摘要:

Beryllium oxide platelets and whiskers have been grown by heating beryllium metal in a silica furnace tube and boat with a hydrogen atmosphere for 16 hr at 1500°C. Three distinct types of whiskers formed: one type was parallel to the crystallographiccaxis, another in the basal plane ([1¯010] direction), and the third in an intermediate direction (approximately the [3¯032] direction). The first type are called ``flagpole'' whiskers because they are topped by small balls of metallic appearance; they grew at the site of the original metal charge. These whiskers have pores along their axes, except in rare instances in which, instead of a pore, a whisker may have disconnected voids along its axis. Their axial growth rate was not observed directly, but was at least 0.02 &mgr;/sec. The other two types have the more normal whisker appearance and grew at a distance of from 2 mm to 2 cm from the original metal charge. They have no pores or voids. Their growth rate was at least 0.2 &mgr;/sec. The larger platelets, which grew in the vicinity of the normal whiskers, were long in [1¯010] direction and wide in the [0001] direction. Some of the very smallest platelets grew in the basal plane. A mechanism of growth for the flagpole whiskers is proposed. It is assumed that molten beryllium balls are splashed onto a BeO substrate, and then react with water vapor to form whiskers which push the balls away from the substrate. The normal whiskers and platelets grew at a distance from the beryllium metal, and therefore their growth involves a vapor transport mechanism.

ISSN:0021-8979    

DOI:10.1063/1.1777195

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The fiber texture and magnetic anisotropy of evaporated iron films have been studied as a function of film thickness. It is found that there are three textures present: [110], [111], and [221]. In thin films, the [111] texture is dominant. It is also found that the magnetic anisotropy is of the order of 2×104ergs/cm3for 350‐A films and decreases with increasing thickness.On the basis of this experiment and information from earlier experiments, several theories of the origin of magnetic anisotropy in films are examined, and shown to be inadequate for iron films. A theory for the origin of the anisotropy is proposed, based primarily on the magnetic energy associated with an array of vacancy needles. These vacancy needles can also qualitatively explain the resistivity anisotropy and dichroism observed by other workers.

ISSN:0021-8979    

DOI:10.1063/1.1777196

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Single crystals of the brittle refractory‐hard‐metal TiC have been plastically deformed at temperatures from 800° to 2200°C. Dislocation etch‐pit studies on {100} cleavage surfaces after bending showed that the slip plane is {111} in the rocksalt structure. The slip direction is taken to be that of the shortest Burgers vector, ⟨110⟩. The slip system is then the same as that of fcc metals and diamond cubic semiconductors. The resolved shear stress for slip in TiC at 1100°C was found to be large: ∼10 kg/mm2. TiC crystals loaded at room temperature did not deform plastically, but did accommodate elastic strain up to 1.2% if the surfaces were electropolished. A shear stress of 0.4 of the theoretical strength was obtained. These results are consistent with the long‐held hypothesis that the binding in hard metal carbides is partially covalent and not exclusively metallic. The Peierls stress resisting dislocation motion should then be large, as in the covalent crystals Ge and Si, and thermal activation would be required for plastic flow. The observed formation of debris by jogs in moving dislocations might alternatively be responsible for the large flow stress. The effects of impurities, precipitates, and composition differences are being investigated.

ISSN:0021-8979    

DOI:10.1063/1.1777197

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

99.999% copper crystals were deformed in tension using an Instron tensile tester, and the dislocation density and arrangement in the crystals were determined before, during, and after the deformations using an etch pit technique. For crystals of low initial dislocation density, it was found that a large amount of dislocation multiplication occurred prior to yielding. Experimental relationships of dislocation density versus applied stress and versus shear strain were determined. It was found that the yield stress was not related to the initial dislocation density or arrangement. The yield stress was postulated to be determined by the stress necessary to break the gliding dislocations through impurity atom barriers in the crystal.

ISSN:0021-8979    

DOI:10.1063/1.1777198

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Trajectories of electrons in a field emission microscope have been calculated for the case of a tip and screen taken as confocal hyperboloids of revolution. The calculations were done in prolate spheroidal coordinates by an iterative method utilizing Hamilton's equations. An IBM digital computer has been programmed to accept values for the initial position and momentum of the electron, the tip and screen radii (each measured at the apex), the tip‐to‐screen distance and the applied voltage. A calculation yields the final values of position and momentum components at the screen as well as the transit time for the electron. The results of the calculation have been used to predict a field emission pattern which is compared with an experimental pattern. Good agreement is obtained without the use of any adjustable parameters.

ISSN:0021-8979    

DOI:10.1063/1.1777199

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Argon crystals are grown with Bridgman's method, and the free surface of the crystal is observed with a microscope in reflected light. In order to observe the crystal at various depths, pumping and sublimation operations are effected until the entire crystal sublimates layer after layer. All the crystals obtained showed many coherent and noncoherent twin boundaries; some of them did not show any grain boundary.

ISSN:0021-8979    

DOI:10.1063/1.1777200

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

It was found that with a particular 10‐cm electron linear accelerator power radiated from undulating electrons in the 8‐mm band increased as (current)1.7. At higher frequencies there was only an approximately linear increase. A large undulator, designed to radiate in the fundamental mode at 8 mm gave a half‐watt power output. This is in general agreement with the theoretical radiation from electrons combined with the experimental power law.

ISSN:0021-8979    

DOI:10.1063/1.1777201

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Profuse and rapid bismuth‐whisker growth from thin bismuth films occurring only in the presence of manganese is reported. This growth was observed during the heat treatment of thin bismuth‐manganese double layers in the vacuum hot stage on a metallurgical microscope. Optimal conditions for whisker growth are described. The presence of manganese required for whisker growth strongly suggested that the whiskers might be composed of a bismuth‐manganese compound. However, chemical microanalytical tests, melting point determinations, magnetic and magnetoresistivity measurements definitely proved that the whiskers grown were bismuth whiskers. Measurements of magnetoresistance as a function of the orientation of the whiskers in the magnetic field showed that the whiskers were essentially bismuth single crystals with their long axes normal to the principal crystallographic axis The results of exploratory measurements of such additional physical properties of the whiskers as electrical resistivity, temperature coefficient, maximal fracture strength, and strain sensitivity factor are also reported.

ISSN:0021-8979    

DOI:10.1063/1.1777202

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A novel technique of analysis of excess carrier behavior in semiconductors, based upon conservation of carrier fluxes, after allowing for generation and recombination, is applied to semiconductorp‐njunctions and simple junction devices. It is assumed that the junction acts as a source of excess minority carriers with respect to the bulk material on either side of the junction, and that the flux strength associated with the junction is proportional to exp (eV/kT), whereVis the bias voltage appearing across the junction. In the case of the planarp‐njunction in an infinite semiconductor, the usual exponential current‐voltage dependence is obtained, but a more general expression for the saturation current than that obtained from the conventional diffusion calculation is exhibited. In particular, it is shown that for sufficiently low‐carrier lifetime in the bulk material adjacent to the junction, the saturation current is less than that predicted by the conventional diffusion calculation, and becomes independent of lifetime in the low‐lifetime limit. The application of the method to simple device structures is also discussed, and a simplep‐nphotovoltaic cell is considered as an example. Here again the current‐voltage dependence (which is related to the boundary condition at the junction rather than to diffusion and recombination phenomena in the bulk) is unaltered, but modified expressions for saturation and generation currents are obtained. Applicability of the method is currently limited to one‐dimensional, field‐free, steady‐state situations.

ISSN:0021-8979    

DOI:10.1063/1.1777203

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The invariance of the initial potential of ZnO xerographic layers with respect to the potential of the corona source, and the increase of the initial potential with increasing layer thickness appear to be a consequence of the dielectric breakdown of small regions of the layer during charging. The variation of initial potential with the layer thickness seems to be a result of a positive space charge in the volume of the layer. This space charge probably comes from normally full electron traps withinkTof the dark Fermi level which are ionized during charging. Typical space‐charge densities are about 1014/cm3.

ISSN:0021-8979    

DOI:10.1063/1.1777204

出版商:AIP    

年代:1962

数据来源: AIP