bluuebunny/crossref_metadata_2025 huggingface dataset:
Minority Carrier Properties of GaAs on Si Grown by Metalorganic Chemical Vapor Deposition
Authors: Soga Tetsuo , Jimbo Takashi , Umeno Masayoshi
Published: October 2002

Minority carrier properties of 3-µm-thick n-type GaAs on Si with a strained layer superlattice and thermal cycle annealing grown by metalorganic chemical vapor deposition (MOCVD) have been characterized by cathodeluminescence (CL) and time-resolved photoluminescence (TRP). The calculated TRP decay curve is investigated by changing the material parameters (bulk lifetime and surface recombination velocity). The minority carrier lifetime of GaAs on Si has been determined by fitting the experimentally obtained TRP curve to the calculated one. The minority carrier lifetime increases and the dark-spot defect density decreases with increasing number of thermal cycle annealings. The longest minority carrier lifetime of GaAs on Si in this study is 0.38 ns, which is about one order of magnitude smaller than that of GaAs grown on the GaAs substrate under similar conditions. The minority carrier lifetime is increased as the dark-spot defect density is decreased.
Single-Molecule Detection by Laser-Induced Fluorescence Technique with a Position-Sensitive Photon-Counting Apparatus
Authors: Ishikawa Mitsuru , Hirano Ken-ichi , Hayakawa Tsuyoshi , Hosoi Shigeru , Brenner Sydney
Published: October 2002

A new method of detecting single-molecule fluorescence has been implemented using a conventional optical microscope and a position-sensitive photon-counting apparatus. The samples were solvent-free fluorescent dyes adsorbed on a solid substrate in air at room temperature by spraying microdroplets of a dye solution followed by solvent evaporation. At the concentration used, each droplet contained a very small number of dye molecules. Quantized fluorescence intensity was determined and the number of occurrences of the quantized intensity agreed well with that calculated from Poisson's formula, thus confirming success of the position-sensitive single-molecule fluorescence detection.
Present Status and Prospects of Ion Trap Frequency Standards
Authors: Günter Werth Günter Werth
Published: October 2002

Present experiments on ion trap frequency standards in the microwave, optical and infrared spectral regions are described, and new ions are considered with respect to their potential as possible candidates. The present status strongly suggests that fractional frequency instabilities of about 10-16 will soon be obtained. Furthermore miniaturization of practical devices seems possible in the near future.
Two-dimensional Analysis of Resonant Tunneling Using the Time-dependent Schrödinger Equation
Authors: Hideaki Taniyama Hideaki Taniyama , Masaaki Tomizawa Masaaki Tomizawa , Akira Yoshii Akira Yoshii
Published: October 2002

Numerical solution of the time-dependent two-dimensional Schrödinger equation  is used here to analyze resonant tunneling in double-barrier structures. One-dimensional simulation is shown to be insufficient even for a system with a perfect barrier, which is regarded as one-dimensional because it does not include the two-dimensional effect attributed to the effective mass difference between the barrier and well regions. The effect of barrier roughness on tunneling characteristics is also analyzed and the transmitted fraction is calculated for various systems with different structural parameters, including the roughness of the barrier. Decomposition of the fraction into transverse momentum clarifies tunneling characteristics in two dimensions, and two-dimensional calculation is shown to be necessary for accurate analysis.
Crosstalk in Photon-Mode Photochromic Multi-Wavelength Recording
Authors: Tsuyoshi Tsujioka Tsuyoshi Tsujioka , Yoshiaki Shimizu Yoshiaki Shimizu , Masahiro Irie Masahiro Irie
Published: October 2002

The mechanism of crosstalk in photon-mode multi-wavelength recording has been theoretically analyzed, and a new method to reduce the crosstalk is proposed in this paper. The crosstalk has linear components of superposition and nonlinear components due to intermodulation. Both can be reduced by linear and nonlinear mixing of the readout signals at λ
i
(i=1,2,…). This reduction method was applied to photochromic optical media having two broad absorption bands which were superimposed with each other. Thus 2-wavelength recording (writing and reading) was achieved.
Selective Lateral Growth Mechanism of GaAs by Liquid-Phase Electroepitaxy
Authors: Shiro Sakai Shiro Sakai , Yasuno Ohashi Yasuno Ohashi
Published: October 2002

Selective lateral growth of GaAs over SiO2-covered GaAs substrate by liquid-phase electroepitaxy (LPEE) is analyzed using a simplified model, and the analysis is compared with the experiment. The aspect ratio defined as the ratio of lateral to vertical growth rate is shown to be greatly enhanced by flowing current during LPE growth, and an aspect ratio of more than 10 is experimentally obtained. The enhanced lateral growth is caused by the increased transport of the growing species by the electric field. The simplified growth model discussed in this paper agrees with the experimental results reasonably well and expresses most of the important features of the LPEE.
Dynamics of Step Bunching Induced by DC Resistive Heating of Si Wafer
Authors: Stoyanov Stoyan S. , Hitoshi Nakahara Hitoshi Nakahara , Masakazu Ichikawa Masakazu Ichikawa
Published: October 2002

Step dynamics has been studied through numerical integration of the equations of motion of the steps at a vicinal surface during evaporation with dc resistive heating. The equations have been derived under the assumption that the surface processes involve drift of the adatoms in the dc direction perpendicular to the steps, in accordance with the hypothesis for Si adatom electromigration on Si surfaces. The calculated trajectories of the steps show bunching in the step-up direction of the drift velocity of adatoms when the interstep distance is at least two times longer than the mean diffusion distance. The formation of slow-moving pairs of steps is a key process in the electromigration-induced instability of vicinal surfaces. These pairs move at a rate which is lower than the rate of motion of the steps involved in bunching. As a result, steps detach from the bunch trail and the resulting pairs cross the terraces to attach to the front edge of the next bunch. The time evolution of the step array manifests a new kind of repulsive interaction between the moving steps, originating from the interplay of the surface transport and kinetics at the steps. The numerical analysis predicts that the instability develops rather slowly and evaporation of thousands of monolayer is necessary for detection of step bunching.
ESR Investigation of a Spin 1/2 Chlorine-Associated Defect in Synthetic FeS2 Crystals
Authors: Wu Ching-Jiun , Yu Jiang-Tsu , Huang Ying-Sheng , Chung-Hsien Lee Chung-Hsien Lee
Published: October 2002

A new type of spin 1/2 chlorine-associated defect species has been observed by ESR in as-grown, sulfur-deficient FeS2 crystals grown by the method of chemical vapor transport using ICl3 as the transport agent. The ESR spectrum of this defect species exhibits a low symmetry and a weak hyperfine interaction with a single chlorine nucleus. The g-factor anisotropy indicates that this species is most likely a hole species, having a p
5 electron configuration and localized at a sulfur atom. We assign this defect species as an (SCl)2- impurity defect, replacing (S-S)2- and locally associated with a Fe2+ vacancy created probably to compensate for the substitutional Cr3+ impurities.
Laser-Induced Reduction of Carrier Activation Energy in Zn-Implanted GaAs
Authors: Vitali Gianfranco , Pizzuto Cesare , Rossi Marco , Zollo Giuseppe , Karpuzov Dimitry , Kalitzova Maria
Published: October 2002

It has been recently established that the crystallinity of ion-implanted GaAs samples can be restored by using a low-power pulsed-laser annealing (LPPLA) technique. In this paper we report an improvement of carrier activation achieved after low-temperature processing (added to LPPLA) at temperatures low enough to avoid substantial losses of As. By using this combination of techniques we have reduced the sheet resistivity to values comparable with those obtained by standard techniques without any specimen encapsulation (or similar) processing. The pretreatment by LPPLA seems to reduce the Zn activation threshold down to values which prevent the sublimation of As.
Effects of Vibration in Storage Ring of Pohang Light Source*
Authors: Moohyun Yoon Moohyun Yoon , Jinhyuk Choi Jinhyuk Choi , Taeyeon Lee Taeyeon Lee
Published: October 2002

Effects of vibrations in a storage ring are described. For convenience, vibrational sources are categorized as internal and external sources depending on their locations. Internal sources are likely to cause a random vibration of magnets, and their effects on the motion of a circulating beam are described well by the conventional closed orbit amplification factor. External sources cause all or some magnets to vibrate in a coherent manner, and their effect on the beam motion requires separate treatment. In this paper, we discuss the effects of both internal and external vibrational sources on the motion of a stored beam in a storage ring. The results are applied to the Pohang Light Source (PLS) 2 GeV storage ring, currently under construction in Pohang, Korea. Some recent measurement results of the PLS storage ring floor vibration are also presented.
A New Photochemical Selective Silylation Technique for Resist Materials
Authors: Kotaka Yoshiaki Mimura
Published: October 2002

A new selective photochemlcal silylation technique for resist materials has been developed. When deep-UV light is irradiated on resist films in either the vapor- or liquid-phase of monochloroalkylsilanes, many commercially available resist materials, both those that have phenolic hydroxy groups like DNQ/novolak and those that do not like polymethylmethacrylate (PMMA), can be sufficiently silylated. The silylated resist layer shows marked improvement in its durability against O2 dry etching. The silylation mechanism is presumed to be that alkylsilane radicals are firstly generated by deep-UV light irradiation, then the radicals diffuse into the resist film and chemically incorporate with the functional base radicals of the resist that are also generated by deep-UV light irradiation. The mechanism is clearly different from conventional one where the diffusion of the silylating agent is carried out after the UV-light irradiation.
New Method of Time Series Analysis and Its Application to Wolf's Sunspot Number Data
Authors: Ohtomo Norio , Terachi Saburou , Tanaka Yukio , Kaneko Kazuo Tokiwano
Published: October 2002

A newly devised procedure of time series analysis, which is a linearized version of the nonlinear least squares method combined with the maximum entropy spectral analysis method, was proposed and applied to the annual sunspot number data from 1700 to 1991. Multiple periodicities of the temporal variation were elucidated in detail. The solar cycle of a 11.04-year period accompanied with the solar cycle multiplets, the periods of 50.41 years, the so-called “Yoshimura cycle”, and 107.11 years corresponding to the cycle of century-scale minima, for example, were clearly observed. The optimum least squares fitting curve for the data was extended over the past two millennia and the next millennium. The past grand minima such as the Maunder minimum were confirmed in the past extrapolation curve, and the next centennial minimum was predicted to occur between 2000 and 2030.
Time Advance and Delay of Phonon Packets Scattered off Superlattice Systems
Authors: Seiji Mizuno Seiji Mizuno , Michihiro Ito Michihiro Ito , Shin-ichiro Tamura Shin-ichiro Tamura
Published: October 2002

We study numerically the time development of the phonon packets propagating through the single- and double-superlattice systems. In a single superlattice system, we find the time advance and delay for the transmitted and reflected phonon packets, respectively. In a double superlattice system in which the resonant transmission occurs, we find large time delays for both the transmitted and reflected packets when the spectrum of the incident packet has a large component at the resonance frequency. These results are well understood in terms of the phase time defined by the stationary phase analysis.
Ionic Conduction and Ultrasonic Velocity in Na1+2ninmbixZr2-xMnx(PO4)3
Authors: Inoue Naoki , Ogawa Yoshihiro , Nakanishi Toyohiro , Yasuhiro Matsumoto Yasuhiro Matsumoto , Takahi Hasegawa Takahi Hasegawa
Published: October 2002

We studied the electrical impedance as a function of frequency ranging from 75 kHz–20 MHz at temperature ranging from 30–253°C, and the ultrasonic velocity dependence on x at room temperature in order to investigate ionic conduction mechanisms of Na1+2
x

Zr2-
x

Mn

x

(PO4)3 with a bottle-neck structure. In the complex impedance representation, we observed either one or two semicircles strongly dependent on x, and a transition from single semicircle to double semicircles at x=0.5. Ultrasonic velocity showed an anomaly at x=0.5. Based on these results, we concluded that we observed the bulk conduction and grain boundary diffusion of the sodium ion.
Wavefront Distortion of Acoustic Beam in Pressurized Superfluid 4He
Authors: Kishi Hidenobu , Sasaki Yasuo , Karaki Koichi , Yuichi Okuda Yuichi Okuda
Published: October 2002

It has been observed that a focused ultrasonic beam in superfluid 4He under high static pressure of 18–24 atm shows a unique nonlinear phenomenon. This phenomenon strongly depends on pressure. As a result of the new experiment, we found that the wavefront of a spherical wave passing through the focal point is greatly distorted. The phase shifts discontinuously by about π radians in the center of the beam under 24 atm. The main features of this effect are explained by a model that involves an incident component and another component whose phases differ by about π.
Fabrication of Weighted Conical Transducer for Generation of Quasi-Nondiffracting Beam
Authors: Ken Yamada Ken Yamada , Katsumi Tasei Katsumi Tasei , Kiyoshi Nakamura Kiyoshi Nakamura
Published: October 2002

The use of conical transducers with weighted velocity distribution has been proposed by the authors as a simple and practical approach for generating Bessel-type quasi-nondiffracting beams. In this paper we present the fabrication of a weighted conical transducer employing a dielectric layer of varying thickness. The dielectric layer is used for applying a radially diminishing voltage to the piezoelectric material, which will create the desired weighting on the vibration amplitude. It is shown from the experiments that the weighted conical transducer has the capability of generating a narrow-beam ultrasound over a long range along the central axis.
Electrical Properties of Piezoelectric Transducers with Space-Periodic Charge Distribution and Control of Properties
Authors: Ohki Michio , Yagi Tadao , Shiosaki Tadashi
Published: October 2002

Space-periodic charge distribution formed optically in a semitransparent LiNbO3:Fe piezoelectric transducer depresses the linear vibration of the transducer. The Q-value decreases and nonlinear phenomena such as nonlinear jump and hysteresis of the admittance often occur under some experimental conditions. Dependence of piezoelectric and dielectric properties on the internal electric field involved with the space-charge distribution was examined. These properties could be changed by changing the intensity of the internal electric field. In addition, the present nonlinear vibration could be controlled by the difference in the methods for driving the piezoelectric vibration.
Performance of Multilayered Ultrasonic Transducers Comprising Vinylidene Fluoride and Trifluoroethylene Copolymer Films and Ferroelectric Ceramic Plates
Authors: Omote Kenji , Park Kang-Sik , Li Guorong , Hiroji Ohigashi Hiroji Ohigashi
Published: October 2002

Frequency and impulse response characteristics of multilayered ultrasonic transducers comprising forward films of vinylidene fluoride and trifluoroethylene copolymer (P(VDF-TrFE)) and backward ferroelectric ceramic plates of lead-zirconate-titanate (PZT) and a backing load, are studied both theoretically and experimentally. These transducers can be driven in three operation modes: (1) P(VDF-TrFE) as a transmitter and a receiver, (2) PZT as a transmitter and a receiver, and (3) PZT as a transmitter and P(VDF-TrFE) as a receiver. It is found that, owing to the great difference in their acoustic and dielectric properties, PZT plates and P(VDF-TrFE) films operate independently at different frequencies, and that, in operation mode (3), the multilayered transducers exhibit broad frequency bandwidth or shorter impulse response characteristics with high sensitivity and high S/N ratio.
Relationship between Speed of Lamb Wave and Measurement Error on Distance
Authors: Katsuyuki Kobayashi Katsuyuki Kobayashi
Published: October 2002

It is possible to calculate a distance from the propagating time and the speed of sound, and the distance measurement accuracy depends on how accurately the speed of sound can be determined. When using Lamb waves with different phase velocity V
p and group velocity V
g, this becomes especially important since the speed of sound depends on the frequency as well as the thickness of the plate. Therefore, an algorithm to calculate the distance using approximated speeds of sound without decreasing the distance measurement accuracy is established through an experimental and theoretical study on the nature of anti-symmetric 0-order-mode Lamb waves.
Analysis of Subsurface Imaging and Effect of Contact Elasticity in the Ultrasonic Force Microscope
Authors: Yamanaka Kazushi , Ogiso Hisato , Kolosov Oleg
Published: October 2002

We examined, both theoretically and experimentally, the characteristics of subsurface imaging with nanometer resolution and the effect of contact elasticity in the ultrasonic force microscope (UFM). In particular, the effect of the surface energy and effective elasticity on the maximum tip-sample force and the shift of the averaged tip-sample distance were examined. Furthermore, kink formation in the cantilever deflection (z
a) against the ultrasonic frequency vibration (UFV) amplitude (a) characteristics was predicted. This model was used to explain experimental observations in UFM, such as the features of the measured z
a(a) curve and the damping of the cantilever torsion vibration by the UFV. Moreover, the previously reported lateral ultrasonic force microscope image of subsurface features was explained by the response of subsurface edge dislocation to a large instantaneous force enhanced by the UFV.
Analysis of Deposits Evaporated from Sb-Doped Si Melts
Authors: Huang Xinming , Terashima Kazutaka , Tokizaki Eiji , Hitoshi Sasaki Hitoshi Sasaki , Shigeyuki Kimura Shigeyuki Kimura
Published: October 2002

To investigate the composition of oxygen-bearing species evaporated from Sb-doped Si melts, a carefully designed deposit collector was used. The collected deposits were analyzed by electron probe microanalysis (EPMA), gas fusion analysis (GFA), X-ray diffraction, and diffuse reflectance infrared (DR-IR) spectroscopy. The results showed that the compositions of the deposits depended on the temperatures of various regions within the collector. Different deposits, with various amounts of antimony oxide, silicon oxide, silicon, and antimony, were found in different temperature regions. In particular, it was discovered that antimony oxide was deposited only in the region where the temperature was lower than 450°C. Thus the present investigation gave evidence showing that oxygen depletion from Sb-doped Si melt probably arose from enhanced antimony oxide evaporation.
Formation Kinetics and Infrared Absorption of Carbon-Oxygen Complexes in Czochralski Silicon
Authors: Hideki Yamanaka Hideki Yamanaka
Published: October 2002

The study of nucleation kinetics and infrared absorption measured at 8 K provides the models of nucleation reactions of carbon-oxygen complexes formed during annealing at 500°C and 650°C. We have, for the first time, found that the reduction ratio of interstitial oxygen in the 450–650°C range obeys the Johnson-Mehl-Avrami equation with a reaction rate constant expressed byk= 83.9 exp (-1.0 eV/kBT) cm-1. Nucleation at 650°C follows first-order kinetics, while that at 500°C follows third-order kinetics. The 1104-cm-1band due to carbon-oxygen pairs formed above 1000°C decreases throughout annealing at 650°C, whereas it increases upon annealing at 500°C for up to 64 h. Five bands appear at 1026, 1052, 1099, 1107.5 and 1112 cm-1, and their intensities increase throughout the annealing process at 500°C for up to 64 h and remain constant from 64 to 128 h, and decrease beyond 128 h. From these findings, carbon-oxygen complexes formed at 650°C and at 500°C are concluded to be Cs–Onwithn= 1, 2, 3, … and Cs–Oi–O2, respectively.
Analysis of P and Sb Diffusion during Thermal Oxidation in Silicon
Authors: Onishi Takahisa Okino
Published: October 2002

Using experimental results of oxidation-enhanced/retarded diffusions (OED/ORD) for P/Sb in silicon, OED and ORD equations are rewritten into differential equations for self-interstitials and vacancies (I and V). An extended relation of the local equilibrium between I and V, V
I

m
= n, is derived from asymptotic forms of formal solutions of OED and ORD equations. The differential equations are solved using V
I

m
=n, i.e., OED and ORD equations are simultaneously solved without any assumptions. Consequently, OED/ORD were governed by only the interstitialcy/vacancy mechanism. The local equilibrium between I and V did not occur in the present diffusion time range. From the obtained results, diffusivities of I and V, i.e., D
I=2.4×10-9 cm2 s-1 and D
V=2.1×10-10 cm2 s-1, and also their thermal equilibrium concentrations, C
I
0=3.3×1016 cm-3 and C
V
0=2.2×1017 cm-3, were determined at 1100°C.
Optical Beam Induced Current Techniques for Failure Analysis of Very Large Scale Integrated Circuits Devices
Authors: Hirotaka Komoda Hirotaka Komoda , Katsusuke Shimizu Katsusuke Shimizu
Published: October 2002

In failure analysis of complementary metal oxide semiconductor (CMOS) very large scale integrated (VLSI) circuits using optical beam induced current (OBIC) techniques, circuit analysis was carried out by studying the flow path of detected photocurrents for the first time. This circuit analysis revealed that the OBIC current can be detected even on a good unit. Furthermore, this gave a clear explanation as to the reason why the suspected failure site detected by OBIC and emission microscopy analyses did not always occur at the same site as the defect. This study showed that there is a high possibility of detecting a failure due to metal-metal short by OBIC analysis.
Alignment of Crystallites in Obliquely Deposited Cobalt Films
Authors: Hara Kazuhiro , Itoh Kikuo , Kamiya Masao , Fujiwara Hiroshi , Okamoto Kunito , Hashimoto Takashi
Published: October 2002

The geometric alignment of crystallites was investigated using ellipsometry for evaporated cobalt films. The incidence angle was 45° and the gas pressure ranged from 0.008 to 2 Pa during argon gas inflow. The anisotropy of the reflection coefficient showed that above 0.6 Pa, crystallites preferentially align in the direction parallel to the incidence plane. The parallel alignment of crystallites is also found in sputtered films and is always accompanied by a c-axis preferred orientation. Replica electron microscopic observation and X-ray analysis revealed that the top of columnar grains constituting the parallel alignment is surrounded by the {101̄1} habit planes, and the side of the columnar grains is truncated by the {0001} habit planes. Thus, we concluded that the parallel alignment is determined by the crystal habit.
Waveguiding Characteristics of Optical Waveguide with Claddings Having Negative Nonlinear Refractive Coefficient
Authors: Ohke Shigeaki , Satomura Yutaka , Umeda Tokuo , Cho Yoshio
Published: October 2002

Waveguiding characteristics of the optical waveguide with claddings having a negative nonlinear refractive coefficient are investigated theoretically. The relationship between the total light intensity and the effective refractive index is obtained by means of numerical computation based on the multisegmentation procedure. As the result, an anomalous optical power-limiting action of this nonlinear waveguide is revealed.
Dual-Ring Double Scattering Method for Proton Beam Spreading
Authors: Yoshihisa Takada Yoshihisa Takada
Published: October 2002

A dual-ring double scattering method has been proposed to obtain a large uniform beam field in the proton rotating gantry used for cancer treatment. This method makes it possible to reduce the distance for beam field formation and to use the larger part of the beam. A flat beam field can be formed at a position on the patient by scattering the beam more strongly at the inner part of the dual-ring second scatterer than the outer part. Using this method we can form the beam field of 20 cm in diameter with the uniformity of ±1.7%p-p using the first scatterer made of 2.6-mm-thick Pb and the second dual-ring scatterer (inner part: 4.6-mm-thick Pb; outer part: 12.6-mm-thick Al) with an additional 0.7-mm-thick iron sheet for the 230 MeV incident pencil-like proton beam at the distance of 3.000 m. It was found that precise beam alignment (typically 1 mrad) on the center of the second scatterer is required to obtain the uniform beam field.
Energy Spectra of Displaced Atoms in High-Energy Electron-Irradiated Si: Views on Electron Beam Doping and Damage Factor
Authors: Wada Kyoichiro Yasuda
Published: October 2002

Electron energy spectra as a function of depth have been computed by means of a Monte Carlo simulation for Si samples with a diameter of 20 µm irradiated by electron beams at 2 to 9 MeV. The energy spectra of primary displaced atoms were calculated from the electron energy spectra and found to be similar to the electron energy spectra. Values of the average energy transfer at the peak of the spectra at a normalized depth of 0.1 (=z/R), where z is depth from the Si surface and R is range of electrons, are about 53, 82, 108 and 120 eV for 2, 4, 7 and 9 MeV electron beams, respectively. It was suggested that the displaced atoms with effective average energy transfer were produced, which contributed to the electron beam doping. There is a proportional relationship between the measured damage factor and nonionizing energy loss, calculated based on respective depths of Si sample irradiated by electrons.
Observation of Initial Growth of In on Silicon(100) Surface
Authors: Zhu Changxin , Hayashi Tohoru , Shunji Misawa Shunji Misawa , Sonoko Tsukahara Sonoko Tsukahara
Published: October 2002

The initial growth of In on a Si(100) surface as a function of the coverage has been investigated using scanning tunneling microscopy (STM). In(2×2) is a frequently observed phase at coverages below 0.5 monolayer (ML), the In(2×1) phase appears at the coverage above 0.5 ML, and the coexistence of the In(2×2) and In(2×1) reconstructions becomes a dominant phase at the coverage between 0.5 ML and 1.0 ML. Further deposition of In above 1.0 ML gives rise to the onset of three-dimensional island nucleation and growth associated with layer-by-layer growth. The island is highly oriented with major axes along the <011> directions. The island is located on the terrace adjacent to the step edge, suggesting that the step edge should be a preferred site for island nucleation.
Scanning Tunneling Microscope Image of Thioguanine Molecules on Au(111) Surface
Authors: Shunji Katsumata Shunji Katsumata , Atsushi Ide Atsushi Ide
Published: October 2002

We have studied 6-thioguanine, a substituent of deoxyribonucleic acid (DNA) bases, adsorbed on a Au(111) surface by scanning tunneling microscopy (STM) under ambient condition in air. Observation of the STM image of the molecule suggests that thioguanine is bound to the Au substrate through the Au-S bond formation described in STM studies of alkanethiolate molecules. Our STM images obtained under ambient condition are much more similar to those of a planar two-dimensional hydrogen-bonded array of guanine molecules on a MoS2 substrate rather than those of a disordered array of guanine on a Au substrate in solution.
Atomic Force Microscopy Images of Natural Zeolite Surfaces Observed under Ambient Conditions
Authors: Yashima Masaharu Komiyama
Published: October 2002

Atomic force microscopy (AFM) images of the (010) faces of two natural zeolites, stilbite and heulandite, were obtained under ambient conditions. They show corrugations close to atomic resolution. For stilbite, crystallographic defects on its surface were observed for the first time. Heulandite images did not match with the surface structure expected from its bulk crystallographic data.
Density Variation of Molten Silicon Measured by an Improved Archimedian Method
Authors: Sasaki Hitoshi , Tokizaki Eiji , Kazutaka Terashima Kazutaka Terashima , Shigeyuki Kimura Shigeyuki Kimura
Published: October 2002

The temperature dependence of the density of molten silicon was determined in the range from about 1,420° C to 1,650° C using a technique for accurate Archimedian density measurement. The temperature range was found to be divided into three regions in terms of the temperature coefficient of the density. An anomalous value in the thermal volume expansion coefficient of about 7.6×10-4°C-1 was observed just above the melting point. A thermal volume expansion coefficient of about 1.0×10-4°C-1 was obtained for the range from about 1,430° C to 1,540° C. Scattering of the density data was observed for temperatures higher than 1,540° C, for which the thermal volume expansion coefficient was estimated to be about 2.8×10-4°C-1. The time dependence of the density of molten silicon has also been examined. It was found to clearly increase for few hours after completion of melting, reaching a maximum, and thereafter decrease slowly.
Effect of Hydrogen Radicals on the Reduction of Carbon Incorporation into GaAs Grown by Using Trimethylgallium
Authors: Goto Shigeo , Nomura Yasuhiko , Morishita Yoshitaka , Ohno Yoshifumi Katayama
Published: October 2002

Carbon incorporation into GaAs grown under an ultra-high vacuum (UHV) environment was investigated in a trimethylgallium (TMGa)-As4 or AsH3 (cracked at 850° C) system with hydrogen molecules ( H2) or hydrogen radicals ( H•). The residual carbon concentrations in GaAs layers grown at a substrate temperature of 490° C were measured by secondary ion mass spectrometry (SIMS). In the case of GaAs growth by simultaneous source supply, the introduction of H• reduced the residual carbon concentrations in epitaxial layers from 8×1019 to 7×1018 cm-3 for TMGa-As4, and from 4×1019 to 5×1018 cm-3 for TMGa-AsH3. In the case of an alternating source sup- ply of TMGa and AsH3 without hydrogen, a higher level of carbon concentrations ( 1–2×1020 cm-3) than that of the simultaneous source supply case was observed irrespective of the purge duration (10–250 s) of TMGa in UHV. The residual carbon concentrations were reduced to 6×1018 cm-3 by the injection of H• after TMGa-exposure in an alternating supply cycle, although H2 did not affect the carbon incorporation. This result indicates that the adsorbed carbon-containing species derived from TMGa, which has a residence time of more than 600 s on GaAs surfaces, can be desorbed by a reaction with H• .
Effects of Plasma-Substrate Distance on Properties of Hydrogenated Amorphous Silicon Deposited from Hydrogen-Diluted Silane
Authors: Motoaki Kawase Motoaki Kawase , Takao Masuda Takao Masuda , Masayuki Nagashima Masayuki Nagashima , Taisuke Maki Taisuke Maki , Yasushi Miyamoto Yasushi Miyamoto , Kenji Hashimoto Kenji Hashimoto
Published: October 2002

Hydrogenated amorphous silicon (a-Si:H) was prepared on substrates located away from rf plasma of hydrogen-diluted silane at 3 Torr. Physical and chemical structures of the films were changed by altering the distance between the plasma and the substrates. An optimum separation distance between the plasma and the substrates was found. The effects of substrate temperature and hydrogen dilution on film properties were also examined. The changes in film properties were explained by taking into account three types of film precursors: favorable radicals of lower sticking probability, unfavorable sticky ones and unfavorable polymerized ones.
Interfacial Study of Tl2Ba2Ca2Cu3O10 Thin Films on Silver Foil
Authors: Hsu Shih-Nan , Lin Ran-Jin , Jefferson Ru-Shi Liu
Published: October 2002

An interfacial study of Tl2Ba2Ca2Cu3O10 thin films on silver foil has been carried out. There is a guest phase, composed of a 2.4-nm-thick unit cell up to 10 nm thick in total, formed between the interface of the 2223 phase and the substrate. It is fitted, with our proposed model, to Tl2CaCu2O6. This kind of guest phase in the TBCCO and silver system is found for the first time. This non-superconducting Tl2CaCu2O6 phase did not affect the superconducting property, and T
c=102 K was found for this sample.
Magnetic Properties of Codeposited Fe/MgO Composite Films
Authors: Susumu Matsuo Susumu Matsuo , Tomohiro Matsuura Tomohiro Matsuura , Isao Nishida Isao Nishida , Nobuo Tanaka Nobuo Tanaka
Published: October 2002

Small Fe particles of nm size were formed in MgO films by a codeposition technique. Static magnetization and ferromagnetic resonance were measured. Magnetic couplings between the particles are discussed on the basis of experimental data of ferromagnetic resonance and magnetization measurement. The data show that the particles in high Fe concentration film are strongly coupled, while those in low concentration films consist of two types of particles: strongly coupled ones and independent ones. Static magnetization measurement strongly suggests enhanced magnetism at the interface of the Fe particles and MgO matrix, which has been theoretically predicted.
Refractive Index of Organic Photochromic Dye-Amorphous Polymer Composites
Authors: Norihisa Tanio Norihisa Tanio , Masahiro Irie Masahiro Irie
Published: October 2002

Refractive indices of organic photochromic dye-amorphous polymer composites and their changes upon photo- irradiation were measured. The packing coefficients of the dyes in amorphous polymers were determined, and it becomes possible to estimate the refractive indices of the polymer composites containing various amounts of dyes. Molar refractions [R] at 633 nm were also determined for both isomers of the dyes.
Raman Characterizations of Ruthenium Dichalcogenides
Authors: Hwang Song-Tzer , Lee Ming-Chih , Huang Jeng-Kuang , Huang Ying-Sheng
Published: October 2002

Raman scattering of single-crystal RuTe2has been carried out with good frequency resolution and wide wavelength coverage. In this article, our results are presented and compared with those for other ruthenium dichalcogenides ( RuSe2, and RuS2) reported previously. We found a good linear relationship between all Raman shifts and the reciprocal chalcogen mass. We also observed resonant scattering related to inter-electronic-band transitions.
Magnetic Properties and Phase Stability of Icosahedral Al–Pd–Mn–B Quasicrystals
Authors: Yokoyama Yoshihiko , Inoue Akihisa , Yamauchi Hiroshi , Kusuyama Masashi , Tsuyoshi Masumoto Tsuyoshi Masumoto
Published: October 2002

The magnetic properties and the effect of B content on the appearance of ferromagnetism, as well as the phase stability of the icosahedral phase, were examined for the icosahedral Al70-
x

Pd15Mn15B

x

( x=0 to 6 at.%) alloys. As the B content increases, freezing temperature (T
f) and ferromagnetic Curie temperature (Θ f) increase markedly, accompanying the drastic increase in M, increase the transition of the magnetic nature of Mn from paramagnetism to ferromagnetism. The phase diagram between the transition temperature of each magnetic state and B content was constructed. The ferromagnetic state was obtained in the B range above 3 at.% B at temperature between 480 K and 550 K. It is thus concluded that the replacement of Al by B causes a drastic change in the magnetic properties though the change in magnetic interaction of Mn–Mn pair and creation and Mn–B pairs.
Origin of Dark Regions in Scanning Tunneling Microscopy Images Formed by Thermal Oxidation of Si(111) Surface
Authors: Hiroyuki Kageshima Hiroyuki Kageshima , Yukinori Ono Yukinori Ono , Michiharu Tabe Michiharu Tabe , Takahisa Ohno Takahisa Ohno
Published: October 2002

We report on the theoretical analysis of dark regions in scanning tunneling microscopy (STM) images formed on a Si(111) surface oxidized at room- and high-temperatures. We have found that the darkness of surface Si atoms in STM images depends on whether or not the dangling bond of the outermost Si atom is terminated by an O atom. The reason for this is that STM current flows through dangling bond states, which are eliminated by termination with O atoms. Based on calculations, we have found the dark regions to be oxidized regions and the darker regions to be more deeply oxidized regions. This is consistent with experimental results previously reported.
Reactive Ion Etching of Gallium Arsenide in CCl2F2 and SiCl4 Plasmas: Influence of Chamber Material and Etching Mask
Authors: Jackie Jean-Pierre Etrillard Jackie Jean-Pierre Etrillard
Published: October 2002

This paper describes the influence of the masking techniques and of the reactor chamber material in reactive ion etching of gallium arsenide in CCl2F2 and SiCl4 plasmas. The etching characteristics are explained by redeposition on surfaces or sidewalls of etched patterns and by interaction with the reactor. Analysis of the etched surfaces by Auger electron spectroscopy (AES) and energy dispersive X-ray spectroscopy (EDX) shows the importance of the masking technique used. Very high-definition GaAs patterning has been performed employing a combination of a SiCl4 gas at a pressure of 5 mTorr, a pure aluminum cover plate material and a nickel mask. A pending issue remains with the hard sidewall film resulting from the high ion energy necessary to achieve anisotropic etching.
Fundamental Study on a Long-Duration Flash X-Ray Generator with a Surface-Discharge Triode
Authors: Takahashi Kei , Sato Eiichi , Sagae Michiaki , Oizumi Teiji , Tamakawa Yoshiharu , Yanagisawa Toru
Published: October 2002

Fundamental studies on a long-duration flash X-ray generator are described. This generator consisted of the following components: a high-voltage power supply with a maximum voltage of 100 kV, an energy-storage condenser of 500 nF, a main discharge condenser of 10 nF, a turbo molecular pump, a thyratron pulser as a trigger device, and a surface-discharge triode. The effective pulse width was less than 30 µs, and the X-ray intensity approximately had a value of 0.6 µC/kg at 1.0 m per pulse with a charged voltage of 60 kV. The maximum tube voltage was equivalent to the initial charged voltage of the condenser, and the peak tube current was less than 40 A. With this generator, we could obtain stable X-ray intensity maximized by preventing damped oscillations of the tube voltage and current.
On Schlomilch's Integral Equation for the Ionospheric Plasma
Authors: De S. S. , Sarkar B. K. , Mal Manasi , De M. , Adhikari B. Ghosh
Published: October 2002

The analytical form of the absorption index appropriate to the D- and E-region of the ionospheric plasma is derived. It has been utilised to build up Schlomilch's integral equation. The corresponding solution is obtained in terms of certain ionospheric parameters. The variation of effective collision frequency with height has been computed numerically from the derived solution. The results are presented graphically along with an earlier work.
CFX(X=1–3) Radicals Controlled by On-Off Modulated Electron Cyclotron Resonance Plasma and Their Effects on Polymer Film Deposition
Authors: Takahashi Kunimasa , Hori Masaru , Shigeru Kishimoto Shigeru Kishimoto , Toshio Goto Toshio Goto
Published: October 2002

The CF, CF2 and CF3 radical and F atom densities and the polymerization were investigated in an on-off modulated CHF3 electron cyclotron resonance plasma. Using infrared diode laser absorption spectroscopy, the remarkable changes of the CF
X
(X=1–3) radical densities were observed by varying duty cycle at microwave powers of more than 300 W. The mechanisms of these behaviors of CF
X
(X=1–3) radical densities were discussed on the basis of the results of the dissociation degree of the CHF3 molecule. The polymer deposition rates on Si and SiO2 surfaces were also investigated, and it was found that the CF2 radical contributed greatly to the growth of polymer films. Furthermore, X-ray photoelectron spectroscopy measurement showed that the -CF2 component in the polymer films decreased markedly and the -C-CF

X

component increased as the CF2 radical density in the plasma decreased.
Time-of-Flight Scattering and Recoiling Spectrometry Study of Plasma-Cleaned Silicon Surface
Authors: Masahiko Ishii Masahiko Ishii , Yasunori Taga Yasunori Taga
Published: October 2002

The cleaning process of a Si(100) surface using electron cyclotron resonance hydrogen plasmas was observed by time-of-flight scattering and recoiling spectrometry (TOF-SARS). The effects of substrate temperature and plasma density on the cleanliness and the damage including roughness of the surface were clarified by the observation, because both impurities and damage of the surface were detected by TOF-SARS. The substrate temperature had effects on reduction of the damage and the exposure time to obtain a clean surface. The hydrogen-terminated clean surface with nominal damage was obtained by exposure to the plasma with the electron density on the order of 109 cm-3 at 300° C for 1–5 min.
Very Long and Large-Area RF Plasma Productions by Odd Surface Waves for Online Mass Production of Amorphous Silicon Solar Cells or Mirrors
Authors: Shigehiko Nonaka Shigehiko Nonaka
Published: October 2002

Very long and large-area plasmas are confirmed to be produced by means of RF discharge between a pair of very long or large-area electrodes. The electrodes are separated from plasma by dielectric layers. The length of long plasma is 11 m in the case of using a long cylindrical dielectric tube with 28 mmφ. The area and thickness of large-area plasma are 73 cm× 176 cm and 2.5 cm, respectively, in the case of using a large-area rectangular dielectric tube. The plasmas are thought to be produced via interaction between two electromagnetic waves, odd metal surface wave ( MSW
o
) and odd plasma surface wave ( PSW
o
), propagating between electrodes.
Large-Diameter Reactive Plasma Produced by a Plane Electron Cyclotron Resonance Antenna
Authors: Takeshige Ishida Takeshige Ishida , Yukito Nakagawa Yukito Nakagawa , Takashi Ono Takashi Ono , Satoru Iizuka Satoru Iizuka , Noriyoshi Sato Noriyoshi Sato
Published: October 2002

A large-diameter and uniform SF6 (sulfur hexafluoride) plasma is produced by a plane slotted antenna with permanent magnets for electron cyclotron resonance. The plasma is fairly homogeneous similarly to the case of an argon plasma, and the uniformity is within ±3% for a diameter of ∼20 cm at a distance of 20 cm from the antenna. Similar uniformity is obtained in the etching process of polysilicon. The etching rate is enhanced by the assistance of ion acceleration using the RF self-bias technique.
Deposition Characteristics and Properties of SiO2 Films Prepared by Reactive Sputtering in Hydrogen-, Oxygen- and Nitrogen-Argon Mixtures
Authors: Tadashi Serikawa Tadashi Serikawa , Seiiti Shirai Seiiti Shirai
Published: October 2002

Films are deposited by reactive sputtering in hydrogen-, oxygen- and nitrogen-argon mixtures from an SiO2 target in order to obtain device quality SiO2 films at low temperature. Deposition characteristics and film properties of SiO2 films sputtered in the mixtures are examined. Oxygen and nitrogen mixing with the sputtering gas leads to a large decrease in deposition rate compared with argon-only sputtering gas and hydrogen mixing. The SiO2 film properties of the etching rate in BHF solution, surface morphology and resistivity are found to be greatly affected by mixing these gases with sputtering gas. Mixing of oxygen and a small amount of hydrogen provides excellent SiO2 films, whose properties are superior to thermally grown films, even at low temperatures. These SiO2 films have been used to successfully fabricate silicon electronic devices. The effects of mixing the reactive gases with the sputtering gas are also discussed qualitatively through plasma-surface interaction on growing film surfaces.
Preparation of Cu–O Films by Sputtering Using He Gas
Authors: Fujii Takamichi , Koyanagi Tsuyoshi , Morofuji Kouji , Tetsuya Kashima Tetsuya Kashima , Kakuei Matsubara Kakuei Matsubara
Published: October 2002

Cu–O films have been deposited by rf sputtering using a mixture of Ar, He and O2as a sputtering gas. When He was mixed with the sputtering gas, highly oxidized Cu–O films were obtained with low O2content of the sputtering gas, compared with those deposited without He. Activated particles in the plasma were investigated by optical emission spectroscopy analysis. This enhancement of oxidation of Cu–O films is related to an increase in O2+and O*generated through the Penning ionization process by Hemin neutral excited metastable states.
Warp Reduction of High-Electron-Mobility-Transistor on Si Wafer by In-Doped Selectively Doped Heterostructure and Strained-Layer Superlattice Buffer Layer
Authors: Ohori Tatsuya , Suehiro Haruyoshi , Kazumi Kasai Kazumi Kasai , Junji Komeno Junji Komeno
Published: October 2002

Structure to reduce warp of high electron mobility transistors (HEMT) on Si wafers is investigated. The proposed structure consists of an In-doped selectively doped heterostructure and a strained layer superlattice buffer layer. Upon reducing the stress and the total epitaxial layer thickness, the warp of our proposed HEMT structure grown on a 3-inch-diameter Si wafer was reduced to about 1/3 of that of the conventional structures. Using the Fox-Jesser strain relaxation theory, we analyzed the stress reduction mechanism. We found that the frictional force acting on dislocations is important for stress reduction of In-related compounds. We fabricated HEMT ring oscillator circuits with gate length of 0.4 µm. The circuits had a delay time of 19.1 ps/gate and power consumption of 0.175 mW/gate. These values are comparable with those on GaAs substrates.
Effect of Annealing in Air on Electrical Resistances of B-Doped Polycrystalline Diamond Films
Authors: Koichi Miyata Koichi Miyata , David L. Dreifus David L. Dreifus
Published: October 2002

The temperature dependent electrical behavior of as-deposited B-doped polycrystalline diamond films was investigated. Diamond films with various atomic B concentrations were deposited using a microwave plasma chemical vapor deposition technique. The atomic B concentrations were determined using secondary ion mass spectroscopy. Resistances were measured between 25 and 525° C in air. Similar electrical behavior was observed for films with atomic B concentrations less than 3×1017 cm-3 in which the resistance increased over 6 orders of magnitude after heating to 525° C. The variation in resistance between the heating and cooling cycles decreased with increasing B concentration. Little or no variation in the resistance was observed for films with atomic B concentrations higher than 4×1018 cm-3. The variable temperature dependent behavior can be explained by a surface conduction mechanism.