bluuebunny/crossref_metadata_2025 huggingface dataset:
Transverse Magnetoresistance of n-Type Germanium for High Electric Fields Applied in the 〈111〉 Direction
Authors: Nag B. R. , Paria H.
Published: April 2005

The transverse magnetoresistance of 5-Ω·cm n-type germanium at different magnetic fields for an electric field applied in the 〈111〉 direction up to 5 kV/cm has been measured. It has been found that (i) magnetoresistance at a particular electric field decreases with increase of magnetic fields, (ii) at small magnetic fields magnetoresistance decreases with increase of electric field, and (iii) the ratio of the square root of magnetoresistance and the conductivity mobility is independent of electric fields up to 5 kV/cm.
Capacitance of p-n Junctions: Space-Charge Capacitance
Authors: Chang Y. F.
Published: April 2005

Exact calculations of the total space-charge density in a p-n junction reveal it to be unrelated to the charge density assumed in the Schottky theory. The difference can be as large as orders of magnitude. Consequently, the space-charge capacitance is also found, by detailed analysis, to be unrelated to the Schottky result. A simplified closed-form solution is then obtained for the space-charge capacitance using the Shockley injection relation. In symmetrical junctions, there is some agreement between the exact space-charge capacitance and the Schottky result. In asymmetrical junctions, the space-charge capacitance is nearly constant for negative biases. These results indicate the need for further detailed analysis of the capacitance of p-n junctions.
Influence of Waveguide Contact on Measured Complex Permittivity of Semiconductors
Authors: Champlin Keith S. , Glover Gary H.
Published: April 2005

Techniques employing rectangular waveguides to measure complex permittivity generally contain the tacit assumption that the material fills the waveguide uniformly. With semiconductors this assumption may be poorly satisfied near the waveguide walls due to (1) air gaps, (2) oxide layers, (3) potential barriers, and (4) distributed ``screening'' charges. The uniform-filling assumption is removed in the present paper by treating the contact region with perturbation theory. The results are found to be simply represented by a lumped-parameter equivalent circuit. Measurements performed on intrinsic germanium at 10.5 GHz agree well with the theory and indicate that unintentional air gaps and oxide layers dominate the measurements at high conductivities, even for ``tightly'' fitting samples.
An Equivalent Distribution of Surface Currents for the Generation of a Prescribed Static Magnetic Field within the Enclosed Volume
Authors: Laslett L. Jackson
Published: April 2005

It is shown how a specified static magnetic field within a given volume may be generated through use of a current distribution on the surface surrounding this volume. The surface distribution includes a distribution of magnetic moment (oriented tangential to the surface) that may be interpreted as a double-current layer, but no magnetic poles are introduced. No sources are required external to the surface and the exterior field will be zero.
Preparation and Morphology of Boron Filamentary Crystals Grown by the Vapor-Liquid-Solid Mechanism
Authors: Sitarik J. P. , Ellis W. C.
Published: April 2005

α-rhombohedral boron has been grown by the vapor-liquid-solid mechanism using the reduction of BCl3 with hydrogen for transport and platinum as the liquid-forming agent. Both straight and kinked whisker crystals were produced with 〈4̄401〉 growth directions.
Hollow-Cathode Glow Discharge in Hydrogen and the Noble Gases
Authors: Sturges D. J. , Oskam H. J.
Published: April 2005

Properties of a discharge maintained between a planar anode and a cathode consisting of two parallel electrodes have been studied in helium, neon, hydrogen, and helium-argon mixtures at pressures between 1 and 25 Torr. The analysis of the data led to the following main conclusions: (1) The enhancement of the discharge efficiency by the hollow-cathode effect does not vary widely between the gases tested. (2) The presence of metastable excited atoms is not essential for a pronounced hollow-cathode effect to occur. (3) The minimum distance from the cathodes at which the anode fall develops is a function of the cathode dimensions, and is simply related to changes in the electron concentration and average electron energy. (4) The lowest observed cathode fall for a hollow-cathode discharge corresponded closely to the cathode fall of a normal plane-cathode discharge. (5) The general nature of the hollow-cathode effect in the gases tested is sufficiently similar to allow simple design criteria to be developed for plane-parallel hollow-cathode discharge tubes.
Pure Space-Charge-Limited Electron Current in Silicon
Authors: Denda S. , Nicolet M-A.
Published: April 2005

Phosphorus diffusion on π-type silicon is used to fabricate n+πn+ structures of base widths between 3 μ and 60 μ with π-type resistivities of 300 Ω·cm and 8 kΩ·cm. The V-I characteristics of the structures are measured at room temperature and at liquid-nitrogen temperature. The change in current for constant applied voltage is also observed in that temperature range.

The results are interpreted in terms of simple models based on the assumption that pure space-charge-limited current of electrons is present. The models describe well the characteristics measured on 300-Ω·cm samples, except for the range of small biases on the thinnest samples. It is concluded that the drift velocity of electrons at 78°K tends towards saturation at 1.0×107 cm/sec ± 10%. The current observed at this temperature actually reaches this value. The critical electric field at 78°K is 103 V/cm±30% but the meaning of this concept for electrons in silicon is vague. The temperature dependence of the current at fixed bias voltages is in general agreement with the variation of the low field mobility. Results obtained on 8-kΩ·cm samples need clarification. Effects of breakdown and trapping are not observed.
Measurement of Strains at Si-SiO2 Interface
Authors: Jaccodine R. J. , Schlegel W. A.
Published: April 2005

When Si is thermally oxidized, the SiO2 resulting is in a state of compression on the surface. This paper reports an experimental determination of the magnitude of this stress and its dependence on the temperature of oxidation.

Samples of (111)- and (100)-oriented Si were oxidized at several temperatures between 875°–1200°C to thicknesses of 2000 Å-20 000 Å. Stress determination was made by two techniques: (a) the thin Si sample was used as a beam, and the amount of bowing under the strain exerted by oxide left on one surface was measured; (b) the unsupported SiO2 window was used as a balloon, and strain was measured as a function of air pressure inflating the balloon. Results of these measurements are in agreement with the stress expected from thermal mismatch of Si and SiO2. For an oxidation carried out at 1200°C the measured stress is 3.1×109 dyn/cm2. The data from the SiO2 balloons showed that the strain grown in the oxide was greater than 10−3. In addition, determination was made of Young's modulus from the stress-strain curves of the unsupported films. The value of 6.6×1011 dyn/cm2 obtained compares favorably with the value 7±1.5 1011 dyn/cm2 found for silicate glasses.

Some implications of this stress are briefly discussed. Dislocation generation at borders of holes cut into oxide, bowing and slip processes of slices, impurity segregation, and precipitation are all possible results of this mismatch between the two materials.
Experiments on Surface Wave Propagation along Annular Plasma Columns
Authors: Paik S. F. , Briggs R. J. , Osepchuk J. M.
Published: April 2005

The propagation of surface waves along a plasma column of annular cross section was investigated experimentally. The laboratory plasma used for the experiment was a mercury-vapor dc discharge. The properties of the experimental discharge tube were examined to show some basic differences between the laboratory plasma and the idealized model of the plasma used for the analysis. In particular, a radially non-uniform density distribution and the variation of the distribution with the applied magnetic field was noted. In spite of the radial-density inhomogeneity, the experimentally determined phase constants of the backward-surface wave are in good agreement with values predicted from the uniform density theory. The attenuation in the absence of the magnetic field is consistent with collisional losses, predominantly with the walls of the container. The effect of an axial magnetic field on the surface-wave characteristics is examined. Experimental results show that in the presence of a magnetic field the attenuation of the backward wave is markedly increased; this enhancement of the damping is not consistent with simple collision theory within the framework of the uniform-density model.
Flow and Self-Diffusion of Gases in Capillaries. Part II
Authors: Lund L. M. , Berman A. S.
Published: April 2005

A variety of experimental data on the pressure dependence of the flow of gases through capillaries are examined using the model presented in Part I. The model is found to provide a good description of flow and self-diffusion in capillaries of arbitrary length-to-radius ratio at pressures ranging from the near free molecule to the continuum regimes.

Experimental free-molecule flows are found to differ from those predicted from existing theories based on the diffuse scattering of gas molecules by the capillary wall. The differences, which in general cannot be explained by specular reflection, are found to depend on the geometrical structure of the surface, the length-to-radius ratio of the capillary, and on the gas being transported.

For a given gas flowing through a capillary of given length-to-radius ratio, the slip contribution to the transport is found to be a monotonically increasing function of the ratio of observed-to-theoretical free-molecule transports.
Mössbauer Effect in Co1−xFexSi
Authors: Wertheim G. K. , Wernick J. H. , Buchanan D. N. E.
Published: April 2005

It is shown on the basis of experiments with CoSi(57Co) in a high magnetic field and with magnetically ordered Co0.5Fe0.5Si that iron does not develop a magnetic moment greater than 0.1 μB at low temperature in the system Co1−xFexSi. The results also indicate that the magnetic properties are not directly related to the electron and hole bands pertinent to transport properties. The isomer shift shows that the configuration of Fe is independent of composition over the entire range of composition. The electron concentration dependence of the quadrupole splitting is discussed.
Cesium Ion Sputtering of Aluminum
Authors: Andrews A. E. , Hasseltine E. H. , Olson N. Thomas , Smith Harold P.
Published: April 2005

A neutron activation technique has been developed to investigate cesium-aluminum sputtering in measured, rarefied atmospheres of oxygen. The sputtering yield was measured as a function of cesium ion energy and as a function of the ratio of oxygen molecular flux arriving at the target surface to sputtered aluminum flux leaving the surface. In all measurements the ion beam was normal to the monocrystalline aluminum target surface and to the (110) crystallographic plane. The yield increased monotonically from 0.74 (atoms/ion) at 1 keV to 2.4 at 10 keV and was unaffected by flux ratios less than 0.2. The yield decreased for higher values of the flux ratio and eventually reached a saturation value where it is conjectured that a surface film of Al2O3 is maintained.
Near-Surface Effects in Superconducting Niobium-Zirconium Alloys
Authors: Love Gordon R.
Published: April 2005

At a given magnetic field, critical currents may be induced to flow in the surface layers of a superconductor by the application of a relatively small-amplitude alternating-current field. Many measurements of this induced current have been made as a function of the intensity of the direct-current field, and the frequency and amplitude of the alternating-current field. The results of these measurements may be interpreted by assuming that there is a near-surface layer of a few hundred angstroms thickness which is able to carry extraordinary current densities from 3 to 20 times the bulk current densities at a given field. Current densities calculated for this surface layer exceed 107 A/cm2 at low fields. Details of the observations vary with sample history, but the general features of these measurements have been observed in all samples tested.
Determination of Deep Centers in Conducting Gallium Arsenide
Authors: Williams Richard
Published: April 2005

A technique has been developed for determining the properties of deep centers in conducting, n-type gallium arsenide. A Schottky barrier is produced at the surface by means of a blocking contact of gold or electrolyte. A reverse bias is applied and the ionization of deep centers in the dark causes the barrier capacitance to change with time. After this, electrons may be injected into the barrier by strongly absorbed light and captured by the deep centers that have previously ionized. Again, the kinetics of the process can be determined from measurements of the barrier capacitance as a function of time. The concentration, energy level, and capture cross section of the dominant center have been determined. It is a donor lying 0.74 eV below the conduction band edge and typically present in concentrations around 1016/cm3. From capture-cross-section data it appears to be negatively charged when occupied. This property is sufficient to limit minority-carrier lifetimes to very small values.
Polarization in LaF3
Authors: Solomon R. , Sher A. , Muller M. W.
Published: April 2005

We report the results of measurements of the low-frequency dielectric behavior and of persistent polarization in single-crystal LaF3. This ionic conductor exhibits unusually large polarization effects. The measurements distinguish at least two components of polarization. One component, with a time constant of the order of milliseconds, is linear in the applied voltage; the long-term polarization is proportional to its square. The phenomena are evidently associated with surface effects, but they cannot be described by the accepted space-charge theory of ionic conductors. They appear, however, to be qualitatively consistent with an extension of the notion of ionic surface states introduced by Frenkel.
Measurement of Synchrotron Radiation in the X-Ray Region
Authors: Bathow G. , Freytag E. , Haensel R.
Published: April 2005

Synchrotron radiation has been investigated by means of scintillation counters at electron energies between 4.0 and 6.3 GeV. Measurements were performed of the integrated radiation, the spectral distribution, the polarization, and the angular dependence of them at photon energies between 15 and 300 keV. The results agree with theoretical calculations.
Atom Ejection Studies for Sputtering of Semiconductors
Authors: Anderson G. S.
Published: April 2005

Atom-ejection patterns resulting from the sputtering of semiconductor single crystals have been examined. The annealing temperature Ta (here defined as the minimum target temperature for which single-crystal spot patterns are observed) previously reported for Ge, Si, InSb, and InAs, has now been determined for GaAs and CdTe. For target temperatures below Ta damage remains frozen in and the deposit indicates an amorphous or polycrystalline surface. For GaAs one finds Ta∼130°C for Ar+ and Ne+ ion bombardment; for CdTe no spot patterns are observed up to 510°C where the target begins to evaporate. No clear correlation of Ta with other physical properties is noticeable.

We had previously reported that spot patterns persist even for T<Ta if the bombarding-ion energy is less than some critical energy. We have now demonstrated that no such critical energy exists.

The 〈111〉 and 〈1̄1̄1̄〉 deposits resulting from sputtering of InAs and GaAs (110) surfaces were studied. The 〈1̄1̄1̄〉 spot [the normal to the (1̄1̄1̄) face, which terminates with a triply bonded In or Ga atom] is generally slightly thicker (by∼10%) than the 〈111〉 spot. For GaAs the 〈1̄1̄1̄〉 spot is slightly richer in Ga and the 〈111〉 spot is slightly richer in As. No compositional differences were noted for the deposits from InAs.
Investigation of 1/f Noise Spectra
Authors: Bess L. , Kisner L. S.
Published: April 2005

The observation of the upper turnover frequency for the 1/f noise spectrum in germanium filaments has been corroborated as well as the dependence of its value on sample ambient and temperature. Its value is also found to be dependent on aging of the sample. A theoretical explanation of the results is attempted based on a 1/f noise theory developed by one of the authors. This theory is amended here so as to apply to near-intrinsic semiconductors.
Production of Carbon Plasmas
Authors: Rutowski R. W. , Weimer D. , Marlow W. C.
Published: April 2005

An experimental technique for the production of high-temperature, high-density plasmas in a shocktube-like configuration has been developed. The device consists of an arc chamber (8.6 cm) analogous to a shocktube driver and a test chamber (25.6 cm) analogous to a shocktube receiver. Both sections have the same diameter (2.54 cm) and are joined without a separating diaphragm. Capacitively stored energy (120 000 J) is delivered over a period of 75 μsec to the arc chamber. This energy flow is initiated by introducing a low-pressure gas (100 μ) into the entire system so that the voltage (7000 V) across the arc chamber electrodes causes a discharge. The discharge produces a shock wave in the trigger gas (usually argon) followed by the flow of the arc chamber electrode material, primarily carbon, which acts, in analogy to the shock tube, as a hot-dense driver gas. In analyzing the subsequent flow, the low-density trigger gas is ignored and the dense carbon plasma is treated as if it were the flow behind an incident shock. This incident carbon plasma is reflected from the end wall of the test chamber producing the plasma of principal interest. The properties of the plasma behind the reflected shock have been studied and indicate that temperatures on the order of 25 000°K, pressures of 800 atm, and electron densities of 1020 cm−3 can be achieved.
Injection Mechanism and Recombination Kinetics in Electroluminescent CdTe Diodes
Authors: Morehead F. F.
Published: April 2005

Diffused p—n junctions in CdTe have been shown to emit efficient electroluminescence under forward bias at 77°K. Capacitance measurements, current—voltage characteristics, photovoltaic measurements, and the shift of the emitted photon energies with current and temperature are consistent with a space-charge recombination controlled current. The dependence of the quantum efficiency on temperature and current is consistent with a simple, Schön—Klasens-type model of thermal quenching and with limitations imposed by the second law of thermodynamics. The low average concentration of majority carriers at the junction (∼1016 cm−3) that characterizes these devices is a major limitation in obtaining high efficiencies of electroluminescence at 300°K, even at high current densities.
Measurement of the Very-High-Pressure Properties of Materials using a Light-Gas Gun
Authors: Jones A. H. , Isbell W. M. , Maiden C. J.
Published: April 2005

Equation-of-state data at extremely high pressure is required for the analysis of many problems pertaining to physics, geophysics, astrophysics, etc. The conventional method used to obtain such data is to impact one flat plate of material against another flat plate at a very high velocity. A shock wave is thus produced in the target plate and the pressure can be deduced by measuring the impact velocity and the shock velocity. American, Russian, and British researchers have used explosive to propel the driver plate to velocities of about 5 km/sec; however, the Russians do not indicate how they accelerate their driver plates for their highest velocities (14–15 km/sec).

The present paper describes an experimental technique in which a 20-mm light-gas gun has been used to accelerate a driver plate against a target at velocities up to 8 km/sec. Tests have been conducted using Fansteel 77 drivers, and Hugoniot data have been obtained for Fansteel 77, tungsten, and gold to about 6-Mbar pressure. The technique is very attractive in that x-ray photographs show that the driver plate is not deformed just prior to impact and has an angle of attack less than 0.5 deg. Also, an analysis of all possible errors in measurement of impact velocity, shock velocity, etc. shows that, with the present technique, Hugoniot data can be obtained to an accuracy of about 1%.
Transport Phenomena in Low-Energy Plasmas
Authors: Wilkins Daniel R. , Gyftopoulos Elias P.
Published: April 2005

An extended Chapman-Cowling formalism is used to derive transport differential equations for the charged-particle species in low-energy, three-component, two-temperature plasmas consisting of electrons, ions, and neutrals. The analysis is developed in two parts: (a) the charged-particle Boltzmann equations are solved for the charged-particle distribution functions; (b) these distribution functions are used to reduce the charged-particle hydrodynamic equations into a system of differential equations involving the densities, temperatures, and electrostatic potential of the plasma, and a set of transport coefficients which depend upon the prevailing collision laws. A general procedure for the computation of the transport coefficients is given, and illustrative numerical results are presented for specific collision laws.
Preparation and Properties of Noncrystalline Zinc Oxide Films
Authors: Mickelsen R. A. , Kingery W. D.
Published: April 2005

Noncrystalline films of zinc oxide have been formed by reactively sputtering zinc metal onto a low-temperature substrate in an oxygen-argon atmosphere. The structural state of the films is determined by the temperature of the condensing substrate, and noncrystalline films formed at low substrate temperatures crystallize on heating to 75°–100°C in air or vacuum. A change in optical absorption corresponds to an increase in band gap energy for the crystalline to noncrystalline transition; this is interpreted as resulting from the change in dielectric constant occurring for the same transition. A large reduction in electrical conductivity observed for the noncrystalline material is believed to result mainly from reduced carrier concentration.
Temperature Dependence of the Elastic Constants of Cu, Ag, and Au above Room Temperature
Authors: Chang Y. A. , Himmel L.
Published: April 2005

The adiabatic elastic constants c44, ½(c11−c12), and ½(c11+c12+2c44) have been measured for copper, silver, and gold over the temperature range from 300° to about 800°K using the conventional ultrasonic pulse-echo technique. The room-temperature values of the stiffness coefficients are shown to be in acceptable agreement with previously published data for the noble metals. Over the entire range from 300° to 800°K, it is found that, to a remarkably good approximation, the elastic constants for all three metals decrease linearly with temperature. Additional evidence is presented to show that the linear temperature dependence of the elastic constants for silver extends to at least 1000°K, i.e., to within 80% of the absolute melting temperature. The isothermal compressibilities calculated from the elastic constant data are used to evaluate the dilational term in the specific heat, Cdil=Cp−Cv, and it is established that the approximate Nernst-Lindemann relation for estimating Cdil is valid for Cu, Ag, and Au at least up to 800°K.
Peierls Barrier Analysis
Authors: Hobart R.
Published: April 2005

In an earlier paper a method was described for numerical calculation of the Peierls energy barrier to dislocation motion in the Frenkel-Kontorova model. The present paper reports an approximate analytical calculation of the barrier for the model with a cubic substrate, and compares the barrier analytically calculated with the barrier numerically calculated by the earlier method. The analytical method relates the barrier to poles on an axis of imaginary lattice spacing.
Eddy-Current-Limited Domain-Wall Motion in Thin Ferromagnetic Films
Authors: Patton Carl E. , McGill Thomas C. , Wilts Charles H.
Published: April 2005

The effect of eddy current losses on domain-wall motion in thin ferromagnetic films has been investigated from a theoretical point of view. Earlier calculations neglecting wall shapes and stray demagnetizing fields do not adequately explain existing experimental data. A general expression has been developed for the current distribution about a moving Bloch wall of arbitrary shape in a thin film of infinite extent and arbitrary thickness. Stray demagnetizing field effects have been included in an approximate manner for a simple 180° wall in which the magnetization rotates linearly through a wall whose width is calculated from static energy considerations. The current distribution was evaluated numerically and the eddy-current-limited wall mobility was obtained as a function of film thickness from 400 to 4000 Å, using material parameters typical for Ni–Fe alloy films with 80% Ni. Although the current distributions exhibited a significant dependence on wall width, the mobilities were not significantly different from previous predictions. In order to explain existing mobility data on the basis of eddy current losses, wall widths much larger than calculated static Bloch wall widths must be assumed. Otherwise, some other loss mechanism must dominate.
Stable Space-Charge Layers in Two-Valley Semiconductors
Authors: Copeland John A.
Published: April 2005

When electric fields of several thousand volts are applied to certain samples of n-type GaAs and InP, space-charge layers have been observed which are stable until they drift into the anode. Calculations of the possible stable configurations have been made using the two-valley model of McCumber and Chynoweth for GaAs. Under various voltage and sample length conditions, four types of configurations are possible: a high-field domain (or dipole layer), a low-field domain, an accumulation layer, and a depletion layer. Only in the limit of very high voltages do the domain configurations resemble the superposition of a stable accumulation layer and a stable depletion layer. The calculations show that the high-field domain is the only type that should have been observed under past experimental conditions. When a device contains a high-field domain, an increase in voltage reduces the current. This negative conductance effect is most pronounced in samples of GaAs where the value of doping density times sample length squared (NL2) is about 109 cm−1. The minimum field for sustaining a high-field domain decreases rapidly from the critical field for samples 30 μ long to about one-half the critical field for longer samples.
Residual Resistance Ratio of Pure Iron
Authors: Schindler A. I. , La Roy B. C.
Published: April 2005

The resistance at zero magnetic induction of iron specimens of varying impurity content has been determined by extrapolating the longitudinal magnetoresistance data taken at magnetic fields above saturation. These resistance values may then be used to determine a modified residual resistance ratio which is shown to be a more appropriate index of purity for ferromagnetic metals than that obtained with resistances measured in zero applied magnetic field.
Influence of Oxygen on the Adherence of Gold Films to Oxide Substrates
Authors: Mattox D. M.
Published: April 2005

Models which have been proposed for the mechanism of adhesion between deposited metal films and oxide surfaces correlate the adhesion to the chemical activity of the metal. It is shown that gold, which is usually thought to have little chemical interaction with oxygen, can be made to adhere strongly to fused silica if deposited in the presence of oxygen. The oxygen apparently affects the nucleation of the deposited film. Several deposition techniques are compared to determine the effect of ion bombardment of the surface on the resulting adhesion.
Electron Mobility in Aluminum Antimonide
Authors: Stirn R. J. , Becker W. M.
Published: April 2005

The temperature dependence of the electron mobility in tellurium-doped aluminum antimonide is calculated assuming combined polar optical, acoustical mode, and ionized impurity scattering. The separate mobilities for each mechanism are calculated using effective mass components (which have been given by the authors in a previous publication) in a many-valley model having [100] symmetry. It is found that the dominant scattering mechanism at room temperature is polar optical mode. However, it appears likely that acoustical mode scattering is non-negligible. The calculated temperature dependence of the mobility is found to be in reasonable agreement with the measured mobility behavior of a sample with known compensation. The calculations give a room-temperature lattice mobility of 250 cm2/V·sec. A lower observed Hall mobility than that calculated for temperatures above room temperature in the same sample is attributed to the onset of intra- and intervalley scattering by nonpolar optical modes, and possible nonparabolicity of the band minima.
High-Energy Light Emission from Junctions in GaAsxP1−x Diodes
Authors: Ainslie N. , Pilkuhn M. , Rupprecht H.
Published: April 2005

Spontaneous and stimulated emission from junctions in diodes made of silicon-doped, melt-grown GaAsxP1−x alloys have been studied. Variations of the emission spectra as a function of current and of composition ranging up to 40 mole % GaP were examined both at room temperature and 77°K.
Amplification of Waves due to Quanta with Negative Energy
Authors: Musha Toshimitsu
Published: April 2005

Wave energy moving faster than the phase velocity of the wave in the medium becomes negative. Such a wave field can equally well be treated as an ensemble of quanta with negative energy. Amplification of waves by mode coupling is represented by pair creation of a negative quantum and a positive quantum. Interaction of an electron stream with a dissipative medium creates the negative quanta.
Propagation Characteristics of Capillary Ripples. I. The Theory of Velocity Dispersion and Amplitude Attenuation of Plane Capillary Waves on Viscoelastic Films
Authors: Hansen Robert S. , Mann J. Adin
Published: April 2005

The boundary value problem for velocity of propagation and attenuation of capillary ripples over viscoelastic surface films is set up and solved from the viewpoint of continuum hydrodynamics. Both soluble and insoluble films are treated. Successive approximation methods are used to derive explicit formulas for velocity of propagation and amplitude attenuation; formulas for these quantities, accurate to second order, are given for slightly viscoelastic and highly viscoelastic films, and formulas, accurate to first order, are given for films of intermediate viscoelasticity.
Polarization of Dielectrics by Nuclear Radiation. II. Gamma-Ray-Induced Polarization
Authors: Murphy Preston V. , Gross Bernhard
Published: April 2005

The electrical polarization produced in solid dielectrics by gamma ray bombardment is treated as a space charge resulting from the production and absorption of Compton electrons. For a gamma-ray beam in equilibrium with secondary electrons, the calculated net space charge is negative in sign and decreases with distance in proportion to gamma ray attenuation. The distribution of polarization was studied experimentally by cutting away sections of irradiated carnauba wax and measuring the charge released on heating for each section. The relationship of thermally released charge to sample polarization and the effect of a temperature gradient are discussed.
Effect of Heat Treatment on the Optical Properties of Heavily Doped Silicon and Germanium
Authors: Spitzer W. G. , Gobeli G. W. , Trumbore F. A.
Published: April 2005

An experimental study has been made of the effect of high-temperature vacuum heat treatment on the infrared reflectivity of heavily doped germanium and silicon. The heat treatment produces a layer on the surface with optical properties differing from those of the bulk material. From a Kramers-Kronig analysis of the reflectivity data for an n-type silicon sample, where the time of heating is sufficiently short to make impurity out-diffusion unimportant, it is concluded that the changes in free-carrier electric susceptibility indicate a decrease in the low-frequency-scattering relaxation time. The change in relaxation time is attributed to the introduction of extensive surface fracture from the heating. The extinction coefficient was not obtained over a sufficient spectral range to ascertain whether it follows the classical expression; however, the results for the extinction coefficient indicate an increase in the high-frequency relaxation time.
Electron Extinction Distance in Silicon
Authors: Frankl D. R.
Published: April 2005

A method is described for the measurement of the extinction distance for electrons transmitted through crystals. Results for Si are in excellent agreement with dynamical diffraction theory if relativistic corrections are taken into account.
Stress—Strain Curves of Rubbers in Simple Shear
Authors: Mooney M.
Published: April 2005

It has been stated in a brief report that a gum rubber Hevea stock exhibited a linear stress—strain relationship in two-dimensional shear up to 300% shear. The experimental procedures and results are reported here in detail. Detailed results are reported also of a series of dynamic stress—strain measurements with the St. Joe Flexometer, briefly referred to in 1940. These dynamic shear—shear stress curves are linear within a given stress range. Whenever the greatest previous stress is exceeded, a new linear curve is obtained, of lower modulus.

Nonreversible crystallinity has been generally neglected in theories of rubber hysteresis and in experimental efforts to obtain truly reversible stress—strain curves.
Ultimate Tensile Properties of Elastomers. II. Comparison of Failure Envelopes for Unfilled Vulcanizates
Authors: Smith Thor L.
Published: April 2005

The tensile stress-at-break σb (based on the initial cross-sectional area) and the corresponding ultimate extension ratio λb of unfilled vulcanizates of silicone, hydrofluorocarbon (Viton B), butyl (both sulfur-cured and resin-cured), and natural rubber were determined at many strain rates and temperatures; the latter ranged from slightly above the glass transition temperature Tg, up to a temperature somewhat below that at which chemical degradation affected the results. For each vulcanizate except natural rubber, data obtained over an extended temperature range superposed to give a time- and temperature-independent failure envelope on a plot of log(σb273/T) vs log(λb−1), where T is the test temperature in °K; for natural rubber, data obtained between 90° and 120°C superposed, but those at lower temperatures did not because of strain-induced crystallization. For each vulcanizate, data at elevated temperatures gave, or tended toward, a line of unit slope on a plot of log (λbσb273/T) vs log(λb−1), where λbσb is the breaking stress based on the cross-sectional area at the moment of rupture. The position of each line corresponded to the equilibrium modulus Ee derived from stress—strain curves. Failure envelopes previously obtained for two styrene—butadiene vulcanizates, which had different crosslink densities, superposed to give a master failure envelope on a plot of log(λbσb273/T) vs logEe(λb−1). On this type of plot, failure envelopes for all the vulcanizates except silicone and natural rubber were found to be essentially identical. At a given value of λbσb, silicone had a smaller λb and natural rubber a somewhat larger λb than the vulcanizates of the three other rubbery polymers.
A Theory of Orientation Correlations in Crystalline Polymeric Solids
Authors: Stein Richard S. , Stidham S. N.
Published: April 2005

The scattering of light from crystalline polyolefins results principally from a correlation in crystal orientation described by an empirical Debye-Bueche correlation function f(r)=exp(−r/a) for crystals separated by distance r. A one-dimensional theory is developed in which neighboring crystals may differ in orientation by a small angle ±δ. A random-walk theory results in the exponential correlation function where the correlation distance is given by a=Kd/δ2 for crystals separated by distance d. K is a numerical factor which is ½ for crystals confined to a plane and ⅔ for crystals permitted to orient about a cone of apex angle δ with respect to the preceding crystal. The extension to two dimensions is proposed by means of a computer simulation of the lattice, and preliminary results of such an analysis are presented.
Relationship between Molecular Weight, Radial-Growth Rate, and the Width of the Extinction Bands in Polyethylene Spherulites
Authors: Lindenmeyer P. H. , Holland V. F.
Published: April 2005

To test theories of the twisting or correlated orientation of crystallites along the radial arms of sperulites, we measured the radial growth rates (G) and the extinction spacings (s) of a series of molecular weight fractions of linear polyethylene. At equivalent degrees of supercooling the radial growth rate is faster for the lower molecular weight fractions. Comparison with earlier measurements shows that the critical free energy for the formation of a growth nucleus is essentially the same for a single crystal growing from dilute solution as for a spherulite crystallizing from the melt. The data are not consistent with the hypothesis that s is directly proportional to the parameter δ=D/G, but indicate an additional factor that has the temperature dependence of a nucleation process.
Investigation of the Morphology Associated with the Dissolution Process of Polymer Single Crystals
Authors: Holland V. F.
Published: April 2005

The morphological changes accompanying the dissolution of polyethylene single crystals in solvent have been correlated with the temperature of annealing. By this method, the solution temperatures of crystals of finite thicknesses were accurately determined. Based on these results, a surface free energy of 58 ergs/cm2 was calculated for the fold surface of polyethylene lamellae crystallized at 80°C from dilute solution. In addition, several novel morphological features were observed at intermediate stages of crystal dissolution which may aid in the understanding of folded-chain crystallization.
Morphology of Isothermally Bulk-Crystallized Linear Polyethylene
Authors: Anderson Franklin R.
Published: April 2005

The internal morphology of isothermally bulk-crystallized fractions, and of whole polymer, Marlex 50 polyethylene is revealed by fracture experiments. Three distinctly different types of lamellae are then observable if one uses suitable electron microscopic techniques: (1) regular or type I lamellae which are similar in appearance to solution-grown lamellae, (2) narrow or type II lamellae which have finite widths, and (3) extended-chain or type III lamellae which have step heights approximately equal to fully extended chain lengths calculated from viscosity-average molecular weights. The type I and II lamellae appear to consist of folded chains. The step heights of the type I and type II lamellae are shown to increase from about 150 to 350 Å with increasing crystallization temperature. The widths of the type II or narrow lamellae vary directly with temperature from 350 to 800 Å. However, the step heights of the type III lamellae, which range from 150 to 1050 Å, are essentially independent of temperature but do vary with molecular weight. The melting points of these different types of lamellae are shown to be consistent with presently existing theories and the relationship between morphological parameters of these lamellae and reported low-angle x-ray periodicities are discussed.
Theory and Measurements of the Glass-Transformation Interval of Polystyrene
Authors: Wunderlich Bernhard , Bodily David M. , Kaplan Mark H.
Published: April 2005

Equations for the apparent heat capacity in the glass-transition interval as functions of temperature, heating rate, and thermal history have been developed and programmed for computation. The hole theory of liquids was used as basis for the analysis of the glass transition. Experimental information was derived from dynamic differential thermal analysis, DDTA, on polystyrene.

The maximum of the apparent heat capacities found experimentally agrees with the theory. The peak temperatures Tm can be expressed over four decades of heating rates by logq = A′ − B/Tm, where q is the heating rate, A′ is an approximate constant, and B is the activation energy for hole formation. Higher cooling rates lead to higher activation energies on subsequent heating, indicating the need to recognize a hole size distribution.

The minimum in the heat capacity that precedes the maximum on heating through the glass-transition interval could be detected on quenched samples. Mathematical expressions for the minimum temperature and magnitude were developed.

The temperature of ``half-freezing'' on cooling, equivalent to Tool's ``fictive temperature,'' was found experimentally to occur at constant q·τ, where τ is the relaxation time (q·τ = 6.6° for polystyrene). From the ``half-freezing'' temperatures as a function of cooling rate one can determine the properties of a ``mean hole.'' For polystyrene the activation energy of the mean hole is 157 600 cal/mole of holes.
Investigation of Plasma Boundaries with Electromagnetic Surface Waves
Authors: Wassink H. W. , Estin A. J.
Published: April 2005

Only a few experimental techniques permit the determination of inhomogenities in the electron density of a plasma, and even these lose their usefulness near the walls of the plasma container. A microwave surface wave technique using the container boundary as a propagating surface is described. Under the assumption that the plasma is azimuthally symmetric and axially uniform, perturbation relations for the microwave field permit an integral transform to convert phase shifts into radial electron density. This technique applied to a 2-Torr neon rf-generated plasma in coaxial geometry indicates an electron density near the inner wall as having a square-law distance dependence. This is not in accord with the well-known theoretical models of diffusion-limited plasmas, but can be explained qualitatively.
Measurement of Electron Temperature in Low-Pressure Cesium Thermionic Energy Converters
Authors: Chapman R. A. , Caulfield H. J. , Hemstreet H. W.
Published: April 2005

A dc probe was placed behind a small slit in the collector electrode in each of several cesium-vapor thermionic diodes. These systems were used to study the velocity distribution of the small fraction of the emitted electrons which passed through the collector slit. This technique overcomes several of the inherent disadvantages in the use of the dc Langmuir probe in cesium vapor. The error due to momentum defocusing in the collector slit is calculated with the presence of a plasma in the emitter—collector interspace. The probe log-current vs voltage curves could be accurately fitted to a Maxwell—Boltzmann velocity distribution over several cycles in log-current. In this manner, effective temperatures were defined as a measure of the randomness of the velocity component normal to the collector surface. No fully randomized, high-temperature electron group was detected in the unignited mode of these diodes. The effective electron temperature in the unignited mode became increasingly larger than the emitter temperature as the latter temperature was increased, but the departure was always less than 25%. The effective electron temperature increased rapidly with diode current as the ignited mode was entered and rose to be 470% higher than the emitter temperature.
Estimation of Contact Potential Differences in Thermionic Energy Converters
Authors: Caulfield H. J.
Published: April 2005

The contact potential difference in a low-pressure thermionic energy converter can be written as CPD=[open phi]̃E−[open phi]̃C, where [open phi]̃E and [open phi]̃C are averaged work functions of the emitter and collector, respectively. The estimation of [open phi]̃E and [open phi]̃C from existing work-function data is discussed. As an example, [open phi]̃E values are estimated for well-aged polycrystalline tungsten wire and those estimates are compared with experimental values.
Studies of the Properties of the Hollow Cathode Glow Discharge in Helium and Neon
Authors: Sturges D. J. , Oskam H. J.
Published: April 2005

An experimental tube to obtain accurate and reproducible data relating to the efficiency of the hollow cathode discharge had a cathode of two plane-parallel plates with variable separation, and a movable anode to eliminate the anode fall region. The cathode temperature was kept between 25° and 35°C by employing pulse techniques. Preliminary studies performed in helium and neon at pressures between 2 and 15 Torr gave the following results: (a) The transition from the plane cathode discharge into the hollow cathode discharge is a smooth function of the cathodic plate separation. (b) For each tube current and pressure there exist two or more optimum values of the cathodic plate separation for which the tube voltage has a minimum. The optimum distances depend on type of gas, pressure, and tube current. (c) For fixed tube current, the relative maximum decrease in tube voltage with respect to the plane-cathode discharge voltage is, in most cases, larger in helium than in neon. (d) The variations of the discharge voltage and current with pressure are consistent with the Townsend scaling law for certain values of cathodic plate separation.
Thermal and Electrical Properties of Heavily Doped Ge-Si Alloys up to 1300°K
Authors: Dismukes J. P. , Ekstrom L. , Steigmeier E. F. , Kudman I. , Beers D. S.
Published: April 2005

The thermal resistivity, Seebeck coefficient, electrical resistivity, and Hall mobility of Ge-Si alloys have been measured throughout the Ge-Si alloy system as functions of impurity concentration in the range 2×1018−4×1020cm−3, and of temperature in the range 300°–1300°K. A qualitative interpretation of these properties is given. For power conversion, boron and phosphorus were found to be useful p-type and n-type impurities, respectively, because of their high solid solubilities. At 1200°K, the maximum values of the dimensionless figure of merit zT were 0.8 for p-type Ge0.15-Si0.85 alloy doped to 2.1×1020cm−3 holes, and 1.0 for n-type Ge0.15-Si0.85 alloy doped to 2.7×1020cm−3 electrons. The maximum over-all efficiency of a stable generator operating between 300°–1200°K, using the best p-type and n-type materials was computed to be 10%.
Effect of Thermal Aging on the Electrical Resistivity of Thin Alloy Films
Authors: Dean E. R.
Published: April 2005

Multicomponent alloy films of sheet resistivity between 100 and 600 Ω/sq. have been fabricated on substrates at 300°C, and several substrate temperatures have been investigated for film resistivities of 250 Ω/sq. These films have been subjected to several thousand hours storage in air at elevated temperatures. When aged at 300°C, films of high resistivity increase in resistance until open, while films of low resistivity reach a resistance maximum, then decrease through a minimum, and finally increase in resistance until opening. The use of a protective overcoating of SiO enhances the film stability during extended storage. The normalized resistance of protected films always decreases, with the lower substrate temperature films exhibiting larger decreases. This normalized resistance decrease is accompanied by a linearly related increase in the temperature coefficient of resistance. The electrical properties of these films may be explained if we postulate that the conductivity is the result of several mechanisms, some resulting from normal metallic conduction through a defect film, whereas others result from activated charge transfer between adjacent grains. The electrical behavior of the protected films under thermal aging is the result of defect anneal and grain growth. For the unprotected films we must also introduce the concept of selective oxidation.