Scanning tunneling microscopy has been used to study the initial stages of
room-temperature adsorption of Ba atoms on a clean Si(100)-(2 X 1) surface.
It is found that most Ba atoms an located at type C defects, which stabili
zes the dimer buckling in their vicinity, while the rest are located at sin
gle dimer sites on top of the Si dimer rows. Analysis of the images reveals
that the Ba-Si(100) interactions are mediated by a partial charge transfer
from the adsorbate to the substrate. [S0163-1829(99)03207-5].