Jensen Stephen C, Baber Ashleigh E, Tierney Heather L, H Sykes E Charles
Department of Chemistry, Tufts University, Medford, Massachusetts 02155-5813, USA.
ACS Nano. 2007 Dec;1(5):423-8. doi: 10.1021/nn700243r.
The literature contains many studies of thiol-based, self-assembled monolayers (RSH); however, thioethers (RSR) have barely begun to be explored, despite having the potential advantages of being more resistant to oxidation and allowing for the control of self-assembly parallel to the surface. This paper describes a low-temperature scanning tunneling microscopy investigation of dimethyl sulfide on Cu{111}. Previous work on the adsorption of dibutyl sulfide on Cu{111} revealed that intermolecular van der Waals interactions directed the parallel ordering of dibutyl sulfide molecules in linear rows. Upon annealing to 120 K, small dibutyl sulfide domains reordered into very large, ordered domains free of defects. The current study reveals the effect of the shorter alkyl chain length of dimethyl sulfide on both the rate of diffusion and the packing structure of the molecule. At a medium surface coverage and at 78 K, it was found that dimethyl sulfide is mobile and forms large, ordered islands without the 120 K annealing that was required for dibutyl sulfide to arrange. Also, the molecular packing structure evolves from quadrupole-quadrupole interactions and results in a perpendicular arrangement of neighboring molecules instead of the parallel arrangement observed for dibutyl sulfide. We show high-resolution images of the dimethyl sulfide islands in which submolecular features are revealed. These high-resolution data allow us to propose a structural model for the adsorption site of each dimethyl sulfide molecule within the ordered structures. These results demonstrate that the length of the alkyl side chain is an important factor in determining how thioethers self-assemble on metal surfaces.
文献中有许多关于硫醇基自组装单分子层（RSH）的研究；然而，硫醚（RSR）尽管具有更耐氧化以及能够实现与表面平行的自组装控制等潜在优势，但几乎尚未开始被探索。本文描述了对二甲基硫在Cu{111}上的低温扫描隧道显微镜研究。先前关于二丁基硫在Cu{111}上吸附的研究表明，分子间范德华相互作用引导二丁基硫分子在线性排列中平行有序排列。在退火至120 K时，小的二丁基硫畴重新排列成非常大的、无缺陷的有序畴。当前的研究揭示了二甲基硫较短的烷基链长度对分子扩散速率和堆积结构的影响。在中等表面覆盖率和78 K温度下，发现二甲基硫具有流动性，并且在无需二丁基硫排列所需的120 K退火的情况下就能形成大的、有序的岛状结构。此外，分子堆积结构从四极 - 四极相互作用演变而来，导致相邻分子垂直排列，而不是像二丁基硫那样平行排列。我们展示了二甲基硫岛的高分辨率图像，其中揭示了亚分子特征。这些高分辨率数据使我们能够为有序结构内每个二甲基硫分子的吸附位点提出一个结构模型。这些结果表明，烷基侧链的长度是决定硫醚如何在金属表面自组装的一个重要因素。
