Low-energy ion neutralization at surfaces: Resonant and Auger processes

Abstract

The interaction of He ϩ with a typical metal surface ͑Al or Pd͒ is described, analyzing in detail the different mechanisms that contribute to the neutralization of the projectile when backscattered from the surface. Auger and resonant neutralization processes are considered and analyzed including a detailed quantum-mechanical description of the He-metal interaction, for projectile energies between 100 eV and 3 keV. We show that the promotion of the He-1s level, due to its interaction with the metal-atom-core orbitals, is the crucial mechanism making resonant processes operative. We find, however, that resonant processes are much more important for Al than for Pd. In Al, both Auger and resonant processes are equally important for neutralization of the ion, while for Pd we find that Auger is the dominant mechanism, making the He/Pd system the ideal case for which Hagstrum's exponential law appears to be practically valid for all velocities. We also find qualitative agreement with experimental data, which we consider a satisfactory result in view of the fact that our theory is a complex ab initio calculation free of adjustable parameters.

Auger neutralization and ionization processes for charge exchange between slow noble gas atoms and solid surfaces

“…However, Merino et al [144], More et al [145], and van Someren et al [146] pointed out that the He-1s level shift might be substantially reduced compared to the classical behavior for distances of some atomic units in front of the surface, as a consequence of a breaking down of the classical image-potential concept at close distances. Actually, theoretical calculations of the He-1s level energy shift showed reduced values or even negative shifts close to the surface as a result of chemical interactions with the surface [36,144,145,147]. Similar deviations from the classical behavior were also calculated for the 1s state of H [30,31], for excited states of He in front of an Al surface [148], and predicted for other systems [37].…”

“…This is the relevant configuration to look at since scattering of He is produced in the collision with a target atom. The diabatic level is taken from [36] and the different adiabatic levels are obtained when the hopping interactions between the 1s level of He and the different orbitals of Al are connected. At distances larger that ca.…”

“…1). Resonant processes, being one-electron ones, have been described abundantly in the literature, practically for any atom/solid combination, using different techniques [8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38].…”

Ab initioelectronic stopping power and threshold effect of channeled slow light ions inHfO2

“…Although the empty KS level does not provide the exact description of the real excited states of the nanostructure, this can be considered as the first approximation to the true excitations of the system [58,59]. Since the occupied He-1s level is strongly affected by the interaction distance [60][61][62][63]. So charge transfer behavior may differ for different trajectories.…”

LEIS: A reliable tool for surface composition analysis?

“…From this, the surviving probabilities P + in and P + out for incoming and outgoing trajectories are obtained as In the "reionization regime", collision induced processes, i.e. collision induced neutralization (CIN) and reionization (CIR), become possible for a minimum distance between projectile and scattering centre smaller than a critical value R min (E,θ) due to the evolution of molecular orbitals [7], [8], [9]. In the collision between the projectile and a target atom, a minimum distance smaller than R min is reached if for a fixed scattering angle θ − the projectile energy E exceeds a certain threshold E th .…”