Counting electrons transferred through a thin alumina film into Au chains

Low-temperature STM measurements combined with density functional theory calculations are employed to study the adsorption of gold on alumina/NiAl(110). The binding of Au monomers involves breaking of an oxide Al-O bond below the adatom and stabilizing the hence undercoordinated O ion by forming a new bond to an Al atom in the NiAl. The adsorption implies negative charging of the adatom. The linear arrangement of favorable binding sites induces the self-organization of Au atoms into chains. For every ad-chain, the number of transfer electrons from the support is determined by analyzing the node structure of the corresponding highest occupied molecular orbital

Stability of sub-surface oxygen at Rh(111)

Using density-functional theory (DFT) we investigate the incorporation of oxygen directly below the Rh(111) surface. We show that oxygen incorporation will only commence after nearly completion of a dense O adlayer (\theta_tot = 1.0 monolayer) with O in the fcc on-surface sites. The experimentally suggested octahedral sub-surface site occupancy, inducing a site-switch of the on-surface species from fcc to hcp sites, is indeed found to be a rather low energy structure. Our results indicate that at even higher coverages oxygen incorporation is followed by oxygen agglomeration in two-dimensional sub-surface islands directly below the first metal layer. Inside these islands, the metastable hcp/octahedral (on-surface/sub-surface) site combination will undergo a barrierless displacement, introducing a stacking fault of the first metal layer with respect to the underlying substrate and leading to a stable fcc/tetrahedral site occupation. We suggest that these elementary steps, namely, oxygen incorporation, aggregation into sub-surface islands and destabilization of the metal surface may be more general and precede the formation of a surface oxide at close-packed late transition metal surfaces.Comment: 9 pages including 9 figure files. Submitted to Phys. Rev. B. Related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

Vibrational Frequencies of Cerium-Oxide-Bound CO: A Challenge for Conventional DFT Methods

In ceria-based catalysis, the shape of the catalyst particle, which determines the exposed crystal facets, profoundly affects its reactivity. The vibrational frequency of adsorbed carbon monoxide (CO) can be used as a sensitive probe to identify the exposed surface facets, provided reference data on well-defined single crystal surfaces together with a definitive theoretical assignment exist. We investigate the adsorption of CO on the CeO2(110) and (111) surfaces and show that the commonly applied DFT(PBE)+U method does not provide reliable CO vibrational frequencies by comparing with state-of-the-art infrared spectroscopy experiments for monocrystalline CeO2 surfaces. Good agreement requires the hybrid DFT approach with the HSE06 functional. The failure of conventional density-functional theory (DFT) is explained in terms of its inability to accurately describe the facet- A nd configuration-specific donation and backdonation effects that control the changes in the Câ"O bond length upon CO adsorption and the CO force constant. Our findings thus provide a theoretical basis for the detailed interpretation of experiments and open up the path to characterize more complex scenarios, including oxygen vacancies and metal adatoms.Fil: Lustemberg, Pablo German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. Consejo Superior de Investigaciones Científicas; EspañaFil: Plessow, Philipp N.. Karlsruher Institut fur Technologie; AlemaniaFil: Wang, Yuemin. Karlsruher Institut fur Technologie; AlemaniaFil: Yang, Chengwu. Karlsruher Institut fur Technologie; AlemaniaFil: Nefedov, Alexei. Karlsruher Institut fur Technologie; AlemaniaFil: Studt, Felix. Karlsruher Institut fur Technologie; AlemaniaFil: Wöll, Christof. Karlsruher Institut fur Technologie; AlemaniaFil: Ganduglia Pirovano, Maria Veronica. Karlsruher Institut fur Technologie; Alemani