  A bimodal size distribution of two dimensional islands is inferred during
interface formation in heteroepitaxial growth of Bismuth Ferrite on (001)
oriented SrTiO3 by sputter deposition. Features observed by in-situ x-ray
scattering are explained by a model where coalescence of islands determines the
growth kinetics with negligible surface diffusion on SrTiO3. Small clusters
maintain a compact shape as they coalesce, while clusters beyond a critical
size impinge to form large irregular connected islands and a population of
smaller clusters forms in the spaces between the larger ones.
