Dresden 2006 – scientific programme

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O: Oberflächenphysik

O 21: Phase transitions

O 21.4: Talk

Tuesday, March 28, 2006, 12:00–12:15, WIL C207

Unusual reversible disorder-order transition in Br/Pt(110) below 100 K — •Enrico Donà and Erminald Bertel — Institut für Physikalische Chemie, Innrain 52a, Innsbruck Austria

The temperature dependence of Bromine overstructures on Pt(110) has been investigated by variable-temperature scanning tunneling microscopy (VT-STM). Surprisingly, for the c(2x2)structure formed at a coverage of 0.5 monolayers (ML) at room temperature it was found that the long-range order disappears upon lowering the temperature. Strongly anisotropic domains elongated along the [1-10]directions are formed, which exhibit local (2x1) or c(2x2) symmetry. In addition, areas with a local (3x1) geometry are also observed. While it is known from DFT calculations that the (2x1) phase is energetically slightly favoured with respect to the c(2x2) phase, the (3x1) phase is believed to be distinctly higher in energy [1]. The present data seem to indicate that the three phases are almost degenerate at T ∼ 50 K, whereas at room temperature the c(2x2) phase is stabilised. Possible mechanisms for this phenomenon are entropic stabilisation or an incipient Peierls transition into an incommensurate phase.

[1] J. Redinger, R. Zucca, private communication