Simulation of keV particle bombardment of covalent materials: An investigation of the yield dependence on incidence angle

The dependence of the yield, Y, of ejected particles on the angle of incidence θ is investigated for the keV particle bombardment of Si by molecular dynamics simulations using many-body potentials to describe the atom/atom interactions and a Molière potential to describe the ion/atom interactions. Results are presented for the Si{110} and the dimer reconstructed Si{100}(2 × 1) surfaces. For Ar bombardment of the Si{0110} surface at 1 and 5 keV the Y-θ curve has a number of peaks and troughs, which is a characteristic of many crystal surfaces. It is shown how the peaks and troughs can be explained by examining the interaction of the incoming ions with atoms in the surface layers. The dominant peaks in the yields as a function of incidence angle for bombardment at 1 and 5 keV are shown to agree with the shadow cone model proposed by Chang and Winograd [1]. The predictions of this model are compared with the full molecular dynamics simulations and its limitations are discussed. For the Si{100}(2 × 1) surface and bombardment at 1 keV, crystalline structural information was absent from the Y-θ curve whose form was characteristic of experimental measurements for amorphous Si. The calculated Y-θ curve showed some evidence of surface structure at 5 keV but the peaks in the curve could not he explained in terms of shadow cone yield enhancement.