J.M. Galligan

Electron dislocation drag at low temperatures

Measurements of the influence of a magnetic field on the stress of plastic deformation for a number of materials are presented. These measurements are given for copper, some copper alloys, zinc, cadmium, lead, and bismuth. The measurements, carried out at a number of temperatures between 1.8 and 40 K, show that this change in stress has a monotonic and an oscillatory dependence upon the magnetic field. The oscillatory dependence on field has a temperature dependence which is consistent with a 1/T3 dependence. We also show that the oscillations are strain rate dependent as well as strain dependent. These results are compared with the inertial model of dislocation motion and the agreement is quite good. Measurements of the orientation dependence of the magneto‐oscillations allows us to assess the relative velocities of screw and edge dislocations, showing that, at low temperatures, screw dislocation move faster than do edge dislocations. Agreement is also found between the present measurements of the Fermi ...

Magneto-oscillations in dislocation drag at low temperatures

Abstract Abstract Experimental results are presented which show how dislocation drag varies with an applied magnetic field. We find that the dislocation drag varies roughly as H 2 in high-purity zinc single crystals. This field dependence agrees with previous measurements on Cu and Al Furthermore, we find magneto-oscillations in the dislocation drag process superimposed on the variation of δ[sgrave] with H in zinc single crystals.

Dislocation motion in superconductors

The strain rate sensitivity of the flow stress of pure Pb crystals was measured at 4.2

Porous silicon photoluminescence and quantum confinement

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The magnetic field dependence of the flow stress in niobium

K. It was found that the effects of changing the strain rate on the flow stress is much more pronounced when the crystal is deformed in the normal state than when the crystal is deformed in the superconducting state. (JRD)

Hardening from metal interstitials in a face centered cubic lattice - PbAg

Images obtained from scanning tunnelling microscopy and atomic force microscopy reveal nanoscale features on hydrogen-passivated porous silicon surfaces. These surface features are altered by varying the chemical etching procedure, resulting in shifts in the wire size and consequent variations in the photoluminescence spectra. The morphology consists of wires with associated nodules. Consistent with the quantum confinement model, the widths of these features range from 1 to 7 nm, and the size distribution and photoluminescence peaks agree with theoretical predictions based on a second-neighbour, empirical tight-binding approximation. In toto, these observations demonstrate that such novel surface features are necessary for the photoluminescence of porous silicon and are consistent with the requirements of the quantum confinement model of porous silicon.

Resistive heating in lead, at 4.2K, while in the normal state

It is shown that the difference in flow stress between the superconducting state and the mixed state is more readily identifiable with the attenuation of an accoustic wave than with a simple rule of mixtures. This result is consistent, qualitatively, with the dislocation moving as an underdamped oscillator as has been shown for the case of lead and lead alloys. (GHT)

PHOTOPLASTICITY AND PHOTONIC CONTROL OF DISLOCATION DENSITIES IN TYPE II-VI SEMICONDUCTORS

Observations of pronounced increases in the yield stress of fcc Pb crystals due to Ag doping are reported. The introduction of silver solutes in lead produces a dramatic increase in the yield strength of the crystals. This hardening effect is produced by a solute concentration too small to be associated with substitutional solutes causing the hardening such as the case of tin in lead and is more consistent with solutes which produce interstitial hardening in crystals. The extent of hardening is dependent on the amount of interstitial silver trapped in solution. Further experiments are presently being conducted to more accurately determine the concentration dependence of the yield stress in the light of an observed increased hardening. In addition the influence of interstitials on the difference in flow stress between the normal and superconducting states is also under investigations and will be reported elsewhere. (auth)

Sintering of promoter catalysts

The application of a current through a plastically deforming metal does not influence the deformation process via some interaction between electrons (i.e. the current) and mobile dislocations, the only effect observed was a decrease in stress when the crystal was in the normal state. 15 refs.

The absence of an electroplastic effect in lead at 4.2K

Crystal defects, such as dislocations, introduce electronic states into semiconductors and thereby degrade the desired electronic behavior of semiconductor devices. Special processing precautions are therefore pursued to minimize dislocation densities in semiconductor materials. When light irradiates a semiconductor, incident photons with appropriate wavelengths excite electrons and holes into traps such as point defects and dislocations. This modification of the population of charged defects can modify the flow stress required to propagate dislocations. This effect manifests itself as an inhibition of dislocation motion in type II‐VI compound semiconductors; whereas in type III‐V semiconductors light can enhance dislocation mobility. This effect is known as photoplasticity. In this article we report on the basic characteristics of photoplasticity in CdS and show how it can be exploited to reduce dislocation densities in semiconductor materials.