Adsorption of oxygen on Pt3Sn 110 studied by STM and LEED

The adsorption of oxygen on the Pt3Sns110d alloy surface was studied by means of scanning tunneling microscopy sSTMd and low-energy electron diffraction sLEEDd. After exposure to 2300 L O2 at 750 K LEED shows additional cs232d spots with regard to the substrate ps231d pattern. This agrees straightforward with STM topographies revealing a thin layer of large protrusions, arranged in a pseudohexagonal lattice. This layer is split into domains separated by distinctive zigzagging boundaries. Post-annealing allowed to partially uncover substrate regions. That way it could be shown that the protrusions are located above Sn locations. Further post-annealing restored the original substrate completely. A model of the adlayer structure consistent with all STM and LEED findings is given. These features observed after high temperature oxygen exposure of the Pt3Sns110d surface resemble to a large extent structures obtained on the Pt3Sns111d surface under similar conditions. The observed structures can be understood in terms of Sn-O entities interacting with each other. However, results from the oxidation of Pt3Sns111d indicate the formation of a Sn layer with chemisorbed oxygen on top, but not of separated SnOx entities. The protrusion patterns observed with STM on both surfaces are a topographic signature of such Sn-O layers on Pt3Sn.