The structure of the oxygen-induced p(4 x 4) reconstruction of Ag(111) is determined by a combination of scanning tunneling microscopy, surface x-ray diffraction, core level spectroscopy, and density functional theory. We demonstrate that all previous models of this surface structure are incorrect and propose a new model which is able to explain all our experimental findings but has no resemblance to bulk silver oxide. We also shed some light on the limitations of current density functional theories and the potential role of van der Waals interactions in the stabilization of oxygen-induced surface reconstructions of noble metals.

Using core-level spectroscopy and density functional theory we show that a one-dimensional (1D) oxide structure forms at the steps of the Pt(332) surface after exposure. The 1D oxide is found to be stable in an oxygen pressure range, where bulk oxides are only metastable, and is therefore argued to be a precursor to the Pt oxidation. As an example of the consequences of such a precursor exclusively present at the steps, we investigate the reaction of CO with oxygen covered Pt(332). Albeit more strongly bound, the oxidic oxygen is found to react more easily with CO than oxygen chemisorbed on the Pt terraces.

The formation of one-layer surface oxides on Pd͑111͒ has been studied by scanning tunneling microscopy ͑STM͒ and density functional theory ͑DFT͒. Besides the Pd 5 O 4 structure determined previously, structural details of six different surface oxides on Pd͑111͒ will be presented. These oxides are observed for preparation in oxygen-rich conditions, approaching the thermodynamic stability limit of the PdO bulk oxide at an oxygen chemical potential of −0.95 to − 1.02 eV ͑570-605 K, 5 ϫ 10 −4 mbar O 2 ͒. Sorted by increasing oxygen fraction in the primitive unit cell, the stoichiometry of the surface oxides is Pd 5 O 4 , Pd 9 O 8 , Pd 20 O 18 , Pd 23 O 21 , Pd 19 O 18 , Pd 8 O 8 , and Pd 32 O 32 . All structures are one-layer oxides, in which oxygen atoms form a rectangular lattice, and all structures follow the same rules of favorable alignment of the oxide layer on the Pd͑111͒ substrate. DFT calculations were used to simulate STM images as well as to determine the stability of the surface oxide structures. Simulated and measured STM images are in excellent agreement, indicating that the structural models are correct. Since the newly found surface oxides are clearly less stable than Pd 5 O 4 , we conclude that Pd 5 O 4 is the only thermodynamically stable phase, whereas all newly found structures are only kinetically stabilized. We also discuss possible mechanisms for the formation of these oxide structures.

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The oxidation of a vicinal Pd͑553͒ surface has been studied from ultrahigh vacuum ͑UHV͒ 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 ͑553͒ surface is preserved. In the pressure range between 10 −6 and 1 mbar and at a sample temperature of 300-400°C, a surface oxide forms and rearranges the ͑553͒ surface facets and forming ͑332͒ facets. Most of the surface oxide can be described as a PdO͑101͒ 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 ͑ ͱ 6 ϫ ͱ 6͒ Pd 5 O 4 surface oxide can be observed on ͑111͒ terraces larger than those of the ͑332͒ terraces. Increasing the O pressure above 1 mbar results in the disappearance of the ͑332͒ facets and the formation of PdO bulk oxide.