XPS and ToF‐SIMS characterization of a Finemet surface: effect of heating

Abstract

X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to study the surface composition and electronic structure of Finemet, Fe 73 Si 15.8 B 7.2 Cu 1 Nb 3 , in the original amorphous state and after gradual heating in vacuum to a temperature of 400• C and cooling back to room temperature. It was found that relaxation processes occurring during heat treatment well below the crystallization onset caused the physico-chemical state of Finemet surface to change irreversibly. In the relaxed alloy, the surface originally covered with the native air-formed oxide was significantly enriched with elemental iron and depleted of other alloy constituents compared with the original state. Yet in the as-quenched state, clustering of copper atoms on the Finemet surface was detected which was enhanced by heating. The thermal treatment resulted in the selective reduction of iron oxides and caused noticeable changes in the valence band structure and the Fe L 3 VV Auger spectrum associated with atomic redistribution.

Raman spectroscopy used to inspect relationship between surface and magnetic properties of Fe-Nb-Cu-B-Si(4.5) nanocrystalline ribbons

“…Nevertheless, no morphology study points either to correlation to ribbon chemical composition or to systemic changes due to thermal treatment. Unlike the morphology, surface chemistry is shown to change with basic chemical composition as well as with various thermal treatments [7]. Surface chemistry differences and changes thus appear to be more closely associated with the supposed surface-interior force interaction.…”

“…Anyway, surfaces often differ from ribbon interior, thus we speak about macroscopic heterogeneity (MH). Although Fe oxides and oxyhydroxides are suspect to persist on ribbon surfaces [2,7], these substances have not been clearly identified by CEMS or XRD after standard anneal- . Labels AS, WS are explained in part 2, AS -fresh in part 3.2.1.…”

“…are the most frequently indicated Fe-oxides by XPS [2,7] on as-cast and sub-crystallization annealed (≤ 400…”

Application Potential of Nanocrystalline Ribbons Still Pending

“…In Table 2, the column label "DO3" means in fact, how good is the fit of measured spectrum when a superposition of DO3 components is assumed. Considering eg the XPS results [6] or corrosion studies [8,12], silicon is seen to engage in SiO x oxides and its availability for the DO3-forming Fe 3 Si is thus limited at ribbon surfaces. In the same spirit of oxidation chance for silicon, the surfaces of Ar-or air-annealed samples are more DO3-poor than the vacuum-annealed ones.…”

“…The quoted terms have something common -all point to a largescale heterogeneity across the ribbon thickness, ie to various differences between the surfaces (surface-adjacent layers) and the deeper layers (interior). Another essential common point: No thermal treatment makes the obviously as-cast-based heterogeneity disappear -it merely transforms [6] to give different outcome in different annealing ambience. The term MH should promote as well the distinction from short-range heterogeneity (nanocrystals, interfaces, clusters, rare solitary defects .…”