ABSTRACT Self-assembled monolayers (SAMs) on metal surfaces have inspired many interesting applications, such as chemical and biological sensors, molecular electronics, magnetism and protective coatings. In this respect, SAMs having different head and tail groups have been synthesised which allow the modification of the material properties by tuning intermolecular, monolayer–metal and/or monolayer–solvent interactions. In this respect, we investigate the adsorption of thiols having aromatic, p-mercaptobenzonitrile (pPhCN) or aliphatic, 2-azidoethanthiol (N3S), tail groups on Au(111) surface by means of Density Functional Theory (DFT). Monomer and dimer adsorption configurations of both pPhCN and N3S molecules as well as the modification of the electronic structures upon adsorption are studied. Our results show that different adsorption mechanisms are observed for the molecules under consideration. While monomer and dimer structures of the pPhCN prefer to adsorb laterally on the surface, for N3S vertical arrangement of the molecules enhances the molecular immobilisation. Although, dominant contributions to the adsorption energy of the laterally adsorbed pPhCN are through S–Au chemical bond, phenyl ring–surface and cyano N–surface interactions, π–π stacking of the rings contributes to the stabilisation of the complex in addition to the S–Au chemical bond in the case of vertical attachment. For N3S, on the other hand, only S–Au chemical bond determines the adsorption strength. S–Au interactions result in broad molecular orbital redistribution of the S atoms of both molecules, due to the rehybridisation of S and Au states. Density of cyano-N and cyano-C states present in the pPhCN is affected by the orientation of the rings with respect to each other. In the case of 2N3S, instead, the distribution of the tail group molecular orbitals is not modified by the adsorption.

中文翻译：

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Au(111) 表面的芳香族与脂肪族硫醇：吸附登记和电子结构的 DFT 探索

摘要 金属表面的自组装单分子层 (SAMs) 激发了许多有趣的应用，如化学和生物传感器、分子电子学、磁性和保护涂层。在这方面，已经合成了具有不同头部和尾部基团的 SAM，可以通过调节分子间、单层-金属和/或单层-溶剂相互作用来改变材料特性。在这方面，我们通过密度泛函理论 (DFT) 研究了具有芳香族对巯基苯甲腈 (pPhCN) 或脂肪族 2-叠氮基乙硫醇 (N3S) 尾基的硫醇在 Au(111) 表面上的吸附。研究了 pPhCN 和 N3S 分子的单体和二聚体吸附构型以及吸附后电子结构的改变。我们的结果表明，对于所考虑的分子，观察到了不同的吸附机制。虽然 pPhCN 的单体和二聚体结构更喜欢横向吸附在表面上，但分子的 N3S 垂直排列增强了分子固定。尽管对侧向吸附 pPhCN 的吸附能的主要贡献是通过 S-Au 化学键、苯环-表面和氰基 N-表面相互作用，但除了垂直连接情况下的 S-Au 化学键。另一方面，对于 N3S，只有 S-Au 化学键决定吸附强度。由于 S 和 Au 状态的再杂化，S-Au 相互作用导致两个分子的 S 原子的分子轨道重新分布。pPhCN 中存在的氰基-N 和氰基-C 状态的密度受环相对于彼此的取向的影响。相反，在 2N3S 的情况下，尾基分子轨道的分布不会因吸附而改变。