bluuebunny/crossref_metadata_2025 huggingface dataset:
Computer simulations of the classical one-dimensional XY-model
Authors: Landau D. P. , Thomchick John
Published: February 2003

Results are presented for the static and time-dependent behavior of the classical one-dimensional XY-model at finite temperatures. Equilibrium properties were determined using an importance sampling Monte Carlo method. A spin-dynamics computer simulation method was then used to evaluate spin-spin and energy-energy time-displaced correlation functions out to time t=10J−1 using initial states chosen from the equilibrium distribution. The transverse spin-spin auto correlation function decreases smoothly as a function of time. The longitudinal spin-spin correlation functions, however, show temperature dependent oscillatory behavior. At moderately high temperature the energy-energy correlations show diffusive t−1/2 behavior at long times with only a slow temperature dependence of the diffusion constant.
Abstract: Antiferromagnetic [(CH3)2NH2]MnCl3⋅2H20
Authors: Filho A. Paduan , van der Bilt A. , Carlin Richard L.
Published: February 2003

Measurements of the magnetic susceptibility and phase diagram of orthorhombic [(CH3)2NH2]MnC13⋅2H2O between 1.8 and 30K will be reported; at Tc(0) =6.4K determined by the maximum value of dχ/dt, antiferromagnetic long range order develops, due to three-dimensional interactions. We find that Tc increases as a function of the applied field for the boundary between the spin-flop and paramagnetic phases as has also been observed in other low-dimensional antiferromagnetic systems. (AIP)
Roles of the order parameters M and M
s in the magnetostriction of D
y3A
l5O12(D
A
G)
Authors: Dillon J. F. , Blount E. I. , Chen E. Yi , Gyorgy E. M. , Van Uitert L. G.
Published: February 2003

An analysis has been made of the dependence of the magnetostrictive distortion of DAG on the two order parameters M and Ms. This paper is a brief report of the analysis and of experiments which test the analysis. The ten cases considered included ? parallel to each of the principal directions with gauges parallel, perpendicular and in some cases oblique to the field directions. All cases are predicted to contain terms in M2 and Ms2. In four there is an additional term in MsM. Previous work has put at our disposal techniques for setting Ms to either of the time reverse antiferromagnetic states A+ and A−. Thus we can test whether or not δl/l has a component odd in M and Ms. Experiments on all geometries give results consonant with the theory. In addition, there are two anomalous results which we believe to be artifacts.
C.P.A. theory for a dilute paired antiferromagnet
Authors: Prater J. T. , Egami T.
Published: February 2003

A coherent potential approximation (C.P.A.) theory has been developed in order to examine the bond dilution problem in an antiferromagnet which contains alternating strong and weak magnetic exchange interactions. Specifically, we have calculated the concentration dependence of the transition temperature at which the system displays long-range order. This is done by examining the Green function for the system in the paramagnetic phase. The existence of the strong exchange interaction creates pairs of highly correlated spins in the paramagnetic state. The transition temperature is identified by introducing the weak coupling between these spin pairs and locating the temperature at which the excitation of a pair from the singlet ground state to the lowest excited states becomes soft. When only interpair bonds are broken, a linear concentration vs transition temperature behavior is predicted. This prediction is compared with recent experimental results for the diluted paired antiferromagnet, RbMn1−xMgxCl3.
Spin-orbit electron scattering in AuFe alloys near the percolation limit
Authors: Hurd C. M. , McAlister S. P.
Published: February 2003

We describe measurements of the anomalous Hall effect (AHE) in AuFe alloys in the range from 5 at.% Fe up to the ferromagnetic percolation limit (∼16 at.% Fe). In the more concentrated alloys the AHE is shown to be composed of two competitive contributions. One arises from the asymmetric scattering of electrons by localised moments. The other, which we attribute to the side-jump effect, increases as the mean free path is reduced, and has the same sign as the side-jump contribution to the AHE in pure Fe. The concentration dependence of this side-jump contribution suggests that it arises from electrons moving within magnetic clusters that are formed as the percolation limit is approached.
Abstract: Néel temperature of chromium alloys with local magnetic moments
Authors: Antonoff M. M.
Published: February 2003

Calculations of the Néel temperature as a function of impurity concentration show features which are in qualitative agreement with experimental results. (AIP)
EPR measurements in the one-dimensional anisotropic paramagnet CsNiF3
Authors: Barjhoux Y. , Boucher J. P. , Cibert J.
Published: February 2003

The EPR line has been observed in CsNiF3 at room temperature. The anisotropy of its width is analysed in terms of the dynamics associated with 4-spin correlation functions (4-SCf). The EPR width can be attributed unambiguously to the single-ion coupling. We therefore get the opportunity to obtain information on specific 4-SCf. Their dynamics is discussed in the conclusion.
Fluctuations in the energy-energy correlation function of one-dimensional magnetic models
Authors: Bowman D. , Halley J. W.
Published: February 2003

We computed the variance 〈x2〉−〈x〉2 of the operator x=EqE−q in which Eq=ΣSr⋅Sr+1eiqr for a one dimensional classical Heisenberg chain. We show that (〈x2〉−〈x〉2)/〈x〉2 is of order 1, not of order 1/N as expected for a thermodynamic variable. This differs from earlier reported results for this variance. We find a similar result for the one-dimensional Ising and x-y models and establish a general condition for the correlation functions which causes such a result to oaccur. The large variance means that numerical calculations of 〈EqE−q(t) 〉 must be done carefully to produce reliable results. We introduce a new method to calculate 〈EqE−q(t) 〉 which avoids this problem. The method gives excellent results for the known values at t=0. We present results for 〈EqE−q(t) 〉 using this new method. They contain some features which are not yet fully understood.
A diffusion model for hydrogen-palladium system
Authors: Banerjee S. , Lee M. H.
Published: February 2003

The hydrogen gas is known to rapidly diffuse through palladium. The interstices of the host metal serve as a nonrigid Yang-Lee cell lattice for diffusing hydrogen atoms. The transition of hydrogen atoms from one cell to another is affected by the host lattice phonons, which give rise to long-range two-body forces between hydrogen atoms. We propose a diffusion model for the PdH system assuming that the nonrigidity of the host lattice is a main driving force for the diffusion. Our essential idea is to modify the quantum lattice model by including the hydrogen-lattice interaction. By a unitary transformation, one can decouple the hydrogen system from the host lattice coordinates in such a way that the diffusion now takes place as if in a rigid lattice. The resulting interacting term then assumes what is equivalent to the 4-spin interaction of a compressible Ising model. Under a suitable approximation our model can predict mean-field critical behavior. We also discuss other physical implications of our model.
Landau-Lifshitz equation in itinerant electron ferromagnets
Authors: Korenman V. , Prange R. E.
Published: February 2003

The Landau-Lifshitz equation is the basic equation governing the time evolution of long-wavelength disturbances in ferromagnets. We report here a new microscopic derivation of this equation, valid for itinerant electron ferromagnets. The derivation is valid for the nonlinear case in which the spin fluctuates over a large angular range globally. In particular it includes the time dependence of magnetization fluctuations above the Curie temperature. We also find the generalization of the Landau-Lifshitz equation needed when the magnetization magnitude is not spatially uniform.
Role of electron-electron interactions in the RKKY theory of magnetism
Authors: Cooke J. F.
Published: February 2003

The theory of magnetism in heavy rare earth metals is based on the RKKY theory. In this formalism the indirect exchange interaction between the local 4f spins is mediated by the conduction electrons. When carried to second order in the 4f-conduction electron interaction, traditional pertubation theory leads to a Heisenberg-like interaction between the local spins which depends on the electronic energy bands and 4f-conduction electron exchange matrix elements. This derivation neglects the detailed behavior of electron-electron interaction within the conduction band, which is known to be important in metallic systems. By using an equation of motion method, an expression for the inelastic neutron scattering cross-section has been derived which includes, in an approximate way, this electron-electron interaction. The results of this calculation indicate that spin-wave peaks can be broadened and shifted if the spin-wave band lies near the conduction electron Stoner continuum. The origin of this effect is similar to that found in itinerant electron systems where the spin-wave band actually intersects the Stoner continuum, resulting in the disappearance of the spin-wave mode.
The spin correlation in a ferromagnet with random anisotropy
Authors: Chi Mely Chen , Egami T.
Published: February 2003

A computer simulation technique has been used to study the static spin correlation in a ferromagnet with random magnetic anisotropy. An effective anisotropy constant which enables us to express the spin correlation by the domain wall equation was calculated for various values of single-ion anisotropy constant. Allowing the spin tunnelling or not makes a significant difference in the high anisotropy region. The energy of a relaxed domain wall was calculated and it was shown that the domain wall energy approached to zero in the Ising limit, suggesting the instability of the ferromagnetic remanent state. The ground state can be obtained by creating reverse domains in the ferromagnetic state, and should be classified as the spin-glass state. The temperature dependence of the coercivity of the amorphous magnet was explained by the theory developed for highly anisotropic crystalline magnets.
Conditions for stress induced bulk moments
Authors: Garshelis Ivan J.
Published: February 2003

The conditions under which stress alone can establish bulk magnetic moments in magnetostrictive ferromagnetic bodies are examined. It is shown that net moments may be realized by appropriately applied mechanical stress, in the absence of any coapplied field or existing net moment, if any or all of the factors influencing relative stress anisotropy (λ,σ, K) are unequal in the regions having antiparallel magnetizations. The regions may be compositionally homogeneous and contiguous with classical domain wall boundaries, or contiguous with structural or compositional steps or continuous gradients, or they may be spatially separated. Multiple pairs of such regions cannot be oriented at random in one ferromagnetic body if the net moment from each pair, due to a physically realizable stress distribution, is to add to a bulk moment. This configurational restriction constitutes an initial state of magnetization even though the pre-stress flux closure paths are all internal. As the stress is applied and increased, the local magnetic field, accompanying the developing uncompensated moments, exerts a demagnetizing influence on this magnetization, in addition to that caused by the stress itself. When thresholds of irreversibility are passed, the initial magnetization is not regained during stress relaxation.
Numerical studies of the low temperature spin dynamics in PdMn (10 at%)
Authors: Ching W. Y. , Huber D. L. , Verbeek B. H.
Published: February 2003

Employing both matrix diagonalization and equation-of-motion techniques we have calculated the density of spin wave modes and the dynamic structure factor for the spin glass PdMn (10 at%). We used a functional form for the exchange interaction suggested by high field magnetization measurements with an overall multiplicative factor adjusted to give agreement with the low temperature specific heat. Our results for the dynamic structure factor for momentum transfer Q=0.8 Å−1 are compared with recent inelastic neutron scattering data.
Spin excitations in amorphous transition-metal boron glasses
Authors: Rhyne J. J. , Lynn J. W. , Luborsky F. E. , Walter J. L.
Published: February 2003

Magnetic inelastic neutron scattering studies have been performed on ribbon specimens of amorphous Fe83B16.5Si0.5 and Fe20Ni60B19P1. The samples were prepared from isotopically enriched B to reduce the neutron absorption. The Curie temperatures for the two materials are 613 K and 410 K respectively, and the room temperature saturation magnetizations 4πMs are 16.0 kG and 5.1 kG. In the Fe20Ni60B19P1 specimen, well-defined spin waves were observed at room temperature for neutron wave-vector transfers in the range q=0.06 Å−1 to q=0.20 Å−1. After correcting for instrumental resolution, the data obeyed a quadratic dispersion law with spin stiffness D=80 meV-Å2. Spin waves in the Fe83B16.5Si0.5 amorphous alloy exhibited a D=125 meV-Å2 consistent with the higher Tc of this alloy.
Influence of metal-metalloid elements on the electrical resistance of amorphous materials
Authors: Rao K. V. , Gudmundsson H. , Aström H. U. , Chen H. S.
Published: February 2003

We report systematic studies on the electrical resistivity, ρ, in the amorphous transition metal based alloy series T1−yGy, with T = A1−xBx (where A,B = Fe, Co, Ni, Cr, Mn) and the metalloid G (=P, B, Si, Al) over the temperature range 20 mK to 300 K. All the alloys studied show a minimum in the resistivity at a characteristic temperature Tmin which varies from 8 K to 250 K depending on the system. For a given system the resistivity rise below tmin is found to be a maximum around the critical conc region where the magnetic long-range order parameter →0. Also, in all the alloys below the resistance minimum it is found that dρ (T)/dT∼–ρ (T) with deviations setting in at lower temperatures. The coefficient of the T2 term in ρ above Tmin is strongly influenced by the metalloid concentration.
The effects of processing conditions on magnetic properties of amorphous alloys
Authors: Takayama S. , Oi T.
Published: February 2003

The effects of processing conditions on the physical properties of Fe40Ni40B20 amorphous alloys produced by a single roll-casting technique were investigated. These results are discussed in terms of the cooling rate in the casting and the state of disordered structure quenched into the amorphous alloy.
Effects of Mo on the magnetic properties of amorphous (FexMo1−x)75P16B6Al3
Authors: Chien C. L. , Chen H. S.
Published: February 2003

Amorphous (FexMo1−x)75P16B6Al3 with x=0.7, 0.8, 0.9, 0.95 and 1.0 have been studied by 57Fe Mössbauer spectroscopy. The magnetic ordering temperature decreases drastically from 640 K for x = 1.0 to 26 K for x = 0.7. The result suggests an antiferromagnetic exchange interaction between Fe and Mo. Anomalous magnetic hyperfine interactions have been observed at 4.2 K. The P(H) analyses indicate a two-maxima function of H. The intensity of the low-field component increases with Mo content and at the expense of the high-field component. This indicates that there is a substantial number of Fe atoms which are weakly magnetic or have small moments.
Mössbauer effect in ferromagnetic, metallic glasses: High pressure studies
Authors: Liu C. M. , Ingalls R. , Whitmore J. E. , Rao K. V. , Bhagat S. M.
Published: February 2003

High pressure–Mössbauer studies to 110 kbar on Metglas 2826A are reported. It is found that both Tc and the hyperfine field reduce monotonically with increasing pressure. In contrast to other metglas materials a paramagnetic component is observed at temperatures well below Tc. The splitting of this weaker component roughly follows the temperature and pressure dependence of the hyperfine field observed for the main component.
Magnetic properties of the rare-earth glasses (R65Fe35)100−xBx
Authors: Gerber J. A. , Cornelison S. G. , Burmester W. L. , Sellmyer D. J.
Published: February 2003

Results are reported on the magnetic properties of (R65Fe35)100−xBx glasses, where R denotes Y, Gd, and Er, and x is 10 or 20. Curie-Weiss fits were made to high temperature susceptibility data to determine average effective moments per magnetic ion and Weiss temperatures. Hysteresis loops and modified Arrott plots were used to determine the spontaneous magnetizations, coercive forces, and ordering temperatures. The effective moments and spontaneous moments are compared with those calculated on the assumption of local moments on both magnetic subnetworks, and assuming various spin structures. There is evidence for moment instabilities on Fe atoms in the Y-Fe-B glass, depending on local-environment effects. Local random anisotropy plays an important role in Er-Fe-B but not in Gd-Fe-B.
Evidence for a surface ferromagnetic layer in amorphous YFe2
Authors: Lloyd J. N. , Bhagat S. M. , Knudson A. R. , Gossett C. R.
Published: February 2003

Spin resonance measurement on bulk samples of a-YFe2, grown by d.c. sputtering, and a thin film of Y0.30Fe0.70, grown by co-evaporation, are reported. In agreement with our earlier reports, we observed a multi-line spectrum in which one line has a frequency and angular dependence expected from a thin ferromagnetic layer with (4πM)eff≳6 kOe at 300 K despite the fact that a-YFe2 is known to have no long range order at this temperature. Rutherford back-scattering, chemical etching studies, and temperature dependence of (4πM)eff lead us to conclude that the ferromagnetic layer is not a consequence of segregation, surface contamination or locally crystallized material. We propose that it arises from some kind of an atomic rearrangement which is initiated at the surface and progresses inward on a time scale of weeks.
Piezoelectricity in nylon 11
Authors: Newman B. A. , Chen P. , Pae K. D. , Scheinbeim J. I.
Published: February 2003

At the present time, only poled, drawn poly (vinylidene fluoride) (PVF2) films give evidence of sufficiently high piezoelectric response to be useful in device applications, and for this reason the great majority of research has centered around this polymer. As in the case of PVF2, many odd nylons crystallize in a polar space group with a large net dipole moment in the unit cell. On the basis of the understanding now reached of the properties of poled PVF2 films, it would appear that the odd nylons have the potential to make films with high piezoelectric activity. Piezoelectricity and pyroelectricity in nylon 11 films have been studied previously. The piezoelectric strain constants found were larger than most polymers, but still two orders of magnitude less than the corresponding activity found in poled oriented PVF2 (d31∼20 pC/N). Studies carried out in this laboratory have shown that by appropriate variation of poling conditions and sample microstructure, relatively large piezoelectric constants can be obtained for nylon 11 films (d31∼3 pC/N). The dependence of the piezoelectric strain constant d31 on poling temperature, poling field, and crystal structure will be discussed.
Brightness of LaB6 cathodes
Authors: Noack M. A. , Gibson E. D. , Verhoeven J. D.
Published: February 2003

Single-crystal LaB6 cathodes were prepared by arc float zone refining and their stoichiomerty and impurity level have been determined. The brightnesses of cathodes were evaluated in a SEM modified to allow in situ measurement of the cathode tip temperature. Three crystallographic orientations were evaluated and the relative brightness was found to follow the order (100)≳(321)≳(110) with the value for the (100) orientation being around 106 A/cm2 sr at 1900 °K.
Stripe domain width in bubble garnet films
Authors: Mada Junji , Yamaguchi Kazuyuki
Published: February 2003

A significant difference was found between stripe widths of bubble garnet film observed by different measuring methods. The methods are (1) stripe width Sw(?) arranged with the ac magnetic field perpendicular to the film plane; (2) stripe widths Sw(H) elongated parallel to the in-plane dc magnetic field with the aid of the ac field as in (1); (3) stripe widths Sw(H?) modulated with an additional ac field after obtaining the magnetic domains of Sw(H). The result that Sw(?) =Sw(H?) ?1.1 Sw(H) was obtained. The exchange stiffness estimated using Sw(?) gives reasonable values, while that from Sw(H) does not. It has been concluded that method (3) is superior to the other two methods.
Secondary electron emission from CuInTe2
Authors: Flinn E. A. , Salehi M. , Tomlinson R. D.
Published: February 2003

Measurements of secondary electron emission yield and inelastic reflection coefficient for monocrystalline CuInTe2 have been made using samples freshly cleaved in ultrahigh vacuum. The yield curve exhibits significant structure which may be explained in terms of primary beam diffraction from (310) planes.
Stress relaxation of iron-boron amorphous alloys
Authors: Luborsky F. E. , Liebermann H. H.
Published: February 2003

The stress relaxation of FexB100−x alloys for 72⩽x⩽88 at.% was measured after annealing for 2 h at 225°C on ribbons having thicknesses between 15 and 33 μm. Stress relaxation increases with x and with decrease in thickness. There was no evidence for any discontinuity in stress relaxation versus x as was previously found for the activation energy for crystallization versus x. This implies that different atomic processes are involved in stress relaxation and in crystallization.
Comparison of the secondary-electron spectrum with the electron-loss spectrum on pure Al by low-energy electron-reflection spectroscopy
Authors: Massignon D. , Pellerin F. , Fontaine J. M. , Le Gressus C. , Ichinokawa T.
Published: February 2003

The secondary-electron (SE) spectrum, energy-loss (EL) spectrum, and Auger electron spectrum (AES) for pure Al were measured by low-energy electron-reflection spectroscopy. The SE spectrum taken at primary energies higher than 50 eV is compared to the spectrum at 30 eV when excitation of surface and bulk plasmons is negligible. Both spectra do not change in the peak position and shape. Therefore the contribution of secondary electrons emitted by plasmon decay is negligibly small compared to the contribution of those emitted by the single-electron excitations. Some additional peaks are observed in EL and SE when O2 is sorbed on the surface.
Dependence of the infrared output power of a hollow-cathode Cu+ laser on He and Ar pressures
Authors: Eichler H. J. , Wittwer W.
Published: February 2003

The dependence of the infrared laser power produced by a hollow-cathode copper ion laser on the He and Ar pressure is reported. An argon partial pressure of 1 mbar is found to be optimum and nearly independent of the helium partial pressure and discharge current. The optimum He pressure is about 25 mbar, dependent on the discharge current. A simple rate equation model is given and compared to the experimental results.
Thermal oxidation of InP
Authors: Wager J. F. , Wilmsen C. W.
Published: February 2003

The growth rate and chemical composition of thermally grown oxides on InP in dry oxygen are presented. The oxide is found to grow very slowly below 340 °C and rapidly above this temperature. All the oxides grown in the temperature range 340–450 °C are composed of approximately 70%–75% In2O3 and 25%–30% P2O5. There is also some evidence for low concentrations of another bonding state of phosphorous.
Zn-doped vapor-grown InP
Authors: Chevrier J. , Huber A. , Linh N. T.
Published: February 2003

Zinc-doped p-type InP layers has been grown by the In/PCl3/H2 technique. It has been shown that the zinc atoms, incorporated during the growth, become electrically active after annealing. By photoluminescence study at 4.2 °K, it has been found that the main transition on the Zn level, in low-doped material, was situated at 1.377 eV; this transition shifts to 1.382 eV in higher-doped material.
Effects of interaction fields on the hysteretic properties of assemblies of randomly oriented magnetic or electric moments
Authors: Davis Paul M.
Published: February 2003

Theoretical models of interacting magnetic or electric moments based on the concept of a uniform Lorentz-type internal spatial mean field predict results that are in conflict with experimental observations. Neglect of the nonuniformities in the interaction-field distribution can account for this. In order to test interaction theories, hysteresis measurements have been made on samples containing particles of known intrinsic magnetic properties. Coercivities, susceptibilities, and saturation remanences have been measured for randomly oriented uniaxial single-domained magnetites as a function of packing factor. On the basis of these results, a model is proposed which takes into account heterogeneity in the interaction-field distribution while retaining the simplicity of the mean-field approach. The model is based on the magnetization configuration which most effectively gives rise to internal pole cancellation and minimum anisotropy energy. This occurs when moments segregate into magnetically independent domains within which magnetic moments are nearly parallel and lie along particle easy axes, but which are themselves randomly oriented throughout the assembly. Particle moments would then be subjected to domain-magnetizing fields which are proportional to and oppositely directed to intrinsic demagnetizing fields. The model predicts a reduction of demagnetizing factors of (1−p), so that susceptibility is given by χ (p) = (2/3)[Nb−Na)(1−p)]−1 for particles of average demagnetizing factors Na, Nb, and also that the remanence remains constant with increased packing, i.e., IRS(p) =0.5IS both of which have been observed experimentally. The results lead to the general conclusions that for all noncrystalline polar interactions: moments will tend to form into the pole-cancelling domains described; the average internal field acting on a moment is a constant, which is independent of the net polarization; and, the spatial mean internal field of polarized assemblies of interacting moments exerts no torque on elementary moments and plays no part in determining the net polarization of the assembly.
Properties of Zn-doped VPE-grown GaN. I. Luminescence data in relation to doping conditions
Authors: Monemar B. , Lagerstedt O. , Gislason H. P.
Published: February 2003

Experimental results on optical and electrical properties of VPE-grown GaN doped with Zn under various conditions of growth are presented. The incorporation of Zn into GaN was found to be critically dependent on growth conditions. Four different Zn-related acceptorlike centers A–D were found to occur, with broad radiative emissions peaking at 2.87 (A), 2.6 (B), 2.2 (C), and 1.8 eV (D). Their broad shape was found to be due to a moderate lattice relaxation upon optical transitions. A linear model for phonon coupling was found adequate, with a principal mode resonant with the optical band [h/ω, varying between 74 (A level) and about 84 meV (C level)] and an additional lower-energy mode, yielding Franck-Condon shifts for these centers ΔFC,A =0.25±0.03, ΔFC,B=0.25±0.04, ΔFC,C =0.28±0.04 eV, and ΔFC,D=0.28±0.05 eV. Data for electrical compensation related to the occurrence of these different emissions indicate that the A level could be the ZnGa substitutional acceptor, while the more efficiently compensating B–D levels might be associated with Zn occupying N sites.
Properties of Zn-doped VPE-grown GaN. II. Optical cross sections
Authors: Monemar B. , Gislason H. P. , Lagerstedt O.
Published: February 2003

Experimental data are presented for optical cross sections σ0n(hν) related to the four deep acceptorlike Zn-related radiative levels A–D in GaN. Very accurate spectral data were obtained by the photoluminescence excitation (PLE) technique, at temperatures varying from 4.2 up to 293 K. From a detailed comparison of the spectral behavior of the emission and absorption spectra, the size of electronic broadening effects could be determined in the overlap region. The binding energies for Zn-related acceptor levels were obtained as EA=0.34±0.04, EB=0.65±0.08, EC=1.02±0.05, and ED=1.42±0.08 eV at low temperature. Optical transmission data give estimates of absolute values for optical cross sections at saturation, varying from σ0nA(sat) ?1×10−16 to σnD(sat) ?5×10−18 cm2. Temperature broadening effects in optical cross sections are well explained by a linear model for phonon coupling in the optical transitions, employing the same phonon energies and coupling strengths as were evaluated from emission spectra.
Optical properties of polycrystalline CdS films
Authors: Cook R. K. , Christy R. W.
Published: February 2003

Optical spectra of CdS films vacuum evaporated onto fused silica substrates were measured in reflection and transmission for photon energies from 0.5 to 6.5 eV. For films of about 2000 Å thickness (determined from the optical measurements), the spectral structure, especially from 4 to 6 eV, differs markedly from that of single crystals and depends on the substrate temperature (up to about 200 °C) during deposition. The changes are correlated with critical points in the joint density of states from band-structure calculations and are attributed to grain-boundary disorder in the CdS on room-temperature substrates, together with some surface roughness on the high-temperature substrates.
Sputter-induced isotopic fractionation at solid surfaces
Authors: Watson C. C. , Haff P. K.
Published: February 2003

Elemental and isotopic mass fractionation in both binary and multicomponent media are investigated within the framework of the familiar collision-cascade model for sputtering. Some of the most salient features of the phenomenon are explicable on this basis. It is found that the partitioning of beam-deposited energy among the various target components can account for differentiations in the secondary recoil fluxes only on the order of one part per thousand, indicating the importance of the surface potentials when large enrichment effects occur. A mechanism governing the translation of internal recoil fluxes into external sputtered fluxes is proposed in order to account for isotopic fractionation, for which the surface binding effects are assumed to be negligible. The predicted initial fractionations are δf(40Ca : 44Ca) =33 parts per thousand in the calcium-containing mineral plagioclase and δf(40Ca : 44Ca) =24 parts per thousand in CaF2, in reasonable agreement with recent data on isotopic fractionation.
Phase-sensitive detection of electron-beam-induced desorption from ZnO
Authors: Shapira Y. , Friedenberg A.
Published: February 2003

We report a method of phase-sensitive detection of desorption from surfaces bombarded by a properly modulated electron beam. Mass-spectrometer signals detected by this method assure a high sensitivity and selectivity of the results. This method is used here for studying surfaces of ZnO powders, and it found that CO2 is the only desorbed species during electron bombardment of such surfaces. Following the CO2 desorption kinetics simultaneously with the associated surface conductivity change, we find one-to-one correspondence between both quantitites. Furthermore, the rates of the electron-induced CO2 desportion and the surface conductivity are in a very good agreement with a theoretical model, previously developed for photodesorption. This model predicts a slowing of the desorption rate due to the buildup of an electron accumulation layer and a corresponding band bending which hinder irradiation-generated holes from reaching the surface and neutralizing CO−2 species chemisorbed on it. Our observations seem to support this model together with pointing out the similarities between electron- and photon-induced desorption in this case.
Structural and compositional properties of the PbS-Si heterojunction
Authors: Elabd H. , Steckl A. J.
Published: February 2003

The physical and chemical structure of thin-film PbS deposited from chemical solution on monocrystalline Si substrate was studied by electron microscopy, x-ray diffraction, and Auger electron spectroscopy. The as-grown PbS has been found to consist of a uniform polycrystalline film. The crystallite size and orientation were found to depend on the orientation of the substrate and were observed to vary between 0.25 and 0.4 μm. Low-temperature treatment of the PbS film was found to be an effective method for revealing the film structure, without altering the grain size. A secondary PbS macrostructure consisting of isolated chainlike clusters was found to coexist with the thin film. The dimensions of the clusters were generally up to an order of magnitude larger (∼3–5 μm) than the thickness of the film (0.5 μm). The microstructure of the cluster was found to be similar to that of the film, consisting of crystallites of the same size. The chemical structure of the PbS film and of the PbS-Si interface was investigated by Auger electron spectroscopy in conjunction with argon ion sputtering. Chemical depth profiles indicate a PbS film of uniform composition. No major contaminants were observed in the bulk of the film. A peak in oxygen content was found to exist at the PbS-Si interface and at the surface of the PbS film. Heat treatment in air increased the oxygen peaks substantially and reduced the sulfur concentration at the film surface.
Transient solution for megajoule energy release in a lumped-parameter series RLC circuit
Authors: Barnes Gene , Dannenberg Robert E.
Published: February 2003

A method is developed for optimizing the energy release from a megajoule capacitive discharge in a series RLC circuit with an RL load. Both the resistance and inductance of the load are represented by effective values that characterize their behavior during the discharge. Using Kirchhoff’s laws, equations utilizing the load impedance and the external circuit impedance are derived for determining the instantaneous load voltage and energy characteristics. A program (ERES) computes and displays the load characteristics and the circuit current. Use of the ERES program allows a designer to perturbate values of the circuit elements in order to produce the desired time distribution for the load energy input.
Theory of the electrical and photovoltaic properties of polycrystalline silicon
Authors: Ghosh Amal K. , Fishman Charles , Feng Tom
Published: February 2003

Grain boundary states play a dominant role in determining the electrical and photovoltaic properties of polycrystalline silicon by acting as traps and recombination centers. The recombination loss at grain boundaries is the predominant loss mechanism in polycrystalline solar cells. Cell parameters are calculated based on a transformation of grain boundary recombination centers to a uniform distribution of such states throughout the grain. Effective carrier lifetime is expressed in terms of grain size, allowing calculation of short-circuit current, open-circuit voltage, and fill factor. Excellent agreement is observed between theory and experiment for almost all device parameters. It is indicated that one could fabricate 10% efficiency polycrystalline solar cells from 20-μm-thick material if the grain size exceeds 500 μm.
Maxwell stresses at charged metal surfaces from thin-film elastoresistance
Authors: Lischner D. J. , Juretschke H. J.
Published: February 2003

Thin metal films, when charged electrostatically, show a change of electrical conductance quadratic in the applied surface-charge density. The sign and magnitude of this signal, as well as its sensitivity to mechanical constraints of the sample, are compared to a model based on the elastoresistive response of the metal film to the Maxwell stresses accompanying electrostatic charging. The agreement for Ag, Au, Cu, Al, and Sb on mica is satisfactory. Apart from elucidating one of the basic electrical responses of metals to charging, the effect lends itself to studying the mechanical constraints imposed on metal films by the metal-substrate coupling, and by external surface layers. Some examples of such interactions are discussed.
On the boundary conditions of Schottky-barrier BARITT devices
Authors: El-Gabaly M.
Published: February 2003

A current-dependent boundary condition appropriate for Schottky-barrier BARITT devices is developed. The rf performance of the device based on this boundary condition is theoretically investigated. The computed results are found to be in close agreement with available experimental data. It is shown that the rf performance is greatly degraded at dc currents close to the saturation value of the metal-semiconductor contact. This limitation is due to the depletion of the injected holes at the forward biased contact. The device rf power capability can be improved if the device is made of a metal with low-barrier height for holes and a semiconductor with a high-impurity doping density.
A calculation of the surface potential in the vicinity of a channel stop in a charge-coupled device
Authors: Schechter Daniel
Published: February 2003

Using Green’s function techniques, the surface potential at a channel stop formed by a sharp increase in doping density is calculated. The calculation is done using four models of increasing complexity. Sample numerical computations are done for an uncharged CCD in order to evaluate the different models. The dependence of surface potential on various device parameters is then evaluated.
Magnetic properties and ferromagnetic resonance in amorphous Gd alloys
Authors: Buschow K.H.J. , Algra H. A. , Henskens R. A.
Published: February 2003

An investigation is reported of the magnetic properties of various amorphous alloys of Gd and Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Pt, or Ga by means of magnetic measurements and ferromagnetic resonance. The Curie temperature and the saturation magnetization were determined for each of these alloys, and the crystallization temperature was obtained by means of a differential scanning calorimeter. The presence of hysteresis and a high remanence in the magnetic isotherms of 4.2 K indicate that the coupling between the Gd spins is predominantly ferromagnetic. For Gd70Ru30, the linewidth ΔH of the resonance line was studied as a function of temperature. A substantial increase of ΔH was observed in a broad temperature range around Tc, instead of a sharp divergence as expected in the case of crystalline materials at Tc. This is in keeping with the presence of a broad distribution of local magnetizations in these alloys. From the ferromagnetic resonance experiments it was also possible to estimate the magnetocrystalline anisotropy. The values for the uniaxial anisotropy constants Ku were found, in general, to be positive (∼106 ergs/cm3). It is argued that this anisotropy originates from an anisotropic exchange interaction between the purely S-state spins, proceeding via the 5d electrons.
Particle trajectories in a lattice of parallel magnetized fibers
Authors: Simons William H. , Treat Richard P.
Published: February 2003

Trajectories of paramagnetic particles in infinite rectangular and rhombic lattices of parallel fibers are calculated. The mathematical model for this analysis accounts for the magnetic and fluid perturbations of all the fibers in the lattice. The fluid field is approximated by potential flow, the viscous force on the particle is assumed to be the Stokes force, and particle diffusion and inertia are assumed to be negligible. For closely packed fibers, the particle collision cross section for a fiber in a lattice is found to differ significantly from the isolated fiber cross section. As one expects, they become equal as the filter porosity approaches unity. Channels are formed allowing particles to pass through the lattice. The channels can be made as narrow as desired by increasing the ratio of magnetic to viscous forces; however, they persist for arbitrarily large porosity. The differences between the filter efficiencies obtained from the isolated fiber model and the regular lattice model are compared. It is suggested that the isolated fiber theory, by neglecting shadows in the particle density cast by upstream fibers, predicts an efficiency that is higher than the efficiency of a real filter. On the other hand, the regularity within the lattice model maximizes the effects of shadows, hence the efficiency predicted by that model is too low.
Elastic-constant variability in stainless-steel 304
Authors: Ledbetter H. M. , Frederick N. V. , Austin M. W.
Published: February 2003

Variability of elastic constants in stainless-steel 304 was determined by measuring longitudinal and transverse ultrasonic velocities in 20 samples acquired randomly. Three kinds of variations—sample to sample, directional within a sample, and repeated measurements on a single sample—are reported for four elastic constants: the bulk modulus, Young’s modulus, shear modulus, and Poisson’s ratio. Because of surprisingly small variations, 1% or less, the principal problem became measurement sensitivity and reproducibility. To overcome this problem, a high-resolution measurement system was devised using general-purpose equipment augmented with a very simple impedance-transforming amplifier and an FET transmission gate. With this system the often-reported troublesome transit-time correction disappeared. Effects due to frequency and directionality were negligible.
Coupling of spherical-surfaced LED and spherical-ended fiber
Authors: Hasegawa Osamu , Namazu Ryosuke , Abe Masayuki , Tōyama Yoshikazu
Published: February 2003

The coupling of a spherical-surfaced LED and a spherical-ended fiber is analyzed using a model in which a light source and an aperture stop are on the anterior and posterior focal planes, respectively. The launching efficiency is defined as the ratio of the power launched into a fiber to the optical power generated in the LED. The efficiencies for step- and graded-index fibers are derived. Maximum efficiency can be obtained when d0=dc, where d0 is the emitting diameter and dc is the critical diameter defined by the focal length and the critical angle of the fiber. When d0?dc, the ratio χ of improvement in the efficiency for a spherical-surfaced LED to that for a flat LED is approximately proportional to the square of the lateral magnification β, which is the image diameter divided by d0. χ?β2 is confirmed experimentally with couplings using spherical-surfaced and flat LED’s.
Pulse amplification in high-power iodine laser
Authors: Farcy J. C. , Huguet M. , Guyot J. C. , Savry D. , Guillet H.
Published: February 2003

Amplification of 0.6-, 1.6-, and 100-ns pulses has been measured in a test amplifier up to 3 atm. total pressure and a small signal gain ranging from 5.5 to 19 dB. A simple model based on a Frantz and Nodvick formulation provides good agreement with the experimental results for 0.6–1.6-ns pulse duration and can be useful for an iodine laser system design.
Surface oxidation of Fe from a Cu(Fe) alloy observed by Mössbauer spectroscopy
Authors: Williamson D. L. , Yeatts F. R.
Published: February 2003

A new iron oxide is found to form on the surface of a Cu–0.2 at.% Fe alloy foil between 843 and 919 K under oxygen partial pressures of less than 10−5 Torr. The growth rate is controlled by the diffusion of dissolved Fe to the surface. The 57 Fe Mössbauer resonance of the oxide consists of two quadrupole pairs at 298 K both indicative of the Fe2+ oxidation state. A phase transition occurs in the oxide below 298 K such that only a single quadrupole pair remains at 76 K.
XPS and AES studies on oxide growth and oxide coatings on niobium
Authors: Grundner M. , Halbritter J.
Published: February 2003

Niobium surfaces show features that have been blamed on the unavoidable oxidation that occurs during the preparation of the Nb. To quantitatively measure the oxidation, XPS and AES profile measurements have been carried out for the typical procedures used in the preparation of Nb surfaces, such as ultrahigh vacuum annealing (UHV), oxipolishing (OP), electropolishing (EP), or handling in air, H2O, and H2O2. For the different surface preparations the oxidation proceeds as follows: At the Nb surface an inhomogeneous Nb2O-NbO layer 1 nm or less thick exists which does not seem to depend much on oxidation technique. Then a dielectric oxide Nb2O5 grows homogeneously in UHV (?2 nm) or in OP(?3 nm), whereas EP(?3 nm) yields rough oxide layers that pick up impurities and charges easily. With time, all oxides grow more or less rapidly to a stable thickness of 6 nm. These results explain the observed behavior of Nb surfaces, especially their responses to the most sensitive measurements, namely, in superconducting rf cavities and tunnel junctions.
Optically induced transient electron paramagnetic resonance phenomena in GaAs:Cr
Authors: White A. M. , Krebs J. J. , Stauss G. H.
Published: February 2003

The dynamics of EPR spectra of the charge states of Cr in GaAs during and following optical excitation are profoundly determined by the presence of other traps. Transients are slow, nonexponential, not thermally activated, and sample dependent. We show that the instability of Cr1+ and Cr2+ at low temperatures (< 10 K) is not thermal, but due to interimpurity transitions involving hole traps 0.45 eV from the valence band. The particular complexities of the GaAs:Cr system are described, but still allow the self-consistency of the EPR and earlier data to be demonstrated.
Ion content of air humidified by boiling water
Authors: Carlon Hugh R.
Published: February 2003

Careful measurements have been made of the ion content of air humidified by boiling water. A very sensitive cell of new design was used, having 40 parallel plates with a total area of 6.6×104 cm2 spaced 0.66 cm apart. A compensating cell with much smaller plates but with an identical insulator configuration was used to correct moist air conductivity data and to study insulator leakage. Results show that unexpectedly high concentrations of small ions (106–107/cm3) are present in air humidified by boiling water and that, in a closed container, a high ion concentration can be maintained for several hours after water vapor generation by boiling water has ceased.
Interaction of magnetoelastic wave with drifting carriers in a ferrite-semiconductor hybrid structure
Authors: Yukawa Toshinobu , Ikenoue Jun-ichi , Shingai Shigeru , Abe Kenji
Published: February 2003

The interaction of horizontally polarized shear (SH) magnetoelastic waves with drifting carriers is analyzed in a ferrite-semiconductor hybrid structure. Wave amplification occurs when the drift velocity of carriers exceeds the phase velocity of the wave. The more magnetostatic the wave, the stronger the interaction of the wave with carriers. The imaginary part of the wave number increases linearly as the drift field (or the drift velocity of carriers) increases, is proportional to the conductivity of the semiconductor, and takes a maximum value in the vicinity of the cutoff frequency of ferrite-air (FA) modes. These results are supported by an approximate solution for the imaginary parts of the wave numbers for the magnetoelastic surface wave interacting with a semiconductor. It is clear that elastic waves and carriers can interact through the medium of the magnetostatic surface wave by means of magnetoelastic coupling and interaction between the magnetostatic surface wave and carriers.
Efficient production of hot plasmas through multiple-wire implosion in transmission line generators
Authors: Bloomberg H. W.
Published: February 2003

Model equations for the implosion of multiple-wire arrays mounted across the electrodes of a transmission line generator are used to obtain an expression for the energy-coupling efficiency. For a useful class of imploding loads, the efficiency is shown to depend on a single dimensionless parameter. Furthermore, the efficiency curve has a maximum, and this permits an explicit optimization of the wire load parameters in terms of the machine parameters.