COMPUTER STUDIES OF THE SURFACE MECHANISM OF PREFERENTIAL SPUTTERING OF 2-COMPONENT SOLIDS - ION-BEAM ANALYSIS OF SURFACE-COMPOSITION IN LOW-DOSE REGIME

We investigated the process of collision cascade propagation through t he solid-vacuum boundary for two-component targets: WSI MoSi and VSi. The surface mechanism of preferential sputtering of atoms of light com ponent based on stronger deflection of light atoms towards surface nor mal when scattering by heavy neighbouring surface atoms during ejectio n was studied. Simulations for ejection of 450 000 Si or W atoms from the surface of WSi for cos theta(0)/E(0)(2) and 1/E(0)(2) initial dist ributions gave Si/W sputtering ratio equal to 1.29-1.55 (for 1:1 Si/W concentration ratio at the surface) giving necessary addition to the A ndersen-Sigmund formula which underestimated that ratio in comparison with available experimental data. Analysis of integral energy distribu tions of atoms of the components gave Si/W ratio maximum equal to 3.18 -5.00 for energy interval 0.0-0.4 eV. Maxima of integral energy distri butions of sputtered atoms were observed at 1.8 eV for Si and 3.4 eV f or W in calculations with equal binding energies for atoms of light an d heavy components in good agreement with experiment. The surface mech anism was shown to be the alternative mechanism in formation of observ ed maxima difference with respect to nonidentity of binding energy val ues for atoms of components proposed by Szymonski [Phys. Lett, A 82 (1 981) 203]. The two-cone structure of ejection vs, initial polar angle for Si atoms sputtered was revealed and explained. Results obtained ga ve the new approach to solve the inverse problem of reconstruction of surface composition in low dose SNMS and showed that the surface mecha nism of preferential sputtering is to be accounted for in analytical c alculations of surface composition. Ejection was simulated in the plan e containing the neighbouring surface atom.