MOLECULARLY RESOLVED SURFACE SUPERSTRUCTURES OF SELF-ASSEMBLED BUTANETHIOL MONOLAYERS ON GOLD

Self-assembled monolayers of butanethiol adsorbed onto highly uniform Au/mica films have been studied using in-air scanning tunneling micros copy (STM) and infrared spectroscopy. STM images taken of fully equili brated films show molecularly resolved features that are believed to c orrespond to the methyl terminations of the organic surface. Large dom ains of organized adsorbates and a variant of the previously reported px root 3 superlattice structure are observed on these surfaces; using this nomenclature, the basic repeat unit of the structure reported he rein corresponds to 7x root 3. Lateral variations in the elevations of striped structures are tentatively assigned to thiolates bound into f ee sites of the Au(111) substrate. We have also observed molecular str ucture in regions of the superlattice that were structureless in UHV-S TM studies. These observations suggest that the filling factor of the fully equilibrated surfaces is highly sensitive to the manner of sampl e preparation and storage. Large-scale desorption of thiolates does no t appear to be a necessary step in the formation of highly organized f ilms of these short-chain systems when equilibrated in thiol/methanol solutions, and the sample processing history may have significant effe cts on the ultimate surface topology.