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Journal of Applied Physics

Issue 11 • Date Nov 1983

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Displaying Results 1 - 25 of 118
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Secondary electron emission in the scanning electron microscope

    Page(s): R1 - R18
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    This paper surveys experimental results concerned with secondary electron emission of surfaces bombarded by primary electrons with respect to scanning electron microscopy. The energy distribution, the angular distribution, and the yield of secondary electrons from metals and insulators are reviewed as well as the escape depth of the secondary electrons and the contribution of the backscattered electrons to the secondary electron yield. The different detectors for secondary electrons in the scanning electron microscope are described. The contrast mechanisms in the scanning electron microscope, material, topography, voltage, magnetic, and crystallographic orientation contrast based on secondary electron emission, as well as the lateral resolution, depending among other things on the spatial distribution of the emitted secondary electrons, are discussed. View full abstract»

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  • Elastic wave scattering from irregular voids

    Page(s): 6079 - 6085
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    Results are presented for elastic wave scattering from irregular voids embedded in Ti alloy by the diffusion bonding process. The defects examined are: two overlapping spherical voids of unequal radii, two overlapping voids consisting of a sphere and a prolate spheroid, and a spherical void with an encircling crack. Representative plots are given for the raw waveforms, magnitude of the deconvolved Fourier transform, and in some cases the time impulse response function. The data are compared to and analyzed in terms of two current theoretical approaches. While good quantitative agreement was observed over certain ranges, the comparisons point to definite (in some cases not unexpected) limitations in either the pertaining theory or experiment or both. The results are discussed with an eye toward applications to nondestructive evaluation. View full abstract»

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  • Differential laser Doppler interferometry for high surface velocity measurement

    Page(s): 6086 - 6093
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    A single‐beam Doppler interferometer is described, whereby light scattered by the diffuse target at slightly different directions interfere, producing a differential Doppler frequency which is much smaller than the Doppler shift of either beam. Due to the diffuse nature of the light scattered by the target, the conditions for alignment of the interferometer must include the effects of speckle decorrelation caused by both longitudinal and tilting motions of the target. Error sources, both systematic and random, are discussed. Ways to minimize the systematic error stemming from uncertainty in the actual direction of the motion, are discussed. The interference signals are processed digitally to minimize the effect of random errors, which can be reduced typically to 8% for the acceleration period and to a negligible degree for the constant velocity phase of the motion. A special exploding‐foil accelerator was constructed to test the new measurement scheme. Experimental results show repeatable measurements of velocity profiles up to about 0.4 mm/μs. View full abstract»

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  • Analysis of manganin and ytterbium gauge data under shock loading

    Page(s): 6094 - 6098
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    Experimental results from previous studies on manganin and ytterbium piezoresistance gauges are analyzed. The gauge stresses and strains for the analysis were approximated from geometrical considerations as suggested in the earlier studies. The results of our analysis lead to conclusions that are significantly different from the previous work. The reasons for these differences are discussed and the requirements for a more rigorous analysis are outlined. View full abstract»

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  • Charging phenomena in the scanning electron microscopy of conductor‐insulator composites: A tool for composite structural analysis

    Page(s): 6099 - 6112
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    Useful applications of charging phenomena occuring during scanning electron microscopy (SEM) of conductor‐insulator composites have been investigated. Unlike the charging of insulating particles in conventional SEM techniques, the local field effect in a conductive composite enhances the relative secondary electron emission in the isolated conductive grains. This ‘‘reverse’’ charging characteristic was utilized for the mapping of dispersion, orientation and segregation characterization in conductor‐insulator composite systems. The charging phenomenon directly reflects the relative electrical continuity of the conductive filler particles in the insulating matrix. The photographic display of the conductive filler arrangement in the composite using this charging phenomenon is termed a SEM charging micrograph. Carbon black/polyvinyl chloride composites with both spherical and chain‐like carbon blacks were used in this study. The structural aspects of such composites as revealed by charge display techniques were found to be directly correlatable with the electrical properties of the composites. This technique is applicable to composites with both small (100 Å) and large (over 10 μ) fillers. View full abstract»

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  • Enhancement of ion beam currents through space‐charge compensation

    Page(s): 6113 - 6118
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    Neutralization of the positive ion space charge between the grids of a positively charged‐ion accelerator by injecting negative charges into this region has been studied theoretically. The current density of a beam of charged particles being accelerated between two parallel plate electrodes can be increased substantially by this injection. Multiple beams of oppositely charged particles can be used to produce the most substantial increases in the current density of the primary beam. The current density of this beam increases monotomically with the number of optimally selected, injected particle beams being used. There is an optimum injected particle current density and energy associated with each beam that yields the maximum extracted beam current density for a given number of injection stages. The total required injected particle current density, regardless of the number of stages used, is of the order of the ion current density times the square root of the extracted ion‐to‐injected particle mass ratio. View full abstract»

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  • Model of positive ion sources for neutral beam injection

    Page(s): 6119 - 6137
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    A comprehensive model is presented to describe the physics of positive ion sources used to generate hydrogen isotope neutral beams for the heating of confined plasma in magnetic fusion energy programs. The model considers 11 important atomic and molecular reactions. A set of particle balance equations, together with those for the primary and secondary electrons in the sources, are solved simultaneously. Taking as input the source geometry, gas inlet flow rate, arc current and voltage, as well as the wall recombination coefficient and the measured temperatures of neutral atoms and molecules, the model gives as output the following information: the ion current densities available for extraction, primary electron density and energy distribution, and secondary electron density and temperature. These calculated results are compared with data of several Lawrence Berkeley Laboratory ion sources, both conventional and magnetic bucket types. Exploratory calculations are made for sources of different proposed designs with the aim of improving the source performance. View full abstract»

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  • X‐ray spectral line coincidences between fluorine K‐ and transition‐metal L‐series lines

    Page(s): 6138 - 6149
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    X‐ray spectroscopy was performed in the 12–15‐Å region, recording L‐series lines from selected laser‐irradiated transition metals. Line coincidences and near coincidences were identified between Cr, Mn, Fe, and Ni L spectra, and F viii and F ix K‐shell lines. Wavelengths were determined to accuracies of 1–3 mÅ and will be utilized in selecting potential pumping candidates in future x‐ray lasing schemes. High‐resolution x‐ray spectra were collected under controlled illumination and target conditions, using 1.05‐ and 0.527‐μm laser excitation with the KMS CHROMA laser. Laser intensity varied from 1.2–2.5×1014 W/cm2 in 200‐ps pulses. Three groups of x‐ray spectra were collected with highly dispersive x‐ray crystals at wave bands centered at 12.643, 13.781, and 14.458 Å, corresponding to H‐ and He‐like lines from fluorine. Two specially designed flat crystal spectrographs employing camera shutters were used with pairs of beryl and thallium acid phthalate (TAP) crystals. The spectra from potential lasant and pump candidates could be recorded on the same spectrogram to aid in identifying x‐ray line coincidences. In cases where wavelengths were measured in both the 1.05‐ and 0.527‐μm laser work, agreement within 1–3 mÅ was obtained for the L‐series x‐ray lines. Within this accuracy range, some five L‐series x‐ray lines, mostly 2p‐3d transitions from the metals Cr, Mn, and Ni, had wavelength values coincident with K‐series lines in fluorine. View full abstract»

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  • Monte Carlo studies of attachment in HCl and HCl–N2 mixtures

    Page(s): 6150 - 6153
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    Recent studies of attachment in pure HCl and HCl–N2 mixtures are analyzed by Monte Carlo simulations. The drift velocity and attachment coefficients are calculated as a function of field strength and relative concentration of HCl. Cross sections for momentum transfer, vibrational excitation, and attachment are derived. View full abstract»

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  • Velocity diagnostics of mildly relativistic, high current electron beams

    Page(s): 6154 - 6159
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    We describe two diagnostic methods for measuring the velocity components of mildly relativistic, high current electron beams. The first involves a measurement of the radial electrostatic potential and of the beam current and yields the time resolved, spatially averaged axial beam velocity v. The second requires a measurement of the beam cyclotron wavelength in the guiding magnetic field and yields a spatially averaged product γv, where γ=(1-v2/c2-v2/c2)-1/2 and v is the transverse beam velocity. By combining the two techniques we obtain v and v for a 0.4–1.2 MV electron beam carrying a current of 1–2 kA. View full abstract»

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  • Studies of the effects of a long pulse electron beam on the autoaccelerator

    Page(s): 6160 - 6174
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    The propagation of a long pulse (600–800 ns) electron beam in an evacuated drift tube and accelerator gap geometries has been studied. Particular attention has been focused on the drift tube and gap surfaces since formation of plasma here will effect the operation of accelerators such as the Autoaccelerator. Experimental evidence of energetic electron and ion flux to the wall have been obtained. These and other measurements have led to a model describing the space‐charge neutralization of the beam and its effect on accelerator operation. View full abstract»

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  • Hole formation in tellurium alloy films during optical recording

    Page(s): 6175 - 6182
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    The material transport phenomena of hole machining, which occur during optical recording, are described for metal films such as elemental tellurium and its alloys. It is shown that the temperature gradient resulting from a focused laser beam creates a minimum in the surface tension at the hottest point of the molten spot. Consequently, a shear stress pulls material from the center of the melt towards the edge, forming a rim. It is demonstrated that the film is thin enough to have all material pulled away, thereby forming a hole and that this occurs in a time frame of about 10–50 ns. Also the cross sectional shape of the rim is modeled. Experimental information corroborating this model is obtained by investigating dropouts, which are created by recording close to the threshold. (A dropout is defined as a missing hole; i.e., it is intended to machine a hole but it fails to open.) The surface profile of dropouts indicates that material has retracted from the center to form a rim. Also, it is shown that dropouts are indeed frozen‐in states of the hole opening process. Experimental data on cross sections of rims around fully opened holes and around optical dropouts support the model, showing rounded rims for the first case and very steep edges surrounding dropouts. View full abstract»

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  • Stimulated emission in strained‐layer quantum‐well heterostructures

    Page(s): 6183 - 6189
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    Stimulated emission data are presented on a large variety of strained‐layer quantum‐well heterostructures (QWH’s) and superlattices (SL’s) grown by metalorganic chemical vapor deposition (MOCVD). These structures consist of barrier‐well combinations of thickness LB,Lz ≲150 Å made from GaAs‐InGaAs, GaAsP‐GaAs, and GaAsP‐InGaAs. Also employed are higher band‐gap confining layers of InxAlyGa1‐x‐yAs, AlyGa1-yAs1-xPx, and AlxGa1-xAs. All of the heterostructures are grown on a GaAs substrate with and, in some cases, without a graded layer. The strain range between 0.2 to 12.5×10-3 is examined. Photopumped, these heterostructures operate as continuous (cw) 300 K lasers, with thresholds of 1.6–7.5×103 W/cm2, for periods of time between 0.5 to ≫35 min. Under high‐level excitation, the equivalent of Jeq∼103 A/cm2, laser operation fails or is quenched by networks of dislocations (with 〈110〉 Burger’s vectors) that are generated within the strained‐layer region of the QWH’s or SL’s. These dislocation networks, which are revealed via transmission electron microscopy (TEM), occur at a more rapid rate in higher threshold samples and ones with higher built‐in strain. The TEM data show, however, that no heterointerface defects (dislocations) are present in the as‐grown strained‐layer regions but are present in thick (bulk) graded regions. View full abstract»

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  • First‐order model of the change with refractive index of the frequency of semiconductor lasers

    Page(s): 6190 - 6192
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    The derivative with refractive index of the frequency of a spectral line of a diode laser is deduced from a model of the internal structure as a rectangular dielectric waveguide. It is found that the derivative depends critically on the spreading of the optical field beyond the guide walls. If the field is strictly confined to the interior of the guide, the derivative depends on only the change of the index inside the guide, and it is negative. If the field extends appreciably outside the guide walls, the derivative depends on changes of the index outside as well as inside the guide, and it varies rapidly with guide design. For lasers operating in the fundamental spatial mode, its numerical value can be appreciably less than for a closely confined mode and its sign can be either negative or positive. Relating the results to frequency modulation of the fundamental mode laser suggests that its sign can change with dc bias, and also its magnitude. View full abstract»

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  • Photodynamics and stability of laser active (F+2)A centers

    Page(s): 6193 - 6198
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    In additively colored KCl : Li crystals, the (F+2)A color center laser operates through a photodynamic equilibrium in which UV excitation generates a partial conversion of (F2)A centers to (F+2)A. Evidence is presented which shows that continuous UV exposure is necessary to sustain laser action because of the neutralization of (F+2)A centers which occurs through the capture of FA center electrons. The bleaching of FA centers results directly from absorption of the 1.3‐μm pump radiation. Since the absorption is extremely weak, only modest UV intensities are needed for intense cw laser operation. View full abstract»

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  • Performance of an array of plasma pinches as a new optical pumping source for dye lasers

    Page(s): 6199 - 6212
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    A new optical pumping source consisting of an array of plasma pinches in the hypocycloidal‐pinch geometry is employed to pump a variety of dye lasers. A dye cuvette is inserted along the symmetry axis of the plasma device such that it may be surrounded by the plasma pinch. The light from the plasma pinch is very intense and rich in ultraviolet, which makes it an attractive optical pumping source for dye lasers, particularly in the blue‐green spectral region. Control of the plasma fluorescence is achieved by the choice of gas, its fill pressure, and the capacitor bank voltage and its stored energy. The rise time of this ‘‘plasma flashlamp’’ depends mainly on the gas species and the fill pressure. Output energy of ∼2 mJ per cm3 of lasing medium, or 2 kW/cm3 for a 1‐μs laser pulse, is obtained from rhodamine 6G, coumarin 480, LD 490, and coumarin 504 dyes. That both the coumarin 480 and rhodamine 6G lasers have the comparable output power is a direct proof that the present optical pumping source is more efficient than the commercial xenon flashlamps in pumping lasers in the blue‐green spectral region. View full abstract»

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  • Second harmonic generation with surface guided waves in signal processing geometries

    Page(s): 6213 - 6217
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    The nonlinear mixing of two oppositely propagating waves can be used to perform the convolution of two waveforms. We have examined the nonlinear cross sections for this interaction based on waves guided by both dielectric and metal films. The numerical analysis shows that optimum efficiencies are obtained with dielectric film guided waves and that useful cross sections can be obtained with organic nonlinear materials. View full abstract»

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  • Characterization of proton‐exchange slab optical waveguides in z‐cut LiNbO3

    Page(s): 6218 - 6220
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    We report the results of a systematic study on planar optical waveguides fabricated in z‐cut LiNbO3 by proton exchange in benzoic acid. It was found that the refractive index varied with depth and could be accurately modeled by a step index profile with Δn=0.126. Diffusion coefficients have been calculated from mode effective refractive index measurements, assuming a step index profile, and hence a value for the activation energy for the proton exchange process has been deduced. The lowest measured optical propagation loss in single‐mode waveguide at a 633‐nm wavelength was 2.4 dB/cm. View full abstract»

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  • Strain‐induced effects in GaAs directional coupler switches

    Page(s): 6221 - 6222
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    Metal‐gap directional coupler structures have been fabricated on n/n+ GaAs layers. Coupling lengths measured by a sequential cleaving technique are found to be dependent upon metal thickness. Strain‐induced refractive index changes are shown to be the dominant cause of waveguiding. View full abstract»

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  • Characterization of TiO2, LiNb3O8, and (Ti0.65Nb0.35)O2 compound growth observed during Ti:LiNbO3 optical waveguide fabrication

    Page(s): 6223 - 6231
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    TiO2, LiNb3O8, and (Ti0.65Nb0.35)O2 compounds have been observed and characterized during the fabrication of optical waveguides by Ti indiffusion in LiNbO3, performed in a flowing dry O2 atmosphere. Ti oxidizes by reacting with both O atoms of the surrounding atmosphere and of the LiNbO3 substrate. TiO2 formation is followed by LiNb3O8 and (Ti0.65Nb0.35)O2 phase growth. With further increasing in the annealing temperature the TiO2 and LiNb3O8 compounds are consumed and vanish. After 30 min at 950 °C both Y‐ and Z‐cut substrates appear covered only by a uniform and epitaxial (Ti0.65Nb0.35)O2 layer which behaves as the real source for Ti diffusion. The LiNb3O8 formation and dissolution were also observed in samples uncoated with Ti. Similar results were observed in LiNbO3 samples annealed in dry N, Ar, and static air. View full abstract»

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  • Quantitative study of the aberrations for focused acoustic plane waves obliquely incident upon a plane interface

    Page(s): 6232 - 6239
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    The nonlinearity of Snell’s law induces aberrations for waves focused under oblique incidence. A detailed study of the phenomenon is given here for the case of a water‐steel interface, on which mode conversion occurs. Two approaches are taken: first a coarse geometrical one and second a finer plane wave spectrum expansion. A comparison between the two models shows the validity of the geometrical approach. The fundamental parameters that must be taken into account and their respective influences are deduced, and limits are fixed over which the correction of aberrations prove necessary. The application of these conclusions has made possible the localization of defects inside a steel sample. View full abstract»

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  • Reflective array compressors using 180° reflecting metal dot arrays

    Page(s): 6240 - 6244
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    Recently, a reflective array compressor using 180° grooved reflectors and a 3‐dB multistrip coupler has been described. This has the advantage over conventional 90° reflective devices that the surface waves undergo only one reflection instead of two, and so the insertion loss can be low. This paper reports a new device, using surface acoustic waves propagating on YZ LiNbO3, in which the grooves are replaced by metal dot arrays, removing the need for ion‐beam milling and—through variation of dot density—providing a simple method of weighting. The devices designed had a time‐bandwidth product of 1000, dispersion time of 20 μs, bandwidth of 50 MHz centered at 150 MHz, and a 40‐dB sidelobe six‐term Taylor amplitude weighting. Compared with dot array devices using 90° reflectors the design is simplified since the velocity and scattering anisotropy, important for 90° reflectors, need not be considered. The surface wave velocity change under the metal dot array is potentially a source of phase error, but it is shown that a simple empirical correction in the mask design is sufficient to reduce this to around 5° rms. Deviation of the weighting characteristic from the ideal is typically of the order ±1 dB. View full abstract»

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  • Thermal wave imaging of closed cracks in opaque solids

    Page(s): 6245 - 6255
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    Thermal wave scattering from closed, slanted cracks is investigated both theoretically and experimentally. A Born approximation calculation is carried out for the particular case of gas‐cell detection for three crack angles. Good agreement is found with experimental images of both the magnitude and phase of the gas‐cell signal variation for cracks fabricated in an aluminum alloy at these same angles. Good agreement is also found between theory and experiment for the frequency dependence of the thermal wave scattering from a 45° crack. It is shown theoretically and confirmed experimentally that a strictly vertical, closed crack is not observable by gas‐cell detection, but is easily seen by mirage‐effect (optical beam probe) detection. The results for model cracks are applied to the case of brittle fractures in solids. View full abstract»

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  • Stress measurements using piezoresistance gauges: Modeling the gauge as an elastic‐plastic inclusion

    Page(s): 6256 - 6266
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    A theoretical framework is provided to analyze and interpret piezoresistance gauge measurements. The analytic developments consist of a phenomenological electromechanical model for piezoresistance and an elastic‐plastic inclusion analysis. The combination of these analytic developments can, in principle, explain the main aspects of the gauge response under shock loading. The present work may provide the basis for a complete specification of the stresses in shock wave uniaxial strain experiments and extension of piezoresistance measurements to other loading conditions. Further experiments are required to determine the material constants needed for the model and to permit detailed comparisons with the analytic results. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Meet Our Editors

Editor
P. James Viccaro
Argonne National Laboratory