INSITU OBSERVATION OF WATER-ADSORPTION ON SI(100) WITH SCANNING TUNNELING MICROSCOPY

The room-temperature adsorption of water has been studied on nominally flat and on vicinal Si(100)(2 x 1) surfaces tilted towards [011] using scanning tunneling microscopy. It is observed that water adsorbs in small islands via a molecular precursor state. Its dissociation products are uncapable of breaking Si back- and dimer bonds. Therefore the step structure on the surfaces remains unchanged. On the saturated surface isolated unoccupied Si dangling bond sites are found which can oscillate between the two ends of a dimer. After water adsorption the density of missing dimer defects is much lower than observed on the clean surface and also lower than the values usually reported in literature. From this observation it is suspected that a certain fraction of ''missing dimer defects'' usually seen on Si(100) are actually adsorbate saturated sites.