X-Ray Photoelectron Spectroscopy Study of a Self-Assembled Monolayer of Thiophene Thiol

Abstract
A thiophene derivative containing a thiol group, (3-thienylethyl)-11-mercaptoundecanoate, was deposited on a gold surface. The thiophene monomer formed a self-assembled monolayer (SAM). The structure of the SAM was characterized by X-ray photoelectron spectroscopy (XPS). The molecules were adsorbed at the thiol group with end-on configuration. Using the ratio of signal intensity of the two types of sulfur atoms in the thiol and thiophene groups, the escape depth of a photoelectron of the SAM was estimated to be 30 Å, which is slightly longer than the empirical value of 33 Å for SAMs of alkanethiols. This is because the bulky thiophene ring and the flexible ester group prevent the monolayer from forming a densely packed structure like the alkanethiol SAMs.

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