Intermolecular Repulsion in Molecular Self-Assembly on Bulk Insulator Surfaces

在这个项目中，我们的目标是探索用于控制有机分子在主体绝缘体表面的分子自组装的远程排斥相互作用。虽然短程引力被广泛用于以合理的方式引导表面分子结构的形成，但到目前为止还没有系统地考虑分子间的斥力。在文献中只有很少的例子展示了分子在表面自组装中的长程分子间相互作用。对于这些例子中的大多数，电偶极子的相互作用被认为是排斥力的来源。然而，对这种排斥的一般性质的系统调查仍然是缺乏的。从引导结构形成的角度来看，合理利用分子间相互排斥进行分子自组装有可能扩大可用于控制表面结构形状和分布的参数空间。为了开发合理地利用相互排斥作用在表面分子结构形成中的策略，我们将通过在超高真空中进行变温扫描力显微镜测量来解决三个问题。首先，我们将研究分子间排斥在多大程度上是分子在表面自组装的一般驱动力。显然，即使存在一定的排斥力，实验条件也可能会阻碍这种排斥力在所产生的分子结构中的表现。第二，尽管电偶极子的排斥力似乎是分子间排斥力的一个非常合理的来源，但对这一归属的实验证实仍然很大程度上是缺失的。为此，需要进行与温度和覆盖率相关的实验，以揭示相互作用势的细节。最后，我们希望利用短程吸引和长程斥力之间的平衡来控制得到的结构在表面上的形状和分布。为此，我们将通过改变分子上的官能团和改变底物来系统地改变所涉及的相互作用。除了相互作用的强度和范围之外，这里的一个关键方面是考虑方向性的影响，即所涉及的相互作用的空间各向异性。我们将把我们的实验结果与蒙特卡罗模拟相比较，以验证一定的相互作用特征将导致实验观察到的结构基元。在分子自组装的描述中包括分子间排斥将允许以合理的方式增强在表面形成分子结构时可以获得的结构多样性。

In this project, we aim for exploring long-range repulsive interactions for controlling molecular self-assembly of organic molecules on bulk insulator surfaces. While short-range attractions are widely used to steer molecular structure formation on surfaces in a rational fashion, intermolecular repulsion has so far not been considered in a systematic way. Only few examples exist in literature demonstrating long-range intermolecular interaction in molecular self-assembly on surfaces. For most of these examples, interaction of electrical dipoles has been suggested as the origin of the repulsion. A systematic investigation of the general nature of this repulsion is, however, still lacking. From the prospective of steering structure formation, the rational use of intermolecular repulsion in molecular self-assembly bears the potential to enlarge the parameter space available for controlling the resulting structures´ shape and distribution on the surface.To develop strategies for making use of repulsive interactions in molecular structure formation on surfaces in a rational fashion, we will address three questions by performing scanning force microscopy measurements carried out in ultra-high vacuum at variable temperatures.First, we will investigate to what extend intermolecular repulsion is a general driving force in molecular self-assembly on surfaces. Clearly, even if a certain repulsion is present, experimental conditions might hamper the manifestation of the repulsion in the resulting molecular structures.Second, while repulsion of electrical dipoles appears as a very reasonable origin for intermolecular repulsion, the experimental confirmation for this assignment is still largely missing. To this end, temperature and coverage-dependent experiments are needed that shed light on the details of the interaction potential.Finally, we want to make use of the balance between short-range attraction and long-range repulsion for steering the resulting structures´ shape and distribution on the surface. To this end, we will systematically vary the involved interactions by changing functional groups at the molecule and by changing the substrate. Besides the interactions´ strengths and ranges, a key aspect here is to consider the effect of directionality, i.e., the spatial anisotropy of the involved interactions. We will compare our experimental results with Monte Carlo simulations to validate that a certain interaction characteristics will result in the experimentally observed structural motifs.Including intermolecular repulsion in the description of molecular self-assembly will allow for enhancing the structural variety that can be obtained in molecular structure formation on surfaces in a rational fashion.