bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preliminary Investigation of the Two-Photon Photoelectric Effect
Authors: Bloch Peter 
Published: April 2005

The photoelectric current due to the absorption of two photons has been calculated. Its magnitude is dependent upon the square of the incident radiation intensity, whereas, for the photoelectric effect due to the absorption of one photon, the magnitude of the current is linearly dependent upon the intensity.
The magnitude of the photoelectric current due to the absorption of two photons is small. However, under intense radiation, such as is obtainable from a ruby laser, a photoelectric current due to two-photon absorption should be observed.
Effect of Mechanical Stress on p-n Junction Device Characteristics
Authors: Wortman J. J. , Hauser J. R. , Burger R. M. 
Published: April 2005

A theoretical model is developed for the effect of mechanical stress on the electrical characteristics of Ge and Si p-n junction devices. This model is based upon the stress-induced variations in energy band structure and their effect on minority carrier densities. The changes in minority carrier densities are shown to depend upon the type of stress applied, with anisotropic stresses causing larger changes than hydrostatic stresses. From the calculated dependence of minority carrier densities upon stress, the equations are developed for the current—voltage characteristics of diodes and transistors under stress.
Following the general analysis several examples are given in which stress is applied to a small section of a junction in a diode or transistor. The results show that at stress levels greater than 1010 dyn/cm2, the device currents can change by several orders of magnitude when stress levels are changed by a factor of 2. The theory is compared with published experimental data and found to be in good agreement.
Parallel-Pumped Magnon Instabilities in a Two-Sublattice Ferrimagnetic Crystal
Authors: Morgenthaler Frederic R. 
Published: April 2005

Instability thresholds for parallel-pumped magnons in a two-sublattice ferrimagnet are derived by means of a perturbation method. Cases are considered in which the pump frequency is twice a particular magnon frequency or else the sum of two distinct magnon frequencies—one belonging to each branch of the spinwave dispersion relation. The calculations are made within the molecular field approximation for a single crystal of ellipsoidal shape, and include the effects of the volume dipolar energy as well as those due to unequal g factors of the sublattices. The thresholds appropriate to an ``unflopped'' antiferromagnet are also given when the dc magnetic field is applied parallel to the anisotropy axis.
The prospects for experimentally reaching the thresholds, particularly those occurring at submillimeter wavelengths, are evaluated insofar as is possible; in such cases the possibility exists of utilizing a laser for the pump.
Dynamical Dislocation Theory of Crystal Plasticity. I. The Yield Stress
Authors: Gillis Peter P. , Gilman John J. 
Published: April 2005

The derivation is outlined of a general relation connecting the macroscopic plastic strain rate with the configuration and velocity distribution of dislocations in a monocrystal with a single active glide system. This can be simplified for particular cases, the most simple being the case of parallel straight dislocation lines.
A new form of the dynamical theory of plasticity is applied to detailed calculations and compared with previous work. The major modification is the use of the equation v=v* exp[−D/τ] to express the quasi-viscous behavior of dislocation velocities. Here, v=dislocation velocity, v*= terminal velocity, D=characteristic drag stress, and τ=resolved shear stress. Also, a physical relation between dislocation density and plastic strain is derived.
The nonlinear differential equation that results from combining the strain-rate equation with an equation that describes the loading machine is integrated. Approximate analytic solutions, and numerical calculations, are given for the upper yield stress and the initial portion of the stress-strain curve. The effects of initial dislocation density, characteristic drag stress, crosshead speed, machine stiffness, and dislocation multiplication rate on the upper yield stress are calculated. It is shown that the upper yield stress exceeds the cohesive stress at a critical crosshead speed. Delay times are also calculated for rapid load application followed by constancy of the load and compared with experiments for LiF. The effects of strain hardening are considered in a companion paper.
Magnetization Dynamics in BaO·6Fe2O3 Single Crystals using Pulsed Magnetic Fields
Authors: Asti G. , Colombo M. , Giudici M. , Levialdi A. 
Published: April 2005

Dynamic magnetization processes in BaO·6Fe2O3 single crystals in the easy direction are examined under rapidly varying high magnetic fields. We observe that for large values of dHa/dt (the rate of increase of the applied field) the derivative dM/dt of the sample magnetization as function of time shows a sharp structure with a maximum.
A phenomenological interpretation is given, assuming that the magnetization change is only due to 180° Bloch wall displacement. In the initial stage of magnetization the number of domains remains constant and the wall velocity is directly related to the experimental results. This leads to an estimate of the viscous damping coefficient β which is found to depend very strongly on the value of the magnetic field, and is of the order of a few hundred cgs units when H reaches values comparable with the saturation magnetization Ms. Indeed in an effective field of several hundred oersteds, β appears to be several hundred times larger than it is in a field of a few oersteds. For instance, for dHa/dt=4.4 kOe/μsec and H=0.6 kOe, we obtain β=6.102 dyn·sec·cm−3.
Ferromagnetic Resonance Porosity Linewidth Theory in Polycrystalline Insulators
Authors: Sparks M. 
Published: April 2005

Two sources of ferromagnetic resonance linewidth in polycrystalline samples which are absent in single-crystal samples are: (1) the variation in resonant frequencies of the individual crystallites due to the random orientation of the anisotropy energy axes from crystallite to crystallite, and (2) the demagnetization fields arising from the pores between the crystallites. A theory is developed which explains this second contribution to the linewidth in terms of the two-magnon scattering induced by the demagnetization fields of the pores. Agreement of the theoretical results with experiments is good.
The present theory takes into account the dipole narrowing of the linewidth, whereas the previous independent grain theory of Schlömann does not. A second previous theory by Geschwind and Clogston makes an essential mathematical approximation, while the present theory is based on a physical model.
Surface Reactions of Silicon (111) with Aluminum and Indium
Authors: Lander J. J. , Morrison J. 
Published: April 2005

The chemisorption of indium on a clean silicon (111) surface has been investigated with display-type low-energy electron diffraction (LEED) equipment. Eight two-dimensional phases have been observed. They vary with respect to composition (from one-third to one monolayer) and with respect to dependence on thermal history. Transitions observed in the range between room temperature and several hundred °C occur with change in adsorbate concentration and reconstruction of adsorbate atom configuration, but transitions at much higher temperatures are probably accompanied by reconstruction of the adsorbing silicon atom configuration.
It is noted that LEED provides specific means for determining composition. Combination of this information with the observed translational symmetry of a surface structure, the principle of bond saturation, and a choice of adsorbate sites of maximum symmetry makes the number of likely structures small for the simpler phases. Diffraction intensity data have been, for the most part, neglected as a means for structure analysis.
Three cases of second-order order-disorder transitions were observed. It appears that interactions with the substrate cannot be neglected in order-disorder models for at least one of these transitions. A curious phase with pseudotwelvefold rotational symmetry is described. A remarkable reconstruction of a silicon (100) surface into etch pits with (111) surfaces is illustrated with characteristic diffraction patterns.
Czochralski Growth of Low-Dislocation-Density Zinc Tungstate Crystals
Authors: O'Hara S. , McManus G. M. 
Published: April 2005

Zinc tungstate crystals were grown by the Czochralski method and the effect of growth parameters on crystal perfection was studied. Of the (010) and (100) slip planes, Berg-Barrett photographs showed that the (100) slip plane appeared to be the most active during crystal growth. Observations made on crystals grown in a steep temperature gradient showed that strain due to thermal gradients was responsible for the high dislocation densities in these crystals.
Studies on seeding showed that if no widening occurred, then the perfection of the region of the crystal after seeding was much higher than the seed; the changes in temperature employed to widen the crystal gave rise to very high dislocation densities. X-ray examination verified the observations made by chemical etching. Crystals grown under nearly isothermal temperature conditions provided material with dislocation densities between 0 and 500/cm2. These crystals propagated with facets at the solid-liquid interface which gave rise to impurity distributions similar to those observed in semiconductor crystals. The conditions for growing low-dislocation-density Czochralski crystals of zinc tungstate are similar to those for growing low-dislocation-density semiconductor crystals.
Vacuum Electrical Breakdown between Plane-Parallel Copper Electrodes
Authors: Davies D. Kenneth , Biondi Manfred A. 
Published: April 2005

Measurements have been made of prebreakdown currents between thoroughly outgassed plane-parallel copper electrodes in ultrahigh vacuum, for electrode separations in the range 0.03 cm to 0.2 cm. These currents are found to be in good agreement with the Fowler-Nordheim theory of field emission from the pure metal surface. From combined measurements of prebreakdown current and breakdown voltage at different electrode separations it is deduced that the cathode microscopic field at breakdown is constant and of magnitude (6±1)×107 V/cm.
Spectroscopic measurements of both resonance line absorption and line fluorescence have revealed that the density of neutral copper vapor present in the interelectrode space during the application of electric fields only fractionally (&lt;1%) less than the breakdown field is considerably less than that necessary for volume ionization to occur. For the same experimental conditions, infrared radiation observations have revealed no hot spots on the anode surface.
From the measurements it is concluded that mechanisms involving the amplification of field-emission current in electrode vapor produced by steady evaporation from either the anode or the cathode do not explain the electrical breakdown of vacuum between extended copper surfaces. Further, the production of electrode vapor by the detachment of heated anode material under the influence of the force of the applied electric field is unlikely.
Guardring Probes in Hot-Cathode Hg-Vapor Discharges
Authors: Medicus G. 
Published: April 2005

The probe curves J(V)=Je(V)+Ji(V) for planar guardring probes (GP) are found to approximate ``ideal plane probe'' (IPP) behavior only in Je≈const.≈Je0 [=zero-field electron (e-) current] for e-attraction; for ion (i-) attraction Ji≈const.≳5Ji0, in columnless Hg-vapor discharges with hot cathode. The sharp knee of the IPP is prevented mainly by perturbations of the plasma by the large G whose radius rG≫ Debye length, and rG≫rP. The perturbations are proportional to the surface area of G+P.
The planar GP reacts strongly to a weak fast group of electrons of perpendicular incidence, while small spherical probes (SP) react only weakly.
The probe curves for planar and spherical GP's and for small SP's and their second derivatives (SD) are automatically plotted and discussed. Peculiar distortions of the SD's of the GP's (double hump shape) are found to be caused by the perturbations of the plasma by the GP's.
Nucleation of Solid in an Undercooled Liquid by Cavitation
Authors: Hunt J. D. , Jackson K. A. 
Published: April 2005

Cavitation in an undercooled liquid can nucleate solid. We have demonstrated, by a new experimental technique, that nucleation occurs when a cavity collapses, rather than when it expands. Extremely large pressures, ∼105 atm, are generated by the collapse of a cavity. The change in pressure lowers the freezing temperature of the liquid, and thereby results in nucleation.
It is suggested that nucleation by scratching also takes place through the medium of cavitation.
Magnetohydrodynamic Flows in Closed Regions with Complete Symmetry about an Axis
Authors: Eraslan Arsev H. 
Published: April 2005

A formal perturbational technique was developed to obtain solutions for magnetohydrodynamic flow problems in closed regions with symmetric properties of flow and boundary conditions about an axis. The system of highly nonlinear partial differential equations, governing the problems of this class, was found to reduce to systems of simultaneous linear partial differential equations, thus creating a possibility of obtaining solutions by classical mathematical methods. The technique used was based on a well-known power series type of perturbational expansion in terms of a small parameter, which in the limit was assumed to become the solution of the original system. The general technique was applied to the magnetohydrodynamic flow in a toroid under the influence of a uniform applied magnetic field along the direction of the main axis of the toroid. It was found that the secondary flow caused by the centrifugal body force on the fluid element due to the curvature created induced electromagnetic components and a pressure variation along the radial direction.
The solutions were carried out to include completely the second perturbational equations and the electromagnetic and flow fields were discussed for different values of characteristic parameters appearing in the solutions.
High-Sensitivity Magnetic Resonance by Bolometer Detection
Authors: Schmidt J. , Solomon I. 
Published: April 2005

It is shown that spin magnetic resonance can be observed by a rise in the temperature of the sample, with a sensitivity equal to or better than with the more conventional electromagnetic detection methods.
An experimental demonstration is provided by a crude bolometer made of a thin copper wire with a small sample of DPPH glued in the center. A sensitivity of about 5×1011 spins, for a detector bandwidth of 1 cps has been obtained at room temperature. An important advantage is the absence of a microwave carrier signal, resulting in a very stable baseline and the possibility of using very high microwave power.
A detailed theoretical discussion shows that this method is well adapted for wide electronic lines, high frequency (up to 2-mm wavelength), low temperature, and small size samples. In favorable cases (resonance of conduction electrons in metals or semiconductors) a sensitivity of 106 spins, at liquid-helium temperature, is predicted.
Saturation and Gain of Gas Lasers from Modulation Experiments
Authors: Bolwijn P. T. 
Published: April 2005

It is shown theoretically that an analysis of single mode output power modulation, obtained via excitation density or via resonator Q modulation is a very sensitive method for studying both the unsaturated net gain and the saturation behavior of gas laser transitions. This theoretical description starts from the theory of Lamb.
Experiments with excitation density modulation in a 1.15 μ He–Ne laser are reported. The output power modulation as a function of the detuning of the resonator, which yields information on the saturation behavior, is found to agree partly with the theory if collision effects are taken into account. Deviations from the theory may be due to higher-order saturation terms, which is shown qualitatively by starting from the extended theory of Lamb, derived by Uehara and Shimoda. A detailed quantitative explanation of the observations at higher excitation levels awaits incorporation of collision effects in the higher-order saturation terms. The output power modulation as a function of modulation frequency may give information on the unsaturated net gain. In our case, however, the frequency response is determined by the long metastable lifetimes of He.
Hot Electron Energy Loss in Tunnel Cathode Structures
Authors: Handy Robert M. 
Published: April 2005

A variety of scattering processes occur within the metal—oxide—metal tunnel cathode, with the result that most of the injected electrons fail to escape into vacuum. By considering the over-all behavior it is possible to identify the most important loss mechanisms and where they occur.
Electron emission measurements suggest that the internal hot electron velocity distribution in the exit metal films is isotropic as a result of numerous phonon scattering events. It is also found that the electron attenuation length in the exit metal film is not a strong function of energy over most of the observable range. As a direct consequence one obtains the result that the shape and mean energy of the emitted electron energy distribution are determined principally by the scattering in the oxide layer. Collision ionization is unlikely; hence optical phonon scattering is believed to be the principal oxide energy loss mechanism. If the scattering is random and independent of energy, both the mean energy loss (ΔE) and mean square deviation (δ2) should depend linearly on oxide thickness (x). Within the limits of the available data this is shown to be reasonably correct, and a mean rate of energy loss dE/dx≈0.03 eV/Å is obtained. This corresponds to about one optical phonon emission event for every 4-Å travel measured along the field direction. The consistency of the argument is tested by showing that δ2 also varies linearly with oxide thickness. The minimum ingredients for a model of the hot electron scattering processes are outlined.
Electrical Conductivity in Evaporated Silicon Oxide Films
Authors: Johansen I. T. 
Published: April 2005

Evaporated silicon oxide films can be made with reproducible electrical conductivity when the evaporation rate, the oxygen pressure, the substrate temperature during the evaporation, and the subsequent heat treatment are controlled.
In the high electric field region the conductivity follows a Schottky emission law and it is shown to be bulk limited. The conductivity is also shown to be a function of the degree of oxidation, and a variation in conductivity of a factor of 109 has been accomplished by varying the composition from SiO to SiOx, where x is between 1.5 and 2. At an electric field of 250 V/μ the variation is from 10−7 (Ω·cm)−1 to 10−16 (Ω·cm)−1.
A model for the conduction mechanism is proposed, where the rate-limiting process is assumed to be Schottky emission from small silicon islands into a silica structure in which the silicon islands are imbedded.
Magnetization of Synthetic Filamentary Superconductors. A. The Dependence of Flux Jumping on Temperature and Magnetic Field Sweep Rate
Authors: Watson J. H. P. 
Published: April 2005

Synthetic high-field superconductors have been prepared by impregnating porous glasses of various pore size with indium, using pressures up to 70 000 psi. The magnetic field Hfi at which the first flux jump occurred in the initial magnetization of the sample was measured as a function of temperature T and magnetic field sweep rate dH/dt. Values of dH/dt between 24 and 375 Oe/sec were used. For a given value of dH/dt, Hfi increased initially as T was lowered, reached a maximum, and finally fell with T. For a given T, Hfi was reduced as dH/dt increased.
For large values of dH/dt, Hfi was almost independent of T and dH/dt. Hfi was reproducible to 50 Oe from cycle to cycle except for T &lt;1.5°K, where the behavior became more erratic. After the sample was warmed to room temperature, Hfi was reduced. The samples showed hysteresis in the magnetization. Flux jumping occurred around the hysteresis loop; the values of field at which flux jumps occurred were reproducible from cycle to cycle. The field interval Δ between flux jumps had a temperature dependence similar to Hfi; Δ is slightly reduced for large values of the applied magnetic field. The size of the flux jumps were also reduced for large values of magnetic field. For small values of T, the flux jumping behavior became erratic. Measurements of the critical field and transition temperature have been made using a low-frequency mutual-inductance technique. The critical field, that is the magnetic field for the normal-superconducting transition, for a sample with a 65-Å pore diameter was 25 770 Oe at 2.67°K. At a reduced temperature of 0.6°K, samples with pore diameters of 65, 117, and 250 Å have critical fields of 156, 102, and 39 times the critical field of bulk indium (176 Oe). The transition temperatures for the samples were 4.24°, 4.04°, and 3.61°K, respectively, compared with 3.408°K for bulk indium. The over-all behavior of these samples was similar to inhomogeneous type II superconductors.
Nonlinear Limiting of the Double-Stream Instability
Authors: Mihran Theodore G. 
Published: April 2005

The double-stream instability in finite-diameter beams has been investigated by numerical experiments on a digital computer using the disk electron model. The nonlinear level is found to be a quadratic function of the linear-theory double-stream parameters ωδ/ωq. Computed electron trajectories show electron trapping to be the cause of rf current saturation. A simple analytic trapping theory is given which predicts observed peak nonlinear current levels to within a factor of three.
This investigation suggests that current conversion efficiencies approaching 50% can be achieved by operating near the upper edge of the gain band. On the other hand, nonlinear behavior occurs at perturbation levels of the order of 1% for weak instabilities near the lower edge of the gain band. The time to reach the nonlinear level is surprisingly short in most cases, ranging from 2 to 30 plasma wavelengths, depending on gain and excitation level.
Environmental Factors in the Luminescence and Photoconductivity of Zinc Oxide
Authors: Oster Gerald , Yamamoto Masahide 
Published: April 2005

Oxygen quenches the room-temperature fluorescence of powder zinc oxide but enhances the low-temperature phosphorescence and thermoluminescence. The low-temperature ultraviolet emission (edge emission) is quenched by oxygen. Water in the presence of oxygen is particularly effective and this is ascribed to the production of hydrogen peroxide.
Parallel effects are observed for the photoconductivity but water is less effective due apparently to enhanced contact conductivity.
Flash desorption of oxygen shows a parallel behavior of room-temperature luminescence and photoconductivity.