Formation of Ordered Self-Assembled Monolayer of Octylthiocyanates on Au(111)

Abstract

Octythiocyanate (OTC) self-assembled monolayers (SAMs) on Au(111) were fabricated by both solution and ambient-vapor deposition techniques at room temperature and 50 °C and their surface structures and adsorption conditions were characterized by scanning tunneling microscopy (STM) and x-ray photoelectron spectroscopy (XPS). STM imaging revealed for the first time that the adsorption of OTC on Au(111) in solution leads to the formation of partial ordered SAMs containing small ordered domains, whereas OTC SAMs formed by vapor deposition have a long-range ordered domains, which can be described as (√3 × √19)R5°structure. From molecular-scale STM results and XPS results concerned with the spectra in the S 2p and N 1s regions for OTC SAMs on Au(111), it was found that vapor deposition is more suitable for the fabrication of high-quality thiocyanate SAMs on gold compared to solution deposition techniques. Our results will be very useful in understanding the SAM formation of organic thiocyanates on gold surfaces.