Comparative study of monolayers self-assembled from alkylisocyanides and alkanethiols on polycrystalline Pt substrates.

Abstract

This paper compares the properties of self-assembled monolayers (SAMs) derived from octadecylisocyanide (ODI) and octadecanethiol (ODT) on polycrystalline Pt substrates. Both monolayers formed at a similar rate using 1.0 mM solutions in ethanol and achieved a thickness of 22-23 A after 24 h as determined by ellipsometry measurements. The advancing contact angles of ODI and ODT monolayers were found to be 113 and 117 degrees, respectively, suggesting a slight difference in structure between them. X-ray photoelectron spectroscopy revealed that SAMs of ODT were more stable than those of ODI, which was supported by experiments that probed desorption of these layers in prewarmed hexadecane. Cyclic voltammetry measurements indicated that both monolayer systems could diminish electron-transfer rates substantially, although ODT monolayers were more effective and robust than their ODI counterparts. The resistance of the SAMs to ion penetration differed in a similar way, and a microcontact-printed monolayer of ODT could protect the underlying Pt better in an HCl/Cl2-based etch process than the one formed from ODI.