Oxygen interaction with Ni/Fe surfaces (1) LEED and XPS studies of Ni 76%/Fe 24% (100)

Abstract

The interaction of oxygen with a Ni 76%/Fe 24% (100) surface has been studied at 293 K. XPS measurements were made as a function of emission angle to obtain depth distributions. Slight Fe segregation is observed for a clean annealed surface. It is enhanced by oxygen adsorption. By 0.7 monolayers oxidized Fe species are detected, but the Ni remains metallic until well above one monolayer. The Fe concentration in the outer 4 Å has then increased twofold. At about ∠2.7 monolayers (passivation) the surface Fe concentration is nearly three times the original and entirely oxidized. Heating causes further Fe segregation which reduces the Ni2+ to yield Ni0. LEED shows a c (2×2) pattern which persists above one monolayer. Correlations of the XPS and LEED data and comparison with XPS/LEED studies of oxygen on Fe(100) and Ni(100) show that between 0.7–2 monolayers, the surface must be heavily patched with Fe oxide and metallic Ni aggregations, the Ni being covered with a c (2×2) oxygen superstructure.

Initial oxidation of polycrystalline Permalloy surface

“…When the oxygen exposure is elevated from 100 to 800 L, the intensity of Fe 2+ ox is slowly decreasing while that of Fe 3+ ox is increasing. This observation confirms the data obtained by Brundle et al [10], who concluded that the dominant oxide was Fe 3+ ox at oxygen exposures above 41 L. The FeO species seem to be partly converted into Fe 2 O 3 . These results are in full agreement with the data about Fe (1 0 0) oxidation at room temperature reported by Roosendaal et al in [34].…”

“…Since the final oxide strongly depends on the oxidation conditions, they have evidenced the formation of different oxides including mainly iron oxide and also nickel oxide. In their study of oxidation of a Py (1 0 0) crystal at room temperature, Brundle et al [10] evidenced initial iron segregation. None of these investigations have dealt with the first stages of oxidation kinetics at room temperature.…”

MnFe and NiFe Thin Films and Magnetic Exchange Bilayers

“…9. Oxygen bound as an oxide is found at 530.0 eV and as hydroxide at 531.6 eV (20). The location of the oxidized Ni 2p signal is consistent with the formation of Ni 2+ in NiO, as has been previously observed on oxidized NiFe single-crystal and thin film surfaces (18)(19)(20).…”

“…The Ni 2p, Fe 2p, O ls, and C ls spectra taken from a NiFe sample, which had been exposed to air prior to being loaded into the MnFe deposition system, are shown in Fig. The location of the oxidized Ni 2p signal is consistent with the formation of Ni 2+ in NiO, as has been previously observed on oxidized NiFe single-crystal and thin film surfaces (18)(19)(20). The Ni and Fe 2p XPS spectra show features characteristic of both metallic and oxidized Ni and Fe.…”

X-Ray Photoelectron Spectroscopy Depth Profiling of Electrochemically Prepared Thin Oxide Layers on Duplex Stainless Steel

“…[2,4,[7][8][9]24] The Fe 2p 3/2 was fitted with five peaks in a similar way. [25,26,28,29] The uncertainties of the binding energy values in Table II comprise all binding energy values obtained during the fitting process. XPS depth profiles are shown in Figure 3. A total of 100 pct was calculated without the components corresponding to the surface oxygen and surface carbon contamination because, before renormalization, these two materials decrease below 2 pct after the first 100 seconds of sputtering, thus confirming that they indeed derive from the surface located species.…”