摘要:

The application of a shear stress to a dislocation segment causes not only energy changes of the dislocation but also entropy changes. For a dislocation kink chain, the entropy change leads to a significant increase in the restoring force for dislocations which have small angles against close‐packed directions. For a dislocation string, the entropy contribution to the restoring force is negligible.

ISSN:0021-8979    

DOI:10.1063/1.1714551

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The Peierls stress for dislocation motion causes characteristic nonlinearities of the micro‐stress‐strain law of dislocations. Contrary to the string model, the nonlinear stress‐strain law of kinked dislocations can be the source of amplitude‐dependent internal friction and modulus defect at amplitudes which are below or comparable to the breakaway stress from pinning points. Under the assumption that double‐kink generation can be neglected, in terms of a bias stress experiment, the following points have been found to be the essential difference between the dislocation string model and the kink model: (1) The anelastic strain as measured by low‐amplitude oscillations increases with bias stress for the string model, whereas it decreases for the kink model, due to the exhaustion of geometric kink motion. (2) The restoring force of kinked dislocations is one to three orders of magnitude more sensitive to bias stress than is the restoring force of dislocation strings. The conditions for measurable changes of the restoring force are, for the kink model, &egr;> (10−1b/L) (sin &phgr;+5kT/Gb2a), and for the string model &egr;> 10−1&pgr;b/L(&egr; is the bias stress in units of shear modulusG, Lis the line length, &phgr; is the average angle against close‐packed direction,bis the Burgers vector,ais the lattice constant, andTis the temperature).

ISSN:0021-8979    

DOI:10.1063/1.1714552

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Experiments have been conducted with Ge and Si to define the metallurgical effects of temperature gradients in the alloying technology. These effects are defined in terms of the electrical characteristics of alloyed diodes and transistors and in terms of the physical appearance of thep‐njunction. The presence of temperature gradients during the dissolution phase of an alloy cycle results in near‐planar junctions with identical electrical characteristics on the 111, 110, and 100 alloying surfaces if the melt is hotter than the solid, and results in nonplanar junctions on all alloying surfaces if the melt is cooler than the solid. The presence of temperature gradients during the crystal growth phase of an alloy cycle results in uniform regrowth layers if the melt is hotter than the solid, and results in nonuniform regrowth layers which contain gross crystal defects if the melt is cooler than the solid. The major electrical consequences are due to the gross crystal defects and take the form of soft reverse breakdown behavior and forward lnI‐Vcharacteristics that deviate from the single‐slope model ofp‐njunction theory. It is shown that temperature gradients with the melt cooler than the solid should be avoided and that temperature gradients with the melt hotter than the solid can be used to advantage.

ISSN:0021-8979    

DOI:10.1063/1.1714553

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The field‐desorption of thorium from a thermally smoothed tungsten substrate has previously been investigated in the temperature range between 300° and 1090°K. The present work extends these measurements to 77°K and includes desorption from a field‐evaporated surface as well as a thermally smoothed surface. For both types of surfaces at 77°K the desorption field strength was found to be 263×106V/cm±10%.

ISSN:0021-8979    

DOI:10.1063/1.1714554

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Large numbers of point defects were produced by the room‐temperature bombardment of LiF by 100‐kV oxygen ions. Clusters of these defects were studied in the electron microscope by means of their diffraction effects and their appearance in bright‐field and dark‐field images. Platelets of polycrystalline lithium were observed to form on {100}LiFplanes. The mechanism of formation of these precipitates is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1714555

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The switching of thin anisotropic magnetic films by sinusoidal fields varying in frequency from 103to 106cps and having amplitudes up to 18 Oe has been studied and the results compared with both theory and previous pulse‐field measurements. As the amplitude of the switching field is increased, it is concluded that the reversal mechanism changes from irreversible domain wall motion to nonuniform rotation of the magnetization, the point at which the transition occurs increasing with frequency. This conclusion is in disagreement with previously published work. A possible dependence of the switching coefficients on film thickness is also noted.

ISSN:0021-8979    

DOI:10.1063/1.1714556

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Dilatational wave velocities in Ni‐Mn alloys are measured at 25°C in the composition range 0% to 80% manganese using ultrasonic pulse techniques. Using a value of ⅓ for Poisson's ratio in the alloys, the observed values for the velocities are used to compute the corresponding values of the dynamic elastic moduliE. The dilatational wave velocities, ranging from 5638 in nickel to 3792 m/sec in the alloy with 80% Mn, and the correspondlng elastic moduli, ranging from 19350 to 7570 kg/mm2, are found, almost linearly, to decrease with increasing manganese content over the composition range 0% to 40% Mn; to increase over the range 40% to 50% Mn; and then to decrease again over the range 50% to 80% Mn. The increase in the elastic modulus with % Mn over the range 40% to 50% Mn is associated with the formation of the highly ordered NiMn(&dgr;) phase with a bcc crystal structure. The variation ofVandEwith % Mn in the range of 60% to 80% Mn is found to be an extension of their variation in the range 0% to 40% Mn. This variation where the Young modulus of nickel decreases at an average rate of 125 kg/mm2per atomic percent manganese added, is characteristic of the solid solution &ggr; phase. At the tests' temperature, 25°C, the alloys with up to 25% Mn are in the ferromagnetic state whereas the alloys over the composition range 25% to 80% Mn are in the paramagnetic state.

ISSN:0021-8979    

DOI:10.1063/1.1714557

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The sputtering threshold energy and low‐energy sputtering yields for films of sputtered quartz and Pyrex were measured with Langmuir probes. The probe characteristic is very sensitive to deposits of insulating material because even very thin insulating films cause radical changes in electron acceptance. A thin insulator film of known thickness is deposited on the probe by rf sputtering, and a known fraction of that film is removed by enforcing a dc bias voltage on the probe. Different bias voltages require different times to remove the same amount of material (as monitored in the probe characteristic), and one can use this as a very sensitive method for collecting sputtering yield data. Analysis of the deposit sputtered from a quartz target in a 10−2Torr Ar discharge shows it to be SiO1.6. The sputtering yield curve for this SiO1.6is presented and shows a yield of ∼0.1 molecules/ion at 100 eV with a sputtering threshold of ∼16 eV.

ISSN:0021-8979    

DOI:10.1063/1.1714558

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

An atomically clean and highly ordered Ge (111) surface was bombarded with Ar+ions and the bombardment effects were studied by low‐energy electron diffraction. Degradation characteristics of the (10) beam were most extensively investigated over an ion energy range from 10 eV to 1 keV with ion dosage ranging from 1012to 1016ions/cm2. The degradation characteristics determine the mean area of damage per incident ion. This area is 7×10−14cm2for a 1‐keV Ar+ion and 1×10−15cm2for a 40‐eV ion. At low ion energies, some retention of (10) intensity is noted even for large dosages, indicating in this case that some short‐range order is retained. The minimum ion energy for damage is ∼20 eV. This value is close to the sputtering threshold energy and the reported displacement energy of Ge. A bombardment damage model is proposed to explain the low‐energy ion‐bombardment characteristics. Thermal recovery of the bombarded surface shows a dependence on ion energy and also on total bombardment dose.

ISSN:0021-8979    

DOI:10.1063/1.1714559

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Diffraction studies were carried out near 4°K on the influence of rate and method of growth upon the perfection and microstructure of 99.998% purity argon crystals. The crystallography of the twinning observed was directly verified to be of the type expected for a fcc crystal. Some idea of the dislocation content of a well‐annealed argon crystal was obtained. It was concluded that it should be possible to produce crystals having a perfection adequate for a variety of quantitative lattice studies.

ISSN:0021-8979    

DOI:10.1063/1.1714560

出版商:AIP    

年代:1965

数据来源: AIP