Electron-stimulated desorption of positive ions from Na nanoclusters adsorbed on Pt(111) and Ar, H₂O, and SF₆ spacer layers

Electron-stimulated desorption of positive ions from supported Na nanoclusters has been investigated in terms of the localization or delocalization of valence holes, as well as the reaction of Na with the substrate or coadsorbed molecules. On the Ar substrate, the Na⁺ yield is enhanced markedly at the smallest coverage and decay steeply with increasing coverage. We interpret that Na⁺ is emitted via Coulomb explosion of the adsorbed Na nanoclusters in which valence holes are confined, i.e., localized. Very few Na⁺ ions are emitted from the Na nanoclusters adsorbed on the Pt(111) and H₂O substrates. The complete suppression of the Na⁺ emission is interpreted as a result of neutralization of nanoclusters due to electron transfer from the substrate, i.e., the delocalization of valence holes. Na tends to interact with the H₂O nanoclusters on the Ar substrate as revealed from the evolution of hydrated Na⁺ ions prior to bare Na⁺ ions. The formation of Na nanoclusters is suppressed on the SF₆ substrate due to reactions, resulting in a much smaller Na⁺ yield than that from the Ar substrate.