A model is presented for the formation of excited Ag-* (4d(9)5s(2)) atoms during sputtering of Ag metal by energetic Ar+ ions. The essential part of the formation process is the slow diffusion of 4d holes in the collision cascade from the sites of violent Ag-Ag collisions to the emitted Ag atoms. A computer simulation of Ag cascades and of the 4d-hole transport allows us to quantify the model and to describe all characteristic features of the available experimental data, in particular the fact that the sputtered Ag-* atoms exhibit a narrower kinetic energy distribution than those ejected in the electronic ground state.

Charge state-resolved time-of-flight spectra were collected for 2.0 keV Na-23(+) scattered from Au nanoclusters deposited on TiO2(110). The neutral fraction of Na scattered from metallic Au is low (similar to3%), but it is surprisingly high (up to 50%) for small clusters. The results demonstrate that alkali ions couple to electronic states specific to the nanoclusters, and that the energy of the states is a function of the nanocluster size. This technique provides a new method for the spectroscopy of nanomaterials.

The neutralization of 400-3000 eV Li-7(+) ions scattered from clean and adsorbate-covered Fe(110) and Fe(100) surfaces was measured with time-of-flight spectroscopy. Li singly scattered from bromine, iodine, and cesium adatoms has a consistently larger neutral fraction than that for scattered from substrate sites. This suggests that the local electrostatic potential directly above these adatoms is reduced from that of the clean substrate. The neutral fraction of Li scattered from halogen adatoms is surprising in that it decreases as the emission angle moves off-normal, yet increases in the usual manner for cesium and silver adatoms. This indicates that the charge distribution associated with a halogen adsorbate is nonuniform, most likely due to internal polarization. A semiquantitative theoretical analysis shows that a nonuniform internal electron density would give rise to the observed behavior. The polarization of halogen adatoms is likely responsible for anomalous work function changes observed previously. Alkali-ion scattering is shown to be an effective tool for detecting the internal electronic structure of an adatom.

The absolute ionization probability of energetic ( > 500 eV) particles recoiled from Al(100) by 2 and 5 keV Xe+ bombardment was measured with time-of-flight spectroscopy. These values were then used to calibrate the energy and angular distributions of low-energy (10-600 eV) sputtered ions collected with an electrostatic analyzer. The independent-particle model of nonadiabatic surface-atom charge exchange, which is typically used to analyze single scattering events, was applied to the ion fractions of the recoiled and sputtered atoms. The model describes all the experimental data from a few eV to the keV range if a different surface electronic temperature is used for recoiling and sputtering. This suggests that the ionization process depends on the instantaneous surface condition at the time of ion emission.