Biased Ostwald ripening in site-selective growth of two-dimensional gold clusters

Nucleation, growth, and ripening of nanoscale Au islands formed on the Au(111) substrate have been investigated using variable temperature scanning tunneling microscopy. The Au(111) surface consists of two types of naturally occurring dislocations. After deposition of Au atoms at 115 K, a single nanometer-sized Au island is formed at each dislocation. Thermal annealing to 180 K causes gross mass transport in which Au atoms systematically move from one type of dislocation to the other. This leads to the preferential ripening of Au islands at one of the two types of dislocations, a phenomenon that has not been observed for any other metals deposited in Au(111). With repeated deposition and thermal annealing cycles, we have succeeded in obtaining two types of clusters with very different sizes: large clusters at the bulged elbow site and small clusters at the pinched elbow site.