AVS 50th International Symposium
    Surface Science Thursday Sessions
       Session SS3-ThM

Paper SS3-ThM2
Sodium Segregation and Morphology on Co@sub 3@O@sub 4@ Single Crystal Surfaces

Thursday, November 6, 2003, 8:40 am, Room 328

Session: Oxide Structure, Growth, and Defects
Presenter: S.C. Petitto, University of Nebraska-Lincoln
Authors: S.C. Petitto, University of Nebraska-Lincoln
M.A. Langell, University of Nebraska-Lincoln
Correspondent: Click to Email
The Co@sub 3@O@sub 4@(110) single crystal surface was characterized in its clean and sodium covered states using Low Energy Electron Diffraction, (LEED), X-Ray Photoelectron Spectroscopy, (XPS), and Auger Electron Spectroscopy, (AES). Annealing Co@sub 3@O@sub 4@(110) at T = 650K results in sodium segregation from the bulk material, quantified here by the AES I@sub Na@/I@sub Co@ intensity ratio. LEED analysis of the clean Co@sub 3@O@sub 4@(110) surface shows a well-ordered pattern with sharp diffraction features, whereas the Co@sub 3@O@sub 4@(110)-Na surface presents a more poorly ordered structure with a hexagonal superimposed pattern due to the sodium oxide overlayer. Concurrent with sodium segregation, the Co@sub 3@O@sub 4@(110) surface is reduced and the surface cannot be fully reoxidized as long as sodium remains present even upon extended oxygen annealing. XPS of the clean Co@sub 3@O@sub 4@(110) is characteristic of the spinel structure with Co@super 3+@ occupying the octahedral sites within the lattice and Co@super 2+@ in tetrahedral sites. Co@sub 3@O@sub 4@(110)-Na cobalt XPS, however, shows the cobalt chemical environment is closer to that in CoO with Co@super 2+@ in octahedral sites. Upon flashing to T@>=@ 800K, sodium desorbs from the surface, primarily as NaOH. Pre-dosing with H@sub 2@O does not appear to catalyze NaOH desorption but rather suppresses it, and the hydrogen is assumed to come from the ambient background in the UHV chamber.