摘要:

A numerical method for solving Laplace's equation in spherical coordinates for an axially symmetric geometry has been developed. Dirichlet boundary conditions on a closed surface yield a set of difference equations. The method of successive overrelaxation has been employed to find solutions to those equations. Application of the method is illustrated by finding the field configuration in a new type of electron gun used in a spherical electron monochromator.

ISSN:0021-8979    

DOI:10.1063/1.1659137

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A very slow change in the dc conductivity below 200°C of certain alkali halide single crystals, not previously investigated, cannot be understood in terms of current theory of homogeneous crystals, but follows first‐order kinetics and correlates with dislocation substructure. Electrical decoration of the dislocation substructure suggests that conduction flow is inhomogeneous, a conclusion confirmed by experiments on bicrystals and on specimens containing subboundaries.

ISSN:0021-8979    

DOI:10.1063/1.1659138

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Equations are derived for nonplanar dissociations of dislocations in hcp metals. Various components ofAB, A&mgr;, &phgr;&thgr;, [AB+&phgr;&thgr;], ands′[AB+&phgr;&thgr;]dislocations on the basal, prism, and pyramidal planes meet the criteria for dissociation into twinning partials on{2¯11l}and{1¯01l}planes, and the Burgers vectors of the twinning partials are consistent with minimum shear strain and small atomic shuffling criteria for twinning. The repulsive force &ggr;mon each twinning partial is computed using anisotropic elasticity and compared with estimates of the twin lamella distortion energies &ggr;. For[AB+&phgr;&thgr;]and&phgr;&thgr;dislocations &ggr;mis quite large and &ggr;m/&ggr; > 1 in many cases. In several cases &ggr;m/&ggr; > 1 for dissociation ofABon the basal and prism planes, leading to an increase in dislocation resistance, locking, or twinning at lower temperatures. The results are consistent with the difference in flow behavior of metals like Zr and Ti on one hand and Cd and Zn on the other. Successive dissociations for twin growth and double twinning processes are studied, with the latter shown to be consistent with reported behavior in magnesium.

ISSN:0021-8979    

DOI:10.1063/1.1659139

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Dielectric measurements effected on silver bromide emulsions in the frequency range 102−107Hz show a maximum in the absorption curve. This dielectric absorption is interpreted as a consequence of the conductivity of the interstitials in the AgBr crystals. According to this interpretation, the influence of the morphology and size of the AgBr grains, and of the addition of stabilizing agent on the conductivity of the AgBr grains can be detected in a simple manner. A continuous transition from surface conductivity towards bulk conductivity of the AgBr grain is observed.

ISSN:0021-8979    

DOI:10.1063/1.1659140

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The voltage‐dependent tunneling conductance of trapezoidal potential barriers has been calculated using two extreme models of (1) the WKB approximation and (2) perfectly sharp boundaries between the metal electrode and the insulator. We show that for both models the conductance‐voltage plot is roughly parabolic at low voltages(≲0.4 V). The minimum conductance is not at zero bias unless the barrier is symmetrical and identical Fermi energies are chosen for the two metal electrodes. The inclusion of image forces does not radically alter the shape of the conductance‐voltage dependence. Using reasonable barrier shapes, the asymmetry of the calculated conductance aboutV=0 is not as large as we frequently observe experimentally. We point out that this extreme asymmetry appears to be associated with the presence of organic impurities in the oxide layer of the junction.

ISSN:0021-8979    

DOI:10.1063/1.1659141

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A new topographic method is described to obtain kinematical images of small defects in highly perfect crystals. In this method, x rays diffracted by strain fields around defects are recorded separate from those by perfect regions of crystals. The capability of the method is demonstrated by observing some small defects in a dislocation‐free Si crystal which cannot be revealed by Lang and Borrmann topographic techniques. The observed images are due to defects which are revealed as shallow pits by the Sirtl etching. By assuming that the defects are dislocation loops, their sizes are roughly estimated: the majority of the defects is less than 5000 Å in size. It is concluded that the present technique is capable of detecting short‐range strains in crystals which are very small compared with extinction distances.

ISSN:0021-8979    

DOI:10.1063/1.1659142

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The diffusivity of oxygen in an aluminosilicate glass from 630° to 830°C is derived from optical transmission measurements, wherein the rate of bleaching of Ti3+color centers by the diffusing oxygen at temperature was measured. The finite‐thickness solution to the heat equation is used to interpret the data; the oxygen diffusivity on this temperature range can be represented byD=28.4 exp (−39.6±3.4 kcal/RT)cm1/sec. It is concluded that the oxygen diffuses interstitially as molecular oxygen, because the activation energy is smaller than the energy to split an Si&sngbnd;O bond: 50 kcal/mole. As a check on the technique and results, penetration measurements were made on a moving color boundary, with identical results.

ISSN:0021-8979    

DOI:10.1063/1.1659143

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The diffusivity of Al in ZnSe, ZnSe0.5Te0.5, and ZnTe has been determined in the temperature range of 700°–1000°C. At 1000°C the diffusivities, calculated from the experimental data assuming the Fick's diffusion law to be valid, are (0.66±0.11) × 10−9cm2/sec for ZnSe; (1.2±0.3) × 10−9cm2/sec for ZnSe0.5Te0.5; and (1.3±0.5) × 10−9cm2/sec for ZnTe. The activation energy for diffusion is approximately 2 eV for all three. It is suggested that the diffusion of Al proceeds substitutionally via the Zn sublattice.

ISSN:0021-8979    

DOI:10.1063/1.1659144

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The chemical diffusion coefficients of single crystals of cadmium tellurideDCdTewere determined as a function of temperature and composition using high‐temperature electrical conductivity measurements. In the temperature range 550° to 800°C,DCdTecan be approximated by 4 exp[− (1.15±0.1) eV/kT] and is nearly independent of cadmium partial pressurepCd, forpCdextending over two decades from the cadmium‐rich liquidus. The measured and calculated values ofDCdTeare in good agreement, and the results favor an interstitial mechanism for cadmium self‐diffusion.

ISSN:0021-8979    

DOI:10.1063/1.1659145

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An approximate theory is developed for the charging by heavy ions of submicron aerosol particles in external electric fields. The theory proceeds from a nonintuitive basis established by kinetic theory and reproduces the general features found in the relevant experimental data.

ISSN:0021-8979    

DOI:10.1063/1.1659146

出版商:AIP    

年代:1970

数据来源: AIP