bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Characterization of Low Nitrogen Content Plasma Deposited and Rapid Thermal Annealed Al/SiNx:H/InP Metal-Insulator-Semiconductor Structures
Authors: Castán Helena , Dueñas Salvador , Barbolla Juan , Redondo Estefanía , Mártil Ignacio , González-Díaz Germán
Published: October 2002

The influence of the dielectric composition and post deposition rapid thermal annealing (RTA) treatments on the electrical characteristics of low nitrogen content plasma-deposited Al/SiN
x
:H/InP structures were analyzed. To obtain the interface state density, deep level transient spectroscopy (DLTS) measurements were carried out. We have also evaluated the insulator damage density, the so-called disorder-induced gap states (DIGS), by means of conductance transient analysis. As for the dielectric composition, both the x=0.97 and x=1.43 values provide interfacial state density and DIGS damage values of the same order of magnitude. In the x=0.97 case, RTA treatments reduce the insulator damage moving it towards the interface. In the x=1.43 case this behavior is only observed for RTA temperatures lower than 500°C. So, moderate temperature (<500°C) RTA treatments improve DIGS damage. This is an important result in terms of fabricating bi-layered metal-insulator-semiconductor (MIS) structures that not only have good-quality interfaces, but also good dielectric properties.
Daytime Monitoring of Urban NO2 Column Density by Solar Spectroscopic Method
Authors: Xue Yanqun , Niu Jianguo , Liu Wenqing , Kuze Hiroaki , Takeuchi Nobuo
Published: October 2002

We describe the monitoring of the column density of NO2 using an automated
apparatus equipped with a sun-tracker, an optical fiber, and a monochromator with a
charge-coupled device array. In order to extract a small absorption from the observed
spectra, we introduce a new algorithm in which a spectrum obtained with the same
instrument is employed as a reference. This leads to a better elimination of the noise
due to large Fraunhofer lines in the solar spectrum in a wavelength range of 430–450 nm.
By means of careful spectral matching between the NO2 cross section and the
optical thickness derived from the observation, a sensitivity for NO2
column density as low as 1×1019 molecules/m2 is attained.
The Change of Magnetoresistance Peaks According to the Direction of Sample Relative to the Magnetic Field
Authors: Rhee Ilsu , Kim Chan
Published: October 2002

The change of magnetoresistance (MR) peaks according to the direction of the film sample relative to the magnetic field has been investigated for various angle configurations of the sample relative to the field. When the sample is in the same plane as that of the magnetic flux, the MR peaks are found to change their shapes, as the sample is rotated through an axis perpendicular to the sample surface, and finally to show their minima at the rotation angle of 45°. However, if the sample is inclined relative to the field, the MR peaks show their minima at a rotation angle higher than 45°. This behavior can be explained by the mixing of the negative MR (NMR) and positive MR (PMR) signals in MR. Furthermore, we also observe the increase of the magnetic field difference between two MR peaks (FDMP) as a function of the rotation angle, φ, for the angle configuration of the sample perpendicular to the field. This increase in FDMP is fitted well as a function of 1/cos
φ, which is well explained by the concept of the effective magnetic field.
Radical Formation in Lithium and Magnesium Oxalate
Authors: Hassan Gamal M. , Ulusoy Ulku , Ikeya Motoji
Published: October 2002

Lithium oxalate (Li-oxalate: Li2C2O4) and magnesium oxalate (Mg-oxalate: MgC2O4·2H2O) were investigated by electron spin resonance (ESR) spectroscopy as new ESR dosimeter materials. The ESR spectra of Li- and Mg-oxalates irradiated by γ-rays have a singlet with a spectroscopic splitting factor (g-factor) of g=2.0043±0.0004 and are ascribed to a self-trapped hole, the oxalate radical C2O4
-. A broad signal formed by high dose irradiation is considered to be due to the zero field fine structure splitting, D
S
2 (D/gβ\cong0.65 mT) for the triplet state (S=1) of a dimer of C2O4
- or a pair of electron and hole centers. The response to the γ-ray dose and thermal stability as well as the effect of illumination have been studied with respect to using these materials as ESR dosimeter elements. The radical formation efficiencies (G-value) for Li- and Mg-oxalates were 0.4±0.1 and 0.21±0.06 and the activation energies (E) from the Arrhenius plot were 1.16±0.24 eV and 1.28±0.26 eV, respectively. These lead to the respective lifetimes of 2.6±0.9 and 3.2±1.1 years at 25°C, which are sufficient for practical dosimetry.
Analysis of Generation Mechanism of Photon-Number Squeezed Light Using Ultrashort Pulse and Asymmetric Fiber Loop Mirror
Authors: Junichi Higuchi Junichi Higuchi , Norihiko Nishizawa Norihiko Nishizawa , Masakazu Mori Masakazu Mori , Kazuo Yamane Kazuo Yamane , Toshio Goto Toshio Goto
Published: October 2002

We analyze numerically the generation of photon-number squeezed light using an asymmetric fiber loop mirror. For photon-number squeezed light generation, the maximum squeezing can be obtained using this method. The evolution of the quantum noise for the optical pulse spectra is calculated using the quantized nonlinear Schrödinger equation and linearization approximation. It is shown that the squeezed light is generated by removing the increased quantum noise part of the spectrum and enhancing the decreased quantum noise part of the spectrum, by the interference of two pulses at the beam splitter. Although the mechanism of squeezing is similar to that of a spectral filter, the maximum squeezing is as large as -13 dB due to the interference.
Theory of Optical Amplification with Plasma in Waveguide Structures
Authors: Mizushima Yoshihiko
Published: October 2002

A novel theory of an optical amplifier device is proposed utilizing plasma resonance carried by electrons. The interaction between photons and drifting plasmons is based on a space-charge wave with longitudinal electric field components within a waveguide structure. By solving the wave equations under the waveguide constraint, it is found that within the original cutoff range, an amplifying mode appears. The operating wavelength range is the infrared one, from submillimeter to micrometer waves. Some accompanying considerations are shown for a practical realization of the devices. The present theory of the plasma interaction under a constraint is extended to various waveguide structures. Some examples of optical interconnections on LSI utilizing dielectric waveguides, including photonic bandgap devices, are described. The physical concept of this effect on the constrained plasma wave transmission is discussed from the viewpoint of the eigenvalue problem.
Display Modes in Time-Resolved Terahertz Imaging
Authors: Herrmann Michael , Tani Masahiko , Sakai Kiyomi
Published: October 2002

We have constructed a terahertz (THz) imaging system based on a conventional pump-and-probe setup. With a time-delay line in the probe beam we can record time-resolved THz waveforms at every image position. The resulting time-indexed set of images (the `THz movie') can be mapped to two-dimensional images with `display modes'. Several of these `display modes' are closely related to sample absorption and refraction, others are designed for very specific purposes such as gas detection. Some of the modes map specific features of the THz pulse without particular purpose, yet they prove to be useful in investigating features of THz images. Examples are provided.
Nano-scale Morphology and Crystallography of Laser-Deposited TiN Thin Films
Authors: Wang Hai-Dan , Lu Yong-Feng , Mai Zhi-Hong , Ren Zhong-Min
Published: October 2002

Titanium nitride (TiN) thin films were deposited on hydrogen-terminated silicon (100) substrates by pulsed laser ablation of a ceramic TiN target (purity: 99.9%). The crystallography and properties of the thin films are related to the substrate temperature. In the investigation, scanning tunneling microscopy (STM), X-ray diffraction (XRD) and nanoindentation were used. Nano-scale morphology of the thin films deposited at 600°C was observed by STM using a platinum tip. The STM image showed that the TiN embryos have a uniform size of approximately 17 nm and grow into large clusters. The films grown at 600°C have a full-width at half maximum of the TiN (200) peak in the XRD spectrum close to 0.50°. The hardness of the thin films deposited at 600°C was as high as 26 GPa.
Diagnostics of KrF- and Nd:YAG-Laser Produced Carbon Plumes by Time- and Spatially-Resolved Spectroscopy
Authors: Shinozaki Tatsuya , Ooie Toshihiko , Yano Tetsuo , Yoneda Masafumi
Published: October 2002

Graphite was ablated by three lasers and the resultant carbon plumes were investigated by time- and spatially-resolved spectroscopy. A KrF excimer laser (248 nm) and an Nd:YAG laser (1064 and 266 nm) were used. Near the target surface, C2 (Swan band) and ionic emissions from the plume produced by the 1064-nm laser at a fluence of 6 J/cm2 were stronger than those produced by the 248-nm and 266-nm lasers. The C emission lines (247.9 and 193.1 nm) produced by the KrF excimer laser were stronger than those produced by the other lasers. The most probable velocity of C+ was highly dependent upon the laser wavelength. The dependence of the most probable velocity on the fluence was small. The velocity of C+ ablated by the 248-nm laser was twice as fast as that ablated by the 1064-nm laser, when the fluence of the 1064-nm laser was six times as large as that of the 248-nm laser.
Thin-Layer Ablation of Metals and Silicon by Femtosecond Laser Pulses for Application to Surface Analysis
Authors: Kyu Kim Min , Takayuki Takao Takayuki Takao , Yuji Oki Yuji Oki , Mitsuo Maeda Mitsuo Maeda
Published: October 2002

For the purpose of thin-layer surface analysis, comparison of laser ablation by 24 ns ArF laser pulses at 193 nm and that by 150 fs Ti:sapphire laser pulses at 780 nm for samples ranging from metals to semiconductors is reported. In contrast to nanosecond laser pulses, the ablation threshold for femtosecond laser pulses could be reduced significantly. In particular, the threshold for a Si sample was reduced to about one order of magnitude, and an ablation rate of 0.48 nm/shot was obtained at 5% above the threshold fluence. The root-mean-square (RMS) growth rate in the roughness of the ablated surface was 0.05 nm/shot. These results show the advantages of femtosecond laser ablation for trace element analysis of a wide range of materials, coupled with laser-induced fluorescence (LIF) spectroscopy.
Monte Carlo Simulation on Properties of a Novel Flat-Panel Fluorescent Display Excited by GaN Micro-Ultraviolet-Light-Emitting Diodes
Authors: Sato Yuichi , Sato Susumu
Published: October 2002

Optical emission properties of a novel flat-panel fluorescent display are investigated by the Monte Carlo simulation. In the display device, phosphor films are excited by gallium nitride (GaN)-based micro-ultraviolet-(UV)-light-emitting diodes (LEDs). The GaN micro-UV-LEDs are adhered to the front surface of the phosphor films in this simulation. Fluorescent light emitted from the front surface of the film concentrates within a small area and the intensity is greater than that of the fluorescent light emitted from the back surface. Dependences of the emission intensities on other parameters are also evaluated. GaN micro-UV-LEDs which are transparent or have small areas comparable with the phosphor diameters are preferable for obtaining high resolution and high brightness.
Heteroepitaxial Growth of 4′-Nitorobenzylidene-3-Acetamino-4-Methoxyaniline on the Single Crystal of 4′-Nitrobenzyliden-3-Ethylcarbonylamino-4-Methoxyaniline
Authors: Yamashiki Tomoya , Tsuda Keiji
Published: October 2002

4′-nitrobenzyliden-3-acetamino-4-methoxyaniline (MNBA) is one of the second-order nonlinear optical materials. We studied the heteroepitaxial growth of MNBA on single crystal of 4′-nitrobenzyliden-3-ethylcarbonylamino-4-methoxyaniline (MNBA-Et). To improve the epitaxial layer quality, we employed a two-step procedure for the crystal growth. After the homoepitaxial growth of MNBA-Et, we annealed the sample and discovered the significantly flattened surface of MNBA-Et crystal. A single-domain MNBA heteroepitaxial layer was grown on an annealed MNBA-Et layer.
Change in Transmittance due to Free carriers in Two-Dimensional Photonic Crystals
Authors: Susa Nobuhiko
Published: October 2002

Numerical simulation revealed that photonic crystals consisting of dielectric and air cylinders should have a high contrast at moderate optical power densities (P) (less than 2 kW/cm2) when the number of stacked layers (ST, i.e., thickness) is larger than or equal to 32. The peak wavelength shifted by about -32 to -39 nm when P was increased from 0 to 10 kW/cm2 at ST≧32. The peak wavelength shifted more with P with a smaller ST because the peak wavelength at P=0 became longer for the wavelengths examined.
Size Dependence of Phonon Raman Spectra in Mn2O3 Nanocrystals
Authors: Chen Zhiwen , Tan Shun , Zhang Shuyuan , Wang Jian , Jin Sizhao , Zhang Yuheng , Sekine Hisashi
Published: October 2002

Nanometer manganic oxide (Mn2O3) has been prepared by the chemical liquid homogeneous precipitation (CLHP) method. The size dependence of phonon Raman spectra in Mn2O3 nanocrystals has been investigated. Transmission electron micrographs and X-ray powder diffraction patterns show that the average particle sizes are in the range of 9 to 50 nm. From the Raman spectra patterns of the nanometer Mn2O3 particle, we determined the broadening of the Raman peak in the lower frequency region. This phenomenon was explained by a spatial correlation model. We also found that the intensities of the main Raman peak decrease with the decrease in the grain size of Mn2O3 nanocrystals.
Photoluminescence of CdSnP2 Single Crystals in the Vicinity of the Fundamental Optical Edge
Authors: Medvedkin Gennadiy A. , Nishi Takao , Sato Katsuaki
Published: October 2002

The influence of chemical etching on the emission properties of undoped CdSnP2 crystals has been studied. The appropriate treatment gives rise to integral strengthening of photoluminescence and redistribution of emissions in such a manner that the longest wavelength band disappears and the exciton line flames up. The shortest wavelength line at 1.243 eV with the 2k
T half-width has been observed successfully for the first time. The doublet structure observed near the fundamental optical edge was attributed to the free exciton and bound-to-shallow level state in CdSnP2.
Optical Response in Amorphous GaAs Thin Films Prepared by Pulsed Laser Deposition
Authors: Toshihiko Kiwa Toshihiko Kiwa , Ichiro Kawashima Ichiro Kawashima , Shigeki Nashima Shigeki Nashima , Masanori Hangyo Masanori Hangyo , Masayoshi Tonouchi Masayoshi Tonouchi
Published: October 2002

Femtosecond optical response in GaAs thin films has been studied. We prepared GaAs thin films on MgO substrates and on YBa2Cu3O7-δ (YBCO) thin films using pulsed laser deposition (PLD) at temperatures below 250°C. A photocarrier lifetime of less than 1 ps is measured for the prepared GaAs thin films using femtosecond time-domain reflectivity change measurements. Pulsed electromagnetic wave [terahertz (THz) radiaiton] containing a frequency component of up to 1 THz is emitted from fabricated photoconductive switches using the prepared thin films. We also evaluated the THz radiation properties emitted from the photoswitches on the YBCO thin films.
Simulation of Optical Constants Range of High-Transmittance Attenuated Phase-Shifting Masks Used in KrF Laser and ArF Laser
Authors: Kim Eunah , Moon Seong-yong , Kim Yong-hoon , Yoon Hee-sun , No Kwangsoo
Published: October 2002

Phase-shifting masks (PSMs) have provided us a breakthrough in the future semiconductor industry by extending lithography further to the submicrometer order. PSMs have been used over the past several years, and their requirements have changed due to the development of semiconductor technology. We investigated high-transmittance attenuated PSMs (HT-Att-PSMs) that satisfy the requirements of 20±5% transmittance and 180° phase shift at the exposure wavelength and less than 40% transmittance at the inspection wavelength. Regarding the wavelength, we targeted the inspection wavelength of 248 nm for ArF laser (exposure wavelength of 193 nm) HT-Att-PSM, and 365 nm for KrF laser (exposure wavelength of 248 nm) HT-Att-PSM. In this study, we developed refractive index-extinction coefficient-thickness (n-k-d) charts showing optimum optical constant ranges for HT-Att-PSM using the matrix method. The simulation was verified by comparing calculated transmittance data with measured ones.
Anomalous Sharp Dip of Large Field-Induced Refractive Index Change in GaAs/AlGaAs Five-Layer Asymmetric Coupled Quantum Well
Authors: Arakawa Taro , Tada Kunio , Kurosawa Naoki , Noh Joo-Hyong
Published: October 2002

The five-layer asymmetric coupled quantum well (FACQW) is a new potential-tailored quantum well for ultrafast and low-voltage optical modulators and switches. Almost linear and large electrorefractive index change can be obtained in the transparency wavelength regions. In the GaAs/AlGaAs FACQW, an abrupt change in refractive index change Δn due to an applied electric field F occurs at a certain electric field range, which results in an anomalous sharp dip of Δn versus F. The physical origin and the elimination of the dip are discussed in detail. The abrupt change of refractive index is caused by significant changes of the wavefunction overlap integrals (and exciton binding energies) of transitions between the ground states for an electron (e1) and a heavy hole (hh1), and transitions between e1 and the first excited state for a heavy hole (hh2). The overlap changes are mainly due to shifts of the wavefunction distribution of hh1 and hh2, respectively. The dip can be eliminated by changing the position or Al content of the AlGaAs barrier layer in the FACQW. In addition, the larger negative index change in a modified FACQW structure is demonstrated.
A-Site (MCe) Substitution Effects on the Structures and Properties of CaBi4Ti4O15 Ceramics
Authors: Yan Haixue , Li Chengen , Zhou Jiaguang , Zhu Weimin , He Lianxin , Song Yuxin
Published: October 2002

We investigated the effect of A-site compound substitution on the structures and properties of Ca0.8(MCe)0.1Bi4Ti4O15 (M denotes Li, Na and K) ceramics. The samples were prepared by the conventional ceramic technique. Sintering characteristics of Ca0.8(MCe)0.1Bi4Ti4O15 and CaBi4Ti4O15 ceramics were discussed. X-ray powder diffraction patterns of the three modified CBT-based compounds show a single phase of bismuth oxide layer type structure with m=4. The hysteresis loops of polarization versus electric field of the four compounds were also measured. A-site compound substitution improves the piezoelectric properties and the high-temperature resistivity of these materials. A-site (LiCe) and (KCe) substitution not only improves the Curie temperature but also decreases the temperature coefficient of dielectric constant (T
K
ε). Among the three modified ceramics, only the Curie temperature of Ca0.8(NaCe)0.1Bi4Ti4O15 is lower than that of CaBi4Ti4O15; however, its T
K
ε is the lowest. As a result, all the three modified CBT-based ceramics were found to be excellent high-temperature piezoelectric materials.
Electron Beam Lithography Simulation on Homogeneous and Multilayer Substrates
Authors: Raptis Ioannis , Nowotny Bernhard , Glezos Nikos , Gentili Massimo , Meneghini Giancarlo
Published: October 2002

A fast simulator for electron beam lithography, called SELID, is
presented and applied in the case of homogeneous and multilayer
substrates. For exposure simulation, an analytical solution based on
the Boltzmann transport equation is used instead of the Monte
Carlo. All important phenomena (forward scattering, backscattering,
generation of secondary electrons) have been taken into account for a
wide range of e-beam energies. The case of substrates consisting of
more than one layer (multilayer) is considered in depth as it is of
great importance in e-beam patterning. Results of simulation are
compared with experimental ones in the case of single pixel
exposures. Additionally, simulation results are compared with
experimental ones for isolated and dense patterns in the
sub-half-micron range, on conventional positive resist on homogeneous
and multilayer substrates. By using SELID, forecast of resist profile
with considerable accuracy for a wide range of resists, substrates and
energies is possible. Additionally, proximity effect parameters are
extracted easily for use in any proximity correction package.
Thermoelectric and Thermogalvanomagnetic Properties of NiBi3
Authors: Masashi Sakurai Masashi Sakurai , Takafumi Ono Takafumi Ono , Ikushi Yoshida Ikushi Yoshida , Seiichi Tanuma Seiichi Tanuma
Published: October 2002

We present some results of an experimental study on transport properties of poly-crystalline NiBi3. Resistivity, thermoelectric power and the Nernst coefficient were measured in a magnetic field up to 1.2 T between 100 and 300 K. A large magnetoresistance was observed and it was revealed that the behavior of thermoelectric power changed markedly upon the application of a magnetic field. The carrier mobility was determined to be 0.446 m2V-1s-1 at room temperature and the Fermi energy was estimated to be 0.643 eV. We obtained an expression ρ= ρ0 + d(H) exp
(-(T
0(H) / T)1.36H
2+1) as the temperature and magnetic field dependence of resistivity.
Effects of Cell Parameters on Photothermal Refractive Index Change in Guest Host Liquid Crystals
Authors: Ono Hiroshi , Harato Yoshiro , Kikuhara Junichi
Published: October 2002

The effects of liquid crystal (LC) cell parameters, including the thickness of the guest-host LC (GHLC) layer and the thermal conductivity of substrates, on photothermal self-phase modulation and the resulting self-diffracted beam characteristics were quantitatively investigated by heat conduction analysis and Kirchhoff's diffraction theory. We successfully explained several photothermal phenomena in the GHLC cells with different cell parameters and our experimental and theoretical technique described here was useful for characterizing the photothermal self-phase modulation.
Structural Analysis of 6H–SiC(0001)√3×√3 Reconstructed Surface
Authors: Fujino Toshiaki , Fuse Takashi , Ryu Jeong-Tak , Inudzuka Katsuhiko , Yamazaki Yujin , Katayama Mitsuhiro , Oura Kenjiro
Published: October 2002

Using coaxial impact-collision ion scattering spectroscopy (CAICISS), the structure of the 6H–SiC(0001)√3×√3 reconstructed surface was investigated. As a result of composition analysis, the topmost layer of this surface was found to be covered with Si adatoms. Moreover, from the incidence angle dependence of the scattering intensity due to C atoms, it was found that the √3×√3 periodicity was formed by a one-third monolayer of Si adatoms occupying T4 sites, and the height of the Si adatoms from the first substrate layer was determined to be 1.5±0.2 Å.
Study on Fluorine-Doped Indium Oxide Films Deposited by RF Magnetron Sputtering
Authors: Shigesato Yuzo , Shin Naoko , Kamei Masayuki , Song P. K. , Yasui Itatu
Published: October 2002

Fluorine-doped In2O3 films were deposited by rf magnetron sputtering using an In2O3 target at substrate temperatures from RT to 300°C under Ar gas pressure of 1.0 Pa. The fluorine doping was carried out by the following two methods, (1) placing InF3 pellets on the erosion area of the In2O3 target, and (2) introducing CF4 gas into the sputtering chamber. In both cases a systematic increase in carrier density (n) was observed, i.e. in case (1): n increased from 3.1×1019 to 2.9×1020 cm-3 by placing optimum number of InF3 pellets and in case (2): n increased from 3.1×1019 to 1.1×1020 cm-3 by introducing CF4 gas at CF4/Ar flow ratio of 4%. The fluorine content of the fluorine-doped films was estimated by electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS), where the inclusion of fluorine was observed to increase by about 30% (F/In at.%) in both cases.
Control of Plasma Parameters for High-Quality Hydrogenated Amorphous Carbon Growth
Authors: Azuma Kazufumi , Inaba Hiroshi , Tasaka Kenji , Fujimaki Shigehiko , Shirai Hajime
Published: October 2002

The correlation between plasma parameters and film properties is demonstrated in the growth of device-grade hydrogenated amorphous carbon (a-C:H) from pure methane (CH4) by capacitively coupled plasma-enhanced chemical vapor deposition (CCP-CVD). The deposition rate, refractive index, film stress and film hardness are strongly correlated with the self-bias voltage, V
dc. Hard, rigid, and transparent a-C:H films can be fabricated when the self-bias voltage, V
dc, is around 160–200 V. The ion energy, which is determined by the V
dc, is used to rearrange the film structure. The V
dc of around 160–200 V corresponds to 70–80 eV of the C ion flux in the case of C2H5
+ ions. According to the calculation using a modified Thomas-Fermi potential as the Coulomb screening potential, the incident C ion energy is estimated to penetrate the carbon film of 1.8 g/cm3 density to the depth of about 0.55 nm, which enables the densification of the a-C:H film.
Proposals for Remote Sensing of Electric Fields under Thunderclouds Using Laser Spectroscopy
Authors: Gavrilenko Valeri , Muraoka Katsunori , Maeda Mitsuo
Published: October 2002

Two novel remote sensing techniques based on laser spectroscopy are proposed for measurement of electric fields in atmosphere under thunderclouds. One is to measure Stark splitting of Rydberg states of argon atoms or Stark shifts of energy levels of polar molecules in atmosphere. The other is to detect the resonant sum frequency or second harmonic generation due to four-wave mixing under the electric fields. The possibility of the measurement by means of a long-path or light detection and ranging (LIDAR) technique is discussed.
Measurement of Complex Electrical Conductivity of Metallic Powders in a Sealed Tube
Authors: Maeda Atsutaka , Matsuo Ryoji , Inoue Ryotaro , Kitano Haruhisa , Takenobu Taishi , Iwasa Yoshihiro , Mitani Tadaoki
Published: October 2002

We studied the method of complex-electrical-conductivity measurement for powders placed in a sealed tube at microwave and millimeter-wave frequencies, using a cavity perturbation technique. We applied this technique to a molecular superconductor K3C60, whose electrical conduction is well known in single crystals, and reproduced the metallic conductivity with the magnitude of 0.5–1.2 mΩcm at 20 K which is in good agreement with the data for single crystals. From this result, it was found that the cavity perturbation technique works well for the conductivity measurement of anaerobic powders, with respect to metallic materials.
Reaction of Copper Oxide and β-Diketone for In situ Cleaning of Metal Copper in a Copper Chemical Vapor Deposition Reactor
Authors: Sekiguchi Atsushi , Kobayashi Akiko , Koide Tomoaki , Okada Osamu , Hosokawa Naokichi
Published: October 2002

For in situ cleaning of inner reactor walls of copper chemical vapor deposition chambers used in the copper wiring process of LSI, etching of the deposited metallic copper is carried out by three step processes of copper oxidation, complexation with β-diketone, and vaporization to allow evacuator. In this paper, reactions suitable for the latter two processes are described. Reactions of copper oxide with three kinds of β-diketone, hexafluoroacetylacetone (Hhfac), acetylacetone and dipivaloylmethane, were studied using thermogravimetry in the range from room temperature to 400°C. Only Hhfac reacted with copper oxide showing etching in the temperature range above 170°C. At 350°C the weight ratio etching rate was 0.29 wt%/min at atmospheric pressure and 0.06 wt%/min at 665 Pa. The evaporation rate of the reaction product, Cu(hfac)2, was 5.3 wt%/min at 150°C, which is sufficiently higher than the etching rate of copper oxide. Reactions are as follows: 2CuO→Cu2O+1/2O2, Cu2O+Hhfac→Cu(hfac)+CuOH, 2Cu(hfac)→Cu(hfac)2+Cu, and Cu+CuO→Cu2O.
Electrical Conductivity of Low-Temperature-Deposited Al0.1Ga0.9N Interlayer
Authors: Hayashi Nobuaki , Kamiyama Satoshi , Takeuchi Tetsuya , Iwaya Motoaki , Amano Hiroshi , Akasaki Isamu , Watanabe Satoshi , Kaneko Yawara , Yamada Norihide
Published: October 2002

We have realized a conductive AlGaN interlayer which was deposited at low temperatures ranging from 500 to 600°C. We studied the surface morphology and electrical property of an AlGaN/low-temperature-deposited (LT) AlGaN interlayer/GaN structure, dependent on the growth condition. It was found that the conductive LT-AlGaN interlayer and crack-free over-grown Al0.1Ga0.9N layer with a thickness of 1 µm were obtained with intermediate deposition temperature and SiH4 supply for the interlayer. Using the conductive LT-AlGaN interlayer technology, we demonstrated the low-voltage operation of a light-emitting diode. The conductive LT-AlGaN interlayer is promising technology for the realization of shorter wavelength emitters with high AlN molar fraction AlGaN cladding layers.
Structural Transformation of Screw Dislocations via Thick 4H-SiC Epitaxial Growth
Authors: Kamata Isaho , Tsuchida Hidekazu , Jikimoto Tamotsu , Izumi Kunikazu
Published: October 2002

In this paper, we studied the structural transformation of screw dislocations through gas-phase 4H-SiC epitaxial growth. We confirmed based on the numbers and features of etch pits on a surface after KOH treatment that some micropipes were closed in the epitaxial layer, and were divided into several elementary screw dislocations. We discuss the magnitude of Burgers vectors of micropipes in 4H-SiC substrates in relation to the number of elementary screw dislocations generated by micropipe closing. A depth analysis further revealed that most micropipe closings took place in the initial stage of epitaxial growth.
Elementary Surface Reaction Simulation of Aluminum Chemical Vapor Deposition from Dimethylaluminumhydride Based on Ab Initio Calculations: Theoretical Process Optimization Procedure (2)
Authors: Masakazu Sugiyama Masakazu Sugiyama , Tohru Nakajima Tohru Nakajima , Takeo Tanaka Takeo Tanaka , Hitoshi Itoh Hitoshi Itoh , Jyun-ichi Aoyama Jyun-ichi Aoyama , Yasuyuki Egashira Yasuyuki Egashira , Kohichi Yamashita Kohichi Yamashita , Hiroshi Komiyama Hiroshi Komiyama , Yukihiro Shimogaki Yukihiro Shimogaki
Published: October 2002

This work demonstrates how to develop a qualitative surface reaction model to an elementary surface reaction simulation of deposition for the quantitative examination of model validity. Chemical vapor deposition of Al (Al-CVD) from dimethylaluminumhydride (DMAH) is examined as an example of this method. The surface reaction model of DMAH was deduced from ab initio cluster model calculations and experimental measurements of reaction products. Rate constants of all the elementary reactions were estimated for an elementary reaction model. Transition-state theory enabled the calculation of rate constants using the activation energies obtained from ab initio calculations. Entropy terms, however, were estimated by using an empirical method to reduce the computational effort. This approach minimized the ab initio calculations required to form a reaction data set. Simulated deposition profiles were compared with experimental data for Al-CVD in a tube reactor. Good agreement between the results of simulations and experiments indicate the possibility of constructing surface-reaction data sets for CVD process simulations based on ab initio quantum-chemical calculations.
Critical Current Density–Magnetic Field Curve for Untwinned Orthorhombic Nd1+xBa2-xCu3O7±δ Single Crystal and Its Microstructure
Authors: Oka Akihiro , Koyama Satoshi , Izumi Teruo , Shiohara Yuh , Ma Xiuliang , Yamamoto Takahisa , Ikuhara Yuichi , Sakuma Taketo , Sugawara Yoshihiro , Hirayama Tsukasa
Published: October 2002

Critical current density–magnetic field (J
c–H) curves with H∥c-axis for untwinned orthorhombic Nd1+x
Ba2-x
Cu3O7±δ (Nd123, x=0.07) single crystals were investigated. Untwinned single crystals were prepared by two different fabrication processes under uniaxial stress: a detwinning process and a twin-free process. The peak effects for twin-free crystals were larger than those for detwinned crystals. The results of evaluation of the Nd/Ba configurations in these single crystals by extended X-ray absorption fine structure (EXAFS) spectroscopy and transmission electron microscopy (TEM) suggested that a larger number of pinning centers of Nd-rich phases were distributed more finely in twin-free crystals, so that the peak effects in their J
c–H curves increased. Furthermore, it is possible that the heat treatments under uniaxial stress affected the progress of Nd/Ba ratio fluctuation by means of the spinodal decomposition mechanism, which caused the fine distribution of Nd-rich phases in twin-free crystals.
Analysis of Photon Recycling in Semiconductor Ring Lasers
Authors: Takahiro Numai Takahiro Numai
Published: October 2002

Photon recycling in semiconductor ring lasers is theoretically analyzed. Dependence of threshold current, light output and modulation speed on photon recycling is calculated using rate equations for the carrier density and photon densities of laser mode and spontaneous emission. It is shown that photon recycling improves current versus light output characteristics and does not degrade the modulation speed. Photon recycling efficiencies for circular, square and triangular ring cavities are also examined. Although a circular structure has the largest photon recycling efficiency, it is considered that a square ring cavity, which still has a high efficiency, is the best because the number of oscillation modes is less than that of a circular one.
67-mW Continuous-Wave Blue Light Generation by Intracavity Frequency Doubling of a Diode Pumped Cr:LiSrAlF6 Laser
Authors: Makio Satoshi , Miyai Tsuyoshi , Sato Masayoshi , Sasaki Takatomo
Published: October 2002

We report a new configuration for an intracavity frequency-doubled Cr-doped LiSrAlF6 (Cr:LiSAF) solid state laser, by inserting a nonlinear crystal of LiB3O5 (LBO) for second harmonic generation (SHG). By applying a highiy reflective coating on LBO crystal, blue light of 67.8 mW was obtained. The slope efficiency of the Cr:LiSAF laser was 39.2% and the continuously tunable wavelength range by a birefringent filter was 113 nm.
Reduction of Seek Time of Tracking Actuator with Pulsed Excitation in Optical Disk
Authors: Lim Hyung-Jun , Han Chang-Soo , Kim Soo Hyun
Published: October 2002

Time consumption during the track seek is an important factor which indicates the ability of an optical disk system. In a two-stage tracking actuator, latency time exists before the laser beam follows the destination track because of the vibration of the fine actuator. Modified velocity profiles and control techniques for the actuator have been proposed to reduce the latency time. When a fine actuator is locked to the coarse actuator, another latency time caused by the disk eccentricity cannot be reduced. It becomes possible to forecast the eccentricity as the rotation type of the optical disk changes to constant angular velocity (CAV). Thus the latency time can be reduced by excitation of the fine actuator with the same velocity of the track when the coarse actuator stops. Pulsed excitation is used for the excitation. This method is applied to a compact disk read-only memory (CD-ROM).
Improved Extinction Ratios for Both Cross and Bar States Using Two-Section Ultra Short Vertical Directional Couplers
Authors: Cho Sung-Chan , Kim Boo-Gyoun , Shakouri Ali
Published: October 2002

We show that both cross and bar states with high extinction ratios larger than 30 dB can be achieved in ultra short vertical directional couplers with two sections. Various combinations of the refractive indices in the two sections are studied using the improved coupled mode theory and the beam propagation method. Design guidelines to achieve high extinction ratios with large tolerances are presented.
Dynamic Double-Exposure Interferometer based on Anisotropic Self-Diffraction in BaTiO3
Authors: Sun Ching-Cherng , Wang Bor , Sun Wen-Shing , Chang Jenq-Yang
Published: October 2002

We have proposed a one-dimensional optical forward phase-conjugate mirror with the use of anisotropic self-diffraction in BaTiO3. A dynamic double-exposure interferometer has been constructed based on this diffraction algorithm, and we have demonstrated the application of this interferometer to optical testing. The real-time measurement of the effective focal length of a positive lens is demonstrated and both the theory and the experiment are presented.
Maximum-channel-number Investigation of Limiting-Amplified Multiwavelength Dispersion Compensator Incorporating Chirped Fiber Gratings
Authors: Chen Yung-Kuang , Liang Tsair-Chun , Su Jing-Hong , Tzeng Sohn-Ling
Published: October 2002

We theoretically investigate the design of an optical limiting-amplified multiwavelength dispersion compensator (LDC) incorporating multiple chirped fiber gratings (CFGs) and a common bidirectional erbium-doped fiber (EDF) amplifier. The LDC provides simultaneous dispersion compensation and limiting amplification of multiple dense wavelength division multiplexing (DWDM) signals. The design criteria for multiwavelength LDC are to provide high constant channel output power and low interchannel differential power by optimization of the EDF length. The influence of the CFG's rejection ratio on the LDC is addressed. The dynamic range and maximum channel number of the LDC are studied. The multiwavelength LDC may facilitate easier DWDM system design flexibility and network implementation.
Enlarged Frequency Upshift from DC to AC Radiation Converter using Boundary Effect of Plasma-filled Waveguide
Authors: Higashiguchi Takeshi , Yugami Noboru , Gao Hong , Takahashi Kenji , Ito Hiroaki , Nishida Yasushi
Published: October 2002

Further frequency upshift from a DC to AC radiation converter is analyzed and experimentally observed by taking into account the boundary effect of a plasma-filled waveguide. The radiation frequency depends on both plasma density and cut-off frequency of the waveguide. The observed frequencies of the emitted radiation are in reasonable agreement with the expected theoretical values.
High-Efficiency Polarized Light Illumination System for Liquid-Crystal-Display Projectors
Authors: Chang Chong-Min , Shieh Han-Ping D.
Published: October 2002

We present a new optical system with two identical s- and p-polarized light paths for converting a random polarized beam into a linearly polarized one. The system also provides a uniform and rectangular cross-section beam on the light valve. The geometrical factor of the polarization-conversion efficiency of 190% and the uniformity at the liquid crystal display (LCD) plane of above 90% has been achieved by this optimized optical system.
F(Br-) Center in Na-doped BaFBr
Authors: Inoue Kiyoshi , Kondo Yasuhiro , Mori Nobufumi
Published: October 2002

Absorption spectra of the F(Br-) center perturbed by the nearest neighbor Na+ ion in BaFBr:Na single crystals were measured. By using the dichroic bleaching technique, the doped Na+ ion was confirmed to replace one of the five Ba++ ions surrounding the F(Br-) center below 250 K, keeping the C4 symmetry of F(Br-). Above 250 K, the perturbed F(Br-) center converts to an isolated F(Br-) center.
Dielectric Properties of CaTiO3–Ca(Mg1/3Nb2/3)O3 Ceramic System at Microwave Frequency
Authors: Huang Cheng-Liang , Yang Ru-Yung , Weng Ming-Hung
Published: October 2002

The crystal structures and the microwave dielectric properties of the (1-x)CaTiO3–xCa(Mg1/3Nb2/3)O3 perovskite ceramic system have been investigated. The (1-x)CaTiO3–xCa(Mg1/3Nb2/3)O3 solid solution exhibited orthorhombic crystal structures for all compositions. As the x value increases from 0.2 to 0.8, the dielectric constant ε
r decreases from 109 to 36 and the unloaded quality value Q×f increases from 8600 to 39000 (at 6.7 GHz). The temperature coefficient of the resonant frequency (τf) varies from 298 to -30 ppm/°C as the x value increases from 0.2 to 0.8. A new microwave dielectric material, 0.4CaTiO3–0.6Ca(Mg1/3Nb2/3)O3, applicable in microwave devices is suggested and possesses the dielectric properties of a dielectric constant ε
r∼54, a Q×f value ∼32000 (at 6.7 GHz) and a τf value ∼18 ppm/°C. Further improvement of the τf value is expected by adjusting the x value of (1-x)CaTiO3–xCa(Mg1/3Nb2/3)O3 ceramics.
Evaluation of Charge Passed through Gate-Oxide Films Using a Charging Damage Measurement Electrode
Authors: Watanabe Seiichi , Sumiya Masahiro , Tamura Hitoshi , Yoshioka Ken , Tokunaga Takafumi , Mizutani Tatsumi
Published: October 2002

A charging damage measurement electrode was used to model device structures.
The charge passed through gate-oxide films (Q
p) was measured in a
cavity-resonator-type electron cyclotron resonance (ECR) plasma etcher for 12-inch
wafers and the reduction of charging damage was investigated. Parallel circuits
composed of resistors and condensers were modeled after the current–voltage
(I–V) characteristics of the gate-oxide film. The electron shading effect was
introduced by mounting a Si chip with line and space (L&S)-patterned photoresist on
the probe, which corresponded to the gate electrode. The reduction of charging damage
using the time modulation (TM) bias was determined by evaluating Q
p and
the damaged test element group (TEG) wafer. This charging damage measurement
electrode is effective for investigating the reduction of charging damage in particular,
of the etcher used for 12-inch wafers.
Diffraction Limited Liquid Crystal Microlenses with Planar Alignment
Authors: Scharf Toralf , Kipfer Peter , Bouvier Manuel , Grupp Joachim
Published: October 2002

Liquid crystal microlenses with diffraction limited performance are presented. The micro-lenses consist of a liquid crystal film sandwiched between a pair of conductive substrates where one has hole patterned electrode. The lens diameters are 120 µm and 110 µm and diameter to thickness ratio of the lenses is approximately 2.4. The optical quality was investigated with a Mach-Zehnder interferometer. The behavior of the deformation of the liquid crystal in the inhomogeneous electric field is explained by using three dimensional director field simulations. It is shown that both, the twist and tilt deformations remarkably influence the optical quality. However, over large areas of the lens the waveguide condition is fulfilled and determines the optical properties. The pretilt angle of the liquid crystal is responsible for a tilt of the optical axis of the lens and diffraction-limited off-axis adaptive lens behavior is found.
Corrugations on the Free Surface of Nematic Liquid Crystal Layers
Authors: Virga Epifanio G. , Schadt Martin
Published: October 2002

In this paper we quantitatively treat an equilibrium problem for the free surface of a monomeric or polymeric nematic liquid crystal layer, which has been suggested by some novel industrial applications. Think of a layer deposited on a plane, rigid substrate, whose optical axis is anchored in such a way that the azimuthal angle is everywhere defined, whereas the polar angle may freely vary. Let further the azimuthal anchoring be discontinuous along a line on the substrate. To accommodate this singularity within a continuous field, the optic axis must flip out of the substrate plane and become orthogonal to it at the anchoring discontinuity. Such a distortion entrains a corrugation on the free surface of the layer. Experimentally, the existence of corrugations at the alignment boundaries of nematic liquid crystal polymer films on single glass substrates is demonstrated by photo-aligning and photo-patterning such films by the linear photopolymerization (LPP)-technology of ROLIC.
Studies on the States of Water and Sodium Ions in Poly(N-isopropylacrylamide) Gel
Authors: Masahiko Annaka Masahiko Annaka , Keiko Motokawa Keiko Motokawa , Takayuki Nakahira Takayuki Nakahira
Published: October 2002

The state of water and sodium ions in poly(N-isopropylacrylamide) gel were studied by differential scanning calorimetry (DSC), and 1H and 23Na NMR. The motional state of water in the gel is restricted at the phase transition point. DSC and 1H NMR suggest that the associated water is considered to be transformed into nonfreezing water on increasing the volume fraction of the polymer. 23Na NMR indicates that the sodium environment is distorted at higher temperatures, leading to an increase for the bound values of both linewidth and chemical shift, which is consistent with the finding that the introduction of Na+ ions into a hydrated gel system increases the amount of nonfreezing water.
Fabrication of Low-Stress Plasma Enhanced Chemical Vapor Deposition Silicon Carbide Films
Authors: Lin Tzu-Yin , Duh Jenq-Gong , Chung Chen-Kuei , Niu Huan
Published: October 2002

Low stress silicon carbide films with good uniformity in thickness and composition were deposited by varying the deposition parameters in a plasma enhanced chemical vapor deposition (PECVD) unit. The effects of deposition parameters on structure, chemical state and stress distribution of these films in the as-deposited state were investigated. The as-deposited films were typically amorphous and under compressive stress. A low compressive film with a stress level of -160 MPa was obtained at low substrate temperature (250°C) under an appropriate deposition pressure of 1100 mTorr. The chemical state and stress distribution were studied as a function of annealing temperatures in the range from 400°C to 650°C. The hydrogenated bonds decreased with the increase in annealing temperatures around 500–600°C, causing the outdiffusion of hydrogen. Owing to the breakage of the hydrogenated bonds, the recombination of unsaturated bonds on silicon and carbon atoms was promoted, enhancing the bond density of the Si–C stretching mode. Meanwhile, the stress could be further reduced to achieve a stress-free film (0.7 MPa) by post deposition annealing and shifting from the compressive region to the tensile region. The stress relaxation was ascribed to the dissociation of the hydrogenated bonds and the incorporation of hydrogen. As a result, Si–C bonds were created, leading to the formation of tensile stress.
Thin Films of Carbon Nanocapsules and Onion-Like Graphitic Particles Prepared by the Cosputtering Method
Authors: Osamu Mamezaki Osamu Mamezaki , Hiroaki Adachi Hiroaki Adachi , Satoshi Tomita Satoshi Tomita , Minoru Fujii Minoru Fujii , Shinji Hayashi Shinji Hayashi
Published: October 2002

A method for fabricating thin films of carbon nanocapsules and onion-like graphitic particles was reported. The method consists of cosputtering Ni and graphite, and subsequent thermal annealing in vacuum. Transmission electron microscopic and Raman studies revealed that the films were composed of Ni-filled carbon nanocapsules with graphitic coatings several nanometers in thickness. Ni particles were removed by acid etching, resulting in the formation of thin films composed of onion-like graphitic particles. Electron field emission properties of the onion-like graphitic-particle films were studied.