The oxidation of a vicinal Pd(553) surface has been studied from ultra high vacuum (UHV) to atmospheric oxygen pressures at elevated sample temperatures. The investigation combines traditional electron-based UHV techniques such as high resolution core level spectroscopy, low energy electron diffraction, scanning tunneling microscopy with in-situ surface x-ray diffraction and ab-initio simulations. In this way, we show that the O atoms preferentially adsorb at the step edges at oxygen pressures below 10-6 mbar, and that the (553) surface is preserved. In the pressure range between 10-6 to 1 mbar and at a sample temperature of 300-400 °C, a surface oxide forms and rearranges the (553) surface facets, forming (332) facets. Most of the surface oxide can be described as a PdO(101) plane, similar to what has been found previously on other Pd surfaces. However, in the present case the surface oxide is reconstructed along the step edges, and the stability of this structure is discussed. In addition, the (√6 × √6) Pd5O4 surface oxide can be observed on (111) terraces larger than those of the (332) terraces. Increasing the O pressure above 1 mbar results in the disappearance of the (332) facets and the formation of PdO bulk oxide.
Corresponding author: R. Westerström. Reprints also available from M. Schmid (schmid).
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