bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport characteristics of a window-coupled quantum-wire system in nonuniform magnetic fields
Authors: Sheng Weidong , Xu Hongqi
Published: July 2002

This work reports on a theoretical investigation of magnetotransport in a window-coupled quantum-wire system using a scattering matrix method. The system consists of two parallel quantum channels with magnetic fields of the same strength applied and a ballistic coupling window without being applied with magnetic field. Two magnetic-field configurations in which the magnetic fields have been applied both parallelly and antiparallelly are considered. Various transmissions and two typical four-terminal resistances (a Hall and a longitudinal resistance) are calculated. Predicted for the system in both magnetic field configurations are a general enhancement of the wave coupling in the low strength region of the magnetic fields and sharp resonant and antiresonant peaks in the transmissions through the coupling window in the strong strength region. We attribute this enhancement to the suppression of backscattering of electron waves at the interfaces between the coupling window and the quantum channels and these peaks to resonant transmissions and resonant reflections via localized states formed in the coupling window. The calculated Hall and longitudinal resistances show different behaviors in the low strength region of the magnetic fields, while in the strong strength region they, at a given number of open modes in the quantum channels, depend only on a single nonzero transmission through the coupling window. The electron charge density and electron flux density at selective strengths of the applied magnetic fields are calculated and plotted in order to illustrate the physics associated with the predicted transport properties of the system.
Study of interfaces in Co/Cu multilayers by low-angle anomalous x-ray diffraction
Authors: de Bernabé A. , Capitán M. J. , Fischer H. E. , Prieto C.
Published: July 2002

The innovative method of combining specular and off-specular low-angle x-ray diffraction, along with the anomalous scattering effect, has been used to characterize magnetron-sputtered Co/Cu multilayers. The anomalous dispersion of Co is employed to increase the electron density contrast between the cobalt and copper layer. The use of a simulation program has been proven to be a straightforward and reliable method to analyze x-ray low-angle diffraction patterns in such a nonperfectly ordered metallic multilayer system. This method has been successfully applied to data obtained from synchrotron experiments and the results compared with those performed using a standard laboratory diffractometer. The combination of both specular and off-specular scans has ensured the obtention of a single set of simulation parameters for the structure of the multilayer and its interfaces. In addition, the off-specular scans have permitted us to confirm, in a rather complex system, the validity of the distorted wave born approximation. The mesoscopic structure of this multilayered system has been accurately and self-consistently characterized.
The thermal behavior of atoms in ultrafine-grained Ni processed by severe plastic deformation
Authors: Zhang K. , Alexandrov I. V. , Valiev R. Z. , Lu K.
Published: July 2002

X-ray diffraction investigations in a temperature range from 85 to 295 K were performed on an ultrafine-grained (UFG) Ni sample processed by severe plastic deformation. A significantly enhanced thermal expansion coefficient of 3.75×10−5 K−1 was observed in the UFG Ni sample, which is three times higher than in the conventional coarse-grained Ni polycrystal. The Debye–Waller parameter and its temperature-dependent and temperature-independent components are revealed to be larger in the UFG Ni sample. The obtained Debye temperature in the UFG Ni sample is decreased by 22%. The altered thermal properties in the UFG Ni sample are attributed to the nonequilibrium dislocations that disturb grain boundaries leading to large atomic displacements near interfaces.
Heterodyne interferometric measurement of the thermo-optic coefficients of potassium niobate
Authors: Chang Springfield , Hsu Chia-Chen , Huang Tzer-Hsiang , Lin Sen-Wei , Leaung Chung-Yi , Liu Tsai-Tien
Published: July 2002

A heterodyne interferometric technique is applied to determine the thermo-optic coefficients of a potassium niobate crystal with a GaAlAs diode laser. The heterodyne beats signal, resulting from the beating of the carrier and two side-band frequencies, is related to the phase shift difference between the carrier and the side-bands. This phase shift difference is determined with a phase sensitive detection technique and is found to be temperature dependent. From the temperature dependence, the thermo-optic coefficients of the potassium niobate crystal along the b and c crystallographic axes are determined to be −4.5×10−5 and 6.7×10−5 °C−1, respectively.
Negative differential conductivity of electrons in electron-beam sustained discharge in pure xenon
Authors: Kochetov I. V. , Napartovich A. P. , Ye C. , Lo D.
Published: July 2002

The mechanism of negative differential conductivity (NDC) in an electron-beam sustained gas discharge of pure Xe is investigated by modeling. The drift velocity of electrons in Xe has been calculated using a self-consistent kinetic model. Model calculations involves the self-consistent solution of the Boltzmann equation for electron energy distribution function in the two-term approximation and a complete set of rate equations for the excited and ionic species in the discharge plasma. It is shown that the main factor responsible for the observation of the NDC effect is Coulomb interaction between electrons. Regions in experimentally achievable parameter space where NDC can be observed are determined.
The effect of thermal resistances and regenerative losses on the performance characteristics of a magnetic Ericsson refrigeration cycle
Authors: Chen Jincan , Yan Zijun
Published: July 2002

The effect of the irreversibilities due to thermal resistances and regenerative losses on the performance of a magnetic Ericsson refrigeration cycle is investigated, based on the Curie law and Newtonian heat-transfer law. Some fundamental optimum relations and general performance characteristics of the cycle are obtained. The maximum cooling rate and some important performance parameters are calculated. The optimal operating regions of the cycle are determined. The results obtained will be helpful for the optimal design and operation of real magnetic Ericsson refrigerators.
Probing nanodefects in fused silica by near-field scanning optical microscopy
Authors: Wang Li , Yan M. , Siekhaus W. , Oberhelman S.
Published: July 2002

Nanodefects were artificially introduced into a fused silica surface by nanoindenting with a commercial atomic force microscope. The sample was illuminated in a total internal reflection configuration and evanescent waves were detected by a near-field scanning optical probe in the constant tip-sample separation mode. The observed contrast in optical images was attributed to the strain fields associated with the nanoindents. Thus the optical image directly maps out the strain distributions associated with these nanoindents. Optical images were taken at different polarizations of the incident light (s and p). Due to different field distributions near the sample surface for the two polarizations, strain distributions at different depths were probed. The spatial resolution of this technique was limited by the probe aperture size and detector sensitivity. This technique may be a useful tool to study laser-induced damage mechanisms in optical materials at the submicron scale.
Constructal tree networks for the time-dependent discharge of a finite-size volume to one point
Authors: Dan N. , Bejan A.
Published: July 2002

This paper shows that the time needed to discharge a volume to a concentrated sink can be minimized by making appropriate changes in the geometry of the flow path. The time-dependent flow of heat between a volume and one point is chosen for illustration, however, the same geometric optimization method (the constructal principle) holds for other transport processes (fluid flow, mass transfer, conduction of electricity). There are two classes of geometric degrees of freedom in designing the flow path: the external shape of the volume, and the distribution (amount, location, orientation) of high-conductivity inserts that facilitate the volumetric collection of the discharge. The optimization of flow path geometry is executed in a sequence of steps that starts with the smallest volume elements and proceeds toward larger and more complex volume sizes (first constructs, second constructs, etc.). Every geometric feature is the result of minimizing the time of discharge, or the resistance in volume-to-point flow. The innermost details of the structure have only a minor effect on the minimized time of discharge. The high-conductivity inserts come together into a tree-network pattern which is the result of a completely deterministic principle. The interstices are equally important in this optimal design, as they are occupied by the low-conductivity material in which the energy charge was stored initially. The paper concludes with a discussion of the relevance on this deterministic principle—the constructal law—to predicting structure in natural flow, and to understanding why the geometry of nature is not fractal.
Electric field redistribution and electroluminescence response time in polymeric light-emitting diodes
Authors: Österbacka R. , Juška G. , Arlauskas K. , Pal A. J. , Källman K.-M. , Stubb H.
Published: July 2002

The electric field redistribution due to injected and trapped charge carriers in Langmuir–Blodgett (LB) films of poly(3-hexylthiophene) (P3HT) sandwiched between indium tin oxide and aluminum (Al) electrodes as function of applied voltage has been studied using charge collection measurements by the time-of-flight technique. For μτE<d (the drift distance shorter than the interelectrode distance) the amount of the collected photocharge is a function of electric field near the Al electrode and has been used to probe the time evolution of it. The response time for the field to redistribute inside the P3HT LB film was found to be of the order of 5–200 μs, in good agreement with the delay time observed in time-resolved electroluminescence measurements in light-emitting diodes (LED) of similar LB films. We suggest a model for the response times in organic LEDs based on these results.
Light scattering and enhanced optical absorption in hot wire microcrystalline silicon
Authors: Diehl F. , Schröder B. , Oechsner H.
Published: July 2002

It is attempted to clarify the origin of the enhanced optical absorption in hot wire microcrystalline silicon (hw-μc-Si:H) which is not yet fully understood. We investigated the influence of elastic light scattering on the enhanced optical absorption of hw-μc-Si:H by means of an Ulbricht sphere and angular resolved scattering measurements, respectively. The experiments clearly revealed that elastic light scattering is not mainly responsible for the enhanced optical absorption in hw-μc-Si:H compared to that in monocrystalline material. They confirm the absorption enhancement to be a bulk effect which is determined by the structural properties of the material and the hydrogen incorporation into the samples. With regard to the origin of the absorption enhancement we refer to an absorption model for hw-μc-Si:H being briefly outlined.
Stresses, deformation, and void nucleation in locally debonded metal interconnects
Authors: Shen Y.-L.
Published: July 2002

Three-dimensional analyses of stresses and deformation in metal interconnects were carried out using the finite element method within the continuum framework. Particular attention is devoted to the preexisting local debond between the metal line and dielectric, which serves as the void nucleation site. Thermal mismatch induced stresses in the aluminum line near the interface defect are considered. The local reduction of stresses as well as the stress gradient along the line are quantified for various debond sizes. It is found that, for aluminum lines with an aspect ratio of unity, the influence of local debond on the stress profile along the line direction becomes negligible in regions greater than about one line height away from the debond edge. A unique stress pattern due to the preexisting debond is identified, which forms the basis of constructing a void nucleation model in terms of crystallographic slip. This three-dimensional modeling provides quantitative information on the initial stress field useful for modeling stress and electromigration induced voiding; it also confirms the qualitative features of stress evolution obtained from a previous two-dimensional analysis.
Indium–tin oxide treatments for single- and double-layer polymeric light-emitting diodes: The relation between the anode physical, chemical, and morphological properties and the device performance
Authors: Kim J. S. , Granström M. , Friend R. H. , Johansson N. , Salaneck W. R. , Daik R. , Feast W. J. , Cacialli F.
Published: July 2002

We report combined studies of the influence of chemical and physical treatments on the properties of indium–tin oxide (ITO) thin films. The ITO films were also used as transparent anodes of polymeric light-emitting diodes (LEDs) incorporating poly(p-phenylene vinylene) (PPV) as the emitter material, with, or without, doped poly(3,4-ethylene dioxythiophene) (PEDOT) as a hole-injection/transport layer. Structures based on a soluble green derivative of PPV, poly(4,4′-diphenylene diphenylvinylene) were also tested. We studied chemical (aquaregia, degreasing, RCA protocol) and physical (oxygen and argon plasmas, Teflon, and paper rubbing) treatments and, in contrast to recently published work, we find that for Balzer Baltracon ITO, oxygen plasma and not aquaregia yields the highest efficiencies and luminances and the lowest drive voltages. For oxygen-plasma-treated anodes, the device efficiency clearly correlates with the value of the ITO surface work function, which in turn depends on the time of treatment. Interestingly, we find that work-function variations induced by our oxygen-plasma treatment are unchanged after long-term storage in air and in the dark. Unexpectedly, we also find that devices incorporating a PEDOT layer benefit from an appropriate treatment of the ITO surface, for both efficiency and lifetime. The results shed light on the physics of conjugated, organic semiconductors and related devices, and in particular on the presence and the role of an anodic energy barrier on the LEDs mechanism of operation. We also discuss the implications of our integrated experimental study in relation to the modification of the ITO sheet resistance, surface and bulk composition, and surface morphology.
Nucleation and development of Goss texture and magnetic induction in thin-gauged 3% Si–Fe alloy
Authors: Heo N. H. , Chai K. H. , Na J. G. , Kim J. , Woo J. S.
Published: July 2002

Nucleation and development of Goss texture have been investigated in high-purity 3% silicon–iron alloy strips. During final annealing, under a high vacuum, Goss texture can form independently from cold-rolled matrix at the early stage of primary recrystallization, regardless of any pre-existing Goss texture near the strip surface. The formation mechanism of the new Goss texture probably follows the oriented nucleation theory, which is due to segregated sulfur present on the strips in a final annealing time. Goss texture in the primary recrystallization develops into the final Goss texture or not, depending on cold rolling conditions.
Normal-state magnetic properties and their correlation with Tc suppression and the resistivity anomalies in the (La1−xPrx)1.85Sr0.15CuO4 series
Authors: Musa J. E. , Garcı́a S. , Rothier de Amaral M. , Salim de Amorim H. , Giordanengo B. , Baggio-Saitovitch E. M. , Pagliuso P. J. G. , Rettori C. , Yelon W. B. , Malik S. K.
Published: July 2002

We have investigated the normal-state anomalies observed in the magnetic and transport properties of the (La1−xPrx)1.85Sr0.15CuO4 system with 0⩽x⩽0.5. The resistivity curves showed an increasing deviation from linearity below ∼100 K. This behavior is properly accounted by a logarithmic term, whose coefficient C linearly increases with x. The normal-state magnetic susceptibility measurements evidenced a departure from the Pr3+ Curie–Weiss dependence in the same temperature range for which the resistivity anomaly occurs. A comprehensive picture of the conduction mechanism is presented in terms of a Kondo-like scattering of the mobile holes by the spin fluctuations.
Cubic anisotropic magnets with a random field
Authors: Nicolaides D. , Lisyansky A. A.
Published: July 2002

The critical behavior at phase transitions of m-component random magnets with cubic anisotropy is studied within the context of an exactly solvable model. The presence of a random field suppresses any phase transition for spatial dimensions d⩽4. If one or more of the components of the random field are zero, but with at least one nonzero component, a new second-order phase transition in the anisotropic phase occurs. In the pure case second-order transitions could happen only into the isotropic phase. The critical temperature of this new, random-field-induced second-order transition decreases with increasing randomness.
Long range order in two-dimensional spin models with long range interactions
Authors: Rastelli E. , Carbognani A. , Regina S. , Tassi A.
Published: July 2002

We show that simple spin wave theory does not provide a reliable indication of long range order or no long range order in two-dimensional square models of two-component spins coupled by long range interactions. This failure occurs when accidental soft modes are provided by harmonic approximation owing to accidental infinite degeneracy of the ground state configuration. Indeed simple spin wave theory gives no long range order both for isotropic long range antiferromagnetic interaction decaying as 1/r3 and for dipolar interaction. On the contrary renormalized spin wave theory replaces accidental soft modes by temperature dependent gaps, so providing no long range order in the former case and long range order in the latter case in agreement with Monte Carlo simulation.
Effect of elastic interaction on critical behavior of three-dimensional Ising model
Authors: Boubcheur E. H. , Diep H. T.
Published: July 2002

We study a three-dimensional (3D) Ising model with ferromagnetic interaction and elastic (cohesive) interaction between neighboring atoms by Monte Carlo simulation. When the elastic interaction strength is much larger than that of the magnetic one, the transition from ferromagnetic state to paramagnetic phase is of the 3D Ising universality class. However, the critical behavior of the 3D Ising model changes into a 3D XY universality when the elastic interaction is smaller than a critical value.
Magnetic properties and microstructure of Mn–Al–C thin films
Authors: Kuo P. C. , Ker K. J. , Yao Y. D. , Huang J. H.
Published: July 2002

Mn x Al 100−x−y C y thin films with x=35–65 at. % and y=0–2.4 at. % were prepared by rf magnetron sputtering. Effects of the chemical composition and annealing temperature on the magnetic properties and microstructure of Mn–Al–C films were investigated. X-ray analysis shows that the as-deposited Mn–Al–C thin films are amorphous, and their saturation magnetization is very low. After annealing at temperatures between 400 and 550 °C in vacuum for 30 min, the magnetic phase with higher carbon concentration shows better thermal stability. The best annealing condition was found to be at 410 °C for 30 min. A ferromagnetic τ phase with a grain size of roughly 200–250 nm appeared at a composition range between 40 and 60 at. % Mn for MnxAl99−xC1 thin films; and the sample with Mn50Al49C1 has high coercivity and moderate saturation magnetization. The carbon addition can increase the thermal stability of the coercivity of the Mn–Al thin films.
Back electromotive force enhancement for a new single-phase synchronous motor
Authors: Lin Yin-Kwang , Huang Der-Ray , Chen Shin-Lu , Chiu Kuo-Chi , Ying Tai-Fa , Hsu Chung-I G.
Published: July 2002

In this article, the back electromotive force (emf) of a new single-phase synchronous motor of the two-pole type useful in aquarium application is studied. Based on a two-dimensional model, the finite-element method is used to numerically analyze the magnetic field distribution inside the motors, from which the back emfs can be computed. Three different shaping schemes on the stator are investigated, with the objective of enhancing the back-emf constant as well as eliminating the starting dead point. Experiments are conducted on one of the shaping schemes, where the measured data are found to agree very well with the numerical results. To predict the transient behavior of the motors in the startup period, parameters extracted from the numerical results are built into a database. From this database a set of dynamic equations governing the current and angular speed can be constructed, which provides significant accuracy as compared with the experimental values.
Structure and magnetostriction of PrxDy1−xFe2 and Pr0.4Dy0.6(Fe1−yMy)2 alloys (M=Co, Ni)
Authors: Wang Bo-wen , Guo Zhi-jun , Zhang Zhi-dong , Zhao Xin-guo , Busbridge S. C.
Published: July 2002

The structure, Curie temperature and magnetostriction of PrxDy1−xFe2 (0⩽x⩽0.5) and Pr0.4Dy0.6(Fe1−yMy)2 (0⩽y⩽0.6) alloys (M=Co, Ni) have been investigated using optical microscopy, x-ray diffraction, ac initial susceptibility and standard strain gauge techniques. The matrix of homogenized PrxDy1−xFe2 alloys is a cubic Laves phase (Pr, Dy)Fe2 with MgCu2-type structure, with a small amount of second phase (Pr, Dy)Fe3 when x⩽0.2. The amount of (Pr, Dy)Fe3 phase increases with the increase of Pr content, and it becomes the main phase when x=0.4. When x=0.5, the matrix is found to be the (Pr, Dy)2Fe17 phase coexisting with a small amount of phases (Pr, Dy)Fe2, (Pr, Dy)Fe3 and rare-earth rich phases. For Pr0.4Dy0.6(Fe1−yCoy)2 alloys, the amount of (Pr, Dy)(Fe, Co)2 phase increases with increasing Co content and the phase (Pr, Dy)(Fe, Co)2 becomes the main phase when y=0.6. However, the substitution of Ni for Fe up to 60 at % Ni in Pr0.4Dy0.6Fe2 alloys does not favor the formation of the cubic Laves phase (Pr, Dy)(Fe, Ni)2. The lattice constant of PrxDy1−xFe2 alloys decreases with increasing x, whereas the Curie temperature Tc increases. The magnetostriction of PrxDy1−xFe2 alloys at room temperature exhibits a peak at x=0.3. The lattice constant of Dy0.6Pr0.4(Fe1−yCoy)2 alloys decreases slowly with increasing y; Tc shows a peak when y=0.45, and the room temperature magnetostriction becomes negative when x>0.45. The Curie temperature of Dy0.6Pr0.4(Fe1−yNiy)2 alloys decreses with the increase of Ni content. The room temperature magnetostriction of Dy0.6Pr0.4(Fe1−yNiy)2 also becomes negative when x>0.45.
Patterned growth on GaAs (311)A substrates: Dependence on mesa misalignment and sidewall slope and its application to coupled wire-dot arrays
Authors: Fricke Jörg , Nötzel Richard , Jahn Uwe , Schönherr Hans-Peter , Däweritz Lutz , Ploog Klaus H.
Published: July 2002

During molecular beam epitaxy of (AlGa)As on patterned GaAs (311)A substrates, mesa stripes along [01-1] develop a fast-growing sidewall with a smooth, unfacetted, convex surface profile which has been utilized for the formation of lateral quantum wires. In the present study this growth mechanism is found to be strongly sensitive, both on the misalignment of the mesa stripes from the [01-1] direction as well as on the sidewall slope. For wet chemical etching which produces a 50° steep sidewall of the starting mesa stripe along [01-1], the formation of the convex surface profile is not affected for a misalignment smaller than 20°. Above 20°, the selectivity of growth monotonically decreases and the surface profile continuously develops into that of the slow growing concave sidewall along the perpendicular [-233] direction for misalignment larger than 50°. In contrast, for reactive ion etched vertical sidewalls, almost no growth occurs for [01-1]-oriented mesa stripes while the evolution of the fast growing sidewall is recovered for misaligned mesa stripes. This behavior, which is qualitatively related to the bond configuration of the starting side facets, thus provides a unique parameter to control the selectivity of growth on patterned GaAs (311)A substrates, which is utilized for the formation of coupled wire-dot structures.
Structural dependence of combustion-flame synthesized diamond films on substrate temperatures
Authors: Takahashi Hiroaki , Després Jean-François , Odawara Osamu
Published: July 2002

Structural changes of diamond film surfaces deposited by a combustion-flame method have been investigated with varying temperatures of the substrates made of Mo, Si, and W. The crystal faces of the deposited diamonds have changed from {111} to {100} with increasing substrate temperatures. The appearance of the {100} faces occurred at around 1200 K for the Mo substrate, and at around 1100 K when using the Si or W substrate. Raman peaks of the diamond deposited below 1400 K and the sample deposited at 1400 K on W substrate present a splitting line shape, which indicates a presence of anisotropic stresses in the crystals. However, when deposited above 1400 K and the sample at 1400 K on Mo substrate, no splitting peak existed, which means no anisotropic stresses remained. The results suggest that the peak splitting can be correlated to crystal shapes and anisotropic intrinsic stresses induced by growth defects.
Formation of modified Si/SiO2 interfaces with intrinsic low defect concentrations
Authors: Gosset L. G. , Ganem J. J. , von Bardeleben H. J. , Rigo S. , Trimaille I. , Cantin J. L. , Åkermark T. , Vickridge I. C.
Published: July 2002

The modification by postoxidation NO treatments of the Si/SiO2 interface in thermally grown Si(100)/SiO2 layers has been studied by nuclear reaction analysis and electron paramagnetic resonance spectroscopy. Our results demonstrate a selective incorporation of NO molecules at the Si/SiO2 interface and a drastic reduction in the interface defect density. In this new configuration, the Pb center density, which is typically 2×1012 cm−2 in the as oxidized samples, is reduced to below 1011 cm−2 without any hydrogen passivation. The thermal treatment in NO atmospheres opens the perspective for the formation of hydrogen free low defect Si(100)/SiOxNy interfaces conserving the qualities of the SiO2 dielectric.
Flux penetration measurements and the harmonic magnetic response of hot isostatically pressed (Pb,Gd)Mo6S8
Authors: Ramsbottom H. D. , Hampshire D. P.
Published: July 2002

Detailed flux penetration measurements and the harmonic magnetic response have been measured from 4.2 K up to the critical temperature in dc fields up to 10 T for a hot isostatically pressed Chevrel-phase superconductor (Pb,Gd)Mo6S8. Good agreement is found between experimental results up to the tenth harmonic and calculations derived from a critical-state model which demonstrates that on the macroscopic scale the supercurrents flow throughout the bulk of the material. The field and temperature dependence of the critical current density shows a universal scaling behavior in agreement with Kramer’s pinning law, which suggests that a single grain-boundary mechanism determines the critical current density. Complementary compositional microscopy, x-ray, resistivity, and susceptibility data are presented. When gadolinium is not incorporated into the crystal structure it acts primarily as an oxygen getter in the form Gd2S3, which enhances the density of paths of PbMo6S8 with low oxygen content and high superconducting critical parameters. When the divalent gadolinium replaces the trivalent lead to form (Pb1−xGdx)Mo6S8, it reduces the density of hole states at the Fermi energy which lowers the critical parameters, the critical current density, and the irreversibility field.
Electron cooling by arrays of submicron tunnel junctions
Authors: Leoni R. , Arena G. , Castellano M. G. , Torrioli G.
Published: July 2002

We cooled down the electrons of a 3 μm3 copper strip by using an on-chip electronic microcooler made by a superconductor-insulator-normal-insulator-superconductor (SINIS) structure. We obtained an electron temperature drop ΔT≃−10 mK at a temperature of the bath slightly above Tb=500 mK and we estimated a cooling power slightly larger than 20 pW at this temperature. In contrast to previous experiments, we obtained this result operating with a simple He3 refrigerator. The copper strip temperature change was sensed by measuring the voltage change across a current-biased SINIS junction, with a temperature responsivity ΔV/ΔT≃−500 μV/K. On-chip microcooler and thermometer have been fabricated by two-angle shadow mask evaporation and e-beam lithography.
Electrical and structural properties of Re/GaAs Schottky diodes
Authors: Lin Chia-Chien , Wu Meng-Chyi
Published: July 2002

This article presents the thermal stability of the electrical and structural properties of Re/GaAs Schottky diodes annealed in the temperature range 600–1000 °C. Results of the current–voltage measurement, 2 MeV He2+ ions Rutherfold backscattering, x-ray diffractometer, and transmission electron microscope were analyzed and discussed. The Re/GaAs diode, annealed at temperatures as high as 800 °C, typically has an ideality factor of ∼1.14 and a barrier height of about 0.65–0.71 eV. It also exhibits a low sheet resistance, which is less than 10 Ω/□. With annealing temperature increases up to 900 °C, the interdiffusion between Re film and GaAs substrate was observed. Furthermore, the intermetallic compound Re3As7 is considered to form in the Re/GaAs sample annealed at 1000 °C. The experimental results provide evidence that the Re/GaAs interface is metallurgically inert up to 800 °C and therefore a Schottky barrier with highly thermal stability can be expected.
The effect of thermal activation on the coercivity of domain walls
Authors: Lopez-Diaz L. , Della Torre E. , Moro E.
Published: July 2002

The effect of temperature is rarely taken into account in micromagnetic calculations. However, thermal perturbations are known to play an important role in magnetization reversal processes. In this article, a micromagnetic model that includes thermal perturbations is presented. A stochastic zero-mean Gaussian field is introduced in the Landau–Lifschitz–Gilbert equation and the corresponding Langevin equation is solved numerically. The model is used to study the effect of temperature on the coercivity of domain walls due to exchange and anisotropy wells as well as nonmagnetic inclusions. It is shown that, for exchange and anisotropy interactions, thermal perturbations can lower the critical field for which the wall breaks free from the inclusion. However, when magnetostatic fields are taken into account, thermal perturbations are found to inhibit the unpinning process. This phenomenon seems to be related to the long-range nature of dipolar interactions.
Nonlinear magnetoelastic anisotropy in Cu/Ni/Cu/Si(001) films
Authors: Ha Kin , O’Handley Robert C.
Published: July 2002

A spin-pair model including magnetoelastic terms to second order in strain is used to analyze the magnetic anisotropy of epitaxial Cu/Ni/Cu/Si(001) films. Two adjustable parameters are used to fit the magnetic anisotropy data taken by a torque magnetometer. It is found that the nonlinear bulk magnetoelastic term can contribute up to about 40% of the total anisotropy energy for thinner nickel films.
Substrate, annealing, and Mn excess effects on La–Ca–MnO3 thin films grown by metalorganic chemical vapor deposition: A way to room-temperature Tc
Authors: Tavares P. B. , Amaral V. S. , Araújo J. P. , Sousa J. B. , Lourenço A. A. C. S. , Vieira J. M.
Published: July 2002

Oriented thin films of the La–Ca–MnO3 system with several Mn-excess compositions were prepared by aerosol-assisted metalorganic chemical vapor deposition. Depositions both on MgO (100) and LaAlO3 (100) substrates were performed at temperatures between 700 and 800 °C, with 30 min in situ oxygen annealing at the deposition temperature. The films deposited on LaAlO3 have much better structural quality with rocking curves of 0.3–0.7 full width at half maximum and higher Tc. For films with Mn excess, an ex situ annealing (800 °C for 1 h in flowing oxygen) increases Tc dramatically, from 180–190 K to values in the range 240–296 K, above the maximum Tc of the stoichiometric, optimally doped La0.67Ca0.33MnO3 composition. This behavior may be associated with the presence of La vacancies, which act as self-dopants, and whose role is enhanced after suitable annealing. The films present high magnetoresistance values in the vicinity of the critical temperatures: at 7 kOe, 32% for a film with Tc=279 K and 13% for a film with Tc=296 K. The magnetic properties of the films on MgO were degraded by annealing, probably due to Mg diffusion to the film.
Assessment of dry etching damage in permalloy thin films
Authors: Kim S. D. , Lee J. J. , Lim S. H. , Kim H. J.
Published: July 2002

Permalloy (Ni81Fe19) thin films are etched by ion beam etching (IBE) or reactive ion etching (RIE), and the variation of magnetic properties with etching time is investigated. Magnetic softness of permalloy thin films deteriorates as etching proceeds, i.e., film thickness decreases. Coercivity begins to increase steeply at a thickness of 0.4 μm and reaches 16 Oe for IBE and 8 Oe for RIE at 0.09 μm. Effective magnetization is increased by 0.2 kG with IBE but decreased by 0.7 kG with RIE. From an atomic force microscopy analysis and independent wet etching experiments, the increase of coercivity is proved to be attributed to the increase of surface roughness as a result of etching. Etching-induced defects are also responsible for the increase of coercivity, which is confirmed by a measurement of electrical resistivity and x-ray diffraction analysis. Ion beam etching process appears to affect magnetic properties to a greater extent than reactive ion etching process.
Al substituted Ba ferrite films with high coercivity and excellent squareness for low noise perpendicular recording layer
Authors: Feng J. , Matsushita N. , Watanabe K. , Nakagawa S. , Naoe M.
Published: July 2002

Al substituted BaM (Al–BaM) ferrite films with composition of BaAlxFe12−xO19 (x=0,1,2) were deposited using facing targets sputtering apparatus on SiOx/Si wafers with a Pt seed layer. A postannealing process is necessary to crystallize the films. It was confirmed that the substrate temperature Ts is also one of the important parameters for the magnetic properties of the postannealed films. Al–BaM ferrite films exhibit the Ts dependence of magnetic properties different from that of simple BaM ones. With increase of the Al content x in Al–BaM ferrite films, 4πMs decreased, while Hc and the anisotropy field HA increased. It was found that acicular shape grains formed more easily in Al–BaM ferrite films than in simple BaM ones. The squareness S⊥ increased largely by substitution of Al for Fe. The Al–BaM ferrite films with high Hc⊥ (∼3 kOe) and large S⊥(∼0.9) may be applicable as perpendicular magnetic recording layers with low noise level.
Magnetic properties of single-crystalline Mott insulator YVO3
Authors: Nakotte H. , Laughlin L. , Kawanaka H. , Argyriou D. N. , Sheldon R. I. , Nishihara Y.
Published: July 2002

Single crystals of YVO3 were grown using the floating-zone technique. YVO3 crystallizes in the orthorhombic Pbnm structure, and the structural parameters were determined by means of neutron diffraction. Using a superconducting quantum interference device magnetometer, we have studied the magnetic properties of YVO3 along the three principal directions. Our single crystal exhibits two magnetic transitions at about 115 and 75 K. For temperatures above the magnetic ordering, almost isotropic Curie–Weiss behavior is found for the magnetic susceptibility. Below the ordering, however, we find a highly anisotropic response with the c axis as the easy-magnetization direction. Both magnetic phases exhibit a weak ferromagnetic component along the c axis. A complex low-field magnetization behavior indicates that YVO3 orders ferrimagnetically for temperatures between 75 and 115 K.
Magnetic force and Lorentz transmission electron microscopy analysis of bit transitions in longitudinal media
Authors: Abarra E. N. , Okamoto I. , Suzuki T.
Published: July 2002

Written bits on a 3 kOe CoCrPtTa/Si longitudinal recording medium are investigated by magnetic force microscopy (MFM) and Lorentz transmission electron microscopy (LTEM). For most defocusing distances, the observed signal contrast is greatest at the track edges where the magnetization is antiparallel to the dc-erased intertrack regions. Head-on type “walls” at the transitions show limited contrast indicating small amplitude deviations in the zigzag transition as observed by MFM. Results are markedly different from earlier work on recording media which revealed large zigzag amplitude and or vortex formation at the transition. LTEM images suggest an increase in the track-edge noise and a reduction in the effective track width with density, presumably due to flux leakage of the head field at the pole edges.
Computed electron oscillation inside the duct of a vacuum arc source
Authors: Kwok T. K. , Zhang T. , Chu P. K. , Bilek M. M. M. , Brown I. G.
Published: July 2002

A three-dimensional numerical model has been developed to simulate the motion of electrons inside the duct of a vacuum arc metal source. It is found that electrons will travel back and forth along the center axis inside the duct tube. This phenomenon of electron oscillation can be explained by the combined effects of the electric and magnetic fields. The electron oscillation will increase the charge state of the positive ions and the ions will gain more energy. Due to the influence of electron oscillation, the plasma throughput of the duct will be different from that of a duct under the influence of only the magnetic field. This finding should be taken into account when designing metal arc sources and optimizing their performance.
Configuration of dislocations in lateral overgrowth GaN films
Authors: Hao M. , Mahanty S. , Sugahara T. , Morishima Y. , Takenaka H. , Wang J. , Tottori S. , Nishino K. , Naoi Y. , Sakai S.
Published: July 2002

The dislocation distribution and emission profile of sublimation lateral overgrowth GaN and metalorganic chemical vapor deposition films have been studied using transmission electron microscopy and cathodoluminescence. A close relationship between the emission profile and the dislocation distribution has been observed. The results show that the dislocations not only affect the band edge emission, but also the yellow emission. It is observed that the dislocations propagate laterally in the overgrowth region. The mechanism of the change in the propagation direction of dislocations has been discussed.
Band lineup of a SnS2/SnSe2/SnS2 semiconductor quantum well structure prepared by van der Waals epitaxy
Authors: Schlaf R. , Pettenkofer C. , Jaegermann W.
Published: July 2002

A quantum well composed of layered semiconductors and SnSe2 (Eg=1.03 eV) and SnS2 (Eg=2.18 eV) was grown in several steps by van der Waals epitaxy. After each growth step the electronic structure was characterized by ultraviolet and x-ray photoemission spectroscopy. From these measurements, bandbending and the valence-band offset were determined on both sides of the quantum well. The results show that both wells are of the same magnitude, hence indicating commutativity of the band offset. Small interface dipoles (0.11–0.19 eV) were detected at the interfaces, which could be identified as quantum dipoles.
Distribution of fields and charge carriers in cylindrical nanosize silicon-based metal–oxide–semiconductor structures
Authors: Pokatilov E. P. , Fomin V. M. , Balaban S. N. , Gladilin V. N. , Klimin S. N. , Devreese J. T. , Magnus W. , Schoenmaker W. , Collaert N. , Van Rossum M. , De Meyer K.
Published: July 2002

A quantum–mechanical description of charge carriers is presented for nanoscaled cylindrical metal–oxide–semiconductor structures. The Schrödinger and Poisson equations are solved self-consistently within the framework of the Hartree approximation and the profiles of the electrostatic field and the charge carrier densities are obtained.
In situ optical assessment of semi-insulating iron doped InP grown by liquid encapsulated Czochralski process
Authors: Doğan S. , Tüzemen S. , Gürbulak B. , Ateş A. , Yildirim M.
Published: July 2002

In semi-insulating, Fe doped InP, we demonstrate that infrared absorption technique provides quantitative measurements of Fe concentrations. We show that the quantum efficiency is reduced more than 70% in Fe doped samples, in comparison to undoped samples. Relative near band edge photoluminescence (PL) intensity is antiproportional to Fe concentration. This can provide a calibration method to transform scanning PL images to quantitative Fe distributions. We demonstrate that infrared absorption mapping images Fe distribution in InP, in a similar way to EL2 imaging in GaAs. The images show that the slip-like defects decorated by Fe centers predominantly lie along [011] direction.
Transient exoelectron emission from a clean tungsten tip at 200–450 K triggered by the surface electric field
Authors: Shiota T. , Tagawa M. , Umeno M. , Ohmae N.
Published: July 2002

The temperature dependence of field-stimulated exoelectron emission (FSEE) on a clean W tip was investigated. The increase of the electron emission at the moment of reapplication of the tip voltage was observed at the temperatures 200–450 K. This emission property was similar to the storage effect of exoelectron emission from Al tips reported previously. [Appl. Phys. Lett. 53, 626 (1988).] However, the emission intensity was independent of the voltage interruption period. The change in work function was also indicated at the temperature where FSEE was observed. The FSEE on W tips observed in this study was explained by the exoelectron emission during the surface reconstruction of W{001} and/or W{031} triggered by the high electric field.
Explicit formulas for crack identification in conductors using boundary measurements of direct current fields
Authors: He Sailing , Romanov Vladimir G.
Published: July 2002

The identification of a crack in a conducting half space is considered. The equivalent current distribution model is applied to crack identification using boundary measurements of a dc magnetic field. A general uniqueness theorem is proved, and an explicit formula is given for identifying a surface-breaking crack whose contour is part of an ellipse. An explicit formula is also given for the identification of a long surface-breaking crack using boundary measurements of a dc electric field.
Spin-valve giant magnetoresistance films with antiferromagnetic PtPdMn
Authors: Anderson G. W. , Huai Yiming , Miloslavsky Lena , Qian Chester X. , Feng Yi
Published: July 2002

The antiferromagnetic alloy Pt20Pd30Mn50 has demonstrated a high exchange coupling field to a coupled NiFe film as well as high corrosion resistance, making it a promising candidate for use as the pinning layer of a spin valve. In this work we have investigated the magnetic and structural properties of spin-valve films exchange biased by CoFe/PtPdMn as compared to CoFe/IrMn spin valves. A spin-valve film structure of Ta50 Å/NiFe50 Å/CoFe20 Å/Cu28 Å/CoFe22 Å/PtPdMn300 Å/Ta50 Å annealed at 250 °C for 10 h showed a giant magnetoresistance of 6.5% with an exchange field of 680 Oe. The blocking temperature of this film is about 350 °C, compared to 250 °C for IrMn based spin valves. The remnant blocking temperature was also measured, and showed that for PtPdMn spin valves the exchange field was constant up to a temperature of 300 °C, in contrast to 180 °C for an IrMn spin valve. Structural ordering of the PtPdMn in a face-centered-tetragonal (fct) phase after annealing has been observed using x-ray diffraction and transmission electron microscopy. The x-ray diffraction data exhibits a strong face-centered-cubic (111) and fct (111) out-of-plane orientation for as-deposited and annealed samples. Transmission electron micrographs show a smooth interface between the PtPdMn and CoFe layers, columnar growth structure, and fct ordering of the PtPdMn.
Diffusion and structural modification of Ti:LiNbO3, studied by high-resolution x-ray diffraction
Authors: Avrahami Y. , Zolotoyabko E.
Published: July 2002

The ability of high-resolution x-ray diffraction, as a nondestructive method, to provide information on atomic diffusion is analyzed. The analysis focuses on studying Ti-diffused waveguide layers of LiNbO3 crystals for optoelectronic applications. Samples were prepared by a deposition of a 35-nm-thick Ti layer on the 3-in.-Y-cut LiNbO3 wafer and subsequent annealing at 995 °C for periods of 0.5–6 h. Depth-resolved profiles of the interplanar spacing derived from x-ray diffraction data are compared with the Ti-concentration profiles measured by secondary ion mass spectrometry. It is shown that both results can be used with confidence to determine the Ti-diffusion coefficients in LiNbO3. Comparison of the two techniques allowed us to obtain a numerical factor, K, relating the Ti concentration and the modification of lattice parameters, i.e., to characterize quantitatively the extent of lattice contraction due to Ti incorporation in the LiNbO3 crystal. The K factor was found to increase with annealing time, indicating a variable strain contribution to the structural parameters of the waveguide layer. These variations are attributed to high-temperature phase transformation processes, which accompany Ti diffusion.
Fabrication and magnetic properties of glass-coated microwires from immiscible elements
Authors: Zhukov A. , Sinnecker E. H. C. P. , Paramo D. , Guerrero F. , Larin V. , González J. , Vázquez M.
Published: July 2002

The Taylor–Ulitovski technique has been successfully employed to fabricate glass-coated microwires having internal nucleus made of alloys of various immiscible elements. Series of alloys CoxCu100−x, Co29Ni25Mn1Cu45, and (FeSiBC)50Cu50 have been studied from structural and magnetic points of view. The influence of thermal treatments on the structure and magnetic properties has been moreover studied with a final aim to obtain such type of microwires with enhanced hard magnetic properties. A maximum coercivity of around 750 Oe is achieved in the optimum conditions.
Parameter identification of bimodal, magnetostrictive material model
Authors: Reimers Ann , Della Torre Edward
Published: July 2002

A full identification method is outlined for the ten parameters of a bimodal model for highly magnetostrictive material. In the model, magnetization and strain hysteresis loops are modeled as the superposition of twin hysteresis loops, shifted in critical field activation value by equal amounts in opposite directions. Identification of the parameters for Terfenol-D and Terzinol-D show that the model predicts the behavior of the Terfenol-D better than that of the Terzinol-D, where more low field reversible behavior is evident.
Double transition behavior induced by coherent anisotropy in random anisotropy magnets amorphous HoFe and ErFe
Authors: Saito T. , Mochiduki K. , Masago E. , Shinagawa K. , Tsushima T.
Published: July 2002

Magnetic phase transition in weak random anisotropy magnets amorphous a-HoFe and ErFe thin films with “in-plane” coherent anisotropy are studied by measurements of temperature (T) dependence of ac susceptibility. We observed distinct difference in the ac susceptibilities between samples with the coherent anisotropy and without the coherent anisotropy; double transition behavior from paramagnetic to ferrimagnetic (FWA) to correlated spin-glass-like is induced by the coherent “in-plane” anisotropy field larger than about 8 kOe even without H. Such a behavior is also observed in a-DyGdFe with “perpendicular” coherent anisotropy. But, larger coherent anisotropy field than about 20 kOe is needed to induce the FWA state, which may arise from the symmetry difference in the coherent anisotropy.