Surface oxidation investigation of Ni36Fe32Cr14P12B6 glass using angle resolved XPS

Native oxide and in-situ prepared, dry oxides of Ni₃₆Fe₃₂Cr₁₄P₁₂B₆ metallic glass have been investigated using angle resolved X-ray photoelectron spectroscopy (XPS or ESCA). The core-level binding energies of the various constituents of clean and oxidized samples have been determined accurately. A qualitative as well as quantitative estimation of elements in the outermost surface layers with and without oxidation is given by comparing XPS results obtained at normal and grazing emission angles. Stepwise oxidation leads to growing thickness of the surface oxide layer and to identification of different oxide species. The maximum thickness of the in-situ prepared oxide was determined as 3.5 nm compared to 4.5 nm for the native oxide. The sequence of oxidation is found to be Cr, Fe, B, P and Ni, but only some of the P and Ni atoms in the surface region are oxidized. The oxidation reaction induces diffusion of the constituents in the surface region as monitored by the change of relative intensities of the various peaks. For instance, P and especially Ni are strongly depleted in the oxide layer whereas Fe, Cr, and especially B are enriched. Differences between native and dry oxide have been observed and are discussed. The main difference is the abundance of carbon and oxygen containing species other than oxides in the native layer. Ar⁺ sputtering of the dry oxide layer leads to stochiometric changes in the surface region which are due to preferential sputtering.