Ion-beam mixing at Fe-Si interface: An interface-sensitive conversion electron Mössbauer spectroscopic study

Abstract

The ion-beam-induced and subsequent thermal transformations at the Fe-Si interface are studied by using the technique of interface-sensitive conversion electron Mössbauer spectroscopy (CEMS). The samples used in these experiments have been prepared by depositing a thin (∼50-Å) layer of Fe57 isotope (enriched to 95.45%) on a freshly cleaned surface of a (111) silicon crystal followed by a deposition of a 250-Å-thick overlayer of natural iron containing only 2.2% of the Fe57 isotope. A number of such composites have been bombarded with Xe+ ions having an energy of 10 keV at an ion dose of ∼1–3×1016 ions/cm2. The atomic mixing at the interface is confirmed by Rutherford backscattering (RBS) measurements and the average composition of the mixed layer is also determined. Using the CEMS technique, it is shown that the thin FeSi layer formed at the interface due to the deposition-induced reaction grows upon ion bombardment, along with the incorporation of a large number of vacancies in the structure. It has also been shown that the internal magnetic field of the ion-beam-mixed alloy shows a broad distribution over a range of field values between 100 and 330 kOe with indications of certain preferences for local atomic arrangements and compositions. The ion-beam-mixed sample shows significant changes in the values of hyperfine interaction parameters subsequent to vacuum annealing treatment at 450 °C for 1 h, while precipitation of α-Fe and Fe3Si phases upon annealing at 700 °C. The as-deposited sample exhibits distinctly different features as compared to those of the ion-beam-mixed sample, when subjected to thermal treatments. These thermal transformations in the as-deposited as well as ion-beam-mixed samples have also been monitored by resistance annealing measurements, and the result of these studies agree well with those of CEMS measurements.