Stair rod dislocation

A partial dislocation (called a stair rod dislocation) is formed at the intersection of two stacking faults on different planes with different fault vectors R and R2 and its Burgers vector is bp = Ri—R2. An extended summary of the contrast from partial dislocations in fee metals has been given by Edington (1975). 

Fig. 3.61 A Lomer-Cottrell lock a two partial dislocations before interaction, b after interaction of the leading partials forming a stair-rod dislocation...

FigurelO.il Termination of two li basal stacking faults (BSFs) by PSF (schematic representation), s and —s represent 1 /5[1010] and 1 /6 [1010] stair-rod dislocations.

Regarding PSFs in a-plane GaN, one type has been identified lying on 1210 planes inclined at an angle of 60° with respect to the (1120) growth plane [46], The lateral extension of these PSFs is only a few nanometers and they are terminated by BSFs of Ji-type bounded by l/6[10l0] and 1/6[1010] stair-rod dislocations. 

The process of stacking fault folding involves stair-rod dislocations to mediate between the different prismatic and pyramidal crystal planes because the displacement vectors of the stacking faults on the (1100) and (1102 planes are not the same. An HRTEM plan-view image of the tip of a prismatic/pyramidal stacking fault domain found in an HVPE film is shown in Figure 11.16. The arrows indicate the position of stair-rod dislocations. It is noteworthy that the tip involves the interaction of an fr-type BSF, representative for all such domains found in the film. The tip position coincides with a terminated BSF and consists of two PyS F, each of them subsequently folding onto the m plane. 

Figure 11.16 A plan-view HRTEM image, showing the tip of a folded stacking fault. White arrows assign the positions of stair-rod dislocations.

Figure 11.18 Sketches of stacking faults found in o-plane GaN. Cray arrows indicate stair-rod dislocations mediating between stacking faults on different planes and gray slabs assign terminating partial...

Fig. 21. Defects formed by condensation of vacancies onto dislocation loops formed by collapse of small vacancy clusters, (a) Dislocation loops in 99.999% Al, quenched from 610°C into liquid N2, then aged 1 hr at — 80°C and 2 hr at 60°C. The defect is a Frank sessile dislocation enclosing an intrinsic stacking fault. Magnification 27,000 x. From Dr. K. Y. Chen, Northwestern University, Evanston, Illinois, (b) Stacking fault tetrahedra in 99.999% Au quenched from 1038° into -35°C brine and aged at 25°C. The tetrahedra (some are truncated) are bound by intrinsic stacking faults and dislocations at the edges called stair rod dislocations. Magnification 70,000 X. From Dr. J. A. McComb, Northwestern University, Evanston, Illinois.

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