Dynamics of resonant charge transfer in low-energy alkali-metal-ion scattering

Abstract

We show in this paper that measurements of charge-state distributions for S -1600 eV Li, Na, and K scattered from a clean Cu(001) surface provide an excellent probe of the dynamics of atom-surface charge transfer. The neutralization probabilities, measured as a function of the perpendicular velocities of the scattered atoms, are qualitatively different for the three species. These differences reflect the high sensitivity of the charge transfer in this energy range to the energies and lifetimes of the atomic resonances near the surface. The measured neutralization probabilities are found to depend on the parallel velocity component of the scattered atom, even though the velocities at which these experiments are conducted are relatively low. The data are compared to several models of the charge-transfer process.Agreement with the data is achieved using a model based on the one-electron Newns-Anderson Hamiltonian and using calculated values for the alkali-metal resonance parameters.

Thermally Enhanced Neutralization in Hyperthermal Energy Ion Scattering

“…Above 100 eV, the exponential dependence is no longer present, and P 0 increases. The strong projectile-surface interaction dominates at these higher velocities, giving an increased neutral occupancy, or as we measure it, a larger P 0 value [14]. Therefore, the non-monotonic change observed for P 0 indicates that both energyand coupling-dominated charge transfer occur in this system at 350 K.…”

“…If a projectile leaves the surface slowly, the energetically-favored charge state can be tracked to large distances, where the coupling is very small. In this case, the velocity dependence is classified as energydominated, and an exponential dependence of P 0 on the inverse perpendicular velocity is obtained [14]. Conversely, higher velocity projectiles only track the energetically-favored charge state near the surface where the coupling is large.…”

Internal electronic structure of adatoms on Fe(110) and Fe(100) surfaces: A low-energyLi+scattering study

“…We neglect the parallel velocity effect as it was found to be small in Li scattering. 26 Using this assumption, the velocity v r in Eq. ͑1͒ can be expressed as v cos , where v is the total velocity and is the exit angle with respect to the surface normal.…”

“…26,27 Thus, for a given scattering angle, the neutralization probability changes with the incident ion energy. As the energy decreases, the neutralization process becomes more adiabatic, which in the present case produces more neutrals since the work function of Fe ͑4.6 -5.1 eV͒ is smaller than the ionization potential of Li ͑5.39 eV͒.…”

Charge Transfer Dynamics in Atom-Metal Surface Collisions

“…The first, very often used in the literature, e.g. [11,22], takes into account the image interaction in its canonical form which in atomic units reads where ε A (∞) (A(∞)) is the ionization (affinity) energy level, φ is the work function and z0 is the parameter which takes into account the image shift saturation when the atom gets close to the surface. As the second form for z-dependence of the ionization and affinity levels, we take the expressions given in Ref.…”