Mechanisms of particle ejection from Cu(OO1) induced by the relative orientation of the bombarding primary ion

The effect of the angle of incidence of 600 eV Ar+ ions on the yields and mechanisms of particle ejection from a clean Cu(001) and a c(2× 2) overlayer of oxygen on Cu(001) has been examined. The total yield of particles ejected as a function of polar angle is in qualitative agreement with experiment. The azimuthal dependence of the yields for both the clean Cu(001) and Cu(001) with a c(2×2) overlayer has been predicted. Mechanisms of particle ejection which are specific to a particular angle of incidence have been identified. Of particular interest is a shearing mechanism which contributes to the ejection process at an angle of θ = 45° in the (100) directions. This shearing is responsible for the ejection of a large number of dimers which were originally next nearest neighbors on the surface. By energy selecting the dimers which eject, one can preferentially select the original sites of the two components. The angular distribution of the ejected particles, both substrate and adsorbate, due to normal incidence ion bombardment has previously been found to reflect the original surface site symmetry. The angular patterns of the ejected atoms are still dominated by the site sensitive effects, but the intensity is shifted due to the primary ion's off-normal angle of incidence.