Structure of the Ag/Si(111) surface by scanning tunneling microscopy

We present the first real-space images, obtained by scanning tunneling microscopy, which show the ordered atomic structures of the Ag/Si(111) surface for several submonolayer coverages. The (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} surface is shown to be of the honeycomb structure, and the room-temperature coverage is determined to be theta=(2/3). The (1\ifmmode\times\else\texttimes\fi{}3) overlayer consists predominantly of rows of Ag atoms separated by two empty rows. At low coverage the surface shows long-range 7\ifmmode\times\else\texttimes\fi{}7 order, but patches occur within the 7\ifmmode\times\else\texttimes\fi{}7 cells whree Si adatoms are absent.