MICROMECHANICAL ANALYSIS OF SURFACE-DEFECTS

Many overlayer/substrate systems exhibit a form of thin-film growth, w hich involves a layer-by-layer mode, subsequently switching to a three -dimensional growth (Stranski-Krastanov [SKI). This phenomenon has ser ious material implications because the layer-by-layer growth mode is o ften preferred in a number of important engineering applications. Rece nt experimental evidence suggests that the SK mode and resulting morph ologies are controlled by local interactions among defects on growing crystal surfaces and cannot be properly characterized on the basis of thermodynamics alone. Surface defects corresponding to adatoms, vacanc ies and steps, together with misfit dislocations interact with each ot her affecting and often dominating the kinetic processes. Little work has actually been done in this area and problems of fundamental import ance such as the elastic interaction between an adatom and a step or a misfit dislocation have not been addressed. The theoretical modeling that will be discussed here is focused on the local elastic field in t he vicinity of adatoms, vacancies and steps as well as on issues invol ving their interaction. To obtain the near-the-defect behavior, a modi fied lattice theory is employed; this approach was developed by extend ing the eigenstrain concept into the classical lattice theory. Green's functions for infinite and semi-infinite lattice spaces are derived a nd verified by comparing their asymptotic expressions with the corresp onding continuum solutions. The analysis establishes the fact that dif ferences between lattice and continuum solutions exist only in a small neighborhood of the defect. A Local Lattice Method (LLM) is subsequen tly proposed to study near defect deformation when a lattice level sol ution is required. It is shown through examples that the LLM is a simp le and effective numerical scheme, regardless of the problem geometry.