bluuebunny/crossref_metadata_2025 huggingface dataset:
Height of the energy barrier existing between cathodes and hydroxyquinoline–aluminum complex of organic electroluminescence devices
Authors: Matsumura Michio , Akai Tomonori , Saito Masayuki , Kimura Takashi
Published: July 2002

The properties of organic electroluminescence devices are largely affected by the kind of metals used as the cathode, because the barrier height formed at the interface depends on the electronic and chemical properties of the metals. On the basis of the temperature dependence of currents flowing through the interface between tris(8-hydroxyquinolino)aluminum and a magnesium cathode, the carrier injection mechanism at the interface was ascribed to the thermionic emission with the barrier height of about 0.58±0.03 eV at zero electric field. The barrier height became larger when metals with larger work functions were used as the cathode. The current density was also found to be dependent on the chemical structure of the interfaces.
Electronic oxide polarizability and optical basicity of simple oxides. I
Authors: Dimitrov Vesselin , Sakka Sumio
Published: July 2002

The average electronic oxide polarizability α02− of numerous single component oxides has been calculated on the basis of two different properties: linear refractive index n0 and energy gap Eg, which have demonstrated remarkable correlation. The optical basicity Λ of the oxides has been estimated on the basis of average electronic oxide polarizability calculated from the refractive index Λ(n0) and the energy gap Λ(Eg). A good agreement has been observed between the optical basicity data obtained using independent initial quantities. The simple oxides have been separated into three groups according to the values of their oxide polarizability. The α02− values (above 3 Å) obtained for PbO, Sb2O3, and Bi2O3 have been attributed to the high cation polarizability and the presence of a lone pair in the valence shell of the cation.
Noise characterization and device parameter extraction of a p-type strained layer quantum-well infrared photodetector
Authors: Wang Daniel C. , Bosman Gijs , Li Sheng S.
Published: July 2002

Dark current noise measurements between 101 and 105 Hz were carried out on a compressively strained p-type InGaAs/AlGaAs quantum-well infrared photodetector as a function of temperature and bias voltage. The measured noise can be attributed to number fluctuation noise associated with the generation and recombination of holes from and to the quantum-well bound states and the extended valence-band states. At low bias the number fluctuation noise translates into current fluctuation noise via hole diffusion, where as at higher-bias values the coupling is via the hole drift current component. Our measurements indicate that the field-induced barrier lowering and the Schottky image effect strongly influence the device characteristics. In addition we observe that the thermally generated heavy holes diffuse, at low fields, on the average to the nearest neighboring quantum well where they subsequently recombine. This recombination process is triggered by hole scattering with the acceptor centers.
Characteristics of light-emitting diodes based on GaN p-n junctions grown by plasma-assisted molecular beam epitaxy
Authors: Vaudo R. P. , Goepfert I. D. , Moustakas T. D. , Beyea D. M. , Frey T. J. , Meehan K.
Published: July 2002

We report on the fabrication and physics of mesa-etched light-emitting diodes (LEDs) made from GaN p-n junctions grown by molecular beam epitaxy. Rapid thermal annealing was found to improve the electrical properties of these LEDs. Annealed LEDs turn on at 4 V, exhibit an on-series resistance of approximately 14 Ω, and have only 36 μA of leakage current for reverse bias levels as high as 10 V. Electroluminescence (EL) spectra obtained from devices driven to 15 mA are dominated by a peak at 400 nm, which is attributed to recombination between shallow donors and Mg luminescent centers on the p side of the junction. The full width at half maximum of this peak is only 30 nm, which, to the best of our knowledge, is the narrowest EL peak measured from a GaN p-n junction LED. In other devices, recombination was found to proceed through defect states in the middle of the band gap. The broad emission from these LEDs can be shifted from the orange to the violet spectral region by adjusting the drive current. In addition, these LEDs withstand dc current densities in excess of 700 A/cm2 at room temperature.
Characterization of epitaxially grown Fe-N films by sputter beam method
Authors: Okamoto Satoshi , Kitakami Osamu , Shimada Yutaka
Published: July 2002

We have prepared epitaxial Fe-N martensite (α′) films on α-Fe (001) single-crystal underlayers by the sputter beam method and synthesized a metastable α″-Fe16N2 phase by post-annealing. The saturation magnetization (4πMs) of the α′ phase films is in the range of 21.9–23.3 kGauss which is larger than that of α-Fe. Magnetization of the annealed samples containing α″-Fe16N2 phase have increased with the x-ray diffraction intensity ratio of α″(002) to [α″(004)+α′(002)]. Very careful analysis of x-ray diffraction data gives more reliable value on the volume fraction of the α″ phase in the annealed samples. As a result, it is found that the Fe-N film with magnetization of 24.7 kG contains 32 vol %-α″ phase within it. This result leads us to believe that α″-Fe16N2 phase has a remarkably large saturation magnetization.
Photovoltaic spectroscopy of exciton structures in Zn1−xCdxSe/ZnSe multiple quantum wells
Authors: Anedda A. , Casu M. B. , Serpi A.
Published: July 2002

Exciton transitions in photovoltaic spectra of strained-layer multiple-quantum-well samples of Zn1−xCdxSe/ZnSe grown by molecular-beam epitaxy were observed up to room temperature. Quantum level energies were calculated by means of the envelope-function method including strain. Great care was taken in order to evaluate the band offsets, the band-gap dependence on temperature and alloy concentration, as well as the quantum confinement enhancement of the exciton binding energies. Very good agreement between experimental and calculated values of the exciton energy position was found in the 80–300 K temperature range. Calculated binding energies as high as 35–40 meV account for the occurrence of the exciton structures up to 300 K.
A spin reorientation in Pr2Fe17D3 as revealed by Mössbauer spectroscopy
Authors: Grandjean F. , Hautot Dimitri , Long Gary J. , Isnard O. , Miraglia S. , Fruchart D.
Published: July 2002

The Mössbauer effect spectra of Pr2Fe17D3, which have been measured between 85 and 295 K, indicate the presence of a spin reorientation of the iron magnetic moments at 105±5 K. At this magnetic transition a large increase of ∼50 kOe in the 6c iron magnetic hyperfine field and abrupt changes in all of the remaining hyperfine fields are observed. A study of the changes in the quadrupole shifts at the transition indicates that this spin reorientation takes place within the basal plane of this rhombohedral compound. As expected, the temperature dependence of the isomer shifts does not show any anomaly at the transition. The origin of this spin reorientation is attributed to competing effects between lattice expansion upon deuteration and lattice contraction upon cooling.
Crystal field induced anisotropy in rare earth intermetallics as studied by 155Gd Mössbauer spectroscopy
Authors: Middleton D. P. , Mulder F. M. , van de Straat D. A. , Thiel R. C. , Buschow K. H. J.
Published: July 2002

We have investigated the effect of substitution and nitrogenation on the hyperfine parameters in Gd2Fe17−x(Ga,Al)x (x=1–10) and Gd(Fe,Co)12−xMox(Ny) (x=1.5–3.0 and y≊1) by means of 155Gd Mössbauer spectroscopy. We have observed marked changes in the values of the electric field gradient Vzz, the effective Gd-hyperfine field, and isomer shift. Al substitution in Gd2Fe17 leads to a sign reversal of the electric field gradient. No sign reversal of Vzz has been observed in the Gd2Fe17−xGax compounds. The effective hyperfine fields of the Gd2Fe17−x(Ga,Al)x compounds are decreasing with increasing x, due to the reduction of the 6s electron polarization resulting from the decreasing Fe moments. The ultimate value of the isomer shift based on a simple model on chemical effects that would be reached for x=17 is 0.52 mm s−1 for Al and 0.64 mm s−1 for Ga substitution in Gd2Fe17, respectively. The electric field gradient of the GdFe12−xMox compounds were obtained for x=1.5 and x=3.0. Nitrogenation is shown to lead to a sign reversal of the 4f and Fe sublattice anisotropy. Mo substitution in GdCo12−xMox shows a decreasing negative value of Vzz with increasing Mo concentration x. The values ‖Heff‖ in GdCo12−xMox increase with increasing Mo concentration. This can be attributed to a different near neighbor Gd and 3d-metal contribution to the effective hyperfine field compared to those of GdFe12−xMox.
Field dependence of magnetic relaxation in BiPbSrCaCuO superconductors
Authors: Raposo V. , Flores A. G. , Zazo M. , Torres L. , Iñiguez J.
Published: July 2002

Magnetic relaxation in ceramic cylindrical samples of BiPbSrCaCuO high Tc superconductors has been studied as a function of applied magnetic field for a constant decay rate of that field strength. We have analyzed the variation of the ac susceptibility versus time just after removing the magnetic field. Data have been obtained by means of an inductive technique from 1 to 3600 s, with magnetic fields that range from 10 to 100 Oe, and by switching off the field at a constant rate of 25 Oe/s. The field dependence of the thermally activated parameters has been obtained within the framework of the Anderson–Kim theory and using the so-called box distribution of energies. Anderson–Kim considered a logarithmic decay of the magnetic flux governed by an effective energy U=U0−FVX, where U0 is the pinning energy, V is the activation volume, X the pinning length, and F the driving force density. In this case we have found a field dependence of the form H−n for the pinning energy, with n close to 2 and temperature dependent. However, we have observed that the box distribution, which assumes the existence of a continuous energy spectrum, shows no field dependence for the effective energy.
Giant magnetoresistance effect and electric conduction in amorphous-CoFeB/Cu/Co sandwiches
Authors: Jimbo M. , Komiyama K. , Tsunashima S.
Published: July 2002

Giant magnetoresistance (MR) effects have been investigated for spin valve sandwiches using amorphous(a)-(Co0.9Fe0.1)80B20 alloy layers. In an a-CoFeB/Cu/Co sandwich, a MR ratio as large as 6% was obtained, and a MR curve was found to saturate in a field within 100 Oe. The resistivity is 40–60 μΩ cm. In a CoFeB(4 nm)/Cu(2 nm)/a-CoFeB(2 nm)/NiO(10 nm) sandwich, MR ratios as large as 4% were also obtained. The maximum field sensitivity of the sandwich is about 2.5%/Oe.
Preparation of Co–Fe–P amorphous fine needles with anodization technique and measurement of demagnetizing factor
Authors: Tayaoka A. , Tayaoka E. , Yamasaki J.
Published: July 2002

The amorphous Co–Fe–P and crystalline Co fine needles with diameter 0.1–0.2 μm aspect ratio more than 100 were prepared successfully by applying the dc electrodeposition to the anodization technique and their demagnetizing factors were measured. It was found that the demagnetizing factor of film with needles decreases with increasing aspect ratio and tends to take low constant values around 0.07–0.08. To obtain the low demagnetizing factor by using the shape anisotropy of needle, it was estimated that the aspect ratio more than 100 is needed. The equivalent demagnetizing factor defined by a ratio of a field needed to achieve saturation to the averaged flux density is estimated around 0.6 for the film with Co–Fe–P amorphous needles with 0.1 μm diameter.
Colossal magnetoresistance properties of the manganese perovskites La0.7−xYxCa0.3MnO3−δ
Authors: Maignan Antoine , Simon Charles , Caignaert Vincent , Raveau Bernard
Published: July 2002

Colossal magnetoresistance (CMR) properties have been evidenced for the manganese perovskites La0.7−xYxCa0.3MnO3−δ with 0.01≤x≤0.20. This system is compared to the manganites Pr0.7Ca0.3−xSrxMnO3−δ that exhibit the same Mn(III)/Mn(IV) ratio. Like for this second system, one observes that the transition temperature T1 increases as the size of the interpolated cation increases from 75 to 225 K. This comparison demonstrates that the Mn(III)–Mn(IV) mixed valence (hole carrier density) and the size of the interpolated cations are the two main factors that govern the transition temperature T1. However, the CMR effect characterized by the resistance ratio (RR) R0/RB (R0 resistance in zero magnetic field and RB resistance in a magnetic field, B=5 T) is much lower than that observed for the Pr manganites. The highest RR value is of 40 for La–Y phases for T=120 K (x=0.10) against 2.5×105 for the Pr phase for T=88 K (x=0.05). Thus, it is suggested that the electronic configuration of the interpolated cation may play an important role in the amplitude of the CMR effect.
Optical gain of InGaP and cubic GaN quantum-well lasers with very strong spin–orbit coupling
Authors: Ahn Doyeol
Published: July 2002

In this article, we study the effects of strong spin–orbit (SO) split-off band coupling on the valence-band structure and the optical gain of 70 Å strained InGaP–In(AlGa)P quantum-well lasers and a 100 Å cubic GaN quantum well using the 6×6 Luttinger–Kohn model. We first calculate the optical gain of InGaP quantum wells by comparing the 6×6 and 4×4 Luttinger–Kohn models. In the case of InGaP–In(AlGa)P quantum wells which have a SO split-off energy of 0.1 eV, the peak gain of the strained quantum well is overestimated in the low carrier injection region and is underestimated in the high injection, in the 4×4 model. On the other hand, the peak gain of an unstrained quantum well is overestimated in the 4×4 model over the wide range of carrier densities. Second, we obtain the Luttinger valence-band parameters γ1, γ2, and γ3 for a cubic phase of GaN using a semiempirical five level k⋅p model. Calculated valence-subband structures show that the subbands originated from the ‘‘light hole’’ and the ‘‘SO’’ are strongly coupled even at the zone center because of the very narrow SO split-off energy. It is expected that a very narrow separation (10 meV) between the SO band and the heavy- and light-hole bands causes two undesirable effects on the lasing of the GaN quantum well: (1) the TE and the TM polarizations have comparable magnitudes over the wide range of carrier densities and (2) the SO band will be easily occupied by the injected holes which in turn reduces the injection efficiency or increases the lasing threshold. Band-structure engineering is proposed to reduce the hole and the electron masses and to increase the SO band separation in order to reduce the lasing threshold.
Polar optical oscillations in coupled quantum wells: The electron-phonon interaction and scattering
Authors: Shi Jun-jie , Pan Shao-hua
Published: July 2002

Within the framework of the dielectric continuum model, optical phonon modes and their interaction and scattering with electrons in general coupled quantum wells (GCQWs) are studied. The dispersion relation of interface phonons and the electron-interface-phonon coupling strengths as functions of coordinate z and wave-number k are derived and illustrated. We find that the forbidden-frequency behavior of asymmetric heterostructures exists in GCQWs, which may cause an obvious polarization and interaction with electrons. The scattering rates as functions of quantum well parameters are calculated and numerical examples are given graphically. It is shown that the behaviors of intersubband scattering rates are much more complicated than those of intrasubband scattering ones. The results are useful for subsequent theoretical modeling of optical or transport experiments.
Effect of implanted ion species on the decay kinetics of 2.7 eV photoluminescence in thermal SiO2 films
Authors: Seol Kwang Soo , Ohki Yoshimichi , Nishikawa Hiroyuki , Takiyama Makoto , Hama Yoshimasa
Published: July 2002

Decay kinetics of photoluminescence (PL) existing around 2.7 eV has been studied in various ion-implanted thermal SiO2 films as a function of implantation conditions. The PL observed in many samples shows decay constants shorter than 10 ms, which is a well-observed decay constant for silica glass. The change in the decay constant and that in the PL intensity have been found to be systematically related with the mass and the dose of the implanted ions. Therefore, despite the short decay constant, the present 2.7 eV PL is attributable to a triplet-to-singlet transition of oxygen deficient centers, as in the case of silica glass. The rapid decay is interpreted as the increase in spin-orbit coupling interaction due to structural deformations by ion implantation such as the formation of paramagnetic defects and/or densification.
Electrically active defects in as-implanted, deep buried layers in p-type silicon
Authors: Giri P. K. , Dhar S. , Kulkarni V. N. , Mohapatra Y. N.
Published: July 2002

We have studied electrically active defects in buried layers, produced by heavy ion implantation in silicon, using both conventional deep level transient spectroscopy (DLTS) and an isothermal spectroscopic technique called time analyzed transient spectroscopy operated in constant capacitance mode (CC-TATS). We show that CC-TATS is a more reliable method than DLTS for characterization of the heavily damaged buried layers. The major trap produced in the buried layers in p-type Si by MeV Ar+ implantation is found to have an energy level at Ev+0.52 eV. This trap, believed to be responsible for compensation in the damaged layer, shows exponential capture dynamics. We observed an unusually high thermal activation energy for capture, which is attributed to a macroscopic energy barrier for carriers to reach the buried layer. We observe two other majority carrier traps, and also a minority carrier trap possibly due to inversion within the depletion layer.
New magnetic refrigerants for low temperature region
Authors: Tishin A. M. , Bozkova L. P.
Published: July 2002

Changes in the entropy magnetic of the rare-earth magnets DyAlO3 and ErAlO3 and DyxEr1−xAlO3 are calculated. It is shown that lanthanide orthoaluminate compounds DyxEr1−xAlO3 are promising working materials for magnetic refrigerators using the Carnot cycle principle operating in the temperature region 4.2–20 K.
Monte Carlo calculation of electron initiated impact ionization in bulk zinc-blende and wurtzite GaN
Authors: Kolnı́k Ján , Oğuzman İsmail H. , Brennan Kevin F. , Wang Rongping , Ruden P. Paul
Published: July 2002

Calculations of the high-field electronic transport properties of bulk zinc-blende and wurtzite phase gallium nitride are presented focusing particularly on the electron initiated impact ionization rate. The calculations are performed using ensemble Monte Carlo simulations, which include the full details of the band structure derived from an empirical pseudopotential method. The model also includes the numerically generated electron impact ionization transition rate, calculated based on the pseudopotential band structures for both crystallographic phases. The electron initiated impact ionization coefficients are calculated as a function of the applied electric field. The electron distribution is found to be cooler and the ionization coefficients are calculated to be lower in the wurtzite phase as compared to zinc-blende gallium nitride at compatable electric-field strengths. The higher electron energies and the resulting larger impact ionization coefficients in zinc-blende gallium nitride are believed to result from the combined effects of a lower density of states and phonon scattering rate for energies near and below 3 eV above the conduction-band minimum, and a somewhat higher ionization transition rate compared to the wurtzite phase. The nature of the impact ionization threshold in both phases of gallium nitride is predicted to be soft. Although there is considerable uncertainty in the knowledge of the scattering rates and the band structure at high energies which lead to uncertainty in the Monte Carlo calculations, the results presented provide a first estimate of what the electron initiated impact ionization rate in GaN can be expected to be.
Scattering of ultraviolet radiation in turbid suspensions
Authors: Griffith Michelle L. , Halloran John W.
Published: July 2002

A Beer’s law expression for the penetration depth of ultraviolet radiation in a concentrated suspension of scattering particles is used to model the depth of cure for a suspension of ceramic particles in a medium of photocurable monomers. The cure depth is predominantly controlled by the square of the refractive index difference between the ceramic particles and the medium, Δn2=(np−n0)2. A secondary effect on the cure depth is the ratio of the interparticle spacing to the ultraviolet wavelength. Theoretical results agree with experimental data for 0.40–0.50 volume fraction ceramic-filled suspensions.
Photo-, cathodo-, and electroluminescence from erbium and oxygen co-implanted GaN
Authors: Torvik J. T. , Qiu C. H. , Feuerstein R. J. , Pankove J. I. , Namavar F.
Published: July 2002

Efficient Er-related photo-, cathodo-, and electroluminescence at 1539 nm was detected from Er and O co-implanted n-type GaN on sapphire substrates. Several combinations of Er and O implants and postimplant annealing conditions were studied. The Er doses were in the range (0.01–5)×1015 ions/cm2 and O doses (0.1–1)×1016 ions/cm2. GaN films implanted with 2×1015 Er2+/cm2 at 350 keV and co-implanted with 1016 O+/cm2 at 80 keV yielded the strongest photoluminescence intensity at 1539 nm. The annealing condition yielding the strongest Er-related photoluminescence intensity was a single anneal at 800 °C (45 min) or at 900 °C (30 min) in flowing NH3. The optimum O:Er ratio was found to be between 5:1 and 10:1. Co-implanting the GaN:Er films with F was also found to optically activate the Er, with slightly (20%) less photoluminescence intensity at 1539 nm compared to equivalent GaN:Er,O films. The Er-related luminescence lifetime at 1539 nm was found to depend on the excitation mechanism. Luminescence lifetimes as long as 2.95±0.15 ms were measured at 77 K under direct excitation with an InGaAs laser diode at 983 nm. At room temperature the luminescence lifetimes were 2.35±0.12, 2.15±0.11, and 1.74±0.08 ms using below-band-gap excitation, above-band-gap excitation, and impact excitation (reverse biased light emitting diode), respectively. The cross sections for Er in GaN were estimated to be 4.8×10−21 cm2 for direct optical excitation at 983 nm and 4.8×10−16 cm2 for impact excitation. The cross-section values are believed to be within a factor of 2–4.
Artificially controlled stress anisotropy and magnetic properties of FeTaN thin films
Authors: Deng Hong , Jarratt James D. , Minor M. Kevin , Barnard John A.
Published: July 2002

This article presents a new method of investigating internal stress effects on thin film magnetic properties, in this case magnetically soft FeTaN sputtered films. The FeTaN films were deposited on a series of oxidized silicon (111) substrates prestressed to different degrees. During sputtering all the deposition conditions were kept exactly the same for all the samples. However, anisotropic stresses with different amplitudes are systematically introduced into the films when the prestressed wafers were released. In this way, FeTaN films with compressive stress varying from 80 to 608 MPa are produced. We found that the saturation magnetostriction (λs), anisotropy field (Hk), initial permeability (μi) as well as easy axis orientation of FeTaN thin films are strongly affected by the induced stress anisotropy. A stress ratio concept is proposed as a measure of the degree of the stress anisotropy. Models for easy-hard axis switching induced by stress for magnetic films with positive magnetostriction are discussed.
Anomalous Hall effect in Gd-doped La2/3Ca1/3MnO3
Authors: Jaime M. , Hardner H. , Salamon M. B. , Rubinstein M. , Dorsey P. , Emin D.
Published: July 2002

Ceramic samples of composition (La1−xGdx)2/3Ca1/3MnO3 were prepared and used as targets to grow films onto LaAlO3 substrates by pulsed laser deposition. Comparison of the electrical resistance and thermopower, measured vs temperature and applied magnetic fields, indicates transport dominated by positively charged small polarons in the high temperature paramagnetic state. Nonetheless, the Hall effect, measured in 0.5 μm thick films of composition x=0 and x=0.25, has the sign that is normally ascribed to negatively charged free carriers. The magnitude of the Hall coefficient decreases exponentially with increasing temperature with an activation energy that differs from that of the resistivity. This behavior and its anomalous negative sign are interpreted to result from face-diagonal hopping of small polarons in the Mn sublattice.
Linearly polarized and time-resolved cathodoluminescence study of strain-induced laterally ordered (InP)2/(GaP)2 quantum wires
Authors: Rich D. H. , Tang Y. , Lin H. T.
Published: July 2002

The optical properties of (InP)2/(GaP)2 bilayer superlattice (BSL) structures have been examined with linearly polarized cathodoluminescence (CL), time-resolved CL spectroscopy, and cathodoluminescence wavelength imaging. An In and Ga composition modulation of ∼18% forms during the metalorganic chemical vapor deposition growth of short period (InP)2/(GaP)2 bilayer superlattices. Transmission electron microscopy showed a period of ∼800 Å along the [110] direction, resulting in coherently strained quantum wires. A strong excitation dependence of the polarization anisotropy and energy of excitonic luminescence from the quantum wires was found. The results are consistent with a phase-space and band filling model that is based on a k⋅p and two dimensional quantum confinement calculation which takes the coherency strain into account. CL images reveal that defects in the BSL originate from the GaAs substrate and/or the initial stages of InGaP growth. The effects of defects on the band filling, carrier relaxation kinetics, and nonlinear optical properties were examined.
Optical absorption by Ag precipitates in AlGaAs
Authors: Crouse David , Nolte D. D. , Chang J. C. P. , Melloch M. R.
Published: July 2002

Optical absorption by silver nanoclusters in a dilute metal-semiconductor composite is calculated including the effects of size and shape on the surface plasmon absorption. Strong broadening of the Fröhlich resonance peaks is caused by relatively minor shape variations. Optical transmission experiments and transmission electron microscopy experiments were performed on a Ag–Al0.3Ga0.7As composite formed by ion implantation followed by anneal. Silver precipitates are present in a clearly defined implant layer. A broad featureless optical absorption is observed that extends below the band gap, and which increases approximately linearly with Ag-ion dose.
Distribution of polarized-cathodoluminescence around the structural defects in ZnSe/GaAs(001) studied by transmission electron microscopy
Authors: Mitsui Tadashi , Yamamoto Naoki
Published: July 2002

The spatial distribution of the polarized cathodoluminescence (CL) emissions from thin ZnSe films grown by metalorganic vapor phase epitaxy method on GaAs(001) has been examined by a low-temperature polarized CL measurement system combined with a transmission electron microscope. It is found that the Y0 and Y1 emissions come from the regions near dislocation tangles and near individual dislocations. The polarized CL images of these emissions show changes in intensity distribution when the polarization condition is changed. The observations suggest that the polarization direction of these emissions is parallel to the dislocation line.
The effect of different profiles of the rotor magnet in an aquatic ac synchronous motor
Authors: Chiu Kuo-Chi , Wang Yau-Der , Huang Der-Ray , Ying Tai-Fa
Published: July 2002

The cogging torque of the aquatic ac synchronous motor is sensitive to the magnetization profiles, the relative angular offset, the magnetic field strength of the rotor magnet, and the structure of the stator core. With the same magnetic profile of the rotor magnet, the cogging torque of the motor is proportional to the trough width of the stator core. For different magnetic profiles of the rotor magnet combined with the same stator core, the cogging torque of the motor varied markedly with the magnetic profiles of the rotor magnet. The computed values of the cogging torque of the motor are in excellent agreement with the experimental values.
Interatomic potentials between distinct atoms from first-principles calculation and lattice-inversion method
Authors: Zhang Wen-qing , Xie Qian , Ge Xi-jin , Chen Nan-xian
Published: July 2002

The effective interatomic potentials between distinct atoms in intermetallics, such as FeAl, Fe3Al, NiAl, Ni3Al, FeCr, Al3Cr, AlLi, Al3Li, and AlLi3, are obtained by inversion of first-principles cohesive energy curves based on the lattice inversion method of Chen. The obtained potentials are used to evaluate the phonon dispersions and linear thermal expansion of some intermetallic compounds, as well as the site preference of alloying element Cr in the D03-ordered Fe3Al.
Band offsets at the GaInP/GaAs heterojunction
Authors: Lindell A. , Pessa M. , Salokatve A. , Bernardini F. , Nieminen R. M. , Paalanen M.
Published: July 2002

We have measured current–voltage curves and the temperature dependence of the zero bias conductance for a p-type Be-doped GaInP/GaAs heterojunction grown by the molecular beam epitaxy method. We have determined the valence band offset ΔEν from both measurements and find it to be 310 meV within 5% of accuracy. Similarly, we find for an n-type Si-doped sample that the conduction band offset ΔEC is 95 meV. First-principles calculations have been carried out for the atomic and electronic structures of the interfaces. For the thermodynamically favored interfaces, the valence band offset is found not to be sensitive to atomic relaxations at the interface. The calculated values are in good agreement with the experiments.
Magnetic domain structures of La0.67Sr0.33MnO3 thin films with different morphologies
Authors: Lecoeur P. , Trouilloud P. L. , Xiao Gang , Gupta A. , Gong G. Q. , Li X. W.
Published: July 2002

Using a wide-field Kerr microscope, we have studied the magnetic domain structures of epitaxial and polycrystalline La0.67Sr0.33MnO3 thin films as well as a film having thermally induced 〈110〉 microcracks. The epitaxial film on a (001) SrTiO3 substrate has different magnetic domain behaviors for in-plane fields applied along the 〈100〉 and 〈110〉 directions. Magnetic domain orientation and contrast suggest a biaxial magnetic anisotropy with 〈110〉 easy axes. Defects such as microcracks and grain boundaries have a strong perturbing effect on the local magnetization and can lead to an enhanced and controllable spin-dependent scattering.
Analysis of grain-boundary structure in Al–Cu interconnects
Authors: Field David P. , Sanchez John E. , Besser Paul R. , Dingley David J.
Published: July 2002

The role of crystallographic texture in electromigration resistance of interconnect lines is well documented. The presence of a strong (111) fiber texture results in a more reliable interconnect structure. It is also generally accepted that grain-boundary diffusion is the primary mechanism by which electromigration failures occur. It has been difficult to this point, however, to obtain statistically reliable information of grain-boundary structure in these materials as transmission electron microscopy investigations are limited by tedious specimen preparation and small, nonrepresentative, imaging regions. The present work focuses upon characterization of texture and grain-boundary structure of interconnect lines using orientation imaging microscopy, and particularly, upon the linewidth dependence of these measures. Conventionally processed Al–1%Cu lines were investigated to determine the affects of a postpatterning anneal on boundary structure as a function of linewidth. It was observed that texture tended to strengthen slightly with decreasing linewidth subsequent to the anneal procedure. Grain morphology changed substantially as the narrow lines became near bamboo in character and the crystallographic character of the boundary plane changed as a function of linewidth. These results are contrasted with those obtained from Al–1%Cu lines, which were fabricated using the damascene process. The damascene lines show a marked weakening in texture as the linewidth decreases, accompanied by a more random misorientation distribution. A description of the competing energetics, which result in the observed microstructures, is included.
Growth and fabrication of strained-layer InGaAs/GaAs quantum well lasers grown on GaAs(311)A substrates using only a silicon dopant
Authors: Takahashi Mitsuo , Hirai Manabu , Fujita Kazuhisa , Egami Norifumi , Iga Kenichi
Published: July 2002

The dependence of electrical properties as a function of substrate orientation and growth conditions for Si-doped GaAs grown by molecular beam epitaxy has been studied. A phase diagram concerning conduction type as a function of growth temperature Tg and V/III flux ratio has been examined for GaAs(311)A, GaAs(111)A, and GaAs(331)A. The conduction type of Si-doped GaAs(311)A abruptly changes from p to n type with varying Tg and V/III flux ratio. Furthermore, it was found that the dependence of electrical properties on growth conditions for Si-doped GaAs(311)A is more like GaAs(331)A rather than (111)A. In addition, InGaAs/GaAs strained-layer quantum well lasers have been fabricated on GaAs(311)A substrates using only Si dopant. The p-n junction was formed by changing the V/III flux ratio without growth interruption using the Si doping characteristic in GaAs(311)A as an amphoteric dopant. High crystal quality was maintained even when the V/III flux ratio was changed, and an abrupt p-n junction with a sharp boundary was achieved. Lasing operation at room temperature has been demonstrated for the first time, and a threshold current density of 260 A/cm2 and an external differential quantum efficiency of 67% were obtained for 720-μm-long broad area lasers. The dependence of threshold current density and external differential quantum efficiency on a laser cavity length was also examined. A laser structure with high crystal quality and abrupt p-n junction exhibits an internal quantum efficiency of 90%, an internal optical loss of 6 cm−1, and a transparency current density of 80 A/cm2.
Overall and local distortion effects on the metal–nonmetal transitions of mixed valent perovskite type manganese oxides
Authors: Kwon Young-Uk , Chi Eun-Ok , Kang Jae-Kyoung , Hur Nam Hwi
Published: July 2002

The metal–nonmetal (MN) transition data of mixed valent manganese oxide perovskites A1−xAx′MnO3 (A: trivalent lanthanide metals, A′: divalent metals, 0.2<x<0.5) are analyzed in terms of the tolerance factor (t), and the standard deviation (σ) of the A-site cation sizes. The interplay of these two parameters that measure the overall and atomic scale distortions, respectively, determine whether a compound can show a MN transition or not and its transition temperature (TMN). In order to show a MN transition, a compound should have t>0.906 and σ≲σ=232t−202 (pm). Large t and small σ are favorable for high TMN.TMN data of A0.7Ba0.15Sr0.15MnO3 (A=La, Pr, Nd, Sm), A0.7Ba0.15Ca0.15MnO3 (A=La, Pr, Nd, Sm), (La0.7Ca0.3)x(Gd0.7Ba0.3)1−xMnO3 (x=0.1, 0.3, 0.5, 0.7, 0.9), and (Nd0.7Ca0.3)x(Gd0.7Ba0.3)1−xMnO3(x=0.25, 0.3, 0.5, 0.55, 0.7, 0.75) newly synthesized are reported.
Melting and vaporization for large-area film removal with a chemical oxygen–iodine laser
Authors: Xie J. , Kar A.
Published: July 2002

Large-area film removal with lasers is a physical process of melting and vaporization of films. A mathematical model is developed to simulate the melting and vaporization of films under the irradiation of a chemical oxygen–iodine laser. The cross section of the film after laser scanning and the substrate surface temperature during laser irradiation are presented. There is an optimum laser power at which relatively wide films can be removed by maintaining low temperature at the substrate surface. The optimum laser power is associated with other process parameters. The results of film removal with TEM31 and TEM00 beams are compared, and the laser mode with more uniform intensity distribution is found to be more effective for large-area film removal.
Effect of interface on magnetic anisotropy of Fe/Tb multilayers: Mössbauer effect study
Authors: Freitag Andrea E. , Chowdhury Ataur R.
Published: July 2002

Perpendicular magnetic anisotropy of Fe/Tb multilayers was investigated using Mössbauer effect spectroscopy. Twenty-four multilayered Fe/Tb samples were prepared by planar magnetron sputtering. Results of Mössbauer effect measurements show that Fe/Tb multilayers display perpendicular magnetic anisotropy if the Tb layer thickness is less than 12 Å, and display in-plane anisotropy if the Tb layer thickness is more than 12 Å. Results indicate that the interface between Tb and Fe layers is the cause of the perpendicular anisotropy. Results also suggest that this perpendicular anisotropy is not induced due to the growth processes or the stress at the interface between the sample and the substrate.
Extremely low temperature formation of silicon dioxide on gallium arsenide
Authors: Houng M. P. , Huang C. J. , Wang Y. H. , Wang N. F. , Chang W. J.
Published: July 2002

This article demonstrates the growth of silicon dioxide (SiO2) on a gallium arsenide (GaAs) substrate by use of the liquid phase deposition (LPD) method at extremely low temperature (∼40 °C). This method cannot only grow SiO2 but it can also obtain good quality and reliability due to the suppression of interdiffusion in such a low temperature process. The deposition rate of LPD-SiO2 on GaAs is up to 1265 Å/h. The refractive index of the LPD-SiO2 film on GaAs is about 1.42 with growth at 40 °C. When the LPD-SiO2 film on the GaAs substrate is used to fabricate a metal–oxide–semiconductor capacitor with a device area of 0.3 cm2, the surface charge density (Qss/q) is about 3.7×1011 cm−2 and the leakage current is 43.3 pA at −5 V. A proposed mechanism for the LPD of SiO2 on GaAs is also presented.
Effects of a monolayer on the electron-phonon scattering rates in a quantum well: Dielectric continuum versus hybrid model
Authors: Bennett C. R. , Amato M. A. , Zakhleniuk N. A. , Ridley B. K. , Babiker M.
Published: July 2002

Recent publications have suggested that a reduction in the total electron-phonon scattering rate in a quantum well can be achieved by the inclusion of a monolayer of a different material. The predictions have been based upon two distinct models: the dielectric continuum (DC) model and the hybrid model. In the DC model the symmetric phonon modes are modified upon introducing the monolayer (via the electromagnetic boundary conditions) and hence a reduction in the intrasubband electron-phonon scattering rate is expected. In the hybrid model it is the antisymmetric modes that are modified and a reduction in the intersubband scattering rate is thus expected. It is shown here, however, that when the calculations are done correctly the calculated rates are approximately the same for both models if the thickness of the monolayer is vanishingly small and the electron wave functions are assumed to be unchanged. This implies that the inclusion of a monolayer of a finite thickness in a quantum well will only have a marginal effect on the total scattering rates, even though the mode spectra are changed. Our results also serve as an additional test of the hybrid model when applied to a more complicated system than a single quantum well. Again, an agreement is found between the two models when calculating the total electron-phonon scattering rates. We emphasize, however, that unlike the DC model the hybrid model can also correctly model Raman spectra.
Spin fluctuation in YCo2-based compounds
Authors: Burzo E. , Givord D. , Chioncel L.
Published: July 2002

The magnetic properties of Y(CoxNi1−x)2 compounds were investigated in the temperature range of 5–800 K and fields up to 8 T. Magnetic susceptibilities of Y(CoxNi1−x)2 compounds with x=1.0 and 0.8, at T⩽15 K, are described by a T2 dependence. The temperature range where this behavior is evidenced is gradually diminished as the nickel content increases. At high temperatures, the compounds with x⩾0.2 show a Curie–Weiss type behavior. The effective cobalt moments decrease slightly when increasing nickel content. The magnetic behavior of the above system is analyzed in a spin fluctuation model.
Kinetics and mechanism of low temperature atomic oxygen-assisted oxidation of SiGe layers
Authors: Tételin C. , Wallart X. , Nys J. P. , Vescan L. , Gravesteijn D. J.
Published: July 2002

The rates of low temperature atomic oxygen-assisted oxidation of strained epitaxial Si1−xGex (x=0.05, 0.1, and 0.2) layers have been measured and compared with the rate of oxidation of pure Si. We show that in the linear regime, the oxidation rate of the SiGe layer increases with the Ge concentration in the alloy. On the other hand, Ge/Si (100) structures have been oxidized. We show that this oxidation leads to the formation of pure SiO2 oxide and that the nonoxidized Ge layer is still present at the SiO2/Si interface. The oxidation rate of Si is not affected by the presence of the pure Ge interface layer. This, together with the results of SiGe oxidation, allows us to conclude that the SiGe oxidation rate is enhanced by the presence of Ge in the SiGe alloy. This can be explained by the fact that Si–Ge bonds are weaker than the Si–Si bonds. For longer oxidation times, the oxidation kinetics of SiGe layers follow a parabolic regime. We show that the parabolic constant strongly depends of the composition of the oxide layer.
Evidence for metal interaction in gold metallized polycarbonate films: An x-ray photoelectron spectroscopy investigation
Authors: Patnaik Archita , Li Changlin
Published: July 2002

The interfacial interactions between in situ thermally evaporated Au and polycarbonate (PC) film, a technologically important polymeric material, is studied by x-ray photoelectron spectroscopy (XPS). Angle resolved XPS is performed to investigate the Au reactivity if any, in forming the metal-polymer interface. The spectral evidence from the above suggests that the metal interacts predominantly with the carbonyl carbon of the monomeric unit with only minor interactions with the phenyl carbons without any complex formation. In contrast to previous findings of Au to be inert at the M-polymer interfaces, this work emphasizes the salient charge transfer type interactions of Au (as electron injector) at the C=O as the primary interaction site, distributing a net charge density to C=O with the formation of a Au-CO π-back bond. The conclusions are supported by the observed new C 1s feature at 282.6 eV and the O 1s and Au 4f7/2 XPS spectral changes. The growth mode of Au on PC was proceeded by the metal monolayer deposition with cluster growth on the already weakly bonded Au onto the C=O carbon of the polymeric backbone.
Electric field-temperature phase diagram of Zr0.98Sn0.02TiO4
Authors: Park Yung , Cho Kurn , Kim Ho-Gi
Published: July 2002

With the use of x-ray diffraction, we investigate the phase diagram of Zr0.98Sn0.02TiO4 as a function of temperature and dc electric field. Accurate satellite position measurements confirm the existence of commensurate phases corresponding to the rational values 1/21 and 1/23 for the incommensurate deviation factor. These results are discussed qualitatively in terms of Landau’s and Aubry’s “devil’s-staircase” approach.
Magnetic anisotropy of R2Fe17Nx compounds
Authors: Kou X. C. , de Boer F. R. , Chouteau G.
Published: July 2002

A nearly perfect magnetic alignment of R2Fe17Nx powders (<20 μm) with respect to the c axis was obtained by using the sample-rotation magnetic-alignment technique. The magnetization from 4.2 to 300 K was measured on the magnetically aligned samples by means of the sample-extraction method in a static field up to 23 T. The Fe-sublattice anisotropy was determined by analyzing the magnetization curves of R2Fe17Nx with R=Y, Ce, Gd, and Lu. Compared to corresponding R2Fe17 compounds, the Fe-sublattice anisotropy of R2Fe17Nx is substantially lower. For R2Fe17Nx with R=Pr, Nd, Sm, Tb, and Er, the magnetization curves in the [001] direction show no anomaly whereas a first-order magnetization process (FOMP) was detected in corresponding R2Fe17 compounds, suggesting that the FOMP transition in R2Fe17 is suppressed upon nitrogenation.
Grain boundary effects on transport in metalorganic chemical vapor deposition-grown, Ca-doped lanthanum manganites
Authors: Heremans J. J. , Watts S. , Wirth S. , Yu X. , Gillman E. S. , Dahmen K. H. , von Molnár S.
Published: July 2002

The transport properties of metalorganic chemical vapor deposited films of lanthanum manganite grown on various substrates are investigated. The more disordered films show a magnetoresistance that is both large and relatively temperature independent over a wide temperature range. At low magnetic fields, a linear field dependence is observed and is attributed to spin-polarized intergrain tunneling. In addition, at low fields a hysteretic dependence of resistivity on the magnetic field has been observed. This effect has been attributed to the scattering of spin-polarized carriers at the grain boundary.
High field magnetic properties in single crystal Nd3Co
Authors: Umehara Izuru , Lu Ying , Lu Qing Feng , Adachi Yoshiya , Endo Masato , Sato Kiyoo , Bartashevich Michael , Goto Tsuneaki
Published: July 2002

Magnetization as a function of field was measured in pulsed fields of up to 40 T at various temperatures along the principal axes of single crystal Nd3Co. Along the a axis we observed metamagnetic transitions at fields of 1.9 and 4.5 T at 4.2 K. We also observed a sharp increase in the magnetic moment in applied fields between 9.5 and 14 T. Along the b axis a metamagnetic transition was observed at a field of 1.5 T at 4.2 K. Along the c axis we observed ferromagnetic behavior. The H–T (magnetic field and temperature) phase diagram was obtained using a superconducting quantum interference device magnetometer.
Compositional dependence of the effective magnetic anisotropy in nanocrystalline Fe–Zr–B–(Cu) alloys
Authors: Garcı́a Tello P. , Blanco J. M. , Murillo N. , González J. , Zuberek R. , Slawska-Waniewska A. , González J. M.
Published: July 2002

Results are presented on the evolution with the thermal treatment parameters of the effective anisotropy and dispersion fields and of the saturation magnetostriction of samples having nominal compositions given by Fe93−xZr7BxCuy (x=6–8 and y=0–2). From these data we conclude that the enhancement of the soft magnetic character of the samples induced by the anneals carried out in the temperature range 480–600 °C could be linked both to the decrease of the anisotropy field and to the reduced magnetostriction values resulting from the thermal treatments.
Magnetic induction and surface segregation in thin-gauged 3% Si steel
Authors: Heo N. H. , Chai K. H. , Na J. G. , Woo J. S.
Published: July 2002

A correlation between magnetic induction and surface phenomena has been investigated in a 3% Si steel 0.1 mm thick. During final annealing at several temperatures, the saturation level in magnetic induction increased with increasing final annealing temperature, and reached 1.93 T after final annealing at 1300 °C for 4.9 ks. This is attributed to the formation of complete (110)[001] Goss texture. During final annealing, the magnetic induction of the thin-gauged 3% Si strip was inversely proportional to the sulfur concentration on the surface. The surface segregation of sulfur occurred after a critical time the silicon concentration on the surface dropped to the level obtained from the α-iron matrix containing 3% Si. The drop in silicon level on the thin-gauged strip surface is due to the volatile silicon monoxide, which arises from the reaction between the silicon dioxide and the silicon segregated, or between the silicon segregated and the oxygen from the high vacuum condition.