Laboratory of Solid-State Physics and Magnetism, KU Leuven , BE-3001 Leuven, Belgium.
Langmuir. 2013 Sep 17;29(37):11593-9. doi: 10.1021/la402282x. Epub 2013 Aug 29.
Nowadays molecular nanoporous networks have numerous uses in surface nanopatterning applications and in studies of host-guest interactions. Trimesic acid (TMA), a benzene derivative with three carboxylic groups, is a marvelous building block for forming 2D H-bonded porous networks. Here, we report a low-temperature study of the nanoporous "chicken-wire" superstructure formed by TMA molecules adsorbed on a Au(111) surface. Distinct preferential orientations of the porous networks on Au(111) lead to the formation of peculiar TMA polymorphs that are stabilized only at the boundary between rotational molecular domains. Scanning tunneling microscopy (STM) and spectroscopy are used to investigate the electronic properties of both the molecular building blocks and the pores. Sub-molecular-resolution imaging and spatially resolved electronic spectroscopy reveal a remarkable change in the appearance of the molecules in the STM images at energies in the range of the lowest unoccupied molecular orbital, accompanied by highly extended molecular wave functions into the pores. The electronic structure of the pores reflects a weak confinement of surface electrons by the TMA network. Our experimental observations are corroborated by density-functional-theory-based calculations of the nanoporous structure adsorbed on Au(111).
如今，分子纳米多孔网络在表面纳米图案化应用和主体-客体相互作用的研究中有着广泛的用途。均苯三甲酸（TMA）是一种具有三个羧基的苯衍生物，是形成二维氢键多孔网络的绝佳构建块。在这里，我们报告了在 Au(111)表面上吸附的 TMA 分子形成的纳米多孔“铁丝网”超结构的低温研究。多孔网络在 Au(111)上的明显优先取向导致了特殊 TMA 多晶型的形成，这些多晶型仅在旋转分子域之间的边界处稳定。扫描隧道显微镜（STM）和光谱学用于研究分子构建块和孔的电子性质。亚分子分辨率成像和空间分辨电子光谱揭示了在最低未占据分子轨道范围内的能量范围内，STM 图像中分子的外观发生了显著变化，同时分子波函数高度扩展到孔中。孔的电子结构反映了 TMA 网络对表面电子的弱限制。我们的实验观察结果得到了基于密度泛函理论的吸附在 Au(111)上的纳米多孔结构的计算的证实。
