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

Abstract

The adsorption and desorption of H 2O 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 H 2O 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 H 2O is observed either by MDS or by TDS. The thermal desorption spectrum of H 2 (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 SiO 2 bonds exist. A detailed description of the adsorption and desorption of H 2O is given by comparing both spectra of MDS and TDS and a model is proposed.