CHARGE-TRANSFER AND PROMOTED OXYGEN-UPTAKE AT ALKYLATED SI(100) SURFACES STUDIED BY AUGER DEEXCITATION OF HELIUM METASTABLES

The electronic structure of alkali-metal (Cs, K) plus oxygen co-adsorption layers on the Si(100)2 x 1 surface has been probed by metastable de-excitation spectroscopy (MDS). Upon admission of oxygen to a Cs-saturated Si(100) surface, the emission intensity in MDS due to the Cs 6s approximately states rapidly decreased down to zero, which was compensated for by an increase of the emission from the Cs 5p level. An increase of the O 2p intensity presents a striking constrast to the decay of the Cs 6s approximately intensity, indicating that oxygen uptake is driven by direct charge transfer from the Cs 6s approximately to the O 2p. A metal pre-coverage dependence of the oxygen uptake kinetics was examined with a K/Si(100) system. The results are in favor of a local mechanism for the enhancement of oxygen dissociation due to the alkali-metal overlayer.