bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Atmospheric Pressure Ionization Mass Spectrometer for the Analysis of Trace Gas Impurities in Silicon Source Gases used for Semiconductor Fabrication
Authors: Irie Takashi , Mitsui Yasuhiro , Iijima Shimpei , Mizokami Kazuaki , Kuriyama Katsumi
Published: October 2002

A new atmospheric pressure ionization mass spectrometer (APIMS) was developed for the measurement of trace gas impurities in silicon source gases, such as monosilane and disilane. To prevent ionization instability caused by Si compound formation, the ion source is divided into a discharge chamber and a reaction chamber (bi-compartment). Impurity species are ionized in the reaction chamber by reactant ions which are generated by corona discharge using an inert gas in the discharge chamber. As the deposition was greatly reduced by this method, stable measurement was possible for over 60 h. Ions of SiH3OH+
2 and Si2H5OH+
2 were found to be produced from trace water in monosilane. The detection limit (S/N) for water in nitrogen was found to be 5 ppt, which is comparable to that obtained with our previous single-compartment ion source.
Anisotropic Surface Anchoring Conditions for Gray-Scale Capability in High-Tilt-Angle Ferroelectric Liquid Crystal
Authors: P. Haridas E. , Bawa Sukhwant Singh , Biradar Ashok Manikrao , Subhas Chandra Subhas Chandra
Published: October 2002

In highly anisotropic anchoring surface, the gray-scale capability has been shown in a thin (4 µ m) polymer rubbed samples of high tilt angle ferroelectric liquid crystal, possessing chiral nematic to smectic C* phase transition. The gray-scale characteristics appear due to the reorientation of the ferroelectric liquid crystal molecules linearly with applied electric field. This effect is observed in the samples where the anchoring strength difference between two surfaces is very high. The anchoring strength has been controlled by means of rubbing strokes on polymer surface of the sample. The observed results have been analysed using electrical and optical switching response.
Monte Carlo Simulation of Growth Process of Two-Dimensional Quasicrystal
Authors: Sasajima Yasushi , Ohtsuka Takahiro , Adachi Katsumi , Ichimura Minoru , Ozawa Satoru
Published: October 2002

Simulations of the growth process of quasicrystal and square crystal lattice have been performed by the canonical Monte Carlo method. By varying the deposition rate and dimensionless temperature, the conditions for obtaining defect-free single crystal were investigated. The two-dimensional Penrose pattern was adopted as a model of the quasicrystal lattice where the positions of particles are restricted to the lattice sites and the interaction range between particles was assumed to be only within the nearest-neighbor distance. It was found that the diffusivity of quasicrystal was higher than that of square crystal lattice if attractive interaction was assumed. This tendency is opposite to that in the case of free particles. The conditions for obtaining a defect-free single crystal were that the deposition rate was low, under 6.57×10-6 atom/(site MCS) and the dimensionless temperature was as low as possible but higher than that for polynuclear growth.
Cooling of Ultracold Neutrons by Propagating Magnetic Field
Authors: Yasutaka Sumi Yasutaka Sumi , Nobumichi Akiyama Nobumichi Akiyama , Zensho Yoshida Zensho Yoshida , Yuichi Ogawa Yuichi Ogawa , Nobuyuki Inoue Nobuyuki Inoue
Published: October 2002

Since a neutron has a magnetic moment, it interacts with a magnetic field. A possible configuration to confine ultracold neutrons (UCN) is a combination of a toroidal multipole field and a toroidal field; the latter prevents spin flip at the separatrix of the multipole field. It results in effective cooling to apply an appreciable ripple to the toroidal field which propagates at the resonant phase velocity. The cooling rate which is the power removed by a propagating toroidal magnetic wave was obtained through the quasilinear theory of the transit-time dumping for a plasma, and compared to the particle simulations.
A Wall Stabilized Nitrogen Arc Model at Different Concentration of Silver Vapour and Current Intensity
Authors: Amry Ahmed M. A. , Rasheedy Mahmoud S. , El-Koramy Reda A. , Abdelhalim A. Turky Abdelhalim A. Turky
Published: October 2002

This paper presents theoretical results for a nitrogen arc contaminated with silver vapours emitted from arc electrode in a range from 0 to 10% and current intensity between 5 to 50 A. By solving the equation of conservation of energy, the effect of these vapours on the arc plasma characteristics are studied. In particular it was seen that the presence of 10-4% Ag in the arc column decreases strongly the axial temperature while the presence of 10-1% Ag has an explicit decreases in the electric field at current near 20 A.
Microwave Discharge in Air: Simulation of Artificial Ionization Layer
Authors: Amemiya Hiroshi , Mitsuru Maeda Mitsuru Maeda
Published: October 2002

For simulation of an artificial ionization layer in the upper atmosphere, air breakdown by microwaves is studied using a magnetron of 2.45 GHz at pressures of 0.2-2.5 Torr corresponding to the height of the upper atmosphere above the ozone layer. The electric field necessary for breakdown has been found to be very close to the optimum value predicted by the microwave discharge theory. The plasma consists of a core and an extended diffusion region. In the latter, the plasma density is 105-106 cm-3, the electron temperature is 0.5 to 1.2 eV and negative ions exist.
Full Optical Determination Method of {001} Lattice Plane of Uniaxial Birefringent Chalcopyrite Crystals
Authors: Yamamoto Nobuyuki , Huang Wen-Zheng , Hirooka Hiroyuki , Kazuki Wakita Kazuki Wakita
Published: October 2002

Uniaxial chalcopyrite crystals of the I-III-VI2 group show a strong dichromatism at wavelengths near their absorption edges due to the polarization-dependent selection rule of the direct band optical transition. Using this unique property, a full optical determination method of the {001} lattice plane is developed. This method provides an expedient alternative to conventional X-ray method for cutting out bulk I-III-VI2 chalcopyrite single crystals.
Structure and Nonlinear Optical Properties of Diacetylene Thin Films Vapor-Deposited on Highly Oriented Polytetrafluoroethylene Thin Films
Authors: Ueda Yasukiyo , Kuriyama Toshiaki , Hari Takahiro , Watanabe Mayumi , Ni Jingping , Hattori Yasuhiro , Uenishi Naota , Uemiya Takafumi
Published: October 2002

Five diacetylene compounds were vapor-deposited on a highly oriented thin film of polytetrafluoroethylene (PTFE) prepared by mechanical deposition. 1,6-Di-( N-carbazolyl)-2,4-hexadiyne (DCHD) film was composed of needlelike crystallites along the chain axis of the PTFE macromolecules. The DCHD crystal was oriented with respect to the PTFE crystal substrate in the relation of (100)*[010]
D
C
H
D
||
(100)[001]
P
T
F
E
. Other diacetylenes also formed uniaxially oriented thin layers. Upon photoirradiation, diacetylene films changed to polymer films having extremely high crystallinity and considerable in-plane dichroism. The third-order susceptibility χ(3) of the uniaxially oriented polydiacetylene films were several times larger than those of the randomly oriented films. Crystal growth observed by electron microscopy on local and microscopic scales was confirmed by THG measurement on a macroscopic scale.
Computer Simulation for Molecular Orientation of Vanadyl Phthalocyanine in Epitaxial Form
Authors: Tada Hirokazu , Shinro Mashiko Shinro Mashiko
Published: October 2002

Molecular orientation of vanadyl phthalocyanine (VOPc) adsorbed on KBr and KCl was studied by molecular mechanics simulation. A VOPc molecule with an oxygen atom oriented upward with respect to the substrate surface was found to be more stable than that oriented downward. The central vanadium atom preferred to stay on potassium cations rather than on halogen anions, which is contrary to our expectation. The lattices optimized in this study agree well with the experimental results. In the epitaxial form on KBr and KCl, the angle between the [100] axis of the substrates and the molecular axis passing through two bridge-nitrogen atoms was 39° and 45°, respectively. The dovetail molecular packing was observed on KCl, while some voids existed between molecules in the optimized packing on KBr.
Close-Packed Adsorption of F(ab′)2 Fragment of Immunoglobulin G on Plasma-Polymerized Allylamine Film
Authors: Kurosawa Shigeru , Kamo Naoki , Arimura Takashi , Sekiya Akira , Muratsugu Makoto
Published: October 2002

Plasma-polymerized films were formed on flat glass plates using allylamine, acrylic acid, acrolein, and allylcyanide as monomers. Adsorption of immunoglobulin G (IgG), F(ab′)2-IgG, Fc-IgG and human serum albumin (HSA) on these plasma-polymerized films and on commercially available polymer plates usually used as substrata for immunoassay was measured. Here, F(ab′)2-IgG and Fc-IgG are fragments of IgG.
The adsorption isotherm followed the Langmuir equation, from which the binding constant and saturation binding were estimated. We found that in general, a cationic surface has higher affinity for protein adsorption than an anionic surface. Among the surfaces examined, the plasma-polymerized allylamine surface showed the highest binding capacity for F(ab′)2-IgG. From saturation binding data, diameters of area occupied by adsorbed proteins were calculated assuming that the adsorbed protein formed a monolayer on the film. Comparing these values with molecular size, we inferred that F(ab′)2-IgG took a close-packed “end-on” orientation on plasma-polymerized allylamine while it took a “side-on” orientation on plasma-polymerized acrylic acid.
Analytical Threshold Voltage Formula Including Narrow-Channel Effects for VLSI Mesa-Isolated Fully Depleted Ultrathin Silicon-On-Insulator N-Channel Metal-Oxide-Silicon Devices
Authors: Ker-Wei Su Ker-Wei Su , James B. Kuo James B. Kuo
Published: October 2002

We report an analytical threshold voltage formula taking into consideration narrow-channel effects for mesa-isolated fully depleted ultrathin silicon-on-insulator (SOI) n-channel metal-oxide-silicon (NMOS) devices based on a quasi-two-dimensional approach. From the analytical formula, contrary to LOCOS-isolated bulk NMOS devices, the narrow-channel effects in the mesa-isolated fully depleted ultrathin SOI NMOS devices are due to elevation of the electrostatic potential in the conducting channel near the sidewall.
Numerical Simulation of Silicon-on-Insulator Thin-Film Solar Cells
Authors: Iwata Hideyuki , Ohzone Takashi , Hideyuki Takakura Hideyuki Takakura
Published: October 2002

The properties of thin-film single-crystalline silicon solar cells fabricated on silicon-on-insulator (SOI) substrate have been investigated through two-dimensional numerical device simulation. The SOI film/buried SiO2 interface condition is changed by varying the back-gate bias. When carriers are caused to accumulate the bottom region of the SOI film by application of large back-gate bias, the conversion efficiency is improved compared to that at zero back-gate bias. However, sufficiently high conversion efficiency cannot be obtained using the conventional structure. One proposal to increase the conversion efficiency of SOI thin-film solar cells is to form a very heavily doped region in the bottom of the SOI film. The newly proposed SOI solar cell has a conversion efficiency of about 24% if complete optical confinement is assumed.
Influence of Fe Contamination in Czochralski-Grown Silicon Single Crystals on LSI-Yield Related Crystal Quality Characteristics
Authors: Miyazaki Morimasa , Miyazaki Sumio , Kitamura Takafumi , Aoki Toshihiko , Nakashima Yutaka , Hourai Masataka , Tatsuhiko Shigematsu Tatsuhiko Shigematsu
Published: October 2002

Influence of Fe contamination in CZ-grown silicon single crystal on oxidation-induced stacking fault (OSF) generation density, carrier recombination and generation lifetimes, and gate oxide integrity (GOI) yield characteristics was experimentally investigated. Two Fe-doped silicon ingots were grown and tested. Concentration of Fe-B ([Fe-B]) in these silicon ingots measured by deep level transient spectroscopy (DLTS) was about 5×1011cm-3and 5×1012cm-3, respectively. OSF density generated by three-step annealing showed dependence on [Fe-B]. Carrier recombination lifetime (τr) showed good correlation with [Fe-B], and a quantitative relationship was established. OSF density after one-step annealing, carrier generation lifetime (τg) and GOI yield were not so dependent on [Fe-B].
Polarization and Dielectric Susceptibility of Ferroelectric Superlattice
Authors: Qu Baodong , Zhong Weilie , Peilin Zhang Peilin Zhang
Published: October 2002

The temperature dependence of dielectric susceptibility as well as the spontaneous polarization of a ferroelectric superlattice were discussed based on the Ising model in a transverse field. When the slab thicknesses are larger, the temperature dependence of the spontaneous polarization shows a steplike structure. The dielectric susceptibility becomes infinite at the Curie temperatureTcand shows finite peaks corresponding to the rapid decrease in the spontaneous polarization near the bulk Curie point of each slab. The height of the finite peaks decreases with the decrease in the slab thicknesses. When they become so thin that the polarization profiles are predominantly controlled by the interface, the finite peaks in susceptibility as well as the steps in polarization disappear.
Carrier Transport and Carrier Trap of 8-Hydroxyquinoline Aluminium Thin Films
Authors: Mori Tatsuo , Miyake Seiya , Mizutani Teruyoshi
Published: October 2002

We estimated the trap depth and the trap density of evaporated 8-hydroxyquinoline aluminium (Alq3) thin film using the space charge limited current (SCLC) model and the thermal stimulated current (TSC) method. The current of Alq3 with thickness greater than 200 nm-thickness showed SCLC-like characteristics. The TSC of Alq3 had a peak around -40° C. The trap depth was estimated to be 0.80 eV.
The trap density was estimated to be 1.0×1017 cm-3 (SCLC) and 1.4×1015 cm-3 (TSC). The trap influenced the electrical conduction in Alq3 thin film, but it was not the major contributor to EL of Alq3.
Surface Tension Variation of Molten Silicon Measured by the Ring Method
Authors: Sasaki Hitoshi , Anzai Yutaka , Huang Xinming , Terashima Kazutaka , Shigeyuki Kimura Shigeyuki Kimura
Published: October 2002

The detailed temperature dependence of the surface tension of molten silicon was measured using an accurate ring method. The surface tension data obtained using a SiC-coated graphite crucible showed an approximately linear temperature dependence from 1,430° C to 1,650° C. Although the temperature dependence of the surface tension of molten silicon in a quartz glass crucible was similar to the above, the maximum value of the surface tension was about 20 dyn/cm smaller than that in the case of the SiC crucible. The temperature coefficient of the surface tension became positive at about 1,425° C and returned to a negative value just above the melring point. These results indicate that surface melt flow near the meniscus of a growing crystal tends to be opposite to the crystal.
Synthesis of PbTiO3 Thin Films by Surface-Reaction-Enhanced Metal Organic Chemical Vapor Deposition
Authors: Yamashita Atsushi , Tatsumi Toru , Keiko Miyanaga Keiko Miyanaga
Published: October 2002

Perovskite PbTiO3 thin films were synthesized on Pt/SiO2/Si substrates at substrate temperatures between 500 and 600° C by metal-organic chemical vapor deposition (MOCVD) under high-vacuum conditions using Pb(DPM)2 (bis-dipivaloylmethanato lead) and Ti(i-OC3H7)4. Composition and structure of the films were investigated and a significant behavior wherein the obtained film suddenly changed from PbTiO3 to TiO2 with increasing feed rate of the Ti precursor was observed. Surface morphology of the obtained films was flat, suggesting that surface migration was important in high-vacuum MOCVD.
Good step-coverage was also obtained.
Potential Structure Measurements of ECH Plasma in a Helical Axis Stellarator
Authors: Kitajima Sumio , Kudoh Ryohta , Inagaki Shigeru , Nakamura Eiji , Takayama Masakazu , Hiroshige Watanabe Hiroshige Watanabe
Published: October 2002

ECH plasma potential structures were measured by Langmuir probes in the Tohoku University HELIAC. By adjusting the coil current ratio of the center conductor and the toroidal coils, 2 characteristic configurations were selected, the 1st case with then/m=3/2 rational surface, the 2nd case without the rational surface. A perturbation field was added in the 1st case in order to producem=2 magnetic islands. Before ECH turn-off the potential structure near the ECH antenna strongly depends on MOD B surfaces; on the other hand, away from antenna the potential structure agrees well with magnetic surfaces, but peculiar regions resemblingm=2 islands appear along a rational surface and disappear in the case without a rational surface. After ECH turn-off both potential structures, near and away from the antenna, not only agree very well with magnetic surfaces, but also preserve the magnetic island structures.
Measurement and Calculation of SiH2Radical Density in SiH4and Si2H6Plasma for the Deposition of Hydrogenated Amorphous Silicon Thin Films
Authors: Shirafuji Tatsuru , Tachibana Kunihide , Matsui Yasuji
Published: October 2002

SiH2radical density in SiH4and Si2H6plasmas diluted with He, Ar and Xe has been measured using intracavity laser absorption spectroscopy, and analyzed by a gas-phase reaction simulation. The density of SiH2increases with dilution due to increase in dissociation rate of parent-gas molecules. The increase in the dissociation rate for He and Xe dilution originates in the increase of electron energy and density, respectively, and both of these contribute for Ar dilution.
Temperature Profiles on Liquid Metal Surface during Electron Beam Evaporation
Authors: Ohba Hironori , Takemasa Shibata Takemasa Shibata
Published: October 2002

The liquid surface of copper during electron beam evaporation was imaged by a lens through a band-pass filter and a double mirror system on a charge-coupled-device (CCD) camera. Temperature profiles were obtained from spectral radiance profiles imaged by the CCD camera using Planck's law of radiation. The maximum temperature was 2040±20 K at the electron beam power of 4.5 kW.
The measured surface temperatures agreed with those estimated from the deposition rate measured by a quartz-crystal thickness monitor.
Correlated Electron-Trapping Events in a One-Dimensional Channel
Authors: Toshitsugu Sakamoto Toshitsugu Sakamoto , Yasunobu Nakamura Yasunobu Nakamura , Sungwoo Hwang Sungwoo Hwang , Kazuo Nakamura Kazuo Nakamura
Published: October 2002

We demonstrate correlated trapping events in a GaAs/AlxGa1-xAs one-dimensional (1D) channel. Due to the Coulomb potential of electrons trapped near the 1D channel, continuous trapping-detrapping of these electron causes fluctuations in the bottle-neck potential, and thus random telegraph signals (RTSs) in the conductance of the channel. RTS appears when the Fermi level crosses the single-electron energy levels of traps. Our results show that when two trap states are at the Fermi level, two RTSs do not occur at the same time, but do interact with each other. This implies that there is electrostatic interaction between the two trapping events.
Magnetoresistance Oscillation in Two-Dimensional Electron Gas under Spatially Modulated Magnetic Field
Authors: Shu-ichi Izawa Shu-ichi Izawa , Shingo Katsumoto Shingo Katsumoto , Akira Endo Akira Endo , Yasuhiro Iye Yasuhiro Iye
Published: October 2002

We have obtained clear experimental evidence for the oscillatory magnetoresistance effect in a two-dimensional electron gas under the influence of a spatially modulated magnetic field, which has been theoretically predicted. The magnetoresistance curve contains an oscillatory component due to the magnetic modulation as well as one due to the potential modulation, and their relative amplitudes can be changed by adjusting the gate bias.
Magnetic Electron Focusing Effect in GaAs/AlGaAs Heterostructure with Gate-Controlled Byway Channel
Authors: Shingo Inoue Shingo Inoue , Sadao Takaoka Sadao Takaoka , Kazuhito Tsukagoshi Kazuhito Tsukagoshi , Kenichi Oto Kenichi Oto , Shigetoshi Wakayama Shigetoshi Wakayama , Kazuo Murase Kazuo Murase , Kenji Gamo Kenji Gamo
Published: October 2002

The magnetic electron focusing effect (MEFE) is investigated using a device with two extra probes connected by a gate-controlled byway channel. The focusing peak height is inversely proportional to the byway channel resistance. The results show that the focusing peaks are caused by the current through the byway. It is found that, at most, about 9% of the total current flows in the byway when the focusing effect occurs. Moreover, a countercurrent flows in the byway when the focusing effect does not occur.
Evaluation of Edge Channel Width by Frequency Dependence of Capacitance Minima in Quantum Hall Regime
Authors: Kenichi Oto Kenichi Oto , Sadao Takaoka Sadao Takaoka , Kazuo Murase Kazuo Murase
Published: October 2002

The frequency dependence of the capacitance between two-dimensional electron systems (2DESs) and the gate has been studied at the quantum Hall (QH) plateaus. The capacitance minima at the QH plateaus are highly dependent on the area of edge channels at high frequencies. The residual contribution of bulk channel to the capacitance has been estimated, and the widths of edge channels have been evaluated. The diagonal conductivity σ
x
x
of less than 10-11 S has been obtained accurately by capacitance measurements at the QH plateaus. The relationship between σ
x
x
and capacitance has been discussed.
Study of Scattering Processes in Quantum Wires by a Correlation Field Analysis of the Phase Coherent Interferences
Authors: Yuichi Ochiai Yuichi Ochiai , Kazunuki Yamamoto Kazunuki Yamamoto , Koji Ishibashi Koji Ishibashi , Jonathan P. Bird Jonathan P. Bird , Yoshinobu Aoyagi Yoshinobu Aoyagi , Takuo Sugano Takuo Sugano , David K. Ferry David K. Ferry
Published: October 2002

We have studied the field dependence of the correlation field, B
c, and the amplitude, δg, of the conductance fluctuations in the low-temperature magnetoresistance of split-gate wires. B
c is found to increase as the field increases and δg is also found to show a similar dependence. Two kinds of scattering processes were found to affect phase breaking of electron interference in the quantum wire. These appear at low and high magnetic fields, and are considered to arise from width-dependent and width-independent scattering processes, respectively. In addition, the inelastic scattering length has been obtained from the phase breaking rate, analyzed via the slope of the field dependence of B
c.
Oscillatory Behavior of Nonlocal Electrical Properties in Mesoscopic AlGaAs/GaAs Two-Dimensional Electron Gas Wire Structures
Authors: Kyoung Wan Park Kyoung Wan Park , Seongjae Lee Seongjae Lee , Mincheol Shin Mincheol Shin , Hyukchan Kwon Hyukchan Kwon , El-Hang Lee El-Hang Lee
Published: October 2002

We have measured the magnetoresistances of mesoscopic wires fabricated in AlGaAs/GaAs two-dimensional electron gas. The nonlocal magnetoresistances show oscillatory behaviors in the transition regions between successive quantum Hall states. We find that the nonlocal oscillations are well explained by the mixing effect of edge states, whose longitudinal wave vectors can be obtained by using the linear confining potential approximation near the edge. Our analysis implies that the confining field strength should in effect decrease as the magnetic field increases.
Universal Fluctuations in Spectra of Disordered Systems at the Anderson Transition
Authors: Isa Kh. Zharekeshev Isa Kh. Zharekeshev , Bernhard Kramer Bernhard Kramer
Published: October 2002

Using the level-spacing distribution and the total probability function of the numbers of levels in a given energy interval we analyze the crossover of the level statistics between the delocalized and the localized regimes. By numerically calculating the electron spectra of systems of up to 323 lattice sites described by the Anderson Hamiltonian it is shown that the distribution P(s) of neighboring spacings is scale-independent at the metal–insulator transition. For large spacings it has a Poisson-like asymptotic form P(s)∝exp
(- A
s/Δ), where A ≈1.9. At the critical point we obtain a linear relationship between the variance of the number of levels <[δn(ε)]2 > and their average number  within the interval ε. The constant of proportionality is less than unity due to the repulsion of the levels. Both P(s) and <[δn(ε)]2 > are determined by the probability density Q

n
(ε) of having exactly n levels in the energy interval ε. The distribution Q

n
(ε) at the critical point is found to be size-independent and to obey a Gaussian law near its maximum, where n∼.
Spatial Variation of Local Current Noise Due to Impurity Scattering and Local Charge-Induced Noise
Authors: Yoshihiro Hiraki Yoshihiro Hiraki , Hisanori Nakano Hisanori Nakano , Yoshimasa Isawa Yoshimasa Isawa
Published: October 2002

We analyze the noise characteristics associated with the fluctuation of the number of electrons in two terminal elements. We find that the local current noise on leads around a point contact varies spatially. The local current noise resulting from short wavelength fluctuations differs from the standard one resulting from long wavelength fluctuations. The excess shot noise near the point contact decreases towards the leads, and the characteristic length is the mean free path of electrons ℓ. At distances longer than ℓ from the contact, the local noise approaches the pure thermal noise given by 4kBTGQwith the quantized conductanceGQ. We also find that the tunneling current of resonant tunneling devices (RTDs) is strongly influenced by the existence of the immobile charges captured by the localized traps. By treating the electron capture and emission processes kinematically, we simulate random telegraph noise (RTN).
Effect of Stray Charge on Quantum Cellular Automata
Authors: P. Douglas Tougaw P. Douglas Tougaw , Craig S. Lent Craig S. Lent
Published: October 2002

We study the operation of quantum cellular automata (QCA) devices in the presence of stray charge. The operation of linear arrays of QCA cells, called binary wires, relies on Coulombic interaction between the cells, which is affected by the presence of such stray charge. The position of the charge determines whether or not the devices function properly, and it is possible to determine the “forbidden” region near the array in which the presence of stray charge causes device failure. We calculate this forbidden region by directly diagonalizing the Hamiltonian for the system including the stray charge. We find that the QCA binary wire is unaffected by stray charge at a distance greater than the intercellular repeat distance of the wire.
A Molecular Beam Epitaxy Approach to Quantum Dot Arrays
Authors: Makoto Kaneko Makoto Kaneko , Masashi Shimoda Masashi Shimoda , Yoshitaka Okada Yoshitaka Okada , Mitsuo Kawabe Mitsuo Kawabe
Published: October 2002

GaAs/AlAs quantum dot structures have been fabricated by atomic hydrogen-assisted molecular beam epitaxy (MBE). The substrates used were (111)B GaAs, on which tetrahedral-shaped pits surrounded by three equivalent triangular-shaped {111}A side facets have been produced by an anisotropic wet chemical etching. The deposition of GaAs on (111)A facets were decreased as a consequence of growth selectivity under atomic hydrogen irradiation. A high selectivity in the growth between on (111)B and (111)A has been uniquely utilized for the fabrication of quantum dot structures.
Observation of Tunneling Electron Luminescence at Low Temperatures Using Novel Conductive Transparent Tip
Authors: Tooru Murashita Tooru Murashita , Masafumi Tanimoto Masafumi Tanimoto
Published: October 2002

A novel conductive transparent (CT) tip has been developed that effectively collects tunneling-electron luminescence with a large solid angle of 2 sr in the direction of the most intensive photoemission. Using this CT tip, the spectrum of tunneling-electron luminescence from cleaved Zn-doped GaAs was obtained at 10 K.
Quantum Well Wire Fabrication Method Using Self-Organized Multiatomic Steps on Vicinal (001) GaAs Surfaces by Metalorganic Vapor Phase Epitaxy
Authors: Shinjiroh Hara Shinjiroh Hara , Junichi Motohisa Junichi Motohisa , Takashi Fukui Takashi Fukui , Hideki Hasegawa Hideki Hasegawa
Published: October 2002

Coherent multiatomic steps with extremely straight edges are naturally formed on vicinal (001) GaAs surfaces during metalorganic vapor phase epitaxial growth. GaAs quantum well wires (QWWs) are formed on these self-organized multiatomic steps. In our previous study, a thin AlGaAs layer was grown on GaAs with multiatomic steps as a lower barrier of QWWs. However, the height and spacing of the steps slightly fluctuate on AlGaAs layer surfaces. Therefore, in this experiment, AlAs layer instead of AlGaAs layer was used as a lower barrier layer to improve the uniformity of the height and spacing of the steps. Atomic force microscopy observations and photoluminescence (PL) measurements at 20 K revealed that the underlying coherent GaAs multiatomic steps were well traced by the AlAs barrier layer rather than the AlGaAs barrier layer. Furthermore, we measured the polarization anisotropy of the PL spectra from the QWWs with AlAs. These results suggest that uniform QWWs are successfully formed using multiatomic steps on vicinal (001) GaAs surfaces.
Observation of 77 K Staircase I-V Characteristics in 2DEG's Irradiated by a Focused Ion Beam
Authors: Sung Woo Hwang Sung Woo Hwang , Henri Lezec Henri Lezec , Toshitsugu Sakamoto Toshitsugu Sakamoto , Kazuo Nakamura Kazuo Nakamura
Published: October 2002

Staircase current-voltage (I-V) characteristics, observed at 77 K in narrow 2DEG channels irradiated by a single line scan of a focused ion beam (FIB), is reported in detail. These staircases are interpreted as evidence of single electron tunneling through a naturally occurring specific Coulomb island in the random potential fluctuations created by FIB damage. Clear comparison is made between the I-V's taken from wide channels and those from narrow channels. Based on orthodox calculations of the I-V characteristics, it is shown that highly asymmetric tunnel junctions are needed to explain our data. This is consistent with the random nature of the potential landscape in the FIB damaged region.
Nanostructure Alignment for Hot Electron Interference/Diffraction Devices
Authors: Hiroo Hongo Hiroo Hongo , Jun Suzuki Jun Suzuki , Michihiko Suhara Michihiko Suhara , Yasuyuki Miyamoto Yasuyuki Miyamoto , Kazuhito Furuya Kazuhito Furuya
Published: October 2002

An ultrafine fabrication technique for hot electron interference/diffraction devices was developed. The alignment of two nanostructures by e-beam direct writing before and after crystal growth was reported for the first time. The aligned structure consists of 70 nm pitch grating GaInAs/InP buried structure and 70 nm pitch stripe electrode of Cr/Au.
Quantum Transport Modeling of Mesoscopic Devices: Application of Wigner Distribution Function
Authors: Hideaki Tsuchiya Hideaki Tsuchiya , Tanroku Miyoshi Tanroku Miyoshi
Published: October 2002

The dynamic and nonlinear quantum transport in mesoscopic devices, especially, in a quantum wire and a quantum well laser are studied based on the Wigner function model. In the simulation of a quantum wire, the contacts to the quantum wire are modeled carefully. It is found that in the nonlinear transport regime, the space charge significantly affects the current-voltage characteristics of the quantum wire. Further, the dynamic responses of the quantum wire are studied when the bias voltage is switched abruptly. In the simulation of a quantum well laser, the bipolar quantum transport is discussed by solving the three Liouville equations for electron, heavy-hole and light-hole simultaneously. The bottleneck phenomenon of carrier injection into the multi-quantum wells is discussed.
Coherent Cooper-Pair Tunneling in a Superconducting Single Electron Transistor
Authors: Yuichi Harada Yuichi Harada , Hideaki Takayanagi Hideaki Takayanagi , Arkadi A. Odintsov Arkadi A. Odintsov
Published: October 2002

We investigate how coherent Cooper-pair tunneling depends on the competition between Josephson coupling energy E
J and charging energy E
C. Measurements were performed on a circuit consisting of two dc-SQUIDs in series, with a gate capacitively coupled to the central island. As the E
J/E
C ratio decreased, coherent Cooper pairs tended to tunnel incoherently. Measured data show good agreement with theoretical calculations in strong and weak coupling limits. This experiment implies the manifestation of Heisenberg's uncertainty principle in a superconductor.
Positron Annihilations Associated with Defects in Plastically Deformed Si
Authors: Kawasuso Atsuo , Suezawa Masashi , Hasegawa Masayuki , Yamaguchi Sadae , Koji Sumino Koji Sumino
Published: October 2002

Deformation-induced defects in Si have been studied using positron lifetime measurement. Two lifetime components, 285 ps and 544 ps, which were assigned to dislocation-related defects and vacancy clusters, respectively, were observed. Through annealing experiments, the dislocation-related component was found to consist of two more components: one annihilated after the annealing at around 900° C and the other remaining even at 1100° C. These were attributed to vacancy like parts on dislocations and to dislocations themselves, respectively. Positron trapping rate due to dislocations increased upon cooling and saturated below 80 K. It was approximately proportional to the inverse of the temperature (∼T-1) in the temperature range between 100 and 300 K. These features were interpreted in terms of shallow levels originating from strain fields around dislocations and the one-dimensionality of dislocations.
Effect of Molar Ratio of (CaxBay)F2 Films on Electrical Characteristics of Metal/Fluoride/InP Structures
Authors: Hidaka Atsushi , Hideaki Ikoma Hideaki Ikoma
Published: October 2002

(Ca

x

Ba

y

)F2 (x:y=7:3, 1:1 and 3:7)/n-type InP (100) metal-insulator-semiconductor (MIS) structures were investigated by means of capacitance-voltage ( C-V) measurements and X-ray photoelectron spectroscopy (XPS) to study the effect of the molar ratio (x:y) of the fluoride films on the quality of the interface between the fluoride and InP.
The fluoride films were deposited on the InP substrates by co-evaporating CaF2 and BaF2 powders in a vacuum of about 1-2×10-6 Torr. The best C-V characteristics were obtained for the lattice-matched (CaBa)F2 (Ca:Ba=1:1 in molar ratio)/InP and the next-best, for the (CaBa)F2 (Ca:Ba=7:3)/InP MIS structures. On the other hand, poor C-V characteristics were obtained for the (CaBa)F2 (Ca:Ba=3:7)/InP and the SrF2/InP structures, though their lattice matchings were better than that of the (CaBa)F2 (Ca:Ba=7:3)/InP structure. It is therefore concluded that the lattice matching between the fluoride film and the InP substrate is probably the most important factor for obtaining a good-quality interface; however, the presence of a fair amount of the “stable” Ca-P bonds is also effective to obtain a stable interface between fluoride and InP.
The XPS data indicated that fluoride films with distinct and uniform chemical compositions were formed from the top surface to the interface with the InP substrate even by the conventional vacuum evaporation technique. The peak binding energy of the XPS signal from the Ba 3d core level shifts to the lower energy side, while that from the Ca 2p core level shifts to the higher energy side with increase in the ratio of Ba to Ca. These shifts are nearly linear with the change of the mixed molar ratio. These findings can be explained by a difference in ionic radii between Ba and Ca in the fluorite structure and indicate that the molar ratios in the fluoride films are the same as the mixed molar ratios of the source powders. Native oxides of InP such as In2O3, InPO3 and InPO4 were found to be removed or reduced by the fluoride films during or after deposition of these films. A small amount of oxygen was included in the fluoride film, indicating that the fluoride film reduced the native oxide of InP and became oxidized itself.
Helicon-Wave-Excited Plasma Treatment of SiOxFilms Evaporated on Si Substrate
Authors: Daisuke Kitayama Daisuke Kitayama , Hideaki Nagasawa Hideaki Nagasawa , Hiroyasu Kitajima Hiroyasu Kitajima , Yoshinaga Okamoto Yoshinaga Okamoto , Hideaki Ikoma Hideaki Ikoma
Published: October 2002

A new approach to low-temperature growth of Si oxide was discussed in which SiOxwas first vacuum-evaporated on Si substrate and then treated in a magnetically excited oxygen plasma (helicon wave) at room temperature. Fairly thick oxide film was obtained. However, the quality of the oxide film was somewhat inferior to those of the oxide grown by direct oxidation of Si with helicon-wave-excited plasma.
Intergrain and Intragrain Critical Current Densities of Ag-Doped YBa2Cu3O7-ySuperconductors
Authors: Goto Shin'ichi , Kazuo Shiiki Kazuo Shiiki
Published: October 2002

The effects of Ag doping on the intergrain and intragrain critical current density properties of YBa2Cu3O7-ysuperconductors were investigated. As a result of AC inductive measurement and four-probe DC measurement, it becomes clear that both intergrain and intragrain critical current densities are enhanced below 10 wt% Ag. This improvement suggests that Ag particles which precipitated in YBa2Cu3O7-ygrains act as pinning centers. At high Ag concentration of more than 15 wt%, intergrain critical current density decreases though the intragrain critical current density is enhanced. The influence of pinning force and grain boundaries is discussed at a macroscopic level.
Multiple Magnetic Resonance in Amorphous Co-Nb-Zr Films with Weak Perpendicular Anisotropy
Authors: Shimada Yutaka , Shimoda Mamoru , Osamu Kitakami Osamu Kitakami
Published: October 2002

The initial permeability of Co-Nb-Zr amorphous films was found to exhibit multiple resonance in a relatively low frequency range from a few MHz up to about 100 MHz. This is clearly observed when the films have a perpendicular anisotropy and it results in very fine stripe domains in the films. A calculation assuming spin wave resonance inside the domains well explains the behavior.
A New Organic Nonlinear Optical Material, 4-isobutyl-3-(5-nitro-2-pyridyl)-2-oxazolidinone
Authors: Komatsu Hiromi , Ukachi Takashi , Shigemoto Takeo , Sugiyama Tsunetoshi , Sakaguchi Yoshihiro , Masahiro Niinomi Masahiro Niinomi
Published: October 2002

A chiral nonlinear optical material, 4-isobutyl-3-(5-nitro-2-pyridyl)-2-oxazolidinone (IBNPO), was developed and grown into a single crystal using the seeded slow-cooling method. The molecular hyperpolarizability of IBNPO was determined to be β IBNPO=2.12×10-30 esu by the dc-induced second-harmonic generation technique. IBNPO crystal is monoclinic and belongs to the space group P
21
. The cutoff wavelength of IBNPO crystal is 410 nm. Angle-tuned type II phase-matched second-harmonic generation at 1064 nm, 860 nm and 830 nm was demonstrated in the plane perpendicular to the a-b plane.
Initial Growth of Heteroepitaxial Diamond on Si(001) Substrates via β-SiC Buffer Layer
Authors: Suesada Tsuyoshi , Nakamura Naofumi , Nagasawa Hiroyuki , Hiroshi Kawarada Hiroshi Kawarada
Published: October 2002

Negative substrate-bias effects on diamond heteroepitaxial nucleation have been investigated using microwave plasma-assisted chemical vapor deposition. The density and the percentage of azimuthally ordered particles grown on carburized Si(001) or on high-quality β-SiC(001) have been estimated by varying the bias-treatment conditions (reaction pressure, microwave power and bias voltage). The percentage of azimuthally ordered particles increases under the following conditions: pressure of 50 Torr, substrate temperature of ∼900° C and bias voltage of -50 V. Smooth heteroepitaxial diamond films of ∼4 µ m thickness have been successfully synthesized on high-quality β-SiC(001) by the bias treatment under the above conditions followed by a two-step growth process: <001> fast growth and <111> fast growth. The initial growth of these films has been governed by the Volmer-Weber mode, where [1̄10]- or [110]-directed protrusions have been formed on β-SiC(001). Diamond islands grew along the grooves between the β-SiC protrusions in the initial stage.
Particle Orbit Simulations on Ion Loss at the Edge of a Tokamak with Separatrix Configuration
Authors: Ido Mieko Kashiwagi
Published: October 2002

Particle orbit simulations are carried out to study the ion orbits and loss at the edge of a tokamak plasma with double null magnetic separatrix. The ion loss conditions are examined as a function ofv∥/v0and the distance of ion launching points from the magnetic separatrix in cases both without and with radial electric field. The simulation results are compared with the theoretical ones. Good agreements and detailed features are obtained in the simulations. As a reference study, the effect of a radial electric field profile similar to that obtained in DIII-D is examined.
Change of Temperature and Elastic Stiffness during Dehydration Process of Polyacrylamide Gel
Authors: Takeo Masuike Takeo Masuike , Seiji Taki Seiji Taki , Kazuhiro Hara Kazuhiro Hara , Shoichi Kai Shoichi Kai
Published: October 2002

Temporal changes of the weight, volume, temperature and elastic properties during the dehydration process of a polyacrylamide (PAAm) gel were studied. Both the weight and the volume monotonically decreased in the early stage of the process and then tended to saturate in the late stage. At the crossover point between these two dependencies, the temperature of the gel and its elastic stiffness showed anomalies, which indicated similar aspects to the glass transition often observed in non-crystalline polymers. The water content in gels is an important factor affecting the transition.
The Interaction Video Pulses and Quasi-Harmonic Signals in Periodic Nonlinear Media
Authors: Gorshkov A. S. , Volyak K. I.
Published: October 2002

We have studied the nearly monochromatic reverse wave generated by a video pulse propagating in a nonlinear medium in which the nonlinearity varies periodically with the position. We considered theoretically the one-dimensional case of a medium with quadratic non-linearity depending sinusoidally on position. The intensity and duration of a quasi-monochromatic reverse wave's generation were evaluated, taking into account various characteristics of the video pulse, as well as the length and nonlinear properties of the medium. Our experimental results obtained on a radio-frequency transmission line with nonlinear capacitors confirm the theory.
Preparation of Bi-Based Ferroelectric Thin Films by Sol-Gel Method
Authors: Atsuki Tsutomu , Soyama Nobuyuki , Yonezawa Tadashi , Katsumi Ogi Katsumi Ogi
Published: October 2002

The effects of Bi/Ta and Sr/Ta mole ratios on ferroelectric properties of Sr

x

Bi

y

Ta2O

z

[ SBIT(x/y/2.0); 0.7≤x≤1.0, 2.0≤y≤2.6] thin-film capacitors were investigated. The SBIT films were grown by the sol-gel method using a spin-on coating on Pt/Ta/SiO2/Si and Pt/Ti/SiO2/Si substrates. The films were annealed at 800° C for one hour in oxygen atmosphere. Remanent polarization (Pr) depended strongly on the Sr/Ta mole ratio, and increased with decrease of the Sr/Ta mole ratio. On the other hand, Pr was almost independent of the Bi/Ta mole ratio. Scanning electron microscopy (SEM) images show that crystal grains grew with decrease of the Sr/Ta mole ratio. Electron probe micro analyzer (EPMA) analysis revealed that Bi content in SBIT films increased with decrease in Sr composition from stoichiometry.
Physical Properties of Bi 4Ti 3O 12 Films Grown on Si(100) Wafers
Authors: Masaki Yamaguchi Masaki Yamaguchi , Takao Nagatomo Takao Nagatomo , Osamu Omoto Osamu Omoto
Published: October 2002

Bismuth titanate (Bi4Ti3O12) films were prepared on Si(100) wafers by rf planar magnetron sputtering using a target of Bi2TiO5 ceramic. C-axis-oriented Bi4Ti3O12 films were grown on Si(100) at a low substrate temperature of 550°C. However, these films did not exhibit ferroelectricity, and the dielectric constant ε
r and dissipation factor tan
δ were about 156 and 0.032, respectively. The dielectric constant was reduced with decreasing film thickness. This behavior was assuming supposing a low-dielectric-constant interface layer. These films showed the dielectric breakdown field of about 21 kV/cm.
Low-Temperature Fabrication of Pb(Zr,Ti)O 3 Films by RF Reactive Sputtering Using Zr/Ti + PbO Target
Authors: WeiXiao Zhang WeiXiao Zhang , Kimihiro Sasaki Kimihiro Sasaki , Tomonobu Hata Tomonobu Hata
Published: October 2002

Pb(Zr,Ti)O3 (PZT) films were grown on fused quartz substrates by reactive sputtering using a Zr/Ti (50%/50%) alloy target combined with PbO pellets under argon pressure of 10mTorr and O2/Ar flow rate ratio of 2.1%. Structure and deposition rate of the films have been investigated as functions of substrate temperature and PbO content. When films were grown in near metallic mode using a Zr/Ti + 41%PbO target, perovskite PZT films were successfully prepared at a temperature as low as 450°C, and in the wide range from 450°C to 570°C. It was impossible to obtain perovskite PZT films using only a stoichiometic Pb(Zr0.5Ti0.5)O3 ceramic target, while perovskite PZT films could be obtained between 540°C and 570°C using a Pb(Zr0.5Ti0.5)O3 + 15%PbO target. Deposition rate of perovskite films for the Zr/Ti + 41%PbO target was 2–3 times higher than that for the PZT + 15%PbO target.
Formation of Bi-based Layered Perovskite Oxide Films by a Laser Ablation Technique
Authors: Tabata Hitoshi , Tanaka Hidekazu , Tomoji Kawai Tomoji Kawai
Published: October 2002

Bi-based layered perovskite oxide films ( SrBi2Ta2O9) have been formed on the Nb-SrTiO3 substrate or Bi2Sr2CuO6 superconducting bottom electrode with c-axis perpendicular to the substrate surface. The dielectric constants of the c-axis oriented SrBi2Ta2O9 films deposited on the Nb-SrTiO3 substrate are as high as 100 and remain constant at an applied frequency from 102 to 106 Hz. Furthermore, an artificially Bi-based layered perovskite structure can be constructed by the layer-by-layer successive deposition technique. The BaTiO3 or SrTiO3 layer is inserted artificially between the double Bi2O2 layers. The formation of “artificially constructed ferroelectric films” by a layer-by-layer deposition method will be discussed and an essential approach to elucidate the mechanism of ferroelectricity.
Pyroelectric Property of Pb 5Ge 3O 11 Thin Films Prepared by Laser Ablation
Authors: Yasuyuki Kageyama Yasuyuki Kageyama , Jiro Sakata Jiro Sakata , Yasunori Taga Yasunori Taga
Published: October 2002

Pb5Ge3O1
1 films were prepared by laser ablation, and pyroelectricity was obtained in the films after annealing. Stoichiometric films were formed at oxygen pressures around 5×10-1 Torr during deposition. It was found that an unreported precursor phase was grown on Pt/Ti/SiO2/Si substrates at a temperature of 520°C. Subsequent annealing at 500°C for 2 h in air made it possible for the film to have (001) oriented texture of ferroelectric Pb5Ge3O1
1. This sample showed remanent polarization of 1.4 µC/cm2 with a ferroelectric hysteresis loop of an asymmetric shape and a pyroelectric coefficient of 4.3 nC/cm2K, while these values were about one third of those reported for single crystal Pb5Ge3O1
1 in a polarization direction. The inferiority in this ferroelectricity is thought due to the lead-deficient phase involved in the film. Although this localized second phase still remains, the appreciable reduction in the process temperature for texturing a Pb5Ge3O1
1 film in the c-plane as low as around 500°C is attributed to the sufficient supply of oxygen during the deposition.