bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow of covalent solids at low temperatures
Authors: Gilman J. J.
Published: February 2003

An empirical correlation shows that the activation energy for plastic flow in covalent solids equals twice the energy gap. This provides evidence that the flow rate is controlled by the rate of tunneling of bonding electrons into nonbonding states under the influence of the applied stress. The model yields an explicit expression for the critical shear stress that contains no adjustable parameters, and which agrees quantitatively with observations for silicon. At finite temperatures tunneling is assisted by high-frequency phonons. An explicit equation for the temperature dependence is derived that contains no disposable parameters and which conforms quite well with observations.
Lamb wave in a thin piezoelectric ceramic plate under the influence of static tensile stress
Authors: Toda Kohji
Published: February 2003

The effect of static tensile stress on the output voltage via the zeroth-order symmetrical Lamb wave (s0 mode) and the convolution output were investigated in a thin piezoelectric ceramic plate. The convolution output increases with the cummulative load, while the output voltage via the s0 mode decreases. The results might be explained to arise from nonlinearities due to dislocation and/or via lattice anharmonicities.
Detection of atomic oxygen and atomic hydrogen beams by semiconductors
Authors: Jacob Adir
Published: February 2003

Experimental evidence indicated that semiconductors like Si, Ge, CdS, and ZnO prove to be suitable detectors of atomic oxygen and atomic hydrogen fluxes. With suitable operating conditions detection is possible in the presence of the parent molecular gases. The method described herein is specific, highly sensitive, and characterizied by simple handling.
Electric-field-enhanced conductivity in solids
Authors: Pai D. M.
Published: February 2003

The Onsager theory of dissociation, based upon the solution of Brownian equations of motion of charge carriers interacting through a Coulomb potential in an applied electric field, is shown to account for the electric-field-enhanced conductivity in solids. In contradistinction to often quoted one-dimensional macroscopic Poole-Frenkel theory and its varied three-dimensional modifications, the Onsager theory is microscopic in nature and thus provides a quantitative description of the observed field enhancement of the conductivity.
Microwave thermal emission from a stratified medium with nonuniform temperature distribution
Authors: Tsang L. , Njoku E. , Kong J. A.
Published: February 2003

Using the dissipation-fluctuation approach, the brightness temperature of a stratified medium with inhomogeneous permittivities and nonuniform temperature profiles is solved. The solution is expressed in closed form ready for machine computation. Numerical results are illustrated and compared with closed-form analytical solutions and results obtained from the WKB method for simple profiles.
Surface contamination of active electrodes in plasmas: Distortion of conventional Langmuir probe measurements
Authors: Szuszczewicz Edward P. , Holmes Julian C.
Published: February 2003

Laboratory experiments were conducted to determine the effectiveness of a newly developed pulse technique in eliminating surface contamination effects and associated hysteresis in Langmuir probe current-voltage characteristics. We found that (i) the pulse technique was superior to the conventional continuous sweep approach to Langmuir probe diagnostics; (ii) substantial potentials can develop across contaminating surface layers and that these potentials can vary in the conventional Langmuir procedure resulting in determinations of electron energies higher than actually present in the ambient plasma; and (iii) attempts to achieve ’’clean-probe’’ operation by heating can be of limited value.
Photon-correlation measurements on light scattered by a nematic liquid crystal under a dc electric field
Authors: Zulauf M. , Bertolotti M. , Scudieri F.
Published: February 2003

The photon-correlation technique is applied to study the behavior of the second-order correlation function g(2)(τ) of light scattered by a liquid crystal under an external dc electric field. Different qualitative shapes of g(2)(τ) at varying electric fields are distinguished and their possible relation to different scattering processes are discussed.
The effect of transverse thickness gradients on differential C-V doping profiles
Authors: Coleman D. J.
Published: February 2003

Distortions of differential C-V doping profiles caused by lateral nonuniformities in doping or layer thickness are discussed and considered in particular examples. The distortions include artificial reduction of actual doping profile gradients and undershoot of the actual doping level obtained when profiling into a uniform subsurface layer. The profiling artifacts produced by this mechanism are similar to the features observed in doping profiles obtained from GaAs Read diodes.
Metal photosurface deposition in As-S-Ag glasses
Authors: Maruno Shigeo , Kawaguchi Takeshi
Published: February 2003

A phenomenon of the surface deposition of metallic Ag in the As-S-Ag glasses, exposed to a mercury lamp (500 W), has been found. The photographic images for As15S40Ag45 glass, which consist of a great number of Ag deposits, are shown herein. It is suggested that the fundamental process in this phenomenon is associated with both photoeffects and thermal effects.
Novel technique for measuring nitrogen profiles in GaP : N
Authors: Shah Jagdeep , Leheny R. F. , Dapkus P. D.
Published: February 2003

We describe a high-resolution technique for determining the nitrogen doping profiles in GaP : N which makes use of a laser-pumped dye cell as a broad-band fluorescence source. Results obtained with this technique are presented. They suggest that under some LPE growth conditions vapor-liquid equilibration may be slow and as a result affect the nitrogen incorporated into the solid. Also the implications of these results for high-efficiency LED’s are discussed.
Theoretical and experimental photovoltaic energy conversion in an organic film system
Authors: Reucroft P. J. , Takahashi K. , Ullal H.
Published: February 2003

A theoretical model in which charge separation takes place at an electrode energy barrier has been extended to estimate the photvoltaic energy conversion efficiency as a function of film thickness and energy barrier for an organic film system based on the (1 : 1) PVK-TNF charge-transfer complex. The model predicts that the theoretical efficiency will be determined by space-charge-limited conduction for films of thickness greater than 0.1 μ. The efficiency is proportional to the inverse cube of the film thickness in this film thickness range. In the case of ultrathin films (<0.1 μ), the model predicts that the efficiency will be determined by the photocarrier generation efficiency and can approach 1%. Experimental photovoltaic energy conversion efficiencies for films of thickness 5–25 μ are in agreement with the general features predicted by the model.
Ho laser with 50-W output and 6.5% slope efficiency
Authors: Beck R. , Gürs K.
Published: February 2003

We report the observation of continuous high-power laser emission from sensitized YAG. The crystal was immersed in flowing liquid oxygen precooled to 77 K. With a linear tungsten-halogen lamp in a single-ellipse pumping configuration an output power of 50 W with a 6.5% slope efficiency was obtained.
Experimental characterization of acousto−optical deflection in multimode optical waveguides
Authors: Weller J. F. , Milton A. F. , Giallorenzi T. G.
Published: February 2003

Resolution and efficiency measurements of acousto−optic deflection in optical waveguides are presented and compared to results of previous analysis. Measurements are made on a Ta2O5 film on YX−quartz. Resolution is shown to be limited by coupling, beam divergence, transducer bandwidth, and modal dispersion.
Principles of the stored ion calorimeter
Authors: Wineland D. J. , Dehmelt H. G.
Published: February 2003

The properties of a harmonically bound radiatively thermalized ion gas were investigated by studying the behavior of an electron cloud stored in a Penning trap. A simple model characterizing ions contained in an electromagnetic trap is proposed and tested by investigating the electromagnetic−dynamic behavior of these electrons subject to various external perturbations. The ion calorimeter realized in such a system is also discussed; particular attention is devoted to sensitivity to heat inputs into the various degrees of freedom.
Doping profile measurements from avalanche space−charge resistance: A new technique
Authors: Glover G. H. , Tantraporn W.
Published: February 2003

A new technique, resistance−current (R−I) profiling, is described in detail. The method utilizes measurements of the isothermal space−charge resistance of an avalanching semiconductor junction to determine the doping concentration as a function of depth. The technique extends profiling capability beyond the depth limit of the usual capacitance−voltage (C−V) methods and is thus particularly useful in measuring epitaxial layers which are not ’’punched through’’ at breakdown. In addition, comparison of the R−I profile with the C−V profile allows the effective avalanche area (Aeff) of the junction to be determined. An analysis of the technique is presented based on the ’’two−zone’’ model, which has uniquely defined avalanche and drift zones. This model is justified by comparison with results from a full simulation of the dc I−V characteristics of abrupt−junction avalanche diodes. Techniques for measurement of R are then discussed. Finally, measurement results of typical GaAs−Pt IMPATT diodes are presented. Effective areas as low as one−third of the geometric area are observed in some devices. Measurements of Aeff as a function of diode diameter are shown to be consistent with a model in which breakdown occurs near the outer edge of the diode in an annular region of constant width.
Optical absorption components of light−modulated absorption spectrum of CdS
Authors: Conway E. J. , Long E. R.
Published: February 2003

The amplitude and decay coefficient of light−induced modulation of absorption (LIMA) was measured as a function of wavelength from 535 to 850 nm for single−crystal CdS. The decay coefficient exhibited a discontinuous resonance at 710 nm which was due to the overlap and cancellation of two opposing absorption changes. A method was developed to separate these opposing absorption changes using the measured decay coefficients. The discrete−level−to−band energy for one absorption change was found to be 1.64 eV. An improved model was developed which contains two associated levels in the band gap separated by 0.32 eV.
Reflectance−circular dichroism of the magnetic insulator CoxCd1−xCr2S4
Authors: Ahrenkiel R. K. , Lyu S. L. , Coburn T. J.
Published: February 2003

Large infrared magneto−optic effects are observed in the series of magnetic compounds CoxCd1−xCr2S4 by means of reflectance−circular dichroism. These effects are associated with the crystal−field transitions of divalent cobalt. Comparison of surface and bulk magneto−optic effects indicate that the surface optical coefficients are representative of bulk phenomena. The magneto−optical effects associated with the 4A2(F) −to−4T1(F) transition are nearly linear with cobalt concentration x. The 4A2(F) −to−4T1(P) transition at about 1.0 μm exhibits a red shift of about 900 cm−1 as x increases from 0.05 to 1.00. Also, the magnitude of the magneto−optic coefficient is not linear in cobalt concentration and reaches a maximum value near x=0.25. The unusual magneto−optical effects associated with the 4T1(P) transition may be utilized in tailoring materials for particular applications.
Two−dimensional domain walls in ferromagnetic films. II. Cubic anisotropy
Authors: Aharoni Amikam
Published: February 2003

The general model for two−dimensional domain walls is utilized here for the study of single−crystal cubic films with no magnetostriction, at zero applied field. The Ritz parameters are evaluated for iron films and the resulting of Tsukahara et al., which in turn are quite close to wall structures observed by Lorentz electron microscopy. The use of this model is thus well justified for iron films whose thickness is up to about 2000 Å.
Effective conductivity of two−phase material with cylindrical phase boundaries
Authors: Mendelson Kenneth S.
Published: February 2003

A two−phase material in which the phase boundaries are cylindrical surfaces is considered. The generators of the phase boundaries are parallel to the z axis and the x and y axes are the principal axes of the effective conductivity tensor. If the two phases have conductivities σ1 and σ2, then the effective conductivity σx* (σ1,σ2) (in the x direction) of the material and the effective conductivity σy* (σ2,σ1) (in the y direction) of the material obtained by interchanging the two phases are related by σx* (σ1,σ2) σy* (σ2,σ1) =σ1,σ2. For a statistically isotropic material σx* (σ1,σ2) =σy* (σ1,σ2) =σ* (σ1,σ2). If, in addition, the material is statistically symmetric so that interchange of the two phases yields again the same material, then σ* (σ1,σ2) =σ* (σ2,σ1) = (σ1σ2)1/2.
Magnetic field distributions due to Permalloy bubble propagating circuits
Authors: Kinsner W. , Della Torre E.
Published: February 2003

Distributions of the normalized average magnetic field within a magnetic bubble−domain material due to the T−bar, Y−bar, and chevron high−permeability overlays are presented.
Positive−ion−induced Kossel lines in copper
Authors: Roberto J. B. , Batterman B. W. , Kostroun V. O. , Appleton B. R.
Published: February 2003

Proton beams have been used to generate Kossel lines in single crystals of copper by the excitation of characteristic radiation at atomic sites inside the crystals. The observed lines exhibit a fine structure similar to lines previously generated using incident electrons and x rays. A key advantage of the positive−ion technique is that the bremsstrahlung background associated with the electron generation of Kossel lines is eliminated. The possible application of the positive−ion technique to impurity lattice location is discussed.
Acousto−optic parameters of Bi2(MoO4)3
Authors: Biegelsen David K. , Chen Tu , Zesch James C.
Published: February 2003

Large optical−quality single crystals of α−bismuth molybdate have been grown and the acousto−optic parameters have been measured. The material has been found to be well suited for device applications. The acousto−optic figure of merit for 633−nm light propagating normal to the b axis is isotropic to 1% and equal to 59.3×10−18 sec3/g. The material is transparent between 460 and 5300 nm. Acoustic absorption is 0.5 dB/cm at 300 MHz. A method for measuring relative signs of photoelastic coefficients in optically anisotropic materials is described. Further, a microscopic argument is presented explaining semiquantitatively the measured photoelastic coefficients.
Approximate joint photocount statistics for Gaussian light with arbitrary spectral shape
Authors: Saleh Bahaa E. A.
Published: February 2003

An approximate formula is found for the joint moment generating function of integrated intensity fluctuations of Gaussian light in two time intervals. Some lower−order joint moments generated by this approximate formula are compared to their exact values known in case of Lorentzian light and good accuracy is obtained.
Measuring low background levels by ac photoconductivity
Authors: Aukerman L. W. , Garber W. A. , Millea M. F.
Published: February 2003

A method is presented for measuring the ac conductance of an infrared detector element at low frequencies and low photon flux levels. This alleviates the difficulties sometimes encountered with dc measurement. A slightly sublinear response was found for mercury−doped germanium detectors at 10 °K.
Auger examination of contaminants in thin−film metallizations
Authors: Thomas R. E. , Haas G. A.
Published: February 2003

Gold nichrome metallizations vacuum evaporated at (10−6 Torr) have been examined with Auger electron spectroscopy and argon ion sputtering techniques. The primary contaminants within the films were carbon and oxygen, which were concentrated in the underlying nichrome film. The contaminants were believed to be due to residual gases present during evaporation. The significance of these results for eutectic bonding processes is discussed.
Thermally darkenable photochromic glasses
Authors: Seward III Thomas P.
Published: February 2003

Thermally darkenable photochromic (TDPC) glasses have been produced by precipitating copper−doped silver halide crystallites in certain lanthanum borate base glasses. A TDPC glass is characterized by a darkened state which is stable at room temperature but which can be bleached by visible light. The glass will return to the darkened state with the passage of time. The rate of darkening and the color of the darkened state are affected by temperature. These TDPC glasses are further characterized by the vanishing of the darkened color above a certain high temperature and redarkening of the glass below a certain somewhat lower temperature. These temperatures are believed associated with the melting and crystallization of the silver halide particles.
Mobile fluoride ions in SiO2
Authors: Williams R. , Woods M. H.
Published: February 2003

We have obtained evidence that fluoride ions are mobile in SiO2 at room temperature. The outer surface of a thin layer of the oxide is coated with a fluoride salt and charged by a negative corona discharge in air. From shifts in the C−V curve and changes in the properties of trapping states near the interface we infer that negative ions have moved through the oxide. This is confirmed by an analysis with a secondary−ion mass spectrometer.
Shock−wave propagation in fluid−saturated porous media
Authors: Garg S. K. , Brownell D. H. , Pritchett J. W. , Herrmann R. G.
Published: February 2003

Mechanical constitutive relations for fluid−saturated porous rocks as previously formulated by Morland and Garg within the theory of interacting continua (TINC) have been generalized to include thermodynamic effects. The model is developed by defining effective stress tensors and effective densities in terms of the partial stress tensors, partial densities, and actual volume fractions occupied by each component. It is postulated that the constitutive law for each component as a single continuum relates effective pressure to effective deformation. Relative motion between the constituents is allowed through a simple Darcy−type law. The governing conservation equations together with the constitutive relations for a binary mixture are solved numerically using a so−called ’’leap−frog’’ finite−difference technique. The model is applied to study shock−wave propagation in a mixture of tuff and water.
Strain relaxation in glass by optical correlation and pressure jump relaxation
Authors: Bucaro J. A. , Dardy H. D. , Corsaro R. D.
Published: February 2003

Strain relaxation functions have been obtained for boron trioxide glass in its transformation region by digital correlation of a scattered optical beam and by pressure jump relaxation measurements utilizing a recently developed acoustic densitometer. The results confirm that the light−scattering correlation data is a measurement of the isothermal constant stress compressibility function. These measurements, together with previous ultrasonic results, cover a temperature region for B2O3 in which the structural relaxation time changes by more than 13 orders of magnitude.
An interferometric investigation of laser−supported absorption waves
Authors: Maher W. E. , Hall R. B.
Published: February 2003

Laser−supported detonation waves, other laser−supported absorption waves, and plumes of vaporized material were the subject of interferograms. Both instantaneous ruby laser interferometry and time−resolved argon laser interferometry were used to study these events. Qualitative behavior is seen in the interferograms which was not evident in photographic studies of these phenomena, such as the progress of radial shock waves and structure in the absorption zone. Abel inversion is used to obtain quantitative radial behavior of the change in the index of refraction. The differences between the laser−supported absorption waves ignited at the surfaces of several materials are discussed. Alumina specimens produced vapor plumes under these conditions whose temporal motion can be followed because of AlO absorption of the argon laser wavelength. The changes in the index of refraction were measured for similar events at the different wavelengths of the instantaneous and time−resolved interferometers and were used to determine the density profiles of electrons and neutrals. Compared to STP air densities, an ionization of a few percent is seen near a silica surface at laser beam intensities slightly below the ignition threshold for laser−supported detonation waves. An analysis of observed radial shock wave expansion rates predicts a neutral density which, when compared with the density determined from the Abel inversion technique, indicates that the shock front ionization is also a few precent.
Growth and characterization of liquid−phase epitaxial InxGa1−xAs
Authors: Nahory R. E. , Pollack M. A. , DeWinter J. C.
Published: February 2003

The liquid−phase epitaxial growth of InxGa1−xAs (0<x≲0.15) single and multiple layers on GaAs substrates has been studied. Growth on 111B−oriented substrates results in planar interfaces, although it requires careful control of the growth temperature relative to the liquidus temperature. For this reason, detailed liquidus and solidus data along the 850 °C isotherm have been determined for the In−rich corner of the In−Ga−As system. The phase diagram of the system has been calculated and found to be in satisfactory agreement with the measurements. An accurate determination of the room−temperature band gap of InxGa1−xAs as a function of x has been made using photoreflectance and photoluminescence techniques. The room−temperature electrical properties of doped layers also have been measured, and Zn acceptors and Se or Te donors were found to be useful dopants. Ge was found to be an amphoteric dopant; it is an acceptor for x≲0.07 and otherwise a donor. By making use of stepwise compositionally graded lattice−matching layers between the substrate and the p−n homojunction, In0.15Ga0.85As light−emitting diodes with total external room−temperature efficiencies ∼1% have been fabricated.
Growth, environmental, and electrical properties of ultrathin metal films
Authors: Kazmerski L. L. , Racine Diane M.
Published: February 2003

The conduction mechanisms of ultrathin (10−100 Å) metal films are investigated. The electrical conductivity and activation energy of discontinuous Au films grown in UHV are correlated with island size and separation and average film thickness. The relationship between film conductivity and deposition rate and substrate temperature is presented. Film temperature data indicate the validity of the proposed model. Some anomalous conductivity effects are reported for films deposited below the UHV range. The results are explained in terms of substrate and film surface contamination. Data are presented indicating the sensitivity of the conductivity of discontinuous films to ambient gas concentration. Reversible and irreversible situations are discussed.
Switching times in amorphous boron, boron plus carbon, and silicon thin films
Authors: Charles Harry K. , Feldman Charles
Published: February 2003

Switching time studies in amorphous boron, boron plus carbon, and silicon thin films have been conducted under pulse and steady−state testing conditions at both 300 and 77 K. Measurements show that the transition times are related to the RC time constant of the system and that the transition is always accompanied by filament formation. At low frequencies, two separate switching time constants are observed during the transition. The recovery time is proportional to the power dissipated in the filament. The delay time is inversely proportional to sample thickness and exhibits statistical fluctuations. The time measurements, coupled with sample physical and electrical parameters and filament locations, suggest a model of switching combining both thermal and electronic elements.
Thermal resistance of heterostructure lasers
Authors: Joyce W. B. , Dixon R. W.
Published: February 2003

A GaAs−GaAlAs heterostructure laser is modeled as a stripe heat source embedded in a layered structure, and an analytic expression is given for the steady−state thermal resistance 〈R〉 of the model. Over the range of typical layer thicknesses and conductivities, and for heat generated uniformly in the active region, 〈R〉 varies between 14 and 31 K/W for a 12×375−μ active region. Four types of heat sinks are shown to contribute an additional 3 to 10 K/W. Design implications are drawn for various properties including layer thicknesses, heat−sink and bond parameters, and radiative heat transfer by spontaneous emission. In disagreement with the common tacit assumption of a unique active−region temperature, it is found that about 40% of the temperature drop within the laser occurs in the active region (center to edge).
Direct comparison of ion−damage gettering and phosphorus−diffusion gettering of Au in Si
Authors: Seidel T. E. , Meek R. L. , Cullis A. G.
Published: February 2003

The residual disorder caused by different implanted ions after annealing at elevated temperatures (850−1150 °C) is dependent upon the ion species. The gettering of Au by damaged layers produced by Ar, O, P, Si, As, and B has been quantitatively compared to gettering by phosphorus diffusion. Each individual comparison was made between opposite surfaces of a Si sample by use of Rutherford backscattering. The damage disorder was quantitatively measured by backscattering and structurally studied using electron microscopy. Typically, an ion dose of 1016/cm2 and ion energy of 200 keV were used for implantations. The Au was present in the Si at ’’moderate’’ levels so that solubility in the phosphorus diffused layers was not exceeded. Ar ion−damaged layers were more effective for gettering Au than were phosphorus−diffused layers below ∼1000 °C and equally effective up to 1150 °C. The relative gettering efficiency of the damage produced by other ions studied was less than that of phosphorus diffusion at 1000 °C and was ranked in the order Ar≳O≳P≳Si≳As≳B. In general, the relative gettering efficiency of ion−damaged layers was related to the amount and type disorder after annealing. The initial disorder was of an amorphous nature for 1016 heavy ions/cm2 (As, Si, P, Ar, or O), and the final disorder state was different for different implanted ions after annealing. It is suggested that the disorder (and gettering efficiency) was influenced by size effects of the implanted ion during annealing.
Electron photoemission induced by laser−produced plasma x rays
Authors: Beverly III R. E.
Published: February 2003

Time− and energy−dependent electron photoemission from metal surfaces exposed to laser−produced plasma x rays is predicted. Primary, Auger, and secondary photoemissive processes are considered. Secondary photoemission significantly increases the total current density response of the surface, and alters the photoelectron energy spectrum via downscattering of the primary electrons.
Dislocation model of a plastic tensile crack
Authors: Marcinkowski M. J.
Published: February 2003

An extensive numerical analysis has been made dealing with the energetics associated with the formation and propagation of plastic tensile and shear−type cracks. All of these cracks have been modeled entirely on the basis of dislocation theory. The most important finding of this investigation is that the stress required to propagate a plastic tensile crack is much higher than that for an elastic crack which in turn is greater than that for a plastic shear crack.
Elastic interactions between disclination loops and dislocations
Authors: Chou Tsu−Wei
Published: February 2003

The interactions between disclination loops and dislocation lines are examined in this paper. Detailed analyses are made according to the relative orientations of the dislocation Burgers vectors and the rotation vectors of disclinations. It is concluded that, for the assumed geometric arrangements, resultant interactions exist between screw dislocations and twist disclination loops, as well as edge dislocations and wedge disclination loops. However, local interaction forces do exist for other combinations of defects. Closed−form solutions are obtained for interaction energies and forces. Depending upon their relative orientations, the interaction forces can be infinite, finite, or zero when the defects are close to each other. Numerical results are also presented.
Dislocation mechanisms for stress relaxation in shocked LiF
Authors: Gupta Y. M. , Duvall G. E. , Fowles G. R.
Published: February 2003

A study of shock wave propagation along the 〈100〉 direction in LiF single crystals is presented. Plate impact experiments were conducted to produce elastic impact stresses of approximately 29 kbar. Stress time profiles at the impact surface and rear surface for thicknesses up to 3.2 mm were observed. Experiments were done for two impurity concentrations and three different heat treatments. Material characterization to supplement the shock data was provided by quasistatic yield stress measurements, dielectric relaxation data, initial dislocation density counts, and spectrographic analysis. Elastic wave attenuation is strongly influenced by both Mg++ impurities and heat treatments. Impurity clustering generally reduces the rate of precursor decay. The plastic strain rate at the elastic shock front was computed from the data by a near−exact method which incorporates material nonlinearities. Beyond the first 1 or 2 mm of propagation, significant contributions to stress decay arise from overtaking by relief waves. Application of dislocation theory reveals dislocation densities to be approximately 3 orders of magnitude larger than grown−in dislocations, at least in the region of rapid stress decay. Present analysis contradicts the idea of regenerative multiplication of dislocations causing this large increase in density. A model for heterogeneous nucleation of dislocation based on an energy criterion is proposed which appears to be well suited for explaining large increases in dislocation densities. The present data suggest an applied shear stress of 3−5 kbar as the lower bound at which dislocations can nucleate at heterogeneities present in our crystals. Better material characterization concerning impurity clusters is needed to consider the quantitative aspects of rate and magnitude of heterogeneous nucleation. The mechanism for stress decay in the very soft LiF crystals is still not well understood.
Stress−induced diffusion of point defects to spherical sinks
Authors: Wolfer W. G. , Ashkin M.
Published: February 2003

Radiation damage in metals at elevated temperatures produces small dislocation loops and voids. The growth of these sinks is determined by the steady−state diffusion of point defects migrating in the stress field of these sinks. To obtain the steady−state current of point defects to these spherical sinks a perturbation method is developed to deal with the drift term of the diffusion equation. It is shown that the contribution of the drift term to the current can be expressed by a bias factor which differs from unity if the point defects interact with the spherical sink. Explicit expressions of the bias factors for voids and infinitesimal dislocation loops are given. If the metal is subject to external loads the bias factors of voids depend on the elastic dilatation, whereas the bias factors for dislocation loops depend on the deviatoric elastic strain. These results then provide the basis for stress−induced swelling and irradiation creep of metals. Both of these phenomena are briefly discussed.
Synchrotron−diffraction radiation spectra in the presence of a penetrable sphere
Authors: Pogorzelski R. J. , Yeh C.
Published: February 2003

The radiation from a charged particle orbiting both inside and outside a dielectric sphere is expressed as a series of vector spherical harmonics. The results of numerical computation of the radiated spectra for various situations are presented and discussed. When the particle orbits far outside the sphere, the interaction between the two is weak and the radiation is of the synchrotron type. The radiated power is shown to decrease with increasing sphere size in this situation. However, when the particle orbits close to or inside the sphere, the interaction is very strong; this being characterized by the appearance of resonances of the sphere in the radiated spectrum. The resonances are shown to be responsible for the power in a particular harmonic being radiated almost entirely into a single spherical harmonic in some instances.
Spinning magnetic fields
Authors: Djurić Jovan
Published: February 2003

A possible electrical charge model based on the spinning time invariant point magnetic dipole within the framework of classical physics is outlined, as suggested by the admissible circular trajectory of a test charge around the magnetic dipole in its equatorial plane. The model depends on the moving force line hypothesis which has been claimed to have been disproved. The controversy about that issue at the turn of this century is reanalyzed. The mathematical model of the generalized homopolar generator is presented, which is fully in agreement with all experimental facts concerning the homopolar generator, except for a single result by Pegram which appears to be an error and which violates the Faraday law. It is shown that the moving force line hypothesis was apparently not disproved by Kennard as claimed. Thus the intriguing model of electrical charge is possible. Further experimental research with all kinds of spinning magnets appears to be justified and desirable in view of the potentially high significance of the research line initiated by Jehle with the quantum mechanical model of the charge in terms of spinning flux loop forms.
Light scattering from nematic liquid crystal waveguides
Authors: Giallorenzi T. G. , Sheridan J. P.
Published: February 2003

The light scattering properties of nematic liquid crystal thin−film waveguides are studied both theoretically and experimentally. A Green’s function analysis of the depolarized light scattering induced by thermal fluctuations in the average molecular alignment is presented and it is shown that the power distribution of scattered light is affected by the presence of waveguide boundaries. Scattering coefficients for scattering out of the guide and for mode conversion are derived and predict substantial propagation losses in this type of guide (∼28 dB/cm). The calculations are experimentally verified and predicted structure in the scattered power distribution is clearly seen.
Gain spectra in GaAs double−heterostructure injection lasers
Authors: Hakki Basil W. , Paoli Thomas L.
Published: February 2003

Gain spectra for GaAs double−heterostructure junction lasers have been obtained with high resolution. This is accomplished by using an automated data aquisition system to analyze the Fabry−Perot resonance modulation in the spontaneous emission spectra. For active regions doped with Ge at a level of 4×1017 cm−3, the gain in the TE polarization at a fixed wavelength increases linearly with current, below lasing threshold. However, the peak gain (at a variable wavelength) increases slightly faster than linearly with current. The photon energy at which gain is a maximum increases logarithmically with current. Gain in the TM polarization depicts the same general behavior as that for the TE case, except that it is slightly less than the TE gain. It is concluded that for this particular doping the spectral gain characteristics are intermediate between those for undoped and heavily doped active regions. Above the threshold for lasing in the TE mode the TE gain spectra are well saturated, with new fine details revealed in the saturated spectra. On the other hand, gain in the nonlasing TM polarization is not well saturated above threshold, with marked differences in gain between high and low photon energies relative to the TE lasing energy.
The physics of metal oxide varistors
Authors: Levinson Lionel M. , Philipp H. R.
Published: February 2003

This paper outlines our present understanding of the conduction mechanisms and physical processes relevant to the performance of ZnO−based ceramic varistors. Varistor behavior is determined by the gross ceramic microstructure of the device as well as by the localized conduction processes which occur between grains. We show that the qualitative features of the highly nonlinear conductivity are largely independent of the details of varistor composition or processing but rather appear to be a general effect engendered by a microstructure of conducting grains surrounded by thin insulating oxide barriers. Evidence is presented from a variety of sources that this intergranular layer is ∼100 Å in thickness resulting in grain−to−grain fields of F∼106 V/cm. The conduction mechanism at breakdown is consistent with a Fowler−Nordheim tunneling process obeying a current−density−vs−field relation given by J∝exp(−γ/F), where γ is a constant. At somewhat lower fields (prebreakdown region) the conduction process follows a thermally activated Schottky−type law of the form J∝exp[−(Ei−β√F)/kT], where Ei?0.8 eV. Analysis of measured current−voltage characteristics at various temperatures in terms of these processes is a good representation of the data. The empirical power law behavior J= (F/K)α often used to describe varistor performance is shown to be an approximation of the Fowler−Nordheim relation.
Experimental study of a stationary laser−sustained air plasma
Authors: Keefer Dennis R. , Henriksen Bruce B. , Braerman William F.
Published: February 2003

An experiment was performed to determine the temperature distribution within a stationary plasma in atmospheric air produced by a continuously operating CO2 laser. A peak temperature of 17000 °K (±5%) was found to exist at a point 1.1 cm ahead of the focal point. The radiation surrounding the hot plasma core was found to consist primarily of the first negative system of nitrogen.
Insulated linear antenna: Theory and experiment. II
Authors: King R. W. P. , Lee K.−M. , Smith G. S. , Mishra S. R.
Published: February 2003

Measurements of current and charge distributions and driving−point admittances of insulated monopoles immersed in saline solutions (σ-0, 3.6, and 10, εr-80) are reported when the insulating material is melamine (εr=5.54). These data supplement the previously presented experimental results for air−insulated monopoles. The transmiasion−line−like behavior of the insulated antenna as predicted by the theory is verified experimentally when the ratio of the magnitude of the wave number of the ambient medium to that of the insulating medium is equal to or greater than 3.8.
Amplified−spontaneous−emission suppressor for Q−switched lasers
Authors: Mallozzi P. J. , Epstein H. M. , Applebaum D. C. , Gallagher W. J. , Campbell B. E.
Published: February 2003

A passive device for suppressing amplified spontaneous emission in Q−switched lasers has been developed. The technique is applicable to lasers of any aperture.
Temperature dependence of the maximum Josephson current for Nb−NbOx−Pb junctions
Authors: Paternò G. , Rissman P. , Vaglio R.
Published: February 2003

Measurements of the maximum Josephson current with temperature for Nb−NbOx−Pb junctions differ from the BCS Ambegaokar−Baratoff curve. This cannot be explained in terms of strong coupling effects. A possible explanation might be proximity effect of a normal layer on the niobium surface.
Emission cross section and fluorescence quenching of Nd3+ lanthanum pentaphosphate
Authors: Singh S. , Miller D. C. , Potopowicz J. R. , Shick L. K.
Published: February 2003

The stimulated emission cross section σ for the transitions 4F3/2→4I9/2,11/2 in NdP5O14 and La0.75Nd0.25P5O14 has been measured at 300 °K. For the strongest emission line at 1.0510 μm the value of σE∥b is 18×10−20 cm2, which is to be compared to the value of 46×10−20 cm2 for Nd : YAG. The fluorescence lifetimes of the 4F3/2 state in La1−xNdxP5O14 have been measured at 300 and 77 °K and were found to be independent of temperature. Based on the measured spectroscopic parameters the performance of LED−pumped La0.75Nd0.25P5O14, NdP5O14, and Nd : YAG have been compared both in the end−pumped and side−pumped configurations. In the end−pumped configuration the pentaphosphate has no advantage over Nd:YAG. In the side−pumped case the threshold for La0.75Nd0.25P5O14 is predicted to be lower than that for Nd:YAG.
Laser absorption spectroscopy using a molecular beam
Authors: Chu F. Y. , Oka T.
Published: February 2003

Infrared absorptions spectroscopy has been performed with the laser radiation propagating perpendicular to the molecular beam from a multiple−tube collimator source. A 1.3−MHz linewidth (HWHM) has been observed in NH3 and 13CH3F absorption.
Some comments on recent measurements of the penetration depth in niobium
Authors: Strongin Myron , Varmazis C.
Published: February 2003

A discussion is given of some difficulties of interpretation when the apparent superconducting penetration depth is used to infer the mean
Monte Carlo simulation of energy deposition by low−energy electrons in molecular hydrogen
Authors: Heaps M. G. , Furman D. R. , Green A. E. S.
Published: February 2003

A set of detailed atomic cross sections has been used to obtain the spatial deposition of energy by 1−20−eV electrons in molecular hydrogen by a Monte Carlo simulation of the actual trajectories. The energy deposition curve (energy per distance traversed) is quite peaked in the forward direction about the entry point for electrons with energies above the threshold of the electronic states, but the peak decreases and broadens noticeably as the electron energy decreases below 10 eV (threshold for the b3Σ+u state). the curve also assumes a very symmetrical shape for energies below 10 eV, indicating the increasing importance of elastic collisions in determining the shape of the curve, although not the mode of energy deposition.
Noise in single injection diodes. II. Applications
Authors: van Vliet K. M. , Friedmann A. , Zijlstra R. J. J. , Gisolf A , van der Ziel A.
Published: February 2003

The noise of single injection diodes of varying degrees of complexity is studied: the trap−free insulator, the trap−free semiconductor, structures with traps, and three−dimensional insulators. Where possible, results for hot as well as thermal carriers are derived. The one−dimensional results are consistently obtained with the transfer impedance method and the emphasis is on results valid in the entire characteristic [Ohmic, space−charge−limited (SCL), and mixed conduction]. Agreement with other work in limiting current regimes is generally observed. For devices with traps explicit new formulas for the trapping noise are obtained.
Anion grain−boundary diffusion in soidum chloride
Authors: Sabharwal K. S. , Mimkes J. , Wuttig M.
Published: February 2003

The grain−boundary diffusion of 131I in Harshaw pure and Ca−doped NaCl was investigated in the temperature range between 430 and 560 °C. The Arrhenius plot of the grain−boundary diffusivity parameter Dδ displays a marked dip at around 510 °C. It is proposed that this dip is due to a phase transformation occurring at the grain boundary, possibly calcium segregation.
High−field electron emission from oxide−metal composite materials
Authors: Feeney R. K. , Chapman A. T. , Keener B. A.
Published: February 2003

High−field electron emission from unidirectionally solidified oxide−metal composites has been experimentally evaluated. Multipin arrays with pin diameters of 0.2−1.0 μm and pin densities of (5−50) ×106/cm2 were produced in UO2−W, ZrO2−W, and Gd2O3−Mo systems. Macroscopic current densities in excess of 100 mA/cm2 were routinely obtained and the observed emitter lifetime was in excess of 2000 h.
Electrical resistivity of silver foils under uniaxial shock−wave compression
Authors: Dick J. J. , Styris D. L.
Published: February 2003

The electrical resistivity of silver foils 15−25 μm thick was measured during shock−wave compression between sapphire anvils in the pressure range 25−120 kbar. Comparison of isothermal resistivity vs compression from shock measurement to a simple semiempirical calculation of resistivity under hydrostatic compression shows shock data to be consistently higher than hydrostatic results. Shock results depend on purity and thermal history of the silver foils. Deviation between shock and hydrostatic results is attributed to resistivity of vacant lattice sites generated by high−strain−rate plastic deformation in uniaxial shock compression. Estimated vacancy concentrations at 100 kbar are (1−2) ×10−3 per lattice site and concentrations vary approximately as the three−halves power of total strain. The high vacancy concentrations may be evidence for dislocation speeds near shear−wave speed. Annealing and microscopy studies of foils recovered after shocking give additional support to the above conclusions.
Two−phase equation of state and free−energy model for dynamic phase change in materials
Authors: Kamegai Minao
Published: February 2003

This paper describes the free−energy approach to calculating the dynamic phase change induced by shock waves. A thermodynamic model is developed for the nonequilibrium phase change assuming that the rate of transition is determined by the difference in the Gibbs free energy among all the phases present and that the transition proceeds toward the phase of the lowest free energy. A two−phase equation of state is derived for the Hugoniot states with the pressure and temperature as independent variables. In order to demonstrate the validity of the theory, the analysis of experimental results is made by applying the free−energy model. It is found that in highly ompressible solids. e.g., bulk modulus 280 kbar and 14% change in density at the transition pressure for δ−plutonium, there is no sharply defined transition point. Instead, the transition takes place gradually at the rate increasing with pressure up to the transition point where the process completes very rapidly. DP/DT taken at the transition point is a variable input in the present scheme. The slope of the phase boundary at the transition pressure is determined from DP/DT. The importance of the phase boundary for the shock−loading and shock−unloading processes is explained.
Mechanical behavior of metallic glasses
Authors: Gilman John J.
Published: February 2003

This is a review of the present knowledge of the mechanical behavior of metallic glasses. It begins with a brief discussion of their structures and how these relate to the small change (about 1%) in mass density that occurs when a metallic glass is crystallized. Then the elastic, anelastic, plastic, and strength properties are reviewed. Mechanisms of plastic flow are discussed. A quantitative dislocation model that successfully predicts the observed yield stresses is presented. Needs for producing future understanding are outlined.
Reduction of dislocation densities in heteroepitaxial III−V VPE semiconductors
Authors: Olsen G. H. , Abrahams M. S. , Buiocchi C. J. , Zamerowski T. J.
Published: February 2003

Electron microscope evidence from {011} cross−sectional samples of InxGa1−xP/GaP is presented to demonstrate the reduction of dislocation densities in constant composition regions of {100} III−V samples prepared by vapor−phase epitaxy with compositional grading having over−all misfit strains as high as 3.7%. Dislocations are shown to be confined to the graded region by an abrupt compositional step in both step− and continuous−graded samples. The crystal growth technique described works well for epitaxial layers which are in compression but not for those which are in tension.