Adsorption and desorption of H2O on potassium precovered Si(100)2 × 1 surface

The adsorption and desorption of H2O on a potassium precovered Si(100)2 × 1 surface have been studied using MDS (metastable deexcitation spectroscopy) and TDS (thermal desorption spectroscopy). It is concluded that H2O is dissociatively attached to a 1 ML K/Si(100)2×1 surface as OH and H at a dosing less than 1 langmuir at room temperature, because no molecularly adsorbed H2O is observed either by MDS or by TDS. The thermal desorption spectrum of H2 (mass 2) consists of two peaks. The lower temperature peak at 140°C is attributed to the hydrogen of a OH species bound to a Si atom. The higher temperature peak at 510°C is caused by hydrogen bound to Si dangling bonds. The thermal desorption spectrum of SiO (mass 44) has two peaks. The SiO desorption peak at 280°C suggests that bonds weaker than the usual SiO2 bonds exist. A detailed description of the adsorption and desorption of H2O is given by comparing both spectra of MDS and TDS and a model is proposed.