Plasmon Excitation and Electron Promotion in the Interaction of Slow Na+ Ions with Al Surfaces

We studied the energy distributions of electrons emitted in the interaction of slow Na+ ions with polycrystalline Alsurfaces. To study sub-threshold plasmon excitation we performed measurements as a function of emission angle whichshowed the excitation of bulk plasmons, confirming the kinetic nature of the excitation process.Electron spectra show narrow transition lines due to Auger decay in vacuum of sodium projectiles excited in the2p-shell by electron promotion in collisions with Al target atoms. Several previously unidentified transition lines couldbe attributed to the autoionization of doubly excited projectiles. 2004 Elsevier B.V. All rights reserved.