  The interaction of cobalt atoms with silicon (111) surface has been
investigated by means of scanning tunneling microscopy (STM) and low-energy
electron diffraction (LEED). Besides the Co silicide islands, we have
successfully distinguished two inequivalent Co-induced
$\sqrt{13}\times\sqrt{13}$ reconstructions on Si (111) surface. Our
high-resolution STM images provide some structural properties of the two
different $\sqrt{13}\times\sqrt{13}$ derived phases. Both of the two phases
seem to form islands with single domain. The new findings will help us to
understand the early stage of Co silicide formations.

Materials Science;Other Condensed Matter