bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum tunneling across a domain wall junction (abstract)
Authors: Barbara Bernard , Gunther Leon
Published: July 2002

In this paper, we discuss a system that is appropriately called a ‘‘domain wall junction’’ (DWJ). The DWJ is a close analog of the Josephson junction with respect to the usefulness of both systems in studying switching by thermal activation (TA) and by quantum tunneling (QT). What makes this system especially attractive for experimental and theoretical studies is that it is a single system, with a single set of parameters that characterizes its behavior. The essential nature and behavior of a DWJ has been elucidated by numerous authors. We show through theoretical analysis that it is within our means to fabricate a DWJ that should exhibit switching via quantum tunneling of magnetization. We further provide experimental procedures for looking for quantum tunneling of magnetization in a DWJ; these are based upon those that have been used in observing macroscopic quantum tunneling in Josephson junctions. Two examples of DWJs have been recently made that apparently show a crossover from TA to QT. Results of these experiments will be summarized.
Surface magnetization processes investigated by the combined surface magneto-optical Kerr effects in Fe/Cu(100) thin films
Authors: Yang Z. J. , Healy S. D. , Heim K. R. , Drucker J. S. , Hembree G. G. , Scheinfein M. R.
Published: July 2002

Surface and ultrathin-film anisotropies in epitaxial fcc Fe thin films grown on room temperature Cu(100) single crystals in an ultrahigh vacuum has been investigated, in situ, by the combined surface magneto-optical Kerr effects (SMOKE). When the applied field is perpendicular to the film surface, rotation processes occurring between out-of-plane and in-plane directions suggest the presence of an induced uniaxial (canted) anisotropy directed out of the plane of the film. This hypothesis is tested with a simple coherent rotation model.
Magnetization of thin Gd films on W(110) near the Curie temperature
Authors: Farle M. , Lewis W. A.
Published: July 2002

In situ temperature dependent magneto-optic Kerr effect measurements in ultrahigh vacuum are presented for 80 and 300 Å thick Gd(0001) films. Films were deposited at 300 K and stepwise annealed to 820 K. It was found that the remanent magnetization Mr(T) depends on the annealing temperature. The as-deposited films have a reduced Curie temperature Tc, e.g., Tc(80 Å)=273 K, which gradually shifts up to the bulk Tc of Gd upon annealing. The changes in Mr(T) are correlated with a sharpening of the Gd low energy electron diffraction pattern. The best magnetic homogeneity and structural coherence is found for films annealed to 620 K. At higher temperatures the films break up into large three-dimensional islands with nearly uncovered W areas in between (W Auger is observed). The magnetic behavior was simulated with a model which assumes a Gaussian distribution of Tc values. From these simulations and the known bulk pressure dependence of Tc we estimate the mean strain and the strain distribution within the films.
Controlling spin-wave chaos
Authors: Rezende S. M. , de Aguiar F. M. , Azevedo A.
Published: July 2002

Microwave pumped spin-wave instabilities in YIG spheres were one of the first experimental systems used to demonstrate that chaos can be suppressed by small periodic modulations in an accessible system parameter. Here we show that the equations describing two interacting spin-wave modes account satisfactorily for the experimental results, as long as the field modulation is appropriately introduced in the model. The finite detuning parameters expressing the boundary conditions of the sample provide a natural way for introducing the field modulation. Thus the present results constitute additional evidence of the validity of the two-mode model with momentum-nonconserving driving Hamiltonian used to explain the sample size dependence of the self-oscillations.
Coercivity enhancement in γ-Fe2O3 by surface treatment with phosphate ions
Authors: Nikles David E. , Parker Martin R. , Crook Elizabeth M. , Self Terry M.
Published: July 2002

Significant increases in coercivity were observed for stoichiometric γ-Fe2O3 pigments that were treated with different phosphate ions. The objectives of this investigation were to determine if the effect was specific to the phosphate anions as well as establishing the influence, if any, of induced compressive stress in coercivity enhancement. Stoichiometric γ-Fe2O3 pigments were treated with aqueous solutions containing the sodium salts of different anions and the changes in coercivity measured by vibrating sample magnetometry. The surface treatments were done in an aqueous suspension, followed by water evaporation, and vacuum treatment at 150–160 °C. Sodium phosphate, sodium pyrophosphate, sodium tripolyphosphate, sodium metaphosphate, poly(sodium acrylate), and sodium p-toluenesulfonate were used and the weight ratio of salt to pigment was fixed at 1.5. Within the range of anions in this work, the coercivity enhancement was specific to the polyphosphate anions. The coercivity for pigments treated with sodium p-toluenesulfonate (273 Oe) or poly(sodium acrylate) (280 Oe) was only slightly higher than 265 Oe for the as-received pigments. For the phosphate anions, the coercivity enhancement increased in the order sodium phosphate (268 Oe), sodium pyrophosphate (287 Oe), sodium tripolyphosphate (316 Oe), sodium polyphosphate (336 Oe). To evaluate the effect of stress on the coercivity, samples treated with sodium polyphosphate were ground to a powder and then pressed into pellets. The coercivity for the samples decreased linearly with increasing applied pressure during pellet formation. Therefore applied stress does not account for the coercivity increase.
In situ x-ray diffraction studies of YBa2Cu3Ox/LaAlO3 interfaces
Authors: Williams S. M. , Wang X. K. , Maglic S. , Toellner T. S. , Lin C. T. , Cavanagh M. D. , Duray S. J. , Lundquist P. M. , Chang R. P. H. , Ketterson J. B.
Published: July 2002

We report on the oriented growth by sputtering of YBCO/LaAlO3/YBCO S/I/S trilayers and YBCO/LaAlO3 multilayers using a new synchrotron compatible multisource deposition chamber.
A phenomenological differential-relation-based vector hysteresis model
Authors: Bergqvist A. , Engdahl G.
Published: July 2002

A phenomenological inherently vector hysteresis model employing simple differentials as a means of keeping track of the past history of the magnetic field is proposed. This results in a simple and computationally fairly efficient formulation for vector hysteresis of any dimension. An expression for determining model parameters from experimental data or from the Preisach function is given. The model exhibits rotational hysteresis and reduction of remanent magnetization by an orthogonal field and reduces to the classical Preisach model in one dimension. Details concerning the numerical implementation are discussed and computational examples demonstrating model properties are presented.
Characterization of a-Ge:H with the steady-state photocarrier grating measurement
Authors: Sauvain E. , Chen J. H.
Published: July 2002

The steady state photocarrier grating measurement technique has been used and is shown to be valid for the characterization of steady-state transport properties of minority carriers in undoped improved quality hydrogenated amorphous germanium (a-Ge:H). Deviations from the theoretically predicted behavior of the measurement have been observed on some a-Ge:H samples. At room temperature in a-Ge:H, the ratio of photoconductivity to dark conductivity is less than 1. The high density of thermally generated carrier is observed to affect the measurement by reducing its sensitivity. Whether it is also the cause of the observed deviation will be discussed.
Impact ionization rate near thresholds in Si
Authors: Sano Nobuyuki , Yoshii Akira
Published: July 2002

The impact ionization rate in Si is determined by performing the full-band Monte Carlo simulations with an ionization model that takes into account the correct joint density of states of Si. The ionization model, which is a refined version of the previously reported one [N. Sano, M. Tomizawa, and A. Yoshii, Jpn. J. Appl. Phys. 30, 3662 (1991)], features a finer mesh spacing for discretizing the wave-vector space and a smaller energy interval for the energy-conserving δ function in the transition probability. The impact ionization rate shows significant anisotropy near thresholds (≤3 eV) associated with the complexity of the indirect band structure in Si. When the impact ionization rate is averaged over all directions, good agreement with that extracted from recent experiments [E. Cartier, M. V. Fischetti, E. A. Eklund, and F. R. McFeely, Appl. Phys. Lett. 62, 3339 (1993)] is obtained.
Effect of spatially dependent screening on the binding energy of shallow impurities in spherical GaAs-(Ga,Al)As quantum dots
Authors: Paredes-Gutiérrez H. , Cuero-Yépez J. C. , Porras-Montenegro N.
Published: July 2002

Within the effective-mass approximation and using a variational method the binding energies of hydrogenic impurities in spherical GaAs-(Ga,Al)As quantum dots are calculated considering the effect of a spatially dependent screening through an r-dependent dielectric response. It is found that the r-dependent dielectric response increases the binding energies when compared with those found using constant screening. The effect is more important for acceptors than for donors and must be taken into account in calculations that include the binding energies of acceptors impurities in GaAs-(Ga,Al)As quantum dots.
Accurate measurements of the frequency dependence of photorefractive grating formation in Bi12SiO20
Authors: Norman Jeffrey B. , Hong John H. , Chang Tallis Y.
Published: July 2002

An experiment using phase-locked acousto-optic devices is described in which accurately detuned plane-wave writing beams produce a stable, continuously moving intensity grating for the measurement of the temporal response of photorefractive grating formation and light-induced decay in Bi12SiO20 in the frequency domain. Accurate measurements of the complex rate constant are obtained with this system (average experimental uncertainty 1.7%), making this configuration useful for the characterization of photorefractive materials to be employed as elements in practical information and signal processing systems.
Current generated periodic space charge in semiconductor diodes with non-Ohmic injection
Authors: Zitter R. N. , Zhang Xuesong , Abraham-Shrauner Barbara
Published: July 2002

Calculations are carried out which show minima or quasiminima in the voltage-current characteristics of semiconductor diodes for values of the plasma frequency/scattering time product of the order of unity. In this regime the minima are evident only for non-Ohmic injection conditions. The results are consistent with reported experiments.
Intensity-dependent photorefractive properties in an n-type BaTiO3
Authors: Chang J. Y. , Garrett M. H. , Jenssen H. P. , Warde C.
Published: July 2002

The beam coupling and response time of reduced BaTiO3 are reported. The major carrier changes from hole to electron after reduction. The electro-optic gain and effective trap density increase with the illumination intensity. Although the electro-optic gain varies little, the response time τ decreases by a factor of 2.8 after reduction. Experimental results indicate that at least three energy levels including shallow level(s) exist in this BaTiO3.
A multilayer heat conduction solution for magneto-optical disk recording
Authors: Shih O. W.
Published: July 2002

The Green’s function temperature expressions formulated by McGahan and Cole [J. Appl. Phys. 72, 1362 (1992)] are modified into a form suitable for solving the heat conduction problem encountered in magneto-optical (MO) disk recording situations. The temperature distribution within MO multilayer media heated by a pulsed scanning Gaussian laser beam is calculated by using Fourier-transformed Green’s functions. The linear heat conduction equation is solved exactly not in real space but in frequency space. The temperature in real space is efficiently recovered by the inverse fast Fourier transform; numerical integrations are unnecessary. Optical absorption in MO media is calculated exactly. Realistic and piecewise-linear models of the laser pulse’s time dependence are incorporated directly into the formalism. Elliptically shaped laser-beam cross sections are also easily included. At the same time, the extended method still preserves the conceptual simplicity and computational efficiency of the original theory. This paper describes the extended method, discusses some numerical issues arising from the modifications, and presents comparisons with previously published finite-difference calculations.
Double-barrier tunnel junctions for quasiparticle mixers
Authors: Gundlach K. H. , Billon-Pierron D. , Rosengarten M. , Karpov A. , Lehnert T. , Rothermel H.
Published: July 2002

Double-barrier niobium tunnel junctions with the middle electrode thinner than the London penetration depth were fabricated. Their I-V curves, annealing behavior, response to external magnetic field, and response to 230 and 350 GHz irradiation in mixer experiments is discussed. Junctions with an integrated tuning circuit designed for the 230 GHz frequency range gave double-sideband receiver noise temperatures of 100 K. Vertically stack arrays can be attractive for various applications. Compared to single-barrier devices possible drawbacks were noted. The I-V curve indicates heating and/or nonequilibrium effects. Double-barrier devices became nonuniform after thermal annealing at 200 °C. The response to the external magnetic field is more complex and considerably larger flux densities are needed to suppress Josephson effects.
Two-dimensional electron transport in selectively doped Ga0.25In0.75As0.5P0.5/InP heterostructure
Authors: Bhattacharyya Keya
Published: July 2002

The Hall mobility of the two-dimensional electron gas in selectively doped Ga0.25In0.75As0.5P0.5, lattice matched to InP, is calculated in the temperature range from 4.2 to 300 K. The pseudo-two-mode nature of the polar optic phonons is considered in addition to deformation potential acoustic, piezoelectric, alloy, ionized impurity (remote and background), and surface roughness scattering. The energy-band nonparabolicity and screening effects on the scattering probabilities are incorporated. The Boltzmann equation is solved by an iterative method and compared with the available experimental data. It is found that at low temperature, with a suitable choice of the alloy scattering potential, theory agrees with the experiment while there are discrepancies between the theory and experimental data on mobility as the temperature increases if one considers polar scattering by the longitudinal-optical vibrations. On the other hand, theoretical results for all temperatures can be fitted with the experiment if in addition to the above scattering mechanisms, interaction with the transverse-optical phonons is assumed to take place.
Epitaxial ternary RexMo1−xSi2 thin films on Si(100)
Authors: Vantomme André , Nicolet Marc-A. , Long Robert G. , Mahan John E.
Published: July 2002

Reactive deposition epitaxy was used to synthesize thin layers of RexMo1−xSi2 on Si(100). In the case of x=1, ReSi2 layers of excellent crystalline quality have been reported previously [J. E. Mahan, K. M. Geib, G. Y. Robinson, R. G. Long, Y. Xinghua, G. Bai, and M.-A. Nicolet, Appl. Phys. Lett. 56, 2439 (1990)]. In the case of x=0, however, virtually no alignment of the MoSi2 and the substrate is found, although this silicide is nearly isomorphic to ReSi2. For intermediate values of x, highly epitaxial ternary silicides are obtained, at least for a Mo fraction up to 1/3.
Defects produced in Si p+n diodes by B+ implantation at liquid nitrogen temperature or −60 °C
Authors: Kase Masataka , Kikuchi Yoshio , Kimura Mami , Mori Haruhisa , Liebert Reuel B.
Published: July 2002

Defects induced by B+ implantation (35 keV) at liquid-nitrogen (LN) temperature and −60 °C are examined using transmission electron microscopy (TEM), secondary-ion-mass spectroscopy, and electrical characterization of p+n diodes. B+ implantation at LN temperature produces a 120-nm-thick amorphous layer with a residual surface crystalline region. B+ implantation at −60 °C does not produce an amorphous layer, but damage can be observed as a dark band at the depth of B+ projected range Rp. For RT implantation, cross-sectional transmission electron microscopy reveals no visible damage in contrast to implantation at −60 °C. Frenkel-pair diffusion and annihilation is suppressed during implantation at the low temperature. The damage accumulates to form an amorphous layer for LN temperature. At −60 °C, the defects are confined near Rp. After annealing at 1000 °C for 10 min, near-surface and depth-encountering solid-phase-epitaxy dislocation-loop defects are observed in the sample implanted at LN temperature. The density of these is about several 108 cm−2, which is 10 or 100 times smaller than samples implanted at higher temperature. The annealed samples implanted at −60 °C and RT are mainly 〈111〉-plane directed defects and dislocation loops, respectively. Corresponding to the degree of as-implanted damage, the defects distribute at a shallower depth in the sample implanted at −60 °C than at RT, and have about 10 times higher density. The leakage current characteristics of p+n diodes indicate that the LN temperature and −60 °C implanted samples have lower leakage than RT samples at all annealing conditions. Notably, at 1000 °C for 10 min the leakage current is reduced to 56%. This is consistent with the result of TEM analysis; thus, the defect confinement to shallow layer by cooling contributes to lower the leakage current. Implantation at −60 °C is suitable for modern high-current implanters, due to practical coolant and less mechanical stress by thermoplasticity.
Nanometer thick Si/SiGe strained-layer superlattices grown by an ultrahigh vacuum/chemical vapor deposition technique
Authors: Chang T. C. , Chang C. Y. , Jung T. G. , Tsai W. C. , Wang P. J. , Lee T. L. , Chen L. J.
Published: July 2002

High quality Si/Si1−xGex superlattices having layers as thin as 1.5 nm have been grown by an ultrahigh vacuum/chemical vapor deposition system. High-resolution double-crystal x-ray diffraction, and conventional and high-resolution cross-sectional transmission electron microscopy were used to evaluate the crystalline quality of these superlattices. A dynamical x-ray simulation program was employed to analyze the experimental rocking curves. Excellent matches between experimental rocking curves and simulated ones were obtained for all superlattices with various periodicity. A cross-sectional transmission electron micrograph of an 80 period Si(4.2 nm)/Si0.878Ge0.122 (1.5 nm) superlattice, in which each individual layers was clearly resolved, demonstrated the capability of this growth technique for nanometer thick layer deposition.
Differential photoreflectance of Si-δ-doped GaAs
Authors: Hsu T. M. , Lu N. H. , Tsai S. P. , Wu J. R.
Published: July 2002

The signals from buried layer in Si-δ-doped GaAs of different undoped cap thickness have been studied by differential photoreflectance. The first-derivative-like line shape of differential photoreflectance is attributed to the energy transitions related to the modulations of two-dimensional electron gas density. We have observed a change of line shape at low temperatures. This change of line shape is probably due to the change of potential distribution in the conduction band, which is caused by the surface Fermi-level pinning and surface photovoltaic effect.
Influence of deposition rate and hydrogen/helium dilution on the structural relaxation of a-SiGe:H network prepared at low substrate temperature
Authors: Middya A. R. , Ray Swati
Published: July 2002

Device quality a-SiGe:H alloy has been developed at low substrate temperature (Ts∼180 °C), suitable for solar-cell fabrication using low flow rate of silane and germane and strong hydrogen dilution. The optoelectronic properties of a-SiGe:H films prepared with different substrate temperature and under different deposition conditions, i.e., low flow rate of source gases and with/without hydrogen dilution, high flow rate and with hydrogen dilution, low flow rate and helium dilution, are compared. It is found that both low deposition rate and strong hydrogen/helium dilution are essential to develop a-SiGe:H material with low defect density. Structural properties, midgap defect densities, and Urbach energies of the optimized and unoptimized materials are correlated with their optoelectronic properties. The results very well support the idea that there should be a fine balance between deposition rate and substrate temperature in developing low defect density materials. Quantum efficiencies of three Schottky battier devices were compared where a-SiGe:H layers have been deposited under different deposition conditions. The results show that both the hole and electron transport remains almost unaffected as Ts decreases from 250 to 180 °C.
Scattering of electromagnetic waves from fractals of large amplitudes
Authors: Sanghadasa M. F. M. , Sung C. C.
Published: July 2002

Numerical accuracy of the representation of a Weierstrass structure function based on fractional Brownian motion is examined. We find that this representation is satisfactory for a large range of parameters. This result is applied to the calculation of the scattering of electromagnetic waves from a fractal surface in the limit of a large amplitude. The results of the calculated reflectivity show that a higher fractal dimension implies a larger surface roughness mainly because of the property of the Kirchhoff integral.
Epitaxial spin-valve structures for ultra-low-field detection
Authors: Schuhl A. , Durand O. , Childress J. R. , George J.-M. , Pereira L. G.
Published: July 2002

A new epitaxial ‘‘spin-valve’’-type system for low-field magnetoresistive detection is described. This system is based on Fe/Pd epitaxial multilayers grown on (100)MgO by MBE. These films show a very abrupt transition from positive to negative magnetization as the reverse field is applied during hysteresis measurements. We have used these sensitive magnetic properties to fabricate epitaxial spin-valve structures by epitaxial growth of Fe/Ag, Co/Ag, or Co/Cu bilayers on top of a Fe/Pd bilayer. Hysteresis loops and magnetoresistance curves clearly indicate a significant field range with antiparallel alignment of the two components. Magnetoresistive sensitivities of up to 0.3% per Oe at low temperatures have been observed in these structures. The efficiency of the spin-dependent scattering has subsequently been improved either through the addition of planar Co impurities, in both the soft and hard magnetic layer, or by increasing the number of active Fe/Pd interfaces. This approach leads to a drastic improvement of the sensitivity, up to 1.5% per Oersted at room temperature.
Influence of chemical character on GaAs(111) surface reconstruction
Authors: Ping Jiang Guo , Ruda Harry E.
Published: July 2002

A surface reconstruction model is presented for GaAs(111)A and B surfaces. The surface reconstruction mechanism is investigated using ab initio Hartree–Fock molecular-orbital calculations. Two model clusters, H3Ga3As3H6 and H6Ga3As3H3, are used to reveal different lateral interactions in the vicinity of the first biatomic surface layer for GaAs(111)A and B surfaces. Lateral interactions originating from the site specific atomic character (Ga/As) are shown to determine the Ga—As—Ga and As—Ga—As bond angles, which differ significantly from those for bulk GaAs. This causes each of the three surface nearest-neighbor Ga (As) atomic rings to become considerably larger (smaller) than the three nearest-neighbor As (Ga) atomic rings lying beneath them. The propagation of such lateral interactions across the surface explains a fundamental inability of Ga (As) -terminated surfaces to match to respective underlying As (Ga) atomic layers, providing the driving force for Ga (As) atom removal from Ga (As) -terminated (111) surfaces. Changes in surface reconstruction are thus attributed to this lateral interaction. It is shown how the 2×2 {2×2, √3×√3, 3×3, and √19 ×√19} reconstructed phases of Ga {As} -terminated surfaces depend on this lateral interaction. Our models for GaAs(111)A and B surface reconstruction are shown to be applicable to the polar surfaces of other III-V compound semiconductors.
Monte Carlo simulation of cation transport via vacancies in spinel solid solutions: One type of cation exchange prevails
Authors: Lu F.-H. , Franke P. , Nichols C. S. , Dieckmann R.
Published: July 2002

Monte Carlo simulations have been performed to calculate values for the correlation factors of vacancies fV, and cations diffusing via vacancies, fA and fB, in quasibinary spinel solid solutions of the type (A1−xBx)3−δO4 as a function of jump frequencies and the composition x, primarily at low vacancy concentrations. Because the cations A and B and the vacancies in spinels are distributed on two types of sublattices, an octahedral and a tetrahedral one, different frequencies occur, some of which are interrelated. The background of the Monte Carlo simulations performed is discussed and results for cases in which one type of cation exchange mechanism prevails are presented and compared to the very limited data available on this subject in the literature. The simulation results for cases which involve multiple types of cation exchange mechanisms will be presented elsewhere.
Enhancement of T
c in argon-pretreated NdSrBaCu3O6+z
Authors: Suryanarayanan R. , Nafidi A. , Das A.
Published: July 2002

NdSrBaCu3O6+z prepared in air followed by oxygen annealing showed a Tc of 68 K. The Tc of the sample when treated in argon followed by oxygen annealing increased by 10 K. This could be related to the observed shrinking of the c axis and/or a rearrangement of oxygen atoms in the basal plane.
Two-dimensional inverse problem in estimating heat fluxes of an enclosure with unknown internal heat sources
Authors: Huang Cheng-Hung , Wu Jan-Yue
Published: July 2002

The methodology in estimating the unknown temporal and spatial variation of inside heat fluxes of a heat-generated enclosure is derived by using the conjugate gradient method in a two-dimensional inverse problem. The advantage of the conjugate gradient method is that there is no need to assume a specific functional form for the unknown quantities beforehand, since the solution automatically determines the functional form over the domains specified. Such a technique can be applied to determine the internal wall heat fluxes acting on the inner and upper surfaces in the cylinder of an internal combustion engine, simultaneously, from the knowledge of transient temperature measurements taken inside the cylinder block and head, respectively, which is discussed in detail. The other application is the determination of inside heat fluxes of a nuclear fuel rod. Once wall heat fluxes inside the cylinder are determined, the exhaust heat produced by the cylinder head and block can be calculated. Furthermore, the cooling system for the cylinder can be established from the knowledge of heat transfer rate to it to avoid crack damage.
Pd/Zn/Pd/Au ohmic contacts to p-type In0.47Ga0.53As/InP
Authors: Leech Patrick W. , Reeves Geoffrey K. , Kibel Martyn H.
Published: July 2002

The electrical properties of Pd/Zn/Pd/Au ohmic contacts to p-type In0.47Ga0.53As/InP have been investigated as a function of the ratio of the interfacial Pd and Zn layers and the annealing treatment. For as-deposited contacts, the presence of an increasing thickness of interfacial Zn and Pd to ∼300 Å in the metallization resulted in a reduction in specific contact resistance, ρc, to a low value of 1.2×10−5 Ω cm2. Annealing of all of the contact configurations except the Zn=0 and 20 Å structures produced a reduction in ρc to a minimum value of 7.5×10−6 Ω cm2 at 500 °C. A critical thickness of the Zn≥50 Å and Pd≥100 Å interfacial layers was required in order to produce a significant reduction in ρc during annealing. These results have been interpreted in terms of the reaction between Pd and In0.47Ga0.53As and an associated doping at the near surface region by Zn atoms. Annealing of the contacts at temperatures of ≥450 °C resulted in significant intermixing of the metal layers and the In0.47Ga0.53As as revealed by Rutherford backscattering spectrometry and Auger depth profiling.
Thermal expansion of Ni/Cu multilayers
Authors: Su C. M. , Kim T. , Oberle R. R. , Cammarata R. C. , Wuttig Manfred
Published: July 2002

The coefficient of thermal expansion of electrodeposited Ni/Cu multilayers was obtained by measuring the evolution of membrane resonances and hence the tension as a function of temperature. The apparent thermal expansion coefficient of the multilayer membranes increases as the interface density of the multilayers increases. This increase is analyzed in terms of stress relaxation resulting from sliding of nonperfectly bonded interfaces. The analysis permits the normalization of all thermal expansion data of the Cu/Ni multilayers with layer thicknesses ranging from 20 to 800 nm but not of the thinnest layers, 2 nm thick. The results are consistent with the idea that interfacial adhesion improves as the layer thickness becomes very small, favoring epitaxial growth.
Characterization of Si/Si1−xGex/Si heterostructures by capacitance-transient spectroscopy
Authors: Brighten J. C. , Hawkins I. D. , Peaker A. R. , Kubiak R. A. , Parker E. H. C. , Whall T. E.
Published: July 2002

Deep level distributions have been investigated in B-doped Si/Si1−xGex/Si layers grown by molecular beam epitaxy using deep level transient spectroscopy. Broadening in the deep level spectra is discussed in terms of carrier emission over a band of deep level energies as has been considered for both alloy disorder and dislocations. The distortion observed in the deep level spectra in the vicinity of the upper Si/Si1−xGex heterojunction is suggested to be a consequence of the significant band bending that occurs in this region; the possible causes for this distortion are discussed. The deep states exhibit donor-like behavior and the origin of the electrical activity is considered to lie with metal point-defect/dislocation interactions.
Excimer laser produced plasmas in copper wire targets and water droplets
Authors: Song Kyo-Dong , Alexander D. R.
Published: July 2002

Elastically scattered incident radiation (ESIR) from a copper wire target illuminated by a KrF laser pulse at λ=248 nm shows a distinct two-peak structure which is dependent on the incident energy. The time required to reach the critical electron density (nc ≊ 1.8× 1022 electrons/cm3) is estimated at 11 ns based on experimental results. Detailed ESIR characteristics for water have been reported previously by the authors. Initiation of the broadband emission for copper plasma begins at 6.5 ±1.45 ns after the arrival of the laser pulse. However, the broadband emission occurs at 11 ± 0.36 ns for water. For a diatomic substance such as water, the electron energy rapidly dissipates due to dissociation of water molecules, which is absence in a monatomic species such as copper. When the energy falls below the excitation energy of the lowest electron state for water, it becomes a subexcitation electron. Lifetimes of the subexcited electrons to the vibrational states are estimated to be of the order of 10−9 s. In addition, the ionization potential of copper (440–530 nm) is approximately 6 eV, which is about two times smaller than the 13 eV ionization potential reported for water. The higher ionization potential contributes to the longer observed delay time for plasma formation in water. After initiation, a longer time is required for copper plasma to reach its peak value. This time delay in reaching the maximum intensity is attributed to the energy loss during the interband transition in copper.
Deep levels in alpha-irradiated platinum doped n-type silicon
Authors: Asghar M. , Baber N. , Zafar Iqbal M.
Published: July 2002

The deep level transient spectroscopy technique has been used to study the interaction of 5.48 MeV α particles with deep levels in Pt-doped n-type silicon. Production rates and annealing behaviors of alpha-radiation-induced levels in the presence of platinum have been investigated. Isochronal annealing characteristics of Pt-related levels before and after irradiation have also been studied. Our results are compared to published data on electron irradiation of Si:Pt.
Third-order nonlinear susceptibility in GaAs/AlxGa1−xAs superlattice with a special layered structure
Authors: Dong Hang , Xiong Shi-Jie
Published: July 2002

By taking into account the nonparabolic band structure of the constituents and the coupling between the periods, we calculated the triply resonant nonlinear susceptibility in a specially designed GaAs/AlxGa1−xAs superlattice. It consists of infinite repeated periods, each of which is an alternative stacking of GaAs and AlxGa1−xAs layers with special layer thicknesses, designed in such a way that the minibands of the superlattice are nearly equally separated. The triply resonant susceptibility is produced by a three-photon process. In some cases coupling between the periods may slightly enhance the magnitude of the third-order susceptibility. Possible ways of maximizing the nonlinear susceptibility of the superlattice are also discussed.
Effects of rapid thermal annealing on electrical properties of heavily doped silicon molecular-beam-epitaxial layer with B2O3 doping source
Authors: Xu Qiang , Yuan Jian , Wang Jianbao , Huang Daming , Lu Fang , Sun Henghui , Wang Xun , Liu Rong
Published: July 2002

The effect of rapid thermal annealing (RTA) on the electrical properties of heavily boron-doped silicon epilayer grown at 680 °C by molecular-beam epitaxy and coevaporation of B2O3 is studied. Through the RTA process, the boron clusters in the epilayer break into boron atoms and the interstitial boron enters the substitutional site. These two effects cause the improvement of the electrical properties of the silicon epilayer. After RTA at 1100 °C for 10 s, the hole concentration can reach 3.1×1020 cm−3 with the mobility of 39 cm2/V s, which is about the same as that of the bulk silicon, while the oxygen concentration is less than 1018 cm−3. It is also shown that the full width at half-maximum of the x-ray-diffraction rocking curve decreases as the RTA temperature increases. The RTA process does not affect the steep distribution of carrier concentration at the epilayer/substrate interface which differs by about 6 orders of magnitude across the interface with the leading edge slope of 25–30 nm/decade.
Inelastic quasiparticle scattering and multiplication in superconductors
Authors: Burnell G. , Warburton P. A. , Blamire M. G.
Published: July 2002

We report a theoretical and experimental study of quasiparticle multiplication in superconductors. A model of the multiplication process, based on random quasiparticle-phonon inelastic scattering, has been compared with experimental data obtained from double tunnel junction devices in which the quasiparticle injection energy can be varied by altering the bias voltage. Excellent quantitative agreement has been obtained for a variety of device structures provided that a previously unidentified quasiparticle energy enhancement process is included in the model. The existence of this energy enhancement process has implications for quasiparticle trapping and multiplication in practical energy resolving detector devices.
Theory for itinerant electrons in noncollinear and incommensurate structured magnets (invited)
Authors: Kübler J. , Sandratskii L. M. , Uhl M.
Published: July 2002

Itinerant-electron systems are described that can form a variety of magnetic-moment arrangements. These are dealt with quantitatively by using energy-band theory and the local density-functional approximation; the theoretical and computational basis is briefly reviewed and results are presented for quite general collinear and noncollinear moment arrangements and states having incommensurate helical order characterized by a wave vector q. Some examples presented here are Fe3Pt-Invar, fcc-iron precipitates, and tetragonal iron. Furthermore, finite-temperature effects become tractable; the magnetovolume effect in Fe3Pt-Invar serves as an example. Finally, the problem of biquadratic exchange in Fe-Cr multilayers will be discussed briefly.
Mössbauer study of R2Fe17Cx (R=Tb,Dy) as-quenched intermetallics compounds
Authors: Gong Hua-Yang , Shen Bao-Gen , Kong Lin-Shu , Cao Lei , Zhan Wen-Shan , Cheng Zhao-Hua , Wang Fang-Wei
Published: July 2002

Intermetallics compounds Dy2Fe17Cx (x=1.5,2.0,2.5,2.8) and Tb2Fe17Cx (x=1.5,2.0,2.5) have been successfully prepared by the melt-spinning method. The x-ray-diffraction patterns and the thermomagnetic curves show that they are single phase with the rhombohedral Th2Zn17-type structure, except for Dy2Fe17C2.8 and Tb2Fe17C2.5 which have a small percentage of α-Fe. 57Fe Mössbauer spectra were measured at 12 K and room temperature to study both the magnetic properties of R2Fe17Cx on a local scale and the effect of the interstitial C atom on the Fe atoms. It is found that the effective hyperfine fields of the various Fe sites decrease in the order 6c≳18 f≳18h≳9d. The average effective hyperfine fields Heff at 12 and 293 K do not change much with C concentration x in agreement with the moment of the Fe atoms obtained by magnetic measurements at 1.5 K. It can be concluded that the effect of C is to enhance the exchange interaction between Fe-Fe atoms, which is sensitive to the distance of Fe-Fe atoms. The C has little influence on the moments of Fe atoms.
Influence of microstructure on magnetoresistance of FeAg granular films
Authors: Yu Chengtao , Yang Ye , Zhou Yuqing , Li Shuxiang , Lai Wuyan , Wang Zhenxi
Published: July 2002

The magnetoresistance of FeAg granular films with optimum composition has been systematically studied as a function of film thickness. It was found that the giant magnetoresistance increases rapidly with increasing film thickness in the initial stage, and beyond about 500 Å the improvements become limited. The saturation field was also found to rise with increasing film thickness. Transmission electron microscope studies showed that with the increase of film thickness the microstructure becomes more homogeneous, with smaller grains and fewer structural defects such as twins. A discussion of the influence of microstructure on magnetoresistance and saturation field is presented.
Magnetic-field orientation and coercivity
Authors: Edwards Brandon , Paul D. I.
Published: July 2002

The relationship between the coercive force and the angle of the applied field of an infinite magnetic medium containing a planar defect have been analyzed. A domain-wall pinning dominated coercivity was assumed and the spatial dependence of the magnetization in the direction normal to the plane of the defect was taken into account. The results show that the coercivity must be about two orders of magnitude smaller than the anisotropy field for the inverse cosine curve to be a good approximation. Some of the results with experimental work on Fe77Nd15Bs are compared. In addition, the existence of a decrease in the domain-wall pinning coercivity as a function of the angle between the applied magnetic field and the anisotropy for certain ranges of parameters—a behavior previously thought to have only occurred in the angular dependence of a nucleation dominated coercivity—is shown.
Short period oscillations in the Kerr effect of 4d- and 5d-transition metal wedges on Co films (invited) (abstract)
Authors: Carl A. , Weller D.
Published: July 2002

We report a novel type of short period oscillations in electron-beam evaporated Co films covered with wedge-shaped films of Pt, Au, and Pd. Oscillatory behavior, with periods in the range 2–3 Å, is observed both in the saturation polar Kerr angle and in the high field susceptibility, as a function of the wedge position (see Fig. 1). The structures of the type buffer/Co/X wedge/Y cap were made by high vacuum evaporation using fused silica as substrates. They consist of a 200 Å Pt buffer layer, a thin Co layer revealing a perpendicular easy magnetization axis, a transition metal wedge (X) with thickness in the range 0–25 Å, and a thin Cu or Au cap (Y) layer. The presence of oscillations depends critically on the choice of the cap-layer Y. They are distinctly different from long and short range period oscillations observed in magnetic sandwich or multilayer structures, since there is only one magnetic film involved. The present results will be discussed in the framework of spin polarized quantum well states.
Atomic structure of Si/TbSi2/(111)Si double-heterostructure interfaces
Authors: Luo C. H. , Chen F. R. , Chen L. J.
Published: July 2002

High-resolution transmission electron microscopy (HRTEM) has been applied to study the atomic structure of the Si/TbSi2/(111)Si double-heterostructure interfaces. The unrelaxed geometrical models of Si/TbSi2/(111)Si interfaces can be systematically deduced from the dichromatic constrained-coincidence-site-lattice patterns. The atomic structures were determined by comparing HRTEM images with computer-simulated images. The relationships of interface bonding and structures of epitaxial Si/TbSi2 and epitaxial TbSi2/Si interfaces are discussed.
Seminumerical simulation of dispersive transport in the oxide of metal-oxide semiconductor devices
Authors: Lathi Seema , Das Amitava
Published: July 2002

Understanding and modeling of the device degradation mechanism in a metal-oxide field-effect transistor either due to hot carriers or ionizing radiation require simulation of hole /H+ ion transport in oxides. Because of its dispersive nature continuous-time random-walk-based techniques are used for such simulations. A numerical technique to simulate dispersive transport of holes and H+ ions in amorphous SiO2 is described. Normalized flatband voltage shift and interface-state density were computed as a function of time and compared with published experimental data. Simulation results show that numerical approach is accurate. Numerical simulation results also show that choice of trial functions for arbitrary value of dispersive parameter α is in general accurate; however, compared to trial function solutions, the numerical approach could be easily extended to two dimensions and integrated with conventional device simulators.
Analytic expressions for emission in sharp field emitter diodes
Authors: Jensen K. L. , Zaidman E. G.
Published: July 2002

We present a complete analytical treatment of elliptical field emitting structures in a diode geometry which correctly includes image charge effects off axis and the variation of field along the tip. The methodology may be extended to other geometries. The angular distribution of electron emission along the tip, the total emitted current, and the area factor may all be calculated as a function of emitter to anode distance, tip radius, tip height, and the anode-tip voltage difference. We show not only where errors arise if the planar Fowler–Nordheim (FN) equation is used to govern electron emission, but also how the FN equation may be modified to correctly address the complications due to atomically sharp tips. Finally, we present an analytic form of the area factor and compare it to the exact calculation and the various approximations.
Electrical properties of Schottky contacts to N-type ZnS0.07Se0.93 epilayers
Authors: Wang A. Z. , Anderson W. A. , Haase M. A.
Published: July 2002

Schottky contacts were formed on Cl-doped N-type lattice matching ZnS0.07Se0.93 epilayers grown on (100) N-GaAs substrates by molecular beam epitaxy for metals with different work functions, Yb, Al, Cr, Cu, Au, and Pd. Temperature-dependent current-voltage and capacitance-voltage (C-V) measurements show a clear relation between Schottky barrier height and metal work function which cannot be predicted by the linear Schottky contact theory, ΦSB=ΦM−χ. The pinning effect is believed to exist at the metal-semiconductor interface with a wide range of Fermi level pinning positions. Thermionic emission dominates the current transport mechanism and the current is limited by the ZnSSe/GaAs heterojunction under a relatively high positive bias. A symmetriclike C-V characteristic is explained by the Schottky barrier-heterojunction model and a fairly constant heterojunction barrier height, ΦHJ, is obtained for Schottky diodes using different metals.
Finite-element stress analysis of failure mechanisms in a multilevel metallization structure
Authors: Shi L. T. , Tu K. N.
Published: July 2002

A finite-element method taking into account material nonlinearity was used to calculate the stress distribution in interconnecting lines and studs of a three-dimensional multilevel metallization structure in a microelectronic device. A good correlation was obtained between the location of calculated stress concentration centers and the experimentally observed void sites in the stud. Accordingly, the failure mechanisms of the stress-induced voiding in the stud and the crack formation in the underlying substrate were inferred to be associated with different stress components. Furthermore, the stress concentration centers were found to migrate as the temperature changes, which agrees with the experimental observations.
In situ reflectance anisotropy studies of AlxGa1−xAs layers grown on GaAs(001) by molecular beam epitaxy
Authors: Morris S. J. , Zettler J.-Th. , Rose K. C. , Westwood D. I. , Woolf D. A. , Williams R. H. , Richter W.
Published: July 2002

Reflectance anisotropy spectroscopy was used to examine the surfaces of AlxGa1−xAs layers grown on GaAs(001) by molecular beam epitaxy, where the Al mole fraction was varied across the whole composition range x=(0.0,0.25,0.50,0.75,1.0). All surfaces were also independently characterized using reflection high-energy electron diffraction, and were found to exhibit a c(4×4) reconstruction. After initial changes in the spectra were observed on depositing very thin layers (≤20 monolayers), in the intermediate thickness range a regime was entered in which strong optical interference effects appeared. These effects are accurately accounted for using a four-media model. For thicker layers (≥8000 monolayers), interference effects were seen to diminish and spectra representative of the surfaces of bulk AlxGa1−xAs were obtained.
Motion of species in a laser-ablated Y-Ba-Cu-O plasma plume studied by time-dependent attenuation of a probe beam
Authors: Kubát P. , Engst P. , Zelinger Z. , Wild J. , Boháček P.
Published: July 2002

The time dependence of attenuation of the He-Ne and CO2 laser beams passing through a plume produced by the excimer laser ablation of Y-Ba-Cu-O in the air is characterized by two maxima. The first maximum is apparently caused by a change in the refractive index at the front of the shock wave and is propagated with a velocity of 360 m s−1 comparable with the speed of sound at room temperature and it is independent on laser energy. The initial velocity for the second maximum is ∼20 m s−1 and can be connected with scattering on species ablated from the superconductor surface. The velocity of ablated species increases linearly with laser energy; the change is 81 m s−1 J−1.
The epitaxial growth of evaporated Cu/CaF2 bilayers on Si(111)
Authors: Mattoso N. , Mosca D. H. , Mazzaro I. , Teixeira S. R. , Schreiner W. H.
Published: July 2002

Successful and unexpected epitaxial growth of Cu/CaF2 bilayers on hydrogen terminated Si(111) wafers by thermal evaporation is reported. The bilayers were characterized with conventional x-ray diffraction experiments, grazing angle incidence x-ray diffraction experiments, rocking curves, and χ scans. The growth mode of Cu films on CaF2 epitaxially grown on Si(111) is completely different from that of the Cu film grown directly on Si(111).