Dresden 2009 – scientific programme
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O: Fachverband Oberflächenphysik
O 25: Surfaces and films: forces, structure and manipulation
O 25.4: Talk
Tuesday, March 24, 2009, 15:45–16:00, SCH A118
Second order phase transition and critical fluctuations in a quasi-1D system: Br/Pt(110) — •Michael Cordin1, Barbara Lechner1, Alexander Menzel1, Erminald Bertel1, Cesare Franchini2, Rainaldo Zucca2, and Joseph Redinger2 — 1Institute for Physical Chemistry, University of Innsbruck, Austria — 2Center for Computational Materials Science, Vienna University of Technology, Austria
Deposition of 0.5 monolayers (ML) of Bromine on Pt(110) results in a c(2x2)-Br/Pt(110) structure with almost perfect long-range order at 300 K. Upon cooling this structure to 50 K a reversible, apparent "inverse" order-disorder transition is observed. On a nearly defect-free surface the c(2x2) structure decays into striped c(2x2) and (2x1) domains. The resulting stripe pattern exhibits typical hallmarks of critical behaviour, i.e. a scale-free domains-in-domains structure. We therefore conclude that there is a continuous phase transition between the (2x1) and the c(2x2) structure and the disorder at 50 K is due to the proximity of the critical temperature. The conclusion is supported by DFT calculations, which place the (2x1) as the stable groundstate 17 meV below the c(2x2) structure (at 0 K). Even very small defect concentrations lead to the appearance of a third structural element at 50 K, namely a local (3x2) unit mesh[1]. Possible origins of the continuous phase transition will be discussed.
[1] E. Dona et al., Phys. Rev. Lett. 98, 186101 (2007).