Inversion of growth speed anisotropy in two dimensions.

An inversion of the triangular shapes of the two-dimensional islands observed in a narrow temperature range by scanning tunneling microscopy during growth of Pt on Pt(111) is reported. This phenomenon is due to the inversion of the growth speed ratio of the two types of close packed step edges. It is tentatively traced back to an inversion in the hierarchy of the atom diffusion speeds along the two types of step edges in this temperature range