bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric properties of amorphous Se–Bi and Se–Bi–As films
Authors: Goldstein I. S.
Published: February 2004

The complex dielectric constant frequency spectra of vapor-deposited amorphous Se–Bi and Se–Bi–As films were measured as a function of heat treatment near the glass transition temperature. The observed dielectric dispersions have been attributed to interfacial polarization arising from a layering of alternate high-bismuth and low-bismuth amorphous phases parallel to the surface of the film. Theoretical equations based on this interfacial polarization model have been used to reproduce the observed dielectric behavior. The model can correctly fit the observed loss peak frequencies and amplitudes and the increase of the peak frequencies with increasing time of heat treatment for lower-bismuth-concentration films (<5.0 at.% Bi). At higher bismuth concentrations conducting paths must be proposed in order to account for the very large dispersion peaks and low-frequency dielectric constants which are observed. These paths occur either through individual high-bismuth layers or through the bulk of the film. The addition of arsenic to the low-bismuth-concentration films increases the over-all conductivity and causes a conductivity maximum with heat treatment in the high-conductivity layers. In the high-bismuth-concentration films the arsenic tended to stabilize the amorphous phases of the film.
Electron impact cross sections and rates for one- and two-electron aluminum ions
Authors: Oran E. , Davis J.
Published: February 2004

A semiclassical impact parameter method has been used to calculate the Gaunt factors, cross sections, and rates for electron-impact excitations between selected states of the hydrogenlike and heliumlike ions of aluminum. These results are compared to the ``universal'' values suggested by Allen. For the resonance transitions, agreement with Allen's values becomes poorer as the charge on the target increases. Agreement is good for the nonresonant transitions.
Simple nonequilibrium model for shock-heated monatomic gas irradiated by an intense laser beam
Authors: Cohen Howard D. , Su F. Y. , Boni A. A.
Published: February 2004

In this paper, we present a method of analysis by which the Maxwellianized electron cascade equations are coupled to the fluid-mechanics conservation equations for the purpose of investigating the effect of a shock-induced flow field on breakdown. A particular example of breakdown initiated behind a previously existing blast wave in argon is investigated. It is shown that the breakdown process may be hindered by the rapid hydrodynamic cooling due to geometrical expansion of the mass element under consideration.
Measurement of diffusion length in solar cells
Authors: Reynolds J. H. , Meulenberg A.
Published: February 2004

New procedures are described for analyzing diffusion length measurements obtained by using several methods which, in the past, have shown inconsistent results. These procedures consist of a microwave photoconductive decay method and three techniques in which carriers, generated by γ rays, 1-MeV electrons, or ir light, are collected by a p-n junction. Special attention is given to measurements of solar cells in which the sample thickness may be comparable to the diffusion length. A theoretical analysis of each method is presented, as well as the results of a study in which a set of solar cells with a wide range of diffusion lengths was measured. It is shown that results from all methods are consistent over the entire range. A discussion of the advantages and disadvantages of the various methods is also included.
Effect of surface regions on the electrical conductivity of extrinsic semiconductor films
Authors: Covington D. W. , Ray D. C.
Published: February 2004

Theoretical expressions based on the Boltzmann transport equation, nondegenerate statistics, and Poisson's equation are derived for the electrical conductivity of extrinsic semiconductor films. The theoretical conductivity is presented as a function of film thickness and Fuch's scattering indices for the nondegenerate n- or p -type semiconducting films. The analysis predicts that the conductivity of thin films having quasisymmetrical space-charge layers at the surfaces should be strongly dependent upon the excess carrier density in these layers even under conditions of specular surface scattering. The limited amount of conductivity data reported for epitaxial germanium films are interpreted using the extrinsic film model. Universal curves are presented for normalized film conductivity as a function of normalized film thickness for accumulated n- and p -type films and depleted n- and p -type films having specularly scattering surfaces. The general case analysis yields the symmetrical and flat-band results as previously reported. The symmetrical-field case is briefly reviewed as an aid for comparison.
Gain-narrowing studies with an organic dye laser
Authors: Marowsky Gerd
Published: February 2004

Efficient spectral narrowing of the emission of a flashlamp-pumped dye laser with nonresonant feedback is reported. Line narrowing from 32 nm to less than 2 nm at peak output powers up to 15 kW has been observed.
Concentration dependence of the refractive index for n - and p -type GaAs between 1.2 and 1.8 eV
Authors: Sell D. D. , Casey H. C. , Wecht K. W.
Published: February 2004

The refractive indices of GaAs at room temperature were determined from accurate double-beam reflectance measurements. The uncertainty in the refractive indices obtained by this technique is ±0.005. Measurements were made on high-purity n -type samples, n -type samples with free-electron concentrations from 5×1016 to 6.7×1018 cm−3, p -type samples with free-hole concentrations from 1.5×1016 to 1.6×1019 cm−3, and p -type samples heavily doped with the amphoteric impurity Si. These data agree with Marple's prism refractive data for both of his samples of the same impurity concentration. Analysis of the reflectance for the high-purity samples permitted assignment of the room-temperature energy gap as 1.424±0.001 eV. The shape of the refractive-index-vs-energy curve was found to be strongly dependent on the carrier concentration at energies near the direct energy gap.
Crystal growth and recovery of ferromagnetism during thermal cycle in MnBi films
Authors: Honda Shigeo , Kusuda Tetsuzo
Published: February 2004

this paper reports details of the magnetic domain configuration during crystal growth and the exciting phenomena during the thermal cycle around the Curie temperature. The experiments suggest the conditions for producing large hexagonal single-crystal MnBi platelets: (i) Substrates must be clean; (ii) Bi and Mn should be evaporated in this sequence with the atomic ratio of Mn to Bi between 0.5 and 0.7; and (iii) annealing should be done with the thermal cycle through the critical temperatures Tc1 (about 360 °C) and Tc2 (about 350 °C), under high vacuum. On the other hand, the most useful films for Curie-point writing with high bit density are produced by annealing the double-layer film, with the ratio of Mn to Bi between 1.5 and 2.0, at a low temperature of 200–300 °C.
Influence of the crystalline electric field on the heat capacity and resistivity of PrAl3
Authors: Mahoney J. V. , Wallace W. E. , Craig R. S.
Published: February 2004

Results of heat-capacity and resistivity measurements performed on PrAl3 between 1.5 and 300 K are utilized to reveal and characterize the influence of the crystalline electric field on the ground-state multiplet of Pr+3 in PrAl3. Also reported are the results of heat-capacity measurements on the isostructural nonmagnetic counterpart LaAl3 for which there are only vibrational and electronic contributions to Cp. Below 180 K, the excess heat capacity of PrAl3 over that of LaAl3 exhibits of Schottky-type thermal anomaly peaking at 25 K and is attributable to excitation within the crystal-field states. Resistivity results indicate a temperature-dependent spin-disorder contribution at low temperatures associated with the splitting of the ground-state multiplet by the crystal field. The higher-temperature resistivity behavior is observed to be a linear function of temperature and can be readily assigned to phonon contribution. The crystal-field interaction is analyzed using the crystal-field Hamiltonian, HCF=W246 (1 − |y|)O2/F2 + y[xO4/F4 + (1 − |x|)O6/F6], which incorporates a second-order term to account for the nonideal crystallographic c/a ratio exhibited by PrAl3. Best agreement between experimental and calculated heat capacity, resistivity, and susceptibility was obtained using the parameters x=−0.60 and y=0.65 with a positive value of W246. A singlet ground state results with an over-all splitting of the crystal-field levels of 132 K. The parameters x and y are in reasonable agreement with calculations based on the point-charge model.
An equation for fracture energy determination by double-cantilever cleavage
Authors: Hindman D. L. , Jones J. T. , Determan W. R.
Published: February 2004

With the aid of elementary beam theory a Lagrangian equation of motion was developed to relate the crack velocity to cleavage energy in a double-cantilevered single-crystal specimen when shear contributes significantly to the cleavage energy. For a constant cleavage energy the equation predicts that the square of crack length is proportional to time when the crack is long with respect to transverse specimen dimensions. For shorter cracks, crack length is proportional to time.
Resistivity of Permalloy thin films
Authors: Mayadas A. F. , Janak J. F. , Gangulee A.
Published: February 2004

Data on resistivity at room temperature in polycrystalline and single-crystal Permalloy (80 Ni-20 Fe) thin films are analyzed in terms of grain boundary scattering and the dc size effect, respectively.
Diffusion effects in one-carrier space-charge-limited currents with trapping
Authors: Rosental A. , Sapar A.
Published: February 2004

The one-carrier injection current-voltage characteristics for insulators having two equal metal contacts and containing traps are computed, together with the free-carrier zero-bias spatial distributions, for extrinsic semiconductors. It is shown that the overlap of the contacts may give rise to trap-filled-limit characteristics governed by a power law. The steepness of these characteristics proves to be less than that predicted by Lampert and Edelman. The shallow-trap square-law characteristic may be entirely replaced by an overlap-determined Ohm's law characteristic. The overlap sometimes fails to be removed through impurity conduction.
Galvanomagnetic measurements on thin PbSe epitaxial films as a function of O2 and H exposure
Authors: McLane George F.
Published: February 2004

The effect of O2 and H on the galvanomagnetic properties of p- and n-type PbSe epitaxial films on NaCl substrates is investigated. O2 has been found to make these films p type, while H makes them n type. The Hall coefficient R, the electrical conductivity σ, and the magnetoresistance Δρ/ρH2 are measured as a function of O2 and H uptake by the films. These measurements can be correlated with film parameters such as layer thicknesses, carrier mobilities, and carrier concentrations, and they indicate that the presence of H produces appreciable carrier scattering. O2 appears to cause these films to have a highly p-type surface region that cannot be converted to n type by the H.
Auger analysis of films formed on metals in sliding contact with halogenated polymers
Authors: Pepper Stephen V.
Published: February 2004

The transfer characteristics of polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), and polychlorotrifluoroethylene (PCTFE) sliding on metals were studied by Auger electron spectroscopy. The polymers were slid on atomically clean S-Monel at room temperature in ultrahigh vacuum, and the track of the slider on the metal was subjected to in situ Auger analysis. A discussion of the Auger spectrum of PVC showed that the chlorine was highly susceptible to electron-induced desorption and a part of it exhibited a desorption cross section of ≳10−16 cm2. This high cross section for desorption of the halogen was postulated to be a necessary condition to be satisfied by the Auger spectra of all halogenated polymers and assists in determining whether a polymer transfer film is established on the metal by sliding. It was found that a polymer transfer film was established by sliding PTFE. The film was uniform and continuous, and no buildup occurred with multiple traversals. The film thickness was estimated to be 2–4 atomic layers. A polymer transfer film was not established by sliding PVC or PCTFE. Instead, a chemisorbed film of approximately monolayer coverage was generated on the metal surface. In the case of PVC this film consisted largely of chemisorbed chlorine, whereas PCTFE may possibly have produced chemisorbed chain fragments on the metal surface. This correlates with the thermal decomposition behavior of these polymers and indicates the possibility of decomposition of the polymer surface by frictional heating.
Electron-irradiation-induced damage production effects in lightly doped n - and p -type α-tin
Authors: Myhra S. , Gardiner R. B.
Published: February 2004

Irradiations at 4.5 K using 0.675-MeV electrons have been performed on a number of n - and p -type α-tin filaments, with impurity concentrations from 4×1015 to 2×1017 cm−3. Large and reproducible changes with radiation dose have been observed in the electrical resistivity and the thermoelectric power, resulting from changes in carrier concentrations and carrier scattering. It is shown that a model, which requires that the induced defects behave as acceptor sites, accounts satisfactorily for the experimental results. A carrier removal rate of 0.6±0.1 cm−1 is deduced and is compared to the theoretical damage production rate of 1.6±0.3 cm−1; this indicates that only a fraction of the induced defects are active as carrier removal centers. Mobilities (μe and μh) have been calculated as functions of impurity and defect concentrations. It is found that the observed changes in the polarity of the thermoelectric power with dose can be accounted for qualitatively.
Photoconductivity in the amorphous Ge-rich Gex Te1—x system
Authors: Scharnhorst K. P. , Riedl H. R.
Published: February 2004

Experimental results on photoconductivity, Δσ, in as-deposited and annealed vacuum-evaporated amorphous films of Gex Te1—x, in the composition range 0.5≤x≤0.7, and of Ge are reported and compared with published photoconductivity data for GeTe2 and Te. Whereas Δσ(T) of Te, GeTe2, and GeTe between 100 and 300°K is characterized by only a single maximum typical of multicomponent chalcogenide glasses, Δσ(T) of the as-deposited Ge-rich samples and of as-deposited and annealed amorphous Ge was found to exhibit a minimum as well as a shallow maximum in this temperature range. A comparison of the present data with those for Te and GeTe2 further shows that amorphous Te is the most sensitive photoconductor in this group of amorphous semiconductors and that the photosensitivity decreases monotonically with increasing Ge content. It is suggested that both the new structure in Δσ(T) and the quenching effect of added Ge are results of increasing densities of localized states—in particular, of midgap states—in compositions with increasing Ge content. Possible correlations between localized-densities-of-states distributions and recombination mechanisms are discussed.
Energy spectra of laser-produced ions
Authors: G. E. Bernal , Ready J. F. , Allen F.J.
Published: February 2004

This paper presents results on mass-resolved and time-resolved energy spectra of the ions produced by the interaction of a laser pulse with an absorbing surface. A Q-switched CO2 laser with a pulse width of 775 nsec and a power density at the target of approximately 7 × 106 W/cm2 was used to produce the ion emission inside a time-of-flight mass spectrometer. A method of data reduction was developed that yields the time development of the energy spectrum during each laser pulse with a resolution of approximately 100 nsec. The energy distribution of ions changes from one containing mostly low-energy species during the early part of the laser pulse to a spectrum peaked at its high-energy end near 200 eV later in the laser pulse.
Preparation and properties of high-Tc Nb–Ge films
Authors: Gavaler J. R. , Janocko M. A. , Jones C. K.
Published: February 2004

Using a previously reported low-energy sputtering technique, Nb-Ge films have been prepared with superconducting Tc's up to ∼23 K. High-field, x-ray, and annealing results are reported for these highest-Tc films. A discussion of the critical parameters required to achieve the highest transition temperatures in the Nb–Ge system is given. Also further arguments in support of the theories that these highest Tc's are due to the formation of the stoichiometric Nb3Ge phase in the sputtered films are presented.
Static bubble domain properties of amorphous Gd–Co films
Authors: Hasegawa Ryusuke
Published: February 2004

Metallic Gd1−xCox films (0.75 < × <0.85) obtained in the amorphous state by an rf-sputtering were investigated using the Kerr polar magneto-optic effect. These films exhibit perpendicular anisotropy sufficient to sustain magnetic cylindrical domains. The magnetic properties obtained with a Kerr hysteresigraph from these films can be described in terms of the wall energy model developed originally for nonmetallic single-crystal bubble material. An analysis based on a simple molecular field description of the magnetization and a mean field approximation of the exchange constant A gives estimates of the uniaxial anisotropy energy Ku. The results indicate that for the composition range studied A increases linearly from 5.7 to 6.6 (10−7 erg/cm), while Ku ranges between 1 and 7 (105 erg/cm3). The saturation magnetization Ms varies between 30 and 180 G. The moderate anisotropy (Q=Ku/2πMs2 = 1–9) and low wall motion coercivity of less than 1 Oe are favorable to bubble device applications. The effect of thermal and magnetic annealing on the magnetic properties is also discussed.
Dynamic conversion during magnetic bubble domain wall motion
Authors: Hagedorn F. B.
Published: February 2004

The experimentally and previously observed erratic propagation of an individual magnetic bubble domain during repetitive bubble transport measurements has been attributed to the dynamic conversion of a normal bubble domain wall into a relatively immobile state. A model for dynamic conversion is presented in this paper. The model extends previous work of Slonczewski and Thiele and suggests that the immobile wall state contains both moving horizontal Bloch lines and stationary vertical Bloch lines, the latter of which are parallel with the cylindrical axis of the bubble domain. The model accounts qualitatively for the evolution of this state from a normal bubble and for its return to the normal bubble state when motion ceases. Interactions between the moving domain wall and material inhomogeneities are postulated to be important in initiating dynamic conversion, and it is suggested that the erratic characteristics associated with dynamic conversion arise from the statistical nature of these interactions. Methods of suppressing dynamic conversion are discussed. The three most important methods appear to be to restrict bubble domain velocities to values below a critical value, to use a large in-plane anisotropy, or to employ a special three-layer structure in which the bubble domain wall becomes dynamically stabilized against dynamic conversion.
Correlation functions for predicting properties of heterogeneous materials. II. Empirical construction of spatial correlation functions for two-phase solids
Authors: Corson Peter B.
Published: February 2004

This paper postulates analytic expressions for two- and three-point probability functions of statistically homogeneous and isotropic two-phase materials with differing phase geometries. Sums of exponentials are used to represent the probability functions, and a curve-fitting procedure for fitting the exponentials to the data is indicated. A comparison of the constructed functions with the original experimental data is given for a specific case. Empirical constants of constructed probability functions which have been fitted to existing experimental data are also given for 10 available experimental materials.
Secondary emission and photoemission from negative electron affinity GaP : Cs
Authors: Martinelli Ramon U.
Published: February 2004

Secondary emission and photoemission measurements have been made on a negative electron affinity (NEA) GaP : Cs sample. An analysis of the photoemission data gives a surface escape factor B =0.33 and an electron diffusion length L =0.2 μm. The secondary emission ratio data extended over the primary energies Ep of 0–14 keV. If the range of the primary electrons R is assumed to be of the form R=a Epb μm (Ep in keV), then analysis of the secondary emission data gives a =0.0095 μm and b =2.0.
Texturing: A new effect in the dynamic scattering regime of liquid-crystal cells
Authors: Alt Paul M. , Freiser M. J.
Published: February 2004

A phenomenon observed in homeotropically aligned liquid-crystal cells after prolonged excitation in dynamic scattering is presented. The phenomenon, because of its visual appearance, is called texturing and is found to be associated with the induction of a metastable configuration in the liquid crystal. A model for the metastable configuration which is consistent with the experimental observations is proposed. Texturing is undesirable in display applications and has been found to occur in matrix-addressed liquid-crystal cells.
X-ray diffraction from a vibrating ADP crystal
Authors: Pertmer G. A. , Hansen D. A. , Parkinson T. F.
Published: February 2004

The enhancement and modulation of x rays diffracted from two planes of an ammonium dihydrogen phosphate crystal have been measured with the crystal driven in its fundamental piezoelectric vibration mode. Both effects are qualitatively similar to results obtained with neutrons diffracted from ADP and from quartz crystals.
Halogen vapor deposition of chalcogenide crystals: Lead sulfide
Authors: Kwan S. H. , Fonstad C. G. , Colozzi A. , Linz A.
Published: February 2004

n-type single crystals of lead sulfide, PbS, have been grown by a novel chemical vapor deposition method of potential importance for growing a variety of chalcogenide crystals. A reduced-pressure flowing system was developed based on the following chemical reactions: Pb+Cl2→PbCl2 and PbCl2+H2S→PbS+2HCl. Additional Cl2 is used for fine control of the growth rate. The optimal growth conditions are a temperature of 650 to 750°C and a pressure of 8 Torr. Important to the furnace design is a quartz concentric gas injection arrangement which prevents premature mixing and reacting of the gases. n-type single crystals of PbS having carrier concentrations of the order of 1019 cm−3 and Hall mobilities of 600 cm2/V sec at 300°K and as high as 14 000 cm2/V sec at 77°K have been grown. An isothermal anneal at 850°C for 15 days will convert the crystals to p type. Possible extensions of the technique to mixed lead-tin salts, including tellurides and selenides, and to other chalcogenides are discussed.
Radio-frequency fields in magnetoactive plasma
Authors: Skipping C. R. , McDaniel D. H. , Oakes M. E.
Published: February 2004

Electric field componenets produced by a single-turn current sheet concentric with a finite magnetoactive plasma cylinder are calculated for frequencies corresponding to resonant peaks in the series loading resistance near the lower hybrid resonance. The radial electric fields are found to be quite large and to penetrate well into the plasma. Axial electric fields are not negligible for a variety of conditions. Expressions for the field components permit calculations for any azimuthally symmetric distribution of current in the sheet.
Shock decay in a stress-relaxing fluid in steady plane flow
Authors: Duvall George E.
Published: February 2004

A constitutive relation for a stress-relaxing fluid is combined with equations of motion and continuity for two-dimensional steady plane flow. Coordinates are attached to an arbitrary point on a shock front, and a differential equation is obtained for the decay rate of shock pressure with distance along the shock front. The decay rate depends on the stress-relaxation function, the pressure gradient normal to the shock front, and the curvature of the shock front. Except for the last term, the decay equation is shown to transform to that which applies to plane time-dependent flow. It is suggested that in some cases the relaxation function as a function of pressure can be obtained by measuring the shock-front profile.
Efficient red GaP LED's with compensated p layers
Authors: Bhargava R. N. , Mürau P. C.
Published: February 2004

Efficient red GaP LED's have been fabricated by compensating the p side of the junction with a donor. The observed efficiency in the diodes fabricated remains invariant over a wide range of net acceptor concentration. Utilizing the recombination kinetic analysis of Jayson, Bhargava, and Dixon, it is shown that better injection efficiencies and higher Zn–O complex concentrations are the cause for this invariance. The compensation technique potentially offers a commercial LPE growth process from which high-efficiency low-cost LED's could be fabricated.
Observation of afterglow character and high gain in the laser lines of O(III)
Authors: Pappalardo R.
Published: February 2004

Under short-pulse excitation, 0.5–1.0 μs, O(III) laser emission in the visible and uv is only observed after extinction of the current pulse. The observed high gain and high power (∼100 W) of the 5592.6-Å line is related to the afterglow character of the lasing. Two new lasing lines of O(III) have been observed at 3757.2 and 3773.8 Å. In pulsed discharges through xenon-oxygen mixtures, laser emission from xenon occurs during the current pulse, while the lasing from oxygen occurs 0.8 μs later. The use of the O(III) laser line at 5592.6 Å for the pumping of dye lasers is suggested.
Mössbauer and crystallographic study of DyFe3−x Nix compounds
Authors: Tsai S. C. , Narasimhan K. S. V. L. , Kunesh C. J. , Butera R. A.
Published: February 2004

Mössbauer and crystallographic investigations were carried out on DyFe3−x Nix compounds crystallizing in the PuNi3 type of structure. The hyperfine field observed at the iron sites shows a maximum at x =0.75. The 12-line spectrum observed at room temperature corresponding to the two different kinds of iron in the structure collapsed into a single six-line pattern at 4.2 K. Lattice parameter c shows a rapid decrease when x is increased beyond 2.0, but no such behavior was found in the a lattice parameter. The results of the x-ray and Mössbauer data are explained in terms of site preference and nonlocalized transition-metal moments, respectively.
Singular points in the magnetization curve of a polycrystalline ferromagnet
Authors: Asti G. , Rinaldi S.
Published: February 2004

The reversible magnetization curve M(H) of a polycrystalline ferromagnet has been investigated with the objective of examining the properties of the singularities located at H = −HA, the anisotropy field, along the hard direction. Using a simple model that approximates the system as a continuous assembly of noninteracting particles, we show that the singular point becomes apparent in the successive derivatives dnM/dHn plotted as functions of H. Indeed, differentiation accentuates more and more the singularity hidden in the magnetization curve, and the minimum order n* at which it can be detected is the order for which the function dn*M/dHn* has a discontinuity in the slope at the singular point. The general formula for the dependence of n* on the symmetry properties of the hard direction is given together with the analytical expression for the shape and amplitude of the singularity in the most important cases. The same sort of phenomenon is shown to be present in the reversible transverse susceptibility, and the general expression for nt* is also given. For all the symmetry cases, nt* turns out to be lower than n*. Experimental tests of the theory have been carried out for binary axes of both uniaxial and cubic materials—namely, BaFe12O19, Fe, and CoFe2O4. The singularity appears in d2M/dH2, as expected, and position and amplitude are in good agreement with the values predicted by theory. The suggestion is made that singular point detection (SPD) could be used as a new technique for measuring the anisotropy in polycrystalline samples.
Atomic ordering in A 15-type phases in the vanadium–nickel and vanadium–cobalt systems
Authors: Waterstrat Richard M. , Dickens Brian
Published: February 2004

Atomic ordering in the V–Ni and V–Co A 15-type phases has been studied using neutron diffraction. The V–Ni structure is shown to be ordered to the maximum extent permitted by the ``off stoichiometric'' composition, V77.5Ni22.5. The V–Co structure possessing the ``ideal'' composition V75.0Co25.0 is also highly ordered. However, the V–Co diffraction data are less accurate due to neutron absorption by the cobalt atoms and interference from the sample holder. No magnetic structures were detected in the V–Co phase at 4.2 °K.
Preparation and properties of sputtered MgO/Au, MgO/Ag, and MgO/Ni cermet films
Authors: Fan John C. C. , Henrich Victor E.
Published: February 2004

Finely grained films of three cermets-MgO/Au, MgO/Ag, and MgO/Ni-have been grown by rf sputtering from composite targets. Electron-microscopic studies show that MgO/Au and MgO/Ag films consist of small crystallites (usually <150 Å) of both MgO and Au or Ag. In MgO/Ni films, it appears that amorphous Ni particles are embedded in a polycrystalline MgO matrix. These cermet films are good secondary-electron emitters, especially in cases where differential-sputtering effects are large. In MgO/Au films, the Au particles sputter much faster than MgO resulting in a MgO-rich surface layer. In MgO/Ag films, the differential-sputtering effect is smaller, probably due to stronger interaction between MgO and Ag crystallites. In MgO/Ni, the Ni particles sputter slower than MgO resulting in a slightly Ni-rich surface (and hence in poorer electron-emission properties). The small particle sizes and the presence of metallic particles in the bulk of the films greatly reduce surface charging.
Dielectric response of anisotropic polarized particles observed with microwaves: A new method for characterizing the properties of nonspherical particles in suspension
Authors: Tolles W. M. , Sanders R. A. , Fritz G. W.
Published: February 2004

The dielectric response of zinc oxide particles to applied electric fields in nitrogen has been observed in a microwave cavity designed for this purpose. With phase-sensitive detection it is estimated that, with these zinc oxide samples, densities of one part in 108 (volume ratio) are detectable. Dielectric saturation and relaxation characteristics are observed with particles several microns in length. It is shown that with measurements of sample concentration, change in cavity Q, dielectric relaxation time, and the ratio of absorption to dispersion, these experiments can yield the length, diameter, and conductivity of the particles. These techniques should be useful for determining the conductivity of micron or submicron crystals or polymer units, for nucleation and crystal growth studies, and for obtaining information on nonspherical aerosol particles.
Formation of interface states and defects in GaAs–AlxGa1−xAs DH lasers under room-temperature cw operation
Authors: Yang Edward S.
Published: February 2004

Experimental results of an investigation on the nature of degradation-induced defects in AlxGa1−xAs–GaAs double-heterostructure injection lasers are presented. The variation of junction capacitance data before and after aging indicates that defects are generated initially at the p-n heterojunction interface and later spread into the active layer as traps. The density of interface states is calculated to be on the order of 1012 cm−2 and the density of traps in the active layer is calculated to be greater than 1017 cm−3. In addition, the carrier lifetime is measured by using both the delay-time and voltage-decay methods. After degradation, the carrier lifetime reduces slightly at the appearance of interface states but shows significant changes when traps are detected in the active layer. An explanation is given and correlated with the threshold-current variation.
Electron transport and emission characteristics of negative electron affinity AlxGa1−xAs alloys (0≤x≤0.3)
Authors: Martinelli Ramon U. , Ettenberg M.
Published: February 2004

Photoemission and secondary-emission measurements were made from AlxGa1−xAs (x=0, 0.1, 0.2, and 0.3) surfaces which were activated to negative electron affinity (NEA) using Cs and O2. Values for the diffusion length L and the surface escape factor B were determined from the data for each alloy composition. It was found that B decreases with increasing AlAs composition and that the diffusion lengths for all the alloys examined were at least 6.0 μm.
Effects of spatially inhomogeneous oxide charge distribution on the MOS capacitance-voltage characteristics
Authors: McNutt M. J. , Sah C. T.
Published: February 2004

The commonly assumed linear model of surface potential fluctuation using a Gaussian distribution is shown to be invalid. A macrocapacitor model previously proposed by us is used to analyze the effects of spatially inhomogeneous oxide charge distribution on the MOS C-V characteristics at various rms oxide charge deviations and temperatures. It is shown that a Gaussian oxide charge distribution of rms value of as low as 1011 electrons/cm2 gives rise to a doubly peaked probability distribution of the surface potential fluctuation. Substantial errors in fast surface state density occur using either the low-frequency capacitance (Berglund), the high-frequency capacitance (Terman), or the temperature dependence (Gray-Brown) analysis of the fast surface states from C-V curves. A major source of error is in the value of the average surface potential which is changed substantially from the ideal case by the presence of inhomogeneous oxide charge distributions.
Properties of high-voltage silicon epitaxial diodes
Authors: Kressel H. , Robinson P. , D'Aiello R. V. , McFarlane S. H.
Published: February 2004

Multilayer Si-epitaxial junctions are described with theoretically limited breakdown voltages as high as 1800 V over moderate areas using a vertical mesa configuration. The diodes were grown by the dichlorosilane method on heavily doped substrates. X-ray topography shows the misfit dislocations as lying mostly in the interface region between the substrate and the epitaxial layer.
Theoretical model for an advanced bremsstrahlung converter
Authors: Halbleib J. A.
Published: February 2004

The model described may be used to predict the output of a bremsstrahlung converter system consisting of one or more thin converter foils immersed in a uniform magnetic field whose direction is oblique to the foil normal(s). This model is a superposition of the vacuum helical trajectories of the electrons and a Monte Carlo collisional transport of photons and electrons. Predictions of radiation environments of these ``advanced'' converters are compared with those of more conventional converters. It is shown that one may extract a comparable, if not greater amount of bremsstrahlung energy from the relatively thin advanced converters and that the spectra are considerably softer. Because of the higher solid-angle reduction inherent in the advanced converter geometries, however, it is concluded that they will not lead to significantly higher point bremsstrahlung deposition in irradiated materials. Nevertheless, higher deposition should be possible where large exposure areas are required.
Mobility in epitaxial GaAs under 1-MeV electron irradiation
Authors: Dresner J.
Published: February 2004

Vapor-grown epitaxial layers of undoped n-type GaAs show an anomalous large decrease in apparent mobility upon irradiation with a small dose of 1-MeV electrons. As the dose is increased, the samples become p type. The results cannot be accounted for by a uniform distribution of radiation-induced point defects. It is proposed that spatial inhomogeneity is induced by the irradiation. A possible mechanism is the ionization-induced migration of deep donors to a network of dislocations in the layer. This migration can be reversed by annealing.
Comment on ``Magnetohydrodynamic boundary layer control with suction or injection''
Authors: Chuang Hsing
Published: February 2004

The governing equation for a steady two-dimensional MHD boundary-layer flow is shown to depend upon certain proper assumptions which result in simplification and approximation. Improper assumptions such as a constant free-stream velocity as well as a zero hydrostatic pressure gradient yield an equation which does not actually represent any physical model of an MHD boundary-layer flow on a flat plate.
Effect of the current-phase relationship on the I-V characteristics of weak links: Noise effects
Authors: Falco C. M.
Published: February 2004

When noise effects are considered, the quasiparticle-pair interference current is shown to have an observable effect on the behavior of superconducting weak links even when the I-V characteristics calculated in the absence of noise are indistinguishable from those calculated without the interference current.
NMR Line Shapes and Path Averages
Authors: Fixman Marshall
Published: February 2004

The functional integration techniques of Kac are shown to be applicable to an evaluation of Anderson's relaxation function. The evaluation is worked through for the rotational diffusion model, and the essential features of the Monte Carlo calculation by Saunders and Johnson are confirmed.
Viscoelasticity of Networks Consisting of Crosslinked or Entangled Macromolecules. II. Verification of the Theory for Entanglement Networks
Authors: Chompff A. J. , Prins W.
Published: February 2004

The molecular theory of the viscoelasticity of entanglement networks developed in the first part of this series is refined. From an approximate treatment, the relaxation spectra of these networks can be determined analytically. The predictions are in good agreement with the values obtained from more accurate calculations performed on a computer. Equations are obtained and mathematical procedures developed to determine from experimental data the necessary parameters m and δ, where (m — 1) is the average number of entanglements per molecule, and δ is a slip parameter. The results of the theory are tested on data for the mechanical properties of a high molecular weight sample of poly-n-octyl methacrylate. Calculations are performed with one set of m and δ and a single molecular weight of 3.36 × 106. With the values of 81 for m and 10−5 for δ the calculations carried out on a computer yield the relaxation spectrum of this sample over nine decades of time. Corrections for molecular rotations are taken into account by assuming that the friction factor f is molecular-weight dependent. In spite of the lack of knowledge of the molecular-weight distribution of this sample, it turns out that the agreement between theory and experiment is very good, although some discrepancy is noted. A more precise fit would be expected if the molecular-weight distribution were known.
Multiple Solutions to the Hartree-Fock Problem. I. General Treatment of Two-Electron Closed-Shell Systems
Authors: Stanton Richard E.
Published: February 2004

The number of fully self-consistent, closed-shell solutions to the two-electron Hartree-Fock problem is investigated. With N orbital basis functions the Hartree-Fock wavefunction can be expanded as a superposition of N(N + 1) / 2 configurations. The constraints in the coefficients are analyzed exactly for the case N = 2. The free CI problem corresopnds to finding energy extrema on the surface of a sphere. The Hartree-Fock state point is constrained to lie on a circle on this sphere. There will be two, three or four SCF solutions depending on the manner in which the circle of constraint crosses valleys and ridges on the sphere. This is shown explicitly by detailed calculations for the He atom. These calculations also reveal instances in which aufbau method of solution necessarily diverges. The general problem can be analyzed under the assumption of zero differential overlap. The Hartree-Fock matrix is diagonal in this approximation, but the diagonal elements still involve the orbital coefficients. One can set an upper limit of (3N − 1) / 2 to the number of acceptable solutions for this problem.
Structural Features in Germyl Isocyanate from Infrared Spectroscopy
Authors: Griffiths James E.
Published: February 2004

An infrared spectral study, from 4000 to 33 cm−1, of the product of the reaction between GeH3Br and silver cyanate has been completed. The product is an isocyanate, GeH3NCO, but evidence for a small amount of the normal cyanate form is also presented. Germyl isocyanate, unlike SiH3NCO, has a nonlinear skeleton and an estimate of the deviation from linearity is about 10°. The vibrational spectra of the GeH3 and GeD3 derivatives are assigned in terms of a pseudo symmetric-top model of C3υ≃Cs symmetry. Rotational fine structure in two of the perpendicular-type fundamentals was used to evaluate the nonlinearity in the skeleton.
Calculation of Three-Body Ionic Recombination Rate
Authors: Landon Stephen A. , Keck James C.
Published: February 2004

The three-body ionic recombination rate at low densities is calculated for a slightly ionized gas by considering that the relaxation of the energy of molecules occurs by a “diffusion” process. The effective conductivity in the equivalent diffusion equation is the second moment of the energy transfer.

The moments are derived in closed form using classical mechanics and enable the recombination rate constant to be obtained. The agreement of the results with experimental data is good and suggests that the approach is useful even where relatively large energy transfers are involved.
Minimal-Basis-Set LCAO–SCF–MO Calculations for the Ground State of O3, NO2–, NOF, and OF2 Molecules
Authors: Petrongolo Carlo , Scrocco Eolo , Tomasi Jacopo
Published: February 2004

Ground-state wavefunctions for the nonlinear triatomic molecules O3,NO2–, NOF, and OF2 are computed. The calculation was performed in two versions both using the minimal set of STO's in the LCAO–SCF–MO approximation and differing only in the choice of the orbital exponents. The results of a population analysis are also presented.
Use of Model Potentials in the Study of Molecular Rydberg States
Authors: Hazi Andrew U. , Rice Stuart A.
Published: February 2004

In this paper we investigate the applicability of simple model potentials containing adjustable parameters to the description of molecular Rydberg states. Qualitative criteria for the selection of appropriate potentials are discussed and the results of numerical calculations relevant to the Πu3 states of H2, the Σu1(2Σgcore) states of N2, and some Rydberg states of benzene are presented. It is found that the model potentials proposed adequately describe the effective potential of the positively charged core in the Rydberg states. In the case of benzene, a unique assignment of the experimentally observed Rydberg series is impossible because of the ambiguity of the calculated term values arising from the adjustable parameters in the potential. We also discuss the limitations of semiempirical potentials and suggest the use of model potentials that contain no adjustable parameters.
Accurate Perturbation-Variation Treatment of the Hydrogen Molecule
Authors: Matcha Robert L. , Brown W. Byers
Published: February 2004

A Rayleigh-Schrödinger perturbation treatment of electron repulsion in the ground state of the hydrogen molecule is presented. The perturbation energies were accurately determined from Hylleraas-type variational principles using a 50-term basis. The perturbation series appears to converge rapidly at the equilibrium distance, in a similar fashion to the series for the united atom, helium, obtained by Scherr and Knight (1963). The electronic energy through fifth order is − 1.88872 hartree, which is comparable with the straight variational result of − 1.88876 obtained by Kolos and Wolniewicz (1964).
Photoionization of High-Temperature Vapors. II. Sulfur Molecular Species
Authors: Berkowitz J. , Lifshitz C.
Published: February 2004

The photoionization efficiency curves of the sulfur molecular species generated by various solids have been measured. The ionization potentials (in electron volts) deduced are 9.36 ± 0.02 for S2, 9.68 ± 0.03 for S3, 8.60 ± 0.05 for S5, 9.00 ± 0.03 for S6, 8.67 ± 0.03 for S7, and 9.04 ± 0.03 for S8. No evidence for structures other than rings has been obtained. The threshold for dissociative ionization of S8 is in very good agreement with that deduced by earlier thermodynamic measurements.
Scattering Theory of Pressure Broadening of Rotational and Vibration–Rotation Transitions
Authors: Trindle C. O. , Illinger K. H.
Published: February 2004

An application of the scattering theory of pressure broadening to rotational and vibration–rotation transitions is presented. The coupled equations for scattering in anisotropic potentials are derived for a number of systems of chemical interest; general methods for the solution of the coupled equations are discussed. The equivalence of the lowest (Born) approximation to the scattering theory of collision broadening, in the limit of classical relative motion, and the Anderson perturbation theory is demonstrated.
Mössbauer Studies of the Iron Atom in Cytochrome
Authors: Cooke R. , Debrunner P.
Published: February 2004

Mössbauer spectra of the iron atom in horse-heart cytochrome c were observed in frozen solution and freeze-dried samples for both the oxidized and reduced states. At temperatures above 77°K, the spectrum of the oxidized enzyme consisted of a quadrupole-split doublet, broadened by a temperature-dependent, magnetic hyperfine interaction. The spectrum of the reduced enzyme consisted, at all temperatures observed, of two peaks with a quadrupole splitting of 0.12 cm/sec. Upon freeze drying, the quadrupole splitting of the oxidized enzyme decreased, whereas the spectrum of the reduced enzyme changed very little.