bluuebunny/crossref_metadata_2025 huggingface dataset:
X-Ray Mask Fabrication Using New Membrane Process Techniques
Authors: Uchiyama Shingo , Oda Masatoshi , Ohki Tadahito Matsuda
Published: October 2002

A membrane process, in which the resist and the absorber are patterned after backetching, was developed to produce highly accurate X-ray masks. Two new techniques allow us to use the same equipment as that currently used in our wafer process. One is a one-point holder for electron beam writers that clamps, without causing any deformation, a small area of the wafer from both sides with just one pair of projections. The reproducibility of the pattern positioning obtainable with the new holder is below 36 nm (3σ) in both x and y directions. The other technique is an etching method that uses a heat sink to prevent temperature increases in the membrane during absorber etching. With the heat sink, there is no difference between the etch rate of the absorber film on the thinned membrane and that on the Si wafer. A comparison between the pattern placement accuracies of X-ray masks produced by the above membrane process and by the conventional wafer process confirms that highly accurate X-ray masks can be fabricated by the membrane process when there is extensive absorber coverage.
A-Axis YBCO Thin Films Deposited by DC Magnetron Sputtering
Authors: Wen Chou Tsai Wen Chou Tsai , Tseung Yuen Tseng Tseung Yuen Tseng
Published: October 2002

A-axis YBCO thin films deposited on SrTiO3 and MgO substrates were prepared using the template-layer method by off-axis magnetron sputtering. The thin films deposited on MgO with template layers displayed better electrical properties and crystallinity than those deposited on the substrates without template layers, whereas the crystallinity of films deposited on SrTiO3 by the template-layer method showed no improvement. The surface morphology of the films, observed by high-resolution scanning electron microscopy, indicates that the homoepitaxial growth of the a-axis films on template layers on MgO and SrTiO3 results in rougher surfaces than in the case of heteroepitaxial growth of template layers. The possible mechanisms contributing to these differences in surface roughness were carefully investigated. Atomic force microscopy was also used to characterize the initial growth of a-axis films on MgO and SrTiO3. According to the results, the initial growth of a-axis films on MgO and SrTiO3 resembles that of island growth.
Post-Exposure-Bake Simulation Model with Constant Acid Loss of Chemically Amplified Resist
Authors: Yanagishita Yuichiro , Miyata Shuichi , Kaimoto Yuko , Oikawa Akira , Ei Yano Ei Yano , Isamu Hanyu Isamu Hanyu
Published: October 2002

The post-exposure-bake (PEB) deprotective reaction was investigated as a function of the exposure energy and bake time with FT-IR spectrum measurements of chemically amplified resist. It was found that the PEB deprotection model giving an acid loss rate that is proportional to its concentration cannot describe the suppression of deprotection for relatively low exposure energies. This paper proposes a PEB reaction model that gives an acid loss whose rate remains constant irrespective of the concentration, which can describe the suppression accurately. In addition, a constant acid loss enhances contrast of the resist development, which was observed experimentally over relatively long PEB times.
Advanced Thermal Improvement Method for Chemically Amplified Resists
Authors: Endo Masayuki , Akiko Katsuyama Akiko Katsuyama , Michinari Yamanaka Michinari Yamanaka
Published: October 2002

We have developed a new method to achieve both, thermal durability and critical dimension (CD) control using short-duration, deep UV irradiation for chemically amplified resists at moderate irradiation intensity and moderate substrate temperature. We obtained thermal durability up to 140° C and CD control within ±5% between as-developed resists and those obtained after baking at 140° C.
Hydrogen Effects on Si1-xGex/Si Heteroepitaxial Growth by Si2H6- and GeH4-Source Molecular Beam Epitaxy
Authors: Okada Masahisa , Kondo Masaaki , Ikeda Hiroya , Zaima Shigeaki , Yukio Yasuda Yukio Yasuda
Published: October 2002

The influences of hydrogen atoms on the Si1-
x

Ge

x

heteroepitaxial growth on Si(100) and Si(111) surfaces using Si2H6- and GeH4-source molecular beam epitaxy (MBE) with additional atomic hydrogen has been studied using reflection high energy electron diffraction (RHEED). In the Si1-
x

Ge

x

growth on Si(100) and Si(111) surfaces, it is found that the dissociative adsorption rates of Si2H6 and GeH4 are significantly dependent upon the surface orientation and the atomic element at the adsorption sites. The role of atomic hydrogen irradiation in the growth rate of Si1-
x

Ge

x

on Si(100) and Si(111) surfaces is to reduce the density of adsorption sites for the hydride gases and to suppress the surface segregation of Ge atoms. However, the altered behavior in the growth rate of Si1-
x

Ge

x

on Si(100) and Si(111) is observed due to the difference in the adsorption rates of the gaseous hydrides.
Optimization Method of Memory Characteristics in Antiferroelectric Liquid Crystals
Authors: Watanabe Manabu , Shimano Yutaka , Hiroyuki Okada Hiroyuki Okada , Hiroyoshi Onnagawa Hiroyoshi Onnagawa
Published: October 2002

The memory characteristics of antiferroelectric liquid crystals were studied. The investigation of holding characteristics upon application of a rectangular waveform voltage revealed that hysteresis curve of transmittance versus holding voltage characteristics could be obtained. In the hysteresis range, both the ferroelectric and antiferroelectric states exist stably during a multi-frame periods. The optimization method proposed herein is expected to lead to the development of a display without frame memory.
High Growth Rate for Slow Scanning in Electron-Beam-Induced Deposition
Authors: Hiroshi Hiroshima Hiroshi Hiroshima , Masanori Komuro Masanori Komuro
Published: October 2002

Electron-beam-induced deposition using WF6 gas was used to directly fabricate conductive wires. In view of the gas supply, repeated fast electron beam scanning had been thought to be more efficient than single slow scanning. The results, however, proved otherwise. There are three possible reasons: (1) less beam drift, (2) rise in temperature of beam exposure region, and (3) numerous secondary electrons generated from the inclined growth front of a wire. The first possibility is clearly negated by an experiment where beam drift is negligible. The second possibility is thought to be low because the rise in temperature is estimated to be less than 1° C. Simulation of wire growth using the string model where the secondary electron effect is taken into account gives good agreement with the experimental results. Detailed observation of fabricated wires using an atomic force microscope supports the idea that the high growth rate is most likely caused by the increase in numbers of secondary electrons generated.
KrF Resist Pattern Monitoring by Ellipsometry
Authors: Hoshi Kenji , Arimoto Eiichi Kawamura
Published: October 2002

This is a report on a rapid and accurate optical method for monitoring line widths by ellipsometry. Samples with a KrF chemically amplified positive resist (TDUR-P009) were exposed by a KrF stepper with 0.35-µ m dense line/space patterns (0.70 µ m pitch) and 0.30-µ m sparse line patterns (2.0 µ m pitch), and measured by ellipsometry. Ellipsometry was found to be effective in monitoring changes in resist line widths and cross-sectional shapes due to variations in focus and dose. Multivariable regression analysis was adopted to predict the line width and the focus position of a stepper. Good agreement (3σ=4.3 nm) between CD-SEM measured and predicted widths was achieved. Also, focus positions were accurately predicted. The results of spectroscopic ellipsometry, which provides many ellipsometric parameters in a short period, are shown.
New Ellipsometric Approach to Critical Dimension Metrology Utilizing Form Birefringence Inherent in a Submicron Line-and-Space Pattern
Authors: Seiji Takeuchi Seiji Takeuchi , Minoru Yoshii Minoru Yoshii , Masaki Yamamoto Masaki Yamamoto
Published: October 2002

A new ellipsometric approach to critical dimension (CD) metrology is proposed, which utilizes the form birefringence of the submicron line-and-space (L&S) patterns of a photoresist. With the continued requirement of further narrowing of the period of the L&S to dimensions less than the probing wavelengths, higher-order diffraction will no longer occur and the 0th-order diffraction beam will be the only tool for CD metrology. Since ellipsometry uses this 0th-order diffraction beam, the method is promising for use in the evaluation of L&S patterns in the subwavelength region. We have been able to relate the large variation in the ellipsometric parameter to the form birefringence of the submicron pattern. Using the higher-order effective medium equations for the ordinary and extraordinary refractive indices, the ellipsometric parameter changes due to the linewidth changes are calculated. The calculated results agree well with the experimental results. Furthermore, the linewidths are determined from the best fit between the calculated and experimental data. The same is done for the latent images of the undeveloped resist patterns.
Estimation of the Surface Magnetic Structure of Materials by Scanning Electron Microscopy
Authors: Kotera Masatoshi , Yamaguchi Kiyoshi , Fujita Atsuhiro , Suga Misao Katoh
Published: October 2002

As a visualization technique of the surface magnetic structure, the type-I magnetic contrast in a scanning electron microscope is proposed. Trajectories of secondary electrons emitted from the specimen surface are deflected by the magnetic flux that leaks from the surface magnetic domain. The magnetic flux and an electric field in the specimen chamber are calculated numerically for a given magnetic structure of the specimen, and the spatial deviation of the electrons at the detector is obtained. By an analysis of the relationship between the structure and the deviation, it is expected that the magnetic structure can be estimated by the deviation, as the inverse problem. In the present paper, this relationship is examined under various conditions, and rules are derived to interpret the results into the magnetic structure of the specimen.
Nanometer-Scale Patterning of Polystyrene Resists in Low-Voltage Electron Beam Lithography
Authors: Manako Shoko , Fujita Jun-ichi , Ochiai Yukinori , Eiichi Nomura Eiichi Nomura , Shinji Matsui Shinji Matsui
Published: October 2002

We studied nanometer-scale patterning using a polystyrene negative resist in electron beam lithography. We found that the use of a low-molecular-weight polystyrene enables 10-nm-level patterning at low-acceleration voltage. We also found that the spot dose of such ultrasmall patterns formed at a 5 kV acceleration voltage was one-tenth of that formed at 50 kV. Low-voltage electron beam lithography is a suitable technique for organic resist nanopatterning. The Charlesby theory can still be applied to nanodot formation, and we can therefore estimate the dot sensitivity for various polystyrene molecular weights. We suppose that an exposure model is based on polymer aggregation to explain the formation of a 10-nm-level pattern with a height of 40 nm can be formed by using a small molecule, not a large one.
Effects on CO Oxidation Activity of Nano-Scale Au Islands and TiO2 Support Prepared by the Ionized Cluster Beam Method
Authors: Fukushima Kazunori , Takaoka Gikan H. , Matsuo Jiro , Yamada Isao
Published: October 2002

Catalytic activity in titania-supported gold ( Au/TiO2) is associated with nano-scale Au islands on a substrate coated with TiO2. The Au islands were prepared by the ionized-cluster-beam (ICB) method. Both rutile and anatase types of TiO2 films were obtained by adjusting the deposition conditions of the reactive ICB method. The average diameter of gold islands was kept constant at about a few nm, and their density increased by ionizing and accelerating the Au beams. The measurements of the temperature dependence of CO oxidation indicated that the catalytic activity was enhanced by using an anatase type of support and by using Au islands deposited at an acceleration voltage of 3 kV. The high catalytic activity was obtained at a temperature of 100–150°C. The diameter and density of Au islands and the surface state of TiO2 support play an important role in catalytic activity.
Surface Superstructures of Ce Thin Films on an Mo(100) Surface
Authors: Kamei Masayuki , Yasutaka Mizoguchi Yasutaka Mizoguchi , Yoshihiko Gotoh Yoshihiko Gotoh
Published: October 2002

Surface structures of Ce thin films on an Mo(100) single crystal substrate were investigated using a molecular beam epitaxy system equipped with a reflection high-energy electron diffraction apparatus. Five kinds of surface superstructures (√2×√2 R45°, one-dimensional √2a
Mo periodicity, 3×3/√2×4√2 R45°, C√2×5√2 R45° and 4×4 structures) were observed in the regions with low Ce coverage and their phase diagram was obtained. Four out of five surface superstructures (except the 4×4 structure) showed the same √2a
Mo periodicity along Mo[011]. This periodicity is also dominant in the case of Ce thin films on an Mo(110) surface when the Ce film thickness is smaller than 0.5 nm. This Ce structure with one-dimensional √2a
Mo periodicity along Mo[011] is considered to be very stable.
Stimulated Brillouin Scattering from KrF Laser Produced Plasma
Authors: Fujita Masayuki , Offenberger Allan A. , Capjack Clarence E. , Vick Doug W.
Published: October 2002

Reflectivity and red-shifted spectra of stimulated Brillouin scattering (SBS) from solid aluminum targets irradiated by 0.25 µm laser radiation at various angles of incidence have been measured. Higher reflectivity was observed for a larger angle of incidence (θ), whereas the spectral shift showed no significant dependence on θ. SBS energy reflectivity levels increased from ∼0.1% (θ=0°) to ∼1% (θ=45°) for a focused KrF laser intensity of ∼1014 W/cm2. The observed θ dependence of reflectivity and spectral shift is consistent with predictions of a two-dimensional hydrodynamic simulation code (CASTOR), in particular, a locally planar density profile and spherical plasma expansion. The observed reflectivity levels cannot be quantitatively explained by standard convective gain theory for inhomogeneous plasma.
One-Dimensional Simulation of Microwave Propagation in Electron Cyclotron Resonance Plasmas
Authors: Hiroshi Muta Hiroshi Muta , Tadanori Sakoda Tadanori Sakoda , Yoko Ueda Yoko Ueda , Yoshinobu Kawai Yoshinobu Kawai
Published: October 2002

Recently, there have been many efforts in modeling new processing plasma sources such as electron cyclotron resonance (ECR) plasmas, helicon-wave-excited plasmas and inductively coupled plasmas. In the new sources, ECR plasmas are especially difficult to model because of highly nonlinear coupling between microwaves and the magnetized plasma. Accordingly, appropriate modeling of the interactions between the microwave and the magnetized plasma is the key to resolving the problem. In this paper, we present numerical simulations based on a one-dimensional model using the finite-difference time-domain (FDTD) method and discuss the characteristics of the microwave propagation in ECR plasmas. Furthermore, we compare the simulation results with the experimental results by interferometry measurement and show the validity of the model. As a result, it is found that the model proposed here can simulate the qualitative characteristics of the microwave propagation in the plasma, which strongly depend on gas pressure.
Improved Stability of a Dual-Spin Satellite in Circular Orbit
Authors: Zheng-Ming Ge Zheng-Ming Ge , Hsien-Keng Chen Hsien-Keng Chen
Published: October 2002

Sufficient conditions for the global stability of equilibrium positions of a dual-spin satellite in a circular orbital system in a Newtonian central force field are obtained by Liapunov's direct method. The new results are compared with those already known. The problem is then studied with respect to all variables, including the angular velocity of the rotor. Further, sufficient conditions for the global stability of rotation with arbitrary angular velocity for an axisymmetric dual-spin satellite are presented by Liapunov's direct method, which improve on Kane's result of infinitesimal stability obtained by linearized equations of motion.
Multiple Switching Phenomena of AlGaAs/InGaAs/GaAs Heterostructure Transistors
Authors: Cheng Chin-Chuan , Jung-Hui Tsai Jung-Hui Tsai , Wen-Chau Liu Wen-Chau Liu
Published: October 2002

An interesting multiple negative-differential-resistance (NDR) phenomenon is observed in AlGaAs/InGaAs/ GaAs heterostructure bipolar transistors with abrupt or graded AlGaAs confinement layers under the inverted operation mode. The switching behaviors are mainly due to avalanche multiplication and a two-stage barrier lowering effect. The switching properties of the first S-shaped NDR observed in the device with the abrupt confinement layer are better than those observed in the device with the graded confinement layer, due to the former device's superior confinement effect on holes and electrons. The control voltage efficiency of the second S-shaped NDR is nearly equal in the studied devices because the InGaAs quantum well dominates the properties of this NDR.
Feasibility Study on Ultrafast Nonlinear Optical Properties of 1.55-µm Intersubband Transition in AlGaN/GaN Quantum Wells
Authors: Nobuo Suzuki Nobuo Suzuki , Norio Iizuka Norio Iizuka
Published: October 2002

The feasibility of the intersubband transition (ISBT) in Al(Ga)N/GaN quantum wells (QWs) as a device mechanism for ultrafast optical switches is theoretically investigated. The 1.55-µ m ISBT is shown to be feasible because of its large conduction band discontinuity. The intersubband relaxation time at 1.55-µ m is estimated to be 80 fs, which is about 30 times shorter than that in InGaAs QWs. The third order nonlinear susceptibility is estimated to be 1.6×10-15 m2· V-2 for N=1×1018 cm-3. These characteristics suggest that the ISBT in nitride QWs is a promising mechanism for multi-terabit/s optical switches.
Polarized Reflectance Spectroscopy and Spectroscopic Ellipsometry Determination of the Optical Anisotropy of Gallium nitride on Sapphire
Authors: Guolin Yu Guolin Yu , Hiroyasu Ishikawa Hiroyasu Ishikawa , Takashi Egawa Takashi Egawa , Tetsuo Soga Tetsuo Soga , Junji Watanabe Junji Watanabe , Takashi Jimbo Takashi Jimbo , Masayoshi Umeno Masayoshi Umeno
Published: October 2002

The refractive indices n
⊥(
E
⊥c) and n
∥ (
E
∥c) of the hexagonal GaN on sapphire substrates have been determined in the transparent region using the polarized reflection measurements. It is found that the difference in the refractive indices for
E
⊥c and
E
∥c is below 3% over the entire wavelength range measured, and ε
∞, the high-frequency dielectric constant, is 5.14 for
E
⊥c and 5.31 for
E
∥c. Ellipsometry angles, Δ and Ψ, have been calculated using the results of n
⊥, n
∥ and the thickness of the film, and an excellent agreement has been obtained between the calculated results and ellipsometric measured data.
Optical Switching of Antiferroelectric Liquid Crystal with Azo-Dye Using Photochemically Induced SmC A
*-SmC* Phase Transition
Authors: Koichiro Shirota Koichiro Shirota , Ichirou Yamaguchi Ichirou Yamaguchi
Published: October 2002

We have studied the photochemically induced phase transition from SmC A
* to SmC* by Ar+ laser light irradiation (wavelength 514 nm) in an antiferroelectric liquid crystal doped with photochromic azo-dye molecules. Using this phase transition, we have demonstrated the optical switching under a bias voltage of 6.2 V. A response time of 1.5 s was achieved by 55 mW/cm2 irradiation at 30°C.
Crystallographic Features of ZnO Single Crystals
Authors: Yoshiyuki Ohta Yoshiyuki Ohta , Tetsuya Haga Tetsuya Haga , Yutaka Abe Yutaka Abe
Published: October 2002

The atomic arrangements of ZnO single crystals have been investigated in detail using ion channeling methods. The ZnO crystals were grown by a flux method, and we focused on the channeling properties along the <0001> axis. In particular, to obtain information on O atoms in the crystal, a nuclear reaction induced by D+ ions was observed. As a result, it was revealed that the atomic arrangement of O atoms along the <0001> direction is better than that of Zn atoms in contrast with simple anticipation. This is quite remarkable but is regarded as one of the structural features of the crystal.
Preparation of a Novel Thin Film Utilizing a Magnetic Field: Alignment of Organic Microcrystals as Revealed by Atomic Force Microscopy
Authors: Akita Yasuyuki Tsuboi , Kazushi Yamada Kazushi Yamada , Akira Itaya Akira Itaya
Published: October 2002

Novel organic thin solid films were prepared by casting a tetrahydrofuran solution of nOCB (4-alkoxy-4′-cyanobiphenyls, where n denotes the number of methylenes in the substituent) in the presence of a horizontal magnetic field. Atomic force microscopy of the 8OCB film revealed that needle-type crystals with micrometer dimensions were well oriented with a perpendicular alignment to the magnetic field. This thin film reflected rays of light in a similar manner to a diffraction grating. In the case of 12OCB which forms plate-type crystals, no such crystal orientation was observed, although its molecular magnetic susceptibility is almost the same as that of 8OCB. We consider that crystal form anisotropy is necessary for the observation of the orientational pattern.
Switching Operation of GaInAs/InP Multiple-Quantum-Well Directional-Coupler-Type All-Optical Switch
Authors: Toshiyuki Takizawa Toshiyuki Takizawa , Akira Uchino Akira Uchino , Takehiro Shimizu Takehiro Shimizu , Yasushi Takeuchi Yasushi Takeuchi , Shigehisa Arai Shigehisa Arai
Published: October 2002

A GaInAsP/InP multiple-quantum-well (MQW) directional-coupler-type all-optical switch utilizing carrier induced refractive index variation was fabricated and its low swtiching power operation was demonstrated at a 1.55 µm wavelength. Extinction ratios at each output port of 2.3 dB and 2.6 dB were obtained with switching light power of 5.9 mW at the input fiber end.
Analysis of the Output Enhancement of Coaxial Flashlamp Pumped Rh-6G Dye Mixed Lasers
Authors: Won Kweon Jang Won Kweon Jang
Published: October 2002

The output energies of Rh-6G dye lasers were enhanced by energy transfer in mixtures of Rh-6G/C-545 and Rh-6G/Rh-560. The laser was pumped by a coaxial flashlamp filled with argon gas. The output energies were enhanced by about 70% and 30%, respectively, using 0.4∼1 % C-545 and Rh-560 mixtures with respect to the concentration of Rh-6G. Comparison of experimental results and calculations showed that the dominant energy transfer mechanisms were the nonradiative transfer from S
2→S
0 of Rh-6G to S
0→S
1 of donor, and then the radiative transfer from S
1→S
0 of donor to S
0→S
1 of acceptor, Rh-6G.
Optical Second Harmonic Generation in Alternately Assembled Dye-Polyion Multilayers
Authors: Yamada Sunao , Harada Atsushi , Matsuo Taku , Ohno Shinji , Izumi Ichinose Izumi Ichinose , Toyoki Kunitake Toyoki Kunitake
Published: October 2002

Layer-by-layer alternate adsorption of an SHG-active dye (Erichrome Black T: BT) and polycation (poly(diallyldimethylammonium chloride): PDDA) was successfully applied to the construction of an ultrathin NLO film. Quartz crystal microbalance and absorption spectral measurements revealed satisfactory film growth of BT and PDDA. The optical second harmonic signal increased with the number of PDDA/BT bilayers up to five, indicating anisotropically ordered alignment of BT molecules in the assembly.
InGaN Laser Diode Grown on 6H–SiC Substrate Using Low-Pressure Metal Organic Vapor Phase Epitaxy
Authors: Kuramata Akito , Domen Kay , Soejima Reiko , Horino Kazuhiko , Shin-ichi Kubota Shin-ichi Kubota , Toshiyuki Tanahashi Toshiyuki Tanahashi
Published: October 2002

InGaN multiple quantum well (MQW) laser diodes were fabricated on (0001)Si oriented 6H–SiC substrate using low-pressure metal organic vapor phase epitaxy (LP-MOVPE). The laser oscillation was observed above the threshold current of 800 mA at a peak wavelength of 414.3 nm under pulsed current injection at room-temperature. The pulse duration was 300 ns and the repetition frequency was 1 kHz. The threshold current density and differential efficiency were estimated to be 16 kA/cm2 and 0.03 W/A, respectively. The full width at half maximum (FWHM) of the lasing emission lines was between 0.03 nm and 0.21 nm. Streak-shaped far field patterns were clearly observable. The lifetime of the laser diode was more than 5 hours.
Thermodynamic Study on Metalorganic Vapor-Phase Epitaxial Growth of Group III Nitrides
Authors: Koukitu Akinori , Naoyuki Takahashi Naoyuki Takahashi , Hisashi Seki Hisashi Seki
Published: October 2002

An analysis of the metalorganic vapor-phase epitaxial (MOVPE) growth from a thermodynamic point of view is described for binary nitrides: GaN, InN and AlN. The equilibrium partial pressures are calculated for the input V/III ratios. It is shown that there are three deposition modes, growth, etching and droplet modes, depending on the partial pressures. The phase diagram for deposition is also calculated for the parameters of growth temperature and extent of ammonia decomposition. The conditions required for InN growth are discussed.
Compact Diode-Pumped Cr3+:LiSrAlF 6 Femtosecond Laser
Authors: Shin-ichiro Aoshima Shin-ichiro Aoshima , Haruyasu Itoh Haruyasu Itoh , Yutaka Tsuchiya Yutaka Tsuchiya
Published: October 2002

A novel geometry for dispersion compensation in femtosecond lasers without specific cut of optical parts in a flat/Brewster angle is demonstrated for the purpose of a compact diode-pumped Cr:LiSAF femtosecond pulse laser. In the geometry, the laser medium lies between the dispersion-compensation prism pair. This approach enables the laser to operate at variable repetition rates from 163 to 235 MHz keeping the pulse width less than 90 fs, which is the shortest pulse to our knowledge, achieved in an all-solid-state Kerr-lens mode-locked laser operating at a repetition rate of greater than 200 MHz.
Underlayer Effect on Magneto-Resistance in Spin-Valves
Authors: Hayashi Kazuhiko , Mori Shigeru , Yamamoto Hidefumi , Fujikata Jun-ichi , Masafumi Nakada Masafumi Nakada , Kazuhiko Yamada Kazuhiko Yamada
Published: October 2002

We measured resistivity (ρ) and resistivity change with magnetic field change (Δρ) in spin-valves (SVs) with Ta, Zr and Hf underlayers of various thicknesses and with NiO underlayers. When we varied the underlayer thickness in Ta, Zr and Hf underlayers, the SVs with 0.4–2.0 nm relatively thin underlayers had Δρ/ρ peaks. The peaks were not caused by the Δρ maximum but by the ρ minimum. When we compared the Δρ/ρ in substrate/NiO/NiFe/Cu/NiFe/Ta to that in substrate/Ta/NiFe/Cu/NiFe/NiO structures, the Δρ/ρ in the former samples was higher than that in the latter ones, because of the ρ difference between the former and the latter ones. It was found that Δρ/ρ in SVs can be increased when ρ are decreased by varying the thickness or the kind of underlayer in the SVs.
Enhancement of Second-Harmonic Generation by Helicoidal Distributed Feedback Action in a Ferroelectric Smectic C* Liquid Crystal Using Two Counter-Propagating Fundamental Waves
Authors: Schadt Jeong-Geun Yoo
Published: October 2002

A remarkable enhancement was observed in the second-harmonic generation (SHG) from the helicoidal structure of a ferroelectric smectic C* liquid crystal, when two counter-propagating fundamental waves generate SH light with the same wavelength as the optical pitch of the helicoid. This enhanced signal based on a helicoidal distributed feedback action is proportional to the fourth power of the sample thickness in thick cells, and becomes larger compared with the conventional phase-matched SHG signal in relatively thick samples, i.e., 100 µm.
Generation and RF Phase-Shifting of Millimeter-Wave Subcarriers Using a Hybrid Mode-Locked Monolithic Semiconductor Laser
Authors: Hoshida Takeshi , Masahiro Tsuchiya Masahiro Tsuchiya , Takeshi Kamiya Takeshi Kamiya
Published: October 2002

A method for generation and RF phase-shifting of millimeter-wave subcarrier signals using a single monolithic semiconductor laser device is proposed and demonstrated. Under fundamental or subharmonic hybrid mode-locking conditions, the optical cavity length of the laser is modulated by the thermo-optic effect in the passive waveguide section. As a result, the timing of the generated 33 GHz output optical pulse train was successfully varied over 10 ps, corresponding to phase-shifts over 2.7 and 5.3 rad for 33 and 66 GHz subcarriers, respectively. The mechanism of the RF phase-shift is explained by analogy with the injection-locked electrical oscillator.
Sensitive H 2 Detection Using a New Technique of Photoacoustic Raman Spectroscopy
Authors: Yuji Oki Yuji Oki , Noriyuki Kawada Noriyuki Kawada , Takashi Ogawa Takashi Ogawa , Yoshiteru Abe Yoshiteru Abe , Mitsuo Maeda Mitsuo Maeda
Published: October 2002

A new technique of photoacoustic Raman spectroscopy (PARS) is proposed and demonstrated for the detection of trace gas molecules in the atmosphere. No tunable laser is required in the proposed method. Only a fixed-wavelength pulsed laser is used as a light source, and a Raman shifter, filled with the same gas as that to be detected, automatically generates the Raman-shifted radiation required for the detection by PARS. In the detection of trace H2 gas in the atmospheric pressure mixture with N2, the detection limit of 3 ppm (3×10-6 in partial pressure) was obtained using a Q-switched, frequency-doubled Nd:YAG laser.
The Effects of La and Nb Modification on Fatigue and Retention Properties of Pb(Ti, Zr)O3 Thin-Film Capacitors
Authors: Katsuhiro Aoki Katsuhiro Aoki , Yukio Fukuda Yukio Fukuda
Published: October 2002

The effects of La and Nb modification on fatigue and retention properties of Pb(Ti, Zr)O3 thin-film capacitors with Ir electrodes formed by sol-gel deposition were evaluated. The concentrations of La and Nb are 1 atm%. The columnar-grain-structured Pb(Ti, Zr)O3 was unchanged by La- and Nb-modification on Ir substrates. They showed good fatigue resistance properties. However, marked degradation of polarization density and retention property was observed clearly. Remanent polarization density was decreased markedly by La modification. La and Nb modified Pb(Ti, Zr)O3 thin-film capacitors showed large losses of 39.0% and 37.5% in remanent polarization density in the first second as compared to the loss of 11.4% for a nonmodified one. Furthermore, the secondary loss is increased significantly by Nb modification. Thus, a nonmodified Pb(Ti, Zr)O3 thin-film capacitor with Ir electrodes shows better fatigue and retention properties than La and Nb modified capacitors.
Defect Modes in Two-Dimensional Triangular Photonic Crystals
Authors: Xiao-Ping Feng Xiao-Ping Feng , Yasuhiko Arakawa Yasuhiko Arakawa
Published: October 2002

We propose a simple method of making defects in two-dimensional photonic crystals by radius modification and analyzed energy levels of such defects obtained by the supercell method. In a triangular lattice of the semiconductor-rods-in-air structure, it was found that both a single sharp acceptor level and a single sharp donor level can be achieved with a defect bandwidth of about 5% of the band gap for E-polarized in-plane waves.
High Resolution Structure Imaging of Octahedral Void Defects in As-Grown Czochralski Silicon
Authors: Bender Hugo , Vanhellemont Jan , Schmolke Rüdiger
Published: October 2002

The crystal originated particles (COP's) as revealed by light scattering tools on Czochralski silicon wafer surfaces are investigated by means of high resolution transmission electron microscopy (HREM) on specimens prepared by a focused ion beam tool. The structure imaging of buried defects gives direct evidence for the void nature of the defects leading to the formation of the COP's.
Preparation of Thin Films of Oriented Iron Nanocrystals
Authors: Bo Bian Bo Bian , Yoshihiko Hirotsu Yoshihiko Hirotsu
Published: October 2002

Granular thin films of oriented α-Fe nanoparticles have been synthesized. The oriented α-Fe nanoparticles were prepared by taking advantage of the epitaxial growth of α-Fe on <100> oriented Au “seed” nanoparticles, which were epitaxially grown on a (100)NaCl substrate. The crystallographic orientation between α-Fe and Au nanocrystals is [100]Au//[100]Fe with (010)Au//(011)Fe. It is shown that this method can be applied to control the size, distance and crystalline orientation of Fe nanocrystals in granular films.
Single-Electron Transistors (SETs) with Nb/Nb Oxide System Fabricated by Atomic Force Microscope (AFM) Nano-Oxidation Process
Authors: Shirakashi Jun-ichi , Matsumoto Kazuhiko , Miura Naruhisa , Konagai Makoto
Published: October 2002

An atomic force microscope (AFM)-based anodic oxidation technique, which is based on selective oxidation of metal thin film by anodization, was developed for the fabrication of niobium (Nb)/Nb oxide-based ultra-small tunnel junction devices. Double junction devices without any gate structures and double junction SETs with side-gate structure were fabricated using this technique, and single-electron charging effects were clearly observed at 100 K.
Soluble Three-Dimensional Polysilane with Organosilicon Nanocluster Structure
Authors: Watanabe Akira , Fujitsuka Mamoru , Miwa Osamu Ito
Published: October 2002

Three-dimensional polysilane with an organosilicon nanocluster structure is first synthesized by the reaction of tetrachlorosilane with magnesium metal and by capping the ends of the silicon nanocluster with tert-butyl group in solution. The organosilicon nanocluster is soluble to common organic solvents in spite of the three-dimensional Si skeleton which is demonstrated by CP/MAS 29Si NMR spectra. The optical properties and the structure of the organosilicon nanocluster are located between network polysilane (a quasi-two-dimensional silicon) and silicon nanocrystal.
Spectral Narrowing of Emission in Di-substituted Polyacetylene
Authors: V. Frolov Sergey , Shkunov Maxim , Vardeny Z. Valy , Tada Kazuya , Hidayat Rahmat , Hirohata Masaharu , Teraguchi Masahiro , Masuda Toshio , Yoshino Katsumi
Published: October 2002

We studied spontaneous and stimulated optical emission in films of di-substituted trans-polyacetylene (t-PA). We found that di-substitution of t-PA drastically changes the polymer optical emission properties, so that photogeneration of exciton and photoluminescence (PL) quantum yields become much higher than those measured in unsubstituted and mono-substituted t-PA. The strong PL is accompanied by high optical gain and emission spectral narrowing at high excitation intensities; the emission spectrum changes from a broad PL band of 100 nm at low intensities to a narrow stimulated emission band of ∼ 8 nm at high intensities. These properties show that di-substituted t-PA films can be good candidates for laser medium in the green and blue spectral ranges.
Improvement of Photovoltaic Performance in Copper Phthalocyanine Binder Layer Solar Cells
Authors: Rudiono Rudiono , Manabu Takeuchi Manabu Takeuchi
Published: October 2002

Schottky barrier solar cells consisting of a semitransparent indium electrode and a copper phthalocyanine binder layer were prepared by vacuum deposition and spin coating, respectively. The influence of chloranil doping on their photovoltaic performance was studied. The undoped solar cell showed moderate photovoltaic performance. Chloranil doping increased the current in the cell, but decreased the open circuit voltage drastically, which was consistent with deterioration of the rectifying characteristic of the Schottky barrier cell. It was confirmed that photovoltaic performance could be approximately doubled by modifying the cell structure.
Control of Composition and Growth Rate of ZnMgS Grown on GaP by Molecular Beam Epitaxy Using Excess Sulfur Beam Pressure
Authors: Kunio Ichino Kunio Ichino , Shin-ichiro Akiyoshi Shin-ichiro Akiyoshi , Tsukasa Kawakami Tsukasa Kawakami , Hiroaki Misasa Hiroaki Misasa , Masahiko Kitagawa Masahiko Kitagawa , Hiroshi Kobayashi Hiroshi Kobayashi
Published: October 2002

We have grown ZnMgS ternary alloys on (100) GaP substrates by molecular beam epitaxy. Using excess sulfur beam pressure evaporated from an elemental S source, we successfully controlled the alloy composition and the growth rate around the lattice-match condition to GaP substrates, which were not reproducible when the S beam was not used. From photoluminescence excitation spectra, it is observed that the band gap of Zn0.80Mg0.20S, which is lattice-matched to GaP, is 0.15 eV larger than that of ZnS.
Observation of Gain and Double-pass Amplification of Li-like Al Soft X-ray Transitions in a Recombining Plasma Pumped by a Pulse-train YAG Laser
Authors: Yamaguchi Naohiro , Hara Tamio , Chiemi Fujikawa Chiemi Fujikawa , Yoshiyuki Hisada Yoshiyuki Hisada
Published: October 2002

A pulse-train yttrium aluminium garnet (YAG) laser was used with a shaped envelope, as well as a new lens system for producing a dotted-line irradiation pattern in X-ray laser experiments. Amplified spontaneous emission (ASE) signals of the two Li-like Al transitions (3d-4f, 15.47 nm and 3p-4d, 15.06 nm) were observed with a pumping energy of only 1.5–2 J. The gain coefficient were approximately 3 cm-1 for the 3d-4f line and was maintained for a period of about 1 ns. The double-pass amplification experiment was carried out using a plane multilayer mirror. A clear increase in the above two Li-like Al transition lines was observed. It is highly expected that a strong laser amplification could be achieved in an X-ray laser cavity with two multilayer X-ray mirrors.
Violet Band Emission of Cd2 Excimer by Electron Beam Excitation
Authors: Xing Da , Wang Qi , Ueda Shi-ci Tan
Published: October 2002

Bound-free emissions of the Cd2 excimer, which is a possible long-lived and high energy storage excimer system, have been observed from electron-beam-excited gas mixtures of dense Cd vapor with rare-gas buffers. A continuum emission between 410–430 nm was assigned to be the Cd2 13Σ u
+→11Σ g
+ excimer transition.
Photocarrier Generation Rate Model of Textured Silicon Solar Cells
Authors: Hideyuki Iwata Hideyuki Iwata , Takashi Ohzone Takashi Ohzone
Published: October 2002

A new model of the photocarrier generation rate of regularly textured silicon solar cells with microgrooves and pyramids on the front surface for application to numerical simulation has been described. The photocarrier generation rate has been formulated based on an analytical approach by considering carefully all the optical paths of the incident light into the cells. This model can be simply incorporated into the device simulation program. The two-dimensionally simulated performance parameters of the sample textured solar cells are in considerable agreement with the previously measured results.
Thermal Decomposition of CeO 2 in Ultra High Vacuum as a Cause of Polycrystalline Growth of Si Films on Epitaxial CeO 2/Si
Authors: Yasuhiro Yamamoto Yasuhiro Yamamoto , Satoshi Arai Satoshi Arai , Taketo Matsuda Taketo Matsuda , Masataka Satoh Masataka Satoh , Tomoyasu Inoue Tomoyasu Inoue
Published: October 2002

Epitaxially grown CeO2(111)/Si(111) samples are heated up to 800°C in an ultra high vacuum environment, and it is verified that CeO2 decomposes above 690°C and the CeO2 surface becomes amorphous by means of residual gas analysis using quadrapole mass spectrometry, Rutherford backscattering in conjunction with a channeling technique, and in situ reflection high energy electron diffraction observation. The inherent difficulty of growing single crystal Si on CeO2 is discussed.
Fabrication and Characterization of (Sr, Ba)Nb2O6 Thin Films by Pulsed Laser Deposition
Authors: Nakano Mitsuru , Tabata Hitoshi , Tanaka Katsuhiko , Kawai Yûzô Katayama
Published: October 2002

Thin films of (Sr, Ba)Nb2O6 (SBN) have been fabricated using a pulsed laser deposition technique. The c-axis oriented films were obtained on SrTiO3 (100) substrates at temperatures higher than 650° C in an oxygen atmosphere (containing 8% O3) of 3 mTorr. Phi scans on the (221) plane showed that the films have two antiphase domains. The a-axis of SBN is aligned at ±18.4° with respect to the a-axis of SrTiO3. The epitaxial relationship between SBN and SrTiO3 is SBN <100>// SrTiO3 <310>. The lattice mismatch between SBN films and SrTiO3 substrates is less than 1%, which contributes to the exellent crystallinity of SBN thin films. The rocking curves of the (002) peak of SBN films grown at 700° C showed the FWHM of 0.31°.
Effects of Discharge Frequency on the Ion-Current Density and Etching Characteristics in High-Density Cl2 Plasmas
Authors: Tsukada Seiji Samukawa
Published: October 2002

We investigated the effects of discharge frequency on the characteristics of polycrystalline silicon (poly-Si) etching rates and on the etching selectivity on the gate oxide ( SiO2). An ultrahigh-frequency (UHF) plasma excited at 500 MHz was found to possess a wider process window for highly selective polycrystalline silicon etching than a radio frequency (RF) plasma excited at 13.56 MHz. This result has a strong correlation to the pressure dependence of the ion current density in both plasmas. In the UHF plasma, high ion-current density can be maintained in a wider pressure range, from 3 to 20 mTorr, whereas in the RF plasma the current density is drastically decreased with an increase in pressure. Thus, because the discharge frequency in the UHF plasma is higher than the electron collision frequency, the ionization in the UHF plasma does not depend significantly on the discharge pressure from 3 to 20 mTorr.
A Novel Gain Measurement Technique for Design of Long-Wavelength Vertical Cavity Lasers
Authors: Takemasa Keizo , Hiroshi Wada Hiroshi Wada , Takeshi Kamijoh Takeshi Kamijoh
Published: October 2002

We have developed a novel gain measurement technique based on a surface-normal optical pump-probe arrangement. The sample is optically pumped at 1.48 µ m, and single-pass optical gain is obtained from the transmitted power of a 1.55-µ m probe beam. Using this technique, gain can be measured accurately up to high excitation levels. In addition, the technique allows gain to be measured from as-grown wafers and can be used to optimize the active-layer parameters more conveniently by circumventing complicated device fabrication. The measured gain can also predict the minimum mirror reflectivity for laser oscillation in vertical cavity lasers.
LiGaO 2 Single Crystals for a Substrate of Hexagonal GaN Thin Films
Authors: Takao Ishii Takao Ishii , Yasuo Tazoh Yasuo Tazoh , Shintaro Miyazawa Shintaro Miyazawa
Published: October 2002

We succeeded in Czchoralski pulling of LiGaO2 single crystals and found for the first time unique domains that can be observed only by mechano-chemical polishing. The domains are separated by straight lines belonging to {110}. Since LiGaO2 single crystal is polar along the c-axis, the formation of a unique domain boundary is presumably attributable to the polarity inversion of the c-axis.
Four-Domain Divided Inclined Vertical Alignment by Irradiation of Unpolarized Ultra Violet Light
Authors: Hidefumi Yoshida Hidefumi Yoshida , Tsutomu Seino Tsutomu Seino , Yoshio Koike Yoshio Koike
Published: October 2002

A four-domain divided vertically-aligned liquid crystal panel (LCP) has been realized by irradiating unpolarized UV light on a vertical alignment layer through an optical mask. The liquid crystal (LC) with a negative dielectric anisotropy is filled. As the alignment has no disclination for the black state, the transmittance in the black state is the same as that with mono-domain vertically aligned LCPs, realizing a high contrast ratio of over 300. With a negative birefringence film, the fabricated LCP exhibits a wide viewing range. It has a contrast ratio of over 10 at any inclination angle of within 60° at any viewing azimuth and has almost no gray scale inversion.
Initial Stages of Cubic GaN Growth on the GaAs(001) Surface Studied by Scanning Tunneling Microscopy
Authors: Qi-Kun Xue Qi-Kun Xue , Qi-Zhen Xue Qi-Zhen Xue , Yukio Hasegawa Yukio Hasegawa , Ignatius S. T. Tsong Ignatius S. T. Tsong , Toshio Sakurai Toshio Sakurai
Published: October 2002

Nitridation of the GaAs(001) surfaces using an N-atom radio-frequency plasma source is investigated by in situ scanning tunneling microscopy (STM). Atomically flat (3×3) nitrided surfaces commensurate and coherent with the substrate have been achieved on the As-rich (2×4) and (2×6) surfaces. Nitridation proceeds via competing mechanisms of (3×3) ordering and step-etching caused by the N-atoms. The former simply involves N-As exchange, which does not require significant morphology modification, whereas the latter causes the roughening of the substrate under the standard GaN growth conditions. On the Ga-rich surface, the GaN islands immediately form at the step-edges, suggesting the possibility of self-assembled nanostructures of GaN.
Self Formation and Optical Properties of II–VI Semiconductor Wire Structures
Authors: Zhang Baoping , Wang Wenxin , Yasuda Takashi , Li Yanqiu , Segawa Yusaburo , Yaguchi Hiroyuki , Onabe Kentaro , Edamatsu Keiichi , Itoh Tadashi
Published: October 2002

Based on simultaneous selective growth and composition modulation, Zn1-
x

Cd

x

Se wire structures are spontaneously formed on cleavage-induced GaAs (110) surfaces by deposition of a Zn1-
y

Cd

y

Se (x>y) alloy layer. The wire structures are formed on the top edge of the steps introduced by cleavage. These wires show a strongly polarized emission and a large piezoelectric effect, implying a potential for applications in nonlinear optoelectronic devices. This paper discusses a novel approach to semiconductor nanostructures.
Electrical Characterization of Silicon Dioxide Thin Film Prepared by ArF Excimer Laser Chemical Vapor Deposition from Silicon Tetraacetate
Authors: Maruyama Atsushi , Nakata Kazuhiro , Yukimura Ken , Maruyama Shinzo Yoshikado
Published: October 2002

Silicon dioxide thin films were prepared by low-pressure direct photochemical vapor deposition (CVD) using an ArF excimer laser. A comparison of the relative dielectric constant and dielectric tangent indicated that laser-CVD was effective in lowering the substrate temperature from 200–300°C to room temperature. Moreover, the capacitance-voltage curves of metal-oxide-semiconductor structure exhibited no significant hysteresis, indicating that the laser-CVD-prepared SiO2 films contained a lower concentration of mobile-ion charges compared to the films prepared by thermal decomposition of silicon tetraacetate without laser irradiation.
Formation of Quantum Dot Structures by Atomic Hydrogen Assisted Selective Area Molecular Beam Epitaxy
Authors: Suzuki Yoshiyuki , Shimoda Masashi , Yoshitaka Okada Yoshitaka Okada , Mitsuo Kawabe Mitsuo Kawabe
Published: October 2002

We have fabricated InGaAs/GaAs quantum dot structures by atomic hydrogen assisted selective area molecular beam epitaxy (H-MBE). First, GaAs pyramidal structures with fourfold symmetric {011} facet sidewalls have been formed in (001) GaAs by using SiO2 as a mask with square openings. The shape and width of pyramidal structures observed by using a scanning electron microscope (SEM) and atomic force microscope (AFM) have been determined to be uniform. Using these pyramids, InGaAs quantum dots have been overgrown on top of the pyramids under different growth conditions. Photoluminescence (PL) spectra have been measured in order to study PL peaks arising from quantum dots. Furthermore, we have fabricated GaAs quantum dot array structures coupled to quantum wire networks by our H-MBE selective area growth technique.