Assignment of rest-atom surface core-level shift through adsorption-site selectivity of methoxy on Si(111)-7×7

The formation of the methoxy species on Si(111)-(7×7) upon methanol adsorption leads to a strongly selective extinction of the rest-atom feature in the valence-level photoemission spectrum. The Si $2p$ surface core level at lowest binding energy is likewise removed in this process, demonstrating that this feature is related to charge distribution around the rest atom, an assignment that has been subject to controversy in the literature. The formation of a Si-O bond upon methoxy adsorption leads to marked changes in the Si $2p$ spectrum that are discussed in terms of the characteristics of this chemisorption bond.