Electron-stimulated desorption of positive ions from Na nanoclusters adsorbed on Pt(111) and Ar,H2O,andSF6spacer layers

Abstract

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 ${\mathrm{Na}}^{+}$ yield is enhanced markedly at the smallest coverage and decay steeply with increasing coverage. We interpret that ${\mathrm{Na}}^{+}$ is emitted via Coulomb explosion of the adsorbed Na nanoclusters in which valence holes are confined, i.e., localized. Very few ${\mathrm{Na}}^{+}$ ions are emitted from the Na nanoclusters adsorbed on the Pt(111) and ${\mathrm{H}}_{2}\mathrm{O}$ substrates. The complete suppression of the ${\mathrm{Na}}^{+}$ 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 ${\mathrm{H}}_{2}\mathrm{O}$ nanoclusters on the Ar substrate as revealed from the evolution of hydrated ${\mathrm{Na}}^{+}$ ions prior to bare ${\mathrm{Na}}^{+}$ ions. The formation of Na nanoclusters is suppressed on the ${\mathrm{SF}}_{6}$ substrate due to reactions, resulting in a much smaller ${\mathrm{Na}}^{+}$ yield than that from the Ar substrate.