bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of a Step-Doped-Channel Negative-Differential-Resistance Transistor
Authors: Laih Lih-Wen , Cheng Shiou-Ying , Lin Kun-Wei , Lin Po-Hung , Chen Jing-Yuh , Wei-Chou Wang Wei-Chou Wang , Wen-Chau Liu Wen-Chau Liu
Published: October 2002

An interesting AlGaAs/InGaAs/GaAs step-doped channel negative-differential-resistance transistor (SDCNDRT) has been fabricated. The SDCNDRT is based on a previously reported step-doped-channel field-effect transistor (SDCFET). The N-shaped negative-differential resistance (NDR) are three-terminal-controlled NDR phenomena. We believe that the NDR phenomena can be attributed to the real space transfer (RST). A maximum drain current and peak-to-valley current ratio (PVCR) of 59 mA and 6.6 are obtained, respectively. The high drain current and PVCR indicate the potential of the SDCFET for practical circuit applications.
Preparation of Poly-Ge Considering its Application to a-Si/Poly-Ge Multilayer Structures by a Low-Temperature Solid Phase Crystallization Method
Authors: Maruyama Eiji , Haku Hisao , Tanaka Makoto , Seiichi Kiyama Seiichi Kiyama , Shinya Tsuda Shinya Tsuda
Published: October 2002

Poly-Ge films with good crystallinity were prepared by a low-temperature solid phase crystallization (SPC) method for application to multilayer a-Si/poly-Ge structures. Using a-Ge:H films prepared at just below the thermal decomposition temperature of GeH4 gas as the starting material for SPC, high-quality poly-Ge with Ge<111> peak orientation was obtained after low-temperature annealing at 350°C for 2 h in a nitrogen atmosphere. Furthermore, the selective crystallization of a-Ge:H sublayers in an a-Si:H( ∼50 Å)/a-Ge:H( ∼1000 Å) multilayer film was achieved by annealing at 350°C. The poly-Ge sublayers included large crystal grains with dimensions of about 3000 Å, which were three times as thick as the poly-Ge sublayers.
Fabrication of 0.2 µm Hole Patterns in KrF Excimer Laser Lithography
Authors: Asano Masafumi , Kawano Kenji , Satoshi Tanaka Satoshi Tanaka , Yasunobu Onishi Yasunobu Onishi
Published: October 2002

This paper describes the fabrication of 0.2 µ m hole resist patterns in KrF excimer laser lithography. By using a SiN

x

single-layer halftone phase-shifting mask (PSM) and an in-house chemically amplified positive resist, 0.2 µ m hole resist patterns can be obtained with sufficient depth of focus (DOF). Furthermore, a 0.15 µ m hole resist pattern can also be fabricated by using the PSM.
Anisotropic Resistivity of In-Plane-Aligned La 2-xSrxCuO 4(100) Films on LaSrGaO 4(100) Substrates
Authors: Hiroaki Myoren Hiroaki Myoren , Roger Bergs Roger Bergs , Takashi Tachiki Takashi Tachiki , Jian Chen Jian Chen , Kensuke Nakajima Kensuke Nakajima , Mitsumasa Suzuki Mitsumasa Suzuki , Tsutomu Yamashita Tsutomu Yamashita , Hisashi Sato Hisashi Sato , Michio Naito Michio Naito
Published: October 2002

We prepared in-plane-aligned La2-x
Sr
x
CuO4(100) films using LaSrGaO4(100) substrates by KrF laser ablation. The φ scan of X-ray diffraction and the large anisotropy of resistivity indicate a high degree of in-plane epitaxy. The T
c of the in-plane-aligned La2-x
Sr
x
CuO4 (x=0.15) was 21.6 K. The critical temperatures measured along the c-axis were usually higher than those measured along the a-axis. We also observed voltage peaks at just above T
c, corresponding to the abrupt decrease of the anisotropy of resistivity at T
c.
EuBa 2Cu 3O 7-δ Thin Films Grown on Sapphires with Epitaxial CeO 2 Buffer Layers
Authors: Osamu Michikami Osamu Michikami , Atsushi Yokosawa Atsushi Yokosawa , Hironori Wakana Hironori Wakana , Yasube Kashiwaba Yasube Kashiwaba
Published: October 2002

Epitaxial growth of CeO2 films on Al2O3 (11̄02) substrates and the effect of CeO2 buffer layers on the growth orientation and superconducting properties of EuBa2Cu3O7-δ (EBCO) were investigated. CeO2 and EBCO films were prepared by rf and dc magnetron sputtering, respectively, and were characterized by X-ray diffraction (θ-2θ scan and ϕ scan), atomic force microscopy (AFM) and high resolution scanning electron microscopy. Epitaxial (001) CeO2 films were obtained at an off-center distance (D
on-off) of 3.5 cm and a substrate temperature of 660°C. The structural and superconducting properties of EBCO films deposited at 650°C depended on the thickness of the CeO2 buffer layer. The EBCO films deposited on CeO2 50-400-Å-thick buffer layers had T
ce's of 90 K or above. The high-T
c EBCO films had in-plane epitaxial orientation relationships of Al2O3 [112̄0]\varparallelCeO2 [100]\varparallelEBCO[110]. The EBCO films on the thin CeO2 buffer layers had rectangular grains similar to those on MgO(001) substrates. The critical current density of the EBCO films with T
ce=90 K was about 6 ×105 A/cm2 in zero field at 77.3 K. The T
ce varied largely and decreased with increasing CeO2 buffer layer thickness above 500 Å. AFM observation of a 1000-Å-thick CeO2 film showed growth of bamboo-like crystal grains 1700 Å long and 300 Å wide along the direction of CeO2 [110]. The ravine depths were about 100 Å. The EBCO films on the thick CeO2 buffer layer (>500 Å) exhibited poor superconducting behavior and gave (103) or (110) diffraction peaks.
The Effect of Lithium Intercalation on the Crystal Structure and Magnetic Property of Layered FeWO4Cl
Authors: Choy Jin-Ho , Park Nam-Gyu , Yoon Joo-Byoung , Chang Kyoo-Seung Han
Published: October 2002

LiFeWO4Cl has been prepared by reductive intercalation of lithium into FeWO4Cl. FeWO4Cl crystallizes into a tetragonal system (space group P4/nmm) with cell dimensions of a=6.677(5) Å and c=5.270(5) Å, while lithium intercalation gives rise to the formation of a monoclinic phase ( P21/m) with cell dimensions of a=7.050(0) Å, b=6.926(2) Å, c=5.043(0) Å and β=92.54(2)°. Infrared (IR) spectroscopic analyses of FeWO4Cl and LiFeWO4Cl show that the symmetry of the tetrahedral WO4
2- group in FeWO4Cl becomes reduced as the lithium intercalate into its two-dimensional lattice, indicating an alternately ordered lithium occupancy of half of the octahedral interlayer sites. The effective magnetic moments of FeWO4Cl and LiFeWO4Cl were estimated to be 5.95 and 5.10 B.M., respectively, which can be attributed to the selective reduction of a high-spin ferric ion to a high-spin ferrous one upon lithium intercalation. It was also found that the two-dimensional magnetic property of FeWO4Cl was changed to a three-dimensional one in LiFeWO4Cl owing to the c-axis contraction.
Reverse Mode and Wide Viewing Angle Properties in Polymer Dispersed Liquid Crystal Cells Prepared Using a UV Curable Liquid Crystal
Authors: Rumiko Yamaguchi Rumiko Yamaguchi , Yutaka Waki Yutaka Waki , Susumu Sato Susumu Sato
Published: October 2002

Reverse mode properties have been achieved in novel polymer dispersed liquid crystal (PDLC) cells using a UV curable liquid crystal (LC) as a polymer matrix. A homogeneously aligned PDLC cell is composed of a nematic LC with positive dielectric anisotropy and the UV curable LC. Another type of the PDLC cell where the molecular alignment is homeotropic is prepared using a LC with negative dielectric anisotropy. These PDLC cells have a very wide viewing angle both in a highly transparent off-state and in a light scattering on-state due to the refractive index anisotropy of the matrix. Fast response and recovery properties of a few ms can be obtained in the homeotropically aligned PDLC cell.
Influence of Pt, RuO 2 and SrRuO 3 Intermediate Layers on Characteristics of (Sr 0.5Ba 0.5)Nb 2O 6 Thin Films
Authors: Hsiu-Fung Cheng Hsiu-Fung Cheng , Chen-Ti Hu Chen-Ti Hu , I-Nan Lin I-Nan Lin
Published: October 2002

The influence of Pt, RuO2 and SrRuO3 intermediate layers on the growth of (Sr0.5Ba0.5)Nb2O6 (SBN) thin films and their related electrical properties has been examined. Crystalline SBN films on Pt-coated Si can be obtained at substrate temperatures higher than 720°C (1 mbar), whereas the formation of SBN films on RuO2-coated Si is difficult, due to the instability of the RuO2 layer at high substrate temperatures. On the other hand, SrRuO3 layers deposited at 600°C (0.1 mbar) not only possess good electrical conductivity (ρ s ≈0.5 mΩ·cm), making them suitable for use as base electrodes, but also have good lattice matching with SBN materials, which markedly enhances the formation of SBN films. However, a special procedure including the deposition of SBN thin films at 600°C (0.1 mbar) to preserve the perovskite phase of the predeposited SrRuO3 layers, followed by postannealing at 750°C (1 atm) to fully crystallize the SBN materials, is required to obtain optimum multilayer films. The remanent polarization thus obtained is around P
r=2.8 µC/cm2 and the leakage current density is around J
1 =10-7 A/cm2.
Quantum-efficiency Dependence of the Spin Polarization of Photoemission from a GaAs–AlGaAs Superlattice
Authors: Tsunehiko Omori Masafumi Tawada , Chihiro Suzuki Chihiro Suzuki , Yasunori Takeuchi Yasunori Takeuchi , Kazuaki Togawa Kazuaki Togawa , Masakazu Yoshioka Masakazu Yoshioka
Published: October 2002

We measured the quantum-efficiency (QE) dependence of the spin polarization of photoemission from a GaAs-AlGaAs superlattice over a wide range of QE values. In the QE range from 10-4 to 10-9, a change in the polarization from 76% to 48% was observed at a wavelength of 778.5 nm. The maximum polarization at 778.5 nm was observed at a QE one tenth of the maximum value. We also observed a similar dependence at other wavelengths. Such a behavior suggests that the vacuum level and surface potential barrier play important roles concerning the spin polarization of photoemission.
Seventy GHz Slow Surface Wave Propagation in a Waveguide Containing Transversely Magnetized p-Type and n-Type InSb Slabs
Authors: Yodokawa Shinichi , Satoru Kosaka Satoru Kosaka , Tetsuo Obunai Tetsuo Obunai
Published: October 2002

Wave propagation characteristics in a 70 GHz waveguide containing transversely magnetized p-type and n-type InSb slabs have been studied experimentally. Surface wave resonance occurs in this configuration. It is also shown that the magnetic field required for slow surface wave resonance is greatly reduced by the addition of the p-layer.
Reversible Photo-Induced Structural Change in Hydrogenated Amorphous Silicon
Authors: Shiba Kousaku Shimizu , Takashi Tabuchi Takashi Tabuchi , Hiroaki Okamoto Hiroaki Okamoto
Published: October 2002

A reversible photo-induced change has been observed in the polarization dependence of a transverse electroabsorption signal for hydrogenated amorphous silicon, which is indicative of the occurrence of structural change in the whole material. The change proceeds rapidly under steady light exposure until saturation is reached, while the decrease in the photoconductivity becomes significant just after saturation. These observations convince us that a large-scale photostructural change is involved in the photo-induced degradation of the electronic properties of the material in addition to the creation of metastable dangling bond defects.
Anomalous Ultrasonic Absorption of Liposome Suspensions in the Liquid Crystal Phase
Authors: Etoh Akinori , Yamamoto Kazunori , Okano Shigeki Mitaku
Published: October 2002

Ultrasonic velocity and absorption of liposome suspensions of dimyristoyl phosphatidylcholine in the liquid crystal phase were measured in the megahertz region, varying the temperature and the size of liposomes. Temperature dependence of ultrasonic properties indicated a critical phenomenon due to the gel-liquid crystal transition at about 24° C, which is characterized by a dip in ultrasonic velocity and an anomalous increase in absorption. However, the anomalous frequency dependence of ultrasonic absorption remained significant even at 35° C where the critical phenomenon almost disappeared. This additional absorption anomaly strongly depended on the size of liposomes. The value of viscosity of multilamellar liposome suspensions estimated from the ultrasonic absorption was inversely proportional to the frequency of the ultrasound and diverged to infinity in the low-frequency limit, while this kind of anomaly was not observed for small unilamellar lipid vesicles. This liposome size dependence indicated clearly that the additional absorption anomaly in multilamellar liposomes was due to the fluctuation of their lamellar structure. The possibility of estimating the content of stacked membrane layers in biological tissue by ultrasonic absorption is discussed based on the ultrasonic measurements of liposomes.
Precise Measurement in Laser Ultrasonics by Phase Velocity Scanning of Interference Fringes
Authors: Kazushi Yamanaka Kazushi Yamanaka
Published: October 2002

In laser ultrasonics, the characteristics of acoustic waves, such as mode selectivity and directivity, are not as good as in piezoelectric techniques, and this is a problem in achieving high measurement precision. Thus, we proposed the phase velocity scanning method for selective generation of surface acoustic waves (SAW), and bulk acoustic waves (BAW). For SAW generation, a thermoelastic source of interference fringes is scanned at the phase velocity of the SAW. For SAW velocity measurement, the ratio of the measured SAW frequency and the wave number of the scanning interference fringes is employed. The velocity measurement is very precise (better than 0.1%) because of the amplitude enhancement of desired SAW and suppression of spurious SAW and BAW. For BAW generation, the interference fringes are scanned at considerably higher velocity, and excellent directivity of longitudinal and shear waves has been realized for the first time.
Noncontact Measurement of Surface Tension by Ripplon Light Scattering Spectroscopy
Authors: Atsumi Ozawa Atsumi Ozawa , Akiko Minamisawa Akiko Minamisawa
Published: October 2002

A new method of rapid and non-contact surface tension measurement based on the ripplon light scattering technique is described. A light beam from a cw-YAG laser with 100 mW output was focused on the surface in a small spot of a diameter comparable to the coherent length of ripplon. A very intense signal of the ripplon light scattering was thus obtained and the time required for the measurement was successfully reduced to ∼5 s. High spatial resolution was also obtained using the focused laser beam. The dispersion relation of ripplon on a pure water surface was measured over a wide frequency range from 10 kHz up to 1 MHz, and the surface tension was determined to be within an accuracy of 1%. The result of surface tension measurement obtained for a water/ethanol mixture is also demonstrated.
Effect of Sodium Dodecyl Sulfate on Coil-Globule Transitions of Poly(N-isopropyl acrylamide)
Authors: Ando Makoto , Takahashi Daisuke , Shinichiro Takeda Shinichiro Takeda , Haruhiko Nakajima Haruhiko Nakajima
Published: October 2002

Mechanical properties of aqueous solutions of poly(N-isopropylacrylamide) (PNIPAM) were studied over a temperature range from 25° C to 40° C using a Zimm viscometer. For a PNIPAM/water system a remarkable increase in specific viscosity, η sp, was found at about 31° C. But in the case of PNIPAM (0.1 g/d l )/sodium dodecyl sulfate (SDS) (0.03 g/d l )/water system a clear decrease in η sp from 0.27 to 0.12 was observed on going through that temperature. The translational diffusion constant was also measured by dynamic light scattering (DLS), and a decrease in the effective hydrodynamic radius by a factor of 1/3 was observed over the same temperature range. These results suggest that SDS prevents the aggregation of polymers without hindering the intramolecular phase transitions.
Determining the Size of Colloidal Particles Using Ultrasonic Absorption Measurements
Authors: Matsuoka Tatsuro , Kitano Hideki , Yasuda Keiji , Shinobu Koda Shinobu Koda , Hiroyasu Nomura Hiroyasu Nomura
Published: October 2002

Ultrasonic absorption spectra of colloidal solutions of silica sol, polymer latex sol and hematite sol were measured to test the validity of the method of determining particle size using the oscillator cell (OC) model based on the viscous dissipation mechanism. For the solution of the spherical particles, the OC model reproduced the ultrasonic absorption of silica sol. For the polymer latex of PTFE, the experimental results were reproduced by taking into account the internal absorption effect, although for polystyrene the agreement was less satisfactory. In the case of hematite sol, which has anisotropic shape, the OC model could not reproduce ultrasonic spectra.
Broadband Light Scattering and Dielectric Dispersion of Liquid-Glass Transition in Propylene Glycol
Authors: Seiji Kojima Seiji Kojima , Kenichi Saruta Kenichi Saruta , Akira Yoshihara Akira Yoshihara
Published: October 2002

The liquid-glass transition of propylene glycol was studied using broadband light scattering spectra obtained using the Sandercook-type Fabry-Perot interferometer and the additive triple-grating spectrometer. The depolarized spectra in a liquid phase at 363 K clearly show an α peak and a boson peak. With decreasing temperature α peak shifts rapidly to a lower frequency but the boson peak does not change significantly. The reduced spectra was analyzed by superposition of the Davidson-Cole α relaxation, a Debye fast relaxation and a boson peak. It is found that the fast relaxation frequency does not depend on temperature, and its intensity decreases remarkably on cooling towards 139 K. The temperature variation of the α relaxation was also measured using broadband dielectric measurements.
Transient Phenomenon of Twin Formation in Quartz Plates
Authors: Takehiko Uno Takehiko Uno
Published: October 2002

The transient characteristics of x-axis inversion for AT-cut quartz plates were studied. The resonance frequency of the quartz plate was monitored throughout the thermal treatment process for x-axis inversion. The x-axis inversion can be detected by resonance frequency change. It was observed that the critical temperature, T
c, for the x-axis inversion decreases with the film thickness deposited on the quartz plate. An expansion phenomenon of the x-axis inverted area was observed at temperatures higher than T
c. Degeneration of resonance frequencies corresponding to AT-cut and -35°15′ rotated Y-cut was observed above 553° C.
Piezoelectric Transformer for Cold Cathode Fluorescent Lamp Inverter
Authors: Fuda Yoshiaki , Kumasaka Katsunori , Katsuno Masafumi , Hiroyuki Sato Hiroyuki Sato , Yoshihiro Ino Yoshihiro Ino
Published: October 2002

A piezoelectric transformer of which the structure differs from the Rosen-type structure was investigated. According to the aim of reducing the heat generation of the piezoelectric transformer, the relationship between the heat generation and vibration velocity of the transformer was investigated. The temperature of the transformer rapidly rises when the vibration velocity of the transformer increases to above a critical value. Based on analysis of the electrical equivalent circuit of the piezoelectric transformer, the vibration velocity of the transformer is proportional to the output current and inversely proportional to the force factor of the output part. As a result, new piezoelectric transformers with a strip electrode at the output part which can minimize the heat generation of transformers have been developed. The inverters with these 3, 6 and 10 W piezoelectric transformers showed more than 85% efficiency at 60–80 kHz driving.
Wavefront Generation Using a Dense Array and Multidimensional ΔΣ Modulation
Authors: Yasutaka Tamura Yasutaka Tamura , Osamu Akasaka Osamu Akasaka , Mitsuru Okada Mitsuru Okada
Published: October 2002

We propose a new digital to analogue (DA) conversion technique for acoustical transducer arrays. This technique utilizes the multidimensional band-limited property of array signals. Using the technique, a large dynamic-range wavefront is converted to multiple 1-bit waveforms which are over-sampled temporally and spatially. The 1-bit waveforms are fed into a dense array of transducers. The acoustical wavefront transmitted from the array is approximately equal to the original wavefront, because the spatial high frequency components are eliminated by band-limitation due to wave propagation. This paper describes an over-sampling technique using two dimensional (2-D) ΔΣ modulation for 1-D and 2-D arrays. Results of simulations are presented for evaluation and demonstration of the applicability of the proposed method.
Factors Influencing the Variation of Surface Acoustic Wave Velocity in Lithium Tetraborate
Authors: Vezin Vincent , Inui Shinichiro , Yamaguchi Kunio , Sugawara Tamotsu , Komatsu Ryuichi , Yamanouchi Satoshi Uda
Published: October 2002

Comparison of the resonance frequency of surface acoustic wave (SAW) resonators fabricated on defect-free and highly defective lithium tetraborate wafers was attempted. The intrinsic variation of SAW velocity due to crystal defects, impurities and chemical compositional inhomogeneities for lithium tetraborate wafers is smaller than ±0.011%. In addition, the variation of SAW velocity in a wafer is influenced by the device fabrication process rather than the lithium tetraborate substrate quality.
Surface Acoustic Wave Propagation Characteristics under the Coded Electrodes of Surface Acoustic Wave Matched Filters
Authors: Yoshihiko Takeuchi Yoshihiko Takeuchi , Kazuhiko Yamanouchi Kazuhiko Yamanouchi
Published: October 2002

Surface acoustic wave (SAW) matched filters are advantageous for use as correlators with high data transmission rates and short spreading sequences. We have examined the second-order effect problem in the case of reducing the insertion loss of SAW matched filters, and proposed a new direct time response calculation analysis of the SAW matched filter. Using this method, we can directly calculate the signal time response, the directivity of the coded electrodes and the propagation and reflection properties of SS-modulated SAW signals. It is also possible to calculate the dynamic responses of the programmable SAW matched filters in the case of switching before the time duration of their impulse responses. We analyzed the decreasing slope of the impulse response, which is a problem of low-loss SAW matched filters, and found that the slope is caused by an electrical delay at the common bus bar, which can be corrected by connecting the coded electrodes to each other by capacitors.
Generalized Amplitude Transfer Factor for an Analysis of Transversal Modes in Surface Acoustic Wave Resonator-Type Devices
Authors: Hiroaki Satoh Hiroaki Satoh , Takashi Kokubo Takashi Kokubo
Published: October 2002

A generalized amplitude transfer factor for analyzing the effect of transversal modes in surface acoustic wave (SAW) resonator-type devices is newly presented, taking the arbitrary transversal source distribution into account. The factor is defined as the ratio of the inner product of G and Ψ
n
to the product of their norms, where G is the source distribution function and Ψ
n
is the n-th order eigenmode function in a ΔV/V waveguide. Several concrete analyses clarify the validity of the factor.
High Signal-to-Noise Ratio Ultrasonic Point Detection Method using a Fused Quartz Rod as a Pulse Compression Filter and a Sensor
Authors: Yoshizawa Masasumi , Tagawa Norio , Watanabe Eiki , Moriya Tadashi , Yagi Shin-ichi
Published: October 2002

In this paper we propose a method to detect ultrasound with high signal-to-noise ratio (S/N) at a point on the surface of a material. To obtain high S/N, we applied an frequency-modulation (FM) pulse compression method as used in radar. We also used a fused quartz rod for point detection, at the same time using it for the pulse compression filter. The concept is demonstrated with an image reconstructed using a computer tomography algorithm.
Sensitive Tracking Method for Blood Flow Velocity Estimation Using Pulsed Ultrasound Techniques
Authors: Hongmin Wu Hongmin Wu , Shigeo Ohtsuki Shigeo Ohtsuki
Published: October 2002

A highly sensitive and simple algorithm using ultrasound RF echo signals for blood-flow velocity estimation is presented in this paper. The method determines the best segment match between successive ultrasound echo signals by a simple squared difference operation rather than the cumbersome correlation coefficient calculation executed in conventional time-domain correlation techniques. Since a time shift search is performed with emphasis on the relative amplitude fluctuations of echo signals in temporal, the algorithm is sensitive and effective for the correct extraction of information about the relative movement of the local scatterers during the pulse repetition period. Simulation results indicate that the proposed method has some attractive merits over conventional correlation techniques.
Change in Size and Number of Sodium Laurate Microbubbles with Time in Saline at Different Air Concentrations
Authors: Kawan Soetanto Kawan Soetanto , Man Chan Man Chan , Motoyoshi Okujima Motoyoshi Okujima
Published: October 2002

The study of the annihilation mechanisms of microbubbles is a very important topic in the development of ultrasound contrast agents. To gain better insight into the annihilation mechanisms, knowledge of the change in the number and size of microbubbles with time in saline is necessary. In this study, the use of a Coulter Multisizer is proposed, and the change in number and size of microbubbles is accurately measured. As a result, mechanisms for longevity and annihilation are suggested. Sodium laurate is used for the coating layer of the microbubbles. The measured longevity of sodium laurate microbubbles is compared with the results of a simulation of free air microbubbles. Although the coating layers lower the diffusion rate of air from microbubbles, diffusion still occurs. The diffusion of air contributes to the size of the microbubbles and the dissolution of the surfactant coating layer causes a decrease in the number of microbubbles. The reasons for these assertions are discussed in this paper. When the concentration of dissolved air in saline is close to saturation, the annihilation mechanism of sodium laurate microbubbles changes to the dissolution of the coating layer into the solution. In addition, it is proposed from the experimental results that small particles less than 10 µm in size which dissolve slowly in saline are formed after the shrinking of microbubbles by diffusion.
Observation of Reconstructed Structure of Au(111) Deposited on Mica by Scanning Tunneling Microscopy
Authors: Yasuhiko Terada Yasuhiko Terada , Ken Nakajima Ken Nakajima , Takayuki Ikehara Takayuki Ikehara , Toshio Nishi Toshio Nishi
Published: October 2002

A scanning tunneling microscope was used to study the reconstructed superstructure of an Au(111) thin film deposited on mica. In addition to the herringbone reconstructed structure, another reconstruction perpendicular to the herringbone lines was observed.
Ultrasonic Time-of-Flight Computed Tomography for Investigation of Wooden Pillars: Image Reconstruction from Incomplete Time-of-Flight Profiles
Authors: Yasutaka Tamura Yasutaka Tamura , Kazunari Adachi Kazunari Adachi , Yoshikuni Yanagiya Yoshikuni Yanagiya , Munekazu Makino Munekazu Makino , Katsuaki Shioya Katsuaki Shioya
Published: October 2002

The authors are developing an ultrasonic time-of-flight (TOF) computed-tomography (CT) system for visualizing the inside of historic relics such as the wooden pillars of shrines. The TOF profiles, positions of ultrasound transducers and the outside shape of a pillar are measured to reconstruct a cross-sectional image. In this paper, an image reconstruction algorithm for incompletely determined TOF data is presented. Preliminary evaluation of an ultrasonic receiver made of a piezoelectrical film of vinylidene trifluoroethylene copolymer (P[VDF-TrEE]) is also reported.
Fracture-Mode Classification in Glass-Fiber Composites by Acoustic Emission Source Wave Characterization and Autoregressive Coefficients
Authors: Tetsuo Kinjo Tetsuo Kinjo , Hiroaki Suzuki Hiroaki Suzuki , Mikio Takemoto Mikio Takemoto , Kanji Ono Kanji Ono
Published: October 2002

To study the sequence and dynamics (fracture mode and kinetics) of microfractures in tensile loaded unidirectional glass-fiber reinforced plastics (UD-GFRP), two types of acoustic emission (AE) signal processings were utilized. One is the source wave characterization of the out-of-plane displacement monitored by the system developed. This method enables us to estimate both the fracture mode and kinetics by taking the orientation dependence of wave attenuation and retardation into account. A change of fracture dynamics with loading was quantitatively revealed by this method. Another method is the pattern recognition analysis of AE waves monitored by conventional AE monitoring equipment. Autoregressive coefficients (AR coefficients) obtained by the maximum entropy method were useful to classify AE signals due to different fracture modes.
Numerical Analysis of Long Range Acoustic Propagation Based on Wide Angle Parabolic Wave Equation
Authors: Anada Tetsuo , Fujii Taro , Morita Koji , Takenobu Tsuchiya Takenobu Tsuchiya , Nobuyuki Endoh Nobuyuki Endoh
Published: October 2002

The purpose of this paper is to describe an accurate computational method for underwater acoustic propagation problems based on the wide angle wave equation with the transparent boundary condition. In order to evaluate the present method, we calculate typical examples of a deep underwater propagation model with Munk's sound velocity profile and shallow underwater with the sound profile increasing exponentially from the sea surface to the bottom including the loss in the seabed material. The results are almost the same as the semi-analytical solutions obtained using rays or normal modes. The validity and usefulness of the present method are confirmed.
Hydrogen and Oxygen Plasma Effects on Polycrystalline Silicon Thin Films of Various Thicknesses
Authors: Liou Bor Wen , Lee Chung Len , Tan Fu Lei Tan Fu Lei , Yi Huang Wu Yi Huang Wu
Published: October 2002

This work studied the hydrogen and oxygen plasma effects on the resistivity, effective free carrier concentration, and mobility of As+- and BF2
+-doped polycrystalline silicon (polysilicon) thin films of various thicknesses. It was found that the resistivity of a polysilicon thin film increased with the decrease of the thickness of the film. This was mainly due to the decrease of effective carrier concentration and the mobility through the decrease of the grain size since the thickness limited regrowth of the film. The hydrogen and/or oxygen plasma treatment decreased the effective carrier concentration of the film through the neutralization of boron and arsenic ions. This effect was more evident for the thinner (<60 nm) film. The plasma treatment also decreased the mobility of the film, unless the thickness of the film was thinner than 50 nm, for which, the mobility instead increased since the plasma passivation effect became dominant.
Effects of Tin Doping and Oxygen Vacancies on the Electronic States of Indium Oxide
Authors: Mizuno Masao , Miyamoto Takashi , Takashi Ohnishi Takashi Ohnishi , Hidetaka Hayashi Hidetaka Hayashi
Published: October 2002

The electronic states of indium oxide are calculated by a molecular orbital method. The conduction band consists mainly of oxygen 2p and indium 5p. The valence band consists of O-2p. When there is an oxygen vacancy in the indium oxide, a localized orbital appears at the indium site near the oxygen vacancy, which forms a vacancy level below the bottom of the conduction band. When there are many oxygen vacancies in the indium oxide, the vacancy level is unlocalized. When Sn atoms are substituted for In atoms, localized molecular orbitals of Sn-5p and O-2p appear at the high-energy part of the conduction band. On the other hand, when Sn atoms are inserted into interstitial positions, vacancy levels appear below the bottom of the conduction band. When there are many oxygen vacancies in both cases, the oxygen vacancy levels appear between the conduction band and the valence band. The complex formed by In, Sn and O forms the doping level.
Tunable Intersubband Absorptions by Quantum Well Interdiffusion and Its Application for Wide Bandwidth Infrared Photodetectors
Authors: E. Herbert Li E. Herbert Li
Published: October 2002

Linear and third-order conduction intersubband absorption coefficients are analyzed in interdiffused lattice matched AlGaAs/GaAs and strained InGaAs/GaAs quantum well (QW) structures. The variation of diffusion lengths has imposed a vast change in subband states energies and causes the transition energies between the lowest two subbands to shift in both red and blue depending on the QW structure. This modification provides a wide range of operation wavelengths (5 to 26 µ m) in the mid to far IR region. In order to perform a comprehensive analysis, interdiffused quantum well with different Al or In concentration, well width and optical field intensity are analyzed. The extent of the change of absorption coefficient due to interdiffusion in these QWs are then examined. Devices such as photodetector and modulator operating in this IR regime are proposed by using the interdiffused quantum well materials.
Microwave Surface Resistance of Bi 2Sr 2CaCu 2Ox Thick Films on Large-Area Metallic Substrates
Authors: Yoshizawa Shigemi Inagaki
Published: October 2002

As a feasibility study for application of a high-T
c material to an accelerator cavity, Bi2Sr2CaCu2Ox thick films were formed on large-area metallic substrates. The microwave surface resistance of the films was measured over a temperature range from 4.2 K to 300 K using a demountable cylindrical copper cavity operated at 3 GHz in the TE011 mode. The area of the end plate was 177 cm2 and the thickness of the films was around 50 µm. The films were formed either on silver foils (on copper) or on a silver plate, coated by either a screen-printing or a spray-coating method, sintered either in air or in a Bi2O3 atmosphere, both at 885–890°C, and either annealed in nitrogen gas at 600°C or not annealed. The ratio of the microwave surface resistance of the best film to that of the copper was 0.18 at 10 K and 0.65 at 77.3 K. A comparison of the microwave surface resistance is made between Bi2Sr2CaCu2Ox and YBa2Cu3O7-x
films.
Internal Stress Effect on the Temperature Dependence of the Dielectric and Lattice Constant in Sm-doped BaTiO3 Ceramics
Authors: Kim Yung Park
Published: October 2002

The internal stress effect on the temperature dependence of the dielectric and lattice constant in a Sm-doped BaTiO3 ceramic was investigated using various particle sizes of starting barium titanate, pressure-dielectric spectroscopy and a high pressure X-ray diffractometer. The grain size was nearly proportional to the particle size of the starting barium titanate, while inversely proportional to the internal stress. A sudden change of internal stress occurred at a grain size of ≈2 µ m. Grain size refinement, as well as external pressure, shifts the lattice and dielectric anomaly T
c to a lower temperature, whereas T
2 is shifted to a higher temperature. For ceramics with a grain size of 2.6 µ m, T
1 decreases with increase in pressure, reaches a minimum value at 5 kbar and then increases. Three lattice anomalies existed for small grained ceramics (<2 µ m) irrespective of grain size and at pressures up to 100 kbar. In particular, the temperature dependence of the dielectric and lattice constant for small grained ceramics (<2 µ m) was less sensitive to external pressure in comparison to that of large grained ceramics (>2 µ m), which was attributable to the internal stress (>240 MPa).
Characteristics on the Gate Insulator of Metal Tip Field Emitter Arrays after Wet Etching Process
Authors: Jung Yu Ho , Ju Byeong Kwon , Jung Jae Hoon , Lee Yun Hi , Kim Myung Hwan Oh
Published: October 2002

The effect of wet-etching process on the gate insulator for fabrication of field emitter arrays (FEAs) was examined. Three types of wet-etching process have been performed to fabricate metal tip FEAs, they are Mo (gate metal), oxide (gate insulator) and Al (release layer) etching, respectively. We examined the effect of gate insulator after wet etching through breakdown field strength and rms surface roughness. And the effect by residual ions or atoms was also examined. The breakdown field strength of gate insulator by the measurement of current-voltage for immersing in oxide etchant was rapidly lowered at the expense of large etching time. However in case of Al etchant, the breakdown field strength was lowered slowly. In all cases, it has been validated through Auger electron spectroscopy (AES) analysis that the residual atom was phosphor after wet-etching process when compared cleaned with non-cleaned samples. Also, we obtained excellent result when aluminum etchant was substituted for 3% tetra-methyl ammonium hydroxide (TMAH). In case of TMAH, decrease of the breakdown field strength was the slowest, surface roughness was smoother, and it did not attack gate and tip material.
Structure and Properties of Germanium Carbide Films Prepared by RF Reactive Sputtering in Ar/CH4
Authors: Z. T. Liu , J. Z. Zhu , Xu N. K. and Zheng X. L. Xu N. K. and Zheng X. L.
Published: October 2002

Germanium carbide ( Ge

x

C1-
x

) films have been prepared by RF reactive sputtering at various mixtures of argon and methane from a germanium target. The compositions, structures and properties of Ge

x

C1-
x

films have been investigated using Auger electron spectroscopy (AES), Visible near-infrared photometer, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The AES analyses show the atomic ratio (Ge/C) of the films decreased with increasing the gas flow ratio CH4/( Ar+CH4 ). The XRD and SEM results indicate that the films were generally smooth and featureless, and had amorphous structure. The refractive index of Ge

x

C1-
x

films can be varied between 1.8 and 4.3 by changing the gas flow ratio. The hardness values of the films grew with the augmentation of the amount of carbon content in the films, and were higher than those of IR optical material Ge and ZnS. It can be predicted that Ge

x

C1-
x

films possess excellent abrasion resistance.
Formation of a Positive Photoresist Thin Film by Spin Coating: Influence of Atmospheric Temperature
Authors: Yada Toshio , Aoki Masaru , Maejima Taro , Akira Ishizu Akira Ishizu
Published: October 2002

Experimental formation of a positive photoresist film by spin coating at various atmospheric temperatures was investigated. The weight of the photoresist solution on a wafer during spinning decreases sharply during the first stage of spinning and gradually during the later stages. At a high temperature, the rate of outflow increases and that of solvent evaporation decreases in the initial stage of spinning, but the former decreases and the latter increases in the intermediate stages. In the later stages, both of them decrease. The baked film spun at a high temperature is thin up to the intermediate stages of spinning due to the higher rates of outflow in the initial stage and evaporation in the intermediate stages more than that at a low one. However, it becomes thick in the later stages due to the lower rates of outflow and evaporation.
Ejection Probabilities of Electrons as Result of Reorganization Effects of Inner-shell Ionized Atoms
Authors: Adel El-shemi Adel El-shemi , Ahmed S. Hassan Ahmed S. Hassan
Published: October 2002

Ion-charge state distributions during vacancy cascades followingK- andLI-shell ionization are calculated using a Monte Carlo simulation. The probabilityP(n) thatnelectrons are ejected after primary ionization is given as a function of atomic number in the regionZ= 7 toZ= 60. The calculations are accomplished by tracing successive radiative and non-radiative transitions and the electron shake off process as an additional effect. Radiative and non-radiative transition rates have been calculated as relativistic wave functions.
Study on Spin Precession of Polarized Slow Positrons in Solids
Authors: Jinfeng Yang Jinfeng Yang , Masami Chiba Masami Chiba , Ryosuke Hamatsu Ryosuke Hamatsu , Tachishige Hirose Tachishige Hirose , Mitsuhiro Irako Mitsuhiro Irako , Tetsuro Kumita Tetsuro Kumita
Published: October 2002

We have investigated spin precession mechanisms of polarized slow positrons in materials caused by multiple Coulomb scatterings, Bhabha scatterings and bremsstrahlungs. It is found that the degree of depolarization is strongly dependent on the atomic number of materials, and the depolarizations caused by the Bhabha scatterings and the bremsstrahlungs are negligible compared with those caused by multiple Coulomb scatterings. By incorporating the theoretical formulations of spin precession due to the three processes mentioned above into a Monte-Carlo simulation program, we can successfully describe depolarizations of polarized slow-positron beams in materials, i.e. a target, an absorber, and a moderator which are utilized for slow-positron production facilities. The magnitudes of the polarizations thus estimated are in good agreement with experimental measurements.
The Development of a Highly Selective KI/I2/H2O/H2SO4 Etchant for the Selective Etching of Al0.3Ga0.7As over GaAs
Authors: Lau Wai Shing , Chor Eng Fong , Kek Soon Poh , Abdul Aziz Wan Hamzah bin , Lim Hui Chin , Chun Huat Heng Chun Huat Heng , Rong Zhao Rong Zhao
Published: October 2002

The selective etching of n-Al0.3Ga0.7As with respect to p+-GaAs is useful for the fabrication of AlGaAs/GaAs heterojunction bipolar transistors (HBTs). The KI/I2/H2O/H2SO4 etching solution was found to be superior to the KI/I2/H2O solution in terms of selectivity. The selectivity could be furthered improved by aging the etching solution for 3 days and by lowering the temperature from room temperature to the ice point. The best selectivity achieved was 330 with etch rates of 0.165 µ m/min and 0.0005 µ m/min for Al0.3Ga0.7As and GaAs respectively for a stabilized KI/I2/H2O/H2SO4 at an etching temperature of 3° C.
Theoretical Study of Silicon Adatom Transfer from the Silicon Surface in Scanning Tunneling Microscopy
Authors: Nobuhiko Kobayashi Nobuhiko Kobayashi , Kenji Hirose Kenji Hirose , Masaru Tsukada Masaru Tsukada
Published: October 2002

We have investigated the electronic structures of a silicon adatom displaced from a silicon surface with the tip of a scanning tunneling microscope using the recursion-transfer-matrix method. This method is an effective means of calculation for electronic states of a bielectrode system under electric field and current. The adiabatic potential surfaces of the adatom moving from the surface to the tip and the corresponding induced electron density distributions are presented for several values of bias voltage. A decrease in the activation barrier height is seen for both positive and negative bias cases when the tip-surface distance is 11 bohrs, while a monotonous decrease is seen only for the positive bias case at a tip-surface distance of 8 bohrs.
Structures on Si(100) 2 × 1 at the Initial Stages of Homoepitaxy by SiH 4 Decomposition
Authors: Fehrenbacher Matthias , Spitzmüller Jürgen , Pitter Michael , Hubert Rauscher Hubert Rauscher , R. Jürgen Behm R. Jürgen Behm
Published: October 2002

The initial stages of homoepitaxial island formation on Si(100)2×1 by SiH4 decomposition under ultra high vacuum chemical vapor deposition conditions are studied by scanning tunneling microscopy and kinetic model calculations. The concentrations of the intermediate species formed on the surface during SiH4 decomposition are calculated from the kinetic parameters of the dissociation cascade leading to Si film growth in the temperature regime of 500 to 800 K and for SiH4 pressures in the range of 2×10-7 to 2×10-5 mbar. Experimental results showing the surface topography after interaction with SiH4 at various surface temperatures and deposition rates are presented, and the observed surface structures are related to the different surface conditions, i.e., deposition flux and sample temperature, under which islands are formed.
Si(111) 2 × 2–In ↔ Si(111)√ 3 ×√ 3–In Scanning Tunneling Microscope Tip-Induced Structural Transformation
Authors: A. Saranin Alexander , Toshinori Numata Toshinori Numata , Osamu Kubo Osamu Kubo , Hitoshi Tani Hitoshi Tani , Mitsuhiro Katayama Mitsuhiro Katayama , Kenjiro Oura Kenjiro Oura
Published: October 2002

We have found STM tip-induced 2 ×2–In → √3×√3–In and √3×√3–In → 2 ×2–In structural transformations on a Si(111) surface at room temperature, relatively low bias voltages and large tip-sample separations. The processes were found to be reversible depending on the tip bias voltage polarity. Our results can be explained by STM tip-induced diffusion of In atoms on the √3×√3–In and 2 ×2–In surfaces.
Nanoscale Indentation on Si(111) Surfaces with Scanning Tunneling Microscope
Authors: Hasunuma Ryu , Tokumoto Tadahiro Komeda
Published: October 2002

We have investigated the mechanism of Si atom removal by measuring the current during formation of a point contact between the W tip of a scanning tunneling microscope (STM) and the Si(111)-7×7 surface. The stepwise drops observed in the current during tip retraction may be attributed to the reduction of the contact area in an atom-by-atom manner. Based on the estimation of the contact size, it was concluded that the adatoms were removed by chemical adhesion of the Si atoms with the W tip. The chemical adhesion was assisted by the mechanical force applied to the Si surface, contact potential and current induced local heating. A trilayer was removed by field evaporation with the assistance of electromigration on the Si surface.
Sharpening Processes of Scanning Tunneling Microscopy/Scanning Tunneling Spectroscopy Tips by Thermal Field Treatment
Authors: Minoru Nagai Minoru Nagai , Masahiko Tomitori Masahiko Tomitori , Osamu Nishikawa Osamu Nishikawa
Published: October 2002

In order to prepare a scanning tip suitable for scanning tunneling microscopy (STM)/scanning tunneling spectroscopy (STS) operated in ultrahigh vacuum (UHV) with a reproducible and ideal profile of the [111]-oriented W tip, sharpening and cleaning treatments were carried out by heating the tip while applying high voltage in UHV (thermal field (T-F) treatment). The treated tips were evaluated by field emission microscopy (FEM). The appropriate values to build up the W tip along the [111] axis for a treatment parameter, |V
T-F/V
base|, range from 2 to 2.6 under fixed conditions of tip heating temperature and time of about 1300 K and 60 s, respectively. It has been also realized that the formation of an ideal tip completely surrounded by three {112} facets at its apex requires a successive heat treatment: an initial T-F treatment, simple heating at about 1000 K to develop the {112} facets, and a final T-F treatment.
Identification of Materials using Direct Force Modulation Technique with Magnetic AFM Cantilever
Authors: Yamamoto Shin-ichi , Ishida Takao , Mizutani Wataru , Tokumoto Hiroshi , Yamada and Hirofumi
Published: October 2002

With a direct force modulation technique we measured the regional stiffness of the self-assembled-(SAM) films. A magnetic thin film was deposited at the end of the backside of the AFM cantilever so as to apply forces directly to the tip through the external magnetic field of an electric coil. This technique is able to detect the difference between the phase-separated monolayer films with two similar stiffnesses composed of hydrocarbon and fluorocarbon and identify the components of the film. We obtained the effective spring constant of 4.8 N/m on hydrocarbon SAM and 6.5 N/m on fluorocarbon SAM at the applied force of 1 nN.