摘要:

Dislocations in web silicon have been observed by x‐ray diffraction microscopy. Numerous sources of dislocations originate in the dendrite and form low‐angle grain boundaries within the web. Dislocations propagating along the growth direction have [01¯1] and [101] or [110] Burgers vectors, and dislocations aligned along the [11¯0] and [101¯] directions are product dislocations of a Lomer‐Cottrell reaction. Interactions between the two sets of dislocations are often observed.

ISSN:0021-8979    

DOI:10.1063/1.1702933

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Techniques for using pressure vessels to study the characteristics of shock waves from high explosives detonated under high hydrostatic pressure have provided empirical observations not previously available in the literature. Results indicate that although peak pressure is not affected by hydrostatic pressure, the duration is shortened and the impulse lowered by increasing the hydrostatic pressure. Also, the negative phase of the pressure pulse appears to increase as the ambient pressure increases.

ISSN:0021-8979    

DOI:10.1063/1.1702934

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The cross‐sectional geometry of Nernst—Ettingshausen generators and refrigerators is optimized for essentially rectangular geometry and also for Norwood's spiral screw thread configuration. The magnetic field, heat flow, and electrical current flow are assumed to be mutually perpendicular. The derivation is carried out without any restrictive assumptions concerning electric current distribution. There are no restrictive assumptions about the temperature dependence of &kgr;, &sgr;, or the Nernst coefficient. The expressions for the boundary of the device are given in parametric form with temperature as the parameter. Formulas are given for use in estimating the effect of incomplete optimization.

ISSN:0021-8979    

DOI:10.1063/1.1702935

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The noise pulse rate of microplasmas and uniform avalanche diodes is determined by carrier generation within the space‐charge layer of the breakdown region, and by minority carrier diffusion to the breakdown region. By suppressing the minority carrier diffusion from bulk to breakdown region with a suitable geometry, it is possible to investigate the carrier generation within the space‐charge layer of ap‐njunction. Three contributions to the carrier generation rate are found: (1) thermal carriers from generation centers, (2) re‐emission of carriers trapped during preceding periods of avalanche breakdown, and (3) carrier generation by internal field emission (band‐to‐band tunneling). For the case of uniform avalanche diodes, these three contributions are investigated separately. The density of generation and trapping centers within the breakdown region could be reduced by several orders of magnitude by driving the diodes into secondary breakdown. During this process the breakdown region is heated to a temperature of the order of 1000°C at which trapping and generation centers are partly annealed.

ISSN:0021-8979    

DOI:10.1063/1.1702936

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Experimental measurement of rf electric fields in electron‐beam/plasma interactions requires a non‐perturbing probing technique. Such a technique is described in this paper and has been applied to study cathodic electron beam break‐up and meniscus formation phenomena observed in a low‐pressure mercury‐vapor discharge. Experiments are described in which the deflection of a fine electron‐beam probe directed parallel to the cathode surface is measured to determine the spatial variations of the low‐ and high‐frequency electric fields. A number of supporting experiments are reported which help to clarify the various phenomena occurring in the beam/plasma interaction region.

ISSN:0021-8979    

DOI:10.1063/1.1702937

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

This paper is concerned with the double sheath which is normally present in front of a hot cathode in a low‐pressure dc discharge. The authors present a theory of an idealized form of this sheath, under space‐charge‐limited cathode emission conditions. The discrepancies from this model to be expected in a practical situation are discussed, and comparisons are made with experimental results. To obtain these, an electron beam probing technique was used, and electric field measurements were made directly in the cathode sheath of a low‐pressure mercury‐vapor discharge. Good agreement was obtained between the simplified theory and the experiments.

ISSN:0021-8979    

DOI:10.1063/1.1702938

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The operation of the plasma resonance probe in the absence of a magnetic field is now well understood, and the resonant frequency can be interpreted to give the electron density in the plasma. In many potential applications of this diagnostic technique to laboratory and space plasmas, a static magnetic field is present. This paper considers the resulting modifications to the resonance. The analysis is based on the simplified model of the probe behavior that has been validated for the zero magnetic field case by the work of Harp and Crawford. It is concluded that the technique can be applied to obtain the electron plasma frequency &ohgr;pand the electron density for&ohgr;c2≪&ohgr;p2; and the electron cyclotron frequency &ohgr;c, and hence the local magnetic field when&ohgr;c2≫&ohgr;p2. An approximate correction formula is derived for the intermediate range&ohgr;c2≈&ohgr;p2.

ISSN:0021-8979    

DOI:10.1063/1.1702939

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The dislocation dynamics of Gilman and Johnston are applied to the problem of elastic—plastic flow in Armco iron at very high strain rates. The dislocation velocity is assumed to follow the lawv=v∞exp(−&tgr;0/&tgr;); experimental data support this form of dependence and are used to determine the value of &tgr;0. This value is in reasonable agreement with other measurements taken from Lu¨ders band front velocities. A second quantity which can be evaluated is the initial density of dislocation lines,N0, which is found to be 2.0×108cm−2.

ISSN:0021-8979    

DOI:10.1063/1.1702940

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Hexagonal selenium can be grown from the melt either in the form of spherulites or as single crystals. At normal pressures, the transition from spherulitic to single‐crystal growth habit is usually not seen due to the very slow growth rate of single crystals. At higher pressures, the single‐crystal growth rate is enhanced sufficiently to permit observation of this transition. Examination of melt‐grown crystals by Weissenberg x‐ray techniques disclosed a disorder normal to the ``c'' axis direction. The absence of the disorder in vapor‐grown needles produced at 5 kbar indicates that the disorder is built in during growth from the melt.

ISSN:0021-8979    

DOI:10.1063/1.1702941

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

We have used ann‐body collision computer simulation model with a Gibson #2 potential to examine various ways in which the lattice nature of the slowing down material influences the motion of a medium‐energy copper atom. For normal incidence upon a (110) surface, we found that the lattice has a significant effect upon the scattering angle when a 10‐keV copper atom strikes an atom of a copper lattice. The channel area, which comprises approximately 40% of the representative area in this orientation, is quite insensitive to the copper atom's energy above 1 keV. Total ranges are significantly longer than those reported by Robinson and Oen from calculations based upon a binary collision model. Below 1 keV, total ranges closely approximate theE32law reported by Kornelsenet al. Above 1 keVdE/dx=A−B/Eappears to describe the motion at all positions in the channel if the values ofAandBare specified for the initial point at which the atom enters the channel. This behavior above 1 keV is clearly nonphysical. To be meaningful, even at intermediate energies, computer range studies must include inelastic energy losses. Lattices are known to focus atoms incident near the [110] direction into [110] channels. This mechanism was studied at the center of the channel with 1‐keV atoms. The effect is anisotropic in the azimuthal angle, but we found that atoms inside a 10° cone were always focused, and that 20° focusing occured in one orientation. Angular focusing wasless effectiveat higher energies. Transverse oscillations in the channel were also considered. The ``wavelengths'' are proportional toE½, but oscillations are usuallynotsymmetric about the channel axis. Transverse motion is approximately harmonic, but the ``vertical'' and ``horizontal'' frequencies arenevercommensurable. We have evidence for a skimming mechanism in which high energy atoms are confined between (111) planes, or to a lesser extent between (100) planes. Trajectories of 5‐keV knock‐on atoms are shorter than 40 Å unless the moving atom skims. One true channel event was found in 120 trials in which the moving atom started from a lattice site.

ISSN:0021-8979    

DOI:10.1063/1.1702942

出版商:AIP    

年代:1965

数据来源: AIP