  The interaction of Mn with Ge quantum dots (QD), which are bounded by {105}
facets, and the strained Ge wetting layer (WL), terminated by a (001) surface,
is investigated with scanning tunneling microscopy (STM). Mn is deposited on
the Ge QD and WL surface in sub-monolayer concentrations, and subsequently
annealed up to temperature of 400 C. Bonding and surface topography were
measured with STM during the annealing process. Mn forms flat islands on the Ge
{105} facet, whose shape and position is guided by the rebonded step
reconstruction. The images show a hybridization of Mn-d band and empty states
of the Ge{105} facet. A statistical analysis of Mn-islands on the QD yields a
slight preference for edge positions, whereas the QD strain field does not
impact Mn-islands. The formation of ultra-small Mn-clusters dominates on the
Ge(001) WL, which contrasts the Mn-interaction with unstrained Ge(001)
surfaces. Annealing (<160 C) leaves the Mn-clusters on the WL unchanged, while
the Mn-islands on the Ge{105} facet undergo a ripening process, followed by a
volume gain attributable to the onset of intermixing with Ge. This is supported
by a statistical analysis of island volume, and size distribution. Increasing
the annealing temperature (220- 375 C) leads to a rapid increase in Mn-surface
diffusion evidenced by the formation of nanometer size clusters, which are
identified as germanide Mn5Ge3 by a mass balance analysis. This reaction is
accompanied by the disappearance of the original Mn-surface structures
completing Mn de-wetting. This study unravels the details of Mn-Ge
interactions, and demonstrates the role of surface diffusion as a determinant
in the growth of Mn-doped Ge materials.
