摘要:

The general principles of measuring appearance potentials by the electron bombardment method are reviewed. Recent improvements in the design of an electrostatic electron selector so as to improve the electron bombardment technique are described. The new instrument provides an electron beam with an energy spread of less than 50 mv. By means of it, measurements have been made on the vibrational levels N2+and H2+.

ISSN:0021-8979    

DOI:10.1063/1.1735504

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The photoemissive process in the semiconducting alkali‐antimonides is examined and values are given for the band gaps and electron affinities. The high photoelectric efficiencies of these materials are attributed to the ability of the excited electrons to traverse relatively large distances (250 A) without overwhelming energy losses, rather than to negligibly small electron affinities. The efficiency is found to be strongly dependent on the percentage of the electrons which are excited into states above the vacuum level. The properties of these materials depend to a large extent on the crystal structure. Cs3Sb and Na2KSb have a cubic structure, areptype, and seem to have a relatively simple valence band structure. K3Sb and Na3Sb have hexagonal crystal structures, arentype, and seem to have a relatively complex valence band structure. The evidence for an effect of band bending on the photoemission is considered.

ISSN:0021-8979    

DOI:10.1063/1.1735505

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Low‐energy electron diffraction, with the diffracted electrons post‐accelerated and observed on a fluorescent screen, has been used to study the adsorption of oxygen on a (100) face of a nickel crystal. Upon admitting oxygen to a clean face at room temperature, or at elevated temperatures up to 350°C, the first adsorbed atoms are arranged in narrow bands parallel to [110] directions on the crystal surface. Within one of these bands, atoms lie on lines at right angles to the band; these lines have a uniform separation of 4.98 A, but the atoms along each line are somewhat randomly spaced in multiples of the nickel spacing of 2.49 A. With further oxygen exposure (30×10−6mm Hg sec) sufficient to produce half of a monolayer (one oxygen atom for every four surface nickel atoms), the arrangement is very chaotic unless the crystal has been heated, but after heating the arrangement is a simple square array with edge of 4.98 A. Further exposure to oxygen (100×10−6mm sec) will produce a full monolayer consisting of this same square array with an additional oxygen atom at the center of each square. With still further exposure, oxygen, at least in part as physisorbed molecules, is piled on top of this first monolayer of atoms, the added molecules forming an array with square symmetry and edges parallel to the edges of the square array of surface nickel atoms. At least several layers of oxygen molecules can be adsorbed and are not removed by pumping at room temperature. Heating at 350°C removes a great deal of the adsorbed oxygen, and the structure of the remainder agrees with that of NiO having the orientation of the nickel crystal. This oxide is removed at 830°C, and the first layer of oxygen atoms at 880°C.

ISSN:0021-8979    

DOI:10.1063/1.1735506

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A plane diode model of a low‐pressure cesium‐filled thermionic converter is treated. It is assumed that all ions and electrons are created at the surface of the hot cathode with a Maxwellian distribution corresponding to the cathode temperature. The charged species are then assumed to move through the plasma, consisting of electrons, ions, and neutral cesium atoms, as free particles under the influence of their mutual space charge field. A method is outlined by which the potential distributions corresponding to different operating conditions may be calculated completely. In this fashion the operating characteristics of the converter may be related to the self‐consistent space charge potentials. Instabilities as possible sources of tube oscillations are briefly discussed.

ISSN:0021-8979    

DOI:10.1063/1.1735507

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Some recent results that determine an upper bound on the scattering length, whether or not composite bound states exist, are reviewed. The extension to the determination of an upper bound on (−kcot&eegr;)−1, where only one channel is open, is presented; the method used requires that the potential vanish identically beyond some given point. The results are applicable to the scattering of one compound system by another. Possible extensions and improvements of the method are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1735508

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

At the composition 31.6 at. % gold, the equilibrium diagram shows a two‐phase mixture of ordered and disordered material extending from 320°C to 350°C. However, a long anneal in this interval results in an x‐ray pattern showing superstructure reflections with strong satellites. The satellite pattern is obtained both by lowering and raising the temperature, and hence is believed to represent an equilibrium structure. The satellite pattern is interpreted in terms of a Cu3Au II type structure, which is derived from the ordered Cu3Au I by introducing antiphase domain displacements (a2+a3)/2 at regular intervals along thea1axis, exactly analogous to the development of CuAu II from CuAu I. At 31.6 at. % gold, the period is 18a1(9a1between consecutive domain boundaries). Between 320°C and 335°C, there is a two‐phase mixture of Cu3Au I and Cu3Au II. From 335°C to about 345°C the structure is that of Cu3Au II. From about 345°C to 350°C there is probably a two‐phase mixture of Cu3Au II and disordered material, but this has not been established. The satellite pattern is also obtained at the composition 29.2 at. % gold, and it is likely that the Cu3Au II type structure exists over a range of compositions on the gold rich side of Cu3Au.

ISSN:0021-8979    

DOI:10.1063/1.1735509

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Experimental results are presented to indicate the effects of a thin protective shield on reducing the penetration of simulated meteoroids. The study is mainly of lead impacting lead at 2.5 km/sec. The effects of thickness and separation of the shield are investigated. It is shown that a shield of thickness slightly less than half the projectile diameter at a separation of about five projectile diameters reduces the penetration of shield plus target to approximately one‐third the depth of the unshielded crater. This shield is also effective against hardened steel ball bearings. Based on the assumption that the ``fluid impact'' penetration mechanism of lead at this velocity is qualitatively similar to that of structural materials at meteor velocities, it is concluded that the weight saving potential of ``bumper'' construction will make its use mandatory for space structures designed by the penetration condition.

ISSN:0021-8979    

DOI:10.1063/1.1735510

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

It is shown that solute atom pairs in ferromagnetic alloys, as well as the interstitial atoms in iron, can give magnetic viscosity.The viscosity field of the alloys vs wall displacement is determined for various crystal structures. The maximum value of the viscosity field is related to the anisotropy energy induced in the same materials by heat treating in a magnetic field.

ISSN:0021-8979    

DOI:10.1063/1.1735511

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Dislocations having a Burgers vector in the basal plane and lying in this plane, have been studied in graphite by the use of thin foil transmission electron microscopy. The dislocations are dissociated into ribbons consisting of two partials separated by a stacking fault. Specific models for these dislocations are presented. Hexagonal networks contain extended and contracted nodes. The presence of two types of stacking faults gives rise to singularities which are analyzed in terms of experimentally determined Burgers vectors. The dislocations and even the networks are very mobile along the basal plane. The stacking fault energy is determined as 3 to 5×10−2ergs/cm2.

ISSN:0021-8979    

DOI:10.1063/1.1735512

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Single‐crystal gold films were grown by vacuum deposition on heated (375°C) sodium chloride substrate blanks. Completely oriented films with thicknesses between 1000 and 3000 A were obtained, with the plane of the film being the {100} crystallographic plane. A small hole was drilled through the substrate with a water jet, and the mechanical properties were determined by stressing the unsupported film over this hole. The films were observed to undergo considerable plastic deformation, accompanied by the appearance and growth of mechanical twin bands as the stress was increased. X‐ray diffraction studies were made to determine the twin orientation. Both the ultimate tensile stress and the elastic modulus were found to increase as the thickness of the films was reduced.

ISSN:0021-8979    

DOI:10.1063/1.1735513

出版商:AIP    

年代:1960

数据来源: AIP