bluuebunny/crossref_metadata_2025 huggingface dataset:
Comment on ‘‘Atomistic models of vacancy-mediated diffusion in silicon’’ [J. Appl. Phys. 78, 2362 (1995)]
Authors: Antoncik E.
Published: July 2002

S. T. Dunham and C. D. Wu [J. Appl. Phys. 78, 2362 (1995)] have explained the enhanced diffusion of dopants in silicon at high concentrations using Monte Carlo simulations as well as an assumed form of the effective diffusion coefficient attributed to the interaction of vacancies with several dopant atoms. It is argued that their result is questionable since the authors did not take into account the interaction between dopant atoms which is predominating at very high concentrations and by itself makes it possible to calculate the effective diffusion coefficient in good agreement with experiment.
Vortex pinning in layered organic superconductors: κ -(BEDT-TTF)2Cu[N(CN)2]Br
Authors: Khizroev S. , Zuo F. , Alexandrakis G. C. , Schlueter J. A. , Geiser U. , Williams J. M.
Published: July 2002

Magnetization studies on organic single-crystal superconductors of κ-(BEDT-TTF)2Cu[N(CN)2]Br with the field H parallel to the b axis (perpendicular to the conducting plane) show anomalous field and temperature dependence of vortex pinning in the mixed state. At high temperatures, the magnetization M decays with increasing field with a power-law dependence. The normalized relaxation rate S=d(ln M)/d(ln t) decreases monotonically with H. At low temperatures (T<7 K), a change of sign in the curvature of M(H) is observed, accompanied by a corresponding change in S as a function of H. Measurement of the irreversibility field Hrev shows a universal power-law dependence of Hrev on (1−T/Tc) in the temperature range investigated. We suggest that the magnetic anomaly observed is due to a dimensional crossover in the nature of vortex pinning.
Magnetic properties of BaFe12−(x+y)SnxCoyO19 single crystals (abstract)
Authors: Solé R. , Zhang X. X. , Ruiz X. , Aguiló M. , Díaz F. , Tejada J.
Published: July 2002

BaFe12−(x+y)SnxCoyO19 single crystals, with 0≤x≤2 and 0≤y≤2, have been grown from high temperature solution by slow cooling using the TSSG method. Magnetic properties of these single crystals have been investigated using a commercial quantum design SQUID magnetometer in the temperature range 6 to 320 K and with a varying field from −5 to +5 T applied parallel and perpendicular to their c axis. It is found that the replacement of part of the Fe3+ ions by Co2+ and Sn4+ ones reduces the anisotropy as well as the saturation magnetization of the materials. For a small amount of substitution, the magnetization as a function of applied fields, which were oriented in the c axis, exhibits a hysteresis loop indicating that the magnetic domain wall moving was pinned by the imperfections of magnetic structures. When the substitution was increased to x+y=2.5, long distance magnetic coupling was destroyed, and the sample behaved as a magnetic granular material consisting of randomly distributed magnetic clusters.
Magneto-optic properties and exchange interaction of the macroscopic ferrimagnet Co1−x−yTbx(EuS)y
Authors: Fumagalli P. , Schirmeisen A. , Gambino R. J.
Published: July 2002

Polar Kerr-rotation spectra and hysteresis loops have been measured in Co1−x−yTbx(EuS)y, with 0≤x≤0.21 and 0≤y≤0.21, and compared to the macroscopic ferrimagnet Co1−y(EuS)y and to amorphous Co1−xTbx. The measurements were taken at room temperature and at 7 K over a wide photon energy range of 1.1–4.6 eV in fields up to 2.77 T. The addition of Tb retains the phase-separated nature yielding a material consisting of a Co–Tb matrix containing crystalline EuS precipitate particles with about 2 nm diameter. Up to 8% Tb is substituted for Eu in the EuS phase. The Kerr rotations are rather small reaching −0.25° at room temperature and increasing to −0.85° at 7 K, i.e., no optical enhancement is observed as in Co(EuS). This is most likely due to the much smaller size of the EuS crystallites. An ‘‘s’’-shaped feature in the Kerr-rotation spectra can be assigned to an Eu2+ 4f→5d transition while a contribution from the Tb3+-4f states shows up as a decrease with increasing photon energies. At 7 K, the Tb and Eu magnetic moments are found to be parallel while the Co moment is believed to be antiferromagnetically exchange coupled to both. At room temperature, the Co moment is dominating the Tb moment which is antiferromagnetically coupled as in Co1−xTbx.
Resistivities of sputtered Ag(3.3  nm)/Cu(tCu), Ag(3.3  nm)/Au(tAu), and Ni(4.2  nm)/Co(tCo) multilayers at 4–5 and 295 K
Authors: Henry L. L. , Oonk M. , Loloee R. , Yang Q. , Chiang W.-C. , Pratt W. P. , Bass J.
Published: July 2002

To help clarify the sources of the 67% periodic oscillations in the in-plane saturation resistivity, ρS (ρS varied from 2.5 to 5 μΩ cm at 4.2 K) of molecular beam epitaxy-grown epitaxial Ni/Co multilayers of total thickness, tT≊100 nm recently reported by Gallego et al. [Phys. Rev. Lett. 74, 4515 (1995)] we have measured the in-plane resistivities at 4–5 and 295 K of Ag/Cu, Ag/Au, and Ni/Co multilayers with tT≊100 nm, dc sputtered nonepitaxially onto (001) Si. In no case do we see reproducible periodic oscillations, and any variations are always similar at 4–5 and 295 K. Our results show that oscillations of the size seen by Gallego are not simply a consequence of an average multilayer resistivity as low as 3.5 μΩ cm.
Spin polarized photoemission studies of the 3s core level in ferromagnetic systems (abstract)
Authors: Liu Y. , Xu J. , Huang D-J. , Johnson P. D.
Published: July 2002

Spin polarized core level photoemision studies are capable of providing local site specific magnetic information. 3s core level photoemission spectra are characterized by a main peak and satellite whose separation reflects the exchange interaction between the core level and the net spin in the valence bands. However, there is currently considerable disagreement as to whether the splitting between these two peaks may be taken as a measure of the local moment. An alternative approach is to examine the intensities of the different peaks in the spectra. Indeed analysis of the multiplet intensities in the final state suggests that it should be possible to obtain a reasonable measure of the local magnetic moment through measurement of the spin dependent intensities in the multiplet structure. In detailed spin polarized photoemission studies of the 3s core level of Fe and Co films grown on Ag(001) and Cu(001) substrates, respectively, we find that this is indeed the case. This suggests that studies of the spin polarization of the 3s core level photoemission may provide an important new technique for the measurement of magnetic moments in thin films. Lineshape fitting reveals new information about the lifetime of the core holes. Previous studies have suggested that a majority spin core hole will be shorter lived than a minority spin core hole because of the higher density of majority spin electrons in the valence bands. However, our studies indicate that the lifetime is more complicated and that it shows a strong dependence on the LS in the final state.
Characterization of ultraviolet excited Br*-radical etching of InGaAs/InAlAs material system
Authors: Habibi Soheil , Tanaka Jun , Hattori Hideki , Totsuka Masahiro , Matsumoto Satoru
Published: July 2002

Dry selective photochemical etching of InGaAs/InAlAs material system, in HBr gas excited by a 172 nm excimer lamp, has been characterized. The etching is thought to be due to the formation of reactive Br*-radicals which are photocreated in the gas phase and then diffused into the solid semiconductor to create volatile products. The etching is temperature sensitive with best etching results at 50–110° C. Atomic force microscope and scanning electron microscope pictures reveal that the surface morphology at this temperature range is smooth and fine. Auger electron spectroscopy and x-ray photoelectron spectroscopy measurements show that at low temperatures the etch products are primarily salts of bromide and are in the liquid phase and thus remain at the surface and a desorption process stops further etching. At slightly elevated temperature range, the creation of oxides and deposition of bromine compounds reduces the etch rate and causes the surface quality to deteriorate. Etching at higher pressure range increases the etch rate of InGaAs but results in surface quality deterioration.
Growth mechanism of iron-filled carbon nanotubules
Authors: Zhang G. L. , Ambe F. , du Marchie Van Voorthuysen E. H. , Niesen L. , Szymanski K.
Published: July 2002

Iron-filled nanotubules were synthesized in a carbon arc in the presence of He and Fe(CO)5 gases. The consumption of the Fe(CO)5 inside the arc chamber was controlled by the pressure of the pentacarbonyliron Fe(CO)5 gas. Different shapes and filling extents of nanotubules were found depending on the pentacarbonyliron concentration supplied. Based on high-resolution transmission electron microscope images, we propose a growth model of iron-filled carbon nanotubules. The growth proceeds through the deposition and surface diffusion of carbon on the liquidlike metal. The hollow tubules probably grow spontaneously.
Bordoni peaks in face-centered cubic metals at low temperatures
Authors: Marchesoni F.
Published: July 2002

Two internal friction peaks discovered in pure aluminum at increasingly low temperatures, respectively by Lax and Filson and by Kosugi and Kino, are interpreted as different occurrences of the well-known Bordoni peak. The Lax–Filson peak is attributed to impurity assisted nucleation of thermal kink pairs; the Kosugi–Kino peak marks the onset of a new nucleation mechanism: the geometrical kinks (antikinks) rearrange themselves into superkink–antikink pairs in order to overcome the Schottky barriers. The experimental conditions for the direct observation of such peaks are discussed in some detail.
Ground and excited state exciton spectra from GaN grown by molecular-beam epitaxy
Authors: Reynolds D. C. , Look D. C. , Kim W. , Aktas Ö. , Botchkarev A. , Salvador A. , Morkoç H. , Talwar D. N.
Published: July 2002

The emission and reflection spectra of GaN have been investigated in the intrinsic region and the data have been interpreted in terms of the wurtzite crystal band structure. Three intrinsic exciton transitions have been observed, one associated with each of the valence bands. Exciton excited states associated with the two top valence bands were also observed. The exciton binding energies, the band-gap energies, and the exciton Bohr radii are all reported along with the dielectric constant and the spin-orbit and crystal-field parameters for GaN.
Reflection high-energy electron diffraction analysis of iron silicide growth on Si(110)
Authors: Wu Jie , Shimizu Saburo
Published: July 2002

Reactive deposition epitaxial growth of iron silicides on Si(110) has been investigated by in situ observation of reflection high-energy electron diffraction. The formation of several phases of iron silicides: simple cubic ε-FeSi, β-FeSi2, γ-FeSi2, and/or FeSi1+x (0≤x≤1) in a CsCl structure have been observed and their crystallographic orientations have been identified. By depositing Fe at 600 °C and annealing at 730 °C for 60 min, β-FeSi2 is formed in islands with facet planes β-FeSi2(1̄00)//Si(221) and β-FeSi2(1̄00)//Si(221̄), and a base plane β-FeSi2(4̄10)//Si(110). The peculiar β-FeSi2(4̄10) plane acts as a matching face because of its better lattice matching to the Si(110) surface than the other planes.
Spectroscopic light scattering from electrochromic tungsten-oxide-based films
Authors: Rönnow D. , Kullman L. , Granqvist C. G.
Published: July 2002

Films of W oxide and oxyfluoride were made by reactive sputtering, and electrochromic absorption modulation was obtained by subsequent electrochemical Li intercalation. Total and diffuse transmittance and reflectance were measured in the 0.4–1 μm wavelength range using a newly developed instrument. The ratio between diffuse and total optical response was <0.2% for the transmittance and <1% for the reflectance irrespective of the electrochromic absorption level. These magnitudes of the scattering are acceptable for practical smart windows applications and lend credence to a description of electrochromism in terms of localized absorption centers. Vector perturbation theory for light scattering by a film with rough interfaces could be reconciled with the data, assuming uncorrelated roughness.
Structural investigation of the initial interface region formed by thin titanium films on silicon (111)
Authors: Edwards A. M. , Dao Y. , Nemanich R. J. , Sayers D. E.
Published: July 2002

A structural study of the initial interface region formed by titanium on silicon (111) was undertaken. Thin films (100 Å) of titanium were deposited in ultrahigh vacuum (UHV) conditions onto atomically clean silicon(111) wafers and annealed in situ at 25 °C intervals between 300 and 475 °C. Structural characterization of the evolving interface was performed primarily via extended x-ray absorption fine structure (EXAFS) measurements. Results indicate that a major structural rearrangement takes place between 400 and 425 °C. EXAFS fitting analysis reveals this transition to be from a disordered TiSi-like phase to a more ordered C49-like disilicide state. The results are compared with those previously reported for the zirconium:silicon system.
Transmission electron microscopy and cathodoluminescence of tensile-strained GaxIn1−xP/InP heterostructures. II. On the origin of luminescence heterogeneities in tensile stress relaxed GaxIn1−xP/InP heterostructures
Authors: Cléton F. , Sieber B. , Bensaada A. , Masut R. A. , Bonard J. M. , Ganière J. D.
Published: July 2002

We have determined the origin of the spatial luminescence fluctuations observed between the dark line defects present in tensile strained GaxIn1−xP/InP/n+-InP heterostructures (Part I [F. Cléton et al. J. Appl. Phys. 80, 827 (1996)]). For that purpose, we have undertaken semi-quantitative and spectroscopic cathodoluminescence (CL) measurements on various specimens in areas exhibiting CL contrasts which could be as large as 80%. The analysis of the variation of the CL polychromatic signal with electron beam energy allowed us to get information on the diffusion-recombination (DR) parameters of the areas under study. From the correlation between the local relaxation level of these areas and their DR parameters, we can conclude that the variation of the misfit dislocations density at the GaxIn1−xP/InP interface is at the origin of the luminescence heterogeneities. We also demonstrate that recycling, by the GaxIn1−xP epilayer, of the photons originating from the heavily doped InP substrate, enhances the CL contrast between areas exhibiting different relaxation levels.
Average bond energy model for determining valence-band offsets at strained heterointerfaces Si,Ge,InP,GaAs/GexSi1−x
Authors: Ke San-huang , Wang Ren-zhi , Huang Mei-chun
Published: July 2002

A full description is presented of the ‘‘average bond energy model,’’ which was developed for the determination of valence-band offset at heterojunctions. It is shown that this model is related conceptually to Harrison’s tight binding ‘‘pinned’’ model, while it overcomes all of the shortcomings of the latter. Its final form turns out to be a generalization of Cardona’s dielectric-midgap-energy model. The average bond energy model is also shown related to Tersoff’s charge-neutrality-point model. In this article, this model is used in conjunction with a cluster expansion method to determine systematically the valence-band offsets at four strained alloy type heterointerfaces, Si,Ge,InP,GaAs/GexSi1−x as functions of the alloy composition x. Good agreement is found between our results and available experimental data.
Fully oxygenated RBa2Cu3−xCoxOy, (R=Y, Eu, Pr, and 0≤x≤1)— from high-temperature superconductors to high-resistivity nonmetals
Authors: Fisher B. , Genossar J. , Patlagan L. , Reisner G. M. , Knizhnik A.
Published: July 2002

Reported here are the results of measurements of the resistivity (ρ) up to 300 K and of the thermoelectric power (TEP) up to 400 K of ceramic samples of the title materials. We determined also their room-temperature lattice parameters and oxygen content as functions of Co concentrations. The metal–nonmetal transition in YBa2Cu3−xCoxOy and in EuBa2Cu3−xCoxOy is marked by the onset of the deviation of the maximum absolute TEP from a value calculated from a simple narrow-band formula. The results indicate that the effective valency of Pr in PrBa2Cu3−xCoxOy varies from ∼3.5 at x=0 to ∼3 for x=0.5. For x=0 this material is close to the metal–nonmetal transition. In the nonmetallic regime the electrical transport is by activated hopping. In certain ranges of Co content the results are consistent with two-band hopping conductivity with two branches, a low-temperature and a high-temperature branch of variable-range-hopping (VRH) conductivity. In the VRH regime there is a remarkable correlation between the two resistivity parameters, ρ0 and T0 in Mott’s equation ρ=ρ0 exp(T0/T)1/4. The resistivity of these Co-rich compounds is very high: thus, e.g., ρ(80 K)≳107 Ω cm in PrBa2Cu2.2Co0.8O7.15. These materials may find applications as insulating barriers in thin-film high-temperature superconducting devices.
Electrical conduction in semiconductor junctions with interface dipole layers
Authors: Schmeits M.
Published: July 2002

We have studied the steady-state dc and small-signal ac conduction in semiconductor junctions with interface dipoles. The junctions have been modeled according to the two experimental methods used to fabricate these structures. In the first method, Si or Ge atomic layers are deposited at the interface of a III–V junction; in the second, a closely spaced pair of δ doping layers, one n type and one p type are inserted in the growth process. The numerical study is based on the resolution of Poisson’s equation and of the continuity equation for electrons and holes. It yields the energy band diagrams, the steady state and ac components of the carrier concentrations and current densities as function of position. In particular, it is shown for the case of junctions with δ-doped interface dipoles that the modulation of the ionized dopant concentrations in the δ layers leads to a significant contribution to the total capacitance. As final results, the current–voltage I(V) and capacitance–voltage characteristics C(V) are obtained. Comparison of the I(V) curves with existing experimental data shows good agreement. The analysis of the C−2(V) curve as function of V yields a method to determine the existence and the strength of the interface dipole.
Effect on electron energy on amorphization of ZrCr2
Authors: Faldowski J. A. , Motta A. T. , Howe L. M. , Okamoto P. R.
Published: July 2002

The influence of electron energy on the amorphization of ZrCr2 at 25 K was measured. Amorphization was observed at electron energies from 900 to 330 keV. The dose-to-amorphization increases with decreasing electron energy with two steps, one at 700 keV corresponding to the decrease in the Zr displacement cross section due to the approaching displacement threshold of Zr and one at 500 keV corresponding to an appreciable decrease in the displacement cross section of Cr due to the approaching displacement threshold for Cr. At lower electron energies, it is believed that amorphization occurs principally through a secondary displacement mechanism, where light impurity atoms (mainly O) are displaced by electrons and displace in turn the heavier atoms. By fitting the results using electron displacement cross sections, we find the displacement energies in each sublattice to be EdZr=22 eV, EdCr=23 eV, EdO=4 eV.
Valence intersubband transitions stimulated by polarized light in Si1−xGex/Si multiple quantum wells
Authors: Zhang Xinhui , Chen Zhenghao , Cui Dafu , Zhou Junming , Yang Guozhen
Published: July 2002

The polarization properties of valence intersubband transitions in p-type doped Si0.75Ge0.25/Si multiple quantum wells are investigated using Fourier infrared absorption spectra. It is found that TE and TM polarized light beams both can excite valence intersubband transitions in SiGe/Si multiple quantum wells. Meanwhile, a strong dichroism is also observed for HH1→HH2 transitions because the splitting peaks between TE and TM absorption have different activity under s- and p-polarized states. However, the strong mixing of light- and heavy-hole states in split-off state SO1 weakens the dichroism of HH1→SO1 transitions.
Comparison of collision rates in particle-in-cell, Monte Carlo, and Boltzmann codes
Authors: Verboncoeur J. P. , Parker G. J. , Penetrante B. M. , Morgan W. L.
Published: July 2002

Computational modeling is a key tool for studying collisional plasma discharges, including capacitive, inductive, and dc discharges. This work compares electron-neutral collision rates for a particle-in-cell code, a Monte Carlo code, a convected scheme Boltzmann code, and a spherical harmonic expansion Boltzmann code. In addition, comparisons with swarm experiments are presented where available. The comparison is performed over a range of reduced fields, E/N, appropriate to ac plasma display panels. The background gas is neon, with a simplified set of representative reactions. Ion and space charge effects are neglected.
Switching of surface-stabilized ferroelectric liquid crystal cells by motion of defects
Authors: Seitz Th. , Stelzer J. , Trebin H.-R.
Published: July 2002

Numerical calculations are presented on both equilibrium states and switching processes of surface-stabilized ferroelectric liquid crystal cells. Defect mediated switching by Bloch walls and by disclination lines is studied in particular. Our examinations are based on an idealized bookshelf configuration of the molecules with fixed tilt angle of the director. Numerical solutions for the scalar fields both of the director twist angle and the electric potential have been determined in two spatial dimensions, assuming the fields to be constant along the third dimension. In the bulk we employ the full Frank–Oseen energy (i.e., no one-constant approximation) with electric terms added represented by a uniaxial dielectric tensor and the spontaneous polarization. On the surface the director is anchored by a Rapini–Papoular potential with medium anchoring strength. The calculations were performed in high precision with a multigrid method on an adaptive grid.
State coupling effects in GaAs/InGaAs/AlGaAs modulation doped quantum wells
Authors: Abbade M. L. F. , Iikawa F. , Brum J. A. , Tröster Th. , Bernussi A. A. , Pereira R. G. , Borghs G.
Published: July 2002

Photoluminescence and magneto-luminescence techniques were used to evaluate the optical properties of pseudomorphic GaAs/In0.2Ga0.8As/Al0.25Ga0.75As modulation doped single quantum wells. The data are analyzed using self-consistent calculations that predict a strong coupling between the InGaAs quantum well and the potential well formed in the AlGaAs barrier due to planar-doping. The coupling effect gives rise to additional transitions in the emission spectra. Temperature and magnetic field dependence of luminescence spectra provide strong evidence of indirect transitions in these structures.
Modeling and control of an electric arc furnace using a feedforward artificial neural network
Authors: King P. E. , Nyman M. D.
Published: July 2002

Previous studies have shown that the electric arc furnace is chaotic in nature and hence standard control techniques are not effective. However, human (heuristic) control is used every day on electric arc furnaces. A furnace operator assesses the performance of the furnace and makes judgments based on past experience and intuition. In order to improve the effectiveness of this control, a qualitative understanding of the operating conditions of the furnace is required. Artificial neural networks are capable of learning the system dynamics of the electric arc furnace. This article describes a feedforward neural network trained to model arc furnace electrical wave forms taken from an experimental arc furnace. The output of this model is then used in estimating the future state of the furnace for control purposes.
Transient light absorption in polydiacetylene films
Authors: Zheng L. X. , Feng Z. G. , Knopf F. Carl
Published: July 2002

The sign of the transient transmission in PDA 4BCMU film (polydiacetylene 4-butoxycarbonalmethylurethane) was experimentally investigated as a function of excitation wavelength and intensity. The observed decrease in the transient transmission (ΔT<0) from 2.05 eV (605 nm)<ωex<2.16 eV (574 nm) is attributed to triplet absorption. The triplet is created by a two-photon absorption process followed by a fast fission process.
Reply to ‘‘Comments on ‘Line shape, line width, and configuration coordinate diagram of the Cu band (1.21 eV) in InP’ ’’ [J. Appl. Phys. 80, 1937 (1996)]
Authors: Pal D. , Bose D. N.
Published: July 2002

We have used Gaussian shape of individual phonon replicas for fitting the experimental curve as suggested by Collan and Krustok. Better fit has been obtained using the parameters E0 (zero phonon energy)=1.28 eV, Eph (phonon energy)=0.038 eV, δ (phonon broadening parameter)=0.026 eV and S (Hwang–Rhys factor)=2.13. Thus, the results of Pal and Bose remain unchanged. Fitting parameters used by Collan and Krustok have no physical significance.
Anomalies of ferroelectric domain wall motion near the transition point
Authors: Tikhomirov O. A.
Published: July 2002

Optical measurements of the individual ferroelectric/ferroelastic domain wall oscillations in the ac electric field were carried out up to the transition temperature. The amplitude of the wall vibrations fell abruptly to zero so that the wall was at rest during the phase transition. The change of oscillation characteristics with temperature is shown to be dependent on the history of motion, in part on the initial amplitude and the presence of the shell of mobile defects or charge carriers. Change of material parameters, influence of screening or defects shell, and critical damping are discussed as possible mechanisms of the effect. The last assumption is shown to be in a good agreement with the experimental data. The measurements of the amplitude of domain wall vibrations may be used as a simple method for investigations on critical phenomena in ferroelectrics.
Kinetics of thermal annealing in strained ultrathin Si/Ge superlattices on vicinal Si(100) studied by Raman scattering
Authors: Chen Zhenghao , Xiao Xudong , Au Stanley , Zhou Junming , Loy M. M. T.
Published: July 2002

We report the experimental studies of in situ kinetic thermal annealing process by Raman scattering obtained from very short period Si/Ge superlattices grown on two types of vicinal Si(100) substrates. The experimental results show that the samples grown on double-stepped vicinal Si(100) substrates have well-defined in-plane strain in the epilayers and rather perfect interfaces. The samples grown on single-stepped vicinal Si(100), on the other hand, appear to have strain-relaxed and imperfect interfaces. The former is also thermodynamically more stable than the latter, and a suggested explanation is given.
Resonant tunneling of holes in double-barrier structures in the presence of an in-plane magnetic field
Authors: Zhu Jian-Xin , Wang Z. D. , Gong Chang-De
Published: July 2002

Using the asymptotic transfer-matrix method, we investigate the resonant tunneling of holes in double-barrier semiconductor structures in the presence of an in-plane magnetic field. The transmission coefficients including ll (light to light hole), hl (light to heavy hole), hh (heavy to heavy hole), and lh (heavy to light hole) are calculated as a function of energy. As in the case of nonzero parallel wave vectors, the mixing of hole tunneling can also occur due to the in-plane magnetic field. Moreover, as has been observed by resonant magnetotunneling spectroscopy, we also find that the different resonances have quite different magnetic-field dependences.
Influence of interface effects on the exciton magnetic-polaron energies in quantum wells and superlattices
Authors: Stirner T. , Hagston W. E.
Published: July 2002

Calculations of exciton magnetic-polaron (EMP) energies in semimagnetic quantum well structures and superlattices together with their temperature and magnetic field dependence have been performed. The influence on the EMP energies of the effects of enhanced paramagnetism at the interface and interface roughness are evaluated. It is shown that both these effects increase the theoretical EMP energy values and that interface disorder is the dominant factor in both cases. Furthermore, a more pronounced increase occurs for both effects in superlattices than in single quantum wells. Superlattices can also exhibit an additional type of disorder arising from variations in the barrier/well thickness. It is shown that this kind of disorder gives rise to an increase in the EMP energy values only when it leads to an overall narrowing of the well regions. A comparison with experimental values of the EMP energies in superlattices indicates the presence of small amounts of micro-roughness in the reported structures on a scale that is similar to that required to account for magneto-optical data.
Picosecond nonlinear spectroscopy of quantum-size PbTe films
Authors: Kornienko A. G. , Petnikova V. M. , Shuvalov V. V. , Vereshchagina L. N. , Zherikhin A. N.
Published: July 2002

We propose a new and promising technique to study quantum-size structures. In ultrathin monocrystalline PbTe films with thicknesses L=6, 18, and 30 nm, we have examined this technique, based on two-photon optical excitation of the renormalized electronic structure and revealed a sharp dependence of frequencies of two-photon resonant transitions on L. We explained this result within the framework of a model taking into account the real PbTe band structure, electron–electron and electron–phonon interactions, and interband and intra band redistribution of free carriers. We have estimated the characteristic time of interband polarization decay as T2≥300 fs and have analyzed the transformation of the nonlinear response for the case L→∞.
Degenerate two-photon absorption in lead borotellurite glasses at 532 nm
Authors: Watanabe Yuichi , Miyazawa Hiroaki , Tsuchiya Toshio
Published: July 2002

Lead borotellurite glasses of the system xPbO:(80-x)TeO2:20B2O3 (x=20–70) are submitted to open-aperture Z-scan measurements at 532 nm. Degenerate two-photon absorption coefficient of the glass ranges from 7.4±1.2 to 21.9±3.6 cm/GW; larger value is observed for the glass with higher PbO content. The proportional relationship between the PbO content and the two-photon absorption coefficient in the ternary glass is explained tentatively in terms of the Pb-associated absorption band existing in the deep ultraviolet region.
Laser cutting of wire-wound resistors: Theory and experiments
Authors: Atanasov P. A. , Manolov V. P.
Published: July 2002

The present study discusses cw CO2-laser cutting of wire-wound resistors. Based on the three-dimensional mathematical model developed, we computed the evolution of the temperature field in the sample and the phase change, as functions of the laser beam power and processing speed. The temperature dependence of the thermophysical coefficients and the dependence of light-absorption coefficient on the laser beam angle on incidence are taken into account. Experimental results are presented for the minimum laser power that provides cutting of the sample at different speeds. A reasonable agreement between the experimental and theoretical results is found.
Application of the principle of minimum entropy production to shock wave reflections. II. Pseudosteady flows
Authors: Li H. , Ben-Dor G.
Published: July 2002

The stability of both regular reflection and Mach reflection wave configurations in pseudosteady flows has been investigated by applying the principle of minimum entropy production, in a way similar to that done by us in Part I of this study [Li and Ben-Dor, J. Appl. Phys. 80, 2027 (1996)] where the stability of steady flow reflection configurations was considered. As a result, it was found that Mach reflection wave configurations are stable inside the dual solution domain, although, based on the state of the art when this study started, they were considered not to be stable. Consequently, a new general transition criterion from regular to Mach reflection was proposed. With the aid of this criterion the domains of regular, direct-Mach and stationary-Mach reflections, in the domain of the incident shock-wave Mach number and the reflecting wedge angle, were reestablished. All the analytical findings were supported by experimental results from different sources.
Evidence for photoluminescence band in p-type Al0.67Ga0.33As related to nonequilibrium DX− centers
Authors: Gladkov P. , Ždánský K.
Published: July 2002

The photoluminescence (PL) properties of p-type Al0.67Ga0.33As epitaxial layers grown by metalorganic vapor phase epitaxy technique and doped with residual carbon have been studied at 10 K. The PL spectra show two distinct ranges: one dominated by PL lines related to the X band shallow impurities (acceptor carbon and a background donor, predominantly Si) and the second including a structural broadband (BB), beginning some 300 meV below the band gap. The ionization energies determined for the carbon and the Si are ≊39 and 52±1 meV, respectively. The BB consists of four poorly resolved peaks at 1.8, 1.74, 1.67, and 1.6 eV with a half width ≳50 meV. Their PL intensity shows very specific temperature dependence with a maximum at temperatures where the persistent photoconductivity reported in n-type AlxGa1−xAs is quenched. Experiments with selective above band-gap excitation reveal the existence of a threshold for the BB excitation. The excitation density dependence of the BB exhibits some superlinearity for excitation densities ≳1.5 W/cm−2. These BB properties gave evidence that its origin has to be related to a nonequilibrium DX− centers, resulting possibly in a two-step optical recharging process: D++e→D° and D°+‘‘hot e’’→DX−. Two models are accounted for the BB explanation. One of them assumes radiative transitions (h, DX−), while the second considers internal radiative transitions from the DX° state of the distorted configuration to the DX− state.
Positron backscattering in polymer/metal systems
Authors: Madani M. M. , Granata R. D.
Published: July 2002

Positron backscattering was observed at interfaces of polymer/metal using positron annihilation lifetime spectroscopy in the Teflon and Mylar films and poly (MMA-co-nBMA) acrylic coatings on tungsten (W) and molybdenum (Mo) substrates. Aluminum (Al) used as a comparison substrate did not have significant backscattering. Major changes were observed in the third, I3, and fourth, I4, intensity components of thin layers of Teflon and Mylar films on W and Mo substrates compared to Al. The average value of positron backscattering was estimated at 39% and 32% for W and Mo, respectively, with a 22Na source. A model was presented for calculation of the backscattering coefficient (B) in the polymer/metal systems and compared with experimental results.
Annealing and memory effects in polymer-dispersed chiral liquid crystals
Authors: Magnaldo A. , Nourry J. , Sixou P.
Published: July 2002

A cholesteric liquid crystal with negative dielectric anisotropy and with a visible wavelength selective reflection presents high memory effects when encapsulated in a polymer film. Three states at least are accessible within the same film: reflecting state, memory state, and refreshed state. The last two states are stable over months. When the sample is annealed, the sample goes through an irreversible transformation, after which the memory state is no longer accessible. Through the data collected as the samples were progressively annealed it was guessed how annealing changes the properties of the film, and which phenomena are responsible for such changes.
Size dependences of model nanostructure sound velocity
Authors: Mon K. K.
Published: July 2002

We study by means of numerical simulations the size dependences for sound velocity of model nanostructures. We use molecular dynamics to obtain the zero temperature size dependences of the propagation velocity of mechanical perturbation for rod-shaped nanostructures with free surfaces. The particles interact with the Stillinger–Weber potential for silicon. We consider the longitudinal sound propagation in the (001) direction only. The bulk limit is reached very quickly and the longitudinal velocity is already independent of the cross section for a nanofiber larger than 40×40 Å. We also study velocity for structures without free surfaces and the effect of changing the magnitude of the triplet interaction potentials.
Microwave field distribution in superconducting thin film devices
Authors: Quenter D. , Doderer T. , Huebener R. P.
Published: July 2002

We measured the spatial distribution of microwave fields and dissipative surface currents in various passive and active superconducting thin-film devices during their operation at a temperature of about 4 K. We used low-temperature scanning electron microscopy which offers a spatial resolution of about 1 μm and we present sample response models for interpreting the imaging results. Such investigations may have important consequences for the improvement of the design and preparation of superconducting thin-film microwave devices.
Pulse shepherding in nonlinear fiber optics
Authors: Yeh C. , Bergman L.
Published: July 2002

In a wavelength division multiplexed fiber system, where pulses on different wavelength beams may copropagate in a single mode fiber, the cross-phase-modulation (CPM) effects caused by the nonlinearity of the optical fiber are unavoidable. In other words, pulses on different wavelength beams can interact with and affect each other through the intensity dependence of the refractive index of the fiber. Although CPM will not cause energy to be exchanged among the beams, the pulse shapes and locations on these beams can be altered significantly. This phenomenon makes possible the manipulation and control of pulses copropagating on different wavelength beams through the introduction of a shepherd pulse at a separate wavelength. How this can be accomplished is demonstrated in this paper.
On the unusual electromigration behavior of copper interconnects
Authors: Glickman E. , Nathan M.
Published: July 2002

The present uncertainty in the ability of Cu to substitute for Al as the conductor material in very large scale integration arises from the perplexing electromigration behavior of Cu interconnects: the electromigration activation energy in multigrained lines is often about two times lower than for grain-boundary diffusion, while the pre-exponential factor in the electromigration rate expression is several orders of magnitude smaller than that characteristic of electromigration along grain boundaries. Using literature data, in particular those of drift velocity experiments, we show that regardless of these unusual facts, grain boundaries are still most likely the major electromigration diffusion pathways in Cu interconnects. Based upon recent progress in the theory of grain-boundary grooving with an arbitrary grain-boundary flux [Klinger et al. J. Appl. Phys. 78, 3833 (1995)], and the specific model applying the general theory to electromigration [Glickman, Phys. Low-Dim. Struct. 11/12, 69 (1994)], we explain the major features of electromigration in Cu in terms of the extension of slit-like grooves along the interconnect line, followed by their merging. Fitting the electromigration activation energy reported for pure Cu into the model suggests that surface diffusion along freshly created groove walls is slow, with an activation energy above 2 eV. Most likely, this is due to trace surface contaminations. Having this new key element in the grain-boundary grooving model, with surface diffusion acting in effect as a ‘‘healing’’ mechanism rather than as an independent pathway parallel to grain-boundary diffusion, and using empirical surface diffusion parameters for Cu, enable us to rationalize the major features of Cu electromigration behavior reported in the literature: the values of the electromigration pre-exponents, the island-like morphology of the electromigration displacement region, the current density exponent, and the origin of the Sn effect on electromigration parameters. Our main conclusion is that the full advantages of Cu as the most promising electromigration resistant interconnect material can be realized, provided that trace contaminations responsible for suppressing diffusion along freshly created surfaces are identified, controlled and eliminated. This will allow unalloyed, multigrained Cu interconnects to have an electromigration resistance four orders of magnitude larger than Al(2% Cu) at 100 °C.
Solid phase epitaxy of diamond cubic SnxGe1−x alloys
Authors: Taylor M. E. , He G. , Atwater Harry A. , Polman A.
Published: July 2002

Solid phase epitaxy of amorphous SnxGe1−x films on strain relieved Ge films on Si(001) substrates was investigated for alloy compositions in the range 0.02≤x≤0.26. Films with compositions x<0.05 crystallize by solid phase epitaxy as substitutional, strain relieved, diamond cubic alloys without phase separation or surface segregation of Sn. Films with higher Sn compositions exhibit more complicated behavior in which phase separation is believed to follow solid phase epitaxy. This sequence of transformations for higher Sn compositions yields epitaxial, substitutional, strain relieved, diamond cubic SnxGe1−x films with x∼0.05, and excess Sn is segregated in ∼100 nm size domains within the epitaxial alloy film.
Anomalous magnetic behavior in the grain aligned HgBa2Ca2Cu3O8+δ superconductor
Authors: Kim Gun Cheol , Kim Young Cheol
Published: July 2002

For magnetic fields parallel to the c-axis configuration for a layered structure Hg-1223 compound, the M–H curves displayed the wrong sign of hysteresis (virgin curve lies above the reverse curve) within a certain temperature regime ≥96 K. For the temperature region below 96 K, the magnetic response was caused by a one-component (three-dimensional) system. For 96 K<T<108 K, the interunit cell coupling of CuO2 plane pairs is broken, but the coupling of CuO2 planes inside the unit cell is effective. At the temperature region above 108 K, the magnetic response was caused by the fluctuation of two-dimensional pancake vortices in a decoupled CuO2 plane inside the unit cell.
Deep acceptorlike states in Si doped molecular-beam-epitaxial-grown AlxGa1−xAs
Authors: Jia Y. B. , Grimmeiss H. G. , Dobaczewski L.
Published: July 2002

Acceptorlike states with energy levels in the lower part of the band gap have been observed by photocapacitance measurements in Si-doped molecular-beam-epitaxial-grown AlxGa1−xAs (x=0.30–0.59). The microscopic structure of these defects is still unclear. Their concentration, however, can exceed the net donor concentration. The energy positions of the acceptorlike states as well as their photoionization cross sections of holes and electrons have been studied for different x. Due to their large concentration, these states may disturb experiments performed on DX centers which are often assumed to be the main electronic levels in these materials.
Anodization behavior of Al, and physical and electrical characterization of its oxide films
Authors: Ozawa Kiyoshi , Majima Teiji
Published: July 2002

We have investigated the physical and electrical properties of anodic oxide films treated by a variety of aqueous electrolyte solutions. All anodic oxide diodes revealed consecutive current regimes varying with bias voltage as V, V2, and Vn (n≳2) in the steady-state current-voltage characteristics. Here, the transition voltage from the V2 to Vn current regime and the voltage exponent n varied depending on the oxide forming electrolyte and the bias direction of the diodes. These electrical properties were interpreted as a space-charge-limited current modified by a distributed gap state density in space and in energy. The oxide had a double-layer structure, a layer containing an anion characteristic of each electrolyte and an anion-free layer. The anion-containing layer had a varying gap state distribution. This was due to the anion characteristics, which reduce a deep-lying gap state density and modify a tail state density. We propose two practical anodizing techniques to control the depth profile of the anion. This allows us to form an oxide with a small leakage current equivalent to an anion-free control oxide. We also show that the dielectric loss for the anion-free oxide was reduced through the formation in an organic electrolyte and was increased in an inorganic electrolyte.
The effect of traps at the free surface of GaAs field effect transistors
Authors: Jin Gongjiu , Jones B. K.
Published: July 2002

In a GaAs field effect transistor there are ungated sections of the channel between the gate and the source/drain. The static characteristics and the transients which occur in various parameters after a change in the bias voltages can be shown to be affected by the surface potential in this region. A model is proposed for these effects which involves a surface region with lower effective energy gap. The gate current leakage characteristics and conductance deep level transient spectroscopy measurements on single and dual gate devices are consistent with this model.
Optical properties of LiNbO3 implanted with Ag ions
Authors: Shang D. Y. , Saito Y. , Kittaka R. , Taniguchi S. , Kitahara A.
Published: July 2002

Ag ions were implanted in LiNbO3 at energies of 25 keV and 3 MeV. Optical absorption spectra were measured in the visible range. A large absorption peak due to small colloidal Ag metal was observed at 460 and 510 nm for the as-implanted sample at 3 MeV and 25 keV, respectively. Subsequently, the samples were heated in air up to 600 °C. The absorption peak moved toward longer wavelengths up to 560 nm when the sample was heated at high temperature. Small droplets of metallic Ag expelled from the implanted layer formed on the surface of the sample even when the samples were held at room temperature. The number and size of the droplets grew with time and their growth was accelerated when the samples were heated at high temperature.
Low-temperature iron-nitride phase transformations induced by ion bombardment
Authors: Moreira E. C. , Amaral L. , Behar M. , Foerster C. E.
Published: July 2002

We show that for the Fe–N system the combined use of ion irradiation and thermal annealing can lower the temperature for a given phase transformation. By Ar bombarding N-implanted Fe samples at 250 and 300 °C, we have induced the ε-Fe2N⇒ε-Fe2+xN+ε-Fe3.2N and the ε-Fe2N⇒ε-Fe3N+γ′-Fe4N phase transformations, respectively. These temperatures are 50 °C lower than the ones needed to produce the same transformations by thermal annealing.
Raman scattering study of thermally reduced stabilized cubic zirconia
Authors: Morell G. , Katiyar R. S. , Torres D. , Paje S. E. , Llopis J.
Published: July 2002

We investigated the Raman spectra of thermally reduced and untreated Y- and Ca-stabilized cubic zirconia. A substantial decrease in Raman activity was observed in the acoustic mode region upon reduction. Analyses of these spectra as a phonon density of states and of the observed spectral changes indicate that the reduced states are more ordered than the untreated one. This is consistent with a nonrandom arrangement of vacancies, which produces the superposition of periodic sequences of vacancies within domains. This, in turn, causes the increment in coherence length of phonons that is manifested as a decrease in acoustic mode activity.