THE ROLE OF ALKALI-METAL LAYERS IN THE OXIDATION OF SI AND GE SURFACES - A COMPARATIVE-STUDY

The oxygen uptake and related oxide formation on clean and alkali-metal-covered Si(100)2 x 1 and Ge(100)2 x 1 surfaces have been studied by core-level photoemission spectroscopy. On both substrates, the O(2) sticking probability is drastically increased in the presence of alkali-metal atoms (e.g. by at least four orders of magnitude). However, while on Si the room-temperature oxidation is promoted by the alkali-metal overlayer, an inhibition of the Ge surface oxidation occurs. This situation changes dramatically when the molecular oxygen exposure is performed at slightly enhanced Ge substrate temperatures (greater than or equal to 200 degrees C). In this case, the role of the alkali-metal overlayer is reversed with promotion of the Ge substrate oxidation. These results reveal new insights into the understanding of alkali-metal-promoted reactions.