다이알킬 썰파이드와 피롤 말단기를 갖는 알칸싸이올의 자기조립 및 나노구조

Abstract

Dialkyl monosulfides self-assembled monolayers (SAMs) are more robust to oxidation, and their chemical structures with various alkyl chains can be modified readily by a simple synthetic method compared to alkanethiol SAMs. In this study, dialkyl monosulfide SAMs were prepared by spontaneous adsorption of ethyl octyl sulfide (EOS), hexyl octyl sulfide (HOS), dioctyl sulfide (DOS), dodecyl octyl sulfide (DDOS) on Au(111) using both solution and ambient-pressure vapor deposition methods. The surface structure, adsorption condition, and thermal stability of the SAMs on Au(111) were characterized by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammogram (CV). STM imaging showed that dialkyl monosulfides SAMs have completely different surface structures compared to alkanethiol SAMs. On the other hand, XPS measurements showed that sulfur S 2p peaks for EOS, DOS, HOS and DDOS SAMs are nearly identical with those for alkanethiol SAMs, suggesting that the sulfur atoms would interact chemically with gold surfaces. CV measurements revealed that DOS SAMs with symmetric alkyl chains have single reductive desorption peak, whereas EOS and HOS SAMs with unsymmetric alkyl chains have two desorption peaks. I found that reductive desorption behaviors of dialkyl sulfide SAMs strongly depend on the composition and strength of van der Waals interaction of SAMs. I found that the SAMs of Octanethiol, Dioctyl Sulfide and Dioctyl Disulfide were somposed of well-ordered domains regardless of the chemical structure of sulfur head-groups. In addition, pyrrole-terminated alkanethiols SAMs were formed by the spontaneous adsorption of 6-(N-pyrrolyl)hexane-1-thiol, 8-(N-pyrrolyl)octane-1-thiol, 10-(N-pyrrolyl)decane-1-thiol, and 12-(N-pyrrolyl)dodecane-1-thiol on Au(111) using both solution and ambient-pressure vapor deposition methods. STM observation shows that the SAMs formed in solution have mainly disordered domains, but the SAMs formed by vapor deposition have more uniform surface with clear vacancy islands. And the surface structure of these SAMs was examined using ex-situ and in-situ STM measurements. The clear domains and vacancy islands were visualized through in-situ sample preparation and STM measurements. XPS measurements for pyrrole-terminated alkanethiols SAMs show that sulfur atoms are chemically bond to the gold surface. The thermal desorption behaviors and reductive desorption behaviors of the SAMs on Au(111) were characterized by means of thermal desorption spectroscopy (TDS). TDS measurements reveal that the SAMs were mainly desorbed as decomposed species after dissociative reaction of C-S bond during heating. CV peaks of the reductive desorption spectra about pyrrole-terminated alkanethiols SAMs on Au(111). As the alkyl chain length increases, the desorption peaks shift to high potential position. This is because the intermolecular interaction increases with increasing the alkyl chain length.