A. Bonanno

The excitation of collective electronic modes in Al by slow single charged Ne ions

Abstract We have studied electron emission from decay of plasmons excited in the interactions of slow single charged Ne ions with Al surfaces as a function of incident energy ranging from 0.7 to 8 keV. Bulk plasmon excitation occurs above a threshold incident energy of ∼1 keV and initially coexists with potential excitation of surface modes. The excitation of bulk plasmons in Al is determined by fast electrons traveling inside the solid.

Bulk and surface plasmon excitation in the interaction of He+ with Mg surfaces

Abstract We report on studies of plasmon excitation in Mg under the impact of slow He + ions in the incident energy range 0.1–0.5 keV. Consistent with studies on Al surfaces, a transition from surface to bulk plasmon excitation occurs as the energy of the ion is increased. Previous methods in the literature to obtain information about yields of electron emission from plasmon decay are discussed. A new data analysis procedure is presented, which allows disentangling the contributions to the experimental spectra arising from different emission mechanisms, showing that potential excitation of multipole surface plasmons gives an important contribution to electron emission.

Al target 2p electron excitation in asymmetric collisions with very low energy Ne+ projectiles

Abstract We present a study on the 2p electron excitation in Al target atoms in very low energy asymmetric collisions with lighter Ne+ projectile ions. We show that one of the L-shell vacancies originally present in Ne 2p3, created by double 4fσ electron promotion from Ne 2p5 or 2p53s, can be transferred to the Al partner through a two-electron autoexcitation mechanism. Our results provide an interesting interpretation for the previously observed lower threshold energies for target Al LMM Auger emission for Ne+ impact than for Ar+, Kr+, and Xe+.

On the origin of Ne2+ production in low-energy Ne+ scattering from Al and Si surfaces

Abstract We report an investigation on the inelastic energy loss of doubly charged Ne2+ ions produced in the single scattering of Ne+ from Al and Si surfaces. The inelasticity of 86 ± 5eV found in the binary encounter agrees well with the energy needed to excite two electrons from Ne+ to Ne2+*. Our results suggest that direct decay or autoionization decay of Ne+** formed subsequently by capturing one electron from the solid is the main mechanism for the production of Ne2+ detected in ion-scattering spectroscopy.

Sub-threshold plasmon excitation in free-electron metals by helium ions

Abstract In this work, we re-examine sub-threshold plasmon excitation by ions measuring the energy distributions of electrons emitted from Al and Mg under the impact of 0.16–4 keV single charged Helium ions. Electron energy distributions for the case of He+ projectiles contain well distinguished structures that confirm the excitation of multipole surface plasmons, due to the potential energy released by the neutralization of incoming ions. It is shown that electron emission from multipole plasmon decay is more intense than from Auger neutralization (AN). Our experiments indicate that scattering and cascade in the solid of electrons excited by plasmon decay and by AN may give an important contribution to electron emission.

Atomic versus bulk Al Auger electron emissin induced by noble gas ion bombardment

We present an angle resolved study on the Auger electron emission from an Al surface uneer noble gas ion bombardment along the normal incidence direction for primary energies varying from 5–15 keV. We show that the intensity ratio between the atomic LMM and the bulk LVV features decreases according to an inverse cosine law as the detection goes from normal to grazing directions and that such ratio changes considerably with the primary ions (Ar+, Kr+ and Xe+). These results provide important information on the deexcitation mechanism of the core excited Al particles.

Double 2p electron excitation in low-energy Ne+ single scattering from a Si surface : an energy loss study

Abstract Results of 1950 eV Ne+ single scattering from a Si surface show that all the backscattered Ne+ ions have suffered severe inelastic energy loss and the total inelasticity in the close binary encounter amounts to 45 ± 4eV. This value is well beyond that required for one-electron excitation from the neutralized Ne0, but agrees well with that for the double 2p electron excitation of a neutralized Ne to 2p4(1D)3s2. These findings contrast the re-ionization model proposed by Souda et al. [Phys. Rev. Lett. 75 (1995) 3552; Surf. Sci. 363 (1996) 139], and confirm that the formation of autoionization states which decay far away from the surface is the main mechanism for Ne+ scattered from Si.

Ar L-shell and metal M-shell Auger electron emission for 14 keV Ar+ ion impact on Ca, Sc, Ti, V, Cr, Fe, Co, Ni, and Cu

Abstract Ar projectile L-shell and metal target M-shell Auger electron emission have been studied by 14 keV Ar+ ion bombardment on Ca, Sc, Ti, V, Cr, Fe, Co, Ni, and Cu targets at an incidence angle of 60° with respect to the surface normal. We observe that the width of the Ar Auger peak progressively reduces and its total intensity decreases exponentially with increase of the target atomic number and that the metal M-shell autoionization peaks are completely absent.

Evidence of alkali adatom island formation induced by ion bombardment on a Na covered Pt surface

Abstract We report on adatom island formation induced by Ne + ion bombardment on a Na covered Pt surface. By using the collisionally excited autoionization electron spectroscopy (CEAES) we observe that, for large initial coverages, ion impact causes the Na adatom aggregation creating large surface areas which are relatively Na-rich and Na-depleted. Decay of excited atoms above these alkali islands and above the more or less clean Pt substrate zone with very different work functions results in the splitting of each atomic transition line in two well separated components.

Angle resolved lineshape study of the Al main L2MM Auger atomic peak

Abstract By studying the angle-resolved lineshape of the few keV Ar+ induced Al main L2MM atomic Auger peak we show that the double core electron promotion can occur even in collisions with a relatively large closest approach distance R as long as the interaction time T is sufficiently long. Based on simple calculations using the formalism of classical mechanics we further indicate that the excitation probability can be simplified as a product of two step functions of R and T with unique cut-off values.