Surface composition of Mn_xCo_1-xO solid solutions by X-ray photoelectron and Auger spectroscopies

Authors

Marjorie Langell, University of Nebraska - LincolnFollow
F. Gevrey, University of Framche Comte-Besancon, France
M. W. Nydegger, University of Nebraska - Lincoln

Date of this Version

January 2000

Comments

Published in Applied Surface Science 153:2–3 (January 1, 2000), pp. 114–127. doi:10.1016/S0169-4332(99)00361-X Copyright © 2000 Elsevier Science B.V. Used by permission. http://www.sciencedirect.com/science/journal/01694332

Abstract

Auger and X-ray photoelectron spectroscopies have been used to study the surface composition of Mn_xCo_1-xO (0 ≤ x ≤ 1) solid solutions. The polycrystalline materials, which are bulk homogeneous, present clear signs of deviation in surface composition at x_bulk ≈ 0.2–0.4 to become surface-enriched in manganese at the expense of the cobalt. Whether on stoichiometric or cobalt-depleted surfaces, cobalt retains the characteristic XPS 2p satellite structure and binding energies of the rock salt monoxide (CoO or Mn_xCo_1-xO) environment. Manganese 2p XP spectra are appropriately monoxide-like for the stoichiometric surfaces but broaden and give evidence for a second manganese species with Mn⁴⁺ character for the bulk-enriched samples. Oxygen O 1s spectra also show two different surface species, one the characteristic rock salt lattice oxide at 529.4 eV and a second at 531.3 eV. However, the two peaks are observed for all samples, regardless of whether the surface and bulk compositions were found to differ. The second O 1s peak cannot be unequivocally identified, but is most likely defect-oxide or hydroxyl-like in origin. The 531.3-eV O 1s species forms at the expense of the lattice oxide, and the net oxide-surface concentration is approximately that of the stoichiometric surface.