Determination of the onset of edge diffusion by temperature-dependent time-lapsed scanning tunneling microscopy demonstrated for dendritic Cu islands on Cu(111)

We investigate the shape of monatomic high Cu islands on a Cu(111) surface by variable-temperature scanning tunneling microscopy between 110 and 240 K. Low temperature dendrites evolve towards more compact shapes at increasing temperature; finally reaching the equilibrium shape of a hexagon with rounded corners. Despite a substantial variation for individual islands at each temperature, the mean fractal dimension increases monotonously between 170 K up to 240 K, from the smallest to the largest values feasible for islands grown on surfaces. Time-lapsed imaging at increasing temperature reveals the onset of shape change to be at ≈ 170 K, corresponding to the onset of edge and corner diffusion of atoms along the island's borders.