G. Rosenfeld

Stability of two-dimensional clusters on crystal surfaces: from Ostwald ripening to single-cluster decay

An overview is given of recent work on the decay of two-dimensional clusters on a Ag(111) surface. Experimental studies using scanning tunnelling microscopy are presented, and various approaches to extract quantitative information on the relevant atomic processes from cluster decay experiments are discussed. It is shown that for typical surface morphologies, the decay rate of individual clusters depends critically on their local environment. Quantitative analysis therefore generally requires complex and detailed case-by-case modelling involving numerical methods. This difficulty can be overcome experimentally by preparing well-defined model structures for which an analytical description can be used without any loss of accuracy.

Dynamics of vacancy island coalescence on Ag(111)

The reshaping of two-dimensional vacancy islands during coalescence has been studied experimentally on a Ag(111) surface at room temperature using a fast scanning tunneling microscope. Different stages of the coalescence event have been found: the initial break-up of the narrow region separating the two islands (neck formation), the subsequent widening of the neck until an elongated shape has evolved, and the final relaxation to the equilibrium shape, which is an equilateral hexagon with rounded corners. The relaxation time for reshaping is found to be a strong function of the island size: for coalescence events involving islands of a similar size it scales roughly with the third to fourth power of the island diameter.