bluuebunny/crossref_metadata_2025 huggingface dataset:
A Laser Ionization Time-of-Flight Mass Spectrometric Study of UV Laser Ablation of Polyarylsulfone Films
Authors: Grivas Christos , Niino Hiroyuki , Yabe Akira
Published: October 2002

Neutral fragments from the 248 nm laser ablation of
polyarylsulfone (PAS) were investigated using laser post ionization
(193 nm) time-of-flight (TOF) mass spectroscopy. Three regimes of
ablation fluence were distinguished with respect to detected
fragments and differences in their velocity distributions. Over the
entire fluence range the arrival profiles of the products matched
with a shifted Maxwell-Boltzmann distribution. Interestingly,
average translational velocities revealed a non-monotonical
dependency on ablation fluence. This is probably be due to screening
effects of the ablation pulse by the plume, or to non-thermal
effects that may contribute to the ablation process at high
fluences. The dependencies of both the flight velocities and the
Knudsen layer temperature of the fragments on fluence suggest that
PAS ablation is photothermally driven. However, the excessively high
values for average translational energies (up to 34 eV at high
fluences) and their increases with increasing fragments amu indicate
that the process also has some non-thermal features.
Streaming Induced by Ultrasonic Vibration in a Water Vessel
Authors: Nomura Shinfuku , Murakami Koichi , Sasaki Yuuichi
Published: October 2002

The flow pattern induced by ultrasonic vibration in a water
vessel is investigated experimentally using several liquids. In tap
water, vortex streaming of cavitation bubbles around the pressure
node of a standing wave occurred because of the large number of
cavitation bubbles generated by the ultrasonic vibration. Acoustic
streaming of the Rayleigh type caused by cavitation bubble streaming
is also induced in tap water. In a glycerin aqueous solution of
30%, Eckart streaming, which flowed upward from the vibrator,
occurred due to the dissipation of ultrasonic energy caused by
viscosity. On the other hand, in degassed water, streaming is hardly
generated at all since a uniform and stable standing wave is formed
in the water vessel. The velocity of the acoustic streaming
generated in the water vessel by 27.8 kHz vibration is 1 to
6 mm/s. The cavitation bubble streaming in tap water is completely
independent of normal Rayleigh or Eckart streaming. This bubble
streaming is considerably faster than previous streaming.
Orientation of Fibers in Liquid by Ultrasonic Standing Waves
Authors: Syojiro Yamahira Syojiro Yamahira , Shin-ichi Hatanaka Shin-ichi Hatanaka , Mamoru Kuwabara Mamoru Kuwabara , Shigeo Asai Shigeo Asai
Published: October 2002

The orientation of fibers in a liquid irradiated with ultrasound is studied to realize the noncontact directional control of reinforcing fibers in the molten matrix of a composite material. The equations of translational and rotational motions of a fiber in a standing wave field are derived. The numerical solutions show the movement of the fibers at various initial positions and their stable positions and directions. Experiments are performed using polystyrene fibers of various lengths suspended in an aqueous sugar solution. Both numerical and experimental results indicate that polystyrene fibers shorter than one-fourth of the wavelength are constrained at the pressure node and are oriented in the direction perpendicular to that of wave propagation. On the other hand, fibers ranging from one-fourth to one-half of the wavelength have orientation either parallel to the direction of wave propagation at the pressure loop or perpendicular to that at the pressure node depending on their initial positions and directions.
Early Detection of Salt Stress Damage by Biophotons in Red Bean Seedling
Authors: Tomoyuki Ohya Tomoyuki Ohya , Hideaki Kurashige Hideaki Kurashige , Hirotaka Okabe Hirotaka Okabe , Shoichi Kai Shoichi Kai
Published: October 2002

The optical detection of the stress damage to plants by NaCl solutions was attempted during germination of a seed and growth of a root. We compared the photon intensity of red beans before and after NaCl treatment and found that the photon intensity after NaCl treatment decreased as the NaCl concentration increased. For the saturated NaCl concentration (4.5 M), however, the observed photon intensity drastically increased, and the simultaneous destruction of cell membranes was observed. The intensity of biophoton emission from red beans showed characteristic change with salt concentrations. When the salt stress was applied to the red beans at an early growth stage, their root elongations were suppressed and photon intensity from the root decreased. This was not the case for the root at the late stage. This shows that biophoton intensity due to salt stress depends on not only NaCl concentration but also the growth stage of the plant. We may conclude that the extent of damage to roots by salt stress can be evaluated from biophoton response.
Differentiation of Au Islands on Ni Film by Friction Force Microscopy, Force Curve and New Force Modulation Method
Authors: Yamamoto Shin-ichi , Yamada Hirofumi , Matsushige Kazumi
Published: October 2002

The characterization of metallic electrodes in semiconducting devices with high spatial resolution has become increasingly important. In paticular, the evaluation of metal-metal interactions has been of vital importance in various technologies. Scanning force microscopy (SFM) enables us to observe surface topographies on a nanometer scale along with local mechanical properties such as friction force without any special surface treatment. It has been difficult to obtain high resolutions using conventional methods such as Auger electron spectroscopy, because of their beam size. In this study, we demonstrated the possibility of two dimensional metal mapping of mechanical properties by magnetic force controlled-atomic force microscopy (MFC-AFM), and a new force modulation method to determine the two metals. The Au–Ni system of metallic electrodes is one such example. Here, we also attempted to differentiate mapping of compositional inorganic materials such as Au islands, deposited on a flat Ni substrate. The Hertzian radius is 13.2 nm for Ni, and 23 nm for Au. We estimate the tip-sample deformation to be 2.9 nm for Au, and 0.97 nm for Ni, respectively.
Influence of Force Acting on Side Face of Carbon Nanotube in Atomic Force Microscopy
Authors: Seiji Akita Seiji Akita , Hidehiro Nishijima Hidehiro Nishijima , Takayoshi Kishida Takayoshi Kishida , Yoshikazu Nakayama Yoshikazu Nakayama
Published: October 2002

We have examined the nanomechanics of a carbon nanotube by a manipulation technique using a scanning electron microscope. Young's modulus of the nanotube, estimated from the buckling under force acting on the axial direction of the nanotube, agrees well with the value estimated from the bending under force acting on the side face. This indicates that the nanotube can be treated as an isotropic material in conventional mechanics. The adhesion force between the side face of the nanotube and a pit wall in a 4.7 GB digital versatile disk is estimated to be ∼10 nN using atomic force microscopy. This value is 160 times less than the value estimated using force curve measurement. This discrepancy is due to the finding that the value estimated from the force curve includes not only the adhesion but also the friction force.
Conductivity and Surface Potential Studies in Carbon Films by Conductive Scanning Probe Microscopy
Authors: Zhang Li , Sakai Tadashi , Sakuma Naoshi , Ono Tomio
Published: October 2002

Conductive scanning probe microscopy (SPM) was applied to field-emission carbon films. The microstructures, conductivity and surface potential properties of carbon films were investigated by conductive atomic force microscopy (AFM) and Kelvin probe force microscopy (KFM), as well as a combination of the two techniques. SPM was proven to be very effective for the study of materials with multiple phases and complex structures, and in clarifying the low-field-emission mechanism.
Surface Structure on Ar+-Ion Irradiated Graphite by Scanning Probe Microscopy
Authors: An Bai , Fukuyama Seiji , Yokogawa Kiyoshi , Yoshimura Masamichi
Published: October 2002

The surface structure of a highly oriented pyrolytic graphite
(HOPG), irradiated by Ar+ ions with an ion energy of
0.5–1.0 keV at doses below 5×1011 ions/cm2 during annealing, was characterized by scanning probe microscopy. The ion-induced hillocks
were observed by both scanning tunneling microscopy (STM) and atomic
force microscopy (AFM) after the ion irradiation, the heights of
which, measured by STM, were larger than that measured by AFM in the
tapping mode. The hillocks were recovered distinguishably by
annealing above 470 K. Almost 85% of the hillocks disappeared after
annealing at 1270 K and they disappeared completely after annealing
above 1770 K. The behavior of defects produced by ion-irradiation in
HOPG during annealing is discussed.
Scanning Tunneling Microscopy Observation of Epitaxial bcc-Fe(001) Surface
Authors: Subagyo Agus , Oka Hirofumi , Eilers Guido , Sueoka Kazuhisa , Mukasa Koichi
Published: October 2002

We report the first atomic-resolution scanning tunneling
microscopy (STM) image of epitaxial bcc-Fe(001) films grown on
MgO(001) substrates. A 50-Å-thick Fe film grown at a growth
temperature of 550 K formed square pyramidal islands with
atomically flat terraces. The terraces were found to range between
5 nm and 20 nm in width separated by monoatomic high steps. The
film exhibited a (1×1) unreconstructed structure at a film
thickness below 19 Å; however, a reconstructed surface was
found on thicker films. The atomic-resolution STM image and low energy electron diffraction (LEED)
observation indicated that the reconstructed structure is a
c(2×2) structure.
Formation of Through-Holes on Silicon Wafer by Optical Excitation Electropolishing Method
Authors: Satoh Akinobu
Published: October 2002

Through-holes were formed by selective partial electropolishing in a 2.5 wt% HF electrolytic solution, using an N-type, (100)-oriented Si wafer as an anode, and a Pt plate as a cathode. The obtained holes were square through-holes of 5–35 µm side length, with an aspect ratio of 109. It was possible to form such through-holes with a density of 3,500 holes/mm2in specified areas. It was also confirmed that the pit of the square-based inverted pyramid structure could form deep capillaries. This suggests the possibility of forming microstructures such as pillars and tubes.
Fabrication of Silicon-Based Filiform-Necked Nanometric Oscillators
Authors: Saya Daisuke , Fukushima Kimitake , Toshiyoshi Hiroshi , Fujita Hiroyuki , Hashiguchi Gen , Kawakatsu Hideki
Published: October 2002

For the purpose of improving the resolution of force and mass
detection of a noncontact-mode atomic force microscope (AFM), we are
developing a mechanical oscillator of nanometric size which consists
of a head mass supported by an elastic neck. A silicon-on-insulator
(SOI) wafer with the laminated structure top Si layer/buried
SiO2 layer/base Si is used in the fabrication of the nanometric
oscillators. By selective etching of Si and SiO2, nanometric
oscillators are successfully obtained. The top Si layer is etched to
form a tetrahedral Si dot, which is the mass of the oscillator, and
the buried SiO2 layer is etched to form the elastic neck
resting on the base Si. The size of the tetrahedral Si dot is
determined by the thickness of the top Si layer without depending on
the precision of the lithography technique. We found that the
cross-sectional shape of the SiO2 neck is a right-angled
triangle and that the neck is situated at the center of the
tetrahedral Si dot. According to calculations, the oscillators we
obtained have spring constants around 1 N/m and a resonance
frequency from 3 MHz to 300 MHz according to their dimensions.
Structures and Electrical Properties of Fullerene Thin Films on Si(111)-7×7 Surface Investigated by Noncontact Atomic Force Microscopy
Authors: Kei Kobayashi Kei Kobayashi , Hirofumi Yamada Hirofumi Yamada , Toshihisa Horiuchi Toshihisa Horiuchi , Kazumi Matsushige Kazumi Matsushige
Published: October 2002

We have studied the fullerene (C60) multilayer thin film deposited on the Si(111)-7×7 reconstructed surface by noncontact atomic force microscopy (NC-AFM) under an ultrahigh-vacuum (UHV) condition. The double domain structure on a terrace of the crystalline island was successfully imaged. We have also simultaneously measured the contact potential difference (CPD) by the Kelvin probe method. Small CPD variations, which are not due to coupling with the topographic image, were measured at a molecular scale.
Extension of Physical Limit of Conventional Metal-Oxide-Semiconductor Transistor by Double Barriers Formed at the Channel Edges
Authors: Matsuo Naoto , Yamauchi Junya , Kitagawa Yasunori , Hamada Hiroki , Miura Takashi , Miyoshi Tadaki
Published: October 2002

A method to extend the physical limit of the conventional (conv.) metal-oxide-semiconductor transistor (MOST) is presented. Suppression of the direct tunneling (DT) from the source to the drain using double barriers at the channel edges is discussed. The parameters of the operation characteristics for the quantum mechanical channel length are also discussed from the viewpoint of the barrier height of the dielectric films which are formed at both edges of the channel.
The Instability Mechanisms of Hydrogenated Amorphous Silicon Thin Film Transistors under AC Bias Stress
Authors: Huang Chun-Yao , Teng Teh-Hung , Tsai Jun-Wei , Cheng Huang-Chung
Published: October 2002

Hydrogenated amorphous silicon (a-Si:H) thin-film transistors
(TFTs) with silicon nitride (SiN
x
) gates have been stressed under
various AC biases to investigate the instability mechanisms. The
state creation is dominant at low stress voltage although the charge
trapping also occurs in SiN
x
gates, and such cases have also been
found under the DC bias stress. In addition, the degradations of
a-Si:H TFTs are found to be independent of the AC frequency for the
positive polarity but show frequency dependence for the negative
polarity due to the RC effect. Furthermore, the threshold voltage
shift is associated with the duty ratio due to the accumulation of
stress time. Finally, the degradation of the a-Si:H TFTs under
bipolar AC bias stress is also introduced. It is found that the
instability mechanisms of devices are composed of different charge
compensations in SiN
x
and redistributions of defect states in the
a-Si:H layer.
Control of Polycrystalline Silicon Structure by the Two-Step Deposition Method
Authors: Heya Akira , Izumi Akira , Masuda Atsushi , Matsumura Hideki
Published: October 2002

Polycrystalline silicon (poly-Si) films are obtained at temperatures below 400°C by the catalytic chemical vapor deposition (Cat-CVD), often called “hot-wire CVD” method, using two-step deposition (TSD). In TSD, the substrate temperature is changed during deposition from the initial step for a short time of 200 s to the second step of 820 s. A comparative study on the structural properties of Cat-CVD poly-Si films prepared by the TSD method and those of the films prepared by conventional method was carried out using Raman spectroscopy, atomic force microscopy, reflection high-energy electron diffraction and transmission electron microscopy observation. It is found that the surface morphology, grain structure and thickness of the amorphous Si incubation layer are all correlated, and the structures are changed by TSD method.
Dehydration after Plasma Oxidation of Porous Low-Dielectric-Constant Spin-on-Glass Films
Authors: Eiichi Kondoh Eiichi Kondoh , Tanemasa Asano Tanemasa Asano , Hiroki Arao Hiroki Arao , Akira Nakashima Akira Nakashima , Michio Komatsu Michio Komatsu
Published: October 2002

In this paper, the dehydration behavior of hydrogen-methyl-siloxane-based porous spin-on-glass (SOG) films after oxygen plasma exposure is reported. The resultant loss of hydrophobic groups from the plasma exposure makes the films hygroscopic and thus the film dielectric constant can significantly increase. We employed a simple method consisting of spin-on coating of hexadimethyldisilazane (HMDS) with successive hotplate baking so as to dehydrate the films and decrease the film dielectric constant.
Dielectric Confinement Effects on Nonlinear Optical Susceptibilities of Semiconductor-Dielectric Composites
Authors: Inoue Michiko
Published: October 2002

The dielectric confinement effect on the nonlinear optical properties of composite materials is studied using the effective medium approximation. It is shown that both off-resonance and resonance dielectric enhancement of nonlinear susceptibilities occur in semiconductor particles doped in linear dielectric materials. Resonance enhancement of third-order susceptibility is associated with excitations of the surface exciton polaritons of the electric multipole modes in the semiconductor particles. The resonance frequency shows a blue shift with the volume fraction of the semiconductor. The effect is numerically evaluated for direct band-gap semiconductors such as CuCl,CdS and GaAs nanocrystals doped in glass.
Improvement of Current Injection Uniformity and Device Resistance in Long-Wavelength Vertical-Cavity Surface-Emitting Laser Using a Tunnel Junction
Authors: Sekiguchi Shigeaki , Miyamoto Tomoyuki , Kimura Tadayoshi , Okazaki Gen , Koyama Fumio , Iga Kenichi
Published: October 2002

A uniform current injection is important in long-wavelength vertical-cavity surface-emitting lasers (VCSELs) for low-threshold, high-efficiency, and stable-mode operation. The utilization of a tunnel junction can solve these problems by employing an n-type highly conductive material for an anode. In this study, the electrical property of a long-wavelength VCSEL with a tunnel junction is analyzed using an equivalent circuit model. The optical absorption loss of a tunnel-junction-embedded VCSEL is also investigated. This results in the quantitative estimation of lasers with a tunnel junction in terms of device resistance, carrier distribution in the active region and optical absorption loss. The introduction of a tunnel junction may improve the output power, power-conversion efficiency, and mode stability of long-wavelength VCSELs.
Effects of Te Doping on Ordering and Antiphase Boundaries in GaInP
Authors: Choi Chel-Jong , Spirydon R. , Seong T.-Y. , Lee S. H. , Stringfellow G. B.
Published: October 2002

Transmission electron microscope (TEM) and transmission electron diffraction studies have been performed to investigate the effects of Te doping on ordering and antiphase boundaries (APBs) in organometallic vapour phase epitaxial Ga0.5In0.5P layers grown on (001) GaAs singular and vicinal substrates at 670°C. TEM results show that the behaviour of APBs for the singular samples differs from that of the vicinal samples. The density of APBs in the vicinal samples is increased by roughly a factor of 2, whilst that of the singular samples is slightly increased, as the Te concentration increases. APBs are inclined 10–57° from the (001) growth surface. As for the singular samples, the angle seems to remain virtually unchanged with increasing doping level. However, for the vicinal samples, the angle decreases significantly with increasing concentration. A simple model is presented to explain the dopant concentration dependence of the behaviour of APBs in the ordered GaInP.
Effect of Surface Oxidation on Raman Spectroscopy of β-FeSi2
Authors: Maeda Yoshihito , Miyake Kiyoshi
Published: October 2002

It was shown that imperfection (deficiency of iron atoms in the lattice) due to
surface oxidation undoubtedly introduces degradation of Raman spectra of
β-FeSi2. After removal of the oxidized layer by chemical etching, a clear
Raman spectrum could be obtained and the shift of the Ag-mode Raman line
around 250 cm-1 toward a higher frequency was observed. The surface sensitivity
of Raman scattering depending on the excitation wavelength is discussed.
Effect of Radio Frequency Power on the Properties of Hydrogenated Amorphous Carbon Films Grown by Radio Frequency Plasma-Enhanced Chemical Vapor Deposition
Authors: Krishna Kalaga Yasuhiko Hayashi , Tetsuo Soga Tetsuo Soga , Masayoshi Umeno Masayoshi Umeno , Takashi Jimbo Takashi Jimbo
Published: October 2002

We have studied the influence of radio frequency (RF) power on material properties of hydrogenated amorphous carbon (a-C:H) films prepared by RF plasma-enhanced chemical vapor deposition (CVD). The RF power has a significant impact on film properties such as electron spin resonance (ESR) spin density, the optical band gap, chemical bonding and photoluminescence (PL). Raman spectroscopy, infrared (IR) absorption and ESR measurements reveal that the residual defect density (ESR spin density) increases with increasing RF power due to the increase of sp
2 C–Hx components. We obtained an ESR spin density as small as 8 ×1016 spins/cm3 at a low RF power, which is comparable to that of high-quality amorphous silicon films. Plasma optical emission spectroscopy indicates that the intensity ratio (I
C–H/I
H) between hydrogen peaks (I
H) and hydrocarbon peaks (I
C–H) significantly decreases with increasing RF power. The optical band gap, obtained from UV-visible spectroscopy, varies from 3.0 to 1.9 eV with increasing RF power. The broad emission band centered around 2.4 eV was observed in the PL spectra of the samples deposited at lower RF powers. We found a 0.5–0.3 eV Stokes shift by comparing the PL emission and the absorption coefficient spectrum from the films deposited at ≤100 W RF powers, whereas, we failed to observe a clear Stokes shift from the films deposited at >100 W RF powers. A weak correlation between the PL peak and the optical band gap is demonstrated.
Film Bulk Acoustic Resonator Fabrication for Radio Frequency Filter Applications
Authors: Park Sang-Hyun , Seo Byeng-Chul , Park Hee-Dae , Yoon Giwan
Published: October 2002

In this paper, a two-step radio frequency (RF) sputtering deposition technique for
piezoelectric ZnO film formation and its successful application for film bulk acoustic
resonator (FBAR) devices are presented. Several critical parameters of the RF
sputtering process such as deposition pressure, RF power and O2 concentration
were studied to clarify their effects on the material characteristics of the ZnO films.
The ZnO films deposited by the proposed two-step deposition are shown to have the
growth characteristic of strongly preferred orientation toward the c-axis. The FBAR
devices with the ZnO films showed a large return loss of ∼50 dB at the center
frequency of 1.49 GHz. It was also found that the impedance matching of the FBAR
could be easily achieved simply by controlling the resonance area of the resonator.
Reaction at the Outermost Surface Selectively Induced by Metastable-Atom Beams
Authors: Yasufuku Hideyuki , Meguro Kazuyuki , Okudaira Koji K. , Ueno Nobuo , Harada Yoshiya
Published: October 2002

This paper reports the first spectroscopic observation of changes in surface electronic states that originate from a chemical reaction at the outermost surface which is selectively induced by the impact of slow metastable atoms. Using metastable-atom electron spectroscopy, structural changes of titanyl phthalocyanine (OTiPc) molecules as a result of the impact of slow He*(23S) were observed for an oriented OTiPc monolayer on a graphite substrate where the molecule is oriented flat with the oxygen atom protruding outside the surface. Unlike photons and electrons, metastable atoms do not penetrate into the bulk of solids. Therefore, they interact only with electrons distributed at the outermost surface of the film, and excite these electrons selectively. The observed spectral change in metastable-atom electron spectrum indicates that the surface reaction can be realized by the selective ionization of the outermost surface with the impact of slow metastable atoms.
Theoretical Study of Orientation Dependence of Piezoelectric Effects in Wurtzite Strained GaInN/GaN Heterostructures and Quantum Wells
Authors: Takeuchi Tetsuya , Amano Hiroshi , Akasaki Isamu
Published: October 2002

We calculated the crystal orientation dependence of piezoelectric fields in wurtzite
strained Ga0.9In0.1N/GaN heterostructures. The highest longitudinal piezoelectric field of 0.7 MV/cm can be generated in (0001)-oriented biaxial-strained Ga0.9In0.1N layer coherently
grown on GaN. On the contrary, no longitudinal piezoelectric field is induced in strained
layers grown along orientations at an off angle of 39° or 90° from (0001). The high
symmetry planes with these angles are, for instance, (1124) and (1012) for 39°, and (1120)
and (1010) for 90°. We also calculated the crystal
orientation dependence of the transition probability in a 3-nm
strained Ga0.9In0.1N/GaN quantum well, which indicated that
the transition probability with these non-(0001) orientations becomes
2.3 times larger than that with the (0001) orientation. We conclude
that high-performance strained nitride-based optical devices can be
obtained by control of the crystal orientation.
Influence of Sustaining Pulse-Width on Electro-Luminous Efficiency in AC Plasma Display Panels
Authors: Cho Tae-Seung , Ko Jae-Jun , Kim Dae-Il , Lee Chun-Woo , Cho Guangsup , Choi Eun-Ha
Published: October 2002

The influence of sustaining pulse-width on electro-luminous efficiency has been experimentally investigated for the surface discharge of AC plasma display panels. A square driving voltage pulse with a variable duty ratio and a fixed rise time of 300 ns has been used in this experiment. It is found that the firing voltage decreases as the sustaining pulse-width increases from 2 µs to 8 µs under a given driving frequency, and also decreases as the frequency increases from 10 kHz to 50 kHz. The memory coefficient is found to be significantly increased from 0.16 to 0.71, as the sustaining pulse-width increases from 3 µs to 4 µs, beyond which it maintains a nearly constant value of approximately 0.8 for the driving frequency range from 30 kHz to 50 kHz. The optimal sustaining pulse-width is shown to be in the range of 3 µs and 4 µs for driving frequencies of 30 kHz and 50 kHz, based on the observations of memory coefficient, wall charge, wall voltage and luminous efficiency.
Stable Microstructures on a GaAs(111)A Surface: the Smallest Unit for Epitaxial Growth
Authors: Akihito Taguchi Akihito Taguchi , Kenji Shiraishi Kenji Shiraishi , Tomonori Ito Tomonori Ito
Published: October 2002

We investigated the stability of various microstructures constructed by several Ga and As adatoms on a GaAs(111)A surface by using first-principles calculations.
We estimated the formation energies of the structures as a function of the chemical potential and found a very stable structure composed of one Ga adatom and three As adatoms.
Investigations of the elemental growth process imply that this structure is the smallest unit able to initiate epitaxial growth on the GaAs(111)A surface.
Based on the calculation results, we propose a growth mechanism for the (111)A surface, which is characterized by the formation of a stable structure and the subsequent coalescence of the structure.
This mechanism qualitatively explains the observed differences in the properties of the growth islands on (111)A and (001) surfaces.
Monte Carlo Simulation of ZnSe/GaAs Heterovalent Epitaxy
Authors: Kazuaki Sano Kazuaki Sano , Takashi Nakayama Takashi Nakayama
Published: October 2002

Heteroepitaxy of ZnSe on GaAs As-rich surface is investigated by conventional growth simulation based on the interatomic bonding energy. The model takes into account both the surface-atom dimerization and the electron transfer between surface dangling bonds, Ga-Se donor bonds and Zn-As acceptor bonds. It is shown that, due to the heterovalency between ZnSe and GaAs, antisites and vacant defect structures are produced at the interface and these defects are suppressed when Zn atoms are first supplied on the GaAs surface. These results are in good agreement with experimantal observations.
Fabrication and Characterization of Various Carbon-Clad Silicon Microtips with Ultra-Small Tip Radii
Authors: Tarntair Fu-Gow , Hong Wei-Kai , Ku Tzu-Kun , She Nan-Jie , Chen Chia-Fu , Cheng Huang-Chung
Published: October 2002

Various types of ultra sharp Si microtips and multitips with
carbon-clading films were fabricated by microwave plasma chemical
vapor deposition (MPCVD). The radii of these Si tips prepared by bias
assisted carburization (BAC) can be reduced below 300 Å under a
low deposition temperature (<550°C). Field emission
characterization was performed in a high vacuum environment. With an
applied anode voltage of 1100 V, emission currents of 169 µA,
198 µA, and 385 µA can be achieved from an array of
50×50 BAC-clad Si monotips, Si multitips via high bias, and Si
multitips via the Ar presputtering technique, respectively. Both the
auger electron spectroscopy (AES) and X-ray photo-electron
spectroscopy (XPS) studies of the C 1 s peak suggest that the
BAC-cladding is more likely to be a carbon-rich SiC layer or a SiC
layer mixed with a small amount of diamond nuclei. This BAC-carbon can
be used as an effective nucleation layer for further diamond
nuclei. Due to the low field emission, low temperature, and large area
growth capability, the sharp BAC-clad Si multitip field emitter arrays
are attractive for flat panel display applications.
X-Ray Photoelectron Spectroscopic Study on γ-Bismuth Molybdate Surfaces on Exposure to Propene and Oxygen
Authors: Ayame Akimi , Iwataya Masazumi , Uchida Kiyotaka , Igarashi Naoki , Miyamoto Masaaki
Published: October 2002

γ-Bismuth molybdate (γ-Bi2MoO6) surfaces
reduced by C3H6,
reoxidized by oxygen, on exposure to C3H6-jet and subsequently
O2-jet were time- or temperature-dependently measured by X-ray
photoelectron spectroscopy (XPS). The C3H6 molecule interacted
simultaneously with two different lattice oxide ions to result in
almost equivalent amounts of Mo5+ and Mo4+, but reduced species of bismuth were not found. The Mo5+ appeared likely to be formed by
oxygen abstraction from Bi3+–O-Mo6+ and the Mo4+
from those of O=Mo6+ along with the elimination
of two oxide ions bound on both sides of the [MoO2]2+ layer. A part of Mo5+ was reoxidized faster than Mo4+, below 373 K, while above 473 K Mo4+ was reoxidized preferentially. On exposure to
C3H6-jet and O2-jet under ultrahigh
vacuum (UHV), only Mo5+ was detected on the surface and the core
spectrum intensity of Mo5+ oscillated with respect to exposure
time. The oscillation phenomena were interpreted by the time lags
between the surface reduction rate with C3H6 and the diffusion rate of oxygen from the oxide bulk, and by the difference between the
surface reoxidation (oxygen incorporation) rate and the diffusion
rate of newly incorporated oxygen into the bulk anion vacancies. It
was also clarified that incorporation of oxygen occurred on the
lattice oxide ion vacancies bridging Bi and adjacent Mo atom.
A General Method of Characterizing Base Resistance of Bipolar Junction Transistors
Authors: Hong Gia M. , Gong Jeng , Lu Shin C.
Published: October 2002

In this work, bipolar junction transistors with two separate
base terminals and the dc method were used to determine the intrinsic
base resistance (R
int), the extrinsic base resistance
(R
ext), and the value of an effective resistance
(R
P) that is in parallel with R
int of such a
device. Transistors with different emitter widths (W
E)
while all other device parameters were kept constant are used. The
current of one of the base terminals was set to zero to trace the
internal base potential of the device. A device simulator was used to
analyze the detailed mechanism of the Kirk effect and the
current-crowding effect on base resistance. The results show that for
current short-width transistors under normal operating conditions the
base resistance is mostly influenced by the Kirk effect, not the
current-crowding effect.
Substrate-Structure Dependence of Ag Electromigration on Au-Precovered Si(111) Surfaces
Authors: Shi Fangxiao , Shiraki Ichiro , Nagao Tadaaki , Hasegawa Shuji
Published: October 2002

Electromigration of Ag on Au-precovered Si(111) surfaces was investigated by in-situ ultrahigh vacuum scanning electron microscopy and µ-probe reflection-high-energy electron diffraction (RHEED). Migration behaviors of a Ag-film patch strongly depended on Au coverage θAu and corresponding surface structures. When θAu<0.7 monolayer (ML), the patch expanded preferentially towards the cathode to attain a maximum area in which the sum of Ag and Au coverages were always about 1 ML irrespective of θAu, resulting in two-dimensional (2D) alloy phases (showing √3×√3 RHEED patterns) with different Au/Ag concentration ratios. The largest expansion of the patch area was achieved on a (5×2+α-√3×√3)-Au mixed phase structure (θAu∼0.7 ML). However, when θAu>0.7 ML, the patch expansion was greatly reduced. Especially on the β-√3×√3-Au surface (θAu∼1.0 ML), the patch showed no directional expansion towards the cathode. But Ag atoms were observed to migrate inside the patches on all substrates (including the β-√3×√3-Au surface) to form 3D islands near terrace edges.
Electron-Ion Coincidence Spectroscopy as a New Tool for Surface Analysis –an Application to the Ice Surface
Authors: Shin-ichiro Tanaka Shin-ichiro Tanaka , Kazuhiko Mase Kazuhiko Mase , Mitsuru Nagasono Mitsuru Nagasono , Shin-ichi Nagaoka Shin-ichi Nagaoka , Masao Kamada Masao Kamada , Eiji Ikenaga Eiji Ikenaga , Tetsuji Sekitani Tetsuji Sekitani , Ken-ichiro Tanaka Ken-ichiro Tanaka
Published: October 2002

Electron-ion coincidence (EICO) spectroscopy
[K. Mase, M. Nagasono, S. Tanaka, M. Kamada, T.Urisu and Y. Murata: Rev. Sci. Inst. 68 (1997) 1703]
has recently been developed to investigate the process of ion desorption induced by the core level
excitation. In the present study, we apply EICO spectroscopy
to determine the O1s level of condensed
H2O (ice) at 100 K. The kinetic energy of O1s photoelectrons
which gives the highest coincidence yield of H+ desorption
is shifted by about -0.7 eV compared to the O1s peak observed
in the conventional core-level photoelectron spectroscopy.
It is ascribed to a core-level shift
in the O1s level from which hydrogen ions desorb.
The results indicate the advantages and the possibilities
of the EICO spectroscopy for surface analysis.
Work Function of Scratched Silicon Surface during O2 and N2 Adsorption
Authors: Nakayama Keiji , Zhang Lulu
Published: October 2002

The Si(111)7×7 surface was scratched under an ultrahigh-vacuum (UHV) of 10-8 Pa. Oxygen and nitrogen gas molecules were then adsorbed on the scratched silicon surface at a gas pressure of 10-6 Pa for various exposure times. The distribution of the contact potential difference (CPD) on the scratched surface was measured using a scanning Kelvin probe force microscope (SKPM). When scratched under UHV, the work function of the Si surface increased. With oxygen exposure time, the work function of both the scratched and nonscratched Si surfaces first increased and then decreased after reaching a peak. The rate of work function increase of the scratched silicon surface in the initial period was lower than that of the nonscratched surface. Nitrogen exposure produces a negligible effect on the work function of both the scratched and nonscratched silicon surfaces.
Reduced Density of Missing-Dimer Vacancies on Tungsten-Contaminated Si(100)-(2×n) Surface by Hydrogen Termination
Authors: Shinobu Matsuura Shinobu Matsuura , Taro Hitosugi Taro Hitosugi , Seiji Heike Seiji Heike , Ayumu Kida Ayumu Kida , Yuji Suwa Yuji Suwa , Toshiyuki Onogi Toshiyuki Onogi , Satoshi Watanabe Satoshi Watanabe , Koichi Kitazawa Koichi Kitazawa , Tomihiro Hashizume Tomihiro Hashizume
Published: October 2002

A Si(100) surface with missing-dimer vacancies forming (2×n) phase was prepared by tungsten deposition and the morphological change was observed by scanning tunneling microscopy when the surface was terminated by hydrogen. The density of dimer vacancies was significantly reduced by the hydrogen termination, suggesting that the density of subsurface W atoms decreased. We discuss the mechanism of this morphological change based on the traditional theory of chemisorption-induced surface segregation and on the energetic instability of W atoms buried in the subsurface of the hydrogen-terminated Si surface.
I–V Characteristics of Schottky/Metal-Insulator-Semiconductor Diodes with Tunnel Thin Barriers
Authors: Sugimura Tomoyuki , Tsuzuku Tatsutoshi , Kasai Yuhki , Iiyama Kouichi , Takamiya Saburo
Published: October 2002

Current–voltage (I–V) characteristics and their temperature dependence, of Schottky and metal-insulator-semiconductor diodes with tunnel thin insulating layers, are theoretically and experimentally studied. The effective barrier height of a Schottky diode becomes low and strongly dependent upon the applied voltage, when the impurity density of the semiconductor increases such that the tunnel current dominates the total curent. The I–V curves and their temperature dependence, of the tunnel thin MIS diodes strongly reflect the characteristics of the Schottky diodes, although the insulating layers suppress the currents, depending upon their I-layers thickness.
Electrochemical Formation of Uniform and Straight Nano-Pore Arrays on (001) InP Surfaces and Their Photoluminescence Characterizations
Authors: Fujikura Hajime , Liu Aimin , Hamamatsu Akihito , Sato Taketomo , Hasegawa Hideki
Published: October 2002

Recently, <001>-oriented nanometer-sized pores (nano-pores) without side branches, unlike porous Si, have been realized by our group on (001) n-InP surfaces by means of electrochemical anodization in 1M HCl solution. However, they exhibit large structural nonuniformity including the presence of an irregular top layer, random pore positioning and wavy pore walls. In this study, attempts have been made to improve pore uniformity and to clarify their optical properties. Anodization in 1 M HCl+HNO3 solution realized highly uniform nano-pore arrays consisting of square-shaped straight pores defined by four crystalline (011) facets. This improvement is explained in terms of preferential etching along the vertical <001>-direction at the pore tip due to the slow etching rate along the lateral <011>-direction as well as the uniform supply of reactant species to pore tips realized by the removal of the irregular top layer during the anodization process. The nano-pore arrays show strong blue- and red-shifted photoluminescence emissions at high and low temperatures, respectively. These are assigned as emissions due to the transition between electron and hole quantum states inside the pore walls and that involving a broad surface state continuum at pore wall surfaces, respectively.
Selective Manipulation of Ag Nanoclusters on a Passivated Silicon Surface Using a Scanning Tunneling Microscope
Authors: Park Kang-Ho , Ha Jeong Sook , Yun Wan Soo , Ko Young-Jo
Published: October 2002

A precise nanofabrication method using a scanning tunneling
microscope (STM) tip as nanoscale tweezers was
devised. With the aid of surface passivation by Sb, we could form Ag
nanoclusters on a Si(100) surface. It was found that self-organized
Ag clusters can be selectively detached and manipulated at room
temperature by field application because of the weak bonding
strength between the clusters and an Sb-terminated Si surface.
Dielectric Cylinder Optical Amplifier
Authors: Yi Soung-soo
Published: October 2002

An optical amplifier is described using an active dielectric
cylinder. A theoretical investigation of plane-wave electromagnetic
scattering in active dielectric cylinder predicted the existence of
anomalously resonances occur at discrete plane-wave angles of
incidence. In this paper, the active cylinder is viewed as an optical
amplifier with finite incident and scattered fields. These resonances
may be understood from a “leaky wave” phase matching boundary
condition. Experiments using finite-diameter pump and probe laser
beams verified the existence of these resonances with amplifications
of the field intensities. Optical pumping of dye solution was used to
provide the gain. The threshold of the each resonant mode was found to
be a function of the radius of cylinders used.
Chemical and Electrochemical Nanofabrication Processes for Schottky In-Plane Gate GaAs Single and Coupled Quantum Wire Transistors
Authors: Iwaya Masanobu , Kasai Seiya , Okada Hiroshi , Nakamura Jin , Hasegawa Hideki
Published: October 2002

Chemical and electrochemical nanofabrication processes used for fabricating GaAs-based single and coupled quantum wire transistors (QWTrs) utilizing Schottky in-plane gate (IPG) structures are described. IPG and metal dot formation processes using a wet chemical etching and an in situ electrochemical process were optimized for a novel nanodevice fabrication. Fabricated single and coupled QWTrs showed conductance quantization and oscillation characteristics at low temperatures, demonstrating the tight gate control capability.
Analysis of Interface Microstructure Evolution in Separation by IMplanted OXygen (SIMOX) Wafers
Authors: Ishiyama Toshihiko , Omura Yasuhisa
Published: October 2002

We have examined the evolution of interface microstructures in Separation by IMplanted OXygen (SIMOX)
wafers during annealing, and have proposed a model that can reasonably explain the kinetics of interface
evolution. There are two dominant mechanisms in the evolution of a square microstructure: coalescence in
the early stage of annealing and diffusion after a sufficient period of annealing. The diffusion of oxygen
is the driving force in the evolution of interface flatness.
Comparison of Breakdown Behavior in Electron-Irradiated and Proton-Irradiated Silicon pn Junctions
Authors: Jo Jungyol , Park Jun , Shen Zhi Yuan , Lee Ho Sung , Lee Jun Ho , Nishihara Yoshiaki
Published: October 2002

We compared the turn-off transient characteristics of
electron-irradiated and proton-irradiated silicon pn
junctions. Three types of irradiations were carried out: by 270 keV
electrons, 2 MeV electrons, and 2 MeV protons. P-type silicon
irradiated with 2 MeV electrons shows very large current peaks
during turn-off. Proton-irradiated p-type silicon shows much weaker
current peaks, while n-type silicon does not show these peaks. It is
generally considered that a 270 keV electron energy is not strong
enough to introduce defects. However, our dc and transient data show
that a 270 keV electron can also introduce defects. Among the three
types of irradiations mentioned above, 270 keV electron irradiation
shows the lowest forward voltage drop and lowest turn-off charge.
Nitrogen Depth Profiling in Ultrathin Silicon Oxynitride Films with High-Resolution Rutherford Backscattering Spectroscopy
Authors: Kenji Kimura Kenji Kimura , Kaoru Nakajima Kaoru Nakajima , Yasutaka Okazaki Yasutaka Okazaki , Hajime Kobayashi Hajime Kobayashi , Shiro Miwa Shiro Miwa , Kotaro Satori Kotaro Satori
Published: October 2002

Nitrogen depth profiles in ultrathin silicon oxynitride films (2.5–8 nm) are measured by high-resolution Rutherford backscattering spectroscopy (HRBS). In order to reduce the large background due to the substrate silicon, HRBS spectra are measured under [111] channeling conditions. It is demonstrated that the HRBS/channeling technique provides the absolute concentration values and a depth resolution of sub-nm can be achieved. The nitrogen profiles are also measured by secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES). The AES result roughly agrees with the HRBS result, while the SIMS result underestimates the nitrogen concentration.
Influence of AlN Buffer on Phase Structure of GaN on GaAs (001) Grown by Radio-Frequency Molecular Beam Epitaxy
Authors: Li Zhiqiang , Chen Hong , Liu Hongfei , Yang Ning , Zhang Manhong , Wan Li , Huang Qi , Zhou Junming , Tao Kun
Published: October 2002

The influence of an AlN buffer layer on the phase structure of GaN is studied. Cubic GaN grown on a GaN buffer layer present on a GaAs (001) substrate, and secondary hexagonal GaN in the sample is grown according to GaN[0001]∥GaAs[111]B; when an AlN buffer layer is introduced, the single hexagonal GaN crystal is obtained with the growth direction of GaN[0001]∥GaAs[001]. X-ray diffraction and photoluminescence measurements are used to analyze the phase structure and orientation of the two epilayers. Atomic force microscopy is used to analyze the surface characteristics and it is revealed that the morphologies of the two samples differ. The results reveal different nucleation mechanisms of GaN on the GaN buffer layer and AlN buffer layer.
Magnetocaloric Effect of Super-paramagnetic Nanocomposite Composed of Iron-Oxide and Silver
Authors: Yamamoto Takao A. , Tanaka Masato , Nakayama Tadachika , Nishimaki Katsuhiro , Nakagawa Takashi , Katsura Masahiro , Niihara Koichi
Published: October 2002

The magnetocaloric effect of super-paramagnetic nanocomposites composed of iron-oxide nanograins dispersed in a silver matrix was studied by evaluating the magnetic entropy change ΔS induced by demagnetization. The nanocomposites were synthesized by inert gas condensation techniques, and their grain sizes are 10–35 nm. The values of ΔS obtained by calculation from magnetization data sets and from a theoretical formula based on the Langevin super-paramagnetism model were compared. The behavior of ΔS agrees fairly well with that predicted by the Langevin model at relatively higher temperatures T and lower magnetic fields H. At lower T or higher H, ΔS deviated from the model. The deviation was examined and ascribed to exchange coupling and crystalline anisotropy, which hinder the fully random spin orientation state at zero field. The evaluated ΔS values of the nanocomposites were larger than those of the paramagnet containing Fe3+ by about two orders of magnitude, indicating a clear enhancement of the magnetocaloric effect due to the nanostructure.
Effects of Substrate Surface Topology on NiFe/Cu/Co Spin Valve Characteristics
Authors: Kim Hyeong-Jun , Jeong Won-Cheol , Cho Kwon-Ku , Kim Young-Keun , Joo Seung-Ki
Published: October 2002

In order to control the crystallinity of sputter-deposited NiFe/Cu/Co spin valve thin films, surface topology of 4°tilt-cut Si(111) substrates was modified in various ways prior to formation of the spin valves. In case of the mirror polished substrate, NiFe and Co showed fcc (110) preferred orientation with in-plane uniaxial magnetic anisotropy. The easy axes of these magnetic layers were aligned in 90° to each other and giant magnetoresistance (GMR) was measured to be 4.5% at room temperature. The spin valves formed on the amorphized substrate by Ar ion mass doping, however, did not show magnetic anisotropy due to the loss of crystallinity and no appreciable GMR could be observed. The spin valves deposited on the unpolished substrate, of which the average surface roughness was measured to be a few microns, turned out to show a sound multilayeredness as well as crystallinity, but GMR was reduced to 3.5%. Tailing in the magnetoresistance (R–H) curve occurred in the spin valves formed on the unpolished substrate, and it was thought to be attributed to the shape anisotropy related to the interface roughness of the films. Detailed discussion on the relationship between GMR and crystallinity of the magnetic layers has been made with the results of simple simulation.
Development of High-Performance Solenoid-Type RF Chip Inductors Utilizing Low-Loss Al2O3Core Materials
Authors: Jung Myung-Hee , Kim Jae-Wook , Yun Eui-Jung
Published: October 2002

In this study, small size, high-performance, solenoid-type RF chip inductors utilizing low-loss Al2O3core materials were investigated. Copper coils with a diameter of 40 µm were used and the dimensions of the RF chip inductors fabricated were 2.1×1.5×1.0 mm3. The high-frequency characteristics of the inductance, quality factor, and impedance of the developed inductors were measured using a RF impedance/material analyzer (HP4291B with a HP16193A test fixture). The developed inductors have a self-resonant frequency of 1 to 3.5 GHz and exhibit an inductance of 22 to 150 nH. The inductors have a quality factor of 60 to 90 over the frequency ranges of 500 MHz to 1.5 GHz. The capacitance–frequency data is well described in the experimental data. It was suggested that reducing the number of turns of the coil and increasing the space between the coils are important measures for improving the high-frequency limit of the RF chip inductors.