ESCA studies of Ni‐25 At% Fe alloy. 1—surface preparation treatments and oxidation

The surface compositions of Ni‐25 at% Fe single crystals ((100) and (110)) were analysed by ESCA. The spectra were interpreted by comparison with reference spectra obtained from Ni, Fe, NiO, Fe 2 O 3 prepared in situ . Various surface pretreatments were investigated. The appropriate treatment to obtain a surface composition identical to the matrix composition is electropolishing and subsequent ion etching; the etching time is critical because the electropolished surface is enriched with nickel. Annealing at 800 °C can also be used to obtain the correct surface composition, but ion etching is then required to remove sulphur segregated to the surface during annealing. Oxidation at 25 °C and 500 °C (PO 2 = 10 −4 Torr) gives an iron enriched oxide. At 500 °C, nucleation and lateral growth of oxide islands were observed. Both the islands formed in the early stage and the final oxide covering the whole surface have the composition of the spinel NiFe 2 O 4 .