bluuebunny/crossref_metadata_2025 huggingface dataset:
RECENT ADVANCES IN ELECTRONIC STRUCTURE THEORY
Authors: NAKAJIMA TAKAHITO , TSUNEDA TAKAO , NAKANO HARUYUKI , HIRAO KIMIHIKO
Published: October 2002

Accurate quantum computational chemistry has evolved dramatically. The size of molecular systems, which can be studied accurately using molecular theory is increasing very rapidly. Theoretical chemistry has opened up a world of new possibilities. It can treat real systems with predictable accuracy. Computational chemistry is becoming an integral part of chemistry research. Theory can now make very significant contribution to chemistry.

This review will focus on our recent developments in the theoretical and computational methodology for the study of molecular structure and molecular interactions. We are aiming at developing accurate molecular theory on systems containing hundreds of atoms. We continue our research in the following three directions: (i) development of new ab initio theory, particularly multireference-based perturbation theory, (ii) development of exchange and correlation functionals in density functional theory, and (iii) development of molecular theory including relativistic effects.

We have enjoyed good progress in each of the above areas. We are very excited about our discoveries of new theory and new algorithms and would like to share this enthusiasm with readers.
CALCULATION OF TRANSITION AMPLITUDES WITH A SINGLE LANCZOS PROPAGATION
Authors: GUO HUA , CHEN RONGQING , XIE DAIQIAN
Published: October 2002

We review in this article a recently proposed energy-global method that is capable of calculating the entire transition amplitude matrix with a single Lanczos propagation. This method requires neither explicit computation nor storage of the eigenfunctions, rendering it extremely memory efficient. Procedures are proposed to handle situations where "spurious" eigenvalues aggregate around true eigenvalues due to round-off errors. This method is amenable to both real-symmetric and complex-symmetric Hamiltonians. Applications to molecular spectra and reactive scattering are presented. Its relationships with other methods are also discussed.
Specific Heat of a Regenerator Material Er3Ni
Authors: Takahashi Akiko , Tokai Yoichi , Hashimoto Masashi Sahashi
Published: October 2002

Specific heat measurement was performed in the temperature range from 800 mK to 62 K on the regenerator material Er3Ni which is an antiferromagnet with a Néel temperature of 6.1 K and possesses a large volumetric heat capacity even at temperatures aboveTN. The magnetic contribution to the specific heat has been carefully divided into two parts, one of which is caused by entropy change due to the magnetic ordering and the other a contribution from higher energy level states (Schottky anomaly). The energy levels of the 4f electrons for Er3+were calculated using the point-charge model, and compared with the experimental data. The entropy change of the Schottky anomaly is large compared with that of magnetic ordering and important for the regenerator material.
Photorefractive Effect in a Polymer Molecularly Doped with Low-Molecular-Weight Compounds
Authors: Yokoyama Kenji , Arishima Koichi , Toshiyuki Shimada Toshiyuki Shimada , Ken Sukegawa Ken Sukegawa
Published: October 2002

The photorefractive effect is observed in poly (methylmethacrylate) molecularly doped with three types of low-molecular-weight compounds, carrier transport (CTM), carrier generation (CGM) and nonlinear optical (NLO) materials. With these materials as dopants, the polymer exhibits both photoconductivity and the electro-optic (EO) effect under DC electric fields. The EO coefficient r
33 is found to be linearly dependent on applied fields because of the lower glass-transition temperature (T
g). In two-beam coupling and diffraction measurements, refraction gratings are written in the polymer. A phase shift of 90° between a refraction grating and a fringe pattern with applied fields proves the existence of the photorefractive effect, which is distinguished from heating effects. A maximum diffraction efficiency η of 4×10-6 is obtained in the photorefractive polymers.
Analysis of Mode Conversion at Discontinuities between K+–Na+ and Ag+–Na+ Ion-Exchanged Waveguides in Glass
Authors: Blagoy Pantchev Blagoy Pantchev , Zdravko Nikolov Zdravko Nikolov
Published: October 2002

The analysis of mode conversion caused by discontinuity between K+–Na+ and Ag+–Na+ ion-exchanged waveguides in glass is carried out. The experimentally obtained refractive index profiles of the waveguide regions are considered. Structures consisting of single-mode potassium and 2-, 5-, or 11-mode silver waveguides are studied using the least squares boundary residual method. The power coefficients of light propagation through the interface between the two waveguide regions are evaluated. In the case of structure consisting of a single-mode potassium waveguide and 11-mode silver one, the power transmittance coefficient for the lowest-order transverse electric mode reaches a value of 98.9%.
Anode Electropolished Stainless Steel with an Oxidized Surface as a New Substrate Material for the Langmuir-Blodgett Technique
Authors: Ohnishi Michihiro , Masahiro Aoki Masahiro Aoki , Coe Ishimoto Coe Ishimoto
Published: October 2002

The suitability of the electropolished stainless steel whose surface oxidized by thermal treatment, which has been developed for use in super-clean rooms, as a substrate for the Langmuir-Blodgett (LB) technique was investigated. This metallic material could be used as either a hydrophilic or a hydrophobic substrate. The properties of the LB films deposited onto the substrate were as good as those onto a glass substrate. X-ray photoelectron spectroscopy showed that LB layers were deposited in a highly ordered manner. The plasma polymerization replica of LB layers was prepared and observed using transmission electron microscopy. It was shown that the image of the LB layers on the prepared substrate was the same as that on a quartz substrate. It was found that this substrate is suitable for purposes of making measurements and observations of the LB film.
Origins of Spurious Peaks of Total Reflection X-Ray Fluorescence Analysis of Si Wafers Excited by Monochromatic X-Ray Beam W-Lβ
Authors: Yakushiji Kenji , Ohkawa Shinji , Yoshinaga Atsushi , Harada Jimpei
Published: October 2002

Spurious peaks such as Fe-Kα or Ni-Kα radiations are observed in the analysis of trace metallic impurities on a Si wafer by monochromatic total reflection X-ray fluorescence. These peaks seriously influence the accuracy in the quantitative analysis of the trace impurities. Intensities of these peaks are shown to depend on the intensity of the elastically scattered primary beam ( W-Lβ) whose intensity varies with the incident azimuth. It is found that impurity radiations are included in the primary X-ray beam, and contaminations in the Be window of the X-ray detector are also a source of spurious peaks. The impurities deposited on the Be window, in and/or on the Si(Li) crystal of the detector and the casing material of the X-ray detector can also contribute to these spurious peaks.
Step Coverage, Uniformity and Composition Studies Using Integrated Vapour Transport and Film-Deposition Models
Authors: Steven Dew Steven Dew , Tom Smy Tom Smy , Michael Brett Michael Brett
Published: October 2002

A Monte Carlo sputter flux transport model has been developed for efficient generation of angular, energy, and thickness uniformity distributions for application to integrated circuit metallization films. The model allows for arbitrary target erosion profiles and emission angular distributions and uses an energy-dependent gas-scattering model. Verification of the model using aluminum and copper pinhole images has been obtained. The resulting sputter distribution information can be input into a topography-level film-deposition model to provide step coverage and microstructure depictions. The combination of these two models has been used to examine metallization issues such as film thickness uniformity, step coverage, compositional variations in alloy films, and magnetron source design.
Wall Deposition of Ultrafine Aerosol Particles by Thermophoresis in Nonisothermal Laminar Pipe Flow of Different Carrier Gas
Authors: Manabu Shimada Manabu Shimada , Takafumi Seto Takafumi Seto , Kikuo Okuyama Kikuo Okuyama
Published: October 2002

Deposition of ultrafine aerosol particles by Brownian diffusion and thermophoresis in a nonisothermal laminar pipe flow is investigated theoretically and experimentally. The deposition rates of Ag and TiO2particles of 8–30 nm in diameter suspended either in N2, Ar or He gas are measured using a circular pipe with a nonuniform wall temperature distribution. The numerical calculation results considering the gas flow, temperature and particle distributions in the pipe show good agreement with the measured values. The particle deposition is enhanced with the increase of the wall temperature variation, but does not depend on the particle material. The difference in the deposition rates among the carrier gases is mostly attributable to the values of the Brownian diffusion coefficient. The enhancement of deposition by thermophoresis is of a similar magnitude among the carrier gases, which is explained in terms of the temperature distribution of the gases in the pipe.
Device Simulation of Novel In-Plane-Gated Field-Effect Transistors
Authors: Stenzel Roland , Klix Wilfried , Dittmann Ralf , Pigorsch Carsten , Meiners Ulrich , Brugger Hans
Published: October 2002

The first three-dimensional numerical device simulation of the novel in-plane-gated field-effect transistor with a quasi-one-dimensional electron channel is reported. Information about the electrical characteristics is obtained by a calculation of the output and the transfer behavior of the device on the basis of a classical drift-diffusion model. The quasi-one-dimensional current path is defined laterally by two thin insulating lines on a pseudomorphic, modulation-doped AlGaAs/InGaAs/GaAs heterostructure with a high-density two-dimensional electron gas. Gate leakage currents and a parasitic bypass current flow can be avoided by deep isolation lines and a modified cap layer sequence, respectively. High transconductance values are expected only for highly p-doped isolation regions. Room temperature operation of a single channel device is demonstrated with a measured transconductance of 18 µ S and a maximum current of above 0.11 mA.
An Investigation of the Inconsistency in Barrier Heights for PNP and NPN Polysilicon Emitter Bipolar Transistors Using a New Tunneling Model
Authors: Post Ian R. C. , Nouailhat Peter Ashburn
Published: October 2002

A new tunneling model is proposed for polysilicon emitter bipolar transistors in which the interfacial layer is modeled as a wide band-gap semiconductor. This model predicts that potential barriers are formed in both the conduction and valence bands. The shapes and sizes of the barriers are dependent upon the amount of band-bending within the interfacial layer, which is in turn dependent on the amount of dopant segregation in the interfacial layer. Measurements of base current and emitter resistance are made on pnp polysilicon emitter bipolar transistors with deliberately grown interfacial oxide layers. These electrical characteristics are then modeled using the new heterojunction tunneling model, from which values of electron and hole barrier heights are extracted. Specifically, a hole barrier height of 0.31±0.02 eV is obtained, and an electron barrier height of either >0.68±0.08 eV or >0.44±0.06 eV, with the value depending on the band-gap narrowing model used in the calculation. These values of electron and hole barrier height are shown to be different than the values obtained when similar measurements are made on npn devices. The new heterojunction tunneling model is used to model these devices, and it is shown that it is capable of fully explaining this discrepancy between the values of barrier height obtained from measurements on npn and pnp transistors.
Preparation of Acicular Fine Particle of Fe–Co Alloy and Its Magnetic Characteristics
Authors: Tagawa Kimiteru , Utuno Noritoshi , Tasaki Hideki Umehara
Published: October 2002

Acicular fine particles of Fe–Co alloy were prepared by reducing hydrogen of α FeOOH and were coated with Co ferrite precipitate. Co ferrite precipitate was prepared by means of mixing the solution of Fe(NO3)3 and Co(NO3)2 whose molecular ratio was 2:1 and the alkaline (pH 11 to 13) solution suspended α FeOOH particles. The amount of the precipitated Co ferrite was 75% of αFeOOH. The saturation magnetization (σ s) and coercive force (H
c) of the obtained Fe–Co particles increase with increasing Co concentration. The rate of increase of σ s was about 2 emu/g per at.% of Co, which is twice as large as that of the bulk. It was concluded that the large σ s was caused by the thickness of the oxide layer which covered the Fe–Co particle. The magnetic anisotropy of the Fe–Co particle was considered to be due to shape anisotoropy, because the rates of increase of H
c and σ s are almost the equal.
High-Density Video Disc Using Superresolution and Green Laser
Authors: Ichiura Shuichi , Tsuchiya Yoichi , Hitoshi Terasaki Hitoshi Terasaki , Osamu Ota Osamu Ota
Published: October 2002

Development of a high-density multiple sub-Nyquist sampling encoding (MUSE) video disc with a playback time of 2 h per side has been achieved using an optical head which utilizes the superresolution technique and a green laser, and by quadrupling the recording density of the analogue video disc. The focused spot size of the main lobe in the superresolving direction of the optical head was 0.63 µ m ( 1/e2 full width). With this optical head, using the slit detection method, a carrier to noise (CN) ratio of 56 dB was obtained at a pit length of 0.3 µ m which is the cut-off pit length of the 670 nm optical head. Compared with an optical head using only a green laser, the CN ratio at a pit length of less than 0.3 µ m was improved by 2 to 3 dB. An SN ratio of 41.5 dB was obtained for the quad- ruple φ300 mm MUSE video disc which has a 0.8 µ m track pitch and a 10.1 m/s linear velocity.
Long-Wavelength (1072 nm) Strained InGaAs Quantum-Well Lasers Grown on 1.0° Misoriented (111)B GaAs
Authors: Akihiro Ishihara Akihiro Ishihara , Hideo Watanabe Hideo Watanabe
Published: October 2002

The operation of InGaAs/GaAs/AlGaAs strained quantum-well lasers on 1.0° misoriented (111)B GaAs substrates is reported. The laser structures are grown by molecular beam epitaxy (MBE). Threshold current densities of 164 A/cm2 at 1072 nm were obtained for broad-area, uncoated devices with cavity lengths of 700 µ m.
Aspheric Lens Laser Diode Collimator Design for Optical Intersatellite Communications
Authors: Nohara Mitsuo , Inagaki Keizo , Koyanagi Hideaki , Ishibai Isao
Published: October 2002

A design for a laser diode collimator using aspheric lens technology was employed to achieve a 5-mm-diameter circular output beam with minimal wavefront aberration, and the minimum number of lenses of the smallest size. The presently designed collimator can achieve a wavefront aberration of better than λ/100 with a pair of aspheric anamorphic lenses, and a total length of 30 mm.
Electret Motor Having Rotor Employing Plastic Substrate
Authors: Yasufusa Tada Yasufusa Tada
Published: October 2002

We have attempted to reduce the weight of our original electret motor by using, as the substrate of the rotor, a plastic disk instead of an aluminum disk. The theoretical calculations show that the torque exerted on the plastic rotor is less than that on an aluminum rotor and approaches that exerted on the aluminum rotor with the decrease in thickness of the plastic rotor; however the torque per unit weight of the acrylic rotor is greater than that of the aluminum one. This type of electret motor has been fabricated. An experimental torque near the theoretical torque has been obtained.
The Homeotropic Surface Anchoring Effects on the C-H Phase Transition
Authors: Allender Jong C. Lee
Published: October 2002

Two simple models are introduced to explane the homeotropic surface anchoring effects on the cholesteric to homeotropic (C-H) phase transition in the absence of an applied field. The calculations are extended to include the effect of an external field perpendicular to the surfaces. The results predict the C-H phase transition with analytical expressions involving the product of cell thickness and inverse pitch.
Switching Experiments with a Mach-Zehnder-type All-Optical Device Based on the Band-Filling Nonlinearity in a GaAs Waveguide and Reduction in Its Relaxation Time
Authors: Tajima Kazuhito , Nakamura Shigeru , Noboru Hamao Noboru Hamao , Yoshimasa Sugimoto Yoshimasa Sugimoto
Published: October 2002

We examine switching characteristics of an all-optical device in Mach-Zehnder configuration, that is based on the band-filling nonlinearity in a GaAs waveguide. Switching waveforms corresponding to π (full switching), 2π, and 2.7π have been obtained and they were compared with theoretical curves. Good agreement has been observed between experimental and theoretical results. The control light pulse energy required for full switching is estimated to be approximately 6 pJ. The switching speed of the above device is limited by the slow relaxation time of photogenerated carriers. In order to reduce the switch-off time determined by the carrier relaxation, we investigated a method which involves application of a DC electric field across the thin core layer of the waveguide in order to sweep photogenerated carriers away from the light-guiding region and effectively reduce the relaxation time. With this technique, the usual switching speed of approximately 1 ns was reduced to approximately 24 ps.
Formation and Thermochromism of V O2Films Deposited by RF Magnetron Sputtering at Low Substrate Temperature
Authors: Ping Jin Ping Jin , Sakae Tanemura Sakae Tanemura
Published: October 2002

Thermochromic VO2films were deposited on substrates of silicon and Pyrex glass by reactive rf magnetron sputtering and characterized by thin-film X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), atomic force microscopy (AFM) and spectrophotometry. Films with a VO2single phase were formed above a fairly low temperature of 300° C by controlling precisely the oxygen flow ratio. The use of a nucleated substrate improved the crystallinity of the VO2films deposited at low temperature. A negative substrate bias appeared to have an effect of favoring the formation of a VO2single phase at a substrate temperature as low as 250° C.
Deposition Profile of RF-Magnetron-Sputtered BaTiO3 Thin Films
Authors: Lee Nam-Yang , Sekine Tomoyuki , Ito Yukio , Uchino Kenji
Published: October 2002

BaTiO3 thin films were fabricated using an rf-magnetron sputtering technique and an oxide target. In spite of depositing on an amorphous fused quartz substrate, the preferentially oriented thin films were obtained without any post-annealing process. The preferred orientation of the thin films changed with sputtering gas pressure, gas composition and substrate temperature. At a lower gas pressure, the thin films crystallized well and preferentially oriented to the [100] direction. With increasing gas pressure, the preferred orientation changed to (110). On the other hand, at a lower substrate temperature or higher argon partial pressure, the preferred orientation changed to (111). The variation of the preferred orientation, lattice constant, and crystallite size with sputtering conditions was explained by assuming a thermal-vibration model.
X-Ray Diffraction and Electron Microscopy Study of Cr/Sb Multilayered Films
Authors: Hitoshi Dohnomae Hitoshi Dohnomae
Published: October 2002

Structures of [Cr(2 Å)/Sb(50 Å)]nmultilayered films have been investigated by X-ray diffraction and transmission electron microscopy (TEM) of cross sections. When the substrate temperature (Ts) was 90° C, an epitaxial structure with a coherent stacking of Sb and compound (CrSb) layers was formed by the interfacial reaction. On the other hand, atTs=-50° C, a non-epitaxial structure composed of crystalline Sb layers and amorphous Cr metal layers was obtained. Interfaces of multilayers observed by TEM are very flat for both samples. The structures of very thin Cr layers depend on the reactivity of interfaces and greatly affect on the orientations of Sb layers.
Application of a Thermally Evaporated WO3 Film to a Shadow Mask for the Suppression of Mislanding in Color Cathode Ray Tubes
Authors: Morio Yamamoto Morio Yamamoto
Published: October 2002

A thermally evaporated WO3 film with higher electron-reflecting rate was investigated for application to a fine-pitch shadow mask aperture of a color cathode ray tube (CRT). The film adhered strongly to the mask and covered the entire mask surface uniformly without blocking the apertures. The amount of mislanding of the mask with the WO3 film was about 35% less than that of a conventional mask with a Fe3O4 film under a local scanning mode. The film thickness necessary to obtain this value was more than 2 µ m. From these results, it was found that the WO3 film was applicable to a color CRT with higher resolution and higher brightness in a large flat screen.
Frequency Stabilization of Two Diode-Pumped Nd:YAG Lasers Locked to Two Fabry-Perot Cavities
Authors: Noboru Uehara Noboru Uehara , Ken-ichi Ueda Ken-ichi Ueda
Published: October 2002

We describe frequency stabilization of two laser-diode-pumped Nd:YAG lasers independently locked to two high-finesse Fabry-Perot cavities. The frequency noise (FM noise) is reduced to the shot noise limit of 0.37 mHz/√H
z at the error signal. A heterodyne beat note between two locked lasers is used to measure the frequency stability, and the beat linewidth of 16 Hz and the root Allan variance of 19 Hz at time interval of 3 ms are measured. We also measured an effect of angular ground vibration to FM noise. The sensitivity of 3.38 mHz/√H
z / nrad below 10 nrad
r
m
s
is obtained in our system.
Frequency Chain to 3.39 µ mCH4-Stabilized He–Ne Laser Using Josephson Point Contact as Harmonic Mixer
Authors: Miki Yukinobu , Onae Atsushi , Kurosawa Tomizo , Yoshiaki Akimoto Yoshiaki Akimoto , Eiichi Sakuma Eiichi Sakuma
Published: October 2002

A frequency-multiplication chain to the 3.39 µ m CH4-stabilized He–Ne laser has been constructed using the Josephson point contact as a harmonic mixer. The Josephson harmonic mixer simplifies the chain because it can directly connect the 90 GHz microwave and the 4.25 THz far-infrared frequencies. Tracking oscillators, which track the beat notes by phase locking and regenerate clean signals, also have been developed to correctly count the beat frequencies. The frequency fluctuations of free-running lasers are canceled by counting the beat frequencies with coincident gate timing. The absolute frequency measurement of the He–Ne laser is reported with a standard deviation of about 5 kHz (τ=8 s).
New Millisecond Pulsar Observation System at Communications Research Laboratory
Authors: Hanado Yuko , Imae Michito , Sekido Mamoru , Hama Hitoshi Kiuchi
Published: October 2002

Millisecond pulsars are attracting attention as future reference clocks because of their highly stable pulse timing. Communications Research Laboratory (CRL) has started a project which applies millisecond pulsars to time and frequency standards, and developed a basic observation system. Using this system, we can observe a millisecond pulsar, PSR1937+21, and obtain an observation precision of 10 µ s/τ which is primarily influenced by system noise. In order to improve the precision, a new observation system is now being developed. This system uses an acoustooptic spectrometer (AOS) for expansion of observation bandwidth, and high-speed devices for practical construction of the AOS. This is a new type of observation system for millisecond pulsars, and is expected to improve the observation precision. In this paper, we introduce the concept of this system and current situation in the development.
Chemical Etching of Thermally-Grown SiO2 Films on SiC Studied by Spectroscopic Ellipsometry
Authors: Susumu Ninomiya Susumu Ninomiya , Sadao Adachi Sadao Adachi
Published: October 2002

Chemical etching characteristics of thermally grown SiO2 films on 6H-type SiC in aqueous HF solutions have been studied using spectroscopic ellipsometry. Aqueous HF (1.5%) solution can etch thermally grown SiO2 layers on the (0001)Si and (0001̄)C faces of SiC at a rate of ∼90 Å/ min. A linear regression analysis and an effective medium approximation indicate that the SiO2/(0001)Si interface formed by thermal oxidation, followed by aqueous HF etching, is much rougher than the SiO2/(0001̄)C interface produced by the same procedure.
Diffusion Length of Holes in n-ZnSe Measured by Schottky Barrier Photovoltage Method
Authors: Hironobu Kariyazono Hironobu Kariyazono , Toshiyuki Ido Toshiyuki Ido
Published: October 2002

The diffusion length (L ) of holes in undoped n-type ZnSe has been measured by using the Schottky barrier photovoltage method. The samples measured were single crystals and epitaxial layers which were prepared by metalorganic chemical vapor deposition. The values of L were 1 µm for single crystals and 0.15 µm for epilayers. The lifetimes estimated from those values were 4.5 ns and 0.10 ns, respectively.
Dynamics of Photoexcited Carriers and Space-Charge Field by Picosecond Two-Beam Excitation in Photorefractive Semiconductors
Authors: Yasuo Tomita Yasuo Tomita , Hidemoto Ishii Hidemoto Ishii
Published: October 2002

Dynamics of space-charge field formation and its decay, as well as those of photoexcited electrons and holes, by picosecond two-beam excitation in photorefractive semiconductors are calculated by means of the band transport rate equations. Approximate analytic solutions that describe the transient behaviors of carriers, deep level donors and the space-charge field at the onset of pulse incidence and after the pulse are obtained. The result is applied to a semi-insulating undoped GaAs crystal with an input of two single-shot 20 ps pulses at 1.064 µm. It is found that two-photon absorption enhances the transient peak of the space-charge field but suppresses the long-lived space-charge field component significantly. The result is also compared with a numerical simulation.
Numerical Evaluation of Silicon-Thin Film Growth from SiHCl3-H2 Gas Mixture in a Horizontal Chemical Vapor Deposition Reactor
Authors: Hitoshi Habuka Hitoshi Habuka , Masatake Katayama Masatake Katayama , Manabu Shimada Manabu Shimada , Kikuo Okuyama Kikuo Okuyama
Published: October 2002

An evaluation of silicon epitaxial thin film growth using the SiHCl3-H2 system in a horizontal chemical vapor deposition (CVD) reactor is discussed. The transport equations for gas velocity, temperature and concentration of chemical species are solved, taking account of the dependence of gas properties on temperature and composition. By comparing the measured and predicted growth rates under atmospheric pressure, the increase in growth rate with temperature and SiHCl3 concentration can be explained by assuming an Arrhenius-type expression for the chemical reaction of SiHCl3 and H2 on a substrate. The calculated growth rate of the Si film increases nonlinearly with SiHCl3 concentration because the flow, temperature, and concentration distributions in the reactor depend on the SiHCl3 concentration. Suppression of the growth rate due to thermal diffusion, which transports SiHCl3 gas away from the hot surface, is found to become significant as the SiHCl3 concentration in the reactor increases.
High Rate and Highly Selective SiO2 Etching Employing Inductively Coupled Plasma
Authors: Fukasawa Takayuki , Nakamura Akihiro , Shindo Haruo , Yasuhiro Horiike Yasuhiro Horiike
Published: October 2002

Plasma and SiO2 etching characteristics employing inductively coupled plasma (ICP) were studied with respect to distance from an antenna. Measurement of the ratio of electron to ion saturation currents in CHF3 plasma shows an increase in negative fluorine ions in the downstream regions. The intensity ratio of C2 (516.5 nm)/F(685.6 nm) also indicates high carbon-concentration in the downstream region. Further more, addition of H2 to C4F8, which has more carbon species, yielded higher C2/F ratio. Accordingly, it was found that selectivity of SiO2/Si was remarkably enhanced by adding a higher concentration of H2 to C4F8 in the downstream region. The favorable results are due to the sheetlike characteristics of ICP. Since the plasma is confined near a quartz plate, HF molecules generated from the reaction of H atoms with F atoms do not undergo dissociation in the diffusive region. Thus high-speed pumping of HF is considered to suppress Si etching and in turn, to allow highiy selective SiO2 etching.
Charge Build-Up and Uniformity Control in Magnetically Enhanced Reactive Ion Etching Using a Curved Lateral Magnetic Field
Authors: Satoshi Nakagawa Satoshi Nakagawa , Tomoyuki Sasaki Tomoyuki Sasaki , Hajime Mori Hajime Mori , Takashi Namura Takashi Namura
Published: October 2002

The effectiveness of a curved lateral magnetic field has been examined in magnetically enhanced reactive ion etching (MERIE). It is demonstrated that both charge build-up and etching nonuniformity are suppressed at the same time when the offset angle of dipole magnets is adjusted to 10°. Theoretical analysis of electron flow in the curved lateral magnetic field suggests that the plasma electron multiplication effect along E×B drift motion is compensated by the divergence of the drift motion at the optimum condition, and it results in uniform plasma generation. Although the definite mechanism of charge build-up is still not clear, this study indicates the importance of plasma uniformity in controlling the charge build-up in a MERIE system.
Generation of Electron Cyclotron Resonance Neutral Stream and Its Application to Si Etching
Authors: Tsuchizawa Tai , Yoshito Jin Yoshito Jin , Seitaro Matsuo Seitaro Matsuo
Published: October 2002

A low-energy (10–20 eV) neutral stream generated by charge exchange reactions in an electron cyclotron resonance (ECR) plasma stream is extracted by eliminating charged particles and used for Si etching. The formation of a cusp magnetic field over the substrate eliminates charged particles because electrons are led outside the substrate by the magnetic field. In addition, residual ions are repelled by a positive voltage supplied to the substrate, and it becomes possible to irradiate the etching samples with only the neutral stream. The etch rate for Si is about 100 Å/min with a gaseous mixture of Cl2 and a small amount of SF6, and a microwave power of 400 W. We confirm that neutral stream etching allows us to attain anisotropic etching shapes without distortion, and that it can be used for delineating fine patterns.
RF Glow Discharge and Ion Transport: Effects of Applied Frequency, Gas Pressure and Method of Power Coupling
Authors: Harafuji Kenji , Atsuhiro Yamano Atsuhiro Yamano , Masafumi Kubota Masafumi Kubota
Published: October 2002

Spatiotemporal structures in a parallel-plate RF glow discharge using argon plasmas have been simulated based on fluid approximation. For unchanged RF and DC bias components of voltage applied at an electrode, ion density, ion flux and mean electric power density increase as frequency f and gas pressure P become higher, whereas sheath length and its variation amplitude are inversely proportional to √f and √P. When two independent RF power supplies having identical frequency and applied voltage to each other are coupled to two electrodes, ion density and ion flux have their maximum values when the phase difference between the two RF power supplies is 180°. Energy and angular distributions of ions striking the electrode are also studied based on the Monte Carlo technique for the simulated parameters of the RF glow discharge. Since the ratio of sheath length to ion mean free path is proportional to √P/f, high-frequency operation under a low-pressure condition is preferable to achieve less attenuated, centered energy and less scattered angular distributions of ions.
Enhancement of Emission of Si Atoms from Si(100) Surface by Low-Rate Br Exposure: A New Model of Dry Etching Based on Defect-Adsorbate Interaction
Authors: Keun Yu Jun'ichi Kanasaki , Yasuo Nakai Yasuo Nakai , Noriaki Itoh Noriaki Itoh
Published: October 2002

We report experimental results of the enhancement of Si emission from the Si(100) surface by submonolayer Br adsorption and by the exposure to Br at exposure rates as low as 10-3L/s. The results were explained in terms of selective breaking of bonds of atoms at defect sites by interaction with adsorbed Br atoms. Semi-empirical calculation of the emission rate per pulse as a function of laser intensity and Br exposure rate explained semiquantitatively the results of not only the low-coverage and low-exposure-rate experiments but also high-exposure-rate experiments under conditions employed in the conventional dry etching.
Abrupt Si/Ge/Si(001) Interfaces Fabricated with Bi as a Surfactant
Authors: Sakamoto Kunihiro , Matsuhata Hirofumi , Kyoya Ken'ichi , Kazushi Miki Kazushi Miki , Tsunenori Sakamoto Tsunenori Sakamoto
Published: October 2002

Fabrication of atomically abrupt Si/Ge/Si heterointerfaces was demonstrated using Bi as a surfactant. Cross-sectional high-resolution transmission electron microscopy shows that the surfactant improves the abruptness at the Si/Ge/Si heterointerface through the suppression of Ge surface segregation. The existence of distinct atomic steps at the heterointerfaces indicates that the flatness at the heterointerfaces is degraded by the surfactant due to the suppression of surface migration. A growth procedure to fabricate abrupt and flat Si/Ge/Si interfaces by alternating adsorption and desorption of Bi atoms is proposed.
Cyclotron Resonance in Ge Layers of Ge1-xSix–Ge Strained Heterostructures
Authors: Gavrilenko Vladimir I. , Kozlov Igor N. , Moldavskaya Mariya D. , Nikonorov Vyacheslav V. , Orlov Lev K. , Kuznetsov Oleg A. , Chernov Alexander L.
Published: October 2002

Cyclotron resonance of photoexcited carriers in Ge/Ge1-
x

Si

x

multilayer strained undoped heterostructures (HSs) was investigated for the first time. Cyclotron resonance line of positive charge carriers with the effective mass m
c≈0.07m
0 corresponding to that of holes in the upper subband in the strained quantum wells in Ge layers was observed in the absorption and mm-photoconductivity spectra. The persistent photoconductivity is shown to arise after interband illumination owing to the free holes remaining in the sample.
Intersubband Transition in Si-based Quantum Wells and Application for Infrared Photodetectors
Authors: Gamani Karunasiri Gamani Karunasiri
Published: October 2002

Intersubband transitions in quantum wells and superlattices have attracted a great deal of interest because of their potential applications in infrared detection and imaging. This is particularly important in Si-based heterostructures due to the advantage of monolithic integration with the conventional silicon signal processing electronics. In this paper, experimental observations of intersubband transition in SiGe/Si quantum wells and δ-doped layers in Si will be reviewed. In addition to intersubband transitions, two normal incident absorption processes; intervalence band transition and internal photoemission from two-dimensional hole gas in the quantum well will also be discussed. Finally, the progress in the application of SiGe/Si multiple quantum well structures for the fabrication of infrared detectors will be discussed.
Growth, Superconductivity and Anisotropy in the Electrical Resistivity of Pb2Sr2Ho0.5Ca0.5Cu3O8 Single Crystals: The Effect of Contamination from the Crucible on Tc
Authors: Noji Takashi , Koike Yoji , Ohtsubo Kunihiro , Shiga Shunsuke , Kato Masatsune , Akihiko Fujiwara Akihiko Fujiwara , Yoshitami Saito Yoshitami Saito
Published: October 2002

Single crystals of Pb2Sr2Ho0.5Ca0.5Cu3O8 have been grown in Pt, Al2O3 and Au crucibles by means of the flux method. The effect of contamination from the crucible on T
c has been investigated by studing the effects of Cu-site substitution on T
c and magnetic properties for sintered polycrystals of Pb2Sr2R0.5Ca0.5( Cu1-
y

M

y

)3O8 with R= Ho or Y and M= Pt or Al. Consequently, it has been found that use of a Pt crucible leads to growth of single crystals of the best quality with high T
c values and that Al2O3 and Au crucibles contaminate the single crystals to decrease T
c. Anisotropy in the electrical resistivity of the single-crystal Pb2Sr2Ho0.5Ca0.5Cu3O8 has been found to be comparable to that of YBa2Cu3O7 in spite of its thick blocking layer, suggesting that the wave functions of conduction electrons moderately overlap along the c-axis in Pb2Sr2Ho0.5Ca0.5Cu3O8.
Magnetic Properties of Mechanically Alloyed Al-doped Fe3Sn
Authors: Pan Chi-Wen , Yen-Hwei Chang Yen-Hwei Chang , Ming-Pan Hung Ming-Pan Hung
Published: October 2002

When Fe3Sn powders were milled for 30 h, the X-ray diffraction pattern of the as-milled powders revealed a broad peak typical for an amorphous phase. Nanocrystals appeared after 30-h milling for Al-doped Fe3Sn powders and the amount of nanocrystals increased with the increase of the amount of aluminum doped. Owing to the formation of nanocrystals, the saturation magnetization of the as-milled powders increased with Al doping. However, the coercivity exhibited an opposite tendency compared with the saturation magnetization. The crystalline phases were obtained by annealing as-milled powders at 800°C for 0.5–5 h. The crystalline Fe3Sn phase was formed for an Al (3.63 wt%)–Fe3Sn sample after 0.5-h annealing with a saturation magnetization of 105 emu/g.
Kinetics of Droplet Formation in UV-Cured Polymer-Dispersed Liquid Crystal Films
Authors: Vasilii G. Nazarenko Vasilii G. Nazarenko , Seshu Sarala Seshu Sarala , Nelamangala V. Madhusudana Nelamangala V. Madhusudana
Published: October 2002

The kinetics of liquid crystal (LC) droplet formation in a UV-cured polymer has been studied using differential scanning calorimetry (DSC). We discuss a physical mechanism for the change in refractive index of the polymer matrix. The influence of initial condition of polymerisation on the optical characterstics of polymer-dispersed LC (PDLC) films has been investigated. The extremely important problem of optimising the contrast of PDLC displays is also discussed.
Effect of Na2O Addition on the Optical Properties and Chemical Durability of Li2O–CaO–Al2O3–GeO2 Glass
Authors: Wang Moo-Chin , Wang Jenn-Shing , Hon Ming-Hsiung
Published: October 2002

By progressive weight percent substitution of Na2O for Li2O, at a constant ratio of concentration of CaO, Al2O3, and GeO2, the Li2O(–Na2O)–CaO–Al2O3–GeO2 system is prepared for infrared transmitting germanate glasses. The optical and chemical durability properties of these glasses have been studied. The infrared cutoff for these germanate glasses is about 7.2 µm longer than that of 5 µm for silicate glasses. The ultraviolet absorption edge for these glasses is near 306 nm, except for the glass which contained 6.44 wt% Na2O at 295 nm. The refractive indexes of these germanate glasses increase as Na2O content is increased. The Abbe number for all glass samples is about 62.03±4.07. The absorption coefficients for these germanate glasses at 2.5 µm and 500–700 nm are 0.023 mm-1 and 0.019 mm-1, respectively. The leaching results indicate that the glass with 3.22 wt% Na2O ( C3 glass) has the minimum weight loss in the chemical durability test.
Brillouin Scattering Study on Dynamic Properties of a Viscoelastic Liquid Propylene Glycol Using a Tandem Fabry-Perot Interferometer
Authors: Takanashi Katsutoshi , Kojima Akira Yoshihara
Published: October 2002

Dynamic properties of propylene glycol have been investigated using a (3+3) pass vernier tandem Brillouin spectrometer in a temperature range between 291 K and 372 K and a frequency range between 2 GHz and 480 GHz. In this report, we discuss the sound velocity dispersion observed below 20 GHz, the structural relaxation mode observed in a middle frequency range between 20 GHz and 200 GHz, and a fast relaxation mode observed above 200 GHz. From these measurements, covering a very wide frequency range, the dynamic susceptibility for light scattering has been successfully determined at several temperatures and compared with the one obtained from Raman scattering.
Postdeposition Annealing Influence on Sputtered Indium Tin Oxide Film Characteristics
Authors: Higuchi Masatoshi , Uekusa Shinichiro , Nakano Ryotaro , Yokogawa Kazuhiko
Published: October 2002

The influence of postdeposition annealing on sputtered indium tin oxide (ITO) film characteristics were investigated. The annealing experiments were carried out in air or vacuum atmosphere. Both air and vacuum annealing decreased the resistivity up to heat treatment of 200° C. Over 300° C treatment, air annealing increased resistivity whereas vacuum annealing decreased it. It was clarified that the resistivity depended on the carrier concentration. The lowest resistivity attained was 1.3×10-4 Ω·cm, with film deposited on a 250° C heated substrate and annealed in vacuum atmosphere at 300° C. Transmittance was improved in both air and vacuum annealing. In air and vacuum annealing, crystallinity improved with increasing annealing temperature. The surface topography showed no changes with air or vacuum annealing.
Phase-Shift Control of Resonant Frequencies of Magnetostatic Wave Resonators
Authors: Takuro Koike Takuro Koike , Hiroaki Nakazawa Hiroaki Nakazawa
Published: October 2002

We discuss a possible technique to control the resonant frequencies of a straight-edge magnetostatic wave (MSW) resonator without changing the external applied magnetic field and the circuit parameters of a feedback load circuit. The method is to use two additional microstrip electrodes at the edges of the resonator and two varactor diodes connected in series. Upon varying the bias voltages to the varactor diodes, the input admittance at the center electrode can be changed. Theoretical investigation reveals that very large resonant frequency shifts can be obtained by changing only the bias voltage change to the varactor diodes, which may be useful in mobile telephone applications in the gigaherz frequency range.
Destruction Mechanisms in Ceramic Multilayer Actuators
Authors: Aburatani Hideaki , Harada Shuichi , Uchino Kenji , Furuta Atsushi , Fuda Yoshiaki
Published: October 2002

Destruction mechanisms were investigated in electrostrictor, piezoelectric and phase-change antiferroelectric ceramic multilayer actuators with an interdigital electrode configuration. Simultaneous observations were done by three different methods; visual observation with a charge coupled device (CCD) microscope, field-induced strain and acoustic emission (AE) measurements. During a cyclic electric field application, the crack was initiated from the edge of an internal electrode and propagated obliquely to another electrode in the piezoelectric sample, while in the antiferroelectric, the crack was initiated between a pair of electrodes and propagated parallel to the electrodes. The field-induced strain curve exhibited asymmetric and enhanced strains in all the samples during the crack propagation, probably due to the internal delaminations. The AE count also increased drastically before the destruction.
Development of Three-Dimensional Ultrasonic Simulation and Its Application
Authors: Yamawaki Hisashi , Saito Tetsuya , Chitoshi Masuda Chitoshi Masuda , Hiroaki Fukuhara Hiroaki Fukuhara
Published: October 2002

A computer simulation technique for 3-dimensional ultrasonic waves was developed for visualization and investigation of ultrasonic propagation in isotropic and anisotropic solids with defects. The technique is similar to a finite-difference method (FDM) and a mass-particle model method, but uses a new nodal calculation method based on fundamental consideration of an elastic wave equation. The new method simplifies calculations on boundary nodes, so that it requires no pseudonodes as in the FDM, and is applicable to not only anisotropic but also complex materials including defects. A program has been developed for 3-dimensional calculation, but it requires the huge memory and high speed of supercomputers. Due to the limitation in computer performance, we present here conventional applications under the 2-dimensional condition including 3-dimensional motion. Some simple applications are shown for ultrasonic propagation in anisotropic (hexagonal) materials and layered materials, and wave scattering at a crack.
Relationship Between Speed of Sound in and Density of Normal and Diseased Rat Livers
Authors: Hiroyuki Hachiya Hiroyuki Hachiya , Shigeo Ohtsuki Shigeo Ohtsuki , Motonao Tanaka Motonao Tanaka
Published: October 2002

Speed of sound is an important acoustic parameter for quantitative characterization of living tissues. In this paper, the relationship between speed of sound in and density of rat liver tissues are investigated. The speed of sound was measured by the nondeformable technique based on frequency-time analysis of a 3.5 MHz pulse response. The speed of sound in normal livers varied minimally between individuals and was not related to body weight or age. In liver tissues which were administered CCl4, the speed of sound was lower than the speed of sound in normal tissues. The relationship between speed of sound and density in normal, fatty and cirrhotic livers can be fitted well on the line which is estimated using the immiscible liquid model assuming a mixture of normal liver and fat tissues. For 3.5 MHz ultrasound, it is considered that the speed of sound in fresh liver with fatty degeneration is responsible for the fat content and is not strongly dependent on the degree of fibrosis.
Analysis of Ventricular Wall Motion Using Color-Coded Tissue Doppler Imaging System
Authors: Yamazaki Nobuo , Mine Yoshitaka , Sano Akihiro , Hirama Makoto , Miyatake Kunio , Yamagishi Masakazu , Tanaka Norio
Published: October 2002

We developed a new color Doppler system by which Doppler signals associated with tissue motion can be determined, and called it the tissue Doppler imaging (TDI) system. Using high-speed scanning, the frame rate was 26–38 F/s, and the pulse repetition frequency was 4.5–6.0 kHz. Under these conditions, the lowest measurable velocity was improved to 2 mm/s. Wall motion toward the transducer was coded as red, and that away from the transducer, as blue. To examine the accuracy and validity of the measured velocity of ventricular wall motion, we performed in vitro and in vivo studies. The results demonstrate that the present TDI system accurately represents the tissue velocity, and is applicable for creating two-dimensional images of the ventricular wall motion in real time, facilitating the visual assessment of abnormal ventricular wall motion.
High Frequency Surface Acoustic Wave Filter Using ZnO/Diamond/Si Structure
Authors: Nakahata Hideaki , Higaki Kenjiro , Hachigo Akihiro , Shikata Shinichi , Fujimori Naoji , Takahashi Yoshihiro , Kajihara Takaharu , Yamamoto Yasushi
Published: October 2002

Diamond films grown by chemical vapor deposition (CVD) method is receiving much attention as surface acoustic wave (SAW) substrate material, due to its remarkable characteristics of large SAW velocity to offer much attraction in fabrication of high frequency SAW devices. The basic properties of SAW propagating in a ZnO/diamond/Si structure were studied utilizing thin film poly-crystalline diamond. Phase velocity, group velocity, electro-mechanical coupling coefficient (K
2), and temperature coefficient of frequency ( TCF) were examined by experiments and theoretical calculations. And it was confirmed that this structure provides high phase velocity up to 10000 m/s, high K
2 up to 4.8% and pratical TCF value of -28 ppm/° C. An 1.3 GHz SAW filter of a ZnO/diamond/Si structure was fabricated for the first time.