bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of Stacking Faults and Prismatic Dislocation Loops in Device-Processed Silicon Wafers
Authors: Prussin S.
Published: February 2004

Stacking faults are generated by sequential wet thermal oxidation of damage-free silicon surfaces. The concentration of stacking faults is dependent upon the nature of the back surface, upon the rate of cooling from the first oxidation, and upon whether the thermal oxide is removed between oxidations. A model is presented in which stacking-fault nuclei are generated during cooling from the first oxidation. On the basis of etching behavior, it is suggested that while the defects generated on 〈111〉 wafers are stacking faults, 95% of the defects for 〈100〉 wafers are prismatic dislocation loops. A model is presented for the creation of stacking faults on thermally oxidized mechanically damaged surfaces based on the effect of surface tensile stress in stabilizing dislocation loops generated at elevated temperatures.
Microwave Absorption in Erbium at 24 and 100 GHz
Authors: Hart L.W. , Stanford J.L.
Published: February 2004

Microwave absorption studies in Er single crystals were made at 24 and 100 GHz. Temperatures from 4.2 to 300 K, and magnetic fields up to 20 kOe at 24 GHz, and up to 50 kOe at 100 GHz were used. No spin-wave resonance absorption was observed with a magnetic field along the 〈0001〉, 〈101̄0〉, or 〈112̄0〉 directions in Er at either of our two experimental frequencies, in accord with theory. Several previously reported magnetic transitions were observed: (i) the cone-ferromagnetism-fan-ferromagnetism magnetic transition for Hdc in the hexagonal plane (T<18 K); (ii) the antiferromagnetic-ferromagnetic transition for Hdc in the 〈0001〉 direction (T>18 K); (iii) the antiferromagnetic-paramagnetic transition for Hdc in the 〈0001〉 direction (T≅80 K). Magnetic phase transitions not previously reported for Er were observed for Hdc in the (101̄0) plane for T=7–42 K. Microwave absorption associated with magnetostriction is also observed in Er for an applied field in the hexagonal plane for T=18–51 K.
Control of the Magnetization of Bubble Garnets by Annealing
Authors: Kurtzig A.J. , Dixon M.
Published: February 2004

It is known that the magnetization of Ga- or Al-substituted garnets can be reversibly altered by annealing and quenching. These treatments result in a redistribution of the substituted ions between the tetrahedral and octahedral iron sites. Changes of 4πMs by about 100 G can be achieved in bubble materials such as Eu2Er1Fe4.3Ga0.7O12. In an oxygen ambient, these changes occur in a few minutes at high temperatures such as 1200°C but require many hours at low temperatures such as 700°C. The times required for the low-temperature anneals have been reduced by roughly two orders of magnitude by the use of a ``forming-gas'' ambient. The anneals in this H2–N2 ambient do not result in major changes of the noncubic anisotropies of flux grown or LPE bubble garnets. This indicates that this anisotropy is not associated with the presence of Fe4+ ions which would be reduced to Fe3+ by the anneals. The use of this low-temperature annealing procedure to tailor the magnetization of bubble garnets along with the previously reported high-temperature annealing to control growth-induced noncubic anisotropy can be very useful for bubble device research and development.
Variance Noise Spectra of 1/f Noise
Authors: Purcell W. Ernest
Published: February 2004

Experimental measurements of 1/f noise variance fluctuations show the spectrum to depend on frequency to the −0.75 power over the frequency interval 10−5–1 Hz. The variance noise at 1 Hz is 10−14 V4/Hz in the case of current noise in a semiconductor diode, and 10−18 V4/Hz for current noise in a carbon resistor. The probability amplitude distributions of the variance for two different 1/f noise sources have the same magnitude and skewed shape as those previously reported. That is, the variance exhibits fluctuations as large as 200% and the most probable value is much less than the mean value. For band-limited 1/f noise, the variance noise decreases with increasing averaging time.
High-Frequency Signal Processor for Simulation of Superposed Coherent and Chaotic Radiation
Authors: Lachs Gerard , Koval Richard K.
Published: February 2004

Recently there has been reported a technique for simulating coherent and chaotic radiation utilizing laser beam modulation. The frequency response of that system was severely limited by the use of operational amplifiers. In this paper we describe a method which avoids the use of operational amplifiers and results in a great improvement in the attainable bandwidth of the simulation process.
Hall Coefficient in Long Needles of Anisotropic Conductors
Authors: Boon M. R.
Published: February 2004

An expression is given for the Hall coefficient of an infinitely long needle of anisotropic conducting material in which space-charge effects and ambipolar conductivity have been taken into account.
Determination of Lattice Disorder Profiles in Crystals by Nuclear Backscattering
Authors: Ziegler James F.
Published: February 2004

A detailed analysis is presented for the determination of lattice disorder in crystals by nuclear backscattering. By means of models and numerical integration, calculations are performed to determine, as a function of depth, the energy loss of projectiles in crystals, their critical angle for dechanneling, their nuclear elastic scattering cross section, and the effects of lattice disorder on the specific energy loss of channeled ions. These calculations are more detailed than those previously used. The efficacy of the analysis is tested with experiments at 1500 and 2500 keV, and it is shown that these detailed calculations are necessary to extract accurate lattice disorder profiles. The effects of misalignment of the target during channeling experiments are determined. The error introduced by misalignment can be made small.
Relativistic Electron Beam Propagation in Low-Pressure Gases
Authors: Miller P. A. , Gerardo J. B. , Poukey J. W.
Published: February 2004

Studies of the propagation of pulsed relativistic electron beams through initially un-ionized background gases are reported. At very low pressures, pronounced beam front erosion occurs owing to the slow buildup of radial force neutralization of the beam electrons. Numerical simulation and an approximate analytical model are used to describe this beam-loss process. The results of experiments with two different electron accelerators (ν/γ ∼ 0.05 and 1) are shown to be in good quantitative agreement with the mathematical descriptions over the pressure range of ∼ 1 μ to ∼ 1 Torr in a large variety of gases. Propagation characteristics are found to scale in pressure from gas to gas inversely with the high-energy ionization cross sections of the gases. The study shows that direct ionization alone is sufficient to explain the experimental results. The theoretical calculations indicate that the low-pressure propagation characteristics of the lower ν/γ beam are sensitive indicators of the beam's transverse energy. The calculations also indicate that this is not the case for the higher ν/γ beam.
Voltage Pulse Profile Characteristics with Space Charge of a Loaded Pulsed Ionization Chamber
Authors: Kim S.H. , Ellis W.H.
Published: February 2004

An analytical model describing the voltage pulse profile of a pulsed ionization chamber and its relationship to the electron density in a field drift dominated plasma is formulated. The differential equation derived from the equations of motion and conservation of electron density combined with Poisson's equation for the electric space-charge field in the system is solved analytically for the cylindrical-electrode geometry with an external RC circuit. The numerical analysis for the given initial and boundary conditions yields the anode voltage-signal pulse profiles for the period of electron collection as a function of the initial electron density, the gas pressure, and ion-chamber radii and length. Thus, the theory permits the determination of the electron density from the observed voltage signal.
Measurement of the Conductivity of Metallic Cylinders by Means of an Inductive Method
Authors: Callarotti R.C. , Alfonzo M.
Published: February 2004

The method of measuring conductivities by observing the decay of eddy currents induced in metallic cylinders is analyzed exactly. We consider the case where the primary coil wound around the sample is connected to a circuit that has an arbitrary time constant, and where the sample partially fills the primary coil. Results derived by other authors are shown to be incorrect. The theoretical predictions are checked against experimental results for cylinders of copper, aluminum, and brass. The experiments are done both at room temperature and at the temperature of liquid nitrogen. The experimental results agree with the theory to within ±5%.
Sputter-Deposited CdS Films with High Photoconductivity through Film Thickness
Authors: Fraser D. B. , Melchior H.
Published: February 2004

Photoconductive films of CdS have been sputter deposited by using mixtures of Ar–H2S as the sputtering gas in a diode system. Both rf and dc sputtering yield deposition rates of about 1 μm/h on substrates maintained above 200°C. Dark resistivities in excess of 107 Ω cm have been obtained with decreases of 5 orders occurring in the resistance when illuminated with a tungsten light source of approximately 0.5 W/cm2. As deposited, the CdS films have displayed photoconductive gain and also have much shorter decay times than films which are activated after deposition. Adherence has been excellent on suitably cleaned substrates and films in device structures have tolerated tensile strains in excess of 10−3 without adherence failure. No aging or electrode migration has been observed.
New small-angle x-ray camera with two glass blocks
Authors: Schnabel E. , Hosemann R. , Röde B.
Published: February 2004

The x-ray small-angle camera consists of two glass blocks. One of them is used as a monochromator by total reflection, the other shields the plane of observation from background radiation. In connection with a microfocus x-ray tube, this camera offers high intensity and large resolving power. The primary beam is limited only by the width of the microfocus and by the slit between the glass blocks. A comparison has been made with the intensity scattered by a Lupolen sample recorded by a Kratky camera with a quartz monochromator and by our camera. If both cameras are adjusted to the same resolving power (1000 Å), the parasitic scattering is the same for both cameras and the intensity of the glass camera is 4.2 times larger.
Determination of Burgers vectors in close-packed metals using g·b=2 contrast
Authors: Kestenbach H.-J. , Hren J.J.
Published: February 2004

Dislocation images giving double contrast in the electron microscope for g·b=2 have been reexamined as a possible means for Burgers vector determinations. In fcc foils which have been cut parallel to an active slip plane, the g·b=2 critierion provides a quick positive Burgers vector analysis which can be carried out during observation. The method is also applicable to basal dislocations in hcp. A comparison between calculated two-beam profiles and experimental images in aluminum is discussed and several commonly observed characteristics of g·b=2 contrast are described.
Fixed-bias floating double-probe technique with simple Langmuir-probe characteristics
Authors: Szuszczewicz Edward P.
Published: February 2004

A new floating double-probe method is presented which has advantages over other floated-probe systems heretofore described in the literature. The method utilizes two electrodes, one of constant area and the other with a variable area, and the two-electrode configuration is separated by a fixed bias voltage. The current-voltage characteristics of the new technique, which are generated by varying the area of one electrode, are identical to those of a simple Langmuir probe, thus coupling all the advantages of a floated-probe system with the simple analysis scheme generally applied to the Langmuir probe for the determination of plasma density and temperature.
Photoluminescence of AlxGa1−xAs
Authors: Shah Jagdeep , Miller B.I. , DiGiovanni A.E.
Published: February 2004

We present the results of a detailed study of the photoluminescence spectra of epitaxially grown AlxGa1−xAs for 0.16≤x≤0.58 and for temperatures between 1.6 and 300°K. At helium temperatures, the emission spectrum consists of a narrow band (half-width ∼ 10 meV) and a broad band (half-width ∼ 30 meV) for direct- as well as indirect-gap alloys. From temperature and excitation intensity dependence and from time-resolved spectra, we we have identified the broad band as due to distant donor-acceptor pair recombination. The narrow band is very likely due to free- and bound-exciton recombination. These identifications differ from those suggested by others. At room temperature, the emission spectrum consists of a single peak with a long high-energy tail. This emission is due to the direct band-to-band transition even in the case of indirect band-gap materials with x<0.5. Temperature-dependence data suggest that the temperature coefficient of the direct band gap is a function of x.
Admittance of an MOS device with interface charge inhomogeneities
Authors: Brews J.R.
Published: February 2004

Two small-signal ac equivalent circuits relating the experimental admittance of an entire MOS device to the interface-state admittance are derived from a small-signal analysis of the three-dimensional Poisson equation for the device. One equivalent circuit, the original Nicollian-Goetzberger equivalent circuit, is shown to be valid for a random interface charge distribution, provided the device is operated in depletion where the ac-induced change in surface potential fluctuations is small compared to the fluctuations themselves. The other is shown to be valid for a very smooth quasi-uniform interface charge distribution.
Enhanced diffusion in Si and Ge by light ion implantation
Authors: Minear Roger L. , Nelson Daniel G. , Gibbons James F.
Published: February 2004

This paper presents theoretical and experimental results of investigations of impurity-atom diffusion enhancement in Si and Ge crystals under light ion bombardment. Using existing ion range and displacement mechanism theories, a continuity equation for bombardment-generated defects is written and solved to give an expression for the steady-state excess defect concentration as a function of depth in the crystal. With the aid of existing diffusion theory, this is interpreted as a spatially varying atomic diffusivity which is a function of the bombarding beam parameters, temperature, the atomic species, and an experimentally measurable defect diffusion length. This spatially varying diffusivity, inserted in an appropriate diffusion equation, determines the evolution of the distribution of any impurity species diffusing by a defect-related mechanism. Some numerical solutions of this equation and some analytic solutions of interest are given, and a comparison of theory and experiment is presented. Among the results of this comparison are (i) defect diffusion length measurements of 0.27 μ in p-type Ge, and 0.086 μ in n-type Si, (ii) a measured yield of approximately 25 mobile defects/proton in either Ge or Si, mostly clustered at the end of the proton's track. A simple method is presented for the experimental measurement of the required defect diffusion length. Impurity concentration profiles of the proton-enhanced diffusion of P31 in Ge and B in Si were measured, and experimental checks of several theoretical predictions were carried out. There are some indications of a diffusivity saturation at high beam currents in Si which may result from the generation of immobile defect clusters. Impurity diffusivity enhancement by a factor of greater than 105 was observed in Si. Several physical parameter values of interest are calculated. Transmission electron microscopy measurements were undertaken to observe the effects of the bombardment on crystalline order in Si, and V-I and C-V characteristics of p-n diodes produced using enhanced diffusion of B in Si were examined. The uses of bombardment-enhanced diffusion as a device fabrication tool are discussed, and some unresolved topics are indicated.
Exact frequency-dependent complex admittance of the semiconductor-insulator-semiconductor (SIS) diode including surface states and Shockley-Read-Hall (SRH) impurity effects
Authors: Shewchun J. , Temple V. , Clarke R.
Published: February 2004

The transmission-line model of the semiconductor-insulator-semiconductor (SIS) diode is solved exactly to give the frequency-dependent complex admittance. Surface-state effects, fixed oxide-charge effects, and Shockley-Read-Hall (SRH) impurity effects are shown in typical SIS systems. A number of different types of capacitance-voltage and conductance-voltage curves are generated depending on the physical parameters associated with the two semiconductors. Since some of the capacitance and conductance responses are quite different from the typical metal-insulator-semiconductor (MIS) responses, the SIS diode could have many useful applications. For example, a predicted bell-shaped high-frequency capacitance-voltage response is of obvious interest in the area of varactor diodes.
Role of defects in determining the electrical properties of CdS thin films. II. Stacking faults
Authors: Kazmerski L.L. , Berry W.B. , Allen C.W.
Published: February 2004

A correlation of the electrical properties of slowly deposited cadmium sulphide thin films with electronic scattering from stacking faults is presented. Electron diffraction studies indicate that the stacking-fault density depends critically on substrate temperature. ``Cross-plane'' resistivity—film temperature data indicate the stacking-fault barrier potential to be 0.035 eV for these films. Hall investigations were also performed on misoriented-crystallite films and, in this case, stacking faults have a significant effect on the ``in-plane'' mobility. An empirical model, which includes the effects of stacking faults along with those of grain-boundary and surface scattering, has been developed to demonstrate these combined scattering effects.
Zn-diffused laser junctions in InxGa1−xAs and InAsxP1−x grown from In solution at constant temperature
Authors: Macksey H.M. , Campbell J.C. , Zack G.W. , Holonyak N.
Published: February 2004

The growth of InxGa1−xAs and InAsxP1−x at constant temperature from In solution by a modified Bridgman method is discussed. Laser diodes are fabricated by Zn diffusion into the n-type substrates, and threshold currents as low as 2000 A/cm2 (77 °K) are found for InxGa1−xAs (x = 0.16) diodes. Pulsed laser operation has been achieved up to 230 °K. The variation in mode spacing across the spectrum is discussed and comparison is made with photoexcited lasers, on the same substrate material, which do not exhibit a large change in mode spacing and n - λdn/dλ. Observations of a large tunneling zero-bias anomaly in the conductance-voltage characteristic show that there are defects in the junction barrier region.
Pulsed field losses in metal-filled superconducting multifilamentary braids
Authors: McInturff A.D. , Dahl P.F. , Sampson W.B.
Published: February 2004

This paper summarizes work on the application of metallic fillers to insulate and bond individual multifilamentary wires into a fully transposed conductor. As has been reported in earlier papers, conductors of this type have performed excellently in low-frequency pulsed magnets, but become ``coupled'' at relatively low values of Ḃ, leading to high pulsed losses. In this paper data are presented on metallic and intermetallic insulated braids showing excellent performance and exhibiting losses comparable to those of organically insulated braid for rise times less than 10 kG/sec. These conductors are also able to achieve 90% of short sample critical current at Ḃ ≥ 200 kG/sec, although their losses are significantly higher at these high rates of field change.
Attenuation of x rays in interstellar space
Authors: Schocken Klaus
Published: February 2004

Using the cosmic composition of elements as given by Aller and utilized by Bell and Kingston, and the total photon interaction cross sections per atom of the elements as computed by Hubbell and collaborators, the x-ray interaction cross sections are computed for three cosmic mixtures over the range 1 keV (12.4 Å) to 1.5 MeV (0.008 Å). The results are compared with a formula given by Heiles. Approximate agreement exists between 10 to 20 keV.
Anisotropic hot-electron microwave conductivity of n-InSb at 84 K and 134 GHz
Authors: Löschner H.
Published: February 2004

High-precision measurements of the anisotropic complex small-signal microwave conductivity of hot electrons in n-InSb at 84 K and 134 GHz have been performed. An unexpected ``plateau'' in the experimental curve of the real part of the ac conductivity parallel to the dc electric field vs the field strength is found between 50 and 100 V/cm.
Reply to ``Comment on `Transformation twinning of B2(CsCl)-type structure based on an Inhomogeneous shear model' ''
Authors: Wang Frederick E.
Published: February 2004

Wasilewski's criticisms may originate in part in semantic problems.
Surface energy for brittle fracture in metals from phonon frequencies
Authors: Caglioti G. , Rizzi G. , Bilello J.C.
Published: February 2004

The calculations of Caglioti, Rizzi, and Bilello are extended to include second and third neighbors.
Measurements of the acoustic gain parameters in n-InSb
Authors: Gorelik J. , Fisher B. , Pratt B. , Zinman M. , Many A.
Published: February 2004

The drift-velocity dependence of the acoustic gain in n-InSb at 77°K is derived from measurements of the rate of growth of the acoustoelectric field in the sample under constant-current pulses of different amplitudes. The amplified acoustic flux monitored by the acoustoelectric field originates from the thermal-equilibrium phonon distribution in the crystal. Results obtained for samples of different carrier concentrations are compared with the predictions of microscopic theories applicable to InSb (ql> 1). For low drift velocities the agreement between theory and experiment is very good. For drift velocities approaching the thermal velocity, on the other hand, the experimental data deviate markedly from the theoretical predictions. In this range appreciable carrier heating takes place, an effect that has not been adequately taken into account in the existing theories. The data also provide estimates for the nonelectronic (lattice) attenuation factor and for the initial thermal flux density. The values obtained for the latter are within an order of magnitude of those calculated on the basis of the thermal-equilibrium Debye spectrum.
Impurity sensitive etching in sodium fluoride crystals
Authors: Davisson J. W. , von Batchelder F.
Published: February 2004

The recently introduced acetic acid etchant is shown to be a useful tool for investigating the impurity content of individual dislocations and grain walls in NaF crystals, since the degree of their contamination can be judged by visual inspection. In pure NaF crystals individual dislocations do not contain sufficient impurity to be sensed by the etchant, but grain walls can show large variations in their impurity content which may be regulated by the character of their dislocations. To a remarkable extent the contamination in each wall is constant, not changing sensibly with change of wall direction, but showing abrupt changes upon passing through intersections. Impure NaF crystals show impurity-saturated etching at all dislocations. This suggests that the core binding states of edge and screw dislocations are equivalent. The negative etching action of this etchant is shown to be due to the presence of polyvalent metallic impurities such as calcium.
Thermally induced surface and bulk electrical effects in semiconducting Ge15 Te80As5 glasses
Authors: Johnson Ralph T. , Quinn Rod K.
Published: February 2004

Electrical, thermal, and structural studies of bulk Ge15Te80As5 glasses show that formation of thermally induced conductive surface layers is associated with surface-nucleated crystalline Te. Both crystallization and the associated electrically conductive regions extend into the bulk material with annealing. A metalliclike conductivity behavior may result from crystalline GeTe, which is a second-stage crystallization product.
Single-crystal thermoluminescent lithium fluoride for dosimetry prepared by an edge-defined film-fed growth (EFG) technique
Authors: Cocks F. H. , Pollock J. T. A.
Published: February 2004

A novel edge-defined film-fed growth technique (EFG) has been used to prepare doped LiF single crystals. The high-temperature thermoluminescent glow peaks of these crystals are found to be greater than those of the TLD-100 powder used as starting material. The thermal resolution of all the glow peaks of single-crystalline specimens is also greater than that of the powder.
Experimental investigation of the transient formation of a microwave-generated ionized sheath in air
Authors: El-Khamy S. E. , McIntosh R. E.
Published: February 2004

Microwave and photometric techniques are used to study the temporal and spatial behavior of a transient microwave-generated air plasma sheath in a coaxial transmission line. In particular, breakdown times, stabilization times, and thickness of the ionized sheath are investigated at different pressures and generating signal amplitudes.
Nonanomalous energy distribution of electrons emitted by a thermionic cathode
Authors: Franzen W. , Gupta R. , Porter J. H. , Wenstrup R. S.
Published: February 2004

An electron gun with an effective concentric-spheres electrode geometry has been used to investigate the energy distribution of electrons emitted by a space-charge-limited dispenser cathode at four different temperatures. A spherical monochromator is used to select different portions of the initial energy spectrum. Electrons so selected are scattered through 90° by an atomic beam of helium. The initial electron energy is inferred from the accelerating potential needed to attain the 19.3-eV helium resonance energy. Energy spectra so obtained are compared with computed spectra based on an initially half-Maxwellian distribution filtered by the space charge in front of the cathode. The form of this space charge is known from an exact solution of Poisson's equation in the spherical geometry of the gun. The only adjustable parameter in the computation is Richardson's constant which is given a value of A = 7 × 104 A/m2 (°K)2. The close agreement between the observed and computed energy spectra is in disagreement with observations of many other investigators. Reasons for this disagreement are suggested.
Electrical resistivity and Seebeck coefficients of CoSb and NiSb
Authors: Penn John , Miller Edward
Published: February 2004

Electrical resistivity and Seebeck coefficients were determined for NiSb and CoSb as a function of composition. The results indicate that clustering of defects occurs for large deviations from the stoichiometric composition in CoSb, and that these compounds cannot be classified as electron compounds.
Diode-pumped solid-state lasers
Authors: Barnes N. P.
Published: February 2004

Diode pumping of solid-state lasers is analyzed. The analysis differs from more conventional analysis by the inclusion of a detailed calculation of the pumping rate and by the use of a Gaussian transverse intensity distribution as well as a circular approximation. Explicit expressions are obtained for the slope efficiency and the threshold. The temperature dependence of both parameters is investigated. Experimental results are obtained with a Nd : YAG diode-pumped laser. These results are compared with the predictions of the analysis. The experimental results yielded a laser power output of 52 mW in TEM00 modes at 269°K.
Photoconductive gain greater than unity in CdSe films with Schottky barriers at the contacts
Authors: Mehta R. R. , Sharma B. S.
Published: February 2004

Photoconductive gains greater than unity can be obtained by illuminating a homogeneous photoconductor having blocking contacts with band gap radiation. A model is presented, which conceives such a possibility. Au contacts to CdSe form a Schottky barrier at the interface. Upon illumination the photogenerated holes are trapped in the Schottky barrier, shrinking the barrier and allowing injection of electrons in the CdSe. This gives rise to the possibility of gain greater than unity. Experimental evidence supporting the model is presented. Photoconductive gains as large as 300 have been measured when these films were illuminated with a photon flux of 2×1015 photons/cm2/sec.
Doping of silver bromide by ion implantation
Authors: Helling J. O. , Keevert J. E. , Kelly T. M. , Merrigan J. A.
Published: February 2004

The effects of implanting silver, phosphorus, and cadmium ions in silver bromide microcrystals were ascertained using the intrinsic photosensitivity of these devices. Defects caused by implantation controlled the photocarrier trapping. After removal of these defects by annealing, both cadmium and phosphorus were the controlling species and increased the internal photosensitivity of the microcrystals.
Reactions of silicon with surfaces of close-packed metals. II. Silicon on nickel
Authors: Jona F.
Published: February 2004

The reactions of silicon with Ni {001}, Ni {110}, and Ni {111} surfaces have been studied by means of low-energy electron diffraction. On all three surfaces, at room temperature the silicon atoms are distributed at random and resulting films are amorphous. At temperatures of the order of 300∼400 °C ordered structures are formed: a c(2×1) structure on Ni {001} and a c(8×2) structure on Ni {110}. On Ni {111}, the √3 structure that was predicted in a preceding paper is found to occur, but increasing silicon concentration on the surface leads to a 2×2 and then a 2×12 structure, defined in the text, the latter displaying only twofold symmetry. In all cases, the surface concentration of silicon is reduced, at higher temperatures, by the rapid diffusion of the silicon atoms into bulk nickel.
Dependence of the transport properties of n-type Ge at 20 K on impurity concentration
Authors: de Biasi Ronaldo S.
Published: February 2004

Transport properties of n-type germanium at 20 K have been calculated in the donor impurity range 1011–1014 cm−3, for a constant electric field in the [111] direction. The mathematical treatment is based on Boltzmann's equation, taking account of acoustic phonon scattering and impurity scattering between the different valleys. The electron distribution function in each valley is approximated by a drifted Maxwellian. It is found that the threshold field for the onset of negative differential conductivity increases with increasing impurity concentration and the peak-to-valley ratio decreases significantly. The negative differential conductivity region ceases to exist for impurity concentrations larger than 4.5×1013 cm−3.
Magnetization distributions, magnetostatic energy barriers, and drive fields for Permalloy bars
Authors: George P. K. , Archer J. L.
Published: February 2004

In an effort to understand more completely the operation of field-access bubble-domain propagation circuits, the analysis of Copeland for Permalloy thin-film elements is generalized to include the effects of a uniform in-plane drive field and applied to the problem of bubble motion along a simple bar. Results are presented for the magnetization distributions in a bar for various bubble positions and drive field situations along with the corresponding magnetostatic energy wells. The structural and spacing (Permalloy to garnet) dependence of the drive fields and the choice of garnet thickness are examined with an eye toward device optimization.
Thermally and magnetically stable flux flow state in type-II superconductor
Authors: Onishi Toshitada , Miura Kenji
Published: February 2004

Behaviors of flux flow states under thermal or magnetic disturbances have been studied using a Pb–In–Sn superconductor with the property ∂JC/∂T>0. Existence of the previously reported stable flux flow states has been confirmed clearly. When heating the sample the flux flow voltages decrease stably to zero (recovery of superconducting state). Also, flux flow states are found to be stable against magnetic field sweeping. They further indicate that magnetization will increase with increasing field sweep rates.
Temperature dependence of dislocation energy in alumina crystals
Authors: Chou Y. T. , Tsao K. Y.
Published: February 2004

The elastic energy of straight dislocations in and normal to the basal plane of an alumina crystal was studied as a function of temperature in the range 0–900°K. It was found that between 400 and 900°K the temperature dependence of dislocation energy is nearly linear. Approximate formulas for the linear relationships are presented.
Observations on the filamentary growth of graphite
Authors: Wawner Franklin E. , DeBolt Harold E.
Published: February 2004

A study has been conducted to show the dependency of the growth of graphite fibers on a metallic impurity. It was seen that heating carbon monofilament by striking a dc arc utilizing a tungsten electrode in a gaseous environment of Ar, N2, and HCl led to the filamentary growth of graphite. If the tungsten electrode was replaced by a carbon one, fiber growth was not observed. Repeating these experiments after removing HCl from the gaseous environment showed no fiber growth in either case. It is proposed that the growth of the fibers can be attributed to HCl reacting with the tungsten to form WCl6 which is reduced to tungsten on the carbon substrate serving as an impurity site.
Dispersion relations of bounded inhomogeneous anisotropic plasmas
Authors: de Santis Pietro , Franceschetti Giorgio
Published: February 2004

The dispersion characteristics of electrostatic modes in a longitudinally magnetized parallel-plate waveguide completely filled with a transversely inhomogeneous cold collisionless electron plasma, obtained by Poularikas and Perl, are reexamined in the light of some previously published results.
GaAs–Gax Al1−x As heterostructure lasers with amphoterically silicon-doped active regions
Authors: Doerbeck F. H. , Blacknall D. M. , Carroll R. L.
Published: February 2004

Amphoterically silicon-doped GaAs heterostructure lasers were fabricated using solution epitaxial growth of GaAs and GaAlAs in a sliding boat system. LOC lasers and double-heterostructure lasers were obtained. The emission wavelength was between 9040 and 9250 Å. Threshold current densities were typically 12–4 kA cm−2, with 2.4 kA cm−2 as the lowest value observed with a double heterostructure.
Lamb-wave delay lines with interdigital electrodes
Authors: Toda Kohji
Published: February 2004

Propagation characteristics and the equivalent circuit model of delay lines using Lamb waves excited by interdigital transducers on unpolarized PZT ceramic plates have been studied. Dispersive characteristics of phase velocities of Lamb waves excited by the interdigital transducers are in good agreement with the numerical solution from the dispersive equation of phase velocities developed by Worlton. When the product of frequency times plate thickness is below 1.3×106 Hz mm, the zeroth symmetric Lamb wave is strongly excited. The Lamb waves are excited most effectively when the half-period of interdigital electrode is equal to the wavelength of the Lamb wave. Also, the values of the attenuation coefficient and the reflection coefficient from the edge of the specimen are given. It is shown that the generation of symmetrical-mode Lamb waves by our transducer is equivalently represented by a thickness mode transducer of half-wavelength inserted perpendicular to the plate.
Mathematical analysis of factors influencing the skin thickness of asymmetric reverse osmosis membranes
Authors: Anderson J. E. , Ullman Robert
Published: February 2004

The formation of the dense surface skin of asymmetric reverse osmosis membranes is analyzed in terms of a composite process involving solvent diffusion and polymer relaxation. The analysis indicates that films with minimum skin thickness result from (i) rapid polymer relaxation; (ii) strongly concentration-dependent solvent diffusion coefficients. The numerical results are discussed in terms of experimental variables. It indicates great difficulty in producing asymmetric films with extremely thin surface skins. The implications of this finding are discussed. Experimental NMR self-diffusion studies of acetone in cellulose acetate are reported.
Effect of impingement of rods on the Avrami equation
Authors: Price Fraser P. , Thornton John M.
Published: February 2004

Phase transformations involving growth and impingement of randomly centered and oriented rods, fixed in number and cross section, have been studied using computer modeling techniques. As expected, the Avrami equation does not adequately describe the process. Deviations of up to 15% from the Avrami predictions are frequently encountered. The biggest deviations are in the Avrami constant K, which contains the rate constants, rather than in the time exponent n, which reflects growth and nucleation modes.
Luminescence characteristics of epitaxially grown cubic ZnS
Authors: Ghosh Amal K. , Addiss R. R.
Published: February 2004

The luminescence properties of cubic ZnS grown epitaxially on GaAs by both vapor-transport and vacuum-evaporation techniques were investigated. Emission spectra, excitation spectra, temperature dependence of emission, and optical bleaching of thermoluminescence were measured. The results indicate that the dominant defect in this material is the self-activated (SA) center. The strong blue emission exhibited the known behavior of the emission from SA centers, namely, the shift of the emission peak to shorter wavelengths with increasing temperature and the 0.9-μm peak in the optical bleaching of this emission in thermoluminescence. However, the excitation specturm for this emission and the absence of pronounced thermal quenching are different from previously reported results. Only the higher-energy peak at 330 nm of the two excitation peaks previously reported is observed. Evidence is presented which suggests that the difference is due to differences in crystalline perfection. The present material exhibits a higher degree of crystalline perfection than that previously studied. A weak red emission observed around 600 nm is attributed to iron. Its excitation spectrum and bleaching spectrum in thermoluminescence are consistent with this interpretation.
Grain-boundary self-diffusion in Au by Ar sputtering technique
Authors: Gupta D.
Published: February 2004

Grain-boundary self-diffusion measurements over the temperature range 367–444°C have been made in polycrystalline Au using Au195 radioactive tracer and rf backsputtering technique for serial sectioning. The diffusion parameters are Qb = 0.88 eV and δDb0 = 3.1 × 10−10 cm3/sec which are discussed in relation to the possible vacancy diffusion mechanism. Both the parameters may be qualitatively identified with the motional properties of vacancies. The activation energy for grain-boundary self-diffusion in Au is in close agreement with that for low-temperature electromigration in thin Au films reported in the literature.
Multiphonon absorption by ionic crystals: Temperature dependence
Authors: Rosenstock Herbert B.
Published: February 2004

We consider the part of the temperature dependence of the multiphonon absorption in the ir that is not dependent on the mechanism from which the absorption arises. Several phonons must act together to provide absorption at high frequencies; the availability of each phonon alone provides a temperature dependence that is the same whatever the mechanism for coupling them together may be. These availability factors must then be summed over the existing frequency distribution in a particular crystal, subject to the condition that the sum of frequencies equal that of the incoming light. Numerical results are given for KC1 and NaC1 at 10.6 μ. We find the temperature dependence to be different depending on whether the incoming photon couples to a lattice or an impurity phonon of higher frequency. This suggests experiments that could reveal whether the residual absorption found in nominally ``pure'' crystals is in fact intrinsic or due to unknown impurities.
Transfer of energy to light ions from the ion-acoustic-wave instability developed in a heavy-ion plasma
Authors: Anastassiades A. J. , Karatzas N. Th.
Published: February 2004

The energy transfer to light ions interacting with the ion-acoustic-wave instability developed in a heavy component plasma is studied. It is shown that the temperature of the light-ion component increases strongly with the rate of energy transfer per particle.
Mechanisms of electrical discharges in high vacuum at voltages up to 400 000 V
Authors: Prichard Benjamin A.
Published: February 2004

High-voltage electrical discharge mechanisms were studied in a stainless-steel and alumina-ceramic vacuum system evacuated by an orbitron getter-ion pump. The high-voltage terminal was charged by a pelletron generator, and its voltage was measured by a generating voltmeter. A moveable ground plate was used to vary gap length. For gaps larger than 2 in., the voltage was limited by regularly spaced discharge pulses and conditioned to a maximum of 230 kV independent of field strength. Mass-spectrometer studies were made of ions emitted from the terminal during discharges with positive and negative terminal polarities. Ions ejected from the terminal by a beam of Na+ ions were also examined. Results of these and other studies led to the conclusion that the regularly spaced discharge pulses were the result of an ion-exchange multiplication process. Measurements demonstrate that gas hinders this mechanism by stripping electrons from negative ions. Electrons were found to be only by-products in the multiplication process. In contrast to the whisker mechanism, the ion-exchange multiplication was found to depend only on total voltage and not on electric field strength. Experiments with gaps smaller than 2 in. supported the conclusions that the voltage is limited by field emitting whiskers and the presence of gas damages these whiskers.
Effective blackbody temperature of high-current gas-filled flashlamps
Authors: Gusinow M. A.
Published: February 2004

Under the assumption that a high-current gas-filled flashlamp is a fully ionized plasma and radiates as a blackbody, an expression for the effective blackbody temperature of the flashlamp is derived. This calculation is compared with the experimental results from several sources.
Redistribution of charged particles and self-distortion of high-amplitude electromagnetic waves in a plasma
Authors: Prasad S. , Tripathi V. K.
Published: February 2004

A steady-state situation of plasma-electromagnetic wave interaction has been studied in detail when the wave feeds energy to the electrons and they loose it to the neutral particles in collisions. For finite width of the wavefront, the electronic concentration is redistributed and owing to strong Coulomb interaction, ions are also dragged to the regions where energy is fed at a slower rate. The perturbations in electron density give rise to focusing of waves and severe over-modulation of an amplitude-modulated wave occurs.
Polycrystalline ceramic lasers
Authors: Greskovich C. , Chernoch J. P.
Published: February 2004

Polycrystalline ceramic laser rods, composed of a cubic solid solution of 89 mole% Y2O3, 10% ThO2, and 1% Nd2O3, were made by a conventional ceramic sintering approach. Rods of this material, called Nd-doped Yttralox (NDY) ceramic, have lasing thresholds between 16 and 30 J when employing a 95% output mirror reflectivity and a pump pulse of 150 μsec; the lasing slope efficiencies are approximately 0.1%. As a reference for comparison, a commercially available Nd-doped glass laser exhibits a threshold energy of 9 J and a lasing slope efficiency of 0.44% under the same testing conditions. Active attenuation coefficients for the NDY rods examined were between 5 and 7% cm−1. The lower values are within a factor of 6 of that found for laser glass. The major contribution to the attenuation coefficients for NDY laser rods, as currently produced, is a result of unidentified submicroscopic scattering centers. Direct observation of the pore size distributions in these highly transparent sintered ceramics reveals that (i) the volume fraction of pores is of the order of 1 ppm, (ii) there is a peak in the pore size distribution between 1 and 2 μm, (iii) pore growth to this size most likely occurs during the sintering process, and (iv) pores are not the major scattering centers responsible for high scattering losses.
Niobium thin-film Josephson junctions using a semiconductor barrier
Authors: Keller W. H. , Nordman J. E.
Published: February 2004

Thin-film superconductive tunnel junctions were fabricated using rf-sputtered germanium or indium antimonide films as barrier layers on photoetched rf-sputtered niobium patterns with evaporated lead counter electrodes. Tunneling characteristics similar in quality and shape to those of niobium-oxide-lead junctions were obtained, large Josephson currents occurring in the higher-conductance devices. Stability of the characteristics with time was also found to be comparable to oxide junctions. Reducing the thickness of the semiconductor film appears to produce an increase in the effective tunneling barrier energy, and a model is proposed to explain this. This behavior is of importance when considering the relative merits of semiconductor barriers compared to oxide barriers for Josephson junctions.
Comment on ``Hot carriers in Si and Ge radiation detectors''
Authors: Antončík E.
Published: February 2004

Drummond and Moll have recently suggested a new method for calculating the radiation ionization energy ε and the Fano factor F in Si and Ge detectors. It is argued here that this procedure is not general enough to give reliable results. A general formulation of this problem is briefly discussed.
Elastic energy flow in crystals of general symmetry
Authors: Neighbours John R.
Published: February 2004

A method of calculating the angle between the propagation direction and the direction of energy flow of a plane wave is developed. The method is suitable for any crystal symmetry, and the necessary transformations are given in the Appendix. Calculations are carried out for calcium sulfate which is an orthorhombic crystal that shows the full number of pure vibration directions.
Electron beam and dense plasma focus interaction heating experiments
Authors: Mather Joseph W. , Carpenter James P. , Freiwald David A. , Ware Kenneth D. , Williams Arthur H.
Published: February 2004

Several attempts to transiently heat a dense plasma focus discharge using intense electron beams at voltages of 280 to 300 keV and 3.6 MeV are discussed. The results, although requiring further confirmation, suggest a positive interaction and indicate that low ν/γ beams are required for injection into the plasma focus column.
Dynamic response of pulse-heated porous copper by the double interferometer technique
Authors: Perry F. C.
Published: February 2004

A new interferometer concept has been successfully applied to the measurement of dynamic response associated with thermally induced stress waves. The technique involves the use of two Michelson interferometers to simultaneously measure front and back surface displacements of a specimen exposed to an intense electron pulse. Application of the method to porous copper (86 and 70% of the theoretical density) has resulted in dynamic data over an energy range spanning elastic and plastic behavior of the porous material. These data were compared to the predictions based on a hydrodynamic model for stress wave generation and propagation in a porous medium. The results indicated semiquantitative agreement, complete agreement not being possible using a single set of porous material model parameters. The study demonstrated that some important differences exist in porous material response to constant volume heating and planar plate impact loading. Finally, the results indicated that the double interferometer technique is uniquely suited to simultaneously studying thermally generated stress and attenuation in complex materials.