| Abstract
| - In order to find factors which determine the two-dimensionalstructure of self-assembled monolayers(SAMs), several classes of thiols and disulfides on gold (111) havebeen investigated by atomic force microscopy(AFM). SAMs were formed from a series of symmetrical andasymmetrical diethylalkanoate disulfides,ω-hydroxy- and ω-carboxyalkanethiols, diacetylene disulfides, anddifferent anthracene terminated thiolsand disulfides. In all the cases, two-dimensional crystallinestructures could be resolved; even for anasymmetrical diethylalkanoate disulfide that had a chain lengthdifference of five methylene units. Thelattices were analyzed quantitatively. Two distinctly differenttypes of crystalline structures were observed,namely, a hexagonal and a centered rectangular lattice. For thediethylalkanoate disulfides with shortalkyl chains (n ≤ 10) both structural phases were observed,domains with a hexagonal lattice existingsimultaneously with centered rectangular domains. The length ofthe alkyl chain determined the probabilityof finding disulfides in the hexagonal structure. This dependenceon the shape of the molecules as wellas the clear contrast of SAMs of asymmetric disulfides suggest that theAFM tip penetrates into the SAMsand probes, at least partially, the interior of the layers. Withthe atomic force microscope no differencewas observed between SAMs formed from thiols and those fromdisulfides.
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