Sputtering of Ag atoms into metastable excited states
Physical Review B (Condensed Matter)
We have investigated the processes that lead to the ejection of excited neutral silver atoms upon sputtering of a polycrystalline silver surface under bombardment with keV rare gas ions. Resonant multiphoton ionization in combination with time-of-flight mass spectrometry was used in order to allow a state-selective detection of the sputtered species. As a result, excited atoms in both states of the metastable multiplet 4d 9 5s 2 ( 2 D J ) with excitation energies of 3.75 eV ( 2 D 5/2 ) and 4.30
... 2 D 5/2 ) and 4.30 eV ( 2 D 3/2 ) have been detected. The total population of both states is determined to be of the order of 1%, which is surprisingly high in view of the large excitation energy. The velocity distribution of atoms ejected in both states reveals that the metastable atoms are ejected with lower average velocity than those emitted in the electronic ground state, thus indicating a mechanism populating this state which becomes less efficient with increasing emission velocity. The results are discussed in terms of a two-step model describing the formation of an excited neutral atom as a combination of collective excitation processes within the collision cascade followed by resonant electron transfer between the surface and the escaping particle.