The role of a Cu buffer layer on the formation of iron silicide nanostructures is investigated using scanning tunneling microscopy and Mossbauer spectroscopy. The deposition of 1 angstrom Fe on the Si(111)-7 x 7 and the Si(111)-5 x 5-Cu surfaces results in the self-organization of nanoscale islands. Increasing the deposition temperature (300-600 degrees C) leads to an exponential decrease in island density and to an increase of the average island size. At 475 degrees C, the preferential nucleation site changes from the terrace to the step edges, i.e., step flow growth is observed. The self-assembled nanostructures exhibit the metastable CsCl-FeSi1+x structure. Due to the enhanced diffusion, nanodots formed on the 5 x 5 surface are significantly larger and more separated compared to growth on the bare 7 x 7 surface. These results show that a buffer layer provides an additional, experimentally controllable parameter, besides temperature, to tailor the size and distribution of nanodots. (C) 2008 American Institute of Physics.