An anisotropic charge distribution on individual atoms, such as σ-holes, may strongly affect the material and structural properties of systems. However, the spatial resolution of such anisotropic charge distributions on an atom represents a long-standing experimental challenge. In particular, the existence of the σ-hole on halogen atoms has been demonstrated only indirectly through the determination of the crystal structures of organic molecules containing halogens or with theoretical calculations, consequently calling for its direct experimental visualization. We show that Kelvin probe force microscopy with a properly functionalized probe can image the anisotropic charge of the σ-hole and the quadrupolar charge of a carbon monoxide molecule. This opens a new way to characterize biological and chemical systems in which anisotropic atomic charges play a decisive role.

中文翻译：

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开尔文探针力显微镜对σ孔各向异性电荷的真实空间成像

单个原子上的各向异性电荷分布，例如 σ 空穴，可能会强烈影响系统的材料和结构特性。然而，原子上这种各向异性电荷分布的空间分辨率是一个长期存在的实验挑战。特别是卤素原子上的σ-空穴的存在，只能通过含卤素有机分子的晶体结构的测定或理论计算间接证明，因此需要直接的实验可视化。我们表明，具有适当功能化探针的开尔文探针力显微镜可以成像 σ 孔的各向异性电荷和一氧化碳分子的四极电荷。