Atomic structural study of a Br-chemisorbed Si(111)-7 x 7 surface by using scanning tunneling microscopy

The atomic structure of a Br-chemisorbed Si(111)-7x7 surface is investigated by scanning tunneling microscopy. At low coverage, Br-reacted adatoms are distinguishable from unreacted adatoms in topographic images. The bias-dependent imaging suggests that the lowest tail of the antibonding state of the Br-Si bond is located about 1.5 eV above the Fermi level. At saturation coverage, a 7x7 structure is perfectly retained at room temperature and most adatoms remain after annealing at 400-630 degrees C. These results indicate that additional Br atoms cannot insert themselves into the Si-Si backbond between a Br-bonded adatom and a rest atom; therefore, SiBr is the only surface species present even at saturation coverage, which is not the case for F- or Cl-saturated Si(111) surfaces. (C) 1999 American Institute of Physics. [S0021-8979(99)05114-2].