Link between local iron coordination, Fe 2p XPS core level line shape and Mg segregation into thin magnetite films grown on MgO(001)

Abstract

A well ordered Fe(001) ultra thin film epitaxially grown on MgO(001) has been oxidized by post deposition annealing in oxygen atmosphere. LEED patterns indicate the formation of magnetite (Fe 3 O 4 ) after one hour of oxygen exposure. The LEED pattern remains stable despite annealing the sample for further four hours. In contrast X-ray Photoelectron Spectroscopy (XPS) of the Fe 2p core levels suggests the formation of an iron oxide comprising mostly of merely trivalent iron. This discrepancy is analyzed and discussed employing charge transfer multiplet calculations for the Fe 2p XPS spectra. We find that Mg ion segregation from the substrate into the magnetite thin film replacing octahedrally coordinated Fe 2+ ions and the excess occupation of octahedral sites which are unoccupied in the ideal inverse spinel structure are driving forces for the altered shape of the Fe 2p XPS spectra. Different potential models which might explain the nature of the Mg ion segregation into the magnetite films are discussed.

Sulfur-Doped Fe–N–C Nanomaterials as Catalysts for the Oxygen Reduction Reaction in Acidic Medium

“…42 The high-resolution spectra for Fe 2p (Figure 4c) of FeN 4 /NSC-1 deconvoluted into four peaks, including Fe 2+ (710.5 and 722.6 eV) and Fe 3+ (715.3 and 729.5 eV); similar peaks were also observed in FeN 4 /NC with a small shift, and the exception of a supplementary peak at 708.9 eV corresponding to Fe 0 . 22,25,43,44 The atomic structure of Fe sites in the samples was determined by XAS. Figure 4d shows the Fe K-edge X-ray absorption near-edge spectroscopy (XANES) spectra of the FeN 4 /NSC-1 sample and Fe foil, FeO, and Fe 2 O 3 used as standards.…”

CO2 Hydrogenation to Higher Alcohols over K-Promoted Bimetallic Fe–In Catalysts on a Ce–ZrO2 Support

“…Regarding the Fe 2p spectra (Figure S6a), peaks at 710.0 and 723.6 eV for the uncalcined K-0.82-FeIn/Ce−ZrO 2 are assigned to the Fe 2p 3/2 and Fe 2p 1/2 bands of octahedrally coordinated Fe 3+ , peaks at 711.5 and 725.1 eV to tetrahedral Fe 3+ , and peaks at 717.4 and 731.0 eV to Fe 3+ satellites. 54 These results illustrate that Fe exists in the form of Fe 2 O 3 , in line with the Raman spectra (Figure 2). Peaks at 443.9 and 451.5 eV are attributed to In 3d 5/2 and In 3d 3/2 of In 3+ and peaks at 292.6 and 295.4 eV to K 2p 3/2 and K 2p 1/2 of K + (Figure S6b,c).…”