摘要:

The effect of exceeding the critical current in one film of a superconducting tunnel junction is examined. The position of the normal superconducting boundary is calculated for a simplified model, and the form of the current‐voltage relation is discussed. Nonuniformity of the film is shown to cause anomalous characteristics observed in Pb‐PbO‐Al junctions.

ISSN:0021-8979    

DOI:10.1063/1.1709957

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Below 30°K zinc‐doped germanium exhibits a number of unusual photo and temperature effects when the lowest zinc‐acceptor levels have been filled by electrons from compensatory antimony impurities. These effects include negative photoconductivity, a discontinuity in the temperature dependence of the sample conductivity, as well as the storage of free electrons produced by intrinsic photoexcitation. Hole trapping by the Zn atoms which are singly or doubly ionized is the prime source of these effects. A simple theory is presented which qualitatively explains all of the observed effects and quantitatively fits the data in those areas that are accessible to rigorous measurement.

ISSN:0021-8979    

DOI:10.1063/1.1709958

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The results of an extensive investigation into the nature of slip‐induced directional order in Fe‐Ni alloys near the 75% Ni composition are reported in this paper. Single crystal rods of 4–79 moly‐Permalloy were swaged in the [111] and [001] orientations, as were crystals of the following orientations subjected to plane strain compression: (001) [100], (001) [110], (110) [001], (110) [1¯12], (110) [1¯10], (111) [1¯12], (112) [1¯10] and (112) [1¯1¯1]. Magnetic torque measurements show that all crystals developed a uniaxial anisotropy upon deformation, with the easy magnetic direction in good agreement with our previous theoretical deductions. In the [001] swaged crystal, deviation of the observed easy axis from the calculated value was rationalized in terms of unequal participation of the expected slip systems.In all cases of plane strain compression, the induced anisotropy constant rose to a maximum value, and then decreased, as the thickness reduction was increased. In one experiment, crystals of a 2%Mo‐76% Ni‐22%Fe alloy received a long‐range‐ordering treatment at 475°C for 190 h prior to plane strain compression in the (110) [1¯12] orientation. The anisotropy energy reached a maximum value of 460 000 erg/cm3, the highest value of slip‐induced anisotropy thus far reported in Fe‐Ni alloys. As for the anisotropy decrease at large reductions, reorientation of slip‐induced atom pairs as a result of lattice rotation, is undoubtedly a factor. However, this explanation is not valid for the (110) [1¯12] orientation, which remained stable even after 98% reduction. A more widely applicable mechanism is advanced, whereby the decrease in anisotropy is attributed to randomization of the atom pairs through slip across antiphase ordered domain boundaries, both those grown‐in and those created by intersecting slip.Additional observations have been made of the crystallographic texture and magnetic squareness in cold‐formed polycrystalline Permalloy tapes, which are currently used as magnetic memory elements in storage devices. The results are satisfactorily explained in terms of slip‐induced directional‐order theory. Implications of seeded single crystals to these results are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1709959

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Quantitative thermal emission microscope studies of cesium surface ionization on porous tungsten emitters show under clean surface conditions a surface migration length in the 2‐&mgr; range. The migration length from the pore exit is under this condition fairly independent of the flow rate per pore and the emitter temperature. It is therefore concluded that 107pores/cm2(traverse counting technique) yield maximum ionization efficiency on porous tungsten.Clean surface conditions were checked by Richardson work function measurements with the built‐in Faraday cage. Also, the ion‐current transition pattern in the threshold region was used for judgement of the surface condition. In case of a contaminated surface, a smooth transition from high to low ion current with decreasing temperature was observed in contrast to the steep ion‐current change‐over in the threshold region under clean surface conditions. Also the surface migration length increased on the contaminated surface.Molybdenum, sputtered onto the porous tungsten substrate, showed a uniform work function over the entire emitter area with &phgr;=4.20 eV.

ISSN:0021-8979    

DOI:10.1063/1.1709960

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A dead‐weight piston gauge was used to determine the bismuth I‐II transition pressure and the volume change at the transition. The transition pressure at 25°C for one sample, believed to contain less than 0.001% impurities, was found to be 25 306 bar, with an estimated uncertainty of 60 bar. With another sample, of substantially less purity and of larger grain size, a transition pressure of 25 500±60 bar was measured. The average relative volume change was 0.035.

ISSN:0021-8979    

DOI:10.1063/1.1709961

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Evidence is reported for the existence of damage regions in Si, GaAs, and InSb irradiated with mono‐energetic 14‐MeV neutrons. The regions were revealed by using a chemical etch and observing carbon replicas of the surface with an electron microscope.

ISSN:0021-8979    

DOI:10.1063/1.1709962

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A new type of cell for investigation of the Costa Ribeiro effect in water is described. The rate of change of water to ice can be controlled and measured, while the associated current is measured. The current is found to be proportional to the rate of change of water to ice and between 1 and 10&mgr;C of charge are liberated for each gram of water frozen. The possible importance of the effect for the explanation of atmospheric electricity is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1709963

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Flash‐evaporated cermet films (Cr‐SiO) with 77 wt % Cr were examined by x‐ray diffraction. Bragg peaks corresponding to extremely small particles of Cr were observed. For specimens deposited onto room‐temperature Pyrex substrates, a particle size of 20 Å was calculated from the breadths of the peaks. For specimens deposited at 400°C, the Bragg peaks took on an unusual form, consisting of a central peak flanked by strong subsidiary peaks, or sidebands. These sidebands are interpreted as evidence for a strong crystal‐lographic correlation, in both separation and orientation, between chromium particles. A model consisting of short chains of touching Cr particles, with correlation only between nearest‐neighboring particles, and a particle size of 15 to 20 Å, is consistent with the observations on the 400°C specimens.

ISSN:0021-8979    

DOI:10.1063/1.1709964

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The marginal‐stability boundary for spontaneous generation of ion‐acoustic waves in a nonequilibrium plasma is investigated experimentally. The transition from inverse Landau damping to normal Landau damping of the acoustic wave modes is demonstrated by observing the change in forward‐scattering cross section of microwave electromagnetic energy. The measured scattering cross section is compared with that predicted by Ichimaru, using a simple relaxation‐time collision term in the Boltzmann equation. In addition, the collision term of Bhatnagaret al.is used to construct a new marginal‐stability boundary. The latter expression seems to give a better comparison with the observed microwave scattering and demonstrates the superiority of the more realistic collision‐term model.

ISSN:0021-8979    

DOI:10.1063/1.1709965

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Coherent longitudinal phonons at 9.0 GHz in X‐cut quartz rods have been detected by means of high‐speed superconducting bolometers. This type of detector is responsive to ultrasonic intensity and is insensitive to the ultrasonic phase distribution over the endface of the quartz rod, which often disguises the true nature of the echo‐decay envelope when piezoelectric detection of microwave phonons is employed. These bolometers are also capable of detecting the incoherent phonons produced in the dissipation and thermalizing of the coherent microwave phonons.

ISSN:0021-8979    

DOI:10.1063/1.1709966

出版商:AIP    

年代:1967

数据来源: AIP