bluuebunny/crossref_metadata_2025 huggingface dataset:
In situ growth of superconducting MgB2 thin films with preferential orientation by molecular-beam epitaxy
Authors: Jo W. , Huh J-U. , Ohnishi T. , Marshall A. F. , Beasley M. R. , Hammond R. H.
Published: July 2002

We report the synthesis of superconducting MgB2 thin films grown in situ by molecular-beam epitaxy. Mg-rich fluxes are deposited with B flux by electron-beam evaporation onto c-plane sapphire substrates. The films exhibit c-axis oriented peaks of MgB2, and a full width at half maximum of 3° in their rocking curves. In-plane alignment of MgB2 shows 12-fold symmetry, which is observed by the selected area diffraction pattern in transmission electron microscopy. The MgB2 films show a superconducting transition at 34.5 K with ΔTc<1 K. Even though the residual resistivity of the films is quite high (∼60 μΩ cm), the normal-state resistivity has a very similar temperature dependence but is five times larger than that of a single crystal, implying that conduction through the whole sample is imperfectly connected or inhomogeneous. Upper critical fields are obtained from measurement of the field dependence of the resistivity. It is estimated that the upper critical field at 20 K is more than 15 T, which is one of the largest values ever reported.
Tunable diode-pumped continuous-wave Cr2+:ZnSe laser
Authors: Sorokin Evgeni , Sorokina Irina T.
Published: July 2002

A midinfrared broadly tunable around 2.5 μm room-temperature continuous-wave diode-pumped Cr:ZnSe laser is reported. The laser is tunable over 350 nm and delivers up to 70 mW of the output radiation at 460 mW of the absorbed pump power and 17.5% slope efficiency. We observe the analog of the optical switching process, where the laser output is strongly modulated by only a few milliwatts of the visible radiation.
On-chip vacuum microtriode using carbon nanotube field emitters
Authors: Bower C. , Zhu W. , Shalom D. , Lopez D. , Chen L. H. , Gammel P. L. , Jin S.
Published: July 2002

We show a fully integrated, on-chip, vacuum microtriode fabricated via silicon micromachining processes using carbon nanotubes as field emitters. The triode is constructed laterally on a silicon surface using microelectromechanical systems (MEMS) design and fabrication principles. The technique incorporates high-performance nanomaterials in a MEMS design with mature solid-state fabrication technology to create miniaturized, on-chip power amplifying vacuum devices, which could have important and far-reaching scientific and technological implications.
Characterization of superconducting structures designed for qubit realizations
Authors: Il’ichev E. , Wagner Th. , Fritzsch L. , Kunert J. , Schultze V. , May T. , Hoenig H. E. , Meyer H. G. , Grajcar M. , Born D. , Krech W. , Fistul M. V. , Zagoskin A. M.
Published: July 2002

We implement the impedance measurement technique in order to characterize superconducting structures designed for applications in quantum computing. We report an experimental study of the circuit consisting of three small Josephson junctions incorporated in a low-inductance superconducting loop. Measurements of the circuit response to an applied weak ac bias as a function of the external magnetic flux φe yield complete information on the properties of the circuit. We found that the system displays two metastable states. From experimental data, we have determined the magnetic field dependent Josephson energy U(φe) of these states, the potential barrier ΔU between these states, as well as the difference of the critical currents of the junction in the loop.
Spectral and stability aspects of quantum chaos
Authors: Jauslin H. R. , Lebowitz J. L.
Published: July 2002

The relation between the spectrum of a generalized quasienergy operator and the stability of quantum systems driven by quasiperiodic time-dependent forces is discussed.
Concentration dependence of UV and electron-excited Tb3+ luminescence in Y3Al5O12
Authors: van der Weg W. F. , Popma Th. J. A. , Vink A. T.
Published: July 2002

The emission spectrum of Tb3+ substituted in YAG to various concentrations (x in Y3−xTbxAl5O12 ranges from 3×10−5 to 3×10−1) has been measured on samples prepared by two different methods. These methods are powder preparation by coprecipitation and growth of crystalline layers by liquid-phase epitaxy. The spectrum consists of two groups of lines, one group around 550 nm originating from the 5D4 level and one group around 450 nm from the 5D3 level. The intensity of the two groups of lines depends on the method of excitation. In the case of UV excitation (λ=254 nm) the emission intensity for low Tb concentrations is mainly governed by the absorption of the incident radiation. With electron excitation, the energy loss of incoming electrons to ‘‘killer sites’’ in the lattice is found to influence the emission. The ratio, however, of 5D4 to 5D3 intensity is independent of the excitation mode. This ratio tends to a constant value at low concentrations and increases strongly with increasing concentration. These effects are explained by feeding of the 5D3 and 5D4 states from 5d levels, followed by cross relaxation, i.e., 5D3 to 5D4 excitation transfer.
Proton, deuteron, and helium implantation into GaAs and LiNbO3 for waveguide fabrication
Authors: Wilson R. G. , Betts D. A. , Sadana D. K. , Zavada J. M. , Hunsperger R. G.
Published: July 2002

Hydrogen and helium implantation into GaAs, LiNbO3, and other crystals has been shown to produce planar or channel waveguides via defects/damage and/or carrier removal or compensation. We have measured implanted depth distributions of 1H, 2H, and 4He in GaAs and LiNbO3 as functions of ion energy, ion fluence, substrate temperature, and annealing temperature using secondary ion mass spectrometry. We have studied the defect depth distribution for hydrogen-implanted GaAs by transmission electron microscopy. We have determined the lateral spread of 1H and 2H ions implanted into GaAs by varying the angle of implantation; this relates to the increase in width of closely spaced parallel channel waveguides made using patterned masks.
X-ray photoelectron and Auger electron spectroscopic analysis of surface treatments and electrochemical decomposition of CuInSe2 photoelectrodes
Authors: Cahen David , Ireland P. J. , Kazmerski L. L. , Thiel F. A.
Published: July 2002

CuInSe2 photoanodes can be optimized for use in electrochemical photovoltaic cells, containing aqueous polyiodide as the electrolyte, by wet chemical etching in Br2MeOH and subsequent thermal treatment (air oxidation). Surface analyses show the formation of a rather clean, Cu-depleted surface with some adsorbed oxygen after Br2/MeOH etch, and the formation of indium-oxygen bonds after thermal treatment, in accordance with previous studies that show indium oxides to be the native ones on this semiconductor. Samples that underwent photoanodic decomposition in the iodide electrolyte and those that were purposely decomposed in acetonitrile showed severe to near-total Cu depletion near their surface and the presence of lower valent Se. These data complement those from solution analyses and from electrochemical studies, to characterize the preferred decomposition path of CuInSe2 sufficiently to stabilize this type of photoelectrochemical cell. Our conclusions are based on the use of Auger parameters and, to a lesser extent, on empirical comparison of x-ray induced Auger electron line shapes, because of the difficulty in extracting unambiguous conclusions from x-ray photoelectron binding energies only.
Short wavelength laser calculations for electron pumping in Be I and B I isoelectronic sequences (18≤Z≤36)
Authors: Feldman U. , Doschek G. A. , Seely J. F. , Bhatia A. K.
Published: July 2002

Level populations of the 2s3p and 2s23p configurations in ions of the Be I and B I isoelectronic sequences can be inverted, with respect to populations of the 2s3s and 2s23s configurations, by electron collisional pumping. In the case of B I ions, the process is analogous to the process for Ne-like ions, which has lately received considerable attention. In the case of Be I ions, the inversion is a consequence of the slow radiative decay of the 2s3p 3P2 and 2s3p 3P0 levels. Level populations are calculated for Be- and B-like ions with atomic number Z between 18 and 36. For each sequence, 20 levels are involved with principal quantum number n equal either to two or three. Using the level populations, gain coefficients are calculated for transitions of the type 2s3s−2s3p and 2s23s−2s23p. Finally, the opacity of the 2s2p−2s3s and 2s22p−2s23s transitions are discussed, for plasma parameters for which a reasonable gain can be achieved.
Thermomechanical equilibrium in solid-fluid systems with curved interfaces
Authors: Alexander J. Iwan D. , Johnson William C.
Published: July 2002

A virtual variational approach for deducing the conditions for thermomechanical equilibrium is extended to solid-fluid systems with curved interfaces. A surface excess energy density is introduced which depends on excess entropy, number densities of the excess constituent components, the surface deformation gradient, the surface orientation and the principal curvatures. The coupling and roles of the surface stress and the Cahn–Hoffman ξ-vector in stressed solid-fluid systems is identified. Results are used to examine the case of a solid isotropic sphere immersed in a fluid.
Softening of hard bremsstrahlung by Compton backscattering
Authors: Whittaker D. A. , Kerris K. G. , Litz M. , Gorbics S. G. , Pereira N. R.
Published: July 2002

Multimegavolt bremsstrahlung backscattering from paraffin yields a photon spectrum mainly below 0.6 MeV. The measured dose in the backscattered radiation agrees with Monte Carlo computations to within 10%.
Diffusion of As and Ge during growth of GaAs on Ge substrate by molecular-beam epitaxy: Its effect on the device electrical characteristics
Authors: Chand N. , Klem J. , Henderson T. , Morkoç H.
Published: July 2002

Owing to surface-exchange reaction and diffusion of As and Ge species during crystal growth by molecular-beam epitaxy, the electrical characteristics of n-GaAs/p-Ge heterojunctions are found to be affected significantly. The junctions grown at temperatures higher than 500 °C become thyristorlike npnp structures. The junctions grown below 500 °C exhibited normal current–voltage characteristics with the p/n junction apparently displaced into the Ge.
Theoretical analysis of efficiency scaling laws for a self-sustained discharge pumped XeCl laser
Authors: Ohwa Mieko , Obara Minoru
Published: July 2002

By using a kinetic model developed for a self-sustained discharge pumped XeCl laser (B→X, 308 nm) with the Ne/Xe/HCl mixture, we determined operational conditions of the XeCl laser with commonly used pulse width of about 100 ns for attaining efficient lasing. According to the analysis of electron kinetics in the laser discharge, the XeCl* formation, the XeCl* relaxation, and the absorption of the B→X laser radiation, it is found that the discharge and kinetic characteristics are affected predominantly by the electron number density which is determined mainly by the ratio of Xe to HCl concentrations. Although the XeCl* formation, the XeCl* collisional quenching, and the absorption of the laser radiation increase with increasing total gas pressure, the optimum Xe and HCl concentrations which are almost independent of the total gas pressure can be determined. Furthermore, since the laser output energy does not increase linearly with the excitation rate, the optimum excitation rate can be determined for a given total gas pressure as it shifts to a higher value with increasing total gas pressure. As a result of the analysis by using the most reliable rate constants and cross sections for the reactions published so far involved in the XeCl laser kinetics, the maximum intrinsic efficiency of 12.5% is found to be obtainable with a 3-atm laser mixture of 0.2% HCl and 1% Xe in the Ne diluent pumped with an excitation rate of 3.5 MW/cm3.
Point-to-plane corona: Current-voltage characteristics for positive and negative polarity with evidence of an electronic component
Authors: Ferreira G. F. Leal , Oliveira O. N. , Giacometti J. A.
Published: July 2002

A series of measurements carried out with the point-to-plane symmetry has shown that positive corona confirms the Townsend relation while for the negative corona this happens only at large point-to-plane distances (greater than 1.5 cm). In this case, the ratio of the prefactors in Townsend relation, for the same geometry, approaches the expected constant (the ratio of the mobilities) at larger distances, around 6 cm. For distances below 1.5 cm, the square root of the current is linear with the voltage, with an intercept of ∼1.4 kV. The results are interpreted as giving evidence of an electronic component at small distances, as suggested by Sigmond. The characteristics change to Townsend at higher distances when the electronic component becomes small as compared with the ionic one.
Zener–Stroh crack, Zener–Hollomon parameter, and other topics
Authors: Weertman J.
Published: July 2002

Zener’s best known contributions to mechanical metallurgy undoubtedly are his theories and experimental research in the field of anelasticity of metals. He has, in addition to his anelasticity discoveries, made very significant contributions to the understanding of other aspects of mechanical metallurgy. This paper considers his other major contributions to mechanical metallurgy. One of these is the introduction of the Zener–Hollomon parameter. Another is the Zener–Stroh crack, the crack which complements the Griffith crack. (Physical parameters that are symmetric for the Griffith crack are antisymmetric for the Zener–Stroh crack and vice versa.) Our paper primarily is concerned with the Zener–Stroh crack. Some additional results are found for this crack.
Laser-induced fluorescence study of silicon etching process: Detection of SiF2 and CF2 radicals
Authors: Matsumi Yutaka , Toyoda Satoru , Hayashi Toshio , Miyamura Masao , Yoshikawa Hideshi , Komiya Souji
Published: July 2002

Using a laser-induced fluorescence (LIF) technique, SiF2 and CF2 radicals are detected during the downstream etching of silicon with a discharge of CF4 gas. It is confirmed that SiF2 radical is desorbed from the surface in the etching of silicon by fluorine atom. Addition of O2 gas to the CF4 discharge enhances the LIF intensity of SiF2 radical and extinguishes that of CF2. Mechanism of the increase of etching rate of silicon by addition of O2 is discussed on the basis of the results of LIF measurements. The etching rate of silicon is proportional to the LIF intensity of SiF2, when the microwave power of the discharge is changed. The relationship between the intensity of chemiluminescent continuum and the concentration of SiF2 is revealed, which suggests that the chemiluminescence is attributed to the emission of SiF*3 which is produced by the reaction between SiF2 and fluorine atoms in the gas phase. There is no signal of SiF2 during the etching of either SiO2 or SiNx.
Liquid-phase-epitaxial growth of Ga0.96Al0.04Sb: Electrical and photoelectrical characterizations
Authors: Luquet H. , Gouskov L. , Perotin M. , Jean A. , Rjeb A. , Zarouri T. , Bougnot G.
Published: July 2002

Ga0.96Al0.04Sb layers have been grown by liquid-phase epitaxy on GaSb substrates at 400, 450, and 550 °C. The 450 °C growth leads to the best control of the layer’s quality. At 450 °C the natural p-type doping of the layers is limited by the thermal acceptors ( p∼4×1016 cm−3) and the lowest reproducible uniform electron concentration obtained by Te compensation is n∼1016 cm−3. Electrical and photoelectrical properties of Schottky diodes and mesa Zn-diffused homojunctions realized on these layers are described. They are strongly affected by surface effects attributed to the band bending of n-type GaAlSb. Some parameters can be deduced from the various characterizations: the carrier lifetime in the space-charge region of Zn-diffused p+/n junctions, τ∼3×10−10 s; electron diffusion lengths in the as-grown Ga0.96Al0.04Sb layer, Ln=5 μm, and in the Zn-diffused layer, Ln=1.5 μm; and the hole diffusion length in the n-compensated layers, Lp=1 μm.
Photoluminescence in AlGaAs/GaAs heterojunction bipolar transistors
Authors: Eda Kazuo , Inada Masanori
Published: July 2002

Photoluminescence in AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with heavily doped GaAs layers and a p+-GaAs/n-AlGaAs heterojunction grown by molecular beam epitaxy at a low temperature of 600 °C is discussed. Each photoluminescence signal in the HBT is identified, and the relationship between performance as a transistor and photoluminescence discussed. A novel photoluminescence signal related to the p+-GaAs/n-AlGaAs heterojunction in the HBT was identified. This signal is thought to originate in the transition of the two-dimensional electrons in the notch formed at the heterojunction to the acceptor and acceptor-related defect levels.
Sintering of silver interlayers in polyimide films
Authors: Reich S. , Mazur S. , Avakian P. , Wilson F. C.
Published: July 2002

Annealing at 220–420 °C and exposure to laser light were used to induce sintering of silver metal interlayers in polyimide films. The sintering process was followed by transmission electron microscopy, electrical conductivity, optical reflectivity measurements, and x-ray scattering. We find that upon sintering at temperatures below Tg≂380 °C of the polymide film, sintering of the silver interlayer is induced. A dramatic increase in both the optical reflectivity (from 32% to 95%) and a hundredfold increase in electrical conductivity are observed upon sintering. Both the average size and the connectivity of the silver particles in the interlayer are increased in the process; however, there is no apparent change in the polymer. High-speed (∼100 ns) high spatial resolution laser writing (∼1 μm) is feasible by a selective sintering process. It is, therefore, of potential interest as a basis for write-once, high-density optical information storage. It is suggested that a surface diffusion mechanism is responsible for the observed sintering process.
Investigation of GaAs/(Al,Ga)As multiple quantum wells by photoreflectance
Authors: Reddy U. K. , Ji G. , Henderson T. , Morkoç H. , Schulman J. N.
Published: July 2002

Room-temperature photoreflectance has been used to investigate a series of GaAs/(Al,Ga)As multiple quantum-well structures. In addition to the allowed (as high as n=5) and symmetry forbidden transitions, we have observed transitions involving the so-called ‘‘unconfined’’ states, which have received less attention so far. We have examined these transitions more carefully by studying a low barrier multiple quantum-well structure and observed transitions as far as 200 meV beyond the barrier gap. By using a simple two-band tight-binding model, the energies and matrix elements for these unconfined transitions were calculated and shown to agree with the experimental values determined by fitting the photoreflectance spectra to the theoretical line-shape expression.
Nonlinear dielectric constant and ferroelectric-to-paraelectric phase transition in copolymers of vinylidene fluoride and trifluoroethylene
Authors: Ikeda Susumu , Kominami Hiraku , Koyama Kiyohito , Wada Yasaku
Published: July 2002

Second- and third-order dielectric constant ε2 and ε3 of three copolymers of vinylidene fluoride and trifluoroethylene were measured over a temperature range from 20 °C to higher than the ferroelectric-to-paraelectric phase transition temperature Tc . The thermodynamical theory predicts that ε2 is negative below Tc  and vanishes at Tc , whereas, for the second-order transition, ε3 is positive below Tc but turns to negative at Tc and, for the first-order transition, ε3 does not change its sign below and above Tc . According to this criterion, it is concluded that the transition is of the second order for a copolymer with vinylidene fluoride fraction of 52 mole %, but of the first order for 65 and 73 mole % copolymers. This conclusion can explain the difference in slope of ε2 versus remanent polarization among the copolymers.
Analysis of He-implanted LiNbO3 by elastic recoil detection
Authors: Al-Chalabi S. A. M. , Weiss B. L. , Barfoot K. M. , Arnold G. W.
Published: July 2002

He-implanted samples of LiNbO3 have been analyzed by 24-MeV 28Si elastic recoil detection. For 50-keV He implants, the Li and H profiles show a depletion of Li from the sample near-surface region which coincides with a gain of H. The Li loss is seen to increase with increasing ion fluence and implantation temperature.
Photoabsorption due to excitons for InGaAs-GaAs superlattice quantum wells in the presence of an applied electric field
Authors: Coffey D.
Published: July 2002

We calculate the absorption at the band-gap edge due to excitons in InGaAs-GaAs superlattice quantum wells. We use a finite square well model and investigate the dependence of the calculated exciton states on the parameters in the model. The behavior of the absorption coefficient as a function of the strength of an electric field applied perpendicular to the layers is investigated and we find that the results of the model give a good description of the measurements of the absorption coefficient on InGaAs-GaAs quantum wells.
The equilibrium properties of a 6m
m polycrystal exhibiting transverse isotropy
Authors: Ferrari Mauro , Johnson George C.
Published: July 2002

The effective thermoelectromechanical properties of an aggregate of 6mm crystals exhibiting transverse isotropy are determined by averaging the corresponding crystal properties over all orientations. The orientation distribution function is expressed in terms of symmetric generalized spherical harmonics and is employed as a weighting function in the averaging procedures, which are applicable to any physical property. The averaging is carried out under a generalized Voigt-type assumption. The physical relevance of the odd-order texture coefficients is demonstrated through their relation to pyro- and piezoelectric phenomena. The discussion is centered on the determination of the physical behavior of zinc oxide, dedicating particular attention to thin films.
The intercalation and exfoliation of tungsten disulfide
Authors: Miremadi B. K. , Morrison S. R.
Published: July 2002

The exfoliation of WS2, the separation of this layer compound into single molecular layers suspended in solution, was found more difficult than the exfoliation of MoS2 reported earlier. The difficulty was found to be the resistance of the WS2 to intercalation. By ultrasonic treatments while exposed to hexane plus n-butylithium, the lithium was found to intercalate, and exfoliation by immersion in water became possible. Restacking the WS2 by drying in a basic solution led to much larger crystallites than the as-received material, while flocculating by decreasing the pH led to small crystallites with a high density of edge planes. Nickel and aluminum inclusions lead to poor restacking, with no regular c spacing between WS2 basal planes. The more vigorous exfoliation procedure applied to MoS2 also leads to loss of regular c spacing (the x-ray diffraction pattern is essentially that of single molecular layers).
Wide domain walls and Bloch lines in Permalloy and Co-Fe films using Kerr effect microscopy
Authors: Ryan P. J. , Mitchell T. B.
Published: July 2002

The recent development of scanning electron microscopy with spin polarization analysis has led to the observation of wide domain walls in thin films of Permalloy. This investigation provides further evidence for the existence of domain walls greater than 1 μm. The domain structure of patterned Permalloy and Co-Fe films was observed with longitudinal Kerr effect microscopy and high-speed image processing (video). The Permalloy films investigated have a thickness range of 0.5–5 μm and square dimensions of 100 μm. Surface domain wall width measurements over the range of film thicknesses are presented. Observations show chirality changes in the domain wall (Bloch lines) as well as Bloch line propagation in the presence of fields.
Complex plane analysis of trapping phenomena in zinc oxide based varistor grain boundaries
Authors: Alim Mohammad A. , Seitz Martin A. , Hirthe Richard W.
Published: July 2002

The origin of the frequency-dependent Mott–Schottky behavior observed in a wide range of ZnO-Bi2O3 varistor systems has been investigated. Lumped parameter/complex plane analysis of two-probe ac electrical data indicates that several trapping relaxations contribute to the measured MOV grain-boundary admittance in the frequency range, 10−2 Hz≤f≤107 Hz. Furthermore, this approach allows the development of an equivalent circuit representation which incorporates these trapping phenomena in a systematic manner.
Experimental and calculated results for the dynamics of oriented nematics with twist angles from 210° to 270°
Authors: van Sprang H. A. , Koopman H. G.
Published: July 2002

A series of experimental data is presented on the switching of nematic liquid crystals with high twist, high tilt director configurations for step-voltage and pulse-voltage addressing. In order to describe the observed phenomena using a simple model containing a single viscosity coefficient only, we introduce an empirical correction to the rotational viscosity coefficient γ. The description appears adequate for step-voltage addressing but less so in the case of decay under specific pulse-voltage addressing conditions. Possible reasons are discussed.
Low-temperature photoluminescence studies of chemical-vapor-deposition-grown 3C-SiC on Si
Authors: Choyke W. J. , Feng Z. C. , Powell J. A.
Published: July 2002

26 cubic SiC (3C-Sic) films grown on (100) Si by way of chemical vapor deposition (CVD) with SiC film thicknesses ranging from 600 Å to 25 μm have been studied by photoluminescence at 2 K. The ‘‘defect-related’’ W band near 2.15 eV appears in very thin-film samples. The G band near 1.90–1.92 eV and its phonon side bands G1 and G2 are believed to be related to dislocations and extended defects. The ratio ρ of the intensities of the G band and the strongest nitrogen-bound exciton (N-BE) TO(X) line may be used as a figure of merit for crystalline perfection in CVD 3C-SiC films. General formulas for the band-gap shift due to an axial stress, including three special cases—hydrostatic pressure and uniaxial and biaxial stress—are derived and applied to the CVD 3C-SiC/Si system. An experimental relationship of stress in these epitaxial films of 3C-SiC as a function of depth is obtained. It is shown that a 1–3 μm transition layer greatly reduces the interface misfit strain. For films thicker than 3 μm the film stress decreases slightly with increase of film thickness. The effects of biaxial stress on the relative intensities of N-BE lines are experimentally studied. It is reported that biaxial stress in the SiC/Si system depresses the intensity of the no-phonon line as well as the TA, LA, and LO phonon transitions of the N-BE spectrum.
Ferromagnetic switching in elongated γ-Fe2O3 particles
Authors: Schabes Manfred E. , Bertram H. Neal
Published: July 2002

Results of numerical micromagnetic calculations of the switching process in elongated γ-Fe2O3 particles are reported. The particles are represented by square rectangular prisms of aspect ratio 3:1 and 5:1, respectively. The crystalline anisotropy is cubic with K1=−4.6×104 erg/cm3 and with the [110] direction in the long particle axis. The application of a reverse field leads to formation of vortices at the ends of the particle. As the reverse field is increased in magnitude the vortices expand from the ends of the particle inwards. Equilibrium and transient magnetization states are computed as a function of particle size. The resulting dependence of the switching field on the particle size and on the angle of the applied field is similar to what has been suggested by experimental evidence.
Effects of mixing materials on losses and cost of operation of three-phase transformer cores
Authors: Moses A. J. , Hamadeh S.
Published: July 2002

It has been previously shown that the building factor of three-phase transformer cores can be improved by using materials with different permeabilities for limbs and yokes. This paper presents results of a comprehensive experimental study of the effect of using conventional, high-permeability, and domain-refined grain-oriented 3% silicon iron in various parts of a small three-phase, three-limb stacked laminated transformer core. It is shown that the core building factor can be improved using certain mixtures of material and that the absolute core loss can be minimized only by using combinations of materials with suitable permeability and texture. The operating flux density and joint geometry are shown to be important factors in controlling the degree of improvement obtained. The results obtained from the models are used to predict the losses in a range of larger transformers and their costs of operation are compared by considering the capitalized cost of losses and the cost of the core materials. It is shown that it is possible to reduce the cost of operation, particularly at low or medium flux density levels, by using suitable mixtures of low- and high-permeability steel in the transformer yokes and limbs.
Light-scattering observation of anomalous parametric spin-wave character in subsidiary absorption
Authors: Wilber W. D. , Booth J. G. , Patton C. E. , Srinivasan G. , Cross R. W.
Published: July 2002

The technique of Brillouin light scattering has been used for the characterization, in terms of wave number and direction of propagation, of parametric spin waves associated with subsidiary absorption in thin films of yttrium iron garnet. Measurements at 7.99, 8.47, and 9.90 GHz have revealed a spin-wave character consistent with theory, with two notable exceptions. First, the data show no evidence for a predicted flip in the azimuthal propagation angle. Second, the measured magnon wave numbers at high fields are inconsistent with the theoretical values. The wave number and polar angle results imply that the change to low-k spin waves is not a discontinuous transition as indicated by the model.
Standing-wave-assisted extended x-ray absorption fine-structure study of a Ni-Ti multilayer
Authors: Heald S. M. , Tranquada J. M.
Published: July 2002

Extended x-ray absorption fine structure (EXAFS) measurements have been made while simultaneously exciting x-ray standing waves in a multilayer structure. This allows the EXAFS signal from selected regions within the multilayer unit cell to be enhanced. The technique is applied to a Ni-Ti multilayer in which it is verified that strong standing-wave fields can be excited in the presence of substantial interfacial roughness. The measurements reveal little Ni-Ti intermixing and a strong low-Z impurity signal in the Ti layers. The standing-wave analysis indicates that the low-Z impurity is distributed throughout the Ti layers.
Moderate energy flash x rays with large dose-area product produced by Aurora
Authors: Kerris K. G. , Agee F. J. , Whittaker D. A. , Gorbics S. G. , Pereira N. R.
Published: July 2002

Compton backscatter of Aurora’s flash gamma rays produces a pulse of moderate energy x rays over a 1 m2 area, dose per shot of 25 Gy (2.5 krad), and uniformity better than 20%. The x-ray spectrum is similar to direct bremsstrahlung from a 1-MeV electron beam, with an additional low-amplitude tail of high-energy photons beyond 1 MeV. Advantages of the Compton backscatter technique over direct bremsstrahlung include a high shot rate, 6–8 shots per day at Aurora, and a spectrum that does not vary during the shot or from shot to shot.
Study of the excitation of magnetostatic modes in yttrium-iron-garnet films by a microstrip line
Authors: Barak J. , Lachish U.
Published: July 2002

Magnetostatic modes in a rectangular yttrium-iron-garnet film, magnetized by a normal or parallel magnetic field, were excited using a microstrip line. The modes spectra are used to investigate the coupling between the microstrip and the magnetostatic waves in the film and to examine the theory of the dispersion of these waves. It is shown that when the microstrip is lifted off the film it excites magnetostatic waves in all directions whereas when it is close to the film waves are emitted only in the directions close to the normal to the microstrip line. These results are discussed in view of their implications to magnetostatic wave devices.
Influence of oxygen on the structural stability and superconducting properties of ceramic (Bi,Pb)2Sr2Ca2Cu3Oδ
Authors: Green S. M. , Mei Yu , Manzi A. E. , Luo H. L.
Published: July 2002

By post-annealing ceramic samples in various partial pressures of oxygen, the structural stability and superconducting properties of (Bi,Pb)2Sr2Ca2Cu3Oδ are demonstrated to be sensitive to δ. The small decrease of Tc with increasing oxygen partial pressure is in agreement with previously reported results on Pb-free samples and may be connected to an optimization of the charge carrier concentration. The collapse of the 2223 phase when post-annealed above 700 °C in pure argon is also documented. It is suggested that this decomposition and the stabilization of the 2223 phase by Pb substitution are both related to the amount of oxygen contained in the (Bi,Pb)-O layers which separate the Sr-Ca-Cu-O perovskite units.
Spatial distribution of a-Si:H film-producing radicals in silane rf glow discharges
Authors: Doughty D. A. , Gallagher A.
Published: July 2002

Film growth on glass fibers (40 μm diameter) is used to probe the distribution of SiH4 decomposition products that produce a-Si:H films in silane rf glow discharges. The film thickness on fibers spanning the electrodes is measured versus position to map the spatial variation of the film-precursor (radical) density. The optical emission from the discharge, which is shown to be essentially equivalent to the distributed source of SiH4 decomposition products, is compared to the density maps. This comparison shows that the SiH3 radical dominates deposition, that this SiH3 is produced in the optically bright regions of the discharge, and that H atoms react rapidly with SiH4 before diffusing significant distances in the discharge. The perturbative nature of the probes on the discharge environment is also addressed.
Kerr effect of two-medium layered systems
Authors: Chen Liang-Yao , McGahan William A. , Shan Z. S. , Sellmyer D. J. , Woollam John A.
Published: July 2002

Detailed and practical expressions are given for the magneto-optical Kerr effect (MOKE) for various configurations of two media. One is a magneto-optic (MO) one, and the other is a nonmagnetic (NM) medium. For a system of two thick media with a single interface, with a first-order approximation in MOKE term Q, the Kerr function is determined by the product of a MOKE term Q and an optical term η. A second type of system includes a thin MO (or NM) layer deposited on a thick NM (or MO) substrate. For a MO/(NM-substrate) configuration, the Kerr function is related to the Kerr effects from the air/MO and MO/NM interfaces, and to the Faraday effects of the MO layer, as well as to interference effects. The enhancement factor can be expected to be large by proper choice of materials. For a NM/(MO-substrate) configuration, the total Kerr function is related to the Kerr effect from the NM/MO interface and can be enhanced by interference. The enhancement factor is expected to be less than one if the NM layer is strongly absorbing. Calculations of Kerr effects for examples of the PtMnSb/AuAl2 and Fe/Cu configurations are given. These indicate that the peaks shown in the onset region of the interband transitions of Cu can be attributed to a dramatic change of the refractive index in that region. The merits of a MO/(NM-metallic) structure have been evaluated, and indicate that a better Kerr enhancement effect can be achieved if the refractive index of the MO layer is larger than one and is much larger than that of the metallic material. A drawback to this configuration comes from the fact that a MO material with a large refractive index value usually is not expected to have a large intrinsic Kerr effect.
Valence-electron contributions to the electric-field gradient and the crystal field at rare-earth sites in intermetallic compounds
Authors: Coehoorn R. , Buschow K. H. J.
Published: July 2002

From first-principles band-structure calculations, the electric-field gradient Vzz at Gd nuclei in Gd2Fe14B, Gd2Co14B, Gd2Fe17, Gd2Co17, GdCo5, GdNi5, GdFe3, and elemental Gd has been calculated. The crystal-field parameter A02 has been calculated for Gd2Fe14B. A02 and Vzz are mainly determined by the asphericity of the charge density of the 5d and 6p valence shells of the Gd atoms. We discuss the validity of a frequently used proportionality relation between A02 and Vzz.
Hysteresis in lithographic arrays of permalloy particles: Experiment and theory (invited)
Authors: Smyth J. F. , Schultz S. , Fredkin D. R. , Kern D. P. , Rishton S. A. , Schmid H. , Cali M. , Koehler T. R.
Published: July 2002

We have investigated the effects of particle size and aspect ratio on the hysteresis in controlled arrays of small magnetic particles. The arrays of permalloy particles were fabricated via electron-beam lithography. Each array consists of ∼ 106 identical, uniformly spaced particles. Hysteresis loops measured with an alternating-gradient magnetometer for particles ∼5–0.1 μm are presented. We find an increase in the coercive force as the particle width decreases below 0.3 μm due to a change in the switching mechanism from domain-wall nucleation and wall motion to vortex nucleation and vortex motion. A novel angular dependence of the loops is described in detail. Results from ab initio micromagnetic calculations on isolated rectangular Permalloy particles are compared, where applicable, with the measurements. We find excellent qualitative and, in selected cases, quantitative agreement between the experiments and calculations.
Substrate effects on the crystalline orientation of barium hexaferrite films
Authors: Lacroix E. , Gerard P. , Marest G. , Dupuy M.
Published: July 2002

In situ crystallized barium hexaferrite films have been deposited with a target-facing sputtering system under previously optimized conditions on four different substrates which are: SiO2, ZnO, Gd3Ga5O12, and Al2O3. By using several structural and magnetic characterizations different growth mechanisms were put forward according to the chosen substrate. On amorphous silica there is an important Ba affinity for SiO2, resulting in the formation of a glass layer with high Ba and Si concentrations. Then comes a (111) spinel which is magnetite and above it there is the well c-oriented Ba hexaferrite (Δω=2.3°). Under progressive annealings, magnetite changes into maghemite and then into hexaferrite. On (001) ZnO, another (111) spinel is formed, that is ZnFe2O4 on which textured Ba hexaferrite film is grown (Δω=1.3°). Under high-temperature annealings ZnO decomposes little by little, on the one hand into ZnFe2O4 and on the other hand, through a diffusion process across the Ba hexaferrite into a surface layer rich in Ba and Zn. On GGG and Al2O3 there are no intermediate layers. In the former case a well c-axis-oriented Ba hexaferrite (Δω=3.6°) was observed whereas for the latter case the orientation of the hexaferrite was found to be random.
Ion flux and ion power losses at the electrode sheaths in a symmetrical rf discharge
Authors: Godyak V. A. , Piejak R. B. , Alexandrovich B. M.
Published: July 2002

Ion flux and ion acceleration power have been measured at the electrode sheath in a capacitively coupled argon discharge driven at 13.56 MHz. Two independent methods have been used to evaluate the ion power. One method is based on measuring the ion current to an rf electrode and the dc component of the rf sheath voltage. The other method is based on measuring the discharge power as a function of the total discharge current. Measurements were performed at gas pressures between 3 mTorr and 3 Torr and at discharge powers between 10−2 and 102 W. Over the entire range of operation the ratio of the ion to discharge current varied between 1% and 3%, whereas the percentage of the ion power loss was between a fraction of a percent and 95% depending upon the total discharge power. The series equivalent resistance corresponding to the ion power loss was found experimentally and corresponds well with predictions based on a dynamic sheath model.
Elastic constants and hardness of ion-beam-sputtered TiNx films measured by Brillouin scattering and depth-sensing indentation
Authors: Jiang X. , Wang M. , Schmidt K. , Dunlop E. , Haupt J. , Gissler W.
Published: July 2002

TiNx films of various composition have been prepared by reactive-ion-beam sputtering at a deposition temperature of 50 °C. Young’s modulus E and hardness H of these films were measured by a depth-sensing nanoindentation technique, whereas the shear modulus G was obtained by a measurement of the velocity of the acoustic surface wave by Brillouin light scattering. The study was extended over a wide range of stoichiometries, 0≤x≤0.8. A proportionality between E and H has been observed.
On the diffusivity-mobility ratio in small-gap semiconductors in the presence of a strong magnetic field: Theory and suggestion for experimental determination
Authors: Ghatak K. P. , Biswas S. N.
Published: July 2002

An attempt is made to study the Einstein relation for the diffusivity-mobility ratio of the electrons in degenerate n-type small-gap semiconductors under strong magnetic field on the basis of three-band Kane model without any approximations of band parameters and incorporating the electron spin and broadening of Landau levels, respectively. It is found, taking n-Hg1−xCdxTe as an example, that the Einstein relation exhibits an oscillatory magnetic field dependence due to Shubnikov–de Haas effect and decreases with increasing alloy composition. Besides the same ratio increases with increasing electron concentration and is in close agreement with the suggested experimental method of determining the Einstein relation in degenerate semiconductors having arbitrary dispersion laws. In addition, the corresponding well-known results of parabolic semiconductors both in the presence and absence of magnetic field have been obtained from the generalized expressions under certain limiting conditions.
Electrical transport in thin films of copper silicide
Authors: Aboelfotoh M. O. , Krusin-Elbaum L.
Published: July 2002

Electrical properties of thin films of η′-Cu3Si phase with a tetragonal crystal structure are reported on. Electrical transport in these films is found to be very sensitive to oxygen exposure. Cu3Si reacts with oxygen at room temperature to form both Si and Cu oxides, resulting in high-room-temperature (∼60 μΩ cm) and even nonmetallic resistivity. This behavior is contrasted with that of low-resistivity (∼5 μΩ cm at room temperature) Cu3Ge, which is inert in an oxygen environment.
Effects of gamma-ray irradiation on cubic silicon carbide metal-oxide-semiconductor structure
Authors: Yoshikawa M. , Itoh H. , Morita Y. , Nashiyama I. , Misawa S. , Okumura H. , Yoshida S.
Published: July 2002

Radiation effects on cubic silicon carbide (3C-SiC) metal-oxide-semiconductor (MOS) structures have been studied with high-frequency capacitance-voltage measurements. It was found that interface traps are generated at the 3C-SiC/SiO2 interface and oxide-trapped charges are built up in the oxide by 60Co gamma-ray irradiation. The generation of the interface traps and the oxide-trapped charges are affected by bias polarity applied to the gate electrode during the irradiation. Absorbed dose dependencies of their generation are discussed comparing with those of Si MOS structures.
Temperature dependence of the photoreflectance of a strained layer (001) In0.21Ga0.79As/GaAs single quantum well
Authors: Huang Y. S. , Qiang H. , Pollak Fred H. , Pettit G. D. , Kirchner P. D. , Woodall J. M. , Stragier Hans , Sorensen Larry B.
Published: July 2002

We have measured the photoreflectance spectra of a strained layer (001) In0.21Ga0.79As/GaAs single quantum well as a function of temperature in the range 10 K<T<500 K. The details of the lineshape of the fundamental conduction to heavy-hole feature (11H) demonstrates its excitonic nature even up to 500 K. From the temperature dependence of the 11H linewidth we have obtained important information about the quality of the material and interface. The variation of the 11H energy gap with temperature agrees with that of bulk material. Comparison of the energies of 11H and higher lying transitions with an envelope function calculation yields a conduction band offset parameter Qc=0.65±0.07.
Sm2(Fe,M)17Nx compounds and magnets
Authors: Endoh M. , Iwata M. , Tokunaga M.
Published: July 2002

The effect of additives has been studied for the Sm2Fe17Nx compounds. Only Co addition increases the Curie temperature. The Ti, V, or Co additions increase the anisotropy field. The additions of these elements are favorable for the magnet fabrication. The magnet fabrication has been carried out by the Zn metal bonding and mechanical alloying. The (BH)max is 8.7 MGOe and the iHc is 14 kOe for the Zn-bonded magnet. The (BH)max is 10.8 MGOe and the iHc is around 25 kOe for the mechanical alloy magnet.
Influence of hydrogen dilution on the optoelectronic properties of glow discharge amorphous silicon carbon alloys
Authors: Alvarez F. , Sebastiani M. , Pozzilli F. , Fiorini P. , Evangelisti F.
Published: July 2002

This work reports the influence of diluting with hydrogen the gaseous mixture of methane and silane on the electrical and optical properties of silicon–carbon alloys deposited by glow discharge. Impressively high secondary photoconductivities, low density of gap defects states and Urbach energy parameter were found in materials prepared in suitable hydrogen dilution conditions. Experiments on temperature dependence of dark and under white light illumination conductivity are also reported and interpreted. Depending on the dilution and substrate temperature, the Fermi level shift toward the conduction band, suggesting a combined effect of low density of defects and sensitization as the causes of the high photoconductivities. IR studies show that appropriate hydrogen dilution and substrate temperature prevent the silicon atoms from forming high order hydrides. Consequently, a more compact structure with better electronic properties is obtained.
An infrared dielectric function model for amorphous solids
Authors: Brendel R. , Bormann D.
Published: July 2002

For the modeling of infrared spectra it is a common approach to use a dielectric function that treats the vibrational modes as damped harmonic oscillators. This model was found to be rather crude for some applications to amorphous solids. A dielectric function model yielding a Gaussian shape of the absorption lines and satisfying Kramers–Kronig relations is suggested. The model function is constructed by a convolution of a Gaussian function with the dielectric function of the damped harmonic oscillator model. An analytical solution of this integral is given. It is demonstrated that this model describes the spectra of thermally grown ultrathin (1.3 nm) silicon oxide films, plasma-deposited silicon films, plasma-deposited silicon nitride films, and amorphous aluminum oxide films very well. The physical motivation of the dielectric function model suggested is the randomness of the vibrational frequencies in an amorphous structure.