By Topic

Journal of Applied Physics

Issue 9 • Date Nov 1985

Filter Results

Displaying Results 1 - 25 of 74
  • Scalar scattering characteristics of impenetrable, periodic surfaces using the T‐matrix method: Effect of medium inhomogeneity

    Page(s): 3275 - 3281
    Save to Project icon | PDF file iconPDF (597 KB)  

    A general T‐matrix is formulated to study the scalar scattering response of an impenetrable, biperiodic surface in the presence of a z‐directed medium inhomogeneity, and reductions thereof are discussed. A numerical scheme for constructing potential reflection coefficients used for generating an appropriate Green’s function has also been described. Numerical results presented demonstrate that the effect of the inhomogeneity cannot be ignored without inducing severe errors. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Nonequilibrium thermostatics

    Page(s): 3282 - 3294
    Save to Project icon | PDF file iconPDF (1896 KB)  

    A self‐consistent thermodynamics is developed for nonrelaxation hysteretic processes. This theory, nonequilibrium thermostatics, is based upon macroscopic empirical descriptions of hysteretic behavior and the laws of thermodynamics. It is shown that the empirical behavior of hysteretic systems does not satisfy the conditions required for application of either equilibrium or relaxation nonequilibrium thermodynamics. Therefore, modified thermodynamic assumptions are proposed which are consistent with empirical hysteretic behavior. The principal new assumptions are (1) that processes (energy dissipation permitted) consists of a differential sequence of nonequilibrium states; (2) that three new ‘‘state variables’’ describe all of the ‘‘history dependence of a state;’’ (3) that at least some ‘‘reversible’’ processes exist; (4) that the time‐independent ‘‘modified Gibbs relation’’ can be used to describe the Second Law constraints. With these assumptions, it is shown that the thermodynamic relationships derived from the First Law are identical to those for standard equilibrium thermodynamics, but Second Law implications are significantly different, e.g., a new ‘‘dissipation’’ state function is derived; it is proven that hysteretic behavior is a positive indication of a dissipative process and that dissipation always causes hysteresis. It is concluded that nonequilibrium thermostatics provides a self‐consistent theory which extends the useful domain of thermodynamics to include nonrelaxation, hysteretic (dissipative)processes. A comparison of detailed predictions and experimental measurements of heat capacities, adiabatic paths, etc., for a hysteretic system is provided in a separate paper. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Two‐photon‐ionization coefficients of CS2, SO2, and (CH3)3N

    Page(s): 3295 - 3301
    Save to Project icon | PDF file iconPDF (829 KB)  

    Electrons produced by two‐photon ionization of CS2, SO2, and (CH3)3N in N2 and CH4 buffer gases at 193 nm were investigated using a parallel‐plate drift‐tube apparatus. At a low charge density, the transient voltage induced by electron motion between the electrodes is proportional to the gas pressure and the square of laser power. The two‐photon‐ionization coefficients measured from the number of electrons produced are 3.3×10-27, 8.3×10-30, and 1.7×10-27 cm4/W for CS2, SO2, and (CH3)3N, respectively. The coefficient for (CH3)3N agrees with the earlier value measured by ion current. At a high charge density, the number of electrons observed deviates from the square dependence of laser power. The numbers of ions and electrons are greatly reduced by charge recombination whose reaction rate is enhanced in the presence of space charge. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Theory of microwave pulse propagation during gas breakdown: Linear approximation

    Page(s): 3302 - 3313
    Save to Project icon | PDF file iconPDF (1440 KB)  

    We develop a theory describing the propagation of a pulse of electromagnetic energy through a gas in which breakdown is occurring (by means of the pulse‐induced electron cascade). The theory is based on solutions to a model wave equation for the pulse electric field, which incorporates the electron cascade in an approximate fashion, and which is derived from the appropriate Maxwell equations coupling the pulse fields to the cascading electron current. Nonlinear effects are ignored, but solutions to the model wave equation appear useful in identifying major trends in the pulse propagation, such as the pulse attenuation and its dependence on the input pulse nominal frequency, spectral breadth, width, rise time, and overall shape. Our results are of relatively simple analytical form, they semiquantitatively confirm available data, and they imply that the pulse energy transport through the electron cascade can be enhanced by choice of certain combinations of the input pulse parameters. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Quantum model of the free‐electron laser in a uniform magnetic field

    Page(s): 3314 - 3321
    Save to Project icon | PDF file iconPDF (880 KB)  

    A quantum model of the single particle free‐electron laser in a uniform magnetic field is given. Here the classical electron current due to electrons in helical orbits (caused by a uniform magnetic field) interacts with a quantized radiation in the interaction volume of finite extent. The description of this free‐electron laser is through the S matrix which incorporates the quantum recoil completely and yields directly the full ‘‘quantum mechanical’’ gain. Taking the relativistic electron factor γ to be approximately equal to 2.4 and the magnitude of the magnetic field in the range of 0.6–1.6 T, this free‐electron laser should be capable of generating radiation in the far infrared‐microwave spectral region. From the analysis of the asymptotic (classical limit) gain (a gain due to the ‘‘infinite’’ number of photons in the interaction volume V), we conclude that it is generally easier to generate radiation in the forward, rather than backward, direction. We also discuss the dependence of the gain on the electron velocity in the z direction, the strength of the uniform magnetic field, and the fact that our (asymptotic) gain scales as L3, which is similar to the gain of the usual (wiggler) free‐electron laser. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Scattering of linearly polarized light from randomly oriented cylinders and spheroids

    Page(s): 3322 - 3327
    Save to Project icon | PDF file iconPDF (575 KB)  

    The Shifrin perturbation theory is applied to the scattering of light from finite cylinders and spheroids, and a procedure is described for averaging over the possible orientations of the symmetry axes of these various target shapes. The possible axis orientations of very long cylinders is limited by the conical shape of the scattering patterns, and the manner of taking this into account in the averaging process is detailed. It is found that the scattering intensities for the scattering of light from randomly oriented long cylinders, with aspect ratios (length/diameter) less than about 200, show differences compared with infinite cylinders of the same radius and dielectric constant (m=1.5). This is especially true for high and low scattering angles and when the plane of linear polarization is changed by the scattering. Moreover, the scattering intensities for the scattering of light from randomly oriented short cylinders and spheroids, with aspect ratios ranging from 0.1 to 10 and the same volume, show significant differences when the plane of polarization is changed by the scattering. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Theory of transverse multimode generation in a laser with a loss guiding structure

    Page(s): 3328 - 3332
    Save to Project icon | PDF file iconPDF (479 KB)  

    A theoretical consideration is given of the transverse multimode generation in a laser which is equipped with a lossy layer below an active layer for mode control, e.g., the buried twin‐ridge substrate laser, the channeled substrate planar laser, and the V‐shape inner stripe laser. The multimode generation occurs as a result of the reduction of the first‐order mode threshold to the fundamental mode threshold. It is shown that even a small asymmetry of the lossy layer causes large reduction of the first‐order mode threshold. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Improved theory of ultrasonic diffraction at large angles

    Page(s): 3333 - 3339
    Save to Project icon | PDF file iconPDF (561 KB)  

    A systematic theoretical study of approximations to the Kirchhoff diffraction integral is presented, stressing the improved behavior at large angles. This work was motivated by consideration of diffraction in dual tilted dispersive interdigital transducers for surface acoustic wave generation, but the salient features are applicable to diffraction problems in general. Previous treatments of surface acoustic wave (SAW) propagation were limited to nearly forward directions perpendicular to transducer fingers, where the simple Fresnel diffraction theory was adopted. Improvement of the theory for nonforward angles is obtained in which both the Fraunhofer and Fresnel diffractions are correctly included. The conventional diffraction treatment used in optics (as in the textbook by Born and Wolf) is found inaccurate and a new form is presented. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Flux formulation of hyperbolic heat conduction

    Page(s): 3340 - 3345
    Save to Project icon | PDF file iconPDF (627 KB)  

    The development of the general flux formulation for heat conduction based on the modified Fourier’s law is presented. This new formulation produces a hyperbolic vector equation in heat flux which is more convenient to use for analysis in situations involving specified flux conditions than the standard temperature formulation. The recovery of the temperature distribution is obtained through integration of the energy conservation law with respect to time. The Green’s function approach is utilized to develop a general solution for hyperbolic heat conduction in a finite medium. The utility of the flux formulation and the unusual nature of heat conduction based on the hyperbolic formulation are demonstrated by developing analytical expressions for the heat flux and temperature distributions in a finite slab exposed to a pulsed surface heat flux. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Vacuum surface flashover from bipolar stress

    Page(s): 3346 - 3349
    Save to Project icon | PDF file iconPDF (501 KB)  

    A simple model is employed to explain the anomalous surface‐flashover characteristics observed when insulators in vacuum are stressed with bipolar voltage waveforms. Under unipolar stress, the flashover field is found to vary as the inverse square root of the prebreakdown time delay over the first few tens of nanoseconds, thereafter becoming less dependent on delay. The short‐delay behavior, according to our model, results from the accumulation of ionic charge adjacent to the insulator‐vacuum interface. At longer delays ions are swept away nearly as rapidly as they are created. Flashover data from conventional insulator assemblies subjected to unipolar stress is consistent with ions being swept away. With the application of a roughly 10 MHz, bipolar voltage waveform a different behavior is observed. The holdoff is unexpectedly low and an anomalous inverse‐square‐root dependence on delay persists over hundreds of nanoseconds. Analysis of ion motion indicates that some fraction of the ions follow small‐amplitude oscillatory trajectories and continue to accumulate for relatively long periods of time. An insulator has been modified to enhance ion removal by decreasing the thickness of polystyrene segments fourfold to 4.7 mm. A 50% improvement in performance is found, although the holdoff remains below standards applicable to unipolar stress. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Frequency dependence of ion bombardment of grounded surfaces in rf argon glow discharges in a planar system

    Page(s): 3350 - 3355
    Save to Project icon | PDF file iconPDF (699 KB)  

    The energy distribution of positive ions incident on a grounded surface in a low‐pressure argon planar rf glow discharge system has been measured as a function of excitation frequency from 70 kHz to 13.56 MHz for both capacitive and direct coupling of the rf power to the excitation electrode. The results are interpreted by taking into consideration both the transit time for the ion to traverse the sheath relative to the period of the rf excitation voltage, and the resistive or capacitive characteristics of the sheaths. The importance of system geometry and of the dc potential of the excitation electrode (as determined by external circuitry) on the maximum energy of ions incident on grounded surfaces is shown. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Heat loading on the components of multimegawatt ion sources

    Page(s): 3356 - 3363
    Save to Project icon | PDF file iconPDF (842 KB)  

    The underlying mechanisms involved in the heat loading on the accelerator grids and plasma chamber components of multimegawatt ion sources are experimentally identified. Utilizing numerical techniques, a new accelerator geometry is designed to minimize the heat loading on various source components and maximize the beam brightness. Measurements on an ion source employing this accelerator geometry, during extraction of quasi‐steady‐state beam pulses of 3.2‐MW power, show significantly reduced heat loadings on all its components. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Surface discharges as intense photon sources in the extreme ultraviolet

    Page(s): 3364 - 3367
    Save to Project icon | PDF file iconPDF (448 KB)  

    We are investigating surface discharges as XUV photon sources for in situ cleaning and preionizing of anode surfaces in light‐ion‐fusion accelerators. In these experiments the surface discharge was formed by discharging a capacitor bank across a spark gap which consisted of two copper electrodes attached to an insulator and facing each other across a 5.5‐mm gap. The surface discharge and its power feeds were constructed in a stripline configuration to minimize overall system inductance. When the surface discharge was driven by a 2.9‐μF, 45‐kV capacitor bank, the peak current thru the discharge was ∼250 kA. When driven at these levels, a single discharge radiated with a peak power of over 80 MW of 10–70 eV photons and had a total extreme ultraviolet output energy of 60 J per pulse. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Thermally activated peroxy radical dissociation and annealing in vitreous SiO2

    Page(s): 3368 - 3372
    Save to Project icon | PDF file iconPDF (556 KB)  

    Isochronal and isothermal annealing results for peroxy radical defects induced in Suprasil W1 by γ irradiation are reported. The activation energy for annealing is estimated to be ∼2 eV and argued to be due to OO bond dissociation rather than gaseous interstitial or network diffusion. The results are shown to be consistent with those obtained from annealing/reactivation studies on oxygen vacancy defect centers. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • X‐ray diffraction studies of thermal treatment of GaAs/InGaAs strained‐layer superlattices

    Page(s): 3373 - 3376
    Save to Project icon | PDF file iconPDF (391 KB)  

    We analyze in this paper the effect of thermal treatment on structural properties of GaAs/InGaAs strained‐layer superlattices grown by molecular beam epitaxy. The superlattices are analyzed using double‐crystal x‐ray rocking curves. In order to model the satellites intensity variation as a function of the heat treatment time at a temperature of 850 °C, we have calculated the structure factors of the superlattices, taking into account both composition and lattice spacing modulation. The latter is found to be more influent in the calculation in this particular case. The deduced values of the diffusion coefficient, about 2×10-18 cm2/s, is discussed and compared to those determined on GaAs/AlAs structures. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Projected range and damage distributions in ion‐implanted Al, Si, Al2O3, and GaAs

    Page(s): 3377 - 3387
    Save to Project icon | PDF file iconPDF (1038 KB)  

    Substrates of Al, Si, Al2O3, and GaAs were implanted with 100 to 420‐keV Al, Ar, Mn, Ni, Zn, Te, and Xe ions at low temperature of about 100 K. The reduced energies range from 0.2 to 4. The implantation energies were calibrated accurately using a nuclear resonance reaction of 19F( p,αγ)16O. The depth distributions of the implanted ions and the induced damage were determined by means of backscattering (including channeling) combined with computer‐simulated spectrum analysis. The results are compared with the theoretical predictions given by Gibbons et al. (GJM) and Winterbon et al. (WSS). For the latter theory, optimum WSS parameters are determined to give a good fit to the experimental data. The systematic investigation reveals that the reduced projected range and damage depth are proportional to reduced energy ϵ for Al, Si, and Al2O3, whereas they are expressed in the form ϵ2/3 for GaAs substrates. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Atomic and microstructural characterization of metal impurities in synthetic diamonds

    Page(s): 3388 - 3393
    Save to Project icon | PDF file iconPDF (643 KB)  

    The phase and microstructure of Ni, Co, and Fe impurities found in synthetic diamonds have been characterized in some detail using a combination of extended x‐ray absorption fine structure (EXAFS) utilizing intense synchrotron radiation as a light source, and conventional transmission electron microscopy (TEM), x‐ray diffraction, and fluorescence analyses. In all three cases, the metal impurity exists as an fcc metallic phase dispersed in the diamond matrix. The particles are submicron in size and not facetted. There was no evidence of a metal carbide phase in these systems. Quantitative simulations of the first‐shell EXAFS signal showed that the Co and Ni particles contain, respectively, 2.3 and 1.5 at. % of carbon in solution. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A model for time dependence in shock‐induced thermal radiation of light

    Page(s): 3394 - 3399
    Save to Project icon | PDF file iconPDF (579 KB)  

    High‐speed optical pyrometry has seen increasing application in the measurement of shock temperatures in initially transparent solids and liquids; however, the information contained in the time‐dependent intensity of the emitted light has frequently been overlooked. A model has been developed for this time dependence in the observed intensity of light emitted from materials undergoing high‐pressure shock loading. Most experimental observations of this time dependence can be explained on the basis of geometric effects only, without having to invoke intrinsic time dependences of the source intensity (due to changes in temperature, emissivity or shock‐wave structure). By taking advantage of this fact, observed time dependences can be used to determine the absorption coefficient of shocked materials and their effective emissivities, thereby providing more precise temperature measurements. The model is invoked under various limiting conditions to explain time dependences previously observed in NaCl, CaO, Mg2SiO4 (forsterite), SiO2 (quartz), MgO, and CaAl2Si2O8 (anorthite) glass. As an example, the linear absorption coefficient at 650 nm of NaCl shocked to 75 GPa is found to be 13 cm-1, close to previously published values based on a similar but less general model. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Calculation of the crack tip opening displacement of a crack lying in a subsurface layer

    Page(s): 3400 - 3403
    Save to Project icon | PDF file iconPDF (405 KB)  

    Crack tip opening displacement of a crack lying parallel to a free surface is calculated by counting the number of dislocations emitted into the plastic zone from a crack tip. A discrete dislocation model was used to simulate the crack, while varying the strength of dislocations so as to satisfy the boundary condition. The result coincides numerically with the predictions made in a previous paper, in which the stress intensity factor appearing in a theory of bulk materials was replaced with the one which includes the surface correction. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Unreacted Hugoniot of Composition B‐3 for stresses of 0–16 kbar

    Page(s): 3404 - 3408
    Save to Project icon | PDF file iconPDF (491 KB)  

    A light gas gun has been used to measure the unreacted Hugoniot of both pressed and cast Composition B‐3. Transmitted stress and wave speeds were determined from quartz gauges placed on the rear surface of explosive disks. Both pressed and cast Composition B‐3 exhibited elastic–plastic behavior. Good agreement was found between the elastic and plastic shock wave speeds and those determined ultrasonically. The elastic constants for pressed Composition B‐3 were evaluated ultrasonically. Apparently, reaction in Composition B‐3 has not occurred in the Hugoniot measurements described in this work. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Refractory amorphous metallic (W0.6Re0.4)76B24 coatings on steel substrates

    Page(s): 3409 - 3414
    Save to Project icon | PDF file iconPDF (781 KB)  

    Refractory metallic coatings of (W0.6Re0.4)76B24 (WReB) have been deposited onto glass, quartz, and heat‐treated AISI 52100 bearing steel substrates by dc magnetron sputtering. As‐deposited WReB films are amorphous, as shown by their diffuse x‐ray diffraction patterns; chemically homogeneous, according to secondary ion mass spectrometry (SIMS) analysis; and they exhibit a very high (∼ 1000 °C) crystallization temperature. Adhesion strength of these coatings on heat‐treated AISI 52100 steel is in excess of ∼20, 000 psi and they possess high microhardness (∼ 2400 HV50). Unlubricated wear resistance of such hard and adherent amorphous metallic coatings on AISI 52100 steel is studied using the pin‐on‐disc method under various loading conditions. Amorphous metallic WReB coatings, about 4 μm thick, exhibit an improvement of more than two and a half orders of magnitude in the unlubricated wear resistance over that of the uncoated AISI 52100 steel. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Study of spall and recompaction of ceramics using a double‐impact technique

    Page(s): 3415 - 3418
    Save to Project icon | PDF file iconPDF (463 KB)  

    A new plate impact technique for studying the dynamic properties of shock‐damaged materials has been developed. The technique is based on impacting the specimen with two flyer plates which are separated by a small gap. Impact of the first plate causes spall in the target. Impact of the second plate closes the spall. The transmitted shock wave is monitored with a VISAR and/or manganin stress gauge. Analysis of the waves gives the properties of the damaged region. Preliminary results for copper and polycrystalline aluminum oxide have been obtained. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Precipitation of oxygen at 485 °C: Direct evidence for accelerated diffusion of oxygen in silicon?

    Page(s): 3419 - 3424
    Save to Project icon | PDF file iconPDF (1126 KB)  

    Prolonged annealing of Czochralski silicon at 485°C leads to the formation of a number of defects which is accompanied by a reduction in the concentration of oxygen interstitials in the matrix. High‐resolution electron microscopy has been used to investigate the structure of these defects which are basically of three types: (1) ribbonlike, (2) looplike defects which result in local lattice strains and hence are also visible in conventional transmission electron microscopy, and (3) dark regions visible in high‐resolution micrographs with no lattice strains. Based on image characteristics and a comparison of the reduction in interstitial oxygen, from infrared spectroscopy, with the sizes of the ribbons, estimated from high‐resolution micrographs, it is proposed that the ribbonlike defects are, in fact, the coesite phase which forms at prolonged anneals of the same material at the higher temperatures of 630–650°C. Using a simple model for the diffusion of oxygen to ribbons, the diffusivity of oxygen in silicon is estimated to be enhanced by nearly four orders of magnitude at 485°C! It is proposed that the looplike defects are extrinsic Frank loops which act as sinks for the interstitial silicon ejected during the oxygen precipitation. The fading away of the dark regions under electron irradiation in the microscope suggests that they are agglomerates of point defects. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Interdiffusion in the Ta‐W system

    Page(s): 3425 - 3429
    Save to Project icon | PDF file iconPDF (675 KB)  

    Interdiffusion in the Ta‐W system, a continuous body‐centered‐cubic solid solution, has been investigated in the temperature range 1300–2100 °C with single‐phase diffusion couples prepared by chemical vapor deposition. Fine inclusions, presumably oxides or carbides, decorated the couple interfaces and served as Kirkendall markers. The diffusion annealing times ranged from 16 h to 220 days. The resulting concentration profiles were measured with the electron microprobe and analytical electron microscope. The chemical diffusion coefficient was determined by the classical Boltzmann–Matano technique. The intrinsic diffusivities were determined by the technique of Darken. In the composition range 20–80 at. % W, the activation energy Q for chemical diffusion was constant at 130.5±1.5 kcal/mole. The activation energies for the intrinsic diffusion coefficients at the composition of the Kirkendall marker plane, approximately 70 at. % W, were Q(Ta)=132.3±0.5 kcal/mole and Q(W)=122.0±0.5 kcal/mole. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Mobility and diffusivity for vacancy‐solute diffusion in a simple cubic edge dislocation

    Page(s): 3430 - 3433
    Save to Project icon | PDF file iconPDF (445 KB)  

    An edge dislocation in a simple cubic crystal is considered as the basis for a model for vacancy‐induced transport. The Burgers vector for the dislocation is [01¯0], and a solute atom moves along the compressed region of the core by vacancy exchanges along the edge of the extra half plane of atoms. The length of the dislocation is carried to the limit of an infinite number of lattice sites. Consequently, when the vacancy is tightly bound to the dislocation, that limit of tight binding becomes exact. In the tight binding limit, the correlation factor goes to zero for self‐diffusion as expected. With vacancy solute tight binding, this result is not altered. Vacancy‐solute repulsion can override vacancy‐dislocation attraction and change the limit. In the case of dislocation and solute binding to the vacancy, the diffusivity becomes indefinitely large due to the abundance of defects increasing the jump frequency at a rate faster than the correlation factor decreases it. The mobility for electromigration also shows unusual limits. When the solute and dislocation both bind the vacancy, the ratio of the mobility to diffusivity becomes indefinitely large. So long as there is large dislocation vacancy binding, the ratio remains large even with solute vacancy repulsion. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

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

Full Aims & Scope

Meet Our Editors

Editor
P. James Viccaro
Argonne National Laboratory