Formation and surface structure of Dialkyl Sulfide Self-Assembled Monolayers on Au(111)

Abstract

Self-assembly of organosulfurs has been studied extensively due to their value of application in nanoelectronics, surface passivation, and biointerfaces. The characteristics of dialkyl sulfide SAMs (DAS) are poorly understood compared to those of alkanethiol SAMs. Surface structures, electrochemical properties, and binding conditions of symmetrical and asymmetrical DAS self-assembled monolayers (SAMs) with various alkyl chain lengths (CH3(CH2)nS(CH2)nCH3, n=0,3,7,9,11) were investigated by means of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) measurements. STM imaging showed that the surface structures of DAS SAMs were markedly different from those of alkanethiol (AT) SAMs or dialkyl disulfide (DADS) SAMs. AT and DADS SAMs have well-ordered domains containing a c(4 × 2) structure and many vacancy islands (VIs), whereas DAS SAMs have large ordered domains showing a line structure and a few VIs. The formation of DAS SAMs was markedly influenced by immersion time, dipping temperature and annealing effect. From this study, we have clearly demonstrated that the adsorption process of DAS molecules on Au(111) differs from that of DADS molecules during molecular self-assembly.