Complex Frank Loops and Fault Climb

Abstract

SummaryThe Burgers vectors of the dislocations bounding steps in the stacking fault in Frank dislocation loops in quenched silver and copper-aluminium alloys have been identified by comparison of experimental electron microscope images and images computed using the Head-Humble technique. The steps in the fault are generally acute, faulted, and bordered by t<llO) stair-rod dislocations. However, obtuse unfaulted steps bordered by t<1l2) Shockley dislocations have also been observed. A characteristic configuration for a stepped loop consists of a triangular region within the main loop with one edge, a dissociated Frank dislocation, forming an edge of the main loop, and the other two edges, acute fault bends bordered by t<llO) dislocations, forming steps in the fault.The formation of steps may occur by the union of separate loops involving dissociation of parallel edges on a common {Ill} plane. However, the formation of the triangular configuration and of steps bordered by t<1l2) dislocations is not compatible with this mechanism. An alternative mechanism, fault climb, is compatible with all observations. It is concluded that vacancy supersaturation is reduced in quenched materials of low stacking fault energy by fault climb, the formation of steps in the fault resulting from climb up and climb down in different portions of a loop.

Generation of degradation defects, stacking faults, and misfit dislocations in ZnSe-based films grown on GaAs

“…The degradation of the Frank-type stacking fault starts in areas close to the QW and propagates toward the II-VI/GaAs interface as shown by the partially collapsed stacking fault in Fig. 18 Thus, the small faulted defect b in Fig. The bugs are clusters of vacancies that form since II-VI compounds have a low stacking fault energy, 17 and the supersaturation of local clusters of vacancies can be reduced by fault climb to form steps in different portions of a simple faulted defect.…”

Apparent Anomalous Absorption and Image Matching

“…However, even in this case, the approximation would be inadequate if quantitative matching of fringe intensity were required. Clarebrough and Morton (1969) and Morton and Clarebrough (1969) have used the approximation d = 0·1 in image matching to determine the Burgers vectors and separations of stair-rod dislocations in complex Frank dislocation loops and the extent of dissociation of Frank dislocations in copper-aluminium alloys and in silver.…”

“…However, a value of d of 0·1 has usually been used when comparing theoretical profiles with experimental images (Humphreys and Hirsch 1968) and this value has also been used in comparisons of experimental images with images computed using the methods of Head (1967) and Humble (1968a) (e.g. France and Loretto 1968;Morton and Clarebrough 1969). Humphreys and Hirsch (1968) have shown theoretically that the assumption d = 0·1, irrespective of g and the material, is often a very poor approximation.…”

The Reconstruction of Displacement Fields of Defects in Crystals from Electron Micrographs

“…The analysis is once again restricted to those displacement fields for which there is a direction along which displacements are constant so that all fault planes must contain the constant direction, and hence the trace of each fault plane on a longitudinal section of the object will be in the constant direction. Within this limitation a large number of configurations of interest are included, not only single fault planes in an otherwise perfect crystal but all the cases of multiple fault planes with dislocations for which Humble (1968) and Morton and Clarebrough (1969) have shown computer-generated micrographs.…”