bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Observation of Localized Strain Pulsation Generated in the Plastic Deformation Process by Electronic Speckle Pattern Interferometry
Authors: Toyooka Satoru , Widiastuti Rini , Zhang Qingchuan , Kato Hiroshi
Published: October 2002

An electronic speckle pattern interferometry (ESPI) system, which makes it possible to observe dynamic phenomena, was applied to investigate the plastic deformation process in tensile experiments of aluminum alloy samples. The dynamic behavior of a strain-localized band which propagated through a specimen was thoroughly investigated. A pulsating fringe variation of the order of 1 Hz was discovered to be the fine structure of the propagating band. Fringe pulsation is caused by localized strain pulsation which suggests that the stress relaxation process propagates periodically with a time constant which governs the dissipative characteristics of a heterogeneous material.
Simulation of Step Frequency Imaging Technique Processed by the Least Squares Method
Authors: Tanaka Kazuo , Iizuka Keigo
Published: October 2002

The least squares method was applied to the step frequency technique for processing two-dimensional images. The advantage of the method is that once the QR decomposition of the matrix is performed for a given target, it is not necessary to repeat this computation for other targets. Numerical simulations which show the validity of the method have been presented.
Influence of Electron Density Distribution at the Electron Source in a Projection Exposure System
Authors: Kotera Masatoshi , Sakai Masahiko , Shimizu Isao , Tomo Youichi , Yoshida Akira , Kojima Yoshinori , Yamabe Masaki
Published: October 2002

The influences of the size and the density distribution at the electron source on the electron exposure characteristics in a projection lithography system are studied. The individual electron trajectory is traced in a realistic optical system considering the Coulomb interaction effect among electrons along with the lens aberration to discuss these effects quantitatively. The uniform, the Gaussian, and the ring density distributions are calculated as the spatial distribution of the electron density at the source. Based on the results obtained above, the most preferable conditions for the electron source are clarified for the projection exposure system. A simple equation is obtained for estimating the most preferable diameter and the broadness of the ring. If the ring source is used in the projection electron optical system, it is shown that the minimum displacement distance at the wafer surface can be largely improved, and it may be approximately 50 nm at the acceleration voltage of 50 kV with the current density of 10 A/cm2.
Nondestructive Depth Profiling by Specimen Tilting Using Scanning Electron Microscope-Energy Dispersive X-Ray Spectrometer
Authors: Ogai Keiko , Ueda Kazuyuki
Published: October 2002

In order to perform nondestructive depth profiling, a glancing incidence method has been attempted by specimen tilting using a scanning electron microscope-energy dispersive X-ray spectrometer. Two-dimensional (2D) compositional mapping was carried out using double/triple-layered specimens at various tilt angles, namely glancing incidence angles. It was confirmed that the visibility of the compositional map clearly varied depending on the incidence angle and the depth distribution. The X-ray intensity dependence on the incidence angle at each observation point is obtained from a series of compositional maps and that enables qualitative 2D depth profiling of spatial resolution in the micrometer range and depth resolution of a few tens of nm.
Film Density Dependence of Polymethylmethacrylate Ablation under Synchrotron Radiation Irradiation
Authors: Fujimura Tsuyoshi , Kuroki Yukinori , Hisakado Tohru , Ikeda Akihiro , Hattori Reiji , Hakiai Yousuke , Hidaka Masanori , Choi Jae-Young , Chang Suk Sang
Published: October 2002

Variations in the etch depth and refractive index of polymethylmethacrylate (PMMA) films of different molecular weights after synchrotron radiation (SR) irradiation are investigated. Reduction of the PMMA film molecular weight, density and thickness are observed after SR irradiation. The amount of film thickness loss depends on not only initial molecular weight but also film density. The PMMA density difference at the start of SR exposure affects the etch depth after SR ablation.
Pulsed Power Technology and Its Applications at Extreme Energy-Density Research Institute (EDI), Nagaoka
Authors: Yatsui Kiyoshi , Jiang Weihua , Suematsu Hisayuki , Harada Nobuhiro , Imada Go , Suzuki Tsuneo , Kinemuchi Yoshiaki , Yang Sung-Chae
Published: October 2002

Recent activities conserning pulsed power technology and its applications are reviewed. Using high-density ablation plasma produced due to the short range of an ion beam in targets, we have successfully prepared crystallized B4C thin films by ion-beam evaporation, which are characterized by hardness, wear resistance, and stability at high temperatures. Fullerenes have been prepared as well. Ultrafine nanosize powders were synthesized by pulsed wire discharge. Flue gas treatment of NO
x
was achieved by intense pulsed relativistic electron beam. Foil acceleration was observed to be ∼8 km/s at the ablation pressure of 13 GPa. Pulsed laser deposition was used to prepare (Cr1-x
, Al
x
)N films. The AlN solubility limit was found to be 77 at.% AlN. The hardness of the films increases with x up to 0.75, and decreases rapidly due to their being amorphous in structure. A highly repetitive, new pulsed power generator is operational, with the specifications of 400 kV, 13 kA, 120 ns, and 1 pps.
Characterisation of Electron Beams Produced by Crossed-Field Secondary Emission Diodes
Authors: Saveliev Yuri M. , Sibbett Wilson , Parkes David M.
Published: October 2002

The crossed-field secondary emission (CFSE) diode is a compact, simple and cheap source of tubular electron beams. The physical mechanism of current production is a self-sustained secondary electron emission. In this study, voltage-current, temporal and spatial characteristics of electron beams produced by axisymmetric and non-axisymmetric CFSE diodes have been investigated. The highest current obtained at the present stage of research is ∼240 A generated with a diode having a cathode diameter of 64 mm and operated with an applied voltage of ∼20 kV. The electron beams are characterised by extremely high temporal stability and narrow (∼1.4 mm) radial current density distributions. In axisymmetric diodes, the azimuthal current density distribution j(φ) is uniform but this is only achieved by careful adjustment of the cathode-anode assembly. In non-axisymmetric diodes, the j(φ) distributions are strongly non-uniform and depend not only on the magnitude but also on the direction of the magnetic field.
Calculation of Ion Sputtering Yield of Solid Sample with Cylindrical Cavities and Rectangular Trenches on the Surface
Authors: Bondarenko G. G. , Kristya V. I. , Prassitski V. V.
Published: October 2002

Analytical expressions which determine the probability of sputtered atom escaping from a cylindrical cavity and a rectangular trench on the target surface bombarded by an ion beam are obtained for sputtered atoms cosine and over-cosine angle distributions. It is shown that the sputtering yield can be substantially reduced by creation a relief of cylindrical cavities on the sputtered surface.
Code for Studying Physical Processes in Magnetic Self-Insulation Diodes
Authors: Valentin Chorny Valentin Chorny , Anatoly Pashchenko Anatoly Pashchenko , Ivan Shapoval Ivan Shapoval , Valery Novikov Valery Novikov
Published: October 2002

We present a solver for magnetic self-insulation diodes (SMID) Code, developed for studies on high-current relativistic diodes, and supply examples of its applied usage. In order to analyze experimental data and numerical simulation results an in-circuit approach has been developed with an appropriate theory elaborated.
The Resistance of a High-Current Pulsed Discharge in Nitrogen
Authors: Takaki Koichi , Akiyama Hidenori
Published: October 2002

The primary objective of this article is to propose a method for accurate prediction of the resistance of a high-current pulsed arc discharge. The nine theoretical and empirical formulas of arc resistance, which have been reported, are compared using the measured values of arc resistance for unipolar arc discharges in nitrogen gas with various maximum currents. The arc resistance was obtained accurately by solving the circuit equation using measured values of the current and breakdown voltage. Each arc resistance equation was numerically evaluated and then normalized by the arc resistance at the time of maximum arc current. The results indicated that Kushner et al..'s predictions [rf1] provided the best overall results with the lowest accumulation of errors. Additionally, the measured arc resistance takes the minimum value at the time of arc maximum current, and the value can be expressed by a function of the maximum current.
Optical Observation of the Instability in Microsecond Gas-Puff Z-Pinch Plasmas
Authors: Katsuki Sunao , Murayama Koichi , Akiyama Hidenori
Published: October 2002

The occurrence of fluid instabilities in gas-puff z-pinch plasmas have been investigated using laser diagnostic systems. An interferometer system was employed to investigate the temporal evolution of the structure in the plasma column during the pinch. The z-pinch plasma was driven by a fast bank, which provided a current of 160 kA for 1.5 µs quarter period of oscillation. Initially the plasma was formed in a conical shape due to the initial gas distribution. The plasma layer moved toward the z-axis and its shape gradually changed into columnar. The plasma layer splits into two layers on the way to implosion. The inner layer, which was indicated to be shock front, propagated toward the z-axis faster than the outer layer. The outer layer seemed quite smooth while the implosion by the inner layer took place at the z-axis. After the blast from the implosion expanded and came across the outer layer, the disturbance occurred at the outer layer. It is concluded that the plasma instability is significantly influenced by the shockwave rather than the initial gas formation in the case of a microsecond implosion.
Preferred Orientation Controlled Giant Grain Growth of Platinum Thin Films on SiO2/Si Substrates
Authors: Lee Dong-Su , Park Dong-Yeon , Woo Hyun-Jung , Kim Seung-Hyun , Ha Jowoong , Yoon Euijoon
Published: October 2002

Platinum thin films were deposited by reactive magnetron sputtering on SiO2/Si substrates. Argon-oxygen sputtering gas mixtures were used to control the microstructure and the preferred orientation of platinum films. As the oxygen fraction in the sputtering gas increased, the preferred orientation of as-deposited film was changed from (111) to random orientation. Post-sputtering anneal was done at 750–1,000°C range in air ambient to study the effects of the incorporated oxygen on the grain growth behaviors of platinum films. After sputtering and anneal at optimum conditions, the 1-µm thick Pt films completely transformed to giant grains with sizes as large as several millimeters. Furthermore, the preferred orientation of the giant grains could be controlled to either (111) or (200).
Direct Growth of [100]-Oriented High-Quality β-FeSi2 Films on Si(001) Substrates by Molecular Beam Epitaxy
Authors: Hiroi Noriyoshi , Suemasu Takashi , Takakura Ken'ichiro , Seki Naoki , Hasegawa Fumio
Published: October 2002

We have directly grown [100]-oriented high-quality β-FeSi2 films on Si(001) substrates with a β-FeSi2 template by molecular beam epitaxy(MBE) at 470°C. It was found that the crystalline quality of the as-grown β-FeSi2 film was as good as that of the film grown by the multilayer method as far as X-ray diffraction intensity was concerned. However, the electrical property of the as-grown β-FeSi2 film was very poor. The crystalline quality and the electrical property were much more quickly improved by 900°C annealing compared to the films grown by the multilayer technique. The [100] orientation of MBE-grown β-FeSi2 film was preserved even for a 1-µm-thick film.
Improvement in Electrical Properties of 4H-SiC Epilayers by Micropipe Dissociation
Authors: Kamata Isaho , Tsuchida Hidekazu , Jikimoto Tamotsu , Izumi Kunikazu
Published: October 2002

In this study, the effect of micropipe dissociation via 4H-SiC vapor phase epitaxy on the electrical properties of the epilayer was investigated. Ni/4H-SiC Schottky barrier diodes (SBDs) were fabricated on a 21-µm-thick epilayer, and their reverse blocking characteristics were examined. Some micropipes dissociated into closed core screw dislocations during epitaxial growth and some of them propagated into the epilayer. The SBDs that included a propagated micropipe showed poor reverse blocking performance, as reported previously, while the breakdown voltages were below -400 V. On the other hand, the SBDs that included a dissociated micropipe withstood breakdown up to -1000 V, where the leakage current density was 10-2 to 10-6 A/cm2. This demonstrated that a great improvement of the electrical properties could be achieved by the structural transformation of micropipes into closed core screw dislocations.
Structural Study of Single {111}-Facetted CoSi2/Si Interface Incorporated in a Silicon-on-Insulator Metal-Oxide-Semiconductor-Field-Effect-Transistor
Authors: Ichimori Takashi , Hirashita Norio
Published: October 2002

Metal-oxide-semiconductor field-effect transistors (MOSFETs) with single {111}-facetted silicide/silicon joints have been fabricated on silicon-on-insulator (SOI) substrates, using cobalt salicide. The interface structure is determined to be {111}Si//{111}CoSi2 and <110>Si//<110>CoSi2 by transmission electron microscopy. This report explains the formation mechanism of an atomically-flat interface, which involves the lateral growth of silicide in the channel direction of the MOSFET. This mechanism also enables the fabrication of a novel MOSFET structure where the SOI beneath the sidewall is silicided, which is expected to be a highly effective method for reducing the series resistance.
Influence of d-Wave Symmetry on Irreversibility Line and Critical Current Densities
Authors: Satoshi Awaji Satoshi Awaji , Kazuo Watanabe Kazuo Watanabe
Published: October 2002

The enhancement of the upper critical field, B

c2, in a low temperature and high magnetic field region has been proposed theoretically, due to the mixing of d

x
2-y
2
- and d

x
y
-symmetries for two-dimensional (2D) d-wave superconductors. Based on the B

c2 enhancement theory, the irreversibility field, B
i, and the critical current density, J
c, for high-T
c superconductors were calculated using the power law of B
i ∝B

c2
n. It is found that both B
i and J
c for chemical vapor deposition (CVD)-processed YBa2Cu3O7 can be well interpreted by the present model. This fact suggests that the concave temperature dependences of B
i and J
c originate from B

c2 for 2D d-wave superconductors. Moreover, the qualitative temperature dependence of B
i for high-T
c superconductors changes slightly with the anisotropy but the value of B
i decreases drastically with increasing the anisotropic parameter γ2.
Noise-Shaping Characteristics of Superconducting Band-Pass Sigma-Delta Modulators
Authors: Hashimoto Tatsunori , Hasegawa Haruhiro , Nagasawa Shuichi , Suzuki Hideo , Miyahara Kazunori , Enomoto Youichi
Published: October 2002

The noise-shaping characteristics of superconducting band-pass single-loop sigma-delta modulators were clearly observed for the first time at 4 K using a 2.86 GHz sampling clock and a 0.69 GHz signal. The modulator consisted of a Josephson comparator, a driver, and a lumped-element-circuit superconducting resonator. The modulator chips were fabricated using NEC's Nb standard process. Digital data from the modulator were consecutively acquired using a semiconductor data acquisition system. By using a fast Fourier transform (FFT) software, the output spectrum of the noise-shaping characteristics was calculated from the measured data. Also, the input-output characteristics were measured experimentally, and the modulator's linearity was confirmed.
Photoemission Spectroscopy of the Interface between Indium-Tin-Oxide and Copper Phthalocyanine for Transparent Organic Light-Emitting Devices
Authors: Isomura Noritake , Satoh Toshikazu , Suzuki Motofumi , Ohwaki Takeshi , Taga Yasunori
Published: October 2002

We investigated chemical and electronic structures of copper phthalocyanine (CuPc) for the electron-injection layer between indium tin oxide (ITO) and emission layers in transparent organic light-emitting devices (TOLEDs). Metallic Cu or dicopper oxide (Cu2O) is formed at the ITO/CuPc interface as a damaged layer during the sputtering deposition of ITO and plays a significant role in efficient electron injection from ITO to the emission layer. Sophisticated photoemission experiments revealed that the cause of the formation of the damaged layer is due to the exposure of CuPc to the oxygen plasma, while no significant damage is introduced by argon plasma and reaction with indium and tin atoms. To achieve efficient TOLEDs, the control of the oxygen plasma is essential.
Band Alignment of Molecular-Beam-Epitaxy-Grown GaS/GaAs Structure Using a Single [(t-Bu)GaS]4 Precursor
Authors: Okamoto Naoya , Tanaka Hitoshi , Hara Naoki
Published: October 2002

We report on the band alignment of a molecular-beam-epitaxy (MBE)-grown GaS/GaAs structure using a single tertiarybutyl-gallium sulfide cubane [(t-Bu)GaS]4 precursor. The optical band gap of epitaxial GaS film grown at a growth temperature (T
S) of 500°C is estimated by spectroscopic ellipsometry to be 2.7 eV, whereas that of amorphous GaS film grown at a T
S of 350°C is only 2.2 eV. X-ray photoemission spectroscopy (XPS) was used to estimate the band discontinuity between GaS and GaAs. Consequently, epitaxial and amorphous GaS/GaAs structures, respectively, reveal straggling type-I and staggered type-II band alignments.
Formation of Solid Solution of Al1-xSixN (0<x≤12%) Ternary Alloy
Authors: Kasu Makoto , Taniyasu Yoshitaka , Kobayashi Naoki
Published: October 2002

When Si was doped into an AlN layer during metalorganic vapor-phase epitaxial growth, the Al density (NAl) in the AlN layer decreased but the N density (NN) did not change. The decrease in NAl was almost the same as the Si density (Nsi). As Nsi increased in Si-doped AlN, the lattice constant decreased. These results can be explained by Si atoms replacing Al atoms in Si-doped AlN and subsequent Si–N bond formation. Thus, Si-doped AlN becomes a substitutional solid solution of Al1-x
Si
x
N ternary alloy. The highest Si density at which the x-ray diffraction peak still appears was 5.8×1021 cm-3 (x=12%).
Surface Defect Formation in Epitaxial Si Grown on Boron-Doped Substrates by Ultrahigh Vacuum Chemical Vapor Deposition
Authors: Furukawa Taisuke , Nakahata Takumi , Maruno Shigemitsu , Tanimura Junji , Tokuda Yasunori , Satoh Shinichi
Published: October 2002

We have investigated the formation mechanism of surface defects in a Si epitaxial layer grown on BF2
+-implanted Si(100) substrates by ultrahigh vacuum chemical vapor deposition. The density of surface defects increases linearly with the BF2
+ dose. It is found that surface defects are generated at the interface, although neither stacking faults nor dislocations are formed in the epitaxial layer. X-ray photoelectron spectroscopy measurements revealed that surface segregation of boron occurs. We propose a model of the defect formation in which inhomogeneous distribution of segregated boron across the substrate surface causes the difference in the epitaxial growth rate between high and low boron concentration regions.
Microcrystal Structures in Titanium Oxide Films Produced by Pulsed UV-Laser Irradiation
Authors: Ichikawa Yo , Setsune Kentaro , Kawashima Syun-ichiro , Kugimiya Koichi
Published: October 2002

Effects of ultraviolet (UV) light irradiation on the crystal structure have been investigated for amorphous Ti–O films by means of a pulsed KrF excimer laser. The crystal structure of the films was characterized by transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) analyses. The results obtained from the analyses suggest that microcrystalline structures of 5–10 nm in diameter are produced in the Ti–O film by the irradiation, and that TiO2 crystal with rutile structure is gradually formed with increasing number of pulses.
Large Anisotropy of Electron Mobilities in Laterally Modulated Two-Dimensional Systems Grown on the (775)B-Oriented GaAs Substrates by Molecular Beam Epitaxy
Authors: Ohno Yasuhide , Kitada Takahiro , Shimomura Satoshi , Hiyamizu Satoshi
Published: October 2002

We have investigated the transport properties of electron gas in a GaAs/(GaAs)4(AlAs)2 quantum well with a regularly corrugated upper interface formed on (775)B-oriented GaAs substrates by molecular beam epitaxy (MBE). The electron mobility perpendicular to the corrugation (µ⊥) was suppressed to 1/70th of that parallel to the corrugation (µ∥) for a quantum well with a well width of L
w=5 nm at a temperature of 10 K, and µ⊥ with a thin L
w of 5 nm monotonically increased with increasing temperature (10–300 K). These results suggest that the lateral potential induced by the thickness modulation is so strong in the nominally 5-nm-thick quantum well that the electron gas has a quasi-one-dimensional nature.
Formation and Structural Evolution of Magnesium Oxide Clusters under Electron Irradiation
Authors: Kizuka Tokushi
Published: October 2002

Magnesium oxide (MgO) clusters were formed by fracture of protrusions at the edges of MgO films under electron irradiation. The fracture was caused by pressing with gold clusters along the incident electron beam direction. The formation and subsequent surface structural evolution of the MgO clusters were observed by dynamic high-resolution transmission electron microscopy. The surface atoms on steps or edges preferentially desorbed, and chair-shaped and rectangular prism clusters appeared. An NaCl structure was stable until the cluster size was reduced to 1 nm.
Needle-Like SiC Nanorods
Authors: Gao Yihua , Bando Yoshio , Sato Tadao , Kitami Yoshizo
Published: October 2002

SiC nanorods with a needle-like shape have been synthesized by carbothermal reduction of SiO at 1410°C, where the reductant is highly curled carbon nanotubes (CNTs) containing Fe nanoparticles approximately 10 nm in size. Each SiC nanorod has a rounded Fe–Si single crystalline tip 120–250 nm in size and a sharp SiC tip approximately 10 nm in size. Along the nanorod axis, the diameter decreases gradually from approximately 100 nm on the Fe–Si tip side to approximately 10 nm on the sharp SiC tip. A revised vapor-liquid-solid mechanism from Wagner's mechanism is proposed to explain the formation of the SiC nanorods.
Exciton Dynamics in Organic Semiconductor Devices: Investigation of Exciton-Charge Carrier Interactions as Revealed by Photoluminescence Responses
Authors: Ichikawa Musubu , Naitou Ryusuke , Koyama Toshiki , Taniguchi Yoshio
Published: October 2002

We measured the photoluminescence decay curves of an organic semiconductor device when the device was electrically driven, and we investigated its exciton dynamics when there were a large number of electrons. The device consisted of a transparent electrode (indium tin oxide), a tris (8-quinolinolato) aluminum layer (Alq, 100 nm), and a metal cathode (Mg:Ag or Al, 200 nm). It was demonstrated experimentally that a singlet exciton of Alq was quenched by electrons through a bimolecular process. The rate constant of the PL quenching was estimated to be of the order of 10-9∼10-10 cm3/s.
Self-Organized Cohesion of Organic Molecular Dots on Chemically Patterned Surface
Authors: Hieda Hiroyuki , Gemma Nobuhiro , Naito Katsuyuki
Published: October 2002

Self-organized pattern formation of nonpolymeric amorphous molecules on substrates, which have nanometer-scale chemical patterns, is demonstrated. It is observed that droplet-like molecular dots deposited by vacuum evaporation cohere selectively onto hydrophilic regions by annealing processes. This selective cohesion of organic dots is thought to be attributable to Ostwald ripening which drives selective growth of dots on hydrophilic region on which the organic dots have large radius of curvatures at the expense of the small dots on hydrophobic regions.
Strain-Fields Effects and Reversal of the Nature of the Fundamental Valence Band of ZnO Epilayers
Authors: Gil Bernard , Lusson Alain , Sallet Vincent , Said-Hassani Said-Assoumani , Triboulet Robert , Bigenwald Pierre
Published: October 2002

We examine the influence of strain fields in ZnO epilayers. We show that a reversal of the nature of the fundamental valence band can be observed similarily to what was reported in GaN epilayers.
Ballistic Spin Transport in Four-Terminal NiFe/In0.75Ga0.25As Structure
Authors: Sato Yuuki , Gozu Shin-ichiro , Kita Tomohiro , Yamada Syoji
Published: October 2002

Spin-injection experiments in NiFe/two-dimensional electron gas (2DEG)/NiFe four-terminal devices are described. The 2DEG was confined at a modulation-doped In0.75Ga0.25As/In0.75Al0.25As heterojunction interface. NiFe source-drain electrodes were located ∼ 1 µm apart and two voltage probes were fabricated between them. The separation between the NiFe electrodes was thus almost less than both the mean free path (∼ 2 µm) and the spin-diffusion length (> 1 µm) of the 2DEG. In nonlocal four-terminal measurements, where a constant current (i) was sent through one NiFe to one ohmic electrode, the two-terminal magnetoresistance (R
2t
=V
2t
/i) exhibited a spin-valve-like effect, while R
4t
=V
4t
/i showed a resistance hysteresis. The amplitude of the latter amounted to almost 12% of the R
4t
(B=0) at 1.5 K, the extent of which was one order of magnitude larger than those so far reported. These results suggest the importance of a quasi-ballistic as well as a spin-coherent coupling between the two NiFe electrodes, which may crucial in the future operation of spin field-effect transistors (FETs).
Terahertz Beam Profiler Using Optical Transmission Modulation in Silicon
Authors: Kitoh Yoshiaki , Yamashita Masatsugu , Nagashima Takeshi , Hangyo Masanori
Published: October 2002

A new type of beam profiler in the terahertz region using optical modulation of transmission in a silicon wafer is proposed and demonstrated. The profile of the beam emitted from a photoconductive antenna and focused by paraboloidal mirrors is obtained as a function of frequency. The beam profile at each frequency can be fitted well with a Gaussian function. The diameter of the beam at a focal plane decreases with increasing frequency. The spatial resolution of the beam profiler is approximately determined by the optical beam size on the silicon wafer.
Fabrication of Adenosine Triphosphate-Molecule Recognition Chip by Means of Bioluminous Enzyme Luciferase
Authors: Tanii Takashi , Goto Tomomi , Iida Tomoyuki , Koh-Masahara Meishoku , Ohdomari Iwao
Published: October 2002

We have succeeded in detecting the adenosine triphosphate (ATP) concentration in a solution quantitatively using an ATP-molecule recognition chip. The ATP-molecule recognition chip is composed of a silicon photodiode on which bioluminous enzyme luciferase is immobilized. When the chip was immersed in an ATP-containing solution, the luciferase emitted light and the photoinduced current detected by the photodiode was in proportion to the ATP concentration. We found that the photoinduced current fits the Michaelis-Menten plot. These results indicate that the luciferase is successfully immobilized on the silicon chip without losing the bioluminous activity and that the proposed device enables us to detect the ATP concentration in a solution by measuring the photoinduced current.
Parallel Optical-Transmission Module Using Vertical-Cavity Surface-Emitting Laser Array and Micro-Optical Bench (MOB)
Authors: Shimada Yuji , Aoki Yasuhiko , Iga Kenichi
Published: October 2002

In this paper, we present a scheme of a parallel optical transmission module using a vertical-cavity surface-emitting laser (VCSEL) array and a micro-optical bench (MOB). We have fabricated a prototype using a VCSEL array emitting at 850 nm and a MOB for the first time, and demonstrated the feasibility of a two-dimensional alignment-free optical interconnect module. No noticeable degradation of I–V, and I–L characteristics of the packaged VCSEL array was observed after the proposed packaging process. The excess loss of the MOB alignment scheme using a multi-mode fiber was evaluated to be about 0.5 dB.
Combined Isothermal and Non-Isothermal Techniques to Analyze Charge Trapping and Stability in Insulating Materials
Authors: Neagu Eugen R. , Marat-Mendes Jose N.
Published: October 2002

Taking into account the time-consuming trapping and detrapping of electric charge in insulating materials, a sequential protocol for the investigation the trapping sites and trapped charge stability is proposed. The method is demonstrated for Teflon FEP-A. Elemental peaks are obtained whose maxima shift with increasing field from 456 to 486 K and are characterized by activation energies that increase from 1.1 to 1.9 eV. The relaxation time of the trapped charge, at 523 K, increases as the amount of charge stored in the material decreases and explains the good charge stability for Teflon FEP-A electrets.
Effect of Electric-Field-Induced Polarization on Positive Temperature Coefficient of Resistivity Characteristics of Semiconducting Barium Titanate Ceramics
Authors: Hamamoto Kouichi , Kuwabara Makoto
Published: October 2002

We observed distinct electric-field-induced birefringence in the vicinity of single-grain boundaries of semiconducting BaTiO3 above the Curie temperature (T
c; 120°C); the single-grain boundaries exhibited a distinct positive temperature coefficient of resistivity (PTCR) anomaly in the same temperature range. The highest temperature at which we could observe birefringence shifted to higher temperatures with increasing electric field, and the maximum resistivity temperature of the PTCR characteristics also shifted to higher temperatures with increasing electric field. Electric field dependencies of the highest temperature of observed birefringence and the maximum resistivity temperature were found to be quite similar to each other. These results suggest that polarization induced by residual strain and/or electric field can exist in the vicinity of grain boundaries in semiconducting ceramics even above 120°C (the inherent T
c of the bulk), and that the occurrence of the PTCR characteristics is closely related to the induced polarization.
First-Principles Study on Electronic Structure and Thermodynamic Stability of Sr(Ti,Ru)O3
Authors: Tatsuo Shimizu Tatsuo Shimizu , Takashi Kawakubo Takashi Kawakubo
Published: October 2002

Not only the electronic structure but also the thermodynamic stability of Sr(Ti,Ru)O3 is investigated using the first-principles method. For the electronic structure with small Ru concentration, the Ru t
2g states appear below the middle of the band gap of SrTiO3. In this case, the wave functions of the Ru t
2g states are localized at the Ru site. As a Ru concentration increases to more than 50 mol%, the inside-gap states gradually become delocalized. Therefore, a conductive Sr(Ti,Ru)O3 thin film is expected. On the other hand, thermodynamic stability of a Sr(Ti,Ru)O3 thin film is enhanced drastically relative to that of SrRuO3, as Ru concentration decreases. Sr(Ti,Ru)O3 with Ru concentration of more than 60 mol% may oxidize the neighboring (Ti,Al)N layer, which is often used as a barrier metal in memory-cell capacitors. In short, Sr(Ti,Ru)O3 with Ru concentration of about 50 mol% is proposed as a promising candidate material for new electrodes.
Suppression of GaInN/GaN Multi-Quantum-Well Decomposition during Growth of Light-Emitting-Diode Structure
Authors: Ishikawa Hiroyasu , Nakada Naoyuki , Mori Masayoshi , Zhao Guan-Yuan , Egawa Takashi , Jimbo Takashi , Umeno Masayoshi
Published: October 2002

Growth of GaN-based light-emitting-diode (LED) structures with GaInN/GaN multi-quantum wells (MQWs) has been explored by metalorganic chemical vapor deposition. GaInN/GaN MQW structures were found to decompose during the subsequent growth of a Mg-doped GaN top layer. This was prevented by adding 5% hydrogen in the growth of the GaN quantum barrier (QB) layer. Photoluminescence (PL) analysis of the grown GaInN/GaN MQW shows a PL peak shift caused by a reduction of the GaInN quantum well (QW) thickness. To prevent the variation of the GaInN QW thickness, a GaN cap layer with varying thickness has been inserted between the GaInN QW and the GaN QB layer. Both strong PL intensity and suppression of the peak shift were obtained for a 1-nm-thick GaN cap layer.
Hydrogen Segregation and Its Detrimental Effect in Epitaxial Growth of Ge Thin Film on Hydrogen-Terminated Si(001) Surface
Authors: Fujino Toshiaki , Okuno Tomohisa , Katayama Mitsuhiro , Oura Kenjiro
Published: October 2002

We have performed real-time monitoring of Ge thin film growth on a hydrogen-terminated Si(001) surface at growth temperatures ranging from room temperature to 350°C, to clarify the influence of hydrogen atoms on Ge/Si(001) heteroepitaxy. Hydrogen atoms segregated to the surface and a portion of them desorbed from the growth front during Ge deposition, depending on the growth temperature. The existence of hydrogen atoms on the growth front increased the growth temperature for Ge/Si(001) heteroepitaxy, while the flatness of the deposited Ge thin film was improved, indicating that hydrogen atoms suppress the surface migration of deposited Ge atoms.
10 keV X-Ray Phase-Contrast Microscopy for Observing Transparent Specimens
Authors: Kagoshima Yasushi , Ibuki Takashi , Yokoyama Yoshiyuki , Tsusaka Yoshiyuki , Matsui Junji , Takai Kengo , Aino Masataka
Published: October 2002

Hard X-ray phase-contrast microscopy has been performed with phase plates of tantalum using an X-ray beam from an undulator in SPring-8. The photon energy was set at 10 keV near the L
3 absorption edge of tantalum (9.9 keV) in order to increase the phase contrast. To demonstrate its capability, a transparent specimen was imaged clearly in the reverse contrast with phase plates to shift the phase by one-quarter and three-quarters of a period, while conventional absorption imaging showed little contrast. Further, an image contrast as high as approximately 40% can be obtained for the cell walls of another specimen.
Ferromagnetism in Co-Doped TiO2 Rutile Thin Films Grown by Laser Molecular Beam Epitaxy
Authors: Matsumoto Yuji , Takahashi Ryota , Murakami Makoto , Koida Takashi , Fan Xiao-Juan , Hasegawa Tetsuya , Fukumura Tomoteru , Kawasaki M. , Koshihara Shin-Ya , Koinuma Hideomi
Published: October 2002

Epitaxial TiO2 rutile films were fabricated on α-Al2O3 (1012) substrate in the layer-by-layer fashion by laser molecular beam epitaxy. Ablation with a Co-doped TiO2 target produced single phase of rutile film with the concentration of Co between 0 and 5%. Some ferromagnetic domain structures were observed in Co
x
Ti1-x
O2 rutile films by a scanning superconducting quantum interference device microscope at 3 to 90 K. The magnetic hysteresis could also be observed even at room temperature with a magnetic moment of ∼ 1 µB/Co atom.
Composition Dependence of Thermal Annealing Effect on 1.3 µm GaInNAs/GaAs Quantum Well Lasers Grown by Chemical Beam Epitaxy
Authors: Makino Shigeki , Miyamoto Tomoyuki , Kageyama Takeo , Ikenaga Yoshihiko , Arai Masakazu , Koyama Fumio , Iga Kenichi
Published: October 2002

The thermal annealing process is effective to improve the optical quality of GaInNAs/GaAs quantum wells (QWs). However, a blue shift of the emission peak wavelength occurs during the annealing and it is strongly related to the annealing condition and the composition of GaInNAs/GaAs QWs. In this study, we investigated the dependences of both the annealing condition and the composition on the lasing characteristics of 1.3 µm GaInNAs/GaAs QW lasers.
Binding Energies of Amorphous CN and SiCN Films on X-Ray Photoelectron Spectroscopy
Authors: Yamamoto Kazuhiro , Koga Yoshinori , Fujiwara Shuzo
Published: October 2002

SiCN and CN films were prepared by nitrogen ion-assisted pulsed-laser deposition. The dependence of silicon addition in CN film on the chemical bonds between carbon and nitrogen was examined. The formation of the sp3 bond between carbon and nitrogen is promoted by the addition of silicon. The binding energies in X-ray photoelectron spectra have been identified, and the bonding states of 286.1 eV in C1s and 400.0 eV in N1s are contributions of the sp2 bond between carbon and nitrogen. Other subpeaks of 287.7 eV in C1s and 398.3 eV in N1s are due to an sp3 bond between carbon and nitrogen.
Ferroelectricity and Amorphous Structure in Quenched Nylon 6 Film
Authors: Yanagisawa Teruaki , Itoh Takashi , Hashimoto Masato
Published: October 2002

The electric displacement versus electric field (D–E) hysteresis appeared for the as-quenched nylon 6 film approximately 30 µm thick. Maximum remanent polarization was 60 mC/m2. Temperature dependence of the d-spacing of the amorphous phase was measured by a high-temperature X-ray camera to show continuous decrease in the d-spacing from 0.439 to 0.434 nm with increasing temperature from 330 to 340 K without appearance of the crystalline phase. It was found that the D–E hysteresis disappeared when the d-spacing became smaller than approximately 0.42 nm with annealing the specimen, where no crystalline phase was observed. Such results suggest that ferroelectricity is caused in the amorphous phase with d-spacing larger than 0.42 nm.
A Spin Esaki Diode
Authors: Kohda Makoto , Ohno Yuzo , Takamura Koji , Matsukura Fumihiro , Ohno Hideo
Published: October 2002

We demonstrate electrical electron spin injection via interband tunneling in ferromagnetic/nonmagnetic semiconductor Esaki diodes. An interband tunnel junction between ferromagnetic p+-(Ga,Mn)As and nonmagnetic n+-GaAs under reverse-bias allows spin-polarized tunneling of electrons from the valence band of (Ga, Mn)As to the conduction band of n+-GaAs. The spin polarization of tunneled electrons is probed by circular polarization of electroluminescence (EL) from an n-GaAs/InGaAs/p-GaAs light emitting structure integrated with the diode. Clear hysteresis loop with ±6.5% remanence is observed in the magnetic-field dependence of the EL polarization at 6 K, below the Curie temperature of (Ga, Mn)As.
Effect of Cooling Process after GaN Epitaxial Growth by Radio-Frequency Molecular Beam Epitaxy
Authors: Shuichi Kubo Shuichi Kubo , Satoshi Kurai Satoshi Kurai , Tsunemasa Taguchi Tsunemasa Taguchi
Published: October 2002

The effect of carrying out a cooling process after GaN epitaxial growth by radio-frequency molecular beam epitaxy (RF-MBE) has been investigated. Nitrogen plasma irradiation with high-density radical components during the cooling process improved the crystalline quality of the GaN epitaxial layer markedly as evidenced by surface morphology, X-ray diffraction (XRD) and low-temperature photoluminescence (PL) measurements. This is because the active nitrogen species restrained nitrogen desorption from the surface of the GaN epitaxial layer. The 3 ×3 reflection high-energy electron diffraction (RHEED) reconstruction patterns were not observed from a N-polarity GaN epitaxial layer cooled under nitrogen plasma irradiation. This suggests that the 3 ×3 reconstruction occurs through nitrogen desorption.
Stripe Geometry Ultraviolet Light Emitting Diodes at 305 Nanometers Using Quaternary AlInGaN Multiple Quantum Wells
Authors: Khan Muhammad Asif , Adivarahan Vinod , Zhang Jian Ping , Chen Changqing , Kuokstis Edmundas , Chitnis Ashay , Shatalov Maxim , Yang Jin Wei , Simin Grigory
Published: October 2002

An ultraviolet light emitting diode with quaternary AlInGaN/AlInGaN multiple quantum wells and peak emission wavelength at 305 nanometers (nm) is reported for the first time. The peak emission wavelength can be tuned from 305 nm to 340 nm by varying the alloy compositions of the quaternary AlInGaN active layers using a pulse atomic layer epitaxy process. At 340 nm, for a 20 µm×1000 µm stripe geometry device an output power as high as 1 mW was measured from the sapphire substrate side.
Quantum-Confinement Effect in Ultrathin Si Layer of Silicon-on-Insulator Substrate
Authors: Tabe Michiharu , Kumezawa Minoru , Ishikawa Yasuhiko
Published: October 2002

We have studied the evolution of valence-band spectra during Si layer thinning in a silicon-on-insulator (SOI) substrate by X-ray photoelectron spectroscopy (XPS) in order to observe the quantum-confinement effect in two-dimensional Si. It was clearly observed that the valence-band maximum (VBM) shifts towards higher binding energies with decreasing Si thickness (< ∼10 nm). The VBM shifts were ascribed to vertical confinement of heavy holes in the quantum-well structure of a vacuum/single-crystalline Si/buried amorphous SiO2.
Improvement of Superconducting Properties in YBa2Cu3O7-δ Liquid Phase Epitaxy Thick-Film by Ca Doping
Authors: Yao Xin , Huang Daxiang , Nomura Katsumi , Nakamura Yuichi , Izumi Teruo , Shiohara Yuh
Published: October 2002

Ca-doped YBa2Cu3O7-δ (Ca-YBCO) thick films were grown on YBCO-seeded MgO substrates by liquid phase epitaxy (LPE) in air. The critical superconducting transition temperature (T
c) value over 90 K was achieved even with a small thickness of 0.5 µm. Using energy-dispersive X-ray spectroscopy (EDX) analyses, we detected Mg in a nondoped YBCO thick film, while it was nondetectable in a Ca-doped film. It was evident that Ca-doping into the solution for LPE growth plays a role in suppressing the Mg contamination in YBCO LPE thick films, leading to the improvement of T
c. Furthermore, the high irreversibility field (H
irr) value of up to 5 T was obtained by Ca-YBCO samples.
Solution Electrochemiluminescent Cell with a High Luminance Using an Ion Conductive Assistant Dopant
Authors: Nishimura Kazuki , Hamada Yuji , Tsujioka Tsuyoshi , Matsuta Shigeki , Shibata Kenichi , Fuyuki Takashi
Published: October 2002

Conventional solution electrochemiluminescent (SECL) cells have a low luminance. In this paper, we propose an ion conductive assistant dopant (ICAD) system to improve the luminance of SECL cells. The SECL cell is assumed to have a simple structure of [transparent electrode/emitting solution/transparent electrode]. The solution of the cell consists of a mixed solvent (o-dichlorobenzene/acetonitrile=2/1 (vol/vol)), rubrene used as the emitting material, and 1,2-diphenoxyethane used as the ICAD. When voltage is applied to this SECL cell, the cell achieves a luminance of 183 cd/m2 and a luminous efficiency of 1.5 cd/A at 8 V with yellow emission. On the other hand, an SECL cell without an ICAD results in a low luminance of 0.3 cd/m2 at 8 V, corresponding to a conventional SECL cell. The ICAD improves the luminance 600 times by enhancing the ion conduction of rubrene cations in the solution.
Furthermore, when the mixed solvent (o-dichlorobenzene/toluene=2/1 (vol/vol)), which has a high voltage resistance, is used in the SECL cell, the cell obtains a maximum luminance of 986 cd/m2 at 80 V. The features of the SECL cell are a simple cell structure and a transparent emitting area. SECL cells are expected to be used in unique displays with a see-through function for automobiles, windows, information equipment, and so on.
The Effects of Low-Pressure Rapid Thermal Post-Annealing on the Properties of (Ba, Sr)TiO3 Thin Films Deposited by Liquid Source Misted Chemical Deposition
Authors: Yang Ming-Jui , Chien Chao-Hsin , Leu Ching-Chich , Zhang Ren-Jian , Wu Shich-Chuan , Huang Tiao-Yuan , Tseng Tseung-Yuen
Published: October 2002

The technique of low-pressure post-annealing process with additional second-step annealing for preparation of the Ba0.7Sr0.3TiO3 thin films deposited by liquid source misted chemical deposition (LSMCD) has been proposed. With employing this annealing procedure, the leakage current density can be significantly eliminated by approximately one order of magnitude at 2 V. In particular, process temperature can be reduced from 650°C to 600°C without suffering deteriorated crystallinity issue, which is identified by both C–V measurement and X-ray diffraction spectrum. The extracted dielectric constant is 310 with extreamly low loss tangent of 0.005. The spectrum of atomic force microscopy (AFM) shows that this low-pressure process results in smoother surface topography. Moreover, thermal desorption spectrums assure that less residual organics and contaminations were left after low pressure post-annealing. This may be one of the reasons for lowering crystallization temperature and the improved electrical properties.
Alignment and Orientation of Diamagnetic Materials under Magnetic Levitation Condition
Authors: Hamai Miho , Mogi Iwao , Awaji Satoshi , Watanabe Kazuo , Motokawa Mitsuhiro
Published: October 2002

The behavior of levitating diamagnetic materials is investigated in gradient magnetic fields produced by a hybrid magnet. The levitating alignment of bismuth particles and the levitating orientation of a paraffin rod are reported, and these behaviors are discussed based on their potential energy curves in the magnet, the interaction among diamagnetic moments and the shape anisotropy.
Characterizations of Simultaneously Fabricated Silicon and Silicon Monoxide Nanowires
Authors: Jifa Qi Jifa Qi , Takahiro Matsumoto Takahiro Matsumoto , Yasuaki Masumoto Yasuaki Masumoto
Published: October 2002

Silicon and silicon monoxide (SiO) nanowires have been simultaneously fabricated by simply sublimating a pressed silicon powder plate (Si and Fe mixtures) at 1200°C in a flowing argon gas environment. The length of the SiO wire exceeds 0.8 mm and its average diameter varies from 70 nm to 1.35 µm, while the length of the silicon nanowire reaches 5 micrometers, with its average diameter varying from 20 to 40 nm. Both wires possess uniform diameters throughout the entire lengths, and smooth surfaces.
Pulsed Laser Epitaxy and Magnetic Properties of Single Phase Y-Type Magnetoplumbite Thin Films
Authors: Ohkubo Isao , Matsumoto Yuji , Hasegawa Tetsuya , Ueno Koichiro , Itaka Kenji , Ahmet Parhat , Chikyow Toyohiro , Kawasaki M. , Koinuma Hideomi
Published: October 2002

Single phase, c-axis oriented thin films of Y-type magnetoplumbite (Ba2Co2Fe12O22; Co2Y) with a very large c-axis length as 43.5 Å were grown successfully by pulsed laser deposition technique. The key points were high temperature deposition and the use of CoO buffer layer inserted between the film and MgAl2O4(111) substrate. From the transmission electron microscope (TEM) analysis, the CoO buffer layer was consumed to make an atomically sharp interface of Co2Y and substrate. Superconducting quantum interference device magnetometer was used to verify the high magnetic properties of the epitaxial thin films.
Ga Polarity Preference in Halide Vapor Phase Epitaxy of GaN on a GaAs (111)B: As Polar Substrate
Authors: Fumio Hasegawa Fumio Hasegawa , Makoto Namerikawa Makoto Namerikawa , Osamu Takahashi Osamu Takahashi , Tomonari Sato Tomonari Sato , Ryutaro Souda Ryutaro Souda
Published: October 2002

Halide vapor phase epitaxy (HVPE) of hexagonal GaN can give a high growth rate with high crystal quality. To clarify the reason, the polarity of GaN grown on GaAs (111)A and (111)B surfaces was investigated. It was found that a low temperature GaN buffer layer sometimes exhibits N polarity by the treatment of the GaAs (111)B surface with ammonia (NH3), but GaN grown on it at high temperatures always exhibits Ga polarity independently of the polarity of the buffer layer. This is probably due to the fact that the HVPE is surface kinetic limited growth with the reduction of GaCl.