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Showing papers in "Journal of Applied Physics in 1985"


Journal ArticleDOI
TL;DR: In this article, a review of the properties of the Al x Ga1−x As/GaAs heterostructure system is presented, which can be classified into sixteen groups: (1) lattice constant and crystal density, (2) melting point, (3) thermal expansion coefficient, (4), lattice dynamic properties, (5) lattices thermal properties,(6) electronic-band structure, (7) external perturbation effects on the bandgap energy, (8) effective mass, (9) deformation potential, (10) static and
Abstract: The Al x Ga1−x As/GaAs heterostructure system is potentially useful material for high‐speed digital, high‐frequency microwave, and electro‐optic device applications Even though the basic Al x Ga1−x As/GaAs heterostructure concepts are understood at this time, some practical device parameters in this system have been hampered by a lack of definite knowledge of many material parameters Recently, Blakemore has presented numerical and graphical information about many of the physical and electronic properties of GaAs [J S Blakemore, J Appl Phys 5 3, R123 (1982)] The purpose of this review is (i) to obtain and clarify all the various material parameters of Al x Ga1−x As alloy from a systematic point of view, and (ii) to present key properties of the material parameters for a variety of research works and device applications A complete set of material parameters are considered in this review for GaAs, AlAs, and Al x Ga1−x As alloys The model used is based on an interpolation scheme and, therefore, necessitates known values of the parameters for the related binaries (GaAs and AlAs) The material parameters and properties considered in the present review can be classified into sixteen groups: (1) lattice constant and crystal density, (2) melting point, (3) thermal expansion coefficient, (4) lattice dynamic properties, (5) lattice thermal properties, (6) electronic‐band structure, (7) external perturbation effects on the band‐gap energy, (8) effective mass, (9) deformation potential, (10) static and high‐frequency dielectric constants, (11) magnetic susceptibility, (12) piezoelectric constant, (13) Frohlich coupling parameter, (14) electron transport properties, (15) optical properties, and (16) photoelastic properties Of particular interest is the deviation of material parameters from linearity with respect to the AlAs mole fraction x Some material parameters, such as lattice constant, crystal density, thermal expansion coefficient, dielectric constant, and elastic constant, obey Vegard’s rule well Other parameters, eg, electronic‐band energy, lattice vibration (phonon) energy, Debye temperature, and impurity ionization energy, exhibit quadratic dependence upon the AlAs mole fraction However, some kinds of the material parameters, eg, lattice thermal conductivity, exhibit very strong nonlinearity with respect to x, which arises from the effects of alloy disorder It is found that the present model provides generally acceptable parameters in good agreement with the existing experimental data A detailed discussion is also given of the acceptability of such interpolated parameters from an aspect of solid‐state physics Key properties of the material parameters for use in research work and a variety of Al x Ga1−x As/GaAs device applications are also discussed in detail

2,671 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied the dielectric properties, lattice and microstructure of ceramic BaTiO3 showing grain sizes of 0.3-100 μm and showed that at grain sizes <10 μm the width of ferroelectric 90° domains decreases proportionally to the square root of the grain diameter.
Abstract: Dielectric properties, lattice‐ and microstructure of ceramic BaTiO3 showing grain sizes of 0.3–100 μm were studied. At grain sizes <10 μm the width of ferroelectric 90° domains decreases proportionally to the square root of the grain diameter. The decreasing width of the domains can be theoretically explained by the equilibrium of elastic field energy and domain wall energy. The smaller the grains, the more the dielectric and the elastic constants are determined by the contribution of 90° domain walls. The permittivity below the Curie point shows a pronounced maximum er ≊5000 at grain sizes 0.8–1 μm. At grain sizes <0.7 μm the permittivity strongly decreases and the lattice gradually changes from tetragonal to pseudocubic.

1,742 citations


Journal ArticleDOI
TL;DR: In this article, X-ray diffraction indicates the films are single-phase, orthorhombic, β-FeSi2, and single-crystal silicon wafers and with low pressure chemical vapor deposition (LPCVD) polycrystalline silicon thin films.
Abstract: Iron disilicide thin films were prepared by furnace reaction of ion beam sputtered iron layers with single‐crystal silicon wafers and with low‐pressure chemical vapor deposition (LPCVD) polycrystalline silicon thin films. X‐ray diffraction indicates the films are single‐phase, orthorhombic, β‐FeSi2. Impurity levels are below the detection limit of Auger spectroscopy. Normal incidence spectral transmittance and reflectance data indicate a minimum, direct energy gap of 0.87 eV. The apparent thermal activation energy of the resistivity in the intrinsic regime is about half of this minimum optical gap. With such a direct band gap, the material may be suitable for the development of both light‐sensitive and light‐emitting thin‐film devices within the silicon microelectronics technology.

447 citations


Journal ArticleDOI
TL;DR: In this paper, the second-order term in the Fourier development of Esc was interpreted by including the second order term in a second order Fourier term in Fourier analysis of BSO crystals.
Abstract: Large values of the exponential gain coefficient Γ are obtained (Γ≂8–12 cm−1) when recording with a moving grating in photorefractive BSO crystals (nearly degenerate two‐wave mixing; drift recording mode). The resolution of the Kukhtarev’s equations with a moving grating shows a resonance effect which at the optimum velocity makes the modulation of the photoinduced space charge field Esc higher. An optimum of the grating spacing also exists: Λopt:2π(E0/NA)(μe/eγR)1/2. In such conditions, the space charge field is phase shifted by π/2 with respect to the incident fringe pattern; this allows an efficient beam coupling between the two recording beams. The dependence of the gain Γ versus the incident beam ratio β of the two interfering waves is interpreted by including the second‐order term in the Fourier development of Esc. The conditions allowing one to obtain a reasonable agreement between the theory and experiments are presented and discussed, as well as the adopted values of the crystals’ parameters.

419 citations


Journal ArticleDOI
TL;DR: In this paper, a review of recent literature dealing with radiation-induced point defects distributed volumetrically in thermally grown SiO2•on-Si or superficially at the silicon interface is made, with particular emphasis on the results of electron spin resonance experimentation.
Abstract: A review is made of recent literature dealing with radiation‐induced point defects distributed volumetrically in thermally grown SiO2‐on‐Si or superficially at the silicon interface, with particular emphasis on the results of electron‐spin‐resonance experimentation. The observed defect types and their anneal kinetics are then compared with recent advances in the understanding of similar species and processes in irradiated bulk fused silica. It is concluded that radiolytic molecular hydrogen is formed in thermally grown SiO2 layers, just as it is in bulk fused silica, and that the diffusion of this hydrogen determines the temperature and time dependencies of the post‐irradiation interface state buildups.

385 citations


Journal ArticleDOI
TL;DR: In this article, the formation of TiSi2 thin films on silicon substrates has been investigated with several transmission electron microscope techniques, and it was shown that a metastable phase (C49 or ZrSi2 structure) forms prior to the equilibrium phase (TiSi2 (C54 structure).
Abstract: The formation of TiSi2 thin films on silicon substrates has been investigated with several transmission electron microscope techniques. For films formed either by reacting titanium with a silicon substrate or by sintering a codeposited (Ti+Si) mixture, electron diffraction patterns show that a metastable phase—TiSi2 (C49 or ZrSi2 structure)—forms prior to the equilibrium phase—TiSi2 (C54 structure). High‐resolution images indicate that the metastable TiSi2‐silicon interface is atomically sharp, with no ‘‘glassy membrane’’ layer present. The annealing temperature required to transform the metastable TiSi2 to the low resistivity, equilibrium TiSi2 increases as the thin‐film impurity content increases. Previous studies of TiSi2 formation are discussed in light of these results.

375 citations


Journal ArticleDOI
TL;DR: In this paper, the capacitive sheath approximation is used to relate the measured voltages to the measured plasma potential, and the effects of superimposing dc voltages on the excitation electrode are discussed.
Abstract: The plasma potential of 13.56‐MHz low‐pressure argon glow discharges has been measured for various modes of applying the rf power in a geometrically asymmetric planar system. The plasma potential is determined from the energy distribution of positive ions incident on the grounded electrode. The voltages on the excitation electrode (target electrode) are carefully measured and the capacitive sheath approximation is used to relate these measured voltages to the measured plasma potential. This approximation is successful in most of the situations encountered in this low‐pressure (20 mTorr) relatively low‐power density regime. The effects of superimposing dc voltages on the excitation electrode are discussed.

373 citations


Journal ArticleDOI
TL;DR: In this paper, it was reported that thin films of polyimide are efficiently etched in air at pulsed excimer laser wavelengths of 248, 308, and 351 nm, and the absorbed energy density required to initiate significant etching was found, within experimental error, to be independent of the wavelengths examined.
Abstract: It is reported that thin films of polyimide are efficiently etched in air at pulsed excimer laser wavelengths of 248, 308, and 351 nm. Etch rate versus incident fluence data are found to obey a Beer–Lambert etching relation. Sharp laser fluence thresholds for significant etching are found to correlate with the wavelength‐dependent absorption coefficient. The absorbed energy density required to initiate significant etching is found, within experimental error, to be independent of the wavelengths examined. It is felt that this information demonstrates the predominantly thermal nature of the laser etching mechanism. Additionally, infrared spectroscopy and coupled gas chromatography/mass spectroscopy were used to identify several gases evolved during pulsed laser etching of polyimide in both air and vacuum.

373 citations


Journal ArticleDOI
TL;DR: Amorphous Si and Ge layers, produced by noble gas (Ar or Xe) implantation of single crystal substrates, have been crystallized in a differential scanning calorimeter (DSC) as discussed by the authors.
Abstract: Amorphous Si and Ge layers, produced by noble gas (Ar or Xe) implantation of single crystal substrates, have been crystallized in a differential scanning calorimeter (DSC). The MeV implantation energies resulted in amorphous layers of micron thickness whose areal densities were determined using the Rutherford backscattering and channeling of 1‐MeV protons. These techniques allow determination of the amorphous‐crystal interface velocity (which is proportional to the rate of heat evolution ΔHac) and the total enthalpy of crystallization ΔHac. Amorphous Ge was found to relax continuously to an amorphous state of lower free energy, with a total enthalpy of relaxation of 6.0 kJ/mol before the onset of rapid crystallization. The interface velocity for crystallization on (100) substrates, was found to have an Arrhenius form with an activation energy of 2.17 eV. The value of ΔHac was found to be 11.6±0.7 kJ/mol, the same as for samples prepared by deposition. For Si, ΔHac was determined to be 11.9±0.7 kJ/mol wit...

364 citations


Journal ArticleDOI
TL;DR: In this article, the effective thermal conductivity of a misoriented short fiber composite was examined based on the equivalent inclusion method for steady-state heat conduction in composite which was recently proposed.
Abstract: This paper examines the effective thermal conductivity of a misoriented short fiber composite The analysis is based on the equivalent inclusion method for steady‐state heat conduction in composite which we have recently proposed The present approach is unique in that it takes into account the interaction among fibers at different orientations Closed form solutions are given for the thermal conductivity of a misoriented short fiber composite Then, numerical results are presented to demonstrate the effects of volume fraction, fiber aspect ratio, and distribution function of fiber orientation on the thermal conductivity

358 citations


Journal ArticleDOI
TL;DR: In this paper, a review of the work done in the field of nonlinear integrated optics is presented, focusing on second and third order phenomena occurring in planar geometry structures and several applications are discussed.
Abstract: We review the work done to date in the field of nonlinear integrated optics. Emphasis is placed on (intrinsic) second‐ and third‐order phenomena occurring in planar geometry structures and several applications are discussed. All of the nonlinear interactions are discussed in a single notation.

Journal ArticleDOI
TL;DR: In this paper, the magnetic scattering of x rays is discussed in a way which allows consideration of the effects of electron binding, and the cross section is reduced by (ℏω/mc2)2 (about 5×10−4).
Abstract: The scattering of x rays is used to determine the electric charge distribution in matter. Since x rays are electromagnetic radiation, we should expect that they will be sensitive not only to the charge distribution, but also to the magnetization density. That this is indeed the case has been pointed out and studied experimentally. In this paper the magnetic scattering is discussed in a way which allows consideration of the effects of electron binding. The cross section, compared with that for neutron scattering from magnetically ordered materials, is reduced by (ℏω/mc2)2 (about 5×10−4). With a synchrotron radiation source, however, this factor can be made up, and magnetic x‐ray Bragg peaks can be collected in the same time as neutron peaks. Special effects of interest include high momentum resolution, polarization phenomena which separate spin and orbital densities, and resonance effects which give a large enhancement of the x‐ray cross section and which may make the study of surface magnetism possible.

Journal ArticleDOI
TL;DR: In this article, the authors focused on viscous-like behavior of solids during large-amplitude compressive stress-wave propagation and determined the maximum strain rate in the plastic wave for 30 steady or near steady wave profiles obtained with velocity interferometry methods.
Abstract: The present study is focused on viscouslike behavior of solids during large‐amplitude compressive stress‐wave propagation. Maximum strain rate in the plastic wave has been determined for 30 steady‐ or near steady‐wave profiles obtained with velocity interferometry methods. The materials include six metals, aluminum, beryllium, bismuth, copper, iron, and uranium, and two insulating solids, magnesium oxide and fused silica. A plot of Hugoniot stress versus maximum strain rate for each material is adequately described by η=aσmh. The exponent m is approximately 4 for all materials while the coefficient a is material dependent. A model is developed which incorporates the observed trends of the shock viscosity data in a three‐dimensional framework. Finite‐difference calculations using the model reproduce the experimental wave profile data.

Journal ArticleDOI
TL;DR: In this paper, a one-dimensional theory is presented, which describes the dependence of the pyroelectric signal on the optical, thermal, and geometric parameters of the solid/pyroelectric system.
Abstract: Light absorption by a solid material and conversion of part, or all, of the optical energy into heat due to nonradiative deexcitation processes within the solid can give rise to an electrical signal in a pyroelectric thin film in contact with the sample. This effect forms the basis of a new spectroscopic technique for the study of condensed phase matter. A one‐dimensional theory is presented, which describes the dependence of the pyroelectric signal on the optical, thermal, and geometric parameters of the solid/pyroelectric system. Specifically, the theory examines the conditions under which the photopyroelectric signal exhibits a linear dependence on the optical absorption coefficient of the solid. Thus a theoretical basis for the technique of photopyroelectric spectroscopy is established. Qualitative comparisons between predictions of the theory and preliminary experimental observations are used to test the applicability of the theory to experimental configurations of practical interest.

Journal ArticleDOI
TL;DR: In this article, a negative conductance device consisting of a heterojunction bipolar transistor with a quantum well and a symmetric double barrier or a superlattice in the base region is proposed.
Abstract: We propose a new negative conductance device consisting of a heterojunction bipolar transistor with a quantum well and a symmetric double barrier or a superlattice in the base region. The key difference compared to previously studied structures is that resonant tunneling is achieved by high‐energy minority carrier injection into the quantum state rather than by application of an electric field. Thus this novel geometry maintains the crucial, structural symmetry of the double barrier, allowing unity transmission at all resonance peaks and higher peak‐to‐valley ratios and currents compared to conventional resonant tunneling structures. Both tunneling and ballistic injection in the base are considered. These new functional devices have significant potential for a variety of signal processing and multiple‐valued logic applications and for the study of the physics of transport in superlattices.

Journal ArticleDOI
TL;DR: In this article, the authors examined the one-dimensional fragmentation problem as a random Poisson process and provided comparisons with expanding ring fragmentation data, and found that size distributions from random geometric fragmentation are construction dependent, and a conclusive choice between the two distributions cannot be made.
Abstract: The present study is focused on the distributions in particle size produced in dynamic fragmentation processes. Previous work on this subject is reviewed. We then examine the one‐dimensional fragmentation problem as a random Poisson process and provide comparisons with expanding ring fragmentation data. Next we explore the two‐dimensional (area) and, less extensively, the three‐dimensional (volume) fragmentation problem. Mott’s theory of random area fragmentation is developed, and we propose an alternative application of Poisson statistics which leads to an exponential distribution in fragment size. Both theoretical distributions are compared with analytic and computer studies of random area geometric fragmentation problems, including those suggested by Mott, the Voronoi construction, a variation of the Johnson–Mehl construction, and several methods of our own. We find that size distributions from random geometric fragmentation are construction dependent, and that a conclusive choice between the two distributions cannot be made. A tentative application of the maximum entropy principle to fragmentation is discussed. The statistical theory is extended to include a concept of statistical heterogeneity in the fragmentation process. Finally, comparisons are made with various, dynamic fragmentation data.

Journal ArticleDOI
TL;DR: In this article, the anchoring energy function at the interface between 5CB(pentylcyanobiphenyl) and an obliquely evaporated SiO was determined by measuring the birefringence and the capacitance of a 56μm-thick cell up to 150 V rms at 0.23°C below the clearing temperature.
Abstract: We show that the anchoring energy function, i.e., the anisotropic part of the interfacial free energy, at a nematic liquid crystal‐wall interface can be determined uniquely without a numerical fitting procedure, when the integrated birefringence of a liquid crystal cell with a thickness much larger than the extrapolation length is measured as a function of an electric or magnetic field well above the Freedericksz threshold. The precision of the present method is closely argued, showing that the resulting anchoring energy function is reasonably insensitive to the uncertainties in the material parameters and in the cell thickness. As an example, the anchoring energy function at the interface between 5CB(pentylcyanobiphenyl) and an obliquely evaporated SiO was determined for the first time, by measuring the birefringence and the capacitance of a 56‐μm‐thick cell up to 150 V rms at 0.23 °C below the clearing temperature. A saturation of the field‐induced distortion was clearly observed at about 100 V rms. The...

PatentDOI
James R. Matey1
TL;DR: In this article, a scanning capacitance probe is used to identify the topography and material properties of the surface layer of a human body in microscopic imaging using a single image of the body.
Abstract: Variations in topography and material properties of the surface layer of a body are observed in microscopic imaging using a scanning capacitance probe. The acronym SCaM identifying the process and apparatus is derived from the phrase scanning capacitance microscope. The material properties observable by SCaM are the surface-electric property representative of the complex dielectric constant of the surface material and the surface-mechanical property representative of the elastic constant of the surface material.

Journal ArticleDOI
TL;DR: In this article, a model for growth of secondary grains into a uniform matrix of columnar normal grains is presented, which indicates that secondary grain growth rates should increase with grain boundary energy, surface energy anisotropy, grain boundary mobility, and temperature.
Abstract: Secondary grain growth in thin films can lead to grain sizes much greater than the film thickness. Surface energy anisotropy often provides an important fraction of the driving force for secondary grain growth, especially in the early stages of growth. Surface‐energy‐driven secondary grain growth leads to the development of large grains with restricted crystallographic textures. A model is presented for growth of secondary grains into a uniform matrix of columnar normal grains. The model indicates that secondary grain growth rates should increase with grain boundary energy, surface energy anisotropy, grain boundary mobility, and temperature. While final secondary grain sizes will decrease with film thickness, their growth rates will increase. The final secondary grain sizes and orientations will be strongly affected by grain sizes and orientations in the initial film. The models presented here provide analytical tools for experimental study of secondary grain growth in thin films. They will be used in for...

Journal ArticleDOI
TL;DR: In this article, the authors show that free standing, doubly supported micromechanical beams which are fabricated from films with built-in compressive strain fields buckle at critical geometries.
Abstract: Free standing, doubly supported micromechanical beams which are fabricated from films with built‐in compressive strain fields buckle at critical geometries. Experimental determination of the onset of buckling for known geometries leads to a direct measurement of the strain level in the films. This idea is supported by appropriate theory for experimental structures which form clamped, doubly supported beams with constant cross section and varying lengths. Application to low pressure chemical vapor deposition polysilicon leads to the conclusion that strain fields of 0.2% reduce to 0.05% during annealing.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated ionic conductivity σ and mobility σ in amorphous network polymers from poly(propylene oxide) (PPO) containing lithium perchlorate (LiClO4) at the concentration of 0.042 and 0.076.
Abstract: Ionic conductivity σ and mobility μ in the amorphous network polymers from poly(propylene oxide) (PPO) containing lithium perchlorate (LiClO4) at the concentration of [LiClO4]/[PO unit]=0.042 and 0.076 were investigated by means of complex impedance and time‐of‐flight methods. The σ values of the PPO–LiClO4 complexes reached 10−5 S cm−1 at 70 °C. The temperature dependence of σ deviated from a single Arrhenius behavior above a critical temperature (−1 °C and 11 °C) which approximately corresponded to the glass transition temperature Tg. The μ values were relatively high and changed from 10−6 to 10−5 cm2 V−1 s−1 in the temperature range of 40–100 °C. The Nernst–Einstein equation correlated μ with the ionic diffusion coefficient D. The Williams–Landel–Ferry equation with C1≂5 and C2≂30–50 held with a temperature dependence of D in the order of 10−8–10−7 cm2 s−1. The change in the number of ionic carriers n with temperature obeyed the Arrhenius equation with the activation energy of 0.26 and 0.34 eV. The deg...

Journal ArticleDOI
TL;DR: In this paper, the metalorganic chemical vapor deposition (MOCVD) of epitaxial III-V semiconductor alloys on III-v substrates is reviewed in detail.
Abstract: The metalorganic chemical vapor deposition (MOCVD) of epitaxial III‐V semiconductor alloys on III‐V substrates is reviewed in detail. The emphasis is placed on both practical and theoretical knowledge of the equipment and deposition process. The chemistry of the source alkyls and the dynamics of the transport process are discussed. The growth of the GaAs and AlxGa1−xAs systems are treated as prototypical examples (and the most studied) of the III‐V materials. Latter sections review InP, Ga1−xInxAs, and related alloys. Finally, the antimonide and the other systems are reviewed. Electronic and optical devices fabricated from MOCVD‐grown materials are used as examples of the capabilities of the growth technique.

Journal ArticleDOI
TL;DR: In this paper, an Nb-Sn filament mounted on a flexible glass beam can be broken to form an electron tunneling junction between the fracture elements, which can be continuously adjusted by varying the surface bending strain of the beam.
Abstract: An Nb‐Sn filament mounted on a flexible glass beam can be broken to form an electron tunneling junction between the fracture elements. Breaking the filament in liquid helium prevents oxidation of the freshly exposed fracture surfaces. A sharp superconducting energy gap in the I‐V characteristics measured at 4 K indicates the formation of a high‐quality tunneling barrier between the fracture elements. The resistance of the junction can be continuously adjusted by varying the surface bending strain of the beam. An estimated 0.1 nm change in the barrier thickness produces about an order of magnitude change in the resistance over the range from 105 to 108 Ω. The exponential character of this dependence shows that the tunnel junction is freely adjustable without intimate contact of the junction elements. ‘‘Break’’ junctions made in this way offer a new class of tunneling experiments on freshly exposed surfaces of a fractured sample without the oxide barrier previously required for junction stability. Such expe...

Journal ArticleDOI
TL;DR: In this article, the authors investigated the contribution of the ionization from the two metastable and the two resonance levels of argon to the total ionization rate in a low-pressure argon positive column.
Abstract: The contribution of the ionization from the two metastable and the two resonance levels of argon to the total ionization rate in a low‐pressure argon positive column is investigated theoretically and experimentally. A simple yet self‐consistent discharge model is developed by coupling the balance between the electron total production and loss rates to the steady‐state rate balance equations for the excited states. The predictions of this model, i.e., the maintenance field for the positive column and the populations in the individual excited states as a function of the gas pressure and the discharge current are compared with the experiment (0.05

Journal ArticleDOI
TL;DR: In this article, the basic physical mechanism responsible for the general behavior of eddy current losses versus magnetizing frequency fm is recognized in the competition between the external field and local internal fields, due to magnetostatic, coercive, and eddy currents effects.
Abstract: The basic physical mechanism responsible for the general behavior of eddy current losses versus magnetizing frequency fm is recognized in the competition between the external field and local internal fields, due to magnetostatic, coercive, and eddy current effects. The concept of magnetic object, corresponding to a group of neighboring walls evolving in a highly correlated fashion, is introduced in order to take into proper account the role of short‐range internal correlation fields. With a random spatial distribution of magnetic objects, the dynamic loss is essentially a function of the number n of magnetic objects which are simultaneously active at each value of fm. It is shown that the dynamic balance between applied field and local eddy current counterfields leads, with increasing fm, to a progressive increase of n governed by the simple linear law n=n0+Hexc/V0, where Hexc represents the part of the applied field in excess of the hysteresis and classical contributions. Under these conditions, a general law of losses is derived, which turns out to be in excellent agreement with several experimental results concerning different iron‐based ferromagnetic alloys. On the basis of the general validity of the obtained loss equation, a bidimensional map of dynamic losses is defined and constructed, in which the parameters n0 and V0 are used as orthogonal coordinates of representative points characterizing the loss behavior of different materials. This map provides the proper basis for a general classification of dynamic losses, which might also be useful from the applicative point of view.

Journal ArticleDOI
TL;DR: In this article, a procedure for using digital image processing techniques to measure the spatial correlation functions of composite heterogeneous materials is presented, and methods for eliminating undesirable biases and warping in digitized photographs are discussed.
Abstract: A procedure for using digital image processing techniques to measure the spatial correlation functions of composite heterogeneous materials is presented. Methods for eliminating undesirable biases and warping in digitized photographs are discussed. Fourier transform methods and array processor techniques for calculating the spatial correlation functions are treated. By introducing a minimal set of lattice‐commensurate triangles, a method of sorting and storing the values of three‐point correlation functions in a compact one‐dimensional array is developed. Examples are presented at each stage of the analysis using synthetic photographs of cross sections of a model random material (the penetrable sphere model) for which the analytical form of the spatial correlations functions is known. Although results depend somewhat on magnification and on relative volume fraction, it is found that photographs digitized with 512×512 pixels generally have sufficiently good statistics for most practical purposes. To illustrate the use of the correlation functions, bounds on conductivity for the penetrable sphere model are calculated with a general numerical scheme developed for treating the singular three‐dimensional integrals which must be evaluated.

Journal ArticleDOI
TL;DR: In this paper, the photoluminescence peak energies of the epilayers with the best experimental relation of band gap versus composition for unstrained layers were determined by comparing the peak energy of the Epilayers.
Abstract: Interfacial elastic strain induced by the lattice parameter mismatch between epilayer and substrate results in significant energy–band‐gap shifts for III‐V alloys. The epilayers used in this study are GaxIn1−xAs on (100) InP and GaxIn1−xP on (100) GaAs prepared by organometallic vapor phase epitaxy. For layer thicknesses between 1 and 1.5 μm, and Δas.f./a0≤3.5×10−3 the misfit strain is assumed to be accommodated elastically. The energy–band‐gap shifts are determined by comparing the photoluminescence peak energies of the epilayers with the best experimental relation of band gap versus composition for unstrained layers. A calculation of the energy–band‐gap shift due to biaxial stress made for GaxIn1−xAs is found to agree with the photoluminescence measurements. In addition, a comparison of the energy–band‐gap shift for GaxIn1−xP shows a clearly different dependency for tensile and compressive strain, in good agreement with calculated results.

Journal ArticleDOI
TL;DR: In this article, the perturbation expansions of the effective electrical conductivity σe of any two-phase isotropic composite medium of arbitrary dimensionality d (where d = 2,3) are derived.
Abstract: Perturbation expansions of the effective electrical conductivity σe of any two‐phase isotropic composite medium of arbitrary dimensionality d (where d=2,3) are derived. It is shown that certain Pade approximants of a particular series representation of σe yield known rigorous bounds on the conductivity of the composite. The relationships between the conductivities of certain models that are exactly realized by some of these bounds and the perturbation expansions are discussed. A new expression for the conductivity of a broad class of three‐dimensional dispersions of inclusions is derived. The formula for σe, which depends upon, among other quantities, a certain three‐point probability function of the composite medium, is shown to accurately predict σe of both periodic and random arrays of impenetrable spheres, for a wide range of phase conductivities and inclusion volume fractions.

Journal ArticleDOI
TL;DR: In this article, anisotropic behavior of the magnetization versus magnetic field curves in the basal plane has been observed for Sm2Fe14B, indicating large amplitude of the high order coefficients, K2 and K3.
Abstract: Static magnetic measurements have been carried out on single crystals of Nd2Fe14B, Sm2Fe14B, and Y2Fe14B from 4.2 to 590 K. Values of K1 estimated from high field measurements at room temperature are 4.5, −12, and 1.1 MJ/m3 for Nd2Fe14B, Sm2Fe14B, and Y2Fe14B, respectively. Anisotropic behavior of the magnetization versus magnetic field curves in the basal plane has been observed for Sm2Fe14B, indicating large amplitude of the high order coefficients, K2 and K3. In Nd2Fe14B, the magnetization has been found to tilt from the c axis and simultaneously increase in magnitude. Average Fe moment is estimated to be 2.23 μB/Fe at 4.2 K from the saturation magnetization of Y2Fe14B.

Journal ArticleDOI
TL;DR: In this paper, the effect of focusing in the plane of the electron's wiggle motion is provided by parabolically curved magnet pole faces and the focusing and resonance effects of curved pole faces are analytically calculated and numerically confirmed.
Abstract: In a free‐electron laser with a long, linear wiggler, the external focusing required to keep the electron beam from dispersing can seriously degrade the performance of the laser. The transverse focusing modulates the longitudinal velocity of each electron, periodically and nonadiabatically changing the phase of the electron with respect to the electromagnetic wave. Phase changes of order unity over a betatron period can strongly detrap or debunch electrons and greatly reduce the gain of a linear wiggler amplifier. The modulation of the electron’s longitudinal velocity can be prevented if focusing in the plane of the electron’s wiggle motion is provided by parabolically curved magnet pole faces. The focusing and resonance effects of curved pole faces are analytically calculated and numerically confirmed. Numerical simulations of linear wiggler amplifiers are presented to illustrate the effect of the curved pole faces on amplifier performance.