bluuebunny/crossref_metadata_2025 huggingface dataset:
Existence and Origin of a Polarization Threshold Field in Bismuth Titanate
Authors: Hamilton Dale L.
Published: January 2005

A new method is proposed to demonstrate the existence of a true polarization threshold field in materials that demonstrate ferrielectric properties. The detection of small changes in the Bragg diffraction angles of a diffracter x-ray beam has been used to show the existence of a true polarization threshold field in one such material, namely bismuth titanate (Bi4Ti3O12). It is shown that the x-ray diffraction method effectively establishes the polarization threshold field of bismuth titanate at 3 kV/cm. This value of polarization threshold field agrees with that found previously using direct electrical methods. Prior to this work, the demonstration of a true polarization threshold field has been shown only by direct electrical methods.
A Light-Activated Semiconductor Switch
Authors: Meyerhofer D. , Keizer A. S. , Nelson H.
Published: January 2005

A GaAs p-n-i-n diode which operates as a light-activated light-coupled switch is described. The i-region is compensated semi-insulating GaAs and is obtained by diffusing Cu, Fe, or Cr into low-doped n-GaAs. The electrical and optical properties of this diode have been studied as well as its switching behavior. The diode exhibits a current-controlled negative resistance region with ratio of off- to on-resistance as high as 106. Turn-on voltages range from 10 to 200 V, and the turn-on time can be made as short as 10 nsec with sufficient overvoltage. The current is limited in the high-resistance mode by intrinsic or one-carrier space-charge-limited conduction in the i region. At higher currents the light emission at the p-n junction causes photoconduction in the i region which is enhanced by the trapping of holes at acceptor levels. In the low-resistance mode all the traps (approximately 1016 cm−3) are filled and remain that way because of the high efficiency of light emission from the junction at the high currents. A model is developed which semiquantitatively describes both the static and dynamic properties of the diode.
Indeterminacy of the Analytic Method for Calculating Molecular Field Coefficients in Ferrimagnets
Authors: Gianino Peter D. , Grossbard Neil
Published: January 2005

It is demonstrated that instead of yielding unique values of α and β for yttrium iron garnet (YIG) and lithium ferrite, the analytic method of calculating molecular field coefficients in ferrimagnets yields only one of many possible (α, β) pairs from a linearly related set. The magnitudes of the internal magnetic fields, total magnetic moment, and the two sublattice magnetic moments, computed from any of the possible coefficients, remain relatively unchanged even though (α, β) and n are extremely sensitive to the input parameters and number of experimental data points. It is shown how this manifold of (α, β) pairs can exist, how the pairs can be linearly related, and how an analytic expression for this dependency can be derived, using low-temperature data. A procedure for testing whether the coefficients for other ferrimagnets can be uniquely determined is discussed. ``Best'' values of (α, β), obtained by minimizing a least-squares percentage error, not only fall along a straight line but are in good agreement with those usually generated by the analytic method. The use of the ``linearity'' test in the X-Y graph as a criterion for judging the appropriateness of the selected value of the Curie point is shown to be invalid.
Theory of Thermionic Converter Extinguished-Mode Operation with Applications to Converter Diagnostics
Authors: Wilkins Daniel R. , Gyftopoulos Elias P.
Published: January 2005

An analysis of thermoionic converters operating in the extinguished mode is presented. Expressions for the forward and reverse saturation output current densities, and for the open circuit voltage are derived for the first time from a single set of transport equations and boundary conditions. Agreement between theoretical and experimental results is established. It is shown that the output current density cannot exceeed a certain upper limit which depends only upon the emitter temperature and the interelectrode spacing, and is independent of the emitter work function and the cesium pressure. It is shown that, under certain operating conditions, measurements of the forward and reverse saturation output-current densities and of the open circuit voltage can be used to infer values of the emitter temperature, emitter work function, collector work function, and electron and ion mobilities.
Imperfections Due to Double Diffusions in Epitaxial Silicon
Authors: Jungbluth E. D.
Published: January 2005

An investigation of imperfections due to selective-area planar double diffusions of n- and p-type impurities on epitaxial silicon has shown that elastic and inelastic lattice strain exists at the edges of oxide windows. This strain may act as nucleation sites for precipitating metallic impurities. High-surface-concentration emitter impurities (phosphorus) cause residual, inelastic strains at oxide edges, while base diffusions (boron) normally cause elastic lattice strains. X-ray transmission topography reveals both elastic and inelastic strains. Surface reflection x-ray topography is slightly more sensitive than x-ray transmission topography for detecting defects due to shallow phosphorus diffusion. Chemical etching techniques delineate line defects which are unresolved by x-ray techniques. The line defects are confined to the emitter area and extend in 〈110〉 and 〈112〉 directions. Differences in the results obtained by both x-ray techniques are discussed in terms of defects observed by etching techniques.
Electrical Properties of Epitaxial Ge Films Deposited on (111) CaF2 Substrates
Authors: Sloope Billy W. , Tiller Calvin O.
Published: January 2005

The temperature dependence of the Hall constant, resistivity, and Hall mobility was measured for Ge films deposited on polished (111) CaF2 substrates at substrate temperatures of 200°–700°C, deposition rates of 100–15 000 Å/min, and for film thicknesses between 800 and 170 000 Å. For formation conditions which improved film structures, electrical properties likewise improved. For single-crystal films the Hall constant and Hall mobility increased as the defect density decreased with increasing deposition temperature and decreasing deposition rate. Similarly, for films thicker than 4000 Å, as the density of defects intersecting the surface decreased with increasing thickness, the Hall constant and mobility increased. Hole-carrier concentrations of 1016–1018 per cm3 and room-temperature Hall mobilities of 100–1100 cm2/V·sec were observed. The results indicate that defects are the source of acceptors and contribute significantly to scattering.
Structure of CdS Evaporated Films in Relation to Their Use as Ultrasonic Transducers
Authors: Foster N. F.
Published: January 2005

The crystallographic orientation of obliquely evaporated CdS films has been investigated by x-ray and electron diffraction to provide the information required to control the fabrication of shear mode thin film ultrasonic transducers. Some degree of preferred orientation, with the c axis normal to the film plane, was observed in the initial layers of all of the films examined. The degree of preference was primarily dependent upon the structure of the substrate. As the films increased in thickness, on all except highly (111)-oriented gold substrate, an oblique orientation developed with the c axis of the crystallites strongly inclined towards the incident vapor beam. On the highly (111)-oriented gold-film substrates, the CdS films remained c-axis preferred. The effects of substrate structure and of the rate and angle of the deposition have been examined. Ultrasonic transducer data are presented and compared with the crystallographic structure of the transducer films showing the expected correlation between the c-axis orientation and the ultrasonic mode generated.
Plasma Frequency and Velocity Spread in Bunched Electron Beams of Finite Diameter
Authors: Mihran Theodore G.
Published: January 2005

The velocity spread existing on a velocity-modulated electron beam of finite diameter is investigated as a function of drive, drift length, and perveance using a digital computer program based on a disk electron model. At small signal levels the velocity modulation decreases cosinusoidally to zero with drift distance in accordance with one-dimensional bunching theory. At higher signal levels, however, the velocity spread does not go to zero due to aberrations introduced by the finite diameter of the beam.

The minimum velocity spread at maximum bunching is found to be proportional to the square of the fundamental component of rf current, up to an optimum drive level. Above this drive level the velocity spread increases rapidly with no corresponding increase in rf current. Trajectories of electrons of all initial phases are found to undergo a basic transition from nonovertaking to overtaking at a new characteristic distance λpq/4, which is given approximately by the geometric mean of the infinite beam quarter-plasma wavelength λp/4 and the reduced (due to finite beam size) quarter-plasma wavelength λq/4. This characteristic distance is found to be a key parameter in the prediction of velocity spread, drift length and drive for optimally bunched electron beams for use in klystron amplifiers, harmonic generators, and in linear accelerators.
Families of Chain Configurations on the Quadratic Lattice and on Narrow Lattice Channels
Authors: Rothstein Jerome , James Paul
Published: January 2005

The set of admissible configurations and diffusive motions of chain molecules (beads and rigid links) on the quadratic lattice are considered with respect to a set of ``flip rules''; these permit configurations to change and the molecules to diffuse by flipping one bead at a time consistent with the excluded volume requirement. The set of configurations splits up into families such that configurations within a family can flip into each other but no transitions between configurations in different families are possible under the flip rules. The families are designated as mobile or sessile, the former including those that are able to diffuse to arbitrarily large distances; the sessiles must remain within a restricted region under the flip rules no matter how many flips are permitted. A complete discussion of chain configurations on a channel one link wide is given and the general situation for wider channels and the infinite plane is discussed. The importance of such considerations for entropy calculations and their possible relevance for biological phenomena are indicated.
Metastable Measurements in Flowing Helium Afterglow
Authors: Huggins R. W. , Cahn J. H.
Published: January 2005

Microwave and optical techniques have been used to measure the decay of the neutral metastable and the charged species in a flowing helium afterglow. Impurity gases, oxygen and argon, are introduced into the afterglow, and measurements of the resulting ionization and excitation yield values for the triplet metastable diffusion coefficient and three-body combination coefficient of 490 cm2 sec−1 Torr and 0.25 sec−1 Torr−2, respectively. In addition, the ambipolar diffusion coefficient of the molecular helium ion was found to be 724 cm2 sec−1 Torr. The mean helium pressure was in the range of 5 to 35 Torr and the gas nominally at room temperature. Absolute triplet metastable densities early in the afterglow were also measured.
Bistable Current Fluctuations in Reverse-Biased p-n Junctions of Germanium
Authors: Wolf D. , Holler E.
Published: January 2005

In base-to-emitter diodes of p-n-p germanium transistors biased in reverse direction far below breakdown, bistable current fluctuations have been observed. These fluctuations show the typical waveform of a random telegraph signal. Its statistical properties have been analyzed. The mean-value crossing-time intervals of current measured by a multichannel pulse-height analyzer turned out to be independent of reverse voltage but dependent upon temperature. Detailed experimental data are given.
Electrostatics of Slender Bodies
Authors: Miles John W.
Published: January 2005

The electrostatic field in the neighborhood of a slender, axisymmetric conductor is expanded in prolate-spheroidal harmonics to obtain approximations to the capacitance, the dipole moments induced by both axial and transverse fields, and the induced charge on a grounded boss in a uniform field. The capacitance calculated for a right-circular cylinder with δ=diameter/length<1 is found to be within 5% of the more accurate results calculated by Smythe. The corresponding comparisons for the dipole moments and the induced charge on a cylindrical boss are less impressive for non-small δ but suggest the general utility of the slender-body approximation for δ of the order of 10−1 or less.
Influence of Reforming Processes on the Fracture Strength of Solids
Authors: Kausch von Schmeling H. H. , Moghe S. R. , Hsiao C. C.
Published: January 2005

The macroscopic strength of an oriented medium is investigated under the assumption that processes of breaking and reforming of microscopic components in the medium may occur. The differential equation governing the time-dependent variation of the number of load-carrying components is considered. Emphasis is placed on the study of the effect of the reformation processes on the stress-time-to-fracture behavior. It is suggested that under small loads these processes may be responsible for the frequently observed phenomena of the deviation from linearity of the strength and logarithm of time-to-fracture relationship. An attempt is also made to compare theoretical results with some reported experimental data.
Energy Dependence of Neutron Damage in Silicon
Authors: Stein H. J.
Published: January 2005

The carrier removal produced in 10- and 100-Ω·cm, vacuum-floating-zone, n-type silicon by neutrons from a bare 235U reactor was measured and compared with that produced by 14-MeV neutron irradiation of the same samples. Carrier removal rates were obtained from conductivity measurements at 283°K following irradiations at 300°K. The measured 14 MeV-to-reactor-neutron-damage ratio is 2.8±0.5 for the 10-Ω·cm silicon, and 2.9±0.6 for the 100-Ω·cm silicon. Very similar isochronal annealing was observed between 300 and 500°K following 14-MeV and reactor-neutron irradiation. This suggests that 14-MeV and reactor-neutron irradiation produce the same kinds of defects in n-type silicon. Total scattering cross-section data for silicon, information on nonisotropic scattering, and the Lindhard model for silicon recoil energy loss to ionization were used to calculate the average energy per cm spent in silicon displacement collisions per incident neutron between 0.2 and 14 MeV. There is general agreement between the calculated energy spent in silicon displacements as a function of neutron energy and the energy dependence of the reported monoenergetic neutron irradiation-produced carrier removal rates in n-type silicon. Dividing the predicted energy spent in collisions per neutron-cm by the carrier removal rate gives an average of 0.85 keV with a standard deviation of 0.38 keV per carrier removed for previously reported monoenergetic neutron irradiations. Using the carrier removal rates measured at 283°K for the 10-Ω·cm n-type silicon of this investigation, the average energy spent in collisions per carrier removed is 1.25±0.15 keV for the reactor neutron irradiation and 0.94±0.08 keV for the 14-MeV neutron irradiation.
Measurement of Stacking-Fault Energies by X-Ray Diffraction
Authors: Otte Henry M.
Published: January 2005

A critical evaluation is made of the procedure and the important parameters involved in estimating the stacking-fault energy Γ from x-ray diffraction measurements of deformed materials. The published data for the Ag-In and the Cu-Zn system are carefully analyzed and compared with results obtained by transmission electron microscopy. For deformed filings, the dislocation density, and hence the mean square strain 〈ε2〉hkl, vary with composition, as does the stacking-fault probability α. Since Γ∝α−1〈ε2〉hkl, the value for the proportionality constant must be known to obtain Γ. This requires a knowledge of the dislocation configuration, principally in terms of barriers and pile-ups of extended dislocations. Within the limits of uncertainty of this information, an assessment of the proportionality constant can be made so that reasonably good consistency with transmission electron microscopy results is obtained. In this way, estimates (good to ±25%, probably) of Γ=18 erg/cm2 for pure silver and Γ=65−74 erg/cm2 for pure copper could be calculated.
Effect of Alloying on the Aluminum K and Iron L X-Ray Emission Spectra in the Aluminum-Iron Binary System
Authors: Fischer David W. , Baun William L.
Published: January 2005

The aluminum K and iron L emission bands and the aluminum Kα3 and Kα4 satellite lines from a series of aluminum-iron binary alloys have been studied using 6-kV electron excitation and a flat crystal x-ray vacuum spectrometer equipped with a flow proportional counter. It is found that the AlK band energy position and the AlKα4/Kα3 intensity ratio are both linearly dependent on alloy composition. As the aluminum concentration is lowered, the AlK band intensity maximum shifts to lowery energy and the band becomes more symmetrical in shape. In general, these results are very similar to those obtained previously from the aluminum-nickel system. The FeLIII band undergoes very little change in shape but shifts to higher energy as the aluminum-to-iron ratio is increased. The spectral changes are interpreted as indicating that the predominately metallic bond in the pure metals acquires a certain amount of covalent-like character in the alloys with the aluminum atoms behaving as electron donors.
Generalized Formulation of Electrostatic Oscillations and Streaming Instabilities in Bounded and Unbounded Inhomogeneous Vlasov Plasmas
Authors: Lee Kai Fong
Published: January 2005

A general formulation for the study of electrostatic oscillations and streaming instabilities in bounded and unbounded Vlasov plasmas with transverse density gradients in a strong axial magnetic field is presented. It is found that the behavior of the plasma depends on a parameter which is a function of geometry, scale of inhomogeneity, and wavelength. Using this formulation, several experimentally realistic configurations have been studied. Two results obtained are of special interest. They are (1) for waves with the same wavelength, a density inhomogeneity and/or boundary increase Landau damping. (2) Under appropriate conditions, depending on the geometry and the degree of inhomogeneity, it is not possible to excite the two-stream instability for any drift velocity. Previous theories of uniform plasmas appear as special cases in this general treatment.
Calculated Size Distributions for Gas Bubble Migration and Coalescence in Solids
Authors: Gruber E. E.
Published: January 2005

Bubble coalescence in solids is assumed to result when collisions occur between bubbles as they migrate by surface diffusion through the solid. The migration of an isolated pore is examined in detail and the results are applied in a finite-difference approach, programmed for a digital computer, to predict the variation of the number of bubbles per unit volume as a function both of bubble size and of post-irradiation annealing time. Two idealized models of bubble coalescence have been treated. The first model considers coalescence resulting from random migration of the bubbles, and the second considers coalescence resulting from unidirectional, biased migration, such as would result in the presence of a thermal gradient. Both models are based on surface diffusion migration of randomly distributed bubbles in a perfect, infinite solid. The results give the predicted variation with time of the entire distribution of bubble sizes, so that various parameters, including the mean bubble radius and volume change, can be predicted. Comparison of the predicted values to parameters measured in appropriate experiments could provide a means of measuring fundamental properties of materials. The results can also be applied to the problem of swelling of reactor fuel materials because of trapped fission gases. Although the present analysis is limited by a number of simplifying assumptions, it is clear that the presence of a thermal gradient can greatly enhance the swelling rate.
Effect of Pressure on Crystal Structure and Lattice Parameters of Iron up to 300 kbar
Authors: Mao Ho-Kwang , Bassett William A. , Takahashi Taro
Published: January 2005

Lattice parameters of the bcc and hcp phases of iron have been determined as a function of pressure up to 300 kbar at 23°±3°C by means of x-ray diffraction techniques. The c/a ratio for hcp iron has been determined to be 1.603±0.001 at pressures between 80 and 300 kbar and is independent of pressure. Based upon the extrapolation of the high-pressure data using an exponential form of the Murnaghan equation of state, the volume of hcp iron at zero pressure is 6.72±0.06 cm3/mole. The volume change for the bcc-hcp transformation at 130 kbar is −0.34±0.01 cm3/mole. This value satisfies the triple point conditions for the bcc-hcp-fcc triple point when published values for the other phase transformations are used.
Metastable F Aggregate Color Centers in Irradiated KCl
Authors: McCall Robert T. , Grossweiner L. I.
Published: January 2005

The absorption spectra and decay lifetimes of the M center triplet state (3M) and R center quartet state (4R) measured in irradiated KCl are similar to previous results in additively colored crystals. The wavelength dependence of the light-induced decay indicates that the 3M center is deactivated by illumination in its absorption bands at 505, 590, and 685 mμ (85°K), and pumped by illumination in the M1 band and also in the F band and K band regions. The initial yield of 3M centers induced by pulse illumination is proportional to the M center density, both for crystals of different initial F center density bleached to maximum M band and for a crystal that was bleached through the growth and decline of the M band. The temperature dependence of the dark decay follows a configuration coordinate model in which a transition of 45-sec half-time competes with a thermally-activated step of 0.064 eV activation energy. The 14-sec dark decay half-time of the 4R center absorption at 710 mμ was found to be independent of temperature from 85° to 200°K. Possible mechanisms of metastable center formation and decay are discussed.
Kikuchi Maps for hcp and bcc Crystals
Authors: Okamoto P. R. , Levine E. , Thomas G.
Published: January 2005

Kikuchi maps have been obtained for bcc and hcp crystals, and their applications to the determination of orientations and Burgers vectors are described. The hcp map is particularly useful and time-saving, and enables orientations to be rapidly and uniquely determined. These cannot be readily obtained from hcp spot patterns in many cases. It is shown that the basal-plane orientation, which can be tilted by about 20 deg to any of the six 〈11̄03〉 poles, is sufficient to provide the unique solution for determining any of the possible 21 Burgers vectors in hcp structures, and that the forbidden 〈1̄21̄1〉 reflections formed by double diffraction can be utilized to simplify such determinations. Kikuchi maps become increasingly valuable for investigating materials of crystal structures which have lower symmetry than that of the cubic systems.
Evaluation of CdTe by Nuclear Particle Measurements
Authors: Mayer J. W.
Published: January 2005

The properties of CdTe have been evaluated by investigating the pulse-height response of surface-barrier devices to monoenergetic alpha particles incident normal to the surface. The energy ε required to form a hole-electron pair was found to be 4.65±0.2 eV. The count rate efficiency and energy resolution that have been obtained indicate that crystals can be grown without major fluctuations in the densities of trapping or recombination centers. The effective lifetime values within the high field regions range from less than 10−9 sec to 4×10−8 sec for holes and electrons. These values represent a marked increase over the previously established value of 10−10 sec.
Energy Dependence of Fission-Fragment Damage in Gold Films
Authors: Merkle K. L.
Published: January 2005

Transmission electron microscopy was used to study the effects of fission fragment irradiation on single crystalline gold films as a function of the fission-fragment energy. It is found that the density of black spots increases as the average energy of the fission fragment decreases. The observations indicate that black spots are produced in displacement cascades initiated by energetic primaries. The results are consistent with a model based on the assumption that only those events are observed in which the primary energy is greater than 2.5×104 eV.
Shear Stresses and Strain Energies of Edge Dislocations in Anisotropic Cubic Crystals
Authors: Duncan Theodore R. , Kuhlmann-Wilsdorf Doris
Published: January 2005

Analytic solutions for the shear stress and energy factors of three basic types of edge dislocations in cubic anisotropic crystals have been published previously based on the general solution of Eshelby, Read, and Shockley. Naming the slip plane and Burgers vector in order, the dislocation types referred to are {010}, 〈100〉; {1̄10}, ½〈110〉; and {001}, ½〈1̄10〉. The most important kind of edge dislocation in fcc metals and diamond-type crystals, however, is of type {111}, ½〈11̄0〉, belonging to by far the most important slip system. This problem has previously been considered by Seeger and Schöck. In the present paper, analytic solutions are derived for the shear stresses and energy factors of the {111}, ½〈11̄0〉 edge dislocation and are evaluated numerically for the cases of aluminum, α-brass, copper, gold, lead, nickel, silver, thorium, diamond, germanium, and silicon. The results are compared to those obtained from isotropic elasticity theory and an approximation introduced by Aerts, Delavignette, Siems, and Amelinckx.
Phase-Locking of Laser Oscillators by Injected Signal
Authors: Tang C. L. , Statz H.
Published: January 2005

The condition for frequency locking of a laser oscillator by an externally injected signal is derived. The results allow one to estimate the minimum-frequency separation in rotation sensing ring lasers as a function of scattering in the beam path. The formula may also be used as a design criterion in phase-locking arrays of laser oscillators.
Electron Attachment-Detachment Processes in Dry Air
Authors: Ryżko Henryk , Åström Ernst
Published: January 2005

The pulses due to electron avalanches released in dry air from a cathode of a uniform field gap (6 cm) by photoelectrons in a time interval of about 40 nsec are investigated. Using a new method of evaluation which yields simpler formulas, the attachment coefficient η for formation of unstable negative ions and the mean lifetime τ of these ions are determined. In the pressure range 4–60 Torr, η/p is independent of pressure and increases in the E/p range 33–53 V cm−1 Torr−1 from 0.006 cm−1 Torr−1 to 0.017 cm−1 Torr−1. In the same pressure range, τp is independent of pressure and decreases from 35 μsec Torr to about 2 μsec Torr.

Our results confirm the earlier assumption of one prevailing kind of unstable negative ion. The value of η/p agrees with that obtained earlier at E/p close to 40 V cm−1 Torr−1. A distinct variation of η/p with E/p, not reported earlier, is obtained.
Gas Desorption Produced by a Giant Pulse Laser
Authors: Levine L. P. , Ready J. F. , Bernal G. E.
Published: January 2005

The gases desorbed when a tungsten target in vacuum of the order of 10−8 Torr is struck by a Q-switched laser beam are studied. The apparatus used in the experiment is described. The data presented are for water vapor, carbon monoxide, and carbon dioxide. Analysis is presented to demonstrate that the data are compatible with a model in which the laser is considered to be no more than a pulsed heat source for laser energy densities up to 50 MW/cm2.
Electron Spin Resonance in Semiconducting Diamonds
Authors: Bell M. D. , Leivo W. J.
Published: January 2005

Electron spin resonance (ESR) was studied in five semiconducting diamonds in the temperature range 108°–370°K and at 4.2°K. The g factor is 2.0030±0.0003, and the linewidth varies from 0.3 to 8 Oe at room temperature. The number of spins contributing to the ESR absorption varies between 1013–1014 and agrees with the number of uncompensated acceptors in the case of two diamonds on which Hall and resistivity measurements were made. The number of spins varies as 1/T in the temperature range 108°–370°K. The spin-lattice relaxation time was estimated to be of the order of 10−8 sec at 300°K. The results indicate that the spin center is associated with the acceptors in the p-type diamonds. The effect of heat treatment on the ESR absorption (g=2.0029) observed in crushed nonconducting diamond was measured. The intensity and linewidth (2.9 Oe) for the crushed diamond was reduced on heating at 600°C; further heating at 1100°C did not change the ESR line after the initial decrease.
Surface Barrier Diodes on Semiconducting KTaO3
Authors: Wemple S. H. , Kahng D. , Braun H. J.
Published: January 2005

A combination of capacitance, I-V, and photoresponse data is presented for metal-semiconductor junctions on KTaO3. Results are in good agreement with the Schottky theory for doping levels below 1018 cm−3. Substantial deviations occur for higher doped samples. Measured barrier potentials do not correlate with either the metal work function or the metal electronegativity, and appear to be strongly affected by strains at the metal-semiconductor interface. In the case of Cu and Au, structure in the photoresponse data associated with an energy-dependent density-of-states is observed.
Parametric Excitation and Amplification of Magnetoelastic Waves
Authors: Van De Vaart H. , Lyons D. H. , Damon R. W.
Published: January 2005

A series of experiments is described showing parametric amplification of traveling magnetoelastic waves in single-crystal YIG in the frequency range 1–10 GHz. The process involves a pump field at right angles to the dc field, with almost exactly twice the signal frequency. Pulse echo techniques were used to observe amplified echoes in both axially and transversely magnetized rods and in normally magnetized disks. The time delay of the echo is a function of applied magnetic field strength and amplification is observed only if the pump is provided at a particular time. The amplification in a rod is largest when the field is directed ≈15° off the rod axis and in this case the pump must be applied approximately when the signal is in the magnetoelastic crossover region. A net gain exceeding 55 dB was obtained at 1.5°K for X-band signals with 10-μsec delay. At room temperature, 6-dB net gain was obtained in X-band at 3-μsec delay with 250 W of pump power, and 17-dB net gain was obtained in L band with only 0.6 W of pump power. The observed echo behavior indicates that the transverse pumping process involves a pair of shear magnetoelastic waves on the same branch of the dispersion curve and occurs near the magnetoelastic crossover point. The theoretical instability thresholds are derived for several processes involving transversely pumped, magnetoelastic shear waves, but the results do not agree with the most direct explanation of the experimental observations.
Measurement of Diffusion Lengths in Direct-Gap Semiconductors by Electron-Beam Excitation
Authors: Wittry David B. , Kyser David F.
Published: January 2005

In semiconductors having high efficiency for radiative recombination, the voltage dependence of cathodoluminescence may be used to determine the diffusion length and to estimate the surface recombination velocity of excess carriers. Theoretical calculations are based on a knowledge of the Laplace transform of the distribution of excitation with depth as determined from the target absorption correction in electron probe microanalysis or, alternatively, on a Gaussian approximation to the distribution of excitation with depth. Experimental results with accelerating voltages of 5–50 kV indicate values of diffusion length in n-type GaAs ranging from 3.0 μ at low-carrier concentration (5.1×1016 cm−3) to 0.65 μ at high-carrier concentration (3×1018 cm−3). The estimated accuracy for diffusion lengths between 0.5 and 4 μ is ±30%. Information is also obtained on the surface recombination velocity and the thickness of a ``dead layer'' at the surface.
Impulse Response of Active Coupled Wave Systems
Authors: Bobroff D. L. , Haus H. A.
Published: January 2005

The impulse response of active contraflow (backward) two-wave systems of infinite and finite lengths are obtained. The infinite system without loss exhibits a nonconvective instability. With sufficient loss in one wave this instability becomes convective and with sufficient loss in both waves the system becomes stable. The impulse response to the finite system is obtained in two forms. One of these is in terms of the discrete normal modes of the system, the other is in terms of repeated reflections at the two ends of the system. The interesting connection between this latter method and the method of images is discussed.
Theory of Ultrasonic Pulse Measurements of Third-Order Elastic Constants for Cubic Crystals
Authors: Holt Albert C. , Ford Joseph
Published: January 2005

The equations of motion for an elastic nonisotropic solid are reduced to a form useful for determination of third-order elastic constants by means of ultrasonic pulse distortion measurements. Values of the coefficients in the reduced equations of motion are tabulated for two cubic materials. The tables are used to show that for cubic materials one should be able to measure C111, C112, and C166 with reasonable accuracy. An argument is given which shows that the equations of motion for a single plane wave in a cubic crystal depend on the five parameters C111, C112, C166, (2C144+C123), and (½C144+C456) instead of all six third-order elastic constants.
Electron Mobilities in SiC Polytypes
Authors: Patrick Lyle
Published: January 2005

Electron-scattering mechanisms in SiC polytypes are discussed. It is shown that the mechanism which limits mobility from 300° to 800°K in n-type SiC is probably intervalley scattering (in relatively pure samples). The dependence of electron mass on polytype enables one to study the scattering mechanisms by a comparison of Hall mobilities in two polytypes.
Electron Mobility Measurements in SiC Polytypes
Authors: Barrett D. L. , Campbell R. B.
Published: January 2005

Electron mobilities were measured in a number of n-type SiC samples selected and prepared in such a way as to ensure that they were single polytype specimens of 6H, 15R, or 4H. In the purest samples from the same growth preparation the ratio of 15R to 6H mobilities was found to be about 1.7 with both polytypes having a temperature dependence of mobility near T−2.4 between 300° and 800°K. Room-temperature mobilities of these specimens were about 300 and 500 cm2 V−1 sec−1, respectively, for 6H and 15R. Only two 4H samples were measured, but these showed even higher mobilities than 15R polytype samples.
Optical and Electrical Properties of Epitaxial and Diffused GaAs Injection Lasers
Authors: Pilkuhn M. H. , Rupprecht H.
Published: January 2005

GaAs injection lasers were prepared by an epitaxial solution growth method and their properties compared with those of diffused junctions. The optical gain factor β was up to a factor of 7 higher for the epitaxial diodes at 300°K. This resulted in threshold current densities as low as 26 000 A/cm2 (3.8×10−3 cm length) at 300°K. At 77°K, gain factor and loss numbers were similar for the two laser types. The spontaneous line-width of the epitaxial lasers was unusually large (∼300 Å at 77°K) and increased with decreasing junction voltage. The internal quantum efficiency of epitaxial diodes drops from 100% at 4.2°K to 40% at 300°K. The vertical beam spread was found to be between 20°–30° half-width at 77°K as well as at 300°K. Diffused diodes frequently show a delay between the current pulse and the stimulated emission of up to 30 nsec, dependent on the current value at higher temperatures. No such delay was observed in epitaxial lasers.
Luminescence from GaP containing Silicon
Authors: Lorenz M. R. , Pilkuhn M. H.
Published: January 2005

An emission line in GaP of previously unexplained origin peaking at about 1.96 eV (6300 Å) at 77°K was studied in electroluminescence of forward biased p-n junctions and in photoluminescence. We attribute this band to the presence of Si. The peak energy position of the 1.96-eV band is dependent on the identity of the dominant shallow donors, thereby indicating that the deep center is an acceptor. The results indicate that Si substitutes at Ga sites and acts as a shallow donor. At high-electron concentrations, Si causes the appearance of an acceptor with a level about 0.25 eV above the valence band. The dependence of current and light intensity on voltage was studied. The 1.96-eV line has an external quantum efficiency at 77°K of up to 1.4×10−2 but is rapidly quenched with increasing temperature.
Spectrographic Measurements on an Arc Discharge
Authors: Barach John Paul
Published: January 2005

An arc discharge of 60-μsec duration and peak current of 2×104 A in an initial pressure of 3 Torr of helium was studied spectroscopically. Time resolution was obtained by Kerr cell shuttering a 1.5-m spectrograph. The spectra were analyzed by Stark broadening and line-to-line intensity ratios. The arc was found to quickly evolve many times the initial density in wall and electrode materials, to decrease in degree of excitation after the first 10 μsec, and to lack thermodynamic equilibrium. The doubly ionized species were found to have roughly consistent temperatures of 7±1.5 eV and the singly ionized species 4±1.5 eV. The ratio between the two populations was more appropriate to excitation energies of 1 or 2 eV.
Electroviscous Fluids. I. Rheological Properties
Authors: Klass Donald L. , Martinek Thomas W.
Published: January 2005

Electroviscosity is defined in this introductory paper as an essentially instantaneous reversible change in apparent viscosity when a fluid is subjected to an externally applied electric field. The electroviscous properties of silica and calcium titanate dispersions are typical of most electroviscous systems and were found to be a function of many parameters such as composition, shear rate, field strength, frequency, and temperature. When only one parameter is varied, electroviscous effects increase with increasing volume fraction of disperse phase, field strength, and temperature, but decrease with increasing shear rate and frequency. Electroviscosities are proportional to the square of the field strength and inversely proportional to the first power of the shear rate. Induced interfacial polarization on and near the particle surface and the resulting interactions between the polarized double layers, and the polarized double layers and particles are used to explain the electroviscous phenomenon.
Diffusion-Induced Defects in Silicon. I
Authors: Levine E. , Washburn J. , Thomas G.
Published: January 2005

Dislocations introduced into the surface layers of silicon crystals by boron and phosphorus diffusion treatments of the type used in device manufacture were studied by transmission electron microscopy. Edge dislocation arrays were found for {110} and {111} surface orientations as was the case for previous observations on {100} specimens. The maximum density of dislocations was located at a depth corresponding to the steepest solute concentration gradient. The observations suggest that the glide mechanism for motion of edge dislocations into a crystal, previously proposed for diffusion into a {100} surface, does not operate for a {111} surface orientation. Most of the edge dislocations making up the accommodation network for the latter orientation apparently had moved into the crystal nonconservatively.
Electrodeless Determination of Semiconductor Conductivity from TE01°-Mode Reflectivity
Authors: Champlin K. S. , Holm J. D. , Glover G. H.
Published: January 2005

Microwave conductivity of semiconductors determined from transmission or reflection of the dominant mode of rectangular waveguide may contain a significant error caused by the impedance of the contact between the sample and the broad waveguide wall. This error increases with increasing bulk conductivity. The present paper describes a technique which eliminates this source of error by utilizing the TE01° mode of circular waveguide in a ``reflection coefficient bridge.'' Measurements of intrinsic germanium at 48 GHz show no contact influence over the conductivity range between 2 and 2×103 mho/m. In contrast, the conductivity measured with a conventional rectangular waveguide transmission bridge saturates at about 50 mho/m.
Scanning Electron Diffraction Observations on Diffuse Inner Rings from Very Thin Vapor-Deposited Films
Authors: Denbigh P. N. , Dove D. B.
Published: January 2005

Observations on small-angle diffraction rings from very thin vapor-deposited layers have been carried out using a direct-recording electron diffractometer. The rings are due to the island structure of the deposited layers. A detailed correlation has been made between ring location and island/island interferences by statistical evaluation of electron micrographs. (The occurrence of inner diffraction rings from various types of specimens was first noted by Mahl and Weitsch using an electron-microscope technique.)
Two-Stream Instability in Plasma
Authors: Uberoi C. , Bhatnagar P. L.
Published: January 2005

The problem of two-stream instability in plasma is studied by specifying the importance of initial magnetic field associated with the motion of the charged particles and the boundary effects. In Part I the accurate initial steady state is studied when the streams of electrons and ions move with different uniform speeds in plasmas with plane and cylindrical geometry. In Part II, in order to show the effects of finiteness and inhomogeneity of the system, small transverse plasma oscillations are studied in the case of plane plasmas. The role of plasma-sheath oscillations at the boundaries is found to be very important in driving the instabilities associated with the electromagnetic modes. The numerical estimates of the growth rates of the instability are given for the specific case of the physical data in discharge tubes.
Use of Boundary Sources in Problems of Heat Conduction
Authors: Reitzel John
Published: January 2005

A method is presented for solving problems of one-dimensional heat flow in regions with plane, spherical, or cylindrical boundaries. It is based on the physical concept of a uniform continuous-source distribution on the boundary, whose strength varies with time in such a way as to meet the prescribed boundary condition. Examples of the method are given, including the solution for the temperature in a half-space with an initial steady gradient of temperature and the boundary condition (∂T/∂x) − w(∂T/∂t) − hT = − hθ.
Peak Effect in Superconducting Nb-15 at.% Zr-45 at.% Ti Alloys
Authors: Doi T. , Ishida F. , Kawabe U.
Published: January 2005

The H-Ic characteristics of Nb-15 at. % Zr-45 at. % Ti alloys are experimentally discussed in relation to metallurgical structure, particularly, precipitation. Peak effect may be due to the random distribution in barrier heights and the interaction between flux lines at the magnetic fields near Hc2.
Acoustic-Wave Propagation in Tetragonal Crystals and Measurements of the Elastic Constants of Calcium Molybdate
Authors: Alton W. J. , Barlow A. J.
Published: January 2005

A complete analysis is given of the propagation of acoustic waves in crystals of the tetragonal system. The determination of the elastic constants from measurements of longitudinal- and shear-wave velocities in selected directions is discussed and experimental results for calcium molybdate are presented. The elastic constants in units of 1011 dyn/cm2 at 25°C are found to be c11=+14.47 ±2%,c33=+12.65±0.17%,c44=+3.69±0.17%,c66=+4.51±5%,c16=+1.34±50%,c12=+6.64±50%,c13=+4.46±2%.
Optical Study of Ultrasonic Diffraction and Focusing in Anisotropic Media
Authors: Cohen M. G.
Published: January 2005

This paper describes an investigation of the diffraction of 100–500-Mc/sec longitudinal elastic waves in anisotropic materials, using the techniques of optical (Bragg) scattering, which allow direct measurement of ultrasonic intensity distributions along the path of the beam. Such measured distributions for beams propagating along pure mode axes in crystal quartz, silicon, and potassium bromide are shown to agree very well with intensity distributions predicted using a diffraction integral derived from a rigorous solution of the related problem of electromagnetic diffraction in uniaxially anisotropic media. In addition, it is demonstrated that cylindrical crystal surfaces, symmetric about the proper pure-mode axis, are appropriate excitation surfaces for cylindrically focused ultrasonic beams. The focusing properties of thin-film CdS and ZnO transducers evaporated on cylindrical surfaces of crystal quartz and silicon are described and compared with the properties of focused beams in isotropic materials.
Initial Shock-Front Interaction with Solid Models
Authors: Zagieboylo Walter
Published: January 2005

The initial response of solid models to low-Mach, high-mass-flow shock waves was analyzed. A rapid-response piezoelectric load cell was mounted in a series assembly behind the models to directly measure resultant loading. The load history was analyzed and correlated with model geometry and shock-wave velocity for rectangular wood models of various length and weight and for the effects caused by changing the front surface material. The front surface of the model was in some cases bare and in other cases covered with plastic foam or thin foam rubber. It was observed that the coatings produced increased loading effects. The maximum loading force was determined for various overpressures and found to be in linear relationship to a dimensionless ratio involving shock-tube and shock-wave pressure parameters.
Ionic Diffusion at the Aluminum-Aluminum Oxide Interface
Authors: Christian J. H. , Taylor H. L.
Published: January 2005

Ionic diffusion currents measured in a metal-insulator-metal structure yield an activation energy of 1.60 eV at 550°K for alumium ions diffusing into alumium oxide. Aluminum evaporated at 10−10 Torr on aluminum oxide, formed by chemical reaction of pure oxygen with the base electrode, produces a structure with a graded alumium-concentration profile at the lower interface and a relatively abrupt aluminum-concentration profile at the upper interface. Thermal activation of aluminum ions from the electrodes produces a transient current of diffusing metal ions when an external short circuit prevents charge accumulation on the electrodes. Analysis of the diffusion-current data of aluminum into aluminum oxide gave values of 1.60 eV for activation energy and 5.8×10−19 cm2/sec for the diffusion constant.
A Moments Methods for Describing the Diffusion of Radiation from a Cavity
Authors: Pomraning G. C.
Published: January 2005

A moments method is applied to the non-self-similar problem of the diffusion of radiation from a cavity, in the case that the transport of energy is purely radiative. The energy in the cavity is assumed to be introduced instantaneously, and the diffusion into the surrounding wall, particularly the motion of the radiation front, is followed for subsequent times. The moments method used has the characteristic that it gives, for the physical model assumed, exact results for the position of the front in both the short- and long-time limits for all geometries.

Both plane and spherical cavities are treated in detail. Series solutions which apply in the limits of short and long times are given. Equations describing the first-order departure of spherical radiation flow from plane flow are derived, and the short-time solution is given. In plane geometry all quantities of interest can be written in parametric form in terms of elementary functions, and numerical results are presented in this case. Spherical geometry yields a more complex parametric solution, which is also given.