Real-space imaging of anisotropic charge of σ-hole by means of Kelvin probe force microscopy

Resolution of the σ-hole Anisotropic distribution of charges on atoms plays an important role in intermolecular interactions, yet direct experimental imaging remains a long-standing challenge. A good example is the σ-hole, an anisotropic charge distribution on a halogen atom covalently linked to carbon atoms. The σ-hole gives rise to the halogen-bonding mechanism, which is well known in supramolecular chemistry despite its existence being confirmed only indirectly. Mallada et al . developed Kelvin probe force microscopy with a specifically functionalized tip and report direct real-space visualization of the σ-hole, revealing its strong anisotropic charge distribution. The authors show that this technique, which relies entirely on electrostatic interactions, may be a powerful tool with which to study anisotropic atomic charge distributions. —YS