π-컨쥬게이션 분자들에 의한 자기조립단분자막의 형성과 나노구조

Abstract

The formation and structure of self-assembled monolayers (SAMs) by the adsorption of acetyl-protected tolanethioacetate (TTA) and octylthioacetate (OTA) on Au(111) in a catalytic tetrabutylammonium cyanide (TBACN) solution were examined by means of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). We found that SAM formation by TTA on Au(111) strongly depends on experimental conditions for the deprotection of acetyl group. Molecular-scale STM imaging revealed that TTA molecules on Au(111) can form better-ordered SAMs in tetrabutylammonium cyanide salt (TBACN) catalytic medium compared to in pure solvent. TTA molecules on Au(111) at 50 ?C for 24 h in catalytic TBACN solution formed unique ordered phase, which can be described as a (2 ? √7)R62? structure. TTA molecules on Au(111) room temperature (RT) for 24 h in catalytic TBACN solution is described as a (3 ? √8)R50? structure. In addition, XPS measurements showed a strong S 2p peak at 162 eV for TTA SAMs on Au(111), implying that the SAMs were formed via chemical reactions between the sulfur atoms and gold surfaces. We also conformed that OTA molecules on Au(111) in a pure solvent form disordered SAMs, whereas they form well-ordered SAMs showing a c(4 ? 2) structure in a catalytic TBACN solution. XPS and CV measurements also revealed that OTA SAMs on Au(111) formed in a TBACN solution have a stronger chemisorbed peak in the S 2p region at 162 eV and a higher blocking effect compared to OTA SAMs formed in a pure solvent. From these results, we clearly revealed that TBACN can be used as an effective deprotecting reagent for obtaining well-ordered SAMs of thioacetyl-protected organic molecules on gold. On the other hand, TDS SAMs formed after 24 h immersion at RT were composed of 2D ordered phases with inhomogeneous surface morphologies and no clear domain boundaries, whereas TDS SAMs formed after 2 h at 50?C contained two-ordered phases with clear domain boundaries, a high coverage c(3 ? √3) structure, and a unique intermediate phase with low coverage. After 24 h immersion at 50?C, only the uniform c(3 ? √3) domains with a corrugation that may reflect surface reconstruction of Au(111) was observed. From our STM study, we revealed that 2D ordered TDS SAMs with large and uniform domains on Au(111) can be achieved by controlling the solution temperature and immersion time. In addition, we checked effect of microwave for SAM formation of aromatic thiols (biphenylthiol (BPT) and benzenethiol (BT)). We found that gold adatom islands appeared during SAM formation can be effectively removed from the surfaces by microwave treatment. Therefore we suggest that microwave technique is very useful for obtaining aromatic thiol SAMs with high quality.