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1 Dec 1960

Volume 31, Issue 12, pp. 2071-2317

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Recent Appearance Potential Measurements Using an Electrostatic Electron Selector

Larkin Kerwin and Paul Marmet

J. Appl. Phys. 31, 2071 (1960); http://dx.doi.org/10.1063/1.1735504 (6 pages) | Cited 8 times

Online Publication Date: 16 June 2004

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The general principles of measuring appearance potentials by the electron bombardment method are reviewed. Recent improvements in the design of an electrostatic electron selector so as to improve the electron bombardment technique are described. The new instrument provides an electron beam with an energy spread of less than 50 mv. By means of it, measurements have been made on the vibrational levels N2+ and H2+.

Photoemission and Related Properties of the Alkali‐Antimonides

William E. Spicer

J. Appl. Phys. 31, 2077 (1960); http://dx.doi.org/10.1063/1.1735505 (8 pages) | Cited 55 times

Online Publication Date: 16 June 2004

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The photoemissive process in the semiconducting alkali‐antimonides is examined and values are given for the band gaps and electron affinities. The high photoelectric efficiencies of these materials are attributed to the ability of the excited electrons to traverse relatively large distances (250 A) without overwhelming energy losses, rather than to negligibly small electron affinities. The efficiency is found to be strongly dependent on the percentage of the electrons which are excited into states above the vacuum level. The properties of these materials depend to a large extent on the crystal structure. Cs3Sb and Na2KSb have a cubic structure, are p type, and seem to have a relatively simple valence band structure. K3Sb and Na3Sb have hexagonal crystal structures, are n type, and seem to have a relatively complex valence band structure. The evidence for an effect of band bending on the photoemission is considered.

Oxygen on Nickel

L. H. Germer and C. D. Hartman

J. Appl. Phys. 31, 2085 (1960); http://dx.doi.org/10.1063/1.1735506 (11 pages) | Cited 34 times

Online Publication Date: 16 June 2004

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Low‐energy electron diffraction, with the diffracted electrons post‐accelerated and observed on a fluorescent screen, has been used to study the adsorption of oxygen on a (100) face of a nickel crystal. Upon admitting oxygen to a clean face at room temperature, or at elevated temperatures up to 350°C, the first adsorbed atoms are arranged in narrow bands parallel to [110] directions on the crystal surface. Within one of these bands, atoms lie on lines at right angles to the band; these lines have a uniform separation of 4.98 A, but the atoms along each line are somewhat randomly spaced in multiples of the nickel spacing of 2.49 A. With further oxygen exposure (30×10−6 mm Hg sec) sufficient to produce half of a monolayer (one oxygen atom for every four surface nickel atoms), the arrangement is very chaotic unless the crystal has been heated, but after heating the arrangement is a simple square array with edge of 4.98 A. Further exposure to oxygen (100×10−6 mm sec) will produce a full monolayer consisting of this same square array with an additional oxygen atom at the center of each square. With still further exposure, oxygen, at least in part as physisorbed molecules, is piled on top of this first monolayer of atoms, the added molecules forming an array with square symmetry and edges parallel to the edges of the square array of surface nickel atoms. At least several layers of oxygen molecules can be adsorbed and are not removed by pumping at room temperature. Heating at 350°C removes a great deal of the adsorbed oxygen, and the structure of the remainder agrees with that of NiO having the orientation of the nickel crystal. This oxide is removed at 830°C, and the first layer of oxygen atoms at 880°C.

Potential Distributions in a Low‐Pressure Thermionic Converter

Peter L. Auer

J. Appl. Phys. 31, 2096 (1960); http://dx.doi.org/10.1063/1.1735507 (8 pages) | Cited 40 times

Online Publication Date: 16 June 2004

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A plane diode model of a low‐pressure cesium‐filled thermionic converter is treated. It is assumed that all ions and electrons are created at the surface of the hot cathode with a Maxwellian distribution corresponding to the cathode temperature. The charged species are then assumed to move through the plasma, consisting of electrons, ions, and neutral cesium atoms, as free particles under the influence of their mutual space charge field. A method is outlined by which the potential distributions corresponding to different operating conditions may be calculated completely. In this fashion the operating characteristics of the converter may be related to the self‐consistent space charge potentials. Instabilities as possible sources of tube oscillations are briefly discussed.

Bounds on Low‐Energy Scattering Parameters

Larry Spruch and Leonard Rosenberg

J. Appl. Phys. 31, 2104 (1960); http://dx.doi.org/10.1063/1.1735508 (8 pages) | Cited 2 times

Online Publication Date: 16 June 2004

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Some recent results that determine an upper bound on the scattering length, whether or not composite bound states exist, are reviewed. The extension to the determination of an upper bound on (−k cotη)−1, where only one channel is open, is presented; the method used requires that the potential vanish identically beyond some given point. The results are applicable to the scattering of one compound system by another. Possible extensions and improvements of the method are discussed.
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New Complex Phase in the Copper‐Gold System

R. E. Scott

J. Appl. Phys. 31, 2112 (1960); http://dx.doi.org/10.1063/1.1735509 (6 pages) | Cited 24 times

Online Publication Date: 16 June 2004

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At the composition 31.6 at. % gold, the equilibrium diagram shows a two‐phase mixture of ordered and disordered material extending from 320°C to 350°C. However, a long anneal in this interval results in an x‐ray pattern showing superstructure reflections with strong satellites. The satellite pattern is obtained both by lowering and raising the temperature, and hence is believed to represent an equilibrium structure. The satellite pattern is interpreted in terms of a Cu3Au II type structure, which is derived from the ordered Cu3Au I by introducing antiphase domain displacements (a2+a3)∕2 at regular intervals along the a1 axis, exactly analogous to the development of CuAu II from CuAu I. At 31.6 at. % gold, the period is 18a1 (9 a1 between consecutive domain boundaries). Between 320°C and 335°C, there is a two‐phase mixture of Cu3Au I and Cu3Au II. From 335°C to about 345°C the structure is that of Cu3Au II. From about 345°C to 350°C there is probably a two‐phase mixture of Cu3Au II and disordered material, but this has not been established. The satellite pattern is also obtained at the composition 29.2 at. % gold, and it is likely that the Cu3Au II type structure exists over a range of compositions on the gold rich side of Cu3Au.

Experimental Investigation in Lead of the Whipple ``Meteor Bumper''

Arnold E. Olshaker

J. Appl. Phys. 31, 2118 (1960); http://dx.doi.org/10.1063/1.1735510 (3 pages)

Online Publication Date: 16 June 2004

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Experimental results are presented to indicate the effects of a thin protective shield on reducing the penetration of simulated meteoroids. The study is mainly of lead impacting lead at 2.5 km∕sec. The effects of thickness and separation of the shield are investigated. It is shown that a shield of thickness slightly less than half the projectile diameter at a separation of about five projectile diameters reduces the penetration of shield plus target to approximately one‐third the depth of the unshielded crater. This shield is also effective against hardened steel ball bearings. Based on the assumption that the ``fluid impact'' penetration mechanism of lead at this velocity is qualitatively similar to that of structural materials at meteor velocities, it is concluded that the weight saving potential of ``bumper'' construction will make its use mandatory for space structures designed by the penetration condition.

Magnetic Viscosity Due to Solute Atom Pairs. Part I. Theory of the Effect

G. Biorci, A. Ferro, and G. Montalenti

J. Appl. Phys. 31, 2121 (1960); http://dx.doi.org/10.1063/1.1735511 (5 pages) | Cited 18 times

Online Publication Date: 16 June 2004

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It is shown that solute atom pairs in ferromagnetic alloys, as well as the interstitial atoms in iron, can give magnetic viscosity.
The viscosity field of the alloys vs wall displacement is determined for various crystal structures. The maximum value of the viscosity field is related to the anisotropy energy induced in the same materials by heat treating in a magnetic field.

Electron Optical Study of Basal Dislocations in Graphite

S. Amelinckx and P. Delavignette

J. Appl. Phys. 31, 2126 (1960); http://dx.doi.org/10.1063/1.1735512 (10 pages) | Cited 36 times

Online Publication Date: 16 June 2004

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Dislocations having a Burgers vector in the basal plane and lying in this plane, have been studied in graphite by the use of thin foil transmission electron microscopy. The dislocations are dissociated into ribbons consisting of two partials separated by a stacking fault. Specific models for these dislocations are presented. Hexagonal networks contain extended and contracted nodes. The presence of two types of stacking faults gives rise to singularities which are analyzed in terms of experimentally determined Burgers vectors. The dislocations and even the networks are very mobile along the basal plane. The stacking fault energy is determined as 3 to 5×10−2 ergs∕cm2.

Mechanical Properties of Thin Single‐Crystal Gold Films

Avery Catlin and Walter P. Walker

J. Appl. Phys. 31, 2135 (1960); http://dx.doi.org/10.1063/1.1735513 (5 pages) | Cited 25 times

Online Publication Date: 16 June 2004

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Single‐crystal gold films were grown by vacuum deposition on heated (375°C) sodium chloride substrate blanks. Completely oriented films with thicknesses between 1000 and 3000 A were obtained, with the plane of the film being the {100} crystallographic plane. A small hole was drilled through the substrate with a water jet, and the mechanical properties were determined by stressing the unsupported film over this hole. The films were observed to undergo considerable plastic deformation, accompanied by the appearance and growth of mechanical twin bands as the stress was increased. X‐ray diffraction studies were made to determine the twin orientation. Both the ultimate tensile stress and the elastic modulus were found to increase as the thickness of the films was reduced.

Experimental Investigations of the Cesium Plasma Cell

W. A. Ranken, G. M. Grover, and E. W. Salmi

J. Appl. Phys. 31, 2140 (1960); http://dx.doi.org/10.1063/1.1735514 (14 pages) | Cited 7 times

Online Publication Date: 16 June 2004

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Some aspects of the performance of a cesium plasma cell with tantalum emitter are evaluated in terms of experimental determinations of the effects of variations in such parameters as cesium vapor pressure, emitter temperature, and emitter‐collector separation distance. Experiments relating to the effect of collector serrations and to the feasibility of radiation shielding are described. Voltage‐current characteristics are presented for several emitter temperatures and for a wide range of cesium vapor pressure.

Correlation of Low‐Temperature Caloric and Magnetic Effects in TiFe

K. Schröder and C. H. Cheng

J. Appl. Phys. 31, 2154 (1960); http://dx.doi.org/10.1063/1.1735515 (2 pages) | Cited 19 times

Online Publication Date: 16 June 2004

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Magnetic measurements by Nevitt on TiFe can be interpreted on the assumption that his specimen is superparamagnetic. It is possible to calculate from his measurements approximate values of the size and number of ferromagnetic clusters. The magnetization vector of these clusters oscillates at very low temperatures within directions given by the energy of crystal anisotropy. This gives rise to the term Ccl in the specific heat at low temperatures, due to the clusters, which is to be added to the lattice and electronic terms. The calculation gives reasonable agreement of Ccl with experimental values found in specific heat measurements.

Effects of Irradiation on the Thermal Conductivity of Synthetic Sapphire

R. Berman, E. L. Foster, B. Schneidmesser, and S. M. A. Tirmizi

J. Appl. Phys. 31, 2156 (1960); http://dx.doi.org/10.1063/1.1735516 (4 pages) | Cited 15 times

Online Publication Date: 16 June 2004

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The thermal conductivity between 2° and 100°K has been measured on synthetic sapphire single crystals and on sintered alumina, before and after reactor and γ‐ray irradiations. Reactor irradiation appears to introduce two types of thermal resistivity‐producing defects, one of which is dominant at low temperatures. The only effect of γ irradiation is an extra thermal resistivity at low temperatures which saturates for quite small doses. This saturation value seems to depend on the initial perfection of the crystal and is increased by reactor produced damage. At present, detailed information about the defects cannot be derived from thermal conductivity measurements alone.

Measurement of Thermal Conductivity by Utilization of the Peltier Effect. II. Correction for Wire Radiation and Determination of Specimen Radiation Emissivity

R. Simon, R. T. Bate, and E. H. Lougher

J. Appl. Phys. 31, 2160 (1960); http://dx.doi.org/10.1063/1.1735517 (5 pages) | Cited 6 times

Online Publication Date: 16 June 2004

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The analysis in the first article on measurement of thermal conductivity by utilization of the Peltier effect [T. C. Harman, J. H. Cahn, and M. J. Logan, J. Appl. Phys. 30, 1351 (1959)] is extended to correct for radiation of heat from the lead wires. It is shown how the radiation emissivity of the semiconductor specimen can also be determined from the measured temperatures.

Determination of Electrode Shapes for Axially Symmetric Electron Guns

Kenneth J. Harker

J. Appl. Phys. 31, 2165 (1960); http://dx.doi.org/10.1063/1.1735518 (6 pages) | Cited 14 times

Online Publication Date: 16 June 2004

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The determination of the electrode shapes for an electron gun involves solving Laplace's equation subject to specified boundary values of voltage and normal field on an open curve. Past attempts to solve this problem for the case of axial symmetry by mathematical methods have met with considerable difficulties because the problem is improperly set and leads to unstable solutions. Following Garabedian, we have reformulated the problem in such a manner that it becomes properly set, and have applied it to a curvilinear space‐charge limited flow gun. First, a conformal transformation is made which maps the beam boundary into a coordinate axis. The second step, which constitutes the essence of the method, is accomplished by making an analytic continuation of Laplace's equation and its boundary values into a fictitious complex domain. Laplace's equation, which is elliptic in the real domain, is thereby converted into a set of hyperbolic equations. This leads to a stable scheme of computation by finite differences. This method should find particular application to curvilinear flow guns, where the use of analogs, such as the electrolytic tank, requires the use of involved experimental techniques. The method is very general, however, being applicable to any configuration where the boundary conditions are given through analytic functions. If one desires, these specifications for the boundary conditions may be given implicitly, as, for example, through a set of differential equations.

Multiple Tube Collimator for Gas Beams

G. R. Hanes

J. Appl. Phys. 31, 2171 (1960); http://dx.doi.org/10.1063/1.1735519 (5 pages) | Cited 24 times

Online Publication Date: 16 June 2004

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A multiple tube gas collimator is described which consists of a bundle of tubes with 20‐μ radii, made by electrolytic removal of copper wires from the plastic matrix in which they were embedded. Details of construction are given, as well as measurements of the angular distribution of gas flow from the collimator, which are determined with a helium mass spectrometer leak detector. The theory of flow through multiple tube sources is discussed, and a figure of merit giving relative values of beam intensity for fixed collimator area and flow rate is derived. The collimator described in this paper compares favorably with those used by previous workers.

Corbino Disk

D. A. Kleinman and A. L. Schawlow

J. Appl. Phys. 31, 2176 (1960); http://dx.doi.org/10.1063/1.1735520 (12 pages) | Cited 12 times

Online Publication Date: 16 June 2004

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When a disk with concentric inner and outer electrical contacts is placed in a magnetic field parallel to its axis, and current is made to flow through the disk, the lines of current flow have a spiral shape. This spiral current flow produces its own magnetic field, which interferes constructively or destructively with the applied field, depending upon whether the carriers spiral inward or outward, respectively. For ordinary conductors and ordinary currents the effect of the self‐field of the current is very small. But the effect should be large in materials of very high mobility such as has been recently reported for bismuth at 4.2°K. In this paper the theory of the effect is given for the case in which the mean free path of the carriers is small compared to the inner radius of the disk. The analysis shows that the disk behaves as a rectifier. The easy direction of flow corresponds to outward spiraling of the carriers, which at large currents results in the explusion of the magnetic field from the disk. In the hard direction of flow the magnetic field at the center of the disk may be several orders of magnitude larger than the applied field. It is suggested that the corbino disk may be a useful rectifier in applications requiring extremely low impedance. It may also be a useful voltage regulator in a very low‐voltage high‐current power supply. A device consisting of the disk and a coil to provide the magnetic field is discussed in some detail. The static characteristics when the coil is connected through a suitable resistance in parallel with the disk exhibits a negative resistance. This negative resistance is useful in ac operation if a condenser is also connected in series with the coil. The equations and boundary conditions which determine the electrical properties of the disk in the time‐dependent case are formulated. In the small‐signal approximation the complex impedance is obtained for the limiting cases of low and high frequency. At low frequency the reactance is that of a negative inductance (‐iωL). At high frequencies there is a skin effect on the tangential component of current, which causes most of the signal current to be radial and causes the impedance to reduce to the resistance of the disk.

Study of Initial Conditions in Constant Velocity Impact

James F. Bell

J. Appl. Phys. 31, 2188 (1960); http://dx.doi.org/10.1063/1.1735521 (8 pages) | Cited 18 times

Online Publication Date: 16 June 2004

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Diffraction grating measurements are made of dynamic plastic strain within a few thousandths of an inch from the impact face of 1‐in. diameter, annealed aluminum specimens in free flight undergoing constant velocity impact. From these data it has been established that initial nondispersive shock fronts are present, even in low‐velocity impact. This initial nondispersive front develops in the first ¼ diameter in two sections, each involving ☒ the initial kinetic energy; the first section is that of the deviatoric, or shear, component, and the second is associated with the hydrostatic stress. It is shown that the dynamic stress‐strain curves obtained experimentally in annealed aluminum and copper may be computed directly from the theory, using information supplied by the static stress‐strain curve. The von Karman critical velocity for annealed aluminum is found to be a dividing point between two types of initial wave development.

Prediction of Fatigue Life

A. M. Freudenthal

J. Appl. Phys. 31, 2196 (1960); http://dx.doi.org/10.1063/1.1735522 (3 pages) | Cited 5 times

Online Publication Date: 16 June 2004

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On the basis of the relation between the ``reliability‐function'' (probability of surviving beyond age N in cycles or t in time) and the ``risk'' of failure (as a function of age), the physical interpretation of the latter can be used to extrapolate the former beyond the range of possible observation. It is shown that the asymptotic distribution of smallest values is compatible with the physical concept of (dynamic or static) fatigue, while the logarithmic‐normal distribution is not.

Electron Microscope Observations of Fission Fragment Tracks in Thin Films of UO2

T. S. Noggle and J. O. Stiegler

J. Appl. Phys. 31, 2199 (1960); http://dx.doi.org/10.1063/1.1735523 (10 pages) | Cited 41 times

Online Publication Date: 16 June 2004

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Electron microscope studies of the tracks produced by fission fragments in thin films of UO2 have established a 100% detection efficiency for fission events in films 100 A or less in thickness. A background texture decreases the efficiency in thicker films. The tracks register in the films primarily as a result of a redistribution of surface material arising from the disturbance produced by the continuous loss of energy of the fragment by electron excitation and ionization. The minimum rate of energy loss which registers as a track in the film is on the order of 1000 ev∕A. Track length distributions, however, suggest that as yet unrecognized free surface effects may also contribute to the track registration.

Direct Measurements of the Surface Energies of Crystals

John J. Gilman

J. Appl. Phys. 31, 2208 (1960); http://dx.doi.org/10.1063/1.1735524 (11 pages) | Cited 294 times

Online Publication Date: 16 June 2004

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By means of quantitative cleavage experiments, the surface energies of several simple crystals have been measured at −196°C. The crystals and their cleavage planes are: LiF (100), MgO (100), CaF2 (111), BaF2 (111), CaCO3 (1010), Si (111), and Zn (0001). Measured values of their respective surface energies (ergs∕cm2) are: 340, 1200, 450, 280, 230, 1240, and 105. The measured values for LiF and MgO are in good agreement with simple ionic lattice theory. Values for the other crystals seem consistent with their binding energies.
Under irreversible conditions an effective surface energy is measured. This quantity increases rapidly with increasing temperature for the metallic crystals, Zn and Fe (3% Si). The increase correlates with increasing plastic flow in these crystals. In contrast, the effective surface energy of LiF and MgO is only moderately dependent on temperature.
A small amount of cadmium (0.1 at.%) markedly increases the cleavage surface energy of zinc.

Production of Dislocation Loops by a Combined Climb and Glide Mechanism

J. T. Fourie and H. G. F. Wilsdorf

J. Appl. Phys. 31, 2219 (1960); http://dx.doi.org/10.1063/1.1735525 (5 pages) | Cited 28 times

Online Publication Date: 16 June 2004

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Studies of dislocations in elongated aluminum crystals by diffraction electron microscopy revealed narrow dislocation loops lying parallel to 〈112〉. These loops formed only behind screw dislocations, their long parts then having edge character. Four mechanisms have been proposed to account for the formation and stabilization of the narrow loops through the condensation of point defects.

Electron Microscope Studies of Colloids in KCl

R. E. Simon and R. L. Sproull

J. Appl. Phys. 31, 2224 (1960); http://dx.doi.org/10.1063/1.1735526 (2 pages) | Cited 7 times

Online Publication Date: 16 June 2004

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Electron microscope studies were made of surfaces of potassium chloride crystals containing excess potassium. The crystals were cleaved in a vacuum and the surfaces replicated in the same vacuum. Large potassium colloids were observed with distinctive shapes and orientations determined by the host lattice.

Some Effects Occurring in Dislocated Tellurium

J. S. Blakemore, J. W. Schultz, and K. C. Nomura

J. Appl. Phys. 31, 2226 (1960); http://dx.doi.org/10.1063/1.1735527 (6 pages) | Cited 36 times

Online Publication Date: 16 June 2004

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Dislocation densities as small as 1000 cm−2 are sometimes found in carefully produced single crystals of tellurium, but since the material is very soft a quite mild stress can introduce 106 dislocations∕cm2 or more. Dislocation etch pits of sharply geometric shape can be developed on the cleavage (1010) planes by the slow attack of sulphuric acid; their planar surfaces correspond to (1100), (1013), (0111), and (0111) faces. Effects are noted on faces exposed by cleavage at 77°K which suggest that even at this temperature the material can suffer localized plastic damage, for brief etching of such faces produces small flat‐bottomed pits; these may be interpreted by supposing that the mild stress of cleavage at 77°K generates shallow dislocation loops. The flat‐bottomed pits disappear when a surface layer ≥25 μ is etched away. A marked increase in electron‐hole recombination rate is noted in plastically deformed crystals. If the additional recombination occurs through the dislocations themselves, then each has a capture radius of some 4×10−8 cm at 300°K. Dislocated crystals also show more prominent trapping effects at low temperatures than structurally pure samples, and contain additional readily ionizable acceptor sites; these may be derived from the dislocations themselves or from other defects created or activated by plastic flow.

Filled and Empty Dangling Bonds in III‐V Compounds

D. B. Holt

J. Appl. Phys. 31, 2231 (1960); http://dx.doi.org/10.1063/1.1735528 (2 pages) | Cited 10 times

Online Publication Date: 16 June 2004

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It is pointed out that the model of dangling bonds from the {111} and {111} surfaces of III‐V compounds proposed by Gatos, Moody, and Lavine is open to serious objection. The idea of resonance is introduced in order to develop a model which is not subject to the same difficulties. Certain implications of this model for dislocation theory are discussed.
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