Estimate of repulsive interatomic pair potentials by low-energy alkali-metal-ion scattering and computer simulation

Abstract

Low-energy ion scattering is used in combination with computer simulation to study the interaction potential between 600-eV potassium ions and atoms in metallic surfaces. A special algorithm is described which is used with the computer simulation code marlowe. This algorithm builds up impact areas on the simulated solid surface from which scattering cross sections can be estimated with an accuracy better than 1%. This can be done by calculating no more than a couple of thousand trajectories. The screening length in the Molière approximation to the Thomas-Fermi potential is fitted in such a way that the ratio between the calculated cross sections for double and single scattering matches the scattering intensity ratio measured experimentally and associated with the same mechanisms. The consistency of the method is checked by repeating the procedure for different incidence conditions and also by predicting the intensities associated with other surface scattering mechanisms. The screening length estimates are found to be insensitive to thermal vibrations. The calculated ratios between scattering cross sections by different processes are suggested to be sensitive enough to the relative atomic positions in order to be useful in surface-structure characterization.