Formation and Structure of Highly Ordered Self-Assembled Monolayers by Adsorption of Acetyl-Protected Conjugated Thiols on Au(111) in Tetrabutylammonium Cyanide Solution

Abstract

The surface structure and binding conditions of self assembled monolayers (SAMs) on Au(111) derived from 1-acetylthio-4-[(phenyl)ethynyl]benzene (OPE2-SAc) without and with tetrabutylammonium cyanide (TBACN) as a deprotection reagent were examined using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM observation revealed that OPE2-S SAMs on Au(111) formed from direct adsorption of OPE2-SAc in 1 mM methanol solution at room temperature (RT) for 24 h were composed of short-range, ordered phase separated by a disordered phase. In contrast, adsorption of OPE2-SAc SAMs on Au(111) at a higher solution temperature of 50 degrees C for 24 h led to formation of a fully ordered phase with slightly increased domain size. The structural quality of OPE2-S SAMs on Au(111) was remarkably enhanced when TBACN was used. OPE2-S SAMs at RT had a well-ordered (root 3 X root 7)R30 degrees structure with a domain size larger than 80 nm. The SAMs deposited at 50 degrees C contained very uniform and highly ordered domains with a size exceeding 100 nm, which can be assigned to a (2 X 3 root 3)rect structure. XPS measurements showed that OPE2-S SAMs were mainly formed via chemical interactions between sulfur and the Au(111) surface regardless of the use of a TBACN deprotection reagent. In this study, we reported the first molecular-scale features of OPE2-S SAMs on Au(111) with highly ordered domains derived from OPE2-SAc and clearly demonstrated that TBACN can be used as an effective deprotection reagent for formation of uniform and well-ordered OPE2-S SAMs with long-range domains derived from thioacetyl-protected OPE2-S molecules on Au(111).