AES STUDY OF AMORPHOUS FE100-XBX (X = 14-25 AT-PERCENT) ALLOYS

Auger electron spectroscopy in conjunction with argon ion sputtering was used to study the sputtering behaviour of melt-spun amorphous Fe100-xBx (x = 14-25 at.%) alloys. Measurement of equilibrium surface composition using the low energy peak of iron Fe (47 eV, MVV) indicated an enrichment of boron in the sputter altered layer in all alloys for argon ion energies of 1 keV and 3 keV. The corresponding sputtering yield ratio (Y(Fe)/Y(B)) had a value between 1.3 and 1.6. The surface composition, calculated by using the high energy iron peak (651 eV, LMM), indicated depletion of boron in the sub-surface region in comparison to that measured by using the low energy peak. It appears that binding effects rather than mass play a significant role in determining the preferential sputtering behaviour of these alloys and the possible sputtering mechanisms could involve cascade sputtering and/or surface segregation. The plot of surface composition or the sputter yield ratio versus boron atom fraction in the bulk showed a break at 18 at.% boron. This is attributed to the known structural differences in Fe-B amorphous alloys. Analysis of native oxide films on these alloys showed enrichment of boron near the oxide-alloy interface and the film thicknesses were approximately in the range 4-6 nm. It was inferred from an analysis of the low energy Auger peaks that the oxide films consisted of Fe3+, Fe2+ and B3+ species.