摘要:

The simultaneous diffusion of two isotopes of a given ionic impurity in an electric field is considered, and an improved method of analyzing the experimental data to obtain &Dgr;D/Dis discussed. (HereDis the diffusion coefficient of one of the isotopes, and &Dgr;Dthe difference between those of the two isotopes.) As noted by Chemla, an electric field increases the accuracy with which &Dgr;D/Dcan be determined. Equations are found giving this increase in accuracy as a function of field and diffusion time. If the ratiow2&agr;/w2&bgr;of the jump frequencies of the two isotopes is known, relative values of the vacancy or interstitialcy jump frequencies near an impurity can be calculated from &Dgr;D/Dand &mgr;/D, where &mgr; is the drift mobility. As an example, data in the literature for Na22and Na24diffusing in KCl are considered. For self‐diffusion,w2&agr;/w2&bgr;may be calculated from &Dgr;D/Dand known values of the correlation factor. When data in the literature are used to estimatew2&agr;/w2&bgr;for Na22and Na24diffusing in NaCl, a value smaller than that predicted by classical rate theory is found.

ISSN:0021-8979    

DOI:10.1063/1.1728919

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The friction of sliding metal surfaces is often attributed to the formation and shearing of welded junctions between the surfaces. This paper describes a more detailed investigation of the phenomena which occur in the junctions. Experiments were performed with a hemispherically ended copper rider sliding against the surface of a large cylindrical copper drum. Observation of the sliding contact through the microscope shows that most of the time during sliding, the drum and rider are held apart by a wedge of displaced metal from the drum, which becomes trapped between them. Whenever a wedge escapes from between the drum and rider, another wedge forms rapidly to replace it. The wedges are also observed with several other combinations of metals, and with pairs of flat copper surfaces. Sections cut through the wedges and adjacent copper contact members were examined. It is found that the shearing of the metal by which the sliding proceeds occurs in a direction slightly inclined to the drum surface. This causes the formation and growth of the wedges. The shearing is primarily a continuous plastic deformation process somewhat similar to the shearing process by which the chip is generated in the cutting of ductile metals with machine tools. It is possible that the adhesion between the rider and wedge may often be weaker than the junctions usually assumed to be responsible for friction. Wear debris is observed to be produced in a number of different ways.

ISSN:0021-8979    

DOI:10.1063/1.1728920

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A one‐dimensional, small‐amplitude analysis is presented of alternating‐current generation by a stationary electromagnetic circuit coupling to waves in a moving, perfectly conducting fluid. In a uniform applied dc magnetic field the waves in the fluid are either compressional waves if the time‐average velocityv¯0is transverse to the dc magnetic field, or Alfve´n waves if it is along the dc magnetic field. It is shown that, for velocitiesv0greater than the velocity of propagationcof the compressional or Alfve´n waves, self‐excited oscillations may be produced in a resistively loaded coil coupling to the fluid. In a traveling‐wave circuit and in a resistively loaded distributed circuit coupling to the fluid, growing waves are found which result from a transformation of the fluid energy into electromagnetic energy. There is a close analogy between these power‐generation mechanisms and those employed in microwave electron‐beam tubes.The results of two‐ and three‐dimensional analyses are summarized in order to show that the phenomena predicted by the simplified one‐dimensional analysis occur in less idealized geometries. Possible applications are briefly discussed with reference to ac power generation by using combustion gases or a flow of a high‐temperature plasma.

ISSN:0021-8979    

DOI:10.1063/1.1728921

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Fine rod and whisker‐type crystals of undoped CdS whose dark conductivity was of the order of 10−10(&OHgr;‐cm)−1were bombarded with 100‐keV electrons. Following bombardment dark conductivity of the order of 10−3(&OHgr;‐cm)−1was observed. Heat treatment to about 200°C reduced the conductivity to near its original value. Because of the high efficiency with which the electron beam raised the conductivity of the crystals, an explanation based on the redistribution of electrons and holes over existing levels rather than the production or removal of defects is required.

ISSN:0021-8979    

DOI:10.1063/1.1728922

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Dislocation multiplication and motion in NaCl was studied using etch pit and birefringence techniques. The observations show that dislocations in glide bands of NaCl are in the form of large concentric loops with sources staggered in the center of the bands. They propagate and multiply by cross‐slip and are braked through intersection jogs. The slip distance parallel tobis estimated to be 2–3 mm and that normal tob0.5–1 mm, at a stress of 30 g/mm2in crystals having 5×104dislocations/cm2. ``Deformation bands'' form normal to the operating system during the latter part of stage I by ``glide polygonization'' of edge dislocations on closely spaced slip planes. These limit dislocation motion to shorter distances in stage II. Stage III appears when significant flow occurs on a secondary system oblique to the primary operating one.

ISSN:0021-8979    

DOI:10.1063/1.1728923

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The effects of surface sources, ozonized surface films, and surface dissolution, on the nature of plastic flow in NaCl single crystals were studied using etch pit and birefringence techniques. Slip steps increase in depth and become rounded as the slip band broadens. This is also often accompanied by a bending of the steps as much as 3° off ⟨100⟩. These effects are explained in terms of both internal and surface cross‐slip mechanisms. Ozonization of NaCl for short periods restricts the action of surface sources and for longer times provides barriers to the egress of dislocations. The ``Suzuki effect'' (formation of a work‐hardened surface layer) is found to depend upon the existence of a multiplicity of surface sources such as is produced by polishing on wet silk. Cross‐slip of screw dislocations at the surface is found to be greater and flow more homogeneous when the surface is dissolved during deformation. This is proposed as a likely mechanism to explain the ``Joffe effect'' when atmospheric variables are eliminated.

ISSN:0021-8979    

DOI:10.1063/1.1728924

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The phase diagram for the Bi2Te3&sngbnd;Sb2Te3pseudo‐binary system is of the solid‐solution type, where the distribution coefficientkis equal to unity at 33.3 and 66.7 mole % Sb2Te3. Theclat tice parameter remains essentially constant across the diagram at 30.49 Å for both slowly crystallized and quenched alloys. For quenched alloys thealattice parameter decreases almost linearly, from a value of 4.487 Å, for pure Bi2Te3, to a value of 4.275 Å, for pure Sb2Te3; however, a significant contraction from linear variation is found in slowly crystallized materials.EGdiminishes in an essentially linear fashion from 0.16 eV, for pure Bi2Te3, to 0.12 eV at 24.2 mole % Sb2Te3in both slowly crystallized and quenched materials.EGremains approximately constant from 24.2 to 66.7 mole % Sb2Te3for slowly crystallized materials but continues to drop for quenched materials.

ISSN:0021-8979    

DOI:10.1063/1.1728925

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

This paper presents a theoretical discussion of the results to be expected from magnetic aftereffect measurements on Ni containing a sufficient number of divacancies. Calculations are made of the stabilization energy for 109°−⟨001⟩ and 180°−⟨110⟩ Bloch walls, the walls expected to be most mobile at low magnetic fields. The results show features characteristic of the ⟨110⟩ symmetry of the divacancies that are not shared by centers with ⟨100⟩ symmetry: (1) The existence of two relaxation modes having different relaxation times and different interaction energies with the magnetization vector, and (2) the nonvanishing of the stabilization force on 109° walls at large Bloch wall displacements.

ISSN:0021-8979    

DOI:10.1063/1.1728926

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The surface and bulk properties of semiconductors have been studied by a two‐terminal method using dirty contacts. These contacts are defined as ones that are easily applied and removed and that are separated from the bulk by surface states, oxides, adhered gasses, and chemical films. The method essentially involves measuring the resistance‐voltage (R‐V) characteristics from the millivolt range up to about 100 V, and from these data the sample resistivity can be obtained directly. The effect of work damaging or etching the semiconductor surface can be readily evaluated. By observation of the shape of theR‐Vcurves it is possible to separate the bulk from the surface effects, calculate the surface barrier height and thickness from tunneling equations, and determine whether the barrier is a surface film or due to metal‐semiconductor contact potential difference. An application of the theory of electric field tunneling of Holm to the data of silicon carbide gives values of about 2.4 eV for the barrier height and 13 Å for the barrier width of the film on the surface. Sufficient information is included on electrode techniques and pitfalls so that the experimentalist can readily make the measurements. Efforts were concentrated on silicon carbide and silicon, but the techniques are applicable to all types of semiconductors.

ISSN:0021-8979    

DOI:10.1063/1.1728927

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Some unusual properties of the porous graphite contact onp‐type silicon are described. Current through the sample reaches a saturation level that is inversely proportional to the amount of adhered water vapor. Other gases such as ammonia, H2S, and HCl modify the shape or amplitude of the saturation current. There is a hysteresis loop in the low voltage region which is similar in appearance to that of a ferroelectric. The general method of measurement can be applied to studying the semiconductor surface as well as the contact phenomena. The possible applications include such devices as current regulators, humidity detectors, and surface‐barrier radiation detectors.An electronic band model, which includes a trap‐dominated inversion layer, is presented to explain the phenomena. This model also integrates various conflicting theories of metal‐semiconductor contacts.

ISSN:0021-8979    

DOI:10.1063/1.1728928

出版商:AIP    

年代:1962

数据来源: AIP