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Journal of Applied Physics

Issue 1 • Date Jul 1989

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Displaying Results 1 - 25 of 87
  • New field emission gun with energy filtering effect

    Page(s): 1 - 4
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    We have developed and tested a new kind of field emission gun. This electron gun is an energy filtering field emission gun that is able to reduce the energy spread of the beam. An energy spread as small as ΔE=0.16 eV full width at half maximum has been measured, at an accelerating voltage V=10 kV, for a probe current Ip=2.1 nA and an illuminating half‐angle α=1.2 mrad. View full abstract»

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  • Monte Carlo study of backscattering of β rays from various monoatomic slabs

    Page(s): 5 - 9
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    A Monte Carlo study of the backscattering coefficients and backscattering intensity of β rays from 204 Tl and 90 Y sources from slabs of Al, Cu, Sn, Tb, and Pb of different thicknesses is carried out. The results for angles of incidence 0°, 30°, 45°, and 60° and absorber thicknesses of 3, 5, 10, 15, 30, and 50 mg/cm2 for 204 Tl β rays and thicknesses of 3, 5, 10, 20, 50, 100, 150, and 190 mg/cm2 for 90 Y β rays are given in tabular form. On using normalization factors good agreement with the measurements of Sharma and Singh is obtained. A phenomenological attempt to investigate a relationship between the backscatter intensity and atomic number Z of the backscatterer indicates that the backscattered intensity is a linear function of ln Z(Z+1). A partial theoretical justification for this relationship is given. View full abstract»

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  • Measurement of electron energy deposition necessary to form an anode plasma in Ta, Ti, and C for coaxial bremsstrahlung diodes

    Page(s): 10 - 22
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    Measurements are made of surface doses necessary to initiate an anode plasma by electron bombardment of Ta, Ti, and C anodes for coaxial geometries characteristic of high‐power electron‐beam diodes. Measured lower and upper bounds of doses necessary to form an anode plasma are 54±7–139±16 J/g in Ta, 214±23–294±71 J/g in Ti, and 316±33–494±52 J/g in C. Within these bounds, probable values for the threshold are given under specific assumptions. The measurements are consistent with a thermal desorption model for plasma formation. View full abstract»

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  • Diffraction and bremsstrahlung radiation from a loop charge in a cylindrical pipe with a step change in wall radius

    Page(s): 23 - 36
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    A theory is developed to model diffraction and bremsstrahlung radiation in the transverse magnetic mode from a loop of charge in a cylindrical pipe with a discontinuous change in wall radius. The beam kinetics is assumed a priori. A consistent definition of the longitudinal coupling resistance is developed. Scattering effects peak at the cutoff frequencies of the modes of the larger pipe. When kinetic losses are sufficiently large, a change in loop charge radius may alter the propagation of the dominant mode when the charge moves from a larger to smaller diameter pipe. This effect is not present if the charge motion is in the reverse direction. View full abstract»

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  • Long‐pulse transversely excited 12CO2 and 13CO2 lasers

    Page(s): 37 - 42
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    A conventional, transversely excited CO2 discharge module is fitted with a pulse‐forming network to produce current and laser pulses with a duration of ≥20 μs. Detailed measurements of laser pulse energies and small‐signal gain coefficients are made for both 12CO2 and 13CO2 gas mixtures, and the results compared with a computer model. In the long‐wavelength band, the two isotopes are found to give very similar performance; the ratio of gain coefficients is measured as 1.00±0.05, while the 12CO2 pulse energy exceeds that of 13CO2 by approximately 20%. View full abstract»

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  • Nonlinear power coupling in the birefringent fiber form birefringence effect

    Page(s): 43 - 46
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    Nonlinear power coupling between two linearly polarized modes in birefringent fibers is examined. In asymmetrically shaped optical waveguides, such as rectangular and elliptical waveguides, which are typical models for polarization beam splitters making use of form birefringence, it is found that the intrinsic critical power of the antisymmetric mode, marking the nonlinear instability, approaches zero at a given aspect ratio; this aspect ratio is 1.587 for the rectangular shape and 1.376 for the elliptical shape. View full abstract»

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  • Phase‐shift measurement in photorefractive holographic recording

    Page(s): 47 - 49
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    A simple direct method for measuring the interference pattern of a light‐to‐recorded hologram phase shift in photorefractive crystals is reported. The method is used for studying the recording in Bi12SiO20 under an externally applied electric field. The results are then compared with theory and used for computing the density of photoelectron traps. View full abstract»

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  • Thermal stresses in multilayer optical‐storage media

    Page(s): 50 - 56
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    Previously, it has been shown that thermal stresses may have a significant role to play in optical‐storage media. Calculations have shown that thermal stresses are produced in single‐layer optical‐storage thin films sufficient to cause interlayer failure and blister formation. In this paper, more realistic multilayer thin films are modeled and it is shown that considerably higher stresses can be produced depending on the layer geometry and material properties. These effects are important both in the initial writing process and in subsequent reading or writing processes, and may result in long‐term‐accumulated, stress‐induced damage. View full abstract»

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  • Frequency locking and quasiperiodicity in a modulated external cavity injection laser

    Page(s): 57 - 60
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    We report the observation of frequency locking and quasiperiodicity in a modulated external cavity injection laser. The order of appearance of the frequency‐locked regions follows a Farey sequence as the modulation frequency is scanned at a fixed value of the modulation depth. Quasiperiodic behavior is observed when the modulation frequency is incommensurate with the external cavity round‐trip frequency. The observed behavior is found to be in good agreement with a rate equation model. View full abstract»

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  • Spatial light modulation by nonlinear absorbers

    Page(s): 61 - 68
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    A novel spatial light modulator (SLM) based on nonlinear absorption of light by excited molecules is suggested. A kinetic analysis is applied to calculate the relative populations of molecular levels in singlet and triplet manifolds. It is shown that for many actual cases a probe light can be modulated by propagating through a medium excited by another light source. The dependence of the molecular SLM on the photophysical parameters of the SLM medium is discussed. View full abstract»

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  • Direct and efficient solutions of integral equations for scattering from strips and slots

    Page(s): 69 - 80
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    Singular integral or integro‐differential equations (SIE or SIDE) are often used for the analytical formulation of two‐dimensional boundary‐value problems. The methods for solving them depend primarily on the complexity of their kernel and on the kind (first or second) of the SIE itself. First‐kind SIEs with a Laplacian kernel are characteristic in electrostatics. A successful method for solving them is a regularization approach based on the transformation of the SIE to an equivalent Fredholm regular integral equation of the second kind. Well‐known inversion formulas are essential to this approach. In electromagnetics, a Hankel‐type kernel complicates matters considerably; inversion formulas and regularization techniques end up as cumbersome indirect procedures making necessary the recourse to a more direct method. Such a method is developed in this paper in combination with a very suitable expansion of the Bessel function, that multiplies the logarithmic singularity of the Hankel kernel, into a series of Chebyshev polynomials of the first or second kind. It is essentially a direct analytical approach that requires fewer expansion functions per wavelength than the method of moments and whose matrix elements are not numerical integrals of singular functions, but quite concise and rapidly convergent series expansions. The efficiency of the method is shown by applying it to scattering of E‐polarized waves from a strip conductor right on the interface between two different dielectric half‐spaces and of E‐ or H‐polarized waves from a slot in the presence of a uniaxially gyrotropic half‐space. Asymptotic expressions for the far‐scattered field are given in all these cases and numerical results are plotted and compared with existing similar ones in certain special situations. View full abstract»

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  • Theoretical analysis of nonlinear optical phenomena taking into account the beating vibration of the electron density in semiconductor lasers

    Page(s): 81 - 89
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    Nonlinear optical phenomena in semiconductor lasers are induced by two types of mechanisms. The first mechanism is beating vibration (i.e., pulsing modulation) on spectral distributions of injected carriers (i.e., electrons and holes) due to lasing frequencies, which is observed as the spectral hole burning effect and whose relaxation is characterized with the intraband relaxation time on the order of 10-13 s. This effect occurs even when the numbers of injected carriers are constant. The second mechanism is beating vibration on the number of injected carriers, whose relaxation is characterized with the electron lifetime on the order of 10-9 s due to band‐to‐band transition. Master equations including these two nonlinear phenomena are obtained in this paper in a general form based on the density matrix formalism. As examples of the equations, characteristics of the saturated gain profile in a laser oscillator and the four‐wave mixing effect (or generation of the phase‐conjugate wave) in a traveling‐wave laser amplifier are analyzed. A saturated gain profile on optical frequency in a laser oscillator contains both symmetric and asymmetric properties induced by the first and the second mechanisms, respectively, where the strengths of these properties are almost the same. While in the case of the four‐wave mixing effect in a traveling‐wave laser amplifier, the second mechanism is more effective than the first mechanism. These results coincide well with previous analyses by other authors which treated the above‐mentioned phenomena individually. View full abstract»

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  • Surface acoustic wave properties of aluminum gallium arsenide

    Page(s): 90 - 96
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    Surface acoustic wave (SAW) properties are measured for {100}‐cut, 〈100〉‐propagating aluminum gallium arsenide (AlxGa1-xAs) with x=0.2 and 0.4. The parameters used to characterize these properties are SAW velocity, SAW attenuation, and piezoelectric coupling coefficient. The measured velocities are found to be substantially higher than those on GaAs in agreement with the theoretical predictions of Adachi. The attenuation is close to the corresponding attenuation on GaAs which is approximately 1 dB/μs. The piezoelectric coupling coefficient is measured using two independent methods and is found to be significantly higher than that of GaAs. This means that the transduction of energy from electrical to acoustical is more efficient and hence acoustic charge transport devices on AlxGa1-xAs substrates will require considerably less rf drive power. An extensive literature search has revealed no previous work, theoretical or experimental, characterizing attenuation or piezoelectric coupling of SAW on AlxGa1-xAs. The velocity has been predicted by Adachi based on a model formulated by Keyes, and has been measured by Sapriel, but the measured velocities reported herein correspond to the predicted values much better than the values measured by Sapriel. The measurement technique described has not, to the authors’ knowledge, been previously used for measurement of the piezoelectric coupling coefficient, and represents a convenient method of obtaining the SAW parameters experimentally. View full abstract»

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  • Photoacoustic investigation of iodine‐doped polystyrene

    Page(s): 97 - 102
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    The kinetics of iodine doping of atactic polystyrene films is investigated using photoacoustic spectroscopy. The changes in the photoacoustically measured physical properties, such as nonradiative relaxation time and thermal diffusivity, are present as a function of the doping time. The results show strong evidence that an order‐disorder transition is taking place as a function of the doping time. The suggested order‐disorder transition is also evident in the dielectric constant measurements of the doped films. View full abstract»

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  • Diffuse discharges at high‐current density

    Page(s): 103 - 107
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    Diffuse discharges were studied in an impedance‐matched experimental system. A traveling‐wave transmission line system was used to produce a high‐voltage pulse (up to 40 kV), with a rise time of approximately 2 ns and a total pulse width of approximately 100 ns. Gas mixtures of C3F8 and c‐C4F8 with He in a pressure range between 100 and 600 Torr were investigated. Plane parallel electrodes with 10‐cm diameter and electrode spacings from 0.25 to 1.5 cm provided uniform field conditions in the discharge region. UV radiation produced by a flashboard placed behind a perforated anode surface provided the volumetric preionization necessary for maintenance of the diffuse discharge. A low ionization potential seedant was used to assure a uniform preionization. High‐current‐density diffuse discharges were maintained for approximately 100 ns. At low‐current density, the diffuse discharge in an electronegative gas mixture operated under balanced electron growth conditions with constant voltage. At high‐current densities (above 100 A/cm2), the discharge operating voltage decreased and was found to be as much as two times lower than the low‐current glow‐discharge voltage. The operating voltage also decreased with time during individual discharge under such conditions. View full abstract»

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  • Influence of the return current effects on the diocotron instability of a relativistic hollow electron beam

    Page(s): 108 - 114
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    Influence of the return current effects on the diocotron instability of a relativistic hollow electron beam propagating through a background plasma is investigated within the framework of a cold fluid model. The return current density induced in the background plasma is taken to be steadily proportional to the axial electron beam current density. By making use of the linearized fluid‐Maxwell equations, a dispersion relation for the eigenfrequencies of the system is derived and used to examine instabilities. It is found that as the fraction of current neutralization increases, lower mode instabilities become dominant while higher mode perturbations are stabilized except in the case of very thin beams. It is also observed that for all values of the fraction of current neutralization, increasing the plasma density gradient or decreasing the beam thickness causes a destabilizing influence. View full abstract»

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  • Measurements of mass separation in a vacuum arc centrifuge

    Page(s): 115 - 118
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    A vacuum arc centrifuge is described which produces a rapidly rotating metal plasma column by means of the Lorentz force between the arc current and an applied axial magnetic field. Analysis of samples deposited on collector surfaces indicates mass separation of elements that increases with the radius. For the plasma formed from a brass cathode, the mass separation of zinc with respect to copper depends on the configuration of the power supply and applied magnetic field and can exceed 50% at the outer radius of the plasma. View full abstract»

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  • Spatial profiles of reactive intermediates in rf silane discharges

    Page(s): 119 - 124
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    Spatial concentration profiles of ground‐state SiH and electronically excited SiH* radicals are measured using laser‐induced fluorescence and emission spectroscopy, respectively. The measurements are made in pure silane, as well as in mixtures with helium, hydrogen, and argon, in a capacitively coupled rf glow‐discharge apparatus used for the deposition of a‐Si:H. Low‐power–low‐depletion conditions are maintained throughout, whereas pressure is varied from 20 to 400 mTorr. Our observations indicate a close relationship between concentration profiles of the species and local electron energy distribution. We conclude that spatial concentration profiles represent stationary generation rates of the radicals. In the case of diluted silane the process is strongly influenced by diffusional transport of detected species to the deposition electrode. The dependence of this effect on dilution grade and buffer gas used is presented. View full abstract»

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  • Intense 1.315‐μm atomic iodine emission from TlI/Xe discharges

    Page(s): 125 - 128
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    Results are presented showing that cw, rf discharge excitation of low‐pressure gas mixtures of TlI and Xe produce very strong atomic iodine emission at 1.315 μm. An examination of previous electron beam excitation observations coupled with these results suggest that there exist two pumping processes for the excited atomic iodine. These are resonant energy transfer of Tl metastables to the excited iodine level and photolytic excitation/collisional TlI dissociative excitation from excited Xe metastable atoms. The overall results suggest a potential for this system as a cw, completely cyclic, self‐contained atomic iodine laser at 1.315 μm. View full abstract»

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  • Anisotropic defect distribution in ZnSe/ZnS epitaxial layers grown by metalorganic vapor‐phase epitaxy on (001)‐oriented GaAs

    Page(s): 129 - 136
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    Epitaxial layers of ZnSe/ZnS have been grown by metalorganic vapor‐phase epitaxy on (001)‐oriented GaAs. A microstructural study of the defect content of these layers was performed using the combined techniques of scanning electron microscopy, reflection high‐energy electron diffraction, transmission electron microscopy, and microdiffraction. Investigation of the epilayers in the [110] and [11¯0] orientations highlighted the strong anisotropy in the defect content of these ZnSe/ZnS layers. Microtwins were found exclusively in the [11¯0] sample orientation, while examination of the same layers along the orthogonal [110] projection revealed only misfit dislocations. The influence of the differential motion of α and β dislocations in the sphalerite structure is discussed in connection with these observations. View full abstract»

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  • The impact of various annealing methods on silicon implant activation properties for GaAs crystals

    Page(s): 137 - 140
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    Wafers obtained from undoped, semi‐insulating GaAs crystals grown by liquid‐encapsulated Czochralski and vertical gradient freeze techniques were implanted with 29Si at a dose of 3×1012 ions/cm2 and an energy of 60 keV. Activation of the implanted region was carried out by furnace or rapid thermal annealing methods, with and without the use of an SiO2 encapsulant. Profiles of the electron concentration and distribution were obtained by the capacitance‐voltage method. Significant variations in the donor distributions were found to be dependent upon the annealing technique employed. The dissimilarities in implant activation properties for GaAs wafers grown by the two techniques, and subjected to identical annealing cycles, have been attributed to variations in melt stoichiometry and native point defects. View full abstract»

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  • The complexing of silicon impurities with point defects in plastically deformed and annealed GaAs

    Page(s): 141 - 145
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    Si‐doped GaAs crystals grown by the horizontal Bridgman method were plastically deformed at 450 °C and then annealed at various temperatures up to 800 °C. Localized vibrational mode (LVM) absorption due to Si‐related defects was investigated using infrared Fourier‐transform spectroscopy with the samples at liquid He temperature. Two LVM lines near 367 cm-1 due to a complex labeled Si‐Y increased in strength in deformed samples which were subsequently annealed around 650–700 °C for 1 h. A new result was the observation of an LVM line from Si‐Y superposed on the absorption from SiAs. Thus three separate lines occur at 366.8, 367.5, and 397.8 cm-1. It is proposed that the Si‐Y center is a SiGa-VGa complex. View full abstract»

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  • Fractal models for the autocatalytic growth of amorphous thin films

    Page(s): 146 - 151
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    Fractal models are proposed for the autocatalytic growth of amorphous thin films. The models give good agreement with the growth kinetics measured for electroless deposited films of amorphous nickel‐phosphorus. A universal result obtained from the models is discussed, and only self‐similarity is found to be important; randomness is effectively eliminated in the model. View full abstract»

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  • Crystalline to amorphous transformation in GaAs during Kr ion bombardment: A study of elastic behavior

    Page(s): 152 - 155
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    A marked softening in the shear elastic properties of GaAs following 1.5‐MeV Kr ion irradiation is observed. Ion channeling and Raman scattering are used to monitor the accumulation of damage, which for 1.5‐MeV incident energy extends to a depth of ∼8000 Å. Both techniques show that the sample is amorphized by a dose of 2×1014 ions/cm2. Brillouin scattering reveals that a shear elastic modulus of this near‐surface irradiated region decreases by 43% as the material transforms from crystalline to amorphous. The observed results are discussed and compared with similar measurements on Si and intermetallic compounds. View full abstract»

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  • Photoreflectance measurements of unintentional impurity concentrations in undoped GaAs

    Page(s): 156 - 160
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    Modulated photoreflectance is used to measure the unintentional impurity concentrations in undoped epitaxial GaAs. A photoreflectance signal above the band gap spreads with the unintentional impurity concentrations and shows well‐defined Franz–Keldysh peaks whose separation provide a good measure of the current carrier concentrations. In samples less than 3 μm thick, a photoreflectance signal at the band edge contains a substrate‐epilayer interface effect which precludes the analysis of the data by using the customary third derivative functional fits for low electric fields. 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