Evolution of threading dislocations in passivated thin film.
Abstract
Crystalline films grown epitaxially on substrate consisting of different crystalline material are of considerable interest in optoelectronic devices and the semiconductor industry. The film and substrate have in general different lattice parameters. This lattice mismatch affects the quality of interfaces and can lead to the formation of very high densities of misfit dislocations at the interface. Here we study the strengthening of a thin film on a substrate. In particular we consider the motion of a single dislocation gliding on its slip plane within the film and its interaction with multiple obstacles and external stress is calculated and the motion in response is determined. It is assumed that the passivation layer and the substrate to be of infinite strength compared to the metallic thin film. A phase field theory of dislocations for the evolution of single threading dislocation is used and simulated using 2D Fast Fourier Transform. This theory accounts for the interactions between the dislocations and an applied stress and between the dislocations lines and obstacles. The results obtained show a relation between the thin film thickness and the critical stress needed to move the threading dislocation. As the film thickness decreases it is observed that the yield stress increases in agreement with the experiments. The evolution of threading dislocations in a passivated metallic thin film is simulated and it shows that as the dislocation travels within the thin film region, it leaves a misfit dislocation at the interfaces of the thin film on the substrate covered with the passivation layer. The effect of various obstacles placed in the path of the evolution of the single threading dislocation in a metallic thin film is also determined. It is observed from the results that the presence of the obstacles impedes the motion of the threading dislocations.
Degree
M.S.M.E.
Advisors
Koslowski, Purdue University.
Subject Area
Mechanical engineering
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