Jeindl Andreas, Domke Jari, Hörmann Lukas, Sojka Falko, Forker Roman, Fritz Torsten, Hofmann Oliver T
Institute of Solid State Physics, NAWI Graz, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria.
Institute for Solid State Physics, Friedrich Schiller University Jena, Helmholtzweg 5, 07743 Jena, Germany.
ACS Nano. 2021 Apr 27;15(4):6723-6734. doi: 10.1021/acsnano.0c10065. Epub 2021 Mar 17.
The fabrication of nanomaterials involves self-ordering processes of functional molecules on inorganic surfaces. To obtain specific molecular arrangements, a common strategy is to equip molecules with functional groups. However, focusing on the functional groups alone does not provide a comprehensive picture. Especially at interfaces, processes that govern self-ordering are complex and involve various physical and chemical effects, often leading to unexpected structures, as we showcase here on the example of a homologous series of quinones on Ag(111). Naively, one could expect that such quinones, which all bear the same functionalization, form similar motifs. In salient contrast, our joint theoretical and experimental study shows that profoundly different structures are formed. Using a machine-learning-based structure search algorithm, we find that this is due to a shift of the balance of three antagonizing driving forces: adsorbate-substrate interactions governing adsorption sites, adsorbate-adsorbate interactions favoring close packing, and steric hindrance inhibiting certain otherwise energetically beneficial molecular arrangements. The theoretical structures show excellent agreement with our experimental characterizations of the organic/inorganic interfaces, both for the unit cell sizes and the orientations of the molecules within. The nonintuitive interplay of similarly important interaction mechanisms will continue to be a challenging aspect for the design of functional interfaces. With a detailed examination of all driving forces, we are, however, still able to devise a design principle for self-assembly of functionalized molecules.
纳米材料的制备涉及功能分子在无机表面的自组装过程。为了获得特定的分子排列，一种常见的策略是给分子配备官能团。然而，仅关注官能团并不能提供全面的情况。特别是在界面处，控制自组装的过程很复杂，涉及各种物理和化学效应，常常导致意想不到的结构，正如我们在此以Ag(111)上的一系列醌同系物为例所展示的那样。天真地说，人们可能会期望这些都带有相同官能化的醌形成相似的图案。与之形成显著对比的是，我们的理论与实验联合研究表明形成了截然不同的结构。使用基于机器学习的结构搜索算法，我们发现这是由于三种相互拮抗的驱动力平衡发生了变化：支配吸附位点的吸附质 - 基底相互作用、有利于紧密堆积的吸附质 - 吸附质相互作用以及抑制某些在能量上原本有利的分子排列的空间位阻。理论结构与我们对有机/无机界面的实验表征在晶胞尺寸和内部分子取向方面都显示出极好的一致性。同样重要的相互作用机制之间这种非直观的相互作用对于功能界面的设计仍将是一个具有挑战性的方面。然而，通过对所有驱动力的详细研究，我们仍然能够设计出功能化分子自组装的设计原则。
