bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of Efficient Silicon-Compensated AlxGa1−xAs Electroluminescent Diodes
Authors: Kressel H. , Hawrylo F. Z. , Almeleh N.
Published: February 2004

The properties of p-n junctions fabricated by Si compensation in the AlxGa1−xAs alloy system have been investigated. The radiative emission is shown to occur via centers substantially removed from the band edges. At 300°K, E0-hvp varies from 0.12 eV at a bandgap energy of 1.49 eV to a maximum of 0.33 eV when E0=1.86 eV. A deep acceptor level due to a Si complex is believed to be involved. As a result internal reabsorption of the emitted light is small compared to Zn-doped junctions where the emission is closer to the absorption edge. External efficiencies of 1%–2% on uncoated, edge emission diodes are observed in the near-infrared portion of the spectrum (8600 Å), at current densities as low as 5 A/cm2. The highest efficiency obtained is 7% at 8800 Å with an encapsulated diode. The radiative efficiency at 300°K is shown to vary with the bandgap energy (i.e., separation between direct and indirect conduction band minima). For Eg=2 eV (when the indirect band is lower than the direct one by about 0.1 eV), the efficiency is reduced to 0.025% at a peak emission wavelength of 7000 Å. However, at 77°K, the efficiency varies by only a factor of ∼5 between Eg=1.49 eV and Eg=2 eV. The difference between 300° and 77°K is explained by free-electron-to-acceptor-recombination at 300°K, which changes to donor-to-acceptor recombination at 77°K. In comparison with other methods of diode preparation by vapor phase epitaxy or diffusion, (in AlxGa1−xAs or GaAs-P) the present devices offer the convenience of a one step growth process in simple apparatus. The low internal reabsorption further simplifies the diode fabrication process because high efficiency devices are obtained even with edge emission structures. Thus it is possible to have large surfaces available for Ohmic contact which results in minimal diode series resistance.
Silicon Carbide Light-Emitting Diodes
Authors: Potter Ralph M. , Blank John M. , Addamiano Arrigo
Published: February 2004

Electroluminescent diodes were prepared by the simultaneous diffusion of boron and aluminum at 2150° to 2250°C into nitrogen-doped, n-type 6H SiC crystals. These diodes exhibit a typical brightness of 50 ft·L (170 nit) at a current density of 5 A/cm2 for temperatures of 25° to above 200°C. The results of various measurements on these diodes are presented and the anomalous nature of the diffusion is discussed.
Resistivity Anomalies in Gadolinium
Authors: Nellis W. J. , Legvold S.
Published: February 2004

Anomalous behavior has been observed in the electrical resistivity of gadolinium single crystals in the region 210°–250°K. The results are correlated with the rapid deviation of the magnetic moment from the hexagonal axis in this temperature range.
Higher-Order Images Reconstructed from a Sampled Sound-Wave Hologram
Authors: Aoki Yoshinao
Published: February 2004

A sound-wave hologram was constructed by sampling the acoustic field with a microphone and simulating a reference wave electronically. The frequency of the sound wave was chosen as 18 kHz. The optical reconstruction of image from the obtained hologram was carried out using the 6328 Å laser light. A zero-order image and higher-order images were reconstructed from a grating-like sound-wave hologram produced by the scanning of the microphone.
Injection Electroluminescence from Diffused Gallium-Aluminum Arsenide Diodes
Authors: Linden K. J.
Published: February 2004

Injection electroluminescence from diffused diodes of gallium-aluminum arsenide has been investigated. These diodes were prepared from material deposited epitaxially from the liquid state onto oriented gallium arsenide substrates. Diffused diodes emitting radiation at wavelengths as short as 7150 Å have been prepared from material estimated to contain 0.28 mole fraction of AlAs. Microscopic examination has shown that the recombination radiation originates within approximately 1 μ of the junction region. Data on measurements of wavelength and efficiency vs aluminum melt concentration are presented. On the basis of the measured emission wavelengths, the mole fractions of AlAs in the deposited gallium-aluminum arsenide layers are given.
Improved Technique for Electrical Measurements on Ice and Other Doped Solids
Authors: Young Irving G.
Published: February 2004

It is of great interest to establish the relationship between the conductivity and the concentration of dopants in ice, as in semiconductors in general. In a widely employed technique, the electrodes are placed perpendicular to the direction of sample growth, which is also the direction of the concentration gradient invariably present. This arrangement is called a resistance measurement. In the improved technique, the electrodes are placed parallel to the concentration gradient; this arrangement is called a conductance measurement. The error in estimation of the bulk conductivity resulting from these distinct methods of measurement is computed, using as the reference, the conductivity associated with the average concentration. Three types of dopant concentration gradients are dealt with: the Pfann, the exponential, and the linear. In addition, the cases where the conductivity is proportional to the first power and to the square root of the concentration are considered. It is found that the improved technique always leads to a smaller error than the usual one, other factors being equal. Furthermore, the techniques recommended for improving doping uniformity (stirring of solution during freezing and freezing only a portion of the sample) are shown to have a sound theoretical basis. The partition coefficient of HCl between ice and water has been calculated based on the Pfann equation and measurement of the average concentration of HCl in doped ice and the known initial solution concentrations. k is of the order of 0.01.
Correlation of Electroacoustic Properties with Resistivity Inhomogeneities in CdS Single Crystals
Authors: Parsons M. K. , English F. L. , Hickernell F. S.
Published: February 2004

The electromechanical coupling constants k31 and k15 of single-crystal, photoconductive CdS were obtained, respectively, by resonance-antiresonance and shear wave velocity measurements. The correlation between the magnitude of these measured electromechanical coupling constants and the presence of thermal equilibrium resistivity inhomogeneities observed with the electron mirror microscope is described.
Purification and the Growth of Gd Crystals
Authors: Cadieu F. J. , Douglass D. H.
Published: February 2004

A method of growing large high-purity Gd single crystals has been developed utilizing a distillation chamber completely sealed by molten Gd. Resistance ratios [ρ(294 K)/ρ(4.2 K)] up to ∼160 have been attained from a starting point of ∼30 in a single distillation run with the resultant crystal grains approaching a cubic centimeter in volume.
Inverse Strain-Rate Effects
Authors: Gillis Peter P.
Published: February 2004

Decrease of stress level at a given strain with increase of strain rate is discussed in terms of three theories: the Johnston-Gilman theory of yield and flow, diffusional aging mechanisms, and stress induced structural instability. None of these theories explain inverse rate effects. However, a modified concept of stress-induced structural instability in conjunction with the Johnston-Gilman theory provides a physical mechanism whereby a material is expected to display ordinary rate effects at high or low strain rates, but may exhibit inverse effects over some intermediate range of strain rates, depending upon the degree of structural instability.
Some Thin-Film Properties of a New Ferroelectric Composition
Authors: Chapman D. W.
Published: February 2004

Thin polycrystalline films made from a base composition of Pb0.92Bi0.07La0.01 (Fe0.405Nb0.325Zr0.27) O3 exhibited a spontaneous polarization of 10 to 20 μC per square centimeter, hysteresis-loop squareness ≥0.75, coercivity≤15 kV/cm, Curie temperature≃150°C, resistivity≃1011 Ω·cm, and initial dielectric constant of about 1000. In a pulsed-life test, one such film was repetitively switched in 300 nsec by 20-V applied pulses for more than 2×1011 polarization reversals before the test was terminated for convenience.
Mass Dependence of Self-Diffusion in Iron
Authors: Graham D.
Published: February 2004

The self-diffusion isotope effect has been measured by serial sectioning in the α, γ, and δ phases of iron. Values for the isotope effect assuming a single vacancy exchange are 0.71±0.06 at 1452°C (bcc); 0.79±0.05 at 1338°C (fcc); 0.69±0.14 at 869°C (bcc). Thus, in each case the isotope effect equals the correlation factor within experimental error. Measurements at 720° and 770°C appear to be influenced by diffusion along grain boundaries producing a marked reduction in the apparent isotope effect.
Arsenic Isoconcentration Diffusion Studies in Silicon
Authors: Masters B. J. , Fairfield J. M.
Published: February 2004

Arsenic radiotracer diffusions have been performed both in intrinsic and in homogeneously doped extrinsic silicon single crystals. Under intrinsic conditions, the tracer diffusion coefficient may be represented by the expression Di=60 exp (−4.20 eV/kT) cm2/sec. Measured in extrinsic silicon, in the absence of a concentration gradient, the tracer diffusion coefficient conforms with the relationship D=Di(n/ni), in which (n/ni) in the ratio of the free electron concentration in the extrinsic sample to that of intrinsic silicon at the diffusion temperature.
Interstitial-Like Diffusion of Copper in Lithium
Authors: Ott Aadu
Published: February 2004

The tracer diffusion of 64Cu in lithium has been measured. The results are expressed by DCu–Li=(0.47±0.11) exp[(−9.22±0.22)/RT] (cm2/sec). Copper diffuses faster than any other hitherto investigated impurity in lithium; close below the melting point D is about 2×10−6 cm2/sec. From the magnitude of the diffusivity, from the systematics among the noble metals, and from parallels with diffusion results in certain polyvalent matrices, it is inferred that Cu, Au, and Ag impurities in Li diffuse as interstitials.
Optical Determination of Cs Ground-State Depletion in Cs–Ar Low-Pressure Discharges. II. Radial and Axial Cs-Atom Distributions
Authors: Bleekrode R. , Laarse J. W. V. D.
Published: February 2004

The radial and axial distributions of Cs ground-state (62S1/2) atoms in Cs–Ar low-pressure discharges are studied by absorption spectroscopy. The results show that there is appreciable Cs-atom depletion at the center of the discharge. Within experimental accuracy the Cs(62S1/2) concentration is found to be constant over the whole length of the positive column of the discharge.
Energy Distribution of Electrons in a Cesium Thermionic Discharge
Authors: Shaw David Tai-Ko
Published: February 2004

The electron energy distribution is obtained for a cesium plasma in a thin region close to the emitter of an ignited-mode thermionic converter. Assuming that the steady-state plasma is spatially uniform, the Boltzmann equation with only the electric field and the collision terms is solved by the use of WKBJ method. The collision terms include the elastic, inelastic and electron-electron Coulomb interactions. A parameter p which is proportional to the ratio of the degree of ionization and the electric field, is used to characterize the effect of the electron-electron interaction on the energy distribution. The stability of the present solution depends on the position of a singular point, a so-called turning point in the wave equation. The present method gives a stable solution when p≥3. When p<3, the ``turning point'' moves inside the inelastic region, and the equation has multivalued solutions. Thus the present method cannot be applied to those cases with very large induced electric field and small degree of ionization. The solution is examined in various values of p, and the effect of nonequilibrium ionization in the energy distribution function is discussed.
Use of a Passive RC-Analog for the Study of Glass Pressing
Authors: Steere Robin C.
Published: February 2004

The passive analog technique is applied to cyclic glass pressing. Design details of an analog of a plunger-glass-mold system are given. The analog is used to provide results on plunger temperature profiles, heat contents, glass temperature gradients near the glass-mold boundary, and rates of attainment of normal mold running temperature. These results are substantiated by practical pressing machine experience. The method is therefore of use in the assessment and design of glass-pressing systems.
Reversible Photodissociative Laser System
Authors: Giuliano C. R. , Hess L. D.
Published: February 2004

Laser action at 2.7 μ from atomic bromine was produced by flash photolysis of gaseous iodine monobromide. The output consists of a series of sharp pulses having peak powers up to 50 W and a total duration of 5 μsec. Optical gain was estimated to be ∼1 dB/m. Chemical reversibility of the system is very good; regeneration of the starting material occurs spontaneously and requires about 3 msec. The fact that excited bromine rather than excited iodine atoms are formed leads to clarification of previous conflicting spectroscopic assignments.
Nuclear Magnetic Resonance Study of the Niobium-Nitrogen System NbNx
Authors: Bennett Robert A. , Hooper H. O. , Roy U.
Published: February 2004

Nuclear magnetic resonance has been employed to identify the phases of the system NbNx in several samples of niobium nitride. The ε phase has been identified by a characteristic second-order quadrupolar broadened central transition with two sets of satellite lines also being observed. The quadrupole coupling constant has been determined for the ε phase (e2qQ/h=10.6±0.1 MHz) and for the δ phase (e2qQ/h=4.3±0.4 MHz). The relative amounts of the phases present in a sample were also determined in two samples.
Two-Dimensional Bloch-Type Domain Walls in Ferromagnetic Films
Authors: LaBonte A. E.
Published: February 2004

The structure of a two-dimensional 180° Bloch-type domain wall in a ferromagnetic film has been generated directly from an iterative micromagnetic energy minimization. The resultant magnetization distribution (which varies through the thickness of the film as well as in the plane of the film perpendicular to the wall) is observed to be significantly different from previous one-dimensional models. The equilibrium wall structure is characterized by extensive flux closure internal to the film, very low pole densities on the film surfaces, asymmetry in the magnetization distribution perpendicular to the wall, and an approximately linear dependence of the over-all wall width on film thickness. Finally, it is found that the total wall energy in this two-dimensional model is less than one-half the comparable value predicted from the most accurate one-dimensional treatment for 1000 Å Permalloy films and less than one-third the corresponding one-dimensional value at 2000 Å.
Magnetic Properties of 3d Transition Metal Ion Substituted CdCr2S4 Spinels
Authors: Robbins M. , Miksovsky M. A. , Sherwood R. C.
Published: February 2004

Substituted CdCr2S4 spinels containing Ni, Co, V, and Ti were prepared for magnetic study. Substitution of In3+ for Cd2+ was used for charge compensation when divalent transition-metal ions were substituted for Cr3+. In the spinels Cd0.8In0.2[Cr1.8Ni0.2]S4, Cd0.8In0.2[Cr1.8Co0.2]S4 and Cd0.8In0.2[Co0.2Cr1.8]Se4 the Ni2+ and Co2+ were both found (by magnetic measurements) to interact negatively (antiferromagnetically) with the Cr3+ ion. The V3+ and Ti3+ ions in CdV0.2Cr1.8S4 and CdTi0.2Cr1.8S4 appear to have no magnetic moment. The measured magnetic moments of these spinels are in excellent agreement with theoretical values based only on the moment of Cr3+. In the compound Cd0.8In0.2[Cr1.8V0.2]S4 the measurements indicated that the V2+ ion is not stable with respect to the Cr2+ ion. The resulting ionic distribution would be Cd0.8In0.2[V0.23+Cr0.22+Cr 1.63+]S4 instead of Cd0.8In0.2[V0.22+Cr1.83+] S4. Two additional compositions containing 0.1 and 0.3 mole of vanadium exhibited magnetic moments which are consistent with the formation of V3+ and Cr2+.
Magnetoelastic Wave Instability Threshold in an Axially Magnetized YIG Rod
Authors: van de Vaart H.
Published: February 2004

The instability threshold has been derived for transversely pumped magnetoelastic waves in YIG for the case where the equilibrium position of the magnetization vector is in an arbitrary direction with respect to the crystal axes. It is shown that the threshold has a finite value for magnetoelastic waves propagating parallel to the direction of the internal magnetic field and that the threshold is minimum near crossover. It is also shown that the threshold is lowest when the internal field is rotated ∼15° with respect to one of the 〈100〉 cubic axes of YIG. The recently developed geometrical ray theory analysis is used to determine the exact propagation path of the magnetoelastic waves in an axially magnetized rod and to compute the magnitude of the angle θ between the wave vector k and the direction of the internal magnetic field. Results show that the magnetoelastic waves focus about the direction of the field and that θ≅1° or less. The ray theory analysis and the nonlinear theory have been combined, and the threshold has been determined at each point along the ray. The results satisfactorily explain the experimental observations on parametric amplification of magnetoelastic waves in YIG, reported in an earlier paper.
Constitutive Equation for the Dynamic Compaction of Ductile Porous Materials
Authors: Herrmann W.
Published: February 2004

A simple phenomenological constitutive equation for porous materials is proposed, which allows a detailed description of irreversible compaction behavior at low pressures and reduces to the correct Hugoniot description at high pressures. The theory is compared to some existing data on Hugoniots of porous aluminum and iron, and fairly simple functional forms of the compaction relation are found to be adequate to fit the data. The constitutive relation is suitable for use with finite difference methods of solution of the one- and two-dimensional equations of motion governing stress wave propagation. Examples of such solutions in one dimension are given to illustrate some of the features of the theory.
Elastic Torsion in Wires Under Tension
Authors: Allen Mildred , Saxl Erwin J.
Published: February 2004

An experimental study of the effect of axial tension on the torsional stiffness of circular wires was made under static conditions and well within the elastic limits for both twist and stretch. The method used was to apply a constant couple to the bottom of a vertical wire and to note optically how the angle of twist changed as the tension on the wire was varied. It was carried out with four different alloys. Variations in angle were observed to be related linearly to the applied tensions and to be in excess of those which arise from the change in dimensions, except for one alloy for which the effect is either nonexistent or too small to be detected. In all cases there is an initial residual twist. In general, an increase in axial tension produces a decrease in torsional stiffness, except where the effect of the residual twist is greater than and opposed to this decrease. The results are also shown to be in qualitative agreement with the classical experiments on the Poynting effect, an effect which can be explained by modern second-order theory of elasticity.
Steady-State Theory of Backward-Traveling-Wave Parametric Interactions
Authors: Meadors John G.
Published: February 2004

The three nonlinear coupled differential equations for a three-frequency backward-traveling-wave parametric interaction in a lossless dielectric are solved for the power density in the three fields as a function of position in the crystal. When the theory is applied to a single-pass oscillator, it predicts the existence and magnitude of a threshold pump power even for lossless media. The theoretical curves showing the power outputs in the signal and idler waves for the single-pass oscillator as a function of pump power and crystal parameters are given.
Electroluminescence of ZnS Lumocen Devices Containing Rare-Earth and Transition-Metal Fluorides
Authors: Chase E. W. , Hepplewhite R. T. , Krupka D. C. , Kahng D.
Published: February 2004

ZnS LUMOCEN (luminescence from molecular centers) films typically 2000-Å thick doped with rare-earth and transition-metal fluorides have been fabricated by vacuum coevaporation. Details of the fabrication techniques are presented for the 12 fluorides studied: PrF3, NdF3, SmF3, EuF3, TbF3, DyF3, HoF3, ErF3, TmF3, YbF3, CrF3, and MnF2. Concentration dependence of the brightness has been investigated for the ZnS/TbF3 device, the maximum occurring at 1.8 at.% Tb. Studies of brightness as a function of input power indicate that the ZnS/TbF3 device is the brightest with 50 foot-lamberts readily obtained. The power efficiency for ZnS:TbF3 is about 10−4. Emission spectra of the devices have been measured from 0.35 to 1.1 μ and related to known energy level schemes where possible. The intensity distributions of the spectra generally differ from those obtained by doping ZnS with the bare ions; the ZnS:CrF3 device yields a spectrum radically different from any Cr3+ luminescence previously investigated.
Nucleation and Growth of Gas Bubbles in Elastomers
Authors: Gent A. N. , Tompkins D. A.
Published: February 2004

An experimental study is described of the formation and growth of gas bubbles in crosslinked elastomers. A critical condition for bubble formation is found to hold in most cases: The gas supersaturation pressure must exceed 5G/2, where G is the shear modulus of the elastomer. The kinetics of bubble growth are shown to be in good accord with a simple diffusion-controlled growth relation for a variety of gases, elastomers, temperatures, and pressures. The number of bubbles depends strongly upon the degree of supersaturation above the critical level. This effect is attributed partly to kinetic factors and partly to the presence initially of internal holes of a range of sizes.
Charge-Carrier Capture and Its Effect on Transition Capacitance in GaP–Cu Diodes
Authors: Grimmeiss H. G. , Olofsson G.
Published: February 2004

The induced photovoltaic effect and the change in transition-layer capacitance in alloyed GaP–Cu diodes have been investigated. Both effects can be explained by hole capturing in acceptor levels with large binding energy. The holes can be released by ir illumination which generates a transient shortcircuit current and quenches the change in capacitance. The spectral sensitivity of the transient photoeffect and of the capacity change is in agreement with other experimental results obtained in homogeneous material. Due to the large binding energy, thermal ionization of acceptor levels is very small at room temperature. Finally, the voltage dependence of the transition-layer capacitance is compared with theoretical considerations, taking into account not only deep lying acceptor levels but also donor levels with large binding energy.
Studies of the Early Afterglow in Helium and Argon Plasmas
Authors: Gerardo J. B. , Gusinow M. A.
Published: February 2004

Spatially resolved measurements of parameters during the early afterglow of helium and argon plasmas are presented. The investigated plasmas were contained in a vessel with a wall temperature much less than the electron temperature at the center of the plasma. All measured parameters developed nonuniformly. In spite of the high thermal conductivity of the free electrons, a temperature gradient was supported; the electron temperature being highest in the center of the vessel. The mechanism by which these gradients were supported is discussed. Both the electron and neutral gas temperatures remained elevated at several thousand degrees for at least 200 μsec into the afterglow. Attention is also focused on the effect of spatially nonuniform plasma parameters on transport processes as well as the dependence of the net decay on the cold walls.
Spectroscopic Studies of a Laser-Produced Plasma in Helium
Authors: Braerman W. F. , Stumpfel C. R. , Kunze H.-J.
Published: February 2004

A highly ionized plasma was produced by laser-induced breakdown in helium at a pressure of 360 Torr. Line and continuum emission from the plasma were studied as a function of time and of position along the axis of the laser beam. Plasma parameters were then deduced from Stark widths, line-to-continuum, and line-to-line intensity ratios. The applicability of the various methods used to the case of a rapidly decaying laser-produced plasma is discussed. The decay of the plasma is analyzed and the observed decay coefficients are compared with theoretical calculations.
Ionization Expansion of Pile-Exposed Vitreous Silica
Authors: Primak William , Kampwirth Robert
Published: February 2004

Exposure of vitreous silica in a nuclear reactor is shown to introduce ionization expandability which is superimposed upon the ionization contractibility of ordinary vitreous silica and upon the ionization expandability associated with certain impurities. The ionization expandability developed in pile exposure consists of two parts. The principal part requires ∼104 eV of ionization for a volume increase of an oxygen ionic volume (O.V.) and can exceed 5×1019 O.V./cm3. Capacity for an earlier phase of ionization expansion, pre-evident expansion, grows on pile exposure to a maximum ∼5×1018 O.V./cm3, requires ∼32 eV/O.V., and declines when electron irradiation is intermitted. Accompanying the reversion is a recuperation phenomenon resulting in an increase in principle expansion on resumption of irradiation. The recuperation phenomenon is explained as caused by a redistribution of bond strain in the reversion of the pre-evident expansion. The supervenient expansion observed after maximum compaction during pile exposure is explained as predominantly associated with the slowing down of atoms scattered by fast neutrons (also the cause of the original compaction) and indicates the existence of structure in the microregion being compacted.
Rapid Annealing in n-Type Silicon Following Pulsed 10 MeV Electron Irradiation
Authors: Arimura I. , Freeman R. R.
Published: February 2004

The forward voltage Vf across a p+-n silicon diode, biased at constant current, was used to monitor the rapid annealing of damage introduced by a 5-μsec pulse of 10 MeV electrons. Silicon diodes (1N648) were irradiated at various temperatures from 90° to over 350°K. The large increase in Vf observed immediately after the irradiation pulse recovered partially to its preirradiation value in times varying from a few milliseconds at 300°K to a few hundred milliseconds at 100°K. The ratio of the change in Vf at 100 μsec after the irradiation pulse to the change after recovery had been completed varied from approximately three at 300°K to nearly seven at 100°K. The large degree of recovery indicates that defect annihilation is most likely responsible for the recovery process. The recovery kinetics of the rapid annealing are closely described by Waite's theory of diffusion-controlled annealing involving recombination of correlated and uncorrelated defects. Particularly for temperatures above 170°K, the initial stage of recovery proceeds at a rate proportional to (t)1/2 for nearly 50% of the annealing, as the theory predicts. The temperature dependence of the diffusion constant for this initial recovery is governed by an activation energy of approximately 0.12 eV. Comparison with other results indicates the possibility that diffusion of an interstitial into a divacancy, whereupon annihilation occurs, is responsible for the recovery mechanism. The low activation energy obtained is the result of the large injection of holes used in the measurements, that the injection level alters the charge state of the interstitial and recovery is enhanced.
Analytical Treatment of Bulk and Surface Recombination in Minority Carrier Mobility Measurement in p-Si
Authors: Cresswell M. W.
Published: February 2004

Previous measurements of minority carrier mobility by the Haynes-Shockley technique have ignored one or more of the effects of the three-dimensional nature of the ambipolar diffusion, and bulk and surface recombination. In some cases, the experimental conditions were tailored so that the effects of these factors were truly negligible, imposing restrictions on the respective experimental configurations. In general, each factor does influence the drift time from which mobility estimates are made. This paper shows how their effects may be conveniently and systematically included in the data analysis and gives examples of the processing of experimental data acquired from p-type silicon samples of different geometries. The suitability of the new technique for measurement of mobility in thin wafers of material is pointed out.
Epitaxial Films of Silicon on Spinel by Vacuum Evaporation
Authors: Itoh Tadatsugu , Hasegawa Shinichi , Kaminaka Nobuyuki
Published: February 2004

By using the vacuum evaporation method single-crystal silicon films have been epitaxially grown on (111) spinel substrates at the substrate temperature range of 850° to 1000°C with the deposition rate of a few angstroms per second. Antimony-doped n-type epitaxial films of silicon having the carrier concentration ranging from 1.3×1016 to 2.1×1018 cm−3 were obtained by evaporating antimony during the evaporation of undoped silicon with the resistivity of 1600 Ω·cm. The Hall effect and the resistivity measurements on those films were carried out over the temperature range from 77°K to room temperature. Electron Hall mobilities of films over 800 cm2/V·sec at room temperature were achieved. It was found that these film mobilities corresponded to approximately 75% of the mobilities expected on the bulk silicon with similar carrier concentrations, and that electron Hall mobilities of the n-type films with the carrier concentrations over 3×1017 cm−3 corresponded to about 100% of those of bulk silicon. It was also found that the n-type epitaxial films of silicon as well as the p-type epitaxial films of silicon grown on (111) spinel substrates had higher Hall mobilities than those grown on (0001) and (1̄012) sapphire substrates with the deposition rate of a few angstroms per second by using the vacuum evaporation method.
Lithium-Ion Drift Mobility in Germanium
Authors: Sher A. H.
Published: February 2004

The mobility of lithium in germanium has been determined for temperatures between 23.8° and 61.2°C by measuring the change in the capacitance with time of a reverse-biased p-i-n diode. The mobilities of lithium thus obtained (at the specified temperatures) were 3.04×10−10 cm2/V·sec (23.8°C), 5.30×10−10 cm2/V·sec (36.2°C), 7.96×10−10 cm2/V·sec (46.2°C), and 16.86×10−10 cm2/V·sec (61.2°C). These values are higher than those that are obtained by the extrapolation of the results of others determined at higher temperatures into this temperature range. The results also suggest that a third distinct field configuration exists during the early stages of the lithium drifting in addition to the two normally considered.
Effect of the Bandgap on the Elasto-Optic and Electro-Optic Properties of Hexagonal Semiconductors
Authors: Kohn Elliott S.
Published: February 2004

The contribution of energy band deformation to the elasto-optic coefficients of hexagonal semiconductors is calculated. It is shown that this contribution accounts for the large dispersion previously observed in certain elasto-optic coefficients near the band edges of CdS and ZnO. The results are also shown to apply, at least qualitatively, to cubic semiconductors. The effect of the bandgap on the Pockels coefficients of hexagonal semiconductors is also treated.
Effect of Pressure on Al–I–Bi Tunnel Junctions
Authors: Vaisnys J. R. , McWhan D. B. , Rowell J. M.
Published: February 2004

Measurements of resistance (dV/dI) versus bias (V) have been made for Al–I–Bi junctions at 77°K up to pressures of 30 kbar. The junctions were prepared by evaporation upon freshly cleaved mica and the pressures generated in a girdle die using AgCl as the pressure transmitting medium. The results are reversible with pressure cycling. A conduction maximum occurs at ≈0.13 V and a kink at ≈−0.15 V. The maximum changes with pressure at a rate dV/dP=−1.7×10−6 V/bar. A change in the tunneling curve is observed at the semimetal to semiconductor transition.
Recombination Lifetimes in High-Purity Silicon at Low Temperatures
Authors: Leadon R. , Naber J. A.
Published: February 2004

Transient recombination lifetimes have been measured in high-purity, n-type, float-zone silicon from 4.2°K to room temperature. Photoconductivity decay curves and quiescent electrical conductivity values have been obtained by a microwave reflection technique which does not require electrical contacts to the sample. Experiments were performed at low injection levels on unirradiated samples and after irradiation with 30-MeV electrons. An unusual feature of the data is a pronounced increase in lifetime with decreasing temperature below 45°K, similar to a trapping effect. This variation of lifetime with temperature has been explained using the two-lifetime transient analyses of Sandiford and Wertheim. The temperature dependences of the capture cross sections are calculated and compared with the theoretical predictions of Lax and with other experimental results.
Dynamic Compressive Behavior of a Strain-Rate Sensitive, Polycrystalline, Organic Solid
Authors: Wasley R. J. , Walker F. E.
Published: February 2004

The rheological behavior of a brittle, strain-rate sensitive, polycrystalline, organic solid explosive (pressed TNT) was investigated under conditions of uniaxial compressive strain. The wave structure of shocks introduced into the specimen material was determined by examining quartz stress transducer records. An ``elastic precursor'' wave forms in the specimen if the driving stress is below approximately 10 kbar. The length, shape, magnitude, risetime, and velocity of the precursor wave and the risetime of the follower wave are functions of both the specimen thickness and driving stress. Stress-strain-variable-strain-rate curves and corresponding Hugoniot curves were experimentally determined for two specimen thicknesses. All sets of curves were found to be related to specimen thickness. Shock hydrostats were estimated at the lower strain levels from those stress-strain-constant-strain-rate curves most closely in agreement with the Hugoniots. A simple elastic-plastic theory that incorporated the results from an associated uniaxial stress study was used to determine the deviatoric stress component. The isentropic and isothermal hydrostats were deduced from the shock hydrostats; the isothermal curves were compared with experimentally obtained results. A numerical study indicated that transducer data were not significantly affected by wave reflections and interactions. Also verified was the adequacy of the simple elastic-plastic model used to describe the loading response.
Shock-Wave Strengthening of Copper and Nickel
Authors: Grace F. I.
Published: February 2004

Final yield strengths of metals plastically deformed in one-dimensional strain by shock compression are calculated from the theory of shock propagation and work hardening. An energy analysis of the shock-relief cycle employs a Mie-Grüneisen-type equation of state and appropriate Hugoniot compressibility curve to determine the thermodynamic states of the material and the plastic work done. The residual elastic strain energy stored in the metal was estimated assuming that a portion of the plastic work remains in the form of lattice defects. Results for copper and nickel are found to be in reasonable agreement with experimental data.
Surface Waves in Piezoelectrics
Authors: Ingebrigtsen K. A.
Published: February 2004

The effect of various electromagnetic boundary conditions on the propagation of surface waves in piezo-electrics is considered. Basic for the analysis is the introduction of an electric ``surface impedance'' which relates the electric potential to the normal component of electric displacement in the surface. An analytic expression for this impedance is found in the case of weak piezoelectric coupling which permits the calculation of the phase velocity for arbitrary values of the impedance. It is also shown that within the weak coupling approximation the surface impedance contains the information on material parameters necessary for calculating the power transferred to surface waves from an impressed electric current.
Attenuation of 5.9 keV Photons by Air
Authors: McCrary J. H. , Ziegler L. H. , Looney L. D.
Published: February 2004

The narrow beam attenuation coefficient of air was measured at 5.895 keV. An 55Fe source of Mn x rays with a CrKβ filter and a collimated low-energy sodium iodide counter were used. The photon intensity as a function of the source-detector distance was determined in vacuum and in atmospheric air. The value of the measured coefficient is 24.55±0.25 cm2/g.
Gel Cusps and Crystal Growth in Gels
Authors: Hanoka J. I.
Published: February 2004

Observations on the cusp-shaped ``cracks'' which form around crystals growing in gels are reported. It is shown that the cusps are interconnected, that the most common shape of the cusps is three-sided, that the cusp sides have a ridged structure, and finally, that the disposition of cusps around a growing crystal often displays a good deal of symmetry. It is concluded that the crystal is completely surrounded by liquid as it grows, and that this liquid is contained within a womb-like enclosure formed by the cusps surrounding a crystal. It is proposed that the surface of the womb made of the gel cusps acts like a membrane, and additional nutrients enter the womb through osmosis.
Extrinsic-Intrinsic Stacking-Fault Pairs in an Fe–Cr–Ni Alloy
Authors: Latanision R. M. , Ruff A. W.
Published: February 2004

Transmission electron images of extrinsic-intrinsic fault pairs in a Fe–Cr–Ni alloy are shown to be sensitive to changes in the sign of (g·b)s for reflections producing either line or stacking-fault contrast. This is interpreted in terms of the overlapping strain fields of the three closely spaced partial dislocations. A differential treatment of the measured widths of the intrinsic and extrinsic faults indicates that the stacking-fault energy ratio γe/γi=1.6 in this alloy.
Elastic, Piezoelectric, and Dielectric Properties of Rubidium Dihydrogen Phosphate
Authors: Adhav R. S.
Published: February 2004

The elastic, piezoelectric, and dielectric constants of single crystals of rubidium dihydrogen phosphate (RbDP) have been measured in the temperature range of 20°–80°C. The six elastic constants, in mks units, measured at 25°C are S11=18.3×10−12,S12=2.2×10−12,S13=−1.3×10−12,S33=22.9×10−12,S44=87.6×10−12,S66=285.8×10−12,The relative dielectric constants K11 and K33 are 47 and 28, respectively. The piezoelectric constants d14 and d36, in mks units, are 3.0×10−12 and 26.7×10−12, respectively. As in ADP, piezoelectric activity in the X plane is very small. Since the temperature coefficients of frequency of cuts in the Z plane are in excess of −200 ppm/°C, these crystals are not useful for electromechanical application.
Electrical Pulse Breakdown of Silicon Oxide Films
Authors: Klein N. , Burstein E.
Published: February 2004

Pulse breakdown tests on individual specimens with self-healing breakdowns resulted in information on both the thermal and the electric breakdown properties. Thermal breakdown due to Joule heat was found to occur nearly uniformly over the whole specimen at voltages generally lower than the electric breakdown. voltages. Calculations with relations derived for the thermal breakdown field agreed well with observations showing increase of breakdown field with decreasing pulse duration. Electric breakdown was found to be a chance event producing breakdown holes tens of microns in diameter. The process was interpreted to consist of three consecutive stages: (1) the field produces a very small charge pulse causing a temperature rise of a few hundred degrees centigrade in a breakdown channel; (2) this induces thermal runaway in the channel; and (3) the energy stored in the specimen discharges through the channel causing destruction. The magnitude of the charge pulse, duration of the process, and the size of the breakdown hole were calculated.
Self-Diffusion in Indium Antimonide
Authors: Kendall Don L. , Huggins Robert A.
Published: February 2004

Self-diffusion in InSb was studied, using radiotracers and refined sectioning techniques. The diffusion coefficients of neither In nor Sb seemed to depend on the ambient Sb pressure. A few pits several microns in depth were found to develop during diffusion of both In and Sb in InSb. Radioactivity associated with these pits led to tails in the diffusion profiles. The In:Sb divacancy is proposed as the defect primarily responsible for self-diffusion of both components in InSb. The activation energy for diffusion for both In and Sb was found to be 4.3 eV. This consisted of effective enthalpies of formation and motion for the divacancy of 3.2 eV and 1.1 eV, respectively. The enthalpy of formation of the single vacancies was estimated to be 1.76 eV. The pre-exponentials D0 in the Arrhenius relation for diffusion of In and Sb were 1.76×1013 and 3.1×1013 cm2 sec−1, respectively. These high values are attributed primarily to the large vibrational entropy contributions of a divacancy.
Secondary Leader Channels in the Impulse Breakdown of Air and Nitrogen
Authors: Nasser Essam , Schroder D. C.
Published: February 2004

In impulse gaseous breakdown, it has never been quite established how the transition from the low ion density of the primary streamers to the high carrier density of the pre-spark channel occurs. This phase of development was investigated for air and N2 by employing the Lichtenberg figure technique. Gas pressure varied between 50 and 760 Torr. It was surprising to detect an ionization process, termed a ``secondary leader,'' that is distinctly different from the primary streamer. During this process a relatively highly ionized channel is formed. Similar channels were previously observed only under static voltages and in very long gaps. The paths of the secondary channels were found to be narrow and to follow a radial pattern; they terminate in ``threads'' of low intensity that have an irregular circular pattern. Measurements were made of their onset voltage and their rate of growth as a function of the voltage and pressure. Their onset voltage in air lies between 4 and 12 kV for 100 and 400 Torr, respectively; in N2 it is about 15% lower. Their length is linearly dependent upon the voltage, though the rate of growth varies with pressure.
Melting of Silver Halides at High Pressure
Authors: Akella Jagannadham , Vaidya S. N. , Kennedy George C.
Published: February 2004

The melting curves of silver chloride, bromide, and iodide are determined up to 68 kbar. The present silver chloride and bromide melting curves are higher by 5°–20°C than those of Deaton. The triple point of silver iodide (I)-silver iodide (III) is at 19.1±0.5 kbar and 678°±1°C whereas Deaton reported the triple point at 22 kbar and 680°C. The volume compression versus the melting-temperature plots are linear at low compression and begin to curve towards ΔV/V0 axis at higher pressures.
Rotational Transition of CO2 Molecule by Collisions
Authors: Chan F. T. , Tang C. L.
Published: February 2004

The quantum-mechanical method of distorted waves for calculating the rotational relaxation rates in H2 as developed by Brout is used here to calculate the relaxation time for the ΔJ=±2 rotational transitions of linear polyatomic CO2 by taking into account the higher partial wave contributions. The intermolecular potential used consists of a spherical part and a nonspherical part with a constant parameter to characterize the deviation of the potential from spherical symmetry. The results obtained indicate that the collision number Z (and hence the relaxation time τ) is a monotonically decreasing function of the temperature T for a given J and is a monotonically increasing function of J for a given T. Except for small values of J, Z and τ for a given T are both approximately proportional to exp(aJ), where a is a constant. Detailed numerical results are also obtained and compared with known experimental results. It is shown that the method used here is not valid when the temperature is too high or whenever Z becomes too close to 1.
Excitation Mechanisms in Pulsed CO2 Lasers
Authors: McKnight William B.
Published: February 2004

Experimental studies were carried out on laser systems to investigate the excitation mechanisms of the upper laser level (0001) of carbon dioxide in an electrical discharge, and the parts played by helium and nitrogen in mixed systems. Used as constituent gases were carbon dioxide, carbon dioxide-nitrogen, and carbon dioxide-helium. Pulsed electrical excitation was used with an arrangement for varying the time delay between the discharge pulse and the alignment of a Q-switch mirror. The upper-level-to-ground radiation was observed from the side of the tube to study the behavior of the upper level following the current pulse and when the upper level population is suddenly decreased by the Q-switch. It is concluded that the primary excitation mechanism is electron impact for pure carbon dioxide. Nitrogen is shown to contribute by acting as a storage mechanism for energy prior to resonant transfer, and a value of 1.6×104 sec−1 Torr−1 was obtained for the rate constant of the N2→CO2 vibrational energy transfer process. Helium was found to contribute to increased output primarily through causing a favorable shift in electron temperature.
Equivalent Circuit of a Superconducting Bolometer
Authors: Maul M. K. , Strandberg M. W. P.
Published: February 2004

The theory of superconducting bolometer operation is presented and a small-signal equivalent circuit developed. This circuit contains a portion that represents dynamic thermal effects and a portion resulting from superconductive phenomena. It is shown that the incremental impedance is greater than the dc resistance even for the limit of zero-frequency modulation. A peaking phenomenon is predicted in the incremental impedance versus temperature for this circuit. The characteristic parameters of a tin superconducting bolometer are presented to indicate the usefulness of incremental impedance measurements in determining these parameters.
Resolving Power of the Scanning Electron Microscope
Authors: Simon Rene
Published: February 2004

The geometrical aberrations of the objective lens of a scanning electron microscope limit the electron beam diameter to a few tens of angstroms. However, the resolving power generally obtained is of the order of 200–500 Å. This discrepancy is explained by the noise coming from the secondary electron emission which must be considered as a supplementary aberration.
Interference of 10.6-μ Coherent Radiation in a 5-cm Long Gallium Arsenide Parallelepiped
Authors: Weil Raoul
Published: February 2004

An experiment was performed to show that the coherence of a laser beam can be maintained over a 5-cm path in a GaAs parallelepiped. The temperature coefficient of the refractive index was measured from the temperature dependence of the intensity of radiation transmitted through the sample. The value of this coefficient was found to be (5.64±0.28)×10−5 (°C)−1 for semi-insulating GaAs at room temperature and 10.6-μ wavelength. The absorption coefficient of the material used was measured calorimetrically and found to be 0.012±0.002 cm−1.
Stimulated Brillouin Scattering: Phonon-Frequency Dependence of Steady-State Gain in Dispersive Liquids
Authors: Barocchi F.
Published: February 2004

The phonon-frequency dependence of S.B.S. steady-state gain in dispersive liquids is derived by means of the hydrodynamic theory of absorption and dispersion of elastic waves and by means of the coupled wave equation method of the Tang theory of S.B.S. It turns out that the relaxation properties of the medium strongly affect the steady-state behavior in C6H6 and CCl4.