Ion beam induced atomic mixing in a single interface Fe-Ge structure: conversion electron Mossbauer spectroscopy study

Abstract

Ion beam induced atomic mixing and subsequent thermal reactions are studied in the single interface Fe-Ge structure, using the technique of conversion electron mossbauer spectroscopy (CEMS). Use has been made of a thin ( 50 Å) layer of ⁵⁷Fe mossbauer isotope (enriched to 95.45%) at the interface of the germanium substrate and a post-deposited 300 λ film of natural iron, to enhance the interface sensitivity of the mossbauer signal. Annealing studies have been carried out at various temperatures upto a maximum of 625°C, to allow for phase transformations. The ion beam mixed samples exhibit the presence of the magnetic FeGe phase along with Fe atoms situated in interstitial positions having a tetrahedrally symmetric environment in Ge. A small fraction of Fe atoms is also found at substitutional sites of the Ge matrix. The as-deposited as well as ion beam mixed composites show significant structural relaxations upon annealing at 350°C, leading to the onset and growth of the Fe enrichment process. When annealed at 625°C for one hour, these composites indicate the segregation of Fe atoms as well as the nucleation and growth of magnetic phases such as FeaGe and Fe₅Ge₃. Such features are not observed in the case of the as-deposited samples. An attempt is made to understand the similarities and differences in the results obtained in the case of the Fe-Ge system and two other systems viz. Fe-Al and Fe-Si, on which work of similar nature has already been reported.