MOLECULAR-STRUCTURE AND DYNAMICS WITHIN SELF-ASSEMBLED HEXAKISALKOXY-TRIPHENYLENE MONOLAYERS AND ALKANE WETTING FILMS

Scanning tunneling microscopy (STM) has been employed to investigate two classes of ultrathin molecular layers on the basal plane of highly oriented pyrolytic graphite (HOPG). First, molecules with three-fold symmetry were studied at solid-fluid interfaces. Structure and dynamics within the first monolayer of hexa-substituted triphenylenes with two different substitutions, -OC7H15 and -OC16H33, could be readily observed, since the molecules exhibit a strong contrast between the triphenylene cores and the alkyl side chains. While the dynamic disorder prohibited atomic-scale resolution imaging, sub-molecular resolution images were suitable to determine packing patterns together with a number of characteristic packing defects. No ordered monolayers could be observed from unsymmetrically substituted triphenylenes like triphenylene dimers, which in bulk materials do only exhibit glassy but no crystalline phases. Secondly, long chain alkanes have been observed, for the first time, in the vicinity of the edge of a solidified alkane-melt drop. The data indicate frozen disordered lamellae at the drop-edge, where the alkane phase is still many monolayers thick, while a columnar phase is found in a thin precursor layer some millimeter away from the drop-edge.