Monolayer formation of 6-deoxy-6-thiol-beta-cyclodextrin on a Au(111) surface studied by scanning tunneling microscopy

Mono(6-deoxy-6-thiol) beta -cyclodextrins (beta -CyD-SH) were grown on a Au (111) surface in ethanol solution, and monolayer formation process of which was studied by scanning tunneling microscopy for the first time. At the in itial stage, beta -CyD-SH molecules were adsorbed on the Au(111) surface no t only randomly, but also partially in a linear ordering. In the following stage, islands were formed and resulted in a uniform monolayer. The observe d mechanism is completely different from the model predicted on the basis o f the macroscopic result, the Langmuir model. An attractive interaction exi sts between beta -CyD-SHs, contrary to the prediction by the model. The obs erved growth processes are quite similar to what was previously observed fo r lipoamide-beta -cyclodextrin (LP-beta -CyD). However, in the case of beta -CyD-SH, the islands did not grow in size as compared to the case of LP-be ta -CyD, and the number of the islands increased to form a uniform monolaye r. This characteristic indicates that the interaction strength ratio of CyD -Au to CyD-CyD is larger for beta -CyD-SH than that for LP-beta -CyD. (C) 2 001 American Vacuum Society.