The Dynamics of Resonant Charge Exchange in Low Energy Ion-Surface Interactions
Abstract
I have studied the dynamics of resonant charge exchange for low and hyperthermal energy alkali ions scattered from clean and adsorbate-covered copper surfaces as a function of incident species, incident energy, scattering geometry and adsorbate coverage. The experiments were performed in an ultra high vacuum chamber which is equipped with a low and hyperthermal energy beamline. I measured neutralization probabilities for potassium and lithium scattered from alkali adsorbate-covered Cu(110) and Cu(001). As expected from most models of resonant charge transfer, I found experimentally that very small coverages of alkali adsorbates on the surface can dramatically increase the neutralization probability. However, the dependence of the neutralization probability on adsorbate coverage is qualitatively different from that expected on the basis of the adsorbate-induced work function change. A treatment of the charge transfer based on the spinless Newns-Anderson Hamiltonian explains the data only if the local electrostatic potential of the adsorbate overlayer is included in the calculations. I also measured the neutralization probability of low and hyperthermal energy (5 {rm eV}<= E_{i}<=1600 eV) lithium (Li), sodium (Na) and potassium (K) scattered from clean Cu(001) as a function of energy and scattering geometry. For these experiments, I developed a time-of -flight neutral detector to measure the velocity- and angle -resolved flux of scattered ions and neutrals. The neutralization as a function of the final velocity of the scattered atoms is found to be qualitatively different for the Li, Na and K. Several models of resonant charge exchange are considered, and a model based on the Newns-Anderson Hamiltonian gives the best agreement with the data. The models depend on the lifetimes and energies of the atomic state in the vicinity of the metal surface, and comparing the models to the data places tight constraints on the magnitude of the lifetimes. I also observed that the neutralization of Na is very sensitive to the parallel velocity component of the scattered atom even at velocities which are quite small compared to the Fermi velocity.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- January 1992
- Bibcode:
- 1992PhDT.......135K
- Keywords:
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- CHARGE EXCHANGE;
- Physics: Condensed Matter