bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of the Particle Sizes and the Correlational Sizes of Dipoles Introduced by the Lattice Defects on the Crystal Structure of Barium Titanate Fine Particles
Authors: Wada Satoshi , Suzuki Takeyuki , Tatsuo Noma Tatsuo Noma
Published: October 2002

Barium titanate single-crystal particles with various average particle sizes (20-100 nm) were prepared by a hydrothermal method. In the particles as prepared, there were a lot of hydroxyl group and barium vacancies as the lattice detects, and the concentration of the lattice defects increased with decreasing particle sizes. But most of the hydroxyl group in the particles desorbed by the thermal treatment at 600° C. The crystal structure of the barium titanate particles as prepared was an expanded cubic. (a∼4.02 Å), but after a thermal treatment above 600° C to remove the hydroxyl group, the cubic phase changed to tetragonal phase (c/a≪1.011). This phenomenon was observed in the particles with average particle sizes from 20 to 100 nm, and the crystal structure was independent of the particle sizes. This result could be explained using the following model, that as the physical quantity, with a finer dimension than the particle sizes, there are the correlational sizes of dipoles introduced by the lattice defects, and the correlational size can determine the stability of the lattice vibration and then the stability of the crystal structure.
Nonstoichiometry Effects and Their Additivity on Anomalous Photovoltaic Efficiency in Lead Lanthanum Zirconate Titanate Ceramics
Authors: Nonaka Kazuhiro , Akiyama Morito , Takase Akira , Baba Toshiyuki , Yamamoto Keisuke , Ito Hirotaka
Published: October 2002

(Pb0.97, La0.03)(Zr0.52, Ti0.48)1-0.03/4O3 ceramics doped with various amounts of Ta were sintered at 1200° C for 2 h and then heat-treated in nitrogen at 900° C for 1 h to investigate the nonstoichiometric effects on the anomalous photovoltaic effect (APE). In the samples pretreated in nitrogen, both the photovoltaic current and the photovoltage were increased by the doping of Ta, and showed maxima around 1.5 mol% of doped Ta. Similar photovoitaic change with various amounts of Ta was observed in the nitrogen-treated samples. They, however, showed markedly higher values of the photovoltaic current and voltage than those in the doped samples pretreated in nitrogen. From this result, additivity is confirmed to hold for the effect of Ta doping and that of nitrogen treatment on the APE, indicating the coexistence of two types of contributions to the APE through different mechanisms. The spectral responses showed peak shifts and curve extension of the photovoltaic current to different directions according to the two effects. The mechanisms of those effects were discussed.
Aging Behavior of Ni-Electrode Multilayer Ceramic Capacitors with X7R Characteristics
Authors: Nomura Takeshi , Kawano Naoki , Yamamatsu Junko , Arashi Tomohiro , Nakano Yukie , Akira Sato Akira Sato
Published: October 2002

Capacitance aging under dc field has been studied on BaTiO3-based dielectrics with X7R characteristics for multilayer ceramic capacitors with Ni internal electrodes. Capacitance change strongly depends on additives and firing conditions as well as microstructure. Aging behavior under no dc field is well explained by Richter's relaxation curve. On the other hand, aging under dc field cannot be fitted by Richter's curve. Therefore, a new model which assumes two factors that affect relaxation is proposed. According to the new model, capacitance changes in two stages, short-term and long-term relaxations. Capacitance change in short-term relaxation strongly depends on applied dc field. On the contrary, that of long-term relaxation does not depend on dc field.
Development of High-Efficiency CuInxGa1-xSe2 Thin-Film Solar Cells by Selenization with Elemental Se Vapor in Vacuum
Authors: Kushiya Katsumi , Shimizu Akira , Yamada Akira , Konagai Makoto
Published: October 2002

Achievements in the development of CuInSe2 (CIS) and CuIn

x

Ga1-
x

Se2 (CIGS). thin-film absorbers with efficiency over 12% by the two-stage method are reported as follows: 12.3% efficiency with CIS, 13.3% efficiency with CIGS (Ga/III ratio=0.25) and 10.1% efficiency with CIGS (Ga/III ratio=0.40, graded band-gap structure). These results clearly indicate that the simple two-stage method developed in this study has high capability to fabricate high-quality CIS and CIGS thin-film absorbers. The Se content in the precursor layer and the Se beam flux intensity during the selenization stage are key factors that must be controlled precisely in order to achieve a high efficiency of over 15%. It is reported, for the first time, that the spontaneous formation of a graded band-gap structure is possible by changing Se and Ga contents in the precursor layer, which should be applicable to the preparation of a high-quality CIS or CIGS thin-film absorber. The formation chemistry models of CIS and CIGS thin films related to this study are proposed.
Curie Temperature of BaTiO3
Authors: Sakayori Ken-ichi , Matsui Yasunori , Abe Hiroyuki , Nakamura Eiji , Kenmoku Mikihiko , Hara Tomoyuki , Ishikawa Daisuke , Kokubu Akihiro , Hirota Ken-ichi , Takuro Ikeda Takuro Ikeda
Published: October 2002

The Curie point (T
C) of BaTiO3 was earlier reported to be 120° C and has been recently believed to be 130° C. Some experiments have been performed here to reconfirm the T
C. Firing conditions used for preparing BaTiO3 were examined first with the use of pure BaCO3 or Ba(NO3)2 and TiO2. The x-dependence of T
C in (BaO)1-
x

(TiO2)1+
x

solid solution was measured. Data were scattered and suffered from individual variations. According to probability considerations, T
C of BaTiO3 was evaluated from the intercept at x=0. On the other hand, composition dependence of T
C in some related solid solution systems, (Ba1-
y

Pb

y

)TiO3. (Ba1-
y

Sr

y

)TiO3 and (BaTiO3)1-
y

(KF)

y

, was examined and the T
C of BaTiO3 was estimated by extrapolation toward the limit y→0. In conclusion, the Curie point of BaTiO3 is determined as 123.0±0.6° C.
X-Ray and Dielectric Studies of the Phase Transitions in Pb(Yb 1/2Nb 1/2)O 3-PbTiO 3 Ceramics
Authors: Jin Kim Hoon Lim , Woong Kil Choo Woong Kil Choo
Published: October 2002

Phase analysis and dielectric measurement have been conducted for a comprehensive study of the phase transition in the whole composition range of (1-x)Pb(Yb1/2Nb1/2)O3-xPbTiO3 (PYN-PT) ceramic system. For all compositions, a continuous series of complete solid solutions of the antiferroelectric (AFE) and the ferroelectric (FE) compounds was found. With increasing PT concentration x, the phase transition in this system can be categorized as three distinct classes in connection with the degree of the structural ordering. The PYN-rich solutions showed a relatively sharp first-order paraelectric (PE)–AFE transition behavior and the transition temperature decreases rapidly with increasing x. For 0.10 < x < 0.25, the phase transition is broadened and frequency-dependent. Beyond x = 0.25, the normal PE–FE phase transition was observed and the transition temperature increases rapidly with increasing x. In the FE side, it was also revealed that the morphotropic phase boundary between pseudocubic and tetragonal structure lies in the vicinity of x = 0.5. Moreover, the resultant phase diagram with temperature and PT concentration is presented.
Microanalysis of Grain Boundary on Low-Temperature Sintered Pb(Zr, Ti)O3 Ceramics with Complex Oxide Additives
Authors: Murakami Kenji , Dong Dunzhuo , Suzuki Hisao , Kaneko Shoji
Published: October 2002

Microstructural and compositional analyses of the low-temperature sintered Pb(Zr, Ti)O3-based ceramics have been carried out using scanning and transmission electron microscopies. A continuous amorphous grain-boundary phase is observed in 0.5 wt% MnO2-added 0.92Pb(Zr0.53Ti0.47)O3-0.05BiFeO3-0.03Ba(Cu0.5W0.5)O3 ceramics during the sintering at 935° C. The composition of the phase is concluded to be lead, copper and possibly iron oxides. Therefore, lowering of the sintering temperature on the ceramics is explained by an enhancement of the densification via the formation of this amorphous phase.
Effects of Grown-in Hydrogen on Lifetime of Czochralski Silicon Crystals
Authors: Akito Hara Akito Hara
Published: October 2002

I studied the effects of grown-in hydrogen on the lifetime of Czochralski-grown silicon crystals. It was found that grown-in hydrogen degraded the electrical properties of Czochralski-grown silicon crystals by enhancing the formation of recombination centers, which had a high thermal stability (∼800° C) and acted as nuclei of oxygen precipitates. I found that the concentration of recombination centers was highest at the center along the radius of the ingot and decreases with increasing distance from the center along the radius of the ingot. This is caused by the distribution of grown-in hydrogen along the radius. Its profile is formed by the out-diffusion of hydrogen during crystal growth.
Se-doped GaN Films Grown by Low-Pressure Metalorganic Chemical Vapor Deposition
Authors: Guo J. D. , Feng M. S. , Pan F. M.
Published: October 2002

Se-doped GaN films are grown for the first time by low-pressure metalorganic chemical vapor deposition (LP-MOCVD), in which H2Se is used as the Se source gas. Effects of Se doping on electrical properties of GaN films are reported. Se atoms tend to out-diffuse to the surface of the GaN film at high temperature. The N atomic percentage is influenced by the incorporation of H2Se in the MOCVD process. The carrier concentration was found to be significantly affected by the surface defects which develop at high H2Se dosages. The highest free electron concentration obtained is about 1.5×1018 cm-3. Increasing the growth temperature from 1000° C to 1050° C reduces the maximum carrier concentration to about 7×1017 cm-3.
Microcrystalline SiC Films Grown by Electron Cyclotron Resonance Chemical Vapor Deposition at Low Temperatures
Authors: Cheng Kuan-Lun , Cheng Huang-Chung , Liu Chih-Chien , Lee Chiapyng , Yew Tri-Rung
Published: October 2002

The characteristics of microcrystalline silicon carbide (µ c-SiC) films deposited using an electron cyclotron resonance chemical vapor deposition system at low temperatures have been investigated. The effect of microwave (MW) power on the SiC crystallinity is studied. According to the results of Fourier transform infrared absorption spectra, plan-view transmission electron microscopy, and the plasmon loss peaks in X-ray photoelectron spectroscopy, Si-C bonds form when the MW power is above 500 W for deposition at 500° C. The SiC crystallinity improves monotonically with MW power. The amount of incorporated carbon atoms in the grown films increases with MW power up to the concentration of 50% at 1500 W.
The dependence of the surface morphology and the mean roughness of the films on MW power is examined using the contact mode atomic force microscopy.
Observation of Electrical Write/Erase Operations for a Memory-Type Polymer-Dispersed Cholesteric Liquid Crystal
Authors: Kato Kinya , Tanaka Keiji , Tsuru Shinji , Shigenobu Sakai Shigenobu Sakai
Published: October 2002

A polymer-dispersed cholesteric (chiral nematic) liquid crystal (PDCLC) with a memory effect is effective for color display devices. The PDCLC stably maintains both selectively reflective and transparent states without holding techniques, and the states can be changed electrically. A high-frequency electric field writes to the reflective state, and a low-frequency field erases to the transparent state. To understand the details of transition between the states, we observed the intensity of light transmitted through a PDCLC cell during operation using a digital oscilloscope. Furthermore, the frequency-dependent current in the PDCLC cell was also measured to evaluate ion movement. The results show that ion movement in the PDCLC layer plays an important role in the electrical erase operation.
Two-Dimensional Numerical Simulation of Si Schottky/Two-Dimensional Electron Gas Barrier Diode Using Boundary Element Method
Authors: Luo Ying-Che , Wang Shui-Jinn , Chiou Yueh-Guey , Lin Jia-Chuan , Ching-Yuan Cheng Ching-Yuan Cheng
Published: October 2002

In this work, we report on the simulation and physical insight of a Schottky/two-dimensional electron gas (2DEG) silicon barrier diode using a boundary element method (BEM) for the first time. The BEM can effectively reduce the dimensions of equation systems and the computation time as compared to conventional numerical methods such as finite-element or finite-difference methods. Using an efficient algorithm for depletion layer width estimation, the potential and electric field distributions, the dependence of the depletion layer thickness on the applied voltage, and capacitance-voltage ( C-V ) characteristics of the Schottky/2DEG junction under different bias conditions are investigated. It is found that the free boundary condition along the top surface of the Schottky/2DEG barrier diode exerts a strong effect on both the electric field distribution and C-V characteristics. In addition, the calculated results show that the Schottky/2DEG diode has a high C-V nonlinearity which increases with decreasing i-Si layer thickness around the 2DEG layer.
Current-Voltage and Capacitance-Voltage Characteristics of Metal/Oxide/6H-Silicon Carbide Structure
Authors: Tokura Norihito , Hara Kazukuni , Miyajima Takeshi , Fuma Hiroo , Kunihiko Hara Kunihiko Hara
Published: October 2002

Current-voltage ( I-V ) and capacitance-voltage ( C-V ) characteristics of metal/ SiO2/6H-SiC structure fabricated on the concave surface in (0001̄)C-face 6H-SiC p/n double epitaxial wafers were studied. Breakdown field of thermally grown gate oxide and effective charge density at SiO2/6H-SiC interface on sloped surface of the metal/oxide/semiconductor (MOS) structure were measured for the first time to be 9.2 MV/cm and 2.2-2.5×1012 cm-2, respectively, for both p- and n-epilayers. Fabricated SiC CONCAVE-MOS field-effect-transistor (FET) including the concave MOS structure achieved FET operation with blocking voltage of 250 V.
Temperature dependence of the threshold voltage was -27 mV/K, which is considerably larger than the ideal value of -1.6 mV/K, due to high interface state density.
Functional Characteristics of Optical Neural Computing Device Using Graded Index Waveguide
Authors: Junichi Minamoto Junichi Minamoto , Yasumitsu Miyazaki Yasumitsu Miyazaki
Published: October 2002

New optical neural computing devices consisting of a thin film with graded refractive index distribution are described. Neural signal processing is controlled by an inhomogeneous refractive index distribution in a very small region in this device. We investigate the inhomogeneous index distribution of waveguide-type neural coupling devices for the cases where the neural signals correspond to Gaussian beams. The neural coupling characteristics attained by applying the inhomogeneous index distributions are evaluated.
Superconductivity and Electrical Transport in YBa2Cu3O7-δ-PrBa2SnO5.5 Percolation System
Authors: Kumar Krishnan Sudarsana , Koshy Jacob , Kurian Jose , Yadava Yogendra P. , Alathoor D. Damodaran Alathoor D. Damodaran
Published: October 2002

Percolation behaviour of the normal state resistivity and superconductivity of YBa2Cu3O7-δ-PrBa2SnO5.5 composites have been studied by X-ray diffraction and temperature-resistivity measurements. No detectable chemical reactivity was observed between YBa2Cu3O7-δ and a ceramic insulator PrBa2SnO5.5 even when the two materials were mixed thoroughly and sintered at 1020° C. The normal state percolation threshold is 21 vol% of YBa2Cu3O7-δ and the superconducting percolation threshold is 30 vol% of YBa2Cu3O7-δ in the composite. The values obtained for the critical exponents describing the normal state transport behaviour of the system matched with theoretically expected values for an ideal conductor-insulator system. The implications are discussed.
Preparation and Properties of Sol-Gel Derived La-Doped PbTiO3 Thin Films
Authors: Shyu Jiin-Jyh , Kom-Lin Mo Kom-Lin Mo
Published: October 2002

Lanthanum-doped lead titanate thin films with perovskite phase were fabricated by sol-gel spin-on process. Effect of lanthanum doping on the crystal structure, film orientation, microstructure, and ferroelectric/dielectric properties of the films were studied. The films showed various degrees of (100) orientation, depending mainly on the substrate used and the La content. The addition of La caused changes in the film microstructure. Rosettes distributed in a matrix were observed for the (Pb0.7La0.2)TiO3 films. The dielectric constant of the films generally increased with the increasing La content and the heating temperature. (Pb0.7La0.2)TiO3 film heated at 800° C has a dielectric constant of about 650.
Electric Field Effect on Layer Structure in Surface-Stabilized Ferroelectric Liquid Crystals
Authors: Nomura Kenji , Terauchi Hikaru , Kasatani Hirofumi , Itoh Nobuyuki , Miyoshi Shuji
Published: October 2002

Electric field dependence of the layer structure in surface-stabilized ferroelectric liquid crystals (SSFLCs) was investigated by means of an X-ray diffraction experiment. With increasing amplitude of the applied electric field (square wave, 20 Hz), in the SmC* phase, the layer structure in our SSFLCs changed from the chevron layer structure to bookshelf layer structure. In the SmA phase (high temperature than the SmC* phase), the tilted bookshelf layer structure changed to a nontilted bookshelf one. The layer structure in the SmC* phase changed from an “asymmetric” chevron layer structure to “symmetric” chevron layer structure when the samples were cooled from the SmA phase. The application of electric field to SSFLCs in the SmA phase induced the well-oriented bookshelf layer structure, and it is also useful to obtain the symmetric chevron layer structure in the SmC* phase.
Accuracy of Nematic Visco-Elastic Constant Measurement Using Rayleigh Scattered Light
Authors: Masaki Hasegawa Masaki Hasegawa , Kouichi Miyachi Kouichi Miyachi , Atsuo Fukuda Atsuo Fukuda
Published: October 2002

We calculated the accuracy of the Frank elastic constants and Leslie's viscosity constants obtained by photon correlation spectroscopy of Rayleigh scattered light (PSRS) for 5CB. The visco-elastic ratio, K
i/ηi, can be determined with an error of less than 1%. The value of K
2 obtained by using electric-field-applied PSRS (EFPSRS) is accurate to within 2.5%. Although K
1/K
2 can be obtained to within 2.5% by parameter fitting, the measurement error of K
3/K
2 was more than 20%. To improve the accuracy with which K
3/K
2 can be determined, we developed a new method that uses EFPSRS to obtain an absolute value of K
3 directly. According to our simulation, this method reduced the measurement error of all of the elastic constants and the viscosity coefficients η splay, η twist, and η bend to less than 5%. We also calculated the measurement error of Leslie's viscosity constants. The value of µ2 can be determined with an error of less than 5%, while other viscosity constants have errors of more than 15%. Our error estimation can be applied to measurements of any other liquid crystals obtained by using PSRS.
Defects in TiN Films Probed by Monoenergetic Positron Beams
Authors: Uedono Akira , Nanao Susumu , Tanigawa Shoichiro , Suzuki Ryoichi , Ohdaira Toshiyuki , Mikado Tomohisa , Ishibashi Shoji
Published: October 2002

Vacancy-type defects in nonstoichiometric TiNxfilms (0.901≤x≤1.04) grown by a reactive ion-plating method were probed by monoenergetic positron beams. Doppler broadening profiles of the annihilation radiation and lifetime spectra of positrons were measured as a function of incident positron energy. In the TiNxfilms, positrons mainly annihilated from the trapped state by vacancy-type defects. In the subsurface region ( <200 nm), two annihilation modes associated with the annihilation of positrons in vacancy clusters and in voids located at grain boundaries were observed. The species of vacancy clusters was found to be influenced by nonstoichiometric conditions. For ion-implanted TiN films, the importance of the focusing collision mechanism in superlattice structures was discussed.
Infrared Spectroscopy and Thermal Studies of As-Grown L-Arginine Phosphate Monohydrate Crystals
Authors: Mazumder Aditi , Kar Tanusree , Siba Prasad Sen Gupta Siba Prasad Sen Gupta
Published: October 2002

Single crystals of L-arginine phosphate monohydrate (LAP) ( C6H14N4O2·H3PO4·H2O) were successfully grown from aqueous solution of L-arginine and phosphoric acid at an ambient temperature of 28.5° C for different pH values ranging from 2.1 to 5.04. As-grown single crystals were characterized by chemical analysis, density measurement and X-ray powder diffraction studies. Infrared (IR) spectroscopy, thermo-gravimetric (TG) and differential thermal analyses (DTA) measurements were performed to study the molecular vibration and thermal behaviour of LAP crystals.
Ultra High Vacuum Reflection Electron Microscopy Study of Step-Dislocation Interaction on Si(111) Surface
Authors: Latyshev Alexander , Minoda Hiroki , Tanishiro Yasumasa , Yagi Katsumichi
Published: October 2002

Interaction between monatomic steps and dislocation emerging at the surface has been studied byin situultra high vacuum reflection electron microscopy (UHV REM). It was shown that during sublimation the motion of the step was suppressed in the dislocation strain field around dislocation core regions. The energy of the step-dislocation interaction was estimated from a mechanical analogy with pinning phenomenon of an infinitely long string moving in uniform medium. The relaxation time was measured from relaxation processes of the step shape after passing across the dislocation core at the high temperature of sublimation. Dynamical step stiffness was evaluated from measurements of the relaxation time. The data obtained are discussed in the framework of recently developed theories.
Simulation of the Electrical Characteristics of Field Emission Triodes with Various Gate Structures
Authors: Ku Tzu-Kun , Chen Ming-Shang , Wang Chih-Chong , Feng Ming-Shiann , Hsieh Iing-Jar , Huang Jammy C. M. , Huang-Chung Cheng Huang-Chung Cheng
Published: October 2002

A new two-dimensional numerical simulation which can accurately reproduce the empirical electrical characteristics of vertical field-emission triodes (FET's) with various gate geometries has been developed. The electrical characteristics of volcano-shaped-gate FET's were simulated for the first time and compared with those of planar-gate ones. Volcano-shaped-gate FET's exhibit significant advantages over planar-gate ones due to their superior current-voltage ( I-V ) properties and larger tolerance of fabrication error. A reasonable definition of emission area was obtained by applying the non-uniform current density model. For sub-micron gate aperture, the gate current is obvious only if the device structure is deeply tip-recessed. On the basis of the evaluation of the device structures including the tip cone angle, the related tip-to-gate height, the emitter shape, and the shrinkage of gate aperture, a high-aspect-ratio conical emitter with a small tip radius will be the optimum structure of FET's for low-voltage operation.
Work Function Change Measured by Electron Beam Chopping Technique as Applied to Oxygen-Adsorbed W(100) at High Temperature
Authors: Lee Suchan , Irokawa Yoshihiro , Inoue Masahiko , Ryuichi Shimizu Ryuichi Shimizu
Published: October 2002

The electron beam chopping technique has enabled the true secondary electrons to be extracted from the overcoming background of thermionic and stray electrons, leading to a precise assessment of the work function change from the measurement of the onset of the spectrum. This technique was applied to the O/W(100) system at ∼1100 K. The work function has revealed a stepwise change against the oxygen exposure time.
Improvement of Frequency Variability of the Folded-Coaxial Radio-Frequency Quadrupole Linac by Installing a Detachable Stem in Its Resonator
Authors: Kamigaito Osamu , Goto Akira , Miyazawa Yoshitoshi , Chiba Toshiya , Hemmi Masatake , Kase Masayuki , Kohara Shigeo , Yasushige Yano Yasushige Yano
Published: October 2002

The beneficial effect of adding a detachable stem to the folded-coaxial resonator of the frequency-variable radio-frequency quadrupole (RFQ) linac previously reported was examined experimentally using a half-scale model as well as by numerical analyses. As a result, this simple modification was found to extend variable frequencies to a high region without increase of rf power consumption.
The Electric Behavior of a Capacity-Transfer-Type Pulsed Gas Laser
Authors: Persephonis Peter , Giannetas Vasilis , Parthenios John , Ioannou Athanasios , Charalambos Georgiades Charalambos Georgiades
Published: October 2002

In the present work the electric behavior of a Capacity-Transfer-Type N2 laser has been studied in relation to storage and peaking capacitors. The results showed that the resistance and inductance of discharges in the ignition system and in the laser chamber vary as the values of the capacitors change. This occurs because the driving circuit, and particularly its capacitances, affect the formation of the two discharges and finally the laser output. The coupling of the two circuit loops is weak and is achieved through laser channel inductance. Finally, the behavior of the laser output versus storage and peaking capacitors is determined from a) the electric energy deposited in the laser channel, as a short pumping pulse and b) the laser oscillation time delay which depends on the upper laser level and the Q factor of the cavity.
Analytic Study on High-Voltage Crowbar System
Authors: O. Campos Delton , Y. Honda Munemasa Machida , A. Aramaki Em\iilia , Luiz A. Berni Luiz A. Berni
Published: October 2002

Crowbar switches are largely used in plasma devices, such as field-reversed configuration (FRC) machines and tokamaks, to avoid energy return from the discharge coil to the capacitor bank. A method of identification of all resistances, inductances and currents involved in capacitor bank discharges using a crowbar is proposed based on the derivation of the general analytical form of the coil current. This analysis can also be used for optimization of the discharge, reducing the ripple amplitude inherent in the crowbar-switched current. Fitting results of the TC-1 UNICAMP FRC device are also presented in this work.
Nuclear Reaction Rates of Non-Isothermal Plasmas
Authors: Hitoshi Hojo Hitoshi Hojo
Published: October 2002

Nuclear reaction rates of deuteron-triton reaction in non-isothermal plasmas with bi-Maxwellian or loss-cone distribution are computed by the Monte Carlo method. The effects of temperature anisotropy and the temperature difference between the deuteron and triton are investigated.
Kerr Cell System for the Measurement of High Voltage Transient Pulses
Authors: Rajagopal Krishnamurthy , Tetali Ananda Prasada Rao Tetali Ananda Prasada Rao
Published: October 2002

An optical method using the Kerr effect is reported for the measurement of high voltage transient pulses with benzonitrile, acrylonitrile, propionitrile, butyronitrile and m-nitrotoluene for the first time along with nitrobenzene and acetone that are well known. These investigations have been performed using high voltage pulse fields ranging from 5×105vm-1to 107vm-1. The experimentally measured values of the electric field from the Kerr signals are found to be in excellent agreement with applied field.
Control of X-Ray Beam Fluctuation in Synchrotron Radiation Lithography Beamline
Authors: Shimano Hiroki , Tanaka Hirofumi , Ozaki Yoshihiko , Kenji Marumoto Kenji Marumoto
Published: October 2002

Using the focusing property of beamline optics, we have presented a new technique to directly measure the position and emission angle drifts of the synchrotron radiation (SR) source which may deteriorate the optical performance of a beamline consisting of focusing mirrors. A new methodology is also proposed to correct the SR source drifts, combining the above measuring technique, a SR beam position monitor (SRBPM) mounted on the beamline and the excitation of two steering magnets installed in a storage ring.
Development of Energy-Filtered Reflection High-Energy Electron Diffraction Apparatus
Authors: Yoshimi Horio Yoshimi Horio , Yasuyuki Hashimoto Yasuyuki Hashimoto , Katsuyuki Shiba Katsuyuki Shiba , Ayahiko Ichimiya Ayahiko Ichimiya
Published: October 2002

A new type of reflection high-energy electron diffraction (RHEED) apparatus equipped with an energy filter has been developed. The apparatus can exclude the inelastically scattered electrons from the RHEED pattern for the first time. Performance of the apparatus is demonstrated using a Si(001)2×1 surface. The energy-filtered RHEED (EF-RHEED) can extract valuable information from the background. Furthermore, it can be used to measure energy loss spectra of diffraction spots.
Impurity Diffusion in Silicon Based on the Pair Diffusion Model and Decrease in Quasi-Vacancy Formation Energy. Part One: Phosphorus
Authors: Yoshida Masayuki , Arai Eisuke
Published: October 2002

The binding energy,Eb, between a vacancy and a P atom or an As atom in Si is large. Therefore the pair diffusion model (PDM) and the decrease in quasi-vacancy formation energy are applicable to P and As diffusions. With the decrease in quasi-vacancy formation energy,Ebalso decreases. Fermi level obtained from the Boltzmann statistics is used. Anomalous diffusion of P consists of two components, a tail and a plateau. The tail has been attributed to excess vacancies, the generation of which is a characteristic of PDM. The plateau has been explained by PDM and the decrease in quasi-vacancy formation energy. The reason for this is given for the first time. It is emphasized that the large value of the phosphorus effective diffusion coefficient at the plateau is not anomalous but normal.
Low-Temperature Si Selective Epitaxial Growth Using Electron-Beam-Induced Reaction
Authors: Hirose Fumihiko , Hitoshi Sakamoto Hitoshi Sakamoto
Published: October 2002

Low-temperature Si epitaxial growth has been achieved by irradiating electrons and Si2H6 molecules simultaneously onto Ge(100) and Si(100) surfaces. The growth takes place exclusively on the electron-irradiated area. The electron stimulation of the surface enables growth rate enhancement and improvement of crystallinity. Si growth is governed by surface reactions induced by electron beam irradiation.
Selenium Passivation of GaAs with Se/NH4OH Solution
Authors: Tsuchiya Kensuke , Sakata Minoru , Funyu Akihiro , Ikoma Hideaki
Published: October 2002

GaAs surfaces were passivated with selenium using Se/NH4OH solution. Selenium powder of 99.8% purity was dissolved in NH4OH and the GaAs substrates were immersed in this solution. The extent of passivation was studied by electrical measurements (current-voltage characteristics) of the Schottky diodes. The experimental results indicated that the surface properties were substantially improved without requiring a succeeding Na2S treatment. The degradation of the ideality factor, n, of the Schottky diodes was efficiently retarded by this selenium passivation. The surface chemistry of the passivated GaAs surface was investigated with X-ray photoelectron spectroscopy (XPS). The XPS data indicated that both the oxidation of the GaAs surface (formation of Ga2O3 and As2O3) and segregation of elemental arsenic ( As0) at the surface were suppressed or retarded by this passivation. This corresponds well to retardation of degradation of the n value. As2Se3 was observed in the Se/NH4OH-passivated surface, which suggests that the segregated As was removed by chemical reaction between As and Se to produce As2Se3. There is a possibility of the formation of Ga2Se3 (Ga-Se bond), though it is not observed in our XPS data. The formation of As-Se and/or Ga-Se bonds is suggested as the reason for suppression of oxidation of the GaAs surface. When the Se-passivated surface was exposed to air ambient, the total amount of selenium and the amount of As2Se3 decreased. This may be due to oxidation of As2Se3 to form As2O3. The extent of Se/NH4OH passivation and the degree of degradation due to air exposure are similar with those of the ( Na2Se/NH4OH+Na2S) passivation reported by Sandroff et al. [J. Appl. Phys. 67 (1990) 586].
Radical Fluxes in Electron Cyclotron Resonance Plasma Chemical Vapor Deposition of Amorphous Silicon
Authors: Zhang Mei , Yoshikazu Nakayama Yoshikazu Nakayama
Published: October 2002

The precursors of a-Si:H films in electron cyclotron resonance plasma chemical vapor deposition have been investigated by analyzing the deposition profile on a trench. The profile of the film prepared from radicals produced in the gas phase by electron collision with SiH4is simulated by a Monte Carlo method using a sticking probability of 0.8 for Si, SiH and SiH2radicals and of 0.1 for SiH3radicals. A comparison between the experimental result and the simulation has shown that the ratio of the total flux of SiHx(x=0-2) to the flux of SiH3in the radicals reaching the surface is 0.82 at 3 mTorr. The flux of radicals which maintain the momentum of SiH4emitted from a nozzle is also compared with that of radicals with a random direction of momentum.
Chemical States of Crystalline Silicon Carbide Surfaces
Authors: Tsuchida Hidekazu , Kamata Isaho , Kunikazu Izumi Kunikazu Izumi
Published: October 2002

Chemical states of 6H polytype crystalline silicon carbide (6H-SiC) surfaces were investigated using X-ray photoelectron spectroscopy (XPS). Surface contaminants such as C-C, C-H and C-O species were evaluated from C1s photoelectron spectra after treatment under various conditions. Clean SiC surfaces were found to appear after the chemical etching of a thermal oxide ( SiO2) film using a buffered HF solution. Furthermore, to clarify the chemical etching characteristics of SiO2 formed on 6H-SiC substrates, the depth profiling of the SiO2 was also performed using XPS.
The C1s peak at a binding energy of about 286.2 eV was detected on the surfaces of the 6H-SiC substrates at the moment when only the SiO2 was completely removed, and the C1s peak was characterized as due to the C-O bonds formed near the SiO2/SiC interface.
Rapid Thermal Post-Metallization Annealing in Thin Gate Oxides
Authors: Jeng Ming-Jer , Lin Huang-Sheng , Jenn-Gwo Hwu Jenn-Gwo Hwu
Published: October 2002

Rapid thermal technique was used in the post-metallization annealing (PMA) of thin gate oxide devices. A suitable choice of the rise rate, the setting temperature, and the hold time in the rapid thermal PMA (RTPMA) process is helpful to improve the oxide quality. It was found that the samples subjected to appropriate RTPMA conditions exhibit almost the same initial characteristic in flatband voltage V
FB and midgap interface trap density D
itm as those subjected to conventional furnace PMA (FPMA). However, the RTPMA samples exhibit longer time-to-breakdown t
BD and higher time-zero-dielectric-breakdown (TZDB) field E
BD than the FPMA ones. In addition to the known spiking effect caused by aluminum penetration into silicon, which seriously degrades the breakdown property, formation of aluminum oxide near the Al/SiO2 interface in the early stage and then aluminum silicon alloy in the later stage was proposed to explain the experimental observation.
Role of Interface States in Temperature Dependence of Capacitance in Amorphous Silicon Solar Cells
Authors: Murthy R. V. R. , Dutta V. , Singh S. P.
Published: October 2002

The temperature dependent variation of capacitance in amorphous silicon solar cells is found to have different behaviours at low frequency (100 Hz). The variation at high temperature has been shown to arise due to the interface states at p-i junction. The density of states at p-i junction and in the whole i-region have been estimated to be 7×1016 eV-1 cm-3 and 5×1016 eV-1 cm-3, respectively, in as-deposited samples. The effect of the reverse biased annealing on the interface states has been observed.
Examination of Correlation of Surface Morphologies of Top-Silicon and Buried Oxide Layers in High-Temperature-Annealed Separation by IMplanted OXygen Wafers
Authors: Ishiyama Toshihiko , Masao Nagase Masao Nagase
Published: October 2002

We examine whether there is a correlation between the morphologies at the cap SiO2 layer/top Si layer interface and the top Si layer/buried SiO2 layer interface of SIMOX (Separation by IMplanted OXygen) (100) wafers during high-temperature annealing. The morphologies were evaluated by scanning a marked position with an atomic force microscope (AFM). From the AFM observation, although some similarities were observed in the mosaic morphologies, squares were not positioned at corresponding locations at the two interfaces. Therefore, it is concluded that there is no correlation of the morphologies between the two interfaces. The squares on each interface grow independently.
Magnetic Relaxation Studies on Grain-Aligned HgBa2Ca2Cu3Oy Superconductor
Authors: Kim Gun Cheol , Young Cheol Kim Young Cheol Kim
Published: October 2002

Temperature dependent critical current density and flux-creep measurement were carried out in magnetically aligned HgBa2Ca2Cu3O

y

. For 20 K<T<60 K, we observed quasi-exponential behavior of the critical current density J
c. The normalized relaxation rate S vs T curve has an N-like shape with the minimum around T=15 K and the peak at 50 K.
The theoretical U(J) given by the collective flux creep model describes the experimental result well.
Structure and Temperature Dependence of Magnetic Properties in the Nanocrystalline Fe74SixB22-xCu1Nb3 Alloys
Authors: Ikeda Shoji , Nagai Masaru , Yuji Ueda Yuji Ueda
Published: October 2002

We have examined the structure and magnetic properties in terms of the temperature dependence of magnetic permeability and magnetization for the Fe74Si

x

B22-
x

Cu1Nb3 (x=8-18) alloys. The temperature dependence of the permeability of the alloys shows various characteristic behaviors depending on the alloy composition (x=8-18) and annealing temperature (450-630° C). The permeability of the samples having coexisting α-Fe(Si) and amorphous phases decreases abruptly near the Curie temperature of the amorphous materials, while the permeability of the samples containing precipitated Fe-B compounds is not appreciably affected by the magnetism in the residual amorphous region. The precipitation of Fe-B compound depends on the composition of the mother alloys. The Fe-B compounds precipitated in the amorphous region upon annealing at high temperature are mainly Fe23B6 for x=14, Fe3B for x=18, and Fe2B for the composition x less than 12.
0.85-µm Vertical-Cavity Surface-Emitting Laser Array Grown on GaAs and AlGaAs Substrates by Metal Organic Chemical Vapor Deposition
Authors: Ohiso Yoshitaka , Kohama Yoshitaka , Takashi Kurokawa Takashi Kurokawa
Published: October 2002

We report very uniform characteristics of 0.85 µ m vertical-cavity surface-emitting lasers (VCSELs) array grown by metal organic chemical vapor deposition (MOCVD) at a high growth rate. For a 16 µ m diameter pixel, the threshold current is 3.29±0.25 mA and the emission wavelength is 850.9±0.6 nm at 6 mA along the 8×8 pixels. Considering the offset gain and Al content of the spacer layer, the threshold voltage is 2.1 V.
By growing VCSELs on an AlGaAs substrate, we were able to acheive a bottom-emitting 0.85 µ m VCSEL array where all elements operated successfully. We also discuss the modulation speed limit and the thermal interference problem of VCSEL arrays. The modulation limit is shown to depend on the capacitance and resistance (CR) time constant of electrodes, and the maximum temperature increase is about 15° C around the center of the chip when the other pixels are driven at the threshold current.
Analysis of Pulse Compression with Perturbation Method
Authors: Zhang Tiejun , Kato Yoshiaki , Hiroyuki Daido Hiroyuki Daido
Published: October 2002

The amplitude and phase of the chirped pulse leaving an optical fiber in a chirped-pulse amplification laser system are derived using the perturbation method. They facilitate understanding of actions of linear and nonlinear portions of the chirped pulse on the pulse compression. The contrast ratio of the compressed pulse can also be evaluated by using spectral and temporal filterings.
Feasibility of Vacuum Microelectronics Voltage Comparator
Authors: Py Christophe , Itoh Junji , Seigo Kanemaru Seigo Kanemaru
Published: October 2002

Field-effect microtips are more coherent electron sources than hot filaments, and are well suited for electron optics applications such as low-energy electron interference. We propose to use this physical phenomenon in an integrated vacuum voltage comparator whose structure is derived from the classical Möllenstedt-type electron biprism. Our setup is separated into two independent parts, and acts both as a biprism and as a deflector for the fringe pattern. The deflection, proportional to the voltage we want to measure, is known with high precision thanks to the fine structures of the pattern. We conclude that it is possible to fabricate a device with a precision of 25 meV, a response time of 110 ps and a very high input resistance.
Gate Oxide Breakdown Phenomena in Magnetron Plasma
Authors: Sekine Makoto , Horioka Keiji , Yoshida Yukimasa , Haruo Okano Haruo Okano
Published: October 2002

Gate oxide breakdown phenomena in a magnetron plasma were investigated from the viewpoint of the effect of magnetic field distribution on the radiation damage. It was found that strong parallel and normal magnetic field regions simultaneously present on a wafer induced surface potential difference along the wafer, and could cause gate oxide breakdown. An optimized magnetic field, consisting of flux lines parallel to the wafer, was found to reduce the degradation of the gate oxide.
Microstructure Observation of “Crystal-Originated Particles” on Silicon Wafers
Authors: Miyazaki Morimasa , Miyazaki Sumio , Yanase Yoshio , Ochiai Takashi , Tatsuhiko Shigematsu Tatsuhiko Shigematsu
Published: October 2002

Microstructure shape of “crystal-originated particles” (COP's) on mirror-polished silicon wafers (a) as received, (b) cleaned with NH4OH/H2O2/H2O solution (SC-1), and (c) annealed at high temperature (∼1150° C) in O2/N2 mixture or in H2, were observed using a scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM). Elemental analysis of the COP's was also made using TEM-energy dispersion X-ray spectroscope (EDX). The COP was a pyramidal pit with {111} sidewalls, or a vertical cave having some facets of {111}. In a part of the COP, oxygen was detected by TEM-EDX.
It was suggested that the microstructure shape of the COP's has been determined until the mirror polishing is finished. The size of the COP becomes larger and the slopes of the COP become gentler after an anneal in 3% O2/N2 at 1150° C for 4 h and removal of the SiO2 layer by HF solution. The depth of the COP becomes shallower, its size larger and its corners rounder by annealing in H2 at 1100° C for 1 min. The COP's disappear by anealing in H2 at 1150° C for 4 h.
Simultaneous Temperature Measurement of Wafers in Chemical Mechanical Polishing of Silicon Dioxide Layer
Authors: Sugimoto Fumitoshi , Arimoto Yoshihiro , Takashi Ito Takashi Ito
Published: October 2002

The wafer temperature in chemical mechanical polishing (CMP) of silicon dioxide layers was measured. When the temperatures of both the polishing slurry and the polishing pad were controlled at 8° C, the measured wafer temperatures were 10-20° C. The temperature distribution affected the thickness of the polished oxide layer. When the wafer temperature was high, the oxide layer removal rate increased because of the increased reaction of the slurry with the oxide layer. It was clear that there was a linear relationship between the measured wafer temperature and the oxide layer removal rate. The effects of grooving several typical polishing pads for oxide layer polishing were investigated. It was found that grooves on the pad increased the uniformity of the removal of the oxide layer from the wafer.
Surface Passivation of Thin Silicon Solar Cells Using Silicon-on-Insulator Wafer
Authors: Takato Hidetaka , Toshihiro Sekigawa Toshihiro Sekigawa
Published: October 2002

Solar cells with various cell thicknesses were fabricated using silicon-on-insulator (SOI) wafers, and effects of applied bias voltages (V
B) at the SOI layer/SiO2 back interface on cell performance were investigated. A surface passivation effect was obtained by applying negative V
B to accumulate holes at the interface. Both open-circuit voltage (V
oc) and short-circuit current were improved by applying negative V
B. This effect becomes more dominant for thinner cells. V
oc of 20- and 50-µ m-thick cells at V
B=-15 V increased compared to that of a 100-µ m-thick cell. Surface recombination velocity (S) was estimated from the dependence of internal quantum efficiency on cell thickness. It was found that S decreased from about 106 to 104 cm·s-1 when V
B changed from 0 to -15 V. The improvement of cell performance by V
B was due to this reduction in S. Therefore, the surface passivation by applying bias voltages is noted as an important technique to realize high-efficiency thin silicon solar cells.
A New Driving Method for Reducing Cross-Talk in High Resolution Thin Film Transistor Liquid Crystal Displays
Authors: Libsch Frank R. , A. Lien A. Lien
Published: October 2002

A new driving scheme to compensate for cross-talk in thin film transistor liquid crystal displays (TFT-LCDs) that is image pattern independent and has no background grayscale variation is presented. In addition, we examine the tradeoffs of existing commercially used cross-talk compensative driving schemes. Results correlating crosstalk capacitor magnitude as a function of display size and density scaling to various types of cross-talk display driving schemes is presented.
A Novel Surface-Site Model for the Oxide/Aqueous Electrolyte Interface
Authors: Meng-nian Niu , Zhi-meng Teng , Tao Xiang , Xin-fang Ding , Qin-yi Tong
Published: October 2002

A novel surface-site model with clear physical configuration for the process of the H+-ion dissociation-association in the oxide/aqueous electrolyte (OAE) interface is derived from statistical physics, in which two-layer adsorption is considered. The derived expression between the charge and potential of the OAE interface is thorough described by microscopic physical parameters, and its fitted result with experimental data corresponds with experimental results nearby the point of zero charge ( pH
p
z
c
) of the OAE interface.
Laser Heating Mechanisms Including Evaporation Process-Semiclassical and Kinetic Theory Approaches
Authors: Bekir S. Yilbas Bekir S. Yilbas , Muhammad Sami Muhammad Sami
Published: October 2002

Microscopic level study of the laser heating process is essential to predict the temperature profiles accurately. Consequently, the present work deals with the analysis of the heating mechanism on a microscopic scale through semiclassical and kinetic theory approaches. In the analysis, statistical and quantum behaviour of electrons, phonons, vacancies and molecules are considered. The probability of collision of each species is taken into account to describe the conduction, melting and evaporation processes occurring due to laser irradiation. A numerical method using the explicit scheme is introduced to solve the energy equations resulting from both approaches. Finally, the temperature profiles predicted from both approaches are compared to the experimentally obtained temperature data. It is found that the results obtained from kinetic theory are in good agreement with the experimentally obtained temperature data.
Picosecond VUV Pulse Generation by Dual-Wavelength-Pumped Raman Shifting
Authors: Nakata Tsuneo , Yamada Tadashi , Fumihiko Kannari Fumihiko Kannari
Published: October 2002

A novel scheme for generating collimated picosecond pulses based on dual-wavelength-pumped Raman conversion is proposed and numerically analyzed. We have numerically obtained VUV pulses with durations as short as 25 ps, from nanosecond primary pump pulses with the same wavelength and moderate intensity, by applying intense picosecond secondary pump pulses with longer wavelength simultaneously with the primary pump. Dependence of generated picosecond pulse shape on primary and secondary pump laser parameters as well as that on the phase mismatch is investigated.