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Galvinoxyl layers on Au͑111͒ have been studied by scanning tunnelling microscopy ͑STM͒, electron paramagnetic resonance ͑EPR͒, and cyclic voltammetry ͑CV͒. We observe two phases: configuration I having a molecular density of 1.57± 0.16ϫ 10 −10 mol/ cm 2 and a rectangular lattice ͑15 Å by 7 Å͒ observed at room temperature and down to 140 K; configuration II with a slightly smaller molecular density of 1.37± 0.14 ϫ 10 −10 mol/ cm 2 and oblique cells ͑22.5 Å by 5.4 Å͒ arranged alternatingly in stacks yielding a molecular layer with lower symmetry and comparatively large crystallographic unit cell. The latter is only observed upon cooling down to 40 K and subsequent annealing to room temperature. For both assemblies typical domain sizes in the range of 100 nm have been found. The EPR results confirm that the radical character is preserved upon adsorption and that the intermolecular distance is smaller than 11 Å. The interaction between the overlapping singly occupied spin orbitals is high, indicating no participation of the unpaired electron in the binding to the surface or laterally between neighboring radicals. The average surface concentration deduced from CV measurements is in excellent agreement with the surface coverages deduced from STM topographies. In aqueous electrolyte the adsorbate undergoes a one-electron oxidation with concomitant loss of a proton as determined from oxidation potential vs pH curves in a similar fashion as known for the free radical in solution. This indicates no dramatic change of the electronic properties of the radical upon adsorption. Structure models are proposed with molecules standing upright like "bicycles in rows."

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A model for core-level shifts in metallic overlayers is introduced. The model is based on a decomposition of the shift into partial shifts which are related to specific structural aspects of the interface system. The model is applied to the Yb/Ni(100) overlayer system which has been studied by He II and Al Ka excited photoelectron spectroscopy. The deposition of Yb is investigated at two substrate temperatures, room temperature and 670 K. At 670 K ordered low-energy electron diffraction structures are seen, and at higher Yb depositions intermixing with the substrate occurs.At room temperature no ordered structures are seen. The 1ow mobility of the atoms furthermore prevents strong intermixing with the substrate. It is shown that an analysis of the divalent and trivalent Yb shifts provides detailed structural information about the Yb/Ni(100) overlayer system.

We study the structural properties of ultrathin Ag x Pd 1−x films on top of a Ru͑0001͒ substrate. Effective interatomic interactions, obtained from first-principles calculations, have been used in Monte Carlo simulations to derive the distribution of the alloy components in a four-monolayer ͑4-ML͒ Ag-Pd film. Though Ag-Pd alloys show complete solubility in the bulk, the thin film geometry leads to a pronounced segregation between Ag and Pd atoms with a strong preference of Ag atoms toward the surface and Pd atoms toward the interface. The theoretical prediction of this double-segregation effect is strongly supported by photoelectron spectroscopy experiments carried out for 4-ML thin films. We also show, in an additional experiment, that even in the case where initially 1 ML Ag is buried under 6 ML Pd, the whole Ag ML segregates to the surface.