Abstract
The halogen-adsorbed Si(111) surfaces were investigated at the very low coverage with scanning tunneling microscope (STM) and surface differential reflectance (SDR). From SDR spectra, we determined the densities of the reacted adatom dangling bonds and the broken adatom back bonds. At the initial stage, STM images showed that the bromine atoms tended to be adsorbed on the site adjacent to the bromine adsorbed ones, in contrast to the behavior of chlorine atoms. The poly-bromide formation was found with STM above 0.1 ML. This coverage is consistent with that shown by SDR spectra, which revealed bromine atoms begin to break adatom back bonds at lower coverage than chlorine does. In the case of chlorine atoms, the back bond breaking does not take place until 0.3 ML. The origin of the different behavior was discussed in terms of the local modification of electronic states and the reactivity between Si surface and each halogen atom.
