bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Speed Laser Probing System for Surface Acoustic Wave Devices Based on Knife-Edge Method
Authors: Kamizuma Hiroshi , Yang Liyan , Omori Tatsuya , Hashimoto Ken-ya , Yamaguchi Masatsune
Published: July 2005

This paper describes the development of a high-speed laser probing system for surface acoustic wave (SAW) devices. For the optical detection, the phase-sensitive knife-edge method was employed, by which the system is made very insensitive to low-frequency mechanical vibration. This enables fast stage translation without disturbing the measurement. A fast scanning rate of 240 points/s was realised by continuous stage translation and by successive data acquisitions of instantaneous sampling positions, in addition to the detector output. The position is measured by a high-precision linear-scale installed in the translation stage. Since the measured intervals between two adjacent sampling positions may not be uniform, the measured data are resampled at equal intervals for data processing. By applying the system to the characterisation of spurious resonance modes, it is shown how the present system is effective in designing and developing SAW devices.
Construction of Reference Data for Tissue Characterization of Arterial Wall Based on Elasticity Images
Authors: Inagaki Jun , Hasegawa Hideyuki , Kanai Hiroshi , Ichiki Masataka , Tezuka Fumiaki
Published: July 2005

Previously, we developed the phased tracking method [H. Kanai et al.: IEEE Trans. Ultrason. Ferroelectr. Freq. Control 43 (1996) 791] for measuring the minute change in thickness during one heartbeat and the elasticity of the arterial wall. By comparing pathological images with elasticity images measured with ultrasound, elasticity distributions for respective tissues in the arterial wall were determined. We have already measured the elasticity distributions for lipids and fibrous tissues (mixtures of smooth-muscle and collagen fiber) [H. Kanai et al.: Circulation 107 (2003) 3018]. In this study, elasticity distributions were measured for blood clots and calcified tissues. We discuss whether these elasticity distributions, which were measuerd in vitro, can be used as reference data for classifying cross-sectional elasticity images measured in vivo into respective tissues. In addition to the measurement of elasticity distributions, correlations between collagen content and elasticity were investigated with respect to fibrous tissue to estimate the collagen and smooth-muscle content based on elasticity. Collagen and smooth-muscle content may be important factors in determining the stability of the fibrous cap of atherosclerotic plaque. Therefore, correlations between elasticity and elements of the tissue in the arterial wall may provide useful information for the noninvasive diagnosis of plaque vulnerability.
Characteristics of Ultrasonic Suction Pump Without Moving Parts
Authors: Hasegawa Takeshi , Friend James , Nakamura Kentaro , Ueha Sadayuki
Published: July 2005

If an ultrasonically vibrating pipe is dipped into a liquid, the liquid is pumped up inside the pipe. We found in a previous study that the maximum pressure was improved from 1 kPa to 7.2 kPa if the end of the pipe was installed on a plate with a small gap. In this study, the configuration is modified for a practical design in which a still pipe is located at a right angle to a piston-vibrated surface. We investigate the difference in the pump characteristics between the former and new configurations. Our experiments show that a maximum pressure of 20.6 kPa is obtained by optimizing the inner and outer diameters of the pipe as well as the gap between the pipe end and the vibrator.
Radiation Characteristics of Hexagonal Transducer Array
Authors: Yokoyama Tomoki , Asami Tomohiro , Mori Kazuyoshi , Hasegawa Akio
Published: July 2005

A staggered transducer array such as a hexagonal transducer array is one of structures used to effectively suppress grating lobes. Some advantages of hexagonal array are outlined. The directivity of a hexagonal array consisting of circular sound sources is derived and compared with that of a conventional square array. Due to the suppression of grating lobes, a hexagonal array can use a larger sound source element than a square array and therefore the number of elements can be reduced. The hexagonal array emits a greater effective radiation power than the square array. In the case where an omnidirectional array is required, the hexagonal array is more effective than the conventional square array.
Range Step Size Analysis of Parabolic Equation Method in Megarange Propagation
Authors: Naoi Jun , Saito Hideaki , Hiyoshi Yoshihisa , Tsuchiya Toshio , Kikuchi Toshiaki
Published: July 2005

It is important to check the calculation accuracy of the simulation model when calculating sound propagation loss in the ocean. Conventionally, simulation of propagation loss has often been calculated for ranges shorter than several hundred km. In such cases, the result has been compared with a benchmark or standard result, for example those obtained by the normal mode method. However, a benchmark result is not available for long-range propagations exceeding 1000 km. Furthermore, it is difficult to make the range interval of calculation into a wavelength using the normal mode method. The parabolic equation (PE) method must have the calculation interval set shorter than the wavelength. Therefore, it is difficult to compare the results of the normal mode method and the PE method in the same calculation environment. On the other hand, with the PE method it is known that the error of division decreases when the calculation step size is set to small. However, the calculation time increases according to the reduction of calculation step size. Thus, we propose a calculation step size that is most suitable for megarange propagation simulation using the PE method.
Reverse Short-Channel Effect of Body Factor in Low-Fin Field-Effect Transistors Induced by Corner Effect
Authors: Nagumo Toshiharu , Hiramoto Toshiro
Published: July 2005

The impact of Fin-corner shape on the body factor γ of low-Fin (tri-gate) field-effect transistors (FETs) in both cases of highly doped channel and undoped channel has been investigated by three-dimensional device simulation. The behaviors of both threshold voltage (V
th) and γ depend on whether V
th is derived from on-state or off-state characteristics. In highly doped low-Fin FETs, γ derived from off-state characteristics (γI0) is strongly affected by corner shape, and the increase in γI0 with the reduction in gate length (reverse short-channel effect of γ) due to the corner effect has been observed in devices with sharp corners. The variation in off-current due to gate length fluctuation can be suppressed by applying a negative substrate bias thanks to the reverse short-channel effect of γ in highly doped low-Fin FETs with sharp corners. On the other hand, in undoped low-Fin FETs, the corner shape dependence is weaker and short-channel characteristics become considerably worse than those in highly doped FETs.
Nanometric Interfacial Polarization Phenomena in Organic Monolayer Films Studied by Maxwell Displacement Current-Second Harmonic Generation Spectroscopy
Authors: Tamura Ryousuke , Manaka Takaaki , Iwamoto Mitsumasa
Published: July 2005

Optical second-harmonic generation (SHG) and Maxwell displacement current (MDC) spectroscopy for the study of the dielectric polarization phenomena in organic monolayer films is described. It is shown that a spontaneous polarization and a nonlinear polarization are induced in monolayers due to symmetry breaking at the interface, and this leads to the generation of an MDC and an SH signal, respectively. The spontaneous and nonlinear polarizations are specified using orientational order parameters expressed using Legendre polynomials of orientational angle. The MDC-SHG experiments were carried out for mesogenic liquid crystal (LC) monolayers of 4'-n-octyl-4-cyanobiphenyl (8CB) on the air-water interface. It is shown that an MDC and an SH signal were generated reversibly in 8CB monolayers by compression and expansion.
Extremely High Degree Photoinduced In-Plane Reorientation in Azobenzene-Containing Polymer Liquid Crystal Film Using 633 nm Light
Authors: Uchida Emi , Kawatsuki Nobuhiro , Ono Hiroshi , Emoto Akira
Published: July 2005

The thermally enhanced photoinduced reorientation behavior of liquid crystalline (LC) polymethacrylate films comprising 4-methoxyazobenzene side groups with different spacer lengths between the azobenzene group and the polymer backbone was investigated based on axis-selective Z-to-E photoisomerization using linearly polarized (LP) 633 nm light and thermal amplification of the photoinduced anisotropy. A high-order in-plane reorientation parallel to the polarization (E) of LP 633 nm light was accomplished regardless of the spacer length. We found that the initial orientation of the mesogenic groups played an important role in the reorientation, and clarified the reorientation mechanism by polarization absorption spectroscopy.
Development of an Apertureless Near-Field Optical Microscope for Nanoscale Optical Imaging at Low Temperatures
Authors: Taniguchi Katsuya , Kanemitsu Yoshihiko
Published: July 2005

We have developed an apertureless scanning near-field optical microscope (apertureless SNOM) operating at low temperatures. The apertureless SNOM system is based on the atomic force microscope using a frequency modulation detection technique. The SNOM images reflect local optical properties of the sample surface, and optical images of a ferroelectric material are successfully obtained at low temperatures below a Curie temperature. The SNOM system developed in this work is a powerful tool to image local fields on the sample surface and to study phase transitions under high spatial resolution.
Optical Absorption of Highly Oriented Pc Derivatives/Arachidic Acid Mixture Langmuir-Blodgett Films
Authors: Yamaguchi Souki , Katayama Kuori , Hashimoto Takuya , Iwata Nobuyuki , Yamamoto Hiroshi
Published: July 2005

Langmuir-Blodgett (LB) films from the mixture solution of phthalocyanine (Pc) derivative/arachidic acid (AA) were accumulated on indium tin oxide (ITO) substrates with a Y-type structure. The layered structure of obtained films was investigated by AFM and XRD. The Hetero-type film, which was alternately accumulated by the mixture and pure AA layer, revealed highly orientation. A roughness Ra was 10.5 nm in the Y-type, 1.6 nm in the Hetero-type film. Bragg reflections from the lattice space of 5.4 nm were clearly observed in the Hetero-type film, while those were not obvious in the Y-type film. The absorption peak at ca. 760 nm, which was attributed to the Pc derivative, was broadened and/or vanished in the Hetero-type film. The results indicate AA layers might change the configuration of electrons of the Pc derivative.
Surface Plasmon Emission Light Property due to Molecular Luminescence and Molecular Interaction
Authors: Shinbo Kazunari , Toyoshima Susumu , Ohdaira Yasuo , Kato Keizo , Kaneko Futao
Published: July 2005

Surface plasmon (SP) emission light was observed for a merocyanine (MC) Langmuir-Blodgett (LB) film and an MC/crystal violet (CV) hetero-LB film in the ATR Kretschmann configuration. Intense photoluminescence of CV and quenching of MC were observed due to an energy transfer from MC to CV in the hetero-LB film. SP emission light due to CV was also observed for the MC/CV hetero-LB film. Furthermore, the emission light properties of the MC/CV hetero-LB film did not depend on the polarization direction of excitation light and were considered to be a result of the molecular shape of CV.
High-Efficiency Color and White Organic Light-Emitting Devices Prepared on Flexible Plastic Substrates
Authors: Mikami Akiyoshi , Koshiyama Tatsuya , Tsubokawa Tetsuro
Published: July 2005

Blue, green and white organic light-emitting devices doped with fluorescent dyes have been successfully fabricated on high-refractive-index plastic substrates and characterized in terms of their electrical and optical properties. The devices consist of a wide-band-gap polymer emissive layer stacked with several small-molecule layers and were designed considering carrier balance, carrier confinement, dye-guest doping and optical characteristics. It was demonstrated that dye-doped polymer devices are effective for the improvement of color and emission efficiency. We demonstrated deep-blue-, bright-green- and pure-white light-emitting devices having external quantum efficiencies and color coordinates (x,y) of 6.0% (0.15,0.07), 5.5% (0.20,0.60) and 4.0% (0.33,0.33), respectively.
Poly(3-hexylthiophene) Field-Effect Transistor with Controllable Threshold Voltage
Authors: Nishimura Haruka , Iizuka Masaaki , Sakai Masatoshi , Nakamura Masakazu , Kudo Kazuhiro
Published: July 2005

Poly(3-hexylthiophene) field-effect transistors (P3HT-FETs) have been prepared by an electric-field casting method. P3HT was cast onto a substrate with source and drain electrodes in nitrogen atmosphere saturated with CHCl3 vapor. An electric-field was applied between the electrodes during film formation. Thermal treatment and electric-field application were performed after film formation to control the device parameters. The threshold voltage (V
th) of P3HT-FETs without electric-field application during film formation was almost invariable after the thermal treatment. On the other hand, the V
th of P3HT-FETs formed with electric-field application can be controlled using thermal treatment. The device parameters can also be controlled by a post-electric-field application. These variations are a result of the doping or dedoping of O2. Two types of inverter showing different inversion points were fabricated using such controlled P3HT-FETs.
Investigation of Surface Damage in Si Exposed to Ar Plasma by Spectroscopic Ellipsometry and Grazing X-Ray Diffraction
Authors: Yamada Takahiro , Mizuno Kaoru , Kitahara Kuninori , Moritani Akihiro
Published: July 2005

Low-damage processes in plasma-surface interactions, particularly lattice deformation and the degree of damage in a single-crystal Si surface exposed to Ar plasma, are investigated by spectroscopic ellipsometry (SE) and grazing X-ray diffraction. The dielectric function spectrum of the damaged Si layer in nano-depth is obtained by use of damage depth estimated by a method based on SE model analysis and confirmed by step etching combined with SE measurement. The third-derivative lineshape of the imaginary part ε
2 of the complex-dielectric function provides the damage dependences of interband transition energy and broadening parameter for the E
1 (Λ3→Λ1) optical interband transition. The result shows that the surface damage proceeds through lattice expansion and relaxation. The lattice deformation in the damaged surface is also investigated by grazing X-ray diffraction. The X-ray rocking curve around (422)Si is asymmetric and involves small subsidiary curves corresponding to the lattice expansion and relaxation. These observations are in good agreement with the lattice deformation process obtained from the SE analysis.
Characterization of Nitride Layer on 6H-SiC Prepared by High-Temperature Nitridation in NH3
Authors: Liu YingShen , Hashimoto Susumu , Abe Katsuya , Hayashibe Rinpei , Yamakami Tomohiko , Nakao Masato , Kamimura Kiichi
Published: July 2005

The nitride layers were prepared by direct thermal nitridation of 6H-SiC substrates at 1200–1570°C in a NH3 atmosphere. The layer was characterized by using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Raman scattering spectroscopy. The thickness of the nitride layers prepared at lower than 1400°C was estimated to be less than 10 nm. The higher nitridation temperature resulted in the formation of a thicker surface layer. XPS measurement showed that the surface layer was composed of N, Si, C and O. Peaks corresponding to α-Si3N4 were detected in the Raman spectra and the XRD patterns of the sample prepared at higher than 1500°C, indicating the crystallization of the nitrided layer.
Growth Temperature Dependence of SrTiO3 Thin Films by Molecular Beam Epitaxy
Authors: Bhuiyan Md. Nurul Kabir , Kimura Hiroaki , Tambo Toyokazu , Tatsuyama Chiei
Published: July 2005

The effect of Sr deposition on the chemically formed SiO2 layer of Si(001) substrates and consequently the growth of SrTiO3 thin films on the Si(001)-Sr(2×1) surface have been studied using reflection high-energy electron diffraction (RHEED), X-ray diffraction and atomic force microscopy. After Sr deposition on the chemically formed SiO2/Si surface, a stable and well ordered Si(001)-Sr(2×1) surface is formed. The SrTiO3 film grown on the reconstructed Si(001)-Sr(2×1) surface at 350°C is amorphous. The sharp, streaky RHEED patterns and the strong STO (002) diffraction peaks and the smooth surface with root mean square roughness of approximately 4 Å suggest that high-quality SrTiO3 films are fabricated at temperatures (400–500°C) using molecular oxygen in molecular beam epitaxy.
Extinction of Large Droplets in Ion-Beam Ablation Plasma Produced by Ion-Beam Evaporation
Authors: Shishido Hiroaki , Yanagi Hideki , Kawahara Hideki , Suzuki Tsuneo , Yunogami Takashi , Suematsu Hisayuki , Jiang Weihua , Yatsui Kiyoshi
Published: July 2005

The extinction of large droplets in ablation plasma produced by intense pulsed ion-beam evaporation (IBE) has been proposed to improve the surface morphology of Al thin films on Si substrates. After the ion-beam irradiation of an Al target, a lot of spherical objects with diameters of approximately 20 to 100 µm were observed on the Al target surface, they are considered to be a possible origin of droplets commonly observed on Al thin films. However, the number of large droplets decreased with increasing distance between the Al target and Si substrate. The following model was considered to explain the obtained results. When a spherical object flies in the ablation plasma, it seems that the object fragments into small pieces or is evaporated. As a result, the number of large droplets decreases with increasing flight distance.
Kinetics of Ultrathin Thermal Oxide Growth on Si(001) Surfaces
Authors: Shimizu Hirofumi , Sato Taku
Published: July 2005

The oxidation kinetics and the effect of aluminum (Al) on the surface oxidation of silicon (Si) (001) in the temperature range from 600 to 900°C in a dry oxygen ambient have been investigated using spectroscopic ellipsometry and X-ray photoelectron spectroscopy. A nonlinear dependence of the thermal oxidation rate on temperature was observed at 760°C. At temperatures lower than 760°C, the activation energy was determined to be 0.27–0.57 eV for the first and/or second atomic layer of Si. The activation energy above 760°C was found to be 1.47–1.60 eV, approaching the value of bulk oxidation (∼2 eV), implying that the SiO2–Si interface moves deeper. It was found that the inclusion of Al reduces the oxide growth by 20 to 30% of that obtained on “clean” oxide. A schematic illustration that takes into account the mechanism by which a thin Al rich layer inhibits oxygen diffusion is presented.
Experimental and Numerical Analysis of An Inhibitor-Containing Slurry for Copper Chemical Mechanical Planarization
Authors: Zhuang Yun , Li Zhonglin , Shimazu Yoshitomo , Uotani Nobuo , Borucki Leonard , Philipossian Ara
Published: July 2005

A slurry containing Benzotriazole (BTA) as the inhibitor was analyzed in terms of its frictional, thermal and kinetic attributes for copper CMP applications. The frictional analysis indicated that `boundary lubrication' was the dominant tribological mechanism. Due to the presence of the inhibitor in the slurry, copper removal rate exhibited a highly non-Prestonian behavior. Based on the measured coefficient of friction (COF) and pad temperature data, a proven thermal model was used to predict wafer temperature. The Preston Equation was used to describe the polishing rate when p×V was lower than 11,000 Pa·m/s; while a modified Langmuir–Hinshelwood kinetic model was used to simulate the copper removal when p×V was higher than 11,555 Pa·m/s. Assuming that the adsorbed inhibitor layer was abraded off instantly from the copper surface when p×V was higher than 11,555 Pa·m/s, the modified Langmuir–Hinshelwood kinetic model indicated that copper polishing was chemically limited in this polishing region.
Free Carrier Concentration Gradient along the c-Axis of a Freestanding Si-doped GaN Single Crystal
Authors: Yoon M. , Park Il-Woo , Choi H. , Park Sung Soo , Koh Eui Kwan
Published: July 2005

The charge carrier concentration variance in a freestanding Si-doped GaN single crystal grown by hydride vapor phase epitaxy (HVPE) has been investigated. A transverse micro-Raman scattering measurement along the [0001] c-axis on the cross section of the n-type GaN was performed to obtain the profile of the free carrier concentration. The analysis of the coupled modes of plasmons and longitudinal optical (LO) phonons revealed the presence of a free carrier concentration gradient along the c-axis, which gradually varies from 2.3×1017 (N face) to 9.3×1017 cm-3 (Ga face). The possible physical origins of the charge carrier concentration gradient in the GaN crystal were discussed on the basis of current theories and experimental results of the growth mechanism of an n-doped GaN single crystal.
Theoretical Analyses of Oxide-Bypassed Superjunction Power Metal Oxide Semiconductor Field Effect Transistor Devices
Authors: Chen Yu , Liang Yung C. , Samudra Ganesh S.
Published: July 2005

The performance merit of silicon unipolar power devices is best described by a trade-off relationship between specific on-state resistance (R
on,sp) and breakdown voltage (V
br), which leads to the establishment of an ideal unipolar limit on device performance. Recently, engineering the electric field in the device drift region to break this unipolar silicon limit for superior performance has become an important research topic. The superjunction (SJ) structure achieves this by paralleling precisely matched higher doping alternate p–n layers to replace the typically low doping drift region. Alternatively, for fabrication simplicity in an oxide-bypassed (OB) structure, an oxide layer of predetermined thickness together with a polycontact is used to replace the p-column of the SJ structure to modulate the electric field. The further improved gradient OB (GOB) structure with slanted oxide sidewalls delivers a performance similar to ideal SJ devices. In this paper, detailed theoretical analyses in closed-form equations on OB and GOB devices are made for the first time to model the performance in various operating regions. The theoretical analyses were also carefully verified through two-dimensional numerical simulations.
On the Origin of Improved Conversion Efficiency of Solar Cells Based on SiGe with Compositional Distribution
Authors: Usami Noritaka , Fujiwara Kozo , Pan Wugen , Nakajima Kazuo
Published: July 2005

We report on the theoretical investigation of photovoltaic power conversion of SiGe with a compositional distribution by a simple approach. The absorption coefficient and the intrinsic carrier concentration, which greatly affect photovoltaic properties, are treated as macroscopically uniform parameters and expressed using the compositional distribution. By solving a steady-state continuity equation under solar light illumination, the performance of the solar cell based on SiGe with the compositional distribution is predicted. As a result, the existence of a compositional window where the conversion efficiency of the solar cell based on SiGe can surpass that of the solar cell based on Si is suggested. Such a window appears due to the increased absorption coefficient when the diffusion length of minority carriers is finite. This prediction agrees with the experimental results of the performance of SiGe solar cells with a systematically varied average Ge composition.
Growth of AlN by the Chemical Vapor Reaction Process
Authors: Hashimoto Tadao , Fujito Kenji , Samonji Katsuya , Speck James S. , Nakamura Shuji
Published: July 2005

AlN was grown by a chemical vapor reaction process with metallic Al and ammonium chloride as source precursors. A detailed parameter study was performed for direct growth on sapphire substrates. Specular films were obtained with optimum ammonium chloride supply for a given temperature. Due to lack of optimization of initial growth conditions, these specular films on sapphire contained polycrystalline inclusions. These inclusions were successfully avoided by regrowing on metalorganic chemical vapor deposition (MOCVD)-grown AlN templates. Inversion domains which existed in the MOCVD templates were eliminated at the interface of regrowth although the density of edge-type dislocations was not reduced, and remained at 9.3×109 cm-2. Growth on grooved sapphire resulted in AlN domains with their c-axis perpendicular to the sidewalls of the grooves. The top free surface which was inclined by about 20° to the basal plane of the sapphire substrate was m-plane. The top portion of this domain showed reduced dislocation density, as low as 8×108 cm-2.
Analysis of Heat Release from Gain Medium of Chemical Oxygen Iodine Laser
Authors: Takeuchi Noriyuki , Sugimoto Daichi , Tei Kazuyoku , Nanri Kenzo , Fujioka Tomoo
Published: July 2005

Heat release into the operating gas of a chemical oxygen iodine laser is analyzed on the basis of stagnation and cavity pressures. The energy of excited oxygen molecules is released as heat in this device through pooling reactions, iodine dissociation, and the interactions of these processes with water vapor. The proposed estimation method is applied to the analysis of subsonic and transonic iodine injection schemes to examine energy loss during iodine dissociation. The results also provide the number n of excited oxygen molecules consumed in each iodine dissociation. The values of n were estimated to be n≥10 and n≥6 in the subsonic and transonic injection schemes, respectively.
High-Pressure Nozzle Bank for a Chemical Oxygen Iodine Laser
Authors: Takeuchi Noriyuki , Sugimoto Daichi , Tei Kazuyoku , Nanri Kenzo , Fujioka Tomoo
Published: July 2005

A new nozzle bank for an ejector-chemical oxygen-iodine laser consisting of two-dimensional slit nozzles with a trip-jet mixing system was designed, fabricated, and tested with a nitrogen flow operation regime. Computational fluid dynamics (CFD) was used to optimize the trip system design. Horizontal Pitot scan experiments demonstrated that the mixing ability of the trips is excellent. The Mach number of the mixed flow was approximately 3. The average Pitot pressure at the laser cavity was more than 100 Torr. Backpressure tests were conducted, and the results of these tests revealed that the static pressure in the cavity remains constant at approximately 10 Torr until the supersonic diffuser breaks back and the cavity unstarts at a backpressure of approximately 80 Torr.
Offset of Multiple-Beam Interference inside Anisotropic Multilayered Structure: Determination of Polar Anchoring Strength at Nematic Liquid Crystal-Wall Interface
Authors: Hung La Trong , Kimura Munehiro , Akahane Tadashi
Published: July 2005

An optical technique for eliminating the inaccuracy in the measurement of retardation caused by multiple-beam interference in anisotropic multilayer-structured thin film is developed by the detailed analysis of obliquely incident transmission ellipsometry. The director distribution of a nematic liquid crystal inside a conventional sandwich-type cell which constitutes glass substrates, alignment films and transparent electrodes can be accurately determined without taking complicated multilayer analysis into account. As a typical application, a novel method of determining of the polar anchoring strength at the nematic liquid crystal-wall interface is proposed. The accurate measurement of the director distortion of a NLC without information on the refractive indices of ITO films, alignment films and glass substrates results in the realization of polar anchoring strength with a high accuracy. This technique can be used to achive a strong polar anchoring reaching the order of 10-3 J/m2.
Friction of C60 Molecules at Noble Metal Surfaces Detected by Change in DC Resistivity
Authors: Nouchi Ryo , Kanno Ikuo
Published: July 2005

To test the applicability of the friction model to the vibrational damping of adsorbed molecules via the excitation of electron–hole pairs, the change in DC resistivity induced by C60 adsorption onto polycrystalline noble metal films (Au, Cu, and Ag) was measured. The friction coefficients were found to be 1.1×1010, 1.7×1010, and 2.8×1010 s-1 for C60/Au, C60/Ag, and C60/Cu systems, respectively. The obtained friction coefficients increase in the order Au, Ag, and Cu; the order correlates with the charge transfer effect across C60/noble metal interfaces. The values deduced from the resistivity data were ten times higher than that predicted by the friction model, indicating that the friction model is not appropriate for obtaining accurate estimations in cases of the adsorption of rather heavy molecules such as C60.
1.1 mW Single-Mode Output Power of All-Monolithic 1.3 µm InAlGaAs/InP Vertical Cavity Surface Emitting Lasers Grown by Metal Organic Chemical Vapor Deposition
Authors: Park Mi-Ran , Kwon O-Kyun , Yoo Byueng-Su , Lee Ki-Hwang , Song Hyun-Woo , Han Won-Seok , Park Sang-Hee Ko , Kim Jong-Hee , Park Seong-Joo
Published: July 2005

We present all-monolithic InAlGaAs/InP vertical cavity surface emitting lasers (VCSELs) emitting wavelength of 1.3 µm grown by metal organic chemical vapor deposition (MOCVD). The devices with tunnel junction (TJ) and the air-gap aperture showed the performances as high as output power of 1.1 mW and as low as threshold current of 1.9 mA operating in single-mode at room temperature. We obtained the emitting transverse wavelength of 1333.1 nm with side mode suppression ratio (SMSR) of 40 dB, the continuous wave (CW) operation of temperature over 80°C, and modulation bandwidth exceeding 2.5 Gbit/s.
Peltier Effect in Sub-micron-Size Metallic Junctions
Authors: Fukushima Akio , Yagami Kojiro , Tulapurkar Ashwin A. , Suzuki Yoshishige , Kubota Hitoshi , Yamamoto Atsushi , Yuasa Shinji
Published: July 2005

Resistance (R)–current (I) curves in trilayer CPP-GMR (current perpendicular to plane-giant magnetoresistance) elements show a parabolic baseline because of Joule heating, and abrupt jumps due to magnetization reversals. The bottom of the parabolic baseline shifts in one current direction for reasons that were previously unclear. Our study of the R–I characteristics of CPP elements with various structures showed (i) the shift in the R–I curve originates from Peltier cooling in the CPP elements; (ii) the cooling power per unit area of the CPP elements (∼105 W/cm2) is much greater than that of conventional thermoelectric materials (∼5 W/cm2).
Ge-Dot Formation on Si(111)-7 ×7 Surface with C Predeposition Using Monomethylsilane
Authors: Narita Yuzuru , Sakai Masashi , Murata Takeshi , Endoh Tetsuo , Suemitsu Maki
Published: July 2005

The effects of carbon (C) predeposition using monomethylsilane (MMS) on germanium (Ge) dot formation on a Si(111)-7 ×7 surface have been investigated. As a result, the C gas source was found to be effective, equally as the solid source, in reducing and densifying the Ge dots. In addition, the Si adatoms supplied from MMS show a positive effect in aligning the Ge dots. Raman spectra evaluation indicated that the Ge dots at higher MMS exposures (>80 L) were nearly dislocation free.
Effects of Abrasive Size and Surfactant Concentration on the Non-Prestonian Behavior of Ceria Slurry in Shallow Trench Isolation Chemical Mechanical Polishing
Authors: Kang Hyun-Goo , Katoh Takeo , Park Hyung-Soon , Paik Ungyu , Park Jea-Gun
Published: July 2005

We examined the dependence of a non-Prestonian behavior on surfactant concentrations in ceria slurries that contained abrasives of various sizes by performing chemical mechanical polishing (CMP) tests using blank wafers. We found that both the surfactant concentrations and the slurry abrasive sizes influence the non-Prestonian behavior. In this paper, we explain in detail a factor that can be used to quantify relation on the non-Prestonian behavior of a slurry, βNP. This non-Prestonian factor βNP was determined to be almost independent of the surfactant concentration in slurry A (large abrasive), but increased with the surfactant concentrations in slurries B (medium-sized abrasive) and C (small abrasive).
Electronic Structure Characteristics of MBE (molecular beam epitaxy)-Grown Diluted Magnetic Semiconductor Ga1-xCrxN Films
Authors: Takeuchi Tomoyuki , Taguchi Munetaka , Harada Yoshihisa , Tokushima Takashi , Takata Yasutaka , Chainani Ashish , Kim Jung-Jin , Makino Hisao , Yao Takafumi , Tsukamoto Takeyo , Shin Shik , Kobayashi Keisuke
Published: July 2005

We study the electronic structure of newly discovered MBE-grown diluted magnetic semiconductor Ga1-x
Cr
x
N(x = 0.0, 0.06, 0.29, 1.0) films, using X-ray absorption spectroscopy across the N 1s and Cr 2p edges. Angle-dependent N 1s absorption results of pure GaN and ferromagnetic Ga0.94Cr0.06N exhibit identical behaviour of the N 2p

x
, 2p

y
and 2p

z
states, typical of the wurtzite structure. In addition, Ga0.94Cr0.06N shows a new feature derived from N 2p states hybridized with Cr 3d states, within the band gap of GaN. Cr 2p absorption spectra show spectral features consistent with tetrahedrally co-ordinated CrN4 cluster calculations. Excess Cr-content shows up as cubic CrN impurity phase, which is confirmed by comparing experimentally with pure CrN spectral features as well as with cluster calculations in octahedral geometry. The results indicate that the new unoccupied states formed in the band gap of the Cr-substituted wurtzite GaN are important for ferromagnetism.
Improvement of Ferroelectric Properties in RF-Magnetron-Sputtered SrBi2Ta2O9 Thin Films by Addition of Si Atoms
Authors: Kikuchi Shin , Ishiwara Hiroshi
Published: July 2005

Si-added SrBi2Ta2O9 (SBT) ferroelectric films were prepared on a Pt/Ti/SiO2/Si(100) structure by an RF magnetron sputtering method. The films were deposited at temperatures below 100°C to suppress the evaporation of Bi atoms and crystallized at 800°C in air. The Si/Ta atomic ratio in the sputtering targets was changed in the range from 0 to 0.1. It was found, for the sample with the Si/Ta ratio of 0.05, that its remanent polarization (2P
r = 20 µC/cm2) and the shape of its hysteresis loop in the polarization vs electric field (P-E) characteristic were not degraded compared to those of a pure SBT sample. It was also found that the leakage current characteristics were improved in the Si-added SBT films. Finally, the Si-added samples were annealed in oxygen ambient at 7 atm and further improvements in the leakage current and imprint characteristics were achieved.
Large Optical Transmission through a Single Subwavelength Hole Associated with a Sharp-Apex Grating
Authors: Ishi Tsutomu , Fujikata Junichi , Ohashi Keishi
Published: July 2005

The effect of grating shapes on optical transmission in a bull's eye structure (a single subwavelength hole surrounded by a concentric grating in a metal) is discussed. Finite-difference time-domain calculations predict that a sharp-apex shape gives as high a reflective structure to the propagating surface plasmon polaritons (SPPs) as does a rectangular shape. Fabricated samples with a sharp-apex grating actually show large optical transmission (a factor of 400 greater than that of samples with a single hole) even when the number of corrugations is three. This result indicates that a sharp-apex grating acts as an effective SPP reflector to confine the energy around the hole, resulting in high optical throughput.
Bridge Mask Growth Using Organomtallic Vapor Phase Epitaxy
Authors: Kim Jeong Soo , Lee Yong-Hee , Chang Kee Joo
Published: July 2005

For the area-dependent epitaxial growth, we propose a new epitaxial growth technique named the bridge mask growth. In this method, growth characteristics are controlled by spatial dimensions such as SiN
x
bridge width and the gap distance between SiN
x
bridges. We have successfully achieved a reduction in the growth rate and an energy band gap shift in multi-quantum-well structure using this technique.
Effect of Dispersant Addition during Ceria Abrasive Milling Process on Light Point Defect (LPD) Formation after Shallow Trench Isolation Chemical Mechanical Polishing (STI-CMP)
Authors: Kang Hyun-Goo , Katoh Takeo , Kim Dae-Hyung , Paik Ungyu , Park Jea-Gun
Published: July 2005

We examined both the dispersant mixing time during ceria slurry synthesis and a method for reducing the quantity of agglomerated large particles, which influence the number of light point defects (LPDs) formed after chemical mechanical polishing (CMP). We quantified the dispersion stability of slurries with the abrasive particle size by examining with and without ultra-sonic treatment. Without the addition of dispersant before mechanical milling, the dispersion stability was worse than the case with dispersant addition before milling. A lower pH of cerium carbonate improved both the dispersion stability and reduced the number of LPDs formed on an oxide film after CMP.
Critical Current Control in YBa2Cu3O7-δFilms Using Artificial Pinning Centers
Authors: Matsumoto Kaname , Horide Tomoya , Ichinose Ataru , Horii Shigeru , Yoshida Yutaka , Mukaida Masashi
Published: July 2005

High-temperature superconductors can carry high non dissipative currents at low temperatures as long as quantized vortices are pinned. However, the currents in a magnetic field at liquid nitrogen temperature (77 K) are not sufficiently high for practical use due to the weak pinning. For the improvement of nondissipative currents in YBa2Cu3O7-δfilms, linear defects that extended to thec-axis of the film were introduced using a novel nanostructure technology. We observed a marked enhancement of the nondissipative currents even at 77 K and high fields when the fields were applied close to thec-axis. This is a clear demonstration of enhanced pinning using artificially incorporated pinning centers.
Fast Boron Diffusion in Si Crystal under Electron Irradiation at Room Temperature Indicated by the Enhanced Formation of Boron-Hydrogen Pairs
Authors: Suezawa Masashi , Kojima Ken-ichi , Kasuya Atsuo
Published: July 2005

We observed the enhanced formation of boron-hydrogen (BH) pairs during electron irradiation of Si crystals co-doped with boron and hydrogen. Such formation was not observed in case of GaH pairs. These results indicate that the BH formation during electron irradiation is due to enhancement of B motion but not hydrogen motion. The optical absorption spectrum of BH pairs observed in the above experiment was the same as that formed by annealing of similar specimens, in which B occupies a substitutional site, B(s). Hence, the observed spectrum is due to B(s)H pairs in both experiments, even though the above B motion occurs due to motion of interstitial B.
Flexible Transparent Organic Light Emitting Devices on Plastic Films with Alkali Metal Doping as Electron Injection Layer
Authors: Uchida Takayuki , Kaneta Shingo , Ichihara Masahiro , Ohtsuka Masao , Otomo Toshio , Marx Daniel R.
Published: July 2005

Flexible transparent organic light emitting devices (FTOLEDs) with of both mechanical flexibility and transparency to visible light were fabricated. For the design of FTOLEDs, the electron and hole injection layers and carrier blocking layers have to be taken into consideration. By the insertion of BCP as a hole blocking layer, carriers and excitons were confined to increase recombination rate. Moreover, by alkali metal doping of 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), the electron injection of FTOLEDs was improved. The device showed 70% transparency at 520 nm, and the total external quantum efficiency from both surfaces of the device was 0.36%. The radius of curvature of FTOLED cells was approximately 2.5 cm.
Direct Modification of Magnetic Domains in Co Nanostructures by Atomic Force Microscope Lithography
Authors: Takemura Yasushi , Hayashi Satomi , Okazaki Fuminori , Yamada Tsutomu , Shirakashi Jun-ichi
Published: July 2005

The direct modifications of magnetic domain structures and magnetic anisotropy in Co-based nanostructures were studied. A Co rectangular structure of 5.1 µm length × 0.8 µm width was fabricated from a 15-nm-thick Co thin film deposited on a Pt layer on a SiO2/Si substrate by conventional processes of electron beam lithography and lift-off. The magnetic domain structure of the Co rectangle was divided by atomic force microscope (AFM) nano-oxidation. It was found that the magnetic domain structures could be controlled by AFM lithography. It was also proposed that the magnetic anisotropy could be directly modified by the nanolithography technique.
Two-Dimensional Crossed Polarization Gratings in Photocrosslinkable Polymer Liquid Crystals
Authors: Ono Hiroshi , Hatayama Akira , Emoto Akira , Kawatsuki Nobuhiro , Uchida Emi
Published: July 2005

Various types of two-dimensional crossed polarization gratings have been prepared in a photocrosslinkable polymer liquid crystal substituted with a 4-methoxycinnamoyloxybiphenyl side group by the use of orthogonally polarized ultraviolet interference light and subsequent annealing. The phase grating is almost invisible after irradiating the ultraviolet interference light without annealing and is thermally enhanced during the subsequent annealing. The two-dimensional crossed polarization gratings can generate two-dimensional diffraction patterns with various types of polarization states. The experimental results are in good agreement with the theoretical expectations on the basis of the Jones calculus.
Hetero-Epitaxial Growth of CeO2 Films on MgO Substrates
Authors: Mukaida Masashi , Miura Masashi , Ichinose Ataru , Matsumoto Kaname , Yoshida Yutaka , Horii Shigeru , Saito Atsushi , Hirose Fumihiko , Takahashi Yutaka , Ohshima Shigetoshi
Published: July 2005

High quality hetero-epitaxial CeO2 films are grown on MgO substrates using BaSnO3 buffer layers. CeO2 films and BaSnO3 buffer layers are grown by a pulsed laser deposition method. It is found that the crystallinity of the CeO2 films directly grown on MgO substrates is quite poor. However when we grow CeO2 films on MgO substrates with a BaSnO3 buffer layer, the crystallinity of CeO2 films is improved from that of the directly grown CeO2 films. Also the estimated in-plane crystallinity (δφ) of the CeO2 films on the BaSnO3 buffer layers is much improved by the introduction of the buffer layers. One of the reasons for high quality CeO2 films are grown on MgO substrates by the introduction of BaSnO3 buffer layers is the lattice matching between the CeO2 films and the MgO substrates. The CeO2 films grow in a 45° rotated mode to the BaSnO3 buffered MgO substrates, then the lattice mismatch between the sublattice of the CeO2 films and the MgO substrates is calculated to be 9.3%, while that of the CeO2 films on MgO substrates in a cube on cube mode is over 25%.
Air Stable n-type Top Gate Carbon Nanotube Filed Effect Transistors with Silicon Nitride Insulator Deposited by Thermal Chemical Vapor Deposition
Authors: Kojima Atsuhiko , Shimizu Mitsuyasu , Hyon Chan , Kamimura Takafumi , Maeda Masatoshi , Matsumoto Kazuhiko
Published: July 2005

The air stable n-type carbon nanotube channel filed effect transistor (CNT-FET) with the top gate structure was successfully fabricated using the silicon nitride gate insulator deposited by the thermal chemical vapor deposition. The effects of the silicon nitride insulator on the electrical properties of the CNT-FET have been investigated. The p-type characteristics of the CNT-FET can be converted to the n-type characteristics in high yield of 90% only by depositing the silicon nitride insulator. The drain current is as high as few µA order. The n-type top gate CNT-FET stably operated even in ambient air.
Fabrication of Hf(C)N Films on SiO2 by Metal Organic Chemical Vapor Deposition (MOCVD) Using TDEAHf Precursor
Authors: Wang Wenwu , Nabatame Toshihide , Shimogaki Yukihiro
Published: July 2005

Hafnium carbonitride Hf(C)N was fabricated as a gate metal electrode on SiO2 by the metal organic chemical vapor deposition (MOCVD) technique with tetrakis-diethylamido-hafnium Hf[N(C2H5)2]4 (TDEAHf) precursor. The chemical composition and electrical resistance of the films were evaluated using X-ray photoelectron spectroscopy (XPS) and four-point probe techniques, respectively. NH3-free growth with H2 carrier gas proved an effective method to fabricate metallic Hf(C)N films, although the composition and electrical properties of the films strongly depended on the growth temperature. Above 600°C, the resistivity decreased to about 104 µΩ-cm. Based on the chemical analysis by XPS, the formation of HfN
x
and HfC
x
resulted in metallic characteristic in the fabricated films.
Application of Dopant-Induced Laser Ablation to Site-Selective Modification of Sea-Island Structures of Polystyrene-block-poly(4-vinylpyridine) Films
Authors: Wang Zhixiang , Masuo Sadahiro , Machida Shinjiro , Itaya Akira
Published: July 2005

Dopant-induced laser ablation was applied to thin polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymer films doped selectively with tetrakis(4-carboxyphenyl)porphine (TCPP) into the nanoscale spherical domain of P4VP-island parts. Under dry-film conditions, the ablation of the island parts was not induced. On the other hand, in methanol solvent, only the P4VP-island parts doped with TCPP were ablated selectively. The dopant-induced laser ablation is attributed to the fact that the P4VP-island parts are in the swollen state, where P4VP chains cross-linked by TCPP-dopant molecules exist with a high density in methanol. This is the first report concerning the site-selective laser ablation of diblock copolymer films.
Resistivity of Thin Copper Interconnection Layers
Authors: Hara Tohru , Shimura Yasu , Namiki Ken
Published: July 2005

Resistivity is observed quantitatively in a thin electroplated copper layer. A resistivity of 2.6 µΩ·cm is observed in a 600-nm-thick as-deposited copper layer by conventional electroplating. This resistivity increases rapidly with decreasing thickness and reaches 7.8 µΩ·cm at a thickness of 75 nm. This rapid increase is mainly due to the increase in the orientation ratio of the copper (111)/(200). The resistivity in the as-deposited layer is maintained at 2.2 µΩ·cm in a 75 nm low resistivity layer with a low orientation ratio. Such a low-resistivity thin layer is electroplated practically by newly developed process. The preparation of a low-stress seed layer is also required in this electroplating process.
Generation of MeV-Order Deuterons by Focusing Low-Terawatt Tabletop Laser Pulses onto Microporous Polytetrafluoroethylene Film Loaded with Deuterated Polystyrene
Authors: Takahashi Hironori , Okihara Shin-ichiro , Fujimoto Masatoshi , Okazaki Shigetoshi , Ito Toshiaki , Ohsuka Shinji , Aoshima Shin-ichiro , Tsuchiya Yutaka
Published: July 2005

By focusing 2.4 TW, 50 fs laser pulses onto a microporous polytetrafluoroethylene film loaded with deuterated polystyrene, we successfully generated MeV-order deuterons. The number of over-1-MeV deuterons generated during 640 shots is estimated to be about 8 ×106.
MoO2 Hollow Fiber with Rectangular Cross Sections
Authors: Suemitsu Maki , Abe Toshimi , Na Hyoung-Jun , Yamane Hisanori
Published: July 2005

Molybdenum oxide hollow fiber with rectangular cross sections has been discovered. The fibers grow on a Mo substrate heated with an acetylene-oxygen combustion flame from the backside. The edge length of the cross-sectional rectangle ranges from ∼0.1 to 10 µm. The material, as determined from the X-ray photoelectron spectroscopy and X-ray diffraction, is of monoclinic MoO2.