Ion-beam mixing in Fe/Si bilayers by singly and highly charged ions: evolution of phases, spike mechanism and possible effects of the ion-charge

Silicide formation and ion beam mixing of Fe/Si bilayers due to Ar-, Xe- and Au-ion irradiations at room and liquid-nitrogen temperatures were investigated. For the study of silicide phase formation, the Fe/Si bilayers were irradiated with 100-keV Ar+, 250-keV Xe+, 700-keV Xe2+ or 400-keV Au+ ions at fluences of 1 x 10(15) to 2 x 10(16) ions/cm(2). The influence of the ion-charge state on the mixing process was studied in Fe/Si by 100-keV Ar8+-ion implantation, in addition to the corresponding irradiations with singly charged ions at the same energy. Changes in the samples were analyzed by Rutherford backscattering spectroscopy, conversion electron Mossbauer spectroscopy, X-ray diffraction and atomic force microscopy. Pronounced structural changes and the intermixing of the components at the Fe/Si interfaces were measured as a function of the ion species, ion fluence and, sample temperature. A linear correlation between the interface broadening and the fluence was observed for all the cases. Mossbauer analysis with enriched Fe-57 layers revealed the onset of phase formation out of the solid solution. In order to interpret the mixing rates in this most general case, we considered mixing through thermal local or global spikes and compound formation. The highly charged Ar8+-ion irradiation produced a higher athermal mixing rate compared to singly charged Ar+ ions, and this result could not be explained by the above models