Oxidation of Pd(553): From ultrahigh vacuum to atmospheric pressure

Abstract

The oxidation of a vicinal Pd(553) surface has been studied from ultrahigh 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 ${10}^{\ensuremath{-}6}\phantom{\rule{0.3em}{0ex}}\mathrm{mbar}$ and that the (553) surface is preserved. In the pressure range between ${10}^{\ensuremath{-}6}$ and $1\phantom{\rule{0.3em}{0ex}}\mathrm{mbar}$ and at a sample temperature of $300\char21{}400\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, a surface oxide forms and rearranges the (553) surface facets and 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 $(\sqrt{6}\ifmmode\times\else\texttimes\fi{}\sqrt{6})$ ${\mathrm{Pd}}_{5}{\mathrm{O}}_{4}$ surface oxide can be observed on (111) terraces larger than those of the (332) terraces. Increasing the O pressure above $1\phantom{\rule{0.3em}{0ex}}\mathrm{mbar}$ results in the disappearance of the (332) facets and the formation of PdO bulk oxide.