bluuebunny/crossref_metadata_2025 huggingface dataset:
An electronic heat capacity, magnetic and crystallographic study of the YFe3−xNix system
Authors: Moskaitis R. J. , Butera R. A.
Published: February 2003

The electronic heat capacity, magnetic and structural properties of the ternary YFe3−xNix system, with 0<x?3, have been investigated. All compounds have been found to crystallize in the PuNi3 type structure. The variation of the lattice parameters, saturation magnetization values and electronic heat capacity coefficients with increasing nickel content has been obtained over the entire range of x. The heat capacity and magnetic results can be discussed in terms of the rigid band model.
Energy splittings of transition metal ions in non-cubic hosts
Authors: Hedgcock F. T.
Published: February 2003

A number of recent experiments have shown evidence for energy splittings of paramagnetic ions in metallic hosts. Although theoretical attempts have been made to calculate so called ’’crystal field effects’’ in metals from first principles very little qualitative progress has been made on this very difficult subject. In this paper we wish to present a short summary of experimental results on the energy splittings of the manganese ion in h.c.p. hosts: Mg, Zn and Cd and also the energy splittings of two species of transition metal ions Mn and Cr in the same host-metal, zinc. This summary of results will be compared with the recent theoretical work of Smith who considers spin-orbit effects in metals. At least semi-qualitative agreement is found in that the observed energy splittings scale with the spin-orbit parameter of the host and the magnitude of the local moment-conduction electron exchange interaction strength.
Crystal field properties of Yb2Ti2O7
Authors: Dunlap B. D. , Shenoy G. K. , Friedt J. M. , Meyer M. , McCarthy G. J.
Published: February 2003

Electronic properties of Yb3+ in Yb2Ti2O7 have been investigated using the 84.6 keV Mössbauer transition in 170Yb. The crystal field parameters have been deduced by analyzing spectra taken in various externally applied magnetic fields up to 32 kG at temperatures of 4.2 K and 1.6 K. Because of the hexagonal point symmetry at the Yb ion, the crystal field levels are sensitive to the direction of the applied field relative to the c axis. As a result, a proper discussion of the field and temperature dependence of the hyperfine parameters is not possible for a powder sample without a careful average over angles. Such an analysis then yields a value for the crystal field parameter B02 in the range 15–21 K and B04/B02 ?0.01. These parameters and the resulting crystal field eigenfunctions have been used to explain the small quadrupole interaction present in this material.
Redistribution of the conduction band density of states near ferromagnetic saturation in EuS
Authors: Schoenes J. , Nolting W.
Published: February 2003

We report new absorption measurements on (100) textured EuS films in the 4f7→4f65dt2g transition energy range. For low fields (H<0.2T) the whole absorption peak shifts continuously to lower energies between 70 K and 5 K. If the magnetic field is increased at T=5.5 K so as to saturate the sample, a striking change of the spectrum is observed. The absorption increases in the low energy part of the peak, while it diminishes at higher frequencies, leading to the appearance of a pronounced shoulder in the spectrum. A new theoretical approach is presented, which indicates that the conduction band splits into 12 quasiparticle bands due to the exchange interaction. The spectral weights of these subbands are strongly dependent on the magnetization 〈Sz〉 of the f-system and on the population of the conduction band. A numerical estimate for the 〈Sz〉 dependence of the spectral weights of these subbands agrees qualitatively with the observed behavior of the absorption spectrum of EuS.
Thermodynamic behavior of quenched random magnets from a position-space renormalization group
Authors: Wortis Michael , Jayaprakash C. , Riedel Eberhard K.
Published: February 2003

The inhomogeneous generalization of the Migdal-Kadanoff approximate recursion relations is used to study the properties of Ising magnets with spatially random (quenched) couplings. Simple calculations in two dimensions produce qualitatively reasonable phase diagrams and critical exponents for both a dilution problem (nearest-neighbor couplings 0 and J) and a spin-glass system (nearest-neighbor coupling +J and −J. Other related work is briefly reviewed.
Study of the bicritical region of the biaxial antiferromagnet MnCl2⋅4H2O
Authors: Butera R. A. , Rutter D. R.
Published: February 2003

The bicritical region of the phase diagram of manganous chloride tetrahydrate has been investigated by the determination of the heat capacity as a function of temperature at constant applied magnetic field. The experiments were repeated at field increments of 10 to 50 G in the region of the bicritical point. Plots of the heat capacity maxima in the H-T plane clearly exhibit an umbilicus at the bicritical point. These data have been fit to the expression given by Fisher and Nelson following the procedure for locating the appropriate scaling axes given by Fisher. The ratio of the amplitudes of the slope of the phase boundaries in the region of the bicritical point has been determined to be 1.000±0.006, which is not consistent with the theoretical prediction of 2.51 for a uniaxial antiferromagnet. These results and also the variation of the behavior of the phase boundaries in the bicritical region as a function of the angle between the applied magnetic field and the spin axis is discussed.
Dynamic scaling and corrections to scaling near bicritical and tetracritical points
Authors: Dohm V. , Janssen H. K.
Published: February 2003

We study the critical dynamics of stochastic models appropriate for describing bicritical and tetracritical points in anisotropic antiferromagnetic systems. The dynamic exponents and the transient exponents are calculated by renormalized field theory up to two-loop order. In the presence of reversible mode-coupling terms, two-loop contributions establish bicritical dynamic scaling in the restricted sense and invalidate recent predictions based on mode-coupling arguments. In the case of an n-component relaxational model total dynamic scaling is found to O (ε2) both at the bicritical (n≲3) and the tetracritical (4≲n<11) points.
Tricritical scaling in the spherical model limit
Authors: Sarbach Stephane , Fisher Michael E.
Published: February 2003

The tricritical scaling properties of the n-component continuous-spin model are investigated in the sphercal model limit, n→∞, with special emphasis on the odd fields h and h3. A full scaling description of the tricritical region for 3<d<4 necessitates the recognition of a dangerous irrelevant variable, p, related to the inverse range of the pair interaction. As the lambda line in zero field (h=h3=0) is approached, p becomes important and determines the correct spherical model exponents. Setting p=0 gives only classical theory; away from the lambda line p yields corrections to scaling of Gaussian character. The wing critical exponents arising for h≠0, h3=0 and T<Tt are classical. Furthermore, for h3≠0 classical behavior is found even on the lambda line above Tt which, in fact, continues into one of the wing critical lines. Some consequences for real tricritical behavior are reviewed.
Scaling functions for quantum crossover
Authors: Lawrie I. D. , Fisher Michael E.
Published: February 2003

The critical properties of d-dimensional Ising models in a transverse magnetc field, Hx=Γ, are considered. A quantal generalization of the Landau-Ginzburg-Wilson free-energy functional, introduced by Hertz and Young, has been treated by a variational approximation of the Hartree type. Behavior near the critcal line, Γ=Γc(T), is governed by the exponents of the d-dimensional spherical model. However, quantal crossover occurs on approach to the T=0 multicritical point at Γ=Γc(0) and this is characterized by the exponents of the (d+1) -dimensional spherical model (which are mean-field-like for d+1≳4). Crossover scaling functions, valid near the multicritical point, are reported for the susceptibility. The quantal crossover exponent φT, is equal to νd+1=1/(d−1), the (d+1) -dimensional correlation length exponent for 2⩽d⩽3, as suggested by ideas of Suzuki, but for 3<d⩽4 we find instead φT= (1/2)(4−d); for d≳4 no crossover occurs.
Critical behavior of a 3-D Ising model in a random field
Authors: Landau D. P. , Lee H. H. , Kao W.
Published: February 2003

A Monte Carlo method has been used to study a simple cubic Ising ferromagnet in a random quenched magnetic field. The Hamiltonian for this model is ℋ==JΣ(ij)σiσj−ΣiHiσi, where σi,σj=±1, J is the nearest-neighbor interaction constant, and the field Hi=tH is fixed at each site with ti=±1 at random and Σti=0. L×L×L lattices with periodic boundary conditions have been studied for a range of H and T. As expected we find a ferromagnetic ordered state which for small H undergoes a second order phase change to the paramagnetic state with increasing temperature. A finite size scaling analysis of the preliminary data suggests that the critical exponent β is substantially smaller (β∼0.2) than the usual 3-dim Ising value of 0.31. Results obtained for small lattices indicate that below kT/J-2 the transition becomes first order suggesting that a tricritical point appears on the critcal field curve.
Percolation and magnetic order in diluted spinels
Authors: Hubsch J. , Gavoille G. , Bolfa J.
Published: February 2003

This paper is concerned with the magnetic range order in diluted ionic compounds of spinel structure. When the concentration of magnetic ions decreases, long range order decays into short range order and disappears for a critical concentration. The critical concentrations are calculated from the de Gennes approximation for the (A) and (B) sublattices and for the whole crystal. That allow us to derive the phase diagram of magnetic range order. Neutron diffraction experiments as well as magnetic measurements reveal the disappearance of long range magnetic order with the dilution on both sublattices and the transition between two different magnetic orders with the dilution on one sublattice only. In both cases, short range magnetic order is already present well above the percolation threshold. Experimental results are in good agreement with the diagram.
New method for investigating the magnetic phase diagram of metamagnets
Authors: Shang H-T. , Huang C-C. , Salamon M. B.
Published: February 2003

A new method of determining the phase diagram of metamagnets has been developed and applied to the tricritical region of FeCl2. The specific heat, measured by an ac method, shows discontinuities at the phase boundaries. The phase boundaries in the applied field-temperature plane, the critical exponent βu, and the specific heat along the mixed-phase boundaries have been determined.
Tricritical behavior in randomly disordered Fe1−xCl2 : Cdx
Authors: Egbert Wm. C. , Yen W. M. , Farge Y. , Jamet J-P.
Published: February 2003

We have determined the magnetic phase diagrams of Fe1−xCl2 : Cdx (x=0, 0.09, 0.11, 0.17, 0.24). Below the tricritical temperature Tc the antiferroparamagnetic mixed phase is easily detectable because it strongly scatters visible light. This light scattering allowed us to map the first order phase boundaries up to Tc. Above Tc the optical density of the 426.8 nm absorption line changes at the continuous phase transition. Well defined tricritical and Néel temperatures were observed in each sample. Randomly quenched disorder introduced by the cadmium impurities reduced Tn and Tc but did not destroy the tricritical behavior. We present phase diagrams for each of the doped samples and plot Tn, Tc, and Hc (the critical field) as functions of Cd concentration.
Forced magnetostriction of dysprosium aluminum garnet (DAG)
Authors: Dillon J. F. , Gyorgy E. M. , Blount E. I. , Chen E. Yi , Van Uitert L. G.
Published: February 2003

Using double strain gauges, the mangetostriction parallel and perpendicular to the applied field of the Ising-like antiferromagnet DAG has been measured as a function of applied field below TN=2.54 K. A magnetic field along [111] couples to the antiferromagnetic order parameter, and the two time reversed states at zero field (A+ and A−) can be separately prepared by specific field-temperature treatments. The parallel and perpendicuar strains may be combined to give a volume magnetostriction ? and an axial distortion ?. For A+ and A−, ? is flat with field; there is an abrupt increase in volume at the metamagnetic transition. In contrast, for A+ ? is odd in field, and shows a contraction along [111] for increasing field. In the paramagnetic state the contraction continues with increasing ‖H‖. The results will be compared with earlier birefringence data and discussed in terms of (a) the modification of g values on individual sites and (b) the modification of spin-spin interactions by strain.
Phase diagrams of the isotropic antiferromagnets RbMnF3 and KNiF3 from ultrasonic measurements
Authors: Shapira Y. , Oliveira N. F.
Published: February 2003

The magnetic-field dependence of the order-disorder transition temperature Tc in RbMnF3 and KNiF3 was measured in fields H up to 180 kOe. In both of these very nearly isotropic cubic antiferromagnets, Tc(H) increases with increasing H at low H, as predicted by Fisher, Nelson and Kosterlitz. The values for the crossover exponent φ obtained from the data for two RBMnF3 samples are 1.278±0.026 and 1.274±0.045, compared to the theoretical value 1.250±0.015.
Electronic spin-dynamics at a structural phase transition by cooperative Jahn-Teller effect: An Al27 NMR study in PrAlO3
Authors: Borsa F. , Corti M. , Rigamonti A.
Published: February 2003

The temperature dependence of the Al27 nuclear spin-lattice relaxation rate has been measured in PrAlO3 in the temperature range 77–700 °K, and particularly around the structural transitions at 205 °K and at 151 °K driven by cooperative Jahn-Teller effect (CJTE). The Al27 relaxation is caused by the fluctuations in the nuclear-electron magnetic dipolar interaction and it is proved that the fluctuations are not directly driven by the exchange interaction but result from transitions among the crystal field (CD) levels of the Pr3+ ion. The main temperature behavior of the relaxation rate has been analyzed by extending the theory by Myers and Narath for the nuclear relaxation in the RE monophosphides. Values of the effective exchange interaction of the order of 𝒞J/h/=1012–1013 rad sec−1 are derived for NdAlO3 and PrAlO3. The main features of the Al27 T−11 temperature dependence in PrAlO3 are explained by referring to the known CF levels and their modifications at the CJTE phase transitions. No sizeable anomaly directly associated to a possible softening of electronic phonon coupled modes was detected, probably because the ground orbital doublet of Pr3+ is non-magnetic.
Riedel anomaly and nonlinear effects in Josephson point contacts
Authors: Thome H. , Couder Y. , Libchaber A.
Published: February 2003

We present experiments on photon-assisted tunneling and ac Josephson effect using microwaves in an energy range 1.05<hν<2.2 meV of the same order of magnitude as the superconducting gap 0.6<2Δ<4 meV. We show that, whereas the photon-assisted tunneling shows no anomaly in this region, the amplitude of the Josephson steps is strongly affected by the Riedel anomaly. Furthermore, the results under strong irradiations show an indirect evidence of a decrease of the gap value by the creation of quasiparticles.
Stirling-cycle rotating magnetic refrigerators and heat engines for use near room temperature
Authors: Steyert W. A.
Published: February 2003

The application (or removal) of a magnetic field to the ferromagnetic Gd metal near its Curie point (293 K) will produce adiabatic heating (or cooling) of 14 K or isothermal expulsion (or absorption) of 32 kJ of heat per liter of Gd metal. A refrigerator and a heat engine are described for which porous Gd metal forms the rim of a wheel rotating into and out of a magnetic field region. Fluid forced to flow through the porous metal exchanges heat; the field and flow configurations are such that the metal executes a magnetic Stirling cycle allowing a very wide temperature span (many times 14 K) while maintaining the 32-kJ/l capacity. Efficiencies approaching that of Carnot are expected at 1-Hz rotation rates, resulting in 32-kW/l refrigeration or heating capacity.
Rotating Carnot-cycle magnetic refrigerators for use near 2 K
Authors: Steyert W. A.
Published: February 2003

The application or removal of a magnetic field of order 5 T to some Gd compounds at low temperatures results in 10–20 K adiabatic temperature changes or the isothermal expulsion or absorption of heat. In particular, the heat absorbed by 1 liter of appropriate magnetic material at 2 K is several hundred J. A rotating device is decribed which will allow cycle times of much less than 1 sec, resulting in approximately 1-kW refrigeration capacity for each liter of paramagnetic Gd compound. This heat could be expelled with better than 80% of Carnot efficiency into a helium refrigerator operating at 10–14 K.
Visual ion-beam images produced by electron and ion-beam interaction on surfaces
Authors: Fine Joseph , Gorden R.
Published: February 2003

Two-dimensional images of 1–5-keV ion beams incident on solid surfaces have been obtained by a method similar to that used in a scanning electron microscope. This easily applied technique produces visual real-time images, whose size correlates well with beam-current profile measurements; actual photographs of two such images obtained for different width ion beams are presented. Various target materials have been examined, but only insulators were found effective in producing ion-beam images by this method. Some mechanisms that may relate to the interaction of ion and electron beams on surfaces are discussed. Those processes that seem to be basic to understanding the surface interactions responsible for this imaging effect are enhanced surface conductivity and charge neutralization. The technique itself has direct application to ion-beam alignment and diagnostics. The use of coincident ion and electron beams presents a new technique that is potentially useful for the investigation of surface interactions.
The structure and composition of rf reactively sputtered MoSx films
Authors: Reichelt K. , Mair G.
Published: February 2003

Molybdenum sulfide films have been deposited by reactive sputtering of molybdenum in a hydrogen sulfide/argon atmosphere and by sputtering of molybdenum disulfide in pure argon atmosphere at substrate temperatures between room temperature and 480 °C. The structure and composition of the films have been determined as a function of hydrogen sulfide partial pressure and substrate temperature by transmission electron microscopy (TEM) and Rutherford ion backscattering, respectively. The experiments showed that at hydrogen sulfide partial pressures above 2×10−4 Torr, MoSx films had a rhombohedral structure with 0<x<2.2. The dependence of the film thickness on the hydrogen sulfide partial pressure has been studied. The dependence of the composition on the substrate temperature is interpreted by a different dependence of the sticking coefficient of the components on the temperature.
Multiple photon absorption of anharmonic molecules in cw laser beams
Authors: Steverding B. , Dudel H. P. , Gibson F. P.
Published: February 2003

The average excitation level of anharmonic molecules in cw beams is determined as well as the distribution of excited states. The deactivation process consists of relaxation, diffusion, and convection. For low excitation levels, a closed solution can be obtained for constant cross section. For higher excitation levels, the variation of the cross section has to be considered and numerical results are presented.
Matched plasma heating mode with moving boundaries
Authors: Harris Paul
Published: February 2003

The problem of a confined plasma created by laser interaction with a thin metallic layer is investigated for the case of time-dependent confinement boundaries. The self-regulating ablative (SRA) model is applied to obtain the time dependence of plasma pressure, temperature, and density. Krokhin’s time-independent boundary solutions are obtained as special cases.
Electron density distribution in a conical laser plasma tube
Authors: Ventrice Carl A.
Published: February 2003

The electron density distribution is determined for a low-pressure gas in a conical plasma tube. The distribution is found to vary in the radial direction as a spherical Bessel function and in the ϑ direction as a Legendre polynomial, the order of which is proportional to L/a.
Plasma deposition of GaP and GaN
Authors: Knights J. C. , Lujan R. A.
Published: February 2003

We report the preparation of thin films of gallium phosphide and gallium nitride by deposition from low-pressure rf-excited plasmas in mixtures of trimethylgallium with ammonia and phosphine, respectively. With the deposition conditions used, the gallium phosphide is found to be amorphous, while the gallium nitride is polycrystalline. We present preliminary measurements of optical and electrical properties.
Photovoltaic properties of ZnCdS/CdTe heterojunctions prepared by spray pyrolysis
Authors: Yin Shaiw-Yih , Fahrenbruch Alan L. , Bube Richard H.
Published: February 2003

A series of photovoltaic heterojunctions of the type n-Zn0.1Cd0.9S/p-CdTe have been prepared by spray pyrolysis of ZnCdS films on single-crystal CdTe with variation of the CdTe substrate temperature and of the postdeposition heat-treatment temperature in hydrogen. Open-circuit voltages as high as 0.82 V are observed compared to maximum values of 0.74 V observed for n-CdS/p-CdTe junctions also prepared by spray pyrolysis. Cell efficiencies are in the 6–8% range without correction for reflection losses.
Experiments on simple magnetic model systems
Authors: de Jongh L. J.
Published: February 2003

A number of experiments on magnetic insulating systems is reviewed which bear upon the following subjects: (i) the magnetic XY model, (ii) the quadratic Heisenberg magnet, (iii) magnetic double-layers, (iv) lattice-dimensionality crossovers, (v) singlet–ground state systems, (vi) magnetic systems doped with magnetic or nonmagnetic impurities.
Theory of spin-Peierls transition in Heisenberg and Hubbard models
Authors: Penson K. A. , Holz A.
Published: February 2003

A spin-lattice dimerization occurring in a system of one-dimensional (1D) magnetic spins coupled to the lattice (Spin-Peierls instability) is studied for classical and quantum Heisenberg and for one- and two-band Hubbard models. Using the exact solutions it is shown for the classical case that second or first order lattice phase transitions (PT) are possible. For the isotropic quantum s=1/2 Heisenberg and Hubbard models using the variational principle it is shown that PT can only be of second order while the spin anisotropy and the presence of a second electronic band yield the first order PT. Some applications to PT in VO2 are also made.
Magnetic susceptibility of CuCl2⋅TMSO, a ferromagnetic spin 1/2 linear chain
Authors: Willett R. D. , Landee C. , Swank D. D.
Published: February 2003

The crystal structure of the title compound (TMSO≡C4H8SO) consists of linear chains of Cu ions with three bridging ligands (2 Cl, 1 O) between each pair of Cu ions. The susceptibility of the salt has been measured between 2.0 and 120 K on a PAR vibrating sample magnetometer and from 80 to 300 on a Faraday balance. The high temperature data shows positive deviation from Curie behavior, with a Curie-Weiss constant of 18.7 K. However, considerable interactions between chains exist and the χT vs T plot shows a maximum at T=7.5 K. The data has been analyzed with several one-dimensional models. At present, the best fit is obtained with an Heisenberg linear chain (J=24.6 cm−1) with a mean field correction for interchain interactions (ZJ′=−1.3 cm−1).
Piezoelectric method of determining viscosity at 40 kHz
Authors: Robinson William H. , Smedley Stuart I.
Published: February 2003

The torsional composite oscillator enables the viscosity, shear modulus, strain rate, and fluid thickness of nonelasticoviscous and elasticoviscous fluids to be determined quickly and accurately, making it a powerful technique for measuring both static and transient phenomena. In this paper the equations relating the measured Q and period to the fluid viscous properties are derived and the resulting viscosity for four nonelasticoviscous fluids from 10−3 to 2 Pa s is confirmed to 1/2% and better by comparison with literature values. Experimental arrangements and procedures are described which indicate how this technique can be used for strain rates from as low as ∼10−5–10−3 s−1 to as high as ∼105–107 s−1.
Convection in vertical high-pressure mercury arcs
Authors: Zollweg R. J.
Published: February 2003

Convection in wall-stabilized high-pressure arcs is found to be highly sensitive to the relative material properties of the discharge gases. A method has been found to experimentally determine net-radiative-emission coefficients that are consistent with more reliably calculated electrical and thermal conductivities. The electrical conductivity of mercury arcs obtained using the electron scattering cross section for mercury derived by Rockwood gives better agreement with experimental temperature profiles than does that obtained by use of McCutchen’s cross section. Using these material properties with a theoretical convection model, good agreement was obtained with measured arc-temperature profiles in the midplane, with the conical appearance at the bottom of the vertical arc and with the electrical properties. For 18-mm-i.d. walls and mercury pressures up to 13 atm, the reduction in radiation found for high mercury pressures was found to be caused by self-absorption and not by an increase in radial thermal conduction because of turbulence or shear-induced eddies. No evidence was found for such eddy diffusion, turbulence, or for multicellular convection.
Model for the unstable-resonator carbon monoxide electric-discharge laser
Authors: Milonni P. W. , Paxton A. H.
Published: February 2003

A computer model of the unstable-resonator CO electric-discharge laser is presented. The molecular kinetics model treats CO/Ar/He mixtures and includes the processes of VV and VT energy transfer, spontaneous and stimulated emission, electron collisions of the first and second kind, and one-dimensional gas flow with heat addition. Optical propagation in the unstable resonator is treated with diffractive calculations based on the Fast Fourier Transform. An assumed initial field distribution is propagated back and forth between the mirrors of the resonator and allowed to interact with the laser medium according to a thin-sheet gain model. These propagations are continued until successive ones yield nearly identical values for intensities, saturated gains, temperature, etc. These are the values predicted for the laser operating under the assumed conditions. The results of sample calculations are presented and discussed.
An embedded stripe DH laser monolithically integrated with a strip waveguide
Authors: Itoh Kunio , Ishikawa Kiyotsugu , Teramoto Iwao
Published: February 2003

Monolithic integration is described of an embedded stripe DH laser with an embedded strip waveguide of vapor-phase-grown GaAsP. The waveguide is composed of high-resistivity GaAs0.9P0.1 and surrounded by GaAs0.85P0.15, whose refractive index is slightly lower, to provide the optical confinement in both directions parallel and perpendicular to the guide plane. The intensity modulation of the output light was efficiently achieved by applying an electric field to the waveguide.
A study of lateral modes in wide double-heterostructure GaAs-GaAlAs laser diodes
Authors: Lengyel G. , Wolf H. D. , Zschauer K. H.
Published: February 2003

Higher-order lateral modes produced in wide GaAs-GaAlAs DH lasers were spectrally analyzed and photographed by the use of spatially resolved spectroscopy. These modes behave differently in mesa- and stripe-geometry lasers. They were studied in detail as a function of pumping current for the mesa structure. The spacing between lateral modes could be approximated by a simple model based on a sandwich-type symmetrical dielectric waveguide. Stripe-geometry lasers follow Hermitian-Gaussian mode patterns which are produced by parabolic refractive-index profiles. An anomalous development of mode intensities near threshold was observed in the mesa diode. Immediately above threshold, higher orders dominated the near-field patterns. Explanation for this could be found in the lateral optical gain profile produced by the interaction of the nonlinear characteristics of the p-n junction and the geometrical series spreading resistance of the substrate.
A note on the formation of the fireball plasma
Authors: Silberg Paul A.
Published: February 2003

A model for the formation of the fireball arc or spark discharge, sometimes called a fireball plasma, is developed based on the nonlinearity of the voltage-current characteristics of a high-current arc discharge. A nonlinear transmission line equation for the discharge current is obtained which is solved in terms of the Jacobi elliptic functions. Under certain prescribed conditions the current field collapses into a small region. This collapse of the current field is taken to be the fireball. It is additionally pointed out that nonlinearities other than the voltage-current characteristics of the high-current arc could produce similar results. Finally, it is suggested that Ball Lightning may have the same origin.
Self-focusing of a non-Gaussian laser mode in a dense plasma
Authors: Nayyar V. P.
Published: February 2003

This paper presents a study of the self-focusing of a high-power non-Gaussian laser beam operating in TEM01 mode in a strongly ionized plasma. The nonlinearity in the dielectric constant is caused by the nonuniform redistribution of carriers due to their inhomogeneous heating by the laser beam having transverse variation of intensity along its wave front. It is found that when the power of the beam exceeds the critical power, focusing effects are observed in the Y direction, whereas divergence of the beam takes place in the X direction. In the reverse case (when P<Pcr) the normalized beam-width parameter f2 first increases in the Y direction, after penetrating a certain depth it reaches a broadened maxima and then starts decreasing with the distance of propagation inside the medium. The beam continues diverging in the X direction. It has also been found that absorption brings about a reduction in the extent of self-focusing. When the absorption length is less than the self-focusing length appreciable self-focusing does not take place.
Crystalline to amorphous transformation in ion-implanted silicon: a composite model
Authors: Dennis John R. , Hale Edward B.
Published: February 2003

The transformation of silicon to the amorphous state by implanted ions was studied both experimentally and theoretically. Experimentally, the amount of transformed silicon and the critical ion dose necessary to amorphize the entire implanted layer were determined by ESR. How the critical dose varies with ion mass (Li, N, Ne, Ar, and Kr), ion energy (20–180 keV), and implant temperature (77–475 K) was determined. Theoretically, several phenomenological models were used to analyze these data. The overlap-damage model was used to determine the critical dose from the data, the size of the amorphous region around the ion track, and the degree of overlap damage required for amorphization. For all implants, the first ion created only predamage, while the second or third ion into the same region caused the amorphous transformation. The critical-energy-density model was in good agreement with the measured critical doses. This model assumed that a region would become amorphous if the energy density deposited into atomic processes by the ions exceeded the critical energy density of 6×1023 eV/cm3. For high-temperature implantations, out-diffusion models can explain the temperature dependence of the critical dose. Although the analysis is not completely definitive, the critical-energy-density model may also be valid at high temperature if diffusion of the damage energy is taken into account. This out-diffusion of energy from around the ion track occurs via a thermally activated process. Probably, the energy moves with the out-diffusion of the vacancies from the ion track.
The piezoresistance effect and dislocations in III-V compounds
Authors: Booyens H. , Vermaak J. S. , Proto G. R.
Published: February 2003

General expressions for the changes in resistivity and conductivity around 60°, edge, and screw dislocations as a consequence of the piezoresistance effect were calculated for III-V compounds. These expressions are discussed with reference to the symmetry of the crystal. The specific case of n-type GaSb is considered and it is shown that 60° and edge dislocations are surrounded by regions of increased and decreased conductivity parallel to the lines of the dislocations. It is also shown that the conductivity parallel to the line of a screw dislocation is increased irrespective of the sign of the Burgers vector. The results indicate that the dislocations can alter the bulk conductivity parallel to their lines and that they can play an important role in the threshold behavior of laser devices. Finally, it is shown that there are charging effects associated with the dislocations during device operation.
Current-crowding effect on current noise of planar resistors
Authors: Yoshida Hiromichi
Published: February 2003

A current-noise equation has been derived as a function of resistor geometry under some assumptions which are acceptable in usual cases. This equation is described by the integral formula. We can estimate the magnitude of current noise of an arbitrarily shaped planar resistor by integrating the square value of current density with current and field potentials. Application of numerical integration of the equation to an L-shaped resistor is described for instance.
Single thin-active-layer visible-spectrum In1−xGaxP1−zAsz heterostructure lasers
Authors: Chin R. , Holonyak N. , Kolbas R. M. , Rossi J. A. , Keune D. L. , Groves W. O.
Published: February 2003

Single active-layer visible-spectrum In1−xGaxP1−zAsz heterostructure lasers are described that exhibit quantum size effects (QSE) in photoluminescence and by means of diode injection (λ<6300 Å). Liquid-phase epitaxial (LPE) quaternary layers as thin as ∼300 Å have been realized. It is demonstrated that single thin-layer recombination wells (Lz<1000 Å) are very effective in the capture and recombination of carriers, even if injection occurs at some distance (a<1 μm) from the thin layer. On the other hand, optical confinement and absorption are weak in diodes with single active layers thin enough to exhibit QSE. This behavior indicates that the type of thin-active-layer diodes described here are not optimum as lasers, but may lead to improved light emitters.
Near-infrared laser action from acetone vapor
Authors: Barry J. D. , Brandelik J. E.
Published: February 2003

CO and CO2 laser activity has been produced by acetone decomposition in a glow discharge. A gas mixture of He-CH3COCH3-N2 was used. An oxidant was not introduced. Molecular decomposition allows a nonexplicitly introduced molecule to be involved in the laser process.
Birefringence of viscoelastic dielectrics under combined stresses
Authors: Nishitani T.
Published: February 2003

A birefringence relation for a nonlinear viscoelastic dielectric is theoretically deduced from the optical theory. The nonlinear viscoelastic dielectric is defined, i.e., the index tensor in the dielectric field is a function of the elastic strain tensor and the viscous strain tensor. Moreover, validity of the deduced relation is discussed with the results of experiments performed under the combined stresses of tensile stress and hydrostatic pressure.
Current limitation by an electric double layer in ion laser discharges
Authors: Torvén S.
Published: February 2003

A theory for current limitation in ion laser discharges is investigated. The basic mechanism considered is saturation of the positive-ion flux at an electric double layer by the limited flux of neutral atoms. The result is compared with a recently published synthesis of a large number of experimental data which agree well with those predicted by the double-layer model.
Stimulated Brillouin backscatter detection from a ϑ-pinch plasma
Authors: Armstrong W. T.
Published: February 2003

Detection of prompt stimulated Brillouin backscatter is reported from an experiment in which a high-power pulsed CO2 laser irradiates an independently produced ϑ-pinch plasma. Analysis of the backscatter signal indicates that significant SBS gain is limited to a time period near peak incident power. The restriction on SBS gain is attributed to a varying temperature gradient.
Dependence of the compaction of vitreous silica on the ionization dose
Authors: Primak William
Published: February 2003

Earlier data for the relationship of negative dilatation of vitreous silica to the ionization dose of 0.3 and 0.6-MeV electrons are clarified and corrected. Values are given for the maximum and the mean dilatations along the electron path in the material.
Reflection of a Gaussian ultrasonic beam from Al2O3 layer–stainless steel in water at the Rayleigh angle
Authors: Adler Laszlo , McCathern D. A.
Published: February 2003

The problem of ultrasonic wave reflection at a Rayleigh angle from Al2O3 layer–stainless steel in water was investigated. The so-called leaky Rayleigh velocity was measured by using an optical schlieren technique to identify the Rayleigh angle. The magnitude of the measured leaky Rayleigh velocity for the coated surface is smaller than the corresponding leaky Rayleigh velocity for either stainless steel or for Al2O3.
Profile of the carrier lifetimes in illuminated GaAs as a function of depth
Authors: Papaioannou G. I. , Euthymiou P. C.
Published: February 2003

The carrier lifetimes τ of illuminated semiconductors depend on the depth due to surface-recombination effects. In this paper the existence of this effect has been proven. The method is based on measurements of mean lifetimes ? as they are obtained from photoconductivity and the photomagnetoelectric effect for various penetration depths z of the illuminating irradiation. The form of the plots ?=f (z) is found to depend on the ratio of the ambipolar length over the Debye length showing a minimum of ? for La?lD (where La is the ambipolar diffusion length and lD is the Debye length). The results can be explained on the basis of a profile of carrier lifetime versus depth which has a minimum near the surface. Its position depends on the light penetration and, of course, on the surface-recombination velocity.
Radiation dose at the silicon-sapphire interface due to electron-beam aluminization
Authors: Galloway K. F. , Mayo S.
Published: February 2003

Recently, the process of metallization in an electron-beam evaporator has been shown to result in a buildup of trapped positive charge at the silicon-sapphire interface during the fabrication of silicon-on-sapphire devices. This charge buildup can be attributed to radiation damage produced by x rays generated by electron impact on the aluminum to be evaporated. This paper gives the results of calculations of the radiation dose in the sapphire near the silicon-sapphire interface due to the electron-beam-metallization process.
Hydrogen partial pressure in water photolysis
Authors: Rüfer H. , Würfel P. , Ruppel W.
Published: February 2003

The electric current flow upon illumination of the TiO2 electrode in an n-TiO2/KOH/Pt photolytic cell without auxiliary external voltage is related to the production of hydrogen or the reaction with dissolved oxygen at the Pt electrode depending on the electrolyte and the atmosphere above the electrolyte. Since hydrogen is produced with a pressure of much less than atmospheric pressure, no bubbles appear at the Pt electrode. The pressure and the production rate of the generated hydrogen are determined by the depth of immersion of the Pt electrode. The increase of both pressure and production rate of hydrogen upon application of an auxiliary voltage, as well as the energy-level diagram of the photolytic cell, are discussed on the basis of the experiments carried out without auxiliary voltage.
Resistance changes induced by electron-spin resonance in ion-implanted Si : P system
Authors: Murakami K. , Namba S. , Kishimoto N. , Masuda K. , Gamo K.
Published: February 2003

The ESR-induced changes in the dc resistance, Δρ/ρ‖ESR, of P-ion-implanted silicon have been observed for the first time. The transfer of absorbed Zeeman energy at liquid-He temperature has been investigated. The Δρ/ρ‖ESR signals observed were a narrow line with a g value of 1.9988 for light-dose implantation and a new broad line with a little larger g value for heavy-dose implantation. The line shape of these Δρ/ρ‖ESR signals was Lorentzian as well as the ESR signal, but the linewidth ΔH1/2 of the broad Δρ/ρ‖ESR signal was about 10 times as broad as the ESR linewidth. It is suggested that the anomalously broad line of Δρ/ρ‖ESR originates from the transfer of the Zeeman energy absorbed by the localized donor electrons at the tail regions with low donor concentration (5×1017<ND≲1.5×1018 P/cm3) to the layer with intermediate donor concentration (1.5×1018<ND≲3.7×1018 P/cm3) where the resistance changes take place. This transfer is caused by the existence of the peak regions with high donor concentration (ND≳2×1019 P/cm3) which act as Zeeman energy absorbers.
Stability of amorphous transition-metal films
Authors: Collver M. M. , Hammond R. H.
Published: February 2003

We have observed the temperature stability of the amorphous structure in many transition-metal-alloy systems (Nb-Mo, Ta-W, Nb-Zr, Mo-Ru, W-Re, Mo-Rh, Ta-Re, Zr-Mo, Ta-Ir, and Zr-Ru) prepared by electron-beam evaporation onto liquid-helium-cooled substrates. Past observations which established criteria for the formation of amorphous metallic alloys were largely limited to close-packed elements. In this paper, which includes a large number of bcc elements, we find that the crystalline-state immiscibiltiy of the elements is a stronger factor in determining the stability, as well as the ease of formation of the amporhous structure, than is the difference in atomic size of the constituent elements.
Thermal stresses and cracking resistance of dielectric films (SiN, Si3N4, and SiO2) on Si substrates
Authors: Sinha A. K. , Levinstein H. J. , Smith T. E.
Published: February 2003

In device-manufacturing technology, it is important to understand why dielectric films crack. With this objective in mind, we have constructed an apparatus for measurement of thermal stresses in thin films (25–500 °C), obtained results on various reactively plasma deposited (RPD) Si-N and CVD SiO2 films, and developed a model which quantifies the cracking resistance of different types of RPD Si-N films. Measurements were made of the coefficient of thermal expansion α (T), which increases on going from SiO2→Si3N4→SiN→Si and the intrinsic stress, which is compressive for RPD Si3N4, nearly zero for thermal SiO2 and tensile for RPD SiN and CVD SiO2. The cracking resistance of Si-N film at a given temperature is functionally related to its density, intrinsic stress, thermal mismatch with Si, and the deposition temperature.
The upper critical field of NbN film
Authors: Ashkin M. , Gavaler J. R.
Published: February 2003

It is proposed and experimentally verified that the anomalously high superconducting critical field normal to the surface of NbN films possessing a column-void microstructure is Hc3, the field appropriate for surface superconductivity. It is also proposed that because the coherence length is much less than the lateral column dimension that the resistivity of the column and not the film enters calculations of the Maki parameter α. A previously noted discrepancy in α is removed by these proposals.
Self-resonant modes in Nb-NbOx-Pb Josephson junctions
Authors: Paternò G. , Nordman J.
Published: February 2003

Measurements of the magnetic field dependence of Fiske steps and ’’zero-field’’ steps in Nb–Nb oxide–Pb Josephson junctions are described. By the use of a simple variable dc bias scheme, the measured ac volt-ampere characteristics are made to clearly exhibit the step structure even in the presence of a large dc Josephson current. A comparison with the theory of Kulik for the magnetic field dependence of Fiske steps is shown and the correlation is very good for small L/λj ratios. Deviations for larger ratios include the appearance of zero-field steps.
The nucleation of magnetic domains during the hcp to fcc phase transition in cobalt
Authors: Lewis W. F.
Published: February 2003

Recent experiments have reported difficulties in nucleating the transformation of domains during the hcp to fcc phase transition in cobalt at 400 °C. By writing the energy associated with these domain patterns explicitly in terms of anisotropy, magnetostatic pole, and domain-wall energies, in addition to the energies associated with an applied external field and domain-wall pinning, a condition of instability, i.e., a free transformation of the domain structure, is obtained. It was found that the field needed to nucleate this domain transformation is increased by the effects of magnetostatic energies and wall pinning, but decreased by the effects of anisotropy. Furthermore, it was found that for an internal planar defect, such as a stacking fault, the transformation between the domain structures indigenous to each crystal phase occurs spontaneously in agreement with experimental observations.
Thermal depolarization current study of polystyrene composites containing mica flakes
Authors: Tanaka T. , Hayashi S. , Hirabayashi S. , Shibayama K.
Published: February 2003

Thermal depolarization current (TDC) of a cross-linked polystyrene composite whose conductive phase is mica has been measured in order to study in detail interfacial polarization (Maxwell-Wagner effect) in polymer composites with stratified structure. The volume fraction of mica flakes in the composite was varied from 0.16 to 0.37. A peak characteristic of the composites is observed at a temperature above the Tg of the composites. The maximum current of the peak increases with the fraction of mica flakes. The behavior of the peak is different from that of TDC due to dipole polarization and the space-charge polarization of injected electrons. The beginning of a dielectric dispersion corresponding to the peak is observed below 1 Hz at 164 °C. The TDC peak can be explained by Maxwell-type interfacial polarization. It is proposed that the TDC peak is attributed to interfacial polarization due to trapping or localizing of conductive ions in mica flakes at boundaries between the polymer matrix and mica flakes.
Effect of electrical state on mechanical and electrical response of a ferroelectric ceramic PZT 95/5 to impact loading
Authors: Dick J. J. , Vorthman J. E.
Published: February 2003

Ferroelectric ceramic specimens 2–10 mm thick were impact loaded in uniaxial strain to a stress of 1.6 GPa. Material velocity-time wave profiles were measured using a laser interferometer system. Specimen states studied were unpoled, poled and shorted, and poled with a high resistive load (E?2 kV/mm). The results show clearly the effect of the specimen electrical state on the mechanical response. Evolution of the mechanical wave was studied by measuring profiles for several different thicknesses with the same electrical state. For poled specimens, simultaneous measurements were made of the depolarization current during the impact loading. Measured wave speed of the first detectable disturbance was sonic in some but not all cases. Measurements of Hugoniot states for unpoled material were also obtained.