We present a detailed investigation of the c(2ϫ2)-Br/Pt(110) adlayer structure supplemented by the analysis of the (1ϫ2) missing-row ͑MR͒ structure of the clean Pt͑110͒ surface. Quantitative low energy electron diffraction analyses and first-principles calculations are in impressive agreement in both cases. The clean surface reconstruction is determined with unprecedented accuracy. For the adsorbate, the analysis retrieves a simple Br-adlayer structure with the Br atoms residing in every second short bridge position on the closepacked Pt rows with the MR reconstruction lifted. The Br-Pt bond length Lϭ2.47 Å is almost equal to the sum of the atomic radii. The substrate below the adsorbate exhibits a contraction of the first layer spacing which amounts to half of that calculated for an unreconstructed clean surface.

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.

After our recent report on the formation of a (3ϫ1) charge-density-wave phase in the quasi-onedimensional system Br/Pt͑110͒ we present a detailed investigation of the c(2ϫ2)⇒(3ϫ1) transition in the Br/Pt͑110͒ adsorption system. This includes the atomic structure of the (3ϫ1) phase as determined by quantitative low-energy electron diffraction ͑LEED͒ and density functional theory calculations. While in the parent c(2ϫ2) phase with coverage ⌰ϭ1/2 ML the Br atoms occupy every second short-bridge site on the unreconstructed (1ϫ1)-Pt͑110͒ surface, the adatoms in the (3ϫ1) phase at coverage ⌰ϭ2/3 ML reside in every third short-bridge and long-bridge sites. Charge densities and vertical relaxations of the Pt atoms forming the short-and long-bridge sites are different, thus yielding a modulation of both, the charge and the position of the outermost Pt atoms with a period of three nearest-neighbor spacings. For 1/2 MLϽ⌰р0.58 ML LEED intensity and scanning tunneling microscope ͑STM͒ measurements reveal the nucleation of (3ϫ1) islands surrounded by areas with a local coverage of 1/2 ML. Within the latter areas the STM measurements indicate dynamical fluctuations of the Br positions at room temperature. In the time average every short-bridge site is sampled by the mobile Br atoms, but in the neighborhood of (3ϫ1) islands every third short-bridge site seems to be preferentially occupied.

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