bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study of the Pseudospark Switches*
Authors: Luo Chengmu , Zhao Huiliang , Xie Zifeng
Published: October 2002

The self-breakdown characteristics (SBC) of pseudospark switches (PSS) with different structure have been experimentally investigated. Two kinds of double-stage PSS with unique structure have been developed. One possesses intermediate cavity electrode and there are two co-axial holes on the upper and lower walls. The another one possesses a plane intermediate electrode with three holes arranged in an equilateral triangle about the center. The SBC of the two kinds of two-gap PSS are shifted to higher-pressure range compared with the single-gap PSS and the ordinary two-gap PSS. They are suitable for developing high hold-off voltage PSS.
Optical Observation of Gas Discharge Induced by High-Power and Short-Pulsed Microwave
Authors: Onoi Masahiro , Azuma Kingo , Fujiwara Etsuo , Yatsuzuka Mitsuyasu
Published: October 2002

The temporal and spatial evolution of gas discharge induced by a high-power, short-pulsed microwave (HPM) was observed using a high-speed image converter camera. The HPM with the peak power of 20 MW, frequency of 13 GHz, and pulse duration of 14 ns was irradiated uniformly into a gap between two spherical electrodes biased to a DC voltage less than the gap breakdown voltage. The streak images show two different breakdown mechanisms depending on air pressure. In the high-pressure region above about 300 Torr, the microwave-induced discharge begins at several points on the gap axis. When these local discharges increase sufficiently to link together with each other, the gap breakdown occurs. The gap breakdown is delayed by 30–300 ns depending on gas pressures and applied DC voltages. In the low-pressure region less than 300 Torr, on the other hand, a two-stage breakdown occurs. In the first stage, a single large discharge luminescence appears in the gap center at the time of the microwave injection and is followed by another discharge between the first discharge and two electrodes. After approximately 0.1–20 microseconds of the first stage discharge, the second-stage discharge appears followed by the gap breakdown.
Study of the Carbon VI 18.2 nm Line in a Capillary Discharge
Authors: Gotou Toyokazu , Takahashi Yasuo , Kobayashi Hirokazu , Taniike Akira , Kitamura Akira
Published: October 2002

In order to develop short-wavelength (extreme ultra violet (XUV) or soft X-ray) laser devices of tabletop size, the characteristics of a capillary tube discharge are examined. The polyacetal (CH2O)
n
capillaries with diameter and length of 2 mm and 60 mm, respectively, are filled with methane (CH4) gas up to 5 Pa, and powered by a Marx generator pulse-forming line system. Time-integrated XUV spectra are analyzed using a flat-field grazing-incidence spectrometer equipped with a 1200 line/mm grating. Although the experimental conditions are rather different from those published, spectral shapes with the same features are obtained. The spatial distribution of the 18.2 nm transition intensity of Carbon VI and its dependence on the discharge parameters such as the capillary length, the diameter and the discharge voltage are discussed.
Order of the Formation Reaction and the Origin of the Photoluminescence W Center in Silicon Crystal
Authors: Nakamura Minoru
Published: October 2002

The origin of the photoluminescence (PL) W center (or I1 center) in silicon crystal was investigated by observing the change of the PL intensity of the center with implantation fluence for proton-implanted silicon crystals with fluences between 1×1011 and 1×1016 ion/cm2 at an energy of 180 keV. The second-order reaction with respect to the fluence was analyzed for the formation of the W center. From the consideration of the symmetry, thermal behaviors and the order of the formation reaction of the W center, the center was determined to be well explained by the <111> split interstitial model.
Crystal Growth and Piezoelectric Properties of Mn-Substituted Pb(Zn1/3Nb2/3)O3 Single Crystal
Authors: Priya Shashank , Uchino Kenji , Viehland Dwight
Published: October 2002

Crystals of Mn-doped Pb(Zn1/3Nb2/3)O3 (PZN) were grown by a flux technique. The dielectric and piezoelectric properties were investigated for <001> oriented crystals. Mn-substitution resulted in combinatory hardening and softening effects. Under high power resonant drive, the mechanical quality factor (Q
m) and vibration velocity showed a considerable improvement, compared to the unmodified PZN crystals. Also, the longitudinal piezoelectric coefficient (d
33) was increased by Mn substitution. The combinatory effect is explained on the basis of mixed valence states of Mn.
Evaluation of Parameters in Atmospheric-Pressure Chemical Vapor Deposition of Borophosphosilicate Glass Using Tetraethylorthosilicate and Ozone
Authors: Nishimoto Yuko , Tokumasu Noboru , Maeda Kazuo
Published: October 2002

The effective parameters for the atmospheric-pressure chemical vapor deposition (APCVD) of borophosphosilicate glass (BPSG) using tetraethylorthosilicate (TEOS) and ozone were evaluated by designing an experiment. Source efficiencies of the deposition and doping were evaluated at constant boron and phosphorus concentrations. Each parameter was also characterized in terms of uniformity and film properties, such as thermal shrinkage and wet etch rate. Interactions between boron and phosphorus were discussed in terms of the difference in influential parameters and reaction rates. The deposition was controlled by the deposition temperature and the deposition rate, which are the dominant parameters of the film quality and deposition efficiency. The balance between gas flow rate and temperature is important to improve deposition and doping uniformity.
10 Gbit/s Data Generation by 4-Channel Optical Time-Division Multiplexing of Direct Pulse-Modulated Gain-Switched Distributed-Feedback Laser Outputs
Authors: Myong Seung-Il , Yeon Je-Sun , Uom Jung-Hyun , Park Chong-Dae , Seo Dong-Sun
Published: October 2002

For the first time, we generate a 2.5 Gbit/s pulse-modulated signal by direct modulation of a gain-switched distributed-feedback semiconductor laser using a 223-1 pseudo-random bit sequence. Comparison of the modulated pulses with the same gain-switched pulses ensures the pattern independent, nearly penalty-free operation of the laser. Then we generate a 10 Gbit/s (2.5 Gbit/s×4) return-to-zero modulated data by optical time-division multiplexing of the directly modulated gain-switched laser outputs.
High-Transconductance AlGaN/GaN High-Electron-Mobility Transistors on Semi-Insulating Silicon Carbide Substrate
Authors: Arulkumaran Subramaniam , Egawa Takashi , Ishikawa Hiroyasu , Jimbo Takashi
Published: October 2002

Epitaxial layers of AlGaN/GaN were grown on semi-insulating (SI) silicon carbide (SiC) by metalorganic chemical vapor deposition (MOCVD) with a very high electron sheet carrier density n
s=1.2×1013 cm-2 and a Hall carrier mobility as high as µH=1281 cm2/Vs at room temperature. High-electron-mobility transistors (HEMTs) have been demonstrated using an AlGaN/GaN heterostructure on a SI-SiC substrate. The fabricated 2.2-µm-gate-length Al0.26Ga0.74N/GaN HEMTs exhibited extrinsic transconductance as high as 287 mS/mm with drain-source current density as high as 857 mA/mm. This is the first report of such high transconductance achieved so far for 2.2-µm-gate-length Al0.26Ga0.74N/GaN HEMTs on SI-SiC substrates. A very small percentage (3%) of drain-source current density reduction at the gate voltage of +1.5 V has been observed for HEMTs on SI-SiC substrates. The observation of high extrinsic transconductance can be explained with the help of intrinsic transconductance values.
Photoenhanced Electrochemical Etching of n-GaN Forced by Negative Bias
Authors: Seo Jae Won , Oh Chang Suck , Yang Jeon Wook , Yoon Chang Joo , Lim Kee Young , Lee Hyung Jae
Published: October 2002

Bias-dependent photoenhanced electrochemical etching of n-GaN using CH3COOH solution and KOH solution is described. During etching of n-GaN under an illumination of 90 mW/cm2, n-GaN was etched at a rate of 8 nm/min in 0.04 M of KOH solution, and negligible etching was shown in 1% CH3COOH solution at zero substrate bias. However, n-GaN was successfully etched by applying negative bias, and an etch rate of 286 nm/min resulted from the etching in 1% CH3COOH solution at a bias of -9 V and an illumination intensity of 125 mW/cm2. Etch rate increased with negative bias and illumination intensity for etching in both solutions.
Preparation of Superconducting Magnetostatic Wave (MSW) Devices Consisting of High-Tc Superconductor (HTS)/Perovskite-Type Manganite Heterostructures: Application of Pr0.85Ca0.15MnO3 as a MSW Waveguide
Authors: Hontsu Shigeki , Sakatani Tomotaka , Nishikawa Hiroaki , Nakamori Masaya , Fujimaki Akira , Kawai Tomoji
Published: October 2002

Electric and magnetic properties of Pr0.85Ca0.15MnO3 (PCMO) have been investigated in order to apply the material to superconducting microwave devices. PCMO films are prepared on (100) surfaces of a (La0.3Sr0.7) (Al0.65Ta0.35)O3 (LSAT) single crystal by a pulsed laser deposition technique. By optimizing the deposition conditions, c-axis oriented PCMO epitaxial films are obtained. The Curie temperature (T
C) of these PCMO films is approximately 130 K. The remanent magnetization and the coercive field for the sample measured at 77 K are about 240 G and 250 Oe, respectively. The relative dielectric constant and loss tangent are significantly decreased below T
C and are about 13 and 6×10-3 at 30 K, respectively. Furthermore, magnetostatic wave (MSW) excitation is observed in a PCMO film by constructing a band elimination filter based on the MSW mode with YBa2Cu3O7-δ(YBCO)/PCMO heterostructure. These results indicate that PCMO is applicable for magnetic microwave devices including MSW devices with superconducting thin films.
1.5-µm-Wavelength Distributed Feedback Lasers with Deeply Etched First-Order Vertical Grating
Authors: Kim Hyo-Chang , Wiedmann Jörg , Matsui Kensuke , Tamura Shigeo , Arai Shigehisa
Published: October 2002

1.5-µm-wavelength distributed feedback lasers with a deeply etched first order vertical grating were realized for the first time. It was shown that we can obtain an effective coupling by reducing the stripe width. The sample with the cavity length of 430 µm, 1.8 µm stripe width and 0.2 µm grating depth on each lateral side exhibited a 12.5 mA threshold current, 37% total differential quantum efficiency and 35 dB submode suppression ratio at a bias current of two times the threshold.
Hybridized Microcrystals Composed of Metal Fine Particles and π-Conjugated Organic Microcrystals
Authors: Masuhara Akito , Kasai Hitoshi , Okada Shuji , Oikawa Hidetoshi , Terauchi Masami , Tanaka Michiyoshi , Nakanishi Hachiro
Published: October 2002

We have successfully prepared hybridized microcrystals composed of polydiacetylene microcrystals and silver fine particles by means of the co-reprecipitation method, and investigated their hybridized structure and optical properties. It was revealed experimentally for the first time that the core domain of metal fine particles may interact optoelectronically with the shell layer of polydiacetylene in the hybridized microcrystals to give different electronic states from those of the original compounds.
Stress Measurements of Polished Surface of 4′-Nitrobenzylidene-3-Ethylcarbonylamino-4-Methoxyaniline Single Crystal by Laser Raman Spectroscopy
Authors: Yamashiki Tomoya , Tsuda Keiji
Published: October 2002

Stress applied by mechanical polishing processes to the surface of 4′-Nitrobenzylidene-3-Ethylcarbonylamino-4-Methoxyaniline (MNBA-Et) single crystals has been measured using laser Raman spectroscopy. It has been proved that the position shift of the MNBA-Et Raman spectrum around 1580 cm-1 originating from the phenyl ring increases linearly with increasing the stress applied to MNBA-Et. Stress applied by the polishing process is proportional to the surface roughness of MNBA-Et, however, the applied stress is determined to be about 390 MPa independent of relation to the surface roughness of each polished MNBA-Et single crystal.
Mechanically Tunable High-Temperature Superconducting Microwave Filter with Large Shift of Resonant Frequency
Authors: Hontsu Shigeki , Sakatani Tomotaka , Fujimaki Akira , Nishikawa Hiroaki , Nakamori Masaya , Kawai Tomoji
Published: October 2002

We propose a mechanically tunable superconducting microwave filter using a floating dielectric or magnetic plate which can be displaced by an actuator above the resonator for frequency tuning. We also examine the transmission and tunable characteristics of the mechanically tunable filter numerically and experimentally. The electromagnetic field simulation based on the moment method shows that a large shift in the resonant frequency by about 1.8 GHz is obtained by displacement of the (La0.3Sr0.7)(Al0.65Ta0.35)O3 [LSAT] floating dielectric plate by 0.1 mm. In the experiment, we obtained a 1.36 GHz shift from the initial center frequency of 7.05 GHz with little increase in the insertion loss by application of an electric voltage to the electromagnetic actuator. These results suggest that the mechanical tuning of superconducting microwave components is useful for optimizing frequency response and for the functioning of RF filter at the front end of the base station receiver of a software-defined radio (SDR).
Optical Emission Spectroscopy of Pulsed Inductively Coupled Plasma in Ar
Authors: Hioki Kazuya , Itazu Naoki , Petrović Zoran Lj. , Makabe Toshiaki
Published: October 2002

Optical emission spectroscopy has been used to study the properties of pulsed inductively coupled plasma in Ar. Both spatially resolved computerized tomography and time resolved spectroscopy have been applied. In the range between 5 mTorr and 300 mTorr, it was found that the ratio of time averaged excited state densities in pulsed and CW conditions increases from 1:3 to 3:4. This is larger than the 1:2 ratio which may be expected from the duty cycle. The variation of the emission in the OFF period requires excitation during that period, and its time dependence may be understood by following the decay of the density and mean energy of electrons, and the decay of the metastable density. In the pulsed mode the radial uniformity is generally improved at lower and slightly worse at higher pressures.
Formation of Self-Assembled Nanocrystalline Silicon Dots by SiCl4/H2 RF Plasma-Enhanced Chemical Vapor Deposition
Authors: Fujimura Yukihiro , Jung Sughoan , Shirai Hajime
Published: October 2002

Self-assembled nanocrystalline silicon (nc-Si) dots have been directly fabricated on thermally grown SiO2/c-Si at low temperatures of 150–200°C by controlling the early stages of a conventional parallel plate RF (13.56 MHz) plasma-enhanced chemical vapor deposition (PE-CVD) process using tetrachlorosilane (SiCl4) and H2. The number density of nc-Si dots, and their sizes and heights were controlled by adjusting deposition time, substrate temperature T
s, pressure, RF power and pulse duty ratio of RF plasma. These specific features originate from the low sticking probability of deposition precursors and chemical stability of the chlorine-terminated surface under the hydrogen plasma, which results in the direct formation of nc-Si dots on SiO2 at low temperatures.
Thermoelectric Thick-Film Hydrogen Gas Sensor Operating at Room Temperature
Authors: Shin Woosuck , Imai Kiyohisa , Izu Noriya , Murayama Norimitsu
Published: October 2002

A sensor of thick film NiO doped with alkali ions was fabricated and coated with Pt as the catalyst on half of its surface. When this sensor was exposed to air mixed with hydrogen gas, the catalytic reaction heated up the Pt-coated surface, and then thermoelectric voltage appeared across the hot and cold region of the oxide film. At 22°C, the sensor showed the built-up temperature difference and voltage signal of 0.12°C and 0.087 mV, respectively, for the 100 ccm flow of 3% hydrogen/air mixed gas, with the full response time, T
90, of 55 s.
Dynamic Properties of Polar Molecules Confined in Electrostatic Trap
Authors: Masatoshi Kajita Masatoshi Kajita , Takayuki Suzuki Takayuki Suzuki , Hitoshi Odashima Hitoshi Odashima , Yoshiki Moriwaki Yoshiki Moriwaki , Maki Tachikawa Maki Tachikawa
Published: October 2002

We theoretically investigate the dynamics of linear polar molecules in static quadrupole electric fields. Numerical calculation shows that molecules rotating in a specific direction experience a restoring force, being three-dimensionally trapped in the center of the field distribution. We formulate the probability of Majorana transition and the trapping lifetime with a simple model of a rotating dipole. Potential depth of the electrostatic trap is quantum-mechanically estimated to be in the order of 100 mK.
A Spin-Polarized Scanning Electron Microscope with 5-nm Resolution
Authors: Kohashi Teruo , Koike Kazuyuki
Published: October 2002

For studying sub-10-nm-scale magnetic structures, a high-resolution spin-polarized scanning electron microscope (spin SEM) was developed. It has a specially designed, compact secondary-electron collector that produces a finer probe beam than that of a conventional spin SEM. By observing a narrow magnetic domain wall of SmCo5, the developed spin SEM was shown to have a high resolution of 5 nm.
Ideally Ordered Anodic Porous Alumina Mask Prepared by Imprinting of Vacuum-Evaporated Al on Si
Authors: Masuda Hideki , Yasui Kenji , Sakamoto Yasuhisa , Nakao Masashi , Tamamura Toshiaki , Nishio Kazuyuki
Published: October 2002

Application of imprinting of vacuum-evaporated Al on a Si substrate using an SiC mold with an ordered array of hexagonally arranged convexes and subsequent anodization yielded an ideally ordered porous alumina mask on the substrate. The obtained alumina mask has sufficient adhesion to a Si substrate, and was used as a mask for vacuum evaporation of metal and ion milling of the Si substrate.
New Superconducting Sr2CuO4-δ Thin Films Prepared by Molecular Beam Epitaxy
Authors: Shin-ichi Karimoto Shin-ichi Karimoto , Hideki Yamamoto Hideki Yamamoto , Tine Greibe Tine Greibe , Michio Naito Michio Naito
Published: October 2002

We report the synthesis of new superconducting Sr2CuO4-δ thin films (T
c
onset∼75 K) using molecular beam epitaxy (MBE). This superconductor has a tetragonal structure with an in-plane lattice constant a
0∼3.79 Å and a c-axis lattice constant c
0∼13.55 Å. This c-axis lattice constant is significantly larger than previously reported for this system. Strong oxidation using ozone gas at a low temperature of around 350°C is essential to the realization of phase conversion from the orthorhombic insulating phase (Sr2CuO3) to the tetragonal superconducting phase (Sr2CuO4-δ).
Zirconium Diboride (0001) as an Electrically Conductive Lattice-Matched Substrate for Gallium Nitride
Authors: Kinoshita Hiroyuki , Otani Shigeki , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu , Suda Jun , Matsunami Hiroyuki
Published: October 2002

Zirconium diboride (ZrB2) has a hexagonal crystal structure with an in-plane lattice constant of 3.168 Å, very close to that of GaN (3.189 Å). It is a metalloid compound and a very good electrical conductor, with a resistivity of 4.6 µΩ·cm. We propose ZrB2 (0001) as an electrically conductive lattice-matched substrate for GaN. Firstly, bulk crystal growth of ZrB2 using a radio frequency (rf)-heated floating zone (FZ) method is presented. Relatively large crystals (φ10 mm×60 mm) were obtained using this method. The thermal expansion coefficient and thermal conductivity of ZrB2 were evaluated using this crystal. Characterization of ZrB2 (0001) mirror-polished substrate was carried out by optical microscopic examination and X-ray diffraction. Finally, the results of heteroepitaxial growth are briefly mentioned.
Comparison of InAs/GaAs Quantum Dot Infrared Photodetector and GaAs/(AlGa)As Superlattice Infrared Photodetector
Authors: Lin Shih-Yen , Tsai Yao-Jen , Lee Si-Chen
Published: October 2002

A 10-stacked InAs/GaAs quantum dot infrared photodetector (QDIP) is compared with a 20-period GaAs/(AlGa)As superlattice infrared photodetector (SLIP). The 2–10 µm wide detection window and 187 mA/W high peak responsivity of InAs/GaAs QDIP at 7 µm at an applied voltage of 1.1 V are superior to the 7–10 µm detection window and 140 mA/W responsivity of GaAs/(AlGa)As SLIP at 9.4 µm at an applied voltage of 1.3 V. The photocurrent of SLIP is temperature-independent, whereas the photocurrent of QDIP increases with increasing temperature from 20 to 100 K. The polarization-dependent response ratios of 0.22 and 0.39 are observed for SLIP and QDIP, respectively.
Two-Dimensional Growth of AlN and GaN on Lattice-Relaxed Al0.4Ga0.6N Buffer Layers Prepared with High-Temperature-Grown AlN Buffer on Sapphire Substrates and Fabrication of Multiple-Quantum-Well Structures
Authors: Ohba Yasuo , Sato Rie , Kaneko Kei
Published: October 2002

Lattice mismatch effects on AlN and GaN growth were studied, aiming at the realization of multiple-quantum-well (MQW) structures. Lattice-relaxed AlN, GaN and Al0.4Ga0.6N were prepared as buffer layers. Microcrystal islands were observed for AlN and GaN respectively grown on the GaN and AlN buffer layers, due to lattice mismatch. However, two-dimensional growth was observed for both layers on the Al0.4Ga0.6N buffer layer. This growth-mode change was ascribable to the fact that a lateral lattice constant for the Al0.4Ga0.6N surface, with residual in-plane compression, is almost the center between those of AlN and GaN. For the MQW structures grown on Al0.4Ga0.6N, it was thought that the AlN and GaN grew two-dimensionally and coherently without significant dislocation generation.
Fine Structure of DNA Bundles: Atomic Force Microscopy Study
Authors: Li Guanglai , Zhang Yi , Li Bin , Hu Jun , Li Minqian
Published: October 2002

Direct observations of fine structure of DNA bundles were presented in this paper. These DNA bundles existed originally in λ-DNA solution with a high concentration of 480 ng/µl. When this solution was diluted, DNA bundles finally split into individual DNA molecules. DNA bundles were stretched on mica treated with 3-aminopropyl triethoxysilane (APS) and observed by an atomic force microscope (AFM). A method was developed to avoid the possible artifacts during the drying process in sample preparation. It was found that in a bundle composed of two individual DNA molecules, these two molecules wound around each other in a helical path.
Cardiac Chaotic Attractors of Ultrasound Echo Signals
Authors: Yoshikawa Yoshihiro
Published: October 2002

We found a human cardiac chaotic attractor in ultrasound RF echo signals of an ultrasound diagnostic system. Proof of these kinds of cardiac chaos was obtained by the reconstruction of the dynamics in phase space and confirmation of the evidence of the validity of Lyapunov exponents. The goal of our study is to develop novel diagnostic indices using chaotic echo signals. We calculated the correlation dimension of attractors, the dimension of which increased linearly with time as determined by stress echocardiography.
Theoretical Prediction of Magnetic Properties of Ba(Ti1-xMx)O3 (M=Sc,V,Cr,Mn,Fe,Co,Ni,Cu)
Authors: Hiroyuki Nakayama Hiroyuki Nakayama , Hiroshi Katayama-Yoshida Hiroshi Katayama-Yoshida
Published: October 2002

We have performed ab-initio total energy calculations for the system of BaTiO3 doped with 3d transition metal (from Sc to Cu), within the framework of the local spin-density approximation (LSDA). Total energies corresponding to the nonmagnetic, ferromagnetic, and anti-ferromagnetic configurations of the magnetic ordering were calculated to examine the magnetic stability. The results predict that the Cr-, Mn-, and Fe-doped BaTiO3 are candidates for ferromagnetic fabrication. Above all, Mn-doped BaTiO3 is the most promising, although carrier doping is necessary.
Low-Temperature Fabrication of High-Coercivity L10 Ordered FePt Magnetic Thin Films by Sputtering
Authors: Takahashi Y. K. , Ohnuma M. , Hono K.
Published: October 2002

We report that fully ordered L10 FePt magnetic thin films with high coercivity can be fabricated by a simple sputtering method at a substrate temperature of 300°C. Although fcc→L10 ordering proceeds only above 600°C in ex situ annealing of disordered FePt films, the ordering occurs spontaneously by surface diffusion during the sputtering process of FePt alloy upon heating the substrate at 300°C. High coercivity larger than 7 kOe was achieved from the as-sputtered state.
A Novel Simulation Algorithm for Si Valence Hole Quantization of Inversion Layer in Metal-Oxide-Semiconductor Devices
Authors: Hou Yong-Tian , Li Ming-Fu
Published: October 2002

A novel simulation algorithm to investigate the 2-D valence hole quantization effect within the inversion layer of a metal-oxide-semiconductor (MOS) structure is illustrated. A 6×6 hole Hamiltonian for a superlattice with a zigzag electric potential is introduced. The method involves the accurate band mixing of the valence bands, as well as simple and highly efficient computation. Mixing of the heavy, light and split-off hole bands is expected as a result of the symmetry property of the Hamiltonian. Due to band mixing, the energy dispersion, density of states, and charge distribution exhibit very different behaviors than those derived by the one-band effective-mass approximation. The impact on the electrical characteristics of MOS devices is demonstrated by an example of the threshold voltage shift. The results are in good agreement with those of the reported experiments.
Spin-Glass Freezing above the Ordering Temperature for the Kondo Antiferromagnet CeNi2Sn2
Authors: Sung Li-Ru , Yao Yeong-Der , Lee Wun-Hsin , Chen Yang-Yuan
Published: October 2002

Measurements of electrical resistivity, magnetic susceptibility and specific heat on an as-cast polycrystal sample CeNi2Sn2 are reported. From the frequency and field dependence of the χac and χdc above T
N, a spin glass state with two freezing temperatures T
f1=3.9 K and T
f2=4.4 K corresponding to the tetragonal and monoclinic phases of CeNi2Sn2, separately, are proposed. Some comparable intriguing experimental facts are the behaviors with anomalies observed in C(T), χac(T) and χdc(T) measurements. A qualitative description for the anomalous physical properties of CeNi2Sn2 compound is provided from the viewpoint of spin glass.
Field Induced Stratification of a Cholesteric Mesophase
Authors: Tolédano Pierre , Neto Antonio Martins Figueiredo
Published: October 2002

A new effect is described theoretically which is proper to liquid crystals formed from achiral molecules having a transverse dipolar order. It consists in the stratification, under application of a transverse electric field, of a cholesteric structure which is shown to stabilize below the isotropic liquid state.
Tantalum Aluminum Alkoxide as a Double-Metal Precursor for Metalorganic Chemical Vapor Deposition of Sr2AlTaO6
Authors: Zama Hideaki , Takahashi Yoshihiro , Tanabe Keiichi , Morishita Tadataka
Published: October 2002

We proposed resolving the poor controllability in the metalorganic chemical vapor deposition (MOCVD) of a complex oxide film consisting of a few metal elements, Sr2AlTaO6 (SAT) film, by using a double-metal source, tantalum aluminum isopropoxide TaAl(O–iC3H7)8. It had a melting point as low as 93°C and generated suitable vapor pressure for MOCVD at a temperature of 100°C. The supply metal ratio, Al/Ta, was ∼1, because it remained a double-metal structure in the vapor phase. We grew stoichiometric SAT films using it as a metal source.
Surface Potential Images of Microstructured Organosilane Self-Assembled Monolayers Acquired by Kelvin Probe Force Microscopy
Authors: Hiroyuki Sugimura Hiroyuki Sugimura , Kazuyuki Hayashi Kazuyuki Hayashi , Nagahiro Saito Nagahiro Saito , Osamu Takai Osamu Takai , Nobuyuki Nakagiri Nobuyuki Nakagiri
Published: October 2002

Kelvin probe force microscopy (KFM) has been applied to acquiring surface potential images of a coplanar microstructure composed of two self-assembled monolayers (SAMs) prepared from octadecyltrimethoxysilane (ODS) and fluoroalkylsilane (FAS), that is, heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane. The regions terminated with ODS and FAS could be clearly distinguished by KFM with a surface potential difference between the ODS and FAS-terminated surfaces. The surface potential of the FAS-terminated region was 190 mV lower than the potential of the ODS-terminated surface due to a larger dipole moment of the FAS molecules induced by the electron negativity of F atoms.
Investigation of Electrical and Optical Properties of Phosphine/Hydrogen-Plasma-Exposed In0.49Ga0.51P Grown on Si Substrate
Authors: Wang Gang , Akahori Kimiya , Soga Tetsuo , Jimbo Takashi , Umeno Masayoshi
Published: October 2002

The defect passivation effects of In0.49G0.51P grown on Si substrates (In0.49G0.51P/Si) have been investigated by exposure to a radio-frequency (RF)-excited PH3/H2 plasma. It was found that the defect hydrogenation effect of In0.49G0.51P/Si was achieved without dissociation of phosphorus (P) from the surface by adding P into hydrogen plasma. The optical and electrical properties of In0.49G0.51P/Si were effectively improved by exposure to PH3/H2 plasma. A significant enhancement of the photoluminescence (PL) intensity on the In0.49G0.51P/Si surface was observed after PH3/H2 plasma exposure, which was attributed to the hydrogenation of defect-related nonradiative recombination centers in the In0.49G0.51P/Si epitaxial layer.
Characterization of Overgrown GaN Layers on Nano-Columns Grown by RF-Molecular Beam Epitaxy
Authors: Kusakabe Kazuhide , Kikuchi Akihiko , Kishino Katsumi
Published: October 2002

We report on the successful growth of free-standing GaN films on (0001) sapphire substrates by RF-molecular beam epitaxy. The key to obtain unstrained GaN layers is employing self-organized GaN nano-columns which involve an air gap structure as a footing layer of overgrown GaN. The residual strain in overgrown GaN films is evaluated by measuring the lattice constant by X-ray diffraction. It is found that the c-axis length of overgrown GaN is estimated to be 5.1848 Å, which is close to the value of strain-free GaN even with a layer thickness of 2.7 µm. Overgrown GaN peeled arbitrarily from GaN nano-columns is observed due to the cleaving process.
Fracture of AlxGa1-xN/GaN Heterostructure –Compositional and Impurity Dependence–
Authors: Terao Shinji , Iwaya Motoaki , Nakamura Ryo , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu
Published: October 2002

Grown-in stress and subsequent fracture in Al
x
Ga1-x
N/GaN heterostructures with or without impurity doping were studied in situ. It was found that the critical thickness of Al
x
Ga1-x
N depends not only on its composition but also on the concentration of impurities such as Si or Mg. Increase in tensile stress during growth at a constant AlN molar fraction can be explained by the increase in the biaxial modulus of Al
x
Ga1-x
N due to impurity doping.
Ti–O Hybridization Effect of Nb-Doped SrTiO3 by Resonant Photoemission Spectroscopy
Authors: Higuchi Tohru , Tsukamoto Takeyo , Yamaguchi Shu , Tezuka Yasuhisa , Shin Shik
Published: October 2002

The electronic structure of Nb-doped SrTiO3 (SrTi1-x
Nb
x
O3) has been investigated by resonant photoemission spectroscopy (RPES). The valence band is well described by the band calculation. The RPES spectra show that the Ti 3d partial density of states in the valence band increases with increasing Nb dopant concentration. This finding suggests that the hybridization effect between the Ti 3d and O 2p states depends on the Nb dopant concentration.
All-Optical Switching in a Dye-Doped Liquid Crystal Fabry-Perot Device
Authors: Hiroshi Ono Hiroshi Ono , Masaki Ito Masaki Ito
Published: October 2002

We present an all-optical switching device using both large optical nonlinearity of dye-doped liquid crystals and Fabry-Perot cavity. The phase retardation change due to the refractive index change in the dye-doped liquid crystal was converted into the light intensity change using the Fabry-Perot cavity. The optical switching phenomena were explained by theoretically calculating the optical properties of the Fabry-Perot device.
Thermally Stable Photoalignment Layer of a Novel Photo-Crosslinkable Polymethacrylate for Liquid Crystal Display
Authors: Kawatsuki Nobuhiro , Takatsuka Hirohumi , Yamamoto Tohei
Published: October 2002

This letter describes the thermal stability of a photoalignment layer conposed of a polymethacrylate consisting of a methyl 4-(4′-hexyloxy)benzoyloxy-cinnamate side group for liquid crystal (LC). The axis-selective photoreaction of the cinnamoyl group induced a negative dichroism, while the photo-Fries rearrangement caused a small positive one. The negative dichroism became positive when the film was annealed at 150°C as a result of self-organization of the side groups, and the annealing treatment at 210°C did not change its spectroscopic characteristics. The nematic LC was aligned on the exposed films in a direction parallel to the electric vector of linearly polarized (LP) UV light and the alignment layer showed thermal durability of the orientational characteristics of the LC up to 200°C.
Electrochemical Deposition of Regioregular Head-to-Tail Poly(3-hexylthiophene-2,5-diyl) and Characterization of the Obtained Film
Authors: Kokubo Hisashi , Kuroda Shin-ichi , Sasaki Shintaro , Yamamoto Takakazu
Published: October 2002

Films of p-doped regioregular head-to-tail-type poly(3-hexylthiophene), HT-P3HexTh, were formed on a Pt plate by electrochemical deposition of HT-P3HexTh in a tetrahydrofuran solution of [NBu4]Y (Bu=butyl; Y=BF4, PF6, or ClO4). The p-doped HT-P3HexTh molecules were oriented in the film with the hexyl group arranged essentially perpendicular to the surface of the Pt plate.
Optimization of GaN Growth with Ga-Polarity by Referring to Surface Reconstruction Reflection High-Energy Electron Diffraction Patterns
Authors: Shen Xu-Qiang , Ide Toshihide , Cho Sung-Hwan , Shimizu Mitsuaki , Hara Shiro , Okumura Hajime , Sonoda Saki , Shimizu Saburo
Published: October 2002

GaN films with Ga-polarity on (0001) sapphire substrates grown by plasma-assisted molecular beam epitaxy were investigated. The optimization of the growth conditions was performed referring to reflection high-energy electron diffraction reconstruction patterns during the cooling processes. Three kinds of surface reconstruction patterns, named (5×5), (1×2) and (2×2), were observed during the cooling processes. Structural, optical and electrical properties of the GaN films, identified by different reconstruction patterns, were characterized to determine the optimal growth conditions. It was found that high-quality films can be obtained when the films show the (1×2) pattern. Under this condition, we obtained an electron mobility at room temperature of as high as 567 cm2/Vs without using a GaN template.
Doppler Shift of Ripplon Spectrum Observed under Surface Flow
Authors: Hosoda Maiko , Sakai Keiji , Takagi Kenshiro
Published: October 2002

We observed the ripplon spectrum on the flowing liquid surface by the optical beating ripplon light scattering technique. The ripplon spectrum, which is composed of Stokes and anti-Stokes components, is expected to be asymmetric with respect to the center frequency due to the Doppler effect. In the observed spectrum, these two components have clearly different peak frequencies, and the difference agrees well with the value predicted from theoretical calculation. This technique can be applied to the noncontact measurement of the surface flow speed that provides important information on the dynamic adsorption phenomena of surfactant molecules. The sensitivity of the flow speed measurement was also discussed.
Formation of Flat Monolayer-Step-Free (110) GaAs Surfaces by Growth Interruption Annealing during Cleaved-Edge Epitaxial Overgrowth
Authors: N. Pfeiffer Masahiro Yoshita , W. West Ken
Published: October 2002

We have characterized, by means of atomic force microscopy, the as-grown and subsequently in situ annealed surfaces of 5 nm GaAs layers grown by molecular beam epitaxy (MBE) on a vacuum-cleaved (110) GaAs surface, and find that a high temperature growth interruption and anneal remarkably improves the surface morphology of the (110) GaAs layer. Interruption of the 490°C epitaxial GaAs growth by a 10 minute anneal at 600°C under an As4 overpressure produces an atomically-flat surface free of monolayer step edges over areas measuring several tens of µm on a side. These results suggest that the (110) GaAs surface has much higher stability under annealing conditions than under MBE growth conditions.
Efficient Free-Exciton Recombination Emission from Diamond Diode at Room Temperature
Authors: Horiuchi Kenji , Kawamura Aki , Ide Takahiro , Ishikura Takefumi , Nakamura Kazuo , Yamashita Satoshi
Published: October 2002

Free-exciton recombination emission of 235 nm in wavelength is obtained by current injection at room temperature from a diamond-based pn junction diode composed of B-doped crystal grown by high-temperature, high-pressure synthesis and a S-doped homoepitaxial layer grown by the chemical vapor deposition method. The diode shows a clear rectification characteristic and a high external quantum efficiency of excitonic emission, 8×10-5, which indicates that the excitonic emission of diamond is a good candidate for application to semiconductor UV-light-emitting devices. A defect-induced light emission and large leakage current indicate that a higher UV emission efficiency is expected with improvement of the junction quality.
Mechanism of Potential Profile Formation in Silicon Single-Electron Transistors Fabricated Using Pattern-Dependent Oxidation
Authors: Horiguchi Seiji , Nagase Masao , Shiraishi Kenji , Kageshima Hiroyuki , Takahashi Yasuo , Murase Katsumi
Published: October 2002

The origin of the potential profile in silicon single-electron transistors (SETs) fabricated using pattern-dependent oxidation (PADOX) is investigated by making use of the geometric structure measured by atomic force microscope (AFM), the bandgap reduction due to compressive stress generated during PADOX obtained using the first-principles calculation, and the effective potential method. A probable mechanism for the formation of the potential profile responsible for SET operation is proposed. The width reduction in the silicon wire region in the SET produces a tunnel barrier, while the compressive stress lowers the bottom of the conduction band through the bandgap reduction and forms a potential well corresponding to an island in the tunnel barrier.
Transmission Electron Microscopy Investigation of Dislocations in GaN Layer Grown by Facet-Controlled Epitaxial Lateral Overgrowth
Authors: Honda Yoshiaki , Iyechika Yasushi , Maeda Takayoshi , Miyake Hideto , Hiramatsu Kazumasa
Published: October 2002

We investigated the propagation of the threading dislocations in the GaN layer grown by facet-controlled epitaxial lateral overgrowth (FACELO). The mixed-type dislocations were bent toward the mask areas and they were terminated at the voids on the SiO2 masks. On the other hand, the pure edge dislocations were bent in the direction of the mask stripe. No dislocations originating from the GaN/sapphire interface propagated to the surface. As a result, it was confirmed that a large reduction of dislocation density was achieved. Therefore, FACELO seems to be a promising technique for the realization of a GaN wafer of low dislocation density.
Fabrication of InP-Based Reflection Type Arrayed Waveguide Grating with Metal Coated Reflection Facet
Authors: Churl Kim Dong , Mun Kim Hyung , Soo Kim Jeong , Ro Choo Heung , Eue Pyun Jeha Kim , Keon-Ho Yoo Keon-Ho Yoo
Published: October 2002

We have fabricated a reflection type arrayed waveguide grating that consists of one free propagation region and arrayed waveguides which are all strainght waveguides. Each arrayed waveguide has a reflection facet formed by lithography. All reflection facets were coated with metal for high reflection. The device is an 1×8 multi/demultiplexer with 1.6 nm channel spacing. The chip size is as small as 0.83 ×2.7 mm2. The on-chip loss is about -13 dB and the crosstalk is less than -13 dB.
Propagation Characteristics of Ultrahigh-Δ Optical Waveguide on Silicon-on-Insulator Substrate
Authors: Atsushi Sakai Atsushi Sakai , Go Hara Go Hara , Toshihiko Baba Toshihiko Baba
Published: October 2002

A submicron rectangular waveguide with a relative refractive index difference Δ of 45% was fabricated on a silicon-on-insulator substrate, and its propagation characteristics were evaluated using the Fabry-Perot resonance method. The propagation loss was of the order of 10 cm-1, and was dominated by light scattering at rough interfaces. However, a large modal effective index of more than 4.5 and a low bend loss of less than 1 dB at a 0.5-µm-radius bend were also observed. These results suggest the potential of an ultrasmall and high-density lightwave circuit, which accepts the relatively large propagation loss.
Pulsed Laser Deposition of Transparent Conducting Indium Tin Oxide Films in Magnetic Field Perpendicular to Plume
Authors: Akio Suzuki Akio Suzuki , Tatsuhiko Matsushita Tatsuhiko Matsushita , Takanori Aoki Takanori Aoki , Yoshitaka Yoneyama Yoshitaka Yoneyama , Masahiro Okuda Masahiro Okuda
Published: October 2002

In2O3 doped with 5 wt% SnO2 (indium-tin oxide(ITO)(5 wt%)) films have been deposited on glass and quartz substrates in a magnetic field generated from three pieces of rare–earth permanent magnets (1.25 T flux density) placed at every 120° angle to surround the plume produced by pulsed laser deposition using an ArF laser (λ=193 nm). In all experiments, a repetition rate of 10 Hz, an energy density of 1.5 J/cm2, and an irradiation time of 20–30 min (12000–18000 shots) were used. The lowest resistivity of 7.2×10-5 Ω·cm and an optical transmittance of more than 90% in the visible region of the spectrum were obtained for approximately 30-nm-thick ITO (5 wt%) films deposited at a substrate temperature of 300°C in oxygen with a flow rate of 2 sccm. Very smooth surfaces with an average surface roughness of 0.61 nm were observed by scanning electron microscope (SEM) and atomic force microscope (AFM).
High-Performance X-Ray Mask Fabrication Using TaGeN Absorber and Dummy Pattern Method for Sub-100 nm Proximity X-Ray Lithography
Authors: Iba Yoshihisa , Taguchi Takao , Iizuka Takashi , Kumasaka Fumiaki , Aoyama Hajime , Nakayama Yoshinori , Horiuchi Kei , Matsui Yasuji
Published: October 2002

We have developed an X-ray mask using TaGeN as the X-ray absorber and the dummy pattern method. Variation of the absorber pattern etching shift width was only 3.3 nm (3σ) in a chip and mask pattern critical dimension (CD) variation was less than 4.5 nm (3σ) for a 70 nm future pattern size. Mask distortion due to absorber etching was less than 8 nm in each mask. This combination of TaGeN and the dummy pattern method is an excellent candidate for use in the fabrication of an X-ray mask for sub-100 nm X-ray lithography.
Complex Nature of Acceptor Levels in Aluminum Gallium Nitrides Doped with Magnesium
Authors: Zohta Yasuhito , Iwasaki Yoshitaka , Nakamura Shuji , Mukai Takashi
Published: October 2002

Frequency (ω) dependent conductance (G) has been measured of the reverse-biased blue and green light-emitting diodes consisting of nitride semiconductors, in order to study the electronic behavior of the Mg acceptor in metalorganic chemical vapor deposition grown p-Al0.2Ga0.8N. Four peaks with activation energies of 14, 63, 115, and 166 meV were found in the G/ω vs ω characteristics of the diodes. Although these activation energies do not correspond directly to the energy depths above the valence band edge, it is likely that they reflect the complex electronic structure of the Mg acceptor levels.
Fabrication of a Micropatterned Ridge Embedded in a Magnetooptic Film
Authors: Yasuyuki Okamura Yasuyuki Okamura , Sadahiko Yamamoto Sadahiko Yamamoto
Published: October 2002

We report the fabrication of a crystal or an amorphous micropatterned ridge buried in a magnetooptic film by use of the selected-area sputter epitaxy. The ion-beam bombardment on the deposited amorphous film was found to be influential in crystal growth on an amorphous region. We successfully formed a crystalline single patterned-ridge with 3 µm width, whose cross section was inverted-trapezoidal, into an amorphous region, and an amorphous single patterned-ridge, whose cross section was triangular, into a crystal region.
1.12 µm Polarization Controlled Highly Strained GaInAs Vertical-Cavity Surface-Emitting Lasers on GaAs(311)B by Metal Organic Chemical Vapor Deposition
Authors: Nishiyama Nobuhiko , Arai Masakazu , Shinada Satoshi , Azuchi Munechika , Matsutani Akihiro , Miyamoto Tomoyuki , Koyama Fumio , Iga Kenichi
Published: October 2002

A highly strained GaInAs vertical-cavity surface-emitting laser (VCSEL) emitting at 1.12 µm has been realized on a GaAs(311)B substrate by metal organic chemical vapor deposition (MOCVD) for the first time. The threshold current of an 8 µm oxide aperture device was as low as 0.9 mA. This device operated at up to 170°C without a heatsink under the CW condition. The polarization direction of the oscillation mode was stable and the orthogonal polarization suppression ratio (OPSR) was 30 dB. The operating lifetime of over 2000 under room-temperature CW conditions was confirmed without any degradation in spite of high strain of over 2%.
Perylene Orange Doped Acrylic Polymer for Solid-State Dye Laser
Authors: Fukuda Makoto , Kodama Kunihiko , Mito Keiichi
Published: October 2002

Perylene orange doped acrylic polymer has been applied successfully to the solid-state dye laser system. Its optical properties and laser characteristics have preliminarily been measured. Its superior photostability has been demonstrated as compared to the solid-state dye laser systems reported thus far.
A Low-Temperature Dehydration Method of Silica Films
Authors: Tatsuya Fukumura Tatsuya Fukumura , Satoshi Sugahara Satoshi Sugahara , Masakiyo Matsumura Masakiyo Matsumura
Published: October 2002

XeF2 has been proposed as a catalyst for low-temperature dehydration of SiO2 films. The critical dehydration temperature was about 200°C less XeF2 dehydration-annealing than for vacuum dehydration-annealing. The SiO2 film deposited from tetraethylorthosilicate (TEOS) and ozone at 270°C showed OH-free and good insulating characteristics after XeF2-annealing at 400°C.
Growth of β-FeSi2 Thin Film on Si (111) by Metal-Organic Chemical Vapor Deposition
Authors: Akiyama Kensuke , Ohya Seishiro , Takano Hiromichi , Kieda Nobuo , Funakubo Hiroshi
Published: October 2002

We succeeded for the first time in preparing a high-quality (101)-oriented epitaxial β-FeSi2 film on Si(111) wafer by metal-organic chemical vapor deposition (MOCVD) using Fe(CO)5 and SiH4 as source materials. The full width at half maximum (FWHM) of the rocking curve of the β-FeSi2 (202) peak was 0.46 degree for the film deposited at 750°C at a rate of 4 nm/min. Moreover, a smooth-surface film of up to 650 nm thickness could be deposited by this method. Carbon content in the film was less than 0.1 at%.
Atomically Flat MgO Single-Crystal Surface Prepared by Oxygen Thermal Annealing
Authors: Zama Hideaki , Ishii Yukie , Yamamoto Hiroshi , Morishita Tadataka
Published: October 2002

Single-crystal MgO is a good candidate substrate for growing metal oxide films, even though it has a few drawbacks, such as surface degradation caused by its easy reaction with H2O and CO2 and high concentration of impurities originating from the method by which it is grown. We propose a thermal annealing carried out under novel conditions, 700°C and 1 atm O2 atmosphere, for resolving these drawbacks. An atomically flat surface with a half-unit-cell-high step-and-terrace feature was realized on a MgO(100) substrate with a reduced surface segregation of impurities.