bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Properties of Dielectric Material on the Temperature Dependence of Tunnel Current in a Metal-Insulator-Metal Junction
Authors: Antula J.
Published: February 2004

The temperature dependence of the forbidden energy gap of the insulator and the positive ionic space charge in the insulator are discussed as possible explanations for the previously measured temperature dependence of the potential barrier height in a metal-insulator-metal tunneling junction. Theoretical results suggested the measurement of the temperature dependence of tunnel current as a function of the thickness of the insulating film. These measurements, carried out on an Al–(Al-oxide)–Al tunneling junction, are compared with theory and discussed. The Al-oxide was prepared by electrolytic anodization.
Reflectivity of Metals at High Temperatures
Authors: Ujihara Kikuo
Published: February 2004

The reflectivity and other optical constants of metals at high temperatures are discussed on the basis of the Drude theory and the theory of electron-phonon collision. The electron-phonon collision frequency is dependent on the temperature through the temperature dependence of the phonon population. The temperature dependence of the collision frequency determines that of optical properties of metals. Variations of the real and the imaginary parts of the dielectric constant and of the complex refractive index with temperature are considered. General expressions for the temperature coefficients of the optical constants are given. The reflectivity is shown to decrease with increasing temperature. Numerical calculations were carried out for several metals at a few wavelengths and at temperatures from room temperature to their melting temperatures. The results are given in graphs and in a table. Curves for the reflectivity show that the absolute value of the temperature coefficient of the reflectivity is greater for a metal having a lower reflectivity at room temperature. Calculated values of the reflectivity at room temperature are in reasonable agreement with handbook data. However, the calculated reflectivity for silver at its melting point is not coincident with the reported experimental data (the only data available at present), in spite of the qualitative agreement between our results and the experiment. A brief discussion on possible explanations of the discrepancy is made.
Role of Copper in the Degradation of GaAs Electroluminescent Diodes
Authors: Bahraman Ali , Oldham W. G.
Published: February 2004

The degradation associated with prolonged operation of GaAs diodes under large forward bias has been investigated. It is observed that the degradation rate increases with temperature and that the fractional percent degradation per unit time interval increases as exp (−E0/KT) for most devices. The value of E0 is about 0.45 ± 0.1 eV. It is shown that contamination of devices with copper increases the degradation rate. The 1.28-eV emission band in the degraded Cu-contaminated devices is enhanced relative to the band-edge emission at low temperatures. A Cu-contamination model for the degradation is considered which shows agreement with experimental data. Accordingly, the degradation is attributed to the diffusion of interstitial copper ions in the p region of the devices toward the junction during operation at high-current densities.
Magnetic Properties of Amorphous Fex Gdy Alloy Thin Films
Authors: Orehotsky J. , Schröder K.
Published: February 2004

The magnetism of pure iron and gadolinium films, and of Fex Gdy alloy thin films with 15 to 94 at.% iron prepared by codeposition on a cold (77 °K) substrate were measured at 77 °K and at room temperature. All the alloys had an amorphous structure that was stable to room temperature. The amorphous alloys were found to be ferrimagnetic. The magnitude of the magnetization in rare-earth transition-metal alloys does not appear to be structure sensitive since the magnetization of the amorphous alloys follows a linear concentration dependence calculated from an antiparallel coupling of the magnetic moments of crystalline iron and gadolinium.
Bialkali (K2 CsSb) Photocathode as a High-Gain Secondary Electron Emitter
Authors: Sommer A. H.
Published: February 2004

It has been found that the K2CsSb photocathode material has much higher secondary emission gain than the conventional Cs3Sb dynode material. Gain factors as high as 30 have been measured.
Thermodynamic Model for Porous Materials with Vacuous Pores
Authors: Cowin S. C.
Published: February 2004

A simple thermodynamic model for a porous material with vacuous pores is proposed. Shear stresses are neglected. The model is used to obtain formulas for the pressure and velocity of sound in the bulk porous material for small porosities. As a first approximation for small porosity, it is shown that the pressure in the bulk material is equal to what the pressure in the matrix material without pores would be times one minus the porosity and that the velocity of sound in the bulk material is equal to the velocity of sound in the matrix material.
Acoustic Convolution and Correlation and the Associated Nonlinearity Paramaters in LiNbO3
Authors: Luukkala M. , Surakka J.
Published: February 2004

The parametric interactions of two oppositely propagating modulated acoustic surface waves can be used to produce acoustic convolution and correlation in YZ-cut LiNbO3 crystals in the 100–200-MHz range. Since the performance of these nonlinear devices depends critically upon the nonlinear properties of the materials used, the interaction is investigated in terms of the associated nonlinear free energy and the relevant expressions for the parameters are derived and also measured experimentally. The measured nonlinearity constants are K = 6.7 N/V m for convolution and Λ = 0.16×10−10 m/V for correlation. Several related factors are also discussed.
Piezothermoelectric Effects in Anisotropic Media
Authors: Tinder R. F.
Published: February 2004

The effect of stress and strain on the thermoelectric effects is generalized for anisotropic media. This leads to the development of the piezo- and elastothermoelectric power, Peltier heat, and Thomson heat effects which are fourth-rank tensor properties. Their aeolotropism is specified for the 32 crystal classes. Emphasis is placed on measurement techniques for common metals and on a phenomenological interpretation of data from previous experimental work.
Steady-State Theory of a Discharge Column in a Magnetic Field: Separable Solutions for a Finite Cylinder
Authors: Ilić D. B. , Self S. A.
Published: February 2004

The problem of the steady state of a magnetized discharge of the positive column type, in the case of a finite cylinder, is shown to have separable solutions for the radial and axial dependence of plasma density, potential, and electron and ion velocities. Consequently, the results of the corresponding one-dimensional theory may be directly applied to the two-dimensional case. In particular the theory is applicable to the case of a low-pressure discharge in a strong magnetic field, where the radial flow is collision dominated but the axial motion is collisionless.
Proposed Experiment to Determine the Effect of Pressure on the emf of Thermocouples
Authors: Waxman Meyer , Hastings John R.
Published: February 2004

A new experimental procedure to determine the effect of pressure on the emf-vs-temperature behavior of thermocouples has been conceived and tested with simulated data on a computer. An important advantage of this procedure is that the temperature of the hot junction can be accurately evaluated without the necessity of measuring it directly. Instead, the emf of the pressurized thermocouple is expressed parametrically as an appropriate function of several variables: (i) a measurable property related to the hot-junction temperature, such as the electric power to the pressurized furnance; (ii) the cold-junction temperature; and (iii) a reference temperature, such as 100°C, at which the pressure effect is known. By variation of the experimental conditions, a set of overdetermined equations is obtained from which the parameters can be evaluated, and thus the emf-vs-temperature relationship of the pressurized thermocouple can be determined. Our experience with simulated data indicates that for the temperature range from 100 to 1200°C and for pressures to about 7 GN/m2 (70 kbar), the procedure should not introduce a temperature error greater than the error associated with the measurements of the emf, power, and cold-junction temperature.
Dependence of Spherical and Chromatic Aberration upon Magnification in an Immersion Lens
Authors: Wardly G. A.
Published: February 2004

Spherical and chromatic aberration as functions of lens magnification have been computed for an immersion lens with a ``bell-shaped'' axial field distribution.
Serially Deposited Amorphous Aggregates of Hard Spheres
Authors: Bennett Charles H.
Published: February 2004

Aggregates of several thousand equal hard spheres were constructed by depositing additional spheres, one at a time, at surface sites on a small seed cluster, placing each new sphere in contact with three already present and not moving it afterward. Always choosing the site closest to the center of the original seed results in an aggregate showing no evidence of crystallinity, with a pair correlation function quite similar to that of the dense random packings which have been prepared from ball bearings, and to the pair correlation functions calculated from x-ray diffraction work on amorphous alloys. The packing density ⅙πNσ3/V and the mean coordination number both decrease with distance from the center; the large-aggregate limits are, respectively, 0.61 (extrapolated, 4% lower than the ball-bearing value), and exactly 6.0 (in agreement with the ball-bearing value). The apparent difficulty of homogeneously nucleating crystallization in hard-sphere systems, even when simultaneous relaxation of many particle positions is allowed, is attributed to the fact that small hcp and fcc fragments are more bulky and have no more hard contacts than amorphous arragements of the same number of atoms.
Spontaneous- and Stimulated-Emission Spectra of CdSnP2
Authors: Shay J. L. , Schiavone L. M. , Buehler E. , Wernick J. H.
Published: February 2004

We report the band-edge photoluminescence spectra of CdSnP2 crystals lightly doped with Cu or Ag. The emission from CdSnP2:Cu is dominated by a broad band 0.13 eV below the band gap at 1.240 eV (2°K). The emission from CdSnP2:Ag is much stronger and is dominated by a narrow band-to-band emission with three impurity peaks at slightly longer wavelengths. At the very high excitation levels, possible with a pulsed N2 laser, a new band appears ∼ 15 meV below the band gap in CdSnP2:Ag, grows superlinearly in the excitation level, and has other features indicating stimulated emission. Indeed, in crystals suitably prepared to form Fabry-Perot cavities, narrow-line laser emission is observed. Studies in a magnetic field reveal that the spontaneous band-to-band transition and the new stimulated line shift to higher energies at precisely the same rate indicating that they result from the same recombination mechanism. From the observed shift to higher energies, it is argued that exciton-exciton scattering can be unambiguously eliminated as the laser mechanism. As briefly reported previously, it is shown that the magnitude and field dependence of the shift requires proper account of electron-plasmon (plasmaron) coupling.
Addendum to ``Microwave Measurement of the Velocity—Electric Field Characteristic of Inhomogeneous Epitaxial GaAs with Conducting Substrate''
Authors: Glover G. H.
Published: February 2004

An error in the relation of microwave field amplitude to absorbed power in a previous paper is discussed. A much simpler alternative method is presented.
Piezoresistance and Hole Transport in Beryllium-Doped Silicon
Authors: Littlejohn M. A. , Robertson J. B.
Published: February 2004

The resistivity and piezoresistance of p-type silicon doped with beryllium have been studied as a function of temperature, crystal orientation, and beryllium doping concentration. It is shown that the temperature coefficient of resistance can be varied and reduced to zero near room temperature by varying the beryllium doping level. Similarly, the magnitude of the piezoresistance gauge factor for beryllium-doped silicon is slightly larger than for silicon doped with a shallow acceptor impurity such as boron, while the temperature coefficient of piezoresistance is about the same for material containing these two dopants. These results are discussed in terms of a model for the piezoresistance of compensated p-type silicon.
Predicted Effect of Exponential Charging Profiles on Photoinjected Currents in Silicon Dioxide
Authors: Lynch W. T.
Published: February 2004

Photocurrents produced by electron photoinjection over a contact interface barrier into an insulator are significantly affected by any charging which occurs in the insulator. The photoinjection is most seriously affected by negative charging near the maximum of the interface barrier potential. In this paper normalized photocurrent solutions are derived for negative exponential charging distributions at the injecting interface. With the aid of the normalized solutions the photocurrent I-vs-V measurements can be used to directly determine (or approximate to) the peak charge density at the interface (N0) and the exponential decay distance (xc). A plot of the ratio of the barrier distance with charging (x0) to the barrier distance without charging (x00) vs voltage has a maximum for x0 equal to 2xc. The N0 value may then be calculated from the quadratic dependence of N0 on the magnitude of the maximum ratio of x0/x00. Total electron charge densities (N0xc) as low as 109 cm−2 can be measured.
Stored Energy Function of Rubberlike Materials Derived from Simple Tensile Data
Authors: Peng T.J , Landel R.F
Published: February 2004

An explicit formulation to obtain the stored energy function W from simple tension experiments alone, based on the Valanis-Landel separable symmetric stored energy function, W(λ1, λ2, λ3) = w(λ1) + w(λ2) + w(λ3), is developed. For a simple extension stress-strain law of the form λσ=Eε, the analytical formula of W in the limited range 1≤λ≤2.5 is found to be W=E ∑ i=l3 [λi−1−lnλi−16 (lnλi)2+118 (lnλi)3−1216 (lnλi)4],where the limitation originates with the stress-strain law. The expression is used to verify the validity of the Valanis-Landel postulation through prediction of the stress-strain behavior in multiaxial deformations.
Bidirectional Scattering of Electromagnetic Waves from the Volume of Dielectric Materials
Authors: Leader J. C. , Dalton W. A. J.
Published: February 2004

A series of optical-scattering experiments was performed on dielectric materials of various pigmentation and surface roughnesses. Cross-section data obtained by these experiments were then analyzed to ascertain the angular, spectral, and polarization behavior of radiation scattered from the volume of the samples. The division of the scattered intensity into a surface and volume component was accomplished by deduction from previous knowledge of the surface-scattering behavior and analysis of the cross-polarized cross-section variation with scattering angle. It was found that a consistent accurate description of observed scattering in the plane of incidence for all polarization combinations could be obtained by assuming a volume-scattered component added incoherently with a surface-scattered term which has already been described. The volume-scattered term was found to be independent of surface roughness. Theoretical fits to the depolarized cross-section data were also made with a model assuming scattering from media with random fluctuations of the refractive index. Although excellent agreement was obtained between the theoretical and observed angular behavior, the identification of such a random fluctuation process as being responsible for observed depolarization must be considered tentative.
Some magnetoelastic interactions in yttrium iron garnet
Authors: Daniel Michael R.
Published: February 2004

Some absorption effects of high-frequency sound waves in a single crystal of yttrium iron garnet (YIG) are described. Two absorption bands as a function of temperature have been observed and are attributed to a dissipative motion of domain walls within the YIG. The domain walls initially pinned and rendered immobile by crystalline dislocations are released under thermal excitation. Other resonancelike absorptions as a function of magnetic field are seen and are consistent with ferroacoustic resonance. These resonances are shown to vary in strength in a way proportional to the absolute temperature squared and sound frequency cubed.
Acoustic surface wave loss mechanisms on Bi12GeO20 at microwave frequencies
Authors: Slobodnik A.J. , Budreau A.J.
Published: February 2004

Measurements of the acoustic surface wave propagation loss in vacuum on both 001-cut and 111-cut 110-propagating Bi12GeO20 have been made between 200 and 2000 MHz. Approximate f-squared frequency dependence was obtained with a value at 1 GHz of 1.45 dB/μsec. Temperature-dependence measurements illustrate the loss peaks in the vicinity of 50–100 K which are characteristic of Bi12GeO20. The difference in loss between 298 and 4.2 K agrees with over-all room-temperature data indicating attenuation is inherent to the crystal itself and not due to imperfections. Air loading contributes an additional loss of 0.19 dB/μsec at 1 GHz. Beam steering and diffraction considerations illustrate the superiority of the 001 cut over the 111 cut. For linear operation at 320 MHz, surface wave devices on 001-cut 110-propagating Bi12GeO20 should be limited to power densities of 9 mW/mm.
Elastic constants of niobium-molybdenum alloys in the temperature range −190 to +100°C
Authors: Hubbell W.C. , Brotzen F.R.
Published: February 2004

The adiabatic elastic constants were determined for niobium and niobium-molybdenum alloys of the following nominal compositions: 15, 25, 35, 50, 75, and 90 wt.% Mo. The c11, c12, and c44 elastic constants of these bcc alloys were tabulated between −190 and +100°C. The effects of compositional changes on the elastic constants were far greater than those due to temperature. An anomalous temperature dependence for c44 was found for the niobium-rich alloys. An analysis of the elastic constants in terms of central forces revealed that nearest-and second-nearest-neighbor force constants rise with molybdenum additions, with the latter tending towards a maximum as the composition of pure molybdenum is approached. This is thought to be associated with the filling of a d subband. The Debye temperatures were computed and found to be generally in good agreement with the calorimetrically determined values reported in the literature.
High-power electron beam deposition studies on aluminum and graphite
Authors: Farber Milton , Robin James E. , Srivastava R.D.
Published: February 2004

The deposition phenomena produced by a 25–-135-MW electron beam have been studied experimentally on aluminum and graphite targets. Large concentrations of multicharged ions of Al and C were produced. The parameters which were obtained quantitatively included momentum transferred to the target by the blow-off material, total mass loss, species velocities, radiation losses, and enthalpy rise in the target materials. From these data the energies of sublimation for aluminum and graphite were calculated, together with the distribution between spall and vapor species in the blow off. Some of the results are compared with laser data.
The resistivities of liquid mixtures: Zn–Sn and Zn–Pb
Authors: Mitchell George R. , Hartmann W.M.
Published: February 2004

The electrical resistivities of molten Zn–Sn and Zn–Pb alloys at 500°C were measured and the experimental results compared with calculations made from the Ziman—Ashcroft-Langreth theory for binary liquid alloys.
Structure analysis of silicon dioxide films formed by oxidation of silane
Authors: Nagasima Naoyuki
Published: February 2004

The structure of a silicon dioxide film deposited on a silicon substrate by oxidation of silane at 340°C was analyzed by using electron-diffraction and infrared absorption techniques. The Si–O, O–O, and Si–Si distances were determined by the radial-distribution analysis to be 1.62, 2.6, and 3.1 Å, respectively. The deposited film consists of SiO4 tetrahedra, but its atomic arrangement is more irregular than that in a thermally grown silicon dioxide film. As the deposited film is heated in nitrogen at 1000°C, the density increases and approaches that of thermally grown silicon dioxide film. No change occurs in average atomic distance by heating, but the atomic arrangement approaches that in the thermally grown silicon dioxide film. This is also explained from the narrowing of the Si–O–Si bending vibrational band near 450 cm−1 (22 μ) in the infrared-absorption spectrum.
Surface damage of GaAs from 0.694- and 1.06-μ laser radiation
Authors: Smith J. Lynn
Published: February 2004

A study of GaAs surface damage due to ruby and Nd-glass laser radiation is presented. The laser wavelengths chosen represent photon energies both above and below the band gap. Garich material develops on the surface to a greater extent with conventional mode operation than with the Q-switched mode. Although the nature of the surface preparation was seen to influence the damage threshold for the case of Q-switched pulsing, no correlation was found to exist between the threshold and the absence, presence, or type of doping. The damage threshold for Nd-glass laser radiation was approximately 107 W/cm2, only a little higher than that for ruby laser radiation. For Nd-glass laser radiation, the damage appears to be connected with material flaws which are especially susceptible to damage due to their proximity to the surface.
Influence of plasma kinetic processes on electrically excited CO2 laser performance
Authors: Fowler Michael C.
Published: February 2004

Reported values of electron-molecule energy-transfer rate coefficients are combined with heavy-particle and radiative energy-transfer rate coefficients in an analysis of the factors influencing the conversion of electron energy to optical energy at 10.6 μm in an electric discharge containing CO2, N2, and He. The analytical procedure and the important energy-transfer processes involved are described in detail, and the parametric behavior of small-signal gain, saturation intensity, and optical power density is presented as a function of electron number density, gas temperature, pressure, and mixture composition. The temperature and pressure dependence of the cross section for stimulated emission of 10.6-μm radiation is also illustrated for a typical CO2 electric discharge laser gas mixture. Maintenance of gas temperature below approximately 700°K is shown to be of fundamental importance to CO2 laser operation.
Near-confocal optical scan amplifier
Authors: Beiser Leo
Published: February 2004

A near-confocal resonator is described which provides iterative enhancement of angular deflection, while conserving the size of the optical aperture. Elemental resolution is increased through periodic reimaging of the deflecting apertures as the optical wave reflexes a countable number of times within this near-resonator. Two experimental variations of the split confocal prototype are described as the concave and plano-conjugate near-confocal systems.
Noise considerations for infrared quantum counters: the oxygen-fired CdF2 : Er3+ IRQC
Authors: Byer N.E.
Published: February 2004

The contributions to the noise equivalent power (NEP) from various noise sources have been analyzed for the oxygen-fired CdF2 : Er3+ infrared quantum counter (IRQC) proposed recently as a detector for 1.5-μm radiation. The noise from photomultiplier dark current and from thermal, Raman, or two-photon excitations are estimated to produce comparable contributions to the NEP, approximately 10−13 W Hz−1/2, which is superior to that of conventional uncooled 1.5-μm detectors. The IRQC is expected to be background noise limited at 385 K. Methods to improve the performance of the IRQC are discussed.
Statistical properties of acoustic waves in bounded media
Authors: Poularikas A.D. , Dandreta W.J.
Published: February 2004

The statistical properties of the acoustic wave propagation constant in bounded media with random properties were found. The bounded medium was assumed to be infinite in the yz plane and finite in the x direction. It was found that the statistics of the wave propagation constant for the different modes depends on the assumed correlation function of the sound velocity profile. At frequencies close to the cutoff frequency the variance of the propagating constant depends primarily on the assumed statistics of the sound velocity profile in the x direction.
Growth of copper-nickel alloy films suitable for use as substrates
Authors: Olsen G.H. , Botha J.C.
Published: February 2004

The structure of copper-nickel alloy films grown via simultaneous deposition on air-cleaved rocksalt has been studied by transmission electron microscopy. The epitaxial temperature of the alloy films was determined as a function of composition. Alloy films grown and annealed at 350 °C exhibited a relatively high density (∼ 1 × 1010/cm2) of twins. The twin density could be reduced to ∼ 1 × 108/cm2 through growth of the alloy film at 540 °C followed by a 10-min anneal at this temperature.
Domain structure of SrTiO3 under uniaxial stresses
Authors: Chang T. S.
Published: February 2004

Tetragonal domain structure of SrTiO3 is studied at 2 °K under uniaxial stresses along [001] and [110] directions. A single-domain crystal with [001] tetragonal axis is obtained by compressively stressing along [110] and is confirmed by Cr3+ fluorescence. Only domains with axis along [100] and [010] are observed under [001] stress.
Amplification of surface shear-wave mode in GaAs
Authors: Ludvik S. , Quate C. F.
Published: February 2004

The amplification characteristics of a surface shear wave mode in GaAs has been investigated and shown to be closely approximated by the bulk wave theory, where trapping effects are included. At a frequency of 205 MHz, relative electronic gains from 35–50 dB/cm have been observed.
Stimulated Brillouin scattering in plastics
Authors: Dietz D. R. , Wiggins T. A.
Published: February 2004

Hypersound speeds, the power threshold for stimulated Brillouin scattering (SBS), steady-state and transient gains for SBS, and the phonon lifetime have been studied in the plastics of polymethylmethacrylate and polyethylmethacrylate as a function of temperature. Damage thresholds were investigated and the effects of annealing are discussed. An extension of current theory allows a determination of phonon lifetimes and relative gains to be determined without absolute calibration of the laser power.
Coupled lenses and their combinations
Authors: Bliamptis Emmanuel E.
Published: February 2004

Electric or magnetic quadrupole lenses and their thin lens analogues, or coupled lenses, are examined for double focusing. The compatibility conditions for double focusing are similar to the stability conditions of betatron oscillations. When the double-focusing conditions are satisfied, a quadrupole lens doublet or a pair of coupled thin cylindrical lenses is equivalent to a single thick converging lens with unequal focal lengths in two orthogonal meridian planes. Specific double-focusing examples are given and a nomogram is developed for facilitating the calculations when combinations of coupled lenses are considered.
Mutual admittance of two collinear antennas
Authors: Hurd R. A.
Published: February 2004

An asymptotic theory for the admittance of two collinear antennas is developed. The antennas can be of unequal lengths, and the feedpoint locations are practically arbitrary. The only restrictions are that the radii must be equal and small; while the smallest feedpoint-end distance and the separation between the antenna ends must be fairly large [i.e., (2π/λ) (distance) > 1, roughly]. The expressions obtained for the self-admittance and mutual admittance are in closed form and contain only elementary or known functions. Where comparison is possible, the results agree with previous theories. A few curves showing the effect of varying different parameters are presented, while some general conclusions about the behavior of the mutual admittance are drawn.
Idealized spatial emission distribution of secondary electrons
Authors: Everhart T. E. , Chung M. S.
Published: February 2004

The spatial distribution of secondary electrons generated by a primary electron beam incident at a point of the sample surface is calculated for samples of varying thicknesses. The current density generated under these conditions is also calculated for several different angles of incidence. According to the calculations, which are based on a commonly used idealized model, most secondary electrons leave the sample within a mean free path of their point of excitation, which is 10–20 Å for metals. Because thin metal coatings are used to prevent many insulating samples from charging, these results relate to the ultimate resolution that one can expect in secondary emission scanning electron microscopy.
Calibration procedure to correct for the effects of dielectric containers in microwave plasma density measurements
Authors: Wellenstein H. F. , Frommhold Lothar , Robertson W. W.
Published: February 2004

It is shown that dielectric containers interfere with plasma density determinations and render them too low by large percentages. A way to avoid such errors is described and its usefulness demonstrated.
Far-infrared dielectric dispersion in barium sodium niobate
Authors: Lurio Allen
Published: February 2004

The room-temperature reflectivity of single-crystal Ba2NaNb5O15 has been measured in the range from 10 000 to 70 cm−1. Separate measurements were taken for the electric field of the light polarized parallel to the c axis and perpendicular to the c axis. The data were analyzed by using the Kramers-Kronig relations and also by fitting the reflectivity spectrum to a classical independent oscillator dispersion model. The results are compared to previous Raman and infrared measurements. The linewidths obtained from the infrared measurements are found to be considerably broader than the Raman linewidths.
Ion-backscattering analysis of tungsten films on heavily doped SiGe
Authors: Borders J. A. , Sweet J. N.
Published: February 2004

The technique of ion backscattering has been used to obtain information on the reactions taking place at the interface between a sputtered tungsten film and a heavily doped silicon-germanium alloy substrate. Significant differences were observed for n-type and p-type SiGe substrates. In both cases silicon was observed to migrate into the tungsten at temperatures above 650 °C and form a layer of atomic composition, WSi2. There was little or no diffusion of silicon beyond the WSi2 layer for the samples on n-type substrates, but on p-type SiGe, silicon diffused through the WSi2 layer to the surface of the tungsten film. Tungsten films on single-crystal silicon showed small amounts of tungsten-silicon diffusion and little or no WSi2 formation for anneals at and below 700 °C. Samples with n-type SiGe substrates exhibited little or no tungsten-germanium diffusion; whereas, samples on p-type substrates annealed to 675 °C or higher showed significant migration of tungsten and/or germanium. The oxidation of the sputtered tungsten films was also investigated by ion backscattering. A 1200-Å-thick W film was completely converted to tungsten oxide (atomic composition WO3) by annealing at 650 °C, which inhibited WSi2 formation. In addition, the growth of WO3 on a thick W film was observed as a function of time.
Effects of tunneling on an IMPATT oscillator
Authors: Kwok S. P. , Haddad G. I.
Published: February 2004

A phenomenological formulation which incorporates both avalanche and tunneling mechanisms in an IMPATT diode is given. Here tunneling is viewed as a field-dependent carrier source. An electron after being field emitted may gain sufficient energy from the field to cause ionization. In this formulation, pure avalanche and pure tunneling appear as the two extreme cases of the general problem. The resultant general dc I- V characteristic shows the dominance of tunneling at low voltages and the onset of the multiplication at higher voltages as observed experimentally. A small-signal admittance of an IMPATT oscillator with tunneling has been calculated. Under some conditions tunneling may increase the negative conductance. However as tunneling dominates, the negative conductance deteriorates and the oscillator will operate in the tunnel transit-time mode. Tunneling invariably shifts the frequency for optimum negative conductance upwards. The threshold frequency for negative conductance varies as the square root of current density for large multiplication factors as expected. However, for small ones it converges to a value determined only by the drift transit time. The general admittance expression reduces to that of pure avalanche and pure tunneling under the prescription ωa → ω as M → ∞ and ωa → ωaz as M → 1, respectively. ωa, ωa0, and ωaz are the modified avalanche frequencies for the general case, pure avalanche, and pure tunneling, respectively.
Mass and critical velocity of domain walls in thin magnetic films
Authors: Schlömann Ernst
Published: February 2004

It is shown that the structure of domain walls moving at constant velocity ν can be obtained by maximizing a Lagrangian L= T− E, where the kinetic energy T is proportional to ν and E is the usual (potential) energy. For thin films having a uniaxial anisotropy axis in the plane of the film an approximate solution of the dynamic micromagnetic equations is obtained by maximizing L relative to a class of variational trial functions that describe one-dimensional domain walls (previously used for the static case by Dietze and Thomas). The dynamic solution obtained in this manner applies for wall velocities smaller than a certain critical velocity, at which the derivative of the wall energy with respect to velocity becomes infinite. For very thick and very thin films the critical velocity calculated using the Dietze-Thomas model approaches the known bulk value (approximately 8 × 104 cm/sec for permalloy) to within 1%. At intermediate film thicknesses, near the transition from Néel to Bloch walls, the critical velocity is much smaller (approximately 1/20 of the bulk value in the case of Permalloy). In this thickness range the predicted effective mass per unit area of the wall is larger than the bulk value by approximately 100 for Permalloy.
Inelastic photon scattering by a polyatomic molecule: NO2
Authors: Fouche D. G. , Herzenberg A. , Chang R. K.
Published: February 2004

When NO2 is illuminated by monochromatic visible light, the frequency distribution of the photons scattered inelastically consists of discrete spikes superimposed on a broad continuum. This scattered intensity has been compared with the Raman scattering from N2 with respect to the following variables: (i) argon-ion laser wavelengths; (ii) NO2 pressure; (iii) air pressure. The intensity scattered by a molecule of NO2 is found to be 116 times the Raman intensity from a molecule of N2, NO2 being in air at STP; (the broad continuum intensity from NO2 was measured at 720 cm−1, from the 4880-Å laser wavelength, with a spectrometer slit width of 10 Å). The quenching constant for the NO2 continuum by air is found to be 67 Torr−1. The observed dependence of the scattered intensity on wavelength and pressure can be explained qualitatively in terms of an expected dense distribution of energy levels in NO2.
Proposed anti-Stokes light converter with heterojunctions
Authors: Takahashi K.
Published: February 2004

A heterojunction device composed of pGe-vZnSe-p+GaAs-p+ AlxGa1−xAs is proposed for efficiently converting infrared radiation of 1.5-μm wavelength into radiation of 0.9-μm wavelength. Conceptually, this is a possible approach to the development of a high-efficiency anti-Stokes light converter.
Production of hot plasmas of solid-state density by ultrashort laser pulses
Authors: Salzmann Hans
Published: February 2004

Ultrashort laser pulses emitted by a neodymium glass laser system were focused on the surface of solid targets situated in a high-vacuum environment. The laser pulse duration as measured by the two-photon fluorescence technique was less than 10−11 sec. Pulse energies up to 3 J were obtained corresponding to a maximum energy release of 3×104 J cm−2 in the focal area. The plasmas produced from targets of solid deuterium, carbon, and thin foils of Mylar were investigated by x-ray measurements, time-of-flight measurements using charge collecting probes, and, in the case of deuterium, by neutron counting measurements. Only 10% of the incident light energy was found to be reflected from the targets. Electron temperatures of 500 and 200 eV were measured for deuterium and carbon plasmas, respectively. The experimental results are found to be consistent with the predictions of the model of a thermal wave penetrating into the solid.
Thermoelectric and photothermoelectric effects in semiconductors: CdS single crystals
Authors: Kwok Harry B. , Bube Richard H.
Published: February 2004

The quantitative reliability of theoretical expressions for Hall and thermoelectric effects has been tested under thermal equilibrium conditions in high-conductivity, nondegenerate, and degenerate CdS single crystals, and under nonequilibrium steady-state and transient conditions in low-conductivity photosensitive CdS crystals. The thermal equilibrium measurements were made as a function of temperature, hence of scattering and degeneracy, and the nonequilibrium measurements were made as a function of excitation intensity and temperature. Good agreement is found in every case between the values of the electron density and mobility calculated from the Hall effect and the values of these quantities calculated from the thermoelectric effect. The results confirm both the reliability of the present state of the theory for materials like CdS, and the extension of this theory far from equilibrium conditions provided that the equilibrium Fermi level is replaced by the steady-state or quasi-Fermi level.
Low-temperature epitaxy of Ge films by sputter deposition
Authors: Khan Imdad H.
Published: February 2004

The crystallographic structure and orientation of Ge films formed by sputter deposition onto Ge (111) substrates have been investigated as a function of various deposition parameters. Important parameters affecting the film structure include growth rate, substrate temperature, substrate-surface cleanliness, and sputtering-gas purity. The structure of the sputter-deposited films was examined by HEED, while the substrate surface was characterized by HEED, LEED, and Auger electron spectroscopy. Results show that epitaxy of Ge can be obtained by sputter deposition at substrate temperatures as low as 100 °C, provided the deposition conditions are properly optimized. A plot of the film structure as a function of substrate temperature and growth rate defines the three regions of crystallinity (amorphous, polycrystalline, and single crystalline), indicating the existence of a triple point. The amorphous-polycrystalline and epitaxial transitions occur at temperatures considerably lower than those reported by previous investigations. Thermal regeneration of the substrate surface results in a considerable reduction of the transition temperatures. Oxygen in the sputtering atmosphere plays a significant role in determining the epitaxial temperature.
Electromagnetic scattering from a radially moving spherical discontinuity
Authors: Pogorzelski Ronald J.
Published: February 2004

The scattering of a spherical electromagnetic wave from a radially moving spherical discontinuity in index of refraction is analyzed. The Doppler shifts are found to depend on the radius as well as the velocity of the discontinuity. As an example the scattering from a tenuous evaporating dielectric sphere is found. The plane-wave scattering problem is formulated and it is shown that the scattered frequencies have a satisfying physical interpretation in the geometrical optics limit.
Elastic constants of holmium between 78 and 300 K
Authors: Salama K. , Brotzen F. R. , Donoho P. L.
Published: February 2004

The adiabatic elastic constants of holmium were determined in the temperature range from 78 to 300 K, using high-purity single crystals. The constants were obtained from the ultrasonic-wave velocities (20 MHz) measured by the pulse-superposition method. The values of the constants at room temperature in units of 1011 dyn/cm2 are c33 =8.015, c44=2.592, c11 =7.612, c12=2.600, and c13 =2.072. Using these values, the Debye temperature was computed to be 181 K. The sound velocities tend to vary with temperature in an anomalous fashion near the Néel temperature (TN=131 K). Attenuation and sound-velocity measurements near TN permit an estimate of the relaxation time for spin fluctuations, which was found to be 3×10−10 sec.
Epitaxially grown AlN and its optical band gap
Authors: Yim W. M. , Stofko E. J. , Zanzucchi P. J. , Pankove J. I. , Ettenberg M. , Gilbert S. L.
Published: February 2004

Single-crystal layers of AlN have been grown on sapphire substrates between 1000 and 1100 °C by vapor-phase reaction of aluminum chlorides with ammonia. The purity, color, crystallinity, growth morphology, and electrical resistivity of the epitaxial layers have been investigated. Infrared specular reflection measurements showed the presence of an appreciable strain at the AlN-sapphire epitaxy interface. Optical absorption data strongly suggest the AlN is a direct band-gap material with a value of about 6.2 eV at room temperature.
Preservation of threshold on-regime in amorphous semiconductor threshold switch
Authors: Vezzoli G. C. , Calella Patrick , Doremus William
Published: February 2004

Chalcogenide amorphous threshold switching devices have been pulse switched and studied in the on-regime by applying cw functions. A 1-MHz square, sine, or triangular test wave of maximum amplitude ±7 V applied to a device which is then pulse switched (65, 30, or 10 V threshold), will cause the device to remain in the on-regime after the set pulse turns off. Lowering the cw frequency or lowering the wave amplitude beneath critical values causes the specimen to turn off. At frequencies significantly above the turn-off value, the positive and negative high-current segments of the V-I on-regime curve are connected by a very high-resistance essentially linear region passing through zero. The on-regime can be preserved in this manner at ambient temperatures varying from at least −196 to + 150 °C; however, increasing ambient temperature causes a decrease in the turn-off frequency. Decreasing the wave amplitude causes an increase in the turn-off frequency.
Growth-induced anisotropy of some mixed rare-earth iron garnets
Authors: Gyorgy E. M. , Sturge M. D. , Van Uitert L. G. , Heilner E. J. , Grodkiewicz W. H.
Published: February 2004

We have measured the growth-induced noncubic magnetic anisotropy under (110) facets of flux-grown garnet crystals at 300°K. The garnets studied have the general formula RM2Fe5O12, where R represents Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu, and M represents Y, Lu, or Gd. Measurements were made at room temperature in the (110) plane. The contribution of Gd and of all ions heavier than Tb is found to be small. The growth-induced anisotropy of all garnets containing Pr, Sm, Eu, or Tb is consistent with a model in which site preferences on the rare-earth sublattice are smooth functions of the ionic radius mismatch, and the single-ion magnetic anisotropy is due to anisotropic exchange. The anisotropy of the exchange appears to have the same sign and order of magnitude for all four ions. The behavior of Nd is anomalous and can be attributed to crystal field effects.
Zero-crossing intervals of Gaussian processes
Authors: Mimaki Tadasi
Published: February 2004

The correlation between successive zero-crossing intervals and their probability densities is experimentally studied for Gaussian processes having power spectra of Butterworth type. The assumption that successive zero-crossing intervals from a Markov chain in the wide sense is found valid only for a process having a narrow-band spectrum. The correlation coefficients between the lengths of several successive zero-crossing intervals of a Gaussian process having a broad-band spectrum decay slowly and reveal a peculiar oscillatory behavior as the number of intervals is increased. These results are interpreted by introducing a model. Results for Gaussian processes having power spectra of type (f/f0)2m[1+ (f/f0)2]−n are also given. The correlation of intervals is also determined by means of a single interval counter making efficient use of the so-called bias effect, and its results agree closely with those from ordinary measurements using two interval counters.
Variation of dc domain threshold in a nematic liquid crystal under continual dynamic scattering
Authors: Wargocki F. E. , Lord A. E.
Published: February 2004

Data are presented indicating a change in threshold for domain formation in MBBA as a function of time maintained under dc dynamic scattering. These changes are correlated with observed changes in dielectric constant.
Calculated elastic constants for stress problems associated with semiconductor devices
Authors: Brantley W. A.
Published: February 2004

Theoretical estimates or experimental determinations of stress fields associated with semiconductor devices are generally simplified with the aid of two elastic constants, Young's modulus E and Poisson's ratio ν. In this paper, a generalized expression for ν has been derived for arbitrary orientations of cubic semiconductor crystals, and the variation of E, ν, and E/(1-ν) for directions within the important {111}, {100}, and {110} planes is examined. The results show that isotropic elasticity theory is exact for all directions within {111} planes and that the composite elastic constant E/(1-ν) which frequently occurs in problems of practical interest is also invariant for all directions within {100} planes. Numerical values for the various elastic constants are tabulated for GaAs, GaP, Si, and Ge.
Ultraviolet radiation from electrical discharges in water
Authors: Robinson James W. , Ham Mooyoung , Balaster Ammon N.
Published: February 2004

Ultraviolet radiation is one of the principal forms of energy which is dissipated from an electrical discharge in water. For a stored capacitor energy of 1500 J, up to 28% or 420 J has been converted to uv radiation with a peak radiant power of 200 MW. Of the energy transferred to the plasma, 36% was converted to radiation. The efficiency of radiation was maximum for a length of the discharge channel of approximately 3.8 cm. Scaling rules are given.
Reaction kinetics of tungsten thin films on silicon (100) surfaces
Authors: Locker L. D. , Capio C. D.
Published: February 2004

The rate of reaction between Si (100) surfaces and tungsten films deposited by rf diode sputtering depends on the preparation of the silicon surface. If rf substrate bias is used to clean the silicon, then the rate of reaction in the temperature range 700–850 °C is independent of time, with an activation energy of 3 eV/mole W. The native oxide layer between the silicon and tungsten, that exists when sputter cleaning is not used, can act as a barrier to WSi2 formation. In this case, the time-independent region is preceded by a period when the reaction rate increases with time. The rate is then controlled by two-dimensional spreading of discontinuous WSi2 regions that originate at sites where the reaction barrier can be penetrated. After a continuous WSi2 layer is formed, additional growth can produce a stage where the increased path length for silicon diffusion causes the transport step to control the over-all rate of the reaction. Quantitative models are presented for each of the three stages in the reaction. The models explain some of the macroscopic observations made on reacted layers.