bluuebunny/crossref_metadata_2025 huggingface dataset:
Focused Ion Beam Process for Formation of a Metal/Insulator/Metal Double Tunnel Junction
Authors: Masayoshi Nakayama Masayoshi Nakayama , Junichi Yanagisawa Junichi Yanagisawa , Fujio Wakaya Fujio Wakaya , Kenji Gamo Kenji Gamo
Published: October 2002

An improved method to fabricate a small lateral double
tunnel junction which utilizes
focused ion beam (FIB) etching and lift-off techniques is proposed.
A double layer resist consisting of nitrocellulose and
germanium layers was used.
Narrow grooves with widths comparable to or narrower
than the FIB diameter were formed
in a ferromagnetic layer of Ni,
and Ni/Ni-oxide/Au/Ni-oxide/Ni and
Al/Al-oxide/Ni/Al-oxide/Al double junction structures
were fabricated using the proposed method. The measured voltage and current
characteristics of the latter structures
indicated that double tunnel junctions with a barrier height
of 0.61 eV were fabricated and suggest that this is a promising method
to fabricate
island structures for devices utilizing Coulomb blockade or spin blockade
effects.
Investigation of Scanning Electron Microscope Overlay Metrology
Authors: Koike Toru , Ikeda Takahiro , Abe Hideaki , Komatsu Fumio
Published: October 2002

Compared with optics-based measurement, overlay measurement using scanning
electron microscope (SEM) is more suitable for small overlay marks. Small overlay
marks can be located freely in a chip. This method realizes highly accurate measurement.
SEM overlay metrology has been studied in recent years. It has been reported that SEM-based overlay metrology is capable of making accurate measurements. Overlay marks of
grooves were used in that case and signals were obtained easily from marks with
topographic structure. We have investigated SEM overlay metrology using marks
covered with flat oxide film and anti+reflection coating. Using voltage contrast images,
we demonstrated that SEM is also capable of making accurate measurements in such a
case. In this work, we examine the accuracy and precision of SEM-based overlay
metrology using a mark covered with thick resist film. In addition, we investigated the
effect of small overlay marks.
Optimization of Sample Plan for Overlay and Alignment Accuracy Improvement
Authors: Hong Jinseog , Lee Junghyeon , Park Joonsoo , Cho Hanku , Moon Jootae
Published: October 2002

The overlay control requirement for a sub-0.15 µm design
rule device is nominally less than 40 nm. To meet this demand,
every factor known to affect the overlay budget should be analyzed
in detail and corrected as much as possible. One of the major causes
degrading the overlay budget is the nonoptimized wafer sample
plan. Compensated but undercorrected overlay errors fitted as linear
terms can be amplified in case of using improper sample plan
(e.g., an asymmetric plan). In this study, we investigated
the sample plan dependency of global alignment repeatability and
overlay measurement accuracy. The achievement of better alignment
repeatability is critical for improving not only in-wafer overlay
but wafer-to-wafer overlay control. Global alignment repeatability
and its results are significantly affected by which chips in a wafer
map are selected for global alignment use. Several sample plans
which are limited to the symmetric group (i.e., translation,
inversion, rotation and symmetric), are tested. The criteria for
selecting the optimum sample plan were the residuals and linear-term
reproducibility, both of which are significantly affected by raw
data noise. Raw data variations include stage positioning errors and
process-induced alignment signal abnormality. From among the
candidates, we determined an optimal sample plan which leaves the
least residuals and exhibits repeatability as good as that in full
chip measurement. Similar results could be obtained for an overlay
sample plan.
Analysis of the Spin Polarization of Secondary Electrons Emitted from Permalloy Polycrystals
Authors: Tamura Keiji , Yasuda Masaaki , Murata Kenji , Koike Kazuyuki , Kotera Masatoshi
Published: October 2002

The spin polarization of secondary electrons scattered from a
permalloy material is calculated using a Monte Carlo simulation of
electron scattering based on the single scattering model. The
simulation model takes into account not only the conduction-band
polarization but also the inelastic mean free path depending on the
electron spin. The calculated primary energy and incident angle
dependences of the polarization of the secondary electrons show
reasonable agreement with the experimental results.
Two-Dimensional Control of Shape-Memory-Alloy Actuators for Aligning a Si Micromachined Pinhole of Spatial Filter
Authors: Minoru Sasaki Minoru Sasaki , Wataru Kamada Wataru Kamada , Kazuhiro Hane Kazuhiro Hane
Published: October 2002

The automatic alignment of a pinhole is realized in two dimensions and its function as a spatial filter is confirmed.
A pinhole device surrounded by four photodiode cells fabricated by Si micromachining techniques is placed on a movable x
y stage which consists of four shape-memory-alloy actuators.
The feedback control based on the signal obtained from the integrated photodiode is confirmed to be feasible for aligning a pinhole in two dimensions even if the shape-memory-alloy actuators are disadvantageous for controlling its displacement including cross-interaction.
The spatial filtering function of an automatically aligned pinhole is confirmed.
Fatigue Tests of Ni–P Amorphous Alloy Microcantilever Beams
Authors: Maekawa Satoshi , Takashima Kazuki , Shimojo Masayuki , Higo Yakichi , Sugiura Shinsuke , Pfister Bruno , Swain Michael V.
Published: October 2002

Fatigue life and fatigue crack propagation tests have been performed on microsized
Ni–P amorphous alloy specimens to investigate the fatigue properties of this material.
The material used was a Ni–11.5 wt%P amorphous thin film. The specimens tested
were cantilever-beam-type specimen with dimensions of 30×12×50 µm3 prepared
by focused ion beam machining. Notches with a depth of 3 µm were introduced in
some specimens. The entire set of fatigue tests was performed using a newly developed
fatigue testing machine in air at room temperature under a constant load ratio of 0.1.
The fatigue life curve was obtained for unnotched specimens, and the fatigue strength of
the specimen was determined to be approximately one-third of the static bending
strength. Fatigue crack propagation tests were performed using notched specimens.
Fine equispaced markings were observed on the fatigue surface. These markings are
aligned perpendicular to the crack growth direction, and are considered to be striations.
Therefore, even in microsized amorphous alloys the crack is deduced to propagate by
cyclic plastic deformation at the crack tip.
Quantum-Dot Cellular Automata: Line and Majority Logic Gate
Authors: Snider Gregory L. , Orlov Alexei O. , Amlani Islamshah , Bernstein Gary H. , Lent Craig S. , Merz James L. , Porod Wolfgang
Published: October 2002

An introduction to the operation of quantum-dot cellular automata is presented, along with recent experimental results. Quantum-dot cellular automata (QCA) is a transistorless computation paradigm that addresses the issues of device density and interconnection. The basic building blocks of the QCA architecture, such as AND, OR, and NOT are presented. The experimental devices presented are QCA cells where the dots are metal islands, coupled by capacitors and tunnel junctions. A line of three two-dot cells is presented, which demonstrates that there are no metastable states in a QCA line. The final experiment presented is a QCA majority gate, a programmable AND/OR logic gate.
Electrical Characteristics of Air-Bridge-Structured Silicon Nanowire Fabricated by Micromachining a Silicon-on-Insulator Substrate
Authors: Fujii Hideo , Kanemaru Seigo , Matsukawa Takashi , Itoh Junji
Published: October 2002

A new air-bridge-structured silicon nanowire was fabricated by micromachining a
silicon-on-insulator (SOI) substrate and was then electrically characterized. The
nanowire, which is isolated from the substrate by an air gap, is 15–100 nm in diameter and
300–600 nm in length. Electrical characteristics of p-type silicon nanowires under
vacuum showed ambient dependency of conductance and anomalous electric conductivity
such as negative resistance and hysteresis at room temperature. The change in the
effective channel width resulting from the surface depletion of p-type silicon nanowire is
considered to be a dominant characteristic.
High Resolution Transmission Electron Microscopy Study on the Structure of Ge Nanoparticles by Using an Ultrahigh Vacuum-Molecular Beam Epitaxy-Transmission Electron Microscope System
Authors: Wu Yuan , Takeguchi Masaki , Furuya Kazuo
Published: October 2002

Ge nanoparticles were deposited on thinned Si substrates in an ultrahigh vacuum
molecular beam epitaxy instrument (UHV-MBE) and transferred into an UHV-field emission
transmission electron microscope (UHV-FE-TEM) through an UHV-transferring system.
TEM observation indicated that the Ge nanoparticles had a round shape and were 2 to 5 nm in
diameter. The crystalline Ge nanoparticles exhibited single crystals, single-twinned crystals,
and decahedral multi-twinned particles (MTPs). It was found that the crystal structure of some
nanoparticles changes from a diamond structure to a novel structure, which is proposed to be
a β-Sn structure, with a=0.38 nm and c=0.71 nm. The particles with the new structure are not
formed when the substrate temperature is above 370°C. The structure of MTPs has been
discussed. Some Ge nanocrystals even became amorphous and then fluctuated continually
during HRTEM observation.
Domain Motion of Ferroelectricity of Bi2SrTa2O9 Single Crystals under an AC-Voltage Electric Field
Authors: Machida Akio , Nagasawa Naomi , Ami Takaaki , Suzuki Masayuki
Published: October 2002

A novel phenomenon, which increases the remanent polarization of Bi2SrTa2O9
single crystals, a promising candidate for ferroelectric random access memories
(FeRAM), has been identified. The single crystals, grown in vapor phases using the
self-flux method, have a composition characterized as
Bi
x
Sr
y
Ta2O9 (x=2.08±0.09, y=1.04±0.06). In
contrast to Bi
x
Sr
y
Ta2O9 (x=1.91±0.05, y=1.27±0.08) single crystals grown by the self-flux method, the coercive field of the present
single crystals is smaller. Observing optical anisotropy in the c-plane, we found
that this material has a paraelectric phase, which might originate from the partial
distortion of the crystal. After voltage was applied, the paraelectric phase
disappeared and the crystal became a ferroelectric domain structure. Measuring the
electrical properties in the c-plane, the remanent polarization of the Bi2SrTa2O9
single crystal was increased by applying ac-voltage. One-hour annealing over the Curie
temperature also produced a paraelectric phase in the crystal but it was confirmed
that this paraelectric phase can also be decreased by applying ac-voltage. Using
this ac-voltage application, we can clearly observe the domain structure of BiSTa
single crystal for the first time.
Study of Reflection High-Energy Electron Diffraction Oscillation for Optimization of Tertiarybutylphosphine-Based Molecular Beam Epitaxial Growth of In0.48Ga0.52P on GaAs
Authors: Sai Hironobu , Fujikura Hajime , Hasegawa Hideki
Published: October 2002

A detailed study of reflection high-energy electron diffraction (RHEED)
oscillation was made for the tertiarybutylphosphine (TBP)-based gas-source
molecular beam epitaxial (GSMBE) growth of In1-x
Ga
x
P on GaAs in order to
obtain lattice-matched layers (x=0.52) with high electrical qualities. For growth of
InGaP on conventional As-rich c(4×4) GaAs surfaces obtained by cooling under As4
flux irradiation after GaAs growth, no RHEED oscillation was observed. On the
other hand, by growing InGaP layer on As-stabilized (2×4) GaAs surfaces obtained
by exposure to low As4 pressures, clear and persistent RHEED oscillations were
successfully observed for the first time. Growth under a sufficient TBP flow rate
with careful adjustment of the substrate temperature within a narrow range was
found to be important for realizing stable layer-by-layer growth of InGaP layer and
for obtaining high-quality layers. The optimal InGaP layers achieved minimum
full-width at half maximum (FWHM) values of X-ray diffraction (XRD) and
photoluminescence (PL) peaks of 18 s and 15.5 meV, respectively. Nondoped layers
grown under the optimal conditions realized high electron mobility values of 3,300 cm2/Vs at 300 K and 21,000 cm2/Vs at 77 K with low residual carrier
concentration values of 5×1014–5×1015 cm-3. These are the best values reported so
far for InGaP layers grown by GSMBE using TBP and are comparable to the best
values reported so far for InGaP layers grown by other methods.
Effect of Cd Reservoir on the Composition (y) of Cd1-yZnyTe Epilayers Grown by Hot Wall Epitaxy
Authors: Koo Bonheun , Wang Jifeng , Ishikawa Yukio , Isshiki Minoru
Published: October 2002

The relation between the composition (y) and the growth condition is
examined for hot wall epitaxy (HWE) of (100) Cd1-y
Zn
y
Te (CZT) using a CZT (y=0.2) source and Cd reservoir. A good linear relation between the compositions and
their partial pressure ratio is obtained. The composition can be effectively controlled
by varying both the source composition and vapor pressure of the Cd reservoir.
Structural Evolution of Colloidal Particles in Porous SiO2 Coatings
Authors: Bernal R. , Manzanares J. , Espinoza-Beltrán F. J. , Ramirez-Bon R. , Vorobiev Y. V. , González-Hernández J.
Published: October 2002

The sol-gel method has been used to produce samples having
colloidal copper-based particles embedded in a SiO2 matrix. The
particle composition depended on: the atmosphere in which the samples
were annealed, the annealing temperature and the time after the
treatment. The optical properties of the colloidal system were
determined, as a function of the sample history. For that, the model
proposed by Mie was used with effective values for the optical
constants of the colloidal particles. From this analysis,
characteristic parameters of the colloidal system and particle
composition were determined.
Deposition of Polyethylene Thin Films Using Synchrotron Radiation Ablation
Authors: Nakanishi Kota , Suzuki Hiroyuki , Katoh Takanori , Imai Shigeru , Nakayama Yasuyuki , Miki Hidejiro
Published: October 2002

Crystalline polyethylene thin films were deposited on Si substrates using the
synchrotron radiation(SR) ablation method. The deposited films were
characterized by X-ray diffraction and Fourier-transform infrared spectroscopy. In
order to understand the mechanism for the decomposition that occurs due to SR
ablation, analysis of gases resulting from the decomposition was performed using
the quadrupole mass spectrometric method. The mechanism involved in the
carbonization was clarified.
He Atomic Beam Scattering Study of Pt(111) Super-Structure Surface Induced by High Energy Molecular Beam of H2O
Authors: Murakami Yasunobu Kino , Yagyu Shinjiro , Yamamoto Shigehiko
Published: October 2002

The super-structure, Pt(111)-(2×2), is investigated both by He atomic beam scattering (HAS) and low energy electron diffraction. The structure is produced by irradiation of a high energy H2O molecular beam, which is accelerated up to about 300 meV by dilution in He gas molecules. The HAS result shows that the structure is stable at 200 K and becomes unstable as the sample temperature is raised to 300 K. The observed structure is believed to be due to reconstruction of the Pt(111) surface, which is caused by H atoms produced during the collision process of H2O molecules with sufficiently high energy for dissociation.
Optical Properties of Anamorphic Liquid Crystal Microlenses and Their Application for Laser Diode Collimation
Authors: Michinori Honma Michinori Honma , Toshiaki Nose Toshiaki Nose , Susumu Sato Susumu Sato
Published: October 2002

Anamorphic liquid crystal (LC) microlenses are fabricated using elliptical hole-patterned
electrodes of various sizes and ellipticity. The relationships between their optical properties
and electrode structure are investigated experimentally and summarized as follows. 1) The
maximum values of the numerical aperture (NA) in the directions parallel and perpendicular
to the rubbing direction simultaneously depend on the diameters in the direction parallel and
perpendicular to the rubbing direction (D∥ and D⊥), respectively. 2)The normalized
longitudinal aberrations, which are closely related to the spherical aberration, in the directions
parallel and perpendicular to the rubbing direction strongly depend on D∥ and D⊥, respectively.
3)The astigmatism strongly depends on the ellipticity (D∥/D⊥) of the electrode pattern. Finally,
an optical setup for collimating an astigmatic beam emitted from a laser diode (LD) is
realized using an anamorphic LC microlens. As a result, a round collimated beam is obtained,
and the potential of the anamorphic LC microlenses for collimating a laser diode beam is
confirmed.
Electrical Properties of a Semiconducting Layer Formed on SrTiO3 Single Crystal by Excimer Laser Irradiation
Authors: Yoon Jong-Won , Miyayama Masaru
Published: October 2002

Effects of excimer laser irradiation on electrical properties were investigated for
insulating SrTiO3 single crystals, and the mechanism was discussed. A drastic drop of surface
resistance from >1013 Ω/cm2 to about 104 Ω/cm2 was observed after irradiation by KrF and XeCl laser light with fluences of about 100 and 200 mJ/cm2, respectively. For laser irradiation
with a fluence above these critical values, the surface resistance remained at almost the same,
low values. Traces of local melting, in the form of microcracks, were recognized on the
surfaces with low resistance. The low-resistance surface had n-type semiconductivity, and the
resistivity, electron concentration and mobility were estimated to be 0.2 Ωcm, 5.4×1018 cm-3,
5.4 cm2V-1s-1, respectively, by the Hall coefficient measurement assuming a semiconductive
layer thickness of 0.3 µm. On the basis of the result of X-ray photoelectron spectroscopic
analysis, the drastic decrease in resistivity is attributed to the generation of oxygen vacancies.
Determination of the Optical Constants of the Photostimulable BaFCl: Eu2+ and KCl:Eu2+ Crystals
Authors: Toshio Kurobori Toshio Kurobori , Shuichi Kozake Shuichi Kozake , Yukio Hirose Yukio Hirose , Masato Ohmi Masato Ohmi , Masamitsu Haruna Masamitsu Haruna , Taku Kimura Taku Kimura , Katsuyuki Inabe Katsuyuki Inabe , Karnati Somaiah Karnati Somaiah
Published: October 2002

A new method to determine the concentration of the defect centers in
photostimurable luminescent materials is demonstrated. The method is
representatively applied to BaFCl:Eu2+ and KCl:Eu2+ single
crystals, which exhibt the photostimulable luminescence.
Thereby the values of the oscillator strength, f, are calculated
utilizing the results of the defect center concentrations as well as
the measured refractive indices and the corresponding absorption bands
by using the Smakula's formula. The values obtained are f=0.80 for
the F(Cl-) centers in BaFCl:Eu2+ and f=0.60 for the F centers
in KCl:Eu2+.
Measurement of Optical Activity using a Photoelastic Modulator System
Authors: Wang Charn-Kuo , Chao Yu-Faye
Published: October 2002

Adjusting the analyzer at 90° to the strain axis of a
photoelastic modulator, one can determine the optical activity
by measuring the slope of its DC intensity distribution under
various phase modulation amplitudes. This technique was
applied to measure the ellipticity of few quartz quarter-wave
plates and the optical rotation of an optical active crystal. A
multiple reflection enhancement effect in the wave plate was
observed and discussed. By considering the photoelastic
modulator as an elliptical retarder, we also determined its
intrinsic ellipticity and static phase retardation, to increase the
accuracy of measurements.
High-Resolution AC Calorimeter for Measuring the Heat Capacity of Small Amounts of Liquid Samples
Authors: Yao Haruhiko , Ema Kenji , Hatta Ichiro
Published: October 2002

A high-resolution AC microcalorimeter has been developed to
measure the heat capacity of liquid samples. A very stable AC heat
flux is supplied to a sample by applying an AC electric current
to a tubelike sample cell made of metal. The fluctuation of the
AC temperature of the cell caused by heat leakage from the cell
to the surroundings is corrected using the phase of the AC
temperature together with its amplitude. Consequently, heat
capacity can be measured with a precision of ±0.01%.
Molecular Beam Epitaxial Growth of InP Using a Valved Phosphorus Cracker Cell: Optimization of Electrical, Optical and Surface Morphology Characteristics
Authors: Yoon Soon Fatt , Zheng Hai Qun , HuaZhang Peng , Mah Kia Woon , Ng Geok Ing
Published: October 2002

We report the molecular beam epitaxial (MBE) growth of epitaxial InP using a valved
phosphorous cracker cell at a range of cracking zone temperature (T
cr=875°C to 950°C),
V/III flux ratio (V/III=1.2 to 9.3) and substrate temperature (T
s=360°C to 500°C). From
Hall measurements, the as-grown epitaxial InP on InP (100) substrate was found to be n-type.
The background electron concentration and mobility exhibited a pronounced dependence on
the cracking zone temperature, V/III flux ratio and substrate temperature. Using a cracking
zone temperature of 850°C, the highest 77 K electron mobility of 40900 cm2/Vs was achieved
at a V/III ratio of 2.3 at a substrate temperature (T
s) of 440°C. The corresponding background
electron concentration was 1.74×1015 cm-3. The photoluminescence (PL) spectra showed
two prominent peaks at 1.384 eV and 1.415 eV, with the intensity of the low-energy peak
becoming stronger at higher cracking zone temperatures. The surface morphology
deteriorated following a reduction in the V/III ratio or an increase in the substrate
temperature. In the extreme case, formation of free indium droplets and severe surface
faceting occurred.
Fe Doping and Preparation of Semi-Insulating InP by Wafer Annealing under Fe Phosphide Vapor Pressure
Authors: Uchida Masayuki , Asahi Toshiaki , Kainosho Keiji , Matsuda Yuko , Oda Osamu
Published: October 2002

Semi-insulating (SI) InP has been industrially produced by doping Fe atoms as deep acceptors. Fe concentrations in InP are, however, largely varied from top to tail along the crystal growth axis due to impurity segregation. In the present work, we have examined the possibility of vapor-phase Fe doping for fabrication of 50- and 75-mm-diameter SI InP wafers with constant Fe concentrations using a wafer annealing procedure. A small amount of Fe was charged with red phosphorus in ampoules in which InP wafers were annealed. It was found that the vapor-phase doping is effective for Fe doping of InP. The present technology can be applied for the fabrication of low Fe-doped SI InP wafers with similar Fe concentrations of all wafers from one InP ingot.
Silicon Crystal Growth by the Electromagnetic Czochralski (EMCZ) Method
Authors: Watanabe Masahito , Eguchi Minoru , Hibiya Taketoshi
Published: October 2002

A new method for growing silicon crystals by using electromagnetic force to rotate
the melt without crucible rotation has been developed. We call it electromagnetic Czochralski
(EMCZ) growth. An electromagnetic force in the azimuthal direction is generated in the
melt by the interaction between an electric current (I) through the melt in the radial direction
and a vertical magnetic field (B). The rotation rate (ωm) of the silicon melt is continuously
changed from 0 to over 105 rpm under I = 0 to 8 A and B = 0 to 0.1 T. Thirty-mm-diameter
silicon single crystals free of dislocations could be grown under two conditions: I = 2.0 A and
B = 0.05 T (ωm = 105 rpm); and I =0.2 A and B = 0.1 T (ωm = 15 rpm). The oxygen
concentration in the crystals was 8 ×1017 atoms/cm3 for the high rotation rate and 1×1017 atoms/cm3
for the low rotation rate. The oxygen-concentration distributions in the radial
direction in both crystals were more homogeneous than those in the crystals grown by
conventional CZ and/or MCZ growth. This new crystal-growth method can be easily
adopted for growing large-diameter silicon crystals.
A New N-Channel Junction Field-Effect Transistor Embedded in the i Layer of a Pin Diode
Authors: Hideharu Matsuura Hideharu Matsuura , Kenji Akatani Kenji Akatani , Michihisa Ueda Michihisa Ueda , Kazushige Segawa Kazushige Segawa , Hidemasa Tomozawa Hidemasa Tomozawa , Katsuhiko Nishida Katsuhiko Nishida , Kazuo Taniguchi Kazuo Taniguchi
Published: October 2002

We experimentally confirmed a basic operation of the n-channel junction field-effect transistor (JFET) embedded in the i layer (n- substrate) of a pin diode for X-ray detectors, which was proposed in Jpn. J. Appl. Phys. 37 (1998) L115.
To electrically isolate the n-channel from the n- substrate, a p+ ring is formed around the JFET and is reverse-biased, instead of a deep p layer under the n-channel (i. e. , the conventional structure).
In the proposed structure, only one type of donor is ion-implanted in the n-channel, while in the conventional structure, both donor and acceptor are ion-implanted there.
For the first time, the role of the p+ ring in the electrical characteristics of the n-channel JFET is experimentally elucidated.
Excitonic Emissions under High Excitation of Hexagonal GaN Single Crystal Grown by Sublimation Method
Authors: Satoshi Kurai Satoshi Kurai , Akira Kawabe Akira Kawabe , Taiichi Sugita Taiichi Sugita , Shuichi Kubo Shuichi Kubo , Yoichi Yamada Yoichi Yamada , Tsunemasa Taguchi Tsunemasa Taguchi , Shiro Sakai Shiro Sakai
Published: October 2002

Excitonic emission lines from hexagonal-structured GaN single crystals grown by the sublimation method have been studied at 4.2 K. A dominant I
2 line at 3.4706 eV, which is probably ascribed to the radiative recombination of an exciton bound to a neutral donor, has a linewidth of 2.1 meV under low excitation. Fine structures around 3.475 eV and 3.479 eV appear with increasing excitation power density. These positions correspond to those of A-free exciton and B-free exciton in strain-relaxed GaN crystal, respectively. A new line at 3.454 eV can be observed above 270 kW/cm2 and gradually shifts towards the low-energy side with a further increase in excitation power density. It is suggested that the origin of this line is due to the inelastic exciton-exciton interaction. The emission related to dense exciton gas was observed in the excitonic luminescence from bulk GaN for the first time.
Terahertz Radiation from (111) InAs Surface Using 1.55 µm Femtosecond Laser Pulses
Authors: Takashi Kondo Takashi Kondo , Masanao Sakamoto Masanao Sakamoto , Masayoshi Tonouchi Masayoshi Tonouchi , Masanori Hangyo Masanori Hangyo
Published: October 2002

We report the first observation of terahertz (THz) radiation from an undoped (111) InAs surface excited by 1.55 µm femtosecond laser pulses.
The surface illuminated by an unfocused beam at an incidence angle of 45 degrees measured with respect to the surface normal emits THz radiation with weak dependence of the amplitude on the azimuthal angle.
The results indicate that the radiation excited by the unfocused beam at a power density less than ∼1 W/cm2 is mainly explained by the surge current effect accompanied by a small component associated with the optical rectification effect.
Scanning Tunneling Microscopy (STM) Study on Morphology of Regioregular Poly(3-alkylthiophene) Deposited on A(111) Surface
Authors: Keiichi Kaneto Keiichi Kaneto , Kazuyuki Harada Kazuyuki Harada , Wataru Takashima Wataru Takashima , Ken Endo Ken Endo , Masahiro Rikukawa Masahiro Rikukawa
Published: October 2002

Molecular alignments of poly(3-alkylthiophene)s deposited on the Au(111) facet are studied by scanning tunneling microscopy (STM). In regioregular poly(3-hexylthiophene) and poly(3-dodecylthiophene), the individual polymer is clearly imaged as a silkworm. On the other hand, regiorandom poly(3-octadecylthiophene) does not show any distinguishable image of the individual polymer. The molecular shapes and the preparation method of the structurally aligned regioregular poly(3-alkylthiophene)s are described.
Oxidation of Terthiophene Substituted with Ferrocenyl Groups
Authors: Sato Masa-aki , Kashiwagi Shin-ichiro , Taniguchi Hiroyuki , Hiroi Masao
Published: October 2002

Terthiophenes substituted with ferrocenyl or methyl groups were prepared by a
palladium-catalyzed cross-coupling reaction. The oxidation processes and the oxidized states of the
compounds were investigated by cyclic voltammetry, coulometry, and electronic absorption
spectroscopy. The first oxidation of the ferrocenyl-terthiophenes took place on the ferrocene
moiety; the resultant oxidized states spread over the terthiophene moiety. This implies the
charge transfer from the ferricinium ion moiety to the terthiophene moiety.
High-Speed Optical Near-Field Photolithography by Super Resolution Near-Field Structure
Authors: Kuwahara Masashi , Nakano Takashi , Tominaga Junji , Lee Myung Bok , Atoda Nobufumi
Published: October 2002

We propose a new lithography technique using the optical near field. This technique
makes use of a super-resolution near-field structure (Super-RENS) which was first proposed
by us for high-density data storage. Using this structure, we have fabricated narrow
grooves in a photoresist film spin-coated on a Super-RENS disk at a constant linear
velocity of 6 m/s and about 400 rotations with a mercury lamp (λ=365 nm) for exposing
the photoresist film and a semiconductor laser (λ=635 nm) for generating a small optical
aperture. By adjusting the laser power, narrow grooves with a full-width at half-maximum
(FWHM) of less than 200 nm could be fabricated in the photoresist film. Moreover, a
fabrication speed 104 or 105 times greater than that with the conventional
techniques using a near-field scanning optical microscope was achieved.
Effects of Tungsten Polycide Process and Post-Polyoxidation Rapid Thermal Process on Electrical Characteristics of Thin Polysilicon Oxide
Authors: Huang Kuo-Ching , Fang Yean-Kuen , Yaung Dun-Nian , Hsieh Jang-Cheng , Liang Mong-Song
Published: October 2002

The effects of the tungsten polycide technologies and rapid thermal annealing (RTA)
on thin polyoxide electrical characteristics have been investigated. It is found that a thin
polyoxide with dichlorosilane (DCS)-based chemical vapor deposition (CVD) WSi
X
exhibits both good J-E characteristics and
reliability. This is due to moderated fluorine incorporation, which improves poly-Si/SiO2
interfaces region but not degrades the bulk polyoxide. Moreover, the post-polyoxidation
RTA is also found to improve the polyoxide quality. According to the results, the
DCS-based CVD WSi
X
with post-polyoxidation RTA is a good candidate for polycide gate
technique in high-density nonvolatile memories.
Electrical Contacts for n-Type Diamond
Authors: Teraji Tokuyuki , Koizumi Satoshi , Mita Seiji , Sawabe Atsuhito , Kanda Hisao
Published: October 2002

Electric properties at metal/n-type diamond interfaces are investigated. Homoepitaxial diamond thin films with n-type conduction are grown on {111} diamond substrates by microwave-enhanced plasma chemical vapor deposition. Gold, copper and aluminum, which have a low reactivity for diamond, are deposited on diamond films. Au and Cu contacts are found to give good n-type rectification properties with a small reverse current. However, a large reverse current is observed for Al contacts. This large reverse current may originate from the lowering of the Schottky barrier height at the Al/n-type diamond interfaces.
High Average Power Mode Locked Ti:Sapphire Laser with Intracavity Continuous-Wave Amplifier and Strained Saturable Bragg Reflector
Authors: Liu Tze-An , Huang Kai-Fung , Pan Ci-Ling , Liu Zhenlin , Ohtake Hideyuki , Sarukura Nobuhiko
Published: October 2002

We demonstrate a new scheme for the generation of high average power femtosecond pulses by incorporating an intracavity amplifier and a strained saturable Bragg reflector with low saturation fluence for self-starting mode locking. When the Ti:sapphire oscillator and intracavity amplifier are pumped at 10 W and 15 W, respectively, the average output power is as high as 1.62 W. The pulse duration is about 145 fs, and the peak power reaches 160 kW at a 68 MHz repetition rate. The pulse-formation time of 400 µs is sufficiently short to sustain stable mode locking.
Wear-Resistant Thin Films of Amorphous Carbon Nitride Prepared by Shielded Arc Ion Plating
Authors: Nobuhiro Tajima Nobuhiro Tajima , Hiroki Saze Hiroki Saze , Hiroyuki Sugimura Hiroyuki Sugimura , Osamu Takai Osamu Takai
Published: October 2002

Amorphous carbon nitride (a-C:N) thin films were synthesized by means of shielded arc ion plating using a graphite target and pure nitrogen gas. The mechanical properties and chemical structures of these a-C:N films were studied through nanoindentation and X-ray photoelectron spectroscopic analysis. Nanohardness of the a-C:N film prepared at a substrate bias voltage of 0 V was ≈10 GPa. It was increased to 13–14 GPa when the substrate was biased negatively in the range of -100 to -500 V. The a-C:N film prepared at a bias of -300 V was particularly wear-resistant such that the film did not wear at all when rubbed with a diamond tip at a contact force of 20 µN. This highly wear-resistant a-C:N film was found to contain almost equal amounts of two C-N phases: β-C3N4-like and graphitelike phases.
Self-Aligned Surface Tunnel Transistors Fabricated by a Regrowth Technique
Authors: Chun Yong Jin , Uemura Tetsuya , Baba Toshio
Published: October 2002

A self-aligned process for fabricating surface tunnel transistors (STTs)
has been developed in an attempt to improve both miniaturization and
integration of STTs. In this process, the keys to obtaining a flat regrown
layer and fine tunnel junctions are to keep from contaminating the surface
during the lithography process before regrowth and to control the side-wall
profile of the gate region in which tunnel junctions are formed. The carbon
contamination can be reduced significantly by using a double hard mask
consisting of Si3N4 and SiO2, and oxygen contamination can be removed by
atomic hydrogen irradiation. The side-wall profile, that is etched surface
morphology and side-wall angle, can be optimized by adjusting the composition
of the H3PO4:H2O2:H2O etching solution. During regrowth, a flat surface
morphology and fine tunnel junctions were obtained at the low temperature of
400°C. Self-aligned InGaAs-based STTs with gate-controlled negative
differential resistance (NDR) characteristics showing a peak-to-valley (P/V)
ratio of 2.5 were obtained.
Disappearance of Peak Effect in Critical Current Density of NdBa2Cu3O7-δ Single Crystals Grown under Very Low Oxygen Partial Pressures
Authors: Shibata Susumu , Pradhan Aswini K. , Koshizuka Naoki
Published: October 2002

NdBa2Cu3O7-δ(Nd123) single crystals were grown by horizontal Bridgman-like
method under various partial O2 pressures (0.1–0.04%) in Ar atmosphere. High
quality Nd123 single crystals with superconducting transition temperature, T
c∼95.0 K were obtained using yttrium stabilized ZrO2 boats. The enhancement of the
magnetization with increasing field, i.e., fishtail or peak effect was observed in the
magnetization hysteresis at around 77 K in the field parallel to the c-axis of the
Nd123 single crystals grown under 0.1–0.06% partial O2 pressures, but not for the
crystals grown under 0.05 and 0.04% O2 pressures. This indicates the existence of
certain partial O2 pressures under which the amount of Nd/Ba substitution is
remarkably reduced in Nd123 single crystals.
Optical Parametric Oscillator on 1-mm-Thick Periodically Poled LiNbO3 with 29 mm Interaction Length
Authors: Nakamura Masaru , Tsunekawa Takashi , Taniguchi Hirokazu , Tadamoto Kazuyuki
Published: October 2002

A 1-mm-thick periodically poled LiNbO3 (PPLN) crystal with a domain-inverted period of 29.8 µm and an interaction length of 29 mm has been successfully fabricated by an electric field poling process. The average ratio of the domain-inverted width to the domain-inverted period (duty cycle) on a +Z surface and a -Z surface were 54.01% and 57.10%, respectively. To investigate the uniformity of domain-inverted structures in the Y-Z plane, the distribution of the optical parametric oscillator (OPO) idler output energy was measured, and an almost constant OPO idler output energy was obtained at all positions on the Y-Z plane. Therefore, the 1-mm-thick periodically domain-inverted structure can be uniformly obtained over the entire aperture. Finally, the OPO using this PPLN crystal with a large aperture of 1 mm×1 mm was demonstrated.
Wavefront Reconstruction from Intensity Measurements Using Fresnel Phase Retrieval Method
Authors: Matsuoka Shinichi , Yamakawa Koichi
Published: October 2002

We experimentally demonstrate the wavefront measurement of a continuous-wave He-Ne laser beam using the Fresnel phase retrieval method, in which the wavefront is reconstructed from the measurement of only two intensity profiles, without additional optics. The reconstructed wavefronts are compared with results obtained with a phase profilometer consisting of two lateral shearing interferometers in order to confirm the accuracy of the method.
Observation of Superconducting Device Using Magnetic Imaging System with a Micro-DC Superconducting Quantum Interference Device Magnetometer
Authors: Morooka Toshimitsu , Nakayama Satoshi , Odawara Akikazu , Chinone Kazuo
Published: October 2002

A magnetic imaging system with a micro-DC superconducting quantum
interference device magnetometer has been developed to evaluate
superconducting films and to inspect a superconducting device with a high
spatial resolution. A superconducting device, i.e., a DC-SQUID made of a
superconducting Nb thin film, was observed using the system. The shape
of the device was identified by applying the Meissner effect. The
trapped fluxes in the device were clearly visible. In addition, the input
current and the shielding current flowing on the device were detected by
feeding a current to the device. It was confirmed experimentally that the
magnetic imaging system was effective in studying superconducting devices.
Correction of Velocity Profiles on Thin Specimens Measured by Line-Focus-Beam Acoustic Microscopy
Authors: Ohashi Yuji , Kushibiki Jun-ichi
Published: October 2002

A new method of correcting apparent velocities of leaky surface
acoustic waves (LSAWs), measured by line-focus-beam acoustic microscopy,
for thin specimens having elastic inhomogeneities is proposed to eliminate
serious errors due to back reflection. This method estimates and removes
the apparent measurement errors using the frequency dependence of LSAW
velocities measured at a reference position on the specimen with a certain
thickness, and also using the relationship between two LSAW velocity values
measured at two frequencies and apparent velocity changes included in those
values. This correction method is more efficient for a number of
measurement positions than the previously developed method of
moving-average processing. Measurements of LSAW velocities along the
crystal pulling-axis (Z-axis) direction of a Y-cut, X-axis
propagating 5-mol% MgO-doped LiNbO3 substrate, with a thickness
of about 0.5 mm, are demonstrated.
Effects of Magnetic Field on Metabolic Action in the Peripheral Tissue
Authors: Kawakubo Tatsyuki , Yamauchi Kazue , Kobayashi Takashi
Published: October 2002

The effect of magnetic field on metabolic action in the
peripheral tissue was examined in 12 subjects by measuring skin
temperature with a thermographic tracer and the binding ratio
of oxygen to hemoglobin using an apparatus for detecting
concentrations of oxyhemoglobin and deoxyhemoglobin. The skin
temperature was found to increase by 0.4–1.2°C after a 5-min
exposure to a magnetic field of 0.45 or 1.2 T. The binding ratio
of oxygen showed a rapid decrease with application of magnetic
field, which indicated the release of oxygen from hemoglobin.
p-Type Electrical Conduction in ZnO Thin Films by Ga and N Codoping
Authors: Joseph Mathew , Tabata Hitoshi , Kawai Tomoji
Published: October 2002

We report the realization of p-type behavior in ZnO thin films,
which are prepared by codoping method using Ga (donor) and N
(acceptor) as the dopants. Especially, using active N formed by
passing N2O gas through an electron cyclotron resonance (ECR) plasma
source is quite effective for the acceptor doping. We have observed a
room temperature resistivity of 2 Ω·cm and a hole concentration of
4×1019 cm-3. These values are enough high for practical applications in
various oxide electronic devices.
Three-Horned Multishell Fullerene
Authors: Yukihito Kondo Yukihito Kondo , Kunio Takayanagi Kunio Takayanagi
Published: October 2002

A new type of three-horned multishell fullerenes with C
3 symmetry has been discovered in deposits on arc discharge electrode using a high-resolution electron microscope. The observed images indicate that these fullerenes consist of three horns and concave horn joints. We also propose a model that involves three seven-membered rings at the horn joints and fifteen five-membered rings at horn caps. The formation of the fullerenes with negative curvature is accompanied by minimum numbers of unstable five-membered and seven-membered rings.
Effects of Seed Layer on YBa2Cu3Ox Films Grown by Liquid Phase Epitaxy
Authors: Zama Hideaki , Miyakoshi Masayuki , Yamamoto Hiroshi , Morishita Tadataka
Published: October 2002

Crack-free YBa2Cu3O
x
(YBCO) films were grown by liquid phase
epitaxy (LPE) on MgO(100) substrates with a YBCO seed layer. The
crystalline property of LPE was crucially dependent on that of the
seed layer. On the purely c-axis-oriented seed layer, reasonable YBCO
films were grown with a full-width at half maximum of the (005)
reflection rocking curve, Δω, of 0.07°. In the case of the seed
including an a-axis-oriented grain, the value of Δω of LPE films was
poor in reproducibility and larger than 0.1° on average. For the
a-axis-oriented seed, no YBCO films grew under the growth conditions
in this study. X-ray topographic observations revealed that the
crystalline quality of MgO substrates limited the Δω of LPE films grown
on them.
Ramp-edge Josephson Junction with Indium-Tin-Oxide Barrier
Authors: Hato Tsunehiro , Aso Hiroyuki , Ishimaru Yoshihiro , Yoshida Akira , Yokoyama Naoki
Published: October 2002

We fabricated a ramp-edge Josephson junction with a 17-nm-thick indium-tin-oxide (ITO) (1 wt%)
barrier. ITO is considered to be a useful barrier material for Josephson junctions because it has a low
permittivity of 20, a mobility of 100 cm2/V·s, a carrier density of 1.1×1020 cm-3, and (100) orientation on
YBa2Cu3O7-x
(YBCO) (001). We examined 8 junctions with widths ranging from 6 µm to 10 µm at
temperatures varying from 20 K to 80 K. All of the junctions showed resistively shunted junction (RSJ)-type I-V characteristics at temperatures between 20 K and 77 K. The maximum critical current density, J
c,
and critical current normal resistance products, I
c
R
n, were 4.0×104 A/cm2 and 2.2 mV, and the averages of
these values at 20 K were 2.7×104 A/cm2 and 1.7 mV, respectively. The standard deviation of I
c and
I
c
R
n were σ
I
=33% and σ
I
c
R
n
=21%, respectively. I
c was suppressed well by a magnetic field.
Quasi-Phase-Matched Optical Parametric Oscillator Using Periodically Poled MgO-Doped LiNbO 3 Crystal
Authors: Masaru Nakamura Masaru Nakamura , Masahisa Sugihara Masahisa Sugihara , Masahiro Kotoh Masahiro Kotoh , Hirokazu Taniguchi Hirokazu Taniguchi , Kazuyuki Tadatomo Kazuyuki Tadatomo
Published: October 2002

A 0.5-mm-thick periodically poled MgO-doped (5 mol%) LiNbO3 (PPMgLN) crystal with domain-inverted periods of 26.2–32.0 µm and an interaction length of
30 mm has been successfully fabricated by an electric field poling process.
The average ratios of the domain-inverted width to the domain-inverted period (duty cycle) were approximately 50%.
Experiments on quasi-phase-matched (QPM) optical parametric oscillation (OPO) using a PPMgLN crystal were performed.
During QPM-OPO, the PPMgLN crystal exhibited a higher resistance to photorefractive damage than did a periodically poled LiNbO3 (PPLN) crystal.
OPO properties of the PPMgLN crystal at 20°C were comparable to those of a PPLN crystal heated to ∼100°C to prevent photorefractive damage, which
enables operation in the steady state at room temperature.
Continuous Wave Operation of 1.55 µm GaInAsP/InP Laser with Semiconductor/Benzocyclobutene Distributed Bragg Reflector
Authors: Madhan Raj Mothi , Yoshikazu Saka Yoshikazu Saka , Jörg Wiedmann Jörg Wiedmann , Hideo Yasumoto Hideo Yasumoto , Shigehisa Arai Shigehisa Arai
Published: October 2002

The room temperature CW operation of a 1.55 µm wavelength
GaInAsP/InP laser with a deeply etched third-order Bragg reflector
consisting of a semiconductor/Benzocyclobutene periodic structure was
obtained for the first time. A threshold current as low as 13.5 mA
and differential quantum efficiency of 28% for a cavity length of 330
µm and a stripe width of 5 µm was obtained
with 10 elements of the Bragg reflector on one side.
Chloro-Fluorinated Polyimides for Low Loss Optical Waveguides Application
Authors: Han Kwansoo , Kim Dug-Bong , Jang Woo-Hyuk , Rhee Tae Hyung
Published: October 2002

Optical polymers which exhibit good thermal stability, controllable refractive index,
and low optical loss in the optical communications wavelength of 1.55 µm were prepared
using fluorinated and chloro-fluorinated polyimides. As the chlorine moiety is increased,
the refractive indices of polymer are increased from 1.5176 to 1.5714 for TE polarization
and from 1.5076 to 1.5590 for TM polarization at 1.55 µm. Single mode rib type polymer
optical waveguides were fabricated using fluorinated and chloro-fluorinated polyimides.
These waveguides exhibit a low propagation loss of less than 0.4 dB/cm at 1.55 µm,
and a very low polarization dependent loss of less than 0.01 dB/cm.
Interface and Domain Structures of (116)-Oriented SrBi2Ta2O9 Thin Film Epitaxially Grown on (110) SrTiO3 Single Crystal
Authors: Suzuki Toshimasa , Nishi Yuji , Fujimoto Masayuki , Ishikawa Katsuyuki , Funakubo Hiroshi
Published: October 2002

The interface and domain structures in epitaxial (116)-oriented
SrBi2Ta2O9 films on (110) SrTiO3 substrates were
investigated by high-resolution transmission electron microscopy. The
film contains domain boundaries due to the formation of two types of
(116)-oriented crystallites with symmetrical tilted c-axis
directions and numerous wavy c/6 translational boundaries
originating from the domain boundaries. Each epitaxial crystallite
forms a semicoherent interface accompanying periodic lattice strain,
where the alternate continuity of perovskite layers in the film to the
perovskite structure of SrTiO3 is found. Such a quasi-stable
interface structure may be the primary cause of difficulty in the
preparation of epitaxial SrBi2Ta2O9 films with the
tilted c-axis.
Observation of Heat Diffusion across Submicrometer Metal Thin Films Using a Picosecond Thermoreflectance Technique
Authors: Naoyuki Taketoshi Naoyuki Taketoshi , Tetsuya Baba Tetsuya Baba , Akira Ono Akira Ono
Published: October 2002

We have observed heat diffusion across submicrometer metal thin films for the first time using a picosecond thermoreflectance method.
The boundary between a film and a transparent substrate is heated by a picosecond laser pulse.
Heat generated by the pump laser pulse diffuses towards the front surface of the thin film.
The temperature change on the front surface opposite to the heated area is probed by the reflectivity of another picosecond laser pulse.
Thermoreflectance signals of a molybdenum thin film and an aluminum thin film with nominal thickness of 100 nm deposited on Pyrex 7740 glass substrates were observed at room temperature.
Thermal energy transfer inside the molybdenum and aluminum thin films under picosecond heating can be explained by the classical heat diffusion equation.
Thermal diffusivity values are close to those of bulk molybdenum and bulk aluminum, respectively.