Scanning tunneling microscopy of charge transfer on the Si(111)7 × 7 surface

The sodium-adsorbed Si(111)7 × 7 surface has been imaged using a scanning tunneling microscope. Center adatoms initially reacted with sodium atoms and appeared dark in the filled state image. When the sodium coverage reached about 0.04 monolayer, the empty state image showed bright maxima at the rest atom sites. We suggest that this image is due to the charge transfer from the rest atom to the adatom induced by sodium adsorbates.