Early stages of H 2O adsorption on clean Si(100)

Abstract

Clean and smooth Si(100) surfaces have been exposed to low doses of water vapor, up to 100 L at most, under ultra-high vacuum. Structural and electronic property changes of the surface have been studied by LEED, AES and photoemission yield spectroscopy. Special attention has been payed in order to get a quantitative indication of the oxygen coverage, by a careful calibration of the Auger lines. It is found that the first stage of adsorption saturates when all the dangling bonds are removed, at an oxygen coverage of 0.25 monolayer. This result is in contradiction with the model where H 2O dissociates into H and OH, each one removing one dangling bond, which would give 0.5 monolayer at saturation. In agreement with similar observations made in the dissociative interaction of NH 3 with Si(100), we propose that either H or OH is able to remove the two dangling bonds of a surface Si dimer.