Nucleation of semicircular misfit dislocation loops from the epitaxial surface of strained-layer heterostructures

Zou, Jin; Cockayne, D. J. H.

doi:10.1063/1.361527

Cited by 20 publications

(8 citation statements)

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“…3͑b͒ and 4͑b͒, in agreement with previous studies. 16,18 Surface nucleation of partial dislocations in areas of enhanced stress is well supported experimentally, 20,21 and theoretical models of surface dislocation nucleation at stress concentrators [22][23][24][25] are well established. The corners of the contact region act as stress concentrators and serve as the sources for nucleation of Shockley partials on the surface.…”

Section: First Yield: Defect Nucleationmentioning

confidence: 96%

Atomistic studies of defect nucleation during nanoindentation of Au(001)

Gannepalli

Mallapragada

2002

Phys. Rev. B

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Atomistic studies are carried out to investigate the formation and evolution of defects during nanoindentation of a gold crystal. The results in this theoretical study complement the experimental investigations [ J. D. Kiely and J. E. Houston, Phys. Rev. B 57, 12 588 (1998)] extremely well. The defects are produced by a three step mechanism involving nucleation, glide, and reaction of Shockley partials on the {111} slip planes noncoplanar with the indented surface. We have observed that slip is in the directions along which the resolved shear stress has reached the critical value of approximately 2 GPa. The first yield occurs when the shear stresses reach this critical value on all the {111} planes involved in the formation of the defect. The phenomenon of strain hardening is observed due to the sessile stair-rods produced by the zipping of the partials. The dislocation locks produced during the second yield give rise to permanent deformation after retraction. Atomistic studies are carried out to investigate the formation and evolution of defects during nanoindentation of a gold crystal. The results in this theoretical study complement the experimental investigations ͓J. D. Kiely and J. E. Houston, Phys. Rev. B 57, 12 588 ͑1998͔͒ extremely well. The defects are produced by a three step mechanism involving nucleation, glide, and reaction of Shockley partials on the ͕111͖ slip planes noncoplanar with the indented surface. We have observed that slip is in the directions along which the resolved shear stress has reached the critical value of approximately 2 GPa. The first yield occurs when the shear stresses reach this critical value on all the ͕111͖ planes involved in the formation of the defect. The phenomenon of strain hardening is observed due to the sessile stair-rods produced by the zipping of the partials. The dislocation locks produced during the second yield give rise to permanent deformation after retraction.

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Section: First Yield: Defect Nucleationmentioning

confidence: 96%

Atomistic studies of defect nucleation during nanoindentation of Au(001)

Gannepalli

Mallapragada

2002

Phys. Rev. B

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“…In addition, it has been shown that, in a stressed solid, a surface step is a source of local stress concentration [17,18,19], although not as efficient as a crack tip. Therefore, a number of continuum models have been developed, taking into account the energy gain associated to the step elimination in the process of dislocation nucleation [20,21,22,23]. Atomistic calculations have also been performed for characterizing the energetics, the processes involved, and the role of surface defects [24,25,26,27,28,29,30].…”

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confidence: 99%

Dislocation formation from a surface step in semiconductors: Anab initiostudy

et al. 2006

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The role of a simple surface defect, such as a step, for relaxing the stress applied to a semiconductor, has been investigated by means of large scale first principles calculations. Our results indicate that the step is the privileged site for initiating plasticity, with the formation and glide of 60• dislocations for both tensile and compressive deformations. We have also examined the effect of surface and step termination on the plastic mechanisms. The plasticity of semiconductors has been extensively studied for the last decades in both fundamental and applied research, leading to significant progresses in the understanding of the key mechanisms involved. Several issues remain unsolved, however, one of the most essential being the formation of dislocations in nanostructured semiconductors such as nano-grained materials, or nanolayers in heteroepitaxy, systems extensively used in devices. While in bulk materials the few native dislocations are able to multiply via Frank-Read type mechanisms to ensure plasticity, the situation is different in nanostructured materials where dimensions are too small to allow dislocation multiplication [1]. The presence of dislocations in these materials appears to be more controlled by nucleation than by multiplication processes. It has been proposed that surfaces and interfaces, which become prominent for small dimensions, play a major role. Several observations support this assumption, especially for strained layers and misfit dislocations at interfaces [2,3,4]. The formation at surfaces is also relevant where large stresses exist, like near a crack [5,6,7,8,9].Since in situ experimental observations of dislocation nucleation is not yet possible due to the very small dimensions and short observation timescales, the formation of dislocations at surfaces has been mainly investigated theoretically, particularly with continuum models and elasticity theory [10,11,12]. However, in these approaches, the predicted activation energy is very large, in disagreement with experiments. It has been proposed that surface defects, such as steps, help the formation by lowering the activation energy. This is supported by experimental facts in the context of dislocation nucleation at or near crack fronts, with dislocation sources located on the cleavage surface and coinciding with cleavage ledges [13,14,15,16]. In addition, it has been shown that, in a stressed solid, a surface step is a source of local stress concentration [17,18,19], although not as efficient as a crack tip. Therefore, a number of continuum models have been developed, taking into account the energy gain associated to the step elimination in the process of dislocation nucleation [20,21,22,23]. Atomistic calculations have also been performed for characterizing the energetics, the processes involved, and the role of surface defects [24,25,26,27,28,29,30].These studies led to a better knowledge of the dislocation formation from surface steps or cleavage ledges, but we are still far from a complete understanding of the phenomenon. Fu...

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“…Theoretically, dislocations are usually described within the theory of elasticity, 2 where they are treated like singularities in a continuum. Within this framework, the formation of dislocation loops near a free surface or interface has been widely discussed, [14][15][16][17][18] providing evidence of a competition between loop expansion favoring the stress release and the attraction of the dislocation by the free surface. There are therefore a critical size and an energy barrier to overcome for the dislocation to propagate throughout the system.…”

Section: Introductionmentioning

confidence: 99%

Determination of activation parameters for dislocation formation from a surface in fcc metals by atomistic simulations

et al. 2008

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Defects in free surfaces are expected to be seeds for the nucleation of dislocations, which is the likely way nanoscale materials suffer plastic deformation. The nucleation results in the competition between the image force attracting the dislocation to the surface and the applied strain. In this work, two methods based on molecular dynamics simulations using an embedded atom method ͑EAM͒ potential are used to determine the activation energy and the critical radius for the formation of dislocations from a surface defect in a typical fcc metal.

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Nucleation of semicircular misfit dislocation loops from the epitaxial surface of strained-layer heterostructures

Cited by 20 publications

References 20 publications

Atomistic studies of defect nucleation during nanoindentation of Au(001)

Atomistic studies of defect nucleation during nanoindentation of Au(001)

Dislocation formation from a surface step in semiconductors: Anab initiostudy

Determination of activation parameters for dislocation formation from a surface in fcc metals by atomistic simulations

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