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Journal of Applied Physics

Issue 5 • Date Mar 1984

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

    Page(s): toc1
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    Freely Available from IEEE
  • Fundamental noise limits of thermal detectors

    Page(s): 1243 - 1253
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    This paper examines the fundamental noise limit in arrays of uncooled thermal detectors which must change temperature to produce signals. This limit is shown to be the statistical fluctuations of the temperature of the detectors (temperature noise). The noise spectrum associated with these temperature fluctuations is derived. The spectrum’s strong dependence on thermal coupling between the detectors and their environment is also shown. This spectrum explicitly accounts for lateral heat conduction which occurs when detectors in the array are thermally coupled to each other. The detectivity is also derived which is shown to depend strongly on the spatial frequency of the signal being detected. In the ideal limit when the thermal coupling is radiation only, the detectivity of these thermal detectors is shown to be D*=1.8×1010 cm Hz1/2 W-1. This closely approaches the maximum D* of a cooled photoconductive detector when its limiting noise is also the noise in the photons from 300 K background radiation. Using the autocorrelation function in both space and time, an expression is derived for the mean square noise‐induced temperature change that occurs during the time interval between two samplings of signal and noise. Finally, it is shown that the signal‐to‐noise ratio, as derived in this paper, may be a better measure of thermal detector performance than the often‐used detectivity. View full abstract»

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  • Self‐magnetic‐field‐enhanced ion diode

    Page(s): 1254 - 1266
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    An intense ion source has been developed utilizing an ion diode that partially suppresses electron flow using the self‐magnetic field of the diode current. This is an extension of a diode class known as pinch reflex ion diodes. In this case the diode was coupled to the particle beam fusion accelerator and was configured in two different cylindrical designs. The first pinch ion diode was a straight, 42‐cm‐diam cylinder and the second, Obi, was a focusing, 26‐cm‐diam, aspheric barrel. In the Obi diode a central gas cell provided current‐neutralized beam transport. In addition, the accelerator was run in a low‐voltage, 0.8 MV, and a high‐voltage, 2.0 MV, mode. The best results showed that the Obi diode produced 3 TW of protons at 34% efficiency in the high‐voltage mode. We present an analytic model of ion efficiency, compare various diode impedance models, and discuss beam divergence mechanisms. The limitation of this ion source as a fusion driver is presently the 2–3° divergence that we measure using a shadow‐box technique. A companion paper contains numerical simulations and further analytic modeling. View full abstract»

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  • Electromagnetic particle simulations of self‐magnetic‐field‐enhanced ion diodes

    Page(s): 1267 - 1273
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    Electromagnetic particle simulations of equatorial self‐magnetic‐field‐enhanced ion diodes have been performed. These simulations complement recent experiments on the particle beam fusion accelerator using the pinch ion diode (pid) and the Obi diode. Those experiments are detailed in a companion paper. The simulations have provided useful information concerning the operation of the diode. This paper will describe many of the simulation findings in such areas as current and charge neutralization, virtual cathode formation, diode impedance, ion divergence, and electron temperatures. In addition, a model for ion efficiency has been obtained that is based upon the simulation results. This model is compared to various other efficiency models. View full abstract»

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  • Molecular stopping powers and effect of chemical bonding in gaseous amine compounds

    Page(s): 1274 - 1277
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    Molecular stopping powers of methylamine, ethylamine, dimethylamine, and trimethylamine have been measured for 0.3–2.0 MeV He+ ions. A single‐bonded atomic stopping power ϵSB(N) for nitrogen is calculated and found to be 6%–20% lower than its triple‐bonded counterpart (1/2)ϵexpt(N2). This disagreement is quite similar to a 6%–17% difference in single‐ and double‐bonded carbon and oxygen atomic stopping powers previously calculated. A lower stopping power peak energy is also observed for the atom in a molecular configuration of higher bond order. These trends demonstrate clearly the effect of chemical bonding upon stopping powers. View full abstract»

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  • Development of an atom buncher

    Page(s): 1278 - 1284
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    An ‘‘atom buncher’’ for controlling the concentration of gaseous samples has been conceptualized, evaluated theoretically, fabricated, and tested with excellent results. In effect, the atom buncher greatly increases the probability that a free atom will be in a small detector volume at a desired time. This was accomplished by using cryogenic techniques to condense atoms on a small spot and a pulsed laser to momentarily heat the spot to release the atoms at the desired time. Our work on noble gas atom counting by using resonance ionization spectroscopy is discussed as one example of the applications of the atom buncher. View full abstract»

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  • Resonant helically distorted relativistic electron beam equilibria for free electron laser applications

    Page(s): 1285 - 1298
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    This paper extends the development of a self‐consistent kinetic description of helically distorted relativistic electron beam equilibria for free electron laser applications to include particular conditions of beam propagation, not treated heretofore, which are of considerable practical interest. Radially confined equilibria are considered for a helically distorted electron beam propagating in the combined transverse wiggler and uniform axial guide fields described by B0=B0z +δB=B0z-δB cos k0z êx -δB sin k0zêy, where B0=const., δB=const., and λ0=2π/k0=const. is the axial wavelength of the wiggler field. It is assumed that the beam density and current are sufficiently small that the equilibrium self fields can be neglected in comparison with B0. In this context, it is found that there are three useful (and exact) invariants (C, Ch, Cz) associated with single‐particle motion in the equilibrium field B0z +δB. These invariants are used to construct radially confined Vlasov equilibria F0b (C, Ch, Cz) for an intense relativistic electron beam propagating in the z direction. Examples of both solid and hollow beam equilibria are considered, and it is shown that the transverse wiggler field can have a large modulational influence on the beam envelope, depending on the size of δB/B0 and other parameters. In the present work, no a priori assumption is made that the gyrofrequency (ωc=eB0bmc) of electron motion in the guide field and the frequency of axial electron motion (ω0=k0Vb) in the wiggler field are well separated. Thus the condition of beam‐cyclotron resonance with ω0≂ωc can be treated. Numerical procedures for the determination of boundaries of both solid and hollow beam equilibria are developed, and calculations of solid and hollow beam boundaries at resonance are presented. View full abstract»

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  • On the electron‐beam pumped KrF laser

    Page(s): 1299 - 1307
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    The paper deals with the complex kinetics of excitation, quenching, and absorption in an electron‐beam pumped KrF laser. The effect of the pressure dependence of the ionic recombination rates, the role of the metastables, and the formation of ArKr+ are investigated and compared with our experimental results. From the model the maximum power density together with the optimized densities of argon, krypton, and fluorine are calculated as a function of the beam‐current‐to‐outcoupling ratio. Finally, the pressure dependencies of the individual components near the optimized conditions are investigated. View full abstract»

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  • Experimental study of the lasing P/N junction as an electro‐optical transducer

    Page(s): 1308 - 1321
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    An experimental study of the small signal equivalent circuit of the lasing P/N junction itself is presented. The usual study examines the behavior of the packaged device through measurement of the dependence on dc current and on frequency of the modulus of the transfer function relating the stimulated power to the drive current. The present work features the study of the P/N junction itself through a new technique, the direct measurement of the modulus, and the argument of the ratio of the modulation of the stimulated power to the modulation of the spontaneous emission. The frequency modulation of the optical power is also studied, and the results compared with deductions from the present study of the spontaneous emission and from a published study of the amplitude and frequency transfer functions of a similar laser. All the studies support the new finding that the modulations of the junction voltage and the power are in phase with each other for frequencies up to the gigahertz range. The experimental values of the circuit elements show that the damping of the response is due to dissipation in the resistance representing the change in voltage with stimulated power. Comparison of the values of the circuit elements to the solutions of the multimode rate equations gives insight about the utility and limitations of existing formalism, in particular about the extent to which the formalism yields a single set of circuit elements which describes the transient response of all observables and about whether the observed responses are better modelled as those of a classical noise amplifier or a free running oscillator. View full abstract»

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  • An electrically triggered 200 kV rail‐gap switch for wide aperture excimer lasers

    Page(s): 1322 - 1331
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    A wide aperture (7×7 cm2), high output energy (5 J in KrF and 13.8 J in XeC1), UV preionized excimer laser is described. A self‐breakdown rail gap was employed as an output switch with the maximum voltage and current up to 230 kV and 300 kA, respectively. To solve the switching jitter problem associated with the self‐breakdown, an electrical triggering was investigated. The measured minimum switching time delay and gap closing time were 40 and 10 ns, respectively. The number of channels up to 50 was observed with a uniform distribution over the 80‐cm electrode length. The triggering jitter was measured to be less than a nanosecond. The maximum operation voltage of the triggered rail gap was 200 kV. The successful trigger operation was obtained in the range 30%–98% of the self‐breakdown voltage. View full abstract»

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  • Chemical modification of near‐surface charge trapping in polymers

    Page(s): 1332 - 1338
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    The surfaces of three polyolefin films, low‐density polyethylene, high‐density polyethylene, and polypropylene, were chemically modified by etching with permanganic acid, and low‐density polyethylene by etching with chromic acid and by staining with chlorosulphonic acid. Polytetrafluoroethylene (Teflon) was treated with a sodium naphthalene complex in glycol ether. The surfaces were examined with a scanning electron microscope, and chemical groups identified by attenuated total reflectance infrared measurements. The surfaces were then corona charged, and the charge stability and trap distributions determined by the methods of thermally stimulated charge decay and thermally stimulated current, respectively. Scanning electron micrographs revealed a nodular surface structure in polyolefins etched with permanganic acid, a rough surface without nodules in low‐density polyethylene etched with chromic acid, isolated corroded surface spots in low‐density polyethylene stained with chlorosulphonic acid, and a web‐like surface in etched Teflon. Permanganic acid removed amorphous and defective regions of the polymer surfaces, exposing more crystalline regions and crystalline‐amorphous boundaries, both of which provided trapping sites, producing better charge storers than the virgin equivalents. Lifetimes, and hence usable temperatures in device application, were increased for both negative and positive charge. The other acids reduced the lifetimes in low‐density polyethylene. Etching made Teflon as good a positive charge storer as the virgin negatively charged material, a result important to practical applications. While attenuated total reflectance measurements showed the presence of various chemical groups, charge stability seemed to depend more on surface morphology than on which active groups were added to the polymers by the etchants and staining agent. View full abstract»

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  • Deformation‐induced work function changes in Cu single crystals. I. Experiment

    Page(s): 1339 - 1345
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    Tensile deformation‐induced work function change experiments were conducted in the elastic and plastic regimes on Cu single crystals. Simultaneous measurements of load, displacement, and contact potential difference changes were made on the samples in an ultrahigh vacuum. The work function change to deformation modulus may be as large as 24 μV/MPa in the elastic regime and varied from +1.7 to -11.8 mV/% strain in the plastic regime for different surface orientations. View full abstract»

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  • Deformation‐induced work function changes in Cu single crystals. II. Theory

    Page(s): 1346 - 1352
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    The jellium model of work function change with elastic deformation has been compared to the cellular and electronegativity models and was found to give the best fit to the experimental data. A point and patch effect model has been developed to account for the work function change with plastic deformation. The single slip variant of the model provides a better fit to the experimental data than the equal cross slip variant of the model. View full abstract»

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  • Temperature dependence of 1/f noise in thin bismuth films

    Page(s): 1353 - 1358
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    We have measured the 1/f noise in thin bismuth films in the temperature range of 80–300 K. The experimental results are described in terms of mobility fluctuations. The influence of several scattering mechanisms on the noise is discussed. View full abstract»

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  • Cluster center formation in neutron‐damaged silicon

    Page(s): 1359 - 1363
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    The production of vacancy clusters in neutron‐damaged silicon has been investigated by electron spin resonance. It is found that the production of P3 four vacancies and P6 di‐interstitials is independent of oxygen concentration, suggesting that these defects are formed in the primary cascade. Approximately two P3 centers were formed per primary cascade independent of the primary mean recoil energy for irradiations in varying fast neutron spectra. This suggests that these defects are associated with the Brinkman spike which terminates the cascade. Low energy primaries from thermal neutron capture and subsequent gamma recoil are very inefficient in producing these centers. View full abstract»

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  • Strong fluctuation theory for electromagnetic wave scattering by a layer of random discrete scatterers

    Page(s): 1364 - 1369
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    The strong fluctuation theory is applied to the study of electromagnetic wave scattering from a layer of random discrete scatterers. The singularity of the dyadic Green’s function is taken into account in the calculation of the effective permittivity functions. The correlation functions for the random medium with different scatterer constituents and size distributions are derived. Applying the dyadic Green’s function for a two‐layer medium and using the bilocal and distorted Born approximations, the first and the second moments of the fields are then calculated. Both the backscattering and bistatic scattering coefficients are obtained, and the former is shown to match favorably with experimental data obtained from snow fields. View full abstract»

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  • Evolution towards thermalization, and diffusion, of sputtered particle fluxes: Spatial profiles

    Page(s): 1370 - 1378
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    Particles sputtered from solid targets in plasma deposition systems, under typical vacuum conditions, slow down in collisions with the gas phase. The spatial profiles of particle fluxes at given instantaneous energy are calculated with a simple model of a particle slowing down along straight‐line trajectories, subject to a continuous energy‐loss process. In particular, the profiles of flux thermalization are given. Model distributions in energy and direction of sputtered fluxes, with a reasonable physical basis, are used. The accumulation and diffusion of thermalized material in the gas phase is studied also, and the stationary spatial profiles are obtained. Diffusion particle currents back to the source, or towards the substrate, can then be estimated. Scaling laws are obtained that allow the analysis of any specific deposition conditions through the masses of the sputtering and sputtered particles, the binding energy of the target, and the working pressure. Because of the simplifying assumptions of the analytical model, predictions in the particular case of light targets sputtered in a comparatively heavier atmosphere should be only regarded on an orientative basis. View full abstract»

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  • Oxygen‐enhanced thermionic emission pattern of hemispherical single‐crystal LaB6

    Page(s): 1379 - 1387
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    With the application of Martin’s experimental arrangement for direct observation of thermionic emission patterns from a hemispherical single‐crystal LaB6 cathode, it has been determined that oxygen‐enhanced thermionic emission does occur for the (210) plane at the rather low partial pressure of oxygen, i.e., in the 10-9‐Torr region, at sample temperatures of 1050 °C. For further quantitative assessment, work‐function measurements by Richardson plots were done for different crystal planes of clean surface by attaching a photomultiplier. The result clearly shows that the values of the work function increases in order from (100), (210), (110), and (111). The measurements were also extended to the oxygen‐enhanced surface of the (210) plane and it was found that the results follow, phenomenologically, the Richardson plot as well. View full abstract»

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  • X‐ray photoemission of polynuclear aromatic carbon

    Page(s): 1388 - 1393
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    The evolution of the C(1s) x‐ray photoelectron spectrum is examined as a function of the size of the polynuclear aromatic molecules. The transition from a symmetric line shape to an asymmetric one occurs in the narrow range of the layer size between 10 and 22 Å. It is shown that the asymmetry reflects the area of the layer over which the π electrons can be delocalized and that it is more closely related to the actual physical size of the layer than measurements from x‐ray diffraction. The latter is illustrated in coal tars which have undergone heat treatment. The effect of the evolution of the line‐shape asymmetry on the determination of the fraction of polynuclear aromatic carbon in heterogeneous carbon materials by x‐ray photoelectron spectroscopy is also discussed. View full abstract»

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  • Characterization of fiber orientation in short‐fiber composites

    Page(s): 1394 - 1403
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    A method for measuring intermediate states of fiber orientation in short‐fiber composites is described. The technique is based on the observation that a representative fiber distribution, for example, the negative of a photomicrograph from a specimen, resembles a collection of diffraction apertures. Diffraction masks for a Fraunhofer diffractometer made from the representative fiber distributions produce diffraction patterns characteristic of the state of orientation. Analyses are presented which relate the features of the diffraction pattern to (i) the orientation distribution, (ii) shape, and (iii) aspect ratio of the fibers. The results from these analyses are in good agreement with experimental diffraction patterns from masks made from simulated fiber distribution patterns. View full abstract»

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  • Rapid Mössbauer‐based methods for the determination of iron‐bearing phases

    Page(s): 1404 - 1409
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    The variation of Mössbauer γ‐ray resonant absorption with the velocity amplitude of a vibrating γ‐ray source is examined theoretically in connection with Mössbauer‐based methods for rapid, nondestructive determination of iron‐bearing phases in different materials. The theoretical analysis can be used to simulate such methods, which are based on the difference in the Mössbauer resonant absorption by a sample with the γ‐ray source stationary and in rapid oscillation. Methods for the determination of pyrite in coal and metallic forms of iron in steels and slags are examined both theoretically and experimentally to illustrate the advantages and limitations of such rapid Mössbauer‐based methods. View full abstract»

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  • Compact coaxially excited high energy density KrF laser

    Page(s): 1410 - 1412
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    A coaxial electron beam generator is described operating without a pulse‐shortening line. It delivers pumping pulses with a length ranging from 150 up to 500 ns (FWHM). For a laser volume of 0.6 l, a pulse duration of 250 ns and a current density of about 50 A/cm2, a maximum output of 13 J is obtained. The present experiments show that this relatively high current regime is also applicable to long pulses. View full abstract»

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  • Optically pumped GaSb/Al0.6Ga0.4Sb multiquantum well lasers operating in the λ=1.5–1.6 μm region

    Page(s): 1413 - 1415
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    Multiquantum well structures of GaSb/Al0.6Ga0.4Sb were grown by molecular beam epitaxy and their spontaneous and stimulated emission properties were studied. The luminescence spectra exhibited high efficiency with the upward energy shift from λ=1.72  μm of GaSb up to λ=1.31  μm for the well width of ∼40 Å. Optically induced lasing has been obtained at the wavelength as short as λ=1.207  μm at 80 K and in the spectral region of λ=1.5–1.6  μm at temperatures as high as 80 °C. The optical thresholds of the quantum well lasers are similar to that of the more conventional GaSb/AlGaSb heterostructures. View full abstract»

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  • Nanosecond laser‐induced transient and permanent gratings and ultrasonic waves in a smectic film

    Page(s): 1416 - 1418
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    Using nanosecond laser pulses, we have observed for the first time optically induced transient and (erasable) permanent gratings in a smectic‐A film. The transient grating is accompanied by strong high frequency acoustic waves. View full abstract»

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  • Critical current uniformity and stability of Nb/Al‐oxide‐Nb Josephson junctions

    Page(s): 1419 - 1421
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    The critical current stability of Nb Josephson junctions using thin Al oxide layers as the tunneling barrier has been investigated with respect to repeated thermal cycling, aging, and annealing at elevated temperatures as a function of time. The Nb electrodes and in situ thermally oxidized Al barriers were deposited by dc magnetron sputtering prior to the lithographic formation of the individual junctions. The arrays of junctions were formed by standard photolithography techniques, reactive ion etching, and anodization. A population of 400 20‐μm‐square junctions were thermally cycled from room temperature to 6 K 4880 times with no failures due to shorts and no change in the average critical currents. These same unpassivated junctions were annealed at elevated temperatures for various periods of time until the critical currents had decreased by 50% at temperatures near 275 °C. 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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Editor
P. James Viccaro
Argonne National Laboratory