Dendritic to non-dendritic transitions in Au islands investigated by scanning tunneling microscopy and Monte Carlo simulations

We investigated the structures of the two-dimensional Au islands grown on $\mathrm{Ir}(111)$ and $\mathrm{Pt}(111)$ using scanning tunneling microscopy and Monte Carlo simulations. We found that the Au islands have dendritic, triangularly compact, and irregularly compact shapes depending on the underlying substrate. We also found a strong layer dependence of the island density. Monte Carlo simulation results demonstrate that the fractal dimensions of these dendritic islands are determined by competition between terrace diffusion and edge diffusion of adatoms. Furthermore, the fractal dimension changes continuously from about 1.7 to 2 as a function of the edge diffusion barrier, which is discussed on the basis of the generalized diffusion limited aggregation model.