摘要:

The elastic moduli of cadmium telluride at 25°C have been determined by measurement of ultrasonic wave velocities in the frequency range 40–300 Mc/sec. Preparation of the crystal specimens is described, and factors affecting the accuracy of results are considered. The question of possible piezoelectric stiffening and its effect on measured wave velocities is also considered. Based on a density of 5.854 g/cm3as computed from the lattice constant (and taken as exact with respect to uncertainty estimates) the zero field elastic moduli are:ModulusValue d/cm2Uncertainty in %c115.351×10110.15c123.6810.2c441.9940.15

ISSN:0021-8979    

DOI:10.1063/1.1728527

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

An exact solution to the nonlinear difference equation which describes a static configuration in the Frenkel‐Kontorova dislocation model is given. The solution is in terms of a power series which is proved convergent. Previously, only approximate solutions had been obtained by replacing the difference equation by a differential equation. A numerical comparison is made between the exact and the approximate solutions and the Peierls energies they give.

ISSN:0021-8979    

DOI:10.1063/1.1728528

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A single crystal undergoing plastic bending develops constraints due to the gradient in lateral contraction across the beam. These constraints result in lateral stresses which may be relieved by the process of anticlastic kinking. Anticlastic kink boundaries in rocksalt structure solids consist of arrays of {121}⟨110⟩ edge dislocations formed by the interaction of two systems of {110}⟨110⟩ glide dislocations, one system being responsible for slip in the main part of the crystal beam, the other confined to its corner.Temperature affects the structure of kink boundaries and their subsequent role in initiating fracture.I. At high temperatures (∼0.3Tm). The resultant edge dislocations in the boundary can move over their {121} slip planes and the kinks become sharp. The resultant dislocations are ineffective barriers to slip and the crystals are ductile.II. At low temperatures (∼0.1–0.2Tm). The resultant edge dislocations are immobile and the kinks consist of a diffuse array. The resultant dislocations provide strong barriers to slip and cracks nucleate at the kink boundary.III. At very low temperatures (∼0.1Tm). Fracture occurs before the second set of {110}⟨110⟩ glide dislocations have been activated to generate anticlastic kinks. Relaxation of the lateral stress results in a complex fracture.

ISSN:0021-8979    

DOI:10.1063/1.1728529

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A theoretical correlation is derived to account for the variation of the work function of refractory metals coated by metallic films for all degrees of coverage. This correlation is based on an extension of the concept of electronegativity to composite surfaces and use of Pauling's rule about electronegativity and dipole moment of complex molecules. A series of theoretical curves is given for different crystallographically ideal surfaces of refractory metals such as W, Mo, and Ta coated by Cs, Sr, Ba, and Th.The derived correlation is compared with available experimental data for which the experimenters specify the exact conditions under which the experiment is performed and excellent agreement between theory and experiment is established.It is shown for the first time that the maximum work function variation does not necessarily always occur either when a full monolayer is reached or at a definite fractional coverage. The exact position of the maximum variation is a function of the adsorbate and substrate materials and the type of the substrate surfaces. It is also shown that it is erroneous to characterize a monolayer as the point at which maximum emission (or maximum work function variation) is achieved because such a maximum may be flat and extend from half a monolayer to one monolayer.

ISSN:0021-8979    

DOI:10.1063/1.1728530

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The electrical conduction mechanism in the film plane of ultrathin, evaporated metal films was investigated. These films consist of a planar array of many small discrete islands. The conduction process consists of, first, charge carrier creation which is thermally activated and involves charge transfer between initially neutral particles, and, second, the drift velocity of these charges in an applied field. Charge transfer between particles occurs by tunneling. The following features were predicted and can be verified experimentally: the conductivity depends exponentially on reciprocal temperature, and it should be independent of field at low fields. Deviations from the exponential temperature dependence can be understood in terms of a spectrum of activation energies, while deviations from Ohm's law at high fields can be explained readily in terms of a field dependent activation energy.

ISSN:0021-8979    

DOI:10.1063/1.1728531

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Small tantalum carbide objects may be made by heating the objects made from tantalum in dilute hydrocarbon atmospheres at temperatures >2000°K. Carburization proceeds quite rapidly above 2300°K by diffusion of carbon initially deposited on the surface into the metal, principally along grain boundaries, to form a thin layer of Ta2C which is quickly converted to the TaC. The latter has a tensile strength of 21–25 kg/mm2, a work function &phgr;=3.17 ev, an emissivity of 0.40–0.46 between 2400° and 3500°K, rising with increasing temperature, and a resistivity &rgr;=102+0.0178T(°K) ohm cm between 1400° and 3500°K.

ISSN:0021-8979    

DOI:10.1063/1.1728532

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The focusing properties of the multi‐stage system of weak lenses, such as in the accelerating tubes, are considered. The lens system is treated as one thick lens in the paraxial ray approximations. By assuming that the field distribution of each lens is the same, the simple expressions for the focal lengths and the locations of the focal points of this lens system as a whole are given.

ISSN:0021-8979    

DOI:10.1063/1.1728533

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The field electron microscope has been used previously to measure the work function of thermally smoothed single‐crystal tungsten planes. In this work the field ion microscope is used to create atomically perfect single‐crystal planes by field evaporation and then to observe and preserve these clean surfaces. The slope of the field emission Fowler‐Nordheim plot then gives the ratio of the three halves power of the work function to the field. Two techniques have been developed in order to obtain a second relationship between work function and field: (1) temperature dependence of field‐emission current density and (2) energy distribution of field‐emitted electrons. While investigating temperature dependence it was found that a reinterpretation of the Gel'berget al.data for the work function temperature dependence of molybdenum up to 1100°K revealed the following unexpected cubic temperature dependence: &phgr;T=&phgr;0+0.44×10−10T3ev.

ISSN:0021-8979    

DOI:10.1063/1.1728534

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

If the Cranberg hypothesis for breakdown in vacuum is valid, measurements made using impulse and dc voltages may yield different results depending in part upon the rate of rise of the impulse and the nature of the attachment of the clumps to the parent electrode. It is assumed that metallic clumps areinstantaneouslydetached from an electrode surface at a voltage dependent upon gap length as described by Cranberg. Consideration of the rise in impulse voltage occurring during the transit time of the clump to the opposing electrode yields the following results. For an over‐volting impulse ofconstant rise ratethe breakdown voltage of a vacuum gap depends upon the ⅚ power of the gap length in the limiting case of large gap length and clump radii, and fast rise impulses. For the same limiting conditions, with an impulse ofconstant rise time, breakdown voltage was found to be related to the52power of the gap length. A brief comparison of calculated results with experimental data in the literature indicates limited, although not conclusive, support for the Cranberg hypothesis in its application to impulse breakdown in vacuum.

ISSN:0021-8979    

DOI:10.1063/1.1728535

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

An explanation of the ``excess current'' up to and including the valley point, observed in tunnel diodes, is suggested in terms of tunneling between impurity band states of the heavily dopedpandnregions. Density‐of‐states curves are constructed, based on several different models of impurity bands, and the tunneling current between such bands is computed and compared with experiment. The effect of different base materials and impurities on the valley current is discussed. Some aspects of impurity band formation in heavily doped semiconductors are considered, and possible modifications and difficulties of the present approach are indicated. The possibility of obtaining information about impurity band structure from tunnel diode measurements is discussed. Experimental evidence is presented about the position of the Fermi level in heavily doped semiconductors and is shown to agree with that postulated by the present model. The Appendix gives the theory of locating the Fermi levels from measurements of the temperature variation of the diode characteristic.

ISSN:0021-8979    

DOI:10.1063/1.1728464

出版商:AIP    

年代:1962

数据来源: AIP