bluuebunny/crossref_metadata_2025 huggingface dataset:
Hot electron spin polarization and Schottky barrier in spin-valve transistor
Authors: Hong Jisang , Wu R. Q.
Published: March 2004

We have explored phenomenological temperature dependence of hot electron magnetotransport in a spin valve transistor. We stress spin polarization of hot electrons and spatial inhomogeneity of Schottky barriers to explain the peculiar temperature and spin dependence of collector currents. Qualitative trends are established for collector current with changes in temperature, thickness of spin-valve base, along with height and width of Schottky barriers.
Temperature effects on Ge condensation by thermal oxidation of SiGe-on-insulator structures
Authors: Sugiyama N. , Tezuka T. , Mizuno T. , Suzuki M. , Ishikawa Y. , Shibata N. , Takagi S.
Published: March 2004

The Ge depth profile and generation of dislocations associated with oxidation of SiGe-on-insulator (SGOI) substrates are examined from the viewpoint of the temperature dependence. It is found that Ge profiles in SGOI layers after oxidation are strongly dependent on the oxidation temperature. This fact is explained by the competitive process between the accumulation of Ge atoms at the SiGe/thermal oxide interface, determined by the oxidation rate, and Ge diffusion toward substrates during oxidation of SGOI substrates. While the abrupt Ge profile obtained by low-temperature oxidation causes the generation of dislocations, SGOI layers with high Ge content and no dislocations can be achieved by high-temperature oxidation.
Effects of the buffer layers on the performance of (Al,Ga)N ultraviolet photodetectors
Authors: Mosca Mauro , Reverchon Jean-Luc , Omnès Franck , Duboz Jean-Yves
Published: March 2004

The fabrication of (Al,Ga)N-based metal–semiconductor–metal (MSM) photovoltaic detectors requires the growth of high-quality (Al,Ga)N films. Inserting a low-temperature deposited buffer layer enables the growth of an epitaxial layer with a reduced density of defects. Two structures using GaN and AlN buffer layers have been deposited by low-pressure metalorganic chemical vapor deposition and used to fabricate MSM interdigitated detectors. The devices have been characterized to investigate the effects of the buffer layers on the detector performances.
Charge dynamics of MgO single crystals subjected to KeV electron irradiation
Authors: Boughariou A. , Blaise G. , Braga D. , Kallel A.
Published: March 2004

A scanning electron microscope has been equipped to study the fundamental aspects of charge trapping in insulating materials, by measuring the secondary electron emission (SEE) yield σ with a high precision (a few percent), as a function of energy, electron current density, and dose. The intrinsic secondary electron emission yield σ0 of uncharged MgO single crystals annealed at 1000 °C, 2 h, has been studied at four energies 1.1, 5, 15, and 30 keV on three different crystal orientations (100), (110), and (111). At low energies (1.1 and 5 keV) σ0 depends on the crystalline orientation wheras at high energies (30 keV) no differentiation occurs. It is shown that the value of the second crossover energy E2, for which the intrinsic SEE yield σ0=1, is extremely delicate to measure with precision. It is about 15 keV±500 eV for the (100) orientation, 13.5 keV±500 eV for the (110), and 18.5 keV±500 eV for the (111) one. At low current density J⩽105 pA/cm2, the variation of σ with the injected dose makes possible the observation of a self-regulated regime characterized by a steady value of the SEE yield σst=1. At low energies 1.1 and 5 keV, there is no current density effects in MgO, but at high energies ≈30 keV, apparent current density effects come from a bad collect of secondary electrons, due to very high negative surface potential. At 30 keV energy, an intense erratic electron exoemission was observed on the MgO (110) orientation annealed at 1500 °C. This phenomenon is the result of a disruptive process similar to flashover, which takes place at the surface of the material.
Two-dimensional measurements of cell parameter distributions in reflective liquid crystal displays by using multiple wavelengths Stokes parameters
Authors: Kawamura Marenori , Goto Yoshiaki , Sato Susumu
Published: March 2004

We propose a two-dimensional measurement method of cell parameters such as a cell thickness, twist angle, and pretilt angle in reflective liquid crystal (LC) cells by using Stokes parameters of reflected light at several wavelengths. The cell thickness of the reflective LC cells can be measured by calculating the Stokes parameter equations at only one wavelength, and both the cell thickness and twist angle can also be determined at two wavelengths, where the twist angle and/or pretilt angle of designed values are used. Three cell parameters including the pretilt angle as well as the cell thickness and twist angle can also be measured by using three wavelengths Stokes parameter equations. Two-dimensional LC cell parameters are easily obtained and their mapping results are successfully demonstrated.
Nanostructural and mechanical properties of nanocomposite nc-TiC/a-C:H films deposited by reactive unbalanced magnetron sputtering
Authors: Zehnder T. , Schwaller P. , Munnik F. , Mikhailov S. , Patscheider J.
Published: March 2004

Thin films of nc-TiC/a-C:H nanocomposite have been deposited by reactive magnetron sputtering at substrate bias values of −240 and −91 V. The grain size and grain separation, which together define the nanostructure, are correlated to the amount of the amorphous phase. From the size of the TiC grains measured by x-ray diffraction and the amorphous hydrogenated carbon (a-C:H) phase content determined by x-ray photoelectron spectroscopy, the mean grain separation is estimated using a simple model for the nanostructure. Films deposited at −240 V show a hardness enhancement for a-C:H phase contents in the range 10% to 30% with TiC grain sizes around 5 nm. The mean grain separation for such films was estimated to be 0.3 nm. Films with higher a-C:H phase contents still have 5 nm small grains, but their mean grain separation is larger than 0.5 nm; their hardness is thus determined by the properties of the amorphous matrix. A less pronounced hardness enhancement is observed for films deposited at −91 V. They have larger grains and larger mean gain separations and show smaller hardness values. The hardness of the films, among other mechanical properties, is controlled by the nanostructure. Raman measurements have shown that a-C:H is present in films with mean grain separation down to 0.2 nm. Coefficients of friction against steel lower than 0.3, independent of the substrate bias, are found for films with mean grain separations as low as 0.15 nm. Self-lubrication due to a-C:H can explain the observed friction behavior, although the presence of a-C:H cannot be proved by Raman spectroscopy for films with mean grain separations smaller than 0.2 nm. It is shown that the substrate bias is crucial in obtaining increased hardness of nc-TiC/a-C:H nanocomposite thin films. In contrast to the hardness of the coatings, their friction behavior is not affected by the substrate bias.
Electromagnetic wave properties of polymer blends of single wall carbon nanotubes using a resonant microwave cavity as a probe
Authors: Roberts J. A. , Imholt T. , Ye Z. , Dyke C. A. , Price D. W. , Tour J. M.
Published: March 2004

A resonant microwave cavity operating in the TM010 mode was used to determine the microwave susceptibility of single walled carbon nanotubes (SWNT) that are blended in polymer matricies. The frequencies of the probe signal were 9.8, 11.4, and 35.93 GHz. Samples of 3%–19% blends of SWNT in polycarbonate were tested to determine the best blends for shielding of devices from microwaves at these frequencies. It appears that blends of 9%–11% are very effective in shielding the electric vector of electromagnetic waves. Both the electric vector and the magnetic vectors were probed by the process to determine the nature of coupling between the SWNTs and the applied fields. Some details are given about the apparatus design that enables computer collection and processing of the data to be achieved. An electronic differentiation technique was used to allow the second derivative of the cavity absorption profile to be displayed for precise measurement. Data are presented to show the relative microwave absorption for different blends of the SWNTs with polycarbonates.
Circular surface electrode on a piezoelectric layer
Authors: Wang B. L.
Published: March 2004

This article considers a piezoelectric ceramic layer with a circular electrode attached to its surface. Exact solution is given for a piezoelectric medium whose thickness is considerably larger than the diameter of the electrode. Numerical solution for a piezoelectric layer of finite thickness is obtained. Field intensities near the edge of the electrode are established. Possible cracking initiation behavior is also discussed. Solutions are obtained for the maximum electric potential that the piezoelectric medium can be applied without catastrophic failure according to the criterion that the maximum stress intensity factor equals the fracture toughness of the ceramics.
Diffusion of Cu, In, and Ga in In2Se3/CuGaSe2/SnO2 thin film photovoltaic structures
Authors: Djessas K. , Yapi S. , Massé G. , Ibannain M. , Gauffier J. L.
Published: March 2004

This article is a study of copper, indium, and gallium interdiffusions in In2Se3/CuGaSe2/SnO2/glass thin film heterostructures annealed at different temperatures. The use of CuGaSe2 material in place of Cu(In,Ga)Se2 is only required by the indium diffusion studies. The CuGaSe2 layers were grown by close-spaced vapor transport for two types of sources having different grain sizes. The In2Se3 films were deposited by thermal evaporation. The heterostructures were annealed in vacuum at different temperatures and analyzed by secondary ion mass spectroscopy (SIMS). The copper, indium, and gallium SIMS concentration profiles show that the copper diffuses up to the In2Se3 film surface and that the indium can diffuse far away from the In2Se3/CuGaSe2 interface towards SnO2. The copper, indium, and gallium diffusions were studied and the interdiffusion parameters were computed. The simultaneous interdiffusions of copper and indium induces the formation of a p–n junction responsible for the photovoltaic effect of the Zn/In2Se3/CuGaSe2/SnO2/glass photocells, the SnO2 side being lighted. This hypothesis is supported by results carried out from electron beam induced current measurements, showing a notable shift of the junction from the In2Se3/CuGaSe2 interface through the CuGaSe2 layer in terms of the annealing temperature, resulting in an increasing of the photovoltages up to 650 mV.
Determination of electric field-dependent effective secondary emission coefficients for He/Xe ions on brass
Authors: Sosov Yuriy , Theodosiou Constantine E.
Published: March 2004

Effective secondary emission coefficients, γeff, for He+ and Xe+ ions are determined from the experimental Paschen curves of Postel and Cappelli [Appl. Phys. Lett. 76, 544 (2000)] through Townsend’s condition for a self-sustained discharge. The γeff dependence on the reduced electric field E/p, where p is the gas pressure, is obtained using the calculated dependence of the reduced Townsend’s ionization coefficient α(E/p)/p on the reduced electric field. Average values of the secondary emission coefficients are also estimated for brass and atomic and molecular ions as well as excited atoms and molecules of He and Xe, through a best fit of the simulated Paschen curves to the experimental ones. The found average values of the secondary emission coefficients are 0.1 for He and 0.0016 for Xe. Comparison is made with the limited available experimental results.
Structure and electrical properties of Bi3.15Nd0.85Ti3O12 ferroelectric thin films
Authors: Wu Di , Li Aidong , Ming Naiben
Published: March 2004

Polycrystalline Bi3.15Nd0.85Ti3O12 (BNdT) ferroelectric thin films were deposited on platinized Si substrates by chemical solution deposition. Dense and uniform BNdT films with pure Bi-layered perovskite structure were achieved by rapid thermal annealing the spin-on films at 700 °C for 3 min. Well-saturated hysteresis loops with remanent polarization around 10 μC/cm2 were obtained on Pt/BNdT/Pt capacitors. Typical values of dielectric constant and loss tangent of BNdT films at 10 kHz were 525 and 0.028, respectively. Curie temperature of BNdT films was determined to be around 450 °C from temperature dependent dielectric measurement. Pt/BNdT/Pt capacitors showed excellent fatigue resistance with no polarization reduction up to 1010 switches. Imprints, shifts of hysteresis loops along voltage axis, were observed along with the loss of retained polarization after heat treatment of poled Pt/BNdT/Pt capacitors. However, data loss due to imprint is negligible for BNdT capacitors. The dc leakage current density of BNdT capacitors is in the order of 10−7–10−6 A/cm2 below 100 kV/cm.
Investigation of a distribution function suitable for acceptors in SiC
Authors: Matsuura Hideharu
Published: March 2004

The distribution function suitable for an acceptor in p-type SiC is investigated using lightly or heavily Al-doped SiC samples. From the temperature dependence of the hole concentration, the density and energy level of the acceptors are estimated using two different distribution functions. The proposed distribution function, which considers the influence of the excited states of acceptors, can be applied to both the samples, while the Fermi–Dirac distribution function, which does not include this influence, can be applied only to the lightly doped sample. In order to elucidate this result theoretically, the dependencies of both distribution functions on the temperature or the acceptor density are simulated. From these simulations, the proposed distribution function is found to be appropriate for determining the density and energy level of dopants with a deep dopant energy level for any dopant density.
Current spread and overheating of high power laser bars
Authors: Laikhtman B. , Gourevitch A. , Donetsky D. , Westerfeld D. , Belenky G.
Published: March 2004

The heating of a semiconductor laser bar imbedded between two heat spreaders has been studied theoretically and experimentally. The model included the p-cladding layer, active region, n-cladding layer, and n-substrate. Heat sources from the active region and both cladding layers were considered. An analytical relation was obtained between the temperature distribution in the laser and the bar geometry. The analytical approach revealed features that are usually missing in purely numerical modeling. It was shown that the current density across the active region is nonuniform, and that the magnitude of the nonuniformity grows when the resistance of the p-cladding layer decreases. This nonuniform current distribution can lead to higher temperatures at the edges of the laser stripe than in the middle. It was found that mutual heating of the individual lasers in the bar is controlled mainly by the overlap of the temperature fields in the heat spreaders. The theoretical results obtained without any fitting parameters show good agreement with the experimentally measured dependence of the active region temperature on pumping current.
Diffuse x-ray scattering and transmission electron microscopy study of defects in antimony-implanted silicon
Authors: Takamura Y. , Marshall A. F. , Mehta A. , Arthur J. , Griffin P. B. , Plummer J. D. , Patel J. R.
Published: March 2004

Ion implantation followed by laser annealing has been used to create supersaturated and electrically active concentrations of antimony in silicon. Upon subsequent thermal annealing, however, these metastable dopants deactivate towards the equilibrium solubility limit. In this work, the formation of inactive antimony structures has been studied with grazing incidence diffuse x-ray scattering, and transmission electron microscopy, and the results are correlated to previous high-resolution x-ray diffraction data. We find that at a concentration of 6.0×1020 cm−3, small, incoherent clusters of radius 3–4 Å form during annealing at 900 °C. At a higher concentration of 2.2×1021 cm−3, deactivation at 600 °C occurs through the formation of small, antimony aggregates and antimony precipitates. The size of these precipitates from diffuse x-ray scattering is roughly 15 Å in radius for anneal times from 15 to 180 seconds. This value is consistent with the features observed in high-resolution and mass contrast transmission electron microscopy images. The coherent nature of the aggregates and precipitates causes the expansion of the surrounding silicon matrix as the deactivation progresses. In addition, the sensitivity of the diffuse x-ray scattering technique has allowed us to detect the presence of small clusters of radius ∼2 Å in unprocessed Czochralski silicon wafers. These defects are not observed in floating zone silicon wafers, and are tentatively attributed to thermal donors.
Light-induced modification of a-SiOx:H. I: Metastability
Authors: Janotta Andreas , Dikce Yavuz , Linder Susanne , Schmidt Matthias , Janssen Rainer , Stutzmann Martin
Published: March 2004

Amorphous hydrogenated silicon suboxides (a-SiOx:H) were deposited by plasma enhanced chemical vapor deposition from the source gases SiH4, H2, and CO2. The band gap of the samples can be tuned from 1.9 to 3.0 eV by varying the oxygen content from 0 to 50 at. %. The light-induced degradation of the photoconductivity and the generation of metastable dangling bond defects, known as the Staebler–Wronski effect in hydrogenated amorphous silicon (a-Si:H), were studied in a-SiOx:H for a wide range of oxygen contents up to 44 at. % as a function of illumination time and intensity. Upon intensive illumination above their respective band gaps for several hours at comparable light intensities, all silicon suboxides displayed a similar increase of the subgap defect density and a corresponding decrease of the photocurrent. Also the temporal evolution of the dangling bond density and photoconductivity were found to resemble those of pure amorphous silicon. Apart from an irreversible redshift of the absorption edge for higher oxygen contents (comparable to the effect of photodarkening in chalcogenide glasses), the effects of light degradation could be reversed by an appropriate annealing at temperatures below 200 °C for all oxygen concentrations studied. However, for higher oxygen concentrations ([O]≳30 at. %) partial irreversibilities were observed after repeated degradation cycles.
Effect of critical thickness on structural and optical properties of InxGa1−xN/GaN multiple quantum wells
Authors: Lü W. , Li D. B. , Li C. R. , Shen F. , Zhang Z.
Published: March 2004

InGaN/GaN multiquantum-well (MQW) structures grown by metalorganic chemical-vapor deposition on n-type GaN and capped by p-type GaN were investigated by cross-sectional transmission electron microscopy, double crystal x-ray diffraction, and temperature-dependent photoluminescence. For the sample with strained-layer thicknesses greater than the critical thicknesses, a high density of pure edge type threading dislocations generated from MQW layers and extended to the cap layer was observed. These dislocations result from a relaxation of the strained layers when their thicknesses are beyond the critical thicknesses. Because of indium outdiffusion from the well layers due to the anneal effect of Mg-doped cap layer growth and defects generated from strain relaxation, the PL emission peak was almost depressed by the broad yellow band with an intensity maximum at 2.28 eV. But for the sample with strained-layer thicknesses less than the critical thicknesses, it has no such phenomenon. The measured critical thicknesses are consistent with the calculated values using the model proposed by Fischer, Kühne, and Richter.
Ceria nanoparticles: Size, size distribution, and shape
Authors: Zhang Feng , Jin Qiang , Chan Siu-Wai
Published: March 2004

Nanocrystalline ceria particles have been prepared by mixing aqueous solutions of cerium nitrate and hexamethylenetetramine at room temperature. The smallest size of nanoparticles synthesized is 2 nm. For each batch prepared, a narrow size distribution is found with a standard deviation less than ±15%. A transmission electron microscopy (TEM) investigation shows that these particles are single crystals having either an octahedral shape with eight {111} surfaces, or with an additional {200} surface-truncated octahedral shape. In-situ ultraviolet-visible light absorption has been performed to measure the absorption edge and to monitor the growth of nanoparticles. The results from light absorption correlate well with those of the TEM images, providing an in-situ method to measure the particle size during synthesis.
Effect of doping SiO2 on high-frequency magnetic properties for W-type barium ferrite
Authors: Wu Yuping , Li Z. W. , Chen Linfeng , Wang S. J. , Ong C. K.
Published: March 2004

The microstructure, static and dynamic magnetic and dielectric properties of BaCo1.3Zn0.7Fe16O27 doped with small amounts of SiO2 have been investigated. The results show that the crystal structure and static magnetic properties have no obvious changes as SiO2 varies from 0 to 1 wt %. However, the complex permittivity and complex permeability could be significantly modified by SiO2 doping. Due to the doping, both real and imaginary permittivity are greatly increased. The increase has its origin in the formation of Fe2+, due to minor Si4+ ions entering the crystal lattice of barium ferrites. The complex permeability spectra can be decomposed into two components, which are associated with natural resonance and wall resonance. By doping with SiO2, the contribution of wall resonance to the static permeability increases, while the contribution of the natural resonance decreases. The overall static permeability is increased as a result.
Anode/organic interface modification by plasma polymerized fluorocarbon films
Authors: Tang J. X. , Li Y. Q. , Zheng L. R. , Hung L. S.
Published: March 2004

We investigated the effects of plasma polymerized fluorocarbon films (CFx) on device performance in organic light-emitting diodes (OLEDs). OLEDs with a 0.3-nm thick CFx film on an untreated indium tin oxide (ITO) anode showed identical current density–voltage characteristics and improved operational stability, as compared to the device with an ultra violet-treated ITO anode. Hole injection was virtually blocked when Au was replaced for ITO as an anode, while an ultrathin CFx film overlaid on an Au anode substantially reduced the barrier height and facilitated hole injection. The enhancement of hole injection was attributed to the manipulation of the energy level offset at the anode/organic interface by the formation of an artificial dipolar layer resulting from rich, negatively charged fluorine. The dipolar interface was fairly stable when being exposed to air, and the improved operational stability of OLEDs was ascribed to the stability of the ITO/CFx anode against atmospheric moisture.
Extrusion of hollow waveguide preforms with a one-dimensional photonic bandgap structure
Authors: Gibson Daniel J. , Harrington James A.
Published: March 2004

An extrusion technique is used to make an all-dielectric, hollow waveguide preform. The structure consists of radially alternating dielectric layers of high/low refractive index pairs. By requiring that the two dielectric materials have a high index contrast, it is possible to make a preform that will have a photonic bandgap structure when drawn into a fiber optic. The preform is made by an extrusion process in which a stack-of-plates, composed of alternating disks of chalcogenide glass and a polymer, is extruded through a die into both solid and hollow-core structures. Laminar flow during extrusion forces the periodicity from an axial to a radial orientation in the final extruded preform. For these experiments the high index material was arsenic selenide glass (As2Se3,n=2.6) and the low index material was polysulfone (PSU,n=1.55), which gives an index contrast of 1.68.
Ferromagnets for integrated atom optics
Authors: Vengalattore M. , Conroy R. S. , Rooijakkers W. , Prentiss M.
Published: March 2004

A ferromagnetic atom chip for trapping neutral atoms above a substrate is fabricated and characterized. The chip is capable of generating an anisotropic quadrupole trap with gradients in excess of 15 kG/cm at a distance of more than 100 μm from the surface. This is a promising route to the study of ultracold low dimensional systems, interferometry, and atom optics which require tight confinement, while alleviating the problems of fragmentation seen in wire-based chips.
Negative corona triggering in air
Authors: Bessières D. , Paillol J. , Soulem N.
Published: March 2004

The role of positive ions and field emission in the negative corona triggering is discussed, in room air, at atmospheric pressure. First, an artificial positive space charge is created in a point-to-plane gap by focusing a pulsed ultraviolet laser beam at a determined distance from the point. The triggered corona current pulse is compared with the natural one. Numerical simulations which are presented take into account the insulating layers charging by positive ions on the cathode surface. The theory of electron emission is based upon a conduction mechanism in the bulk of insulating layers. Second, the role of field emission is enhanced by covering the point with a graphite coating. Field emission is modeled by introducing a field enhancement factor and current instabilities are attributed to the switch-off of emission sites on the cathode surface.
Planar polymer light-emitting device with fast kinetics at a low voltage
Authors: Edman Ludvig , Pauchard Marc , Moses Daniel , Heeger Alan J.
Published: March 2004

Polymer light-emitting electrochemical cells containing a ternary mixture of a soluble phenyl-substituted poly(para-phenylene vinylene) copolymer (“superyellow”), a dicyclohexano-18-crown-6 (DCH18C6) crown ether and a LiCF3SO3 salt as the active material have been assembled. Planar Au/{superyellow+DCH18C6+LiCF3SO3}/Au devices, with an interelectrode gap of 50 μm, were initially charged (i.e., electrochemically p- and n-doped in situ) at T=85 °C and then cooled to room temperature under applied voltage. When operated at T=23 °C charged devices show electroluminescence with fast response (< 1 s) at a low applied voltage (V⩾6 V). Charged devices could be stored under open-circuit conditions at room temperature for a prolonged time without detectable changes in device performance, and they can be completely (reversibly) discharged by raising the temperature to 85 °C. The active material mixtures were studied by atomic force microscopy and differential scanning calorimetry. The results demonstrate that superyellow phase separates from a crystalline DCH18C6–LiCF3SO3 complex on a ∼25 nm scale. The superyellow phase exhibits a glass transition at Tg∼180 °C, while the crystalline DCH18C6–LiCF3SO3 phase melts at Tm≈56 °C. Thus, we attribute the stabilization of charged Au/{superyellow+DCH18C6+LiCF3SO3}/Au devices in going from 85 to 23 °C as being directly related to the passage of Tm of the DCH18C6–LiCF3SO3 phase. The ionic distribution related to the p- and n-doped regions is “frozen-in” by this crystallization allowing for the observed fast kinetics at low voltages at room temperature.
Apparent quantum efficiency effects in CdTe solar cells
Authors: Gloeckler M. , Sites J. R.
Published: March 2004

Quantum efficiency measurements of n-CdS/p-CdTe solar cells performed under nonstandard illumination, voltage bias, or both can be severely distorted by photogeneration and contact-barrier effects. In this work we will discuss the effects that are typically observed, the requirements needed to reproduce these effects with modeling tools, and the potential applications of apparent quantum efficiency analysis. Recently published experimental results are interpreted and reproduced using numerical simulation tools. The suggested model explains large negative apparent quantum efficiencies (≫100%) seen in the spectral range of 350–550 nm, modestly large negative apparent quantum efficiencies (>100%) in the spectral range of 800–850 nm, enhanced positive or negative response observed under red, blue, and white light bias, and photocurrent gain significantly different from unity. Some of these effects originate from the photogeneration in the highly compensated CdS window layer, some from photogeneration within the CdTe, and some are further modified by the height of the CdTe back-contact barrier.
Estimation of dynamical invariants without embedding by recurrence plots
Authors: Thiel M. , Romano M. C. , Read P. L. , Kurths J.
Published: March 2004

In this paper we show that two dynamical invariants, the second order Rényi entropy and the correlation dimension, can be estimated from recurrence plots (RPs) with arbitrary embedding dimension and delay. This fact is interesting as these quantities are even invariant if no embedding is used. This is an important advantage of RPs compared to other techniques of nonlinear data analysis. These estimates for the correlation dimension and entropy are robust and, moreover, can be obtained at a low numerical cost. We exemplify our results for the Rössler system, the funnel attractor and the Mackey–Glass system. In the last part of the paper we estimate dynamical invariants for data from some fluid dynamical experiments and confirm previous evidence for low dimensional chaos in this experimental system.
Highly efficient probe with a wedge-shaped metallic plate for high density near-field optical recording
Authors: Matsumoto T. , Shimano T. , Saga H. , Sukeda H. , Kiguchi M.
Published: March 2004

The distribution of the optical near-field generated by a probe with a wedge-shaped metallic plate was calculated using a finite difference time domain method. The dependence of the distribution on the size and the material of the metallic plate was calculated, and it was shown that a strong optical near-field was generated at the apex of the metallic plate when the size and the material were optimized so that a surface plasmon was excited in the metallic plate. The influence of the recording medium was also calculated. The resonance wavelength shifted toward a longer wavelength and the decay length of the optical near-field increased when the recording medium was placed near the probe. The spot size calculated on the surface of the recording medium was 30 nm, and the efficiency (defined as the ratio between the power of the optical near-field at the surface of the recording medium and that of the incident light) was about 20% when the spacing between the probe and the recording medium was 10 nm. The near-field distribution for a probe with two metallic plates was also calculated, and it was shown that a strong optical near-field was generated between the apices of the metallic plates when the plasmon was excited in the metallic plates.
Electronic properties of antimony-vacancy complex in Ge crystals
Authors: Markevich V. P. , Peaker A. R. , Litvinov V. V. , Emtsev V. V. , Murin L. I.
Published: March 2004

Schottky barriers formed by depositing Au on n-type Ge have been used to study the antimony-vacancy complex (E center). Both hole and electron transitions have been observed because the formation of an inversion layer at the semiconductor surface enables minority carriers to be injected when the Schottky barrier is forward biased. It is argued that the E center in Ge has three charge states: double negative, single negative, and neutral. The free energy of electron ionization for the double acceptor level of the complex has been found to be ΔG(=/−)=0.294−4.2 kT (eV), where k is Boltzmann’s constant. Consequently, the position of the double acceptor level of the E center {E(=/−)=Ec−ΔG(=/−)} is temperature dependent. In moderately Sb-doped (NSb=1013–1015 cm−3) Ge crystals at equilibrium conditions half-occupancy of the double acceptor state of the Sb-V complex occurs when the Fermi level is at about Ec−0.20 eV. The single acceptor level of the E center is in the lower part of the band gap. The activation energy of hole emission from the E(−/0) level has been determined as 0.307 eV. The introduction of one Sb-V defect results in the removal of three free electrons in Sb-doped Ge. It is proposed that this is one of the main reasons for the fast free carrier removal and n→p conversion of the conductivity type in Ge:Sb upon electron- or gamma-irradiation at room temperature.
Thermoacoustic simulation with lattice gas automata
Authors: Chen Y. , Liu X. , Zhang X. Q. , Yan L. , Yang C. X. , Li Z. C.
Published: March 2004

A thermoacoustic engine using a two-dimensional nine-bit lattice gas was simulated. The model engine consisted of a tube with a regenerator and two heat exchangers. The evolution process of self-excited thermoacoustic oscillation and the optimization of the regenerator were studied. The validity of a lattice gas model for a thermoacoustic engine was also verified experimentally.
Nonsteady-state surface plasmons in periodically patterned structures
Authors: Crouse David T. , Lo Yu-Hwa
Published: March 2004

The properties of nonsteady-state surface plasmon modes are analyzed for general grating structures and in particular for short pitch, high aspect ratio gratings and lamellar gratings. Numerical simulations of grating structures are described including a transformed coordinate, coupled plane wave approach known as the Chandezon method. A model of radiating light-surface plasmon coupling is then developed that allows for the extension of steady-state calculations involving time independent incident and reflected intensities to nonsteady-state situations involving no incident light but exponentially time dependent decaying emission intensity. Properties such as surface plasmon dispersion curves, electromagnetic field profiles, incident light-surface plasmon coupling efficiency, surface plasmon-radiating light coupling efficiency, overall radiation efficiency, and lifetime or decay constant are analyzed. It is seen that the surface plasmon modes of several structures couple strongly to incident and radiating light producing high surface plasmon-radiating light conversion and short lifetimes.
Electrical characterization of native-oxide InAlP/GaAs metal-oxide-semiconductor heterostructures using impedance spectroscopy
Authors: Li Xiang , Cao Y. , Hall D. C. , Fay P. , Zhang X. , Dupuis R. D.
Published: March 2004

InAIP native oxide/GaAs metal-oxide-semiconductor (MOS) capacitors have been characterized using bias- and temperature-dependent swept-frequency impedance spectroscopy. An equivalent circuit model has been developed for these MOS capacitors that accurately fits the measured impedance over the full frequency range from 40 Hz to 10 MHz. From the bias dependence of the circuit model parameters, the distribution in energy of the interface states was found to be consistent with an exponential distribution, with a total interface state density of 8×1011 cm−2 and an average activation energy of 0.34 eV below the conduction band edge. The temperature dependence of the impedance spectra was also examined, and an activation energy of 0.44 eV from the conduction band edge was determined, in good agreement with the bias-dependent impedance measurements.
Kinetics of arsenic-enhanced solid phase epitaxy in silicon
Authors: Johnson B. C. , McCallum J. C.
Published: March 2004

The kinetics of intrinsic and arsenic-enhanced solid phase epitaxy (SPE) have been measured in buried amorphous Si (a-Si) layers in which crystallization occurs free from the rate retarding effects of hydrogen. Surface a-Si layers, where H infiltration can occur during crystallization, have also been studied. A single 1.45×1016 As/cm2 implant at 1200 keV was used to form an As concentration profile with a peak concentration of 3×1020 As/cm3 centered at 8000 Å beneath the crystal surface, allowing many different enhanced SPE rates to be examined simultaneously. The SPE rate through this profile and its intrinsic counterpart were measured using time-resolved reflectivity. The effects of hydrogen on the SPE rate can be determined by a comparison between the buried and surface a-Si layers. For the surface a-Si layers, it was found that the As-enhanced SPE rate versus depth curve is offset with respect to the concentration profile. We attribute this offset to the H infiltration in the case of the surface a-Si layer.
The effects of Xe on an rf plasma and growth of ZnO films by rf sputtering
Authors: Nagata T. , Ashida A. , Fujimura N. , Ito T.
Published: March 2004

Sputter deposition of thin films using Xe gas instead of Ar is believed to suppress damage to the films caused by ion bombardment. To investigate the effects of Xe on ionic species in the rf plasma, and on the growth of ZnO thin films, rf plasmas generated using Xe and Ar sputtering gases were analyzed using Langmuir probe methods and optical emission spectroscopy (OES). The Langmuir probe results showed that the electron temperature of the Xe plasma was nearly half of that of the Ar plasma. In addition, the ion density in the Xe plasma was found to be greater than the ion density in the Ar plasma. OES data showed that a significant fraction of the ionic species in the Ar plasma was oxygen, which is thought to be the primary cause of damage to growing films. Ionic molecular oxygen (O2+) was observed only in the Ar plasma, and the concentration of excited atomic oxygen (O*) in the Ar plasma was ten times as high as that in the Xe plasma, for an oxygen partial pressure of 20%. In addition, ions in the Xe plasma were found to have smaller kinetic energies than for the ions in the Ar plasma, and the main ionic species were different. Using Xe as the sputtering gas therefore resulted in higher quality ZnO thin films with smoother surfaces.
Reduction of iron diffusion in silicon during the epitaxial growth of β-FeSi2 films by use of thin template buffer layers
Authors: Liu Zhengxin , Suzuki Yasuhito , Osamura Masato , Ootsuka Teruhisa , Mise Takahiro , Kuroda Ryo , Tanoue Hisao , Makita Yunosuke , Wang Shinan , Fukuzawa Yasuhiro , Otogawa Naotaka , Nakayama Yasuhiko
Published: March 2004

We fabricated continuous highly (110)/(101)-oriented β-FeSi2 films on Si (111) substrates by the facing-target sputtering method. An epitaxial thin β-FeSi2 template buffer layer preformed on the silicon substrate was found to be essential in the epitaxial growth of thick β-FeSi2 films. It was proved that the template reduced the iron diffusion into the silicon substrate during thick β-FeSi2 film fabrication. Even though the annealing was performed at high temperature (880 °C) for a long duration (10 h), iron diffusion was effectively hindered by the template. By introducing this template buffer layer, an abrupt interface without appreciable defects between the β-FeSi2 film and the silicon substrate formed. The mechanism for the reduction of iron diffusion by the template buffer layer is discussed.
Effects of a weak transverse magnetic field on negative ion transport in negative ion sources
Authors: Sakurabayashi T. , Hatayama A. , Bacal M.
Published: March 2004

The effects of a weak transverse magnetic field on negative ion (H−) extraction in a negative ion source have been studied by two-dimensional electrostatic particle simulation. A particle-in-cell model is used which simulates motion of charged particles in their self-consistent electric field. The extraction of H− ions is significantly improved by the weak transverse magnetic field in simulation as well as in experiments. Since electrons are deflected by the weak magnetic field, more H− ions arrive instead of electrons in the region close to the plasma grid in order to ensure plasma neutrality. The presence of the weak magnetic field produces important modifications in positive ion flow and, as a result, in the structure of the spatial potential which collects H− ions.
Numerical analysis of repetitive pulsed-discharge de-NOx process with ammonia injection
Authors: Onda Kazuo , Kusunoki Hironobu , Ito Kohei , Ibaraki Hiroshi
Published: March 2004

Due to its relatively high-performance and compactness, the pulsed-discharge de-NOx process is expected to be an advanced technology to suppress air pollution. Adequate guidelines for optimum operation of the pulsed-discharge de-NOx process have not yet been established however. In this study, we numerically analyze the process subjected to several hundred high-voltage pulses and investigate the effects of by-products and ammonia injection on the de-NOx performance. The electron collision process to produce OH and N radicals to remove NOx is analyzed by the Boltzmann equation for the energy distribution of discharge electrons. The chemical reaction process between the unstable radicals and NOx including combustion flue gas is calculated by considering a total of 1004 rate equations for electron collision and chemical reaction processes and a total of 101 chemical species. In a case without ammonia injection, both the NxOy removal efficiency and the de-NOx energy consumption rate to remove NxOy change with an increase in repeated pulse number because electrons produced by the discharge attach to accumulated by-products, such as H3O+(H2O)2, followed by a decrease in radical concentration, i.e., a decrease in oxidative and reductive removal reaction rates. In the case with ammonia injection, the removal efficiency increases and the electric energy consumption rate decreases with an increase in ammonia concentration because removal reactions such as NO→NO2→HNO3→NH4NO3 and NO→N2 are promoted. When excess ammonia is injected, the de-NOx performance declines because the NH2 radical produced by electron collision with ammonia reacts with NO2 and forms relatively stable N2O. In a case where HNO2 is considered NxOy, the de-NOx performance is also assessed.
Mössbauer study of FeCoSiAlGaPCB amorphous alloys
Authors: Borrego J. M. , Conde C. F. , Conde A. , Roth S. , Eckert J. , Greneche J. M.
Published: March 2004

A Mössbauer spectrometry and magnetic study have been performed on FeCoSiAlGaPCB amorphous alloys in order to get information about the variations in the atomic short range order with the substitution of Fe by Co. The decrease of the Curie temperature with decreasing Fe content was analyzed in the framework of the molecular field theory. The average hyperfine magnetic field at 77 K decreases linearly with increasing Co content as does the average magnetic moment per transition metal atom and a linear dependence between both quantities is found. The standard deviation of the hyperfine magnetic field distribution at 77 K does not change with Fe substitution and the average isomer shift increases linearly with the Co content of the alloy. The hyperfine magnetic field distributions show a bimodal character that evidences the presence of two types of Fe environments in the as-cast alloys.
Self-organized textured surfaces of amorphous carbon
Authors: Zhu X. D. , Narumi K. , Xu Y. , Naramoto H. , Arefi-Khonsari F.
Published: March 2004

We report a simultaneous formation process of textured surfaces for hydrogen-free amorphous carbon (a-C) induced by an ion beam. By adjusting surface reactions via controlling temperature together with ion beams, several kinds of textured surfaces of a-C on mirror-polished Si (111) can be produced during ion-beam assisted deposition. In high-temperature regimes, submicron-sized pyramidlike a-C particles and ripples structures form. The sizes and separations of a-C particles change with substrate temperature significantly. An intrinsic model based on a natural self-organization mechanism is proposed for the production of textured surfaces, where the surface diffusion is shown to play a decisive role. In a low-temperature regime, the films commonly present mounding roughening. Likewise, self-organized nanodots appear at a very low ion flux. These nanodots are about 5±0.5 nm high with a diameter to height ratio close to 15:1 and a density of approximately 290 μm−2. The nanodot production is correlated with ion-induced nucleation. The demonstration of the textured surface formations may open a way to fabricate and tune desirable surface structures on the technically important functional materials.
Finite element analysis of electric fracture properties in modified small punch testing of piezoceramic plates
Authors: Magara Y. , Narita F. , Shindo Y. , Karaiwa M.
Published: March 2004

The fracture behavior of a piezoelectric ceramic under applied electric fields has been the subject of recent studies. We have used finite element analysis to study experiments with the modified small punch (MSP) technique. Nonlinear three-dimensional finite element analysis was employed to calculate the MSP energy and maximum strain energy density. The effects of an applied electric field, 180° and 90° domain switching on the MSP energy, and maximum strain energy density are discussed, and the model predictions are compared with the results of the experiments. The polarization switching zones corresponding to combined mechanical and electrical loads are also obtained.
High-energy proton irradiation induced changes in the linear-kink noise overshoot of 0.10 μm partially depleted silicon-on-insulator metal-oxide-semiconductor field-effect transistors
Authors: Simoen E. , Mercha A. , Rafı́ J. M. , Claeys C. , Lukyanchikova N. B. , Smolanka A. M. , Garbar N.
Published: March 2004

This article describes the impact of a high-energy proton irradiation on the parameters of the Lorentzian noise overshoot, occurring in ultrathin gate oxide 0.10 μm partially depleted (PD) silicon-on-insulator metal-oxide-semiconductor field-effect transistors (MOSFETs), operated in the linear regime. It is shown that the drain current noise spectral density SI exhibits an increase after irradiation, while the Lorentzian time constant τ shows a different response to the 60/65 MeV protons in n- or p-channel transistors. In addition, the excess noise peak develops a pronounced radiation-induced dependence on the back-gate bias VBG, which is different for both device types: a strong increase of SI is found for the PD SOI p-MOSFETs, upon changing VBG into the accumulation regime, while in the first instance, the opposite is found for the n-MOSFETs. These observations are discussed in terms of a RC-filtered shot noise model and of the ionization induced positive charge trapping in the buried and isolation oxides. The results lead to the conclusion that in n-MOSFETs, an additional generation-recombination component becomes active by the charge trapping. In the p-type counterparts, on the other hand, it is believed that irradiation modulates the body-channel coupling factor, giving rise to a strong increase of SI with VBG, while the corresponding τ is in a first approximation not affected.
Monte Carlo simulation on dielectric and ferroelectric behaviors of relaxor ferroelectrics
Authors: Wang X. , Liu J.-M. , Chan H. L. W. , Choy C. L.
Published: March 2004

The dielectric and ferroelectric behaviors of relaxor ferroelectrics over the ferroelectric transition range are simulated using Monte Carlo simulation. The simulation is based on the Ginzburg–Landau ferroelectric model lattice in which a random distribution of two types of defects (dopants) which will suppress and enhance the local polarization, respectively, is assumed. The simulation reveals an evolution of the ferroelectric transitions from a normal first-order mode toward a diffusive mode, with increasing defect concentration. The simulated lattice configuration shows the microdipole ordered clusters embedded in the matrix of paraelectric phase over a wide range of temperature, a characteristic of relaxor ferroelectrics. The relaxor-like behaviors are confirmed by the lattice free energy, dielectric susceptibility, and ferroelectric relaxation evaluated as a function of the defect concentration. Finally, we present a qualitative comparison of our simulated results with the simulation based on the coarse-grain model [C. C. Su, B. Vugmeister, and A. G. Khachaturyan, J. Appl. Phys. 90, 6345 (2001)].