bluuebunny/crossref_metadata_2025 huggingface dataset:
Imaging in an Optical Projection System with a Laser Light Source. II: Multi-Transverse-Mode Laser Light Illumination
Authors: Kiichi Takamoto Kiichi Takamoto
Published: October 2002

Imaging characteristics are analyzed using a one-dimensional model. The second source plane in an illumination system is illuminated by a laser light oscillating in a multitude of transverse modes. Intensity distributions for a line-and-space pattern with 5 lines are calculated. Focal tolerance is examined for intensity distributions due to the light oscillating in only even transverse modes. No linear relationship between the number of transverse modes and focal tolerance is observed. When a phase of the light field for each even transverse mode is randomly given, contrasts of intensity distributions do not deteriorate with defocus.
Threshold Current and Its Temperature Dependence in InGaAsP/InP Strained Quantum-Well Lasers under a Magnetic Field
Authors: Mitsuru Sugawara Mitsuru Sugawara
Published: October 2002

We studied threshold currents of 1.3-1.6 µ m InGaAsP/InP strained quantum-well lasers under a magnetic field of 13 T.
A simple model to relate field strength to the lateral size, L, and area density, N, of quantum boxes is presented. The model shows that 13 T corresponds to L≃30 nm and N≃3000 µ m-2. The threshold current decreased by a few milliamperes, and its characteristic temperature increased by about 10 K at about room temperature.
Piezoelectric and Dielectric Properties of Aromatic Polyureas Synthesized by Vapor Deposition Polymerization
Authors: Wang Xian-Shan , Takahashi Yoshikazu , Iijima Masayuki , Eiichi Fukada Eiichi Fukada
Published: October 2002

Four different kinds of aromatic polyurea were synthesized by vapor deposition of monomers. As a diisocyanate, [4,4′-diphenyl methane diisocyanate] (MDI) was used. As a diamine, [4,4′-diamino diphenyl methane] (MDA), [4,4′-diamino-3,3′-dimethyl diphenyl methane] (MeMDA), [4,4′-diamino diphenyl ether] (ODA), and [4,4′-diamino diphenyl sulfide] (SDA) were used. Poled thin films of P(MDA/MDI), P(MeMDA/MDI), P(ODA/MDI), and P(SDA/MDI) exhibited piezoelectric activity which remained up to almost 200° C. The stable value of the piezoelectric constant for P(ODA/MDI) was 26 mC/m2. The piezoelectric constant plotted against the evaporation temperature of MDI showed a maximum, where the stoichiometrically balanced composition of MDI and diamine monomer was obtained. The curve was sharp for P(MDA/MDI), but broad for P(ODA/MDI) and other polyureas. It was suggested that the high probability of production of balanced oligomers might be due to the longer time of residence of ODA molecules on the substrate.
Properties of the CdSe-Doped Glass Thin Films Prepared by Ion-Beam Sputtering Method
Authors: Suzuoki Yasuo , Matsuno Noriaki , Tabata Akimori , Takeda Masashi , Teruyosi Mizutani Teruyosi Mizutani
Published: October 2002

CdSe-doped silica glass thin films were prepared by the ion-beam sputtering (IBS) method and the ion-assisted deposition method (IAD). Properties of the doped glass were studied by visible-ultraviolet absorption spectrometry and X-ray photoelectron spectroscopy. The particle size could be controlled by the deposition rate, the O2 gas flow rate and the assist ion irradiation, but did not depend on the sputtering ion energy. The SiO2 matrix had the same structure as thermally oxidized SiO2 and the contents of Cd and Se atoms were several at.%. The Se atoms at the surface of a CdSe particle were replaced by O atoms as the O2 gas flow rate increased. The main effect of the assist ion irradiation was resputtering and effects such as chemical activation were not dominant. The CdSe particles increased in size during the annealing at 700° C, but that at 500° C scarcely affected the particle size.
Chemical Stability of HBF4-Treated (100)Si Surfaces
Authors: Levenets V. V. , Beklemishev V. I. , Kirilenko E. P. , Makhonin I. I. , Trifonov A. Yu. , Loginov B. A. , Protasenko V. V.
Published: October 2002

Si(100) surfaces were modified by means of enhanced RCA procedure with “ HBF4-last” and “HF-last”. Nulling ellipsometric (NE) and secondary ion mass spectrometric (SIMS) measurements revealed that HBF4-treated Si surface is more strongly passivated by hydrogen and fluorine than HF-treated one: the oxidation rate of the HBF4-treated Si surfaces in air was found to be lower than that of the HF-treate surface. Scanning tunneling microscope (STM) images of HBF4-cleaned surface after 18 h storage in air were quite stable during observation, scanning could be easily performed over a wide area on every plot we chose.
Novel Amorphous-Silicon-Based Double-Metal Antifuse with Barrier Enhancement Layer
Authors: Fang Yeau-Kuen , Lee Kuen-Hsien , Chen Fu-Yuan , Jun-Dar Hwang Jun-Dar Hwang
Published: October 2002

The electrical characteristics, operating mechanism and reliability of a novel amorphous-silicon-based double-metal antifuse are reported in detail. A very thin α-S
i
C:H layer was inserted on both top and bottom A
l/α-S
i:H interfaces as barrier enhancement layer. With proper adjustment of the thickness of this layer, the programming voltage and leakage current can be controlled. The antifuse offers very low on-resistance (<2 Ω) and low preparation temperature (<250° C), and the characteristics are independent of area, therefore, the device is suitable for integration with field-programmable gate array applications.
Optimization of a-SiGe:H Alloy Composition for Stable Solar Cells
Authors: Terakawa Akira , Shima Masaki , Sayama Katsunobu , Tarui Hisaki , Nishiwaki Hidenori , Shinya Tsuda Shinya Tsuda
Published: October 2002

The film properties and solar cell performance of amorphous SiGe:H (a-SiGe:H) samples have been systematically investigated, using constant optical gap and various compositions of hydrogen and germanium. It was found that the hydrogen content and bonding configurations play important roles in determining both the initial properties and stability. The optimum compositions were clarified for the minimum Urbach tail characteristic energy and defect density in the as-deposited film, and for the maximum conversion efficiency of the solar cells. The stability of a-SiGe single and a-Si/a-SiGe tandem solar cells becomes higher as the hydrogen content of the photovoltaic layer becomes lower. As a result, the optimum composition after light soaking shifts to the region of lower hydrogen content. Applying the above findings to the design of devices, the highest stabilized conversion efficiencies of 3.3% (initial 3.7%) under red light (λ>650 nm) for an a-SiGe single-junction solar cell and 10.6% (initial 11.6%) for an a-Si/a-SiGe tandem solar cell have been achieved (area: 1 cm2).
Failure Analysis and New Design of a Thin-Film Silicon-on-Insulator Power Metal-Oxide-Semiconductor Field-Effect Transistor Based on Emission Microscopy and 2-Dimensional Device Simulation
Authors: Matsumoto Satoshi , Fukumitsu Takao , Kim Il-Jung , Sakai Tatsuo , Toshiaki Yachi Toshiaki Yachi
Published: October 2002

Thin-film silicon-on-insulator (SOI) power metal-oxide-semiconductor field-effect transistors (MOSFETs) with a standard stripe-gate topology and a cellular-gate topology have been fabricated. The breakdown voltage for the stripe-gate topology is half that for the cellular-gate topology in 200-V-class power MOSFETs. Their failure modes are analyzed by emission microscopy and 2-dimensional device simulation for the first time and a new device structure is proposed based on the results of this analysis. The fabricated new device attains a breakdown voltage of 200 V and a specific on-resistance of 2.7 Ω· mm2.
Diffusion Barrier Effects Against Cu of W-N Layer Formed by Electron Cyclotron Resonance Plasma Nitridation on W Layer
Authors: Ono Hideaki , Nakano Tadashi , Tomohiro Ohta Tomohiro Ohta
Published: October 2002

To improve the diffusion barrier effects of W against Cu, W-N/W multilayers formed by electron cyclotron resonance (ECR) N2 plasma exposure on W layers were investigated. Cu/W-N/W/Si multilayer structures were measured using secondary ion mass spectroscopy (SIMS), Rutherford backscattering spectroscopy (RBS), Auger electron spectroscopy (AES), and electric resistance change. The W-N/W films showed a dramatic improvement in barrier properties over those of metallic W films. When the thickness of the W-N/W barrier layer was only 5 nm, the Cu/W-N/W/Si multilayer retained the multilayer structure even after annealing at 873 K for 1 h in H2 without increase of resistivity. The thickness of the W-N layer formed by ECR plasma nitridation was less than 1-2 nm, which provided an excellent barrier effect.
Novel a-SiC/a-Si Heterojunction Filter with Twin-Wavelength Tunability
Authors: Lee Kuen-Hsien , Fang Yeau-Kuen , Chiou Yih-Jen , Kuo Lee-Ching
Published: October 2002

A novel a-SiC/a-Si heterojunction filter with twin-wavelength tunability has been developed successfully by plasma-enhanced chemical vapor deposition (PECVD) system. Using i-a-SiC:H to absorb blue light and i-a-Si:H to absorb red light, the device is able to simultaneously detect two different wavelengths of light. The peak response wavelengths are 630 nm and 450 nm. In addition, utilizing different contact electrodes and various values of reverse bias, the diode can also detect only blue light or only red light. Thus the a-SiC/a-Si heterojunction filter is a good candidate for optoelectronic integrated circuit (OEIC) applications, such as color image sensors and twin-wavelength photodetectors.
Test of the Recombination Model for the Energy Resolution in an Ionization Chamber Filled with Liquid Argon or Xenon
Authors: Eido Shibamura Eido Shibamura , Kimiaki Masuda Kimiaki Masuda , Tadayoshi Doke Tadayoshi Doke , Akira Hitachi Akira Hitachi
Published: October 2002

A test is made of the recombination model proposed by Thomas \et [Phys. Rev. A 38 (1988) 5793] for the energy resolution, of which the experimental value is far worse than that estimated by the Fano theory, in liquefied rare gas detectors. The energy resolution and the charge collection based on the recombination model are calculated for electrons or gamma rays in the liquid chamber doped with photoionizing molecules. The calculated energy resolution does not agree with that obtained by the recent experiments, although the agreement is good for the charge collection. It is suggested that the recombination is not a main cause of the energy resolution. Possible causes of poor energy resolution are discussed.
Dark and Photoconductivity Behaviors of Amorphous and Crystalline C60 Films
Authors: Asakawa Toshiaki , Sasaki Masahiro , Shiraishi Tadashi , Hideomi Koinuma Hideomi Koinuma
Published: October 2002

Deposition and in-situ electrical conductivity measurement of C60 thin films were conducted under high-vacuum conditions to evaluate the intrinsic electrical properties of C60 films without ambiguity due to surface contamination. Amorphous and polycrystalline films were deposited by vacuum evaporation of C60 powders onto fused silica glass, and cleaved NaCl(100) substrates, respectively, on which Al electrodes were deposited in advance. The film conductivity measured in-situ is highly reproducible and strongly dependent on the crystallinity not only in the absolute values of conductivity and its activation energy, but also in the behaviors under light irradiation and air exposure.
Thermonuclear Burn Performance of Volume-Ignited and Centrally Ignited Bare Deuterium-Tritium Microspheres
Authors: Stefano Atzeni Stefano Atzeni
Published: October 2002

A parametric study of the burn performance (measured by the fuel energy gain) of compressed deuterium-tritium fuel microspheres, with parameters of interest to inertial confinement fusion, has been performed by 1-D numerical radiation-hydrodynamics simulations. Both volume-ignited and centrally ignited (either initially isobaric or isochoric) configurations are considered. An overview is given of the relevant ignition conditions. For the first time a scaling law is presented for the limiting gain of volume-ignited fuels. Scaling laws are also given for the limiting gain of centrally ignited assemblies, which have the same functional dependences as predicted by previous analytical models, but different numerical coefficients. The advantage of isochoric assemblies over isobaric ones is confirmed, but found to be smaller than previously reported. The potentials of volume-ignited and of centrally ignited, isobaric assemblies as functions of the energy, density and pressure are also critically compared.
Highly Selective Contact Hole Etching Using Electron Cyclotron Resonance Plasma
Authors: Kimura Hajime , Shiozawa Ken'ichiro , Kawai Kenji , Miyatake Hiroshi , Masahiro Yoneda Masahiro Yoneda
Published: October 2002

The SiO2 etching process is one of the most significant processes in ultra-large-scale integration (ULSI) fabrication. In order to obtain fine contact holes, it is necessary to achieve both highly selective etching of SiO2 over other materials, and non-reactive ion etch (non-RIE) lag. We investigated the etching characteristics and the effect of O2 addition in C4F8+O2 plasma using electron cyclotron resonance (ECR) discharge. In C4F8+O2 plasma, we can obtain dense fluorocarbon films at low pressure, and films are more durable against ion bombardment than at high pressure. This film enables the suppression of O atoms to the Si surface, and the achievement of high SiO2-to-Si selectivity. By additional O2, dissociation of high-mass species such as C2F5 proceeds, and at about 20%O2, low-mass species, such as C, CF, and CF2, increase. Thus we can obtain high SiO2-to-Si selectivity and high-aspect-ratio fine contact holes.
Studies on Reaction Processes of Hydrogen and Oxygen Atoms with H2O-Adsorbed Si(100) Surfaces by High-Resolution Electron Energy Loss Spectroscopy
Authors: Hiroya Ikeda Hiroya Ikeda , Koji Hotta Koji Hotta , Tohru Yamada Tohru Yamada , Shigeaki Zaima Shigeaki Zaima , Yukio Yasuda Yukio Yasuda
Published: October 2002

Surface reactions of H2O-adsorbed Si(100) with atomic hydrogen and oxygen have been examined by high-resolution electron energy loss spectroscopy (HREELS). The surface with saturated coverage of H2O is terminated by H and OH species and the sticking probability of H2O is estimated to be 0.9. This surface is stable for the adsorption of molecular oxygen at room temperature. The presence of dissociation sites of oxygen molecules such as dangling bonds is considered to be essential to the oxidation of Si(100) surfaces. By the reaction of H2O-adsorbed Si(100) with atomic hydrogen, the uptake of oxygen atoms of Si-OH bonds into sites of Si back bonds occurs even at room temperature.
Valence-Band-Edge Energy of Group-III Nitride Alloy Semiconductors
Authors: Nakajima Sadanojo , Yang Tao , Shiro Sakai Shiro Sakai
Published: October 2002

Valence-band-edge energies for group-III nitrides, Ga1-xInxN, Ga1-xAlxN, In1-xAlxN and (GaxIn1-x)yAl1-yN, are calculated using ansp3hybrid-orbital model. Alloy disorder at cation sites is treated within the framework of the coherent-potential approximation. Our results show that the compositional dependence of valence-band edges for these alloy systems is almost linear.
Time-of-Flight Photocurrents in Amorphous Semiconductors under Nonequilibrium Trap States
Authors: Mikitaka Itoh Mikitaka Itoh , Keiji Tanaka Keiji Tanaka
Published: October 2002

Characteristic changes in time-of-flight photocurrents induced with photoelectric bias excitation have been studied in amorphous \asse, Se and Si:H films. If \asse films are exposed to bias illumination under electric fields, the transit time of dispersive carriers increases by a factor of ∼2. In Se and Si:H films, bias excitation makes nondispersive photocurrent signals featureless. In all the materials, bias excitation increases the number of collected carriers. These effects observed in photoelectrically biased amorphous semiconductors have been analyzed on the basis of a multiple-trapping model. The result suggests that bias excitation yields two effects: a density increase in shallow trap states and a modification of electric fields.
Use of Tetraethylgermane in ArF Excimer Laser Chemical Vapor Deposition of Amorphous Silicon-Germanium Films
Authors: Fujio Ishihara Fujio Ishihara , Hiroshi Uji Hiroshi Uji , Tatsuya Kamimura Tatsuya Kamimura , Satoru Matsumoto Satoru Matsumoto , Hirofumi Higuchi Hirofumi Higuchi , Shigefusa Chichibu Shigefusa Chichibu
Published: October 2002

A new organogermanium precursor, tetraethylgermane (TEGe, Ge(C2H5)4) was used with disilane in ArF excimer laser chemical vapor deposition of hydrogenated amorphous silicon-germanium films (a-Si1-x
Gex:H,C). The germanium composition, x, could easily be controlled since it almost coincided with the gas-phase composition. The optical band gap (E
opt) of the film was reduced from 1.8 eV (x=0) to 1.4 eV (x=0.8). This relatively wide E
opt compared with conventional hydrogenated or fluorinated silicon-germanium, was ascribed to the carbon corporation and dominant SiH2 and GeH2 bonds in the film.
Vibrational Local Modes of a-Si:(H, C) Alloys and Shifts of Local Modes under Annealing
Authors: Shu-Ya Lin Shu-Ya Lin
Published: October 2002

We have used the cluster-Bethe-lattice method to study the vibrational local modes of a-Si:(H, C) alloys. The local mode around 780 cm-1 could be assigned to both the Si-C vibrational mode and the wagging/rocking mode of the SiCH3 group. We have studied the variation of the Si-C vibrational modes in relation to the structural change upon annealing. The calculated results are in agreement with the infrared absorption spectra.
Preparations and Some Properties of W2B, δ-WB and WB2Crystals from High-Temperature Metal Solutions
Authors: Okada Shigeru , Kudou Kunio , Lundström Torsten
Published: October 2002

W2B, δ-WB and WB2crystals were prepared from high temperature aluminium and copper solutions using tungsten metal and crystalline boron powders as starting material under an argon atmosphere. Growth conditions for obtaining crystals of relatively large size were established. The crystals were examined by X-ray diffraction and chemical analysis. The Vickers microhardness and electrical resistivity of the crystals was measured, and oxidation at high temperature in air was studied. The microhardness value on (001) planes of δ-WB crystals is in the range of 25.3(±0.4)-26.7(±1.2) GPa. The microhardness value on (0001) planes of WB2crystals is 21.3(±0.4) GPa. The electrical resistivity determined on δ-WB and WB2crystals are as follows: for δ-WB: 171.5 µ Ω · cm; for WB2: 312.6 µ Ω · cm. The oxidation of W2B, δ-WB and WB2crystals begins to proceed with a measurable rate in the temperature range 550-730° C. The final oxidation products contain WO3and probably amorphous B2O3or H3BO3.
Magnetoresistance Effects of Fe-Mn/Ni-Fe-Co/(Au, Ag, Al)/Ni-Fe-Co Sandwiches
Authors: Nakatani Ryoichi , Hoshiya Hiroyuki , Hoshino Katsumi , Noguchi Shin , Yutaka Sugita Yutaka Sugita
Published: October 2002

Magnetoresistance effects and film structures have been investigated in [Hf/Fe-Mn/Ni-Fe-Co/(Au, Ag, Al)/Ni-Fe-Co/Hf/Si] sandwiches. The sandwiches show high magnetoresistance ratios when the Au and Ag spacers are thicker than 2.0 and 4.0 nm, respectively. The resistivity changes are almost equal to those of [Hf/Fe-Mn/Ni-Fe-Co/Cu/Ni-Fe-Co/Hf/Si] sandwiches. The sandwiches with Al spacers show magnetoresistance ratios of almost 0%, although the configuration of magnetisations of the two Ni-Fe-Co layers changes between parallel and antiparallel. Each sandwich has a strong (111) texture. The thickness of the Ag spacer is not homogeneous. The sandwiches show about the same thermal stabilities, whether the nonmagnetic spacer is Cu, Ag or Au.
High-Power InGaAs-GaAs-InGaP Strained Quantum Well Lasers on P-Type GaAs Substrate
Authors: Sin Yong Kun , Horikawa Hideaki
Published: October 2002

We report on device results from channel guide InGaAs-GaAs strained quantum well lasers with InGaP cladding layers. Channel guide lasers are demonstrated with the current blocking scheme using a p-n-p InGaP junction on p+-GaAs substrate. The laser structure is grown by metalorganic vapor-phase epitaxy (MOVPE) on the channeled n-InGaP layer. The uncoated lasers show CW laser threshold of 11 mA at RT, output power over 125 mW, fundamental lateral and transverse modes, and lasing wavelength of 0.98 µ m at 50 mW.
Anti-reflectivity-high-reflectivity (AR-HR) coated lasers show high output powers of 302 mW.
3 kHz XeCl Excimer Laser Using New Type of Electrode
Authors: Ishii Akira , Yasuoka Koichi , Okita Yuji , Tohru Tamagawa Tohru Tamagawa
Published: October 2002

A new type of electrode for XeCl excimer lasers has been developed. In order to produce a stable discharge at a high repetition rate, we calculated the electric field strength distribution of the discharge area, using the finite-element method. On the basis of the calculation results, we fabricated a new type of electrode, applied it to an XeCl excimer laser, and operated the laser at a repetition rate of 3 kHz. The laser power during 3 kHz operation was 18.9 W with the Ernst-type electrode and 24.4 W with the new-type electrode. The space distribution of density variance due to gas expansion in the discharge area could be checked by the laser schlieren method. With the Ernst-type electrode, the energy is concentrated in the center of the discharge area. With the new-type electrode, in contrast, the energy concentration is reduced, making the discharge stable.
Bulk Photovoltaic Effect in Reduced/Oxidized Lead Lanthanum Titanate Zirconate Ceramics
Authors: Nonaka Kazuhiro , Akiyama Morito , Hagio Tsuyoshi , Takase Akira
Published: October 2002

The dependence of the bulk photovoltaic effect (BPE) on illumination intensity and wavelength has been studied in (Pb0.97, La0.03)(Zr0.52, Ti0.48)1-0.03/4O3 ceramics normally sintered at 1200° C for 2 h and then heat-treated in various atmospheres such as nitrogen, air and oxygen at 900° C for 1 h to investigate the enhancement of the BPE in the nitrogen-treated sample. The values of the Glass constant and the photoconductivity increased with decreasing oxygen partial pressure (p O2) during the heat treatments, whereas that of the dark conductivity decreased, indicating the creation of oxygen vacancies. No significant change was observed in ion oxidation states in the heat-treated samples by X-ray photoelectron spectroscopic analysis. The wavelength showing the maximum value of the photovoltaic current became shorter with decreasing p O2 during the heat treatments and simultaneously the value of the maximum current notably increased. At the same time broadening of the current curves was also noted in the spectral responses. It is proposed that some of the electrons originating from the formation of oxygen vacancies can be expected to contribute to the enhancement of the BPE.
Variation in Conductivity of Cadmium Sulfo-Selenide Sintered Films with Vacuum Heat Treatment
Authors: Abdulla Aniwar , Kasai Akinari , Takenaga Mitsuru , Akira Nakamura Akira Nakamura
Published: October 2002

The conductivity of CdS-Se sintered film increases irreversibly about 109-fold with vacuum heat treatment from 100° C to 200° C. The mechanism of such a large variation has been studied using highly sensitive Hall effect and conductivity measurements. The obtained results can be analyzed by the grain-boundary potential-barrier model with the aid of the charge neutrality condition for the grains, the maximum allowable values of surface potential and potential barrier height, and the density of interface states. Increase in conductivity of 8 orders of magnitude is brought about by increase in the free electron density, which occurs in two steps: in the low-temperature region, the release of trapped electrons from the surface state occurs due to desorption of chemisorbed oxygen; in the high-temperature region, the increase in effective doping density through the decrease in acceptor density occurs due to the release of occluded oxygen from the bulk crystallites near the surface. The mobility of free electrons contributes to an increase of one order of magnitude in conductivity, which decreases once to a minimum and then increases. The variation in mobility is attributed to the barrier height at the grain boundary which is produced by trapped electrons at the intrinsic interface state.
Temperature Cycling Influence on Pyroelectric Figure of Merit of Triglycine Sulphate Doped with Alanine and Deuterated Triglycine Sulphate Doped with Alanine and Bivalent Platinum Crystals
Authors: Ramos Saturio , Martí José María , Jaime del Cerro Jaime del Cerro
Published: October 2002

While heating and cooling in the range 20-60° C, the pyroelectric coefficient, the dielectric permittivity and the specific heat of three samples of triglycine sulphate (TGS) family have been measured. These samples were TGS doped with alanine (ATGS), deuterated TGS doped with alanine (ADTGS), and deuterated TGS doped with alanine and bivalent platinum (ADTGS:Pt). Using these data, the thermal hysteresis of the pyroelectric figure of meritFvof these three crystals has been studied in this temperature range. The highest value ofFvwas obtained for the ADTGS:Pt crystal while the widest temperature range in whichFvcan be considered constant was obtained for the ADTGS crystal.
Direct Observation of Electron Charge of Si Atoms on a Si(001) Surface
Authors: Doi Takahisa , Ichikawa Masakazu
Published: October 2002

The electron charge of Si adsorbates evaporated on a Si(001)-2×1 surface is studied by tracing their behavior after heating of the substrate. A reflection electron microscope (REM) is used to observe denuded zones which are created at the terrace edge and grow with heating time. It is shown that two effects affect the adsorbates. One is the thermal effect, where the zone width (x) is proportional to the square root of heating time (t). The other is the electric effect, where x is proportional to t. At the critical time t

c
, the electric effect becomes a dominant force and the Si adsorbates migrate independently on the substrate surface. In the region of t>t
c, the adsorbates show the features of surface electromigration caused by the electric field. The adsorbates migrate in the same direction as that of the electric field applied for substrate heating. The results indicate that Si adsorbates are positively charged on the Si(001) surface.
Effects of Sine Wave Modulation on Tracking of Resonance and Antiresonance of Piezoelectric Resonator
Authors: Shigeo Hayashi Shigeo Hayashi
Published: October 2002

External signals of the form asin
2πf
0
t (t≥0) are applied to the PLL tracking system. The experimental values of the critical amplitude a
c such that the system is unstable for a>a
c vary continuously with f
0, and are in good agreement with the values obtained by numerical analysis. Extra stability due to barrier recrossing is gained in the narrow frequency range above the characteristic frequency f
c at which the system is the least stable. No hysteresis occurs for increasing or decreasing a. The results are free from an error in a preceding paper.
Compressibility of Polymer in Solution in the MHz Range
Authors: Hiroaki Ikeda Hiroaki Ikeda
Published: October 2002

The compressibility of solute obtained from measurements of ultrasonic velocity at 1 or about 3 MHz provided information on intermolecular potentials of segment (mixing unit of a polymer chain) in polymer solutions. The difference in solution properties between the theta and the good-solvent phases was interpreted from the viewpoint of intermolecular potentials of segments using the compressibility model. The new acoustic parameter in the MHz range was found to be proportional to the excluded volume of segments obtained from static measurements at 0 Hz in good solvents.
Effects of Nonlinearity in Development of Acoustic Streaming
Authors: Mitome Hideto , Kozuka Teruyuki , Toru Tuziuti Toru Tuziuti
Published: October 2002

Development of acoustic streaming generated along the beam axis of ultrasound in unbounded medium is discussed using a numerical analysis. Acoustic nonlinearity changes the distribution of driving force of streaming. If fluid-dynamic nonlinearity is neglected, the streaming velocity essentially increases in proportion to the square of source amplitude. Incorporation of acoustic nonlinearity enhances the streaming velocity near the sound source and suppresses it at a farther distance compared to the acoustically linear case. When fluid-dynamic nonlinearity is taken into account, the fundamental trend in the increase of streaming velocity changes from the second power of the source amplitude toward the first power. Thus the fluid-dynamic nonlinearity delays the development of acoustic streaming.
Ultrasonic Motor Using a Large-Diameter Torsional Vibrator with Slant Slits
Authors: Kenji Sato Kenji Sato , Manabu Aoyagi Manabu Aoyagi , Toshiharu Ogasawara Toshiharu Ogasawara , Yoshiro Tomikawa Yoshiro Tomikawa
Published: October 2002

This paper deals with a large-diameter rod-type ultrasonic motor, in which only the torsional vibration is excited piezoelectrically. This new motor is designed to improve the performance of a relatively high-torque motor by increasing the diameter of the stator vibrator. The characteristic feature of the motor construction is that many slits are cut aslant on the vibrator end-face in contact with a rotor in order to form small slanted cantilever beams; that is, these cantilever beams operate in the bending vibration due to coupling with the main torsional vibration of the stator and lift the rotor in the inclined direction to rotate it. Therefore, this motor operates fundamentally one-way, and thus its advantage is that it is easily driven with a single power source. The first part of this paper concerns the simulated results of an aslant slit torsional vibrator, especially on its slanted cantilever beam, and the second part describes the experimental investigation of the prototype motor.
Construction of Torsional-Vibration Systems with a Hollow Cylindrical Bolt-Clamped Langevin-Type Transducer and Their Application to Ultrasonic Plastic Welding
Authors: Kazunari Adachi Kazunari Adachi , Masanaka Saito Masanaka Saito
Published: October 2002

We have previously developed a hollow cylindrical bolt-clamped Langevin-type transducer with a high mechanical quality factor (Q) for excitation of high-amplitude torsional vibrations. In this paper, we propose a construction of vibrating systems that comprise a `stepped horn' (a mechanical transformer of torsional vibration) and the stumpy `twisting' transducer developed by us. The distinctive feature of the construction is that it achieves compactness without sacrificing the volume of piezoelectric ceramics that is important for high-power ultrasonic applications. Through experiments, we have found some crucial points in the procedure for constructing torsional-vibration systems that can be operated at a relatively high frequency. In addition, we have conducted some experiments of ultrasonic plastic welding using one of the vibrating systems for evaluation of the feasibility of the construction in this manufacturing technique
Frequency-Domain Autocorrelator for Estimation of Blood Flow Velocity
Authors: Taibao Li Taibao Li
Published: October 2002

In color Doppler systems the received RF signal is multiplied by a reference signal and subsequently averaged over a short depth range to obtain a sample of Doppler signal. The mean frequency of the Doppler signal, reflecting the mean velocity of the scatterers moving through the depth range, is obtained by a time-domain autocorrelator. An alternative is to evaluate the time shift of range-gated RF signals over subsequent A-lines, and then give the velocity of the scatterers. This paper presents a frequency-domain autocorrelator to estimate the time shift associated with a high-pass filter for removing small time shift components. It has the same mathematical expression as that for the time-domain autocorrelator, and most of the hardware of the conventional color Doppler systems can be used for its implementation. The first results of computer simulations show that the new estimator is superior to the conventional Doppler technique.
Computer Simulation of Ultrasonic Images with Self-Similarity of Tissue Structures
Authors: Akiyama Iwaki , Ohya Akihisa , Taniguchi Nobuyuki , Itoh Koichi
Published: October 2002

A simulation model of reflection source distribution in biological tissues is proposed. The tissue is considered to consist of cells of various sizes. The distribution is computed using the fractal Brownian function. The ultrasound wave is reflected at the center of a cell and the coefficient of reflection is proportional to the area of a cell. The cell distribution is computed for the initial Hurst coefficient range of 0.2 to 0.8. The occupied area of every image is equal, because the cell density is kept constant. The Hurst coefficient of the ultrasonic image which is computed from the cell distribution is dependent on the initial Hurst coefficient for the cell distribution. As a result, it is indicated that the fractal analysis is effective for the characterization of tissue structure.
Ocean Experiments to Discriminate Seabed Materials by Echo Pulse and Neural Network at Uchiura Bay
Authors: Motooka Seiichi , Kitami Mitsumasa , Ogawa Kiyoma , Nobuyuki Takano Nobuyuki Takano
Published: October 2002

The authors used two sets of measurements, the first made in Aug. 1991 at Uchiura Bay, off Numazu City, and the second made in Oct. 1993 at nearly the same place, in an attempt to prove the usefulness of pulse echo and neural network in discriminating different types of seabed material, such as rock, sand and silt. As a result, good discrimination ratios of over 80% for the 3 seabed materials were achieved when learning and discriminating data were obtained by averaging 32 datums from one measuring place and averaging again this average value for more than 3 measuring places.
Time-Domain Analysis of SOFAR Propagation in Low-Latitude Sea Area by Wave Theory and Ray Theory
Authors: Imayoshi Shinichi , Tsuchiya Toshio , Kikuchi Toshiaki , Akio Hasegawa Akio Hasegawa
Published: October 2002

In investigation into the phenomenon of global warming, ocean acoustic tomography (OAT) has been used for analysis. In this analysis method, the most important factor is exact calculation of the sound speed in water, that is, the sound wave propagation time. However, so far, analysis of SOFAR propagations in the low-latitude sea area has been lacking. Such a sea area is very important for analysis of the El Ni
n
o Current and others, although a special sound speed structure appears in the region of uniform sound speed formed around the SOFAR axis. For SOFAR propagation, we have compared time-domain results using two models, based on the measurement of far-range sound wave propagation in the sea east of Mindanao Island. The models chosen for the analysis are Stickler's normal mode method (SNM) and ray approximations. (The SNM time series is obtained via Fourier synthesis.) By this means we examined the characteristics of wave theory and ray theory in the low-latitude sea area.
Observation of 1-nm-High Structures on a Si(001) Surface Using a Differential Interference Optical Microscope
Authors: Doi Takahisa , Ishizaka Akitoshi , Ichikawa Masakazu , Hosoki Shigeyuki , Ken Ninomiya Ken Ninomiya
Published: October 2002

A Si(001) clean surface is oxidized by exposure to air and the step-band structures on the oxidized surface are observed using a differential interference optical microscope in air. The step-bands observed consist of many monatomic steps. Electromigration, induced using alternating-current heating, splits the step-band into steps on the Si(001) surface. The number of monatomic steps is counted after alternating-current heating and the height of the step-band is determined to be about 1 nm. Using a differential interference microscope, it is possible to observe structures with height of nanometer-order on a Si(001) surface.
Low Temperature Resonant Secondary Emission in CuGaS2 by Γ Point Excitation
Authors: Yamamoto Nobuyuki , Kitakuni Masatake , Susaki Masami
Published: October 2002

Resonant secondary emissions are examined on the (100) surface of CuGaS2 crystal. Two bound-exciton luminescence lines and 27 sharp resonant-Raman lines are observed under polarizing excitation of 4765 Å and 4880 Å in <X|Z
Z| \barX> configuration. Resonant enhancement and breakdown of the Raman selection rule for longitudinal E modes are attributed to the intraband Fröhlich interaction. High resolution measurement and accurate polarization evaluation can be performed using a line rejection filter and a polarization compensator, respectively.
Pedestal Reduction by Temporal and Spectral Filterings in Chirped Pulse Amplification
Authors: Zhang Tiejun , Kato Yoshiaki , Hiroyuki Daido Hiroyuki Daido
Published: October 2002

We present numerical calculations on pedestal reduction of high-intensity ultrashort laser pulses generated by chirped pulse amplification. When an optical fiber is used as a pulse expander to generate a chirped pulse, spectral filtering is not effective in reducing the pedestal arising from the nonlinear chirp near the central frequency. The temporal filtering, in contrast, is effective in reducing the pedestals arising from various chirp nonlinearities and amplified spontaneous emission. It is shown that a contrast ratio exceeding 1010 is achievable with appropriate filtering techniques.
Rubbing-Induced Molecular Alignment on an Orienting Layer of Polyimide with and without Alkyl Side Chains
Authors: Huang Jung Y. , Li Jie S. , Juang Youe-S. , Shu-Hsia Chen Shu-Hsia Chen
Published: October 2002

The rubbing-induced molecular alignment on a surface of polyimide with and without branched alkyl side chains was investigated with optical phase retardation measurement, atomic force microscopy (AFM), and second-harmonic generation (SHG). Our AFM results suggest that the rubbing-induced microgrooves play a minor role in aligning liquid crystal (LC) molecules. From the SHG studies, the detailed in-plane distribution of a LC monolayer on rubbed polymers was deduced, and the polar angle of the LC molecules was found to vary with the rubbing strength exerted on an alkyl-branched polymer. The polar angle of the LC monolayer on an alkyl-branchless main-chain polyimide film was observed to be independent of the rubbing strength. We propose a simple molecular model to reconcile these experimental results.
Re-Oxidation of Thermally Nitrided Silicon Dioxide Thin Films
Authors: Kiyotoshi Masahiro , Tsunasima Yoshitaka , Kikuo Yamabe Kikuo Yamabe
Published: October 2002

Re-oxidation of thermally nitrided SiO2 thin films was studied. The SiO2 growth rate at re-oxidation is reduced until a certain time (the “oxidation delay time” or “ODT”) has passed. During the ODT, thermally nitrided SiO2 at the Si-SiO2 interface is re-oxidized. the ODT is the time required for complete oxidation of nitrided SiO2. Re-oxidation of thermally nitrided SiO2 thin films is limited not by diffusion of oxidizing species, but by oxidation of nitrided SiO2. The ODT is proportional to the nitrided SiO2 thickness. Nitrided SiO2 formation at the Si-SiO2 interface is mass-transfer controlled by nitriding species through nitrided SiO2 to Si substrate. As an application of thermal nitridation of SiO2, thermal nitridation of the local oxidation of silicon (LOCOS) pad oxide can shorten the bird's beak of LOCOS.
Scanning Tunneling Microscopy and Atomic Force Microscopy Study on Interface between Molecular-Beam-Grown Pt Film and Si(111) Substrate
Authors: Kouichi Nishikawa Kouichi Nishikawa , Masahiko Yamamoto Masahiko Yamamoto , Katsuyuki Ichimiya Katsuyuki Ichimiya , Yukihiro Umetani Yukihiro Umetani , Toshiki Kingetsu Toshiki Kingetsu
Published: October 2002

A method of observing interfaces using scanning tunneling microscopy and atomic force microscopy is proposed, and the method is applied to observe interfaces between Pt film and Si(111) substrate, and the Pt/Si interface topography is clearly presented. Microstructures of interface such as band structure, island structure and netlike structure are described in detail. Finally, the reaction path at Pt/Si interface is discussed.
Calculation of the Three-Dimensional Field Vectors in Dielectrics
Authors: Takechi Kimihiro , Arii Kiyomitsu , Udo Sadahito , Haruo Ihori Haruo Ihori
Published: October 2002

We have developed a culculation method of the applied electric field in a dielectric by measuring the difference in the output light intensity. At present, the direction of each applied field can be calculated when the dielectric is divided into four cells in which the applied fields are the same in intensity but differ in direction. Firstly, this paper shows how to determine the applied field intensity and direction when the electric field is applied to only one dielectric cell. Secondly, the method of numerical calculation of the applied field is described applying the method for one cell to a case where the dielectric is divided into two cells in which the intensity of the applied field is known but the direction is unknown. Finally, by extending the case of two cells, the flow of the numerical analysis and its result are described when the dielectric is divided into four cells under the same conditions as those for the two-cell case.
Microwear of Silicon Surfaces
Authors: Yasuko Andoh Yasuko Andoh , Reizo Kaneko Reizo Kaneko
Published: October 2002

A silicon surface and a diamond-like carbon film were scanning scratched in the air. The silicon surfaces scratched with a light load upheaved immediately. This upheaval represents the pre-stage of wear. The silicon surface depressed by heavier scratching began to upheave after some time. This implies that the surface was activated by scratching and adsorbed molecules in the air.
Control of Microstructure and Optoelectronic Properties of Si:H Films by Argon Dilution in Plasma-Enhanced Chemical Vapor Deposition from Silane
Authors: Chaudhuri Partha , Ujjwal Kumar Das Ujjwal Kumar Das
Published: October 2002

Structural and optoelectronic properties of thin films of silicon-hydrogen binary alloy (Si:H) deposited from silane and argon mixture in a rf glow discharge plasma have been studied for different argon dilutions and rf powers. It has been observed that with low rf power density ( 30-70 mW/cm3) increase of argon dilution up to 95% reduces the microstructure in the films, as determined from IR absorption spectra. Simultaneously, increase in refractive index and decrease in ESR spin density have been observed. Above 95% argon dilution or with higher rf powers, transmission electron microscopy (TEM) studies reveal a dominance of the columnar growth mechanism, and the optoelectronic properties of the films deteriorate. At 99% argon dilution, microcrystallites appear to form within columnar regions. Addition of a small amount of hydrogen to the silane-argon plasma improves the network significantly, which is manifested by the changes in the dark conductivities in the different rf power regimes.
Low-Noise and High-Power GaAlAs Laser Diodes with a New Real Refractive Index Guided Structure
Authors: Takayama Toru , Imafuji Osamu , Sugiura Hideyuki , Yuri Masaaki , Naito Hiroki , Kume Masahiro , Kunio Itoh Kunio Itoh
Published: October 2002

We demonstrate for the first time a real refractive index guided GaAlAs laser structure that has both very low-noise characteristics at a low output power (reading mode) and a stable fundamental transverse mode up to a high power level (writing mode) sufficient for optical read-write systems. The low-noise characteristics are realized by self-sustained pulsation which is induced by large saturable absorbers outside a stripe, and the high power is achieved by using a thin active layer which confines the optical flux very loosely. In order to optimize the device parameters, numerical simulation of the structure is proposed with consideration of interaction between optical field and carrier diffusion under gain nonlinearity and carrier diffusion taken into account. The calculated results are verified experimentally. The lasers showed relative intensity noise level less than -135 dB/Hz under 0-20% optical feedback and output power higher than 60 mW.
Blue Light Emitting Diode
Authors: Lee Ming-Kwei , Yeh Min-Yen , Huang Hon-Da , Chih-Wei Hong Chih-Wei Hong
Published: October 2002

An n-ZnSe/p-ZnSe/p+-GaAs blue light emitting diode was prepared by low pressure organometallic chemical vapor deposition. Its electroluminescence wavelength was 461 nm with a full width at half maximum 52 meV at 300 K.
It shows that a pure blue ZnSe light emitting diode can be prepared under Zn-rich growth condition for n-type ZnSe epilayer doped with aluminum and under Se-rich growth condition for p-type ZnSe epilayer doped with nitrogen.
Effects of Rubbing and Temperature Dependence of Polar Anchoring Strength of Homogeneously Aligned Nematic Liquid Crystal on Polyimide Langmuir-Blodgett Orientation Films
Authors: Seo Dae-Shik , Kobayashi Shunsuke , Kang Dou-Yol , Yokoyama Hiroshi
Published: October 2002

The effect of rubbing on the polyimide (PI) Langmuir-Blodgett (LB) surface-alignment films has been successfully evaluated by observing the temperature dependence of the polar anchoring strength of nematic liquid crystal 4-cyano-4'-n-pentylbiphenyl (5CB). Upon rubbing, the PI-LB films showed a significant increase in the anchoring strength. The anchoring strength showed a nearly divergent decrease toward the clearing temperature, which is a manifestation of the diminished surface ordering, as previously pointed out for obliquely evaporated SiO films. Based on the van der Waals theory developed by Yokoyama et al. [J. Appl. Phys. 61 (1987) 4501], the intrinsic parts of the anchoring energy have been obtained as a function of temperature and found to undergo nearly one order of magnitude increase on rubbing. The polar anchoring energies for 5CB were strongly related to the surface order parameter on PI-LB films.
Heteroepitaxial Growth of Tungsten Carbide Films on W(110) by Plasma-Enhanced Chemical Vapor Deposition
Authors: Katoh Masahiro , Kawarada Hiroshi
Published: October 2002

Tungsten carbide (WC) layers have been grown epitaxially on tungsten single crystals for the first time by using microwave plasma and electron cyclotron resonance plasma carburization of single-crystalline tungsten. WC on tungsten is grown epitaxially as (0001)WC||
(110)W in the alignment [1\bar210]WC||
[\bar111]W.
Side Wall Roughness Reduction in Deep Silicon Oxide Etching Using C2F6 Based ECR-RIBE
Authors: Achyut Kumar Dutta Achyut Kumar Dutta
Published: October 2002

A process using multilayered mask, consisting of either novolak based resist or special type of light insensitive polymer and thin metal, is developed for improving the side wall smoothness of silicon oxide etching. Different techniques are used to reduce the side wall roughness of the mask prior to the underlying silicon oxide etching. The mask smoothness is reduced down to 25 nm using underlying thin metal layer which not only increases the adhesion of the upper resist/polymer with the silicon oxide, but also acts as the etch stopper during patterning of the upper resist/polymer. The side wall smoothness of underlying silicon oxide etching using the smooth polymer mask, is improved down to 60 nm which is better than conventional process where metal mask is used.
Characterization of Gas Sorption of Plasma-Polymerized Cu-Phthalocyanine Film
Authors: Kurosawa Shigeru , Arimura Takashi , Tamura Masanori , Shibakami Motonari , Sekiya Akira , Kamo Naoki
Published: October 2002

The molecular recognition part of a gas sensor on a piezoelectric quartz crystal is prepared by the plasma polymerization technique. Cu-phthalocyanine (CuPc) was used as the monomer for plasma polymerization. The sorption of gases by the plasma-polymerized CuPc film coated on piezoelectric quartz crystal was measured. The intermolecular interactions between plasma-polymerized CuPc and a series of various gases were characterized on the basis of physicochemical parameters, i.e., the partition coefficient and modified Small's number. A specific interaction other than hydrophobicity occurs in the presence of double bonds, cyclorings, and aromatics. It results from the π-π interaction, because CuPc has a number of double bonds.