Shadow-cone-enhanced secondary-ion mass-spectrometry studies of Ag{110}

Abstract

The yield of particles ejected due to keV ion bombardment of Ag{110} has been observed to depend strongly on the angle of incidence of the primary ion beam. The desorption angles of these particles are found to reflect both the crystallographic and chemical structure of the surface. Molecular dynamics calculations indicate that the desorption yield of all particles is significantly enhanced when the shadow cone of the incident beam of particles created by a surface atom intersects adjacent surface atoms. These angles may be accurately calculated by use of a full three-dimensional trajectory calculation of the scattering or by simple computation of the angle of this intersection using a two-body Moli\`ere interaction potential function. With this approach it is possible to assign all of the angular anisotropies observed from secondary ions ejected from Ag{110}. Moreover, a detailed analysis suggests that the topmost atomic layer is relaxed inward by (7.8\ifmmode\pm\else\textpm\fi{}2.5)% and that the spacing between the first and third layer is contracted by (4.1\ifmmode\pm\else\textpm\fi{}2.1)% relative to the bulk spacings. These results are in excellent agreement with recent Rutherford backscattering experiments. A number of new possible applications of this technique to the analysis of chemisorbed overlayers is also discussed.