Self-Assembly of Carboranethiol Isomers on Au{111}: Intermolecular Interactions Determined by Molecular Dipole Orientations
Self-Assembly of Carboranethiol Isomers on Au{111}: Intermolecular Interactions Determined by Molecular Dipole Orientations
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DOI：
10.1021/nn800673d
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发表时间：
2009-03-01
期刊：
影响因子：
17.1
通讯作者：
Weiss, Paul S.
中科院分区：
文献类型：
--
作者：
Hohman, J. Nathan;Zhang, Pengpeng;Weiss, Paul S.
自组装单分子膜(SAM)的结构和性能主要受两种相互作用的影响：基质与被吸附材料之间的相互作用和被吸附材料本身之间的相互作用。我们在Au{111}上制备了m-1-Carboranthiol(M1)和m-9-Carboranthiol(M9)自组装单分子膜。这两个异构体在几何上几乎相同，但计算的分子偶极矩在气相中的M1和M9分别在1.06和4.08 D处有较大差异。这些分子提供了一个机会，在不改变组装几何结构的情况下，研究不同偶极矩对自组装膜的影响。用扫描隧道显微镜(STM)研究了这些分子的纯自组装和共沉积自组装膜。这些分子在STM图像中是不可区分的，并且六角紧密堆积的附着层结构被发现具有(根19 x根19)R23.4度单位细胞。在与其他SAM系统中的域边界相关联的STM图像中，两个SAM都显示没有突出或凹陷特征的旋转域。分子偶极矩的不同取向会影响SAM的性质，包括SAM的稳定性和竞争结合条件下碳氰硫酸酯的覆盖度。用动态接触角测角仪、开尔文探针力显微镜和掠入射傅里叶变换红外光谱对这些性质进行了研究。
Self-assembled monolayer (SAM) structures and properties are dominated by two interactions: those between the substrate and adsorbate and those between the adsorbates themselves. We have fabricated self-assembled monolayers of m-1-carboranethiol (M1) and m-9-carboranethiol (M9) on Au{111}. The two isomers are nearly identical geometrically, but calculated molecular dipole moments show a sizable difference at 1.06 and 4.08 D for M1 and M9 in the gas phase, respectively. These molecules provide an opportunity to investigate the effect of different dipole moments within SAMs without altering the geometry of the assembly. Pure and co-deposited SAMs of these molecules were studied by scanning tunneling microscopy (STM). The molecules are indistinguishable in STM images, and the hexagonally close-packed adlayer structures were found to have (root 19 x root 19)R23.4 degrees unit cells. Both SAMs display rotational domains without the protruding or depressed features in STM images associated with domain boundaries in other SAM systems. Differing orientations of molecular dipole moments influence SAM properties, including the stability of the SAM and the coverage of the carboranethiolate in competitive binding conditions. These properties were investigated by dynamic contact angle goniometry, Kelvin probe force microscopy, and grazing incidence Fourier transform infrared spectroscopy.