Structures of self-assembled monolayer of alkanes adsorbed on Au(111) surfaces
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The structure of self-assembled monolayers of long n-alkane molecules deposited on an Au(111) surface has been studied by in situ scanning tunnelling microscopy at 300 K, These monolayers are formed on Au(111) either at the interface between gold and a solution of hexatriacontane (C36H74) in tetradecane, or by ultrahigh vacuum (UHV) deposition of octatriacontane (C38H78). At the liquid/solid interface, the monolayer consists of a close-packed arrangement of lamellae separated by troughs. Perfect side-to-side packing of C36H74 molecules, the long axis of which stays parallel to Au  directions, forms each lamella, Lamella present two different widths (4.8 +/- 0.1 and 4.5 +/- 0.1 nm) determined by the molecular orientation with respect to troughs. In contrast, the monolayers obtained after UHV deposition at 300 K show poor organization with meandering lamellae and troughs that present strong variations in width. Nevertheless, all the C38H78 molecules stay parallel to the  directions of Au(111), Annealing such monolayers at 350 +/- 5 K yields a structure that looks like the one observed at the liquid/solid interface. These results show a directional epitaxy relationship perpendicular to the  directions of Au(111) in a monolayer of C36H74 and C38H78 molecules. We discuss the origin of the differences observed between the molecule packing at the liquid/solid interface and the one in monolayers built in UHV at 300 K. Copyright (C) 2000 John Wiley & Sons, Ltd.
CitationSURFACE AND INTERFACE ANALYSIS，2000,30（1）：167-169