Effects of Chain Length on Adhesive Force between Gold Tip and Gold Substrate Covered with Alkanethiol Self-Assembled Monolayers

Abstract

The effects of chain length on adhesive force between a gold-coated tip and a Au(111) substrate covered with alkanethiol self-assembled monolayers (SAMs) were studied. By microcontact printing (µ-CP), we prepared a patterned surface covered with two types of n-alkanethiol that have the same CH3-terminal functional group but different chain lengths. As a method for mapping adhesive force, pulsed-force-mode atomic force microscopy (PFM-AFM) was used. PFM-AFM enables the simultaneous imaging of surface topography and adhesive force. Regardless the use of the same CH3-terminal functional group to modify a surface, a difference in adhesive force corresponding to the printed pattern was observed. The adhesive force on a printed region covered with a longer alkanethiol SAM was slightly smaller than that of an unprinted region covered with a shorter alkanethiol SAM chemisorbed from solution after µ-CP. The possible molecular mechanisms for the difference in the observed adhesive force were discussed in detail.