bluuebunny/crossref_metadata_2025 huggingface dataset:
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.
Dynamical Dislocation Theory of Crystal Plasticity. II. Easy Glide and Strain Hardening
Authors: Gillis Peter P. , Gilman John J.
Published: April 2005

Mathematical descriptions of the stress-strain-time behavior of plastic crystals are developed using a statistical approach to dislocation dynamics. First, the ``easy-glide'' portions of stress-strain curves are described in terms of glide band propagation. Then, three models of strain hardening are developed and used in numerical calculations of stress-strain curves. In one model, the mean density of mobile dislocations first increases and then decreases with increasing plastic strain. In another, strain introduces internal stress fluctuations which decrease the mean velocities of mobile dislocations. In the third (and preferred) model, strain increases the mean viscous drag acting on moving dislocations, thereby decreasing the mean velocity at a given stress. The numerically calculated curves show that the dynamical models provide realistic descriptions.
Temporal Growth of Suppressed Corona Streamers in Atmospheric Air
Authors: Dawson G. A.
Published: April 2005

Suppressed positive streamers are produced in a short (3 cm) positive-point-to-plane gap in air by the discharge of the small anode capacitance. A study is made of the growth of current at the cathode plane, and the growth of luminosity at various positions in the gap with one or two photomultipliers and with a camera. The results are compared with some photographs obtained with an image converter. From a comparison of current and photomultiplier output it is shown that sharp peaks in the current are the result of the arrival of streamer tips at the cathode. The method has allowed measurement of streamer tip velocity at various positions in the gap. It has not proved possible to detect directly any return strokes produced when the streamers reach the cathode, but the subsequent growth of the discharge indicates that they are active in much the same way as previously shown for long (25 cm) gaps.
Anisotropic Spin-Wave Propagation in Ferrites
Authors: Sethares James C. , Purnhagen Tom G.
Published: April 2005

A directional dependence of the propagation of nonlinearly excited spin waves in anisotropic ferrites has been observed by measuring the radiation from the edge of a (110) YIG disk. The disk was excited by a parallel pump field normal to its plane and rotated through 360 deg. Measurements were made at dc field intervals of 10 Oe from 1800 to 2800 Oe (the experimental minimum of the butterfly curve). Radiation was observed at half the parallel pump frequency over a dc field range of 248 Oe (from 2294 to 2542 Oe). The direction for maximum radiation was along a [1̄10] axis in the plane of the disk, and a strong directional dependence was observed when the pump field was less than 4 dB above threshold. The ratio of maximum to minimum output as the disk was rotated was at least 10 dB. The directional dependence was found to be essentially independent of pump field strength up to 4 dB above threshold. Any further increase in pump field strength reduced the amount of radiation, and for pump field strengths higher than 8 dB above threshold no radiation was observed.
Anomalous Thermal Conductivity of the Rare Earth Metals—Gadolinium, Terbium, and Dysprosium
Authors: Gallo C. F.
Published: April 2005

Recent measurements of the thermal (K) and electrical (σ) conductivities of the rare earth metals (gadolinium, terbium, and dysprosium), indicate that the ratio Kσ−1 T−1 is considerably larger than the value predicted by the Wiedemann-Franz law. At low temperatures, a significant lattice contribution to the thermal conductivity (and possibly some magnon contribution) seems to account for the experimental results. At higher temperatures, the bipolar mechanism of heat transport is probably responsible for the observed behavior. If this interpretation is correct, other transport properties should exhibit anomalous behavior. In particular, the Nernst and Ettingshausen effects should be anomalously large and therefore these rare earth metals may be useful in devices for refrigeration or electrical power generation.
Piezoelectric Response of Z-Cut Tourmaline to Shocks of up to 21 Kilobars
Authors: Hearst J. R. , Irani G. B. , Geesaman L. B.
Published: April 2005

The piezoelectric sensitivity of Z-cut tourmaline has been measured for plane shocks with amplitudes up to 21 kbar. There is no evidence of hysteresis or significant effects due to mounting. Two straight lines provide the best fit to the data.
Short-Duration Light Pulse during Electrical Breakdown in Gases
Authors: Pollack S. A.
Published: April 2005

The paper describes and discusses observations of the emission of a light pulse by a Hg-Ar binary system during electrical breakdown, when an impulse potential in the form of a rectified square wave is applied to the electrodes of a flash lamp. By a proper choice of various parameters, the light pulse can be made intense and narrow, i.e., its width can be extended into the nanosecond region. The experimental procedures and results of different measurements are described, illustrated, and substantiated by photographs and charts; and the conjecture about the mechanism responsible for the pulse formation is discussed. Multiple-watt light pulses of 40–60 nsec were produced in a 2-cm gap with point electrodes at V=3 kV, pHg=10−2 Torr, and pAr=70 Torr. The application of the light pulse as an intense, short-duration light source for measuring submicrosecond fluorescence lifetimes is discussed. A simple method of determining lifetimes using electrical analog circuits is described.
Electron Microscope Observation of High-Energy-Neutron-Irradiated Germanium
Authors: Bertolotti M. , Papa T. , Sette D. , Vitali G.
Published: April 2005

The damage regions predicted by Gossick in n-type germanium irradiated with fast neutrons have been directly observed with an electron microscope. The technique employed and the characteristics of these regions are described.
Electrical Resistivity of Niobium—Zirconium Alloys below 273.2°K
Authors: Evans D. J. , Erickson R. A.
Published: April 2005

An apparatus for measuring the electrical resistivity of materials from 4.2°K up to 273.2°K was constructed and used to test niobium—zirconium alloys of the following compositions: Nb+15% Zr, Nb+25% Zr, Nb+33% Zr, and Nb+50% Zr. It was found that the temperature dependence of the electrical resistivity in these alloys is approximately linear, with Matthiessen's rule holding for the lower concentrations. The residual electrical resistivity was shown to depend linearly on zirconium concentration.
Spatially and Temporally Resolved Electron and Atom Concentrations in an Afterglow Gas Discharge
Authors: Gerardo J. B. , Verdeyen J. T. , Gusinow M. A.
Published: April 2005

The use of a modified laser interferometer to measure the temporal and spatial behavior of a medium density (1013–1014 electrons/cc) afterglow plasma is described. In the work described here, the plasma to be studied is located inside the laser cavity. The presence of the plasma changes the laser frequency (within the Doppler-broadened transition) and this frequency shift is determined by coupling an external cavity to the laser. This modification of the interferometer preserves the high sensitivity of using the transverse modes in the external cavity and has a spatial resolution in the medium being studied of less than 1 mm2. Two optical wavelengths, λ0=0.6328 μ and λ0=1.1523 μ, and two microwave wavelengths, λ=4, 8 mm, are used in this study and excellent agreement is obtained between measurements. It is shown that there is a strong migration of the gas atoms away from the discharge vessel axis due to the localized heating during the active discharge. Electron loss processes in such plasmas are discussed. Because of the excellent spatial resolution, the rate of loss of electrons by diffusion can be measured directly, and hence the electron temperature can be estimated. Electron temperatures obtained in this manner agree to within a factor of two with that obtained by the double-probe technique.
Sputtering at Acute Incidence
Authors: Cheney Kenneth B. , Pitkin Edward T.
Published: April 2005

Experimental sputtering yields obtained for incidence angles from 2° to 90° (normal) with incident ion energies of 1.5 to 30 keV are reported. These data were obtained by bombardment of copper, molybdenum, and tungsten surfaces with xenon and argon ions. Brief surveys of low- and high-temperature surface effects are also reported.
Temperature Dependence of the Pressure Coefficients of Elastic Constants for NaCl
Authors: Bogardus E. H.
Published: April 2005

The temperature dependence (25°–250°C) of the pressure coefficients of the elastic constants C11, C44, and ½ (C11+C12+2C44) have been calculated for NaCl from measurements of combinations of third-order moduli. The temperature cofficients of several combinations of these moduli generally agree with Nran'yan's theory.
Investigation of the Contact Angle between Indium (l) and an Aluminum Substrate in Ultrahigh Vacuum
Authors: Aldrich R. G. , Keller D. V.
Published: April 2005

The contact angle of liquid indium resting on an aluminum plate in which both surfaces were presumably atomically clean was measured in ultrahigh vacuum as 170°±10°, at a temperature of 158°±2°C. The deviation in angle was a function of the position around the periphery of the drop due apparently to variations in crystallographic orientation of the aluminum grains in the surface. The surface energy of the liquid indium was determined by the Bashforth and Adams technique in this system as 600 dyn/cm.
Electrical Resistivity and Transverse Electrical Magnetoresistivity of Chromium
Authors: Arajs Sigurds , Dunmyre G. R.
Published: April 2005

The electrical resistivity of an arc-melted chromium sample, having the electrical resistivity ratio ρ(290°K)/ρ(4.2°K) = 160, has been measured 4.2° and 319°K. The only anomaly in the ρ-vs-T curve, where T is the temperature, occurs at the Néel point, which for this sample is found to be 313.0°±0.2°K. The transverse electrical magnetoresistivity has been determined in magnetic fields up to 12 kOe at 4.2, 16.4, 51.4, 81.9, 93.2, 114.9, 134.0, and 170.7°K. Our results do not exhibit anomalous magnetoresistivity behavior of the type recently observed by Kostina et al. Our measurements show that the relative change in the electrical resistivity (Δρ/ρ) due to the applied magnetic field (Ha) is positive at the above-given temperatures. Chromium does not obey the Kohler law. The quantity Δρ/ρ is not proportional to Ha2, as predicted by simple theoretical arguments, at any of the above temperatures.
Perfection of Ruby Laser Crystals
Authors: Birks L. S. , Hurley J. W. , Sweeney W. E.
Published: April 2005

Ruby laser crystals grown by three different methods have been examined by x-ray topography and double-crystal rocking curves. Flame-fusion grown material is the least perfect. It usually has a few zones per centimeter that are tilted from the general matrix by 1 to 2 min of arc; the angular range of misorientation within the matrix is about 20 to 30 sec of arc. Flux grown ruby is intermediate in perfection with few or no gross imperfections and angular misorientation of 15 to 20 sec of arc. The most perfect ruby is grown by the Czochralski method. No gross imperfections have been observed; the angular misorientation is about 5 sec of arc over mm sized areas and 10 sec of arc over cm sized areas.
Influence of Anisotropic Scattering on Stopping by Elastic Collisions
Authors: Baroody E. M.
Published: April 2005

Calculations of spatial moments 〈zn〉 for particles from a plane source in an infinite medium of randomly located target atoms are extended to a scattering cross section which is a product of factors depending on energy and angle separately. It is shown that expressions for Laplace transforms of moments of the flux fnl(s) which were used before for isotropic scattering continue to be valid, provided the definition of the functions Gl(s) is broadened in a natural way. For classical scattering by several inverse power repulsive potentials, and for various ratios of target mass to fast particle mass, spatial moments at zero energy have been calculated through n=4. Deviations of distributions from the Gaussian form prove to be moderate, and Edgeworth expansions may be used to give approximate curves. With certain additional approximations the results can be applied for scattering by a Thomas-Fermi potential. A few comparisons are made with published Monte Carlo results and with measurements on range distributions of kilovolt ions in gases.
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.
Nucleation and Epitaxial Growth of Cu on W
Authors: Melmed Allan J.
Published: April 2005

Nucleation and growth of Cu on W from the vapor phase has been studied by field emission microscopy in the temperature range from −195° to 750°C for a limited range of impingement rates. Nucleation occurs in patches rather than homogeneously, the nucleation sites varying with substrate temperature, becoming very specific above ∼300°C. Cu crystals can readily be grown having surface areas comparable in size with the W field-emitter surface. Epitaxial relationships are determined from the field-emission micrographs. The crystal plane initially formed is {111} Cu superposed on an {011} W plane with either a Cu 〈112〉 direction parallel to a W 〈011〉 direction or a Cu 〈112〉 direction parallel to a W 〈112〉 direction. The crystal growth technique is proposed as a general means of obtaining clean surfaces for field emission microscope studies.
Parametric Traveling-Wave Acoustic Amplification in Ferromagnets
Authors: Auld B. A. , Matthews H.
Published: April 2005

A theoretical evaluation is presented for the amplification of acoustic microwaves traveling in a ferromagnet by means of a parametric interaction with a spatially uniform pump magnetization and a spin-wave idler. In this interaction, the strong frequency dispersion of the idler wave suppresses the degenerative effect of the upper sideband frequency. Although the spin-wave boundary conditions would seem to require a standing-wave idler, the low group velocity, and resulting short decay length, permits traveling-wave operation. By means of a normal mode analysis including losses, expressions are found for the gain per unit length and the interaction bandwidth as a function of pump power. The ultimate interaction bandwidth is determined by the spin wave Q, but the usable bandwidth is reduced by the effect of acoustic mismatches. This amplifier, in common with the maser and laser, is bilateral and the usable gain is limited by regeneration. The range of usable gain is expressed in terms of the acoustic mismatches at the terminals. Nondegenerate operation is possible, permitting reduction of idler-wave thermal noise. Gain, bandwidth, and pump power, and their frequency dependence, are evaluated for a number of available materials. Performance limitations due to Suhl breakdown are also discussed.
Diffusion, Solubility, and Electrical Properties of 64Cu in GaSb Single Crystals
Authors: Fuller C. S. , Wolfstirn K. B.
Published: April 2005

The behavior of 64Cu in as-grown and bent crystals of GaSb has been investigated in order to obtain information on the nature of the native defects supposedly present in this crystal. 64Cu concentrations were determined radiochemically and Hall measurements were made before and after the introduction of the 64Cu. Although interstitial Cu diffuses very rapidly into as-grown GaSb, the rate of substitution of Cu is found to be extremely slow, even at temperatures 30°C from the mp. The rate of substitution is greatly accelerated in bent GaSb specimens. Measurements on these show that ∼1019 cm−3 Cu dissolves at the maximum (650°). Curves for the interstitial and substitutional solubilities are given. Hole concentrations (25°C) in bent specimens saturated with Cu are only ∼⅓ of the 64Cu concentrations over a large Cu concentration range. This suggests that a considerable fraction of the Cu precipitates from solution during quench to room temperature. Hall curves on such specimens show four distinguishable acceptor levels. Hall measurements on as-grown GaSb indicate that the native defect is a double acceptor as previously suggested by others. The low interstitial Cu solubility observed at 250–350°C indicates that the native acceptors are not Ga vacancies. GaSb does not exhibit the ``doubling'' phenomenon toward 64Cu such as found in GaAs.
Effect of High Electric Fields on the Propagation of 24-GHz Microwaves Along the Surface of InSb
Authors: Hasty T. E. , Wisseman W. R.
Published: April 2005

The effect of high electric fields on the propagation of 24-GHz microwaves along the surface of thin slabs of n-type InSb was determined. Measurements were made at 77°K on samples with low-field electron mobilities of approximately 6×105 cm2/V·sec. The properties of the observed wave were found to agree with the surface wave described by Barlow and Cullen. This mode of propagation along the flat InSb surface travels without change of field pattern at a velocity near c. The field pattern is determined primarily by the conductivity of the InSb. Since the conductivity of InSb is a strong function of electric field E because of electron heating, a change in the amount of power propagated as a function of E was anticipated. The results were in agreement with the predicted change for a surface wave.
Magnetocaloric Effect in Dysprosium
Authors: Hudgins A. C. , Pavlovic A. S.
Published: April 2005

The magnetocaloric effect and magnetization of a polycrystalline ellipsoid of dysprosium were measured in magnetic fields up to 20 kOe from the temperature of liquid nitrogen to room temperature. Dysprosium exhibits both heating and cooling upon adiabatic magnetization depending on its magnetic state (ferromagnetic, paramagnetic, or antiferromagnetic) and a change in state is reflected by its magnetocaloric behavior. The magnetocaloric effect has been correlated with temperature, magnetization, and magnetic field intensity. These various behaviors are discussed in terms of some of the existing ideas concerning dysprosium.
Short-Range Order in some Nickel-Base Alloys
Authors: McManus G. M.
Published: April 2005

The first-nearest-neighbor short-range-order and size-effect coefficients have been determined for the solid-solution alloys Ni+12% Ta, Ni+15% W, and Ni+20% Mo by the method of x-ray diffuse scattering. In these alloys a strong preference for unlike nearest neighbors was found, with the Ni+12% Ta, Ni+15% W, and Ni+20% Mo alloys having α1=−0.10, −0.12, and −0.13, respectively. The corresponding size-effect coefficients for these alloys were found to be β1=0.017, 0.015, and 0.000, respectively.
Theoretical Approach to Enhanced Pressure Apparatus Design
Authors: Corll James A. , Warren William E.
Published: April 2005

The possibility of obtaining an enhanced stress level within a solid is investigated for a spherical configuration consisting of a solid homogeneous isotropic core encapsulated by a nonhomogeneous isotropic shell. Utilizing a linear elastic analysis, the enhancement is maximized (1) for the case when the nonhomogeneous shell is composed of a number of concentric homogeneous shells; and (2) for the case where the elastic shell modulus varies as a power of the radius. The dependence of the enhancement on the various parameters is depicted graphically and the results are discussed in terms of presently available materials. It is felt that the attainable enhancement may be significant only in the region up to 10 kbar and very limited above 30 kbar.
Laser-Quenching of Photoconductivity and Recombination Processes in Sensitive Photoconductors
Authors: Saura Jose , Bube Richard H.
Published: April 2005

The optical quenching of photoconductivity in CdS and GaAs sensitive photoconductors has been investigated as a function of quenching intensity using a He-Ne laser as the quenching radiation source. Electron capture cross sections for sensitizing centers of the order of 10−21 cm2 are found in agreement with previous measurements. No indication of a departure from a linear dependence between the free-electron density for the onset of optical quenching and the quenching radiation intensity is found for free-electron densities up to 4×1013 cm−3. It may therefore be concluded that the appropriate Auger recombination coefficient for the sensitizing centers is less than 10−28 cm6·sec−1.
Optical Transmission in Multidomained KH2PO4 : Polarization Scattering
Authors: Hill R. M. , Herrmann G. F. , Ichiki S. K.
Published: April 2005

When cooled below the ferroelectric Curie temperature, KH2PO4 assumes a layered structure of thin domains. Light incident nearly normal to a domain wall and polarized along a principal crystal direction is found to be strongly scattered into a forward wave with polarization perpendicular to that of the incident radiation. This scattering increases as the square of the angle of incidence and is strongly dependent on wavelength. The scattering into the perpendicular polarization is shown to result from the boundary conditions relating the normal waves on both sides of a domain wall, and the wavelength dependence arises from interference effects due to the large number of such walls traversed by the ray. Scattering coefficients for the transmitted and reflected waves are derived. The scattering into the transmitted wave with perpendicular polarization is found to be much larger, in general, than the scattering into the reflected waves. Qualitative and quantitative agreement with observation is obtained. The observed effect is related to a similar effect observed in light reflected from KClO3 crystals which was first noticed and discussed by Stokes and Rayleigh.
Problem of Spike Elimination in Lasers
Authors: Statz H. , DeMars G. A. , Wilson D. T. , Tang C. L.
Published: April 2005

We have investigated theoretically and experimentally the conditions under which spiking in the laser output can be completely suppressed. It is predicted that a nonlinear absorber in the cavity producing greater loss at the higher power levels, and vice versa, should be highly effective. Experimental work was carried out with a single-mode traveling-wave laser, since in this case the predictions can be most easily checked. Instead of using a nonlinear absorber, a Kerr cell controlled by a feedback circuit was used. It was found, in agreement with theory, that the time delay between the build-up of the electromagnetic energy in the cavity and the corrective action of the Kerr cell is a rather important parameter. Spike suppression can only be obtained when this time delay is short as compared to the duration of one oscillation pulse.
Laser-Induced Thermionic Emission from Tantalum
Authors: Verber C. M. , Adelman A. H.
Published: April 2005

We have measured the induced thermionic emission of electrons from tantalum as the result of bombardment with laser beams of up to 105-W/cm2 peak power density as a function of the tantalum temperature. It is shown that within the power range investigated, the results can be described in detail as thermionic emission resulting from a temperature increase which is calculable from classical heat-transfer theory.
Radiative Recombination between Deep-Donor-Acceptor Pairs in GaP
Authors: Gershenzon M. , Trumbore F. A. , Mikulyak R. M. , Kowalchik M.
Published: April 2005

A number of emission bands lying several tenths of an eV below the band gap have been observed in photoluminescence spectra of GaP crystals. These bands shift in peak position as different donors and acceptors are incorporated in the crystals. The emission bands are identified as donor-acceptor pair recombination bands involving deep levels by noting that these shifts correspond directly to changes in the donor and acceptor binding energies and by noting their similarity to shallow donor-acceptor pair bands previously identified as such. One of these bands is due to recombination between the deep donor oxygen and the shallow acceptor zinc. In p-type crystals thermal ionization of minority carriers trapped on the deep donor is small, so that in samples containing optimum concentrations of zinc and oxygen, photoluminescence (external) quantum efficiencies as high as 1.5% have been measured at room temperature.
p-Type Surface Layers in Ion-Bombarded Silicon
Authors: Amadei L. , Gereth R. , Queisser H. J.
Published: April 2005

Silicon is bombarded at 400° to 900°C in a glow discharge of hydrogen with phosphine or diborane admixtures. Below 700°C, bombardment of n-type silicon with an initial resistivity of 200 Ω-cm creates deep (0.5–2.5μ) p-type surface layers regardless of gas composition. The concentration NA(x) of the acceptors in the p layers obeys a simple law: NA(x)=N0 exp(−x/L). N0 is the surface concentration at x=0 which increases from 3.5×1016 acceptors cm−3 to 4×1018 acceptors cm−3 for bombardment temperatures increasing from 500° to 650°C. The decay constant L is found to be 0.2 μ. Annealing experiments rule out the hypothesis that the p layers are caused by fast-diffusing acceptor impurities, e.g. aluminum or boron. It is proposed that the p layers are formed by vacancies which act as acceptor-like defects.
Hg Adsorption Studies Using Atom Ejection Patterns
Authors: Anderson G. S.
Published: April 2005

The effect of Hg adsorption on atom ejection patterns in Hg+ ion bombardment of Ni low-index planes has been studied. The atom ejection patterns observed for single-crystal sputtering become smeared out when a Hg film is adsorbed on the target surface. The transition is unusually sharp and is interpreted to be the result of a two-dimensional condensation. A heat of adsorption of 0.69 eV/atom is derived from the model. The sputtering rate of the adsorbed Hg film seems to be determined more by the substrate than by the surface atom binding energy.
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.
Microwave Impedance of Semiconductor Posts in Waveguides. Part I
Authors: Larrabee Robert D.
Published: April 2005

A method for calculating the impedance of a thin inductive post of semiconductor material placed in a waveguide is presented. The calculation has been simplified by treating separately the geometrical and the material aspects of the interaction. The analytical expressions obtained are evaluated numerically in those cases where only two parameters are needed to characterize the semiconductor.
Lorentz Microscopy of Small Ferromagnetic Particles
Authors: Cohen Mitchell S.
Published: April 2005

Several authors have shown theoretically that a ferromagnetic particle with a diameter less than a critical value will be in a uniformly magnetized, single-domain state. Interesting transition states for particles just above the critical size are also predicted. Using special techniques, specimens have been prepared which contain discrete islands of NiFe film on a nonmagnetic substrate. Each specimen contained islands, usually circular, several hundred angstroms thick with a wide range of diameters (∼1–50 μ). The islands were thus two-dimensional analogs of three-dimensional particles. Lorentz microscopy gave direct evidence of the configurations predicted for small uniaxially anisotropic islands: (a) a circular magnetization configuration, (b) a 180° domain wall separating two oppositely directed domains, and (c) a single-domain, uniformly magnetized state (observed for elongated islands). The magnetization in islands in state b was not uniform, but ``curled'' around the ends of the domain wall near the edges of the islands. The transition from state b to a was noted below a critical island diameter Dc if all other parameters were fixed; theoretical estimates of Dc were made. In addition, the distortion of all three states in the presence of applied fields was observed. Elongated single-domain islands reversed by a process involving ``locking'' of the magnetization.
Rotating Ion Plasma in an External Magnetic Field
Authors: Kim Nak Goo
Published: April 2005

The Vlasov equation is investigated for the case of an ionized gas rotating in a uniform external magnetic field. The distribution function for a cylinder is obtained neglecting particle-particle collisions. The rotation of the ion beam is related to the Larmor and the plasma ion frequencies with resonance when ωi2/ω2=2, where ωi and ω are the ion plasma and angular frequencies.
Compton Current and Polarization in Gamma-Irradiated Dielectrics
Authors: Gross Bernhard
Published: April 2005

Attenuation of a directional flux of gamma radiation in a solid dielectric is accompanied by the production of Compton current and space-charges. Under proper conditions the space-charge field can be high enough to produce breakdown. A phenomenological theory of these effects is developed, which is based on Compton current theory and experimental results of breakdown-induced charge release in glass. It takes into account space-charge formation due to the trapping of high-energy Compton electrons and persistent internal polarization associated with the production of electron-hole pairs by low-energy secondary electrons.
Ferromagnetic Domains in Thin Single-Crystal Nickel Platelets
Authors: De Blois R. W.
Published: April 2005

Ferromagnetic domain observations have been made on single-crystal nickel platelets, ranging from 900 Å to over 10 μ in thickness, that have been grown nonepitaxially by the hydrogen reduction of the bromide. The platelets are generally rectangles or right triangles with (001) faces, 〈100〉 sides or legs, and edges from several microns up to 3 mm in length. Because their degree of perfection is close to that of metal whiskers, reversible domain wall motion occurs with a change of field of less than 0.01 Oe. Thus the domain configurations, observed by Lorentz microscopy and the Bitter technique, are in stable or metastable equilibrium. For platelets less than 1.0 μ thick, the magnetization lies in the plane along 〈110〉 directions, these being the projections of the 〈111〉 directions of minimum anisotropy energy. Echelons form the common closure structure near the edges. Some 180° walls appear to be of a combined Néel-Bloch type. At a thickness of 1.0 μ a striped powder pattern appears within the planar domains, with a 0.7-μ spacing between stripes. Near 2 μ the pattern changes to a coarser one in which the stripes are not parallel to the planar magnetization. Above about 7 μ the surface pattern is essentially that for the bulk crystal. Near 1000 Å, Néel walls and spotted transitional walls are observed. Crosstie walls and individual crosstie spots appear with unusual clarity in single-crystal nickel-cobalt platelets (7% Co). Their creation and transformation are readily observable. Striped and planar domain patterns similar to those for nickel appear on fcc cobalt platelets.
A Two-Position Probe Method of Microwave Impedance Measurements for the Determination of the Electrical Properties of Indium Antimonide. Part II
Authors: Larrabee Robert D. , Woodard D. W. , Hicinbothem W. A.
Published: April 2005

A comparatively simple procedure was developed for measuring the impedance representation of a wave-guide obstacle. The Smith chart location of the impedance representation of the obstacle is derived from voltage measurements at two fixed probe positions. This technique was applied to the case of a thin inductive post of indium antimonide at 77°K. The electrical properties of the post material were inferred from the impedance using the concepts of Part I. Large impedance charges attributable to the pinch effect agreed with theoretical predictions over a small range of applied electric field values.
Measurement of the Refractive Indices of Several Crystals
Authors: Bond W. L.
Published: April 2005

An all-reflector spectrometer is used to measure the refractive indices of the cubic crystals ZnS, GaP, SrTiO3, and Y3Al5O12; the tetragonal crystals rutile, CaWO4, SrMoO4, CaMoO4; the hexagonal crystals LiTaO3, CdSe, ZnO, and AlPO4; and the monoclinic crystal ZnWO4. Most of these are measured in the wavelength range 0.4 to 4 μ.
Growth of Large Single Crystals of Hexagonal Selenium from the Melt at High Pressures
Authors: Harrison D. E. , Tiller W. A.
Published: April 2005

The preparation of single crystals of hexagonal selenium at ordinary pressures is hampered by the very slow rate at which crystals can be grown from the melt under these conditions. As the equilibrium freezing temperature is increased by the application of pressure, single crystals can be grown at rates several orders of magnitude faster than under ordinary pressures. At 5 kbar pressure, single crystals were grown up to 1 cm in diameter by 10 cm long. X-ray and optical studies established that the principal cleavage surfaces were along the {101̄0} and {101̄2} planes.
X-Ray Absorption Factors for Cylindrical Samples in Annular Sample Cells Exposed to Incident Beams of Limited Width
Authors: Kendig A. P. , Pings C. J.
Published: April 2005

Expressions are derived for x-ray absorption factors for a liquid or amorphous sample confined within a cylindrical sample cell. Sufficient geometrical parameters are included in the formulation to cover many experimental cases of practical interest. Various integrals involved are formulated in numerical calculus formulas adaptable to digital computer procedures. The statistical error caused by subtracting the cell background from the scattering of a cell and sample can be reduced substantially by limiting the volume of the cell material irradiated. The absorption factors calculated apply to uniform beams only; the approximation of absorption factors for nonuniform beams is discussed.
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.
Influence of Preferred Orientation on Ultrasonic Grain Scattering
Authors: Papadakis Emmanuel P.
Published: April 2005

The known formulas for ultrasonic attenuation caused by scattering in metals are inapplicable when the metal exhibits preferred orientation. It is shown through the analysis of a two-dimensional mathematical model of the elastic anisotropy of a grain that preferred orientation tends to reduce the anisotropy factor in the grain scattering formulas. It is inferred that the scattering will be nil in heavily rolled hcp metals (where the c axes of the grains are aligned) and in heavily rolled and recrystallized fcc metals (where a ``cube texture'' develops with alignment of all the axes). Experiments on these and other plastically deformed metals will prove valuable. One experiment on zinc bar stock is described to demonstrate the reduction of scattering by preferred orientation. Scattering of longitudinal waves was lower along the bar axis than perpendicular to it since the preferred orientation yielded only a axes of grains along the bar axis but both a and c axes pointing radially.
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.
High-Temperature Deformation of Rutile
Authors: Farb N. E. , Johnson O. W. , Gibbs P.
Published: April 2005

The creep of 44 rutile (TiO2) single crystals was studied as a function of stress (σ), temperature (T), ambient atmosphere, and impurity. For constant ambient and impurity in the range 1100° to 1230°C and σ=3.9–7.26 kg/mm2, the steady-state deformation rate ε̇ could be fitted quite well to ε̇=Aexp(Bσ−ΔH/kT), under conditions of constant or decreasing temperature. However, an ``hysteresis'' was observed for specimens tested with increasing temperature; ε̇ at a given temperature was irreversibly reduced after creep at a higher temperature. Nitrogen and argon atmospheres produced similar results. The ``constant'' A ranged between 1010 and 1019 for undoped specimens in N2, depending on purity. A decreased by a factor of 103 in O2, and fell to 100 and 1011 for doping with Fe and Al, in O2, respectively. B ranged: 1.0–2.2 in N2 and 0.7–1.4 in O2. ΔH ranged: 5.7–7.7 eV in N2, 4.0–7.5 eV in O2, 2.3 and 5.8 eV for doping with Fe and Al, in O2, respectively. In all cases, less than 10% scatter was observed for tests with the same atmosphere and purity. Significant changes in activation energy as a function of stress were found only for the highest-purity specimens (about 30-ppm cation impurities); in these crystals ΔH increased abruptly by ∼2 eV at a stress between 3.9 and 4.5 kg/mm2, with accompanying changes in A and B.
Eigenvalues of a Microwave-Cavity-Lossy-Plasma System
Authors: Shohet J. L. , Moskowitz C.
Published: April 2005

A cylindrical microwave cavity containing a concentric plasma column can be resonated in an infinite number of electromagnetic wave modes. The resonances all shift upward towards coaxial cavity modes as the electron density in the plasma is increased if collisions are neglected. The characteristic eigenvalue equation for all modes including collisional effects is derived and typical graphs for fundamental modes are presented. The solutions of the eigenvalue equation can be explained on the basis of coupled-mode theory. The empty cavity mode and the coaxial (infinite electron density) mode which are originally overcoupled, uncouple from each other for sufficiently large values of electron collision frequency. The imaginary part of the roots, which is inversely proportional to the Q of the plasma cavity system, shows the two modes distinctly.
Research and Development of a Channeled-Electron Image Intensifier
Authors: Theodorou Dimitri G.
Published: April 2005

A brief description is given of the operating principle and possible electrode structures of a channeled-electron image intensifier. Details of the design and construction of the tube are described and the development of the optimum parameters in the design outlined. Investigation of the secondary emitting properties of the KCl, MgO, SbCs3, and BaF2 has led to the choice of KCl as the most practical secondary emitter for the dynodes. A method is also described in which the photocathode is processed in a separate chamber and is then transferred to the intensifier body before seal-off. A thirteen stage tube using KCl as a secondary emitter has been constructed giving an electron gain of 8×105, and with blue light gain of over 106. Resolution is in agreement with the expected theoretical resolution. A net gain of 2.1 in resolution is further obtained by dynamically scanning the tube in the plane of the image with a random amplitude and orientation. Finally, life tests are given on the stability of the electron gain and photocathode sensitivity.
Saturation and Spectral Characteristics of the Stokes Emission in the Stimulated Brillouin Process
Authors: Tang C. L.
Published: April 2005

An analysis is given of the saturation effect in the stimulated Brillouin scattering of coherent light waves. It is shown that the three coupled nonlinear wave equations describing the complex amplitudes of the forward-traveling primary and acoustic waves and the backward-traveling Stokes wave can be replaced for room-temperature situations by two coupled first-order nonlinear equations for the intensities of the primary and Stokes waves. These resulting equations are solved exactly and the solutions describe completely the process of photoelastic amplification of the coherent Stokes wave via stimulated Brillouin scattering in both the linear and the nonlinear saturated regimes. The results also give a more realistic estimate of the intensity of the hypersonic wave generated in the process than that made on the basis of either the Manley-Rowe relationship, which does not take into account the losses, or the usual linear theories, which do not take into account the saturation effect. It is believed that the Stokes emission observed in the usual experiments on stimulated Brillouin scattering of ruby laser light is due to photoelastic amplification via the stimulated process of Stokes noise generated by the scattering of the laser light via the normal Brillouin process by the thermal phonons present throughout the electrostrictive medium. A detailed analysis of this situation is also given. Explicit formulas for the spectral characteristics and the total integrated intensities of the Stokes and acoustic waves are obtained. The results also describe the noise characteristics of the photoelastic backward-wave amplifier. As an illustration, all these results are applied to the case of stimulated Brillouin scattering of ruby laser light in quartz.
Electromagnetic Behavior of Thin-Film Structures
Authors: Pearl Judea
Published: April 2005

A general method is presented for studying the response of thin-film structures to electromagnetic excitations. It is shown that for thin films which can be characterized by a complex, nonlocal conductivity tensor σ, a simple closed-form solution can be obtained relating the secondary sources at the films to the external excitations. From this relation the dispersions and interactions of resonant surface waves, as well as the scattering properties of thin-film geometries, can be studied. Several geometries consisting of plasma layers, dielectric films, and resistive and superconductive films serve to demonstrate the power and simplicity of this method.