bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Molecular Rearrangements on the (0001) Face of C70 Single Crystals
Authors: Jiang Lei , Iyoda Tomokazu , Tryk Donald A. , Kino Nobuhiro , Kitazawa Koichi , Fujishima Akira , Hashimoto Kazuhito
Published: October 2002

Surface molecular rearrangements on the (0001) face of C70 single crystals were investigated using atomic force microscopy (AFM). On the surface of a freshly prepared crystal, the molecules are arranged in a slightly distorted hexagonal close-packed (hcp) structure, with an average nearest-neighbor distance of 10.5±0.3 Å. After the samples were stored for two weeks in dry air, the surfaces of the crystals became relatively rough. A quasi-two-dimensional molecular rearrangement from a purely hexagonal structure to a mixture of hexagonal, cubic, and rhombic structures was observed over a several-nanometer region. For different crystal growth conditions, a superstructure resulting from a quasi-three-dimensional surface molecular rearrangement was grown and observed on the surface of the crystals. The superstructure appears as an ordered array of domain boundaries between surfaces regions with face-centered cubic (fcc)-type stacking (CBA) and hcp-type stacking (ABA) regions. The coexistence of the different phases in a nano-scale area is probably due to the similarity of the cohesive energies of the phases. The AFM images represent the direct observation of a transient state in a surface phase transformation on the C70 single crystals.
Structural Studies on Phosphatidylcholine Liposomes in Various Phases Using Atomic Force Microscopy
Authors: Hideki Iwamoto Hideki Iwamoto , Nobuyuki Wakayama Nobuyuki Wakayama
Published: October 2002

Structural studies on phosphatidylcholine liposomes in various phases were carried out using atomic force microscopy (AFM) by applying a newly proposed fixation method under aqueous conditions. With soybean lecithin liposomes in air at room temperature (liquid crystalline phase), only irregular images were observed under magnification. On the other hand, with dipalmitoylphosphatidylcholine (DPPC) liposomes in air at room temperature (gel phase), regular two-dimensional molecular arrays were observed. With dimyristoylphosphatidylcholine (DMPC) liposomes in water at 18° C (sub-gel phase) on mica substrates immobilized by centrifugation, various types of ripple structures were seen. It was shown that our fixation method using centrifugation is suitable for the AFM observation of artificial membranes under aqueous conditions.
Effect of Quantum Confinement and Lattice Relaxation on Electronic States in GaAs/In 0.2Ga 0.8As/GaAs Quantum Dots
Authors: Katsuji Moriyasu Katsuji Moriyasu , Shinichi Osako Shinichi Osako , Nobuya Mori Nobuya Mori , Chihiro Hamaguchi Chihiro Hamaguchi
Published: October 2002

The effect of quantum confinement and lattice relaxation on electronic states in GaAs/In0.2Ga0.8As/GaAs quantum dots has been studied. The quantum dots were fabricated using electron beam lithography and wet chemical etching, and photoluminescence measurements were carried out to investigate the electronic states of the dots. A blue shift in the transition energy for smaller quantum dots was clearly observed, while the transition energy shifts to lower energy for larger dots. The blue shift is attributed to quantum confinement and the red shift to lattice relaxation. A simple empirical formula is given which well describes the observed energy shift.
Theory of Single Electron Tunneling through a Quantum Dot Dimer
Authors: Kiyoshi Kawamura Kiyoshi Kawamura , Tomosuke Aono Tomosuke Aono
Published: October 2002

Transport spectra of a quantum dot dimer are studied with the assumption that energy levels are quantized in each quantum dot. The splitting of energy levels between bonding and antibonding states is modulated by the coupling with electronic states in an emitter and a collector. When the coupling with external electrodes is strong enough, the spectra of a quantum dot dimer are not necessarily observed by I–V characteristics.
Fundamental Physics of Single Electron Transport
Authors: Shun-ichi Kobayashi Shun-ichi Kobayashi
Published: October 2002

We have studied the critical tunnel resistance for the appearance of the Coulomb blockade in single small-tunnel junctions with electrodes in the normal state and for the phase coherence to appear in the same junctions in the superconducting state. We found that the critical resistances are in accordance with theoretical expectations in both the normal and the superconducting states. For two-dimensional arrays of small junctions, we determined the phase diagram in the parameter space of temperature, Josephson coupling, charging energy and tunnel resistance. It agreed qualitatively with a theoretical diagram based on a competition between charge and vortex Kosterlitz-Thouless transitions.
Charging Effect and Phase Coherence through Parallel Quantum Dots
Authors: Shingo Katsumoto Shingo Katsumoto , Akira Endo Akira Endo
Published: October 2002

We observed the coexistence of the charging effect and the interference effect through a Coulomb oscillation and an Aharonov-Bohm oscillation in a parallel quantum dot system. A rapid decrease in the AB amplitude due to a shift in the gate voltage was observed.
Nonequilibrium Transport Properties through Parallel Quantum Dots
Authors: Mikio Eto Mikio Eto
Published: October 2002

Nonequilibrium transport properties through parallel metallic dots are studied theoretically to elucidate the interdot charging effect. The current and its fluctuation are calculated, as functions of the gate and bias voltages, by solving a master equation numerically and by performing a Monte Carlo simulation. A two-dot system shows a new structure of the Coulomb oscillation owing to the interplay between regular and irregular transport processes. In long arrays of dots, a “crystallization” of charges is observed as a large enhancement of the current fluctuation in which charges are accumulated at every other dot.
Deformation Effects and Recording Characteristics of Compact Disc-Recordables
Authors: Huh Young Jae , Kim Jong Sung , Kim Tae Young Nam
Published: October 2002

The dimensions of the deformed area of a compact disc-recordable (CD-R) were calculated by structural analysis and measured by atomic force microscope (AFM) analysis. From these analyses, the relationship between the deformation of polycarbonate (PC) and the recording characteristics was investigated. The calculated bump height was 26 nm at 7 mW and the actual bump height was 41 nm. The bump was observed from 3.5 mW and the bump height increases with increasing writing power. The carrier to noise ratio (CNR) is related to the bump half-width rather than to the bump height, and the trend of jitter corresponds to that of | 3T-bump half width|1/2.
Conductance Oscillations in Hopping Conduction Systems Fabricated by Focused Ion Beam Implantation
Authors: Kondo Hiroki , Iwano Hirotaka , Nakatsuka Osamu , Kaga Kazutaka , Shigeaki Zaima Shigeaki Zaima , Yukio Yasuda Yukio Yasuda
Published: October 2002

We have investigated the single-electron phenomena in p-Si hopping conduction systems with a gate electrode. The hopping conduction systems have been fabricated on Si(100) substrates by focused ion beam (FIB) implantation of Ga+ ions with a beam diameter of 0.1 µ m. The samples show nearest-neighbor hopping (NNH) conduction below 30 K and the conductance is found to oscillate by changing the gate voltage in the NNH conduction region. From the period of conductance oscillation, the gate capacitance is estimated to be about 0.3–0.4 aF. The evaluated size of a dot based on the capacitance is close to the dimension of localized states in this hopping conduction system. A plateau is also observed in current-voltage characteristics between source and drain electrodes. It is considered that these phenomena originate from a Coulomb blockade and that the chain of localized hopping states acts as asymmetric multiple tunneling junctions.
Collective Superradiation Effects in InGaAsP/InP Liquid Phase Epitaxy-Grown Quasi-0-Dimentional Nanostructures
Authors: Sergy V. Zaitsev Sergy V. Zaitsev , Anatoly M. Georgievski Anatoly M. Georgievski
Published: October 2002

Autocorrelation measurements of the time structure of radiation have been performed on a InGaAsP/InP laser based on self-organized nanostructures under CW pumping. The measurements reveal ultra-short-pulses shorter than the intra-cavity round-trip time in the structure of laser radiation. The first and second order analysis of optical autocorrelation functions prove the pulse nature of CW injection laser radiation. Two different modes of pulse formation has been shown.
Negative Characteristic Temperature of InGaAs Quantum Dot Injection Laser
Authors: Zhukov Alexey E. , Ustinov Victor M. , Egorov Anton Yu. , Kovsh Alexey R. , Tsatsul\`nikov Andrey F. , Ledentsov Nikolay N. , Zaitsev Sergey V. , Gordeev Nikita Yu. , Peter S. Kopèv Peter S. Kopèv , Zhores I. Alferov Zhores I. Alferov
Published: October 2002

The range of negative characteristic temperatures in temperature dependences of threshold current density of low-threshold (In, Ga)As/(Al, Ga)As quantum dot injection lasers has been observed. A model describing the decrease in threshold current density with temperature at low temperatures is proposed.
Optimizing Two-Photon Three-Dimensional Data Storage in Photochromic Materials Using the Principles of Nonlinear Optics
Authors: Akimov Denis A. , Fedotov Andrei B. , Koroteev Nikolai I. , Magnitskii Sergei A. , Naumov Aleksandr N. , Dmitrii A. Sidorov-Biryukov Dmitrii A. Sidorov-Biryukov , Aleksei M. Zheltikov Aleksei M. Zheltikov
Published: October 2002

In the context of designing a three-dimensional optical-memory device, we investigate the cross section of two-photon absorption of a photochromic material as a function of the relative orientation of polarization vectors of light waves involved in two-photon data writing. It is demonstrated that, with an appropriate choice of polarization vectors of writing laser waves, one can considerably increase the efficiency of two-photon data writing.
A Compact I2-Stabilized 532 nm Nd:YAG Laser
Authors: Feng-Lei Hong Feng-Lei Hong , Jun Ishikawa Jun Ishikawa
Published: October 2002

Compact diode-pumped Nd:YAG lasers and 5-cm-long iodine cells are used to establish a portable wavelength standard at 532 nm and 1064 nm. Doppler-free absorption lines of the 127 I2 molecule were found using modulation transfer spectroscopy to have a very high signal-to-noise ratio (5000 in a 50 Hz bandwidth). The maximum frequency excursion of the stabilized lasers was less than 120 kHz (at 1064 nm) over 50 min, with an averaging time τ= 10 s.
Space Charge Effect in Ferroelectric (K 0.50Na 0.50) 2(Sr 0.75Ba 0.25) 4Nb 10O 30 Ceramics
Authors: Sangdon Bu Sangdon Bu , Dukhyun Chun Dukhyun Chun , Gwangseo Park Gwangseo Park
Published: October 2002

The effects of space charges on the ferroelectric properties of (K0.50Na0.50)2(Sr0.75Ba0.25)4Nb10O30 (KNSBN) ceramics have been investigated in the temperature range between 30°C and 800°C. For samples aged at room temperature or poled at temperatures above the Curie point (T
c ∼208°C) in order to induce space-charge polarization, we have observed a broad dielectric peak at around 650°C, a negative depolarization current above 650°C, and a variation of the activation energy at 650°C. This behavior above T
c may be interpreted in terms of mobile space charges such as A-site vacancies or oxygen vacancies which may be formed during the sintering process at high temperatures (∼1300°C). The experimental results are discussed in connection with the interaction between the polarities of domain and space charges.
Hydrogenation of High-Concentration Arsenic-Doped Silicon Using Radio Frequency Hydrogen Plasma
Authors: Katsuhiro Yokota Katsuhiro Yokota , Kouichi Hosokawa Kouichi Hosokawa , Kouichiro Terada Kouichiro Terada , Kiyohito Hirai Kiyohito Hirai , Hiromichi Takano Hiromichi Takano , Masao Kumagai Masao Kumagai , Yasunori Ando Yasunori Ando , Kouji Matsuda Kouji Matsuda
Published: October 2002

n-type layers in silicon with high carrier concentrations have been formed by high-dose (1×1015–1×1016 cm-2) As-ion implantation and subsequently 950°C-annealing. The n-type layers containing many As clusters were exposed to radio-frequency hydrogen plasma for 30 min. While the hydrogenated samples had the same As-atom concentration profile as the as-annealed samples, the carrier concentration profiles approached the As atom concentration profile with increasing substrate temperature. The activation energy obtained from the Arrhenius plot of the carrier concentration agreed well with that of the diffusivity of H atoms in silicon. Thus, the increase in the carrier concentration is a result of H atoms reacting with As clusters.
DC Field Dependence of the Dielectric Characteristics of Doped Ba0.65Sr0.35TiO3 with Various Grain Sizes in the Paraelectric State
Authors: Jih-Wei Liou Jih-Wei Liou , Bi-Shiou Chiou Bi-Shiou Chiou
Published: October 2002

Different grain sizes of ferroelectric Ba0.65Sr0.35TiO3 doped with 1.0 mol% MgO and 0.05 mol% MnO2 were prepared to investigate the DC field dependence of dielectric characteristics. A transition broadening is observed as grain size decreases. The broadening is attributed to the variance of lattice distortion in the materials. As the grain size increases, both the maximum dielectric constant k
max at T
c and the dielectric tunability (percentage change of dielectric constant under a DC field) increase. A phenomenological equation can be fit to the DC field dependence of the dielectric constant. The phenomenological coefficient obtained is strongly dependent on the grain size and the temperature. Above the phase transition, a “behavior-transformation” temperature T
b is observed. At temperatures below T
b, the dielectric loss factor that is dominated by intrinsic loss is reduced when the DC field is applied. While at temperatures above T
b, the loss factor is dominated by the conduction loss and is raised by the DC field.
Preparation and Electrochromism of RF-Sputtered TiO2 Films
Authors: Kitao Michihiko , Yoshihiro Oshima Yoshihiro Oshima , Kazuo Urabe Kazuo Urabe
Published: October 2002

Titanium oxide ( TiO2) thin films were prepared by rf-sputtering in an Ar/O2 atmosphere from a compressed powder TiO2 target and their electrochromic (EC) phenomena were investigated. Films prepared under the sputtering pressures of 1.3, 4.0 and 6.7 Pa were confirmed by X-ray diffraction to be in amorphous state, anatase form and rutile form, respectively. Amorphous and anatase films showed cathodic EC properties. The maximum value of coloration efficiency was 14 cm2/C for the amorphous films in an electrolyte solution of 1N HCl. AC conductance measurements were measured from 110 Hz to 100 kHz for various oxygen contents in the sputtering atmosphere. The ac conductance gradually decreased with increasing oxygen content in the region of up to 30% and was independent of oxygen content in the region of more than 30%. In the films prepared in the sputtering atmospheres of oxygen contents of less than 30%, electronic conduction is interpreted to occur due to lack of oxygen. In the films prepared in oxygen contents of 30% and more, on the other hand, only ionic conduction is considered to exist.
Adsorption of Atomic Hydrogen on the Si(100)-(2×1)-Sb Surface
Authors: Jeong-Tak Ryu Jeong-Tak Ryu , Koichiro Kui Koichiro Kui , Kenji Noda Kenji Noda , Mitsuhiro Katayama Mitsuhiro Katayama , Kenjiro Oura Kenjiro Oura
Published: October 2002

The structural change of a Si(100)-(2×1)-Sb surface caused by atomic hydrogen adsorption at room temperature and 100°C was studied using time-of-flight impact collision ion scattering spectroscopy (TOF-ICISS) and low energy electron diffraction (LEED). In this study, we found from the change of TOF-spectra and α-scans that when atomic hydrogen adsorbs on the Si(100)-(2×1)-Sb surface, (1) a structural transformation from (2×1) to (1×1) occurs, (2) Sb atoms existing on the Si(100) surface partly desorb even at room temperature, and (3) the rest of the Sb atoms are displaced from their original positions and form an almost two-dimensional layer with dispersive distribution of Sb atoms. These results are different from those for other metal adsorbates/Si systems reported previously.
Reduction of Electrical Resistance of Nanometer-Thick CoSi 2 Film on CaF 2 by Pseudomorphic Growth of CaF 2 on Si(111)
Authors: Wataru Saitoh Wataru Saitoh , Kaoru Mori Kaoru Mori , Hidekazu Sugiura Hidekazu Sugiura , Takeo Maruyama Takeo Maruyama , Masahiro Watanabe Masahiro Watanabe , Masahiro Asada Masahiro Asada
Published: October 2002

1.9-nm-thick epitaxial metal (CoSi2) films were grown on relaxed or pseudomorphic CaF2/Si(111) and their electrical resistance was measured. It was found that the electrical resistance of the CoSi2 film on pseudomorphic CaF2 was about half of that on relaxed CaF2. This result can be attributed to the improved of flatness and crystalline quality of the CoSi2 by using of pseudomorphic CaF2 instead of relaxed CaF2 due to the flat pseudomorphic CaF2 surface and the small lattice mismatch between CoSi2 and pseudomorphic CaF2.
New Application of a Magneto-Plasma Dynamic Arc-Jet to Amino Acid Synthesis
Authors: Miyakawa Shin , Tamura Hideki , Kobayashi Kensei , Akira Sawaoka Akira Sawaoka
Published: October 2002

A magneto-plasma dynamic arc-jet (MPD arc-jet) was applied to the synthesis of biomolecules. Fourteen µ mol of amino acid were synthesized by hydrolyzing the film produced from a hot plasma of CO–N2–H2 gas mixture. The amino acids were identified by high-performance liquid chromatography and gas chromatography-mass spectrometry. The gas-phase products and the film were examined by mass spectroscopy and elementary analysis, respectively. Since glycine was found in all samples which were synthesized under different conditions, it became clear that the conditions of glycine synthesis were not strict. After MPD arc discharges, most gas-phase products were the starting gas samples and about 1% of the starting gas samples was deposited. About 1% of the deposit was amino acid precursors.
Crosstalk-Suppressed Readout System Using Shading Band
Authors: Dobashi Hisanobu , Takaya Tanabe Takaya Tanabe , Manabu Yamamoto Manabu Yamamoto
Published: October 2002

A readout system that uses a shading band to suppress crosstalk was developed. In this system, a shading band is placed in the collection path to shade the center part of the reflected beam along the track direction at the aperture plane. Crosstalk could be sufficiently suppressed when the width of the shading band was chosen so the readout signals that are obtained by detecting the resulting beam after this shading band are free from data patterns on adjacent tracks. Computer simulation results show that this method can suppress crosstalk in each track pitch by choosing suitable widths for both the recorded mark and the shading band. Experiments using a magneto-optical readout system that has a shading band in the collection path were performed to demonstrate the crosstalk suppression effects of this method. These results show that this method can reduce crosstalk by about 19 dB compared with conventional methods.
0.8-Numerical-Aperture Two-Element Objective Lens for the Optical Disk
Authors: Yamamoto Kenji , Osato Kiyoshi , Ichimura Isao , Fumisada Maeda Fumisada Maeda , Toshio Watanabe Toshio Watanabe
Published: October 2002

A high-numerical-aperture ( NA) optical pick-up for an optical disk was developed using a two-element lens, a thin disk substrate and a spherical aberration compensation mechanism. We designed a two-element objective lens rather than a conventional singlet objective lens in order to increase the fabrication tolerance of the objective lens for high NA. A disk substrate which is thinner than that of the digital video disk (DVD) was adopted to increase the disk tilt tolerance. A spherical aberration compensation mechanism was realized by controlling the distance between the two lenses of the objective using an actuator in order to cancel the aberration due to the variations in the disk thickness. In the experiment, we fabricated a two-element lens according to our design and confirmed that it performed as a high-quality 0.8- NA objective lens.
A Plasma Source Using Waves in a Lower Hybrid Frequency Range
Authors: Yasuyoshi Yasaka Yasuyoshi Yasaka , Keitaro Ohnishi Keitaro Ohnishi , Tetsuo Kikuchi Tetsuo Kikuchi , Kunihide Tachibana Kunihide Tachibana , Tohru Itoh Tohru Itoh
Published: October 2002

Plasma production using the waves in a lower hybrid frequency range is investigated numerically and experimentally. The radial profiles of wave field and power absorption by electrons are calculated using a one-dimensional kinetic wave code. The two-dimensional fluid simulation code is coupled with the output of the kinetic wave code to predict the plasma production in the designed plasma source. The power deposition profile, and hence the produced plasma density profile, can be controlled by selecting the wave number and the magnetic field. It is observed in the experiment that plasma is produced in the outer radii of the source chamber, and diffuses to form a radially uniform profile in the diffusion chamber in accordance with the simulation.
Mass Spectrometric Detection of F Atoms and CFx Radicals in CF 4 Plasmas
Authors: Schwarzenbach Walter , Tserepi Angeleki , Jacques Derouard Jacques Derouard , Nader Sadeghi Nader Sadeghi
Published: October 2002

Threshold ionization mass spectrometry method has been applied to the study of the neutral radicals present in a microwave generated CF4 plasma. Calibration of the mass spectrometry signals by comparison with the ion signals produced by the dissociative ionization of CF4 allows the estimation of the absolute concentration of the radicals in a 15 mTorr plasma, with an emphasis on the cases of atomic fluorine and CFx (x = 1–3) radicals. The effect, on the gas phase composition, of the introduction of a silicon sample in the plasma chamber is also investigated. Among these effects, the introduction of silicon leads to decrease the concentration of the F and H atoms as well as HF molecules, and to increase the concentration of the SiF3 and CFx radicals.
Ionic Species in 13.56 MHz Discharges in CF 4 Gas and Mixtures of It with Ar and O 2
Authors: Itsuo Ishikawa Itsuo Ishikawa , Shinya Sasaki Shinya Sasaki , Kazuya Nagaseki Kazuya Nagaseki , Yukinori Saito Yukinori Saito , Shinji Suganomata Shinji Suganomata
Published: October 2002

Signal intensities of positive ions were measured in situ by direct sampling from parallel-plate discharges in CF4/Ar and CF4/O2 mixtures using a quadrupole mass spectrometer. Major positive ions in CF4/Ar discharge are CF
x

+ (x=3, 2, 1) and Ar+. Some of the production of CF2
+ and CF+ is considered to be due to the contribution of Ar+. Major positive ions in CF4/O2 discharge are CF3
+, O
y

+ and F
y

+ (y=2, 1). The signal intensity of CO2
+ is of the same order as that of F
y

+. The signal intensities of F
y

+ and O+ in CF4/O2 discharge are higher than those in pure CF4 and O2 discharges, respectively. Intensity ratios of the ions vary with the gas mixing ratios.
Measurement of the Density of OH Free Radicals in Magnetized Sheet Plasma Crossed with Vertical Gas Flow
Authors: Tonegawa Akira , Takatori Masahiko , Kobayashi Yukihiro , Ichiba Masatugu , Miyasaka Hiroaki , Kawamura Kazutaka , Takayama Kazuo
Published: October 2002

We demonstrated the production of hydroxyl (OH) free radicals in an argon plasma, called the magnetized sheet plasma, crossed with vertical gas flow of O2- H2 gas mixture. Number density of OH free radicals n
OH and plasma parameters were measured by laser-induced fluorescence (LIF) and Langmuir probe, respectively. n
OH depends on the electron temperature in the sheet plasma. Above the maximum value of n
OH, the high-energy part of the electron energy distribution function f
e(E) above ∼8 eV decreases. These results suggest that the high-energy part of f
e(E) contributes to the dissociation of O2, producing OH free radicals.
Transport Parameters for Electrons in Carbon Monoxide
Authors: P. Karwasz Jadwiga Mechlińska-Drewko , Lj. Petrović Zoran
Published: October 2002

The measurements of the ratio of transverse diffusion coefficient to mobility (D/µ), the ratio of longitudinal diffusion coefficient to mobility (D
L/µ) and of the drift velocities (W) for electrons in carbon monoxide are presented. The coefficients D/µ and D
L/µ have been determined by applying the Townsend–Huxley method, at an ambient temperature and for the reduced electric fields 50≤E/N≤2500 Td and 50≤E/N≤1750 Td, respectively. The drift velocities were obtained between 0.1 Td and 150 Td by applying the Bradbury–Nielsen technique in the Blevin Hasan version.
Three-Dimensional Simulation of Microwave Propagation in an Electron Cyclotron Resonance Plasma
Authors: Hiroshi Muta Hiroshi Muta , Yoko Ueda Yoko Ueda , Yoshinobu Kawai Yoshinobu Kawai
Published: October 2002

Electron cyclotron resonance (ECR) plasmas which can generate high density under low pressure are widely used in plasma processing applications such as etching for semiconductor and thin-film deposition. In these applications, ECR plasmas are required to be uniform over a large-diameter wafer. For this problem, the analysis of microwave propagation in the plasma is important because the microwaves can have significant influence on the formation of the spatial profiles of the plasma. In this paper, we present a three-dimensional simulation of microwave propagation in an inhomogeneous ECR plasma using the finite-difference time-domain (FDTD) method. As a result, it was found that the wave propagation was sensitive to the spatial profile of the plasma density, and much different from that in an isotropic dielectric medium. In addition, it was found that a three-dimensional model reproduced the experimental results measured by interferometry much better than a one-dimensional model.
Analysis of Three-Dimensional DC Magnetron Discharge by the Particle-in-Cell/Monte Carlo Method
Authors: Kenichi Nanbu Kenichi Nanbu , Shuji Kondo Shuji Kondo
Published: October 2002

The structure of a three-dimensional dc magnetron discharge is clarified by the use of the PIC/MC method. Magnets are placed in the form of a racetrack with the practical dimensions of a commercial sputtering apparatus. The cathode sheath has a three-dimensional structure; the sheath is thinnest in the midst of magnets. As the magnetic field B increases in strength, the sheath thickness decreases. The similarity law for the sheath thickness proposed by Gu and Lieberman [J. Vac. Sci. Technol. A 16 (1988) 2960] works well. The plasma density peaks outside the sheath. As B increases, the location of the peak moves closer to the cathode and the plasma is more widely distributed between the electrodes. The distribution of the peak plasma density on the plane parallel to the electrode has a strong correlation with the distribution of ion flux onto the cathode. Pressure has little effect on the electric field. However, as pressure decreases, the plasma density exhibits a wider distribution.
A Compact-Disc-Compatible Digital Versatile Disc Pickup Using Annular Mask
Authors: Lee Chul Woo , Chung Chong Sam , Cho Kun Ho , Seong Pyong Yong , Kim Tae-Kyung , Jung Soo Yul , Choi Byoung Ho , Yoo Jang Hoon , Joong Eon Seo Joong Eon Seo , Dong Ho Shin Dong Ho Shin
Published: October 2002

An optical pickup has been developed for both digital versatile discs (DVD) and compact discs (CD) using an annular mask on an objective lens. A conventional lens without the annular mask has been optimized only for DVD disc with 0.6 mm-thickness. The intensity of the secondary peaks of the spot focused by the objective lens with an annular mask to a CD is reduced and the pickup is found to have large tolerance for disc tilt variation compared with a conventional objective lens without an annular mask.
The Role of a Resist During O2 Plasma Ashing and Its Impact on the Reliability Evaluation of Ultrathin Gate Oxides
Authors: Chien Chao-Hsin , Chang Chun-Yen , Lin Horng-Chih , Chang Tsai-Fu , Hsien Szu-Kang , Tseng Hua-Chou , Chiou Shean-Guang , Tiao-Yuan Huang Tiao-Yuan Huang
Published: October 2002

Resists are regarded as protective layers for underlying devices during plasma ashing. In previous studies, resists were deliberately removed by a wet etching process prior to plasma exposure in an effort to achieve significant device degradation. In this paper we report that, contrary to conventional belief, devices with a resist overlayer actually suffer from more severe degradation than those without a resist covering. This resist-enhanced degradation effect, although not observed for devices with a thick gate oxide of 8 nm, becomes significant as the oxide thickness is scaled down below 6 nm. The most severe device degradation is found to be located at the center of the wafer and is found to increase with increasing antenna area ratio. Damage is also found to occur not during the overashing period, but primarily during the initial ashing stage when the resist is still on the electrodes. Using a combination of a simple equivalent capacitor circuit model and the self-adjustment behavior of potential between the wafer surface and substrate, good correlation with the experimental results is obtained.
Amorphous Carbon Nitride Hard Coatings by Multistep Shielded Arc Ion Plating
Authors: Yusuke Taki Yusuke Taki , Toshihisa Kitagawa Toshihisa Kitagawa , Osamu Takai Osamu Takai
Published: October 2002

Hard amorphous carbon nitride (a-C:N) films fabricated by shielded arc ion plating break into pieces because of the large compressive stresses in the films when the film thicknesses are more than 200 nm. In the application of these films to practical hard coatings, the development of a technique to grow thicker films (over 1 µ m) is necessary. In this study, we developed a multistep ion plating technique to grow thick hard multilayer films. We formed a-C:N multilayers with a total thickness of more than 1 µ m on Si (100) and high speed steel (SKH9) substrates by stacking hard and soft films alternately in order to relax the large compressive stress in the hard film. The multilayers are extremely hard (Knoop hardness: 3200) and neither break into pieces nor peel off substrates spontaneously.
Preparation of Stable F-Doped SiO 2 Thin Films from Si(NCO) 4/SiF 4/O 2 Gas Mixtures Using a Conventional Capacitively Coupled RF Plasma Source
Authors: Mahito Sawada Mahito Sawada , Yuko Nakagami Yuko Nakagami , Tatsuru Shirafuji Tatsuru Shirafuji , Yasuaki Hayashi Yasuaki Hayashi , Shigehiro Nishino Shigehiro Nishino
Published: October 2002

Stable F-doped SiO2 (SiOF) films have been deposited using a simple conventional capacitively coupled RF plasma-enhanced chemical vapor deposition method using H-free tetraisocyanatesilane (Si(NCO)4: TICS) diluted with oxygen, and tetrafluorosilane (SiF4) having Si–F bonds in itself. The SiO2 films deposited only with TICS have poor water resistivity, which originates in the inclusion of the SiNCO structure in the films. This property has been improved by mixing O2 with the source gases. Although F atoms at the top surface of films desorbed upon air exposure, SiOF films deposited with TICS, SiF4 and O2 exhibit excellent water resistivity. A film with F concentration of 6 at.% exhibited a dielectric constant of 3.3, a resistivity of 3.6×1015 Ωcm and a break-down electric field of 7.7 MV/cm. These values are comparable to or better than the reported values for films prepared using tetraethylorthosilicate. These results indicate that the TICS, SiF4 and O2 system can be used to deposit high quality SiOF films using a much simpler method than those requiring complex high density plasma sources.
Deposition of High-Quality TiO 2 Films by RF Magnetron Sputtering with an Auxiliary Permanent Magnet
Authors: Kunio Okimura Kunio Okimura , Akira Shibata Akira Shibata
Published: October 2002

RF magnetron sputtering with an auxiliary permanent magnet was applied for the deposition of TiO2 films. An auxiliary magnet was installed under a grounded electrode and the magnetic field strength was intensified in the whole discharge space. The film prepared by this sputtering apparatus showed a high value of the refractive index equal to that of bulk TiO2 crystal. The results of several diagnostic techniques showed characteristic changes in the discharge structure. It was shown that a high current of substrate-incident ions brings about growth of high-quality TiO2 films.
Effects of Methyl and Perfluoro-Alkyl Groups on Water Repellency of Silicon Oxide Films Prepared by Microwave Plasma-Enhanced Chemical Vapor Deposition
Authors: Hozumi Atsushi , Kondo Takahiro , Kajita Iwao , Sekoguchi Hiroki , Nobuhisa Sugimoto Nobuhisa Sugimoto , Osamu Takai Osamu Takai
Published: October 2002

Silicon oxide films with water repellency were prepared by microwave plasma-enhanced chemical vapor deposition using multiple gas mixtures of five organosilicon compounds, fluoro-alkyl silane (FAS-17) and Ar as source gases. We studied the effects of methyl and perfluoro-alkyl groups in the reactants on the water repellency of the films. Films of different compositions were prepared by controlling the partial pressures of the reactants. High water repellency was obtained when tetramethylsilane and trimethylmethoxysilane were mixed with FAS-17/Ar. Water repellency depended on the number of methyl groups in the organosilicon compounds and did not depend directly on the fluorine concentrations at the surfaces of the films. The decomposition process of reactants in the plasma was analyzed by optical emission spectroscopy.
Materials Characterization of Plasma Deposited Copolymer Using CFC-113 With C2H4 Monomer
Authors: Tsuji Osamu , Minaguchi Takeshi , Hirohiko Nakano Hirohiko Nakano , Toshiaki Tatsuta Toshiaki Tatsuta
Published: October 2002

Chlorofluorocarbons ( CFC
s
) with C2H4 copolymer films have highly hydrophobic surfaces and good adhesion. We confirmed that the copolymer is highly thermostable in a high-temperature environment. These properties are strongly dependent on the mixing ratio of CFC-113 and C2 hydrocarbon monomers. We report on the influence of process conditions such as monomer composition, r.f. power and pressure on polymer film deposition. The bond strength, contact angle and thermal stability of the polymer thin films at 400° C in an oxygen atmosphere were measured and electrical properties such as a dielectric constant of (ε) 2.2–3.1 and breakdown voltage of 2.62–3.30 MV/cm were obtained.
Heterogeneous Particle Formation during Low Pressure Etching of Silicon Dioxide
Authors: Yoo Won Jong , Nam Byeong Yun , Kim Woo Sik , Shin Kyung Sup , Jung Chan Ouk , Young Bum Koh Young Bum Koh , Moon Yong Lee Moon Yong Lee
Published: October 2002

Particles generated during highly selective SiO2 etching using a magnetically enhanced reactive ion etcher and an inductively coupled plasma etcher are investigated. The pressure ranges from 3 to 60 mTorr in mixtures of CHF3, CF4, C2F6, C4F8, O2 and Ar. Polymers at the reactor surface are the major contributors to particle formation, and particles fall onto the wafer during the etching process. The formation mechanism is heterogeneous. By quadrupole mass spectrometry and optical emission spectroscopy, C2 and C

x

F

y

species can be used to monitor the level of particle contamination in highly selective SiO2 etching. During the Ar/O2 dry cleaning process to decontaminate the plasma chamber, concentrations of C2 and C

x

F

y

radicals and CO products decrease with the removal of the polymers from the chamber wall, while the concentrations of O and O2 radicals increase.
Chemical Kinetic Modelling of Non-Equilibrium Ar-CO 2 Thermal Plasmas
Authors: Thomas G. Beuthe Thomas G. Beuthe , Jen-Shih Chang Jen-Shih Chang
Published: October 2002

A chemical kinetic model has been constructed to predict the gas and electron temperature dependence of the neutral and ionic species composition in Ar-CO2 mixtures under thermal plasma conditions. The model includes electron impact, thermal impact, ion-molecule, and recombination reactions as well as accounting for diffusion. Important metastable and excited states of species have been accounted for as well as the presence of neutral molecules, radicals, and atoms, positively and negatively charged atoms and molecular ions, and electrons. All relevant electron temperature, gas temperature and pressure terms have been included. Under thermodynamic non-equilibrium conditions, Ar, CO, and O were found to be the dominant neutral species, CO4
+ the dominant positive ion, and O- and electrons the dominant negatively charged species.
The Characteristics of Polysilicon Oxide Grown on Amorphous Silicon Deposited from Disilane
Authors: Yeou Ming Lin Yeou Ming Lin , Tan Fu Lei Tan Fu Lei
Published: October 2002

The characteristics of polysilicon oxide (polyoxide) grown on amorphous silicon deposited from disilane as the silicon source are reported on. The rate of amorphous silicon deposition from disilane is comparable to that of polysilicon deposition from silane. Moreover, the obtained polyoxide has the desirable electrical characteristics of lower leakage current and higher breakdown field than those of polyoxide grown on polysilicon deposition from silane, urgently needed for nonvolatile memory application. At the same time, the grown polysilicon oxides have lower electron trapping rates and larger charge-to-breakdown (Q
bd), both attributable to their smoother polyoxide/polysilicon-1 interface than those of polyoxides grown on polysilicon deposition from silane.
Microstructural Optimization of Low-Temperature-Fired Ni–Zn–Cu Ferrites Using Calcination
Authors: Byeon Soon Cheon , Je Hae June , Kug Sun Hong Kug Sun Hong
Published: October 2002

The purpose of this work was to examine the effect of low-temperature sintering on the microstructural optimization of Ni–Zn–Cu ferrites. This behavior was evaluated with respect to calcination temperature. The amount of unreacted hematite produced during calcination was quantitatively analyzed using a new calibration curve obtained using X-ray powder diffractometry. The formation of a spinel phase was initiated above 550° C, and completed above 850° C. The microstructural optimization of Ni–Zn–Cu ferrite samples was achieved using powder calcined at 750° C, and these specimens showed a maximum permeability of 700. A variation in microstructure with the change of the calcination temperature is ascribed as the cause of this optimization. Two mechanisms for the optimization are also suggested. One is the formation of hard agglomerates at high calcination temperatures and the second is the inhibition of grain growth due to the residual hematite in powders calcined at low temperatures. Microstructural optimization was achieved through a trade-off between these two mechanisms.
Single-Frequency Injection Seeded Pulsed Ti:Al2O3 Ring Laser
Authors: Ogino Atsushi , Masayuki Katsuragawa Masayuki Katsuragawa , Kohzo Hakuta Kohzo Hakuta
Published: October 2002

A pulsed Ti:Al2O3 ring laser system injection seeded with a laser diode is presented. The Ti:Al2O3 laser generates single-frequency output with Fourier-limit temporal profiles. Temporal characteristics are systematically investigated, leading to a fact that the temporal stability of pulsed output is essentially determined by the fluctuation of the pump YAG laser output.
Numerical Prediction of the Etched Profile in Pyrolytic Laser Etching of Silicon and Gallium Arsenide
Authors: Wee Teng-Soon , Yong-Feng Lu Yong-Feng Lu , Wai-Kin Chim Wai-Kin Chim
Published: October 2002

A quasi-static two-dimensional heat conduction analysis is used to deduce the geometrical profile of a cavity pyrolytically etched on isotropic silicon and GaAs substrates by a stationary CW argon ion laser with a Gaussian intensity profile. The nonlinear problem is solved using the numerical finite element method. Starting with a substrate having a flat surface, the numerical routine progressively removes regions of the substrate to model the actual etching action. Multiple reflections of the laser beam in the etched cavity are also modeled assuming that the substrate surface is perfectly diffused. Laser etching experiments performed on a silicon substrate in a CCl4 gas ambient are used to verify the numerical routine. Comparison between the experimental and the numerical results indicates that the desorption of SiCl2 radicals is probably responsible for the final etched profile obtained. Numerical results are also compared with the experimental data obtained from previous works carried out on a GaAs substrate.
Structure and Photoelectric Properties of Copper-phthalocyanine/Lead Telluride Multilayer Thin Film Prepared by Laser Ablation and Thermal Evaporation
Authors: Lee Heayeon , Tabata Hitoshi , Takuya Matsumoto Takuya Matsumoto , Tomoji Kawai Tomoji Kawai
Published: October 2002

We prepared highly crystallized copper-phthalocyanine (CuPc)/lead telluride (PbTe) hetero-multilayer structures for the first time. The crystallized CuPc (α-form) and PbTe films are formed by thermal evaporation and laser ablation techniques, respectively. Both films are grown at 300° C, which is a lower growth temperature than that of other transition metal chalcogenide films. We observed the transverse current–voltage characteristics of CuPc/Si, PbTe/Si and PbTe/CuPc/Si junctions in the dark and under illumination. The PbTe/CuPc/Si junction exhibits a strong photovoltaic response with quantum efficiency of 15.4% and a power conversion efficiency of 3.46×10-2. The photocarrier is generated in the CuPc layer and the carriers are separated by the steep incline of the potential near the CuPc/PbTe interface. The CuPc/PbTe multilayers exhibit a high level of photoconductivity in the in-plane direction.
Reduction of Double Positioning Twinning in 3C-SiC Grown on α-SiC Substrates
Authors: Katsushi Nishino Katsushi Nishino , Tsunenobu Kimoto Tsunenobu Kimoto , Hiroyuki Matsunami Hiroyuki Matsunami
Published: October 2002

Crystal growth of cubic silicon carbide (3C-SiC) on α-SiC (6H- and 15R-SiC) substrates was carried out by chemical vapor deposition. 3C-SiC (111) can be epitaxially grown on 6H- and 15R-SiC (0001) substrates. Due to the peculiar stacking sequence of α-SiC, double positioning boundaries (DPBs) appear in the 3C-SiC (111) layers. The layer on 15R-SiC has far fewer DPBs than that on 6H-SiC. Successive etching of a thick grown layer and successive observation of a growing surface revealed that the DPBs decreased anisotropically as crystal growth proceeded. Facets formed along DPBs were analyzed by atomic force microscopy. The angles between the facets and the grown surface (111) varied with the crystallographic orientation of DPBs. DPBs may decrease due to the lateral growth from the facets. The difference in the velocities of the anisotropic decrease in DPBs was discussed on the basis of the number of dangling bonds on the facets.
Dielectric Relaxation Phenomena of a Liquid Crystal Monolayer at the Air-Water Interface
Authors: Majima Yutaka , Yoko Sato Yoko Sato , Mitsumasa Iwamoto Mitsumasa Iwamoto
Published: October 2002

The dielectric relaxation phenomena of a 4-cyano-4′-5-alkyl-biphenyl (5CB) monolayer at the air-water interface have been investigated. Maxwell displacement current (MDC; I)-area per molecule (:A) isotherms and surface pressure (:π)–A isotherms were measured at several monolayer compression ratios. The dipole moment (:m

Z
)–A isotherm and dm

Z
/ dt–A isotherm were evaluated from the I–A isotherm. It was found that in the range (range 2) where the surface pressure is almost zero, m

Z
tends to increase at wide A as the compression ratio becomes small, whereas m

Z
–A isotherms coincide for various compression ratios in the range where the surface pressure increases by monolayer compression. These results indicate that the compression process of a 5CB monolayer in range 2 is a non-equilibrium process. Relaxation time (:τ)–A isotherm and dipole moment at equilibrium state (:m

Z eq)–A isotherm were evaluated for the first time using the equation d(m

Z
–m

Z eq)/ dt=-(m

Z
–m

Z eq)/τ, which represents the dielectric relaxation process.
Wall and Temperature Effects on Electrostatic Oscillations of Spheroidal Non-neutral Electron Plasmas in the Multi-Ring Electrode Trap
Authors: Hiroyuki Higaki Hiroyuki Higaki , Akihiro Mohri Akihiro Mohri
Published: October 2002

Electrostatic oscillations of spheroidal non-neutral electron plasmas are experimentally investigated with the multiring electrode trap which provides an electrostatic quadrupole potential with a long axial extent and enables confinement of plasmas with large aspect ratios. The frequencies of axial modes l = 2 and 3 of trapped plasmoids shifts upwards from those predicted by Dubin's cold plasma theory for the free boundary case, mainly due to the image charges induced on the conducting electrodes. These frequencies continue to increase as the plasma temperature is increased from 0.03 eV to 1.5 eV by rf heating. This temperature dependence can be interpreted as a change in the dielectric tensor caused by the temperature increase.
A Novel Graphical Analysis Method for Double Crystal X-Ray Diffraction Measurements of Strained Layer Superlattices Grown on (100) Substrate
Authors: Kiichi Nakashima Kiichi Nakashima , Hideo Sugiura Hideo Sugiura
Published: October 2002

A novel graphical plot analysis method for double crystal X-ray diffraction measurements is applicable to cubic crystal epilayers grown on (100) substrate. In this method, we introduce a new term: the `difference of the virtual lattice constant, ΔA'. The ΔA values can be obtained by converting the angular difference between the relevant peak and a reference peak. By plotting ΔA values as a function of (k
2+l
2)/h
2, parallel and perpendicular lattice constants can be easily analyzed for any sample with arbitrary relaxation rate. This advantage also reduces estimation error. This novel method and its advantages are experimentally demonstrated using InAsP/InGaAsP SLS samples.
A Study on the Radiation Hardness of Flash Cell with Horn-Shaped Floating-Gate
Authors: Huang Tiao-yuan , Jong Fuh-Cheng , Chao Tien-Sheng , Lin Horng-Chih , Leu Len-Yi , Young Konrad , Lin Chen-Hsi , Chiu Kuang Y.
Published: October 2002

The effects of radiation on the characteristics of split-gate electrical erasable programmable read only memory (EEPROM)/flash cells with recently-proposed horn-shaped floating gates are studied in terms of cell read current, data retention, cycling endurance, program/erase efficiency, threshold voltage and junction leakage. Our results show that the cells appear to survive after 1 Mrad (Si) Co60 irradiation. Moreover, the after-irradiation cell read current actually increases in the “erase” (i.e., low-threshold voltage, high-conducting) state (i.e., improves), albeit the cell read current also increases in the “program” (i.e., high-threshold voltage, low-conducting) state (i.e., a degradation). Our results also show that, despite an improvement in the initial read current in the “erase” state immediately after radiation, the write/erase cycling endurance of the flash cells is significantly impeded after irradiation, due to a much faster “window closure” rate in the “erase” state, although the cell read current is found to remain relatively stable in the “program” state after cycling.