摘要:

Sn films varying in thickness from 200 to 4500 Å have been prepared by vacuum deposition. The surface roughness has been held to a minimum and the grain size restricted to approximately 1000 Å by cooling the substrate to 80°K and depositing the film at an evaporation rate of 100 Å per sec. The film purities have been calculated from residual resistance data. The mean free paths are in the range of 1000 to 5000 Å. Critical fields for films in this thickness and purity range are reported. The London and Ginzburg‐Landau models have been used to calculate from experiment the penetration depth, which has been found to be in general agreement with Ittner's effective penetration depth concept. The temperature dependence of the penetration depth lies between the two temperature‐dependence predictions of the Bardeen, Cooper, Schrieffer (BCS) theory.

ISSN:0021-8979    

DOI:10.1063/1.1728840

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The effect of {111} polarity in the fabrication of alloyedp‐njunctions in InSb was investigated. The fabrication procedure also considers other polarity dependent effects found in III–V compounds. the results of this investigation suggest use of the {1¯1¯1¯} surface over the {111} for obtaining planar, lower reverse current, higher and sharper breakdown junctions. The implication of this study, using the exemplary III–V compound InSb, is that in the use of III–V compounds for the fabrication ofp‐njunction devices, one must regard a concept, polarity, heretofore not embraced in the manufacture of devices made of Ge and Si.

ISSN:0021-8979    

DOI:10.1063/1.1728841

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The locus of points on the (&agr;,&kgr;/&sgr;T) plane for a two‐band (electrons and holes) semiconductor as the concentration of doping agent is changed, is a curve that forms a closed loop, where &agr; is the Seebeck coefficient, &kgr; the thermal conductivity, &sgr; the electrical conductivity, andTthe absolute temperature. The value of the dimensionless thermoelectric figure of meritZT=&agr;2/(&kgr;/&sgr;T) has, in general, two maxima on this loop, either or both of whose values are determinable, in principle, from measurements of &agr;, &kgr;, and &sgr; on a few specimens with different amounts of doping. The shape and size of the loop and its position on the (&agr;,&kgr;/&sgr;T) plane depend upon the values of two dimensionless material parameters of the Chasmar and Stratton type, one for each band, the scattering parameters for the charge carriers in each band, and the value of the band gap inkTunits. The effects of these parameters on the values of theZTmaxima are considered and approximate empirical relationships forZ(max)Tas a function of these parameters are developed to aid in the quantitative evaluation of these effects. The relationships between these parameters and the pertinent physical properties of the material are discussed from the viewpoints of the requirements for improved thermoelectric materials and of the possible existence of an upper limit to the thermoelectric figure of merit.

ISSN:0021-8979    

DOI:10.1063/1.1728842

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Sputtering yields of various metals have been determined for He+‐, Kr+‐, and Xe+‐ion bombardment in the energy range 100 to 600 ev. Yields at 400 ev show a periodic dependence on atomic number similar to that of the reciprocals of the heats of sublimation.

ISSN:0021-8979    

DOI:10.1063/1.1728843

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Nucleation fields for the reversal of magnetization in thin iron‐nickel films were experimentally measured. The reversal was observed by the Kerr magneto‐optical effect. Different regions or types of imperfections were observed at which lower nucleation fields are required than for the more perfect regions. Small regions of study in the ``interior'' of the film were localized by using an inhomogeneous field a millimeter or less in extension. Nuclei formed reproducibly about a center, with a statistical probability of formation which depended on the pulse length and field strength. A mode value of nucleation can be associated with a given center. The average of the mode values for different centers increased somewhat with film thickness, and showed a marked dependence upon composition, with a minimum value for films containing 80–85% nickel.Repeated pulsing with fields smaller than those required for nucleation increased the size of nuclei, while maintaining the same lenticular shape, to limiting dimensions which increased with film thickness. At higher fields, wall motion was observed in detail for two types of motion: (1) the tip of the domain was displaced along the easy axis with an axial or ``endwise'' extension; (2) the ``180° wall'' was displaced along the hard axis with a normal or ``sidewise'' extension. Endwise extension takes place at lower fields than sidewise extension. Evidence was obtained to indicate that an energy barrier exists for sidewise motion, e.g., repeated 1.5‐&mgr;sec pulses caused no motion, whereas a single 20‐&mgr;sec pulse did. With very narrow drive wires or with thick films, additional nucleation took place instead of ``sidewise'' motion of the wall; otherwise, domains could be enlarged at will. Some films were produced which required larger fields to ``erase'' or contract the domain lengthwise than for tip extension.The instabilities and general morphology of the domains as they depend on composition, film thickness, distance of extension of the inhomogeneous field along the easy axis, and the magnitude of the drive field were studied. Certain configurations led to a morphology of many small nuclei, which eventually were dense enough to join into a single domain; other configurations showed domain growth by wall motion and a large domain formed from very few nuclei. Very small nuclei were generally unstable, disappearing in a short time after formation. The smallest stable nucleus observed was about 0.25 mm×0.04 mm. The transition in behavior between 1.0‐ and 0.5‐&mgr;sec pulses stresses the importance of multiple‐nucleation processes in the nonuniform rotation region. The finescale observations on fields for nucleation and wall motion make possible comparisons with the processes taking place when the complete specimen is switched in a B‐H loop tester.

ISSN:0021-8979    

DOI:10.1063/1.1728844

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

It is well known that a three‐level system functions as a mixer for radiation at its three resonant frequencies. Here the topic is treated in detail by analogy to a three terminal‐pair circuit element, one pair for each frequency. To one pair, fixed power is applied from a local oscillator, or ``pump.'' Attention is then centered on the other two pairs to determine their small‐signal response and transfer characteristics. A slight generalization of the impedance concept takes account of the frequency changes and allows the results to be expressed as self‐impedance at each terminal pair, and a transfer impedance between pairs. The damping effect of molecular surroundings is taken into account. The three‐level maser is a special case in which the terminal pair for the idle frequency is open, and the self‐impedance at the signal terminals has a negative resistive part.Quantization of the radiation field is included by expressing quantum uncertainties in the same form as classical noise, i.e., correlation functions and power spectra. The means for doing this comes from a formalism which connects noise theory to quantum theory through the fact that the Wigner density of linear systems, such as modes of the radiation field, varies with time exactly like a classical probability density. The rules for using this technique are stated as needed without proof. The photon concept is not used.The method is extended to include a system pumped by broad‐band noise.

ISSN:0021-8979    

DOI:10.1063/1.1728845

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

In a previous article, a method for obtaining electrode shapes for axially symmetric electron guns was presented. In essence, this method depended upon reformulating the problem according to a method of Garabedian so that the solution can be obtained by finite‐difference methods. This is accomplished by an analytic continuation which transforms the Laplace equation into a form which is hyperbolic. The purpose of this paper is to present improvements in the original formulation. By introducing time as the independent variable, the derivatives in the space‐charge flow equations are made well‐behaved at the cathode. A different set of dependent variables is introduced so that the matrix of the coefficients associated with the system of partial differential equations possesses simple elementary divisors. Finally, the difference equations have been modified to a form more suitable for numerical computation.

ISSN:0021-8979    

DOI:10.1063/1.1728846

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The theoretical problem of determining the Cˇerenkov radiation from an electron traveling in a circle through a medium has been advanced and the fields and resultant radiation from such a geometry have been determined. A solution is achieved by a transformation of the fields as determined by Frank and Tamm in their original article on Cˇerenkov radiation. This transformation results in a solution as a summation of eigenfrequencies each separated by the frequency of the periodic motion of the electron. The radiation expression derived by this transformation method approaches the Frank and Tamm radiation expression in the limit.

ISSN:0021-8979    

DOI:10.1063/1.1728847

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The absorption spectra of Sm3+and Sm2+in CaF2have been measured from 200–800 m&mgr; at room and liquid‐nitrogen temperatures. A strong divalent absorption band at 620 m&mgr; has an effective oscillator strength of 1.1×10−2. This band has been used to study the reduction of CaF2:Sm3+by ionizing radiation. For some samples, the reduction is as large as 50%. The kinetics of the reduction is obscured due to the presence of oxygen and other crystal defects. The data do indicate that the charge compensator for Sm3+in CaF2is an interstitial F−ion.

ISSN:0021-8979    

DOI:10.1063/1.1728848

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Changes in the structure of PTFE produced by different cooling rates from the sintering temperature and following permanent mechanical deformation have been studied with the electron microscope. Slow cooling rates resulted in longer and wider striated bands (which constitute the PTFE) than fast cooling rates, however, there was no apparent change in the relative amount of crystalline material as x‐ray and infrared absorption studies indicate. Permanent strain resulted in severe distortion of the band structure; the striations either slipped past one another or became kinked. The manner in which the deformation occurred indicated it was controlled by a viscous noncrystalline phase. It is proposed that the band structure itself consists of two phases, crystalline striations or platelets separated by viscous noncrystalline matrix.

ISSN:0021-8979    

DOI:10.1063/1.1728849

出版商:AIP    

年代:1962

数据来源: AIP