Generation Of Prismatic Dislocation Loops Research Articles

Initial stages of misfit stress relaxation through the formation of prismatic dislocation loops in GaN–Ga2O3 composite nanostructures

The initial stages of misfit stress relaxation through the formation of rectangular prismatic dislocation loops in model composite nanostructures have been considered. The nanostructures are either spherical or cylindrical GaN shells grown on solid or hollow β-Ga2O3 cores or planar thin GaN films on β-Ga2O3 substrates. Three characteristic configurations of prismatic dislocation loops, namely, square loops, loops elongated along the GaN/Ga2O3 interface, and loops elongated along the normal to the GaN/Ga2O3 interface, have been analyzed. The generation of prismatic dislocation loops from the interface into the bulk of the GaN shell (film), from the free surface into the GaN shell (film), and from the interface into the β-Ga2O3 core (substrate) has been investigated. It has been shown that, for the minimum known estimate of the lattice misfit (2.6%) in some of the considered nanostructures, no any prismatic dislocation loops can be generated. If the generation of prismatic dislocation loops is possible, then in all the considered nanostructures, the energetically more favorable case corresponds to prismatic dislocation loops elongated along the GaN/Ga2O3 interfaces, and the more preferred generation of prismatic dislocation loops occurs from the GaN free surface. The GaN/Ga2O3 nanostructures that are the most and least resistant to the formation of prismatic dislocation loops have been determined. It has been found that, among the considered nanostructures, the planar two-layer GaN/Ga2O3 plate is the most resistant to the generation of prismatic dislocation loops, which is explained by the action of an alternative mechanism for the relaxation of misfit stresses due to the bending of the plate. The least resistant nanostructure is the planar three-layer GaN/Ga2O3/GaN plate, in which GaN films have an identical thickness and which itself as a whole does not undergo bending. The critical thicknesses of the GaN shells (films), which must be exceeded to ensure the growth of these shells (films) so as to avoid the formation of prismatic dislocation loops, have been calculated for all the studied nanostructures and three known estimates of the lattice misfits (2.6, 4.7, and 10.1%).

Prismatic and helical dislocation loop generation from defects

Plastic deformation induced by stress concentrations near crystal defects occurs through the generation of prismatic dislocation loops (PDL). The production of PDLs leads to void growth and particle decoherence. In this work we use dislocation dynamics simulations to characterize two mechanisms for PDL formation. The first mechanism corresponds to a classical model of PDL generation from dislocation nucleation. The second mechanism considers PDL generation through cross-slip of a screw dislocation intersecting the particle. We systematically study the effect of the crystal lattice and defect type on PDL generation for both mechanisms as a function of pressure. The simulations show image stresses produced by the dislocation's interaction with the free surface of a void suppresses PDL generation. The highest PDL generation rates are found for a dislocation nucleated from a void in a body-centered cubic lattice. Our simulations also show helical coiling of screw dislocations produces a continuous emission of PDLs without the need for dislocation nucleation at pressures as low as 1.0 GPa.

Initial stages of misfit stress relaxation in composite nanostructures through generation of rectangular prismatic dislocation loops

Critical (necessary) conditions of misfit stress relaxation in bulk and hollow core–shell nanoparticles, bulk and hollow core–shell nanowires, and flat bi- and tri-nanolayers (composing of a substrate and one or two thin films, respectively) through generation of rectangular prismatic dislocation loops (PDLs) at the inner and outer interfaces of the composite nanostructures with subsequent extension of the PDLs into cores (substrates) or shells (films) are analyzed theoretically and discussed in detail. The critical conditions are considered for different shapes and places of generation of the PDLs. It is shown that the misfit parameter is the principal factor, which determines the energetic preference of PDL generation: the latter is energetically favorable when the misfit parameter reaches its critical value, which depends on the geometry parameters of a composite nanostructure and the PDL type. Regardless of the place of PDL generation, the most energetically favorable case is when the PDL is elongated along the interface. The generation of PDLs from the free surface is the most preferable for small thicknesses of the shells (films). Growth of the shell (film) leads to a change of places of PDL generation while maintains their preferential shape – elongated along the interface. Among the six composite nanostructures under consideration, the tri-nanolayers are the least stable to the PDL generation. The hollow nanoparticles and nanowires are more stable to the PDL generation than the bulk ones. The bi-nanolayers are the most stable to the PDL generation.

Generation of dislocation loops in strained quantum dots embedded in a heterolayer

The generation of prismatic dislocation loops in strained quantum dots is investigated. The quantum dots are embedded in a film-substrate heterostructure with mechanical stresses caused by the difference between the lattice parameters of the film (heterolayer) and the substrate. The intrinsic plastic strain e m of a quantum dot arises from the misfit between the lattice parameters of the materials of the quantum dot and the surrounding matrix. The interface between the heterolayer and the substrate is characterized by a misfit param- eter f . The critical radius of a quantum dot R c at which the generation of a dislocation loop in the quantum dot becomes energetically favorable is analyzed as a function of the intrinsic plastic strain e m and the misfit param- eter f . © 2004 MAIK "Nauka/Interperiodica".

Generation of Prismatic Dislocation Loops in Silicon Crystals

Generation of Prismatic Dislocation Loops in Silicon Crystals