Regensburg 2007 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 20: Symposium: Real Time Growth Studies I
DS 20.6: Vortrag
Donnerstag, 29. März 2007, 10:45–11:00, H32
Coarsening kinetics of facetted 2D islands: theory and Monte Carlo simulations — •Vladimir Kaganer1, Wolfgang Braun1, and Karl Sabelfeld2 — 1Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin — 2Weierstraß-Institut für Angewandte Analysis und Stochastik, Mohrenstr. 39, 10117 Berlin
Two coarsening mechanisms, Ostwald ripening and dynamic coalescence, are studied by means of kinetic Monte Carlo simulations. Ostwald ripening is the leading coarsening mechanism in absence of a step edge barrier, while dynamic coalescence takes place if an exchange of atoms between islands is prohibited by a step edge barrier. We find that the coarsening laws qualitatively change at large bond energies or low temperatures, when the 2D islands become facetted. Ostwald ripening proceeds through a sequence of ’magic’ sizes corresponding to square or rectangular islands and becomes attachment-limited, but the Wagner’s asymptotic law is reached after a very long transient time. The unusual coarsening kinetics obtained in Monte Carlo simulations are well described by the Becker-Döring equations of nucleation kinetics. We show that these equations can be applied to a wide range of coarsening problems. Dynamic coalescence is a result of the Brownian motion of the islands. For large bond energies, the island diffusion coefficient becomes size-independent and the size distribution becomes monotonously decreasing. The results of the kinetic Monte Carlo simulations are supported by numerical solutions of the Smoluchowski equations.