bluuebunny/crossref_metadata_2025 huggingface dataset:
Capture of electrons into Na+-related trapping sites in the SiO2 layer of MOS structures at 77 °K
Authors: DiMaria D. J. , Aitken J. M. , Young D. R.
Published: February 2003

Sodium ions in the SiO2 layer of MOS structures have been completely neutralized at liquid-nitrogen temperatures (77 °K) by avalanche injection of electrons from the Si substrate. Three principal electron capture cross sections (2×10−15, 2×10−19, and 5×10−20 cm2) associated with ionic sodium (Na+) contamination have been observed.
Temperature dependence of avalanche breakdown voltage in Si p-n junctions
Authors: Kajiyama Kenji , Kanbe Hiroshi
Published: February 2003

The temperature dependence of avalanche breakdown voltage in Si p-n junctions is calculated by a simplified method. The calculated results agree with experiments in specifically doped junctions as well as in abrupt junctions. It is also discussed how the doping profile affects the temperature coefficient.
Chemical etching and fabrication of ridge waveguides on Bi12GeO20 single crystals
Authors: Iwasa Tatsuru
Published: February 2003

Chemical etching of Bi12GeO20 was investigated, and the developed technology was applied to the fabrication of ridge waveguides by an easy and rapid chemical etching method. The etching solution was prepared by mixing concentrated HCl, concentrated H2O2, and 5M NH4Cl. Ridge waveguides (0.3 mm to a few microns in size) prepared on the (110) surface had a trapezoidal cross section, and for a higher volume ratio of HCl and a longer etching time the cross section was triangular. Rectangular ridge guides were also prepared on the (100) surface, but this application is limited to small-size (several microns) ridges because with deep etching the surface is covered with etch pits and becomes rough.
High-speed droplet migration in silicon
Authors: Cline H. E. , Anthony T. R.
Published: February 2003

High-temperature thermomigration of aluminum-rich droplets in silicon has results in droplet migration rates up to 10 cm/day. These unexpectedly high rates are an order of magnitude greater than those previously reported in the liturature. The large enhancement of dorplet migration rates at high temperatures is shown to be caused by a substantial increase in the flow of liqudi across the droplet and by a favorable variation in the change of the composition of the liquid at hgih temperatures. The variation of droplet velocity with droplet size is reported over a large range of droplet sizes and temperatures for both the 〈100〉 and 〈111〉 migration directions in silicon. The undersaturation and supersaturation required to make a (111) silicon plane dissolve and deposit, respectively, are calculated from the data. Finally, fromthe velocity of large droplets, the liquid interdiffusion coefficient for the aluminum-silicon system is determined.
Computer simulation of the sputtering of clusters
Authors: Harrison Don E. , Delaplain C. B.
Published: February 2003

The formation of clusters of sputtered copper atoms from an argon-bombarded (100) copper surface has been simulated with a computer program which includes interatomic attractive forces. Dimer formation is very common. Most commonly, dimers are formed from atoms which were next-nearest neighbors in the crystal. Nearest-neighbor atom clustering is rare, and dimer formation by a single atom moving in a channel has not been observed, and could not be forced by artificial means. All multimer formation mechanisms depend strongly upon both the relatively low speed of the sputtered atoms and the relatively high speed of the knock-on atoms involved in the sputtering mechanisms. Strong evidence for trimer formation exists. Pairs of dimers with a common atom have been observed. No quadrimers have been identified, but structures which almost meet the stability criteria have been observed.
Signal processing with surface waves via the double acousto-optic interaction
Authors: Normandin R. , Stegeman G. I.
Published: February 2003

Optical diffraction by two successive surface acoustic waves was used to achieve various signal-processing operations. Expressions were derived for the frequency spectrum and bilinearity factor associated with this double interaction and these formulas were verified experimentally using Fabry-Perot interferometry. An aperture function formalism was used to demonstrate that the doubly diffracted field corresponds in form to that required for real-time convolution. The addition of a simple lens system extended the capability of this technique to a full range of processing functions. The following operations were demonstrated for pulses of the order of 1 μs: squaring convolution, squaring correlation, variable time expansion, variable time compression, time inversion, and image scanning. This processor is characterized by large bandwidth since the diffraction takes place in the Raman-Nath limit up to GHz frequencies.
Epitaxial growth of In1−xGaxSb thin films by multitarget rf sputtering
Authors: Greene J. E. , Wickersham C. E. , Zilko J. L.
Published: February 2003

Single-crystal epitaxial In1−xGaxSb thin films have been grown at compositions ranging from x=0 to x=1 on a variety of substrates including BaF2, NaCl, and InSb using multitarget rf sputtering. The films were deposited on rotating substrates from two targets, InSb and GaSb, with separate discharges allowing independent control of relative sputtering rates. Alloy-film composition was determined by Auger spectroscopy using bulk standards. The results agreed very well with predicted values calculated from a simple theory which is presented in this paper. Within experimental error, measured lattice constants were found to vary linearly with alloy-film composition. The amorphous to polycrystalline to single-crystal growth transition temperatures were found to increase with Ga concentration in the films. Single-crystal InSb films were obtained at substrate temperatures as low as 150 °C. High dislocation densities were observed in In-rich films due to large film-substrate lattice mismatch. Thermoelectric measurements indicated that In-rich films were n type while Ga-rich films were p type with the n-to-p crossover occurring at approximately In0.58Ga0.42Sb. In addition to homogeneous alloy films, intercalated structures consisting of thin (∼100 Å) alternating layers of InSb/GaSb/InSb... were grown, as well as films which were chemically graded from pure InSb to pure GaSb.
Flexoelectricity in nematic and smectic-A liquid crystals
Authors: Prost Jacques , Pershan P. S.
Published: February 2003

Flexoelectric effects are observed in both the nematic and smectic-A phases of p-butoxybenzal-p- (β-methylbutyl) aniline (BBMBA) and p-cyano-benzylidine-p-octyloxyaniline (CBOOA). This is the first reported observation of flexoelectricity in smectic phases. The use of a symmetric interdigital electrode in the homeotropic geometry facilitated the unambiguous separation of linear and quadratic electro-optic effects. Both the interdigital electrodes and those liquid-crystal deformations that are quadratic in the voltage act as optical diffraction gratings with a spacing that corresponds to the repeat distance d for adjacent electrodes. In contrast linear electro-optic effects give rise to diffraction gratings with twice this spacing since adjacent electrodes have opposite voltages. Diffraction maxima due to the linear effects are halfway between the maxima due to the other effects. Using optical heterodyne detection, the intensity of the diffraction maxima believed to arise from the linear effect are indeed observed to be linear in the applied voltage V (ω). With homodyne detection the diffracted intensity is proportional to V (ω)2. Although previous discussions of flexoelectricity in nematics have been in terms of two flexoelectric coefficients e11 and e33, we present theoretical arguments that as long as ∇×E=0 there is only one true volume coefficient and that the other constant can always be included in surface effects. Our measurements of the volume coefficient f=e11+e33 are an order of magnitude larger than previously obtained values for e11 and e33. Measured values of f are also nearly independent of temperature, in contrast to previous theoretical models, and of similar magnitude in the smectic and nematic phases. Measurements of flexoelectric signals versus the frequency of the driving voltage obtain relaxation times for splaylike nematic fluctuations and undulation-type smectic fluctuations.
Dynamic scattering in nematic liquid crystals under dc conditions. I. Basic electrochemical analysis
Authors: Barret S. , Gaspard F. , Herino R. , Mondon F.
Published: February 2003

An analysis of the electrochemical reactions occurring in a pure liquid crystal under dc excitation is presented. The conclusion is that the only way to avoid degradation of liquid crystals is to prevent the nematic molecules from taking part in oxidation reactions. This can be done by using a suitable dopant. The main characteristics to be fulfilled by such an additive are then analyzed; it is shown that only a compound which presents reversible electrochemical reactions can solve the problem, providing that its redox potential is low enough. Some experimental results using these ideas are presented in Paper II.
Cataphoretic distributions in metal-halide–He discharges
Authors: Cross Lee A. , Willis Robert K. , Funk Loren L. , Gokay M. Cem
Published: February 2003

Measurements of the longitudinal distributions of metal atoms and ions in a positive-column helium discharge tube have been made. The source of metal which is cataphoretically pumped down the tube is a sidearm heated by an external oven which contains a metal halide rather than the parent metal itself. Three metal halides, ZnCl2, SnCl2, and AlCl3, have been used as sources and the intensities of neutral and ionic emission lines recorded as a function of longitudinal displacement along the discharge tube. Evidence for cooperative motion of independent gaseous species has been found and it has been shown that considerable concentrations of metal atoms and ions can be obtained when the temperature of the bore is far too low to allow the use of the parent metal itself. It has been shown that such discharge tubes, particularly when they are of small diameter, require a careful appraisal of the temperature of the bore since, contrary to what might be expected, the cataphoresis is less effective at higher temperatures.
X-ray emission from laser-irradiated plane solid targets
Authors: Eidmann K. , Key M. H. , Sigel R.
Published: February 2003

Plane solid targets (D2, C, and Cu) were irradiated with Nd laser pulses of 5-ns duration with energies of up to 50 J giving peak intensities up to 1015 W/cm2 in the focal spot. The x-ray emission of the plasma has been studied by using scintillators together with photomultipliers, x-ray photodiodes, and an x-ray pinhole camera. Detailed results are presented on the emitted x-ray spectra up to 20 keV, on their angular dependence, on the conversion of laser energy into x-ray energy, and on the spatial and temporal behavior of the electron density and temperature. The results are discussed with respect to the hydrodynamics, the absorption of laser light, and the energy transport occurring in the plasma. Two important features are heating at densities larger than critical yielding thermal pressures up to about 1 Mbar, and the development of a large cold plasma by strong lateral heat conduction. The hot electrons observed via the high-energy tail of the x-ray spectrum, were important for transporting the absorbed laser energy.
High-field conduction and oscillations in polymers
Authors: Toureille Alain
Published: February 2003

A study of high-field conduction and oscillations in polymers is presented. It appears that there are two types of oscillations, depending upon the strength of the applied field: the regular oscillations (RO) and the prebreakdown oscillations (PBO). The interpretation shows the importance of the emission of the contact and the determining influence of the traps inherent in the very structure of high polymers.
Large-spot thermal coupling of CO2 laser radiation to metallic surfaces
Authors: Marcus S. , Lowder J. E. , Mooney D. L.
Published: February 2003

Thermal coupling of pulsed 10.6-μm laser radiation to aluminum and titanium targets was measured as a function of incident fluence, focal-spot size, and ambient pressure. Thermal coupling coefficients were measured with both calorimetric and fast-response surface-thermocouple techniques. Thermal coupling coefficients of over 0.3 were observed with the onset of a well-developed plasma at the target surface. The thermal coupling was observed to increase slightly with increasing irradiated spot size and to decrease monotonically with increasing laser fluence. Under conditions of low ambient pressure (∼0.5 Torr) the breakdown threshold was increased by a factor of 5 and at high incident fluences the thermal coupling was roughly a factor of 2 higher than at atmospheric pressure.
The contribution to self-focusing of laser beams from free-carrier heating effects in InSb in the presence of a static magnetic field
Authors: Kumar Awdhesh , Tripathi V. K. , Tewari D. P.
Published: February 2003

In this paper we have studied the self-focusing of a right-handed circularly polarized laser beam in indium antimonide in the presence of a static magnetic field when the nonlinearity in the dielectric tensor arises because of heating and subsequent mass modulation and redistribution of electrons. The paraxial and WKB approximations have been employed to obtain an analytical solution of the wave equation. It is seen that in n-InSb self-focusing of all frequency waves, off the cyclotron resonance, is possible, whereas in compensated InSb only higher frequencies (ω≳ωc) are focused. In the range ω≳ωc the effect of the magnetic field is to enchance the focusing of the beam.
Latent image changes during electrophotographic development
Authors: Junginger H.-G. , Strunk R.
Published: February 2003

The latent image formed at the surface of a photoconductive layer is leveled out during the time of development by means of charge neutralization, due to the finite conductivities of the surrounding media. The representation of the charge distribution in terms of its spatial frequency components, and the assumption of the currents at the image surface being proportional to the local electric field associated, yields an exponential decay of each component. The corresponding ’’spectral time constants’’ derived determine the rate of decrease and the degree of spread of the charge and field distributions with increasing time. Their dependence on the parameters of the electrophotographic system is governed both by static and dynamic boundary conditions. Numerical results for periodic line charge patterns are presented, varying in spatial frequency and electrode spacing. As can be predicted from the frequency dependence of the spectral time constants the charge and field distributions are smeared out remarkably in the case of low spatial frequencies and large electrode spacings. It follows that an edge enhancement will be compensated soon after immersion of the image surface. The resultant time scale is essentially defined by the effective conductivity at the boundary layer.
High-frequency and high-current studies of metal oxide varistors
Authors: Levinson Lionel M. , Philipp H. R.
Published: February 2003

High-frequency, 106≲f≲2×109 Hz, impedance measurements on ZnO-based ceramic varistors are described. Our studies indicate that the ZnO grain resistivity ρg is less than 1 Ω cm for GE-MOVR varistors at room temperature. The high-frequency measurements are compared with estimates of ρg from high-current (J≳103 A/cm2) data and the difference observed is explained in terms of the varistor ceramic microstructure.
X-ray diffraction study of interdiffusion in bimetallic Au/Pd thin films
Authors: Murakami M. , deFontaine D. , Fodor J.
Published: February 2003

An x-ray diffraction technique recently developed by Houska and co-workers was applied to the problem of measuring interdiffusion at 350 °C in 3.3 μ Au–60 at.% Pd bimetallic thin films. The technique consists of matching experimental intensity bands to those calculated from assumed concentration profiles. The profiles which gave best fit were then Boltzmann-Matano analyzed during the first stages of interdiffusion. The later stages were analyzed with the help of a linear diffusion equation applied to a finite slab. Experimentally determined values of D̃ were found to be close to those extrapolated from bulk high-temperature measurements but far from those obtained from 150 Å films.
Theory of acoustic-surface-wave detection of radiative absorption
Authors: Rockwell D. A. , Parks J. H.
Published: February 2003

A new technique is presented to study surface absorption properties by utilizing the interaction of a radiatively heated surface region with an acoustic-surface-wave probe. Surface-wave phase changes are induced by the absorption of 10.6-μm laser radiation. A detailed theory is presented to describe the thermal-acoustic interaction under the condition that the laser-induced temperature change is uniform within the acoustic-wave penetration depth. Where the theory is applicable, calculations in which there are no free parameters agree with quantitative phase-change measurements on yx α-quartz and yz lithium niobate. Phase-change dispersion measurements are shown which indicate a sensitivity to the depth dependence of the absorbed radiation and the resulting temperature distribution.
Equilibrium plasma conditions in electrostatically plugged cusps and mirrors
Authors: Blondin D. G. , Dolan T. J.
Published: February 2003

The goal is to estimate the feasibility of using electrostatically plugged cusps and mirrors to confine thermonuclear plasmas. Assuming the density of ’’trapped electrons’’ to be small, the present work describes a set of equations for determining equilibrium particle densities, temperatures, and potential barrier heights. The equations are solved for specific cases involving neutral beam injection, and the ratio Q of fusion power output to injection power input is determined. Favorable Q values are found for applied voltages exceeding 250 kV.
Reciprocity relations in an isotropic compressible multifluid plasma
Authors: Ishizone Takayuki , Adachi Saburo , Mushiake Yasuto
Published: February 2003

Reciprocity relations in an isotropic compressible multifluid plasma with collisions are theoretically investigated. The reciprocity theorem for current sources and electromagnetic fields which is often employed for a free space is found to be guaranteed in such a medium. The reciprocity is shown to be valid also for the case that an antenna is surrounded by an abrupt vacuum sheath under a physically permissible boundary condition. Furthermore, the reciprocity theorem is established for electric charge sources and number density of wave perturbed particles under the condition that there is no collisions among perturbed particles of different species. It is also shown that the similar reciprocity relation holds for the quasistatic approximation without any restrictions. Finally, as an application of the reciprocity theorem, a general expression giving antenna receiving voltages for incident electrostatic waves such as an electron plasma wave and an ion acoustic wave are obtained.
Effect of phase transition on the dielectric properties of thin organic layers
Authors: Tanguy J.
Published: February 2003

Working with capacitors produced with thin organic layers (orthophenanthroline with three stearic chains) significant variations were observed in parallel conductance and capacitance in the neighborhood of the transition point T=35 °C. An investigation of conductance properties in alternating current revealed that these layers are the site of ion relaxation phenomena between two equilibrium positions separated by a potential barrier. A sudden drop in activation energy was observed at 35 °C, falling from a value E1=1.25 eV to E2=0.65 eV. This variation, attributed to a phase change, leads to a rapid increase in capacitance and conductance G in the neighborhood of 35 °C (ΔG/G≳50%/d °C). The phenomenon is reversible, and the structure oscillates between two stable states, depending on temperature.
Extension of the method of solving potential field problems for complicated geometries
Authors: Yeh Hsu-Chieh
Published: February 2003

This paper extends the recently developed method of solving potential field problems for complicated geometries by Yeh to the case of the mixed boundary condition involving both the potential and the potential gradient. The method is exemplified by solving the heat-conduction problem of a cylinder with a suddenchange in cross-section area.
Dependence of positive corona streamer propagation on air pressure and water vapor content
Authors: Phelps C. T. , Griffiths R. F.
Published: February 2003

Experiments are described in which the ambient electric field required for sustained positive corona streamer propagation is determined as a function of dry air pressure and water vapor partial pressure. This critical field varies approximately as the 1.5 power of the dry air pressure and shows a strong linear dependence on the water vapor partial pressure. These results differ substantially from what would be expected on the basis of Paschen’s Law, but are consistent with a propagation mechanism in which the ionizing streamer tip and a portion of the plasma trail left behind it are treated as an electrically isolated propagating conductor. Energy budget arguments indicate that the critical field is inversely proportional to the length of the trail that is effectively conducting and is dependent, therefore, on the lifetime of low-energy electrons against attachment.
Correct evaluation of the irradiance of reflected light from rough surfaces
Authors: Holzer J. A. , Sung C. C.
Published: February 2003

Numerical results for the simplified irradiance integral are presented. The Gaussian and exponential surface height autocorrelation functions are shown to produce qualitatively different results in the rough surface limit. Several incorrect applications of the theory in the current literature are pointed out.
Impurity effect on the growth of dislocation-free InP single crystals
Authors: Seki Yasuo , Matsui Junji , Watanabe Hisao
Published: February 2003

Dislocation-free InP crystals were pulled in a 〈111〉 %In direction by using a liquid encapsulation technique. InP crystals were free from dislocations only when they were grown from a melt doped heavily with impurities. Zn was found to be the most effective impurity to reduce the grown-in dislocation. Dislocation density was drastically decreased when Zn concentration exceeded a value of 1018/cm3. Donor impurities, such as S and Te, were also effective in reducing the grown-in dislocation. A single-bond energy model for the impurity effect on reduction of dislocations is proposed. Zn and S were presumed to also be effective in making dislocation-free GaAs, in light of this model. These were confirmed by experiment.
Bleaching absorption fronts and beam propagation in laser-heated solenoids
Authors: Burnett N. H. , Offenberger A. A.
Published: February 2003

It is shown that the propagation velocity of bleaching laser-driven heating waves in the supersonic mode is governed by the requirement that the bleached plasma maintains an optical thickness of unity. It is proposed that in the case where the bleached plasma is confined by very large magnetic fields, the diameter of the plasma column may self-regulate so that the bleaching wave propagates at the Alfveń velocity.
Drift-dominated conduction within an Ohmic medium
Authors: Zahn Markus
Published: February 2003

Drift-dominated charge transport within an Ohmic medium is analyzed using the method of characteristics to convert the governing partial differential equations into a set of ordinary differential equations. As for earlier work within a lossless medium, the analysis is generalized to allow any initial and boundary conditions and any terminal constraint or excitation. For imposed currents the equations are exactly integrable, while for imposed voltages, the equations are easily integrated using the Runge-Kutta method of numerical integration. Special cases examined are the charging transients for space-charge-limited conduction for step current and step voltage excitations from rest and the discharging transients for systems in the dc steady state for which the excitation is instantaneously open or short circuited.
A model for reach-through avalanche photodiodes (RAPD’s)
Authors: Kaneda Takao , Matsumoto Hideo , Yamaoka Toyoshi
Published: February 2003

A model for silicon RAPD’s, which have an n+–p–π-p+ structure and are fabricated by using the ion-implantation techniques for forming the p layer, is studied. Useful relations for both an excess noise factor and a temperature dependence of an avalanche breakdown voltage are derived and are found to be in good agreement with experiments. The diodes discussed are useful in optical communication systems because of a relatively low operating voltage for the higher quantum efficiency.
Endurance and memory decay of MNOS devices
Authors: Neugebauer C. A. , Burgess J. F.
Published: February 2003

The endurance of MNOS EAROM-type memory devices toward write/erase cycling is examined using the increase of the memory window decay rate as the criterion. Two decay regimes are identified: a short-term decay in which the window decays linearly with log time, and a long-term decay in which the rate is faster than log time. Beyond 104 write/erase cycles the short-term decay rate increases at a rate of 0.05 V per decade of decay per decade of write/erase cycling per volt of memory window being cycled, at room temperature. Cycling also results in a deeper stored charge centroid in the nitride. Increasing the temperature during writing increases the depth of the stored charge in the nitride at a rate of 1.6±0.3 Å/°C and decreases the short-term decay rate. The degree of temperature dependence of the short-term decay rate is a function of the write temperature and the number of accumulated write/erase cycles. The storage time tB at which the long-term decay commences is found to shift toward shorter times on cycling. These observations can be understood in terms of the back tunneling of stored charge into fast interface states in the short-term decay region, and activated rearrangement of the stored charge within the nitride in the long-term decay region.
Impact ionization and positive charge in thin SiO2 films
Authors: Shatzkes Morris , Av-Ron Moshe
Published: February 2003

The magnitude and the centroid of the positive charge induced in the SiO2 layer of an MOS capacitor have been determined from measurements of deviations of the fields at the electrodes from the average field in the oxide. The field at the metal electron-injecting electrode is found from the current density, which deviates from a Fowler-Nordheim characteristic with respect to the average field at high fields; the field at the SiO2-Si interface is found from the shift of the high-frequency capacitance-voltage curve. For cathode fields ≳10 MV/cm, the charge is linearly related to the cathode field and is the same for both of the film thicknesses used, 494 and 263 Å. The centroid, measured from the injecting electrode, is a decreasing function of the cathode field. From these results, the average field can be derived as a function of the cathode field and the film thickness, even for cathode fields beyond breakdown. A maximum average field is found to exist, which is identified as the average field at breakdown. The average field and the cathode field (and thus the current) at breakdown are determined as a function of film thickness. Good agreement is found between our results and computations based on a model by DiStefano and Shatzkes involving electron impact ionization and electron-hole recombination.
High-field capture of electrons by Coulomb-attractive centers in silicon dioxide
Authors: Ning T. H.
Published: February 2003

Electron capture by Coulomb-attractive oxide-charge centers in thin SiO2 films thermally grown on silicon was studied at room temperature and at 77°K for average oxide fields ranging from 5×105 to 3×106 V/cm. The observed capture cross section varied with the average oxide field, EOX, approximately as EOX −3. Such a strong field dependence cannot be accounted for by the Frenkel-Poole lowering of the potential % barrier alone which predicts an EOX −3/2 dependence. It is suggested that electron heating by the oxide field is likely at these high fields. Electron heating decreases the probability of capture. The observed field dependence can be explained by a combination of Frenkel-Poole and electron-heating effects. Although the zero-field capture cross section is expected to increase rapidly with decreasing lattice temperature, the observed high-field capture cross sections were about the same at room temperature and at 77°K. Such weak dependence of the high-field capture cross section on lattice temperature is consistent with Lax’s model of cascade capture by acoustic-phonon emission.
Analysis of stress and strain distribution in thin films and substrates
Authors: Röll K.
Published: February 2003

Calculations are presented for the distribution of stress and strain in thin films and substrates from inhomogeneous plane stresses developed in the film during deposition. The results can be applied to the ’’bending-plate method’’ of determining the unknown stresses in a film, in which the deformation of the substrate surface is measured. Thereby the local values of the stress tensor within the film plane (averaged through the film thickness) and the center of the stress distribution normal to the film plane can be obtained in principle. A more convenient evaluation based on linear approximations is applicable when the film thickness is small. Restrictions are discussed which result from neglecting the conditions of compatibility for the components of the strain tensor.
Transport-current–induced magnetic field profiles of Nb3Sn superconducting tape
Authors: Migliori A. , Bartlett R. J. , Taylor R. D.
Published: February 2003

We have developed a new Mössbauer-effect magnetic field microprobe and have used it and Hall probes to study the zero-applied-field large-transport-current-density (3×106 A/cm2) magnetic field profiles of Nb3Sn superconducting tapes for T≪Tc. Our data did not agree well with predictions of critical-state models but did fit a model based on an elliptical approximation to the tape’s cross section with a current distribution having the property that where the field is zero the current density is also zero.
Magnetoresistance variation and noise properties of chevron stretcher detectors
Authors: George P. K. , Oeffinger T. R. , Chen T. T.
Published: February 2003

The angular variation of the magnetoresistance of one- and two-level chevron stretcher detectors has been determined and related to the underlying microscopic domain configuration. The origin of the 1ω-2ω transition (where ω is the angular frequency of the rotating field) in one-level detectors is shown to be the result of incomplete magnetization reversal along the detector. The characteristics of this transition and the associated output are discussed for 28- and 20-μm-period devices. Also discussed are the amplitude- and phase-shift modes of operation of these detectors for normal drive fields. Noise measurements made on zero- and one-state detector outputs show that both states exhibit a √N noise dependence with the number of chevrons N and that the drive-field dependence of the noise is approximately 1/Hxy at large drive fields. Comparison of the noise output from different detector geometries is made.
Thermomagnetic switching of ferrimagnetic garnet films at their compensation temperature
Authors: Krumme J.-P. , Hansen P. , Witter K.
Published: February 2003

Thermomagnetic flux reversal by laser heating in (111) -oriented (Gd,Yb)3(Fe,Al)5O12 films and (111) -oriented (Gd,Bi)3(Fe,Ga)5O12 films has been investigated theoretically and experimentally. Local switching is governed by wall nucleation and domain wall motion, the first step requiring the most energy. The nucleation threshold strongly depends on the uniaxial magnetic anisotropy and the induced misfit profile due to thermal lattice expansion. The effective uniaxial magnetic anisotropy is found to change sign at certain temperature distributions resulting in spontaneous switching under zero applied field. The size of the domain nucleus is assumed parabolic and depends strongly on the anisotropy field at a given applied field. The temperature distribution in the laser-heated film volume has been assessed by using the shift of the absorption band edge at 5145 Å wavelength. The present work substantiates the requirement for low-anisotropy garnet films in thermomagnetic/magneto-optic memories.
Theory of optimum linear induction motors
Authors: Dukowicz John K.
Published: February 2003

The performance of linear induction motors is degraded primarily because the finite length of the winding introduces harmful field disturbances originating at the ends. There has been considerable speculation that this effect could be overcome by making modifications to the uniform windings used conventionally. We examine this possibility by calculating the optimum distribution of current in a finite length winding using variational techniques and evaluating the gain in performance that results compared to a uniform winding. The results show that the optimum windings are in general composed of four traveling wave windings; two of which degenerate to concentrated current elements at the end of the winding in the case of optimum efficiency. The ability to improve motor efficiency depends principally on the value of the parameter M=σμ0V2d/ωg. For high values of M, such as occur in typical transportation applications where M≳10, the degradation of performance is due to eddy currents in the secondary and there is no significant improvement over a uniform primary current distribution, while for low values of M, such as in low-speed industrial actuators or liquid metal pumps where M<1, improvements in efficiency are possible. Generally, power density improvements are insignificant for all applications.
The solution of Laplace’s equation in cylindrical and toroidal configurations with rectangular sectional shapes and rotation-symmetrical boundary conditions
Authors: Heerens W. Chr.
Published: February 2003

Basic formulas have been obtained for the contribution to the potential in any point of a cylindrical or toroidal volume with rectangular sectional shapes and rotation-symmetrical boundary conditions. This is done by solving Laplace’s equation in cylindrical coordinates using the method of separation of variables for the cases in which simple but characteristic rotation-symmetrical potential overlays on the boundaries exist. Knowing these solutions and limiting the widths of the areas where the potential overlays are defined, differential contributions to the potential in any point of the observed volumes in analytical form are derived. With these solutions also numerical formulas for the contribution in a point of the volume can be formulated so that the relaxation method can be avoided.
Distribution coefficient of P for growth of Ga1−xAlxAs1−yPy by LPE, determined using Auger spectroscopy
Authors: Chang C. C. , Panish M. B. , Wagner W. R. , Rode D. L. , Sumski S. , Sobers R. G.
Published: February 2003

The effective distribution coefficient of phosphorus during growth of Ga1−xAlxAs1−yPy by liquid-phase epitaxy is of particular importance to the growth of heteroepitaxial structures for injection lasers and light-emitting diodes. In these structures small additions of P (y<0.02) can be used for stress compensation and for lowering of laser threshold. In this work, Auger spectroscopy was combined with ion milling for quantitative chemical analysis and depth profiling. Below y=0.02 (with x=0.36) and cooling rate of 0.1 °C/min for growth, kp was found to be 290 at a growth temperature of 790 °C and remained constant down to at least y=0.002. This high value of kp caused depletion of P from the growth solution and gave rise to P concentration profiles in the epitaxial layer which decreased with distance away from the substrate.
Analysis of lead azide thin films by Rutherford backscattering
Authors: Windawi H. M. , Varma S. P. , Cooper C. B. , Williams F.
Published: February 2003

The Rutherford backscattering technique using 1-MeV protons has been employed to analyze pure and doped lead azide thin films of various thicknessess which had been prepared by vacuum evaporation followed by vapor conversion. The films were found to be approximately homogeneous in composition with depth within the limits of the depth resolution of the experiment. The energy rate loss dE/dx of the films was found to be about 60 keV/μm. The Tl-doped films showed a somewhat different backscattering spectrum from the undoped films.
Low-threshold double heterojunction AlGaAs/GaAs laser diodes: Theory and experiment
Authors: Kressel H. , Ettenberg M.
Published: February 2003

A detailed study is presented of AlxGa1−xAs/GaAs double heterojunction lasers combining very thin recombination regions (d?0.1 μm) with high Al concentration differences at the heterojunctions. These devices have exceptionally low threshold current densities (475–1000 A/cm2 depending on the structural details), which increase by a median value of 1.35 between 22 and 70 °C. The differential quantum efficiency decrease in that same temperature interval is small. The device parameters have been analyzed in terms of available theory connecting the radiation confinement to the width of the recombination region and the dielectric step at the heterojunctions. Both the threshold current density dependence on the width of the recombination region and the far-field beam pattern are in reasonable agreement with theory. Assuming no change in carrier or optical flux confinement for large Al concentration differences, the temperature dependence of the threshold current density is found to be somewhat steeper than calculated.
Concentration dependence of the gain spectrum in methanol solutions of rhodamine 6G
Authors: Urisu Tsuneo , Kajiyama Kenji
Published: February 2003

Concentration dependence of the gain spectra in methanol solutions of rhodamine 6G was measured by the amplified spontaneous-emission method. Peak gain and peak wavelength depended nonlinearly on the dye concentration. The nonlinear dependences were attributed to the concentration dependence of the fluorescence lifetime which is caused by radiation trapping and concentration quenching.
The photodoping sensitivity in As-S and Ge-S films
Authors: Kasai M. , Hajimoto Y.
Published: February 2003

Photodoping sensitivity differs greatly between As-S and Ge-S films. This difference depends on the degree of phase separation and on the degree of crystallization of the films.
Electrical properties of Te-implanted GaAs
Authors: Shin B. K.
Published: February 2003

Tellurium was implanted into Cr-doped GaAs at 250 °C to a dose of 1013 or 1014 Te/cm2 at 120 keV. Sheet-resistivity and Hall-effect measurements were made on the samples for annealing temperatures up to 900 °C. From the temperature dependence of the sheet resistivity, the conduction mechanism of as-implanted samples was found to be due to thermally assisted tunneling in disordered semiconductors. The very small activation energy of <0.1 meV obtained from the sheet-resistivity curves for isochronal annealing temperatures of ≲200 °C indicates that formation of an amorphous layer has been prevented and that the samples have undergone no epitaxial recrystallization. Annealing at ?600 °C produced n-type conductivity with the maximum effective bulk concentration being ∼1018 electrons/cm3 for the 1014 Te/cm2 sample annealed at 800 °C. However, the electrical compensation remained high (NA/ND ?0.6) for annealing temperatures ranging from 600 to 900 °C, the compensating centers being of the VGaTe-complex type. The temperature dependence of the electrical characteristics for well-annealed samples resembled that of bulk material. However, a somewhat larger value of donor ionization energy (∼7 meV) was obtained for the 1013 Te/cm2 sample annealed at 800 °C; this value may arise from the profiling effects.
Electron-hole recombination in nitrogen-doped direct-band-gap GaAs1−xPx
Authors: Nelson R. J. , Holonyak N. , Groves W. O. , Keune D. L.
Published: February 2003

Optical phase-shift lifetime measurements (77 °K) on N-free and N-doped direct-band-gap GaAs1−xPx are studied to determine the effect of the N isoelectronic trap on the lifetime spectrum τ (λ). An analysis of the recombination processes in direct-gap crystal is used to provide estimates for the N-trap carrier capture time and capture cross section, which for the NX state is σt≳10−13 cm2. It is shown that the minority-carrier lifetime is decreased by the addition of N doping. This effect, which is attributed to nonradiative recombination paths fundamental to the N trap, is thought to be the reason for the increased laser thresholds of N-doped In1−yGayP1−zAsz/GaAs1−xPx junction lasers as compared with similar N-free devices.
Stability of amorphous metallic alloys
Authors: Luborsky F. E. , Walter J. L.
Published: February 2003

In a previous paper it was concluded that the migration of phosphorus was causing the embrittlement of amorphous Fe40Ni40P14B6 at temperatures as low as 100 °C. In this paper we compare the stability of the above alloy to amorphous Fe40Ni40B20, Fe50Ni30P14B6, and Fe50Ni30B20. The stability is evaluated from brittleness measurements after annealing at temperatures between 100 and 400 °C. The results confirm the prediction that the removal of phosphorus suppresses the embrittlement at low temperatures; temperatures above 225 °C are required to cause embrittlement in the phosphorus-free alloys. At higher temperatures the fracture strain approaches that of the phosphorus-containing alloy. It is concluded that the replacement of P by B inhibits the low-activation processes involved in the embrittlement process. The changes are not related to the changes in the glass transition temperatures.
Lineshapes of the electron paramagnetic resonance of small silver particles
Authors: Châtelain A. , Millet J-L. , Monot R.
Published: February 2003

The lineshape of the electron paramagnetic resonance of conduction electrons of small silver particles is analyzed in terms of the theory of Kawabata and the size distribution of the particles in the sample. In particular, this analysis explains the observed asymmetry of the signal and its evolution during the heat treatment of the samples.
Magnetic heat pumping near room temperature
Authors: Brown G. V.
Published: February 2003

Magnetic heat pumping can be made practical at room temperature by using a ferromagnetic material with a Curie point in or near the operating temperature range and an appropriate regenerative thermodynamic cycle. Rare earths are found to be much more effective in this application than transition elements, and measurements have been made which show that gadolinium (Curie point: 293 °K) is a reasonable working material. The application of a 7-T magnetic field to Gd at the Curie point causes a heat release of 4 kJ/kg under isothermal conditions or a temperature rise of 14 °K under adiabatic conditions. A regeneration technique is proposed which removes the limits usually expected on the temperature span of a magnetic cycle. The cycle efficiency can approach the Carnot-cycle efficiency.
Elastic constants of neodymium single crystals in the temperature range 4.2–300 °K
Authors: Greiner J. D. , Schlader D. M. , McMasters O. D. , Gschneidner K. A. , Smith J. F.
Published: February 2003

The elastic constants of a single crystal of the double hcp allotrope of neodymium have been measured over the temperature range 4.2–300 °K. The magnetic orderings which occur in neodymium near 7.5 and 19 °K are readily evident as cusps in the temperature dependences of some of the directly measured ultrasonic wave velocities, as well as in the associated elastic constants, and the character of the magnetic interactions is reflected in the differing effects on the various elastic constants. Comparison of the elastic constants of neodymium with those of seven other rare earths shows a trend with atomic number which is similar to trends which have been observed in other physical properties.
Geometry dependence of thin-film transverse thermoelectric voltages
Authors: von Gutfeld R. J.
Published: February 2003

We have measured the transverse voltage from slant-angle-deposited metal films due to laser illumination as a function of film geometry. For a fixed laser spot size, the voltage is found to vary inversely with film width d for d small compared to contact separation a. For d/a ⩾∼1 the voltage approaches a constant. The experimental results are in good agreement with the open-circuit voltage from a finite-current dipole and consistent with the thermoelectric model previously proposed. Useful design parameters for transverse thermoelectric optical detectors are implied by the data.
Vacuum ultraviolet photoemission studies of nucleic acid bases
Authors: Pong W. , Inouye C. S.
Published: February 2003

The spectral quantum yields of adenine, thymine, cytosine, and uracil films were measured at photon energies of 7 to 23 eV. In addition, photoelectron-energy-distribution measurements were made at 21.2 eV. The photoelectron spectra exhibit features which can be associated with density-of-states structures below the vacuum level. The difference between the observed photoemission threshold of a solid film and the calculated energy of the highest occupied orbital for the isolated molecule is found to be 1.5–2.0 eV.
High-power transmission in plasma-filled waveguides
Authors: Chandra Prayag , Tripathi V. K.
Published: February 2003

Using appropriate expressions for the nonlinear dielectric constant of a bounded fully ionized hot plasma, the propagation of high-power electromagnetic waves in the TE10 mode in a plasma-filled rectangular waveguide has been investigated; the nonlinearity in this collisionless plasma arises from the ponderomotive force due to the gradient of the field intensity. After integrating the wave equation once, numerical solution has been carried out. As the power of the beam increases, the plasma is depleted from the center of the waveguide and concentrates near the walls. This allows the transmission of the beam in the waveguide even when the average plasma frequency is much larger than the wave frequency. At very high powers the field around the center of the waveguide possesses a cosine variation but falls very rapidly as the wall is approached. The field patterns in this case are seen to be similar to the linear case of a waveguide, partially filled with plasma.
Trap-modulated mobility of electrons and holes in Teflon FEP
Authors: Sessler G. M. , West J. E.
Published: February 2003

The trap-modulated mobilities of electrons and holes in 25-μm Teflon FEP, charged by application of a high dc field at room temperature, are determined from thermally stimulated current (TSC) measurements performed under open-circuit conditions. Use of the TSC method allows one to evaluate approximately the effect of various trapping levels in the material (corresponding to different TSC peaks) on carrier mobility. For example, the first and second above-room-temperature TSC peaks for positive carriers yield mobilities of 10−11 cm2/V sec at 50 and 80 °C, respectively. Similarly, for negative carriers, the second above-room-temperature TSC peak yields a mobility of 10−11 cm2/V sec at 185 °C. The temperature dependence of the mobilities follows an Arrhenius-type behavior with activation energies of 0.7 and 1.0 eV for the positive-carrier peaks and 1.8 eV for the negative-carrier peak.