bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic susceptibility of A
nRe2 compounds
Authors: Brodsky M. B. , Trainor R. J. , Aldred A. T. , Sowers C. H.
Published: February 2003

The compounds AnRe2, where An=Th, U, Np, and Pu all have the MgZn2-type hexagonal Laves phase structure. Measurements of their magnetic susceptibilities have been made from 2 to 300 K. Whereas ThRe2, URe2, and PuRe2 have essentially temperature-independent susceptibilities, NpRe2 is ferromagnetic with Tc=47 K. The paramagnetic data for NpRe2 follow a modified Curie-Weiss law, χ−χ0=C/(T−ϑ) from 60 to 230 K with ϑ=47.4 K and C equivalent to an effective moment, peff=2.11μB. The ordered moment μ0=0.90μB and the results are consistent with other actinide compounds having good local moment behavior. The electronic specific heat γ of URe2=34 mJ/(mole K2) is large enough to indicate the possibility of spin-fluctuation behavior in this compound.
Magnetic characteristics of R2Al and R2Au compounds
Authors: Sill L. R. , Biggers R. R.
Published: February 2003

The magnetic moments of some polycrystalline R2Al and R2Au (R=rare earth) compounds have been studied between 4.2 and 300 °K in magnetic fields up to 26 kOe. At high temperatures, the measurements indicate that, with the exception of the samarium compounds, the inverse susceptibilities follow a Curie-Weiss type behavior yielding effective moments in good agreement with the theoretical values for free R3+ ions. At low temperatures complex magnetic behavior including saturation, S-shaped magnetization curves, peaks in the σ vs T curves, hysteresis and remanence is exhibited by individual compounds.
Magnetization studies in the system Fe1−xCrxBO3
Authors: O’Horo Michael P. , Muller Olaf
Published: February 2003

Temperature-dependent magnetization studies from 4.2 to 600 °K have been made for the solid solution system Fe1−xCrxBO3 where 0⩽x⩽0.95. A rapid decrease is observed in the saturation magnetization with increasing x at 4.2 °K up to 0.40, after which a broad compositional minimum is found up to x=0.60. Compositions in the range of 0.40⩽x⩽0.60 display unusual magnetization behavior as a function of temperature in that maxima and minima are present in the curves below the Curie temperatures. Possible explanations for these anomalies are discussed.
Ionic model for Cr, Mn and Fe impurities in Cu
Authors: Abbas D. C. , Aton T. J. , Slichter C. P.
Published: February 2003

We have discovered that the NMR frequencies of Cu atoms which are near neighbors to Cr atoms in dilute CuCr have an anomalous temperature dependence. Comparison with data from CuMn and CuFe which display the normal temperature dependence of a Curie-Weiss law lead us to conclude that (a) Hirst is correct in his general picture that magnetic atoms have a d-shell configuration characteristic of a particular ionic state, (b) Cr and Mn appear to be divalent while Fe is monovalent, (c) there is a crystalline electric field at the site of the magnetic atom, but its sign is opposite of that proposed by Hirst, and (d) the Kondo temperature of CuCr is 2.9±1.0 K which is higher than most previously reported values.
Magnetic susceptibility of α-phase noble metal alloys
Authors: Foiles C. L.
Published: February 2003

The magnetic susceptibility of α-phase alloys composed of noble metal solvents and non-transition metal solutes continues to be difficult to interpret. Guided by the fact that the rate of change in susceptibility is proportional to the solute valence, most interpretations have considered changes in the behavior of the conduction electrons. These interpretations are not acceptable because they either predict a paramagnetic change rather than the observed diamagnetic one or they require a strong decrease in the density of states which is not supported by other measurements. Following a brief summary of these inconsistencies, we present a correlation of the susceptibility changes with lattice parameter changes which produces some striking patterns. The data for impurities from a given row of the periodic table lie on a single straight line and the slopes of the lines for different impurity rows are quite similar. The intercepts on the susceptibility axis are consistent with alloy host parameters and form a self-consistent pattern. We suggest that these systematic patterns are evidence for significant, perhaps dominating, changes in the core contributions to susceptibility in these alloys.
Application of the Green’s function diagrammatic technique to complex crystal field systems with bilinear and biquadratic exchange
Authors: Sablik M. J. , Wang Yung-Li
Published: February 2003

A diagrammatic Green’s function technique is used to obtain the elementary excitations in a rare earth system with cubic crystal field and both bilinear and biquadratic couplings. We find three distinct modes of excitations—longitudinal (L) and transverse (T1 and T2). L modes and T1 modes consist of mixed dipolar and quadrupolar excitations below Tc, but above Tc they are either pure dipolar or pure quadrupolar in character. The T2 modes are pure quadrupolar. Dispersion and temperature dependence of the exciton energies are shown for a particular model system, DySb, but the computer program used is general enough to be used on other systems whose molecular field states are known.
Paramagnetic properties of Fe-Al alloys at high temperatures
Authors: Arajs Sigurds , Anderson E. E.
Published: February 2003

Magnetic susceptibility (χ) of binary Fe alloys with Al content between 17 and 27 at.% have been studied as a function of temperature (T) between their ferromagnetic Curie temperature (Tc) and 1500 K. At temperatures slightly above Tc the paramagnetic behavior is strongly influenced by the short-range magnetic ordering. In the high temperature region (between 1350 and 1500 K) χ approximately obeys the Curie-Weiss law. It is found that the paramagnetic moments per Fe atom increase with increasing Al concentration while the paramagnetic Curie temperatures decrease.
Nuclear orientation studies of the manganese in copper Kondo system
Authors: Bakalyar D. , Babcock J. , Kiely J. , Weyhmann W. , Symko O. G.
Published: February 2003

The internal field of 54Mn in Cu at a nominal concentration of 1 ppb has been measured at 4 mK in applied fields of 5 to 40 kG. No temperature shift was observed from 4 to 8 mK. Assuming the hyperfine field (measured internal field plus applied field) to be proportional to the Mn local moment, theoretical expressions by Emery and Luther and Götze and and Schlottman can be fitted to the data with high accuracy, while that of Ishii cannot. (The first of these requires asymmetric exchange for the best fit.) Additional samples containing 1/2 ppm and 10 ppm of stable Mn were prepared for comparison. At 5 kG applied field the addition of 1/2 ppm stable Mn lowered the hyperfine field by 4% and 10 ppm by an additional similar amount. At 40 kG all samples had the same hyperfine field within statistical accuracy. This data indicates the onset of interaction effects at very low concentrations and the increasing magnitude of data shifts from this cause as the applied field is lowered.
LuGd: A system exhibiting positive exchange coupling between conduction electrons and localised magnetic moments
Authors: Cochrane R. W. , Ström-Olsen J. O. , Williams Gwyn
Published: February 2003

We have measured the magnetization and the low temperature resistivity and magnetoresistance of a series of alloys of Lu containing up to 1.6 at.% Gd. The resistivity was found to vary A+D lnT, with A and D scaling linearly with Gd concentration showing that this is a single impurity effect and thus establishing LuGd as the first unambiguous example of a positive exchange Kondo system. Furthermore, the value of the exchange constant deduced from the resistivity data is in excellent agreement with that estimated from e.p.r. measurements. The low field susceptibility data (<5 kOe) confirm the single particle limit, as the impurity suceptibility follows a Curie law with an estimated upper limit on the Curie-Weiss temperature of ±0.5 K. The magnetoresistance is negative, but is much smaller than in systems with a negative J of comparable magnitude; this effect is attributed to the competing field dependences of the second and third order terms in the usual expression for the magnetoresistance when J is positive, in contrast to the negative J situation.
Electronic structure of magnetite at low temperature
Authors: Iida S. , Mizushima K. , Mizoguchi M. , Umemura S. , Yoshida J.
Published: February 2003

Recent progress in NMR analysis of Fe3O4 has revealed the presence of five B site Fe3+ ions, called B-1, B-2, B-4 and B-5. From the symmetry of the NMR lines of these ions, a very new electron ordering was proposed, in which Fe3+-I ions make pairs along [11̄0] direction and Fe2+-II ions also behave in the same way. In this Mizoguchi’s model, all the (001) planes in which B sites align along [11̄0] are composed of these pairs exclusively with two kinds of pairs aligning alternately. The other (001) planes in which B sites align along [011] are composed of Fe3+-II and Fe2+-I ions, which align as 3⋅1⋅3⋅⋅⋅ and 1⋅3⋅1⋅⋅⋅. The significance of this model in contrast to Iida’s model in which all (001) planes have the same alternative sequence of Fe3+ and Fe2+ ions is discussed, concluding that, although the new model is quite promising, the NMR study at the present stage still cannot eliminate the latter model.
The influence of magnetic order on charge delocalization in pure and Zn-doped Fe3O4
Authors: Pan Lu-San , Evans B. J.
Published: February 2003

The unexpected simplicity of the 57Fe Mössbauer spectrum of Fe3O4 above its Néel temperature has been confirmed for pure Fe3O4 and Fe3−xZnxO4, x=0.01, 0.1, and 0.2. The abrupt change in the isomer shifts of the A and B site patterns is observed to take place near the Néel temperature for all samples, despite a 90 K variation in Néel temperatures. The abrupt change in isomer shifts is caused by electron delocalization from the B site to the A site as the spins on these two sites lose their antiparallel arrangement near TN. This facile electron exchange between the A and B sites is possible because of the high thermal energies available at TN and the delocalization mechanism is believed to be hopping in between localized sites.
XPS study of LaCoO3
Authors: Veal B. W. , Lam D. J.
Published: February 2003

X-ray photoelectron spectroscopy (XPS) measurements have been performed on LaCoO3 and related compounds including LaTiO3 and LaCrO3. The XPS spectra of LaCoO3 are analyzed to determine the spin states of the Co ions. Final state multiplets of the d6 electron configuration in the valence band region are apparent near the band edge. The predominately O 2p valence bands are corrected using XPS data from LaTiO3 and LaCrO3 where the 3d electron spectra are understood. The results are discussed in terms of the mixed spin-state trivalent cobalt ion model.
Low temperature spin wave dynamics in classical Heisenberg chains
Authors: Heller P. , Blume M.
Published: February 2003

A detailed and quantitative study of the low-temperature spin-wave dynamics has been made for the classical Heisenberg-coupled chain using computer simulation. Results for the spin-wave frequencies are presented and compared with existing predictions.
A calorimetric study of CoxNi1−xCl2⋅6H2O
Authors: Forstat H. , Lam N. T.
Published: February 2003

Using a standard He4 adiabatic calorimeter, we have measured the specific heats of a series of mixed crystals with chemical formula CoxNi1−xCl2⋅6H2O. All the samples studied show fairly sharp λ-type transitions in the liquid He4 region. The Néel temperatures vary from 2.43 °K to 4.47 °K for x ranging from 0.89 to 0.13. We find that the critical behaviors of the mixed crystals can be explained by assuming that the Ni and Co spins behave like Ising spins randomly distributed on a square lattice. The TN vs concentration diagram can be reasonably well accounted for by (a) the annealed Ising model, (b) the annealed Bethe-Peierls-Weiss (BPW) model and to a lesser extent, (c) the quenched BPW model. The experimental specific heats have also been compared with theoretical predictions. In all cases, the annealed Ising model fits the data the best near and above the critical temperatures. For high Ni concentrations, the quenched BPW model fits the data better than the annealed BPW model but predicts critical temperatures which are too high. We present a quantitative argument to support the view that an exact solution of the quenched Ising model is unlikely to differ significantly from the annealed Ising model.
Neutron diffraction study of magnetic order in the ternary superconductor ErMo6Se8
Authors: Lynn J. W. , Moncton D. E. , Shirane G. , Thomlinson W. , Eckert J. , Shelton R. N.
Published: February 2003

Development of new ternary superconductors has led to materials which also show a strong tendency toward magnetic order when one of the constituent elements is a rare earth. Powder neutron diffraction data on superconducting (Ts∼6 K) samples of ErMo6Se8 taken in the temperature range 0.05–2.0 K show that magnetic Bragg peaks develop at TM=1.1 K, in agreement with specific heat studies. However, it is not possible to index these new reflections using a simple antiferromagnetic unit cell based on the ErMo6Se8 lattice. It is also not possible to index the magnetic reflections based on a single modulation vector, or with a modulation vector along a high symmetry direction including higher order harmonics. Thus either the long range magnetic order corresponds to a more complicated magnetic structure in the ErMo6Se8 lattice, or at least some of the peaks develop in impurity phases. These results are compared with the recent neutron data on the reentrant superconductors HoMo6Se8 and ErRh4B4, in which the development of ferromagnetic order is clearly shown to be responsible for quenching the superconductivity.
Spin polarized tunneling in rare earth ferromagnets
Authors: Meservey R. , Paraskevopoulos D. , Tedrow P. M.
Published: February 2003

We have measured the spin polarization of tunneling electrons in junctions between thin Al films and films of the heavy rare earth metals Gd to Yb. These metals are known from other experiments to have positively polarized conduction electrons. All polarizations measured by tunneling are positive and are approximately proportional to the part of the saturation magnetic moment per atom attributed to the conduction electrons.
Magnetic properties of amorphous alloy films of Fe with Gd, Tb, Dy, Ho, or Er
Authors: Mimura Y. , Imamura N. , Kobayashi T. , Okada A. , Kushiro Y.
Published: February 2003

Amorphous rare-earth RE(Gd, Tb, Dy, Ho, Er) -Fe films prepared by cosputtering were studied. The compositional analysis was obtained from known deposition profiles, x-ray microanalysis, and the stripe-width measurements. The structural variation with composition change was investigated by electron diffraction and dark-field microscopy. The Curie temperature Tc, the compensation temperature Tcomp, the coercive force Hc, the uniaxial anisotropy energy Ku and the static domain properties such as the stripe width Ws, the wall energy σw, and the exchange stiffness constant A were investigated. The systematic variation of Tc and Tcomp associated with a variation of composition and RE species could be described by the Heiman et al. model. The static domain properties could be interpreted in terms of the wall energy model and the mean field approximation of the exchange stiffness constant A.
Optimum discharge parameters for beam-plasma ion sources
Authors: Conrad J. R.
Published: February 2003

An expression for the optimum discharge parameters of beam-plasma ion sources is obtained and compared with experimental data.
The electron temperature in a medium-pressure radio-frequency flowing positive column plasma
Authors: Chang Jen-Shih
Published: February 2003

An expression for the electron temperature in a medium-pressure radio-frequency flowing positive column plasma has been derived for a cylindrical discharge tube. The effect of flow on electron temperature increases as the product of gas pressure and tube radius decreases.
One-dimensional model systems: Theoretical survey
Authors: Bonner Jill C.
Published: February 2003

In the early 1960’s one-dimensional model systems were regarded as amusing toys with the advantage of being far more easily solvable than their ’’real’’ three-dimensional counterparts. Now essentially 1-D (quasi-1-D) magnets can be ’’tailor-made’’ in the laboratory. Even more popular is the field of organic conductors like TTF⋅TCNQ, which are naturally quasi-1-D. Currently solitons and related solutions of non-linear, dispersive 1-D differential equations are ubiquitous in physics, including the area of 1-D magnetism. These developments are discussed in the Introduction. The rest of this paper is concerned with model Hamiltonians, model comparisons, critical singularities in 1-D (quasi-1-D) systems, accuracy of numerical techniques in comparison with exact solutions, brief accounts of dilute and disordered 1-D systems, and 1-D spin dynamics. Finally, a comment is made on a variety of interesting isomorphisms between 1-D magnets and phenomena in several other areas of physics, for example 2-D ferroelectrics, field-theoretic models, and realistic fluids. Comparison of theory and experiment has been the subject of several excellent reviews and is therefore not discussed here.
Phase transitions in two-dimensional systems
Authors: Domany Eytan , Riedel Eberhard K.
Published: February 2003

Relations between two-dimensional physical systems, continuous-spin Hamiltonians, and discrete spin or Potts models are established by Landau symmetry and renormalization-group arguments. Experimental realizations of XY and Heisenberg models with cubic anisotropy as well as of different Potts models are reviewed. Then a unified model encompassing these classes of models is introduced. For the special case of a six-state discrete model a phase diagram is proposed based on duality and Migdal renormalization-group transformations.
Thermal and magnetic study of exchange in the quasi-1-D molecular compound, TTF⋅PtS4C4(CF3)4
Authors: Bonner J. C. , Wei T. S. , Hart H. R. , Interrante L. V. , Jacobs I. S. , Kasper J. S. , Watkins G. D. , Blöte H. W. J.
Published: February 2003

Single crystal magnetic susceptibility results from 2.5 K to 270 K and specific heat results from 3 K to 16 K are reported for TTF⋅PtS4C4(CF3)4, (TTF=tetrathiafulvalene). The combined results are analyzed using a simple model which ignores differences between the two types of S=1/2 spin carriers and involves a system of ferromagnetic chains treated ’’exactly’’, with interchain antiferromagnetic interaction evaluated in a mean field approximation. Above an apparent ordering transition at 8 K, the susceptibility is well described by the model irrespective of whether the ferromagnetic exchange is Heisenberg, Ising or intermediate to these. The magnetic contribution to the specific heat is obtained using earlier results for the isostructural Au compound. Comparison with specific heat calculations for the Heisenberg, Ising and intermediate cases successfully narrows the ambiguity to an intermediate anisotropic exchange close to the Heisenberg limit.
Modes of grating waveguide
Authors: Haus H. A. , Wang K. L.
Published: February 2003

Starting with the coupled-paraxial-wave equations for Rayleigh waves propagating under a SAW grating, modes are derived with characteristic transverse-mode patterns. Modes exist below the first-order Bragg frequency both within a passband (real propagation constant) and a stop band (imaginary propagation constant). Cutoff (disappearance of guided mode solutions) is reached within the stop band above the Bragg frequency. No passband is found immediately above the stop band. Guidance of the waves by the grating is due to reflection at the grating edges and not due to a velocity difference of the Rayleigh waves between the regions outside the grating and underneath the grating. We take up the study of the effect of the velocity difference and find enhancement of guidance (as expected) when the outside region has a higher Rayleigh velocity. When the outside region has a smaller velocity, guided modes do not necessarily disappear. In fact, some guidance is provided by the velocity discontinuity.
Scattering of electromagnetic waves from a rough surface. II
Authors: Holzer James A. , Sung C. C.
Published: February 2003

The mean irradiance reflected from a randomly rough dielectric surface is calculated using the vector Kirchoff integral. The tangent-plane approximation is used to relate the fields on the boundary to the incident fields through the Fresnel reflection coefficients. The averages involving the random surface variables are performed exactly using a spectral representation for the scattering function. The special case of a corrugated surface is treated numerically to gain insight into the more general problem. Our results are compared with previous solutions. An empirical formula is presented for practical applications. Finally, a general expression for the depolarization matrix is derived, retaining terms up to second order in the surface slopes. Our solution is compared with available theories.
Optically enhanced Franz-Keldysh effect
Authors: Ishikawa Kiyotsugu , Itoh Kunio , Takeshima Masumi , Teramoto Iwao
Published: February 2003

A new phenomenon that the electroabsorption of a n-p-n heterodiode is enhanced by the absorbed light is reported. The electroabsorption is essentially based on the Franz-Keldysh effect, where the light absorption edge of the heterodiode shifts towards a longer-wavelength region under the applied voltage. It is shown that the optical enhancement of the electroabsorption is caused by the space charges accumulated through trapping of photogenerated free carriers.
A new model for the flat conductor electromagnetic SAW transducer
Authors: Sethares J. C. , Szabo T. L.
Published: February 2003

Previous models for Rayleigh- and Lamb-wave electromagnetic transducers have been based on the assumption that the current distribution in each transducer conductor is uniform. We present solutions for the dynamic magnetic fields surrounding an array of flat conductors above a ground plane in which the current distribution is allowed to vary. The resulting solutions are used to calculate space-harmonic curves and to derive a new transducer model including electrical inductance, eddy current resistance, acoustic impedance, and transducer efficiency. A direct analogy to the interdigital transducer is established. For fundamental frequency operation, this model is nearly equivalent to previous flat field models, provided the conductor width/spacing ratio is 1/2 or less. For harmonic transducer operation, the present analysis is substantially different from other models and it matches data more accurately. A method for measuring the individual insertion loss of dissimilar transducers in a lossy medium is presented.
Implosion experiments with D2, 3He filled microspheres
Authors: Slivinsky V. W. , Ahlstrom H. G. , Nuckolls J. H. , Larsen J.T. , Weinstein B. W. , Tirsell K. G. , Storm E. K. , Leipelt G. R.
Published: February 2003

Glass microspheres filled with D2 and 3He were imploded using the LLL 1.06 μm Argus laser. The energetic 14.7-MeV protons from the D-3He reactions were measured. By taking the ratio of the number of D-3He reactions to the D-D reactions, ion temperatures were calculated. The results were compared with numerical modeling of the experiments.
Evaluation of doping profiles in ion-implanted PbTe
Authors: Palmetshofer L. , Vierlinger E. , Heinrich H. , Haas L. D.
Published: February 2003

From measurements of the sheet conductivity and the Hall effect in combination with layer stripping by chemical etching, we have evaluated the doping profiles of ion-implanted PbTe. By using thin films grown epitaxially on insulating substrates, we avoided difficulties with the formation of an insulating p-n junction. The carrier profiles of samples implanted in a random direction are deeper and broader than those of the LSS theory. The charge-carrier profiles associated with the implantation damage show a constant value of the maximum concentration largely independent of the implantation dose and the ions used.
Transport of residual ions and rectification in liquid-crystal displays
Authors: Sussman Alan
Published: February 2003

Field-effect devices with evaporated silicon monoxide coatings for liquid-crystal alignment exhibit rectification under dc and ac excitation when the coatings are asymmetric. The rectification mechanism is a polarity- and electrode-dependent depletion of residual ionic carriers from the bulk. Polarity reversal transients offer a novel means of studying the electrode double-layer charging and demonstrate hydrodynamic contributions to the mobility. The threshold conditions for rectification under ac excitation are outlined.
Electro-optic behavior of a field-induced twisted structure with quasihomeotropic boundary conditions
Authors: de Rossi D. , Robert J.
Published: February 2003

A twisted nematic structure is induced by an electric field. The distortion of the structure and the optical activity of the cell is computed for both static and dynamic behavior. Experimental results are given and followed by a tentative interpretation.
Shock-wave compression of an alumina-filled epoxy in the low gigapascal stress range
Authors: Mock Willis , Holt William H.
Published: February 2003

The shock-wave equation of state for a commerically available alumina-filled epoxy has been determined in the stress range from 0.4 to 3.7 GPa via gas-gun-impact experiments. A linear fit to the shock-velocity–particle-velocity data yields U=2.78+1.63u. This curve lies between the U-u curves for an unfilled epoxy and for an alumina-filled epoxy of higher density.
Effects of bimolecular recombination on photocurrent and photoinduced discharge
Authors: Chen Inan
Published: February 2003

The effects of bimolecular (Langevin) recombination of charge carriers on the photocurrent in the constant-voltage mode and on the surface potential decay in the open-circuit (or xerographic) mode are studied. By solving the charge-carrier transport equations numerically, it is possible to treat cases of practical interest, e.g., transport with recombination of more than 1 CV’s worth of charge carriers, field-dependent mobilities, and nonuniform generation of charge-carrier pairs. The calculation of photocurrent in the constant-voltage mode justifies Hughes’s use of the small-signal formula in the interpretation of the large-signal data. In the open-circuit mode, the difference between the small-signal formula and the calculation taking into account the space-charge effects becomes more significant. The natures of the contrast potential and the reciprocity relation are examined.
The anisotropic carrier mobility due to dislocations in III-V compounds
Authors: Booyens H. , Vermaak J. S. , Proto G. R.
Published: February 2003

The anisotropy in the carrier mobility due to the presence of dislocations in III-V compounds is determined using a method based on the equivalence of scattering energy loss and Joule heat created in the crystal. It is found that the mobility is a maximum perpendicular to the slip planes of 60° and 90° dislocations of both the α and β types of dislocations. Screw dislocations do not cause any scattering and consequently do not affect the mobility through this mechanism.
High conductivity ZnSe films
Authors: Aranovich Julio , Fahrenbruch Alan L. , Bube Richard H.
Published: February 2003

Thin films of ZnSe deposited by vacuum evaporation have a high resistivity (≳5×108 Ω cm), even when donor impurities such as Ga or In and additional Zn are coevaporated. High-conductivity films of ZnSe were produced by annealing films, deposited with coevaporated Ga and Zn, in Zn vapor at 500 °C. Film resistivities in the range 0.5–40 Ω cm were obtained in this way, corresponding to degenerate n-type material with electron densities in the 1019-cm−3 range. Heterojunctions of n-ZnSe/p-CdTe and n-ZnSe/p-GaAs were investigated.
Photoelastic constants of germanium
Authors: Feldman A. , Waxler R. M. , Horowitz D.
Published: February 2003

The photoelastic constants of Ge have been measured at 3.39 and at 10.6 μm. Our stress-birefringence data join smoothly to earlier stress-birefringence data at other wavelengths. The acousto-optic figure of merit M2, computed from our data, agrees well with M2 determined for commercial acousto-optic devices. However, our data disagree with some earlier measurements of M2, the elasto-optic constants pij, and the change of refractive index with hydrostatic pressure dn/dP.
Transferred-electron photoemission to 1.65 μm from InGaAs
Authors: Escher J. S. , Gregory P. E. , Hyder S. B. , Sankaran R.
Published: February 2003

Photoemission to 1.65 μm has been achieved in the reflection mode from a bias-assisted p-InGaAs cathode. Quantum yield at 1.55 μm is ∼10−3 at 125 K and ∼10−4 at 300 K.
Approximating the transient response of double-heterojunction devices
Authors: Fonstad C. G. , Armiento C. A.
Published: February 2003

Two techniques of approximating the transient response of a double-heterojunction light-emitting diode or diode laser in which there is a nonzero recombination velocity at the heterojunctions are compared to the results of a recently published exact series solution for the transient behavior of such structures. It is shown that both approximations can lead to large quantitative errors—one overestimating and the other underestimating the speed of response—when the active region is wide and the interface recombination is large, but that both approximations are useful and yield similar results when the active region is narrow and interface recombination is small. For devices with narrow active regions and small recombination velocities, it is shown that the transient response can be represented as a single exponential with a characteristic lifetime given by τ[1+(Sv1+Sv2)/D]−1, where Svi and D are the normalized interface recombination velocities and active region width, respectively.
Doubled-layered polycrystalline cadmium sulfide on lithium niobate
Authors: Kornreich Philipp G. , Mahapatra Amaresh , Kowel Stephen T. , Loh K. W. , Emmer Bruce
Published: February 2003

We have developed a technique for fabricating polycrystalline thin films of CdS on z-cut LiNbO3. A single film will show a light-to-dark–conductivity ratio of approximately unity with very high sheet resistance after curing. To make a good photoconductor, a second film is then deposited. This film is protected during the subsequent curing from out-diffusion from the LiNbO3 by the first film and develops a light-to-dark–conductivity ratio of 10 000 in room light with a sheet conductivity of 10−10 s/⧠ mcd. Films produced by this layered process also possess a remarkably large conductivity-modulation dependence (20%) on the square of an impressed electric field provided by a traveling surface acoustic wave in the LiNbO3 substrate.
In-plane susceptibility of amorphous ferrimagnetic films near the compensation point
Authors: Mizoguchi T. , Malozemoff A. P. , Cox D. E.
Published: February 2003

The in-plane susceptibility χp of several amorphous sputtered GdCoMo films shows a minimum of ∼3×10−4 emu at the compensation temperature. This value is accounted for theoretically by the classical antiferromagnetic susceptibility relation. The contribution to the in-plane susceptibility of composition inhomogeneities is also calculated. The fact that such an increase in susceptibility is not observed in experiment indicates the films are quite homogeneous magnetically. Comparison of the anisotropy in films prepared at high and low deposition rates indicates the effect of rate on anisotropy is weak.
Anisotropy field of small magnetic particles as measured by resonance
Authors: de Biasi Ronaldo S. , Devezas Tessaleno C.
Published: February 2003

The anisotropy field as measured by resonance is calculated for a coherent assembly of small magnetic particles possessing both crystal and shape anisotropy. The theoretical results are compared with experimental data on precipitated cobalt and magnesioferrite particles.
Dielectric breakdown in electrically stressed thin films of thermal SiO2
Authors: Harari Eli
Published: February 2003

A novel technique is described which was used to study the intrinsic breakdown mechanism in films of thermal SiO2 in the thickness range 30–300 Å. It was determined that high-field and high electron injection current conditions existing in the films just prior to breakdown result in the generation of a very high density of defects which behave electrically as stable electron traps. These traps are most likely generated close to the injecting electrode. The internal field in the oxide due to trapped electrons can approach 3×107 V/cm which appears to be the maximum field strength which Si-O bonding can withstand. At all temperatures between 77 and 393 °K, the breakdown mechanism is intimately related to the rate of generation of the electron traps. No evidence was found to support the impact ionization breakdown model. The technique is also described as a tool for yield measurements, with important implications for long-term reliability of MOS IC’s.
Optical absorption and photoconductivity in thermally grown SiO2 films
Authors: Powell R. J. , Morad M.
Published: February 2003

Optical transmission of unbacked thin films of thermally grown SiO2 films were measured in the vacuum uv. The absorption data indicate a band gap of 8.0±0.2 eV for SiO2, and this value is confirmed by measurements of electron and hole photoconductivity and positive charging thresholds in MOS samples. The observation of hole photoconductivity near 8 eV shows that the uppermost valence levels in SiO2 are not nearly atomic, but form a band with sufficient orbital overlap that readily transport holes at room temperature.
TOF atom-probe investigation of metal oxides
Authors: Ng Yee S. , McLane S. B. , Tsong T. T.
Published: February 2003

An energy-focused time-of-flight atom-probe field-ion microscope has been successfully employed to investigate the composition depth profile and the oxides species of metal oxide layers. Depth profiles of p-type semiconducting thin films formed by in situ oxidation of materials of three different crystal structures (bcc iron, hcp cobalt, and fcc nickel) showed, without exception, a metal-rich near surface. After iron has been oxidized in pure research-grade oxygen, iron oxide layers field evaporate mostly as FeO+, Fe2+, Fe+, O+, and O+2. A small number of FeO2+, FeO+2, and FeO+3 have also been observed. However, iron oxide layers formed by oxidation in air field evaporate exclusively as FeH2+2 and Fe(OH2)2+2. No Fe3O4 or Fe2O3 have been detected in both cases. No hydroxides and very few hydrides are found for nickel and cobalt when they are oxidized in air. Cobalt oxide layers field evaporate as CoO+, Co2+, O+2, and O+ as well as a small number of Co+, CoO2+, and CoH+. Although we also expected Co3O4 ions, none was found. Nickel oxide layers field evaporate mainly as NiO+, Ni2+, O+2, O+, and Ni+. In addition to these, some NiO+2 and masses which can be assigned as Ni2O3+3 and Ni2O4+3 are detected. We have also discovered that the oxygen content in the thick oxide layer does not, in general, vary uniformly, possibly due to oxygen diffusion along grain boundaries. The oxide films are polycrystalline in nature, and the adhesive strength of the oxide to the metal is found to be weakest at the oxide/metal interface.
Electromagnetic acceleration of macroparticles to high velocities
Authors: Rashleigh S. C. , Marshall R. A.
Published: February 2003

An inductively driven rail-gun macroparticle accelerator has been built in which velocities of 5.9 km/s have been obtained using an arc as the driving armature. Simple theory is shown to be adequate for predicting rail-gun performance up to that velocity and for designing rail guns for launching large masses.
Closed-form calculation of the transient behavior of (Al,Ga)As double-heterojunction LED’s
Authors: Zucker J.
Published: February 2003

A closed-form approximation to the transient behavior of high-radiance double-heterojunction LED’s is derived based on the assumption of current-independent space-charge capacitance. The resulting expression for the rise time is found to agree with experiment to a useful degree of approximation.
The Faraday effect in Hg1−xCdxTe at CO2 laser wavelengths
Authors: Ahrenkiel R. K. , Weiss P. , Watkins D. , Gulati S. K. , Grannemann W. W.
Published: February 2003

The optical and magneto-optical properties of crystals of Hg1−xCdxTe (x=0.37) have been measured over the CO2 laser wavelength region. The absorption edge of this composition occurs at about 3.2 μm, and the Faraday rotation consists of interband and intraband components. The latter is very large in n-type material due to the small electron effective mass (0.052). The figure of merit of n-type material is about 1.0 deg/kOe at 10.6 μm. Optical-damage studies give a damage threshold of 160 MW/cm2, indicating application to high-power laser isolator devices.
Light scattering on internal reflection from surface acoustic waves
Authors: Sarid Dror , Stegeman G. I.
Published: February 2003

The intensity of light scattered by surface acoustic waves (SAW) on internal reflection has been calculated for the geometry where the incident and scattered light are in a plane perpendicular to the SAW wave vector. The calculation was carried out for an arbitrary piezoelectric crystal having a free or metallized surface. Measurements on a y-cut LiNbO3 crystal and a z-propagating SAW give good agreement with the theory.
Study of the surface acoustic wave properties of lead molybdate
Authors: Rouvaen J. M. , Bridoux E. , Waxin G. , Bruneel C. , Torguet R.
Published: February 2003

The bulk-wave properties of lead molybdate are well known in relation to its applicability as an acousto-optic material. Some new results about its acoustic surface wave propagation properties are reported here, and potential applications of the light diffraction by acoustic surface waves propagating on lead molybdate are studied.
Activation of fracture mechanisms
Authors: Ginman W. H.
Published: February 2003

The method of analyzing the activation of fracture mechanisms under the influence of generalized forces is described, leading to a generalized approach to the problem of time- and temperature-dependent fracture processes. The analysis of complex fracture mechanisms of the type necessary for the simultaneous fracture of two phases is discussed. Fracture processes are described in terms of a network of events that can occur both sequentially and simultaneously.
Stopping cross sections of three-membered ring-structure molecules and their double-bonded isomers for 0.3–2.0-MeV He+ ions
Authors: Chau E. K. L. , Powers D. , Lodhi A. S. , Brown R. B.
Published: February 2003

The stopping cross sections of acetaldehyde, ethylene oxide, propylene oxide, and vinyl methyl ether for 0.3–2.0-MeV accelerated He+ ions have been measured with probable random errors of 0.5–0.9%. The stopping cross sections of the three-membered ring-structure compounds ethylene oxide and propylene oxide were found to be lower than those of their double-bonded isomers, but higher than those of isomers calculated from single-bonded alcohols.
On nonlinear droplet condensation and evaporation problem
Authors: Lou Y. S.
Published: February 2003

Using a four-moment method of the kinetic theory of gases, an analytical expression is derived for the problem of vapor condensation on and evaporation from spherical liquid droplets when the droplet is not in equilibrium with its surrounding vapor in temperature and pressure. Unlike the linearized theories, the result for the mass flux to or from the droplet surface is obtained for a general case of finite temperature and pressure differences between the droplet and its vapor. It is believed, therefore, that the present nonlinear theory should be more realistic in predicting the rate of vapor condensation or evaporation phenomena of a droplet.
Intense relativistic electron-beam trajectories and their effect on beam heating of toroidally confined plasma
Authors: Lockner T. R. , Kusse B. R.
Published: February 2003

The trajectories of an intense relativistic electron beam propagating between a toroidal plasma column and a conducting vacuum wall are calculated theoretically and verified experimentally. Three classes of trajectories are observed, including a set of banana-type orbits. The significance of these trajectories on the ability of the beam to transfer energy to the plasma is discussed.
Electrode surface field and preionization effects on the spatial distribution of arcs in CO2 laser discharges
Authors: Mitchell Robert R. , Denes Louis J. , Kline Laurence E.
Published: February 2003

We have studied the spatial distribution of arcing as a function of electrode spacing and preionization pattern in CO2 laser discharge mixtures, using circular electrodes which allowed a gap of up to 10 cm and a discharge volume of ∼3 liters. We utilized both cathode-field enhancement with uniform preionization and apertured preionization with uniform field to define the discharge boundaries. In both cases, we found a threshold value of cathode-field enhancement below which arcing was uniform and confined to the discharge region and above which arcing became highly nonuniform, with arcs localized to the high-field region.
Theory of the hollow cathode arc
Authors: Ferreira C. M. , Delcroix J. L.
Published: February 2003

A theory of the hollow cathode arc is given which explains the physical mechanisms of operation of these discharges. The following basic phenomena are studied: the gas flow inside the cathode; the formation of the internal plasma column by ionization of the neutral gas by the primary electrons emitted by the cathode, which are accelerated in the cathode sheath; the transport of the ions towards the cathode wall; the transport of current and of kinetic energy towards the exit of the cathode, by the Maxwellian electrons of the plasma; and, finally, the thermal equilibrium of the cathode wall. This theory gives the axial variation of the gas pressure and wall temperature, the electron temperature, the mean number of excitations and of ionizations produced per primary electron, and the radial and the axial variation of the plasma density and plasma potential. The field-enhanced thermionic effect constitutes the basic emission mechanism of the cathode, the wall being heated mainly by ion bombardment. Theoretical results for discharges in argon with a tantalum cathode are in excellent agreement with all the available experimental results.
Experimental thermal coupling of laser beams
Authors: Maher W. E. , Hall R. B.
Published: February 2003

Energy in a laser beam can be transferred to a solid and increase its thermal energy. In a series of experiments, this thermal coupling has been investigated for pulsed CO2 laser beams. Target material, air pressure, focal spot size, and laser pulse separation time were varied. A feature often seen is an enhancement of the thermal coupling process above a fluence or intensity threshold. A method for the determination of the spatial profile of the heat absorbed by the target using a single on-axis thermocouple is presented. For the focal spot size and other conditions in these experiments, this technique shows a heating profile with a width much larger than the focal spot width.
Transverse self-focusing and filamentation of a laser beam in a magnetoplasma
Authors: Sharma Ashok K.
Published: February 2003

In this paper we have studied the problem of self-focusing of a Gaussian laser beam in a collisionless magnetoplasma when the direction of wave propagation is at right angles to the magnetic field. The nonlinearity arises through the ponderomotive force and subsequent redistribution of plasma along the magnetic field. It is seen that as the magnetic field increases the extent of self-focusing increases. The isointensity surfaces of a three-dimensional beam are elliptical. In the case of a plane-uniform laser beam it is seen that it is unstable for small-scale fluctuations, and the growth rate of instability increases very rapidly with magnetic field.
Properties of GaN tunneling MIS light-emitting diodes
Authors: Lagerstedt O. , Monemar B. , Gislason H.
Published: February 2003

MIS structures on GaN consisting of Au-NaI-GaN or Au-Al2O3-GaN with insulator thickness <100 Å have been fabricated with the aim of producing light-emitting diodes with emission in the uv and blue spectral region at low bias. I-V characteristics are consistent with a tunneling carrier transport mechanism, and light emission typically occurs for voltages 2–3 V. The spectral behavior of electroluminescence (EL) is in good agreement with photoluminescence (PL) data in the uv and blue spectral region. Suggestions for further work to improve radiant power output from such devices are presented.
Logic design of Josephson network. II
Authors: Nakajima K. , Onodera Y.
Published: February 2003

By numerical calculations of the differential-difference sine-Gordon equation, we have discussed the discrete Josephson-junction transmission lines which are constructed of a series of small-area Josephson junctions connected by superconducting strips. It is shown that the discrete Josephson lines containing D lines, N lines, T turning points, and S turning points are elementarily characterized by the discreteness parameter (2πLIc/Φ0)1/2. On the discrete Josephson logic circuits there exists a region of forbidden propagation in the (2πLIc/Φ0)1/2-γ (bias-current parameter) plane for single flux quanta. A single flux quantum can be stuffed in a small area of the discrete Josephson logic circuits. The discrete circuits can be conveniently and easily linked to each other, in a practical fabrication of a Josephson network.
Lead silicate optical coatings for GaAs-AlGaAs lasers
Authors: Barnes P. A. , Kyle T. R. , Grodkiewicz W. A. , Van Uitert L. G.
Published: February 2003

Lead silicate glass sputtered onto GaAs-AlGaAs injection lasers facets can yield optical coatings with near-perfect linear-expansion matching or refractive-index matching by adjusting the PbO : SiO2 ratio. Half-wave coatings increase the lasing threshold by less than 5%, while quarter-wave coatings allow a large increase in power output for less than a 30% increase in lasing threshold.
Measurement of 16-μm emission of a two-photon-excited ammonia laser
Authors: Flicker H. , Holland R. F. , Bischel W. K. , Pummer H. , Rhodes C. K.
Published: February 2003

The emission wavelengths at 16 μm of a two-photon-excited ammonia laser has been measured with improved accuracy. The measurement technique involves accurate calibration of the monochromator using well-known spectral lines and boxcar amplifiers to measure the total laser energy per laser pulse and the energy transmitted through the monochromator.
cw room-temperature laser operation of Nd : CAMGAR at 0.941 and 1.059 μ
Authors: Birnbaum M. , Tucker A. W. , Fincher C. L.
Published: February 2003

Continuous-wave laser operation at 300 °K at 941 and 1059 nm has beeen demonstrated using Nd : CAMGAR. Discrimination against the 1059-nm line required only tuned dielectric mirrors because of the strong 941-nm fluorescence. Gain and loss coefficients at 1059 nm were determined.
Broadening of x-ray diffraction lines from small subgrains containing gradients of spacing
Authors: Houska C. R.
Published: February 2003

Recent data on subgrain size and spacing gradients in the Cu-Ni system allow a more critical examination of a technique currently used to obtain the composition profiles of small diffusion zones. These data support the assumption that the broadening from individual subgrains need not include a spacing gradient term when volume diffusion is predominant. However, care should be taken in the interpretation of the earliest stage of diffusion where grain boundaries, surface, and other defects may introduce large spacing gradients.