bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of Atomic Force Microscopy Image Variations along the Surface Normal: Presence of Possible Resolution Limit in the Attractive Force Range
Authors: Masaharu Komiyama Masaharu Komiyama , Kazuya Tsujimichi Kazuya Tsujimichi , Shin'ya Ohkubo Shin'ya Ohkubo , Katsuyuki Tazawa Katsuyuki Tazawa , Momoji Kubo Momoji Kubo , Akira Miyamoto Akira Miyamoto
Published: October 2002

Variations of atomic force microscopy (AFM) images as tip-sample distance is varied were examined using a newly developed AFM simulation code ACCESS (AFM simulation Code for Calculating and Evaluating Surface structures) with a Morse-type pairwise potential. A model system consisting of a single atom tip (an “ideal" AFM tip) and a face-centered cubic (fcc) (100) surface with or without point defect showed perfect atomic resolution when scanning was performed in the repulsive force range. In the attractive force range, image contrast inversion was observed twice with the increase of tip-sample distance. Simulation on the point defect surface indicated that this inversion is due to a collective force from more than one atom being imaged as one bright spot. Exact correspondence between the sample surface registry and the simulated image in this force range appears to be coincidental.
Photon Migration Model for Turbid Biological Medium Having Various Shapes
Authors: Tsuchiya Yutaka , Tsuneyuki Urakami Tsuneyuki Urakami
Published: October 2002

Fundamental, yet novel, formulas representing diffuse re-emission of short-light-pulse incidence on turbid media independent of their shapes are deduced from a simple photon migration model in which the survival probability of a photon is determined by the zigzag photon path length and the absorption coefficient within the medium. The results can be applied to derive the absolute concentration of the absorptive constituent in variously shaped media. The coincidence between our model and the diffusion equation is seen if we adopt a new diffusion coefficient independent of the absorption coefficient.
Characterization of Si Wafer Bonding by Injection-Dependent Recombination Velocity
Authors: Grivickas V. , Thungström G. , Bikbajevas V. , Linnros J. , D. Noreika D. Noreika
Published: October 2002

A new silicon wafer bonding characterization technique, based on depth- and time-resolved free-carrier-absorption measurements is demonstrated. The effective recombination velocity is obtained from the measured excess carrier profiles perpendicular to the interface. Measurements have been performed covering a large range of injection levels for unipolar bond-junctions obtained from (100) and (111) oriented p-type Si wafers. Our results show a dramatic difference between the injection-dependence of the recombination velocity for hydrophobic bond-junctions prepared in different ways.
Interferometry of KrF-Laser-Produced Plasma by Shortened Stokes Pulse
Authors: Takahashi Eiichi , Matsumoto Yuji , Matsushima Isao , Yashiro Hidehiko , Yoshiro Owadano Yoshiro Owadano
Published: October 2002

We have recently built an interferometer for diagnosis of KrF-laser-produced plasma using shortened Stokes pulses as probe light. This probe light is generated by a newly developed technique based on transient gain of stimulated Raman and Brillouin scattering in mixed gas media. With this technique, a Stokes pulse of 2 ns (277 nm) can be generated stably from a KrF laser pulse of 20 to 30 ns duration. The procedure for mixing two kinds of gas is very simple and useful, especially for temporally accurate measurement. We successfully applied the interferometer with the probe light in the measurement of KrF-laser-produced plasma for the first time.
Development of a Precisely Temperature-Programmable Langmuir Trough for Measuring Properties of Insoluble Monolayers at the Water Surface as Functions of Temperature
Authors: Kato Teiji , Tatehana Atsushi , Suzuki Noboru , Iimura Ken-ichi , Araki Toshinari , Iriyama Keiji
Published: October 2002

A new type of Langmuir trough was constructed in which temperature of the water surface is controlled precisely according to a program using a large number of Peltier elements and a microcomputer. We can suppress convection of the water in the trough during linear heating or linear cooling by planning the trough as thin as 2 mm. This trough is very suitable for measuring A-T isobars and π-T isochores of insoluble monolayers which are rarely measured precisely. The newly developed trough can permit observation of Brewster angle microscopic (BAM) images of insoluble monolayers clearly during measurements of A-T isobars by suppressing convection completely.
Large Lateral Modulation in InAs/GaAs In-Plane Strained Superlattice on Slightly Misoriented (110) InP Substrate
Authors: Nishikawa Yuji , Nakata Yoshiaki , Tackeuchi Atsushi , Muto Shunichi , Osamu Wada Osamu Wada
Published: October 2002

An InAs/GaAs in-plane strained superlattice (IPSSL) grown by molecular beam epitaxy (MBE) is investigated using photoluminescence (PL) measurements. The polarization-dependent PL at 0.77 eV (77 K) with a full width at half maximum of 25 meV indicates that a laterally modulated structure is grown. With the use of the empirical nearest-neighbor sp3s*tight-binding energy band calculation for the IPSSL, we deduced that an In0.74Ga0.26As/In0.26Ga0.74As IPSSL was actually grown. This reveals that an indium composition modulation Δxof about 0.48 was achieved, which is more than twice as large as that in in-plane superlattices using other material systems.
Effect of Plasma-Generated Hydrogen Radicals on the Growth of GaAs Using Trimethylgallium
Authors: Michio Sato Michio Sato
Published: October 2002

The effect of hydrogen radicals on the metalorganic chemical vapor deposition of GaAs was investigated by introducing radicals using a downstream-type plasma-cracking cell. The hydrogen radicals enhanced the decomposition of trimethylgallium at the substrate surface. The increase in the growth rates with increasing radical flux at low temperatures, where growth was kinetically-controlled, and the reduction in carbon concentrations in GaAs grown at high temperatures with the addition of radicals were observed.
Valence Band Modulation in InGaAs/InAlAs Superlattices with Tensilely Strained Wells Grown on InGaAs Quasi-Substrate on GaAs
Authors: Tominaga Kouji , Hosoda Makoto , Fujiwara Toshihide Watanabe
Published: October 2002

We have studied structural and optical properties of strained InGaAs/InAlAs superlattices grown on an InGaAs quasi-substrate on GaAs by X-ray diffraction measurement, photoluminescence and photocurrent spectroscopy. The measurements were performed for two sample groups: one was Wannier-Stark type superlattices (SLs) with thin barriers and the other was quantum confined Stark effect type SLs with relatively thick barriers. In each group, we have obtained ample evidence for modulation effects on the SLs' band structure by tensile strain, which is controlled by the lattice constant of the InGaAs quasi-substrate.
Ultra-Thin Fatigue-Free Bi4Ti3O12 Films for Nonvolatile Ferroelectric Memories
Authors: Kijima Takeshi , Satoh Sakiko , Hironori Matsunaga Hironori Matsunaga , Masayoshi Koba Masayoshi Koba
Published: October 2002

We have developed a new low temperature growth technique for Bi4Ti3O12 thin films using a MOCVD method in which an ultra-thin double buffer layer (5-nm thick Bi4Ti3O12/5-nm thick TiO2) is used to control the crystallization and fine grain structure. The 100-nm thick Bi4Ti3O12 thin films fabricated at 400°C showed an extremely smooth surface morphology and good electrical properties, namely, a large remanent polarization of P
r=11 µC/cm2, a coercive field of E
c=90 kV/cm and a low leakage current I
L=7×10-9 A/cm2 at 3 V. Moreover, we successfully fabricated 50-nm ultra thin Bi4Ti3O12 films with P
r=9 µC/cm2 and E
c=120 kV/cm at 3 V. For the first time, the fatigue free property, which is very important for nonvolatile ferroelectric memory (NVFRAM) applications, was confirmed up to 1×1012 switching cycles.
High-Sensitivity SOI MOS Photodetector with Self-Amplification
Authors: Hideaki Yamamoto Hideaki Yamamoto , Kenji Taniguchi Kenji Taniguchi , Chihiro Hamaguchi Chihiro Hamaguchi
Published: October 2002

A high-sensitivity silicon-on-insulator (SOI) metal-oxide-silicon (MOS) photodetector compatible with conventional silicon technology is proposed. Its operation principle is based on that of a lateral bipolar transistor in spite of an SOI MOS device structure. Photodetectors with narrow base width or short channel length have high current gain which is attributed to a self-biased effect under illumination. Current gain as high as 100 has been achieved for the device with a channel length of 1.0 µm. Measured intrinsic response time for optical pulses is 19 µs for the photodetector with a channel length of 0.7 µm.
A Novel Short-Cavity Laser with Deep-Grating Distributed Bragg Reflectors
Authors: Akihiro Matsutani Toshihiko Baba , Toshikazu Mukaihara Toshikazu Mukaihara , Fumio Koyama Fumio Koyama , Kenichi Iga Kenichi Iga
Published: October 2002

We have proposed a novel short-cavity laser with deep-grating distributed Bragg reflectors (DBRs). We monolithically fabricated a 0.98 µm InGaAs/AlGaAs device and 1.55 µm GaInAsP/InP device using electron beam lithography and a reactive ion beam etching technique. The lasing operation of both devices was achieved at room temperature. From a comparison of the threshold current from the experimental result with that from the theoretical result, the reflectivity of formed DBRs was estimated to be less than 30%. The theory also predicts that the ideal DBR exhibits a high reflectivity over 97% even with 3 periods of grating. It achieves lasing operation with a threshold current less than 100 µA using a cavity shorter than 10 µm. This high performance is realized by reducing the surface roughness and damage to etched sidewalls and improving the reflectivity of the DBR.
Thermal Budget for Fabricating a Dual Gate Deep-Submicron CMOS with Thin Pure Gate Oxide
Authors: Suzuki Kunihiro , Satoh Akira , Aoyama Takayuki , Namura Itaru , Inoue Fumihiko , Kataoka Yuji , Yoko Tada Yoko Tada , Toshihiro Sugii Toshihiro Sugii
Published: October 2002

We studied the diffusion of impurities in dual polysilicon gates, and found that this phenomenon can effectively be treated as diffusion from a constant concentration diffusion source for both p+ and n+ polysilicon gates. We derived a model for the critical time required to obtain a flat profile. We then clarified the thermal budget required for suppressing gate depletion and impurity penetration through a gate oxide. According to our study, the thermal budget for n-type metal-oxide-semiconductor-field-effect-transistor (MOSFET) is always wider than that for p-type MOSFET, and the budget for p-type MOSFET is wide enough for realizing a flat profile without impurity penetration using pure SiO2 if B is available instead of BF2.
Low-Temperature Chemical-Vapor-Deposition of Silicon-Nitride Film from Hexachloro-Disilane and Hydrazine
Authors: Yeh Wen-Chang , Ishihara Ryoichi , Shunsuke Morishita Shunsuke Morishita , Masakiyo Matsumura Masakiyo Matsumura
Published: October 2002

We have successfully deposited SiNx:H films at temperatures as low as 350°C by the chemical-vapor-deposition (CVD) method using hexachloro-disilane (Si2Cl6) and hydrazine (N2H4). The atomic ratio (N/Si) of the film deposited at 400°C was 1.26 with a total hydrogen content of about 30 at.%. The breakdown-field strength was 5.3 MV/cm at a leakage-current density of 1 µA/cm2, and the low-field resistivity was more than 1015 Ω·cm. Amorphous-silicon thin-film transistors equipped with this film as the gate dielectric showed clear transfer characteristics.
Structure and Effective Pair Potential of Liquid Silicon
Authors: Waseda Kazuhiko Omote
Published: October 2002

Liquid silicon has a particular structural feature characterized by a small hump on the higher wave vector side of the first peak in the structure factor. The effective pair potential of liquid silicon has been estimated from the experimental structure factor data using the modified hypernetted chain (MHNC) equation. The resultant pair potential shows the ledge-type feature in the repulsive core part, close to the first peak of the pair distribution function, as well as the long-range oscillatory behavior. This pair potential was also compared with the theoretical one calculated using the pseudopotential theory of metals and good agreement was found although there are differences in detail. The basic structural features including a small hump of the structure factor for liquid silicon can be reproduced by this calculated pair potential. In order to consider a possible origin of the characteristic small hump detected in the structure factor of liquid silicon, the calculations were also made using artificially modified pair potentials. The results suggest that the long-range oscillatory part of the pair potential plays a significant role in producing this particular structural feature of liquid silicon.
Fabrication and Electrical Characterization of Pt/(Ba,Sr)TiO3/Pt Capacitors for Ultralarge-Scale Integrated Dynamic Random Access Memory Applications
Authors: Park Soon Oh , Hwang Cheol Seong , Cho Hag-Ju , Kang Chang Suk , Kang Ho-Kyu , Sang In Lee Sang In Lee , Moon Yong Lee Moon Yong Lee
Published: October 2002

Pt/(Ba, Sr)TiO3/Pt capacitors are fabricated using DC and RF magnetron sputtering processes on thermally oxidized silicon wafers for ultralarge scale integrated dynamic random access memory (ULSI DRAM) applications. (Ba,Sr)TiO3 (BST) thin film deposited at 640°C to 20 nm thickness shows an equivalent SiO2 thickness (t
oxeq) of 0.35 nm and a leakage current density, measured at an applied voltage of 1.5 V, of about 100 nA/cm2. t
oxeq of the BST film and leakage current density are further decreased to 0.24 nm and 40 nA/cm2, respectively, by postannealing at 750°C after fabrication of the top electrode.
Characterization of Charged Traps near Si–SiO2 Interface in Photo-Induced Chemical Vapor Deposited SiO2 Film
Authors: Hideaki Yamamoto Hideaki Yamamoto , Shinya Iwasaki Shinya Iwasaki , Katsuhide Okumura Katsuhide Okumura , Takeshi Kanashima Takeshi Kanashima , Masanori Okuyama Masanori Okuyama , Yoshihiro Hamakawa Yoshihiro Hamakawa
Published: October 2002

Charged traps near the Si–SiO2 interface in a SiO2 film deposited by photo-induced chemical vapor deposition (photo-CVD) have been analyzed by the photo I–V method. In the as-deposited film, positively charged traps distribute in the region between 2 nm and 10 nm from the Si–SiO2 interface, and their density decreases monotonically with increasing depth. The density of traps in the region between 2 nm and 4 nm is decreased by annealing in N2 or O2, and that of traps in the region between 4 nm and 10 nm is decreased only by annealing in O2. Furthermore, the results of electron spin resonance (ESR) analysis suggest the possibility that the positively charged traps in the 2–4 nm region are related to the defects observed in ESR.
Low Dielectric Constant Fluorinated Oxide Films Prepared by Remote Plasma Chemical Vapor Deposition
Authors: Lee Seung Min , Park Min , Park Kyu Chang , Bark Jong Tae , Jin Jang Jin Jang
Published: October 2002

Low dielectric constant fluorinated oxide (SiOF) films were deposited using SiF4/SiH4/O2 mixtures by remote plasma chemical vapor deposition (RPCVD). The refractive index and relative dielectric constant decrease with increasing SiF4/SiH4 ratio. The fluorine content in the SiOF film observed by X-ray photoelectron spectroscopy increases with SiF4/SiH4 ratio. With increase of fluorine content in the SiOF film, the peak position of the Si-O stretching mode shifts to a higher wave number and the relative dielectric constant decreases. The SiOF film, deposited with SiF4/SiH4 mixture ([SiF4]/[SiH4]=40), exhibited an F content of 12 at.% and a relative dielectric constant of 3.38.
Enhanced Growth Mechanism in Lateral Solid-Phase Epitaxy of Si Films Simultaneously Doped with P and Ge Atoms
Authors: Oh Jeong-Hee , Kim Chul-Ju , Hiroshi Ishiwara Hiroshi Ishiwara
Published: October 2002

Lateral solid-phase epitaxy (LSPE) characteristics of Ge-and P-incorporated amorphous Si films deposited on SiO2/Si(100) structures have been investigated and a model for explaining the enhanced growth has been proposed. The growth rate is enhanced for the Ge concentration around 0.5 at.% and it is even further enhanced by simultaneous doping of Ge and P atoms. In order to investigate the origin of the enhanced growth, Ge atom profiles and stress distributions along the LSPE direction have been investigated using cross-sectional transmission electron microscopy (TEM), electron probe microanalysis (EPMA) and microprobe Raman spectrometry. A main cause of the enhanced growth was shown to be the residual stress in Ge-incorporated films. From this a model to explain the stress effect due to incorporation of Ge atoms has been derived, in which the critical thickness theory for pseudomorphic growth of SiGe alloy layers is taken into consideration.
Kinetic Study of Silicon Nitride Growth from Dichlorosilane and Ammonia
Authors: Ogata Tamotsu , Sorita Tetsuji , Kobayashi Kiyoteru , Matsui Yasuji , Horie Kazuo , Makoto Hirayama Makoto Hirayama
Published: October 2002

The model of silicon nitride film deposition in a batch furnace from dichlorosilane ( SiH2Cl2; DCS) and ammonia ( NH3) is presented. The gas-phase and surface reaction rates of DCS are estimated from thickness profiles along the gas stream direction, and surface reaction and DCS decomposition are found to be of Langmuir and Lindemann types, respectively. It means that at a normal deposition temperature ( ∼1000 K), some DCS molecules adsorb directly on the Si surface while others decompose into a more reactive intermediate, SiCl2. At higher temperatures, the reverse reaction of DCS decomposition and the subsequent reaction of SiCl2 with NH3 may play significant roles. Using the present reaction rates, we estimate the film thickness profiles across a 12-inch wafer.
Structure and Electric Properties of YBa2Cu3O7-δ/SrRuO3/PtSi on Si Substrate
Authors: Mitsuzuka Tsutomu , Jian-Guo Wen Jian-Guo Wen , Youichi Enomoto Youichi Enomoto
Published: October 2002

We have fabricated superconducting YBa2Cu3O7-δ thin films on a Si substrate with metallic buffer layers, SrRuO3/PtSi. The T
c
on is 90 K and the T
c
0 is 35 K. The interface shows electrical conductivity with contact resistance 3×102 Ω· cm2 at 293 K. Cross-sectional transmission electron microscopy and Auger electron depth profile show that YBa2Cu3O7-δ is protected from reaction with Si. However, SrRuO3 reacts with PtSi and forms an amorphous layer which has high resistance. The SrRuO3 and YBa2Cu3O7-δ are polycrystalline.
Effects of Texturing and Microbridge Length on the IR Responsivity of YBa2Cu3Ox Thin Film
Authors: Bae Sung Joon , Hong Seungbum , Kim Eunah , Shin Woosuck , Cho Chang Hyun , Kim Young Kun , Bea Youn Soo , Sung Tae-Hyun , Kwangsoo No Kwangsoo No
Published: October 2002

YBa2Cu3O

x

(YBCO) superconducting thin films were deposited on MgO(100) single-crystal substrates using the metalorganic chemical vapor deposition (MOCVD) method. The microstructure of the YBCO film was controlled by varying the deposition temperature and pressure. Different shapes and numbers of weak links were observed depending on the microstructure. Bridge-type Josephson junctions of natural grain boundaries were fabricated using photolithography and chemical etching for infrared detection. Effects of the microstructure and microbridge patterns on the IR responsivity of the YBCO thin films were investigated and discussed.
Laser Polarization Effect on Adiabatic Inversion of Degenerate Two-Level System
Authors: Hideaki Niki Hideaki Niki , Iwao Kitazima Iwao Kitazima
Published: October 2002

Coherent excitation dynamics of a degenerate two-level system by a frequency-swept laser were analyzed by solving the optical Bloch equations. Physical parameters (Rabi frequency, laser frequency sweep rate and laser frequency sweep width or pulse width) giving a high excitation efficiency were obtained. Laser polarization also affects the excitation efficiency because the variation of dipole matrix elements depends on the laser polarization and ΔJ, the difference between the J values of the upper and lower levels. It was found that circular polarization is preferable when ΔJ=0 and linear polarization is preferable when ΔJ=±1. This polarization effect was qualitatively analyzed.
Rewritable Near-Field Optical Recording on Photochromic Thin Films
Authors: Mitsuo Hamano Mitsuo Hamano , Masahiro Irie Masahiro Irie
Published: October 2002

Rewritable photon-mode near-field optical recording by the use of an ultra-small light source (diameter ∼100 nm) was performed. Bis(2-methylbenzo[b]thiophen-3-yl)perfluorocyclopentene dispersed in polystyrene and amorphous bis(2,4-dimethyl-5-phenylthiophen-3-yl)perfluorocyclopentene films were used as the recording media. Marks 100 nm in width were recorded on the media by irradiation with 529 nm light, and erased by irradiation with UV light ( 300 nm<λ<400 nm).
Grating Optical Low-Pass Filter
Authors: Fujisawa Katsuya , Nishida Masao Uetsuki
Published: October 2002

The spurious signals appearing in the picture image from a charge-coupled semiconductor device (CCD) camera were removed by means of a novel grating optical low-pass filter (GOLF). By placing the GOLF near the imaging plane of the CCD and adjusting the effective grating period projected onto the imaging plane with respect to the array period, or its integral multiplicative inverse of the picture elements formed in the imaging plane, it was verified that the GOLF eliminated the grating image superimposed on the picture image, which had been a long-standing problem. Photochemical reaction was useful for forming a sinusoidal grating crosssection which increased the MTF value in the region of low spatial frequencies to realize a clear-cut picture image. The GOLF fabricated in the form of a thin plate was promising to realize a new CCD with a built-in optical low-pass filter applicable for downsizing of camera optics.
Improvement of Dark Current Density of AlInAs/InGaAs Metal-Semiconductor-Metal Photodetector Using Phosphine-Plasma-Treated Schottky Barrier
Authors: Daiji Hirata Daiji Hirata , Takashi Sugino Takashi Sugino , Junji Shirafuji Junji Shirafuji
Published: October 2002

AlInAs/InGaAs metal-semiconductor-metal (MSM) photodetectors with a low dark current density are fabricated using a surface modification process with phosphine (PH3) plasma. Phosphidization of the AlInAs cap layer reduces the surface state density and allows formation of high Schottky barrier with a tunnel metal-insulator-semiconductor (MIS) structure. A dark current density as low as 0.021 pA/µm2 at 10 V is obtained.
Electronic States in Edge Quantum Wires on GaAs/AlGaAs Facet Structures
Authors: Yamauchi Miyuki , Nakamura Yusui , Kadoya Yutaka , Sugawara Hiroharu , Sakaki Hiroyuki
Published: October 2002

Quantum states of electrons confined in edge quantum wire structures are theoretically investigated, for the case in which wires are prepared on tilted facet planes of GaAs/AlGaAs quantum well structures. We show that the one-dimensional electron gas has an asymmetric spatial distribution with more electrons accumulating in the top part of the wire than at the bottom. This feature results from asymmetries in both the wire geometry and the distribution of ionized donors in n-AlGaAs. We have also studied how electronic states of the wire depend on structural parameters, such as the spacing of adjacent wires and the tilt angle of facet planes. Energy levels calculated for a 80-nm wire are found to be almost evenly spaced in agreement with the results of our magnetic depopulation experiments.
Correlation between Negative Hydrogen Ion Production and Work Function of Plasma Grid Surface in a Cesium-Introduced Volume-Production-Type Negative Hydrogen Ion Source
Authors: Okumura Katsuhiro Shinto , Toshimitsu Ando Toshimitsu Ando , Motoi Wada Motoi Wada , Hiroshi Tsuda Hiroshi Tsuda , Takashi Inoue Takashi Inoue , Kenji Miyamoto Kenji Miyamoto , Akihito Nagase Akihito Nagase
Published: October 2002

The correlation between the work function of a plasma grid surface in a Cs-introduced volume-production-type negative hydrogen ion ( H-) source and the extracted H- current has been investigated experimentally. The quantum efficiency of a Cs/Mo surface has been measured as a function of the photon energy in a high-vacuum test chamber, and a relationship between the photoelectric work function and the quantum efficiencies at the wavelengths of an Ar+ laser has been obtained. Using this relationship, the work function of the plasma grid surface has been determined by measuring quantum efficiency using an Ar+ laser. When the increment of the H- current is plotted against the measured work function, an exponential dependence on the decrease of the work function is observed. The experimental result cannot be explained by a theoretical H- formation model when one assumes that H- are produced from H atoms leaving from the surface with the energy corresponding to the temperature of H atoms in the plasma. When H- are produced with the kinetic energy substantially larger than thermal energy, the theoretical result shows good agreement with the experimental result.
Velocity, Pressure and Temperature Measurement in Low-Pressure Supersonic Flow
Authors: Takao Tsuboi Takao Tsuboi , Kazuhiro Ishii Kazuhiro Ishii , Yasufumi Mochizuki Yasufumi Mochizuki
Published: October 2002

In order to determine the thermodynamic conditions in supersonic flow, we measured the flow velocity, Mach number, density and temperature, as well as the pressure of unsteady flow in a submillisecond interval. In the cold model the time-dependent gas temperature could be measured at low temperatures in the supercooled condition below 100 K and at low pressures below 1000 Pa using the laser light absorption technique. The measured gas temperature was about 50–70 K, which coincided with the designed temperature range. In the hot model we observed the combustion of liquid spray in the supersonic flow.
Nitrogen Incorporation in a-Ge:H Produced in High-Hydrogen-Dilution Plasma
Authors: Xu Jun , Seiichi Miyazaki Seiichi Miyazaki , Masataka Hirose Masataka Hirose
Published: October 2002

The network of hydrogenated amorphous germanium (a-Ge:H) has been modified with nitrogen by employing the rf glow discharge decomposition of a hydrogen-diluted gas mixture of NH3 and GeH4. It is found that the hydrogen dilution of the material gas hinders the incorporation of three-fold coordinated nitrogen atoms in the network and causes optical bandgap shrinkage. Dramatic enhancement of the conductivity and decrease of the activation energy are observed in the high-hydrogen-dilution regime, and are explained by the incorporation of four-fold coordinated nitrogen in the relaxed network.
Effect of Fermi Level Motion on the Optical, ESR and Transport Properties of CuInSe2
Authors: Katsuaki Sato Katsuaki Sato , Nobuyuki Nishikawa Nobuyuki Nishikawa , Igor Aksenov Igor Aksenov , Takeshi Shinzato Takeshi Shinzato , Hisayuki Nakanishi Hisayuki Nakanishi
Published: October 2002

The infrared (IR) absorption and ESR spectra of the CuInSe2 crystals, grown by the normal freezing technique and subsequently annealed in various atmospheres, have been studied in connection with the annealing-induced motion of the Fermi level relative to the energy band edges. The degenerate n-type crystals exhibited a free-electron absorption, while the p-type crystals showed both an inter-valence-band and a free-hole absorption, from the analysis of which the energy positions of the Fermi level have been evaluated, and the electrical parameters of the respective crystals estimated; these results were then compared with the experimental results. In the ESR spectra the signals from iron residual impurity in both divalent and trivalent charged states, as well as the signals arising from native defects V Cu and In Cu, have been detected, the intensities of the ESR signals being dependent on the composition of the samples and the Fermi level position.
Characterization of Interfaces of Directly Bonded Silicon Wafers: A Comparative Study of Secondary Ion Mass Spectroscopy Multiple Internal Reflection Spectroscopy, and Transmission Electron Microscopy
Authors: Reiche Manfred , Hopfe Sigrid , Gösele Ullrich , Strutzberg Hartmut , Tong Qin-Yi
Published: October 2002

The structure and chemistry of interfaces of directly bonded Si/Si wafer pairs after annealing at 1100°C were investigated by secondary ion mass spectroscopy (SIMS), multiple internal reflection spectroscopy (MIRS), and high resolution electron microscopy (HRTEM). Si–O, SiO–H, and Si–H
x
bonds are shown to be the main atomic bonds at the interfaces of bonded hydrophilic wafer pairs, whereas Si–Si and Si–H
x
bonds are dominant at interfaces of bonded hydrophobic wafer pairs. For bonded hydrophobic wafer pairs a frequency shift of the Si–H
x
modes suggest that fluorine is probably present in Si–F···H–Si configurations. Strongly oriented SiO–H modes detected in bonded hydrophobic wafer pairs appear to be related to oxide islands at the interface.
Occurrence of Metallic Bismuth and Superconductivity in Bi 2Sr 2CaCu 2Oy Crystals Irradiated by N+ Ions
Authors: Wang Liangbin , Wu Wenbin , Li Xiao-Guang , Liu Xianming , Zhu Jingsheng , Shi Lei , Jia Yunbo , Zhou Guien , Zhang Yuheng
Published: October 2002

X-ray photoemission spectroscopy and X-ray diffraction reveal that N+ ion irradiation causes the occurrence of the metallic bismuth and the surface decomposition in Bi2Sr2CaCu2O
y
crystals. We think that such change results in the change of oxygen content. Due to this fact, a possible reason for the decrease of the superconducting transition temperature is suggested as the change of oxygen content.
Thermally Stimulated Luminescence of X-ray Irradiated Sodium Borate Glasses Doped with Cerium(III) and Samarium(III)
Authors: Tanaka Katsuhisa , Hirao Kazuyuki , Tanaka Hideki , Soga Naohiro
Published: October 2002

Thermally stimulated luminescence has been observed in X-ray irradiated sodium borate glasses codoped with Ce3+ and Sm3+. The emission wavelength corresponds to the 5d→4f transition of Ce3+. X-ray irradiation leads to the ionization of Ce3+ to form Ce4+ and an electron, which is released from the Ce4+ and trapped by Sm3+. Thermal stimulation excites this electron, which transfers to the 5d level of Ce4+. The radiative relaxation of this electron to the 4f state gives rise to the observed emission. In contrast, point defects such as a non-bridging oxygen hole center and an electron trapped near Na+ induced by the X-ray irradiation contribute to the thermally stimulated luminescence in glasses doped with only Ce3+. The thermally stimulated emission intensity increases linearly with an increase in the X-ray irradiation time up to 1 h for 25Na2O· 75B2O3: Ce, Sm glass, suggesting that this glass is a promising material for radiation dosimetry.
Effect of Molecular Orbital Distributions on Charge Transport Properties of Polymers Doped with Triphenylamine Derivatives
Authors: Aratani Sukekazu , Kawanishi Tsuneaki , Kakuta Atsushi
Published: October 2002

The hole drift mobilities of polymers doped with triphenylamine derivatives including heterocyclic groups have been measured and the effect of molecular orbital distributions of triphenylamine derivatives on the charge transport properties has been studied. The temperature dependence of the mobilities of polymers doped with two kinds of triphenylamine derivatives has been analyzed using the disorder formalism presented by Bässler and co-workers[H. Bässler, Phys. Status Solidi B 175(1993) 15.] and it has been found that highest occupied molecular orbital (HOMO) distribution of the triphenylamine derivatives has little effect on the diagonal and off-diagonal disorder but has a large effect on the disorder-free mobility in this formalism.
Electrode Dependences of Switching Endurance Properties of Lead-Zirconate-Titanate Thin-Film Capacitors
Authors: Aoki Katsuhiro , Fukuda Yukio , Ken Numata Ken Numata , Akitoshi Nishimura Akitoshi Nishimura
Published: October 2002

Switching endurance properties of lead-zirconate-titanate thin-film capacitors with gold, platinum and iridium top electrodes were investigated using a pulse switching characterization technique. Lead-zirconate-titanate capacitor structure formed with Ir top and bottom electrodes exhibited superior switching endurance to Au/PZT/Ir and Pt/PZT/Ir capacitors. The difference between switched and nonswitched polarizations of an Ir/PZT/Ir capacitor reversed by bipolar pulses was more than 38 µ C/ cm2 after 2×109 switching cycles. Nonswitched polarization of this capacitor for negative read-pulses decreased gradually with increase in the number of switching cycles. When positive and negative unipolar pulses, and DC biases were applied to the top electrodes of Pt/PZT/Ir and Ir/PZT/Ir capacitors, remanent polarizations of each capacitor were not changed significantly. However, nonswitched polarizations for negative read-pulses decreased with increase in the number of negative unipolar pulses applied or DC bias application time. Drastic decrease in remanent polarization of a Pt/PZT/Ir capacitor was caused only by bipolar pulse application. The reduction of nonswitched polarization for negative read-pulses suggested the formation of depletion-layer capacitances at the interfaces between top electrodes and PZT layers.
Electronic Polarization in Mixed Alkali Silicate Glasses: A Molecular Dynamics Study
Authors: Matsumoto Hiroshige , Yuzo Shigesato Yuzo Shigesato , Itaru Yasui Itaru Yasui
Published: October 2002

Molecular dynamics simulation involving electronic polarization was performed for lithium-potassium single and mixed disilicate glasses. Inductive potential was used as well as pairwise additive potential. Oxygen was found to have a large energy of polarization. Total potential energy showed negative deviation from additivity.
Characterization of a DC Arcjet Plasma for Diamond Growth by Measurement of Spatial Distributions of Optical Emission
Authors: Yamaguchi Hiromi , Ishii Masahiro , Kazuo Uematsu Kazuo Uematsu , Shinji Morimoto Shinji Morimoto
Published: October 2002

A DC arcjet plasma for diamond growth was characterized by the in-situ measurement of spatial distributions of the optical emission from atomic hydrogen, C2, CH and Ar. For H and C2 radicals, the distributions of the emission in front of a substrate were found to correlate well with the profiles of the diamond film thickness and the film morphology with the change in background pressure and substrate position. The deposition conditions under which H emission was suppressed and C2 emission was enhanced promoted diamond growth. The profiles of the diamond film thickness could be predicted from the radial distributions of H and C2 emission in front of the substrate.
Slow Surface-Wave Propagation in Partially Filled Coaxial Solid-Plasma Waveguide in r-Dependent Azimuthal Magnetic Field
Authors: Tetsuo Obunai Tetsuo Obunai
Published: October 2002

Propagation characteristics of 70 GHz slow surface waves in a partially filled coaxial solid-plasma waveguide in an r-dependent azimuthal magnetic field have been theoretically analyzed. Results of numerical analyses reveal that the nonuniformity of the magnetic field exerts no essential effect on the existence of the slow surface-wave resonance, but that the magnetic field required for the propagation of the slow wave is considerably reduced.
Formation of van der Waals Tryptophan Clusters in Seeded Beam Expansion
Authors: Tatsuo Arikawa Tatsuo Arikawa , Hisayuki Yazawa Hisayuki Yazawa
Published: October 2002

Stable van der Waals clusters of tryptophan molecules, (Trp)
n
, of up to n=5, were produced in a seeded supersonic beam expansion from a laser desorption nozzle source. Translational beam temperatures of van der Waals tryptophan clusters were measured using a fast optical imaging device. Estimated beam temperatures in carrier argon gas were 27 K for tryptophan dimers (n=2) and 41 K for tryptophan trimers (n=3). A preliminary experiment showed that no significant difference was observed in the yield of van der Waals clusters for L-, D- and racemic-tryptophan molecules.
A New Fabrication Method for Ultra Small Tunnel Junctions
Authors: Ono Keiji , Shimada Hiroshi , Kobayashi Shun-ichi , Youiti Ootuka Youiti Ootuka
Published: October 2002

We have developed a new method for fabrication of microstructures. Using a Si3N4 membrane with small windows as a mask, a metal film with fine structure is vacuum deposited directly onto a substrate. By means of piezoelectric actuators which slide the mask on the substrate, we have fabricated an array of Al/AlO

x

/Al small tunnel junctions. This method has the important advantage that the lift-off process after vacuum deposition is not necessary. The use of rf plasma oxidation to form the tunnel barrier is another advantage of this method. We have fabricated a Ni/NiO/Fe small junction array with a junction area of 0.01 µ m2 using plasma oxidation and double-angle evaporation.
Influence of Poly-Si Potential on Profile Distortion Caused by Charge Accumulation
Authors: Ogino Satoshi , Fujiwara Nobuo , Hiroshi Miyatake Hiroshi Miyatake , Masahiro Yoneda Masahiro Yoneda
Published: October 2002

The appearance of local side etch in polysilicon etching was investigated using a pattern of lines and spaces (L&S) with spaces of various widths. The local side etch is found to appear at lines connected to the silicon substrate even when there is no exposed area of the silicon substrate. It is also found that the degree of local side etch decreases as the area of exposed silicon substrate increases. From these results, it is considered that the cause of the local side etch is the electron supplied from the silicon substrate to polysilicon through the connection, where the source of electrons is, electron irradiation at the sidewall of the lines which have connection and are facing to the wide spaces. The results also show that the electric potential of the silicon substrate in the case when there is no exposed area is lower than the potential of the exposed area of the silicon substrate.
SiO2 Etching in C4F8/O2 Electron Cyclotron Resonance Plasma
Authors: Siozawa Ken-itiro , Tabaru Kenji , Maruyama Takahiro , Nobuo Fujiwara Nobuo Fujiwara , Masahiro Yoneda Masahiro Yoneda
Published: October 2002

We report the application of C4F8/O2 electron cyclotron resonance (ECR) plasma to SiO2 etching. The effect on SiO2 etching characteristics of O2 addition to C4F8 ECR plasma is investigated. In C4F8 ECR plasma (no O2 addition), strong reactive ion etching (RIE) lag effect of SiO2 and poly-Si etching is observed. However, with O2 addition, the RIE lag effect of SiO2 etching decreases markedly whereas the RIE lag effect of poly-Si etching decreases gradually. Consequently, SiO2 etching selectivity to poly-Si increases. The results of mass spectrometric measurement using two orifices indicate that surface reaction probability of fluorocarbon molecules is affected by O2 addition.
Molecular Beam Epitaxial Growth of In0.15Ga0.85As Quantum Wells on (110) GaAs Surfaces
Authors: Takao Someya Takao Someya , Hidefumi Akiyama Hidefumi Akiyama , Hiroyuki Sakaki Hiroyuki Sakaki
Published: October 2002

We report on molecular beam epitaxial (MBE) growth of high-quality In0.15Ga0.85As quantum wells (QWs) on (110) GaAs surfaces. The (110) surfaces are prepared by cleaving (001) GaAs substrates in air. The optimized growth condition is searched by changing the substrate temperature for the growth of In0.15Ga0.85As layers. We have found that the substrate temperature around 430°C is crucial to obtain the good surface morphology without facet structures and the sharp PL peak of an In0.15Ga0.85As QW.
Inelastic Neutron Scattering Studies on the Amorphous and Nanocrystalline Fe76Cu1Nb3Si14B6
Authors: Kepa Seong-Cho Yu , A. Graf Won-Tae Kim
Published: October 2002

Inelastic neutron scattering measurement has been used to study the temperature and wave-vector dependence of the spin wave excitation in the amorphous and nanocrystalline state of ferromagnetic Fe76Cu1Nb3Si14B6 alloy. For the amorphous alloy the spin waves were observed over the accessible wave-vector range of 0.055 Å-1 ≤q ≤0.105 Å-1, for temperature between 300 K (0.49 T
c) and 547 K (0.90 T
c). The magnon dispersion curves exhibit the conventional quadratic relationship E = D(T)q
2 + Δ, typical of an isotropic ferromagnet, where the small energy gap Δ≈0.05 meV is attributed primarily to the dipole-dipole interaction. An estimate of the T = 0 value of D(0) ≈153 meV Å2 was obtained from a plot of D(T) vs T extrapolated to low temperatures, while the Curie temperature of 610 K was obtained from the extrapolation of D(T) to zero at high temperatures. There is the increase of the spin wave stiffness constant D with the transformation of the alloy from amorphous to nanocrystalline state.
Construction of a 100-Hz-Repetition-Rate 28-Channel Thomson Scattering System for the JIPPT-IIU Tokamak
Authors: Narihara Kazumichi , Yamauchi Kenji , Minami Takashi , Yamada Ichihiro , Sato Kohnosuke , Kawahata Kazuo , Hamada Yasuji , Mamoru Kojima Mamoru Kojima , Satoru Hirokura Satoru Hirokura
Published: October 2002

An ASDEX-type Thomson scattering system (YAG Thomson) with an improved performance (100 Hz repetition rate and 1.5 cm spatial resolution) was designed and constructed for the JIPPT-IIU tokamak. Efforts were concentrated on realizing a large solid angle of collection optics (0.08 sr), high throughput of polychromators ( >64%) and high quantum efficiency of detectors (80% at 900 nm), which, together, yield high-quality data even with a small laser energy (0.4 J) delivered by a 100-Hz-repetition-rate Nd:YAG laser and with a short scattering length (1.0 cm). The compactness of the polychromators also contributes to achieving a high spatial resolution.
Gain Characteristics of Optical-Gate Switches Using InGaAs/GaAs Strained-Layer Quantum Wells
Authors: Tatsuya Takeshita Tatsuya Takeshita , Satoshi Oku Satoshi Oku
Published: October 2002

Gain characteristics in single, double and triple InGaAs/GaAs strained-layer quantum-well structures have been measured in a wide wavelength range, and an optical-gate switch with the 0.9 µ m wavelength band has been examined for use in an integrated device with low driving current operation. Gate switches are classified into two types: small-gain switches and large-gain switches. A switch with 0 dB gain is produced by reducing the active layer volume through the use of a single quantum-well structure with 1.8 mA driving current. A large-gain switch with 15 dB gain under a no-gain-saturation condition is achieved using a large optical confinement structure: a triple quantum-well structure with 10 mA driving current. The driving current dependence of the gain spectrum for the single, double, and triple quantum-well gate switches shows that carrier injection to the second quantized state plays an important role in the saturation of the increase in gain when the driving current is increased.
Effects of Dichroic Dye in UV-Cured Polymer Dispersed Liquid Crystal Films
Authors: Wu Jin-Jei , Wang Chih-Ming , Chen Shu-Hsia
Published: October 2002

We study the effects of dichroic dye in “ultraviolet” polymer dispersed liquid crystal (PDLC) films. Experimental data show that for a dye-doped PDLC film the absorption coefficient for He-Ne laser light is different from that for UV light. Transmittance of a PDLC film changes when the UV curing intensity or dye concentration is varied. It is found that under UV the illumination with a constant intensity the dye concentration can be optimized to obtain minimum transmittance and to improve the contrast ratio. Correspondingly, for a fixed dye concentration the UV curing intensity can be optimized to obtain a minimum transmittance. The experimental results can be described by a theory based on Beer's law. Besides, the experimental results show that the curing temperature is an important factor that affects the nematic liquid crystal droplet size in the UV curing process.
Long Term Operation of a CW Doubly Resonant Optical Parametric Oscillator
Authors: Takeshi Ikegami Takeshi Ikegami , Sergey Slyusarev Sergey Slyusarev , Shin-ichi Ohshima Shin-ichi Ohshima , Eiichi Sakuma Eiichi Sakuma
Published: October 2002

Long-term operation of a cw doubly resonant optical parametric oscillator was demonstrated. The minimum threshold was 9mW and the slope efficiency was 25%. Using a rigid structure cavity and a stable pump laser, it operated in a single longitudinal signal-idler mode pair for over 3 h without any mode hopping.
Pyroelectric Properties of Sol-Gel Derived Lanthanum Modified Lead Titanate Thin Films
Authors: No Kwangsoo , Choi Chaun Gi , Yoon Dae Sung , Sung Tae-Hyun , Kim Yong Chun , Jeong In Seop , Won Jong Lee Won Jong Lee
Published: October 2002

Lanthanum-modified lead titanate (PLT) thin films were fabricated on Pt/Ti/SiO2/Si substrate using the sol-gel method and rapid thermal annealing technique. The pyroelectric coefficient, and the infrared responsivity and the detectivity of the films were measured using static and dynamic methods, respectively. The ferroelectric properties were also measured. The pyroelectric coefficient increased from 1.3 to 2.5 nC/cm2· K with increasing La content. However, these low coefficients of PLT films are due to their crystal quality and orientations. The infrared response properties of PLT films depended on their thermal time constants. τ t (thermal time constant) for the PLT films decreased with the La contents increasing. The effects of back surface etching on the responsivity and the detectivity were also discussed.
Determination of Sign of Surface Charges of Ferroelectric TGS Using Electrostatic Force Microscope Combined with the Voltage Modulation Technique
Authors: Ohgami Junji , Sugawara Yasuhiro , Morita Seizo , Nakamura Eiji , Ozaki Tōru
Published: October 2002

The sign of surface charges and the surface topography around a domain wall on a cleaved (010) surface of ferroelectric TGS [ (NH2CH2COOH)3·H2SO4] were studied in air at room temperature. Using an electrostatic force microscope (EFM) combined with the voltage modulation technique, we determined the location of the domain wall and the sign of the surface charges around it. At the domain wall, we found a ridge structure with a large peak in the spatial distribution of a feedback signal used to keep the amplitude of the 2ω component of electric force constant. This means that the dielectric constant has a large peak value at the domain wall. Furthermore, in an atomic force microscope (AFM) image in a contact mode, we observed a small step 2–3 Å high at the center of the domain wall.
Atomic Layer Epitaxy of ZnS by Low-Pressure Horizontal Metalorganic Chemical Vapor Deposition
Authors: Liu Chun Hsing , Yokoyama Meiso , Yan Kuin Su Yan Kuin Su , Nien Chung Lee Nien Chung Lee
Published: October 2002

The self-limiting growth in atomic layer epitaxy (ALE) of ZnS on (100)-GaAs substrate was investigated using a horizontal low-pressure metalorganic chemical vapor deposition (MOCVD) system. The growth rate per cycle was kept constant at one monolayer, independent of the substrate temperature which was in the range of 125° C to 200° C. Under optimal growth conditions, ZnS layers grown in the ALE mode showed good surface morphology. Photoluminescence (PL) showed three peaks; a near-band-edge emission at 349 nm, a self-activated emission at 434 nm and a broad one at around 500 and 600 nm, which is considered to be due to relaxation through dislocation formation.