Interaction Between Dislocations and Misfit Interface
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Interaction Between Dislocations and Misfit Interface A. Kuronen, K. Kaski, L. F. Perondi1 , and J. Rintala Helsinki University of Technology, Laboratory of Computational Engineering P.O.Box 9400, FIN-02015 HUT, FINLAND 1 Permanent address: Instituto Nacional de Pesquisas Espaciais – INPE P.O.Box 515, 12–227–010 S˜ao Jos´e dos Campos – SP, Brazil ABSTRACT Mechanisms responsible for the formation of a misfit dislocation in a lattice-mismatched system have been studied using Molecular Dynamics simulations of a two-dimensional Lennard-Jones system. Results show clearly how the strain due to the lattice-mismatched interface acts as a driving force for migration of dislocations in the substrate and the overlayer and nucleation of dislocations in the overlayer edges. Moreover, we observe dislocation reactions in which the gliding planes of dislocations change such that they can migrate to the interface. INTRODUCTION Dislocations play an essential role not only in strength properties of ductile materials but also in strain relaxation processes of lattice-mismatched hetero-structures [1–3], that are central in todays nanotechnology. When in a lattice-mismatched hetero-structure the thickness of the overlayer is small enough, the mismatch is accommodated by elastic deformation of the overlayer. When the thickness increases, the elastic energy of the overlayer becomes larger and at a certain critical thickness it becomes favorable to relieve the strain by misfit dislocations at the interface. Various mechanisms of dislocation migration and nucleation have been found to affect the strain relaxation process [1, 3]. These mechanisms include the migration of threading dislocation to the interface, nucleation of dislocations, and dislocation multiplication [4– 7]. In all these mechanisms the underlying atomic level cause of the misfit dislocation formation is the attractive force exerted by the interface on dislocations with Burgers vector orientation appropriate for the relaxation of misfit energy. In the present work, we investigate the migration of dislocations and their effect on strain relaxation in an atomistic model of a hetero-structure. We will study the effect of the misfit interface on the migration of dislocations initially present in the system, nucleation of dislocations in the overlayer edges, and the effect of the interface on the interaction between dislocations, by using Molecular Dynamics (MD) simulations. In order to explore the qualitative behavior of dislocation dynamics and for simplicity inter-atomic interactions have been modeled by Lennard-Jones (LJ) potentials. We have restricted our investigations to two-dimensional (2D) systems, thus avoiding the geometrical complexities involved in the simulation of three-dimensional dislocations while retaining salient features of the problem under consideration. COMPUTATIONAL DETAILS In order to get better insight to the dislocation dynamics we have constructed a computational model that is based on an interactive simulation program with a graphical visualB4.9.1
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