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Is silicide formation the decisive factor in impurity induced ion beam pattern formation?

Engler, M.; Müller, S.; Will, M.; Frost, F.; Feder, R.; Spemann, D.; Hübner, R.; Facsko, S.; Michely, T.

Abstract

Recent experiments showed that metal deposition during ion beam erosion causes the pattern formation at low incidence angles.
We performed 2 keV Kr+ ion beam erosion of Si(001) experiments using a scanned fine focus ion source with simultaneous deposition of metal atoms. After ion beam erosion we analyzed our samples in-situ with scanning tunneling microscopy and ex-situ with atomic force microscopy and transmission electron microscopy. The metal concentration on the Si surface was analyzed ex-situ with Rutherford backscattering spectrometry.
To distinguish the effects of collision kinetics versus chemical interaction in metal co-deposition induced pattern formation on Si(001) we conducted Ag and Pd sputter co-deposition from a target mounted on the Si sample. This setup results in a flux and concentration gradient of the co-deposited metals on the Si sample. While for Pd a concentration dependent ripple pattern is observed, no pattern evolves for Ag co-deposition under ultra high vaccum conditions. Since Ag and Pd possess nearly the same nuclear charge and atomic mass, their different ability to form a pattern must be attributed to their different ability to form silicides. While Pd forms a variety of silicides, Ag forms none. Silicide formation of the co-deposited metal appears thus to be a necessary condition to induce a pattern on Si during ion exposure.

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