Open Access Dissertation
Date of Award
Physics and Astronomy
The formation of surface nanostructures such as islands or quantum dots during strained film epitaxy has attracted great interest in recent years. The underlying mechanisms have been attributed to the occurrence of morphological instabilities of the strained films, for which the coupling between film-substrate material properties and growth conditions play a major role. Morphological properties of an epitaxially grown film and the self-organization process of coherent strained islands are analyzed via the development of a continuum elasticity model based on the 2nd order perturbation method. Effects of wetting stress due to film-substrate interactions have been incorporated in the resulting nonlinear dynamic equation governing the film morphological profile. We study the formation and evolution of surface strained islands or quantum dots for different film/substrate misfit strains, via analyzing the time-dependent behavior of the structure factor for surface heights, its various moments, and the surface roughness. Three regimes of island array evolution have been identified, including a film instability regime at early stage, a slow power-law-type coarsening at intermediate time, and the crossover to a saturated state, with detailed behavior dependent on misfit strains but not qualitatively on finite system sizes. It is found to be controlled by the strength of film-substrate wetting interaction which would constrain the valley-to-peak mass transport and hence the growth of island height, and also determined by the effect of elastic interaction between surface islands and the high-order strain energy of individual islands at late evolution stage. The results are compared to previous experimental and theoretical efforts on quantum dots coarsening and saturation. We also study the formation of these nanostructures on a nonplanar patterned substrate. The properties of islands formed are highly affected and controlled by the periodicity and amplitude of the pre-defined substrate patterns and also the initial film thickness, as shown in our analytical results.
Gigiriwala Gamage, Champika, "Continuum Elasticity Modeling Of Nanostructure Evolution In Strained Film Epitaxy" (2012). Wayne State University Dissertations. 594.