement of the photochromism as well as better film formation. The photochromic sensitivity to UV light increased with the amount of PEG added. In addition, the coloration by the irradiation of UV light in the hybrid films faded with heating, but was recovered by the re-exposure of the lights.
Structural Study on Pressure-Induced Phase Transition from β-Po Type to BCC in Selenium at 140 GPa
Authors: Akahama Yuichi , Mototada Kobayashi Mototada Kobayashi , Haruki Kawamura Haruki Kawamura
Published: February 2005

High-pressure X-ray diffraction study of selenium has been carried out in the megabar pressure region. The phase transition from a β-Po type to a bcc structure was observed at about 140 GPa. Relative volume reduction, -ΔV/V
0, at the transition, was less than 0.2%. At 150 GPa, the lattice constant of the bcc phase, a
bcc, was 2.7941(3) Å and relative volume, V/V
0, reached 0.4. The transition has been discussed from a crystallographical viewpoint in terms of structural parameters, which indicate the rhombohedral distortion.
Generation Mechanism of Tensile Stress in a-Si1-xNx:H Films Prepared by Afterglow Plasma Chemical Vapor Deposition Technique
Authors: Nagayoshi Hiroshi , Hoe Wong Chee , Ueno Tomo , Kamisako Koichi , Kuroiwa Koichi , Shimada Toshikazu , Yasuo Tarui Yasuo Tarui
Published: February 2005

Amorphous silicon nitride (a-Si1-x
N
x
:H) films have been deposited by microwave afterglow plasma of NH3. Residual stress and its changes due to annealing were investigated in relation to the hydrogen bond density in the films. The total hydrogen bond density and the change in stress due to annealing show a minimum value when the residual tensile stresses in the films reach a maximum value. The tensile stress decreases and the change in stress due to annealing increases with decrease of deposition temperature. These phenomena can be consistently explained using the gas evolution model.
Molecular Orientation Changes in Thin Solid Films of Long-Chain Compounds Induced by Thermal Treatment
Authors: Yamanaka Mikihiro , Sato Kiyotaka , Inaoka Kimio , Yase Kiyoshi
Published: February 2005

A long chain compound, calcium stearate ((CH3(CH2)16COO)2Ca), was deposited on the substrates of KCl, mica and amorphous carbon film kept at 25°C and then annealed at 50-115°C for several minutes in 1×10-4 Pa. Molecular orientations drastically changed from parallel to perpendicular with respect to the substrate surface. The activation energies for molecular orientation changes were estimated as 76 kJ/mol on KCl and 23 kJ/mol on mica and carbon film.
Diffusion of Gallium Vacancies from Low-Temperature-Grown GaAs
Authors: Ohbu Isao , Mitsuharu Takahama Mitsuharu Takahama , Yoshinori Imamura Yoshinori Imamura
Published: February 2005

Diffusion of crystalline defects from low-temperature-grown GaAs (LT-GaAs) during annealing at 600°C has been studied. Gallium vacancies diffuse from the LT-GaAs layer into an adjacent Si doped GaAs layer, degrading the electrical characteristics of the Si-doped GaAs. An Al
x
Ga1-x
As (x>0.3) barrier inserted between the LT-GaAs and the Si-doped GaAs effectively suppresses the diffusion of gallium vacancies from the LT-GaAs.
Simulation of the Effect of Emitter Doping on the Delay Time in AlGaAs/GaAs Heterojunction Bipolar Transistors
Authors: Kusano Chushiro , Masuda Hiroshi , Mochizuki Kazuhiro , Hiroshi Mizuta Hiroshi Mizuta , Ken Yamaguchi Ken Yamaguchi
Published: February 2005

The influence of the emitter doping level (5×1017-5×1018 cm-3) on the delay time in AlGaAs/GaAs heterojunction bipolar transistors is investigated using numerical simulation based on a drift-diffusion model. The results reveal that the emitter delay time (τE) decreases with higher emitter doping (5×1018 cm-3), allowing a very short delay time (<0.2 ps). It is shown that τE is affected by excess charge accumulation due to the built-in electric field at the cap/emitter (n+-GaAs/n-AlGaAs) isotype heterojunction, more than at the emitter/base (n-AlGaAs/p+-GaAs) heterojunction, under high-current operation (>104 A/cm2).
Preparation of ZnS:Tm Films by Metalorganic Chemical Vapor Deposition Using Thulium β-Diketonates as Dopants
Authors: Hara Kazuhiko , Tominaga Satoshi , Takano Atsushi , Dantani Kyoji , Junji Yoshino Junji Yoshino , Hiroshi Kukimoto Hiroshi Kukimoto
Published: February 2005

ZnS:Tm films have been successfully prepared on glass substrates by metalorganic chemical vapor deposition (MOCVD) by the use of β-diketonates of Tm, tris(dipivaloylmethanato)thulium and tris(hexafluoroacetylacetonato)thulium, as the dopants. The Tm concentration can be controlled by the Tm source temperature. Undoped and lightly Tm-doped films are polycrystals of zinc blende structure with a preferential growth direction oriented towards <111>. On the other hand, heavily Tm-doped films have been found to crystallize in the wurtzite structure. The ZnS:Tm films show blue photoluminescence and electroluminescence due to the transitions of f-electrons in Tm3+ ions.
Development of Excess Y2BaCuO5 during Directional Growth of YBa2Cu3Ox
Authors: Kim Wonbaek , Shim Gunjoo , Jang Daekyu , No Changyoul Suh
Published: February 2005

The superconducting compound YBa2Cu3O
x
was prepared by directional solidification. Composition analysis revealed that directionally grown YBa2Cu3O
x
was heavily enriched with yttrium. When part of YBa2Cu3O
x
melted to Y2BaCuO5 and liquid, Ba-Cu rich liquid wetted the surfaces and pores of adjacent YBa2Cu3O
x
. As a result, the melt zone contained Y2BaCuO5 in excess. These excess Y2BaCuO5 particles are believed to eliminate the unreacted liquid phases which otherwise remain impairing superconducting properties.
Enhancement of the Transport Critical Current Density by Electron Irradiation in a Bi1.5Pb0.5Sr2Ca2Cu3Ox Ceramic
Authors: Shiraishi Kensuke , Sakamoto Hiroshi , Yano Koichi , Otoguro Yasuo
Published: February 2005

A Bi1.5Pb0.5Sr2Ca5Cu3O
x
ceramic was sequentially irradiated with 3 MeV electrons at a dose rate of 8.9×1015 m-2·s-1 up to a dose of 1.8×1020 m-2 at ambient temperature, and the transport critical current density was measured under a magnetic field up to 0.64 T as a function of temperature. The critical current density in zero field was increased by irradiation up to a dose of 1.8×1020 m-2 at temperatures below 45 K. The critical current dcnsity measured under magnetic fields was also enhanced by electron irradiations, which was larger at lower temperature and lower magnetic field up to 0.16 T.
Transport Critical Current Density in a Bi1.5Pb0.5Sr2Ca2Cu3O10 Ceramic
Authors: Shiraishi Kensuke , Sakamoto Hiroshi , Yano Koichi , Otoguro Yasuo
Published: February 2005

The transport critical current density of a Bi1.5Pb0.5Sr2Ca2Cu3O10-y
ceramic was measured as a function of temperature in the range from 90 to 20 K under a magnetic field up to 1.0 T. A critical current density of 2.0 MA·m-2 at 77 K in zero field increased almost linearly to 8.3 MA·m-2 with a decrease in temperature to 50 K, and then to 11.7 MA·m-2 at 20 K. When the current density was measured at 20 K in the zero field after applying a magnetic field of 1.0 T at low temperature, the critical current decreased to 8.6 MA·m-2. The decrease in the critical current density induced by the magnetic field at 20 K recovered gradually with an increase in temperature to approximately 70 K.
Passivation of P-Type Dopants in GaAs by Process Induced Hydrogenation and Reactivation by Thermal Annealing
Authors: Nakajima Osaake , Koichi Nagata Koichi Nagata , Takashi Makimura Takashi Makimura
Published: February 2005

The sheet-resistance of a carbon-doped p-type GaAs epitaxitial layer was increased by silicon nitride plasma-chemical-vapor-deposition (PCVD) using SiH4 and N2 gases. This increase was strongly correlated with the increase in hydrogen concentration in the GaAs epitaxial layer, suggesting that the acceptor arising from the carbon impurity is passivated by hydrogenation during silicon nitride deposition. Thermal annealing in N2 gas at 500°C reactivated the passivated acceptor. On the other hand, acceptor passivation was not observed for beryllium-doped p-type GaAs under the same process conditions. The difference in behavior between carbon and beryllium may be due to the difference in dissociation energy of hydrogen-dopant complexes.
Polycrystalline GaAs Made by Selective Deposition and Its Optical Properties
Authors: Tokunaga Hiroyuki , Hideshi Kawasaki Hideshi Kawasaki , Yumie Yamazaki Yumie Yamazaki
Published: February 2005

Polycrystalline GaAs was grown by selective deposition using metalorganic chemical vapor deposition. The nucleation of polycrystalline GaAs took place on a small seed of polycrystalline Si on the substrate and overgrowth proceeded to SiO2 which covered the substrate. The photoluminescence (PL) intensity from polycrystalline GaAs was in inverse proportion to the seed size. When the seed size was 1 µm2, the PL intensity became six times larger than that for the polycrystalline GaAs on the seed size of 64 µm2. We fabricated a light-emitting diode (LED) on the amorphous substrate (SiO2) using polycrystalline GaAs deposited on the 1-µm2-area seed.
Chemical Vapor Deposition of Cu Film on SiO2 Using Cyclopentadienylcoppertriethylphosphine
Authors: Chichibu Shigefusa , Yoshida Nobuhide , Higuchi Hirofumi , Satoru Matsumoto Satoru Matsumoto
Published: February 2005

Chemical vapor deposition of Cu film on SiO2 has been studied using cyclopentadienylcoppertriethylphosphine (C5H5CuP(C2H5)3), which contains no oxygen atom itself. The deposited Cu films had complete (111) preferred orientation for deposition temperatures below 450°C. From Auger electron spectroscopy measurements, no simultaneous incorporation of oxygen during the deposition has been confirmed. Relatively low temperature deposition is preferable to reduce the condensation of deposited Cu.