摘要:

This paper describes an investigation of the interaction between pairs of flat metal surfaces sliding against one another. The experiments show that the junctions which are formed when the surfaces are first placed in contact do not break when the surfaces begin to slide. The relative motion of sliding is accommodated by plastic deformation of the metal near the contact areas. The plastic shearing takes place in a direction slightly inclined to the surfaces and causes the formation of wedges of displaced metal in much the same manner as was observed in a previous investigation with hemispherical riders sliding against cylindrical drums. With a pair of flat surfaces several wedges are formed simultaneously at various places between the surfaces. The wedges force the surfaces apart, and the separation is often as much as 0.1 to 0.4 mm. The variations in the distance of separation during sliding were measured with a dial indicator. The wedges and the gap between the surfaces were also observed visually with and without the microscope. Metallographic sections cut through the wedges were examined. Differences in the phenomena observed with various metals indicate that with some metals the plastic shearing by which the wedges are generated continues to occur during extended periods of sliding, while with others it occurs mainly during an initial period of sliding, though the wedges once formed remain between the surfaces.

ISSN:0021-8979    

DOI:10.1063/1.1713746

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Permalloy films of composition 83% Ni 17% Fe ranging from polycrystalline to monocrystalline were prepared by evaporation. Conventional electron micrographs, selected area diffraction patterns, and Lorentz electron micrographs were taken to study the average magnetic ripple wavelength (&lgr;0) as a function of the average crystallite size (a) of the film. Below a critical crystallite size, polycrystalline films showed a linear increase of the ripple wavelength with increase in crystallite size. It was found that &lgr;0=4ain agreement with the maximum probable wavelength predicted theoretically by Rother. Films with preferred orientation showed similar behavior with &lgr;0=10a. A plateau was reached (&lgr;0=9000 Å,a=2000 Å, &lgr;0=12 000 Å,a=1160 Å, respectively) after which an increase in crystallite size had no effect on the ripple wavelength. Monocrystalline films did not exhibit ripple structure and it is concluded that in these films &lgr;0=∞.

ISSN:0021-8979    

DOI:10.1063/1.1713747

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Energy distributions have been obtained for atoms sputtered from Cu (100), (110), (111), and polycrystalline surfaces bombarded by 80‐ to 1200‐eV Hg and noble gas ions. Energies of sputtered atoms are found to depend markedly on the angle of ejection. For a (110) surface bombarded by 1000‐eV Kr ions, average energies of ejected atoms are 9.5 eV in the [110] direction (normal to the surface) and 14.2 eV in the [011] direction (60° to the surface normal). Ejection energies decrease for lighter ions in the order Kr+, Ar+, Ne+, and He+. For a (110) surface bombarded by 600‐eV He ions, the average energy of atoms ejected in the [110] direction is 5.5 eV. Dependence on bombarding ion energy is very weak above 1000 eV where average energies of sputtered atoms are found to be in the range 5–15 eV. Ejection energies decrease at lower bombarding ion energies and decrease rapidly below 200 eV. For atoms ejected in the [110] direction from a (110) surface under Kr ion bombardment, the average energy decreases from 5.5 eV at an ion energy of 200 eV to 2.6 eV at an ion energy of 80 eV.

ISSN:0021-8979    

DOI:10.1063/1.1713748

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The adiabatic elastic constants of aluminum have been measured with an ultrasonic pulse technique at liquid‐heluim, liquid‐nitrogen, and room temperatures. The values of the elastic constants at 4°K arec11=11.63,c12=6.48, andc44=3.09 in units of 1010N/m2. The Debye characteristic temperature calculated from these figures is &thgr;=425°K in good agreement with the value obtained from speciffic heat data.The shear elastic constants ½(c11−c12) andc44are discussed with reference to the theory given by Leigh.

ISSN:0021-8979    

DOI:10.1063/1.1713749

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A possible mechanism for uniaxial anisotropy in ferromagnetic films is the magnetoelastic energyW&lgr;which results from the constraint imposed on the film by the substrate. Below some temperatureT′ at which the mobility of the film atoms on the substrate is sufficiently low, the constraint prevents the film from deforming in magnetostriction. An increase in the magnetoelastic energy, therefore, occurs when the film is magnetized in a direction other than that in which the film was deposited.This paper examines this constraint energy in detail and shows that earlier calculations which have been based on the average polycrystalline magnetostriction are not correct in principle, since the correct calculation requires averaging the magnetoelastic energy over a polycrystalline aggregate. For the maximum value ofW&lgr;at room temperature the correct calculation gives 4.2, 1.8, and 42 (103erg cm−3) in nickel, iron, and cobalt, respectively. The value for iron is an order of magnitude larger than that given by earlier calculations. These values are found to be consistent with the experimental results of several groups of workers for films of nickel, iron, and cobalt deposited on amorphous substrates in vacua of less than about 10−5Torr and for electrodeposited films of nickel and cobalt. The particular case of the temperature dependence ofW&lgr;in nickel films is found to be in agreement with the reported experimental behavior when annealing of the constraint is allowed for. The annealing kinetics are discussed qualitatively in the light of observations by Benjamin and Weaver on film‐substrate adhesion. This discussion predicts, in agreement with experiment, the possibility of room‐temperature magnetic annealing in films deposited on unheated glass substrates in good vacua.Evidence is also presented for the presence of constraint energy in evaporated films of the nickel‐iron alloys, particularly near the 50% Ni composition. The calculations for the maximum room‐temperature values ofW&lgr;give a maximum of 3×103erg cm−3at 50% Ni and a minimum of about 20 erg cm−3at 82% Ni.

ISSN:0021-8979    

DOI:10.1063/1.1713750

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Several spurious peaks observed in the x‐ray diffraction patterns of bulk specimens of pyrolytic graphites (PG) have been identified as double Bragg peaks. Their angular position is described by 2&thgr;hkl+2&thgr;h′k′l′, where &thgr;hkland &thgr;h′k′l′ are the Bragg angles of the participating single reflections. The intensity dependence of the peaks on the specimen shape and the specimen orientation is distinctly different from that of single Bragg reflections, but agrees well with predictions based on double Bragg reflections. The concentrations of doubly reflected power which give rise to the unexpected peaks are due to the highly preferential alignment of crystallites. It has been known for some time that double Bragg reflections from polycrystalline samples may be sufficiently strong to contribute significantly to the small‐angle scattering of x rays. The present study demonstrates that in favorably textured specimens they may even become strong enough to show up as peaks in normally recorded diffraction patterns. Techniques are described by which such peaks can be distinguished from single Bragg reflections.

ISSN:0021-8979    

DOI:10.1063/1.1713751

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Thin single‐crystal films of lead sulfide have been prepared by vapor deposition on heated rocksalt substrates in the 0.2–8.0‐&mgr; range. Electrical and optical measurements have established that the properties of the films compared favorably with the bulk material and are suitable for a large number of experimental investigations. The index of refraction for PbS is in good agreement with previously obtained bulk values. The various electrical properties of the films, particularly the Hall mobility, are in very good agreement with those of bulk material.

ISSN:0021-8979    

DOI:10.1063/1.1713752

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A reversible reduction of breakdown voltage is observed when mechanical stress is applied to siliconp‐njunctions. This effect can best be investigated in junctions exhibiting uniform avalanche breakdown. When uniaxial stress is applied the normalized reduction of breakdown voltage &Dgr;V/VBis proportional to stress, the proportionality constant being of the order of 10−12dyn−1cm2. When stress is applied by means of a flat stylus, &Dgr;V/VBis proportional to the load, when a spherical stylus is used, &Dgr;V/VBis proportional to the cube root of load. It can be shown that the relative current change for a given force is to a first approximation independent of diode area and breakdown voltageVB. It is proposed that the effect is caused by reduction of the energy gap.

ISSN:0021-8979    

DOI:10.1063/1.1713753

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

ZnS platelets grown from the vapor phase, bounded by (2¯11), (011¯), and (111) faces, were used. The crystals showed birefringence bands perpendicular to the [111] axis. X‐ray rotation, oscillation, and Laue photographs showed that the bands are due to changes in crystal structure (cubic, hexagonal, and polytypes) and one‐dimensional stacking disorder. The polarity of the common [111] axis of the various bands was determined by several techniques. On the (2¯11) faces, heating with H2O2caused the appearance of triangular etch pits, aligned with bases parallel to the [01¯1] direction and apexes pointing all in the same sense. The (111) face towards which the triangles pointed was attacked faster by the etchant than was the opposite one. The same (111) face became negatively charged if a (2¯11) face was uniformly illuminated by 343 m&mgr; radiation. Furthermore, the same face turned out to be a zinc plane, as revealed by comparing the intensity of two (111) reflections, using wavelengths at both sides of the ZnK‐absorption edge. The sense of the crystal growth along the [111] axis was also determined. A correlation was established between the morphology and crystallographic polarity as well. The results show that in spite of the polytypism, twinning, and one‐dimensional stacking disorder, the sense of the [111] axis remains constant. Moreover, the one‐to‐one correspondence between the sign of the photovoltage and the crystallographic polarity restricts the possibilities of interpretations of the anomalous photovoltaic effect observed along the [111] axis in ZnS crystals favoring Neumark's theory [G. F. Neumark, Phys. Rev.125, 838 (1962)].

ISSN:0021-8979    

DOI:10.1063/1.1713754

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The existence is reported of large reversible changes in the excess current of germanium, silicon, and gallium arsenide tunnel diodes subjected to highly localized stress. The relationship of this effect to the anisotropic stress effect recently reported by Rindner and Braun in conventionalp‐njunctions is discussed. It is suggested that both effects may arise from deep‐lying electronic states associated with strain‐induced lattice defects in the junction region. A consistent interpretation is presented of the tunnel diode excess current in terms of strain‐induced intermediate tunneling states, and of the conventional diode current in terms of strain‐induced generation‐recombination centers.

ISSN:0021-8979    

DOI:10.1063/1.1713755

出版商:AIP    

年代:1964

数据来源: AIP