摘要:

It is shown by an analysis similar to that for the spinodal decomposition of a supersaturated solution that an array of dislocations, modelled by parallel screw dislocations, of uniform density, is unstable; the dislocations move to form a structure having a modulated dislocation density. It is suggested that the instability grows ultimately into a dislocation cell structure and that the cell size is given by the dominant wavelength of the density modulation. This wavelength &lgr;mis found to be proportional to &rgr;−1/2and furthermore the wavelength is given by &lgr;m≈Kc·&rgr;−1/2=rc, whereKcis a constant, &rgr; is the dislocation density andrcis defined as a dislocation‐dislocation interaction distance. Data in the literature relating to cell size are shown to support this result. Restrictions on the applicability of the analysis are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1659399

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The lattice diffusion coefficient of copper in high‐purity nickel single crystals is measured between 775° and 1050°C. The diffusion coefficient satisfies the equationD=0.27 exp(−61.02/RT) cm2sec−1, with an error inD0of ±22% and inQof ±1%. A comparison with the results of other authors is given, showing that the dc measured is considerably lower than in previous investigations. This effect is referred to grain‐boundary diffusion and chemical impurities in the specimens used earlier.

ISSN:0021-8979    

DOI:10.1063/1.1659400

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The rigorous solution of the grain‐boundary diffusion problem has been approximated by a series expansion method. The calculations show that higher‐order terms may be neglected in the bulk adjacent to the grain boundary. Thus, in this region Whipple's and Suzuoka's solutions represent a close approximation to the problem. Inside the grain boundary, however, higher‐order approximations have to be taken into account. These approximations gain importance in the case of wide grain boundaries. The solutions obtained for an instantaneous source have been fitted to available grain‐boundary diffusion data of Ni2+in MgO at 1200°C. Numerical calculations give for the bulk diffusion coefficientD=2.9×10−12cm2sec−1, the ratio of diffusion coefficient &Dgr;=1.5 and for the grain‐boundary widtha=75 &mgr;.

ISSN:0021-8979    

DOI:10.1063/1.1659401

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

This paper deals with electromagnetic wave propagation in a longitudinally magnetized, ferrite‐filled elliptical waveguide. Using the wave equations and boundary conditions for a ferrite‐filled waveguide of arbitrary cross‐sectional shape, it is shown that for an elliptical cross section the characteristic equations for the propagation constant take the form of even and odd infinite determinants. Solutions for the characteristic equations are obtained for various values of applied field strength, saturation magnetization, and waveguide ellipticity. The existence of three types of cutoff conditions is demonstrated.

ISSN:0021-8979    

DOI:10.1063/1.1659402

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Detailed analyses were carried out for the Faraday effect of electromagnetic waves propagating in longitudinally magnetized ferrite‐filled elliptical waveguides. Few resemblances were found between the Faraday rotation effect in a circular waveguide and that in an elliptical waveguide. The circular waveguide features strong coupling between the dominant vertically and horizontally polarized modes, whereas in the elliptical ferrite‐filled guide very little mode coupling occurs for large eccentricities.

ISSN:0021-8979    

DOI:10.1063/1.1659403

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Photoemission yield measurements were made on amorphous selenium from about 6 to 21 eV. The yield curve exhibits a change in slope at about 7.8 eV corresponding to a maximum in the imaginary dielectric constant. The photoemission threshold is obtained by using a threshold law equation derived by Kane,Y = C(E − Et)n, whereYis the yield,EandEtare the photon energy and threshold energy, andCandnare constants. The yield data up to 8 eV are best represented by the equation withn=52resulting in an extrapolated photoemission threshold of 5.86 eV for amrophous selenium.

ISSN:0021-8979    

DOI:10.1063/1.1659404

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The voltage‐current characteristics of Au&sngbnd;MgO&sngbnd;Au thin‐film emission diodes formed by electron beam evaporation of Au and MgO are consistent with an expression derived for Schottky field emission into the conduction band of the oxide. These results however indicate a potential barrier height of about 0.72 eV when determined from the zero‐field intercept of the straight line logIvsV1/2plot and about 0.33 eV when obtained from an Arrhenius plot. These apparent barrier heights were different for devices fabricated by depositing the MgO film in an oxygen atmosphere. The apparent barrier height determined from the zero‐field intercept went up for increasing oxygen pressure and the barrier height determined from the Arrhenius plot went down. Emission of electrons into vacuum was observed from each device at very low sample biases indicating that preferential emission through pinholes in the Au overlayer was occurring.

ISSN:0021-8979    

DOI:10.1063/1.1659405

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Positive ions emitted from heated iron filaments consist mainly of the alkali‐metal atoms, such as lithium, sodium, and potassium, which are present in iron as trace impurities. Changes in the work function with different applied partial pressures of oxygen and hydrogen have been recorded. From the results of measurement it is concluded that the effect of oxygen on the work function of iron is much stronger than that of hydrogen. Kinetic data representing the emission of Na and K ions from Fe were obtained in the temperature range of 1050°–1350°K. Diffusion and ion desorption are discussed as possible rate‐controlling processes. Activation energies, believed to represent the diffusion of Na and K atoms in Fe, are found to be approximately 38 kcal/mole (1.7 eV) and 53 kcal/mole (2.3 eV), respectively. The Richardson work function of iron varies from &phgr;≃4.0 eV atP02≃10−9Torr to &phgr;≃5.6 eV atP02≃10−5Torr. When a diffusion‐controlled process is assumed, the difference between the activation energies, for the above two oxygen pressure conditions, is found to be the same as the difference (I‐ &phgr;); that is, the difference between the first ionization potential of the atom and the work function of the metal surface. The experimentally determined values of (I‐ &phgr;)exDfor K and Na agree within experimental error with the calculated values.

ISSN:0021-8979    

DOI:10.1063/1.1659406

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The conditions necessary to establish a stable hollow‐cathode or cavity mode in a high‐pressure mercury vapor discharge have been studied by analysis of the physical processes at the electrodes. The electron emission is primarily Schottky‐enhanced thermionic, so the cavity mode is favored by a thermally shielded cavity design, at low currents. Techniques have been developed for measurement of the temperature of the arc terminus of the probe contact potential relative to the electrode, of the cathode fall of potential, and of the power input to the electrode. Positive ion current densities, work functions of the dispenser‐type electrode at the arc terminus and other interesting quantities have been obtained by computation. The analysis giving these results has been partially verified by experiment.

ISSN:0021-8979    

DOI:10.1063/1.1659407

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Five possible mechanisms of dc vacuum breakdown are analyzed for rf electric fields. The theories which are considered are the vaporization of a micron‐sized cathode irregularity due to joule heating by field‐emitted electrons, vaporization of the anode due to bombardment by field‐emitted electrons, field‐emission current instability created by the presence of anode ions, exchange of electrode ions, and microparticle vaporization. The analysis indicates that mechanisms which do not involve anode ions in gaps of 0.2–1.0 cm will not be strongly influenced by rf fields in the frequency range of 20–120 MHz. Under similar conditions, the theories involving anode ions predict a very sizable increase in the voltage capability of vacuum‐insulated electrodes. Experimental ratios of vacuum breakdown voltage at 21.5 MHz to that for 60 Hz were experimentally determined for highly polished tungsten electrodes with separations between 0.18 and 0.61 cm. The rf voltages obtained experimentally were less than the values predicted by theory, although the cathode whisker vaporization and ion perturbation by light ions were within experimental uncertainties. From the differences seen in spark conditioning of electrodes, it would appear that micron‐sized particles are involved in the spark threshold at 60 Hz.

ISSN:0021-8979    

DOI:10.1063/1.1659408

出版商:AIP    

年代:1970

数据来源: AIP