bluuebunny/crossref_metadata_2025 huggingface dataset:
Modified Random-Walk Model for 1/f Noise
Authors: Hawkins R. J.
Published: February 2004

Offner's modified random-walk model is shown to be essentially similar to the conventional model for generation-recombination noise at traps with a single time constant. This would exhibit a relaxation power spectrum rather than one of 1/f form, and an analysis of Offner's computed results shows that this is indeed the case.
Comments on ``Modified Random-Walk Model of 1/f Noise''
Authors: Offner Franklin F.
Published: February 2004

The random walk originally proposed to account for 1/f noise has been modified to more nearly correspond to physical phenomena by considering the jump probability to be biased by the potential. Over the range of steps investigated, this results in a broadening of the 1/f region, apparently as the N.
Saturable Absorption and Q Switching in a Triphenylmethane Dye
Authors: Giuliani J. F.
Published: February 2004

Saturable absorption and Q-switching action for the triphenylmethane dye fuchsin pumped by a ruby laser is shown to occur in fluorocarbon solvents and not in water or common organic solvents. These properties are related to a probable change in the bonding structure of the dye by the fluorocarbon solvent.
Effects of Spectral Truncation on Photocount Statistics
Authors: Lachs Gerard , Ruggieri Neil F.
Published: February 2004

For many photocounting experiments, it is desirable to know the theoretical photocount distribution for radiation whose spectral shape may be altered by an optical filter or truncated in some manner. The effect of spectral truncation (band limiting) is investigated by computing the photocount distribution by a method that makes direct use of the power spectral density. Some data are presented for truncated Lorentzian spectra.
Influence of Surface Absorption Characteristics on Reactively Sputtered Films Grown in the Biased and Unbiased Modes
Authors: Winters Harold F. , Kay Eric
Published: February 2004

A series of metals have been reactively sputtered in N2–Ar mixtures. The results indicate that surface adsorption characteristics greatly influence compound growth and/or gas incorporation. It will be shown that the functional relationship between the measured nitrogen concentrations and PN2 places these metals into one of three groups: (1) metals which chemisorb molecular nitrogen and form a nitride, e.g., W; (2) metals which do not chemisorb nitrogen but form a nitride, e.g., Ni; and, (3) metals which neither chemisorb nitrogen nor form a nitride, e.g., Au. It will also be shown that bias sputtering causes the nitrogen content of tungsten and nickel to decrease while it causes the nitrogen content of gold to increase. The increase for gold is caused by bombardment of the film with energetic N2+, which results in increased sorption of nitrogen. The same effect is present in tungsten and nickel but is overshadowed by resputtering of the previously sorbed nitrogen. It is suggested that the high sputtering yield found for chemisorbed gases is related to a poor mass fit between the sorbed atoms and the metal lattice.
Propagation and Amplification of Rayleigh Waves and Piezoelectric Leaky Surface Waves in LiNbO3
Authors: Yamanouchi Kazuhiko , Shibayama Kimio
Published: February 2004

Velocities and attenuations of piezoelectric leaky surface waves in LiNbO3 are analyzed. As a result, we have found that the effective electromechanical coupling coefficient of the leaky surface wave propagating along the X axis of a 64° rotated Y-cut plane is very large, K2 = 0.113, and the attenuation of this wave, caused by radiation of the energy into the solid, is 0.036 dB/wavelength for a free surface and goes to zero for a metalized surface. Moreover, K2 of the elastic surface wave for a 130° rotated Y-cut, X propagation, is found to be larger than that for a Y cut, Z propagation. The theory is verified experimentally. The theoretical analysis and experiments on amplification are performed for these types of waves. In an experiment utilizing the leaky surface wave, net terminal gain of 13 dB/cm is observed for the interaction between the carrier in 200-Ω cm Si wafer (0.3×3×10 mm), separately mounted on a LiNbO3 surface, and the leaky surface wave. The air gap between the Si wafer and LiNbO3 single crystal is about 0.5 mμ.
Mass Spectrometric Study of Sputtering of KB by Low-Energy Ar+ and Xe+ Ions
Authors: Campbell Arthur B. , Cooper C. Burleigh
Published: February 2004

A KBr target was bombarded normally with Ar+ and Xe+ ions, with energies ranging from 25 to 180 eV, in the source of a mass spectrometer capable of detecting neutral and negative sputtered species. A relatively strong signal of Br− ions sputtered from the target was detected, and relative sputtering yield curves were obtained. The yield was greater for Ar+ than for Xe+ ion bombardment at all ion energies. No neutral K0 or Br0 atoms, nor KBr0 molecules, were detected as having been sputtered from the target during bombardment.
Preionization Control of Streamer Propagation
Authors: Bradley Laird P.
Published: February 2004

Streamer velocity is experimentally shown to vary with preionization in N2 and SF6. The velocity has been controlled over orders of magnitude by introducing pulsed preionization ahead of an already propagated streamer. The preionization is produced by pulsed uv irradiation. The pulsed electric field is uniform in the gap. Avalanche-streamer conversion times were observed which agree well with prediction.
CO2 Laser Heating of a Θ-Pinch Plasma by Inverse Bremsstrahlung and Induced Compton Processes
Authors: Martineau J. , Pepin H.
Published: February 2004

The heating of a Θ-pinch plasma by a pulsed CO2 laser is considered. In addition to the inverse bremsstrahlung the induced Compton effect is taken into account as a heating process. The influence of the pulse duration on the maximum temperature attained is studied. The results show that it is preferable to deliver the laser energy slowly. In addition, if one seeks to transfer the greatest fraction of laser energy to the plasma, the pulse shape becomes important. Tailored pulses providing an increase in the energy delivery rate when the power absorbed by bremsstrahlung diminishes will increase the contribution of the induced Compton effect to the heating.
Elastic and Photoelastic Constants of α-ZnS
Authors: Uchida Naoya , Saito Shoichi
Published: February 2004

Elastic constants and acoustic absorption coefficients of hexagonal ZnS single crystal have been measured by the ultrasonic pulse methods. The absorption coefficients are found to be nearly proportional to the square of frequency between 60 and 500 MHz. Photoelastic constants have been determined by the ultrasonic light diffraction technique, in which an abnormal type of the Bragg reflection as well as the normal type has been used. The values obtained at 6328 Å are p11=−0.115, p12=+0.0170, p31=+0.0271, p13=+0.025, p33=−0.13, and p44=−0.0627. The obtained values for α-ZnS have been compared with those of cubic β-ZnS by the adequate rotation of the coordinate system, and the results show great similarity between these materials in the elastic and the photoelastic features.
Positron as a Probe of Imperfections in Quartz Crystals
Authors: Coussot G. , Paulin R.
Published: February 2004

The angular correlation between the two γ quanta emerging from positron annihilation in quartz crystals shows a structure with intensity S = NC + FS composed of a narrow component NC and a fine structure FS, which is characteristic of the symmetry of the quartz crystal. This structure, where the ratio NC/FS remains nearly constant, is sensitive to certain types of imperfections present or created in the quartz samples. Thus, slow growth rate, high Q, and low concentrations of aluminum or alkali impurities enhance S, while electron or neutron irradiation decreases S, which can be restored to its initial value by optical bleaching or thermal annealing of color centers created by irradiation.
Dependence of Conduction-Induced Alignment of Nematic Liquid Crystals upon Voltage above Threshold
Authors: Carroll T. O.
Published: February 2004

The Helfrich theory of conduction-induced alignment in nematic liquid crystals is extended to describe the dependence of alignment upon voltage above threshold. Alignment angle, saturation alignment, flow velocity, and shear are computed. Experimental measurements of these parameters for p-azoxyanisole are in good agreement with the predictions of the theory.
Simulation of Crystal Growth with Surface Diffusion
Authors: Gilmer G. H. , Bennema P.
Published: February 2004

A computer simulation model is described which applies to the molecular processes involved in crystal growth under very general growth conditions. The transition probabilities used for adding and subtracting molecules from the crystal and for surface diffusion are shown to satisfy microscopic reversibility in equilibrium. The computer program uses several internal self-consistency checks, the results of which support the validity of the simulation method. Growth measurements are obtained in a range above and below the surface roughening temperature. The growth rates of the (100) face of a Kossel crystal show a two-dimensional nucleation barrier at low supersaturations and below the roughening temperature. An almost linear dependence on supersaturation is observed above this temperature. This result is independent of the amount of surface diffusion. A simple step model is described and the resulting growth rates are compared with the simulated rates of faces containing a fixed number of steps. Agreement is rather good at the lower temperatures and supersaturations. The same step model is used in conjunction with two-dimensional nucleation theory to obtain growth rates for (100) faces, and the results are consistent with the simulated rates below the roughening temperature. A few simulations of dissolution (or evaporation) are included.
Etch Pits in Natural Molybdenite
Authors: Fairbrother John A. , Cowan Matthew D.
Published: February 2004

Etch pits 50 and more molecular layers deep have been observed on the surface of natural molybdenite crystals exposed to oxygen at temperatures in the region of 650°C. The geometry and manner of growth of the etch pits suggest that etching takes place through the intermediary of a two-dimensional gas of adsorbed oxygen molecules on the surface of the crystal. For the five samples studied this explanation of the etch pits leads to the conclusion that the fraction of adsorption sites occupied by adsorbate molecules lies in the range θ=2.3×10−3−3.6×10−2. The average activation energy of a molecular etch reaction is 33.7 kcal/mole or 1.43 eV.
Anharmonicity Contributions to Dislocation Drag
Authors: Brailsford A. D.
Published: February 2004

A unified theory of the effect of phonon-phonon scattering on the drag force Bv acting upon a dislocation moving with velocity v, much less than the sound velocity, is presented. A formalism is developed in terms of a frequency- and wave-vector-dependent bulk viscosity. Thermoelastic damping, phonon viscosity, phonon scattering, and, in the case of oscillatory motion, reradiation damping are all included in this framework. It is shown that the dominant mechanism is that resulting from phonon scattering and gives rise to the form BS=β [k2R(0)/θΩa2]J5(T/θ) for a straight dislocation. Here R(0)=WDT2/Λ)T→0, where WD is the dislocation contribution to the phonon component of the thermal resistance, Λ the dislocation density, Ωa the atomic volume, κ is the Boltzmann constant, and T and θ the ambient and Debye temperatures, respectively. The function J5(x)5=(x)5/5!)∫ 01/xx5ex(ex−1)−2dx, and the numerical constant β is estimated to be 1.2×104. The physical processes underlying all the above mechanisms are explored in detail and the theory is compared at length with the work of previous authors.
Experimental Study of the Space-Charge Layer in Silver Halide Crystals
Authors: Fatuzzo E. , Coppo S.
Published: February 2004

Using equations developed in a previous paper the properties of surface layers in silver halide crystals have been studied by measuring their low-frequency dielectric constant. It was found that the subsurface space charge depends strongly upon the nature of the material in contact with the crystal surface. Experimental results on the variations of the dielectric constant measured at 1 kcycle/sec as a function of an applied voltage are also reported and a model for the interpretation of these results is provided.
Effect of Microstructure on the Electromigration Life of Thin-Film A1–Cu Conductors
Authors: Agarwala B. N. , Patnaik B. , Schnitzel R.
Published: February 2004

The role of microstructural variables on the electromigration life of A1–Cu conductors is investigated. Experiments show that the lifetime of A1–Cu films is very sensitive to grainsize distribution and is independent of the amount of precipitate phase in the film. These results are explained in terms of a vacancy flux divergence model.
Variation with Depth of the Electrical Properties of Sputtered Tantalum Films
Authors: Waterhouse Neil
Published: February 2004

The variation of the electrical properties with depth in the film has been measured for two sputtered tantalum films using anodization by stages in a citric-acid electrolyte as a method of sectioning the films. Changes in the temperature dependence of the resistivity, between ∼20 and 300°K, and in the room-temperature Hall coefficients with film thickness were measured. A dual conduction model for sputtered tantalum films has been used to assist in analyzing the measurements. The resistivities of the tantalum layers have been calculated from simple parallel-resistor theory, and the functional forms of the ρ-vs-T curves of these layers were closely predicted by this model. The trends of these curves with film depth were accounted for by simply changing the relative ``weighting'' of the model's two conduction mechanisms.
Penetration of Low-Energy Protons through Thin Films
Authors: Cano Gilbert L.
Published: February 2004

Protons of energy 10–30 keV impinged on free-standing films of Au, Er2O3, and Sc2O3 of thickness 150–650 Å. Results are reported of the stopping power, energy, and angular spread of the transmitted beam. Stopping power results obtained and theoretical predictions are only in qualitative agreement.
Linear Transient Response of a Plasma to a Pulsed Electric Field
Authors: Sodha Mahendra Singh , Ghatak Ajoy Kumar
Published: February 2004

The authors have obtained a transient solution of Boltzmann's transfer equation for electrons in a plasma, subjected to a weak pulsed electric field, and used this solution to derive an expression for the transient current density. Explicit expressions for the current density and energy absorbed (during the pulse) have been given when (i) the pulsed field is dc or sinusoidal in nature and (ii) the electron collision frequency is proportional to vs (s=0, 1, 2) (v being the electron velocity). It is seen that the nature of velocity dependence of collision frequency (viz., the value of s) has little effect on the attainment of steady state. The present theory (i) neglects the collective plasma phenomena, which is valid when the frequency of the field is appreciably different from the plasma frequency, (ii) ignores electron-ion and electron-electron collisions, which is valid for weakly ionized plasmas, (iii) ignores nonlinear effects, and (iv) neglects the effects of ion motion (which is appreciable only for highly ionized plasmas and very low frequencies of the field).
Static and Dynamic Pore-Collapse Relations for Ductile Porous Materials
Authors: Carroll M. M. , Holt A. C.
Published: February 2004

Static and dynamic pore-collapse relations for ductile porous materials are obtained by analysis of the collapse of a hollow sphere of incompressible elastic-plastic material, with appropriate pore radius and over-all porosity. There are three phases of the pore-collapse process: an initial phase, a transitional elastic-plastic phase, and a plastic phase. The change in porosity during the first two phases is quite small. In the plastic phase, the static pore-collapse relation is an exponential law that depends only on the yield strength of the material; the dynamic relation is a nonlinear second-order ordinary differential equation that involves the yield strength and a material constant (with the physical dimension of time) that depends on the yield strength, the density, the initial porosity, and the pore radius. Comparison of the theoretical predictions with finite-difference computer-code calculations for pore collapse of a hollow sphere of compressible material indicates that the effect of elastic compressibility on pore collapse is quite small, so that the pore-collapse relations obtained from the incompressible model should have a wide range of validity. Also, the specific internal energy at the pore boundary has a logarithmic singularity as the pore closes.
Measurement of Spontaneous Carrier Lifetime from Stimulated Emission Delays in Semiconductor Lasers
Authors: Ripper José E.
Published: February 2004

An analysis of the delay between the beginning of the excitation of a semiconductor laser and the onset of stimulated emission is carried out. It justifies the use of these delays as a method of measuring the spontaneous carrier lifetime, even when this lifetime is not the same for all carriers. It is also shown that the lifetime thus measured is the average lifetime of all carriers when the population inversion is at the threshold level.
Analysis of Photoconductivity in Amorphous Chalcogenides
Authors: Arnoldussen T. C. , Bube R. H. , Fagen E. A. , Holmberg S.
Published: February 2004

Starting with standard semiconductor recombination statistics and a generalized distribution of localized states within the mobility gap of an amorphous semiconductor, a model for photoconductivity has been developed. Consistency with experimental phenomena requires the inclusion in this model not only of the traditional nonlocalized-to-localized state recombination transitions, but also of two types of localized-to-localized state recombination transitions: (i) from states nearer than a critical energy to the conduction edge, to similar states nearer than a critical energy to the valence edge; (ii) from states near the mobility edges to states near the thermal equilibrium Fermi level. Such a model has general applicability to a variety of different types of amorphous chalcogenides, encompasses previously reported variations of photoconductivity with intensity and temperature, and provides a way of estimating the characteristic parameters of localized states in these materials. Quantitative application of the model is made to photoconductivity data for three amorphous chalcogenides.
Temperature Dependence of Intrinsic Carrier Concentration in InSb: Direct Determination by Helicon Interferometry
Authors: Chen K. K. , Furdyna J. K.
Published: February 2004

The phase velocity of helicon waves depends on the carrier concentration. In intrinsic semiconductors sharp changes in helicon phase can therefore be produced by varying the temperature of the material. Basic features of this effect are analyzed for intrinsic semiconductors of InSb and HgTe type. Helicon velocity in these materials is determined almost entirely by the electronic plasma alone and, within a limited field and temperature region, is described in a simple analytic form. Experiments performed at 35 GHz on intrinsic InSb between 200 and 350°K are discussed. Interferograms obtained by sweeping the sample temperature at constant magnetic field provide a fast and accurate method of directly recording the temperature dependence of intrinsic carrier concentration ni. The agreement between observed and calculated values of ni is very satisfactory over the investigated temperature range.
Continously Tunable Coherent Ultraviolet Radiation
Authors: Sato Takuzo
Published: February 2004

A continuously tunable coherent source has been obtained by the mixing of ruby- and dye-laser beams in an ADP crystal producing the sum frequency in the wavelength range 3044–3272 Å. The rates of wavelength change of the mixed light with temperature and the angle between the z axis of ADP and the direction of the laser beams were evaluated, which were dλM/dT=2.6 Å/°K and dλM/dθM=45 Å deg−1, respectively. Furthermore, the spectral bandwidth of the mixed light was calculated and compared with experimental results.
Thermal Desorption of Na and K from α Iron
Authors: Hill R. V. , Stefanakos E. K. , Tinder R. F.
Published: February 2004

The activation energies for the thermal desorption of Na and K from iron filaments were measured by allowing a flux of Na and K neutral atoms to strike the Fe filament for predetermined periods of time and then applying a linear temperature sweep of 0.895°K/sec. The desorption energies for an unoxygenated iron surface were found to be 2.8 and 2.6 eV for Na and K from iron, respectively. The effect of oxygen application on the desorption energies is also investigated.
Secondary Electron Emission from Ion-Implanted Silicon
Authors: Konrad G. T.
Published: February 2004

A number of single-crystal p-type Si samples were implanted with Cs+ ions to various concentrations and depths. The secondary electron emission coefficient δ of these samples was found to be as much as 28% higher than for untreated Si samples. In particular, the low value of primary voltage needed to obtain δ>1 suggests the use of such emitters in applications where secondary emission buildup at low primary voltages is desired.
Interpretation of the Auger Electron Spectrum from Oxidized Beryllium
Authors: LeJeune E. J. , Dixon R. D.
Published: February 2004

Auger electron peaks at 94 and 87 eV have been observed in the dN(E) /dE of the secondary-electron energy distribution N(E) from oxidized Be. These peaks are explained in terms of 1s2p2p (94 eV) and 1s2s2s (87 eV) transitions. This interpretation is consistent with an energy-level diagram and a total-density-of-states curve constructed using existing experimental data.
Diffusion in Heavily Doped Semiconductors: Local Charge Neutrality and One-Band Approximations
Authors: Hu S. M.
Published: February 2004

Two aspects of diffusion in heavily doped semiconductors are discussed in reference to the suitability of the commonly assumed local charge neutrality approximation and the one-band approximation for the conduction-band density of states. The local electron concentration and internal field have been obtained by solving the Poisson-Boltzmann equation, and are compared to those obtained under the assumption of local charge neutrality. When the impurity diffusion length is several times the Debye length, the discrepancy is small except at the surface. A two-band density-of-states approximation is used to calculate the Fermi level in heavily doped germanium. It was found that the Fermi level thus obtained can be more than 0.1 eV lower than that obtained in the one-bank model.
Attenuation Length of Excited Electrons in Amorphous Selenium
Authors: Pong W.
Published: February 2004

The scattering of electrons in amorphous selenium was investigated by measuring the attenuation of excited electrons passing through selenium films of different thicknesses. The attenuation due to inelastic scattering was determined by observing the decrease of photoemission current when a thin film of amorphous Se was deposited on a semitransparent CuI photocathode. The attenuation length was found to be (40±10) Å for excited electrons of (4.7±1.0) eV in the conduction band. On the basis of observed attenuation length, the relaxation frequency for electron-electron scattering is estimated to be 2.4×1014 sec−1.
Growth Kinetics of Inert-Gas Bubbles in Polycrystalline Solids
Authors: Markworth Alan J.
Published: February 2004

A largely analytical study is presented of the growth kinetics of inert-gas bubbles in polycrystalline solids. Growth is assumed to be gas diffusion controlled, and coupled expressions are thus derived for the instantaneous rates of growth of bubbles situated both within grains and on grain boundaries. Numerical solutions of these expressions are obtained for given values of various parameters using a Runge-Kutta technique, and the results obtained in this manner are found to be consistent with corresponding experimental data describing bubble growth in neutron-activated and annealed UC. In addition, approximate solutions to the coupled growth equations are obtained analytically for a special case and are found to be in relatively good accord with corresponding results obtained numerically.
Localized Vibrational Mode Absorption of Ion-Implanted Silicon in GaAs
Authors: Skolnik L. H. , Spitzer W. G. , Kahan A. , Euler F. , Hunsperger R. G.
Published: February 2004

Infrared absorption bands of localized vibrational modes for ion-implanted Si in GaAs are observed. Room-temperature implants were at energies of 1.0 and 1.5 MeV and fluences ∼ 1017 ions cm−2. The bands previously attributed to SiGa and SiAs defects were observed and the dependence of the absorption at liquid-nitrogen temperature was studied for samples isochronally annealed from 200 to 900 °C. The strongest band due to (SiGa–SiAs) pairs was observed after 400 °C annealing. For most of the temperature range the different defect concentrations were found to either grow or show little change during the annealing cycle. However, between ∼ 500 and 650 °C substantial reverse annealing was observed for both SiGa and SiAs. This effect cannot be explained by direct pair formation and other possible explanations are suggested. For these high-fluence, high-energy implants the electrical data obtained during the anneal cycle show no apparent correlation with the Si defect concentrations as deduced from optical data. The conductivity is probably controlled by residual damage left in the implant layer.
Rayleigh Wave Dispersion on Surface-Treated Glass
Authors: Bucaro J. A. , Davis C. M.
Published: February 2004

Rayleigh wave velocities have been measured as a function of frequency on thermally quenched and ion-exchanged glass samples. A significant dispersion is found indicating that such a technique can be used for studying stress profiles in surface-strengthened glass.
Alfvén Wave Second-Harmonic Generation in Bismuth: Kinetic Theory
Authors: Sharma Satish K. , Tripathi V. K.
Published: February 2004

The possible nonlinear mechanisms for harmonic generation in bismuth have been investigated by solving the Boltzmann transfer equation for free carriers. Space diffusion of carriers has been shown to be as important as the interaction of magnetic field of the wave with current density. The results are compared with the experimental results of Bate and Wisseman for damped Alfvén wave second-harmonic generation. Except for the behavior of harmonic power with static magnetic field, a good agreement is found.
Paramagnetic Resonance and Hall Coefficients in Fe-Doped n-Type GaP
Authors: Suto Ken , Nishizawa Jun-ichi
Published: February 2004

Fe impurities in solution-grown n-type GaP crystals have been studied with the measurements of the paramagnetic resonance and the Hall coefficient at and above 77°K. It is shown that Fe impurities act as electron traps and when they have trapped electrons, reveal the paramagnetic resonance spectrum which the authors already reported as due to the (3d)7 configuration. It is confirmed that the resonance spectra appear only in n-type GaP crystals by doping with various amounts of Fe and Te, Sn, or Zn. The trap level is found to be near the conduction band.
Numerical Solutions to a One-Dimensional Analogue of the Diffusion of Resonance Excitation through a Gas
Authors: McIntyre Robert G. , D'Arcy Edward M.
Published: February 2004

McIntyre and Fowler reported on an equation for the diffusion of resonance excitation through a gas. A one-dimensional analogue of their equation is presented together with illustrations of numerical solutions. In the case where the mean translational distance moved by an atom between absorption and reemission and the expected skip distance of a photon during an emission-reabsorption process are roughly equal, solutions are obtained considering both processes and then suppressing the former. Illustrations are presented to estimate the relative importance of the contribution of the translation of excited states to the total diffusion process.
Induced Fluorescence and Temperature Jump in CO2 by Resonant Absorption of 10.6-μ CO2 Laser Radiation
Authors: Offenberger A.A. , Lidsky L.M. , Rose D.J.
Published: February 2004

Experimentally observed ``jump'' phenomena in gas temperature and detected fluorescence at a well-defined pressure, when a 50-W beam of focused 10.6-μ laser radiation is absorbed in CO2, are reported. A model based on sufficiently fast relaxation of (00°1) vibrational-translational energy and sufficiently slow energy loss out of the laser focus to result in a runaway of temperature is proposed to account qualitatively for the observed features. Calculation of the temperature jump (160°C) agrees with a measured value and establishes the reason for the order-of-magnitude jump in detected fluorescence by means of an increased Boltzmann distribution of absorbing states. The influence of helium on the jump condition was established; in particular, the helium quenching effect via increased thermal conductivity supports the proposed model.
Disturbed Phonon Distribution in Polar Semiconductors
Authors: Kranzer D. , Gornik E.
Published: February 2004

The mobility of n-InSb at cryogenic lattice temperatures is shown to change during approximately 10 nsec after application of a voltage pulse. It increases with time below a certain electric field strength and decreases above this value. This behavior can be understood as resulting from a deviation of the longitudinal optical phonon distribution from its thermal equilibrium; the stationary state being obtained approximately 10 nsec after application of the voltage pulse.
Determination of Optical Energy Gaps from Surface Photovoltage Measurements
Authors: Lile D. L. , Wieder H. H.
Published: February 2004

The spectral photovoltaic response of surface barrier MOS diodes is shown to yield information about the charge carrier dependence and the temperature dependence of the fundamental optical band gaps of pure and doped bulk crystalline and thin-film semiconductors with specific reference to InSb.
Resolution and Sensitivity of the Spherical-Grid Retarding Potential Analyzer
Authors: Huchital D. A. , Rigden J. D.
Published: February 2004

The resolution and sensitivity of the spherical-grid retarding potential difference electron-energy spectrometer are discussed. The resolution is shown to be determined by lens effects at the second grid and to be proportional to the ratio of the grid separation to the grid mesh hole size. The resolution of three experimental systems is discussed and shown to be in agreement with the results of computer analysis. The ultimate sensitivity or signal-to-noise ratio developed by the analyzer is shown to be improved by the addition of a ``postmonochromator'' collector scheme which selectively gathers those electrons which pass through the retarding field with a minimum of kinetic energy. Application of the analyzer to Auger electron spectroscopy and x-ray photoelectron spectroscopy is demonstrated. The retarding potential/postmonochromator combination is shown to possess distinct advantages in terms of simplicity and/or sensitivity for both techniques.
Exploring the Ultimate Efficiency in Infrared-to-Visible Converting Phosphors Activated with Er and Sensitized with Yb
Authors: Rich T. C. , Pinnow D. A.
Published: February 2004

Recently developed visible solid-state light sources made by coating ir light emitting diodes with ir-to-visible converting phosphors appear technologically interesting. However, the ultimate performance of these devices has been uncertain since there was no accurate method for extrapolating the nonlinear characteristics of the phosphors. We have developed techniques for exploring the ultimate efficiencies of these phosphors by exciting them with a tightly focused YA1G:Nd laser operating at 1.06 μ. The results of a series of measurements on the brightest phosphor materials available indicate that the ultimate efficiencies are strongly dependent on the host crystal material. Of the materials we have examined, the most efficient hosts are barium vttrium fluoride, BaYF5, and yttrium fluoride, YF3. The ultimate visible efficiency of the latter, defined as the ratio of visible emitted power to incident ir excitation power, is in excess of 24%. Based on these results and the known performance of GaAs ir light emitting diodes, we conclude that the over-all performance of ir-to-visible converting phosphor-diode devices should be comparable to the direct visible emitting GaP devices.
Harmonic Generation by Resistive Feedback from Superconducting Point Contacts
Authors: Adde R. , Vernet G.
Published: February 2004

The rf emission from a superconducting point contact driven with a constant current source allows the direct observation of harmonic generation by purely resistive feedback. The amplitudes of the harmonics are shown to be in agreement with the theoretical values determined from a simple model of the junction.
Observation of a c-Axis Moment in α-Fe2 O3
Authors: Flanders P. J.
Published: February 2004

The Dzyaloshinsky theory for spin configurations in the rhombohedral weak ferromagnet α-Fe2O3 predicts above the Morin transition temperature a very small c-axis magnetic moment Mc having a threefold symmetry. This property has been experimentally observed for the first time using a rotating sample magnetometer. Mc is found to vary as AMs cos3Ψ when a saturating field rotates through an angle Ψ in the basal plane, being equal to zero when the field is along any of the three twofold axes. For 11 α-Fe2O3 crystals the average value of A is 1.15±0.4×10−3 with Ms equal to the weak spontaneous moment in the basal plane. Since a canting angle for the spins in the basal plane of 10−4 rad will produce Ms, a spin canting toward c of only 10−7 rad can account for Mc.
Charge of the Electret
Authors: Gross Bernhard
Published: February 2004

The polarization of the electret is measured by heating the dielectric in short circuit. Intensity and shape of the depolarization current depend on heating rate; the time integral over the current cannot, therefore, a priori be assumed to be independent of heating rate. This note discusses conditions under which the value of the integral is an invariant that depends only on the initial state of the system, and thus allows one to define the ``frozen-in'' charge of the electret.
Electrical Resistivity of a Composite of Conducting Particles in an Insulating Matrix
Authors: Aharoni Shaul M.
Published: February 2004

A model rationalizing the curve of resistivity vs volume percent of a metal-powder component in a metal/polymer composite is considered. It shows the conductivity to be directly dependent on the surface area of the conducting particles and also shows a 2/3 power dependence on their volume. Comparison with experimental results shows a good fit.
Influence of Deposition Temperature on Composition and Growth Rate of GaAsx P1−x Layers
Authors: Ban V. S. , Gossenberger H. F. , Tietjen J. J.
Published: February 2004

Epitaxial layers of GaAsxP1−x alloys were deposited in an open-tube vapor-transport apparatus. It was found that the growth rate and the composition of the deposited alloy strongly depend on the deposition temperature. Higher deposition temperatures lead to an increase in the P content of the alloy. The growth rate reached a maximum at 830°C and then decreased with further decrease in the deposition temperature, contrary to expectations based on the thermodynamics of the growth system. A time-of-flight mass spectrometer was coupled to the growth system, and the composition and the chemical reactivity of the vapor species was studied. The results of these studies offer an explanation for the observed dependence of the composition of the deposited alloy on the deposition temperature.
Thermomigration of Gold-Rich Droplets in Silicon
Authors: Anthony T. R. , Cline H. E.
Published: February 2004

The thermomigration of gold-rich liquid droplets through solid silicon in a constant thermal gradient of 50°C/cm was studied as a function of temperature. A simple equation based on diffusion control adequately described the variation of the droplet velocity with temperature. The effective diffusion coefficient D* of Si through the Au–Si liquid was found to follow the relation D*=D0 exp(−Q/RT), where Q=5.0 kcal/mole and D0=2.5×10−3 cm2/sec.
Conservation of Acoustic Phase in Ultrasonic Imaging by Bragg Diffraction
Authors: Landry John , Keyani Hormozdyar , Wade Glen
Published: February 2004

Acoustic-phase conservation in ultrasonic imaging by Bragg diffraction is experimentally verified by optical heterodyning. The results suggest the possibility of a phase-contrast Bragg imaging system with simultaneous display of phase and amplitude information.
Dislocation Analysis of Crack Lamellae
Authors: Marcinkowski M. J. , Armstrong R. W.
Published: February 2004

A detailed numerical analysis has been carried out with respect to the equilibrium configuration of both shear and tensile crack lamellae under varying applied stresses. The cracks were assumed to consist of circular concentric glide and prismatic dislocation loops, respectively. Among other things, it was found that under a given applied stress, circular cracks are larger in size than straight cracks and that circular tensile cracks are greater in size and energy than circular shear cracks. In addition, it is shown that the Griffith criterion for crack growth simply corresponds to specifying the lowest energy for a given arrangement and number of dislocation loops.
Attenuation of Microwave Acoustic Surface Waves Due to Gas Loading
Authors: Slobodnik A. J.
Published: February 2004

Experimental measurements of microwave acoustic surface-wave attenuation due to propagation at the boundary of a solid and a monatomic gas are presented. Data illustrate attenuation as a function of frequency, molecular weight, pressure, and temperature. Experimental results are compared to both an approximate and a continuum mechanical theory. For the frequencies of interest (500–2500 MHz) the approximate theory gives better agreement with experiment. A summary of data of attenuation due to air loading at 1 GHz is presented for a number of low-loss acoustic surface-wave substrates. Of practical interest is the fact that microwave acoustic surface-wave delay lines and other signal-processing devices must be encapsulated in either helium or vacuum if minimum insertion loss is desired.
Elastic Surface Wave Guidance by (Δv/v) Effect Guidance Structures
Authors: Hughes A. James
Published: February 2004

The possibility of utilizing guided surface acoustic waves in signal processing devices has generated interest in basic investigations of guidance mechanisms and structures for surface acoustic waves. Surface wave propagation, investigated in detail thus far in guidance structures, has unfortunately proven sufficiently dispersive to rule out many practical device applications. Reported here are theoretical investigations of the basic physical phenomena of a (Δv/v) guidance structure which is substantially nondispersive. Acoustic guidance in the (Δv/v) structure is assumed to be due principally to the velocity reduction Δv of a thin conducting strip on a piezoelectric substrate. With this assumption, major features of (Δv/v) guidance can be predicted theoretically from an isotropic nonpiezoelectric model which incorporates the velocity difference Δv. Numerical results are presented for quartz and lithium niobate. In addition, a generalized description for guided waves is developed which is approximately independent of the (Δv/v) velocity ratio. Thus, with the use of scaling factors, the normalized data are applicable to materials with a range of (Δv/v) ratios. Simply put, our principal conclusion is that for many common piezoelectrics, strong guidance and low dispersion are theoretically predicted. Basic experimental investigations thus appear warranted.
Diffusion-Controlled Breakdown of Gases in Cylindrical Microwave Cavity Excited in the TMn Mode
Authors: Maldonado C. D. , Ayala I. L.
Published: February 2004

The boundary-value problem for diffusion-controlled breakdown of gases in microwave cavities is converted to a variational principle for the square of the reciprocal of the ``effective'' diffusion length. For a cylindrical cavity excited in the TM0n0 mode, the resultant variational principle was minimized by an iterative-variational procedure. This was done for an arbitrary functional dependence on the rms value of the electric field. The resultant hierarchy of approximations to the variational principle obtained by this iterative-variational procedure was applied to a cylindrical cavity excited in the TM010 and TM020 modes, respectively, using the high-frequency ionization coefficient of Herlin and Brown. Calculations were carried out and plots of the ratio of the effective to the characteristic diffusion length as a function of the Herlin and Brown parameter β are given for various ratios of cavity depth to radius. From this theoretical investigation, it is felt that the first ten approximations to the variational principle are sufficient to provide adequate convergence for any situation encountered in practice with regard to β as well as cavity dimensions.
Dark Discharge in Amorphous As2Se3 Films
Authors: Ing S. W. , Neyhart J. H.
Published: February 2004

The dark-discharge rate of corona-charged amorphous films of As2Se3 is dependent upon the electric field, temperature, and the duration of discharge. The dark-discharge current was found to result from both bulk generation of holes and from surface injection of holes. Negative charges are immobile in the material. The surface contribution gradually diminishes over a period of weeks as the film ages, or it can be eliminated by applying a thin organic insulating layer to the photoconductor surface. The bulk generation contribution, identified by its linear dependence upon film thickness, is the subject of more detailed analysis. The discharge rate increases slightly at higher electric fields. During the period of a single discharge measurement, the rate drops faster than can be explained by the field dependence. In addition, the discharge rate increases rapidly with temperature. There is no unique activation energy characterizing the discharge process. To account for the discharge time and temperature dependencies, two sets of generation centers are postulated to lie within the band gap of the material. The first set lies 0.6–0.78 eV above the hole conduction states and the density of centers at each energy increases slowly with increasing energy. The second set is located at 0.8–0.86 eV above the hole conduction states, whose density is more than 2 orders of magnitude greater than that of the shallower centers. A first-order kinetic mechanism is assumed for the hole generation from each energy level. The density of the first set of centers has been calculated to be 1014 cm−3 and the second set is in the range 1016−1017 cm−3. A Poole-Frenkel type of relationship is used to correlate the electric field dependency of the dark-discharge rate. Using this model, the surface potential can be predicted as a function of the discharge time, the temperature, and the initial field, provided no severe internal field distortion exists in the bulk of the photoconductor.
Effect of Aluminum on the Amphoteric Behavior of Silicon in Ga1−xAlxAs
Authors: Rado W. G. , Johnson W. J. , Crawley R. L.
Published: February 2004

The effect of the Al concentration in the melt on the transition temperature at which Si changes from an n- to p-type dopant during the liquid-phase epitaxial growth of Si-doped Ga1−xAlxAs layers has been investigated as a function of the substrate's orientation. It was found that the transition temperature decreased logarithmically with increasing Al-to-As atom fraction ratio in the melt for both (111)-Ga and (111)-As oriented substrates. The effect was more pronounced for the (111)-As oriented substrates. However, electroluminescent diodes fabricated from the grown layers showed no discernible difference in characteristics as a function of the substrate's orientation.
Second-Harmonic Generation and Miller's Delta Parameter in a Series of Benzine Derivatives
Authors: Southgate P. D. , Hall D. S.
Published: February 2004

Second-order nonlinear susceptibilities and refractive index dispersion measurements have been made in six benzene derivative crystals. The nonlinear susceptibility tends to be much greater in crystals with lower energy absorption edges. A simple classical model is discussed in which the enhanced values are due to anharmonic oscillators near the absorption edge.
Automatic Plotting of Langmuir-Probe Susceptance- and Conductance-Voltage Curves
Authors: Olson Robert A. , Nordlund D. R.
Published: February 2004

Langmuir-probe susceptance- and conductance-voltage measurements have been made using a system which automatically plots the in-phase and quadrature components (simultaneously) of a two-terminal complex admittance, as a function of applied dc potential. The operation of the system, which utilizes phase-sensitive detection to separate the admittance components, is discussed. Measurements for a planar guardsleeve probe in a mercury-vapor plasma (collisionless) and for a spherical probe in an argon plasma (collisional) are presented. Positive and negative peaks observed in the low-frequency susceptance-voltage characteristic are discussed in terms of ion-response, probe-contamination, and plasma-perturbation effects.
Emission of Characteristic L and K Radiation from Thick Tungsten Targets
Authors: Storm Ellery
Published: February 2004

A method is proposed for calculating L and K photon emission from thick tungsten targets bombarded by electrons accelerated by potentials of 12–300 kV. Electron energy losses, electron backscatter losses, and photon attenuation in the target are included. Agreement with measured K emission is obtained using the Arthurs-Moiseiwitsch ionization cross sections and an expression of the form CZ(E0−k) 1−exp(−3k/EK)(k/E0)1/3 1−exp(−E0/EK)to describe the bremsstrahlung energy distribution. Satisfactory agreement with L-emission measurements is obtained using the Mott-Massey cross-section formula with constants BLi=4 ELi, bLI=0.25×1.6, bLII=0.25×2.75, and bLIII=0.25×4.2. Indirect radiation contributes 54–82% of the total K emission and 5–8% of the total L emission. The Webster-Clark empirical relation Ii=Ci(U0−1)ni agrees with calculation for U0<3, with CK=5.1×1011 photon/sec mA sr, nK=1.67, CL=2.6×1011 photon/sec mA sr, and nL=1.5.
Energy Spectrum of Slow Monoenergetic Electrons Reflected by Stainless Steel
Authors: Adnot A. , Ballu Y. , Carette J. D.
Published: February 2004

The energy spectra of monoenergetic electrons reflected from a surface of stainless steel have been measured. In the spectra one may detect two types of energy losses: (i) weak and multiple losses which may be associated with the weakly adsorbed phase of the residual gas of the vacuum system; (ii) strong and discrete losses caused by chemisorbed molecules on the surface. The values of these discrete energy losses are compatible with a model of molecular structure of the chemisorbed species on the surface.
Numerical Calculation of the Arc-Driven Supersonic Laser Operating in the Gas-Dynamic Mode
Authors: Howgate D. W. , Roberts T. G. , Barr T. A.
Published: February 2004

Numerical results derived from a theoretical model for the nozzle and cavity sections of a CO2–N2–H2O gas-dynamic laser are compared with the output of an arc-driven supersonic laser operating in the gas-dynamic mode at about 10% CO2 and H2O concentrations ranging from 0.7 to 7%.