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

Scanning tunneling microscopy (STM) has been employed to investigate t wo classes of ultrathin molecular layers on the basal plane of highly oriented pyrolytic graphite (HOPG). First, molecules with three-fold s ymmetry 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 obser ved, since the molecules exhibit a strong contrast between the triphen ylene cores and the alkyl side chains. While the dynamic disorder proh ibited atomic-scale resolution imaging, sub-molecular resolution image s were suitable to determine packing patterns together with a number o f characteristic packing defects. No ordered monolayers could be obser ved from unsymmetrically substituted triphenylenes like triphenylene d imers, which in bulk materials do only exhibit glassy but no crystalli ne phases. Secondly, long chain alkanes have been observed, for the fi rst 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 pha se is found in a thin precursor layer some millimeter away from the dr op-edge.