다이알킬 다이썰파이드와 모노썰파이드 분자의 자기 조립 및 나노구조

Abstract

Formation of self-assembled monolayers (SAMs) by the spontaneous adsorption of dialkyl sulfides (DAS) and asymmetrical dialkyl disulfides (DADS) were examined by means of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) measurements. STM imaging showed that DAS SAMs have completely different surface characteristics, such as ordered structures and density of vacancy island, compared with those of alkanethiol (AT) SAMs or dialkyl disulfide (DADS) SAMs. AT and DADS SAMs have many ordered small domains and defects, whereas, in generally, DAS SAMs have large domains with line structures and a few defects. Interestingly, the adsorption of octanethiol (OT) on Au(111) in a 1 mM ethanol solution at room temperature (RT) for 24 h yields well-ordered SAMs with (√3 × √3)R30˚ or c(4 × 2) structure regardless of immersion time, whereas dioctyl sulfide (DOS) form well-ordered SAMs with quite different packing structure, which can be described as (7 × √3)R20˚ superlattice. In addition, although DDT molecules form well-ordered SAMs with (√3 × √3)R30˚ or c(4 × 2) structure regardless of immersion time and temperature, DDS SAMs form partially ordered domains with line structures. Moreover, we found that long-range ordered DDS SAMs can be prepared at high solution temperature of 70 ˚C for 1h, suggesting that the diffusion rate of DDS is important factor for the formation of monosulfide SAMs. To compare the adsorption behaviors of DAS and DADS SAMs on Au(111), we examined the surface structure of these SAMs prepared by solution and vapor deposition techniques. It was found that the structures of dodecyl octyl disulfide (DDODS) SAMs are also remarkably different from those of dodecyl octyl sulfide (DDOS) SAMs. Especially, we revealed that the DDODS SAMs prepared by vapor deposition have well-ordered line structure or densely packed (√3 × √3)R30˚ structure, whereas DDOS SAMs prepared by solution deposition have short-range line structure. The remarkable structural differences of DAS SAMs are attributed to intact adsorption of DAS molecules on gold surfaces, contrary to the dissociative adsorption of the S-H bond of AT or the S-S bond of DADS.