Interaction of Hollow Atoms with Surfaces

Abstract

Experimental and theoretical methods for studying the formation of hollow atoms during the interaction of slow, highly charged ions with surfaces are reviewed. Particular attention is devoted to the emission of Auger electrons and the creation of plasmons near the surface. To exhibit the static aspect of hollow atoms, Hartree-Fock and Density Functional methods were used to evaluate electron charge densities above and below the surface. The dynamic properties of hollow atoms are revealed by means of cascade models which include the filling of inner shell orbitals via Auger transitions and collisional charge transfer. The theoretical results are compared with experiments of electron emission at energies from a few eV to a few hundred eV. In the electron spectra, Auger peak structures are shown to yield information about the filling of the hollow atom within the first atomic layers of the surface. Low-energy electrons ejected from an Al surface were measured to study spectral structures found near 11 eV attributed to the decay of plasmons. Absolute electron yields from the plasmon decay were primarily studied as a function of the incidence angle of the projectile. Finally, recent experiments revealing spectral structures near 6.5 eV which may be associated with the creation of surface plasmons.