bluuebunny/crossref_metadata_2025 huggingface dataset:
Fe–N Films Prepared by Dual Ion Beam Sputtering
Authors: Nagase Toshihiko , Shiiki Kazuo
Published: October 2002

Fe–N films containing less than about 30 at.% N were prepared on glass substrates and GaAs (100) single crystal wafers by the dual ion beam sputtering (DIBS) method. As nitrogen concentration and substrate temperature increased, α-phase, γ′-phase and ε-phase were formed on both substrates. The phase diagrams of the Fe–N films on both substrates were similar, although there was a slight difference in the crystalline orientation of the Fe–N films. A new α-phase supersaturated with nitrogen was found at concentrations lower than about 15 at.% N, which was much higher than that in the bulk. No α′-phase was detected. The lattice parameter of this phase increased from 2.88 to 2.96 Å at about 15 at.% N. The saturation magnetization decreased monotonically as the nitrogen concentration increased, due to simple dilution.
Local Structures and Structural Relaxation Processes in Supercooled Tetra(ethylene glycol)
Authors: Noudou Takaaki , Matsuoka Tatsuro , Koda Shinobu , Nomura Hiroyasu
Published: October 2002

Raman spectra of tetra(ethylene glycol) have been measured at near
the glass transition temperature, T
g. The spectra from 750 to 950 cm-1
indicate that the conformation in the liquid state depends upon temperature
and may approach to that in the crystalline state with decreasing
temperature down to T
g. A broad peak known as a boson peak is observed
at below 233 K in the low-frequency spectra. The lineshape of the boson
peak is reproduced by the extended disorder-induced scattering model and
structural correlation length is estimated. The correlation between the
local structures of molecules and the structural relaxation processes
obtained by sound velocity and dielectric measurements are discussed.
Rapid Brillouin Scattering Measurement of the Fast Relaxation Process in a Glass-Forming Intermediate Liquid
Authors: Genzou Matsui Genzou Matsui , Seiji Kojima Seiji Kojima , Shin-ich Itoh Shin-ich Itoh
Published: October 2002

The rapid Brillouin scattering method was applied to the giga Hertz
dynamics of the deuterated ethylene glycol-d4 by the combination of a
highly sensitive charge coupled device(CCD) detector and an angular
dispersion type Fabry-Perot interferometer. The temperature variation
was measured on cooling at a constant rate of 1 K/min. The obtained
relaxation frequency was found to obey the Arrhenius law with the
activation energy ∼4.5 kcal/mol, which corresponds to the potential
barrier for the rotational motion of an alkyl group which interacts with
the surrounding molecules. This microscopic picture was discussed in
relation with the cage effect predicted by the mode coupling theory.
Photoacoustic Spectrum and Surface Morphology of Porous Silicon
Authors: Toshio Kawahara Toshio Kawahara , Michiyo Mihara Michiyo Mihara , Jun Morimoto Jun Morimoto , Toru Miyakawa Toru Miyakawa
Published: October 2002

Both the photoacoustic (PA) and the photoluminescence (PL) spectra were studied in porous Si.
The surface morphology was investigated using atomic force microscopy (AFM).
The PA signal intensity was increased as porosity increased.
The enhancement of the PA signal intensity with an increase in the surface area was observed in samples whose porosity was above 60%.
These surface effects were observed in AFM images.
We found a reciprocal correlation between the PA spectrum and the PL spectrum in the same sample.
We also observed the reduction of the red spectrum in the PA spectra of the samples which showed a peak at 600 nm in the PL spectrum.
Annealing of RuO 2 and Ru Bottom Electrodes and Its Effects on the Electrical Properties of (Ba,Sr)TiO 3 Thin Films
Authors: Ahn Joon-Hyung , Choi Won-Youl , Lee Won-Jae , Ho-Gi Kim Ho-Gi Kim
Published: October 2002

Crystalline structures and surface morphologies of annealed RuO2 and Ru thin films were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The annealing was performed in oxygen and argon ambient and high vacuum in the temperature range of 400–800° C. In oxygen ambient annealing, the surface morphology was drastically changed due to the evaporation of ruthenium dioxides in the form of RuO3 and RuO4. Annealed RuO2 thin film in vacuum was reduced to the Ru metal phase. The actual variation of RuO2 bottom electrodes during the deposition of (Ba,Sr)TiO3 (BST) thin films and the effects of the thermal stability of bottom electrodes on electrical properties of BST thin films deposited on RuO2/SiO2/Si were also investigated.
Phase Modulation of the Light Wave Propagating in an Optical Fiber by Acoustic Waves
Authors: Kazuhiko Yamanouchi Kazuhiko Yamanouchi , Kenji Kotani Kenji Kotani , Hiroshi Yao Hiroshi Yao
Published: October 2002

The optical fiber acoustooptic phase modulator offers the advantages of small size, light weight and low diffraction and optical coupling loss. In this paper, we present the fabrication process and results of our proposed device. A ZnO thin-film bulk acoustic wave transducer was fabricated on a glass substrate which was then bonded on the optical fiber. We experimentally obtained an amplitude-modulated lightwave signal with an input of 9 V at 94 MHz with our measurement system.
Characteristics of Rayleigh and Leaky Surface Acoustic WavePropagating on a La3Ga5SiO14 Substrate
Authors: Sato Takashi , Murota Masao , Shimizu Yasutaka
Published: October 2002

The propagation characteristics of Rayleigh waves on a La3Ga5SiO14 substrate are theoretically
investigated for all cuts and propagation directions. The results of the phase velocity, electro-mechanical coupling constant (K
2), power flow angle (PFA) and temperature coefficient of delay
(TCD) are shown as contour maps. The maximum value of K
2 of a Rayleigh wave is 0.55%, and
about 0.5% with zero TCD. These values are about 2–3 times larger than those of quartz. It is found
that some cuts exist, which do not have a Rayleigh wave. The characteristics of leaky surface acoustic wave (SAW) on Z-cut La3Ga5SiO14 are also shown.
A Surface Acoustic Wave Elastic Convolver using a KNbO3 Single Crystal Substrate
Authors: Kazuhiko Yamanouchi Kazuhiko Yamanouchi , Hiroyuki Odagawa Hiroyuki Odagawa , Kenyuu Morozumi Kenyuu Morozumi , Yasuo Cho Yasuo Cho
Published: October 2002

Elastic convolvers are very important in signal processing devices of spread spectrum communication (SSC) systems. Highly efficient convolvers are required in the application of the spread spectrum and next stage communication systems. A high value of the coupling coefficient is very important for wideband and high efficiency surface acoustic wave (SAW) devices, such as SAW convolvers. Potassium niobate (KNbO3) has large piezoelectric constants and a very large electromechanical coupling coefficient (K
2) of 0.53 for surface acoustic waves, which is about 10 times higher than that of LiNbO3. Therefore, highly efficient elastic SAW convolvers using KNbO3 substrates are expected in the future. In this paper, the use of the rotated 60° Y-cut, X-propagating KNbO3 substrates in convolvers is demonstrated. The experimental results show that the efficiency of the convolver using 60° Y–X KNbO3 is 15 dB higher than that of the convolver using Y–Z LiNbO3.
Performance of a Leaky Wave Transducer in a Layered Substrate Composed of a Thin Piezoelectric Plate and a Thin Glass Plate
Authors: Motegi Kenji , Toda Kohji
Published: October 2002

A leaky wave interdigital transducer on a layered substrate composed of
two thin plates, a piezoelectric ceramic thin plate and a glass thin plate, is
described. The transducer has the function of multiple-mode operation for
underwater ultrasound, while retaining sufficient mechanical strength. The
calculated results of the phase velocities are confirmed experimentally, including
the case of using only a piezoelectric ceramic plate as a substrate. The calculated
electromechanical coupling constant and the mode conversion ratio obtained from
the phase velocities under two kinds of electrical boundary conditions are also
presented along with the experimental results of this type of transducer. The
combination of a piezoelectric ceramic plate and a glass plate is a promising method
for realizing a highly effective transducer for underwater ultrasound.
New Techniques for Simulation of Ion Implantation by Numerical Integration of Boltzmann Transport Equation
Authors: Shyh-Wei Wang Shyh-Wei Wang , Shuang-Fa Guo Shuang-Fa Guo
Published: October 2002

New techniques for more accurate and efficient simulation of ion implantations by a stepwise numerical integration of the Boltzmann transport equation (BTE) have been developed in this work. Instead of using uniform energy grid, a non-uniform grid is employed to construct the momentum distribution matrix. A more accurate simulation result is obtained for heavy ions implanted into silicon. In the same time, rather than utilizing the conventional Lindhard, Nielsen and Schoitt (LNS) approximation, an exact evaluation of the integrals involving the nuclear differential scattering cross-section (dσ
n
=2πp
d
p) is proposed. The impact parameter p as a function of ion energy E and scattering angle φ is obtained by solving the magic formula iteratively and an interpolation techniques is devised during the simulation process. The simulation time using exact evaluation is about 3.5 times faster than that using the Littmark and Ziegler (LZ) spline fitted cross-section function for phosphorus implantation into silicon.
Temperature Rise and Welding Characteristics of Ultrasonic Wire Bonding Using 190 kHz Linear, Circular and Square Vibration Loci and 600 kHz Linear Vibration Locus Welding Tips
Authors: Tsujino Jiromaru , Yoshihara Hiroyuki , Itoh Tomohiko , Inujima Kazutoshi , Hirano Yasuyuki
Published: October 2002

Welding characteristics of ultrasonic wire bonding using 190 kHz linear, circular and square
vibration loci and a 600 kHz linear vibration locus are studied. High-frequency systems at 90–780 kHz have been shown to be significantly effective in comparison to a conventional system at
60 kHz. Aluminum wire welding specimens 0.1 mm in diameter have been successfully joined.
Temperature increases at welding parts are measured from the thermoelectromotive force
between the aluminum wire and copper plate specimens, and deformation at welded parts of wire
specimens are measured using a digital height gage. Complex vibration welding tips at 190 kHz,
which vibrate in elliptical to circular or rectangular to square shapes at either the same or different
frequencies, are effective in joining welding specimens successfully in shorter welding times,
under smaller vibration amplitudes and over wider good welding areas. A high-frequency 600 kHz system with a linear vibration locus is also effective for successful wire bonding. Both the
temperature increase and wire deformation correlate well with the weld strength.
Measurement of the Nonlinearity Parameter in Dispersive Liquid using Focused Ultrasound
Authors: Saito Shigemi
Published: October 2002

Taking into account the velocity dispersion in a sample inserted into the focal region of the focused field, the second harmonic component of the acoustic pressure observed beyond the sample is investigated. An amplitude increase due to the
degradation of the cancellation effect of the second harmonic components generated at the pre- and post-focal regions is predicted. When focused ultrasound is applied to the finite-amplitude method to estimate the nonlinearity parameter B/A in
dispersive liquid, the B/A value can, therefore, be overestimated. This prediction is confirmed by the B/A measurement for water-oil mixtures with various oil fractions employed as dispersive samples. The methods used to measure the sound-speed
difference between the fundamental and the second harmonic frequencies using the same focusing system and to measure the B/A accurately are presented in this paper.
Wide-Band Detection of Ultrasonic Wave Pulse Using Optical Evanescent Waves
Authors: Choi P.-K. , Shimizu Soh , Hayashi Kazushi
Published: October 2002

A wide-bandwidth ultrasonic transducer was constructed using optical evanescent fields. Due
to the nonresonant nature of this evanescent waves transducer, a sharp pulse was observed in
a glass sample as compared to that obtained by a piezoceramic transducer. The signal
corresponds to the ultrasonic displacement on the glass surface, and an absolute value of the
displacement was obtained. The sound fields at the glass surface were traced with the
resolution of the laser beam diameter, which qualitatively agreed with the calculated profile
for pulsed fields.
Simulation and Fabrication Process for a Medical Phased Array Ultrasonic Probe using a 0.91Pb(Zn1/3Nb2/3)O3–0.09PbTiO3 Single Crystal
Authors: Saitoh Shiroh , Kobayashi Tsuyoshi , Harada Kouichi , Shimanuki Senji , Yamashita Yohachi
Published: October 2002

Medical array ultrasonic probes using a 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 (PZN-PT)
single crystal exhibiting a high electromechanical coupling factor
(k
33) >90% have been studied
in order to realize both a higher sensitivity and broader bandwidth properties. Pulse echo
characteristics of the array probes, each transducer of which has dimensions of 6.0 mm×0.14 mm
with a center frequency of 3.5 MHz, are simulated using the dielectric and the piezoelectric
constants of the grown PZN-PT single crystals. Simulated echo amplitudes of the PZN-PT
probes have been improved by as much as 7 dB compared with those of the conventional
Pb(Zr1-x
,Ti
x
)O3 (PZT) ceramic ones. Moreover, the bandwidth of the PZN-PT probe is
expected to be about 25% broader than those of the conventional PZT probes. It has been
shown by simulation that the low acoustic impedance as well as the high coupling factor of the
PZN-PT crystal contribute in broadening the bandwidth of the probe. The fabrication process
of the array probe was investigated. A conventional method in which the dicing conditions are
optimized and a novel dicing process are proposed.
Fundamental Examination of Cattle Red Blood Cells Damage with Ultrasound Exposure Microscopic System (UEMS)
Authors: Kawan Soetanto Kawan Soetanto , Masahiro Kobayashi Masahiro Kobayashi , Motoyoshi Okujima Motoyoshi Okujima
Published: October 2002

In order to define the safety limit of the medical ultrasound equipment and to study the ultrasonic bioeffects, ultrasound exposure microscopic system (UEMS) was developed in our laboratory. We intended to observe the tissue damage caused by ultrasound exposure in real time. The change of size and shape of the cattle red blood cells was investigated experimentally with UEMS. It was observed that, at a driving frequency of 2.2 MHz, when the ultrasound intensity I
SPTP was 28.4 W/cm2, the change of shape of the cattle red blood cells, due to the ultrasound exposure, occurred after 30 min of exposure. The change of size of the cattle red blood cells was investigated with a Coulter counter. The results, indicated that the size of the red blood cells after exposure to ultrasound was smaller than before exposure. Moreover, the results also indicated that, there was a tendency of the red blood cells to decrease in size after the ultrasound exposure when the ultrasound intensity was increased. At the two driving frequencies of 2.2 MHz and 0.55 MHz, in this study, the size of the cattle red blood cells decreased when the ultrasound intensities were increased.
Study on Contrast Effect of Microbubbles as Ultrasound Contrast Agents
Authors: Man Chan Man Chan , Kawan Soetanto Kawan Soetanto
Published: October 2002

In this study, the contrast effect from different sized microbubbles is investigated both theoretically and experimentally. Theoretically, the reference backscattered power is defined to evaluate the contrast effect of different sized microbubbles dispersed in the heart. In this study, the calculation results of two kinds of microbubbles of sizes 35 µm and 2.2 µm are discussed. From the calculation results obtained, it is found that the contrast effect from microbubbles of size 35 µm is better than that from microbubbles of size 2.2 µm. The reason being that as the size of microbubbles decreases, a large portion of ultrasonic energy is lost due to absorption. Based on the same reason, microbubbles less than 10 µm will cause an acoustic shadowing effect at a higher concentration of microbubbles, according to the calculation results. Experimentally, microbubbles of an average size of 35 µm are produced, and by filtration, microbubbles of an average size of 2.1 µm are collected. Then, the contrast effect produced from microbubbles before and after filtration are compared. It is observed that for both kinds of microbubbles, a good contrast effect is observed at a relatively low concentration of microbubble dispersion. However, distortion of images occurs at high concentrations. The acoustic shadowing effect is observed for microbubbles of an average size of 2.1 µm which can also be expected from the calculation results. On the other hand, the multiple-scattering effect which results in blurred images, occurs for microbubbles of an average size of 35 µm.
Estimation of Trabecular Bone Axis for Characterization of Cancellous Bone Using Scattered Ultrasonic Wave
Authors: Kiyotaka Kitamura Kiyotaka Kitamura , Hidetaka Nishikouri Hidetaka Nishikouri , Sadayuki Ueha Sadayuki Ueha , Shigeo Kimura Shigeo Kimura , Naoki Ohtomo Naoki Ohtomo
Published: October 2002

A new method has been proposed to measure the thickness and the interval of trabecular bones for diagnosing osteoporosis, in which the ultrasound signals scattered by trabecular bones are analyzed by modeling cancellous bone as a multilayered grating.
For applying this technique to actual diagnosis, the estimation of the direction of the trabecular bone axis is necessary.
In this paper an estimation method for obtaining the direction is proposed, where typical pictures of the frequency spectrum are obtained by changing the angle between the bone axis and the detecting plane.
This method has been proved to estimate the direction successfully.
The principle and the experimental verification are described here.
Ultrasonic Attenuation Image of the Biological Tissues by using the Diffraction Tomographic Technique
Authors: Masaki Kuroiwa Masaki Kuroiwa , Akira Yamada Akira Yamada
Published: October 2002

A novel ultrasonic inverse scattering tomographic technique was recently developed by the authors using the introduction of the backward propagation Rytov approximation to improve significantly the quantitative precision of a sound parameter image of a weak scattering tissue like object. Thus far, examinations were made only for the sound velocity parameter image for lossless case. However, an image of attenuation can be precisely reconstructed as well as the image of the sound velocity is expected to be useful in medical diagnostic applications. To this end, the present paper investigates the quantitative precision of the inverse scattering parameter image with special emphasis on the realization of an image of attenuation.
3D Dynamic Echocardiography with a Digitizer
Authors: Osamu Oshiro Osamu Oshiro , Ayumu Matani Ayumu Matani , Kunihiro Chihara Kunihiro Chihara
Published: October 2002

In this paper,
a three-dimensional (3D) dynamic ultrasound (US) imaging system,
where a US brightness-mode (B-mode) image
triggered with an R-wave of electrocardiogram (ECG)
was obtained with an ultrasound diagnostic device
and the location and orientation of the US probe
were simultaneously measured with a 3D digitizer, is described.
The obtained B-mode image
was then projected onto a virtual 3D space
with the proposed interpolation algorithm using a Gaussian operator.
Furthermore, a 3D image was presented on a cathode ray tube (CRT)
and stored in virtual reality modeling language (VRML).
We performed an experiment
to reconstruct a 3D heart image in systole using this system.
The experimental results indicate
that the system enables the visualization of
the 3D and internal structure of a heart viewed from any angle
and has potential for use in dynamic imaging,
intraoperative ultrasonography and tele-medicine.
Accuracy Evaluation in the Measurement of a Small Change in the Thickness of Arterial Walls and the Measurement of Elasticity of the Human Carotid Artery
Authors: Hideyuki Hasegawa Hideyuki Hasegawa , Hiroshi Kanai Hiroshi Kanai , Nozomu Hoshimiya Nozomu Hoshimiya , Noriyoshi Chubachi Noriyoshi Chubachi , Yoshiro Koiwa Yoshiro Koiwa
Published: October 2002

For the diagnosis of the early stages of atherosclerosis, it is
important to evaluate the local acoustic characteristics of the
arterial wall. For this purpose, it is necessary to increase the
spatial resolution in the axial direction to several millimeters,
which corresponds to the size of the macular lesion on the surface of
the wall. We have proposed a method for measuring small velocity
signals on the intima and adventitia of the arterial wall from the
skin surface using pulsive ultrasonic waves. The small change in
thickness of the arterial wall is obtained by integrating the
difference between the two velocity signals on the intima and
adventitia. The elastic property of the arterial wall is noninvasively
evaluated from the change in thickness and the arterial inner
pressure. In this paper, we evaluate the accuracy of the proposed
method for measuring the small displacement. Moreover, we applied this
method to evaluate the elastic property of the arterial wall of 50
patients and 8 healthy subjects.
Some New Applications of the Scanning Electron Acoustic Microscope for Materials Evaluation
Authors: Fuming Jiang Fuming Jiang , Seiji Kojima Seiji Kojima , Bingyang Zhang Bingyang Zhang , Qingrui Yin Qingrui Yin
Published: October 2002

Several different kinds of materials were investigated by an improved scanning electron acoustic microscope (SEAM). Residual stress distribution in aluminum metal and whisker-reinforced Al2O3–SiCw ceramic induced by Vicker's indentation, domain structures in a ferroelectric Bi4Ti3O12 single crystal, dislocations and defects in the hetero-structure GaAs/GaAlAs epitaxial multilayer were successfully observed. Alternative contrast mechanisms were discussed. The advantages of the scanning electron acoustic microscope for materials evaluation were demonstrated.
Low-Frequency Sound Source with Dual Bending Radiation Surfaces
Authors: Mitsuru Yamamoto Mitsuru Yamamoto , Hiroshi Ishimura Hiroshi Ishimura , Yoshinori Hama Yoshinori Hama , Takeshi Inoue Takeshi Inoue
Published: October 2002

A disk bender sound source with dual radiation surfaces is designed based on the finite element method (FEM) analysis and an equivalent circuit analysis. The results of these analyses results exhibit that the sound source has a low-frequency and high-power radiation capacity and is capable of operating at ten times the normal atmospheric outer water pressure. The sound source comprises of two bending resonators. Each resonator consists of a metal disk and many piezoelectric ceramic segments. Each ceramic segment is firmly bonded to a depression on the metal disk with an epoxy resin adhesive. The sound source has external dimensions of about 80 cm diameter, 9 cm thickness and weighs 130 kg. The resonant frequency obtained is 115 Hz at a depth of 50 m, and the maximum sound pressure level successfully achieved is more than 200 dB re 1 µPa at 1  m. For the purpose of using the sound source at great depths, a pressure-compensation method, in which the inner cavity of the sound source is filled with compressed gas, is theoretically investigated.
A Self-Aligned Gate AlGaAs/GaAs Heterostructure Field-Effect Transistor with an Ion-Implanted Buried-Channel for use in High Efficiency Power Amplifiers
Authors: Nishihori Kazuya , Kitaura Yoshiaki , Tanabe Yoshikazu , Mihara Masakatsu , Yoshimura Misao , Nitta Tomohiro , Kakiuchi Yorito , Uchitomi Naotaka
Published: October 2002

In this paper we report on a self-aligned gate buried-channel Al0.22Ga0.78As/GaAs
heterostructure field-effect transistor (BC-HFET). The BC-HFET comprises a selectively ion-implanted channel and an undoped i-AlGaAs surface layer. In order to realize the buried
channel heterostructure, a combined process of ion-implantation and epitaxial growth is
developed. The post-implantation annealing before the epitaxial growth successfully reduces
the interdiffusion at the heterointerface between the ion-implanted GaAs channel and the
AlGaAs surface layer. The BC-HFET overcomes the disadvantages of a low breakdown
voltage which exists in conventional self-aligned gate MESFETs. The BC-HFET exhibits a
high breakdown voltage of 8 V and a high Schottky barrier height of 0.75 eV. The 1-mm-wide
power BC-HFET demonstrates an output power of 18.2 dBm and a drain efficiency of 50% at
a low adjacent channel leakage power of -59 dBc for a 1.9-GHz π/4-shifted quadrature phase
shift keying (QPSK) modulated input, for use as Personal Handy-phone System handsets.
Below-Gap Spectroscopy of Undoped GaAs/AlGaAs Quantum Wells by Two-Wavelength Excited Photoluminescence
Authors: Katsuyuki Hoshino Katsuyuki Hoshino , Takahiro Uchida Takahiro Uchida , Norihiko Kamata Norihiko Kamata , Koji Yamada Koji Yamada , Masao Nishioka Masao Nishioka , Yasuhiko Arakawa Yasuhiko Arakawa
Published: October 2002

By using an improved method of two-wavelength excited photoluminescence,
we observed a considerable decrease in the band-to-band photoluminescence
intensity of an undoped GaAs/AlGaAs quantum well structure when a below-gap
excitation was superposed on an above-gap excitation.
This intensity quenching was attributed to the enhanced nonradiative
recombination through below-gap states which were activated by the below-gap
excitation.
By changing the energy of above-gap excitation, it was shown that these
below-gap states were formed neither inside GaAs well layers nor at
the GaAs/AlGaAs heterointerface, but inside AlGaAs barrier layers.
Tuning the photon energy of below-gap excitation revealed that the activation
energy of the nonradiative recombination process via these below-gap states is
around 1.2 eV.
Lowering the above-gap excitation density to a single-photon-counting
region enabled us to characterize below-gap states spectroscopically without
the need of a high-power tunable laser source for the below-gap excitation.
Application of a Slow Positron Beam to the PdGe Ohmic Contact on GaAs
Authors: Lee Jong-Lam , Tanigawa Shoichiro
Published: October 2002

The depth distributions of Ga vacancies in the PdGe ohmic contact on GaAs were studied by a slow positron beam technique. The results were compared with the electrical properties, to interpret the mechanisms on both the ohmic contact formation and the degradation at the PdGe/GaAs interface. The magnitude of the S parameter, reflecting the Ga vacancy concentration, at the near-interface GaAs region increases during the PdGe ohmic contact formation on GaAs. This is due to the creation of the n+-GaAs interfacial layer below the contact. The S parameter in the interfacial layer increases with the annealing temperature, which indicates the elevation of the Ga vacancy concentration. The Ga vacancies reduce the electron concentration, resulting in the degradation of the contact resistivity.
High-Temperature and Low-Threshold-Current Operation of 1.5 µm AlGaInAs/InP Strain-Compensated Multiple Quantum Well Laser Diodes
Authors: Lin Chia-Chien , Liu Kuo-Shung , Wu Meng-Chyi , Shiao Hung-Pin
Published: October 2002

High-temperature and low-threshold-current of 1.5 µm strain-compensated
multiple-quantum-well (SC-MQW) graded-index separate-confinement-heterostructure (GRIN-SCH) AlGaInAs/InP laser diodes have been successfully
fabricated. An epitaxial wafer was grown by low-pressure metalorganic
chemical vapor deposition (LP-MOCVD) and the 2-µm-wide ridge-waveguide
(RWG) structure with self-aligned process was adopted. Significant
improvements in threshold current high-temperature operation and characteristic
temperature have been demonstrated. Under CW operation, these laser diodes
exhibited a threshold current of 5.4 mA and 17 mA at 20°C and 100°C,
respectively. Output power exceeding 5 mW was obtained at a temperature as
high as 120°C. Also they have a characteristic temperature T
0 of 90 K between
20°C and 70°C which is as good as the best values of the conventional
InGaAsP/InP lasers.
Ab-Initio Study of Electronic Structure of Dilute Si Alloys Containing I–B Impurity Atoms
Authors: Agarawal Bal K. , Agrawal Savitri
Published: October 2002

We have made a first principles calculation of the electronic
structure and charge density of the dopants I–B group impurities Au,
Ag and Cu in crystalline silicon by employing a full potential self-consistent
linear muffin tin orbital (LMTO) method along with the local
density functional theory. The scalar relativistic effects have also been
included. A supercell containing 54 atoms, Si53X with X as impurity
has been considered for these investigations. The states lying deep into
the energy gap show a fast decaying behaviour and the corresponding
wave-functions of the impurities lying in the neighbouring supercells
show quite small overlap. The impurities lying in the adjacent
supercells are the sixth neighbours among themselves in the direction
of the lattice vectors of the fcc lattice. In all cases, impurity bands
arising from the p-like orbitals appear in the gap region although some
mixing with the d-like states is also observed. This p-like impurity
state is a triply degenerate T state at the Γ-point. The impurity bands
are peaked at 0.65, 0.61 and 0.56 eV for Au, Ag and Cu, respectively.
The d-type impurity states appear in the middle of the valence band.
The results in the valance band region are in good agreement with the
available experimental data.
Enhanced Electrical Conductivity of Indium Tin Oxide Films by Ag Addition
Authors: Masakazu Suzuki Masakazu Suzuki , Yoriko Maeda Yoriko Maeda , Yutaka Sawada Yutaka Sawada
Published: October 2002

Ag-added indium-tin-oxide (ITO) films were prepared using conventional radio frequency (rf) magnetron sputtering with an ITO target on which Ag chips were placed. A small amount of Ag addition (< 1 at.%) lowered the resistivity by ∼30% with only a slight decrease in the visible range transparency. The enhancement in conductivity was equivalent to lowering the substrate temperature by ∼50°C. At a substrate temperature of 250°C, the resistivity (ρ) of 2.0 ×10-4 Ωcm with a carrier density (n) of 7.1 ×1020 cm-3 and Hall mobility (µ) of 44 cm2V-1s-1 was obtained for the ITO (8.1 at.% Sn) film with 0.6 at.% Ag, whereas ρ=2.8×10-4 Ωcm with n=4.9×1020 cm-3 and µ=46 cm2V-1s-1 was obtained for the ITO film without Ag addition. The Ag addition enhanced the crystallinity and the densification of the film. The enhanced electrical conductivity due to Ag addition is explained by the increase in the efficiency of Sn doping.
Light Scattering from a Spherical Nematic Droplet Modulated by an Electric Field
Authors: Shu-Hsia Chen Shu-Hsia Chen , Wang-Yang Li Wang-Yang Li
Published: October 2002

We use finite difference and
relaxation methods to simulate the three-dimensional molecular director configurations in a spherical nematic droplet in the presence of an electric field. Deformation free energy of the nematic droplet is described in terms of tensor representation. Total scattering cross sections of a single nematic droplet modulated by various electric field strengths are calculated using the anomalous diffraction approach light scattering theory. The electrooptical properties are examined with respect to the droplet size, the dielectric anisotropy and the elastic constants of the
nematic liquid crystals.
Changes in Raman Spectra with Deposition Conditions and Plasma Treatment of Diamond Like Carbon Thin Films
Authors: Endo Katsumi , Miyamura Takeshi , Kitaori Noriyuki , Yoshida Osamu
Published: October 2002

A diamond like carbon (DLC) protective thin film was deposited on a Co
evaporated magnetic recording tape by the electron cyclotron resonance chemical
vapor deposition (ECR-CVD) method. The components of the DLC thin films were
measured upon a changing the deposition conditions and plasma treatment
conditions by means of Raman spectroscopy. It was found that the fluorescence
level and graphite/diamond composition ratio in the DLC films influenced the
film characteristics and could be controlled independently. The fluorescence
level was estimated from the fluorescent background of Raman spectra and could
be controlled by the reactive gas (100% C6H6) flow rate of the DLC film deposition
time. In contrast, the graphite/diamond composition ratio could be controlled by
means of the Ar plasma treatment after deposition. The composition ratio is the
estimated parameter S
1/S
2 of the Raman spectrum area, where S
1 is the low
Raman band (nearly 1350 cm-1) area and S
2 is the high Raman band (nearly
1530 cm-1) area. An increase in S
1/S
2 shows a high graphite ratio. The
composition ratio was controlled from 0.43 to 2.04 using plasma treatment.
A Gated Microchannel Plate Soft X-Ray Imaging System for a Laser Plasma Experiment
Authors: Bing Shan Bing Shan , Zenghu Chang Zenghu Chang , Jinyuan Liu Jinyuan Liu , Xiuqin Liu Xiuqin Liu , Shengshen Gao Shengshen Gao , Youlai Ren Youlai Ren , Wenhua Zhu Wenhua Zhu
Published: October 2002

A picosecond soft X-ray imaging system for a laser plasma experiment which is convenient for practical use is developed. The system, based on a gated microchannel plate (MCP) with four 6-mm-wide stripline cathodes is capable of capturing multiframe soft X-ray images at time resolution of 60–100 ps and spatial resolution of 15 lp/mm. During design and construction of the system, emphasis was placed on reliability and operating convenience. The four gating pulses for each stripline were generated by a single avalanche transistor circuit, ensuring a steady time sequence and the same waveform for each pulse. The transmission characteristics of the four striplines were adjusted to be identical by monitoring the time domain reflectometry (TDR) of each stripline. The construction of the pulser and striplines in this manner allowed for both timing and sensitivity consistency of the gating for the four striplines. A pinhole system was equipped in front of the imager with precise control and flexible pinhole illumination, making the alignment and adjustment of the pinhole array very easy. The system was used in a high-power laser plasma experiment and results were obtained both with the pinhole and pinhole grating array.
Proximity Effects Correction for Advanced Optical Lithography Processes
Authors: Tritchkov Alexander , Finders Jo , Randall John , Ronse Kurt , Vandenhove Luc
Published: October 2002

This paper describes the performance of various optical proximity correction (OPC) software
packages in terms of correction accuracy and effectiveness. Although parts of these software
packages have been made commercially available couple of years ago, their performance keeps
improving by the new features and capabilities added continuously in time by the software vendors.
In this study we address mainly the lithographic performance of the OPC techniques implemented
in the software packages, including many of the new features which are still in a development
phase. Corrections using one of these software packages were carried out for an advanced sub-0.3 µm i-line process after poly-Si etching. Corrections for an advanced 0.2 µm deep-UV process were
carried out using two other OPC software packages, representing two different OPC techniques.
Exposures were carried out on state-of-the-art i-line and deep-UV steppers equipped with high
numerical aperture lenses and illuminators allowing the user to vary the coherence factor by
keyboard control. Optimized optical settings towards reducing optical proximity effects have been
used. Results on the effectiveness of reducing linewidth variation and line-end shortening for
various pitches using these OPC techniques are reported.
Perturbation Analysis of Octupoles in Circular Accelerators
Authors: Yoon Moohyun
Published: October 2002

The octupole effects in a circular accelerator are analyzed using a first-order canonical perturbation theory. It is shown that, to the first order, the nonlinear amplitude-dependent tune shifts due to an octupole are composed of two types: terms of second order and terms of fourth order in betatron-oscillation amplitudes. The fourth-order part of tune shifts is expressed in terms of distortion functions. Distortion functions are also expanded in harmonics to express the higher-order tune shifts in harmonically expanded form. Finally, the results are applied to an accelerator and compared with the results of numerical tracking of particles. Laskar's algorithm for numerical analysis of the fundamental frequency is used to determine tunes from the tracking data, in which the error becomes inversely proportional to the cube of the number of data points.
Stability Improvement of Selective Oxidation During the Fabrication of InGaAs/GaAs Vertical Cavity Surface Emitting Laser
Authors: Pan Zhong , Zhang Yi , Du Yun , Wu Ronghan
Published: October 2002

The effects of the carrier gas flow and water temperature on the oxidation rate for different reaction
temperatures were investigated. The optimum conditions for stable oxidation were obtained. Two mechanisms
of the oxidation process are revealed. One is the flow-controlling process, which is unstable. The other is the
temperature-controlling process, which is stable. The stable region decreases for higher reaction temperatures.
The simulation results for the stable oxidation region are also given. With optimum oxidation conditions, the
stability and precision of the oxidation can be dramatically improved.
Temperature Dependence and Numerical Analysis of Negative Nonlinear Absorption Effect in Erbium-Yttrium Aluminum Garnet
Authors: Maeda Yoshinobu , Yamada Toshikazu , Imai Shiho , Migitaka Masatoshi
Published: October 2002

The temperature dependence of the negative nonlinear absorption (NNA) effect was investigated
in an erbium-doped yttrium aluminum garnet (YAG) crystal using a 787.3 nm laser diode. The
NNA effect was obtained in a temperature range of 15 to 400 K. An absorption peak corresponding
to both the 4
I
15/2-4
I
9/2 and 4
I
13/2-2
H
11/2 transitions of Er3+ in the YAG at 400 K was displaced from
that at 300 K. It is considered that the NNA effect weakened at high temperature because the
absorption cross section decreased due to the shift of the absorption peak. In addition, the
dependence of the NNA effect on the modulation degree was investigated. The characteristic of the increase in the incident laser intensity was
almost the same as that for the decrease. It was confirmed that the mechanism of the NNA effect
can be explained by calculating the rate equations based on an analytical model for a five-level
system of the Er3+ ion. It is suggested that the NNA effect weakened at the low temperature because
the number of phonons decreased due to the low temperature.
New Treatment for Tomographic Reconstruction of Refractive Index Profiles of Inhomogeneous Objects from Slope Measurements
Authors: Angeles Rama Maria de los , Susana Ríos Susana Ríos , Eva Acosta Eva Acosta
Published: October 2002

This work deals with a modified formulation of the Radon transform for the evaluation
of refractive index profiles in inhomogeneous media by using data obtained with deflection
tomography techniques. The theoretical results are supported by numerical simulations and
analysis of the noise propagation is presented. Under this formulation we will show that good
reconstructions of index profiles are achieved by using a small number of projections, with a
subsequent fast data processing.
Skew-Free Optical Interconnections Using Fiber Image Guides for Petabit-per-Second Computer Networks
Authors: Kawai Shigeru , Li Yao , Wang Ting
Published: October 2002

Parallel interconnections using vertical-cavity surface-emitting laser (VCSEL)-based
fiber image guides (FIGs) have been proposed. The FIGs consist of many individual optical
fibers. The core in each optical fiber is small, and thus, modal distortions may be small.
All optical fibers in an array are fabricated under the same conditions. Characteristics for
each optical fiber are almost uniform, and skew in FIGs is expected to be small.
Interconnections using FIGs are advantageous for both free-space optics and optical fiber
communications. They may enable the achievement of highly dense and large-channel
communications, and easy alignment. Optical interconnections with FIGs and large-core
fibers are proposed. Experiments and discussions show that the optical interconnections
have very small skew and distortion. The interconnections also have merits for low cost and
light weight. Module concepts and applications to petabit/s optical networks for PetaFLOPS
computing are described.
Barrier-Height Imaging of Si(001) 2 × n
Authors: Hiroyuki Fukumizu Hiroyuki Fukumizu , Shu Kurokawa Shu Kurokawa , Akira Sakai Akira Sakai , Yukio Hasegawa Yukio Hasegawa
Published: October 2002

We have carried out barrier-height imaging on clean Si(001) 2 ×1 and Ni-contaminated 2 ×n surfaces and investigated the local barrier-height variation at and around Ni-related dimer-vacancy (DV) defects which are referred to as (1+2)-DVs. The barrier-height images show atomic contrast which conforms nicely with corresponding constant-current scanning-tunneling-microscopy (STM) topographs. No strong defect-induced modification was observed in the local barrier height at (1+2)-DV. Our direct barrier-height measurements thus provide a negative result on the barrier-height reduction at (1+2)-DV, which was predicted by Ukraintsev et al. [Surf. Sci. 388 (1997) 132)].
A Study of Local Processing on Solid Surfaces with Atomic Force Microscope
Authors: Hai-Ming Wu Hai-Ming Wu , Masaharu Komiyama Masaharu Komiyama
Published: October 2002

With the use of atomic force microscope (AFM), local mechanical processing of molybdenum disulphide (MoS2) crystal surface has been examined. It was found that AFM tip could strip the surface layer-by-layer in a controlled manner. In addition to this tip-induced etching effect, it was also found that AFM tip could adsorb, transfer and redeposit the substrate surface particles. A model based on the adsorption and desorption process of surface particles on the tip was used to interpret the observed phenomena.
Structures and Local Polarized Domains of Ferroelectric Organic Films Studied by Atomic Force Microscopy
Authors: Chen Xinqi , Yamada Hirofumi , Horiuchi Toshihisa , Matsushige Kazumi
Published: October 2002

We have investigated the surface structures and the local polarized domains of the
copolymer thin films of vinylidene fluoride and trifluoroethylene (P(VDF/TrFE)) by
atomic force microscopy (AFM). AFM observation revealed that the films consisted of
“rod-like” grains and that the surface morphology depended strongly on the annealing
condition. We also observed that pairs of “rod-like” grains were gradually formed
depending on the length of the annealing time. The local polarized domains were
fabricated by applying a high electric field to the film with a conducting AFM tip. The
piezoelectric response of the film was detected using the tip with an oscillating electric
field and imaged with the topographic images taken simultaneously. The X-ray profile
suggested that the thin films had a β-type crystalline structure.
Enhanced Grain Growth Phenomena in Excimer Laser Annealed Microcrystalline Silicon Films
Authors: Voutsas Apostolos T.
Published: October 2002

In this work we have investigated the feasibility of microcrystalline silicon as the precursor material for the formation of high crystalline quality polysilicon films. Excimer laser anneal (ELA) process was used for the phase transformation of amorphous to polycrystalline silicon (polysilicon). Polysilicon films, obtained from laser annealed microcrystalline silicon, were found to demonstrate larger grain size than that of laser annealed amorphous silicon films. This grain size enhancement was attributed to an improved microstructure developing during the initial, rapid, solid-phase-crystallization (SPC) stage, preceding the melting process, during laser anneal. Proper engineering of the as-deposited film structure, via optimization of deposition conditions, yielded a twofold increase in the grain size of the post ELA polysilicon films. Based on the findings of this work, one direction for additional improvement is suggested by employing alternative deposition methods that allow for greater control of the as-deposited film structural characteristics.
Front- and Back-Interface Trap Densities and Subthreshold Swings of Fully Depleted Mode Metal-Oxide-Semiconductor Transistors Fabricated on Separation-by-Implanted-Oxygen Substrates
Authors: Yoshino Akira , Ma Tso-Ping , Okumura Koichiro
Published: October 2002

By measuring the charge pumping current (I
CP) and the subthreshold swing,
we examined the front- and back-interface trap densities (D
fit and D
bit) of long
channel N-type metal-oxide-semiconductor transistors fabricated on separation-by-implanted-oxygen (SIMOX) substrates, as a function of the total oxygen implantation
dose. The front-channel subthreshold swing (S
f) measured in the coupled condition
was larger than that calculated with D
fit and D
bit obtained from I
CP. However, dose
dependences of the D
fit and D
bit obtained from I
CP were consistent with those of the
front- and back-channel peak mobilities, while those obtained from the subthreshold
swings were not. These seemingly contradictory results can be satisfactorily
explained by the existence of lateral nonuniformities (LNU) in the front- and the
back-channel local threshold voltages. We propose that the experimentally
determined S
f can be used as an index of LNU in the SIMOX and other silicon-on-insulator substrates, just by comparing it with the theoretical value of S
f.
Atomic Force Microscopy Study of Self-Affine Fractal Roughness of Porous Silicon Surfaces
Authors: Naohisa Happo Naohisa Happo , Makoto Fujiwara Makoto Fujiwara , Masao Iwamatsu Masao Iwamatsu , Kenju Horii Kenju Horii
Published: October 2002

Atomic force microscopy was used to measure the “roughness” exponents of
the rough porous silicon surfaces formed by electrochemical anodization.
It was found that the porous Si surfaces have a self-affine fractal structure
characterized by roughness exponents α=0.53–0.64, fractal dimensions
D=2.36–2.47 and a growth exponent β=0.24 ±0.02.
An Experimental Investigation of the Novel Unstable Resonator with a Stable Resonator Core
Authors: Nanri Kenzo , Matsumura Masaru , Yamaguchi Shigeru , Fujioka Tomoo
Published: October 2002

A new type of laser resonator, a confocal unstable resonator with a stable core, is
experimentally tested. Applying the carefully designed resonator for a relatively low gain
(<1%/cm) transversely excited atmospheric pressure (TEA) CO2 laser device, the laser
output performance was compared with a usual confocal unstable resonator at the same
magnification value (M) of M=1.6. As predicted with the theoretical calculations, the output
energy of the new resonator increased 12% and the superiority of this resonator was clearly
shown.
Relationship between Propagation Loss and Crystallinity in Proton-Exchanged and Annealed LiNbO3 Optical Waveguides
Authors: Ito Kenchi , Kawamoto Kazumi
Published: October 2002

The propagation loss of proton-exchanged and annealed LiNbO3 optical
waveguides was studied in relation to the change in the crystal phase. With annealing
at relatively low temperatures (≤325°C) or for a short time (at 375 or 400°C, ≤15 min),
the propagation loss increases. Annealing at relatively high temperatures (375 to
400°C) for a longer time (30 to 45 min) greatly reduces the propagation loss. The
reasons for the increase in propagation loss with insufficient annealing is the
deterioration of crystallinity due to changes in the crystal phase and the coexistence of
two different crystal phases.