Quasi-one-dimensionally ordered chains of silver and cobalt clusters are grown on the R͑15 ϫ 12͒-C/ W͑110͒ template and investigated by scanning-tunneling microscopy. Both Ag and Co nucleate at the same area within the large template unit cell. We attribute this area to the carbon-poor part of the unit cell. Clusters exhibit a narrow size distribution, peaking at cluster sizes of seven to eight atoms. The strong preference of this cluster size is attributed primarily to the size of favorable adsorption areas in the R͑15 ϫ 12͒ unit cell. For cobalt atoms the adsorption strength seems to be more homogeneous across the unit cell than for Ag, allowing also growth of small clusters on less favorable regions of the unit cell at low temperatures.
When adsorbed on the strongly anisotropic Pt(110) surface Br forms a sequence of (n × 1) structures. In the present study we investigate the (4 × 1) structure by scanning tunneling microscopy, quantitative low-energy electron diffraction and density-functional calculations. We show that the optimal structural model contains essentially the same adsorption sites as the (3 × 1) structure, but with a different preference. The positions of the substrate atom are consistent with a frozen surface phonon of fourfold periodicity, suggesting that the phase diagram can be understood on the basis of a tunable charge density wave (Swamy et al 2001 Phys. Rev. B 86 1299). The structure could also be explained by assuming short-range interactions only, but evidence is presented that adsorbate-adsorbate interactions mediated by quasi-one-dimensional surface resonances play a major role in both cases.
Silver nanoclusters arranged in quasi-one-dimensional chains with a nearest-neighbor cluster-cluster distance of 1.4 nm were prepared on the R͑15ϫ 12͒-C/ W͑110͒ surface. The silver cluster chains form local thermodynamic equilibrium structures. Interactions between neighboring clusters are addressed by investigating the length distributions of silver cluster chains with scanning tunneling microscopy. Comparison with theoretical expectations derived from a one-dimensional Ising model yields evidence for a slightly repulsive interaction energy of about 20-30 meV.
The atomic structure of various indium adlayers at submonolayer coverages on W͑110͒ is investigated by a density functional theory ͑DFT͒ approach as well as by analysis of low-energy electron diffraction intensities ͑LEED I / V͒. Single-atom adsorption is studied by DFT, with the result that adsorption at the pseudo-fourfold coordinated sites of the W͑110͒ is most preferable, followed by bonding to the pseudo-threefold and twofold short-bridge sites. Both theory and experiment reveal that for the ͑3 ϫ 1͒ structure, which corresponds to a coverage of 0.33 monolayer ͑ML͒, indium atoms occupy exclusively pseudo-fourfold coordinated sites, while for the ͑1 ϫ 4͒ phase ͑0.75 ML coverage͒ and ͑1 ϫ 5͒ phase ͑0.80 ML coverage͒, pseudo-threefold and twofold short-bridge sites are also occupied. According to DFT, the ͑1 ϫ 4͒ structure is the most stable one, closely followed by the ͑1 ϫ 5͒ structure. Analysis of DFT studies on free monolayers of In reveals the significant influence of In-In bonding on the formation of these adlayer structures. The low-coverage ͑3 ϫ 1͒ structure is energetically the least favorable one, in agreement with the experimental finding that the ͑3 ϫ 1͒ structure is only metastable and transforms with increasing time or upon annealing into islands of ͑1 ϫ 4͒ patterns. In order to investigate whether the ͑3 ϫ 1͒ structure might be stabilized by contaminants, DFT calculations were also performed for coadsorbing hydrogen and oxygen with indium on W͑110͒. However, the ͑3 ϫ 1͒ structure always remains metastable. Furthermore, we find that phase separated regions of oxygen patches and ͑1 ϫ 4͒ In islands are stabilized by about 1 eV/atom relative to mixed ͑3 ϫ 1͒ In+ O configurations. This is in very good agreement with the experimental observation that the ͑3 ϫ 1͒ → ͑1 ϫ 4͒ transition can be triggered by additional oxygen.
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