bluuebunny/crossref_metadata_2025 huggingface dataset:
GaN/Mirror/Si Light-Emitting Diodes for Vertical Current Injection by Laser Lift-Off and Wafer Bonding Techniques
Authors: Wuu Dong-Sing , Hsu Shun-Cheng , Huang Shao-Hua , Wu Chia-Cheng , Lee Chia-En , Horng Ray-Hua
Published: February 2005

A p-side-up GaN/mirror/Si light-emitting diode (LED) for vertical current injection has been fabricated by laser lift-off and wafer bonding techniques. A variety of metallic mirrors (Au, Al, and Ag) were chosen to improve the optical reflectivity and contact resistance with n-GaN. The GaN/mirror/Si LED with a silver mirror achieved a maximum luminance intensity of 45 mcd (20 mA) with a low forward voltage of 3.5 V. This luminance intensity is over two times that of the original planar GaN/sapphire LED. Under high current injection, the GaN/mirror(Ag)/Si LED also showed a more stable emission wavelength than the planar GaN/sapphire LED. This can be explained by the fact that the Si substrate provides a good heat sink and alleviates the joule heating problem. On the basis of these results, the p-side-up structure confirms the possibility of the simultaneous realization of a lower contact resistance and higher reflectivity for GaN/mirror/Si LEDs.
Lower Voltage Operation of a Phase Change Memory Device with a Highly Resistive TiON Layer
Authors: Kang Dae-Hwan , Ahn Dong-Ho , Kwon Min-Ho , Kwon Hyuk-Soon , Kim Ki-Bum , Lee Kyeong Seok , Cheong Byung-ki
Published: February 2005

The electrical switching behaviors of an offset-type phase change memory device with a highly resistive TiON layer were investigated, where the TiON layer (7 nm thick) was formed at a 70 nm wide contact between Ge1Sb2Te4 and TiN layers. Reversible transitions between crystalline (set) and amorphous (reset) phases were found to occur at relatively lower reset and set voltages, as compared with a device having no TiON layer. These results hold a high promise for a low-power operation of a phase change memory device.
Formation of β-FeSi2 Microstructures by Reactive Ion Etching Using SF6 Gas
Authors: Wang Shinan , Liu Zhengxin , Fukuzawa Yasuhiro , Osamura Masato , Ootsuka Teruhisa , Suzuki Yasuhito , Otogawa Naotaka , Nakayama Yasuhiko , Tanoue Hisao , Makita Yunosuke
Published: February 2005

The reactive ion etching (RIE) technique, using SF6 as reaction gas, was applied for the formation of microstructures of semiconductor β-FeSi2 films. The etching mask is an Al film patterned by photolithography and wet chemical etching. The maximum etch rate of β-FeSi2 is 0.1 µm/min and the etch selectivity of β-FeSi2 to the Al mask is about 1. This attempt suggests that existing RIE techniques for Si process may be applied directly to the micro fabrication of β-FeSi2.
Narrow-Band Thermal Radiation with Low Directivity by Resonant Modes inside Tungsten Microcavities
Authors: Kusunoki Fuminori , Kohama Tatsuro , Hiroshima Takeshi , Fukumoto Satoshi , Takahara Junichi , Kobayashi Tetsuro
Published: February 2005

Narrow-band thermal radiation with low directivity is presented using a periodic array of microcavities on tungsten surfaces. Thermally excited resonant modes inside the microcavities are found to enhance thermal radiation at specific wavelengths. Compared with a flat tungsten surface, thermal radiation from the microcavities has been enhanced by ∼200% at the most enhanced wavelength of λ=5.5 µm. This strong enhancement yields narrow-band thermal radiation with a full width at half maximum of Δλ=0.59 µm. The enhancement peak positions are well explained using a simple cavity resonator model. By measuring thermal radiation at oblique directions, it is also found that this narrow-band radiation has low directivity.
Improvement in Photoluminescence Efficiency of GaInNAs/GaAs Quantum Wells Grown by Metalorganic Chemical Vapor Deposition for Low-Threshold 1.3 µm Range Lasers
Authors: Kawaguchi Masao , Miyamoto Tomoyuki , Koyama Fumio
Published: February 2005

A quality improvement of the III–V dilute nitride semiconductor alloy, GaInNAs, grown by metalorganic chemical vapor deposition (MOCVD) on a GaAs substrate is reported for 1.3 µm-wavelength lasers. GaInNAs wafers were grown at various growth temperatures, V/III ratios, and growth rates. The photoluminescence (PL) efficiency of GaInNAs/GaAs quantum wells (QWs) was increased by lowering the growth temperature and increasing the V/III ratio in the growth conditions conventionally used for nitrogen (N)-free GaInAs/GaAs QW growth. These conditions are important for realizing high PL efficiency because they prevent the inhomogeneity of the immiscible alloy of GaInNAs. It was also observed that the optimal window for the growth temperature, V/III ratio, and growth rate for the GaInNAs is narrower than that of N-free GaInAs QWs. After careful optimization of the growth conditions, GaInNAs/GaAs QW lasers with various emission wavelengths were fabricated. Low-threshold current densities of 0.17 kA/cm2/well, 0.18 kA/cm2/well, and 0.44 kA/cm2/well are obtained for emission wavelengths of 1.25 µm, 1.30 µm, and 1.34 µm, respectively. The results obtained for growth conditions and lasing characteristics are useful in further improving 1.3 µm or longer wavelength GaInNAs lasers grown by MOCVD.
Ultraviolet Lasing Phenomenon of Zinc Oxide Hexagonal Microtubes
Authors: Yuen Clement , Yu Siu F. , Sun Xiao W. , Xu Chun X. , Leong Eunice S. P. , Lau Shu P. , Chen Chung K.
Published: February 2005

Prismatic zinc oxide (ZnO) hexagonal microtubes have been fabricated on silicon substrate using vapor transport. Two morphologies, bell-mouthed and uniform hexagonal microtubes, are obtained from the fabrication process. The ZnO hexagonal microtubes have demonstrated ultraviolet (∼393 nm) lasing emission under 355 nm optical excitation. It is found that the threshold pump intensity and cavity mode spacing of the microtube lasers are ∼500 kW/cm2 and ∼0.7 nm, respectively. The lasing characteristics of the microtube lasers are also investigated. It is shown that high threshold pump intensity of the microtube lasers is due to the high radiation loss arising from the hollow hexagonal structure near the prismatic facets.
Fabrication of Half-Wave Plates with Subwavelength Structures
Authors: Isano Taisuke , Kaneda Yasushi , Iwakami Nobuaki , Ishizuka Ko , Suzuki Noboru
Published: February 2005

Various optical elements with subwavelength structures are currently being developed. Because phase plates require a deep grating structure in which the line width is narrow and the aspect ratio is high, it has been difficult to develop half-wave plates. We have designed and developed λ/2 plates, and evaluated their optical characteristics. The fabricated phase plates have subwavelength gratings the depth of which is 1170 nm with a period of 260 nm. The phase plates achieved a phase retardation of 180 deg. at a wavelength of approximately 850 nm, and 90 deg. at the optical communication wavelength of approximately 1550 nm. The transmittance was approximately 70% around 850 nm and approximately 80% around 1550 nm.
Pulsed-Laser Deposition of LiNbO3 in Low Gas Pressure Using Pure Ozone
Authors: Tsukada Ichiro , Higuchi Sadao
Published: February 2005

Pulsed-laser deposition (PLD) growth of stoichiometric LiNbO3 has been investigated in detail in the low gas pressure region where the mean free path of ablated species is longer than the target-to-substrate distance. We have found that the reduction of gas pressure effectively suppresses Li deficiency, and therefore, is a promising way of overcoming the nonstoichiometory problem that has been inherent to the conventional PLD growth of LiNbO3. In such low-pressure growth, we have found that ozone atmosphere is more favorable than that of molecular oxygen, because the crystallographic quality and surface flatness is better in films grown with ozone than in those grown with molecular oxygen. These results open the way to nanoscale lattice engineering of Li-containing oxide materials.
Enhancement of Data Transfer Rate of Phase Change Optical Disk by Doping Nitrogen in Ge–In–Sb–Te Recording Layer
Authors: Yeh Tung-Ti , Hsieh Tsung-Eong , Shieh Han-Ping D.
Published: February 2005

This work investigated the enhancement of the data transfer rate and/or recrystallization speed of Ge–In–Sb–Te recording material by nitrogen doping. The effects of nitrogen content on the dynamic properties of optical disks and the corresponding microstructural changes of the recording layer were studied. The experimental results showed that nitrogen doping at a sputtering gas flow ratio of N2/Ar = 3% might enhance the data transfer rate of an optical disk up to 1.6 times without severely damaging the signal jitter values. However, the disks failed the dynamic tests when too much nitrogen (N2/Ar ≥ 5%) was introduced. Dynamic testing also revealed that nitrogen doping slightly increased the noise level and jitter of the disks. Transmission electron microscopy (TEM) found that nitrogen doping promoted a phase transformation by generating numerous nucleation sites uniformly distributed in the recording layer and hence increased recrystallization speed.
Depth-Enhanced Integral Imaging with a Stepped Lens Array or a Composite Lens Array for Three-Dimensional Display
Authors: Choi Heejin , Park Jae-Hyeung , Hong Jisoo , Lee Byoungho
Published: February 2005

In spite of the many advantages of integral imaging, the depth of reconstructed three-dimensional (3D) image is limited to around the only one image plane. Here, we propose a novel method for increasing the depth of a reconstructed image using a stepped lens array (SLA) or a composite lens array (CLA). We confirm our idea by fabricating SLA and CLA with two image planes each. By using a SLA or a CLA, it is possible to form the 3D image around several image planes and to increase the depth of the reconstructed 3D image.
Nanometer Photothermal Heating and Cooling Dynamics of Azo Polymer Film Elucidated by Analyzing Nanosecond Laser-Induced Expansion/Contraction Behavior
Authors: Tada Takuji , Asahi Tsuyoshi , Tsuchimori Masaaki , Watanabe Osamu , Masuhara Hiroshi
Published: February 2005

The nanosecond transient expansion and successive contraction dynamics of an azobenzene-substituted urethane-urea copolymer film were studied by nanosecond time-resolved interferometry. In addition, the photoisomerization dynamics of azo dyes during morphological change was investigated by transient absorption measurement. A transiently generated cis isomer absorbed a few photons during laser irradiation and its energy was effectively converted to heat. When the pulse width of the irradiated laser was 8 or 14 ns full-width at half maximum (fwhm), the expansion of the polymer film started with 3–6 ns delay from the temperature elevation, while the film contracted exponentially accompanying a different absorbance change of the transient species. The expansion dynamics was well explained not in terms of volume change due to isomerization dynamics but in terms of thermal expansion involving glass–rubber transition. The film-thickness-dependent contraction dynamics could be mostly interpreted in view of the heat flow toward the quartz substrate, heat dissipation via the film itself, and phase transition of the polymer film from the rubbery to glassy states. The laser-induced transient morphological change of the urethane-urea copolymer film observed below the threshold could be well explained in terms of nanometer heating and cooling dynamics.
Hybrid L-Band Optical Fiber Amplifier Module with Erbium-Doped Fiber Amplifiers and Semiconductor Optical Amplifier
Authors: Yeh Chien-Hung , Lai Kuo-Hsiang , Huang Ying-Jie , Lee Chien-Chung , Chi Sien
Published: February 2005

We propose and experimentally demonstrate a new hybrid three-stage L-band fiber amplifier module composed of a semiconductor optical amplifier and two erbium-doped fiber amplifiers over the gain bandwidth of 1540 to 1600 nm. This proposed amplifier also provides a broadband amplified spontaneous emission light source.
Influence of the Niobium or Fluorine Dopant Concentration on the Properties of Mn-Doped Lead Zirconate Titanate Ceramics
Authors: Boucher Eric , Guiffard Benoit , Lebrun Laurent , Guyomar Daniel
Published: February 2005

In this paper, we report on the effect of donor addition (Nb5+ or F-) on the electrical and piezoelectric properties and crystallographic characteristics of Mn-doped lead zirconate titanate (PZT) ceramics. Samples were prepared chemically by coprecipitation of oxalates and hydroxides. The niobium ion was incorporated in the B site whereas the fluorine ion was introduced in the anionic site. Structural analysis (XRD) and measurement of electrical properties were carried out. Electron spin resonance was used to determined the valency states of manganese in PZT ceramics. From the experimental results, the F–O substitution decreases the amount of oxygen vacancies in the Mn-doped PZT, and the valency states remain unchanged. However, a small number of oxygen vacancies may exist in PZT doped with 1 at.% manganese and 2 at.% fluorine. In the (Mn,Nb) co-doping case, the valency states vary from 4+ to 2+ and the number of oxygen vacancies is lower or even almost equal to zero. Thus the electroneutrality is achieved by lead vacancies.
Microwave Dielectric Properties and Microstructures of CuO-Modified (1-x)(Mg0.95Co0.05)TiO3–xCaTiO3 Ceramic System
Authors: Huang Cheng-Liang , Pan Chung-Long , Hsu Jui-Feng
Published: February 2005

The effects of CuO additives on the microstructures and the microwave dielectric properties of (1-x)(Mg0.95Co0.05)TiO3–xCaTiO3 ceramics were investigated. The CuO additives can effectively reduce the sintering temperature of the ceramics to as low as 1175°C. With x = 0.08, at 1275°C, the 0.92(Mg0.95Co0.05)TiO3–0.08CaTiO3 ceramic possesses excellent microwave dielectric properties: a dielectric constant ε
r of 22.1, a Q×f value of 86400 GHz (at 7 GHz) and a τf value of 5.4 ppm/°C. Sintered ceramic samples were characterized by using X-ray diffraction pattern and SEM. Dielectric constants (ε
r) are not significantly affected by various additives and range from 20 to 23. By properly adjusting the x of (1-x)(Mg0.95Co0.05)TiO3–xCaTiO3 ceramics, small temperature coefficients (< ±3 ppm/°C) of resonant frequency (τf) are obtained for 0.93(Mg0.95Co0.05)TiO3–0.07CaTiO3 with 0.25 wt% CuO additives.
Number of Dielectric Layers Dependence of Dielectric Properties and Residual Stress of Multilayer Ceramic Capacitors with Ni Electrodes
Authors: Nakano Yukie , Nomura Takeshi , Takenaka Tadashi
Published: February 2005

The relationship between the residual stress and dielectric properties of multilayer ceramic capacitors with Ni electrodes (Ni-MLCCs) has been studied. Residual stress measurement by X-ray diffraction revealed that tensile stress inside MLCCs in the thickness direction increased with increasing number of dielectric layers. The increase in the ratio of the c-axis to the a-axis of BaTiO3 in the thickness direction of MLCCs was expected from the results of X-ray diffraction with increasing number of dielectric layers. The increase in dielectric constant and its temperature dependence with increasing number of dielectric layers were expectedly related to crystal structures.
Effect of Annealing on Physical and Electrical Properties of Ultrathin Crystalline γ-Al2O3 High-k Dielectric Deposited on Si Substrates
Authors: Shahjahan Mohammad , Okada Takayuki , Sawada Kazuaki , Ishida Makoto
Published: February 2005

Ultrathin crystalline γ-Al2O3 films with an equivalent oxide thickness (EOT) of 1.3 nm to 2.5 nm have been fabricated on Si substrates by molecular beam epitaxy and annealed in various atmospheres at different temperatures (300–700°C). The effect of the annealing on the chemical composition, crystalline property, surface morphology and electrical properties of the ultrathin γ-Al2O3 films has been studied. An improvement in the electrical properties after annealing was observed. It was also observed that the nitrogen atoms were incorporated into the γ-Al2O3 (γ-Al2O3:N) films during annealing at higher temperatures. No detectable pits or pinholes were observed on the surfaces after annealing and the crystalline property remained unchanged during annealing.
Low-Temperature Deposition of Pb(Zr,Ti)O3 Thin Films on Si Substrates Using Ba(Mg1/3Ta2/3)O3 as Buffer Layer
Authors: Chu Ying-Hao , Liang Chen-Wei , Lin Su-Jien , Liu Kuo-Shung , Lin I-Nan
Published: February 2005

Utilization of Ba(Mg1/3Ta2/3)O3 materials as buffer layers was found to achieve perovskite Pb(Zr,Ti)O3 (PZT) thin film growth on silicon at very low substrate temperature (∼350 °C) by in situ pulsed laser deposition (PLD). Formation of a continuous layer is of critical importance in order to use the Ba(Mg1/3Ta2/3)O3 materials as diffusion barriers for suppressing the PZT-to-Si interaction and, at the same time, as seeding layers for enhancing the crystallization kinetics of the PZT films. Perovskite and amorphous PZT thin films can be obtained by simply adjusting the ambient oxygen pressure or substrate temperature in the PLD process. The amorphous PZT films possess a markedly smaller optical refractive index than the perovskite ones (n
amorphous = 2.02 and n
perovskite = 2.39), such that the perovskite/amorphous PZT films are a good combination for core/cladding materials for planar optical waveguides.
Photoalignment of Ferroelectric Liquid Crystals by Azodye Layers
Authors: Pozhidaev Eugene , Chigrinov Vladimir , Huang Danding , Ho Andrei Zhukov* , Kwok Hoi Sing
Published: February 2005

The photoinduced alignment of ferroelectric liquid crystals (FLCs) onto photochemically stable azo-dye films was studied. The alignment quality of FLC display cells depends mainly on the difference between the FLC surface energy and the aligning substrates surface energy; however, the structure and thickness of FLC layers are also important. The effect of the thickness of photoaligning azodye layer on the alignment quality and multiplex operation of passively addressed FLC display cells has been investigated. An optimal (about 3–5 nm) azo-dye layer thickness that provides both the highest multiplex operation steadiness and the best contrast ratio of the FLC display cells was found. The photoaligned FLC display cells showed the contrast ratio CR>500:1 at the wavelength λ=0.63 µm both in surface stabilized and deformed helix FLC electrooptical modes.
Multiscale Detection of Defect in Thin Film Transistor Liquid Crystal Display Panel
Authors: Song Young-Chul , Choi Doo-Hyun , Park Kil-Houm
Published: February 2005

A new automated inspection algorithm is proposed for detecting blob-Mura defects based on multiscale in a thin film transistor liquid crystal display (TFT-LCD) panel. As such, new kernels with different sizes are defined and then used to detect blob-Mura defects with varying sizes and brightness levels. To extract a seed point, an adaptive multilevel-threshold method is employed. Initially, smaller kernels are used to detect smaller defects, then gradually larger kernels are applied to detect larger defects. Through simulation it was verified that the proposed algorithm has a superior capability for detecting blob-Mura defects.
Modeling of Strain Induced by Compositional Variation in Wafer-Shaped Bulk Mixed Crystals
Authors: Islam Md. Rafiqul , Verma Prabhat , Hiroki Akira , Yamada Masayoshi
Published: February 2005

A radially symmetrical strain model has been proposed to determine the residual strain distribution induced by compositional variation in wafer-shaped bulk mixed crystals. The strain components in cylindrical coordinates are analytically derived by assuming a symmetrical variation of composition along the radial direction and uniform composition along the growth direction. The results obtained from the model demonstrated that the quantitative amount of strain and its distribution are highly dependent on the radial compositional profile and its range. The strain model is confirmed with the combination of micro-Raman scattering and optical transmission experiments, which were performed in single-crystalline Si1-x
Ge
x
mixed material grown by the floating zone method. The experimental results indicated that there exists residual strain due to the compositional variation along the radial direction in Si1-x
Ge
x
wafers, which is well explained by the strain model proposed here.
Observation of Adsorption Phenomena of Dibutyl Phthalate Molecules on Si Surface Using Quartz Crystal Microbalance Method
Authors: Okamura Shigeru , Shimada Manabu , Okuyama Kikuo
Published: February 2005

The adsorption phenomena of dibutyl phthalate (DBP) molecules on the Si surface were observed in detail using a highly sensitive quartz crystal microbalance (QCM) and a new method involving a sliding chamber system. As a result of the precise observation of the adsorption phenomena and an accurate decomposition analysis, the typical Langmuir adsorption phenomenon with a time constant of 350 s was observed following the rapid adsorption phenomenon that occurs within the first 10 s and the next adsorption phenomenon of increasing linearly. After almost reaching the adsorption equilibrium amount, another Langmuir adsorption phenomena for a time constant of 3000 s was also observed; the Langmuir adsorption phenomenon for a time constant of 350 s seems to be that of an isolated admolecule whereas that for 3000 s seems to be one where admolecule cohere by mutual migration on a surface.
Novel Surface Modification of Indium-Tin-Oxide Films Using Ion Implantation for Organic Light-Emitting Diodes
Authors: Choi Nack-Bong , Lee Kwang-Yeon , Yang Myong-Su , Kim Chang-Dong
Published: February 2005

Indium–tin–oxide (ITO) films doped using an ion implantation system were used as the anode electrode of organic light-emitting diodes (OLEDs). Changes in the characteristics of the doped ITO films were observed and measured in terms of sheet resistance, Hall mobility, contact angle, roughness, transmittance and work function. Boron dopant was used as an impurity to modify the surface of the ITO films. The depth profile of boron concentration was monitored by secondary ion mass spectrometry (SIMS) as a function of dose. Optimum dose was 5×1014 atoms/cm3 at which resistance was lowest. The resistance variation from 16 Ω/sq. of the conventional ITO to 11 Ω/sq. of doped ITO shows that the doped ITO films become more conductive after doping and thermal annealing. The Hall mobility and carrier concentration of boron-doped ITO was 40.4 cm2/Vs and -9.32×1020/cm3 respectively. Contact angle and roughness were investigated by the sessile drop technique and atomic force microscopy (AFM). After doping, the water contact angle of the film surface was changed from 55° to 38° and the root-mean-square roughness of the films was similar to that of conventional ITO. Transmittance in the visible spectrum range was increased from 91% to 96%. Work function was improved from 4.66 eV to 4.86 eV. An OLED device fabricated with a multilayer, boron-doped-ITO/CuPc/NPD/Alq3:C545T/Alq3/LiF/Al, was tested. The device had a luminance of 780 cd/m2 and the lifetime was also increased by approximately 25% compared with those of ITO devices produced under the same conditions.
Growth and Surface Morphology of Textured NiO Thin Films Deposited by Off-Axis RF Magnetron Sputtering
Authors: Ryu Hyun-Wook , Choi Gwang-Pyo , Hong Gwang-Jun , Park Jin-Seong
Published: February 2005

Textured crystalline NiO thin films were grown on Si(100) substrates by off-axis RF magnetron sputtering without substrate heating using a NiO target. (100)-textured NiO films were obtained using pure Ar gas. On the other hand, (111)-textured NiO films were obtained using pure O2 gas. Also, the surface morphology and roughness of the NiO thin films were closely related to the type of sputtering gas and RF power.
The Effects of Hydrogen Plasma Treatment on the Plasma-Enhanced Chemical Vapor Deposition a-SiC:H Films
Authors: Chen Chia-Fu , Li Yan-Way
Published: February 2005

Amorphous hydrogenated silicon carbide (a-SiC:H) films were deposited using plasma-enhanced chemical vapor deposition (PECVD) process. Reducing silane flow rate increased the carbon concentration and optical band gap in the a-SiC:H films, but decreased the refractive index and dielectric constant. X-ray photoelectron spectroscopy (XPS) data revealed that the carbon concentration decreased as the methane flow rate increased, but the silicon concentration increased. Increasing the carbon concentration in the a-SiC:H film reduces the dielectric constant of the film. The carbon-rich a-Si0.24C0.68:H
y
films treated with hydrogen plasma for various periods, were converted into films with more silicon content. Increasing the hydrogen plasma treatment period gradually roughened the surface even though the original film had a smooth surface, with a roughness <0.231 nm. The leakage current density of the hydrogen plasma treated a-Si0.24C0.68:H
y
films declined as the duration of the hydrogen plasma treatment period decreased.
Spectroscopic Study on Vibrational Nonequilibrium of a Microwave Discharge Nitrogen Plasma
Authors: Koike Shuji , Sakamoto Takeshi , Kobori Hiroyuki , Matsuura Haruaki , Akatsuka Hiroshi
Published: February 2005

We generate a microwave discharge nitrogen plasma using a rectangular waveguide and a quartz tube (30 mm i.d.) inserted along the vector of the electric field, with an adjustable short-circuited plunger. The typical discharge conditions used are as follows: microwave frequency 2.45 GHz, input power 550 W, nitrogen (99.5%) gas flow rate 0.01–1.6 l/min, and discharge pressure p=0.5–10 Torr. Electron temperature T
e, and density n
e are measured using a double probe. Vibrational temperature T
v is obtained from the population density of the vibrational exited states of N2 C 3Πu by spectroscopic examination. Rotational temperature T
r is obtained from a comparison of the rovibronic spectra observed experimentally with the calculated ones. It is found that T
e≃0.5–2 eV, T
v≃0.45–1 eV, and T
r≃0.06–0.1 eV under the present pressure conditions, whereas n
e≃1011–1012 cm-3 at a low discharge pressure, and n
e≃108–109 cm-3 at a high discharge pressure. We discuss the measured vibrational populations by theoretical calculations in which the variation in their number density is expressed in terms of molecular processes in the nitrogen plasma.
Calculation of Ozone Generation in AC Corona Discharge Reactor
Authors: Yehia Ashraf , Mizuno Akira , El-Osealy Mohamed A. M.
Published: February 2005

The aim of this work is to study the analytical calculation of ozone generation in an ac corona discharge reactor. The corona discharges were generated in a dry air-fed wire-duct reactor stressed by an ac voltage at atmospheric pressure and room temperature. The current–voltage characteristics of the ac corona discharges relative to ozone generation in the reactor were measured under different discharge conditions. Subsequently, an empirical equation was derived for the calculation of the ozone concentration generated in the reactor on the bases of the experimental results. The derived equation can be used to predict the ozone concentration generated by ac corona discharges in the reactor for any values of the parameters that were investigated in the experiment.
On the Amplification Capability of Ne-like Ar Soft X-ray Laser Generated by Capillary Z-Pinch Discharge
Authors: Hayashi Yasushi , Taniguchi Hiroaki , Ghomi Hamid , Chalise Priya , Sakamoto Nobuhiro , Watanabe Masato , Okino Akitoshi , Nakajima Mitsuo , Horioka Kazuhiko , Hotta Eiki
Published: February 2005

We have studied the gain characteristics of an Ne-like Ar soft X-ray (SXR) laser, at a relatively low discharge current, generated by a capillary z-pinch discharge, by changing the plasma length and the gas pressure. It was found that the pressure range of laser amplification varies with plasma length, which then yields different values of the gain at different pressures. For this reason, we suggest a quantity of “the gain-length product at the pressure of maximum laser output”. This quantity is suitable for comparing the amplification capability of soft X-ray laser devices, which use capillary discharge.
Interpenetrating Interface in Organic Photovoltaic Cells with Heterojunction of Poly(3-hexylthiophene) and C60
Authors: Fujii Akihiko , Shirakawa Tomoki , Umeda Tokiyoshi , Mizukami Hiroyoshi , Hashimoto Yuuki , Yoshino Katsumi
Published: February 2005

The optical and photovoltaic properties of a photovoltaic cell with a structure of indium-tin-oxide (ITO)/C60/poly(3-hexylthiophene) (PAT6)/Au have been investigated. The C60/PAT6 heterojunction of this cell was fabricated by spin-coating the chloroform solution of PAT6 onto the C60 thin film formed on ITO. The photovoltaic cell fabricated by this method has demonstrated the high efficiency for a solar cell based on organic polymers. From the optical properties and the direct observation of the C60/PAT6 heterojunction, it has been clarified that the interpenetrating interface of PAT6 and C60 contributes to the high photovoltaic performance.
Highly Sensitive Magnetic Sensing Method Using Magnetoresitance Devices
Authors: Kaiju Hideo , Saisho Kazuya , Shiiki Kazuo
Published: February 2005

A highly sensitive magnetic sensing method using magnetoresistance devices is proposed. An InSb magnetic sensing device was used in the feedback loop of a Hartley oscillator. The oscillation starts when the resistance of the InSb magnetic sensing device changes in the external magnetic field as the oscillation condition is fulfilled. We can detect the magnetic 1 or 0 signal, corresponding to oscillation or nonoscillation, respectively. Output response and error rate in our magnetic sensing for the detection of oscillation were invesitigated. As a result, a high output response of 1 Vpp was obtained even if the electric sensing current which flows into the InSb magnetic sensing device was 450 µA. The resistance change of more than 30 Ω is required in order to maintain an error rate of less than 10-5. Therefore, this magnetic sensing method has potential application in highly sensitive magnetic sensors.
Measurement of Thermal Diffusivity in a Sample with a Certain Thickness by an AC-Calorimetric Distance-Variation Method: IV. Requirements for Measuring by Spot Heating
Authors: Takahashi Fumiaki , Hamada Yukihiro , Hatta Ichiro
Published: February 2005

An ac-calorimetric distance-variation method has a variety of applications in thermal diffusivity measurement of a plate like material. In this method, there are some ac heating configurations. For a periodic band heating and a periodic line heating, we have proposed the requirements for the precise measurement in our previous papers. In this paper, we analyze temperature wave propagation in a plate like sample for a periodic spot heating under the condition in which heat loss between a sample and a heat sink takes place. In such a case, the requirements for measuring thermal diffusivity by spot heating within an accuracy of ±1% are proposed. For the precise measurement, we analyze the requirements in detail for the cases using only the phase of the periodic temperature and both the phase and the amplitude, because these two methods have individual merits.
Biophoton Emission from Kidney Bean Leaf Infested with Tetranychus Kanzawai Kishida
Authors: Kawabata Ryuzou , Uefune Masayoshi , Miike Tohru , Okabe Hirotaka , Takabayashi Junji , Takagi Masami , Kai Shoichi
Published: February 2005

We studied spontaneous photon emission from kidney bean leaves infested with spider mites. Strong photon radiation was observed from the leaf veins where spider mites were crowding. Photon emission intensity increased with the decreases in chlorophyll content and photosynthesis yield; these decreases represented the degree of damage caused by the pest. When both infested and un-infested leaves were put on the same wet cotton, photon emission from the un-infested leaf increased, too. Photon emission from the un-infested leaf might be induced by an aqueous elicitor released from the infested leaf. Such an elicitor activates the plant defense response. Therefore, it is suggested that photon emission from an infested leaf conveys information on the direct injury (physical stresses) and physiological (biochemical) actions associated with the defensive response.
Nonlithographic SiO2 Nanodot Arrays via Template Synthesis Approach
Authors: Cha Young Kwan , Seo David , Yoo In K. , Park Sangjin , Jeong Soo-Hwan , Chung Chee Won
Published: February 2005

We present a method for fabricating SiO2 nanodot arrays through pattern transfer of self-organized tantalum oxide hard masks on to a Si wafer. Tantalum oxide nanopillar arrays are formed at the bottom of anodic aluminum oxide by electrochemical anodization of the Al/Ta films on a Si wafer. Then the tantalum oxide nanopillars were used as hard masks for formation of SiO2 nanostructures. Ion milling was used for the pattern transfer. The density and diameter of the SiO2 nanodot arrays could be controlled by varing the anodizing conditions. The average diameters and areal density of prepared SiO2 nanodisks were 68 nm and 1010/cm2, respectively. Through this approach, it is expected that a wide variety of nanodisk arrays over large areas can be prepared.
Fabrication Technique for Carbon Nanotube Single-Electron Transistors Using Focused Ion Beam
Authors: Kurokawa Yuto , Ohno Yutaka , Kishimoto Shigeru , Okazaki Toshiya , Shinohara Hisanori , Mizutani Takashi
Published: February 2005

We have proposed a technique for fabricating carbon nanotube single-electron transistors using a focused ion beam (FIB). Wiring to a multiwalled carbon nanotube was formed by the ion-beam-assisted deposition of tungsten. Tunneling barriers were formed in the nanotube by ion beam etching. A drain current oscillation originating from the Coulomb blockade effect was observed at 23 K.
Prediction of Thermal Properties and Effect of OH Substituent for Poly(vinyl alcohol)s by Molecular Dynamics Calculations
Authors: Tsuchiya Yooko , Yoshii Noriyuki , Iwatsubo Tetsushiro
Published: February 2005

Since heat storage technology contributes greatly to the effective use of energy, we are attempting to develop latent heat storage materials. If computer simulations enable the estimation of material properties prior to experiments, they will provide us with very effective tools for the development of new materials. We use molecular dynamics calculations to predict the melting points and latent heats of fusion, which are crucial thermal properties for evaluating the suitability of heat-storage materials. As the object of calculation, poly(vinyl alcohol) (PVA) was chosen, because polymer materials are effective in that they can be made to cover all temperature ranges by changing the molecular weight. The melting points were determined from the volume change, and the latent heats of fusion were determined from the internal energy. As for these calculations, it was ascertained that these thermal properties were suitable values in comparison with the results of actual calorimetry. From the comparative calculation of the polymer consistent force field (PCFF) and optimized potentials for liquid simulations (OPLS) force field, it was shown that the intermolecular potential could be simplified. Moreover, the stability of the structural isomer of PVA and the state of the hydrogen bond were evaluated, because a strong intermolecular bond leads to structural stability and a high melting temperature.
Efficient and Practical Modeling of Finite Waveguide Grating Couplers
Authors: Cottier Kaspar , Kunz Rino. E. , Herzig Hans Peter
Published: February 2005

The local interference method (LIME) is introduced as a tool for simulating guided mode excitation by finite gratings in monomode waveguides. This efficient and versatile calculation scheme considers each grating line as a scattering center radiating into and from the forward-traveling waveguide mode, neglecting multiple scattering processes. This approximation considerably speeds up calculation time while delivering very good results for a broad range of calculation tasks, including non-periodic gratings or waveguides exhibiting small variations of the propagation constant. The algorithm is presented in detail, and it is applied to the calculation of the coupling line shapes of waveguide grating structures used for biochemical sensors, having small spatial non-uniformities.
Wide-Range Tunable Microring Resonator Filter by Thermo-Optic Effect in Polymer Waveguide
Authors: Yamagata Shunichi , Yanagase Yuji , Kokubun Yasuo
Published: February 2005

A tunable Add/Drop filter is demanded for a scalable photonic network. A vertically coupled microring resonator (VCMRR) filter has many advantageous characteristics, such as a narrow bandwidth, the possibility of dense integration, and the ease of filter response synthesis. However, since a conventional tunable ring resonator filter utilized the thermo-optic effect of silica waveguides, the tunable wavelength range was not sufficiently wide. Thus, in this study, tunable vertically coupled microring resonator filters were demonstrated utilizing the large thermo-optic (TO) coefficient of polymer materials. The maximum center wavelength shift of 9.4 nm and the low power consumption of 60 mW were achieved.
High-Extraction-Efficiency Blue Light-Emitting Diode Using Extended-Pitch Photonic Crystal
Authors: Orita Kenji , Tamura Satoshi , Takizawa Toshiyuki , Ueda Tetsuzo , Yuri Masaaki , Takigawa Shinichi , Ueda Daisuke
Published: February 2005

We have integrated the surface photonic crystal (PhC) on GaN-based blue light-emitting diodes (LEDs) for the first time in order to enhance the extraction efficiency of the LEDs. With the finite-difference time-domain method, we have calculated 3.6-fold enhancement in light output. The theoretical calculations have revealed that the optimum pitch of the PhC is much longer than the emission wavelength when the distance between the PhC and the active layer of LEDs is short. This design enables PhC formation on chemically stable GaN surfaces. In addition, an indium tin oxide (ITO)-based transparent electrode is formed directly on the surface of PhC to realize light emission from the whole area of the LED. The fabricated PhCs have increased the light output of blue LEDs by 1.5 times compared with the LEDs without PhC. We have demonstrated that PhC will realize highly efficient solid-state lighting with GaN-based LEDs.
Near-Field Evanescent Wave Enhancement with Nanometer-Sized Metal Grating and Microlens Array in Parallel Optical Recording Head
Authors: Goto Kenya , Kim Young-Joo , Kirigaya Takayuki , Masuda Yoshiki
Published: February 2005

To increase the data capacity and data transfer rate in optical data storage, a parallel near-field optical array head has been designed and prepared using the finite-difference time-domain (FDTD) simulation and nanofabrication process. Since the vertical cavity surface emitting laser (VCSEL) microprobe array head reported in our previous paper does not satisfy the required recording power for conventional phase change optical media, we have studied a new array head structure designed to enhance the optical throughput using the surface plasmon resonance effect between the incident light and the metal grating. The theoretical analysis and fabrication of a new integrated optical head were discussed with emphasis on the FDTD simulation for the metal grating structure. An approximately 500 times increase in the resonant power enhancement of evanescent waves was observed when a grating periodicity of 118 nm was maintained with the half-wavelength of the incident light inside the GaP substrate. Grating width and depth also affect the evanescent light enhancement between the incident light and metal grating; such result can be used as a guideline for future applications of near-field optical data storage.
Reflective Microoptical Element Array Fabricated by Photofabrication Technique
Authors: Awatsuji Yasuhiro , Sasada Masaki , Kawano Naoki , Kubota Toshihiro
Published: February 2005

The authors present reflective microoptical element arrays fabricated by a photofabrication technique. The three-dimensional base of the microoptical element array is photofabricated by exposing photopolymerizable resin to a light beam through a grayscale mask. Reflective film on the photopolymerized base of the optical element is introduced to prevent serious problems in photofabricated refractive optical elements, such as when the optical characteristics of the elements fundamentally depends on the spectroscopic property of the material of the photofabricated optical element. The relationship between the pixel value in the grayscale bitmap image used for making the grayscale transparency mask and the cure depth of the photofabricated base is experimentally clarified for a photopolymerizable resin. 15×15 unit convex and concave micromirror arrays, in which each optical element has a diameter of 930 µm, have been batch fabricated. The focusing capability of the fabricated concave micromirror array is demonstrated.
Gratings in GaN Membranes
Authors: Chen Chii-Chang , Hou Chia-Hung , Sheu Jinn-Kong , Chang Jenq-Yang , Li Ming-Hung , Chi Gou-Chung , Wu Chuck
Published: February 2005

In this work, gratings are fabricated on the GaN thin film grown on the silicon substrates. GaN membranes are obtained by removing the silicon below the GaN gratings. The samples are stacked on the GaN diffractive microlenses on sapphire substrates fabricated using gray-level masks. The stacked components are characterized using a He-Ne laser. The laser beam is collimated by the GaN microlenses and diffracted by the GaN gratings. The result demonstrates a stacked microoptics systems in GaN-based materials for the first time.
Calculation of Nonreciprocal Phase Shift in Magnetooptic Waveguide with Si Guiding Layer
Authors: Yokoi Hideki , Shoji Yuya , Mizumoto Tetsuya
Published: February 2005

A nonreciprocal phase shift in a magnetooptic waveguide with a Si guiding layer is discussed. The magnetooptic waveguide was installed in an optical isolator employing the nonreciprocal phase shift. The magnetooptic waveguide had a magnetic garnet/Si/SiO2 structure, which was realized by wafer bonding technique. The nonreciprocal phase shift in the magnetooptic waveguide with the Si guiding layer was calculated at a wavelength of 1.55 µm. A required thickness of the magnetic garnet cladding layer was obtained by calculating the nonreciprocal phase shift. An optical isolator employing the nonreciprocal phase shift, which could be operated under unidirectional magnetic field, was proposed by contriving the layer structures in the interferometer.
Crossed-Si-Wire-Waveguide Optical Switch
Authors: Okayama Hideaki , Furuhashi Kohji , Nakajima Hirochika
Published: February 2005

Si wire waveguides crossing at an angle of 0.5 radians are proposed for a cross-bar-type optical switch matrix. The device uses the evanescent wave coupling of the waveguide surface. The submicrometer movement of the optical waveguides activates the switching function.
Resonant Channel-Dropping Filter with Integrated Detector System Based on Optical Fiber Coupler and Microsphere
Authors: Serpengüzel Ali , Kurt Adnan , B\uil\uic\ui Temel , İşç\ui Şenol , Yilmaz Yi\~git Ozan
Published: February 2005

Dielectric microspheres are used to resonantly couple light from an optical fiber half coupler to a large-area silicon photodetector. Dielectric microspheres possess high quality factor morphology-dependent resonances, i.e., whispering gallery modes. The observed resonances have a channel spacing of 0.14 nm and a linewidth of 0.06 nm. These resonances provide the narrow linewidths necessary for high-resolution optical spectroscopy applications. Optical communication applications of this system are studied experimentally and theoretically.
New Concept of Optical Components of Low Cost and Ultracompactness
Authors: Kawai Shigeru , Yokokura Takashi , Nishizawa Koichi
Published: February 2005

We developed optical fiber collimators, which are the key optical systems for optical components and devices of ultracompactness and low cost. A beam waist diameter of 250 µm through the optical components and devices is chosen, taking into consideration the space between two optical fiber collimators and compactness without any excess insertion losses. We designed and fabricated an aspherical collimating lens with a coupling loss of less than 0.2 dB using a single-mode optical fiber. Several innovative optical components and devices based on this common platform are proposed.
Compact Spectroscopic Imaging Device Using Planar Grating Lens
Authors: Ura Shogo , Okayama Fumikazu , Takegami Kouji , Nishio Kenzo , Nishihara Hiroshi
Published: February 2005

Planar grating lens, fiber array and two-dimensional image sensor were assembled and packaged to be a compact spectroscopic imaging unit. Phase shift function of grating, end position of each fiber and image sensor tilt angle were optimized for suppressing aberration. Spatial resolution of 0.3 mm and spectral resolution of 5 nm were obtained with 100 nm spectral range. Size of the fabricated unit was 65×50×45 mm3.
Facial Recognition System with Compact Optical Parallel Correlator Using Vertical-Cavity Surface-Emitting Laser Array Module
Authors: Watanabe Eriko , Arima Nobuko , Kodate Kashiko
Published: February 2005

The design and trial fabrication of a two-dimensional light-source module is presented for application to an optical parallel correlator for facial recognition. The light-source module is composed of a vertical-cavity surface-emitting laser array and a multilevel zone-plate array as a collimating lens. This module is about 1/10 the size of the conventional light source module and the optical parallel correlator has a size of 16.1×13×23 cm3, weight of 4.4 kg, and a throughput time of 19 faces/s. In an experimental evaluation of the system through one-to-one correlation using a database of 300 front facial images, the false match and false non-match rates were less than 1%. The optical system presented here is therefore robust to a variety of changes in facial expressions and is highly applicable in security systems.
High-Efficiency InGaAs/AlGaAs Quantum Well Distributed Bragg Reflector Laser with Curved Grating
Authors: Uemukai Masahiro , Kitano Kazutoshi , Shimada Naoyuki , Suhara Toshiaki
Published: February 2005

An InGaAs quantum well curved distributed Bragg reflector (DBR) laser designed for high efficiency and high wavelength purity operation is demonstrated. The laser was fabricated by a simple process without regrowth. In order to improve the performance, the quantum well was selectively disordered in the DBR grating region to accomplish low absorption loss. As a result of optimization of the curved DBR grating and low-reflection coating on the facet mirror, single-mode lasing with an external differential quantum efficiency as high as 0.74 and a side mode suppression ratio of 52 dB was achieved. Low noise characteristic of only 0.7 dB above the standard quantum limit was obtained.
Characterization of Single-Wavelength Optically Pumped GaInAsP/InP Vertical-Cavity Surface-Emitting Lasers with Dielectric Mirrors
Authors: Kinoshita Junji , Miyamoto Tomoyuki , Onishi Yutaka , Koyama Fumio
Published: February 2005

In this study, the lasing characteristics of optically pumped vertical-cavity surface-emitting lasers (VCSELs) with dielectric mirrors, which are a fundamental structure of our proposed tunable VCSELs, were investigated. Firstly, the design and fabrication of single-wavelength GaInAsP/InP VCSELs without a tuning mechanism are described. The GaInAsP nine-quantum-well (QW) active region and pump light-absorption region were grown on an InP substrate by metal-organic chemical vapor deposition (MOCVD). SiO2/TiO2 or a-Si/SiO2 dielectric distributed Bragg reflectors (DBRs) were deposited on both sides of a thin cavity formed by etching of the InP substrate. Continuous-wave operation was observed at room temperature. The lowest threshold pump power was 1.8 mW for a 0.98 µm pump light, which corresponds to an equivalent threshold current density of 710 A/cm2. The thermal and polarization characteristics of the fabricated devices are also discussed.