The high performance of ceria (CeO ₂ ) as an oxygen buffer and active support for noble metals in catalysis relies on an efficient supply of lattice oxygen at reaction sites governed by oxygen vacancy formation. We used high-resolution scanning tunneling microscopy and density functional calculations to unravel the local structure of surface and subsurface oxygen vacancies on the (111) surface. Electrons left behind by released oxygen localize on cerium ions. Clusters of more than two vacancies exclusively expose these reduced cerium ions, primarily by including subsurface vacancies, which therefore play a crucial role in the process of vacancy cluster formation. These results have implications for our understanding of oxidation processes on reducible rare-earth oxides.

Photoelectron spectra from sublimed layers of chromatographically separated $\mathrm{La}@{\mathrm{C}}_{82}$ are presented. Using photon energies corresponding to the La $3d$ to $4f$ transition, a resonant enhancement of the La-derived valence states is observed. From the calculated resonant intensities of La $5d$ and $5p$ states in a La atom we estimate that about $\frac{1}{3}$ of an electron charge is left in the La-valence orbitals for $\mathrm{La}@{\mathrm{C}}_{82}$. In contrast to previous interpretations of La core-level photoemission studies our results demonstrate that the La valence electrons are not completely delocalized on the fullerene cage.

We demonstrate that high resolution autoionization studies for core excitations under Auger resonant Raman (ARR) conditions can be used to extract extremely fast charge transfer (CT) relaxation times for chemisorbed molecules on a metal surface. For the $\mathrm{O}1s$ and $\mathrm{C}1s$ bound resonances of CO on Ru(0001), ARR behavior is almost completely suppressed; from its small remnant detectable by its linear dispersion with photon energy, CT times below 1 fs can be determined. For CO on a Xe spacer, only dispersive Raman-type decay is seen; i.e., no CT occurs.

The surface topography and local surface work function of ultrathin MgO(001) films on Ag(001) have been studied by noncontact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM). First principles calculations have been used to explain the contrast formation of nc-AFM images. In agreement with literature, thin MgO films grow in islands with a quasi rectangular shape. Contrary to alkali halide films supported on metal surfaces, where the island heights can be correctly measured, small MgO islands are either imaged as depressions or elevations depending on the electrostatic potential of the tip apex. Correct island heights therefore cannot be given without knowing the precise contrast formation discussed in this paper. KPFM shows a silver work function which is reduced by the MgO islands. The values for the work function differences for one and two layer thin films are −1.1 and −1.4 eV, respectively, in good agreement with recent calculations and experiments.