bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of One Monolayer Thickness Variation in GaAs/AlGaAs Five-Layer Asymmetric Coupled Quantum Well upon Electrorefractive Index Change
Authors: Tada Kunio , Arakawa Taro , Kazuma Kensuke , Kurosawa Naoki , Noh Joo-Hyong
Published: October 2002

The five-layer asymmetric coupled quantum well (FACQW) is a new potential-tailored quantum well (QW) for ultrafast and low-voltage optical modulators and switches. First, the influence of one monolayer (ML) thickness variation of a single layer in the GaAs/AlGaAs FACQW on the electrorefractive index change Δn is theoretically studied. The thickness variation of two thicker GaAs layers has a considerable influence on Δn of the FACQW, while the thickness variation of thin AlAs and AlGaAs barrier layers has a smaller influence on Δn. The ratio of the thicknesses of the two GaAs well layers significantly affects the Δn characteristics of the FACQW. The change Δn does not vary appreciably as long as the ratio is kept constant. Second, the influence of the statistical fluctuation of the layer thickness by 1 ML in all of the layers on the Δn characteristics of the FACQW is also discussed. Even when Δn decreases with the increase of the occurrence probability of a layer being thicker or thinner by 1 ML, the FACQW still has a much larger Δn than conventional rectangular quantum wells do.
Preparation and Magnetooptical Properties of AlN–Fe Granular Film
Authors: Haga Yumiko , Nakaya Noriyuki , Takeda Eishi , Nakamura Yoshio , Nittono Osamu
Published: October 2002

AlN films including Fe nanoparticles have been prepared from sputtered films with Al–N–Fe composition by annealing in a vacuum furnace. Faraday rotation angles and M–H loops of AlN–Fe granular films have been measured. The maximum value of Faraday rotation angle is estimated to be 1.1°/µm at a wavelength of about 500 nm. The microstructures of the films are characterized by transmission electron microscopy and X-ray diffractometry. The structural features are related to the magnetic properties.
Electrochemical Nanolithography on Amorphous WO3 Thin Films Using Scanning Tunneling Microscope in Air
Authors: Qiu Hong , Lu Yong-Feng , Mai Zhi-Hong
Published: October 2002

Tungsten oxide (WO3) thin films have shown interesting properties as lithography resist materials. In this study, the scanning tunneling microscope (STM) was used in air for nanometer etching of α-WO3-x
thin films, an n-type semiconductor. The current–voltage (I–V) curve was found to be affected by the water layer absorbed on the surface. For low voltage (< 3 V) with long duration (∼ 10 s) or high voltage pulse (> 3 V) with short pulsewidth (∼ 200 ms), holes were formed on the film surface at high humidity (> 70%) by applying a pulse voltage. A threshold voltage existed for hole formation. Higher pulse voltage and negative polarity corresponded to larger modified size. All the structures formed in STM images were topographical in nature by comparison with the AFM images. The hole formation was reasonably attributed to electrochemistry and high dissolution of WO3 in high pH solutions, which was co-manifested by links between the holes and eroded materials on the surface. Alkaline solutions instead of deionized water were chosen to act in the tip-surface gap. Alkaline ions being expelled from the tip due to electric polarity demonstrated the ion movement and their effect on etching. Lines of nanometer width were fabricated.
Reduction in Feedback Bandwidth of the Force-Controlled Atomic Force Microscope Using a Polyimide Cantilever
Authors: Kato Nobuhiro , Matsumoto Toshiro , Kikuta Hisao , Nakamura Yasuhiro , Iwata Koichi
Published: October 2002

In this paper we present a method of reducing the bandwidth required in the force-controlled atomic force microscope (AFM) for measuring the force curves. System stability strongly depends on the quality factor of vibration (Q) of the cantilever. As polyimide has a low Q, a cantilever fabricated from it reduces the bandwidth required in the feedback system. A polyimide cantilever with dimensions of 540×155×3.4 µm3 is fabricated to evaluate its Q in vacuum, density and Young's modulus. The measured Q is 50, which is much smaller than those of conventional cantilevers used for AFM. Using the measured mechanical properties of the polyimide, the required frequency response of the feedback system is estimated. Typical force curve measurements are confirmed by some numerical simulations.
Investigation of Etch Rate Uniformity of 60 MHz Plasma Etching Equipment
Authors: Koshiishi Akira , Araki Youichi , Himori Shinji , Iijima Tamotsu
Published: October 2002

When the driving frequency of etching equipment using capacitively coupled parallel-plate plasma (CCP) becomes high, the etch rate tends to indicate a center peak. In this paper we discuss the improvement of the etch rate by leveling the center peak. From the results of numerical simulation using FEM, it can be considered that the center peak shape of the RF electric field distribution, which is enhanced by the resistivity of plasma, causes the center peak shape of the etch rate. Experimental results using an improved CCP, which possesses the ability to control the electric field distribution, demonstrate a refined etch rate. That is to say, the improvement of making a cavity behind the electrode provides the ability to control the electric field distribution. This distribution is governed by the dimensions of the cavity and the resistivity of the electrode. Less than 3% uniformity is obtained at 60 MHz for a wafer of 200 mm diameter using the improved electrode.
Low Operating Voltage and High Efficiency Organic Multilayer Electroluminescent Devices with p-Type Doped Hole Injection Layer
Authors: Huang Jingsong , Pfeiffer Martin , Blochwitz Jan , Werner Ansgar , Salbeck Josef , Liu Shiyong , Leo Karl
Published: October 2002

We demonstrate efficient organic electroluminescent devices with multiple well structure and a p-doped hole injection and transport layer (HTL). The multiple well structure improves the efficiency and the controlled p-doped HTL leads to a lower operating voltage. An amorphous starburst [4,4′,4′′-tris(N,N-diphenylamino)triphenylamine] doped with a strong organic acceptor, tetrafluoro-tetracyano-quinodimethane serves as the HTL material, a spiro-linked compound, 2,2′,7′,7′-tetra-kis-(diphenylamine)-9,9′-spirobifluorene as an interlayer to provide a favorable interface and as a barrier within the multiple well structure and 8-tris-hydroxyquinoline as an emitter and well. The double-well device exhibits low operating voltage, less than 4 V, for obtaining 100 cd/m2 and the highest current efficiency exceeding 5 cd/A. Changes in the spectra due to the different well structures are also discussed.
Development of a Zero Spillover Controller for Broadband Cancellation of Noise in Ducts
Authors: Wu Jian-Da , Bai Mingsian R.
Published: October 2002

In this paper, an active noise control (ANC) system for broadband cancellation of noise in ducts, where a nonacoustical reference is unavailable and thus the ANC structure is “spatially feedforward” is presented. In this structure, acoustic feedback that is known to be detrimental to system stability and performance must be taken into account in controller design. In this case, difficulties generally arise in implementing the ideal controller, or the zero spillover controller due to plant uncertainties. In the present study, an equivalent approach based on the 2-norm (H2) optimal model matching principle is proposed in controller design. The control algorithm is implemented on a digital signal processor (DSP), by finite impulse response (FIR), infinite impulse response (IIR) and hybrid filters. The experimental results indicate that the proposed controller was effective in suppressing periodic noise and random noise sources, without and with airflow.
Accuracy of a Harmonically Operated Single Electron Pump
Authors: Iwasa Akio , Fukushima Akio , Sato Akira
Published: October 2002

We analyzed the behavior of a single-electron pump operated by sinusoidal signals. We determined the expressions of a set of the harmonic gate signals which can operate an N-junction pump. Concerning the three-junction pump and four-junction pump, we analytically derived asymptotic formulas of the error rate against the pumped current caused by cotunneling and missed transition. As a result, the error rate of the three-junction pump operated by harmonic signals was the same as or less than that of the three-junction pump operated by well-known operation methods, namely, the operation by triangular signals or orthogonal sinusoidal signals. Our estimation shows that the error rate of the three-junction pump is sufficiently small to calibrate the 1.000 00 pA range of a commercially available high-sensitivity current meter.
A Novel Resonance in n-GaAs Diodes
Authors: Shiau Yuo-Hsien , Néda Zoltán
Published: October 2002

We consider two external laser beams interfering inside a n-GaAs with a nonlinear feedback. In a given parameter region coexistence of the two unstable periodic domain trains (UPDTs) is found in this system. The UPDT is associated with the formation of intermittent oscillating current in the circuit. By external periodic driving, a novel resonance is observed in both inside one UPDT and the switching between the two UPDTs. The signal-to-noise ratio (SNR) as a function of driving amplitude A is numericaly investigated and the nonmonotonic behavior of the SNR(A) spectrum is observed.
Stress-Induced Level Shift of a Hydrogen–Carbon Complex in Silicon
Authors: Fukuda Kazuhisa , Kamiura Yoichi , Yamashita Yoshifumi , Ishiyama Takeshi
Published: October 2002

We have studied the stress-induced shift of a deep level at E
c-0.15 eV due to a hydrogen-carbon complex in Si using deep-level transient spectroscopy (DLTS) under uniaxial compressive stress. Linear stress dependencies of the ionization energy of the above level were observed for five components of split DLTS peaks altogether for <111 >, <110 > and <100 > stresses. By subtracting the stress shifts of conduction band minima from the stress dependencies of ionization energy, the net stress shifts of the energy level were obtained. Two piezospectroscopic parameters, A
1 and A
2, were determined as approximately 4 and -9.5 meV/GPa, respectively. Considering a molecular-orbital schematic suggested here and throughout, we conclude that the stress-induced level shifts and the split pattern of DLTS peaks reflect the trigonal symmetry and antibonding character of the electronic state of the complex. These properties are completely consistent with the atomic configuration in which a hydrogen atom occupies the bond-centered site between Si and C atoms.
Boron Diffusion and Activation during Heat Treatment in Heavily Doped Polysilicon Thin Films for P+ Metal-Oxide-Semiconductor Transistors Gates
Authors: Mahamdi Ramdane , Mansour Farida , Scheid Emmanuel , Boyer Pierre Temple , Jalabert Laurent
Published: October 2002

In this work, we present a study of heavily doped polycrystalline silicon which is used as a transistor gate in standard complementary metal-oxide-semiconductor (CMOS) technology. Our aim is to study the redistribution and activation of boron during thermal annealing in thin silicon films implanted and deposited by low-pressure chemical vapor deposition (LPCVD) using a disilane (Si2H6) gaseous source. The boron concentration is monitored by secondary ion mass spectrometry (SIMS). The resistivity measurements by the four-probe method show that the films become conductors after annealing. Carrier mobility and active doping fraction are obtained by Hall effect measurements. To investigate the SIMS profiles, we have proposed a model based on the one-dimensional numerical resolution of Fick's laws. This model takes into account phenomena due to effects of very heavy doping such as that of clusters. The boron diffusion coefficient and its activation percentage are deduced from the adjustment of simulated profiles with SIMS experimental ones. We have used SUPREM IV software in order to estimate the boron diffusion coefficients in these films and compare them to our results. A small gap between the profiles simulated by our model and by SUPREM IV has been observed, in particular in the region where the boron limit solubility is exceeded. Nevertheless, the diffusion coefficient values obtained by the two methods are of the same order of magnitude.
Photoluminescence and Thermoluminescence of MgSO4, CaSO4, SrSO4 and BaSO4 Powder Phosphors Activated with Tb3+
Authors: Yamashita Nobuhiko , Hamada Takuya , Takada Makoto , Katsuki Masafumi , Nakagawa Masuo
Published: October 2002

The photoluminescence (PL) spectra and optical excitation spectra of phosphors were obtained at temperatures of 10, 80, 300 and 370 K. Many narrow bands were observed in both the spectra, and were attributed to the transitions within the 4f
8 electron configuration in Tb3+. The quenching of the 5
D
3 emission series assigned to the transitions 5
D
3→7
F

J
(J=6,5,4,3,2,1 and 0) is characteristic of the PL emission spectra. The thermoluminescence (TL) glow curves, TL emission spectra and TL fading properties of the same samples were also observed. The quenching of the 5
D
3 emission series is not observed in the TL emission spectra. The large differences between the features of the TL emission spectrum and the PL emission spectrum are contradictory to the conventional model of the TL emission process. The addition of Na+ to the phosphors as a charge compensator is effective in enhancing the PL efficiency, but causes TL fading because of the shallow electron traps due to Na+.
Effect of Tantalum in Crystal Growth of Silicon Carbide by Sublimation Close Space Technique
Authors: Krastev Lilov Tomoaki Furusho , Satoru Ohshima Satoru Ohshima , Shigehiro Nishino Shigehiro Nishino
Published: October 2002

Investigation into the effect of tantalum on silicon carbide, grown by the sublimation close space technique, was carried out. It was established that in the presence of a small piece of tantalum in the reaction space during the crystal growth process, the surface of the epitaxial layer became extremly smooth and high-crystal-quality epitaxial layers were obtained. It was also shown that the concentrations of aluminum and titanium are different in epitaxial layers grown with and without tantalum. High-quality epitaxial layers, which were comparable to epitaxial layers grown by chemical vapor deposition, could be obtained at a high growth rate by the sublimation close space technique.
Current Peak Characteristics of Triple-Barrier Resonant-Tunneling Diodes with and without Phase Breaking
Authors: Nagase Masanori , Furuya Kazuhito , Machida Nobuya , Kurahashi Masaki
Published: October 2002

We studied peak characteristics in the current–voltage (I–V) curve of triple-barrier resonant-tunneling diodes (TBRTDs). The current peak broadening caused by the well–well and well-electrode couplings is revealed. The electron phase breaking effect is incorporated into the analysis to obtain the I–V curve of TBRTD using the phase correlation method. For strong well–well coupling, the peak current is independent of the phase breaking, while for weak coupling it is dependent of it. The electron coherence can be estimated using TBRTDs designed appropriately.
Analysis of Device Performance by Quasi Three-Dimensional Simulation for Thin Film Polycrystalline Silicon Solar Cells with Columnar Structure
Authors: Ishikawa Yasuaki , Yamamoto Yukie , Hatayama Tomoaki , Uraoka Yukiharu , Fuyuki Takashi
Published: October 2002

In order to realize high efficiency thin film polycrystalline silicon (poly-Si) solar cells, a novel method of quasi three-dimensional simulation using a cylindrical coordinate system was proposed. Optimum design of cell configuration and analysis of device performance have been demonstrated. In this simulation we used realistic physical values for parameters, such as interface recombination velocity at grain boundaries and diffusion length of minority carriers. Interface recombination velocity at grain boundaries (which has a strong effect on cell performance) should be less than 103 cm/s to obtain high cell performance. Even at a relatively short diffusion length of 50 µm, high efficiency of more than 16–18% can be expected at a film thickness of 5–20 µm when grain size is 10 µm, which is appropriate for the utilization of solar grade Si of reasonable material quality.
Electrical Characteristics of TiO2/ZrSixOy Stack Gate Dielectric for Metal-Oxide-Semiconductor Device Applications
Authors: Sim Hyunjun , Jeon Sanghun , Hwang Hyunsang
Published: October 2002

This short note describes a unique process for the preparation of high-quality titanium oxide (TiO2) with zirconium silicate (ZrSi
x
O
y
) as an interfacial layer for use in gate dielectric applications. Compared with conventional chemical oxide and oxynitride as an interfacial layer, titanium oxide (TiO2) metal-oxide-semiconductor (MOS) capacitors with zirconium silicate (ZrSi
x
O
y
) as an interfacial layer exhibit lower leakage current levels at the same equivalent oxide thickness. We were able to confirm the achievement of the TiO2/ZrSi
x
O
y
stack structure by Auger electron spectroscopy (AES) and transmission electron microscope (TEM) analysis. The equivalent oxide thickness (EOT) and leakage current density at the gate bias 1 V below the flatband voltage (V
FB) were 10.3 Å and 1 mA/cm2, respectively. The zirconium silicate is a promising interfacial layer for future high-k gate dielectric applications.
Quantitative Determination of Mixed Anisotropies in Fe(100) Thin Films and Annealing-Induced Magnetic Reorientation
Authors: Calleja Javier F. , Menéndez José L. , Cebollada Alfonso , Contreras Carmen
Published: October 2002

A specific formalism for quantification of magnetic anisotropies using transverse biased initial susceptibility measurements in systems with mixed in-plane biaxial and uniaxial anisotropies has been developed. This formalism has been applied to the study of magnetic anisotropies in epitaxial, partially nitrided Fe thin films that exhibit these coexisting anisotropies. The influence of annealing on the structure and magnetic anisotropies in this system is also studied. A restructurating of N into the Fe lattice with the formation of a nonstoichiometric FeN phase is found after sufficient annealing time. An additional result is a 5° in-plane rotation of the uniaxial anisotropy direction with respect to the as-grown sample, with no reorientation of the film crystal lattice with respect to the substrate. Possible mechanisms to explain the origin of magnetic anisotropy and the rotation upon annealing of the uniaxial anisotropy are proposed.
Eu and Yb Substituent Effects on the Properties of Pb(Zr0.52Ti0.48)O3–Pb(Mn1/3Sb2/3)O3 Ceramics: Development of a New High-Power Piezoelectric with Enhanced Vibrational Velocity
Authors: Gao Yongkang , Chen Yun-Han , Ryu Jungho , Uchino Kenji , Viehland Dwight
Published: October 2002

Improved piezoelectric materials with higher vibrational velocities are needed to meet the demands of advanced high power electromechanical applications. In this paper, the effects of Eu and Yb substituents on the vibrational velocity and the piezoelectric properties of Pb(Zr, Ti)O3–Pb(Mn, Sb)O3 ceramics will be reported. Both of these substituents resulted in a significant increase in the mechanical quality factor Q
m, a decrease in the dielectric constant, and improvements in the electromechanical properties. Root mean square value (rms value) of vibration velocity as high as 1.0 m/s under an electric field of 10 kV/m (rms value) has been found for Yb-substituted specimens, which is 1.7 times higher than that of Pb(Zr, Ti)O3–Pb(Mn, Sb)O3 ceramics and 3 times higher than that of the commercialized hard Pb(Zr, Ti)O3 ceramics.
Effects of Different Dopants on Diffuse Phase Transition and Ordering Degree in Lead Magnesium Niobate
Authors: Yang Yi , Feng Chude , Yao Wenlong , Yu Youhua
Published: October 2002

This work is based on the relaxor ferroelectrics lead magnesium niobate (PMN) system. The influences of different dopants (Li+, Sr2+, Y3+) on diffuse phase transition and ordering degree were studied. X-ray diffraction (XRD), high-resolution electron microscopy (HREM), selected area electron diffraction (SAED) and Raman spectroscopy were used to study small changes of ordering degree in PMN systems. Results showed that diffuse phase transition (DPT) is caused by the formation of an ordered structure at B-sites (Mg2+:Nb5+=1:1). The degree of DPT can be contrasted from dielectric properties, and has a direct relation with ordering degree of the microstructure. It also showed that, when doping with an element of one valence (Li+), the ordering degree of PMN was decreased; when doping with Sr2+ and Y3+, the ordering degree was enhanced to different extents.
Dry Vertical Alignment Method for Multi-domain Homeotropic Thin-Film-Transistor Liquid Crystal Displays
Authors: Cai C. , Lien A. , Andry P. S. , Chaudhari P. , John R. A. , Galligan E. A. , Lacey J. A. , Ifill H. , Graham W. S. , Allen R. D.
Published: October 2002

Multi-domain homeotropic liquid crystal alignment has been recognized as an alignment method to achieve wide viewing angle for thin-film-transistor liquid crystal displays (TFT-LCDs). In the past decade, several types of multi-domain homeotropic TFT-LCDs have been well studied. In all these LCDs, a homeotropic polyimide layer is used to align liquid crystal molecules. In this paper, a new homeotropic alignment method-dry deposition vertical alignment (or vacuum deposition vertical alignment) is introduced. We studied several different vacuum deposited vertical alignment materials and one of them was demonstrated on a high resolution ridge fringe-field multi-domain homeotropic (RFFMH) TFT-LCD. This new method has advantages over the conventional polyimide alignment method: it simplifies the manufacturing process by avoiding wet chemical processes and improves the viewing angle by reducing light leakage.
Formation Mechanism of Incommensurate Epitaxial Crystals of Chloroiron(III) Derivative of Tetraphenylporphine on Alkali–Halide (001) Surfaces
Authors: Takagi Tomohiro , Hoshino Akitaka , Miyaji Hideki , Izumi Kunihide , Kokawa Ryohei
Published: October 2002

We investigate the thickness dependence of the lattice constants of a chloroiron(III) derivative of tetraphenylporphine (ClTPPFe) epitaxial crystals grown on alkali–halide substrates, KCl, KBr and KI, in order to study the accommodation of the misfit strain, and do not observe any obvious dependence. Moreover, the orientational disturbance of the epitaxial crystals on the alkali halides and the formation of amorphous islands on an amorphous carbon film are observed. On the basis of these results, we propose the mechanism that the orientation of surface-diffusing molecules contributes significantly to the epitaxial growth of ClTPPFe on the alkali halides.
Growth of Self-Assembled Monolayer of Thiophene on Gold Surface: An Infrared Spectroscopic Study
Authors: Matsuura Toshihiko , Nakajima Masayoshi , Shimoyama Yuhei
Published: October 2002

The growth process of self-assembled monolayers (SAMs) of thiophene on Au(111) surfaces was revealed by Fourier-transform infrared reflection absorption spectroscopy (FT-IR-RAS). Thiophene spontaneously adsorbs from an ethanol solution onto the gold surface, and forms well-ordered SAM. FT-IR-RAS measurements and Langmuir adsorption isotherms revealed that thiophene SAMs possess two phases with different molecular orientations during SAM growth. In the primary phase, thiophene orients parallel to the gold surface. In the final phase, the molecular orientation changes from parallel to upright configurations with respect to the surface. This suggests that even molecules without alkyl-chain moiety can reorient during SAM growth. A transition of the molecular orientation is caused by a balance between thiophene-thiophene and thiophene-gold interactions.
Dynamic Behavior of Sputtering of Tungsten Implanted in Carbon
Authors: Ohya Kaoru , Kawakami Retsuo
Published: October 2002

Sputtering due to the bombardment of C with 0.5–10 keV W ions is studied as a function of the W ion fluence by computer simulation. The simulation deals with the dynamic composition change in the surface layer due to implantation of the W ions, the associated collisional mixing and diffusion of the implanted W. The calculated results show a clear oscillation in the sputtering yield of the implanted W as a function of the ion fluence. There is a critical energy (∼ 1 keV) for the appearance of the oscillation, where the W emission yield, defined by the sum of the W sputtering yield and W reflection coefficient, is unity. Above the critical energy, the W sputtering yield oscillates around unity, whereas below the energy it monotonically increases towards a value dependent on the incident energy. The oscillation is caused by the dynamic change in the W depth profile, therefore, it is significantly influenced by the diffusion of the implanted W inside the C bulk. The diffusion suppresses the W sputtering and therefore the oscillation of the yield. Furthermore, for strong diffusion, only W deposition is calculated during the bombardment, whereas the transition from deposition to erosion is calculated without diffusion.
Microwave Dielectric Properties and Microstructures of V2O5-Modified Zr0.8Sn0.2TiO4 Ceramics
Authors: Huang Cheng-Liang , Weng Ming-Hung , Wu Cheng-Cher , Wei Chung-Chuang
Published: October 2002

The effects of V2O5 addition on the microwave dielectric properties and the microstructures of (Zr0.8, Sn0.2)TiO4 ceramics have been investigated. It is found that low-level doping of ZnO (1 wt%) and V2O5 (up to 2 wt%) can significantly improve the densification ability and the dielectric properties of (Zr0.8, Sn0.2)TiO4 ceramics. (Zr0.8, Sn0.2)TiO4 ceramics with additives could be sintered to a theoretical density higher than 95% at 1300°C due to the liquid-phase effect of V2O5 addition. The dielectric constant (ε
r) increased with increasing sintering temperature and saturated at 1300°C. The temperature coefficient of resonant frequency (τf) was not significantly affected while the unloaded quality factor Q was promoted by V2O5 addition. The ε
r value of 37.3, the Q×f value of 51500 (at 7 GHz) and the τf value of -2.1 ppm/°C were obtained for the 1 wt% ZnO-doped (Zr0.8, Sn0.2)TiO4 ceramics with 1 wt% V2O5 addition sintered at 1300°C.
Scanning Tunneling Microscopy of Si(100)-c(4×4) Reconstructed Structure Formed by Ethylene Exposure
Authors: Ikeda Masanori , Nagashima Naoyuki
Published: October 2002

Si(100) surfaces exposed to ethylene (C2H4) at 700°C were observed using a scanning tunneling microscope (STM). For surfaces exposed to 10 L (1 L=1.3×10-4 Pa·s) of C2H4, irregular dots appeared in Si dimer rows, and lines of continuous missing dimers appeared that were aligned perpendicular to the Si dimer rows. With increasing C2H4 exposure, densities of both the irregular dots and the continuous missing dimers, as well as the length of the missing dimer rows, increased. For surfaces exposed to 100 L of C2H4, part of the Si(100)-(2×1) surface was reconstructed to a c(4×4) structure. The c(4×4) domain was located preferentially at the atomic step of a terrace and grew in the direction of the dimer rows in a (2×1) structure. The c(4×4) structure basically consisted of two distinct subunits.
Influence of Silicon Wafer Loading Ambient on Chemical Composition and Thickness Uniformity of Sub-5-nm-Thick Oxide Films
Authors: Endoh Tetsuo , Kimura Yasutaka , Lenski Markus , Masuoka Fujio
Published: October 2002

The influence of silicon wafer loading conditions during the vertical furnace oxidation process, on both the chemical composition and thickness uniformity of sub-5-nm-thick oxide films is investigated by secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). Loading wafers in pure nitrogen prior to oxidation effectively suppresses undesired preoxide growth offering controlled oxidation in the sub-5 nm regime. However, these wafers show a pronounced thickness nonuniformity, which correlates to the nitrogen incorporated in the oxide at the central part of the wafer. Loading wafers in a 1%-O2/99%-N2 ambient prior to oxidation results in uniform oxide films. However, film thickness in the sub-5 nm regime is difficult to control due to an excessive preoxide growth during wafer loading. Loading wafers in a chemically inert Ar atmosphere or under controlled preoxidation conditions prior to oxidation results in uniform oxide films with controllable oxide thickness suitable for sub-5 nm thick oxides.
Theory of Morphotropic Phase Boundary in Solid Solution Systems of Perovskite-Type Oxide Ferroelectrics: Engineered Domain Configurations II
Authors: Iwata Makoto , Orihara Hiroshi , Ishibashi Yoshihiro
Published: October 2002

The piezoelectric constants under two types of engineered domain configurations in perovskite-type oxide ferroelectrics were calculated in terms of the Landau-Devonshire-type free-energy function. It was found that the piezoelectric constants under the engineered domain configurations increase on approaching the morphotropic phase boundary, and diverge at the morphotropic phase boundary, if the free-energy function is truncated at the fourth order in the polarization. The physical properties of the engineered domain configurations were discussed.
Production of Stable Isotopes by Selective Channel Photofission of Pd
Authors: Takahashi Akito , Ohta Masayuki , Mizuno Tadahiko
Published: October 2002

A conservative modeling and analysis were attempted to explain the presence of nonradioactive fission-like products with nonnatural isotopic ratios observed in some D2O/Pd electrolysis experiments. The collective deformation of a Pd nucleus by multiphoton E1 resonance absorption in a dynamic PdD
x
lattice was assumed to induce low-energy photofissions via the selective scission channels within the lowest band (11–20 MeV) of channel-dependent fission barriers. Values of channel dependent fission barriers were calculated by using liquid drop model potentials for Pd isotopes. Fission products were analyzed in detail. Major fission products (FPs) are stable isotopes and the isotopic ratios of FP elements are very different from those of natural abundances. The present theoretical results have shown good agreement with the experimental data of Mizuno et al.. [Denki Kagaku 64 (1996) 1660] and others in terms of Z-distribution, mass distribution and isotopic ratios. Selective channel photofissions with positive Q-values are possible for A>90 nuclei, which may provide us with a clean method for the incineration for the radio isotope (RI) waste of nuclear plants.
Electron Energy Distributions in Inductively Coupled Plasma of Argon
Authors: Yonemura Shigeru , Nanbu Kenichi
Published: October 2002

The effects of gas pressure, electron density and coil current on the electron energy distribution functions (EEDFs) in inductively coupled discharges of argon are studied numerically. The EEDF for low gas pressure is close to the Maxwellian, whereas the EEDF for high gas pressure is lower than the Maxwellian in the high energy tail due to inelastic collisions. Since the energy loss due to inelastic collisions is compensated by the energy deposition due to the induced electric field, the EEDF near the quartz wall becomes close to the Maxwellian. However, this EEDF is not the real Maxwellian because the velocity distribution of electrons near the wall is anisotropic in velocity space and hence in nonequilibrium. We proposed the factor ξ which represents the magnitude of the effect of Coulomb collisions. The factor is the ratio of electron–electron collision frequency to electron-atom inelastic collision frequency. The effect of Coulomb collisions on the EEDF is negligibly small for ξ< 0.01. The distribution function for the azimuthal component of electron velocity varies significantly as the radial position changes, whereas the distribution functions for the other components do not vary so much.
Electron Transport across Magnetic Filter in Negative Hydrogen Ion Source
Authors: Fukano Azusa , Ogasawara Masatada
Published: October 2002

Profiles of electron temperature and number density in a negative-ion source are investigated theoretically. Spatial dependence over the magnetic filter region is obtained using the equations of electron flux and electron heat flux that include the effect of interference of forces by the density gradient and temperature gradient. Due to the effect of the magnetic filter, temperature and density of the electron decrease from the source chamber to the extraction chamber, and the decrease depends on the magnitude of the magnetic flux. The effect of the magnetic filter on the production and destruction rates of the negative hydrogen ion is examined. The reaction rate for the dissociative attachment reaction which produces the negative hydrogen ion increases with the decrease of the electron temperature. However, the production rate per one vibrationally excited hydrogen molecule decreases with the decrease of electron density. On the other hand, the destruction probability of the negative ion by the electron detachment reaction decreases significantly by the decrease of the electron density and temperature. The magnetic filter does not enhance the production of the negative hydrogen ion, but it reduces the destruction of the negative ion because of the decrease of the electron density.
Photoisomerization of Azobenzene Dendrimer Monolayer Investigated by Maxwell Displacement Current Technique
Authors: Shimura Daisuke , Manaka Takaaki , Nakamoto Masayuki , Zhao Wei , Majima Yutaka , Iwamoto Mitsumasa , Yokoyama Shiyoshi , Kubota Tohru , Mashiko Shinro
Published: October 2002

Photoisomerization in monolayers of a novel azobenzene compound, azobenzene dendrimer, was investigated for the first time by means of the absorption spectrum and Maxwell displacement current (MDC) technique. According to the absorption spectrum, trans-to-cis conversion ratio was estimated to be approximately 10% for the third generation of azobenzene dendrimer deposited onto a glass substrate. Temperature-dependent induced charge with trans-cis isomerization was also measured by means of MDC technique, and we found that the thermal isomerization process must be taken into account for theoretical analysis of trans-to-cis photoisomerization. The temperature dependence was theoretically treated in terms of the three-state model that takes into account the stimulated thermal isomerization. As a result, we could obtain a ground state energy barrier of 0.93 eV in cis-to-trans isomerization for the first-generation of the azobenzene dendrimer (AZ-G1), and the value is in good agreement with the previous results obtained from the molecular orbital (MO) calculation which suggests that thermal cis-to-trans isomerization in AZ-G1 passes through the inversion process.
Decomposition of N2O by Microwave Discharge of N2O/He or N2O/Ar Mixtures
Authors: Tsuji Masaharu , Tanoue Takeshi , Kumagae Jun , Nakano Kousuke
Published: October 2002

The decomposition of N2O into N2, O2 and NO by a microwave discharge of N2O/He or N2O/Ar mixtures was studied at various total pressures. Although discharge could be maintained only in the low total-pressure range of 1–80 Torr in N2O/He mixtures at N2O and He flow rates of 25 and 2000 sccm, respectively, stable microwave discharge could be maintained in the wide total-pressure range of 1–760 Torr in N2O/Ar mixtures at N2O and Ar flow rates of 25 and 1000 sccm, respectively, at a microwave power of 200 W. The decomposition efficiency of N2O and the branching ratios of products in N2O/Ar mixtures at 760 Torr were measured as a function of the microwave power or the N2O flow ratio at a relatively high N2O concentration range of 9900–47600 ppm. The decomposition mechanism of N2O in the He and Ar discharges is discussed on the basis of mass spectrometric and optical emission spectroscopic data.
Comparative Study of Electrochemomechanical Deformations of Poly(3-alkylthiophene)s, Polyanilines and Polypyrrole Films
Authors: Fuchiwaki Masaki , Takashima Wataru , Kaneto Keiichi
Published: October 2002

Expansion and contraction in regioregular and regiorandom poly(3-alkylthiophene), PAT films (alkyl=hexyl and dodecyl) upon electrochemical oxidation and reduction in organic electrolyte solvents are studied. It is found that the deformed films consist of two components, which respond to electrochemical cycle and creeping. The PAT films with short alkyl chain length show relatively large deformation by the electrochemical cycle, because of the higher density of electroactive π-electron components. The expansion/contraction ratio of PAT films is discussed taking the morphology into consideration and comparing it with the results for the other conducting polymers of polyaniline and polypyrrole films.
Nonempirical Design of Rapid Thermal Processing System
Authors: Habuka Hitoshi , Suzuki Takahiro , Sakurai Takashi , Negishi Youichi , Takeuchi Takashi
Published: October 2002

In order to develop a nonempirical technology to design a rapid thermal processing (RTP) system, a direct approach model using the ray tracing simulation (DARTS) is applied for designing the small RTP system composed of tungsten/halogen filament lamps, specular reflectors and a silicon wafer. The temperature profiles on the silicon wafer surface are theoretically predicted and experimentally evaluated using the two RTP systems. The quantitative agreement of the theoretically predicted and experimentally evaluated temperature profiles on the silicon surface suggests that the nonempirical design of the RTP system is possible using the DARTS model. The reflection-resolved analysis based on this model is considered to provide information on the entire path of the rays from the lamps to the silicon wafer surface and on the heat loss caused by the reflectors in the RTP system.
ArF Chemically Amplified Positive Resist Based on Alicyclic Lactone Polymer
Authors: Maeda Katsumi , Nakano Kaichiro , Iwasa Shigeyuki , Hasegawa Etsuo
Published: October 2002

We developed alicyclic acrylates with a hydrophilic moiety for use as an ArF chemically amplified positive resist. These monomers have an alicyclic unit, a norbornyl group, and a hydrophilic group, such as a hydroxyl, ester, acetate, or γ-lactone group. The acrylate polymer having a γ-lactone unit, 5-acryloyloxy-6-hydroxynorbornane-2-carboxylic 6-lactone, exhibited high thermal stability and high hydrophilicity. A chemically amplified positive resist composed of a terpolymer using the norbornyl acrylate with a lactone structure and a photoacid generator produced a fine resolution of a 0.12 µm L/S pattern at 16.3 mJ/cm2 by ArF exposure. This resist also produced a contact hole resolution of 0.14 µm with a depth of focus of 0.5 µm and exhibited good dry-etching resistance. The oxide etching rate achieved when using the developed resist is 1.29 times that of using a novolac resist, and it produces no resist top roughness after etching.
Functionally Graded Broadband Ultrasound Transducer Created by Forming an Internal Temperature Gradient
Authors: Daisuke Yamazaki Daisuke Yamazaki , Ken Yamada Ken Yamada , Kiyoshi Nakamura Kiyoshi Nakamura
Published: October 2002

A broadband ultrasound transducer composed of a piezoelectric plate with a graded piezoelectric parameter is presented. Grading of the piezoelectric constant is performed by forming an appropriate temperature gradient in the thickness direction of a fully polarized piezoelectric ceramic plate that has a low Curie temperature. It is shown experimentally that the functionally graded transducer is capable of emitting an almost single-pulse ultrasonic wave.
Water Adsorption on Lubricated Carbon Surface
Authors: Yanagisawa Masahiro
Published: October 2002

The fundamental properties of adsorption, i.e., molecular mobility and interaction energy between lubricants, water, and overcoats, are investigated for perfluorinated polyether (PFPE) lubricants on carbon surfaces in order to design mechanically reliable magnetic storage devices. The interaction between PFPE molecules and water molecules on carbon surfaces in dry and humid environments is analyzed using nuclear magnetic resonance (NMR). Two NMR spectrum peaks of water on carbon surfaces on which the PFPE diol is coated are observed when humid air of 90% relative humidity (RH) is introduced. One peak at a low chemical shift corresponds to the adsorbed water on the carbon surface. The other peak at a high chemical shift shows sorbed water molecules in the PFPE diol film. Minimum molecular mobility is observed for OH groups, i.e., adsorption sites, in dry air. However, the molecular mobility increases because of the lubricant desorption when humid air is introduced. The increased spin-lattice relaxation time (T
1) for the proton in the OH group reveals the desorption phenomena. Adsorption energies between the adsorbates (lubricants and water) and the adsorbent (carbon powder) are measured using a flow micro-calorimeter. When water vapor is introduced, the negative heat of adsorption is observed, which indicates the lubricant desorption caused by the water molecules.
Electrical Properties of Diamond-like Carbon Films Deposited Using a Filtered Cathodic Arc System
Authors: Li Yan-Way , Chen Chia-Fu , Tseng Yu-Jen
Published: October 2002

A new filter arc deposition (FAD) system has been developed to satisfy the requirements of magnetic storage devices. This work briefly describes the 45° magnetic filter cathodic arc deposition process and investigates how substrate bias, hydrogenating, and nitrogen-doping affect the electrical properties of amorphous diamond-like carbon films. Experimental results indicate that increasing in substrate bias and/or nitrogen doping into the film during the process would lower the resistance of the film. All these evidences indicate the post-deposited film is more “graphite-like”. The effect of hydrogen flow in the film is less significant. It is believed that the hydrogen can prevent the nucleation of the graphite phase, and can also stabilize of sp3 bonding. The phenomenon clearly indicates that the film is more “diamond-like”.
Intrinsic and Effective Secondary Electron Emission Coefficients in AC Plasma Display Panel
Authors: J. Yoon Sean , Insook Lee Insook Lee , Jong-Wan Lee Jong-Wan Lee , Byungdu Oh Byungdu Oh
Published: October 2002

Ion-induced secondary electron emission from the MgO protecting layer of an AC plasma display panel (AC-PDP) and the successive back-scattering of secondary electrons toward the cathode due to high gas pressure have been studied theoretically. A correlation between the intrinsic secondary electron emission coefficient (γi) and the MgO surface properties such as band gap energy and defect states in the band gap was found. The behavior of the effective secondary electron emission coefficient (γeff) of various ion species as a function of the reduced electric field (E/P) has also been investigated. These relationships can be applied to AC-PDP manufacturing in order to enhance the luminous efficiency and to reduce the breakdown voltage of AC-PDPs.
Terahertz-Time Domain Spectroscopic Measurement of Moderately-Doped Silicon Using InAs Emitter under Magnetic Field
Authors: Alex Quema Alex Quema , Masataka Migita Masataka Migita , Shigeki Nashima Shigeki Nashima , Masanori Hangyo Masanori Hangyo
Published: October 2002

The complex refractive index of silicon using terahertz-time domain spectroscopy (THz-TDS), with an InAs wafer under the influence of a magnetic field as emitter, has been studied. By applying a magnetic field on the InAs emitter, the detected temporal waveform broadens and the spectral weight of its Fourier spectrum shifts toward the low frequency region. Calculating the real (n) and imaginary (κ) parts of the complex refractive index of silicon, it is found that with the application of a magnetic field the plots of these quantities in the low frequency region (sub-terahertz region) are smoother than those without magnetic field. These features indicate that a significant enhancement of the signal-to-noise (S/N) ratio in the low frequency region can be obtained by applying a magnetic field on the InAs emitter.
Electric Field Vector Mapping in Sphere-to-Plane Electrode System using Simultaneous Three-Direction Optical Measurement System
Authors: Haruo Ihori Haruo Ihori , Takao Kawasaki Takao Kawasaki , Kotaro Tanino Kotaro Tanino , Masaharu Fujii Masaharu Fujii , Kiyomitsu Arii Kiyomitsu Arii
Published: October 2002

We have investigated nonuniform electric field vector distributions in liquid dielectrics. We have already reported on measurements of symmetrical and nonsymmetrical electric field vector distribution using the Kerr electrooptic effect and our unique reconstruction method based on the computed tomography technique. For the measurement of a field vector distribution, it was necessary to measure light intensity twice by changing the optical axis of optical wedges. Moreover, the intensity measurement had to be carried out at many points around the electrode system, and therefore it took considerable time to measure an electric field distribution. Thus, we developed a simultaneous three-direction optical measurement system with three optical systems combined with a two-beam method. Using the new measurement system, the electric field vector distribution was measured in about 0.1 min.
Transport Efficiency of Intense Relativistic Electron Beam in Preformed Plasma Channel
Authors: Seo Myoung-Choul Choi , Yun-Ho Seo Yun-Ho Seo , Guang-Sup Cho Guang-Sup Cho , Hi-Myung Shin Hi-Myung Shin , Eun-Ha Choi Eun-Ha Choi
Published: October 2002

Relativistic electron beam (REB: 300 keV, 5 kA, 60 ns) transport efficiency has been investigated by injecting the REB into a preformed argon plasma channel in a drift tube. Transport efficiency was obtained using two Rogowski coils separated 20 cm from each other. In the vacuum drift tube, the transport efficiency is about 20%, in which the propagation beam current is below the space charge limiting current. It is found that the transport efficiency can be increased to 48% when the preformed plasma channel density is 1.3×1011 cm-3, which is close to that of REB.
Suprathermal Electron Generation by an Ultraintensive Laser Pulse in Foil Plasmas
Authors: A. Andreev Kazuhito Satou
Published: October 2002

Suprathermal electrons are produced with energies up to 10 MeV by the interaction of high-intensity laser pulses with overdense plasmas. With the progress in short-pulse multiterawatt lasers, it is now possible to produce MeV electrons in a plasma. These electrons have potential for applications to medicine and other technologies. Particle-in-cell (PIC) simulations were performed to produce suprathermal electrons.
Foil Acceleration by Intense Pulsed Ion Beam Ablation Plasma
Authors: Yatsui Kiyoshi , Shinkai Hiroyuki , Kashine Kenji , Jiang Weihua , Kagihiro Makoto , Harada Nob
Published: October 2002

Foil acceleration by ablation pressure produced by the interaction of an intense, pulsed ion-beam with thick targets has been studied, where the thickness of the target is considerably more than the range of the incident ion beam. The experiments were carried out on solid targets with ion beam energy densities ranging from 100 J/cm2 to 4.3 kJ/cm2. The maximum foil velocity obtained by time-of-flight measurement was ∼7.7 km/s, giving the estimated ablation pressure of ∼13 GPa. The experimental and simulation results were in reasonable agreement.
Magnetic Field Generation in the Crab Nebula by Particle-in-Cell Simulations
Authors: Jyun-ichi Saeki Jyun-ichi Saeki , Toshio Okada Toshio Okada
Published: October 2002

Intense magnetic field generation in the Crab Nebula is studied by two-dimensional (2-D) particle-in-cell (PIC) simulation. We have proposed a mechanism of magnetic field generation based on Weibel-type electromagnetic instability. We apply our theory to simulate the magnetic field generation in the Crab Nebula and obtain an intense magnetic field by 2-D PIC simulation.