Revisiting the origin of low work function areas in pattern forming reaction systems: Electropositive contaminants or subsurface oxygen?

Martin Hesse, Sebastian Günther, Andrea Locatelli, Tevfik O. Mentes, Benito Santos, Ronald Imbihl

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

In pattern-forming reaction systems, the conversion of macroscopic islands of chemisorbed oxygen into low work function (WF) areas has been attributed to formation of a subsurface oxygen species. We prepare micrometer-sized oxygen islands on Pt(100) and Pt(110) by reaction fronts in catalytic CO oxidation in the 10−6 mbar range. By applying electron microscopy with chemical and structural sensitivity, we characterize their chemical composition upon annealing in vacuum. On Pt(100) we reproduce the previously reported transformation from high to low WF, estimating a relative change Δϕ ≈-0.8 eV with respect to the CO covered surface. We demonstrate that the change in WF is due to a strong enrichment of electropositive contaminants, namely Ca and Ti, in the oxygen islands. On Pt(110) predosed with Cs, we find that the alkali metal accumulates in the oxygen islands, producing Δϕ ≈ −0.4 eV relative to CO−adlayer. Our experiments suggest that the interpretation of the low WF areas as due to “subsurface oxygen” should be revised and attributed to the local enrichment of electropositive species.

Original languageEnglish
Pages (from-to)26864-26872
Number of pages9
JournalJournal of Physical Chemistry C
Volume120
Issue number47
DOIs
StatePublished - Dec 2016

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