ENERGY-TRANSFER, TRAPPING, AND THE INTERACTION POTENTIAL IN HYPERTHERMAL NA+ SCATTERING FROM CU(001)

In this paper we present measured energy and angular distributions for Naf scattering from Cu(001) with incident energies ranging from 10 to 100 eV. Excellent agreement with the measured spectra over the full r ange of incident energies is achieved with simulations using a scatter ing potential that consists of two parts, both of which we discuss in detail in this paper. The first is a sum of Hartree-Fock (Na-Cu)(+) pa ir potentials where the sum runs over the surface atoms nearest the sc attering ion. To this we add an attractive potential that approaches t he classical image potential fat from the surface, but saturates close to the surface. From these spectra we extract detailed information ab out the scattering dynamics, such as the scattering trajectories, ener gy transfer to the surface, and particle trapping. For energies below 100 eV we find that the scattering is particularly sensitive to the at tractive term in the potential. In particular, as the incident energy is reduced the scattered angular distributions broaden, the fractional energy transfer to the surface increases, and trapping of the ions by the surface is observed. This sensitivity enables us to put bounds on the depth of the attractive well in the potential. According to the s imulations there is a minimum in the trapping probability at incident energies between 15 and 30 eV. Furthermore, they indicate that the tra jectories that lead to trapping at energies below and above the minimu m differ markedly, particularly in the energy transfer in the initial collision with the surface.