Scanning tunnelling microscopy of various alkanols and an alkanethiol adsorbed onto graphite

Abstract

Scanning tunnelling microscopy has been used to image monolayers of octadecanol, octadecanethiol, docosanol, hexacosanol and triacontanol adsorbed onto graphite under ambient conditions. These studies confirm the ‘herringbone’ and ‘parallel’ packing room-temperature structures observed previously for octadecanol and triacontanol, respectively. Adsorbed layers of docosanol and hexacosanol have been imaged for the first time. Docosanol was found to form monolayers containing both ‘herringbone’ and ‘parallel’ oriented dimers, giving rise to complex domain structures and complex domain boundaries. Hexacosanol has been shown to be adsorbed exclusively in the ‘parallel’ packed structure. A new type of sub-domain structure has been observed in certain triacontanol monolayers. Successive scans of triacontanol monolayers show evidence for the motion of domain walls and molecular rearrangement within domains. Preliminary studies on binary mixtures of octadecanol and triacontanol suggest preferential adsorption of triacontanol. Finally, domain structures have been observed for monolayers of octadecanethiol, although the molecular packing within the domains has not been resolved.