bluuebunny/crossref_metadata_2025 huggingface dataset:
SPIN-DEPENDENT QUANTUM SIZE EFFECTS IN THE ELECTRON REFLECTIVITY OF ULTRATHIN FERROMAGNETIC CRYSTALS
Authors: ZDYB R. , BAUER E.
Published: October 2002

We have studied the spin-dependent quantum size effects in the reflection of 0–20 eV electrons from 2–10-ML-thick Fe microcrystals grown in situ on a W(110) surface in a spin-polarized low energy electron microscope. The goal is to obtain a better understanding of the magnetic ("asymmetry") image contrast and of the limits of spin polarization devices based on the quantum size contrast. The contrast is interpreted in terms of the band structure and of the spin-dependent inelastic mean free path. For the figure of merit of spin polarization devices, an upper limit of 5 × 10-2 is obtained.
INVESTIGATION OF THE ELECTROCHEMICAL BEHAVIOR OF HEAT-TREATED CARBON BLACKS AND Pt/C CATALYSTS
Authors: HUANG C. D. , XIONG Z. T. , LIN J. Y. , TAN K. L.
Published: October 2002

In this paper we report the electrochemical behavior of heat-treated carbon blacks and Pt/C catalysts. Cyclic voltammetry indicates that the heat-treated carbon black as catalyst support does not improve the Pt/C catalyst's activity for methanol oxidation. An XPS study of a Pt-loaded carbon black indicates that the amounts of oxidized platinum and oxygen-functional groups on catalysts are decreased when the platinum particles are deposited on the heat-treated carbon surface. These changes in the surface and crystalline structural properties of carbon materials lead to the catalytic activity change in methanol electro-oxidation.
A STUDY OF THE MUTUAL INFLUENCE OF Cs AND S ON Si(100)-(2 × 1) SURFACES
Authors: PAPAGEORGOPOULOS A. C.
Published: October 2002

In this work we study the adsorption of Cs on S-covered Si(100)-(2 × 1) and Si(100)-(1 × 1) surfaces, as well as the adsorption of S on Cs-covered Si(100)-(2 × 1). The experiment was performed in an ultrahigh vacuum (UHV) chamber with low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and work function (WF) measurements. Predeposited S increases the binding energy and the maximum amount of Cs that can be deposited on the surface. The presence of S inhibits the pattern of the characteristic WF curve of Cs on clean Si(100)-(2 × 1), i.e. an initial decrease to a minimum value, Φmin, followed by an increase toward the value Φmax of metallic Cs. The WF, instead, decreases to a value close to that of saturated Cs on clean Si(100)-(2 × 1), where it forms a plateau. This is characteristic of the covalent bonding of Cs with the semiconductor substrate. Independently of the sequence of Cs and S deposition, (a) the transition Si(100)-(2 × 1) → Si(100)-(1 × 1) occurs when ΘS > 0.5 ML, and (b) the sites of Cs and S remain the same, with the Cs atoms residing between the S atoms. Heating of the S/Cs/Si composite surfaces to ~ 650 K causes a reorganization of the Cs and S adatoms in a tendency to form a Cs–S complex. The issue of site preference for Cs and S adatoms has been discussed in detail in the structural models provided.
Use of Deviations of Purchasing Power Parity and Interest Rate Parity to Clarify the 1997 Asian Financial Crisis
Authors: Hung Mao-Wei , Jan Yin-Ching
Published: October 2002

This study is an attempt to examine whether the deviations of purchasing power parity and uncover interest rate parity Granger-cause the 1997 Asian financial crisis by using vector autoregression and Granger causality tests. The results show that the purchasing power parity and uncover interest rate parity do not hold for most Asian markets. We find weak evidence to support that the deviations of purchasing power parity and uncover interest rate parity have the power to explicate the origin of the financial crisis.
PRESCRIBING A FOURTH ORDER CONFORMAL INVARIANT ON THE STANDARD SPHERE — PART I: A PERTURBATION RESULT
Authors: DJADLI ZINDINE , MALCHIODI ANDREA , AHMEDOU MOHAMEDEN OULD
Published: October 2002

In this paper we study some fourth order elliptic equation involving the critical Sobolev exponent, related to the prescription of a fourth order conformal invariant on the standard sphere. We use a topological method to prove the existence of at least a solution when the function to be prescribed is close to a constant and a finite dimensional map associated to it has non-zero degree
HARDY-SOBOLEV INEQUALITY IN H1(Ω) AND ITS APPLICATIONS
Authors: ADIMURTHI
Published: October 2002

In this article, we have determined the remainder term for Hardy–Sobolev inequality in H1(Ω) for Ω a bounded smooth domain and studied the existence, non existence and blow up of first eigen value and eigen function for the corresponding Hardy–Sobolev operator with Neumann boundary condition.
NON-RADIAL GROUND STATES FOR THE HÉNON EQUATION
Authors: SMETS DIDIER , WILLEM MICHEL , SU JIABAO
Published: October 2002

We analyse symmetry breaking for ground states of the Hénon equation [7] in a ball. Asymptotic estimates of the transition are also given when p is close to either 2 or 2*.
EARLY DETECTION AND VISUALIZATION OF BREAST TUMOR WITH THERMOGRAM AND NEURAL NETWORK
Authors: FOK S. C. , NG E. Y. K. , TAI K.
Published: October 2002

Although mammography is still the benchmark technique for breast cancer detection, many advantages of thermography make it a suitable adjunct tool for early detection. This paper describes the development of a computer-aided system for use together with thermography to assist in the detection and visualization/analysis of breast tumors. The system consists of a detection module for predicting the presence of tumors from thermograms, and a visualization module for generating the 3-D volumetric geometry of the suspected tumor inside the breast based on the 2-D thermogram. Detection is achieved through an artificial neural network taking the thermogram image as input, while the visualization is obtained by generating the 3-D model of the breast that produces a matching thermal image as the thermogram under a 3-D finite element analysis. A study with 200 subjects indicate that the detection sensitivity was good but the specificity was poor, but the reverse performance result was true for another back-propagation neural network which used physiological data instead of thermograms as input. This suggests that overall prediction capability can be improved by appropriate combination of the two results.
Elimination of Fabry-Perot Effect in 4×4 Propagation Matrix Method and Its Application to Liquid Crystal Displays
Authors: Hiap Liew Ong Hiap Liew Ong
Published: October 2002

In the conventional 4×4 wave propagation matrix method, Fabry-Perot effects occur for monochromatic light because of the inherent multiple reflections at the interfaces. However, Fabry-Perot effects are not present in the usual liquid crystal device employing an incoherent light source. We present a simple method to eliminate the Fabry-Perot effects in the 4×4 propagation matrix method. The method gives the exact optical field corresponding to a single reflection at the interfaces. The results are applied to modeling the electrooptics of liquid crystal displays without the Fabry-Perot (FB) effects.
Sensitive Detection of Probing Electron Transport and Magnetic Field Structure in Toroidal Plasma Configuration
Authors: Sakurai Shinji , Noriyasu Ohno Noriyasu Ohno , Shuichi Takamura Shuichi Takamura
Published: October 2002

Novel diagnostic instrumentation for imaging test electron transport in a small tokamak has been developed by using the following techniques: electron beam probing with scanned fluorescent rod and boxcar image integration with repetitive tokamak discharges. In order to detect the electron beam not in vacuum but in a low-temperature plasma, the fluorescence from a phosphor with long fluorescent decay time is discriminated from plasma radiation by taking fluorescent images after each discharge shot. Disturbed magnetic field in a simple torus has been sensitively detected by the distortion of electron orbits. A modification of electron beam transport in a low-temperature tokamak plasma has been detected with high spatial resolution for a slight change in the external magnetic field.
Development of Bolt-Clamped Langevin-Type Transducer with High Mechanical Quality Factor for Excitation of Large Torsional Vibration
Authors: Adachi Kazunari , Yuji Konno Yuji Konno , Shingo Masaki Shingo Masaki
Published: October 2002

We have identified a crucial point for realization of a high mechanical quality factor (Q) of a bolt-clamped Langevin-type transducer used to excite large torsional vibrations of a cylindrical system. A sufficient margin of the static bearing stress over the vibratory shearing one at the interface between the components has been found necessary for a high Q as a result of some numerical simulations and experiments for two models of the transducers. A hollow cylindrical shape of the transducer is seen to have a great advantage in this respect.
Measuring Particle Size Distribution by Digital Image Processing with Inverse Fourier-Bessel Transformation
Authors: Momota Masahiro , Miike Hidetoshi , Hashimoto Hajime
Published: October 2002

An analytical approach based on digital image processing is proposed for measuring the size distribution of circular particles. From an analogy with the light diffraction pattern of a circular aperture, a reduced spectrum of the particles' image can be obtained using a two-dimensional fast Fourier transformation. The reduced spectrum, which is equivalent to the diffraction pattern, is analyzed using the theory of inverse light scattering to evaluate the size distribution of the particles. The usefulness of this method is confirmed not only in binary images but also in gray-scale images created by computer simulation.
Induced Photovoltage Effect on Barrier Height of Au/GaAs from Photoreflectance Spectroscopy
Authors: Dong-Po Wang Dong-Po Wang , Tsong-Lin Shen Tsong-Lin Shen
Published: October 2002

Barrier height of Au/GaAs was measured at various temperatures from Franz-Keldysh oscillations (FKO) of photoreflectance spectroscopy. The temperature dependence of the measured barrier height of Au/GaAs was explained by the theory of Hecht [Phys. Rev. B 41 (1990) 7918]. The photoinduced voltage depends on the temperature and cannot be neglected in the low-temperature range.
Diamagnetic Susceptibility of Donors in Silicon
Authors: Vudan Rao Hari Krishna Vudan Rao Hari Krishna
Published: October 2002

Diamagnetic susceptibility of shallow donors in Si is computed incorporating the multivalley conduction band structure and the spheroidal energy surfaces. Our result is compared with an earlier estimate of Kohn on the one-valley model [Solid State Phys. 5 (1955) 2573].
Relationship between Tc and Cu Valence and Bond Lengths of Cu–Cu and Cu–O for Ba2-xEu1+xCu3O7-y Compounds
Authors: Ohshima Shigetoshi , Tanaka Nobuo , Shiro Kambe Shiro Kambe , Katsuro Okuyama Katsuro Okuyama
Published: October 2002

The relationship between superconducting transition temperature, T
c, and Cu valence as well as Cu–Cu and Cu–O bond lengths for Ba2-
x

Eu1+
x

Cu3O7-δ and Ba2EuCu3O7-
y

compounds as functions of x and y was investigated. For Ba2-
x

Eu1+
x

Cu3O7-δ compounds, Cu(2) valences decreased from 2.3 to 2.2 as x varied from 0 to 0.5, and Cu(1)–Cu(2) and Cu(2)–O(3) bond lengths were almost constant for 0<x<0.3, but decreased for x>0.3. For Ba2EuCu3O7-
y

compounds, the Cu(2) valences decreased from 2.3 to 1.9 as y varied from 0.14 to 0.6, and Cu(1)–Cu(2) and Cu(2)–O(3) bond lengths increased with increasing y. T
c of Ba2-
x

Eu1+
x

Cu3O7-δ compounds decreased rapidly with increasing x; on the other hand, that of Ba2EuCu3O7-
y

compounds decreased gradually with increasing y. The behavior of T
c for Ba2-
x

Eu1+
x

Cu3O7-δ and Ba2EuCu3O7-
y

compounds cannot be accounted for by the change of Cu(2) average valence. The change of T
c depended on the bond length of Cu(2)–O(3), and the maximum T
c for these compounds was obtained at the optimum bond length of Cu(2)–O(3).
Reflection Mode Polymer-Dispersed Liquid Crystal Light Valve
Authors: Takizawa Kuniharu , Kikuchi Hiroshi , Fujikake Hideo , Namikawa Yasuo , Tada Kohji
Published: October 2002

This paper describes the procedure for fabrication of a reflection-mode polymer-dispersed liquid crystal light valve (PDLCLV) consisting of a polymer-dispersed liquid crystal film, a diamondlike carbon film, a dielectric mirror, a Bi12SiO20 photoconductive crystal plate, and transparent electrode films. The many advantages of the PDLCLV include the lack of need for polarizers, high optical transmittance, high-speed response and ease of fabrication. The performance of the device as evaluated experimentally is as follows: optical transmittance 72%; extinction ratio 178/1; limiting resolution 34 lp/mm; and rise/decay times 14/15 ms. These values are suitable for the image converter of an optically addressed projection display. It has also been found that the resolution increases as the frequency of the AC voltage driving the PDLCLV decreases.
Field-Induced Surface Carrier Density in Pt/SrTiO3/p-Si Metal-Insulator-Semiconductor Structure in Excess of 3×1013cm-2
Authors: Masahiro Taga Masahiro Taga , Takeshi Kobayashi Takeshi Kobayashi
Published: October 2002

Highly polarisable (100)SrTiO3 (STO) epitaxial films with permittivity of 313ε
0 were grown on (111)Pt/(100)MgO substrates by reactive rf magnetron sputtering. By contacting a p-Si tip onto the STO surface and using a Pt underlying layer as the base electrode, inverted metal-insulator-semiconductor (MIS) structures were prepared. The field-induced surface carrier density in Si reached as high as 3.5×1013 cm-2 for 8 V applied voltage, being ∼50 times higher than that of the metal/SiO2/Si MOS diode. On the other hand, when STO was directly grown on the Si substrate, field-effect modulation in an ordinary MIS diode was significantly degraded due to the deteriorated interface.
Scanning Tunneling Microscopy of Initial Stages of GaAs Heteroepitaxy on Lattice-Mismatched Substrates
Authors: Ohkouchi Shunsuke , Ichiro Tanaka Ichiro Tanaka , Nobuyuki Ikoma Nobuyuki Ikoma
Published: October 2002

The island-formation processes of GaAs heteroepitaxial growth on InP (lattice constant ( a) is 3.7% larger than that of GaAs) and InAs ( a is 7.2% larger than that of GaAs) surfaces were investigated using a scanning tunneling microscope (STM) multichamber system equipped with a molecular beam epitaxy facility. In the case of GaAs/InP heteroepitaxial growth, two-dimensional (2D) growth was observed when less than 2.0 monolayers (MLs) of GaAs were deposited on the InP surfaces. On the other hand, three-dimensional (3D) growth was confirmed for more than 2.0 ML GaAs deposition. In the case of GaAs/InAs heteroepitaxial growth, the same transition from 2D to 3D island growth occurred when more than 0.75 ML of GaAs was deposited.
Discharge Current Dependences of Laser Parameters of Regular and Sequence Band Transitions of CO2
Authors: Shimizu Fumiko O. , Fujisawa Tadahito , Takahashi Hiroki , Minoh Tadashi Hirata
Published: October 2002

From gain measurement, laser parameters such as rotational temperature, inversion densities, absolute population densities, and excitation and deexcitation rates are determined as functions of the discharge current. The rotational temperature is well defined in both bands and is very close to the gas translational temperature. It is found by rate equation analysis in an ordinary discharge condition, the rates of excitation to the lower laser levels are much larger than those to the upper laser levels. The deexcitation rates of the lower laser levels are evaluated and found to be the most important processes in maintaining the laser gain in both bands.
Evaluation Techniques for Austenitic Stainless Steels through Tensile Deformation by Analyzing Ultrasonic Pulse Waves in the Frequency Domain
Authors: Katsuhiko Honjoh Katsuhiko Honjoh
Published: October 2002

This paper describes a technique for evaluating the structural variations that tensile deformation induces in austenitic stainless steels. By using fast Fourier transform processing to analyze the spectral distributions of ultrasonic pulse waveforms, I quantitatively investigate the relationship between the spectral distributions of pulse echoes and the internal structures of SUS304 and SUS310 stainless steel. The spectral distributions are obtained by the zero-crossing method and the relationship between the spectral distributions and ultrasonic attenuation caused by grain scattering are discussed. With increasing elongation, the spectral peak frequency andQvalue increase for SUS304 steel and are nearly constant for SUS310 steel. The results for SUS304 steel are attributed to martensite transformation, which results in smaller grain size and a corresponding reduction of the attenuation coefficient due to the ultrasonic scatterings.
Laser Cooling of Ca+ Ions and Observation of Collision Effects
Authors: Urabe Shinji , Hayasaka Kazuhiro , Watanabe Masayoshi , Hidetsuka Imajo Hidetsuka Imajo , Ryuzo Ohmukai Ryuzo Ohmukai
Published: October 2002

This paper describes our recent experimental results on trapping and laser cooling of Ca+ ions. The measurement of the characteristics of laser-cooled Ca+ ions in an rf quadrupole ion trap, such as the fluorescence line shape and phase transition, is described. Observation of two types of collision-induced “quantum jumps” of a Ca+ ion in a background gas of H2 or air is also described. Since the rate of the collision-induced jumps is very high for Ca+, it is necessary to achieve an extremely high vacuum condition for frequency standard applications.
Electric Field Effect on ZnSe Thin Films Prepared by Metalorganic Chemical Vapor Deposition
Authors: Hsu Chin Tsar , Su Yan Kuin , Tien Shou Wu Tien Shou Wu , Meiso Yokoyama Meiso Yokoyama
Published: October 2002

Epitaxial layers of ZnSe on ITO/glass (indium-tin-oxide-coated glass) were grown by low-pressure metal-organic chemical vapor deposition. Absorption-edge shifts produced by an applied electric field (Franz-Keldysh) in ZnSe thin films have been studied. As a result, the absorption edge is shifted by about 30 meV toward longer wavelengths.
Second-Harmonic Generation of GaAlAs Diode Laser by Enhanced Doubling in LiIO3 Crystal
Authors: Oh Cha Hwan , Kim Sang Gee , Song Yang Sup , Kim Young Bum Kim
Published: October 2002

The second harmonic of the 794 nm output of a GaAlAs diode laser is generated in a LiIO3 crystal in an external ring enhancement cavity. The dependence of the second-harmonic power on the input power has been measured and compared with the theory. The second-harmonic power of 7.4 µ W at 397 nm has been obtained with an input fundamental power of 28 mW by using an 8-mm-long LiIO3 crystal.
Unique Polarization Caused by Frequency Locking between σ and π Modes in a Transverse Zeeman Laser
Authors: Hiroshi Yasuda Hiroshi Yasuda , Masaru Mamiya Masaru Mamiya , Yuichi Ishida Yuichi Ishida , Tatehisa Ohta Tatehisa Ohta , Takumi Ichinose Takumi Ichinose
Published: October 2002

Experiments on polarization characteristics of a single-longitudinal-mode internal-mirror 633 nm He-Ne laser with very small cavity anisotropy have been performed. A polarization rotating phenomenon from the σ to the π mode direction and to directions other than the σ or π direction by varying magnetic field strength (2.7 to 9.0 mT) has been observed. Here, polarization is independent of the natural axis, and this rotated polarization switches alternately between adjacent longitudinal modes with respect to the σ mode axis. These alternating polarizations are not perpendicular to each other. The rotation and the switching of polarization are unique. Furthermore, we have conducted theoretical analyses on polarization characteristics under the strong coupling condition of σ and π modes based on the theory of the transverse Zeeman laser. Then it is concluded that this unique polarization rotation is caused by the frequency locking of the two modes.
Hollow Glass Waveguides for Mid-Infrared Light Transmission
Authors: Saito Mitsunori , Baba Nobuyoshi , Sawanobori Naruhito , Mitsunobu Miyagi Mitsunobu Miyagi
Published: October 2002

Hollow SiO2- and GeO2-based glass waveguides were fabricated for mid-infrared light transmission. By changing the percentage of Si or Ge atoms in the glass systems, we can control the low-loss wavelength range which appears near the resonance absorption peak. Efficient transmission was demonstrated in the 7–12 µ m wavelength range by using hollow waveguides made of pure- SiO2, (SiO2)63(TiO2)16(Na2O)21, and (GeO2)80(Ta2O5)10(K2O)10glasses. For a CO2laser of 10.6 µ m wavelength, the lowest loss of 1.1 dB/m was attained with the waveguide of 1 mm diameter.
The Role of the Hydrogen Maser for Frequency Transfer from Cesium Fountains
Authors: Derek Morris Derek Morris , Robert James Douglas Robert James Douglas , Jean-Simon Boulanger Jean-Simon Boulanger
Published: October 2002

Primary cesium frequency standards realized as cesium fountains offer the prospect of frequency accuracy in the 10-15 range, or better. Active hydrogen masers are good candidates for the source of a local time scale to disseminate frequency at this level of accuracy after calibration by a cesium fountain that operates intermittently. We develop a procedure for evaluating the frequency uncertainty associated with the resulting calibrated time scale. We apply the procedure to the expected performance of masers and cesium fountains, and find that current hydrogen masers can be used to deliver frequency uncertainties of less than 10-15, and might be used to approach 10-16. The procedure is appropriate to use, for example, when reporting uncertainties for cesium fountain average frequencies delivered to assist the International Bureau of Weights and Measures (BIPM) in steering International Atomic Time (TAI).
Photocapacitance Measurement on Intentionally Undoped n-Type Ga0.9Al0.1As Grown by Stoichiometry Control Method
Authors: Nishizawa Jun-ichi , Motozawa Mitsutake , Oyama Yutaka , Dezaki Kazushi , Fujishiro Hiroyuki , Suto Ken
Published: October 2002

Photocapacitance (PHCAP) measurements have been performed for intentionally undopedn-type Ga0.9Al0.1As grown by liquid-phase epitaxy (LPE) with arsenic vapor pressure controlled in the range from 0.016 to 51 Torr.Eν+0.47 eV andEν+0.7–0.8 eV deep levels are found to be dominant. The density of theEν+0.47 eV deep levels increases with increasing arsenic vapor pressure in proportion toPAs1/2. TheEν+0.47 eV deep levels are considered to be associated with arsenic interstitial atoms.
Hole Accumulation in SiO2/Si3N4/SiO2 Capacitors Prior to Dielectric Breakdown
Authors: Nishioka Masao Sawachi
Published: October 2002

Supporting evidence for the time-dependent dielectric breakdown (TDDB) of an SiO2/Si3N4/SiO2 (ONO) capacitor due to hole accumulation has been obtained: 1) the gate current of the ONO capacitor during constant voltage stress continues to increase prior to dielectric breakdown, 2) after stress with a positive gate bias, the midgap voltage shifts toward the negative voltage direction, and 3) the time-to-breakdown is inversely proportional to the gate current. These suggest that holes injected from the anode accumulate in the vicinity of the Si3N4/SiO2 interface near the cathode, which cause the breakdown of ONO capacitors.
Oxidation of Ultrathin SiGe Layer on Si(001): Evidence for Inward Movement of Ge
Authors: Prabhakaran Kuniyil , Nishioka Takashi , Sumitomo Koji , Yoshihiro Kobayashi Yoshihiro Kobayashi , Toshio Ogino Toshio Ogino
Published: October 2002

An ultrathin SiGe layer prepared by growing Ge epitaxially on Si(001) was oxidized and investigated using X-ray photoelectron spectroscopy (XPS) and medium energy ion scattering (MEIS). Growth at a substrate temperature 550° C leads to the formation of a mixed SiGe layer on Si(001). Oxidation of this sample at 250° C forms predominantly SiO2 and a small amount of GeO. MEIS shows evidence for the diffusion of Ge inwards by 2–3 Å and of Si towards the surface resulting in the pile up of Ge at the SiO2/SiGe interface. On annealing the oxidized surface at 360° C, oxygen leaves the Ge sites and form SiO2 thereby reducing GeO to elemental Ge. The concentration of oxygen remains the same through out this reaction.
Voltage versus Flux Relation of DC Superconducting Quantum Interference Device Using Three Josephson Junctions
Authors: Keiji Enpuku Keiji Enpuku , Hideki Doi Hideki Doi
Published: October 2002

It has been shown that the voltage versus flux (V-Φ) relation of dc superconducting quantum interference devices (SQUIDs) operating at T=77 K is degraded considerably by thermal noise. Since degradation of modulation voltage in the V-Φ relation becomes more significant when inductance increases, a very restricted range of inductance exists which can be used at T=77 K. In order to reduce the degradation due to thermal noise and to enable the use of large inductances, a new SQUID using three Josephson junctions (3J-SQUID) is proposed. Numerical simulation shows that inductance of 3J-SQUID can be increased to twice as large as that of the conventional case without degrading modulation voltage. It is also shown that modulation voltage is highly improved by damping resistance parallel to inductance. As a result, we can expect to use inductances as large as L<500 pH if 3J-SQUID with damping resistance is employed. Large inductances available in 3J-SQUID will be useful in realizing efficient coupling of external magnetic field to the SQUID inductance.
Temperature Dependence of ESR Lines Related to Phosphorus in Silicon
Authors: Morooka Masami , Tokita Masahiko , Tomohiko Kato Tomohiko Kato , Ichiro Tsurumi Ichiro Tsurumi
Published: October 2002

Temperature dependence of ESR in a silicon crystal containing 1.3×1017 phosphorus atoms/cm3 has been investigated at 4–40 K. The ESR signals depend strongly on the specimen temperature. Typical hyperfine structures of the phosphorus ground state were found in the low-temperature region. The hyperfine lines vanished at 20 K and a single line corresponding to the first excited state of phosphorus was observed in the high-temperature region. The amplitudes of the hyperfine lines and the single line show sharp maxima at 11 K and 30 K, respectively. The change of the signal amplitudes is due to the temperature dependence of spin relaxation time. The change of the linewidth for the hyperfine lines can be explained by the temperature dependence of spin relaxation time, and that for the single line is considered to be caused by motional narrowing.
Optical Properties of Ion-Implanted Si layeres Studied by Spectroscopic Ellipsometry
Authors: Adachi Sadao , Takashi Matsumura Takashi Matsumura , Takahiro Suzuki Takahiro Suzuki
Published: October 2002

The damage produced in crystalline Si by As+ion implantation at 80 keV has been studied using spectroscopic ellipsometry (SE). A linear regression analysis (LRA) and a Bruggeman effective-medium approximation (EMA) require a multilayer-structure (four-phase) model: ambient (air), first and second damaged Si layers and Si substrate. Each damaged layer consists of volume fractions of crystalline and amorphous Si and voids. The LRA-EMA analysis suggests that the buried fully amorphized layer with a partially amorphized overlayer begins to form around ∼9×1014cm-2dose. Results on the isothermal annealing have also been presented. SE has been proven to be an easy, fast and nondestructive technique which can be used to assess important ion-implantation parameters.
Influence of Crystal Thermal History on Surface Recombination Lifetime at Elevated Temperatures in Magnetic-Field-Applied Czochralski Silicon
Authors: Daio Hiroshi , Andrzej Buczkowski Andrzej Buczkowski , Fumio Shimura Fumio Shimura
Published: October 2002

Recombination lifetime for wafers prepared from two magnetic-field-applied Czochralski (MCZ) silicon crystals with a different body length was analyzed using a laser/microwave photoconductance (LM-PC) technique with an algorithm to separate the surface and bulk components. It has been shown that the surface lifetime dominantly contributes to the dependence of the effective lifetime at elevated temperatures on the crystal length. It is interpreted that the surface lifetime is strongly affected by the grown-in defects which depend on the thermal history, or the crystal length of the silicon crystals.
Novel Switching with Gray Scale in Surface-Stabilized Ferroelectric Liquid Crystal Devices
Authors: Koden Mitsuhiro , Akira Tagawa Akira Tagawa , Tomio Wada Tomio Wada
Published: October 2002

The apparent tilt angle in surface-stabilized ferroelectric liquid crystals (SSFLCs) is dependent on the applied electric field for monostable and bistable devices. This behavior is attributed to the fact that the director profile of molecules in SSFLC cells is changed by an interaction between spontaneous polarization and the electric field. Based on this behavior, the transmission in SSFLCs can be controlled by the applied voltage, resulting in a smooth voltage-transmission curve.
Characteristics of Grown-In Dislocations in Czochralski-Grown Benzophenone Single Crystals
Authors: Masaru Tachibana Masaru Tachibana , Qi Tang Qi Tang , Naoki Ide Naoki Ide , Kenichi Kojima Kenichi Kojima
Published: October 2002

Systematic studies of crystal growth of benzophenone by the Czochralski method and characterizations of dislocations in the grown crystals were performed. The dislocations introduced during the crystal growth were observed using X-ray topography. The characteristics of these dislocations were determined by an invisibility condition of dislocation images. Furthermore they were analyzed by a minimum energy criterion of preferred directions of dislocation lines. From these characterizations, a shorter Burgers vectorc[001] was found to be generated in crystals grown along directions of [001], [010] and [100]. Several longer Burgers vectors were also found to exist in spite of their higher dislocation energies. These characteristics of grown-in dislocations are discussed in relation to corresponding dislocation energy.
Low-Temperature Atmospheric-Pressure Chemical Vapor Deposition Using 2, 4, 6, 8-Tetramethylcyclotetrasiloxane and Ozone
Authors: Fujino Katsuhiro , Nishimoto Yuko , Noboru Tokumasu Noboru Tokumasu , Kazuo Maeda Kazuo Maeda
Published: October 2002

Tetramethylcyclotetrasiloxane (TMCTS) was studied as a possible silicon source for atmospheric-pressure chemical vapor deposition (CVD) using ozone chemistry. High-quality silicon dioxide films were produced at 400° C with a typical deposition rate of 100 nm/min. During the study, TMCTS was observed to have base material dependent characteristics which varied as a function of both deposition temperature and ozone concentration. The deposition rate vs deposition temperature relationship indicated that the film structure varies slightly as a function of the deposition temperature. Data collected for film shrinkage after annealing supported these structural changes. The typical as-deposited film stress was 2×109 dyn/cm2 (tensile). The step coverage varied from conformal to flow-shaped depending on the deposition temperature and ozone concentration. The results of this study show that TMCTS is a promising precursor for use in intermetal dielectric applications for ultra large-scale integration (ULSI) devices.
Plasma Etching Effect on Dangling Bonds and Nondiamond Components in Low- and High-Quality Diamond Films
Authors: Watanabe Ichiro , Katsuhiko Haruta Katsuhiko Haruta , Yoshikazu Shimamura Yoshikazu Shimamura
Published: October 2002

Two types of diamond film with low and high quality are synthesized from a mixture of alcohol and hydrogen using microwave plasma chemical vapor deposition. Both films exhibit ESR spectra which can be decomposed into two signals with a broad and a narrow linewidth. The low-quality film has a spin density almost one order of magnitude higher for both the broad and narrow components than the high-quality film. The spin density for both the components greatly decreases upon microwave-plasma etching using CF4–O2gas. From the changes in ESR and Raman spectra induced by plasma etching, it is considered that both nondiamond and diamond phase in the film contain both the broad and narrow components, and that the former phase contains higher density of narrow components compared with the latter phase.
Shock Compaction of an Acicular Iron-Alloy Powder to Produce a Nanocrystalline Magnet
Authors: Kondo Ken-ichi , Hisako Hirai Hisako Hirai , Hideaki Oda Hideaki Oda
Published: October 2002

A shock-compaction technique of an acicular magnetic iron-alloy powder was developed to produce a nanocrystalline magnet preserving its magnetic properties and acicular features. Although a precompacted disk of the powder had undesirable initial conditions which were a large porosity of 50% and a wide distribution of pore size, use of a double-plate flyer consisting of copper and aluminum made it possible to produce a good compact having a density 98% of the theoretical value, 6.2 GPa Vicker's microhardness, and maximum energy product of 15.1 kJ/m3. One-dimensional wave-propagation analysis implies effective compression at the initial stage suppressing the total thermal energy and the localization of heat in the vicinity of large pores. The method is discussed for improving the magnetic properties.
Layer Structure Reformation of Surface-Stabilized Ferroelectric Liquid Crystal Treated with Electric Field
Authors: Seishi Miura Seishi Miura , Munehiro Kimura Munehiro Kimura , Tadashi Akahane Tadashi Akahane
Published: October 2002

The smectic layer reformation caused by the electric field treatment (EFT) was studied in terms of X-ray diffraction profiles, electro optical (EO) response, polarization reversal current and transitional dielectric constant (TDC) measurement. From the X-ray diffraction study, it was found that the chevron layer structure was reformed to a quasi-bookshelf structure by applying a suitable amplitude of the EFT voltage. The structural reformation made the threshold characteristics of the EO steep. The shape of the polarization reversal current indicated that the surface molecular switching was delayed as the EFT voltage increased. Furthermore, from TDC measurement, it was found that the amplitude of the dielectric constant variation corresponding to FLC switching was decreased when the EFT voltage was high. These results were consistently examined on the basis of the consideration for the surface anchoring potential barrier.
Application of Ion Doping and Excimer Laser Annealing to Fabrication of Low-Temperature Polycrystalline Si Thin-Film Transistors
Authors: Kawachi Genshiro , Aoyama Takashi , Mimura Akio , Konishi Nobutake
Published: October 2002

Feasibility of the non-mass-separated ion implantation (ion doping) technique followed by excimer laser annealing for fabrication of low-temperature polycrystalline Si thin-film transistors (TFTs) is studied. High-speed doping, less than 10 s for formation of the source and drain of TFT, can be achieved by using a bucket-type ion source. Hydrogen ions incorporated in a non-mass-separated ion beam induce undesirable etching of Si films during implantation. To avoid this, He-diluted gas is used. The fabricated TFTs exhibit excellent characteristics comparable to those of TFTs fabricated conventionally. There is no instability due to contamination which may be introduced from a non-mass-separated ion beam. OFF-state characteristics of TFTs can be improved by increasing laser energy for impurity activation. However, also the avalanche-induced short channel effect is enhanced by increasing laser energy. Adjustment of laser energy is required to optimize the device characteristics. It is concluded that ion doping and excimer laser annealing techniques are promising solutions to problems plaguing poly-Si TFTs.
Free Radicals in an Inductively Coupled Etching Plasma
Authors: Hikosaka Yukinobu , Nakamura Moritaka , Sugai Hideo
Published: October 2002

A high-density (>1011 cm-3) CF4/H2 plasma was produced in an inductively coupled plasma (ICP) reactor where an external helical coil is wound around a quartz tube. Capacitive coupling from the coil to the plasma caused the release of a large number of impurities ( SiF4 and CO) from the warm quartz wall close to the coil. These impurities significantly deteriorate the etch selectivity of SiO2 to Si in the ICP reactor. Water cooling and a Faraday shield are effective to suppress the release of impurities. Neutral radicals CF3, CF2, CF and F were measured in addition to ionic species. The high-density high electron-temperature ICP causes the formation of a large number of F atoms and CF+ ions with fewer CF

x

radicals, in comparison to a low-density capacitively coupled plasma (CCP). H2 addition to the CF4 discharge drastically modifies the CF3 and CF2 densities in the ICP as well as in the CCP. The high etch rates and the low selectivity of SiO2 to Si obtained in the ICP were discussed taking account of the residence time and the dissociation time of reactive species in the etching reactor.
Effect Plasma Transport on Etched Profiles with Surface Topography in Diverging Field Electron Cyclotron Resonance Plasma
Authors: Fujiwara Nobuo , Maruyama Takahiro , Yoneda Masahiro , Tsukamoto Katsuhiro , Banjo Toshinobu
Published: October 2002

Recent studies of electron cyclotron resonance (ECR) plasma etching for fabricating fine patterns of less than a half-micron indicate a serious problem in the etched profiles caused by a charge build-up of the patterns. The relationships between the local pattern distortion and the plasma properties measured by the electrostatic probe are investigated. Lowering the electron temperature perpendicular to the surface normal is one of the most effective techniques for eliminating the local side etch. It is enhanced by setting the wafer at the lower magnetic field. As the large space charge bends the ion trajectories, the higher ion current density also enhances the local side etch. The distribution of plasma potential which accelerates the ions can reduce the local side etch in spite of the higher current density.
Photon-Stimulated Desorption Mechanism of Cl+Ions from Cl/Si(111) Surface
Authors: Takuya Yonezawa Takuya Yonezawa , Hiroshi Daimon Hiroshi Daimon , Kan Nakatsuji Kan Nakatsuji , Kazuyuki Sakamoto Kazuyuki Sakamoto , Shigemasa Suga Shigemasa Suga , Hidetoshi Namba Hidetoshi Namba , Toshiaki Ohta Toshiaki Ohta
Published: October 2002

Photon-stimulated desorption (PSD) of Cl+ions from a Cl/Si(111) surface was studied using synchrotron radiation. The kinetic energy distribution of Cl+ions in PSD agreed with our previous results of electron-stimulated desorption (ESD). The excitation energy threshold of Cl+desorption also agreed within the experimental error. Hence, the desorption mechanisms in both PSD and ESD were considered to be the same. We studied the excitation (photon) energy dependence of the Cl+yield more precisely than ESD to elucidate the excitation mechanism for ion desorption. We found that the lower threshold photon energy was 17eV. Comparison with the ultraviolet photoelectron spectroscopy (UPS) spectrum showed that this energy corresponded to the excitation from the Cl 3s state to the Fermi level. Hence, this PSD process was explained by the KF model, where the Cl 3s core hole was filled by electrons of the Cl-Si bond through the Auger-like process, and then Cl+ions desorbed by repulsive Coulomb force from the adjacent Si+.
Fine SiO2 Pattern Generation by Excimer Laser-Induced Modification of Polysiloxene-Based Thin Films
Authors: Okamoto Katsuhiko , Shinohara Masato , Seiichi Miyazaki Seiichi Miyazaki , Masataka Hirose Masataka Hirose
Published: October 2002

Polysiloxene-based thin films have been grown by the glow discharge of an Si2H6+O2 gas mixture at a substrate temperature of -110° C. Infrared absorption spectra have shown that the matrix is mainly composed of (–SiH2O–)

n

chains which are terminated with SiH3 and partly have Si–Si branches. The bonded hydrogen in the network is effused by ArF excimer laser irradiation, resulting in three-dimensional SiO2 network formation. The nonirradiated region is easily etched off by a 0.16% HF solution, while the etch rate of the irradiated region is extremely lowered. The fine SiO2 pattern is generated by the excimer laser irradiation through a metal stencil mask and subsequent etching of the nonirradiated region.
Transformation of Egg-White Glass into Partially Crystallized Glass Induced by Heat Treatment and Gamma-Ray Irradiation
Authors: Haruichi Kanaya Haruichi Kanaya , Tetsuaki Nishida Tetsuaki Nishida , Masakazu Ohara Masakazu Ohara , Kazuhiro Hara Kazuhiro Hara , Kazumi Matsushige Kazumi Matsushige , Eisei Takushi Eisei Takushi , Yasukuni Matsumoto Yasukuni Matsumoto
Published: October 2002

Egg-white gel is easily transformed into transparent “glass" by drying at ambient temperature, e.g., at 25° C for 140 min. The optical transmittance is increased from 2 to 25% accompanied with a decrease in the weight by more than 70%. Broad and intense IR absorption peaks observed at 3288–3308 and 1653–1657 cm-1 were respectively assigned to ν (NH) and να(C=O) stretching modes in the amido (RCONH-) groups, and the δ(NH) bending mode was observed at 1521–1546 cm-1. Differential thermal analysis (DTA) study showed a distinct endothermic peak due to the glass transition, and the peak position was located at 36, 42, 58 and 69° C when the heating rates were 2, 5, 10 and 20° C min-1, respectively. Heat treatment of egg-white glass at 60° C or γ-ray irradiation resulted in partial crystallization, and the XRD patterns showed a few diffraction peaks superimposed on the halo peak due to the glassy phase.
Growth, Characterization and Device Fabrication of Boron Delta-Doped Structures by Si-Molecular Beam Epitaxy
Authors: Sardela Jr. Mauro R. , Radamson Homayon H. , Lars Hultman Lars Hultman , Göran V. Hansson Göran V. Hansson
Published: October 2002

The material quality of boron delta-doped layers grown by Si-molecular beam epitaxy has been studied. A delta-layer width of three (200) atomic planes was measured by high resolution transmission electron microscopy, even for boron sheet concentrations close to 1 monolayer. Electrical characterization of device structures containing a pair of delta-doped layers and exhibiting negative differential resistance at room temperature is also reported.
High Temperature (77–300 K) Photo- and Electroluminescence in Si/Si1-xGex Heterostructures
Authors: Sturm James C. , Amour Anthony St. , Mi Qun , Lenchyshyn Lori C. , Thewalt Michael L. W.
Published: October 2002

The photo- and electro-luminescence of strained Si1-
x

Ge

x

/Si heterostructures on Si(100) substrates from 77 K to 300 K has been investigated both experimentally and by quantitative modelling. The key experimental features are very broad linewidths and an exponential drop in the luminescence at high temperatures, with a larger Ge fraction corresponding to a higher temperature before the drop begins. These phenomena were accurately explained by an electron-hole plasma from high carrier densities in the quantum well and by an excessively low effective lifetime in the silicon cladding region.
Time-Resolved Optically Detected Magnetic Resonance of Luminescence from Si/Si1-xGex Superlattices
Authors: Glaser Evan R. , Kennedy Thomas A. , Klein Paul B. , David J. Godbey David J. Godbey , Phillip E. Thompson Phillip E. Thompson
Published: October 2002

Time-resolved optically detected magnetic resonance (TR-ODMR) experiments have been performed on Si/Si1-
x

Ge

x

superlattices grown by molecular beam epitaxy (MBE) on (001) Si. These structures exhibit a single, broad (full width at half-maximum amplitude ∼70 meV) photoluminescence (PL) band with peak energy 100 meV below the expected band gap. Fast (τ≤5 µ s) and slow (τ≃20 µ s) processes have been separated with the TR-ODMR. The slow resonances are new and provide more detailed information on the nature of the recombination. These features are tentatively assigned to Ge-rich regions in the SiGe layers based on the resonance parameters and the faster spin-lattice relaxation.
From Relaxed GeSi Buffers to Field Effect Transistors: Current Status and Future Prospects
Authors: Xie Ya-Hong , Fitzgerald Eugene A. , Monroe Donald , G. Patrick Watson G. Patrick Watson , Paul J. Silverman Paul J. Silverman
Published: October 2002

We review the current status of relaxed GeSi buffer layers, high-mobility two-dimensional electron and hole gases fabricated on top of these layers, and GeSi-based field effect transistors (FETs). Recent progress in these fields is emphasized. A brief summary is then given for a variety of GeSi-based FET fabrications to date. Finally, the future prospects of GeSi-based FETs to be integrated into Si VLSI production is discussed.
Sm2+ Photoluminescence and X-Ray Scattering Studies of A- and B-Type Epitaxial CaF2 Layers on Si(111)
Authors: Sokolov Nikolai S. , Hirai Takayoshi , Kawasaki Koji , Ohmi Shun-ichiro , Tsutsui Kazuo , Furukawa Seijirou , Takahashi Isao , Itoh Yobun , Harada Jimpei
Published: October 2002

The crystalline quality and strain in molecular beam epitaxy (MBE)-grown CaF2:Sm/Si(111) structures with type-A (nonrotated) and type-B (rotated by 180° in the plane of the interface) epitaxial relationships were characterized by the bivalent samarium photoluminescence technique. It was found from the analysis of X-ray crystal truncation rod (CTR) scattering that the interface spacings along the [111] direction are (1.30±0.03)a
0 for annealed samples with the type-A and (1.45±0.02)a
0 with the type-B interface, where a
0 is the Si(111) spacing. It was also confirmed that Ca atoms occupy T-sites at the interface (atop the atoms of the first Si layer) for the type-A interface. Both the photoluminescence and X-ray measurements indicate that the crystalline quality of type-A CaF2/Si(111) structures is inferior compared with that of type-B structures.
Growth of 100 GHz SiGe-Heterobipolar Transistor (HBT) Structures
Authors: Kasper Erich , Kibbel Horst , Hans-Joest Herzog Hans-Joest Herzog , Andreas Gruhle Andreas Gruhle
Published: October 2002

The transit frequency f
T of SiGe-heterobipolar transistors (HBT's) was increased from 20 GHz to 100 GHz. This was mainly achieved by thickness reduction of the double heterojunction SiGe-base from 65 nm to 25 nm. The complete vertical structure of the SiGe-HBT's (collector, base, emitter, emitter contact) was grown in one run by Si molecular beam epitaxy (Si-MBE). The growth temperature was varied from 650° C at the collector side to 325° C at the emitter contact side. The different n-type doping levels (1017/ cm3, 1018/ cm3, 1020/ cm3) were obtained by applying three different Sb-doping techniques (secondary implantation, adatom pre build-up, low temperature doping). The p-type base was doped with boron. The doping level in the base (6×1019/ cm3) exceeded the emitter doping level by a factor of 30 (doping level inversion).
Growth and Processing of Relaxed-Si1-xGex/Strained-Si Structures for Metal-Oxide Semiconductor Applications
Authors: Welser Jeffrey , Judy L. Hoyt Judy L. Hoyt , James F. Gibbons James F. Gibbons
Published: October 2002

Epitaxial growth and processing issues related to strained-Si metal-oxide semiconductor field effect transistor (MOSFET) fabrication are discussed. The material quality of the graded Ge composition, relaxed- Si1-
x

Ge

x

buffer layers is analyzed. The ion implants used to form complementary metal-oxide semiconductor (CMOS) “wells” prior to epitaxy are found to degrade the quality of these layers by introducing a high density of misfit dislocation nucleation sites. Rough surface morphology, short misfit dislocation line lengths, and high threading defect densities are correlated with the increased nucleation site density. In addition, the oxidation of strained Si is investigated by Rutherford backscattering and Raman spectroscopy. No measurable strain relaxation is found as a result of thermal oxidation at temperatures up to 850° C.