Formation of Ordered Self-Assembled Monolayers of Octylthiocyanates on Au(111) by Vapor Phase Deposition

Abstract

Self-assembled monolayers (SAMs) were formed by the spontaneous adsorption of octythiocyanate (OTC) on Au(111) using both solution and ambient-pressure vapor deposition methods at room temperature and 50°C. The surface structures and adsorption characteristics of the OTC SAMs on Au(111) were characterized by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM observation showed that OTC SAMs formed in solution at room temperature have unique surface structures including the formation of ordered and disordered domains, vacancy islands, and structural defects. Moreover, we revealed for the first time that the adsorption of OTC on Au(111) in solution at 50°C leads to the formation of SAMs containing small ordered domains, whereas the SAMs formed by vapor deposition at 50°C have long-range ordered domains, which can be described as (√3 × 2√19)R5° structures. XPS measurements of the peaks in the S 2p and N 1s regions for the OTC SAMs showed that vapor deposition is the more effective method compared to solution deposition for obtaining high-quality SAMs by adsorption of OTC thiocyanates on gold. The results obtained will be very useful in understanding the SAM formation of organic thiocyanates on gold surfaces.