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Journal of Applied Physics

Issue 12 • Date Dec 1991

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Displaying Results 1 - 25 of 77
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • The proton stopping power of aluminum and nickel ions

    Page(s): 7213 - 7216
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    Results are presented for the stopping power for protons of 1–100 MeV energy by Ni+n ions with 0≤n≤26. Older Al stopping power results are re‐examined to better estimate and reduce the error, new asymptotic stopping power parameters are obtained from improved Al and Ni ion optical oscillator strengths, and Ni stopping power results are presented with an estimated accuracy of 20%. View full abstract»

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  • Artificial magnetostatic and electrostatic modes

    Page(s): 7217 - 7222
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    Outer surfaces of simple objects such as plates, cylinders, spheres, etc. may be approximately reproduced (in an infinite number of ways) by closely assembling a number of insulated metal stripes or wires. If those stripes or wires are then suitably connected through purely reactive impedances, one obtains a system that exhibits either ‘‘magnetostatic’’ or ‘‘electrostatic’’ modes. These modes are analogous to those predicted and observed in solid bodies of corresponding shapes (plate, cylinder, sphere, etc.) made of respectively magnetic or dielectric materials. The proposed systems can thus constitute models on which a number of basic features characterizing the magnetostatic or electrostatic modes can be easily demonstrated and studied. Two specific examples, the ‘‘magnetic’’ plate, and the ‘‘magnetic’’ cylinder, will be described in detail in this paper, both theoretically and experimentally. Other models exhibiting electrostatic modes will also be presented but only on the theoretical side. View full abstract»

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  • Experimental investigation of a plasma edge cathode scheme for pulsed electron beam extraction

    Page(s): 7223 - 7226
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    A scheme with the potential for generation of an electron beam with high brightness and several μs pulse duration for microwave generation, electron accelerators, or free electron lasers is investigated experimentally. An electron beam is extracted transversely to the flow of a plasma jet. The transverse boundary of the plasma allows extraction of a space charge limited electron current for 7 μs at a current density of 18 A/cm2. At present, a normalized microscopic brightness of 8×108 A m-2 rad-2 is achieved. Closure of the extraction gap by invasion of plasma has been observed with a typical velocity of 0.1 cm/μs. Higher current density and higher brightness are expected for higher plasma densities and larger extraction fields. View full abstract»

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  • Upconversion‐pumped 2.8–2.9‐μm lasing of Er3+ ion in garnets

    Page(s): 7227 - 7239
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    Upconversion‐pumped lasing characteristics near 3 μm on the 4I11/24I13/2 transition of the Er3+ ion in Er:YSGG (erbium‐yttrium‐scandium‐gallium garnet) and Er:YAG (erbium‐yttrium‐aluminum‐garnet), laser state spectroscopy, and population kinetics, are the main subjects discussed. The wide difference in lasing patterns of both garnets can be attributed to the difference in population inversion kinetics which was studied by analyzing the rise and decay of fluorescence starting from the laser states. It is shown that the effective decay times, τ1 and τ2 of the lower and upper laser states, are changed during lasing by the nonlinear energy‐transfer processes such that the resulting ratio becomes τ12≪1. In Er:YSGG this condition is established during the declining phase of the 4I11/2 population, whereas in Er:YAG it occurs only for a short time during the rising phase. Consequently Er:YAG lases in a self‐terminating pulsed mode. The role of various energy‐transfer processes in the upconversion‐pumped population inversion kinetics is discussed and analyzed. It is experimentally shown that the lower 4I13/2 laser state in both garnets is depopulated by the cooperative energy summing due to the di‐ and tri‐ionic interactions. Because of these interactions, the 4I11/2 and 4S3/2 states are populated with ensuing fluorescence from these states at 980 and 550 nm, respectively. The indication that the latter state is populated directly by the tri‐ionic interaction, rather than via the former state by two sequential ion‐pair interactions, follows from the experimental fact that the 550‐nm fluorescence rises faster and - reaches its maximum sooner than the 980‐nm fluorescence. The previously proposed kinetic rate equations for Er:YAG and Er:YSGG were modified by adding a cubic term to represent the tri‐ionic interaction. The steady‐state solutions yielded approximately cubic dependence of green fluorescence intensity on the intensity of pump radiation in agreement with the experiment. These solutions also explained deviations from cubic dependence observed experimentally in several erbium‐doped crystals. View full abstract»

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  • All‐optical switching of solitons in two‐ and three‐core nonlinear fiber couplers

    Page(s): 7240 - 7243
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    We present a numerical investigation of all‐optical switching of solitons in two‐ and three‐core nonlinear fiber couplers. Both self‐switching of solitons and phase‐sensitive switching are considered. The extension of the results to multicore couplers is briefly discussed. View full abstract»

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  • Second‐ and third‐harmonic generations in ultrathin phthalocyanine films prepared by the molecular‐beam epitaxy technique

    Page(s): 7244 - 7248
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    Second‐ and third‐harmonic generations in ultrathin (200‐Å)films of fluoro‐bridged aluminum phthalocyanine polymer have been observed in the geometry of Maker fringe experiment using Nd:YAG laser fundamental light. Two types of films, single‐crystalline and polycrystalline films, with different orientations grown by the molecular‐beam epitaxy technique have been used. Observed dependence of the generated second‐ and third‐harmonic intensities on the polarization of light and the angle of incidence is discussed based on the symmetry of the film structures. Enhancement of the harmonic intensities is realized in the single‐crystalline film. View full abstract»

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  • Second‐harmonic generation by Cerenkov‐type phase matching in a poled polymer waveguide

    Page(s): 7249 - 7252
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    A copolymer of methyl methacrylate and azo‐dye‐substituted methacrylate is corona‐poled. Cerenkov‐type second‐harmonic generation (SHG) of Nd:YAG laser is observed in the poled polymer waveguide even though there is strong absorption of the SHG wavelength. The total SHG conversion efficiency is 1.72 × 10-3%, and the net SHG conversion efficiency in the waveguide is 0.21%. View full abstract»

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  • Output characteristics of an optically pumped Ta vapor laser

    Page(s): 7253 - 7256
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    Output characteristics of an optically pumped tantalum vapor laser and the distribution of tantalum vapor generated by irradiation of a laser have been investigated experimentally. Ta vapor is generated by irradiation of a pulsed YAG laser and then the Ta atoms are optically pumped by a KrF excimer laser. It is observed that the maximum output energy is 160 nJ, the maximum optical conversion efficiency is 0.01%, and the ground‐state Ta atoms are distributed not only in the luminous space of the vapor but also around it. View full abstract»

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  • Application of the transfer function method in calculations of the directivity pattern of ultrasonic transducer

    Page(s): 7257 - 7260
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    In this paper the authors applied an original transfer function method for calculations of radiation patterns in the case of Bessel circular transducers. It is known that the amplitudes of some natural vibration modes of circular plates are Bessel functions of zero order [R. R. Aggarval, JASA 24, 463 (1952)]. In the paper the natural vibrational modes of a circular disk‐shaped ultrasonic transducer were employed. As it follows from the numerical calculations, it is possible to obtain for Bessel‐like transducers the nondiffracting main lobe. The latter is in accordance with the suggestions of the paper [J. Durnin, J. Opt. Soc. Am. 4, 651 (1987)].   View full abstract»

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  • Terawatt fiber pinch experiments

    Page(s): 7261 - 7272
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    Pinch formation in fiber pinch experiments has been investigated in the lower terawatt regime. The main results are: (1) there are upper limits of breakdown voltage (∼700 kV) and current rise rate (∼20 kA/ns) beyond which leak discharges develop within the vacuum feed of the pulseline KALIF; (2) there is a lower limit of fiber radius (∼10 μm) below which pinch disruptions take place at a pinch current of ≳300 kA; (3) the hot (Te≤1 keV) inhomogeneous pinch plasma develops typically 10 ns after local collapses (micropinches) at a pinch current ≳400 kA and lives for more than 50 ns; (4) neutron emission (yield of CD2 fibers ∼1010) appears mostly isotropic; (5) all fiber pinches show global expansion with velocities reaching from typically 10 μm/ns (initial expansion) to ≳100 μm/ns; and (6) the power requirements for the fiber ablation process are contradictory to those for the final pinch phase. View full abstract»

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  • Some features of power balance in normal glow discharge in CO2, N2, and their mixtures with He

    Page(s): 7273 - 7281
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    The results of the theoretical and experimental investigation of a power balance in a normal glow discharge in CO2, N2, and their mixtures with He are given. It is shown that power contributed to this discharge goes essentially to the excitation of the metastable oscillatory levels of the CO2 and N2 molecules and to their dissociation. It is ascertained that the relaxation of the excited levels occurs on the discharge tube walls, while the recombination takes place into the tube space by the triple collisions with the transition of bond energy to the Joule heat. The experimental data enable one to assert also that the shape of the electron distribution function in the discharge considered is invariant with respect to average electron energy into its range 0.3≤〈ϵ〉≤6 eV. View full abstract»

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  • Behaviors of ionization wave packets within finite positive columns

    Page(s): 7282 - 7288
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    Behavior of ionization wave packets was investigated in wave‐free positive columns of Ne‐N2 and He. The position of envelope wave packet launching was displaced with an excitor along the tube axis, while phases of included carrier waves shifted only a little. The anode end of positive column played an important role in propagation of the carrier wave, causing such a phase shift. The influence of anode end on the wave behavior was explained by a phenomenological model. View full abstract»

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  • Computer simulation of dose effects on composition profiles under ion implantation

    Page(s): 7289 - 7294
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    Here is presented a computer code ‘‘dynamic sasamal,’’ which has been developed to simulate the dose dependence of concentration profiles and sputtering yields under ion implantations. The model calculations have been applied for high dose implantations of 50‐keV nitrogen into zirconium and aluminum. The results are compared with composition profiles obtained by Rutherford backscattering spectrometry (RBS) and with semiempirical values. In the case of Zr, agreements between calculated composition profiles and experimental profiles obtained by RBS analysis were excellent for all fluences up to 1018 ions/cm2 and the calculated sputtering yield decreased toward the semiempirical value with the increase of the fluence. In the case of Al, for fluences up to 7.5×1017 ions/cm2, the composition profiles obtained by RBS measurements agreed well with the calculated results, but for a fluence of 1×1018 ions/cm2, the measured profile deviated from the calculated one; while the calculations assume a saturation concentration equal to the saturated nitride phase, nitrogen concentrations of 55% were measured within the mean ion range. View full abstract»

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  • Analysis of Rayleigh light scattering of semidilute polymer solutions and gels

    Page(s): 7295 - 7308
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    This paper deals with two major problems often encountered in analyzing the measured autocorrelation functions in photon correlation spectroscopy of semidilute polymer solutions and gels: partial heterodyning and the interpretation of slow relaxation modes. These topics are discussed in the context of measurements of semidilute aqueous polyacrylamide solutions and gels used as electrophoresis media. Following a review of basic principles of Rayleigh light scattering and photon correlation spectroscopy, data analysis procedures, including the constrained Laplace inversion program contin, are first re‐examined by presenting the results from aqueous latex standard solutions. The method to analyze the partial heterodyne autocorrelation function is then presented and tested against the simulated partial heterodyne autocorrelation functions. Finally, the recently observed slow relaxation modes in polyacrylamide solutions are examined in detail with a test of contin against the simulated autocorrelation functions consisting of a trimodal distribution of relaxation rates. The results confirm that the slow relaxation modes detected in polyacrylamide solutions are indeed physical modes originating from structural relaxation and interdiffusion. View full abstract»

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  • Transient behavior of boron diffusion coefficient in silicon in oxidizing ambient and extrinsic conditions: Influence of point defect recombination

    Page(s): 7309 - 7314
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    We present experimental results that show the variation of the diffusion coefficient of boron in silicon as a function of the oxidation time in extrinsic conditions. A model is then developed that explains quite satisfactorily this experimentally detected dependence. The model assumes that recombination between self‐interstitials and vacancies takes place reducing their number and consequently their contribution to the diffusion of boron. Our results show that this method can fit experimental data using only the interstitialcy diffusion component as a parameter. The best fitting is obtained when fI equals 0.4. View full abstract»

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  • Annealing behavior of Ga and Ge antisite defects in neutron‐transmutation‐doped semi‐insulating GaAs

    Page(s): 7315 - 7317
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    The evaluation of GaAs and GeAs antisite defects in neutron‐transmutation‐doped semi‐insulating GaAs was studied by the photoluminescence measurements at temperatures ranging from 15 to 80 K. The annealing behavior of both the GeAs acceptors and the band‐edge distortion, induced by the neutron irradiation, plays an important role in the detection of GaAs double acceptors. The 200‐meV level of the GaAs double acceptor cannot be observed unless the 30‐meV GeAs and 78‐meV GaAs levels are partially or completely filled with electrons. View full abstract»

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  • The strength behavior of granulated silicon carbide at high strain rates and confining pressure

    Page(s): 7318 - 7326
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    The dynamic Mohr–Coulomb behavior of silicon carbide (SiC) was inferred from symmetric pressure/shear plate‐impact experiments which entail planar impact of two SiC plates inclined at 15° to the impact direction. The transverse velocity of the free rear surface of the target plate was recorded using a laser Doppler velocimeter system, and the experiments were simulated using a postulated viscoplastic constitutive model that accounts for comminution and dilatancy. Model parameters were varied until the computed and measured velocity histories agreed. The results indicate that comminution occurred soon after loading, and thus the experiment measures the behavior of granulated material at shear strain rates of ≊105 s-1 and mean stress ranging from 1 to 9 GPa. A friction coefficient of 0.23 was obtained, which is about half the value for quasistatic compression of precomminuted ceramic reported in the literature. The simulation results were strongly affected by the values chosen for the friction coefficient and yield strength parameters; changes in the dilatancy, rate‐sensitivity, and strain‐hardening parameters had a lesser effect. View full abstract»

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  • The elastic and electromechanical properties of tetragonal BaTiO3 single crystals

    Page(s): 7327 - 7332
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    From velocity of sound measurements, obtained using Brillouin scattering and ultrasound techniques, the elastic and piezoelectric constants at room temperature have been determined on high‐quality monodomain tetragonal BaTiO3 single crystals. The elastic constants are in fair agreement with those measured previously by the low‐frequency equivalent circuit method. However, the electromechanical properties are significantly different. It is suggested that high frequency relaxation may have an influence on the measurements of those parameters.   View full abstract»

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  • A photoemission study of cluster growth and morphology on inert substrates

    Page(s): 7333 - 7341
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    Thin metal overlayer growth on solid xenon was characterized by means of synchrotron radiation photoemission spectroscopy. We employed a simple experimental arrangement in which a closed‐cycle refrigerator and in situ evaporated metal films were used as substrate for Xe condensation. A ‘‘sandwich’’ geometry, in which the overlayer metal was used as substrate for Xe condensation, simplified the isolation of metal and Xe emission features. The evolution of the Xe and metal photoemission intensity and the line shape of core and valence states, as a function of metal coverage, were used to estimate average particle size and nucleation site density. The coverage dependence of the Sm 4f binding energy, as well as a number of newly identified spectral fingerprints of particle coalescence, support the measured film morphology and particle size. View full abstract»

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  • In situ stress measurements of gold films on glass substrates during thermal cycling

    Page(s): 7342 - 7348
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    The stress of thin (100 nm) gold films grown by electron‐beam deposition onto cover‐glass substrates was measured dynamically during heating and cooling cycles between room temperature and 500 °C. The initial tensile stress, 82 MPa of the as‐deposited films increased slowly with temperature up to about 300 MPa at 375 °C, and then decreased to 120 MPa on further heating to 500 °C. When the film was cooled from 500 °C back to room temperature, the final film stress became compressive (-50 MPa). A transmission electron microscope study has shown that when the temperature is raised above ∼370 °C, which is the eutectic temperature of the gold–silicon binary alloy, an interfacial reaction started between the gold film and the glass substrate. This interfacial reaction can account for the stress relaxation occurring at the high temperatures. View full abstract»

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  • Anomalous deuterium trapping in evaporated iron films studied by positron annihilation

    Page(s): 7349 - 7353
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    Forward recoil energy spectroscopy showed that thin, evaporated Fe films trap anomalously large quantities of deuterium. Positron annihilation was used to investigate how the film microstructure influenced this trapping. Polycrystalline films trapped more deuterium and contained more open volume defects than single‐crystal films. Annealing reduced both trap and open volume defect concentrations. These results strongly suggest that coalescence voids produced during the thin‐film deposition were the sites for the trapping of deuterium.   View full abstract»

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  • Coalescence of buried CoSi2 layers formed by mesotaxy in Si(111)

    Page(s): 7354 - 7361
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    Evolution and microstructure of buried CoSi2 layers formed by 100‐keV Co+ implantation at 350 °C into Si(111) are systematically studied in this work. Implant doses ranged from 1 × 1016 to 1.6 × 1017 cm-2. Three types of CoSi2 precipitates are observed during the mesotaxial process: A type (fully aligned with the host lattice), B0 type (twinned on the (111) plane parallel to the surface), and B1,2,3 type (twinned on one of the three {111} planes inclined to the surface). The fraction (probability of occurrence) of each type varies with both the implantation and annealing conditions. The critical dose required to form a continuous layer after 600+1000 °C annealing is found to be the same, ≊ 1.1 × 1017 cm-2, in both (111) and (001) substrates, despite pronounced differences in precipitate morphology. Formation of a continuous, twinned (B0 type), buried layer after 600+1000 °C annealing is shown to be possible in (111) samples implanted at the critical dose. View full abstract»

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  • Structural and optical properties of Al0.48In0.52As layers grown on InP by molecular beam epitaxy: Influence of the substrate temperature and of a buffer layer

    Page(s): 7362 - 7369
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    We have studied the crystalline and optical properties of AlyIn1-yAs ternary alloys grown by molecular beam epitaxy on InP substrates. We obtain Al0.48In0.52As layers with both high structural quality and excellent optical performance by growing (i) at high substrate temperature (600 °C), (ii) on a high‐quality GaxIn1-xAs/AlyIn1-yAs short‐period superlattice buffer, (iii) or on a high‐quality GaxIn1-xAs buffer layer, as attested by double‐crystal x‐ray diffraction and photoluminescence measurements. In addition the experimental results indicate a significant reduction of the clustering level in these samples which is interpreted in terms of a smoothing of the growth front, a thermodynamically controlled growth mode, and the interplay between In segregation and In desorption. Our investigations further show that the improvement of the structural quality and of the optical performance are strongly correlated. Finally, we report the first evidence of excitonic features in photoluminescence excitation spectra of the AlyIn1-yAs ternary alloy. View full abstract»

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  • Structural characterization of Co‐Re superlattices

    Page(s): 7370 - 7373
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    Co‐Re superlattices were prepared with nominal periodicities of 65–67 Å and varying bilayer composition. The structural characterization was made by x‐ray diffraction and Rutherford backscattering spectrometry (RBS). First, second, and third order satellites are observed in the x‐ray diffractogram at 2θ values and with intensities close to those predicted by simulation. This confirms the coherence of the superlattice. RBS measurements combined with RUMP simulations give information on interface sharpness and the absolute thicknesses of the Co and Re layers. Discrepancies between the experimental and simulated diffractograms are found for Co thicknesses below 18 Å. 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