摘要:

Using time‐dependent solutions of the avalanche current generalized for unequal ionization rates and velocities of the two charge carriers, compact formulas for theQand the efficiency of the Read structure are derived, which are valid from zero to very large oscillation amplitudes. A method is developed to properly account for the internal‐field adjustment (which may be variably positive or negative) that is caused by the nonlinearly rectified avalanche‐current component flowing through the drift region. These developments clearly show that the behavior of theQat intermediate and large signals cannot be correctly derived unless the avalanche analysis retains terms related to both the in‐phase and out‐of‐phase components of the avalanche current.The behavior ofQvs oscillation amplitude is numerically calculated for a successfully operated prototype and compared with experimental observation. These experimental observations in conjunction with the analytical development also permit an interpretation and assessment of the effects due to inhomogeneities in multiplication found in junctions.Design considerations of Read structures are discussed, particularly how various parameters that are critical in optimizing the efficiency and stability may be controlled by design of the electric‐field distribution of the avalanche. It is shown how advantage may be taken of the asymmetry of ionization rates of the two charge carriers to achieve even higher efficiencies than the 30% Read predicted for the case of equal ionization rates. Finally, certain circuit criteria for achieving dynamic stability are discussed and solutions given.

ISSN:0021-8979    

DOI:10.1063/1.1710005

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

It is possible to identify portions of the fine structure appearing in the x‐rayKabsorption edges of pure metals with their respective energy bands. The areas of these portions are proportional to the density of unoccupied states in each band and changes in their occupation density accompanying alloying. Face‐centered‐cubic Ni, Co, and Fe have similar fine structures that are characteristically different from that of body‐centered‐cubic Fe. An analysis of the latter suggests that the overlapping 3d+4s+4pbands in &agr;‐Fe are split into two sub‐bands separated by ∼8 eV. A direct comparison of changes in the areas under the curves of Cu‐Ni alloys shows that a systematic decline in Ni 3dholes and Cu 4sholes takes place with increasing copper content. An apparent saturation takes place at 56 at.% copper in agreement with magnetic saturation and NMR measurements.

ISSN:0021-8979    

DOI:10.1063/1.1710006

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Changes taking place in the fine structure of the cobaltKedge in Ni‐Co solid solutions indicate a decline in the 3d‐4shole density at cobalt atom sites. Changes in the NiKedge in the same alloys suggest that the hole density at nickel atoms increases, thus supporting the rigid‐band model for these alloys.Significant changes in the NiKedges of fcc (gamma) Ni‐Fe solid solutions suggest that the rigid‐band model may be valid for these alloys also. It does not appear to be applicable, however, to bcc (alpha) solid solutions. In both alloy types, the fine structure at the FeKedge remained unchanged. Good agreement was obtained with magnetic measurements on bcc Ni‐Fe alloys.

ISSN:0021-8979    

DOI:10.1063/1.1710007

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

General expressions are derived for the stress components due to an arbitrary continuous distribution of dislocations prescribed in a cylindrical coordinate system. Results are obtained for the stress field of a helical dislocation of uniform shape with the Burgers vector along its axis. The additional energy arising from the interaction of a point defect with the helix is obtained and the behavior of the defect examined.It is also shown how results for circular dislocation loops are readily obtained from the general expressions and in particular the problem of a rotational loop, which is formed by twisting the two faces of the slip surface relative to each other, is solved.

ISSN:0021-8979    

DOI:10.1063/1.1710008

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Many properties of polycrystalline yttrium iron garnet (YIG) and reduced single‐crystal YIG have been attributed to the presence of Fe2+ions which provide mobile electrons that can diffuse locally through the lattice. It was the purpose of this research to study the modification to the low‐temperature anisotropy caused by the presence of Fe2+ions in silicon‐doped YIG, Y3Fe5−&dgr;Si&dgr;O12with 0<&dgr;<0.18. Silicon‐doped YIG demonstrates a time‐dependent induced anisotropy proportional to doping when magnetically annealed to low temperatures. The kinetics and temperature dependence of this induced anisotropy have been studied. It is further found that these doped garnets show a constant, high‐field component of rotational hysteresis which is both frequency‐ and temperature‐dependent.The intrinsic, unannealed anisotropy behaves in a novel way. At room temperature the anisotropy coincides with normal YIG, while between 150°K and 300°K |K1| increases above that of pure YIG Below about 150°K the curves develop asymmetry and appear to be no longer purely cubic. At 4.2°K the easy axis has shifted to the [100] direction (>3% doping) indicative of a change in sign inK1. Silicon‐doped lutetium iron garnet and polycrystalline lutetium iron garnet were found to behave in a similar manner.The results are interpreted in terms of an electron‐diffusion model which enables the Fe2+ion to effectively wander among four nonequivalent octahedral sites. A simple kinetic rate theory is at least partially successful in explaining: (1) the time dependence of the torque curves, (2) the rotational hysteresis, and (3) some of the apparent low‐temperature deviations from cubic symmetry.

ISSN:0021-8979    

DOI:10.1063/1.1710009

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Destructive breakdown has been studied in Al‐SiO‐Al capacitors using transmission electron microscopy and electron diffraction, while the capacitors were subjected to controlled electrical stresses. Extensive electrical measurements were made outside the electron microscope on other capacitors. The purpose is to describe destructive breakdown and to relate it to prebreakdown conduction, conditions of fabrication, and capacitor structure.It is found that breakdowns originate at inhomogeneities in the dielectric which appear in electron micrographs as irregularly shaped dark spots about 0.5 &mgr; in diameter. The structure of these dark spots has not been determined. Breakdowns are not concentrated at pinholes, dust spots, or fissures. Breakdown is accompanied by the growth of crystalline silicon. Electrical measurements with a given capacitor reveal two well‐defined polarity‐sensitive threshold voltages, one for the onset of breakdown and one for the cessation of breakdown. Both are virtually independent of temperature from 80° to 380°K. The voltage threshold for the onset of breakdown varies approximately asw1/2, wherewis the dielectric thickness, while the voltage threshold for the cessation of breakdown is found to be independent of dielectric thickness. The diameter of a typical breakdown is 10 to 100 &mgr;. The conductivity of the breakdown site at the onset of breakdown changes by a factor of about 1010in a time less than 0.1 &mgr;sec. Duration of a breakdown is usually about 1 &mgr;sec.A breakdown mechanism is proposed that is based upon an electrochemical solid reaction in the presence of the breakdown electric field:Si−O−Si+(breakdown electric field)→Si−Si++O+e,where the term Si−Si+means the two silicon atoms are in crystalline form and one is singly ionized. A description of the breakdown process is given using this reaction.

ISSN:0021-8979    

DOI:10.1063/1.1710011

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The ion current produced by electron bombardment of the (211) crystal face of a W ribbon is shown to be predominantly O16+. The only impurity detected, H+, was never more than 4% of the total current even when the ribbon operated in hydrogen with a carbon monoxide impurity as low as 1%.

ISSN:0021-8979    

DOI:10.1063/1.1710012

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

This study includes the design of a fully demountable alkaline‐metal‐plasma machine. The plasma is produced by contact ionization of alkaline metal vapor on a refractory metal emitter. The properties of this plasma depend on three parameters: emitter temperature, cesium vapor pressure, and potential of an electrode which sets the electric boundary conditions for the medium. Three movable probes analyze the plasma. Measurements are made and results are discussed in terms of the parameters. The first part of the study is devoted to a description of the machine and the probes. The second part analyzes its different operating modes. There are two fundamental modes. The first covers the case where collisions are predominant. The second is a flux mode in which interactions are very improbable. The machine permits continuous transition from the first to the second mode. In the transition zone complex phenomena arise. The study is primarily concerned with an examination of the inflection potentials given by the second derivative of the current‐voltage characteristics of the probes. Interpretation of this inflection potential will differ greatly from one operating mode to another.

ISSN:0021-8979    

DOI:10.1063/1.1710013

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The galvanomagnetic parameters &rgr;123, &rgr;1111, &rgr;1133, &rgr;1131, and &rgr;1122have been measured at 77°K for two samples ofp‐type (Bi2Te3)5(Bi2Se3)1(Sb2Te3)18and the results fitted to a six‐ellipsoid model similar to that proposed for Bi2Te3. An anomalous rise in the Hall coefficient with temperature and an apparent change in the effective mass ratios are explained by assuming the existence of impurity banding. The thermal conductivity, thermoelectric power, and electrical resistivity were measured over the temperature range from 77° to 300°K.

ISSN:0021-8979    

DOI:10.1063/1.1710014

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The reflection and transmission of electromagnetic waves by a moving dispersive dielectric half‐space or slab are investigated theoretically. The dispersive medium is assumed to be a cold plasma medium. Two cases of the movement are considered: (a) the plasma medium moves parallel to the interface; (b) the plasma medium moves perpendicular to the interface. The electric vector of the incident wave is assumed to be polarized in the plane of incident (parallel polarization). Unlike the normal polarization case which was treated earlier, the reflected and transmitted fields for the present case are functions of the velocity of the moving plasma medium for both cases (a) and (b). An illustrative numerical example is given for case (a) at normal incidence.

ISSN:0021-8979    

DOI:10.1063/1.1710015

出版商:AIP    

年代:1967

数据来源: AIP