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Journal of Applied Physics

Issue 13 • Date Dec 1967

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Displaying Results 1 - 25 of 96
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Substrate‐Condensate Chemical Interaction and the Vapor Deposition of Epitaxial Niobium Films

    Page(s): 4933 - 4937
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    Investigation of films formed by vacuum deposition of Nb on single‐crystal MgO has demonstrated the importance of chemical interaction between the substrate and overgrowth in the epitaxial growth process. The interaction layer is composed of an oxygen‐stabilized face‐centered cubic modification of the normally bcc Nb, or the compund NbO, the thickness of which is controlled by the oxygen diffusion process in the layer. The previously observed nucleation‐coalescence process of thin film formation is replaced by ordered chemical reaction. Defect‐producing misorientations between nuclei, predominant in the nucleation‐coalescence case, are not present in the ordered chemical reaction process. Thin films may thus be produced having defect density no higher than that of the substrate crystal. The effect of interaction between the substrate and condensate, although large in the example presented, should not be overlooked in other considerations of the epitaxial process where chemical reaction cannot be ruled out. View full abstract»

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  • Spot Distortion Caused by Magnetic Deflection of an Electron Beam

    Page(s): 4938 - 4944
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    When a focused electron beam is deflected by a transverse magnetic field through a small angle, the spot shape on the target is distorted. The electron density distribution within it also varies. A novel method of calculating and presenting the characteristics of the distorted spot is presented. The positions of the electrons at the incoming aperture are mapped into the target plane subsequent to the deflection. The resultant density distribution is plotted by the computer. View full abstract»

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  • Simplified Analysis of Point‐Cathode Electron Sources

    Page(s): 4944 - 4957
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    The accelerating field of a point‐cathode electron source is divided into two regions, a diverging spherical‐field region located in the immediate vicinity of the point cathode, and a converging‐field region which occupies most of the cathode‐anode space. Analysis of this model gives the Gaussian source size, axial position of the source, and spherical‐ and chromatic‐aberration constants of the pointed‐cathode electron gun. After including diffraction effects, the electron‐optical parameters are optimized for minimum possible source size. The current density which appears to be emitted by the apparent source is introduced as a figure of merit for this type of electron gun, and the performance of field‐emission and Schottky‐emission pointed cathodes are compared. Source diameters below 100 Å are predicted for oriented‐tungsten field‐emission pointed cathodes, with apparent current densities exceeding 104 A/cm2; source diameter below 1000 Å are predicted for oriented‐tungsten Schottky‐emission pointed cathodes, with apparent current densities of approximately 100 A/cm2. View full abstract»

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  • Computer Simulation of Field‐Ion Images of Hexagonal Structures and Superlattices

    Page(s): 4957 - 4965
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    The simulation of field‐ion images by computation of the position of atoms which lie within an outer shell of given thickness on a spherical crystal has been extended to spherical crystals of a variety of structures. These include the hexagonal lattice, the hexagonal close‐packed structure and a few of the common superlattices. The consequences of the invisibility of one atomic species in ordered alloys has been investigated. The results show that computations are in fact necessary for a detailed interpretation of the field‐ion image. View full abstract»

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  • Wave‐Optical Aspects of Lorentz Microscopy

    Page(s): 4966 - 4976
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    The customary defocused and Foucault modes of Lorentz microscopy of magnetic films are usually described in terms of geometric optics. However, Wohlleben has shown that geometric optics has a restricted range of validity; a more fundamental approach is provided by wave optics. The defocused and Foucault modes may be discussed in terms of wave optics, and for the defocused mode, it can be shown explicitly that the geometric theory is simply the first approximation to the wave‐optics theory. Consideration of wave optics also leads to the proposal of two additional modes of Lorentz microscopy: Zernike phase‐contrast and interference microscopy; these modes cannot be described on the basis of geometric optics. The most fundamental problems in magnetic films which are amenable to study by Lorentz microscopy are investigations of the fine structures of domain walls and magnetization ripple. These problems are discussed in terms of wave optics for all four modes of Lorentz microscopy; in particular, the intensity distribution of the zero‐width divergent domain wall is explicitly calculated for each mode. For practical experiments, the importance of coherence, i.e., of the illumination source size, is emphasized, and the experimental aid of holography is suggested. Since the Wohlleben limit is valid for all four modes, however, there is no resolution advantage inherent in any one mode. The choice of modes for solution of the domain wall and ripple problems therefore depends upon experimental convenience. It is concluded that the defocused mode seems most promising for practical application; Fresnel diffraction is preferred for the domain‐wall problem, while Fraunhofer diffraction using low‐angle electron‐diffraction techniques is fruitful for the ripple problem. View full abstract»

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  • Linear Shock‐Velocity‐Particle‐Velocity Relationship

    Page(s): 4976 - 4980
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    An equation of state, based on a bulk modulus variation with pressure of the form BS=B0S+B0S′P+B0S″P2/2, where B0S, B0S′, and B0S″ are constants, is developed in this analysis. The resultant equation of state is combined with the Rankine-Hugoniot conservation relations to obtain a Maclaurin series expansion for the shock velocity vs the particle velocity us=c+sup+s′up2+.... The coefficients c, s, and s′ are given in terms of the unshocked density and quantities available from ultrasonic elastic constant measurements at high pressures. Using new experimental data for sodium, it is shown that s′ is nearly zero. For ionic crystals such as KBr a theoretical expression is given for B0S″ (in terms of B0S′). In the case of KBr, the value of s′ is also very close to zero. The smallness of s′ depends on the cancellation of a number of terms brought about by the fact that B0S″ is negative. CsI and xenon are also discussed. View full abstract»

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  • Paramagnetic Resonance of Trivalent Iron in Single‐Crystal Potassium Tetrafluoaluminate

    Page(s): 4980 - 4983
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    Single‐crystal potassium tetrafluoaluminate‐doped substitutionally with iron has been prepared. The room‐temperature spectrum of isolated iron ions may be described by a conventional spin Hamiltonian with parameters: g‖=2.005, g⊥=1.999, D=0.1471 cm-1, a=0.0020 cm-1, and F=0.007 cm-1. From the linewidths an upper limit to the fluorine hyperfine structure is estimated. View full abstract»

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  • Capacitance Changes in Thin CdS Crystals under dc Bias

    Page(s): 4984 - 4992
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    Appreciable increases in capacitance have been observed in thin single‐crystal CdS platelets when measured under conditions of dc bias. Data have been obtained in the frequency range 20 cps‐20 Mc/sec. Crystals could be roughly divided into two groups (denoted by I and II). Group I crystals, exhibiting an approximate V2 dependence of the I‐V characteristic, showed low‐frequency‐capacitance increases of up to a factor of ten under bias. These changes could be explained in terms of SCLC. Group II crystals, exhibiting I‐V characteristic with a voltage exponent much greater than two, showed low‐frequency‐capacitance increases of up to a factor of 1000. This behavior cannot be understood in terms of SCLC flow, and a two‐layer model is proposed which provides a satisfactory explanation. View full abstract»

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  • Current Pause in Exploding‐Wire Discharges

    Page(s): 4993 - 4998
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    Experiments with exploding wires made of constantan, copper, and lithium in atmospheric air have shown that the dwell time of an exploding wire for the examined lengths (3.2, 6.5, 9.7, and 13 cm), diameters (0.005 cm for constantan and copper, and 0.025 cm for lithium), and applied voltages (1 to 20 kV) is a function of the average electric‐field strength along the wire. The function relating dwell time to field strength is not single‐valued, but from a certain critical value there are two dwell times corresponding to each field strength. There is evidence that this duality of the dwell times is due to a change in the type of explosion at the critical gradient. Both types of observed dwell times depend in a simple way on the average field strength. View full abstract»

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  • LEED Study of the Growth of Aluminum Films on the Ta(110) Surface

    Page(s): 4998 - 5004
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    Growth of aluminum films on clean Ta(110) surfaces has been investigated by LEED techniques. Five phases of aluminum have been found, which are: (1) disordered Al(111), formed by depositing at T≪600°C; (2) Al(111)c(2×2) formed by heating film, deposited at T≪300°C, to 700°C; (3) Al(100)c(2×2), formed by heating film, deposited 300≪T≪600°C, to 700°C; (4) Epitaxial Al(111), formed by depositing film with substrate T in range 600≪T≪670°C; (5) Diffuse phase, formed by heating any of the preceding to 800°C. Two orientations of each structure have been observed; this results from the close match between primitive unit meshes of aluminum (111), (100) and Ta(110). A mechanism for the growth of Al(111) and Al(100) is suggested. Comparisons with some published LEED data on epitaxy are made. View full abstract»

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  • Theory of Plasma Transconductance due to Landau Waves

    Page(s): 5005 - 5013
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    We present here an N‐pole circuit analysis of a network of parallel plane grids immersed in an isotropic hot‐electron plasma. The associated self‐ and trans‐impedances are expressed in terms of the discrete spectrum of electrostatic waves. Voltage‐transfer ratios and transconductances between pairs of grid assemblies are calculated to study the feasibility of this scheme for launching and detecting Landau waves. Results show that widths of about 5 Debye lengths are optimum for modulator and detector gaps and that close‐range transmission between gaps is predominantly due to the fundamental exponentially damped Landau wave. View full abstract»

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  • Experimental Verification of Landau Waves in an Isotropic Electron Plasma

    Page(s): 5014 - 5020
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    We report here measurements of dispersion and damping of plane electrostatic waves having phase velocities between 1.5 and 3 times electron thermal speed 3×107 cm/sec. These waves were excited and detected at frequencies ωp≪ω≪2.5ωp using gridded rf probes within an isotropic, quiescent, and collision‐free sodium plasma at thermal equilibrium. As plasma electron density (1×107 to 2×108 cm-3) and rf (30 to 180 MHz) are varied, the measured wavelengths and spatial damping rates were scaled to Debye length using independent Langmuir probe data. Full agreement is then found between the experimental results and the fundamental solution of Landau's dispersion relation. View full abstract»

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  • A Cause and Cure of Stacking Faults in Silicon Epitaxial Layers

    Page(s): 5020 - 5026
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    In many applications of silicon epitaxial layers grown on silicon substrates it is necessary to oxidize the substrate and then remove the oxide prior to epitaxial deposition. This oxidation step is found to produce a greatly increased density of stacking faults in the deposit. This anomalous increase in stacking faults can be eliminated if the back (undeposited) substrate surface is treated either to abrasive processes such as lapping and scribing or to a boron‐gettering process prior to oxidation. Both types of treatment are likewise found to eliminate saucer‐like pits observed in oxidized slices after structural etching. The incidence of these pits is closely correlated with the incidence of stacking faults in the grown layer. It is concluded that the pits represent precipitates of fast‐diffusing impurities and are probable nucleation sites for stacking faults. View full abstract»

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  • Properties of Magnetic Materials with a Nonuniform Saturation Magnetization. I. General Theory and Calculation of the Static Magnetization

    Page(s): 5027 - 5034
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    A general theory concerning the properties of magnetic materials having a nonuniform saturation magnetization is developed. In this theory, the local saturation magnetization and the local exchange interaction are assumed to vary in an arbitrary manner throughout the sample. It is further assumed that a dc magnetic field is applied which is sufficiently large to magnetize the sample substantially to saturation. The general theory is then specialized for a calculation of the static magnetization, assuming that the host material contains inclusions of a material with a different saturation magnetization. If all inclusions are fairly large, the effect of the exchange interaction becomes negligible and a result previously derived by Néel is obtained. The inclusion of exchange reduces the deviation of the magnetization from its saturation value, particularly at low values of the internal field. If exchange is neglected, this deviation becomes infinitely large at zero internal field. If exchange is included, however, the deviation remains finite. The theory is, therefore (for suitable materials), still approximately valid at remanence. View full abstract»

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  • Properties of Magnetic Materials with a Nonuniform Saturation Magnetization. II. Longitudinal Susceptibility

    Page(s): 5035 - 5044
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    A theory of the longitudinal susceptibility (response to an rf field applied parallel to the dc field) of magnetic materials with a nonuniform saturation magnetization is described. According to this theory the imaginary part of the longitudinal susceptibility, χ″, considered as a function of dc magnetic field, should show a maximum when the internal magnetic field is approximately equal to (ω/γ)‐π〈M0〉, where ω is the frequency, γ the gyromagnetic ratio, and 〈M0〉 the average saturation magnetization. The height of the absorption peak is calculated to be proportional to the degree of inhomogeneity (mean square deviation of the local saturation magnetization from its average) and approximately inversely proportional to the square of the frequency. The width of the absorption peak is approximately 2π〈M0〉. If the nonuniformity of the saturation magnetization is due to the presence of pores or nonmagnetic inclusions, the absorption at low dc fields (near remanence) is found to be proportional to the total cross‐sectional area of the inclusions (rather than their volume). Thus many small inclusions have a stronger effect than few large ones of the same total volume. The real part of the susceptibility is negative on the low‐field side, positive on the highfield side of the absorption peak. In most of the calculations, the effect of the inhomogeneity‐induced scattering of spin waves has been neglected. This scattering is shown to be substantially equivalent to an additional damping of the spin waves, which is strongly frequency and field dependent. View full abstract»

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  • Electromagnetic Forces in Conductors

    Page(s): 5045 - 5051
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    Relaxation‐averaging formulas are derived for magnetic‐induction problems involving axially symmetric fields with sinusoidal or pulsed time dependence in media which may be linear or nonlinear, homogeneous or inhomogeneous. Solutions have been obtained from a high‐speed digital computer for time‐harmonic fields in linear, inhomogeneous media. From these solutions, the electromagnetic forces are calculated and compared with experimental measurements. It is found that the computed and measured values agree quite well and that most of the discrepancy can be explained by the fact that the permeability of the ferrite used in the measurements was different from that assumed in the calculations. View full abstract»

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  • Electrical Conductivity of Iodine‐Doped Polyethylene

    Page(s): 5051 - 5057
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    Measurements of the electrical conductivity of polyethylene film containing absorbed iodine are described and discussed. The influence of temperature, film thickness, iodine concentration, and voltage is examined. It is believed that carriers arise from a charge transfer between polymer molecules and the iodine. The results suggest that space charge is important. View full abstract»

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  • Current Oscillations in Iodine‐Doped Polyethylene at High‐Field Strengths

    Page(s): 5058 - 5062
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    With applied dc electric fields in excess of 1.2 kV/mil, the current in iodine‐doped polyethylene is found to be no longer invariant with time, but to exhibit continuous oscillations superimposed upon a large background current. These oscillations appear at a well‐defined threshold field, which is found to be independent of temperature, but to depend on the concentration of iodine in the film. The frequency of the oscillations is very temperature dependent, having an activation energy of almost the same value as the conductivity. Increase of iodine concentration increases the frequency, but the frequency decreases with increase of field strength. The frequency is also found to be inversely proportional to film thickness. Transient response characteristics suggest that the formation of space‐charge regions may be important. The experimental results are compared with the theory of recombination waves in dielectrics, which considers the propagation of low‐field domains through the sample. View full abstract»

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  • Optical Determination of Cs Ground‐State Depletion in Cs‐Ar Low‐Pressure dc Discharges

    Page(s): 5062 - 5065
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    The results of an experimental study of the absorption properties of Cs as present in Cs‐Ar low‐pressure discharges under various discharge conditions are presented. The total Cs concentration at zero discharge current was varied between 1.5 and 15×1012 cm-3. Absorption was measured in the 4555‐Å and 8521‐Å lines of Cs from which the stationary concentration of Cs (62S1/2) could be derived. Special attention was paid to determine the Cs concentration as the discharge changed from a low‐burning voltage mode to a high‐burning voltage mode. The pronounced variations of the discharge properties were found to be accompanied by rather drastic changes of the Cs concentration for which variations of a factor of ten or more were found. View full abstract»

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  • Wave Propagation in a Beam‐Plasma System

    Page(s): 5065 - 5076
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    A nonquasistatic treatment is established in order to study wave propagation along beam‐plasma systems in the presence of a dc magnetic field. Solutions to the dispersion equations are given for two cases: The column completely fills a cylindrical waveguide, or it is in an infinite dielectric (vacuum). The results are compared qualitatively to those already obtained by various authors for the same conditions by a quasistatic analysis. View full abstract»

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  • Resonance‐Rectification Effects in Warm Magnetoplasmas

    Page(s): 5077 - 5082
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    This paper extends the study of resonance rectification phenomena in plasmas to the case where a static magnetic field is present. Parallel wire‐probe geometry has been chosen so that the rf electric field is primarily perpendicular to the magnetic field. Under these conditions, experiments show that there are two distinct series of resonance peaks, one occurring between successive cyclotron harmonics, the other precisely at the cyclotron harmonics. Cold‐plasma theory is inadequate to account for the existence of these resonances. An explanation is proposed, based on the form of the warm‐plasma permittivity component perpendicular to the magnetic field, which explains satisfactorily all of the experimental observations. View full abstract»

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  • Nonradiative Relaxation Time between 4T1, 2 and 2E States in Ruby

    Page(s): 5083 - 5086
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    The R‐line fluorescence in ruby was excited with the nanosecond light pulses, and the slope of the rise curve was studied as a function of the pulse width at room temperature. The purpose of the experiment was to determine the value or the upper limit of the nonradiative relaxation time between the pump bands 4T1, 2 and the fluorescence state 2E. The upper limit of 5 nsec was determined. A brief review of previous work is given. View full abstract»

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  • Electrical Properties of Cr‐SiO Cermet Films

    Page(s): 5087 - 5089
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    The Hall coefficient, temperature coefficient of resistance, and conductivity of Cr‐SiO cermet films were measured as a function of film composition. The behavior of the Hall coefficient indicates this material should be treated as a two‐carrier system. A model is proposed which may account for this behavior and for the dependence of the temperature coefficient of resistance on small concentrations of SiO. View full abstract»

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  • Position and Waveform of Light Emission in Reverse‐Biased GaAs Diodes

    Page(s): 5090 - 5094
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    The light emission from reverse‐biased GaAs p‐n junctions was investigated using current pulses. Appreciable light emission was obtained only in the breakdown range. Light‐emission waveform had three components, i.e., emission waveform of nearly the same shape of current pulse (first component), emission wave delaying about 2 μsec from the onset of current pulse (second component), and unstable emission peak near the last part of the current pulse (third component). For the first component, the position of the reverse‐biased emission was the same as that of the forward‐biased emission. The light of the second component was emitted from n‐type region of the diode, and this component will occur from the saturation of recombination rate near the junction. The third component was emitted from the relatively wide range of the n‐type region containing p‐n junction, and this emission peak is the phenomenon preceding the destruction of the diodes. View full abstract»

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Aims & Scope

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

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Editor
P. James Viccaro
Argonne National Laboratory