Promoted oxidation of the K-modified Si(100) (2×1) surface: Electron-energy-loss-spectroscopy and thermal-desorption studies

The interaction of the K-covered Si(100) (2×{}1) surface with oxygen has been investigated by the use of high-resolution electron-energy-loss spectroscopy and thermal-desorption spectroscopy. It was found that the mechanism of enhanced oxidation of the K-modified Si(100) (2×{}1) surface is dependent on the fractional K coverage ΘK. At low coverage (ΘK{≤}1), K atoms reduce the work function of the Si surface, thus increasing the initial sticking probability of oxygen; the oxygen atoms are bonded to Si and potassium oxides are not formed. However, at high coverage (ΘK>1), K adatoms are bonded to oxygen and potassium oxides (K₂{O}₂$, ${KO}₂$) are formed; the promoting mechanism is related to the thermal decomposition of these oxides which play the role of an ``oxygen reservoir.''