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    Surface Science Tuesday Sessions
       Session SS+BI-TuA

Paper SS+BI-TuA9
Alkanethiols on Copper Single Crystal Surfaces

Tuesday, October 30, 2001, 4:40 pm, Room 120

Session: Poirier Memorial Session: Self-Assembled Monolayers II
Presenter: S. Vollmer, Ruhr-Universität Bochum, Germany
Authors: S. Vollmer, Ruhr-Universität Bochum, Germany
G. Witte, Ruhr-Universität Bochum, Germany
C. Wöll, Ruhr-Universität Bochum, Germany
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Ultrathin organic films of self-assembled molecules (SAMs) have attracted considerable interest because of their promising technical applications. Whereas the vast majority of related studies have been focused on alkanethiolate (C@sub n@) films on gold surfaces, which are considered as prototype systems, the structure and properties of SAMs on transition metal surfaces are by far less intense studied. Here we present the results of a comprehensive study of the formation and structure of alkanethiol monolayers of various chain length (n @<=@ 12) on the low indexed copper surfaces [i.e. (111), (100) and (110)]. The films which have been prepared by gas phase adsorption under UHV conditions were characterized by means of XPS, TDS, LEED and HAS. At low temperatures alkanethiol molecules are physisorbed with their molecular axis parallel to the surface without any long range ordering. With increasing temperature (110-250K) a conversion into a copper thiolate species takes place depending on the alkyl chain length which is accompanied by an upright tilting of the molecules. Upon adsorption at room temperature highly ordered thiolate monolayers are observed of which structures depend only on the substrate orientation but not on the chain length. Heating the films above 380K causes a S-C bond cleaving and desorption of the entire alkyl chains leaving the S-atoms on the surface. Surprisingly, the saturation structures are metastable and decompose already at about 250K upon partial desorption of the alkyl chains into a thermodynamically stable mixture of thiolate and sulfide species. The presently observed differences to the case of SAMs on gold surfaces are attributed to the much stronger S-Cu interaction.