STM Investigation of the Y[C 6 S-Pc] 2 and Y[C 4 O-Pc] 2 Complex at the Solution–Solid Interface: Substrate Effects, Submolecular Resolution, and Vacancies
STM Investigation of the Y[C 6 S-Pc] 2 and Y[C 4 O-Pc] 2 Complex at the Solution–Solid Interface: Substrate Effects, Submolecular Resolution, and Vacancies
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溶液中 Y[C 6 S-Pc] 2 和 Y[C 4 O-Pc] 2 配合物的 STM 研究 - 固体界面：底物效应、亚分子分辨率和空位
DOI：
10.1021/acs.jpcc.0c10573
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Hipps, K. W.
中科院分区：
文献类型：
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作者：
Rana, Shammi;Jiang, Jianzhuang;Korpany, Katalin V.;Mazur, Ursula;Hipps, K. W.
众所周知，分子上的取代基可以显著控制固体表面的组装、吸附和取向行为。用扫描隧道显微镜(STM)研究了Y[C6S-Pc]2和Y[C4O-Pc]2双层配合物在固-液界面的自组装。当浓度大于1μ时，Y[C6S-Pc]2在高度定向的热解石墨上形成了规则的、低缺陷密度的单分子膜。另一方面，在Au(111)面上，它与一些孤立的分子形成致密的小岛群。两个岛屿的方位之间明显倾向于15°的倍数。实现了Y[C6S-Pc]2内部分子结构的清晰可视化，包括所有8个连接到顶部的酞菁环的硫原子。当Y[C6S-Pc]2的浓度低于1μM时，Y[C6S-Pc]2只在Au(111)表面观察到稳定的孤立单分子，而在HOPG上没有观察到。硫醇连接的侧链有利于Au(111)表面的强吸附，分离的单分子很容易被观察到，并在几次图像扫描中保持稳定。在形成定义明确的单分子膜的浓度下，我们观察到分子空位形式的缺陷，其数量可以通过偏置电压来控制。通过与Y[C4O-Pc]_2的比较，证明了在O-键合体系中，S键合体系的稳定性增强，并从有机硫化物-金相互作用的角度进行了讨论。在HOPG和Au(111)面上都没有观察到Y[C4O-Pc]2的孤立分子。即使在很低的溶液浓度下，也能在开放的底物表面观察到小的分子筏。在HOPG上，Y[C4O-Pc]2单层结构复杂，既有开放的立方体结构，也有填充的立方结构，呈混合结构。在HOPG上观察到的表面结构可能是由平衡热力学控制的。Au(111)表面的Y[C6S-Pc]2络合物的结构是由扩散的动力学势垒决定的，因此是被动力学捕获的。我们认为，具有外围S链烷烃的核心部分通常对金具有特别强的吸附。密度泛函计算表明，S连接的烷基取代体系在Au上的稳定性可能比类似的O连接体系高1 eV。我们还观察到HOPG上的Y[C6S-Pc]_2单分子膜具有偏置和设定点电流相关的缺陷。在恒定的隧道电流下，与高的负偏压相比，较小的负偏压会产生更多的空位。连续的STM扫描显示了新空位的扩散、消失和出现，这些空位既是由热诱导的，也是由STM针尖诱导的。这项工作证明了分子-底物相互作用、偏置电压、隧道电流和STM针尖在控制和稳定分子组装中的重要作用。
Substituents present on a molecule are known to significantly control the assembly, adsorption, and orientation behavior on solid surfaces. Using scanning tunneling microscopy (STM), self-assembly of the Y[C6S-Pc]2and Y[C4O-Pc]2double-decker complexes was investigated at a solution–solid interface. At concentrations above 1 μM, Y[C6S-Pc]2formed well-defined monolayers with low defect density on highly oriented pyrolytic graphite (HOPG). On Au(111), on the other hand, it formed dense groups of small islands with some isolated molecules. There was a clear preference for multiples of 15° between the orientations of the islands. A clear visualization of the Y[C6S-Pc]2inner molecular structure, including all eight of the sulfur atoms linked to the top phthalocyanine ring, was achieved. At concentrations below 1 μM, stable isolated single molecules of Y[C6S-Pc]2were observed only on Au(111), not on HOPG. The thiol-linked side chains favor strong adsorption on the Au(111) surface, with isolated single molecules being easily visualized and stable over several image scans. At concentrations where well-defined monolayers form, we observe defects in the form of molecular vacancies whose number can be controlled by bias voltage. The enhanced stability of the S-linked system over an O-linked system is demonstrated by comparison with Y[C4O-Pc]2and discussed in terms of the organic sulfide–gold interaction. On both HOPG and Au(111), isolated molecules of Y[C4O-Pc]2are never observed. Even at very low solution concentrations, small rafts of molecules on an otherwise open substrate surface are observed. On HOPG, the structure of the Y[C4O-Pc]2monolayer is complex with both an open and filled cubic structure occurring as a mixed structure. The surface structures seen with either double-decker on HOPG are probably controlled by equilibrium thermodynamics. The structure of the Y[C6S-Pc]2complex on Au(111) is determined by the kinetic barrier to diffusion across the gold surface and is therefore kinetically trapped. We suggest that core moieties with peripheral S-linked alkanes may generally be particularly strong adsorbates on gold. Density functional calculations suggest that the S-linked alkane substituent system may be as much as 1 eV more stable on Au than a similar O-linked system. We have also observed that the Y[C6S-Pc]2monolayer on HOPG has bias and setpoint current dependent defects. At constant tunneling current, less negative bias generates a greater number of vacancies as compared to high negative bias. Consecutive STM scanning shows the diffusion, disappearance, and appearance of new vacancies which are induced both thermally and by the STM tip. This work demonstrates the important role of molecule–substrate interactions, bias voltage, tunneling current, and the STM tip in controlling and stabilizing molecular assembly.