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1 Dec 1977

Volume 48, Issue 12, pp. 4865-5393

Page 1 of 4 Pages Next Page | Jump to Page

Superconductive bolometers for submillimeter wavelengths

J. Clarke, G. I. Hoffer, P. L. Richards, and N. ‐H. Yeh

J. Appl. Phys. 48, 4865 (1977); http://dx.doi.org/10.1063/1.323612 (15 pages) | Cited 59 times

Online Publication Date: 26 August 2008

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Three types of composite superconductive bolometers are described in which the temperature‐sensitive element is a superconducting film at the transition temperature, a superconductor–normal metal–superconductor Josephson junction, or a superconductor–insulator–normal metal quasiparticle tunneling junction. The temperature‐sensitive element is evaporated onto a sapphire substrate on the reverse side of which is a bismuth film to absorb the submillimeter radiation. The noise limitations of each type of bolometer are calculated. The fabrication and measured performance of the transition‐edge bolometer and the Josephson‐junction bolometer are described. The best electrical (noise‐equivalent power) NEP obtained with a transition‐edge bolometer fabricated on a 4×4×0.005‐mm sapphire substrate is (1.7±0.1) ×10−15 W Hz−1/2 at 2 Hz at an operating temperature of 1.27 K. This NEP is within a factor of 2 of the thermal noise limit. The effective absorptivity of the bismuth film is measured to be 0.47±0.05, and the corresponding detectivity D∗ is calculated to be (1.1±0.1) ×1014 cm W−1 Hz1/2. Suggestions are made for further improvements in sensitivity.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
74.78.-w Superconducting films and low-dimensional structures
85.25.-j Superconducting devices

Theoretical consideration on thermoluminescence response

Toshiyuki Nakajima

J. Appl. Phys. 48, 4880 (1977); http://dx.doi.org/10.1063/1.323613 (6 pages) | Cited 3 times

Online Publication Date: 26 August 2008

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See Also: Erratum

Show Abstract
A new model is proposed for explaining the unsolved phenomena in the thermoluminescence properties, which are the nonlinear response to exposure, the postirradiation and test‐irradiation dose dependences of the sensitization phenomena, the dose effect of the energy dependence, and changes in the shape of the glow curve with the exposure. This model is based on the following assumptions: (1) In the first step of the carrier capture reaction, the sum of the number of trapped carriers in each trapping level is restricted to the number of released carriers, (2) the capture reaction between the released carriers and traps is irreversibly consecutive and follows first‐order kinetics, and (3) passage of the charged particle through the phosphor brings about an exothermic effect and reaction temperature is a sum of irradiation and exothermic temperatures. As a result, the number of captured carriers in the ith trapping level is given as a function of irradiation temperature, exothermic temperature, activation energy of the irreversibly consecutive reaction, stopping power and flux of the charged particle in the phosphor, and the number of initial traps. The model can qualitatively explain the unsolved phenomena in thermoluminescence response.
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28.41.Te Protection systems, safety, radiation monitoring, accidents, and dismantling
78.60.Kn Thermoluminescence

Electromagnetic diffraction of an aperture in a planar conducting screen separating partitioned half‐spaces

Chalmers M. Butler, Allen Q. Howard, and Robert D. Nevels

J. Appl. Phys. 48, 4886 (1977); http://dx.doi.org/10.1063/1.323614 (7 pages) | Cited 1 time

Online Publication Date: 26 August 2008

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A vector integro‐differential equation is derived for the problem of electromagnetic diffraction by an aperture in a perfectly conducting planar screen that separates two half‐spaces which are, themselves, divided into quarter spaces of differing electromagnetic properties by planar interfaces perpendicular to the screen. The aperture/screen is excited by specified sources located on both sides of the screen. Due to the partitioning of the half‐spaces, Sommerfeld integrals appear in the integral‐equation kernel. The aperture is specialized to be an infinite slot of uniform width subject to TE and TM (to slot axis) illumination, and the resulting slot equations are solved numerically. Data are presented for representative cases of interest.
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03.50.De Classical electromagnetism, Maxwell equations
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Analysis of alternating current excitation of a wire rope by a toroidal coil

David A. Hill and James R. Wait

J. Appl. Phys. 48, 4893 (1977); http://dx.doi.org/10.1063/1.323615 (5 pages) | Cited 6 times

Online Publication Date: 26 August 2008

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An idealized magnetic sheet current model for a toroidal coil which encircles a conducting ferromagnetic rope is analyzed. This configuration is suitable for the nondestructive testing of wire ropes and cables. Numerical results for the axial electric current density induced in the rope reveal that low frequencies on the order of 10 Hz are required to produced a uniform current in a typical rope. For a toroidal coil which does not completely encircle the rope, the azimuthal symmetry is lost and harmonics in ϕ are produced. These harmonics are large but decay rapidly away from the source.
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03.50.De Classical electromagnetism, Maxwell equations
41.20.Jb Electromagnetic wave propagation; radiowave propagation
84.40.Az Waveguides, transmission lines, striplines

Thermionic return currents in contact electrification

F. R. Ruckdeschel and L. P. Hunter

J. Appl. Phys. 48, 4898 (1977); http://dx.doi.org/10.1063/1.323616 (5 pages) | Cited 6 times

Online Publication Date: 26 August 2008

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It is demonstrated that the contact electrification process is generally a nonequilibrium phenomenon. The electrochemical potential is considered for the case of ion transfer between insulators. It is shown that the thermionic return currents are significantly dependent on the physical separation and the dielectric constants of the materials. A nonequilibrium chemical kinetics formulation is presented in which dielectric constants and surface separation rates are explicitly accounted for. The predictions of the theory are shown to correlate with electrification experiments performed on various glass, lead zirconate, and aluminum oxide beads rolled in an aluminum oxide coated rotating cylinder.
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41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
77.90.+k Other topics in dielectrics, piezoelectrics, and ferroelectrics and their properties (restricted to new topics in section 77)

The Dirichlet problem in a heterogeneous dielectric

Kenneth S. Mendelson

J. Appl. Phys. 48, 4903 (1977); http://dx.doi.org/10.1063/1.323617 (4 pages) | Cited 2 times

Online Publication Date: 26 August 2008

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A Green’s function has been used to discuss the Dirichlet problem in a heterogeneous dielectric. Depending on the boundary condition imposed on the Green’s function, one obtains formal expressions for the potential and the electric field or bounds on the potential and the field components at a point. A formal expression for the effective permittivity of a random statistically homogeneous dielectric has also been obtained. Finally, the Green’s function has been obtained in terms of a Neumann series. A close relation is observed between the Green’s function and the T matrix used in treating effective constants.
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41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
77.22.Ch Permittivity (dielectric function)

Stimulated‐emission cross section at 1064 and 1342 nm in Nd : YVO4

A. W. Tucker, M. Birnbaum, C. L. Fincher, and J. W. Erler

J. Appl. Phys. 48, 4907 (1977); http://dx.doi.org/10.1063/1.323618 (5 pages) | Cited 65 times

Online Publication Date: 26 August 2008

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The stimulated‐emission cross sections at 1064 (4F3/2→4I11/2) and 1342 nm (4F3/2→4I13/2) in Nb : YVO4 were determined by measurement of laser thresholds as a function of output mirror reflectivity. Small samples of Nd : YVO4 and Nd : YAG were end pumped at room temperature with a cw 514.5‐nm argon ion laser in an almost identical geometrical arrangement which permitted comparative values to be obtained. Assuming that the pumping quantum efficiency of Nd : YVO is similar to that of Nd : YAG, the stimulated‐emission cross sections obtained for the 1064‐ and 1342‐nm transitions were respectively 12×10−19 and 6.0×10−19 cm2.
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42.55.Rz Doped-insulator lasers and other solid state lasers

A simple compact high‐repetition‐rate hydrogen vuv laser for scientific applications

John E. M. Goldsmith and Igor N. Knyazev

J. Appl. Phys. 48, 4912 (1977); http://dx.doi.org/10.1063/1.323619 (10 pages) | Cited 3 times

Online Publication Date: 26 August 2008

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The operation of a simple compact high‐repetition‐rate vuv hydrogen laser is described in detail. The laser uses a Blumlein‐type transverse discharge system with a very narrow profiled discharge channel and a low‐inductance nitrogen‐pressurized triggered spark‐gap switch. The laser produces 20−μJ pulses of approximately (1/2) ‐nsec duration at 1600 Å (corresponding to a peak power of about 40 kW). The dependence of the pulse energy on the operating parameters of the laser is reported. Laser action in nitrogen, neon, and XeF∗ has also been observed.
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42.60.By Design of specific laser systems
42.55.Lt Gas lasers including excimer and metal-vapor lasers
33.20.Ni Vacuum ultraviolet spectra

Stability limits of high‐power ion‐laser discharges

H. R. Lüthi and W. Seelig

J. Appl. Phys. 48, 4922 (1977); http://dx.doi.org/10.1063/1.323620 (6 pages) | Cited 10 times

Online Publication Date: 26 August 2008

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Highly ionized plasmas (degree of ionization 0.1,...,0.5) with electron temperatures kTe≳4 eV are required for high‐power generation from ion lasers. In stationary low‐pressure arcs, however, these requirements are limited by discharge instabilities. The stability limits are investigated in the case of Ar and Hg low‐pressure discharges. It is shown that the main limitation processes are due to neutral gas depletion by ionization and axial plasma inhomogeneities. The stability ranges of ion‐laser discharges are represented using the geometry‐independent parameters jR and pR ( j: discharge current density; p: filling pressure; R: discharge radius). These instabilities, together with saturation effects in the laser mechanism, limit the output power of ion lasers by restricting the operational range of the discharges.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
52.80.-s Electric discharges

Transient‐waveguide effects and lasing time delays in electron‐beam‐pumped semiconductor lasers

B. K. Garside, F. Gouin, and J. Shewchun

J. Appl. Phys. 48, 4928 (1977); http://dx.doi.org/10.1063/1.323621 (9 pages) | Cited 1 time

Online Publication Date: 26 August 2008

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The dynamics of electron‐beam‐pumped semiconductor lasers are strongly affected by transient waveguiding. We have investigated the impact of such effects on the time delay from the start of the pumping pulse to the onset of laser emission in GaAs at liquid‐nitrogen temperatures. Time delays were measured as a function of pump current density for three values of the electron‐beam energy (20, 30, and 40 keV). Delays up to 200 nsec were observed which are approximately two orders of magnitude larger than the minority‐carrier lifetime. A theoretical model is presented for the time‐dependent variations of the optical confinement to account for such long delays. The time delay to threshold is determined not by the gain buildup but by the time required to sufficiently decrease the laser‐mode diffraction loss in the active layer. Initially, the presence of gain results in a negative change of the refractive index with respect to the passive material. This is opposed by a growing positive index contribution due to the rise in temperature of the pumped layer. The latter eventually dominates, thereby confining the cavity modes. Under appropriate conditions, the ensuing reduction in loss determines the onset of lasing. The importance of the waveguide effect was confirmed by measurements on devices incorporating a permanent index step at the active‐passive region interface.
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42.55.Px Semiconductor lasers; laser diodes
78.45.+h Stimulated emission
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.60.Hk Cathodoluminescence, ionoluminescence

Coupling losses in laser resonators containing a hollow rectangular dielectric waveguide

Sigrid Avrillier and Jacques Verdonck

J. Appl. Phys. 48, 4937 (1977); http://dx.doi.org/10.1063/1.323622 (5 pages) | Cited 6 times

Online Publication Date: 26 August 2008

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This paper discusses the losses in coupling radiation from the guide into free space and back into the guide for a hollow rectangular dielectric waveguide laser resonator with external spherical mirrors. Computations of the coupling loss for the EH11 lowest‐order mode of a square guide, as a function of mirror curvature and position, are presented in the limit of large mirror aperture. It is shown that some mirror positions and radii provide low coupling losses.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Gn Optical waveguides and couplers

Mechanisms of electromagnetic generation and detection of ultrasonic Lamb waves in iron‐nickel alloy polycrystals

R. Bruce Thompson

J. Appl. Phys. 48, 4942 (1977); http://dx.doi.org/10.1063/1.323623 (9 pages) | Cited 24 times

Online Publication Date: 26 August 2008

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Measurements of the efficiencies of electromagnetic generation and detection of ultrasonic Lamb waves in Armco iron, 1018 steel, nickel, and Invar are presented as a function of both the static and dynamic magnetic field strengths in a geometry in which both are parallel to the surface. Three distinct coupling mechanisms are suggested by the data, and this is confirmed by a quantitative comparison of the amplitude and phase of the generated waves to theoretical predictions. In the iron, 1018 steel, and nickel, Lorentz forces are the primary mechanisms of transduction for static fields above about 2 kOe, whereas Joule magnetostriction is dominant at lower fields. In Invar, a forced volume magnetostriction mechanism is observed in the 1–10‐kOe range that is greater in strength than the Lorentz force mechanism. The data also demonstrate that the amplitudes of waves generated by the Lorentz force mechanism are proportional to the macroscopic magnetic field H rather than the magnetic flux density B.
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43.35.Rw Magnetoacoustic effect; oscillations and resonance
75.80.+q Magnetomechanical effects, magnetostriction

Nonlinear imaging of an edge in the scanning acoustic microscope

H. K. Wickramasinghe and Celia Yeack

J. Appl. Phys. 48, 4951 (1977); http://dx.doi.org/10.1063/1.323624 (4 pages) | Cited 5 times

Online Publication Date: 26 August 2008

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When harmonics are produced in the scanning acoustic microscope, the resultant images have a complex appearance which requires interpretation. A theoretical calculation of the distribution of harmonic radiation has been made for the case of a focused beam scanning across the edge of an object such as a Mylar sheet suspended in water. The results show that most of the harmonic signal is generated in the water, and that diffraction causes the appearance of fringes in the image. Experimental results agree with the theory.
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43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves
42.65.-k Nonlinear optics

Modes in SAW grating resonators

Hermann A. Haus

J. Appl. Phys. 48, 4955 (1977); http://dx.doi.org/10.1063/1.323625 (7 pages) | Cited 8 times

Online Publication Date: 26 August 2008

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A Rayleigh wave of finite width, propagating along the surface of an isotropic medium, is shown to obey approximately a paraxial wave equation if the width is large compared with a wavelength. Results of laser wave propagation can be applied to the Rayleigh‐wave case. Furthermore, an equation is derived for the two‐dimensional Rayleigh‐wave propagation underneath a grating surface. A grating of finite width is shown to provide transverse confinement (guidance) of the wave. The mode patterns are obtained of the fundamental and higher‐order guided modes under uniform gratings of finite width. For a grating resonator formed of two uniform gratings separated by a quarter‐wave section, a variational expression is developed for the resonance frequencies. Using a simple mode pattern for the trial solution, the resonance frequencies of the higher‐order modes are evaluated. They all lie on the high side of the Bragg frequency, increasing with increasing mode number.
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43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
84.30.Vn Filters

A more complete interpretation of optoacoustic data taken with fixed‐frequency lasers

L. A. Farrow and R. E. Richton

J. Appl. Phys. 48, 4962 (1977); http://dx.doi.org/10.1063/1.323626 (6 pages) | Cited 8 times

Online Publication Date: 26 August 2008

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The response of the cylindrical optoacoustic cell when filled with an absorbing gas and irradiated by a laser beam passing along its axis has been studied theoretically and experimentally as a function of the gas pressure and composition. The pressure on the cell microphone has been calculated by solving numerically, for the experimental parameters of interest, the general heat‐diffusion equation with a forcing function which is shown to depend upon both space and time for the realistic case of 50% modulation of the laser beam. It is further shown that if the experimental optoacoustic signal at a given pressure is divided by the signal calculated for that pressure, the ratio is expected to be a constant. The results of a series of experiments using a CO laser to irradiate mixtures of nitric oxide (the absorbing gas) and nitrogen are presented and are shown to confirm the theoretical predictions.
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51.70.+f Optical and dielectric properties
42.62.-b Laser applications

Scattering of relativistic electron beams by magnetic field errors and beam‐induced waves

Gregory Benford

J. Appl. Phys. 48, 4968 (1977); http://dx.doi.org/10.1063/1.323627 (5 pages) | Cited 1 time

Online Publication Date: 26 August 2008

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Relativistic electron beams propagating in long plasma columns must be well focused to cause efficient plasma heating. Expansion of the beam area due to scattering lowers efficiency. We calculate the beam spreading expected from errors in the ambient magnetic field. We then include scattering from both electrostatic and magnetic waves generated by the beam itself. All these effects can be important in contemplated experimental regimes. However, it may prove possible to ’’tune’’ beam‐plasma heating processes to avoid significant beam spreading.
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52.40.Mj Particle beam interactions in plasmas
52.35.Ra Plasma turbulence
52.50.Gj Plasma heating by particle beams

Plasma etching A ’’pseudo‐black‐box’’ approach

Harold F. Winters, J. W. Coburn, and E. Kay

J. Appl. Phys. 48, 4973 (1977); http://dx.doi.org/10.1063/1.323628 (11 pages) | Cited 48 times

Online Publication Date: 26 August 2008

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A framework for understanding plasma etching has been developed (using the CF4 plasma etching of silicon and silicon compounds as an example) which treats the discharge as a ’’pseudo‐black‐box’’ which is characterized by a dissociation rate G of the CF4 molecules and a recombination rate R at which CF4 and other inert molecules are re‐formed by recombination of the active fragments. Expressions based on the conservation of fluorine and carbon in the system have been derived which relate the concentration of the various species in the effluent gas to the etch rate. This approach provides a semiquantitative understanding of several aspects of plasma etching such as the effects of additive gases and the presence of a much larger ’’loading’’ effect for Si than for SiO2.
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52.80.Hc Glow; corona
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Anisotropic production of laser‐plasma soft x rays and fast electrons from thin plastic targets

C. E. Violet and J. Petruzzi

J. Appl. Phys. 48, 4984 (1977); http://dx.doi.org/10.1063/1.323629 (7 pages) | Cited 3 times

Online Publication Date: 26 August 2008

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In separate experiments incident pulses from two different Nd‐glass lasers and a CO2 laser were fired at planar targets of thin plastic, and the angular distributions of the soft x rays and fast electrons were measured. The focused power densities of the first Nd‐glass laser and the CO2 laser were 2×1012 W/mm2, of the second Nd‐glass laser, 2×1013 W/mm2. The electron efficiency of the CO2 laser plasmas is strongly peaked antiparallel to the incident pulse, the backward‐to‐forward ratio being 100. The electron efficiency of both Nd‐glass lasers is less than 150% of their x‐ray efficiency. The x‐ray efficiencies of the Nd‐glass laser plasmas are at least an order of magnitude greater than that of the CO2 laser plasmas. The x‐ray efficiency of the first Nd‐glass laser was isotropic. The x‐ray distribution for both the second Nd‐glass laser and the CO2 laser plasmas had the backward‐to‐forward ratio of 4.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Nc Particle measurements
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Properties of electric discharges sustained by a uniform source of ionization

John J. Lowke and D. Kenneth Davies

J. Appl. Phys. 48, 4991 (1977); http://dx.doi.org/10.1063/1.323606 (10 pages) | Cited 36 times

Online Publication Date: 26 August 2008

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A theoretical examination is made of the class of discharges which are sustained by a uniform source of electron and ion pairs produced between plane‐parallel electrodes. The calculations account for drift, diffusion, and recombination of the charge carriers, ionization of the gas by electrons, and distortion of the applied field due to space charges. It is found that the number and current‐density profiles of electrons and positive ions in the gaseous discharge are of three different types, where (i) the electron density is several orders of magnitude lower than the positive‐ion density at all interelectrode positions, (ii) a plasma region exists, but the electric field in the plasma is negligible compared with that in both electrode sheaths, and (iii) significant ionization occurs in the cathode‐sheath region. Examples of such discharges for which numerical solutions are given are as follows: for type (i), a γ‐ray photoionization chamber with a current density j<1 μA/cm2; for type (ii), a fission fragment ionization chamber used as a neutron detector where j∼1 mA/cm2; for type (iii), a discharge similar to that of a gas laser sustained by ionization from an electron beam where j for the laser ∼1 A/cm2. Derived current‐voltage characteristics for discharges in argon corresponding to types (i) and (ii) are in reasonable agreement with experiment and also with characteristics derived analytically by considering the cathode‐sheath region only and neglecting diffusion and ionization by electrons.
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52.80.Hc Glow; corona
52.25.Fi Transport properties
29.40.Cs Gas-filled counters: ionization chambers, proportional, and avalanche counters

Propagation of ionizing waves in glow discharge

Toshio Suzuki

J. Appl. Phys. 48, 5001 (1977); http://dx.doi.org/10.1063/1.323607 (7 pages) | Cited 10 times

Online Publication Date: 26 August 2008

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Ionizing waves were produced along the positive column of a glow discharge in air by applying an impulse voltage to an electrode at one end of the column. Five photomultipliers and three current‐sensing coils were used to observe how the waves were affected by the rise time and the magnitude of the applied impulses and by the electron density in the positive column of the glow discharge. It is shown that the speed of the ionizing waves increases with the slope of the applied impulses and with the preexisting electron density. The electron density is augmented about 100–200 times due to the buildup of ionization at the front of the waves. The theory was developed to explain the property of ionizing waves.
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52.80.Hc Glow; corona
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
52.35.Tc Shock waves and discontinuities

Sum‐frequency excitation of electron plasma waves

Joseph E. Willett, Behrooz Maraghechi, and Eldon J. Zorinsky

J. Appl. Phys. 48, 5008 (1977); http://dx.doi.org/10.1063/1.323608 (6 pages)

Online Publication Date: 26 August 2008

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Nonlinear mixing of two circularly polarized electromagnetic waves propagating in a plasma along a uniform static magnetic field is considered. Resonant excitation of electron plasma waves is found to be possible at the difference frequency if the incident waves are both extraordinary or both ordinary and at the sum frequency if one incident wave is extraordinary and the other is ordinary. Formulas for the absorption efficiency due to sum‐frequency excitation are derived and the results of a numerical study are presented.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.50.Gj Plasma heating by particle beams

Excitations of wave modes and energy loss by a charged particle passing through a plasma sheet

K. C. Swami and S. R. Sharma

J. Appl. Phys. 48, 5014 (1977); http://dx.doi.org/10.1063/1.323609 (6 pages)

Online Publication Date: 26 August 2008

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Expressions are presented for the field components due to a charged particle passing across a dielectric layer surrounded by the media of different dielectric constants. The case of a cold plasma sheet is discussed in detail. The energy loss due to the space‐wave part of the transition radiation has been reported in a previous paper. In the present paper, the energy loss due to the excitation of surface wave modes is considered. For the large thickness, the energy is lost through the surface wave mode which propagates for frequencies less than ωp/√2. However, for thin sheets, two modes are excited in which the radial wave number depends upon the thickness of the plasma sheet. The power flow per unit angular frequency along the radial direction is calculated for both the thick and thin plasma sheet. The contribution of the particle velocity, the layer thickness, and the frequency on the power flow per unit frequency is investigated in detail.
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52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.40.-w Plasma interactions (nonlaser)
52.25.Fi Transport properties

Oxygen partial‐pressure dependence of the oxidation‐induced surface stacking faults in (100) n silicon

S. P. Murarka

J. Appl. Phys. 48, 5020 (1977); http://dx.doi.org/10.1063/1.323610 (7 pages) | Cited 23 times

Online Publication Date: 26 August 2008

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The effect of varying oxidation rates on the growth of the oxidation‐induced stacking faults (OISF) in (100) silicon has been investigated. Oxidation rates were varied by changing partial pressures of dry oxygen in the oxidizing ambient of oxygen‐nitrogen mixtures. For the first time, it has been shown that in addition to the conventionally observed dependence on time and temperature [i.e., L∝tn exp(−Q/kT)], the length L of the OISF also depends on the partial pressure of oxygen and is given by L∝pmO2. Thus, the length of the OISF is given by L= (const) pmO2tn exp(−Q/kT), where m and n are number exponents. m was found to increase very slightly (from 0.28 at 1050 °C to 0.35 at 1150 °C) with temperature. n decrease very slightly with temperature and was 0.89 at 1050 °C and 0.76 at 1150 °C. At 1119 °C, n was found to increase from 0.78 to 0.84 by changing the oxygen content in the oxidizing ambient from 100 to 10%. The activation energy Q was found to be 2.30±0.05 eV in the temperature range 1050–1150 °C and was independent of variations in the oxygen partial pressures from 10 to 100%. The results have been discussed, and a mechanism incorporating excess of unoxidized silicon at the Si‐SiO2 interface and vacancy mechanism of diffusion has been suggested to explain the experimental results.
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61.72.Nn Stacking faults and other planar or extended defects
81.65.-b Surface treatments
66.30.Lw Diffusion of other defects

Preliminary study for the construction of a low‐energy electron‐diffraction apparatus using a high‐tension source

Colette Berger, Jean Claude Dupuy, Louis Laydevant, and René Bernard

J. Appl. Phys. 48, 5027 (1977); http://dx.doi.org/10.1063/1.323552 (6 pages) | Cited 10 times

Online Publication Date: 26 August 2008

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This paper is a study towards the construction of a low‐energy electron‐diffraction apparatus using a Johansson objective for its optical system. A theoretical study in Gaussian approximation shows that the diffraction pattern is formed in the focus plane of the objective; its dimensions do not depend on the electron energy. By computing courses of electron trajectories, a more accurate investigation is carried out. A variation of 100 eV in electron energy induces broadening less than 7% in the diffraction pattern. The size of each spot in the pattern is lower than 0.6 mm, while the aperture of the primary beam is lower than 1.6 mm. The objective is shown to carry out by itself the filtering of the secondary electrons, the better this filtering the smaller the aperture radius. This study points out important advantages in using this device for the diffraction of low‐energy electrons—advantages which were first perceived in preliminary experiments.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
41.75.Fr Electron and positron beams

Effects of grain size on cation ordering in sintered Mg‐ferrites

Toshio Kimura, Miyoko Ichikawa, and Takashi Yamaguchi

J. Appl. Phys. 48, 5033 (1977); http://dx.doi.org/10.1063/1.323611 (5 pages) | Cited 2 times

Online Publication Date: 26 August 2008

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The effects of grain size on the isothermal cation ordering in sintered Mg‐ferrites have been studied from 400 to 750 °C by thermomagnetic analysis. The observed dependence of ordering behavior on the grain size as well as on the temperature has proposed that the rate‐determining process changes from nucleation growth to homogeneous ordering as the temperature increases. The high rates of ordering in fine‐grained specimens have been interpreted as due to the increased grain‐boundary areas favorable for nucleation. The apparent activation energy of the homogeneous ordering is 36 kcal/mole in the temperature range between 450 and 600 °C.
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61.50.Ks Crystallographic aspects of phase transformations; pressure effects
61.72.Mm Grain and twin boundaries
81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations
68.03.Fg Evaporation and condensation of liquids
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