bluuebunny/crossref_metadata_2025 huggingface dataset:
Azathioprine and UVA Light Generate Mutagenic Oxidative DNA Damage
Authors: O'Donovan Peter , Perrett Conal M. , Zhang Xiaohong , Montaner Beatriz , Xu Yao-Zhong , Harwood Catherine A. , McGregor Jane M. , Walker Susan L. , Hanaoka Fumio , Karran Peter
Published: September 2005

Oxidative stress and mutagenic DNA lesions formed by reactive oxygen species (ROS) are linked to human malignancy. Clinical treatments inducing chronic oxidative stress may therefore carry a risk of therapy-related cancer. We suggest that immunosuppression by azathioprine (Aza) may be one such treatment. Aza causes the accumulation of 6-thioguanine (6-TG) in patients' DNA. Here we demonstrate that biologically relevant doses of ultraviolet A (UVA) generate ROS in cultured cells with 6-TG–substituted DNA and that 6-TG and UVA are synergistically mutagenic. A replication-blocking DNA 6-TG photoproduct, guanine sulfonate, was bypassed by error-prone, Y-family DNA polymerases in vitro. A preliminary analysis revealed that in five of five cases, Aza treatment was associated with a selective UVA photosensitivity. These findings may partly explain the prevalence of skin cancer in long-term survivors of organ transplantation.
People, Stars, and Scopes
Authors: Rubin Vera
Published: September 2005

Miss Leavitt's Stars
. The Untold Story of the Woman Who Discovered How to Measure the Universe.
By George Johnson
. Norton, New York, 2005. 176 pp. $22.95, C$34. ISBN 0-393-05128-5. Weidenfeld and Nicolson, London. £14.99. ISBN 0-297-84647-7. Great Discoveries.

Stargazer
. The Life and Times of the Telescope.
By Fred Watson
. Da Capo, Cambridge, MA, 2005. 352 pp. $24.95, C$32.95. ISBN 0-306-81432-3. Allen and Unwin, St. Leonards, New South Wales, Australia, 2004. A$35. ISBN 1-865-08658-4.

Writing for a popular audience, the authors take a human-interest approach to the history of astronomy. Johnson focuses on the woman whose computations led to the use of Cepheid variable stars as a cos-mic yardstick. Watson highlights people who made important contributions to the development of optical telescopes over the past four centuries.
FbpA-Dependent Biosynthesis of Trehalose Dimycolate Is Required for the Intrinsic Multidrug Resistance, Cell Wall Structure, and Colonial Morphology of
Mycobacterium smegmatis
Authors: Nguyen Liem , Chinnapapagari Satheesh , Thompson Charles J.
Published: September 2005

Ligation of mycolic acids to structural components of the mycobacterial cell wall generates a hydrophobic, impermeable barrier that provides resistance to toxic compounds such as antibiotics. Secreted proteins FbpA, FbpB, and FbpC attach mycolic acids to arabinogalactan, generating mycolic acid methyl esters (MAME) or trehalose, generating α,α′-trehalose dimycolate (TDM; also called cord factor). Our studies of
Mycobacterium smegmatis
showed that disruption of
fbpA
did not affect MAME levels but resulted in a 45% reduction of TDM. The
fbpA
mutant displayed increased sensitivity to both front-line tuberculosis-targeted drugs as well as other broad-spectrum antibiotics widely used for antibacterial chemotherapy. The irregular, hydrophobic surface of wild-type
M. smegmatis
colonies became hydrophilic and smooth in the mutant. While expression of
M. smegmatis fbpA
restored defects of the mutant, heterologous expression of the
Mycobacterium tuberculosis fbpA
gene was less effective. A single mutation in the
M. smegmatis
FbpA esterase domain inactivated its ability to provide antibiotic resistance. These data show that production of TDM by FbpA is essential for the intrinsic antibiotic resistance and normal colonial morphology of some mycobacteria and support the concept that FbpA-specific inhibitors, alone or in combination with other antibiotics, could provide an effective treatment to tuberculosis and other mycobacterial diseases.
DOS
Ec
, a Heme-Regulated Phosphodiesterase, Plays an Important Role in the Regulation of the Cyclic AMP Level in
Escherichia coli
Authors: Yoshimura-Suzuki Tokiko , Sagami Ikuko , Yokota Nao , Kurokawa Hirofumi , Shimizu Toru
Published: September 2005

Heme-regulated phosphodiesterase from
Escherichia coli
(DOS
Ec
) catalyzes the hydrolysis of cyclic AMP (cAMP) in vitro and is regulated by the redox state of the bound heme. Changes in the redox state result in alterations in the three-dimensional structure of the enzyme, which is then transmitted to the functional domain to switch catalysis on or off. Because DOS
Ec
was originally cloned from
E. coli
genomic DNA, it has not been known whether it is actually expressed in wild-type
E. coli
. In addition, the turnover number of DOS
Ec
using cAMP as a substrate is only 0.15 min
−1
, which is relatively low for a physiologically relevant enzyme. In the present study, we demonstrated for the first time that the DOS
Ec
gene and protein are expressed in wild-type
E. coli
, especially under aerobic conditions. We also developed a DOS
Ec
gene knockout strain (Δ
dos
). Interestingly, the knockout of
dos
caused excess accumulation of intracellular cAMP (26-fold higher than in the wild-type strain) under aerobic conditions, whereas accumulation of cAMP was not observed under anaerobic conditions. We also found differences in cell morphology and growth rate between the mutant cells and the wild-type strain. The changes in the knockout strain were partially complemented by introducing an expression plasmid for
dos
. Thus, the present study revealed that expression of DOS
Ec
is regulated according to environmental O
2
availability at the transcriptional level and that the concentration of cAMP in cells is regulated by DOS
Ec
expression.
Phenotypic Convergence Mediated by GGDEF-Domain-Containing Proteins
Authors: Simm Roger , Fetherston Jacqueline D. , Kader Abdul , Römling Ute , Perry Robert D.
Published: September 2005

GGDEF domain-containing proteins have been implicated in bacterial signal transduction and synthesis of the second messenger molecule cyclic-di-GMP. A number of GGDEF proteins are involved in controlling the formation of extracellular matrices. AdrA (
Salmonella enterica
serovar Typhimurium) and HmsT (
Yersinia pestis
) contain GGDEF domains and are required for extracellular cellulose production and biofilm formation, respectively. Here we show that
hmsT
is able to restore cellulose synthesis to a
Salmonella
serovar Typhimurium
adrA
mutant and that
adrA
can replace
hmsT
in
Y. pestis
Hms-dependent biofilm formation. Like
Y. pestis
HmsT overproducers,
Y. pestis
cells carrying
adrA
under the control of an arabinose-inducible promoter produced substantial biofilms in the presence of arabinose. Finally, we demonstrate that HmsT is involved in the synthesis of cyclic di-GMP.
Changes in the circumstances of young mothers in Britain: 1990 to 2000
Authors: Nanchahal Kiran , Wellings Kaye , Barrett Geraldine , Copas Andrew J , Mercer Catherine H , Macmanus Sally , Macdowall Wendy , Fenton Kevin A , Erens Bob , Johnson Anne M
Published: September 2005

Objectives:To assess changes between 1990 and 2000 in the circumstances of women who became mothers before the age of 18.

Design:Two cross sectional probability sample surveys of the general population carried out in 1989–1991 (Natsal 1990) and 1999–2001 (Natsal 2000).

Setting:British households.

Participants:Women aged 18 to 27 years at time of survey (Natsal 1990: 2575, Natsal 2000: 1757).

Main outcome measures:Educational attainment, participation in education/work or training, living in social housing, social class, living as lone adult, parity, ill health, and health related behaviours at the time of the interview.

Results:The proportion of women who were sexually active before 18 increased between 1990 and 2000 from 58.9% to 71.3% (p<0.0001). There was no significant change in the proportion who had a child before the age of 18 (4.7% in 1990, 5.3% in 2000, p = 0.390). The proportion who had attained no educational qualifications and were not participating in education/work or training was significantly lower in 2000 than in 1990 for all women aged 18–27, but higher among those who were mothers before age 18, although the relative difference was not statistically significant. The proportion living in social housing or reporting a recent long term illness at time of interview was higher and this trend was more pronounced among women who did not experience motherhood before 18 than those who did, but the differences between these groups of women were not statistically significant.

Conclusion:Motherhood before the age of 18 continues to be related to a variety of adverse circumstances in adult life, including lack of educational attainment, not being in education/work or training, lone parenthood, and a reduced likelihood of home ownership. There is little evidence of improvement in the circumstances of young mothers between 1990 and 2000 despite improvements in life chances among young women in general.
Circular Polarization Control in Silicon-Based All-Optical Switch
Authors: Yamamoto Naokatsu , Matsuno Toshiaki , Takai Hiroshi , Ohtani Naoki
Published: September 2005

We present all-optical control of the circular polarization of reflected light on photochemically etched silicon (PCE Si). The polarization properties of photoluminescence (PL) from the PCE Si were observed under circularly polarized laser excitation. As a result, we found that the polarization information from the excitation laser is preserved in the polarization of PL observed in the PCE Si. We found that the preservation effect of circular polarization is useful for realizing a silicon all-optical switch (Si-AOS). In addition, we discuss the switching mechanism of a Si-AOS in terms of the interaction between the spin state of carriers and circularly polarized photons.
Dependence of pH, Molecular Weight, and Concentration of Surfactant in Ceria Slurry on Saturated Nitride Removal Rate in Shallow Trench Isolation Chemical Mechanical Polishing
Authors: Kang Hyun-Goo , Lee Myung-Yoon , Park Hyung-Soon , Paik Ungyu , Park Jea-Gun
Published: September 2005

We have investigated how controlling the pH, molecular weight, and concentration of the surfactant in ceria slurry affects the nitride film loss and oxide-to-nitride selectivity in the shallow trench isolation (STI) chemical mechanical polishing (CMP) process. We found that for a surfactant with a higher molecular weight, the oxide removal rate markedly decreased as the surfactant concentration increased, but in the case of a lower molecular weight, the removal rate only slightly decreased. In addition, with increasing surfactant concentration and addition of surfactant with the same molecular weight, the nitride removal rates for all slurries markedly decreased and very quickly saturated at a lower surfactant pH. Moreover, with an increase in the surfactant concentration from 0.1 to 0.3 wt %, the slurries whose surfactants had a medium or the lowest molecular weight maintained higher nitride removal rates than did the slurry whose surfactant had the highest molecular weight.
Hopping Transport of Electrons and Holes at Localized Band Tail States in Amorphous Hydrogenated Silicon and Amorphous Heavy-Hydrogenated Silicon
Authors: Ohno Kazuhiro , Murayama Kazuro , Matsuda Akihisa
Published: September 2005

The electric field dependence of the transit time in a time-of-flight experiment on amorphous hydrogenated silicon (a-Si:H) and amorphous heavy-hydrogenated silicon (a-Si:D) samples with device quality, prepared under different conditions, has been measured at different temperatures. It has been shown that the dependences can be explained by hopping at localized band tail states rather than multiple trapping. The hopping distance is in the range of 15 to 26 Å for both electrons and holes. The thermal activation energy for hopping is in the range of 0.10 to 0.24 eV for electrons and in the range of 0.32 to 0.38 eV for holes. The attempt-to-escape frequency obtained is larger than the phonon frequency, which has been explained by the Eyring theory. The electron mobility in a-Si:H and a-Si:D is in the range of 10-1 to 10 cm2/(V s), while the hole mobility is in the range of 10-3 to 10-2 cm2/(V s). The difference in the mobility between electrons and holes has been explained from the difference in thermal activation energy between the two types of carrier.
Low-Temperature Fabrication of Polycrystalline Si Thin Film Using Al-Induced Crystallization without Native Al Oxide at Amorphous Si/Al Interface
Authors: Sugimoto Youhei , Takata Naoki , Hirota Takeshi , Ikeda Ken-ichi , Yoshida Fuyuki , Nakashima Hideharu , Nakashima Hiroshi
Published: September 2005

Low-temperature fabrication of polycrystalline silicon (poly-Si) thin film has been performed by Al-induced crystallization (AIC), and the structural properties have been investigated. In our experiments, to prevent native oxidation of Al film, an amorphous silicon (a-Si)/Al bilayer was formed on the SiO2/Si substrate by electron beam evaporation without breaking the vacuum. The a-Si/Al/SiO2/Si structure was then heated at a low temperature of 400°C to induce AIC. It was confirmed that layer exchange of the a-Si/Al bilayer is induced even though there is no native oxidation of Al film, which was demonstrated by scanning transmission electron microscopy and energy dispersive X-ray analysis. The mechanism for layer exchange of the a-Si/Al bilayer has been discussed. Furthermore, it was verified by scanning electron microscopy and spectroscopic ellipsometry that the a-Si/Al thickness ratio of roughly 1:1 is suitable to achieve a flat surface morphology of poly-Si. In addition, it was found, by X-ray diffraction and orientation imaging microscopy, that the Si(111)-oriented grain becomes dominant with decreasing thickness of the a-Si/Al bilayer.
Growth, Optical and Structural Characterization of Layered GaS Films Prepared by Reactive RF Sputtering Method
Authors: Ohyama Masanori , Ito Hiroshi , Takeuchi Manabu
Published: September 2005

Good-crystallinity gallium sulfide (GaS) films were prepared on silica glass substrates by RF reactive magnetron sputtering with an Ar and H2 gas mixture with various hydrogen fractions (H
mf=0.1–0.4). The structure and optical properties of the sputtered GaS films were studied. The X-ray diffraction measurements showed that GaS films deposited at 500°C using Ar as the sputtering gas (H
mf=0) had amorphous structures, while those using H
mf=0.4 had polycrystalline structures with the c-axis perpendicular to the substrate plane. The absorption edges of the polycrystalline GaS films showed a direct allowed transition with an optical gap of E
og=3.0 eV, which was in good agreement with those measured in single-crystal GaS by previous researchers.
Sol–Gel-Derived Zn(1-x)MgxO Thin Films Used as Active Channel Layer of Thin-Film Transistors
Authors: Lee Jen Hao , Lin Pang , Lee Cheng Chung , Ho Jia Chong , Wang Yu Wu
Published: September 2005

Sol–gel derived n-type Zn(1-x)MgxO (x=0–0.45) thin films and thin-film transistors (TFTs) with active channel layers made of the films were investigated. The films were prepared at 500°C. The effects of Mg doping on the crystallinity, optical transparency, grain size, and charge-carrier concentration (n) of the films were examined. The Fermi level of the films, as derived from the temperature dependence ofn, was ∼0.12 eV below the conduction band. The donor concentration and donor level (Ed) were derived by a curve fitting method based on the electrical neutrality condition.Edwas found to be ∼0.3 eV below the conduction band. The composition dependence of the TFT output characteristics was interpreted and correlated to the width of the depletion region adjacent to the grain boundaries. When the grains were almost depleted atx=0.2, the TFT showed an enhancement mode and an on/off ratio of 106.
Formation of Nickel Silicide Layer on Strained-Si0.83Ge0.17/Si(001) using a Sacrificial Si Layer and its Morphological Instability
Authors: Jang Chi Hwan , Shin Dong Ok , Baik Sung Il , Kim Young-Woon , Song Young-Joo , Shim Kyu-Hwan , Lee Nae-Eung
Published: September 2005

Nickel silicide was formed on strained-Si0.83Ge0.17/Si(001) using a sacrificial Si capping (cap-Si) layer and its morphological characteristics were investigated. Nickel silicide layers were grown by rapid thermal annealing of the samples with the structure of Ni (\cong14 nm)/cap-Si (\cong26 nm)/Si0.83Ge0.17/Si(001) at the annealing temperature (T
A) range of 400–800°C. The phase formation, surface and interfacial morphologies, and electrical properties of the resulting samples were characterized by various measurement techniques, including X-ray diffraction, atomic force microscopy, scanning electron microscopy, Auger electron spectroscopy, cross-sectional transmission electron microscopy, and the four-point probe method. The results showed the formation of a uniform layer nickel monosilicide (NiSi) with a thickness of \cong30 nm at 400–550°C and sheet resistance values of 6.5–7.9 Ω/□. The sheet resistance values of the samples annealed at T
A≥600°C were found to be increased, however, and this is attributed to the agglomeration of nickel monosilicide leading to discrete large-size NiSi grains. Microstructural and chemical analyses of the samples annealed at elevated temperature, T
A≥750°C, indicated the formation of large agglomerated NiSi grains penetrating into the Si0.83Ge0.17/Si(001) structure and the conversion of the cap-Si layer situated in between the nickel silicide grains into an Sil-u
Ge
u
layer (u \cong0.01–0.03), due to the out-diffusion of Ge from the SiGe layer during agglomeration. However, no NiSi2 phase was observed at these elevated annealing temperatures.
Formation of Novel Silicon Nitride with Face-Centered Cubic Crystal Structure in a TaN/Ta/Si(100) Thin Film System
Authors: Cheng Wei-Chun , Jou Shyan-Kay , Chiu Chuei-Fu
Published: September 2005

We discovered a new silicon nitride with cubic symmetry formed in the silicon at the Ta/Si interface of the TaN/Ta/Si(100) thin film system when the silicon wafer was annealed at 500 or 600°C. The cubic silicon nitride grew into the silicon crystal in the shape of an inverse pyramid after the annealing process. The boundary planes of the inverse pyramid were the {111} planes of the silicon crystal. The orientation relationship between the silicon nitride and silicon crystal is cubic to cubic. The lattice constant of the new silicon nitride is a=0.5548 nm and is about 2.2% larger than that of the silicon crystal.
Fabrication of Spherical Silicon Solar Cells with Semi-Light-Concentration System
Authors: Minemoto Takashi , Okamoto Chikao , Omae Satoshi , Murozono Mikio , Takakura Hideyuki , Hamakawa Yoshihiro
Published: September 2005

A spherical Si solar cell with a semi-light-concentration system was successfully fabricated using a spherical Si crystal produced by a dropping method. The dropping method has great potential for low-waste and low-cost fabrication because the Si spheres can be made directly from dropping melted Si without the cutting and polishing processes of Si ingots. The fabricated Si spheres were generally multicrystalline due to the crystal growth through homogeneous crystal nucleation in containerless states. Spherical Si solar cells were fabricated using a Si sphere with a diameter of 1 mm as a solar cell substrate and then mounted on a reflector cup with a hexagonal aperture to complete the semi-light-concentration system. The current–voltage (J–V) measurement of the cell demonstrated an energy conversion efficiency of 10.4%. The key parameters for achieving higher efficiency are discussed with J–V data analysis, and quantum efficiency and laser-beam-induced current measurements.
Novel 2-Bit/Cell Metal–Oxide–Nitride–Oxide–Semiconductor Memory Device with Wrapped-Control-Gate Structure That Achieves Source-Side Hot-Electron Injection
Authors: Tomiye Hideto , Terano Toshio , Nomoto Kazumasa , Kobayashi Toshio
Published: September 2005

We have proposed a novel 2-bit/cell metal–oxide–nitride–oxide–semiconductor memory device with a wrapped gate. Programming and erasing operations are performed by source-side hot-electron injection and hot-hole injection, respectively. Programming speeds of less than 1 µs, programming currents of less than 0.2 µA/µm, and erasing speeds of 10 µs were achieved. In this paper, we describe the abilities of this device and the mechanism of the operation by using a device simulator.
Impact of Aggressively Shallow Source/Drain Extensions on Device Performance
Authors: Kimoto Kenji , Tada Tetsuya , Kanayama Toshihiko
Published: September 2005

We investigated by numerical simulations the effect of aggressive reduction of the source/drain extension (SDE) depth X

j
on the performance of a metal–oxide–semiconductor field-effect transistor (MOSFET) of the 45-nm technology node. As an extreme case, the charge-transfer-doped SDE MOSFET (CTE-MOS), which has inversion-layer SDEs induced by surface charges, was considered. Assuming that the gate length L
g fluctuation was ±20%, the substrate doping was set so that the off-state current was a specified value at L
g=-20%, and the resulting drive current I
on at L
g=+20% was evaluated. When X

j
was reduced from 9.5 to 2.0 nm under a fixed impurity density of 2×1020 cm-3, I
on increased by ∼27% because the SDE resistance increase was compensated for by the reduction of the short-channel effects. CTE-MOS exhibited a still better performance: 1–1.3 times I
on and 1.1–1.4 times the reciprocal intrinsic delay at L
g=+20% with 1.5–2.5 times the gate oxide thickness compared with the conventional MOSFETs with X

j
=9.5 nm. The feasibility of the CTE was experimentally demonstrated by the formation of electron inversion layers induced with Cs ions implanted into thermal oxide.
Dependence of Time-Dependent Dielectric Breakdown Lifetime on NH3-Plasma Treatment in Cu Interconnects
Authors: Noguchi Junji , Ohashi Naofumi , Yamaguchi Hizuru , Takeda Ken-ichi
Published: September 2005

The time-dependent dielectric breakdown (TDDB) between adjacent Cu wires was investigated. TDDB lifetime strongly depends on the conditions of the chemical mechanical polishing (CMP) surface and of NH3-plasma treatment prior to cap nitride deposition. The condition of NH3-plasma treatment was evaluated in detail. The TDDB lifetime is strongly dependent on the substrate temperature and the duration of NH3-plasma treatment but is independent of the pressure and power. Excessive NH3-plasma treatment degrades the TDDB lifetime. Hillocks on the Cu surface appear abruptly as the substrate temperature rises. The optimum treatment conditions are 10–30 s for a substrate temperature of 360°C, and 10 s for a substrate temperature of 400°C.
Preliminary Study of Polymer Removal in 0.25, 0.3, and 0.5 µm Ruthenium Storage Nodes and 0.11 µm, 10.9:1 High-Aspect-Ratio Trenches by Laser-Induced Etching
Authors: Kim Yong-Gi , Cha Byung Heon
Published: September 2005

The demands for new etching technology are increasing because of new materials, such as, ruthenium (Ru), platinum (Pt), and iridium (Ir), that are now being used, and the strict critical dimension (C/D) controls required in today's ultra large scale integrated (ULSI) circuit technology and dynamic random-access memory (DRAM) fabrication lines. Laser etching technology successfully etched organometallic polymers generated after reactive ion etching and ash processing in 0.25, 0.3, and 0.5 µm Ru storage nodes. In this study, the effects of the incident beam profile on the laser-induced etching of the polymers are investigated. Unevenness of the peak energy in the Gaussian beam profile creates unequal etching and heating effects on the polymer removal depending on the irradiating position of the line beam profile on the sample surface. This article discusses for the first time the preliminary results of laser-induced etching with a KrF laser to remove photoresist (PR) and polymer in 0.11 µm deep contact holes with a high-aspect-ratio 10.9:1 trench hole. How deep can the laser etching technology penetrate and strip the PR at a high aspect ratio (A/R) of 10.9:1 and a 0.11 µm hole size? The penetration depth for the PR removal was approximately 1 µm, which is about a 9.1:1 A/R in a 0.11 µm hole with a 1.2-µm-deep trench. Several promising points are discussed on the basis of laser etching in such a high A/R and small 0.11 µm contact hole. Laser-induced etching technology enabled a very uniform penetration depth without any fluctuations, and it also did not show any attack on the edge of the barrier material TiN.
Observation of Heat-Induced Particle Resuspension and Transport in a Plasma Chemical Vapor Deposition Chamber
Authors: Moriya Tsuyoshi , Shimada Manabu , Okuyama Kikuo , Setyawan Heru
Published: September 2005

The influences of gas viscous force, thermal stress, and plasma electrostatic force on heat-induced particle resuspension and transport in a plasma chemical vapor deposition (CVD) chamber were studied experimentally. Using an in situ particle measurement system in a plasma CVD chamber based on a laser light scattering method, it was observed that silica particles with a diameter of 600 nm dispersed on a wafer were resuspended when the wafer was heated. At a wafer temperature of 573 K, when the pressure in the chamber was being changed, the removal ratio of particles from the wafer exhibited a weak dependence on pressure in the range from 13.3 Pa (0.1 Torr) to 1.33 kPa (10 Torr). A theoretical calculation based on thermophoresis that considers a temperature jump could explain the trend of the experimental results. Since the removal ratio of particles from the wafer is greater with larger difference in the linear coefficients of thermal expansion between the wafer and the particles, it is considered that the particles are separated from the wafer due to thermal stress and are scattered towards the upper electrode by the force of thermophoresis. It has also been revealed that, when plasma discharge is applied, the removal ratio of particles is reduced due to the electrostatic force of charged particles.
X-ray Shielding of an Ionizer using Low-Energy X-rays below 9.5 keV for Ultra-Clean Assembly Line of Electronic Devices
Authors: Suzuki Masanori , Sato Tomokatsu , Matsuhashi Hideaki , Mizuno Akira
Published: September 2005

An ionizer has been developed using a low-energy X-ray for producing ion pairs that are transported by clean air through a shielding plate to objects to be discharged. The shielding plate should shield the X-ray of below 9.5 keV, while it should pass sufficient amount of the ion pairs. In this study, characteristics of the structural condition of the shielding plate has been investigated, on both the shielding effect and the ability to pass the ion pairs. We confirmed the structural condition that the leakage dose rate of the low-energy X-rays could be decreased to less than 1 µSv/h while allowing the passage of enough ion pairs to eliminate the static electricity.
Plasma-Enhanced Chemical Vapor Deposition Growth of Fluorinated Amorphous Carbon Thin Films Using C4F8 and Si2H6/He for Low-Dielectric-Constant Intermetallic-Layer Dielectrics
Authors: Kim Howoon , Shin Jang-Kyoo , Kwon Dae-Hyuk , Seo Hwa-Il , Lee Gil S.
Published: September 2005

The Si2H6/He gas mixture was used for growing fluorinated amorphous carbon thin films (a-C:F) for low-dielectric-constant intermetallic-layer dielectrics by plasma-enhanced chemical vapor deposition (PECVD) with C4F8, which has a lower fluorine/carbon ratio than CF4. Si2H6 captures excessive fluorine ions and carries C4F8 to the substrate. It is also much safer than other carrier gases such as H2 or CH4. To characterize and improve film properties, we changed conditions such as deposition temperature and ambient pressure, and we measured the growth rate, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and C–V characteristics. At a low temperature, the film properties were very poor, although the growth rate was very high. On the other hand, the growth rate was low at a high temperature. The growth rate increased with deposition pressure. The XPS result showed that the carbon peaks shifted to a higher energy level due to a carbon-fluorine combination, and the FT-IR results showed a bonding between C–F and C–F2. The dielectric constants of the samples were in the range of 1.5–5 and the sample with a constant of 2.18 showed relatively good thermal characteristics.
Spectroscopy of a Bulk GaN Microcavity Grown on Si(111)
Authors: Ollier Nadège , Natali Franck , Byrne Declan , Disseix Pierre , Mihailovic Martine , Vasson Aimé , Leymarie Joël , Semond Fabrice , Massies Jean
Published: September 2005

We report the experimental observation of the exciton–photon strong coupling regime in a GaN microcavity. The structure has been grown by molecular beam epitaxy on a Si(111) substrate. The upper mirror is a SiO2/Si3N4 dielectric mirror and the silicon substrate acts as the bottom one. Angle resolved reflectivity and photoluminescence experiments have allowed to demonstrate the exciton–photon strong coupling regime, characterized by a Rabi splitting of 31 meV at 5 K. From the modeling of experiments, the oscillator strengths of excitons A and B are evaluated and compared to the values previously published. Then, the design of the bulk microcavity is optimized in order to maintain the strong coupling regime at room temperature; our calculations predict a Rabi splitting of 33 meV at 300 K in this case. A second kind of structure based on GaN/AlGaN quantum wells is also proposed, leading to an expected splitting of 19 meV at 300 K.
Preparation of High-JcYBa2Cu3O7-yFilms on CeO2-Buffered Yttria-Stabilized Zirconia Substrates by Fluorine-Free Metalorganic Deposition
Authors: Tsukada Kenichi , Furuse Mitsuho , Sohma Mitsugu , Manabe Takaaki , Yamaguchi Iwao , Kondo Wakichi , Fuchino Shuichiro , Kumagai Toshiya
Published: September 2005

Epitaxial YBa2Cu3O7-y(YBCO) films have successfully been prepared by fluorine-free metalorganic deposition on yttria-stabilized zirconia (YSZ) substrates with an evaporated CeO2buffer layer. The YBCO films, prepared using a metal acetylacetonate-based coating solution, were highly (001)-oriented by X-ray diffraction θ–2θ scanning and φ scanning. The 0.21-µm-thick YBCO film demonstrated a high superconducting transition temperature,Tc=90.1 K, and high critical current densities with an average in excess of 4 MA/cm2at 77 K using an inductive method. Transport critical current (Ic) was also measured by a standard four-terminal technique; theIcvalue reached 185 A in a 2.5-cm-wide current path formed on a 5-cm-diameter film. These excellent properties are attributed to the small in-plane fluctuation due to high epitaxy of the YBCO films, which resulted from good matching of the crystal structure, lattice parameter and thermal expansion coefficient among the YBCO film, CeO2buffer layer and YSZ substrate, as well as from the smooth and uniform surface morphology, i.e., average roughness = 0.34 nm, of the CeO2buffer layer. The present deposition conditions, i.e., 700°C andp(O2)=4×10-2Pa, activated by radio frequency plasma at 20 W, are valid for the growth of such CeO2(100) buffer layers on YSZ substrates.
Microwave Properties and Critical Current Density of YBCO Thin Films Deposited on CeO2-Buffered Sapphire Substrates Using Sputtering Targets of Different Compositions
Authors: Kawagishi Kyoko , Komori Kazunori , Fukutomi Masao , Togano Kazumasa
Published: September 2005

The effect of the composition of a YBCO film on the microwave properties deposited on sapphire  substrates with a CeO2 buffer layer was investigated. CeO2 and YBCO films were deposited by RF magnetron sputtering with targets of different compositions. Y-rich crack-free YBCO films with a thickness of 0.5 µm, deposited onto a 25-nm-thick CeO2 film, showed good crystallinity and a low microwave surface resistance. Microwave surface resistances of 0.09 mΩ at 20 K and 0.7 mΩ at 77 K were obtained at a frequency of 12 GHz, and a critical current density of 0.1 MA/cm2 at 77 K was estimated for the 0.5-µm-thick YBa1.5Cu2.5O
y
film.
Characteristics of Whispering Gallery Modes in Single Dielectric Spheroid Excited by Gaussian Beam
Authors: Fujii Masamitsu , Haraguchi Masanobu , Okamoto Toshihiro , Fukui Masuo
Published: September 2005

We have numerically analyzed a coupling between a Gaussian light and spheroids by using a finite-difference time-domain method. In a configuration where the polarization of light is directed along the short axis of the spheroid and light is incident along the long axis, there exists a complex whispering gallery mode (WGM), which cannot be observed for any spheres. The characteristics of such a complex WGM are similar to those produced from a combination of several WGM's. In a configuration where the polarization of light is directed along the long axis of the spheroid and light is incident along the short axis, the Q-factor of a WGM excited there decreases compared with that of the WGM of a sphere because the curvature around the edges of the long axis is considerably large and thus the confinement of light must be weak.
Development of Optical Isolators for Visible Light Using Terbium Aluminum Garnet (Tb3Al5O12) Single Crystals
Authors: Geho Mikio , Takagi Takashi , Chiku Shinichiro , Fujii Takashi
Published: September 2005

We have recently reported the successful growth of incongruently melting terbium aluminum garnet (Tb3Al5O12; TAG) single crystals by the hybrid laser FZ (floating zone) method. Optical property evaluations confirmed a high transmittance and a larger Verdet constant than conventional Tb3Ga5O12 (TGG) crystals and/or Faraday glasses. In this study, we attempted to design, fabricate, and evaluate optical isolators in visible light through near-infrared (NIR) regions using TAG crystals. A finite element method (FEM) simulation of possible models led us to the preferable one based on a radially magnetized magnet. To realize this, we employed a pseudo-radially magnetized magnet. The target wavelengths of the prototype device were 408, 808, and 1064 nm. The typical extinction ratio was more than 30 dB and the insertion loss was less than 0.3 dB for AR-coated devices.
The Cornú Spiral as a Golden Mean Construction
Authors: Castaño Víctor M.
Published: September 2005

The Cornú spiral, the graphical realization of the Fresnel Integrals, is shown to intrinsically contain the golden mean (φ=(1+√5)/2), which is characteristic of quasi-periodic atomic arrangements, Fibonacci sequences, biological structures and a number of mathematical objects.
Improvement of Dielectric Properties in Iron-Containing Ferroelectrics
Authors: Fang Bijun , Shan Yuejin , Tezuka Keitaro , Imoto Hideo
Published: September 2005

Iron-containing ferroelectrics tend to exhibit large dielectric loss accompanied by strong frequency dispersion of the dielectric properties, which is considered to correlate with the partial reduction of Fe3+ to Fe2+ ions during sintering. After sintering in an O2 atmosphere, MnO2 and Li2CO3 dopings exhibit superior behavior in decreasing the dielectric loss of the iron-containing dielectrics. The strong frequency dispersion of the dielectric response and the abnormally recurrent increase of the dielectric constant and loss in the paraelectric region are correspondingly suppressed. An electron compensation mechanism is advanced to interpret the reason for the improvement in dielectric properties in the iron-containing dielectrics, in which the generation of donor electrons is based on different ionization paths.
Ferroelectric and Piezoelectric Properties of (Bi1/2K1/2)TiO3 Ceramics
Authors: Hiruma Yuji , Aoyagi Rintaro , Nagata Hajime , Takenaka Tadashi
Published: September 2005

The dielectric, ferroelectric and piezoelectric properties of bismuth potassium titanate, (Bi1/2K1/2)TiO3 (BKT), ceramics were studied. Single-phase BKT ceramics with a high relative density of 97% were obtained by the hot pressing (HP) method. The resistivities of BKT ceramics hot-pressed at 1060 and 1080°C (hereafter abbreviated as BKT-HP1060°C and BKT-HP1080°C) were fairly high being of the order of 1013 Ω·cm at room temperature (RT). The Curie temperature T
c of BKT-HP1060°C was 437°C, which is relatively higher than those of other lead-free piezoelectric materials. In this study, the ferroelectric properties of BKT ceramics were successfully obtained with fully saturated hysteresis loops. The remanent polarization P
r and coercive field E
c of BKT-HP1080°C were 22.2 µC/cm2 and 52.5 kV/cm, respectively. D–E hysteresis loops for these ceramics were observed even at 260°C. The electromechanical coupling factor k
33 and piezoelectric constant d
33 of BKT-HP1080°C were 0.28 and 69.8 pC/N, respectively. The second-phase transition temperature T
2 of 340°C was determined from the temperature dependence of piezoelectric and dielectric measurements.
Microstructure and Dielectric Properties of Sputtered (Ba0.3Sr0.7)TiO3 Thin Films with Amorphous Interfacial Layers
Authors: Lin Tai-Nan , Chu Jinn P. , Wang Sea-Fue , Wu Cheng-Hui
Published: September 2005

Crystallization behavior, microstructure and dielectric properties of sputtered (Ba0.3Sr0.7)TiO3 thin films have been studied. The crystallization from as-deposited amorphous structure to equilibrium crystalline structure is confirmed as an irreversible, exothermic and first-order transition by differential scanning calorimetry. At a heating rate of 20°C/min, the exothermic peak temperature for crystallization is measured to be 697.3°C. Transmission electron microscopy results reveal layered structures of amorphous and perovskite crystalline phases in the films deposited at temperatures between 450 and 650°C. The amorphous interfacial layer diminishes with increasing substrate temperature and a well-crystallized film is found at 750°C with a dielectric loss of 0.021. Dielectric constant shows an abrupt increase to 187 for the film deposited at 750°C as a result of the fully crystallized structure. The measured dielectric constants at different temperatures are well consistent with those calculated based on the presence of amorphous interfacial layers in the films.
Charging Method of Micropatterned Electrets by Contact Electrification Using Mercury
Authors: Genda Takashi , Tanaka Shuji , Esashi Masayoshi
Published: September 2005

This paper describes a new charging method for micropatterned electrets. The charging is based on contact electrification, and is performed by dipping an electret into mercury. By this method, 0.5-µm-thick silicon-dioxide electrets whose surfaces were treated by hexamethyldisilazane (HMDS) and a fluorinated silane coupling agent were charged up to -50 and -80 V, corresponding to a seventh and a forth of the dielectric breakdown limitation, respectively. Micropatterned electrets with line-and-space features were also charged near the surface charge density of the unpatterned electret, but a part of the charges disappeared from both edges of the electrets. The charge stability was propotional to the square of the electret width. This suggests that the charge stability is not dominated by the electret bulk property, but by surface conduction. To reduce the surface conduction, surface modification by the fluorinated silane coupling agent is effective, improving the charge stability by 100 times compared with HMDS treatment.
Electric Capacitance as Nanocondensers in Zigzag Nanographite Ribbons and Zigzag Carbon Nanotubes
Authors: Harigaya Kikuo
Published: September 2005

Electronic states in nanographite ribbons with zigzag edges and zigzag carbon nanotubes are studied using the extended Hubbard model with nearest-neighbor Coulomb interactions. The nearest-neighbor Coulomb interactions stabilize electronic states with the opposite electric charges separated and localized along both edges. Such states are analogous to nanocondensers. Therefore, electric capacitance, defined using a relation of polarizability, is calculated to examine the nano-functionalities of the system. We find that the behavior of the capacitance varies widely depending on whether the system is in the magnetic phase or charge-polarized phase. In the magnetic phase, capacitance is dominated by the presence of the edge states when the ribbon width is small. Even when the ribbon becomes wider, capacitance remains having a large magnitude as the system develops into metallic zigzag nanotubes. It is proportional to the inverse of ribbon width, when the system corresponds to the semiconducting nanotubes and the system is in the charge-polarized phase also. The latter behavior could be understood by the presence of an energy gap for charge excitations.
Microwave Characteristics of MgTiO3–CaTiO3 Dielectric Ceramics Fabricated Using Spark Plasma Sintering
Authors: Shim Seung Hwan , Choi Bong Geun , Yoon Jong Won , Kim Seong Hun , Kim Byong Chul , Shim Kwang Bo
Published: September 2005

Spark plasma sintering (SPS) was used in preparing dense 0.93MgTiO3–0.07CaTiO3 (MCT) ceramics, and their microstructure and microwave dielectric properties were investigated. Compared with conventional pressureless sintering, SPS was found to be effective in obtaining dense MCT ceramics with uniform microstructures at low temperatures, without any degradation of dielectric properties. The MCT specimen SPS-fabricated at 1150°C for 10 min exhibited excellent dielectric properties: a dielectric constant of 23 and a quality factor (Qf) of 70,000 GHz.
Liquid Phase Epitaxial Growth of Si Layers on Si Thin Substrates from Si Pure Melts under Near-Equilibrium Conditions
Authors: Nakajima Kazuo , Fujiwara Kozo , Nose Yoshitaro , Usami Noritaka
Published: September 2005

The growth of Si epitaxial layers on Si substrates from Si pure melts was attempted under near-equilibrium conditions by dipping-type liquid phase epitaxial (LPE) growth, in order to eliminate the doping effect from metal solutions on the purity of the Si epitaxial layers. Si epitaxial layers can be grown on Si substrates from a Si pure melt only when the temperature of the Si growth melt is kept 1–2°C above the melting point of Si (1414°C) and the growth melt is cooled just after the substrate is dipped in the growth melt. The Si substrate, Si epitaxial layers, and Si polycrystals can be clearly distinguished in the electron back-scattering diffraction pattern (EBSP) image of their cross sections. The growth rate of Si LPE layers during cooling clearly increases as the amount of overheating of the growth melt decreases from 2 to 1°C and the cooling rate increases from 0.4 to 1.0 mm/min.
Thin Films of Single-Crystal Cuprous Oxide Grown from the Melt
Authors: Naka Nobuko , Hashimoto Satoshi , Ishihara Teruya
Published: September 2005

We have grown thin films of cuprous oxide (Cu2O) from the melt in a small gap between paired substrates of MgO or Al2O3 single crystals. The films are characterized by scanning electron microscopy, X-ray diffraction and optical spectroscopy. The thickness of the films is found to range from 16 nm to 20 µm. The domain structure with dimensions of 0.1–1 mm is found and attributed to single crystals oriented into different directions. The narrow peaks in rocking curves and in azimuthal angle rotations indicate the formation of highly oriented single-crystal films. Clear peaks due to yellow, green, blue, and violet excitons are observed in optical spectra. The positions of the peaks depend on the thickness of the film, implying strain-induced shifts of the exciton levels.
Bandwidth Characterization of Pulsed Array Transducer in the Time Domain
Authors: Sung Chia-Chi , Liu Hsuan-Chi
Published: September 2005

A numerical approach is presented for efficiently evaluating the pressure fields radiated by a pulsed linear array transducer in the time domain. Instead of using Green's function, a wide-band time pulse, which is composed of two amplitude-modulated cosines multiplied by the difference between two traveling Heaviside step functions is employed to avoid complicated and time-consuming integration in the frequency domain. A numerical solution for the pressure distribution is obtained and compared with that obtained by the integration of a Gaussian pulse in the frequency domain. Increasing bandwidth causes smoothing of the grating lobes and side lobes, increases the width of the main lobe, and avoids split energy distribution along the axial direction. Finally, for numerical efficiency, we present the first quantitative evaluations of the lateral resolution, contrast resolution and uniformity of the array transducer for various bandwidths.
Enhancement of Crystallization of Hard Spheres by Gravity: Monte Carlo Simulation
Authors: Yanagiya Shin-ichiro , Mori Atsushi , Suzuki Yoshihisa , Miyoshi Yasuo , Kasuga Masashi , Sawada Tsutomu , Ito Kensaku , Inoue Tetsuo
Published: September 2005

We present the effects of gravity on the growth of a hard-sphere (HS) crystal as determined by Monte Carlo simulations. HSs were confined between hard walls at the top (z=L

z
) and the bottom (z=0) of the system with a periodic boundary condition in the horizontal direction. After preparing a melt state as an initial state, the gravity was suddenly switched on. The values of the gravity were m
gσ/k
B
T(≡g
*)=0.1,0.2,...,2.0, where m was the mass of a HS, g the acceleration of gravity, σ the HS diameter, and k
B
T the temperature multiplied by Boltzmann's constant. We observed the enhancement of crystallization due to gravity up to g
*=0.7 and that the crystals of largest size were formed at g
*=0.7–0.9. On the other hand, for g
*≥1.0, the top position of the HS crystal that was grown from the bottom became lower with an increase in the gravity, where crystals with various axis directions coexisted. The polycrystallization is speculated to occur due to polynucleation. These results are qualitatively consistent with those of an experimental study of the centrifugal sedimentation of colloidal crystallization.
A Transparent and Conductive Film Prepared by RF Magnetron Cosputtering System at Room Temperature
Authors: Liu Day-Shan , Wu Chun-Ching , Lee Ching-Ting
Published: September 2005

The electrical and optical properties of transparent and conductive oxide films obtained from a cosputtering system with indium–tin oxide (ITO) and zinc oxide (ZnO) targets have been investigated. The resistivity of these ITO films deposited at an rf power of 150 W was markedly improved with additional simultaneous ZnO target cosputtering at rf powers ranging from 25 to 200 W. A transparent film of lowest resistivity (3.69×10-4 Ω cm) was achieved at room temperature where the rf powers of the cosputtering for the ITO and ZnO targets were 150 and 75 W, respectively. The average transmittance obtained from these cosputtered films in the visible spectrum was over 80%.
Electrical Properties of La0.7Ca0.3MnO3 Thin Films Obtained by Metal-Organic Deposition (MOD) using Excimer Laser and Thermal Annealing
Authors: Daoudi Kais , Tsuchiya Tetsuo , Mizuta Susumu , Yamaguchi Iwao , Manabe Takaaki , Kumagai Toshiya
Published: September 2005

Epitaxial La0.7Ca0.3MnO3 (LCMO) thin films were prepared by thermal and excimer laser (EL) metal-organic deposition (MOD). Using simple thermal annealing (STA) at 800–1000°C, the LCMO films were well epitaxially grown on single-crystalline SrTiO3 substrates. When, using a KrF or an ArF excimer laser irradiation, the LCMO films were also epitaxially grown at a substrate temperature of 500°C. The films produced by STA exhibited metal–insulator transition temperatures T
p's ranging from 282 to 290 K while those obtained by EL irradiation had a T
p of approximately 205 K. For bolometric applications, the temperature coefficient of resistance (TCR) of the films was calculated. The LCMO films obtained by STA have a TCR of 8.5%/K at 228 K. On the other hand, using the EL irradiation, the TCR values are 5.8%/K at 165 K and 6.5%/K at 128 K for the KrF and ArF excimer lasers, respectively.