Lack of surface oxide layers and facile bulk oxide formation on Pd(110)

The oxidation of the Pd(110) surface has been studied from ultrahigh vacuum up to atmospherical pressures by combining scanning tunneling microscopy, low-energy electron diffraction and high-resolution core-level spectroscopy with in situ surface x-ray diffraction, and density-functional theory calculations. Under in situ conditions, we observe a $c(2\ifmmode\times\else\texttimes\fi{}4)$ structure which transforms via the formation of antiphase domain boundaries to a ``complex'' structure with increasing partial oxygen pressure. Contrary to other closed packed and vicinal Pd surfaces investigated so far, no surface oxide is formed, which allows for the formation of the PdO bulk oxide closer to the thermodynamic limit at temperatures relevant for catalysis.