Study of amorphous and crystallised Fe 75B 25 by Auger electron spectroscopy and X-ray photoelectron spectroscopy

Abstract

Auger electron spectroscopy (AES) in conjunction with argon ion sputtering was used to study the sputtering behaviours of an amorphous Fe 75B 25 alloy and its corresponding crystallized alloy forms, namely the single-phase metastable Fe 3B and a two-phase mixture of α-Fe and Fe 2B. Bombardment with the energetic argon ions of energy 1 and 3 keV resulted in the establishment of a boron-rich sputter altered layer in all the alloy forms. The magnitude of enrichment of boron was relatively much higher and similar in the amorphous and the metastable Fe 3B alloys than in the alloy consisting of a two-phase mixture of α-Fe and Fe 2B. The sputter-induced compositional differences in these alloys have been rationalized in terms of their different structural states and are suggestive of a similar local atomic order in the structures of the amorphous and the corresponding crystallized Fe 3B. The binding effects appeared to play a significant role in determining the sputtering behaviours of these alloys and the probable sputtering mechanisms would include cascade sputtering and/or surface segregation. The evidence for the occurrence of bombardment-induced surface segregation is provided by a simple model calculation based on the values of the concentration ratio of iron to boron obtained by using the low energy (47 eV) and the high energy (651 eV) Auger peaks of iron. Native oxide films formed on these structurally different alloy forms were also characterized using AES and X-ray photoelectron spectroscopy (XPS). The oxide films were enriched in boron, the enrichment being maximum near the oxide/alloy interfacial region and incorporated Fe 3+, Fe 2+, and B 3+ species. The oxide films on amorphous Fe 75B 25 and Fe 3B were similar in thickness (3.6 and 3.3 nm) while a relatively thicker film (9.7 nm) was formed on the alloy consisting of α-Fe and Fe 2B.