Self-Assembling Properties of 11-Ferrocenyl-1-Undecanethiol on Highly Oriented Pyrolitic Graphite Characterized by Scanning Tunneling Microscopy

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Molecular resolution scanning tunneling microscope (STM) images the spontaneous self-assembly of 11-ferrocenyl-1-undecanethiol ((C₅H₅)Fe(C₅H₄)(CH₂)₁₁-SH) forming a large striped-phase on highly oriented pyrolitic graphite (HOPG) at a phenyloctane-HOPG interface. In the image, the alkyl chains lying flat on HOPG appear as bundles in groups of five in the moiré pattern due to lattice mismatch with the underlying HOPG. The ferrocene units appearing as either fuzzy or ring-like structures suggest the random rotation of cyclopentadienyl (Cp) rings sandwiching the central iron ion of the ferrocene moieties with their principal axis either oblique or perpendicular to the HOPG. The ferrocene moieties are more clearly resolved in a mixed film with octanethiol, where the fuzzy or ring-like structures of the ferrocene units are asymmetrically distant from the sulfur head-groups forming alternating rows in the phase segregated image. Both molecules can be clearly distinguished by the length of the molecular rows. [DOI: 10.1380/ejssnt.2008.119]