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O: Fachverband Oberflächenphysik

O 67: Metal surfaces: Adsorption of H/O and inorganic molecules

O 67.4: Vortrag

Donnerstag, 29. März 2012, 11:15–11:30, MA 043

Iodine on Pt(110) - competing phases — •Nadja Oberkalmsteiner, Michael Cordin, and Erminald Bertel — Institute of Physical Chemistry, University of Innsbruck, Innsbruck, Austria

The adsorption of halogens on Pt(110) leads to an exceedingly rich phase diagram. This is due in part to the competition between different ordered phases at the same coverage of Θ=0.5 ML. In previous experiments with Br/Pt(110) a c(2x2) structure was observed at room temperature, while a small excess coverage led to the appearance of a threefold periodicity. The latter structure however, was strongly fluctuating, thus neither the exact coverage nor the structure could be determined unambiguously. Here we present STM data on the Θ=0.5 ML room temperature phase of Iodine on Pt(110). Similarly to Bromine, a long-range ordered c(2x2) structure is observed. A minute excess coverage leads to nucleation of a (3x1) structure with local coverage of Θ=0.66 ML. The presence of such a few highly dispersed (3x1) nuclei, however, switches the rest of the surface with Θ=0.5 ML local coverage into a global (3x2) structure. Since the Iodine adlayer does not fluctuate at room temperature, one can determine precisely the excess coverage required to switch the whole surface to the threefold periodicity. The observed transition clearly demonstrates the long-range nature of the interaction in real space, thus arguing for an electronically driven phase transition. Remarkably, the (3x2) structure involves a considerably buckling of the substrate pointing towards an inherent instability of the Pt(110) surface. Apparently both halogens promote a charge density wave/periodic lattice distortion transition of Pt(110).