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Journal of Applied Physics

Issue 4 • Date Feb 1993

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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
  • A new numerical method for computing the optical characteristics of birefringent fibers

    Page(s): 1557 - 1560
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    In this article, we present a new numerical method for solving vectorial Maxwell equations which makes it possible to study the birefringence of any geometric pattern of isotropic optical fiber. The distinguishing feature of this method is its use of an iterative process to determine the modes of propagation. The major advantage is the ease of the procedure since the various mathematical steps required can be performed by commercially available software. View full abstract»

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  • Integral equation solution of low‐pressure transport of gases in capillary tubes

    Page(s): 1561 - 1569
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    The molecular flow, or effusion limit, of transport through a capillary is extended to include the regime where the effects of intermolecular scattering become important. This is accomplished through a generalization of the Clausing equation, which gives a fundamental kinetic theory description of molecular flow. The generalized integral equation obtained is solved numerically to obtain both throughput and angular distribution properties of the gas flow. The results show good agreement with experimental curves which clearly demonstrate the effects of intermolecular scattering. View full abstract»

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  • Aberration calculation for combined magnetic focusing deflection systems with curved axes

    Page(s): 1570 - 1575
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    The general aberration theory for combined electromagnetic focusing‐deflection systems with curved axes will be applied to a scanning electron microscopic system and an electron lithographic system. All third order geometric and first order chromatic aberrations have been calculated along rectilinear/curvilinear axes. The important identities between some aberration coefficients will be verified numerically. The geometric and chromatic aberrations calculated along the matching curvilinear axis will be compared with those along the rectilinear axis. The computational trials may be of help for explaining the mechanism of moving/swinging objective lens and variable axis lens systems. View full abstract»

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  • Spectral optimization of a pulsed HF chemical laser for efficient energy delivery through a low‐loss fluoride glass optical fiber

    Page(s): 1576 - 1580
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    Pulsed HF chemical lasers oscillating in the midinfrared region of the spectrum where water can strongly absorb are suitable for the organic tissue ablation. For such a medical application, a flexible energy delivery system using an optical fiber is indispensable. The fluoride glass optical fiber may be used for low‐loss optical energy delivery of the pulsed HF laser. Using an intracavity CO2 absorption cell, we have optimized pulsed multiline HF chemical laser spectrum for low‐loss energy delivery through a fluoride glass optical fiber whose transmission loss is theoretically estimated to be minimum around 2.5 μm. The fractional output energy of P1‐0(3) and P1‐0(4) lines, which are sitting in the lowest loss spectral region of the practical fluoride glass fiber, exceeded half the multiline output energy using a line selective intracavity CO2 gas cell. The P1‐0(4) line extracted from the resonator with a diffraction grating was successfully delivered through a 3‐m‐long commercial fluoride glass fiber (core/cladding diameter=450/500 μm). The delivered energy of 11.9 mJ was achieved with the corresponding energy fluence of 12 J/cm2 and peak intensity of 22 MW/cm2 at the exit core surface without optical damage. View full abstract»

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  • The propagation of a radar pulse in sea water

    Page(s): 1581 - 1590
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    The propagation in sea water of an electromagnetic field in the form of a semi‐infinite wave train or a radar pulse generated by an electric dipole is investigated analytically for low frequencies. The frequency‐domain formula for the downward‐traveling field of a horizontal electric dipole excited by a sinusoidally modulated electric‐current pulse is Fourier transformed to obtain an explicit expression for the field at any distance in the time domain. Specific application is made to a wave packet of 25.5 cycles in a time duration of 1 s. The amplitude and phase velocity of the wave packet are determined together with the amplitudes of the initial and final transients. Graphs are displayed and discussed for a range of distances; these show that the amplitude of the wave packet decays more rapidly than the amplitudes of the transients. Possible application to remote sensing in the ocean is considered.   View full abstract»

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  • The linear and nonlinear optical properties of the organic nonlinear material 4‐nitro‐4’‐methylbenzylidene aniline

    Page(s): 1591 - 1597
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    The organic crystal 4‐nitro‐4’‐methylbenzylidene aniline (NMBA) was identified as a promising nonlinear material by the powder technique. The material gave a second harmonic intensity 16 times that of urea. Large single crystals of dimensions 5×3×1 cm3 were grown by the temperature lowering of a seeded supersaturated ethyl acetate solution. The principal dielectric axes were defined by orthoscopic examination. The dispersions of the refractive indices were determined to an accuracy of ±0.0015 using the minimum deviation technique and Maker fringe spacings. These dispersion curves were fitted to a Sellmeier equation which allowed the indices to be determined to ±0.0006. The nonlinear d coefficients d11, d33, d31, and d13 were evaluated at 1000, 1064, and 1300 nm using the Maker fringe technique. The coefficient d11 was over 200 times larger than potassium dihydrogen phosphate (KDP) d36. In addition, the nondiagonal coefficient d31 was similar to the phase‐matching coefficient in the organic material 3‐acetamido‐4‐dimethylamino‐nitrobenzene (DAN). Critically phase‐matched second harmonic signals were observed at all fundamental wavelengths. There was excellent agreement between the experimentally determined and theoretical phase‐matched incidence angles. Noncritical phase‐matched conditions have been calculated and are reported. Both angle and wavelength noncritical phase matching is possible with this crystal. View full abstract»

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  • Theoretical modeling of chemical generators producing O2(1Δ) at high pressure for chemically pumped iodine lasers

    Page(s): 1598 - 1611
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    A theoretical model is developed for chemical generators producing O2(1Δ) at high pressure. Such generators are especially important for supersonic chemical oxygen‐iodine lasers. The model treats different types of generators, e.g., bubble‐column, film, aerosol, and jet generators. The main factor affecting the O2(1Δ) yield under high pressure is liquid‐phase quenching enhanced by depletion of HO2- ions near the gas/liquid interface. Simple analytical expressions are derived for the O2(1Δ) yield at the exit of the generator. Output characteristics of different specific generators are calculated and compared with available experimental results. O2(1Δ) yield ≥0.5 can be achieved for oxygen pressure up to 50 Torr and flow rates of 3 mmol/cm2 s. For equal velocities of the gas and the liquid the maximum flux of the energy carried by O2(1Δ) for jet or aerosol generators reaches 200 W/cm2. It can be increased by increasing the liquid velocity in the generator. View full abstract»

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  • Measurements of electron energy distribution function in an asymmetric radio‐frequency discharge plasma

    Page(s): 1612 - 1616
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    Electron energy distribution functions in an asymmetric radio‐frequency (rf) discharge helium plasma were measured using an electrostatic energy analyzer looking opposite ways toward both the powered electrode and the bulk plasma. The grid and collector in the analyzer were connected to a series of parallel inductance‐capacitance (L‐C) filters to minimize rf interference. Electrons with high energies (15–30 eV) flowing from the electrode toward the bulk plasma were observed near the electrode. The energy is caused by the acceleration mechanism due to the rf sheath expansion, which should be the rf discharge sustaining mechanism. The electrons with high energies decreased in number with the distance from the electrode and became Maxwellian far from it. Electrons directed toward the electrode from the plasma were almost Maxwellian, and this situation was almost independent of the distance from the electrode. View full abstract»

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  • Electrostatic forces on small particles in low‐pressure discharges

    Page(s): 1617 - 1620
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    The electrostatic forces on an isolated particulate in a low‐pressure discharge are calculated assuming a screened Coulomb potential profile for the particle sheath. In the absence of particle sheath distortion due to a flowing plasma and assuming that there is no charge ‘‘bound’’ to the particle in the form of ions in trapped orbits, the monopolar and dipolar forces on the particle are essentially identical to the corresponding forces on a charged sphere in vacuum. View full abstract»

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  • Optical ion energy measurements in a radio‐frequency‐induction plasma source

    Page(s): 1621 - 1626
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    In situ, Fabry–Perot interferometry was used to study the translational dynamics of ions in a magnetically confined, radio‐frequency‐induction (RFI) plasma reactor. Radial ion motion was characterized through measurements of the Doppler profile of emission from Ar+ ions. Radial ion energies depend on the operating power, pressure, and magnetic‐field configuration. In a magnetically confined RFI plasma at 1000 W, ion energies increase from 0.08 to approximately 0.25 eV as the operating pressure is lowered from 13 to 0.18 mTorr. Complementary Langmuir probe studies of the plasma potential as well as its variation across the radius of the reactor illustrate the influence of electric fields on the radial motion of ions in the RFI system. These measurements illustrate that radially directed ion motion in the RFI reactor is significantly less than that reported previously for a divergent‐field electron cyclotron resonance system. View full abstract»

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  • Transient current interruption mechanism in a magnetically delayed vacuum switch

    Page(s): 1627 - 1633
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    The capacity of a magnetically delayed vacuum switch to conduct current depends on the density of plasma injected into the switch. Exceeding the current capacity results in the switch entering a lossy mode of operation characterized by a transient interruption of the main current (opening behavior) and a rapid increase of voltage across the vacuum gap. Streak and framing photographs of the discharge indicate that a decrease of luminosity near the middle of the gap precedes the transition to the opening phase. The zone of low luminosity propagates toward the cathode. This evidence suggests that the mechanism causing the opening phase is erosion of the background plasma in a manner similar to that in a plasma‐opening switch. The resulting ion depletion forces a space‐charge‐limited conduction mode. The switch inductance maintains a high discharge current even during the space‐charge‐limited conduction phase, thus producing high internal fields. The high accelerating voltage, in turn, produces electron and ion beams that heat the electrode surfaces. As a result of the heating, jets of electrode vapor issue from the electrodes, either cathode or anode, depending on the selection of electrode materials. View full abstract»

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  • Monte Carlo simulations of electron distributions in the sheath region of reactive‐ion‐etching plasmas

    Page(s): 1634 - 1643
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    The results of a Monte Carlo model for calculating the trajectories of electrons in the plasma sheath region in reactive‐ion‐etching plasmas are described. The calculations illustrate how the oscillating movement of the sheath imparts energy to electrons and alters the electron energy distribution (EED) within the bulk of a 13.56 MHz Ar discharge. The study is limited to low‐pressure discharges of less than about 10 mTorr, where the effects of electron‐molecule collisions can be ignored. Under these conditions it is found that the sheath imparts energy preferentially to low‐energy electrons. Calculated EEDs for electrons striking the electrodes in a radio‐frequency reactor are also presented. Most electrons strike the electrodes with energies of a few eV, but some electrons strike the substrate surface with impact energies as high as 20 eV. This may be an important consideration when modeling etch mechanisms. Secondary electron emission caused by ion bombardment of the electrodes is also modeled. Simulated EEDs for secondary electrons that are produced at the electrodes and accelerated by the action of the sheath potential into the plasma region are presented. These electrons have energies of up to several hundred eV and are therefore important in plasma‐sustaining mechanisms. View full abstract»

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  • Precursor to paramagnetic centers induced in gamma‐irradiated doped silica glasses

    Page(s): 1644 - 1649
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    We prepared silica glasses having various concentrations of chlorine, fluorine, hydrogen (SiO2-x), and oxygen (SiO2+x) to examine the precursors of paramagnetic centers induced by γ rays. In the case of glasses sintered under chlorine and hydrogen ambients, the concentration of the E’ center induced by γ‐ray irradiation scaled with the partial pressure of chlorine and hydrogen. In contrast, the E’ center was suppressed in glasses doped with fluorine. Stress in the glasses was also found to enhance formation of the E’ center. Planar ring structures in the glass are influenced by stress and are proposed as precursors to the E’ center. View full abstract»

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  • A crystallographic methodology for modeling dislocation dynamics in GaAs crystals grown from melt

    Page(s): 1650 - 1656
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    The objective is to develop a quantitative model for simulating dislocation motion and multiplication in gallium arsenide (GaAs) crystals during growth from the melt by taking the crystallography of slip into account. A constitutive model that couples microscopic dislocation motion and multiplication to macroscopic plastic deformation is employed for developing the model. The density of dislocations in the crystal is predicted by assuming the crystal to be grown under quasi‐steady‐state conditions. The thermoelastic stresses are calculated from a two‐dimensional finite‐element analysis, and then transformed into the resolved shear stresses in each slip system for the simulation of dislocation motion and multiplication. A numerical example is presented to verify the validity of the model. The calculated distribution of dislocation density on (001) GaAs wafer shows fourfold symmetry which is consistent with etch pit observations made by Jordan, Caruso, and Von Neida [Bell Syst. Tech. J. 59, 593 (1980)]. Although the emphasis is placed on GaAs, the model can be applied to other electronic and photonic materials. View full abstract»

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  • Bleaching mechanism of silver halide photochromic glasses

    Page(s): 1657 - 1668
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    Thermal bleaching of silver halide photochromic glasses is studied by electron paramagnetic resonance spectroscopy of photoinduced CuII centers. During exposure to ultraviolet light, the only stable CuII species is the (CuIIVAg)A center, which is a CuII‐silver vacancy complex with the vacancy in a nearest position. In the dark, this center rapidly decays via two parallel channels. The first involves the dissociation of the complex by displacement of the vacancy along a [110] direction, with an activation energy E3=0.44 eV and a frequency factor k30=3.4×105 s-1. The second channel involves the conversion of the (CuIIVAg)A center into a (CuIICl-VAg)B center, where the silver vacancy is in the next nearest position along the [100] direction. This process occurs with an activation energy E1=0.44 eV and a frequency factor k10=3.1×105 s-1. The (CuIICl-VAg)B center slowly decays by a vacancy hopping mechanism, with an activation energy E2=0.22 eV and a frequency factor k20=4.6 s-1. To explain these two decay channels, it is proposed that the (CuIIVAg)A and (CuIICl-VAg)B centers annihilate via the formation of a CuI ion and a neutral complex (AgIIVAg)A which migrates to the surface of the silver halide particle, where electron‐hole recombination occurs. View full abstract»

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  • Ion irradiation damage in Er‐doped silica probed by the Er3+ luminescence lifetime at 1.535 μm

    Page(s): 1669 - 1674
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    The effect of MeV ion irradiation damage on the luminescence lifetime of erbium‐doped silica glass films has been studied. The 10‐μm‐thick films were first implanted with 3.5 MeV Er at a fluence of 5×1015 cm-2. When optically pumped at 488 nm, the films show a clear photoluminescence spectrum centered around 1.535 μm, corresponding to the 4I13/24I15/2 transition of Er3+(4f11), with a luminescence lifetime of 5.5 ms. After thermal annealing at 900 °C, the lifetime increases to 14.1 ms. Radiation damage was then introduced in the annealed films using 1 MeV He, 3.5 MeV C, 5.5 MeV Si, or 8.5 MeV Ge ions. The lifetime is decreased by irradiation with fluences as low as 1011 ions/cm2 and continues to decrease with fluence until saturation occurs above ≊1014 ions/cm2. The saturation lifetime is ion‐mass dependent and ranges from 6.6 to 8.5 ms. The lifetime changes are explained in terms of nonradiative energy transfer processes caused by irradiation‐induced defects in the silica. A model for lifetime changes as a function of ion fluence is derived, assuming an inverse relation between the nonradiative lifetime and the defect density. Fits to the data show that the defect generation rate is a sublinear function of the ion fluence. The ion damage effects are governed by the electronic component of the energy loss along the ion trajectories. View full abstract»

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  • Defect reactions by heat treatment of heavily silicon doped gallium arsenide

    Page(s): 1675 - 1680
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    Silicon is an amphoteric impurity of gallium arsenide that is present in different defect configurations. This work reports on the effects of heat treatment on defect reactions of heavily silicon‐doped gallium arsenide crystals. The distribution of segregation, lattice parameter, and electrical properties was studied for several heat treatments. When the crystals were bulk‐annealed at between 700 °C and 1000 °C for 20 h, zone‐distributed segregation was observed at the area with a silicon concentration of about 1×1019 cm-3 by etching and x‐ray topography. Regions observed to have silicon‐related segregation exhibited a decrease in lattice parameter when the crystals were annealed below 850 °C for 20 h then quenched. In addition, such regions exhibited little change in lattice parameter when the crystals were annealed above 850 °C. For electrical properties, the largest decrease in carrier concentration and mobility of such regions was observed when the crystals were annealed at 700 °C. This change in the characteristics of such regions seems to be affected not only by heavily doped silicon but also by excess arsenic. View full abstract»

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  • Dynamic activity of dislocations in gallium phosphide

    Page(s): 1681 - 1685
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    Dynamic activities of α, β, and screw dislocations in a GaP crystal containing sulphur as the main impurity at a concentration of 7×1017 cm-3 are investigated as a function of stress and temperature by means of the etch pit technique. Generation of all types of dislocations from a surface scratch is found to be suppressed at temperatures higher than 500 °C and is interpreted in terms of dislocation locking due to impurities and/or impurity‐defect complexes as has been observed in GaAs and InP. α dislocations move faster than β and screw dislocations and their velocities are expressed with the same type of empirical equation as a function of the stress and the temperature as those in other semiconductors. Roughly speaking, dislocations in GaP move at velocities lower than those in GaAs by about two orders of magnitude. View full abstract»

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  • The effects of ion implantation on the interdiffusion coefficients in InxGa1-xAs/GaAs quantum well structures

    Page(s): 1686 - 1692
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    Photoluminescence coupled with repetitive thermal annealing has been used to determine the diffusion coefficients for intermixing in InxGa1-xAs/GaAs quantum wells and to study the subsequent effects of ion implantation on the intermixing. It is shown that following ion implantation there is a very fast interdiffusion process, which is independent of the implanted ion and that is thought to be due to the rapid diffusion of interstitials created during the implantation. Following this rapid process, it was found that neither gallium nor krypton ions had any effect on the subsequent interdiffusion coefficient. Following arsenic implantation in addition to the initial damage related process, an enhanced region of interdiffusion was observed with a diffusion coefficient that was an order of magnitude greater than that of an unimplanted control wafer. This enhanced process is thought to be due to the creation of group III vacancies by the arsenic atoms moving onto group V lattice sites. This fast process was present until the structure had broadened by about 75 Å when the diffusion coefficient returned to the unimplanted control value. The activation energy for the interdiffusion was measured over the temperature range 1050–750°C and a value of 3.7±0.1 eV was measured. This was found to be independent of the implanted ion. View full abstract»

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  • Interface‐phonon‐assisted Γ–X transitions in short‐period superlattices

    Page(s): 1693 - 1701
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    The dielectric continuum model of longitudinal‐optical phonons in polar semiconductors is used to define the role of interface longitudinal‐optical phonons in affecting phonon‐assisted Γ–X transitions in GaAs–AlAs and GaAs–GaP superlattices. In particular, the dielectric continuum model for interface optical phonons is used in conjunction with a Kronig–Penney model of the superlattice electronic properties for two purposes: to specify superlattice parameters where interface‐phonon‐assisted Γ–X transitions are expected and to estimate relative transition probability amplitudes for interface‐phonon‐assisted Γ–X transitions in selected short‐period superlattices.     View full abstract»

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  • Phase evolution upon ion mixing and solid‐state reaction and thermodynamic interpretation in the Ni‐Nb system

    Page(s): 1702 - 1710
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    The amorphization of Ni‐Nb multilayered alloy films by xenon ion irradiation at room temperature and by high‐temperature solid‐state reaction was studied. The composition range favoring amorphization was carefully determined to be 20–85 at. % Ni by energy‐dispersive spectroscopy attached to the transmission electron microscope. A new metastable crystalline phase (MX) of hexagonal structure was formed in Ni75Nb25 and Ni70Nb30 multilayered films. Interestingly, in the Ni75Nb25 multilayered films, with increasing mixing dose an amorphous phase was first formed and then the MX‐phase was observed, while in the Ni70Nb30 multilayered films the MX phase was formed at relatively low doses and turned amorphous upon further mixing or 400 °C annealing for 2 h. Besides, annealing of the as‐deposited Ni70Nb30 multilayered films at 300 °C for half an hour also resulted in the formation of the MX phase. The thermal stability of the ion‐mixed amorphous alloys was also studied by subsequent annealing. To give semiquantitative interpretation to all the above observations, the Gibbs free‐energy diagram of the system, in which especially the free‐energy curve of the MX phase is added, was constructed on the basis of the model of Nissen et al. [CALPHAD 7, 51 (1981)] and the method proposed by Alonso and Simozar [Solid State Commun. 46, 765 (1983)]. The explanation based on this diagram is in good agreement with our experimental results. View full abstract»

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  • The effective thermal conductivity of composites with coated reinforcement and the application to imperfect interfaces

    Page(s): 1711 - 1722
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    An analytical model is developed to predict the effective thermal conductivity of multiphase composites reinforced with coated fillers. The coated fillers are modeled as confocal spheroids, thus enabling the simulation of a wide range of reinforcement geometry ranging from thin flake to continuous fiber. The orientation of the coated fillers is described by a density distribution function which can simulate completely random, in‐plane random, and aligned distributions as special cases. The analytical approach appears to be the only one in the literature that renders closed‐form predictions of the effective thermal conductivity of composites with misoriented coated reinforcement and thus recourse to a numerical scheme is not required. The analytical approach is specialized to consider the effects of a thermal resistance at the filler‐matrix interface of a composite. Results of the proposed model are compared with those obtained by self‐consistent and differential estimates [Y. Benveniste and T. Miloh, J. Appl. Phys. 69, 1337 (1991)] for the effective thermal conductivity of a composite reinforced by completely random coated short fibers. The proposed model is in close agreement with the other two models for low conductivity coatings, but differs appreciably for high conductivity coatings. Finally, good agreement is shown to exist between analytical predictions and experimental results obtained from the literature for a diamond particle/zinc‐sulfide matrix composite with an interfacial thermal resistance. View full abstract»

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  • Hydrogen diffusion and acceptor passivation in p‐type GaAs

    Page(s): 1723 - 1731
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    Deuterium diffusion profiles in GaAs doped with different acceptors of group II (Mg,Zn,Cd) or group IV (C,Ge) have similar characteristics even though the neutralization of acceptors measured at 300 K is not always efficient. Conductivity and Hall measurements have been used to study the electrical characteristics of hydrogenated p‐type GaAs epilayers. The temperature dependence of the free‐carrier concentration and hole mobility before and after hydrogenation shows that the neutralization of acceptors by atomic hydrogen leads to the elimination of the shallow acceptor states. Infrared‐absorption lines associated with hydrogen‐acceptor complexes are observed for all acceptors except magnesium. It is established that the microscopic structure of hydrogen‐acceptor complexes depends on the acceptor site in the lattice. View full abstract»

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  • Ellipsometry study on refractive index profiles of the SiO2/Si3N4/SiO2/Si structure

    Page(s): 1732 - 1736
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    In this work, the refractive index profiles of SiO2/Si3N4/SiO2/silicon (ONO) structures were measured and analyzed by ellipsometry. The ONO structures were obtained by oxidizing the Si3N4/SiO2/silicon structure in a wet O2 ambient at the temperature range of 900–1050 °C for different lengths of time. It was found that for a nitride film thickness less than 250 Å, oxygen not only oxidized the surface, but diffused through the nitride and oxidized the inner surface of the nitride. This result was confirmed by the Auger analysis. The kinetics of the wet O2 oxidation of nitride at the above temperature range was linear for an oxidation time of 30–120 min. The activation energy was 2.24 eV. 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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P. James Viccaro
Argonne National Laboratory