Regensburg 2010 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 59: Poster Session II (Nanostructures at surfaces: Dots, particles, clusters; Nanostructures at surfaces: arrays; Nanostructures at surfaces: Wires, tubes; Nanostructures at surfaces: Other; Plasmonics and nanooptics; Metal substrates: Epitaxy and growth; Metal substrates: Solid-liquid interfaces; Metal substrates: Adsoprtion of organic / bio molecules; Metal substrates: Adsoprtion of inorganic molecules; Metal substrates: Adsoprtion of O and/or H; Metal substrates: Clean surfaces; Density functional theory and beyond for real materials)
O 59.58: Poster
Mittwoch, 24. März 2010, 17:45–20:30, Poster B1
Ultrathin Epitaxial Molecular C60 Layers on Bi(111):
Morphology, Strain State, and Order-Disorder Phase Transition — •Hichem Hattab, Dennis Meyer, Giriraj Jnawali, and Michael Horn-von Hoegen — Faculty of Physics, University of Duisburg-Essen, Lotharstr.1, 47048 Duisburg, Germany
Using Spot Profile Analyzing Low Energy Electron Diffraction (SPA-LEED) we have studied the order-disorder structural phase transition [1] of C60(111) films on a Bi(111) surface. Initially a smooth Bi(111) base film was prepared on Si(001) [2]. Sub-monolayer coverages of C60 were adsorbed at 80 K and annealed to 450 K. These molecular adsorbate layers exhibit a moiré pattern with a periodicity of 5 nm which is determined by the lattice mismatch of the C60 adlayer and the Bi(111) virtual substrate. The coverage of the C60 film was subsequently increased by additional deposition of C60 at 450 K. For each step LEED spot profiles were recorded at 80 K. Comparing these profiles, we conclude that the initial (1×1) phase changes into the disordered (2×2) phase as soon as the coverage is increased beyond a single layer of C60. The formation of the second molecular C60 layer is accompanied by a sudden relaxation of the lateral lattice parameter of the C60 adlayer. We have additionally confirmed that C60 films thicker than 1 BL show the temperature dependent surface orientational-disordering phase transition from (2×2) to (1×1) at 235 K in analogy to previous studies [1].
[1] A. Goldoni et al., Phys. Rev. B 54, 2890 (1996)
[2] G. Jnawali et al., Phys. Rev. B 74, 195340 (2006)