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O: Oberflächenphysik

O 21: Phase transitions

O 21.5: Vortrag

Dienstag, 28. März 2006, 12:15–12:30, WIL C207

A Low-Energy Electron Diffraction Study of Phase Transitions in Br/Pt(110) — •Simon Penner, Thomas Lörting, and Erminald Bertel — Institut für Physikalische Chemie, Innrain 52a, A-6020 Innsbruck, Austria

Peak shape analysis of low-energy electron diffraction spots recorded as a function of temperature are used to analyse phase transitions in c(2x2) and (3x1) Bromine overstructures on Pt(110). A well-defined one-dimensional order-disorder transition at 370 K in the c(2x2) structure indicates the existence of long-range interactions within the adsorbate layer consistent with a quasi-1D electronic structure. Lowering the temperature to ∼ 100 K leads to an unexpected decrease in the long-range order consistent with observations by variable-temperature STM. It is shown that the decay of the long-range order cannot be attributed to contamination but seems to be related to fluctuations which involve the substrate atoms as well. Similar experiments carried out for various Br coverages 0.5 monolayers (ML) < Θ < 0.67 ML also point to the possibility that the substrate plays an essential role in driving the phase transitions. A possible explanation in terms of a Peierls mechanism is discussed.