  We report a direct STM observation of Ge hut array nucleation on the Si(001)
surface during ultrahigh vacuum molecular-beam epitaxy at 360C. Nuclei of
pyramids and wedges have been observed on the wetting layer MxN patches
starting from the coverage of about 5.1 \r{A} (~3.6 ML). Further development of
hut arrays consists in simultaneous growth of the formerly appeared clusters
and nucleation of new ones resulting in gradual rise of hut number density with
increasing surface coverage. Huts nucleate reconstructing the patch surface
from the usual c(4x2) or p(2x2) structure to one of two recently described
formations composed by epitaxially oriented Ge dimer pairs and chains of four
dimers.
