Regensburg 2002 – wissenschaftliches Programm

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O: Oberflächenphysik

O 34: Organische Dünnschichten

O 34.8: Vortrag

Donnerstag, 14. März 2002, 17:15–17:30, H45

Chain-length dependent structure and stability of tilted-phases of alkanethiols on Au(111) — •Esther Barrena1, Elisa Palacios2, Carmen Ocal2, and Miquel Salmeron31Max-Planck-Institut für Metallforschung, Heisenbergstr. 1, 70569 Stuttgart, Germany — 2Instituto de Ciencia de Materiales de Madrid, Cantoblanco, 28049 Madrid, Spain — 3Lawrence Berkeley National Laboratory, Berkeley, 94720 California, USA

Previously we have shown that alkanethiols and alkylsilanes undergo a series of tilted-phases under compressive stress [1,2]. Here we show the existence of an ordered (2×√3)rect 50 tilted phase spontaneously formed by alkanethiols on Au(111) at a partial coverage. Islands exhibiting this phase coexist with islands in the (√3×√3)R30 structure, which is characteristic of complete monolayers (the molecular tilt is around 30). For C22 and C18, the 50 tilted phase can be irreversibly transformed into the most stable hexagonal structure by mechanical perturbation with the AFM tip. A similarly tilted phase is obtained for C10. However, in this case the transition cannot be induced, i.e. the C10 tilted phase is energetically more favorable than that one for long molecules. Furthermore, a detailed AFM and GIXD study reveals that, in fact, the C10 tilted phase has a different structure (4×√3)rect. This can be understood in terms of the competition between the interaction with the substrate (chemical bonding plus van der Waals interaction) and the van der Waals interaction between the chains. ([1] E. Barrena, S. Kopta, D. F. Ogletree, D. H. Charych, M. Salmeron, Phys.Rev.Lett. 82, 2880 (1999). [2] E. Barrena, C. Ocal, M. Salmeron, J. Chem. Phys. 113, 2413 (2000).)

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