bluuebunny/crossref_metadata_2025 huggingface dataset:
Band-Structure Design of Fluoride Complex Materials for Deep-Ultraviolet Light-Emitting Diodes
Authors: Ono Shingo , Ouenzerfi Riadh El , Quema Alex , Murakami Hidetoshi , Sarukura Nobuhiko , Nishimatsu Takeshi , Terakubo Noriaki , Mizuseki Hiroshi , Kawazoe Yoshiyuki , Yoshikawa Akira , Fukuda Tsuguo
Published: October 2005

The design principle for fluoride-containing optical devices for applications in the deep ultraviolet range is discussed. Variations in band gap energy, band structure and lattice constant of LiBa
x
Ca
y
Sr(1-x-y)F3 and Li(1-x)K
x
Ba(1-y)Mg
y
F3 have been studied. The band structure and transition type of these fluorides are predicted by ab initio band calculations based on the local density approximation. The lattice-matched double-hetero structure of direct-band-gap compounds LiBa
x
Ca
y
Sr(1-x-y)F3 on LiSrF3 and Li(1-x)K
x
Ba(1-y)Mg
y
F3 on either LiBaF3 or KMgF3 is sufficiently feasible to fabricate.
Improved Thermal Stability CrB2 Contacts on ZnO
Authors: Ip K. , Khanna Rohit , Norton D. P. , Pearton S. J. , Ren F. , Kravchenko I. , Kao C. J. , Chi G. C.
Published: October 2005

Most common contact metals show low thermal stabilities on ZnO and there is a clear need for more thermally stable metallization. The formation of rectifying contacts on n-type bulk single crystal ZnO using CrB2 was studied using current–voltage, scanning electron microscopy (SEM) and Auger Electron Spectroscopy (AES) measurements. When a single Au overlayer was used to reduce the metal sheet resistance, the contacts were ohmic for all annealing conditions. Under these conditions, both Zn and O were observed to outdiffuse from the ZnO. When a bilayer of Pt/Au was used on top of the CrB2 layers, rectifying contacts with barrier heights of ∼0.4 eV were obtained after annealing at 600°C, although at this condition the contact showed a reacted appearance and AES showed the onset of intermixing of the metallization. At higher anneal temperatures (700°C) the contact metallization showed blistering and loss of adhesion.
Fabrication of Hybrid n-ZnMgO/n-ZnO/ p-AlGaN/ p-GaN Light-Emitting Diodes
Authors: Yang Hyuck Soo , Han Sang Youn , Heo Y. W. , Baik K. H. , Norton D. P. , Pearton S. J. , Ren F. , Osinsky A. , Dong J. W. , Hertog B. , Dabiran A. M. , Chow P. P. , Chernyak L. , Steiner T. , Kao C. J. , Chi G. C.
Published: October 2005

We report on the fabrication of UV light-emitting diodes (LEDs) based on a p–n junction n-ZnMgO/n-ZnO/ p-AlGaN/ p-GaN semiconductor triple-heterostructure. Radio-frequency plasma-assisted molecular beam epitaxy was used to grow the complete heterostructure on p-AlGaN/ p-GaN c-plane sapphire templates. Cross-sectional transmission electron microscopy showed single-crystal quality of the pseudomorphically grown ZnO active region of the device. The LEDs were fabricated by a process involving both wet and dry etching. Electroluminescence emission most likely associated with ZnO excitonic transition was observed up to 370°C. The results show the potential of ZnO-based materials for UV emitters of potentially lower cost and with comparable or higher emission intensity than comparable AlGaN/GaN devices.
Diamond Sensors Durable for Continuously Monitoring Intense Vacuum Ultraviolet Radiation
Authors: Hayashi Kazushi , Tachibana Takeshi , Kawakami Nobuyuki , Yokota Yoshihiro , Kobashi Koji , Ishihara Hideaki , Uchida Koji , Nippashi Kenji , Matsuoka Mikihiko
Published: October 2005

Photoconducting sensors are fabricated using radiation-hard diamond films to measure the intensity of vacuum ultraviolet (VUV) radiation. They are composed of a pair of interdigitated Pt electrodes on highly oriented diamond surfaces. The sensors are examined as monitors of the intensity of VUV radiation (λ=172 nm) from xenon excimer lamps with an output power of greater than 10 mW/cm2. It was demonstrated that the diamond sensors have practical durability: the output signals from the sensors are reproducible and stable under a continuous irradiation from the xenon lamps for more than 500 h.
Host Isotope Effect on the Local Vibration Modes of VH2 and VOH2 Defects in Isotopically Enriched 28Si, 29Si and 30Si Single Crystals
Authors: Ohya Takeru , Itoh Kohei M. , Pereira Rui N. , Nielsen Brian Bech
Published: October 2005

Local vibrational modes of a vacancy with two hydrogen atoms (VH2) and of a vacancy with one oxygen and two-hydrogen atoms (VOH2) in silicon have been investigated using isotopically enriched 28Si, 29Si, and 30Si single crystals. Infrared absorption spectroscopy revealed shifts in the Si–H stretch frequencies of the two defects when the mass of the silicon host atoms was changed. The observed stretch frequencies can for each defect be accounted for with a simple vibrational model based on two coupled Morse oscillators. The anharmonic contribution to the local vibrational mode frequencies of these two defects is evaluated.
Metal-Organic Vapor-Phase Epitaxy Growth of InP-Based Resonant Tunneling Diodes with a Strained In0.8Ga0.2As Well and AlAs Barriers
Authors: Sugiyama Hiroki , Matsuzaki Hideaki , Oda Yasuhiro , Yokoyama Haruki , Enoki Takatomo , Kobayashi Takashi
Published: October 2005

InP-based resonant tunneling diodes (RTDs) with a strained In0.8Ga0.2As well and AlAs barriers were grown by metal-organic vapor-phase epitaxy (MOVPE). Cross-sectional transmission electron microscopy (TEM) confirmed the successful formation of ultra-thin strained AlAs barriers and In0.8Ga0.2As wells. Atomic force microscope (AFM) observation revealed atomically flat interfaces in the double-barrier (DB) structures of the RTDs. We obtained a peak current density ( j
P) of 1.46×105 A/cm2, high peak-to-valley current ratio (PVR) of 7.7, and a low peak voltage (V
P) of 0.43 V simultaneously in the RTDs with the barrier thickness (L
b) of about 6 monolayers (MLs). Maximum j
P exceeded 4×105 A/cm2 in the RTDs with L
b of about 4 MLs. The AlAs barrier thickness was precisely controlled by the Al-precursor-supply duration. These results indicate the potential of the practical use of MOVPE for high-speed InP-based integrated circuits with RTDs and other devices.
Effects of Tensile Stress on Growth of Ni–Metal-Induced Lateral Crystallization of Amorphous Silicon
Authors: Hou Chih-Yuan , Wu YewChung Sermon
Published: October 2005

The Ni–metal-induced lateral crystallization (NILC) of amorphous silicon (a-Si) has been used to fabricate low-temperature polycrystalline silicon thin-film transistors. Three stages have been identified in the NILC process: (1) the formation of NiSi2 precipitates, (2) the nucleation of crystalline Si (c-Si) on NiSi2 precipitates, and (3) the subsequent migration of NiSi2 precipitates and growth of c-Si. In this study, a bending fixture was used to investigate the effects of tensile stress on the growth of NILC. It was found that tensile stress did not enhance NiSi2 formation and c-Si nucleation stages, but enhanced the c-Si growth stage. It was also found that compressive stress did not change NILC rate.
Analysis of Microstructures in SiGe Buffer Layers on Silicon-on-Insulator Substrates
Authors: Taoka Noriyuki , Sakai Akira , Mochizuki Shogo , Nakatsuka Osamu , Ogawa Masaki , Zaima Shigeaki , Tezuka Tsutomu , Sugiyama Naoharu , Takagi Shin-ichi
Published: October 2005

Microstructures in strain-relaxed SiGe buffer layers grown on silicon-on-insulator (SOI) substrates have been analyzed. The growth of strain-relaxed SiGe layers was achieved by two methods, a Ge-condensation method and a strain-relaxation method using a pure-edge dislocation network. We measured the surface morphology, dislocation structure, and crystalline mosaicity of the strain-relaxed SiGe layers and investigated the influence of various growth parameters. Transmission electron microscopy revealed residual strain-undulation elongating approximately along two orthogonal in-plane <110 > directions in a strain-relaxed SiGe layer formed by the Ge-condensation method. On the other hand, the morphology of pure-edge dislocations buried at the SiGe/SOI interface was dependent on the sample structure as well as the annealing process, both of which critically determine dislocation propagation in the SiGe layer. A clear correlation was obtained between the dislocation morphology in the SiGe layer and the crystalline mosaicity measured by X-ray diffraction analysis.
Terahertz-Induced Impact Ionization Effect in Semiconductor Heterojunctions
Authors: Cao J. C.
Published: October 2005

We have extended the balance equations to account for conduction–valence interband impact ionization (II) induced by an intense terahertz (THz) electromagnetic irradiation in two-dimensional semiconductors. We have studied the effect of II on electron transport and electron–hole pair generation–recombination rate in THz-driven InAs/AlSb heterojunctions (HJs). As many as needed multiphoton channels are self-consistently taken into account. Usually II acts as a cooling mechanism in semiconductors. In the present THz-radiation-driven case with a multiphoton process, the electron temperature with II, however, is higher than that without this process. We propose to explain the counterintuitive behavior of electron temperature in THz-radiation-driven HJs.
Photocarrier Injection and Current–Voltage Characteristics of La0.8Sr0.2MnO3/SrTiO3:Nb Heterojunction at Low Temperature
Authors: Muramatsu Takaki , Muraoka Yuji , Hiroi Zenji
Published: October 2005

An epitaxial heterojunction made of a p-type perovskite manganite La0.8Sr0.2MnO3 film and an n-type strontium titanate SrTiO3:Nb substrate has been fabricated by the pulsed laser deposition technique. The current–voltage (I–V) characteristics and photovoltaic properties are measured under UV light irradiation in a wide temperature range down to 10 K. It is found that the junction acts as an efficient UV photodiode with a large external quantum efficiency of 28%. It is also demonstrated that the manganite film can be doped with a certain amount of holes by photocarrier injection. The maximum surface hole density is estimated to be 3.0×1013 cm-2.
Physical Characteristic Effects of Contact Hole Reflow
Authors: Kim Sang-Kon
Published: October 2005

The thermal reflow process is one of many processes used for pattern shrinkage and resolution enhancement technology. In this study, we try to describe the shrinkage phenomena of linear static in contact hole patterns by the finite element method. The resist of thermal flow is designed as a circular saw blade for linear conduction thermal analysis. Using a commercial tool such as I-DEAS, the values of the modeled parameters corresponding to the resist parameters of shrinkage and deformation due to thermal reflow are extracted from a comparison of the experimental results. The contact hole patterns are linearly reduced due to the increase in temperature and the increase in heat flux. Hence, for the linear static phenomena, these mechanical simulations predict the contact hole patterns after thermal reflow. Also, we describe the effect of surface tension during the thermal reflow. In the thermal reflow process, as the temperature increases, the bottom corner edges of the resist profile are sharper below a specific temperature and more round above the same temperature. Using the description of surface tension effects in spin coating, it is shown that these phenomena are due to the surface tension.
Control of Nitrogen Depth Profile and Chemical Bonding State in Silicon Oxynitride Films Formed by Radical Nitridation
Authors: Kawase Kazumasa , Umeda Hiroshi , Inoue Masao , Tsujikawa Shimpei , Akamatsu Yasuhiko , Suwa Tomoyuki , Higuchi Masaaki , Komura Masanori , Teramoto Akinobu , Ohmi Tadahiro
Published: October 2005

Chemical bonding states and depth profiles of nitrogen in radical nitrided silicon oxide film formed in Ar/N2 plasma excited by microwave has been investigated using X-ray photoelectron spectroscopy with HF step etching. The main chemical bonding state of nitrogen atom is Si3≡N configuration, and the other unknown bonding state (termed Nhigh) is observed, whose peak energy shift is about +4.8 eV. The nitrogen atoms forming Si3≡N configuration accumulate only at the film surface and those forming Nhigh configuration are distributed deeper in the films. The Nhigh bond is very weak because it is desorbed completely at low temperature (300–500°C). Although the nitrogen atoms forming Nhigh configuration are removed by post O2-annealing, those forming Si3≡N configuration migrate toward the film/substrate interface and they increase negative bias temperature instability. In the case of ultra thin film, nitriding species forming Nhigh bond reach the film/substrate interface and form Si3≡N bond at the interface. Suppression of the generation of nitriding species forming Nhigh bond in the plasma is very important. It is clear that Nhigh bond is reduced using Ar/NH3 plasma.
ArF Photoresist Parameter Optimization for Mask Error Enhancement Factor Reduction
Authors: Lee Chang Ho , Oh Hye-Keun
Published: October 2005

The mask error enhancement factor (MEEF) is the best representative index for critical dimension (CD) variation in a wafer which is amplified by real specific mask CD variation. As already clarified in previous reports, MEEF is increased by reducing k1 (process ability index) or pattern pitch. The illumination system, just like lens aberration or stage defocus effects directly the MEEF value, but the leveling or species of a substrate and the resist performance are also strongly related to the MEEF value. In practice, when engineers set up the photoprocess for fabricating the miniaturized structures of current devices, they established minimum shot uniformity target such as the MEEF value within wafer uniformity and wafer-to-wafer uniformity, in addition to the usable depth of focus (UDOF) or exposure latitude (EL) margin. We examined MEEF reduction by checking the differences in resist parameters and attempted to correlate the results between experiment and simulation. Solid-C was used as the simulation tool. The target node is dense line/space pattern (L/S) of sub-80 nm and we used the same illumination conditions. We calculated MEEF values by comparing with the original mask uniformity using the optical parameters of each resist type. The normalized image log slope (NILS) showed us some points of the saturation value with pupil mesh points and the aberration is not considered. We used four different types of resist and changed resist optical properties (i.e., n, k refractive index; A, B, and C Dill exposure parameters). It is very difficult to measure the kinetic phenomenon, thus we chose the Fickian model in post exposure bake (PEB) and the Weiss model for development. In this paper, we suggest another direction of photoresist improvement by comparing the resist parameters with the MEEF values at different pitches.
High Interband Transitions in β-FeSi2 under Pressure
Authors: Sumida Yasunobu , Mori Yoshihisa , Takarabe Kenichi , Udono Haruhiko , Kikuma Isao
Published: October 2005

The effect of pressure on high interband transitions up to 3 eV in β-FeSi2 is studied by measuring reflectivity spectra up to 16 GPa. The evaluated linear pressure coefficients for the interband transitions are all positive and about 8 meV/GPa for the transitions below 1.6 eV and about 16 meV/GPa for those beyond 1.6 eV. The previously determined pressure coefficient of the direct absorption edge (0.875 eV) is 15.9 meV/GPa. This characteristic indicates that the density of states near the energy gap consists of two different bands, with large- and small-pressure coefficients.
Theoretical Investigation of Oxygen Diffusion in Compressively Strained High-Density α-Quartz
Authors: Akiyama Toru , Kageshima Hiroyuki , Uematsu Masashi , Ito Tomonori
Published: October 2005

The microscopic mechanisms of oxygen diffusion in compressively strained high-density α-quartz are investigated on the basis of first-principles total-energy calculations. It is found that both the incorporation energy of oxygen into SiO2 and the energy barrier for its diffusion are dependent on the density of SiO2. The activation energies show that molecular-type oxygen is the dominant diffusion species over the entire density range. Furthermore, the activation volumes estimated from the results of the present first-principles calculations imply the retardation of oxygen diffusion in the high-density region.
Etch-Byproduct Pore Sealing for Atomic-Layer-Deposited-TaN Deposition on Porous Low-k Film
Authors: Furuya Akira , Soda Eiichi , Shimada Miyoko , Ogawa Shinichi
Published: October 2005

Porous low-k and ultrathin atomic-layer-deposited (ALD)-TaN are expected to be useful materials for Cu interconnects in ULSI devices of the 45-nm technology node and beyond. One problem with integrating these into the Cu interconnect is the Ta penetration which occurs during ALD-TaN deposition. In this work, we propose a novel pore-sealing technique using an etch-byproduct that is deposited on a sidewall of the pattern during reactive-ion-etching of the stopper under the porous low-k. It was found that the Ta penetration is completely prevented by the etch-byproduct if the cap insulator for the porous low-k is a SiC/SiO2 multilayer. Two levels of single-damascene Cu interconnects with ALD-TaN and porous low-k were successfully fabricated without the penetration, and good electrical characteristics were obtained for the interconnects.
Temperature Dependence of AC Transport Current Loss of QMG Bulk Superconductor
Authors: Otabe Edmund Soji , Watanabe Tadaaki , Kiuchi Masaru , Matsushita Teruo , Morita Mitsuru
Published: October 2005

The AC transport current loss of a QMG bulk superconductor for a current-limiting device with a rectangular cross section was measured at various frequencies in the temperature range of 40–77 K. Since the AC transport current loss did not appreciably depend on frequency in the range of 35–70 Hz, the pinning loss was dominant. The experimental result was well explained by the numerical calculation by finite element method in which the Irie–Yamafuji model was assumed for the magnetic field dependence of critical current density. The AC transport current loss decreased markedly with decreasing temperature. Therefore, it is beneficial to decrease temperature, since the increase in cooling penalty is not significant. It was also found that cylindrical superconductors have a lower AC transport current loss than rectangular superconductors.
Vertically Aligned Liquid Crystal Cell with Image-Enhanced Reflector for High-Contrast Transflective Displays
Authors: Lee Gak Seok , Oh Min-Cheol , Kim Jae Chang , Yoon Tae-Hoon
Published: October 2005

We propose vertically aligned liquid crystal cell structures with image-enhanced reflectors for transflective displays. Liquid crystal (LC) molecules are aligned vertically so that an excellent dark state can be achieved. Wide-band quarter-wave design is employed to realize broad spectral characteristics over the entire range of visible wavelengths. The display performance in the transmissive mode can be markedly improved compared with that of homogeneous cells.
Low-Threshold-Current-Density, Long-Wavelength, Highly Strained InGaAs Laser Grown by Metalorganic Chemical Vapor Deposition
Authors: Chen I-Liang , Hsu Wei-Chou , Kuo Hao-Chung , Yu Hsin-Chieh , Sung Chia-Pin , Lu Chen-Ming , Chiou Chih-Hung , Wang Jin-Mei , Chang Yu-Hsiang , Lee Tsin-Dong , Wang Jyh-Shyang
Published: October 2005

A long-emission-wavelength laser with multiple InGaAs/GaAs quantum wells without a strain-compensated barrier was grown by metalorganic chemical vapor deposition (MOCVD). InGaAs quantum well (QW) broad-area laser diodes with an emission wavelength of up to 1214 nm were realized. A measured room-temperature threshold current density of only 173 A/cm2 for a 2-mm-cavity device and a transparency current density of 66 A/cm2 were obtained. The internal quantum efficiency and laser cavity loss were 67% and 6 cm-1, respectively.
Relativistic Calculations of Complete 4 fn Energy Level Schemes of Free Trivalent Rare-Earth Ions
Authors: Ogasawara Kazuyoshi , Watanabe Shinta , Ishii Takugo , Brik Mikhail G.
Published: October 2005

A recently developed computer package for a fully relativistic first-principles many-electron method based on a numerical solution of the Dirac equation is consistently applied to the calculations of the 4 f

n
energy level scheme of trivalent rare-earth ions in a free state. The overestimation of the energy levels obtained (which is a common feature of configuration interaction calculations of multiplet energies) is thoroughly dealt with in order to improve the correspondence between calculated and observed energy levels. As a result, the ion-dependent scaling factor is introduced, which significantly increases the accuracy of the calculations for rare-earth ions both in a free state and in a crystal.
Impurity Effect on Electrical Conduction in n-GaSe Doped with Si, Sn and Ge
Authors: Shigetomi Shigeru , Ikari Tetsuo
Published: October 2005

The impurity levels in Si-, Sn- and Ge-doped n-GaSe have been investigated by Hall effect measurements. The carrier transport caused by these group IV dopant atoms in GaSe is governed by the deep donor level of about 0.6 eV below the conduction band. The deep donor level is considered to be related to the defects or defect complexes formed by the dopant atoms in the interstitial site or interlayer.
Molecular Dynamic Study on Structure of Interface Formed by Binding Flat Amorphous Silica Surfaces at High Temperatures
Authors: Kuzuu Nobu , Nagai Ken , Tanaka Mitsuya , Tamai Yoshinori
Published: October 2005

The structure of the interface formed by the binding of flat amorphous silica (a-SiO2) surfaces at high temperatures was investigated by molecular dynamics simulation. The surface before binding was formed by the same method as that previously used for studying the a-SiO2 surface [J. Appl. Phys. 92 (2002) 4408], in which a slab of silica sandwiched by two vacuum regions is used as the unit cell under three-dimensional periodic boundary conditions. The surfaces were contacted by reducing the cell size along the vacuum-sandwiched direction progressively up to the size of the simulation cell being the same as that of the bulk silica. The system was then heated at high temperatures up to 3000 K and quenched to 300 K. Although the coordination numbers of almost all atoms are regular, that is, four for Si and two for O, at temperatures higher than 2500 K, the density of the interface remained lower than that of the bulk region.
Microspheres of Tellurite Glass Formed by Evaporation–Condensation Process under High Magnetic Field
Authors: Kitamura Naoyuki , Makihara Masaki , Mogi Iwao , Awaji Satoshi , Watanabe Kazuo , Motokawa Mitsuhiro
Published: October 2005

Sodium tellurite glass was evaporated by irradiating a CO2 laser beam under a high magnetic field with a large gradient. Glass microspheres were formed as a cloud of soot with the condensation of the vapor from the source glass. The flow of the glass soot due to thermal convection was observed when the glass source was evaporated under a zero field, but was suppressed by applying the high magnetic field with a large gradient, which reduces gravity for the glass by a magnetic force of -0.8g in the gravitational scale. The maximum size of the microspheres decreased to about half that of microspheres formed under a zero field. Sodium concentration in the microspheres was found to increase with magnetic field. A disturbance of the motion of evaporated species due to electromagnetic force was suggested as an origin of the suppression of recondensation to the surface of source glass melt under the high magnetic field, resulting in the increase in the sodium concentration of the microspheres and in the decrease in their size.
Photoinduced Processes of Solid Aromatic Compounds by Mid-IR Free Electron Laser
Authors: Tono Kensuke , Kondoh Hiroshi , Hamada Yasuhiro , Suzuki Takahiro , Bito Kotatsu , Ohta Toshiaki , Sato Shin , Hamaguchi Hiro-o , Iwata Akira , Kuroda Haruo
Published: October 2005

Effects of the irradiation of a mid-infrared (MIR) free electron laser on solid-state aromatic compounds were investigated for anthracene, tetracene, and perylene by time-of-flight mass spectroscopy, time-resolved optical emission spectroscopy, and X-ray absorption spectroscopy. The irradiation induced vaporization and chemical reactions on the sample surfaces, resulting in the formation of graphite-like species, which absorbed IR photons more efficiently than the intact molecules. Successive irradiation on the reformed surfaces induced plasma, which caused the molecular decomposition and ionization.
Friction Force Study on (010) Surface of Polydiacetylene Single Crystal
Authors: Jo Sadaharu , Yoshikawa Hitoshi , Nakashima Naoko , Fujii Akane , Takenaga Mitsuru
Published: October 2005

A friction force study was systematically performed on the (010) surface of a polydiacetylene (PDA) single crystal. The results indicated a decrease in friction forces along the [001], [102], [101], [100], [101] directions. Such frictional features were clarified with respect to the polymerization directions, crystallographic directions and the lines on lattice defects. The [001] direction with a minimum friction force corresponds to the polymerization direction. The result of white beam X-ray topography strongly supports the results of friction force microscope (FFM).
Three-Dimensional Optical Focusing Systems Utilizing Stress-Induced Bending of Concave Micromirrors
Authors: Kuo Ju-Nan , Lee Gwo-Bin , Pan Wen-Fung , Lee Huei-Huang
Published: October 2005

In this study, a three-dimensional optical focusing system utilizing stress-induced bending of concave micromirrors was examined. The shape and thermal effects of micromachined bilayer concave mirrors were first investigated. The characterization of the bilayer concave mirror with different Au distributions was performed to observe out-of-plane deformation. A finite-element model was established to analyze such a deformation. As postprocessing temperature increases, the curvature of the concave mirror increases, resulting in a larger out-of-plane deformation of the concave mirror. Finally, a novel reflective surface-micromachined three-dimensional focusing system was demonstrated. The three-dimensional focusing system comprised two optic fiber guide plates, a Fresnel lens, and a three-dimensional concave mirror. The concave mirror was capable of focusing and collecting light, and could be readily integrated into a micro-optical bench for various optical applications.
Enhancement of Electrokinetically-Driven Flow Mixing in Microchannel with Added Side Channels
Authors: Yang Ruey-Jen , Wu Chien-Hsien , Tseng Tzu-I , Huang Sung-Bin , Lee Gwo-Bin
Published: October 2005

Electroosmotic flow (EOF) in microchannels is restricted to low Reynolds number regimes. Since the inertial forces are extremely weak in such regimes, turbulent conditions do not readily develop. Therefore, species mixing occurs primarily via diffusion, with the result that extended mixing channels are generally required. The present study considers a T-shaped microchannel configuration with a mixing channel of width W=280 µm. Computational fluid dynamics simulations and experiments were performed to investigate the influence on the mixing efficiency of various geometrical parameters, including the side-channel width, the side-channel separation, and the number of side-channel pairs. The influence of different applied voltages is also considered. The numerical results reveal that the mixing efficiency can be enhanced to yield a fourfold improvement by incorporating two pairs of side channels into the mixing channel. It was also found that the mixing performance depends significantly upon the magnitudes of the applied voltages.
Polarized White Emission from Fluorene-Based Polymer Blends
Authors: Yao Yung-Hsin , Kung Liang-Rern , Hsu Chain-Shu
Published: October 2005

Three alternating co-polyfluorenes emitting primary red, green and blue (RGB) colors have been synthesized via a palladium-catalyzed Suzuki coupling reaction. All copolymers reveal good thermal stability and nematic liquid crystalline behavior. The polymers were fabricated to form a polarized electroluminescent device using poly(ethylene dioxythiophene)–poly(styrene sulfonicacid) (PEDOT–PSS) as an alignment layer. For the case of primary colors, a host-guest approach that utilized a blue light emission P1 as a host with a green light P2 or a red light P3 as a guest led to approximately two- to fourfold enhancement in luminescence in comparison with that of a neat film in polymer light emitting diodes (PLEDs), 1039 versus 2205 cd/m2 and 284 versus 1146 cd/m2. In the case of white light, as a consequence of blending, polarized emission peak ratio of up to 4.4 and a pure white luminance brightness of up to 1895 cd/m2 have been attained.
Novel Method for In Situ Monitoring of Thickness of Quartz during Wet Etching
Authors: Lee Chi-Yuan , Chang Pei-Zen , Chen Yung-Yu , Dai Ching-Liang , Chen Ping-Hei , Lee Shuo-Jen
Published: October 2005

In this work, we present a novel method based on a plate wave sensor for the in situ monitoring of the thickness of quartz membranes during wet etching. Similarly to oscillators and resonators, some acoustic devices require the thickness of quartz membranes to be determined precisely. Precise control of the thickness of quartz membranes during wet etching is important, because the thickness strongly influences post processing and frequency control. Furthermore, the proposed plate wave sensor, allows the thickness of quartz membranes from a few µm to hundreds of µm to be monitored in situ, which depends on the periodicity of an interdigital transducer (IDT). In summary, the proposed method for measuring the thickness of quartz membranes in real time has a high accuracy, is simple to set up and can be mass-produced. Also described herein are the principles of the method used, the detailed process flow, the measurement set up and the simulation and experimental results. The theoretical and measured values differ by an error of less than 1 µm, implying a close correspondence.
Microwave Sterilization Using Catalyst Material Filter
Authors: Takashima Hideaki , Wang Huagang , Miyakawa Yozo , Kanno Yoshinori
Published: October 2005

We developed a new microwave sterilization system that can rapidly raise filter temperature by microwave irradiation with a low microwave power. We prepared filters made of A2O3 wool to trap microorganisms. The filters were coated with TiO2 (anatase) by the sol–gel method before use. The filters were impregnated with each of two kinds of metals, Pt and Ag. We also prepared Tyranno-fiber (SiC continuous fiber containing small amounts of Ti, O) cloth and honeycomb SiC as filters. Two microorganisms, Escherichia coli and Bacillus subtilis were the targets in the present study. Cells of E. coli and B. subtilis loaded on the Ag-impregnated filter can be sterilized within 5 s by microwave irradiation. Tyranno-fiber cloth and honeycomb SiC were also effective for microwave sterilization. These results indicated that this technique enables rapid sterilization of E. coli and B. subtilis, and that microwave absorption materials, such as SiC and graphite, are effective for microwave sterilization filters.
Self-Assembled InAs Quantum-Dot Chains on Self-Formed GaAs Mesa-Stripes by Molecular Beam Epitaxy
Authors: Kanto Toru , Yamaguchi Koichi
Published: October 2005

The self-formation of InAs quantum-dot chains (QDCs) was demonstrated on GaAs/InGaAs/GaAs(001) layers by molecular beam epitaxy (MBE). In the MBE growth of a GaAs layer on a corrugated InGaAs/GaAs buffer layer, mesa-stripe structures with the {211}A side wall were spontaneously formed along the [1 10] direction. InAs QDCs were formed on the GaAs mesa stripes along the [1 10] direction. In particular, uniform InAs QDCs were fabricated on the vicinal GaAs(001) substrate, misoriented toward the [110] direction. The self-formation of QDCs was attributed to the misfit dislocation and step structure.
Thermal Behavior of SnO2–5 wt % Pd Composite Nanoparticles Fabricated by In-Situ Synthetic Method
Authors: Han Jeong-In , Hong Sung-Jei
Published: October 2005

In this paper, the thermal behavior of SnO2–5 wt % Pd composite nanoparticles fabricated by an in-situ synthetic method was characterized. The in-situ synthetic method made the composite nanoparticles in one process, which is different from the current method in which Pd catalyst doping is separated from the synthetic process for SnO2. Tin and palladium organic reagents were used for the in-situ synthesis. These materials enable low-temperature processing since the removal of organic components is possible below 300°C. High resolution transmission electron microscope (HRTEM) observation revealed that the size of the synthesized particles ranged from 2 to 7 nm and that the Pd catalyst is uniformly distributed in the lattice of the SnO2 particles. In fact, X-ray diffraction (XRD) analysis certifies a uniform solid solution of the Pd catalyst in SnO2 since a prominent Pd peak was not found. The specific surface area of the synthesized particles measured with a Brunauer–Emmett–Teller (BET) surface analyzer exceeded 100 m2/g. The SnO2–5 wt % Pd composite nanoparticles also exhibit an excellent sensitivity of 0.62, which is defined as a ratio of R
3500/R
1000, after aging at 400°C for 5 h. Thus, ultrafine SnO2–Pd composite nanoparticles can be synthesized by the in-situ synthetic method.
Preparation of Nanostructured TiO2 Powders with Additions of Various Metal–Chlorides for Efficient Photocatalyst
Authors: Kim Sun-Jae , Hwang Doo-Sun , Lee Nam-Hee , Shin Seunghan , Kim Seon-Jin
Published: October 2005

Preparation of nanostructured TiO2 powders for efficient photocatalyst was investigated through a direct crystallization from aqueous TiOCl2 solutions containing various metal–chlorides. The TiO2 powders without any additives and those added with Ni2+, Fe3+ and Nb5+ions, respectively, which has a similar cationic radius to Ti4+, were mainly crystallized to rutile phase, whereas those added with Al3+ and Zr4+ ions, which have a quite different positive ionic radius, were mainly crystallized to anatase phase. On the other hand, the secondary particles in the TiO2 powder consisted of acicular and spherical primary particles corresponding to rutile and anatase phases, respectively. From these results, it seems that the cationic radius of the additives could affect phase formation as well as morphology of TiO2 precipitates. Among the TiO2 powders prepared, Ni2+ doped powder, showing mainly rutile phase, had excellent photocatalytic ability in decomposition of 4-chlorophenol.
Bridging Growth of Single-Walled Carbon Nanotubes on Nanostructures by Low-Pressure Hot-Filament Chemical Vapor Deposition
Authors: Matsumoto Tetsunori , Homma Yoshikazu , Kobayashi Yoshihiro
Published: October 2005

Suspended single-walled carbon nanotubes (SWNTs) bridging between Si- or SiO2 nano-pillars were synthesized at low pressure using hot-filament chemical vapor deposition. The relation between the bridging probability of SWNTs and growth conditions was analyzed statistically. The bridging probability of the SWNTs strongly depends on pillar configuration, including pillar spacing, but is not significantly affected by the pressure, growth method, pillar material, and gas flow. These results indicate that environment in the gas phase has little influence on the suspended growth of SWNTs, and they support our vibratory growth model, in which the vibration of growing nanotubes plays a crucial role in bridging to an adjacent pillar.
Encapsulation of Organic Field-Effect Transistors with Highly Polarizable Transparent Amorphous Oxide
Authors: Kim Woo Jin , Koo Won Hoe , Jo Sung Jin , Kim Chang Su , Baik Hong Koo , Lee Jiyoul , Im Seongil
Published: October 2005

To enhance the stability of pentacene field-effect transistors, a highly polarizable amorphous oxide is used as a gas barrier due to the strong chemical interaction between permeating polar water molecules and an oxide. For a more reliable barrier function, in addition to chemical effects, a dense amorphous microstructure of a barrier is also preferred and achieved by ion-beam-assisted deposition (IBAD) at room temperature in this study. Our OTFTs encapsulated with IBAD SnO2 showed a degraded field-effect mobility of 0.5 cm2/(V s) after encapsulation. However, the field-effect mobility was surprisingly sustained up to one month and then gradually degraded down to 0.35 cm2/(V s) after 100 days in air, which was still three times higher than that of an OTFT without an encapsulation layer. The encapsulated OTFTs also exhibited a superior on/off current ratio of more than 105 to that of the unprotected device (∼104), which was reduced from ∼106 before aging. The effects of encapsulation on the electrical properties of OTFTs are discussed in terms of the physical and chemical properties of barrier films.
Nonlinear Current–Voltages Curves of Noble Metal Quantum Point Contacts
Authors: Yoshida Makoto , Oshima Yoshifumi , Takayanagi Kunio
Published: October 2005

Current–voltage (I–V) curves were studied for the quantum point contacts (QPCs) of gold, platinum, silver and copper at room temperature. Nonlinear I–V curves of a cubic function, I=a
V+c
V
3, were found for all QPCs, that were fabricated between a cleaned Scanning Tunneling Microscope (STM) tip and a cleaned substrate in an ultrahigh vacuum. The nonlinear parameter c/a was found to be positive, and scattered in the range of ∼0 to 1 [1/V2] independent of the conductance at the zero-bias voltage. The average value of c/a showed no strong dependence on the metal elements.
Transcranial Photoacoustic Measurements of Cold-Injured Brains in Rats
Authors: Ueda Yoshinori , Sato Shunichi , Hasegawa Makoto , Nawashiro Hiroshi , Saitoh Daizoh , Shima Katsuji , Ashida Hiroshi , Obara Minoru
Published: October 2005

We performed transcranial photoacoustic measurements of cold-injured brains in rats. Before inducing injury, a signal peak was observed at two locations corresponding to the surfaces of the skull and brain, while after injury, a third peak appeared at a location corresponding to the back surface of the skull; the third peak was found to be caused by subdural hematoma. The signal peak for the brain surface shifted to a deeper region with elapse of time after injury, indicating deformation of the brain. These findings suggest that small hemorrhage and morphological change of the brain can be transcranially detected by photoacoustic measurement.
Influence of KrF Excimer Laser Irradiation on Luminescent Performance of Polymer Light-Emitting Diodes
Authors: Lin Yow-Jon , Chou Wei-Yang , Lin Shih-Ting , Chen Yao-Ming
Published: October 2005

In this study, we find that KrF excimer laser irradiation is an effective treatment for enhancing polymer light-emitting diode (PLED) performance, due to the increase in work function and the amount of oxygen on the indium–tin oxide (ITO) surfaces and the reduction in ITO surface roughness, resulting in a reduction in leakage current at the polymer/ITO interface and an increase in device luminance. It is indeed necessary to minimize the leakage current to prevent unnecessary wasting of power and to increase external quantum efficiency.
Characterization of Spot-Size Dependence of Coarse Wavelength Division Multiplexing Dielectric Multilayer Thin-Film Filters for Planner Lightwave Circuit Platforms
Authors: Suda Satoshi , Koyama Fumio
Published: October 2005

We present the first measurement and modeling on the spot-size dependence multilayer thin-film filters used in coarse wavelength division multiplexing (CWDM) systems. The noticeable spot-size dependence can be seen for use in their multiplexer/demultiplexer based on planner lightwave circuit (PLC) platforms.
Multilayered Domain Control for Surface Plasmon Resonance
Authors: Saito Takao , Haraguchi Masanobu , Fukui Masuo
Published: October 2005

Metal particles are utilized to study surface plasmon resonance. They are regulated in terms of their dimensions to control surface plasmon resonance, and sealed with a dielectric material. In this study, we applied a method of domain growth to form particles. It is an advantage in manufacturing because the entire process is carried out in a sputtering system. We describe a method of multilayered domain control (MLDC), illustrating it with Au, Ag and Cu for particles and SiO2 for dielectric layers in this paper. A remarkable feature of MLDC is its intensification of surface plasmon resonance. Moreover, this intensification enables base metals to substitute for noble metals.
High Power Silicon Schottky Barrier Diodes with Different Edge Termination Structures
Authors: Liou Bor Wen , Chen Tron Min , Chen Chih Wei , Uang Kai Ming , Wang Shui Jinn
Published: October 2005

In this work, the design and fabrication of Au/n-Si Schottky barrier diodes (SBDs) with various edge termination schemes including a reduce surface field (RESURF) type lateral super-junction (LSJ), polysilicon (poly-Si) floating, and guard rings are presented. A novel method using ion implantation through a poly-Si film for guard ring fabrication is proposed to prevent damage to the silicon surface. Experimental results show that the reverse leakage current of the proposed SBDs is reduced by about two orders and the breakdown voltage is increased by more than 4-fold those of conventional SBDs.
Development of Thermoelectric Bi-Based Cobaltites with an Easy Axis of Magnetization Parallel to the C-Axis for Magnetic Alignment
Authors: Kumagai Toshiaki , Horii Shigeru , Uchikoshi Tetsuo , Suzuki Tohru S. , Sakka Yoshio , Okamoto Taichi , Shimoyama Jun-ichi , Kishio Kohji
Published: October 2005

We report the conversion of the easy axis of magnetization from the a-axis to the c-axis in thermoelectric misfit-layered Bismuth-based cobaltites for a magnetic grain-alignment process. The conversion was accomplished by the substitution of Ca for Sr in the block layer of [(Bi0.5Pb0.5)2Sr2O4]0.55CoO2. Moreover, magnetic anisotropy along the c-axis was enhanced by partial substitution of Pr for Ca in [(Bi0.5Pb0.5)2Ca2O4]
z
CoO2. From the analysis of their crystal structures, we concluded that the doping of Pr and Ca played a role in distortion of the block layer, indirectly leading to changes in the local structure of the CoO2 layers and magnetic anisotropy. The c-axis grain-aligned bulk has been successfully fabricated by a magnetic grain-alignment method in 10 T, and a drastic reduction in the resistivity perpendicular to the applied field and the grain-oriented microstructure were observed.
Current-Driven Magnetization Switching in CoFeB/MgO/CoFeB Magnetic Tunnel Junctions
Authors: Hayakawa Jun , Ikeda Shoji , Lee Young Min , Sasaki Ryutaro , Meguro Toshiyasu , Matsukura Fumihiro , Takahashi Hiromasa , Ohno Hideo
Published: October 2005

Current-driven magnetization switching in low-resistance Co40Fe40B20/MgO/Co40Fe40B20 magnetic tunnel junctions (MTJs) is reported. The critical-current densities J
c required for current-driven switching in samples annealed at 270 and 300°C are found to be as low as 7.8×105 and 8.8×105 A/cm2 with accompanying tunnel magnetoresistance (TMR) ratios of 49 and 73%, respectively. Further annealing of the samples at 350°C increases TMR ratio to 160%, while accompanying J
c increases to 2.5×106 A/cm2. We attribute the low J
c to the high spin-polarization of tunnel current and small M
s
V product of the CoFeB single free layer, where M
s is the saturation magnetization and V the volume of the free layer.
Effects of Ag Addition on the Resistivity, Texture and Surface Morphology of Cu Metallization
Authors: Zhao Bin , Kim Hoon , Shimogaki Yukihiro
Published: October 2005

Doping Cu with some elements has been proved to be a promising method to improve the reliability of Cu interconnects. In this paper, Ag was chosen as the alloying element because of its low bulk resistivity and low solubility in Cu. Cu–Ag alloy film was prepared by layered evaporation and postdeposition annealing in vacuum. The resistivity of the films decreased with annealing temperature. After annealing at 400°C, most of the Ag atoms were segregated to the film surface because Cu–Ag system had a negative segregation energy. By comparing the texture evolution of pure Cu film and Cu–Ag films during annealing, it was found that Ag addition usually retarded the texture development of the alloy film. Vacuum annealing resulted in a rougher surface for the Cu–Ag films. The investigation of alloying effect on Cu agglomeration on TaN substrate suggested that Ag addition might impair the Cu wettability on TaN substrate. Possible methods for improving the surface morphology of Cu alloy were also proposed.
Study of Transport and Dielectric of Resistive Memory States in NiO Thin Film
Authors: Kim Min Gyu , Kim Sun Man , Choi Eun Jip , Moon Seung Eon , Park Jonghyurk , Kim Hyoung Chan , Park Bae Ho , Lee Myoung Jae , Seo Sunae , Seo David H. , Ahn Seung Eun , Yoo In Kyeong
Published: October 2005

We have measured the DC resistance R(T) and AC dielectric constant ε(ω) for the bistable high-R and low-R states of NiO thin film. The high-R state shows thermally activated resistance and Debye relaxation of ε(ω). In the low-R state, R(T) exhibits a metallic temperature dependence of R(300 K)/R(5 K)=1.6. The value of ε(ω) is drastically different from that of the high-R state, and we interpret it in terms of the free-carrier Drude dielectric response. The plasma frequency ω
p

2 in the metallic low-R state is estimated to be 1.2×109/cm3.
Chirality Dependence of Mechanical Properties of Single-Walled Carbon Nanotubes under Axial Tensile Strain
Authors: Mori Hideki , Hirai Yoshihiko , Ogata Shigenobu , Akita Seiji , Nakayama Yoshikazu
Published: October 2005

The chiral dependence of the axial tensile strain versus stress characteristics for single-walled carbon nanotubes has been investigated by numerical simulation using a tight binding calculation and a first-principles density functional theory calculation. It is found that the tight binding calculation adopted is accurate. Both calculations show that nanotubes have a Young's modulus of 1.0 TPa and a maximum tensile strength of 0.10 TPa with no chiral dependence. However, the critical tensile strain for breaking has a chiral dependence. This is discussed from the viewpoint of the deformation of six-membered rings.
Fast Ambipolar Carrier Transport and Easy Homeotropic Alignment in a Metal-Free Phthalocyanine Derivative
Authors: Iino Hiroaki , Takayashiki Yukiko , Hanna Jun-ichi , Bushby Richard J.
Published: October 2005

We have investigated charge carrier transport in the various phases of the metal-free phthalocyanine derivative, 1,4,8,11,15,18,22,25-octaoctylphthalocyanine (8H2Pc), by the time-of-flight method. The discotic columnar phase of 8H2Pc easily self-organizes in columns perpendicular to the substrate when cooled from the isotropic phase. We found that well-defined transits were observed, not only for positive carriers, but also for negative carriers. For the columnar rectangular phase at 85°C the hole and electron mobilities were very high at 0.2 and 0.3 cm2/(V·s), respectively. These mobilities depend on neither electric field nor temperature. This ambipolar carrier transport was easily observed even in an ambient atmosphere. Interestingly, the mobility in the isotropic phase was of the order of 10-3 cm2/(V·s) and did not depend on temperature, which suggests that the electronic conduction is governed by charge carrier transport in that phase as well.
Mobility Enhancement in Strained Ge Heterostructures by Planarization of SiGe Buffer Layers Grown on Si Substrates
Authors: Sawano Kentarou , Abe Yasuhiro , Satoh Hikaru , Nakagawa Kiyokazu , Shiraki Yasuhiro
Published: October 2005

Compressively strained Ge channel p-type modulation-doped structures were fabricated on SiGe buffer layers planarized by chemical mechanical polishing (CMP). While the hole mobility of the sample without CMP was drastically reduced with decreasing channel thickness, a much higher mobility was maintained for the sample with CMP, suggesting that atomic-scale interface roughness as well as long-ranged roughness was significantly eliminated by CMP. As a result, mobility enhancement factors of 8 and 1.8 at 10 and 300 K, respectively, were obtained by CMP for a channel thickness of 7.5 nm, indicating that the planarization is very essential for realization of high-mobility strained Si/Ge heterostructures.