Berlin 2005 – wissenschaftliches Programm

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O: Oberflächenphysik

O 27: Phasenüberg
änge

O 27.5: Vortrag

Samstag, 5. März 2005, 16:00–16:15, TU EB107

Order-disorder transition of halogens on Pt(110) by I(T)-LEED — •Thomas Loerting, Clemens Deisl, Mariana Minca, Alexander Menzel, and Erminald Bertel — Institute of Physical Chemistry, University of Innsbruck, Austria

We have recorded low-energy electron diffractograms for halogen overlayers on Pt(110) as a function of temperature at constant coverage and electron gun voltage. A sharp decline of the fractional order spots indicates an order-disorder transition from both the (3×1) and c(2×2) phases to a disordered (1×1) phase at approximately 375 K. The peak profiles and the integrated scattered intensities of various spots on these LEED-films have been investigated according to critical scattering theory both in the [110] and [100] direction. The (3×1) as well as the c(2×2) halogen overlayer show a clear anisotropy in their phase transition behaviour, which corroborates our earlier claim of the quasi-one-dimensional nature of these systems. On the other hand, there are also pronounced differences between the phase transitions. Whereas the c(2×2) superstructure shows the expected behaviour for a continuous second-order phase-transition, e.g., the divergence of the correlation length at the critical temperature, the (3×1) superstructure shows a quite different behaviour, which also involves a change in the platinum substrate. Possible mechanisms for the (3×1)→disorder phase transition will be discussed, in particular with respect to a Peierls transition as previously proposed by us.