Scanning-tunneling-microscope observation of 2 x 1 structure on a homoepitaxially grown Si(111) surface.

We have used scanning tunneling microscopy to study molecular-beam epitaxial growth on Si(111)7\ifmmode\times\else\texttimes\fi{}7 surface. On the homoepitaxially grown surface at 500 \ifmmode^\circ\else\textdegree\fi{}C, we find the small domains of non-DAS (dimer adatom stacking fault) rowlike ordered structures, the periodic rows of which run along the [011\ifmmode\bar\else\textasciimacron\fi{}] and [1\ifmmode\bar\else\textasciimacron\fi{}10] directions. The atomic configuration of these structures seems to be consistent with Pandey's \ensuremath{\pi}-bonded chain model for Si(111)2\ifmmode\times\else\texttimes\fi{}1 structure. We discuss two kinds of \ensuremath{\pi}-bonded chains, and the boundaries along the atomic rows between the 2\ifmmode\times\else\texttimes\fi{}1 and DAS domains.