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The formation and structure of self-assembled monolayers (SAMs) by the adsorption of acetyl-protected 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). Molecular-scale STM imaging revealed 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. In this study, we clearly demonstrate that TBACN can be used as an effective deprotecting reagent for obtaining well-ordered SAMs of thioacetyl-protected molecules on gold.

Decylthiocyanate (DTC) self-assembled monolayers (SAMs) on Au(111) were prepared by solution and vapor phase deposition methods at 50 o C for 24 h. The formation and surface structure of DTC SAMs were examined using scanning tunneling microscopy (STM). STM imaging revealed that DTC SAMs formed in 1 mM ethanol solution at 50 o C were composed of small ordered domains with lateral dimensions of a few nanometers and disordered phases, whereas DTC SAMs formed in the vapor phase at 50 o C contained two ordered phases: a closely packed c(4 × 2) superlattice and a striped phase with an interstripe spacing of 2.6 -2.8 nm. It was also found that the ordered domain and vacancy island formation for DTC SAMs on Au(111) differs significantly from that of decanethiol SAMs, suggesting that adsorption mechanism is different from each other. From this study, it was confirmed that DTC SAMs with a high degree of structural order can be obtained by vapor phase deposition.

Alkanethiol self-assembled monolayers (SAMs) on metal surfaces are key elements for the fabrication of functional organic layers and devices in the broad fields of nanotechnology and biotechnology.1-7 However, it was found that alkanethiol SAMs were usually composed of structural defects such as domain boundaries and vacancy islands (VIs), which make them more amenable to oxidation. 1Compared to alkanethiols, thioethers (RSR') are more robust to oxidation, and their chemical structures with various alkyl chains can be modified readily by a simple synthetic method. Therefore, SAMs prepared using thioethers provide a very useful means for tuning the characteristics of metal surfaces. Despite these advantages, there have only been a limited number of papers involving the formation and structure of thioether SAMs on gold surfaces.9-15 It has been revealed that dioctadecyl sulfides (DODS, CH 3 (CH 2 ) 17 S(CH 2 ) 17 CH 3 ) at the initial growth stage form SAMs with striped phases in which the molecular backbones are oriented parallel to the surface, 9 whereas DODS SAMs formed after long immersion have two mixed phases containing closely packed and loosely packed standing-up phases where the molecular backbones are oriented perpendicular to the surface.10 High-resolution scanning tunneling microscopy (STM) observation revealed that the SAMs of dimethyl sulfides (DMS, CH 3 SCH 3 ) with the shortest alkyl chains on Cu(111) have a herringbone-like packing structure, 13 whereas dibutyl sulfides (DBS, CH 3 (CH 2 ) 3 S(CH 2 ) 3 CH 3 ) with slightly larger alkyl chains form striped phases.14 From these results, we assumed that the formation of dialkyl sulfide SAMs strongly depends on van der Waals interactions between alkyl chains.So far, there no data has been reported on the formation and structure of didodecyl sulfides (DDS, CH 3 (CH 2 ) 11 S(CH 2 ) 11 CH 3 ) with medium alkyl chains from a molecular-scale perspective. In this paper, we report the first STM results showing that the adsorption of DDS molecules at 70 ºC generating long-range ordered SAMs with a 7.5 × √3 striped phase with VIs-free surfaces.Dodecanethiol (DDT, CH 3 (CH 2 ) 11 SH) and DDS were purchased from Tokyo Chemical Industry (Tokyo, Japan). DDT and DDS SAMs were prepared by dipping the Au(111) substrate in 1 mM ethanol solutions of corresponding compounds at room temperature for 24 h. To understand the effect of solution temperature on the formation of DDS SAMs, the SAMs were prepared at 70 o C for 1 h. STM images were obtained using a NanoScope E (Veeco, Santa Barbara, CA, USA) with a commercial Pt/Ir (80:20) tip under ambient conditions.The STM images in Figure 1 show remarkable structural differences in the formation of ordered domains and VIs (dark holes) for DDT and DDS SAMs on Au(111) formed after 24 h immersion at room temperature. Figure 1(a) shows a typical packing structure of DDT SAMs with a c(4 × 2) superlattice formed at saturation coverage. DDT SAMs were mainly composed of ordered phases with three domain orientations (Regions A, B, and C...

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