Molecular-Scale Investigation of Tolane Disulfide Self-Assembled Monolayers on Au(111) Using Scanning Tunneling Microscopy

Abstract

Molecular-scale surface structures of self-assembled monolayers (SAMs) formed by the spontaneous adsorption of tolane disulfides (TDS) on Au(111) in a 1 mM mixed solution of ethanol/N, N'-dimethylformamide (9:1) were examined using scanning tunneling microscopy (STM). The STM study revealed that TDS SAMs formed after a 24 h immersion at room temperature were composed of two-dimensional (2D) ordered phases with inhomogeneous surface morphologies and no clear domain boundaries. However, after 2 h immersion at 50 degrees C, uniform 2D ordered domains with clear domain boundaries were observed, which could be described as c(3 x root 3) structures with centered rectangular unit cell. Interestingly, a unique intermediate ordered phase with a low surface coverage was also observed. After a longer immersion for 24 h at 50 degrees C, only the uniform c(3 x root 3) domains were observed with a corrugation that may have reflected surface reconstruction of the Au(111) surfaces. From this study, we found that 2D ordered TDS SAMs with large and uniform domains on Au(111) can be obtained by controlling the solution temperature and immersion time.