Ion hydration and transport at interfaces are relevant to a wide range of applied fields and natural processes1-5. Interfacial effects are particularly profound in confined geometries such as nanometre-sized channels6-8, where the mechanisms of ion transport in bulk solutions may not apply9,10. To correlate atomic structure with the transport properties of hydrated ions, both the interfacial inhomogeneity and the complex competing interactions among ions, water and surfaces require detailed molecular-level characterization. Here we constructed individual sodium ion (Na+) hydrates on a NaCl(001) surface by progressively attaching single water molecules (one to five) to the Na+ ion using a combined scanning tunnelling microscopy and noncontact atomic force microscopy system. We found that the Na+ ion hydrated with three water molecules diffuses orders of magnitude more quickly than other ion hydrates. Ab initio calculations revealed that such high ion mobility arises from the existence of a metastable state, in which the three water molecules around the Na+ ion can rotate collectively with a rather small energy barrier. This scenario would apply even at room temperature according to our classical molecular dynamics simulations. Our work suggests that anomalously high diffusion rates for specific hydration numbers of ions are generally determined by the degree of symmetry match between the hydrates and the surface lattice.

CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing China

Collaborative Innovation Center of Quantum Matter Beijing China

Department of Physics and Astronomy London Centre for Nanotechnology Thomas Young Centre University College London London UK

Institute of Experimental and Applied Physics University of Regensburg Regensburg Germany

Institute of Physics Czech Academy of Sciences Prague Czech Republic

Institute of Theoretical and Computational Chemistry College of Chemistry and Molecular Engineering Peking University Beijing China

International Center for Quantum Materials School of Physics Peking University Beijing China

Regional Centre of Advanced Technologies and Materials Palacky University Olomouc Czech Republic

State Key Laboratory for Mesoscopic Physics and School of Physics Peking University Beijing China

Nature. 2018 Nov;563(7729):E18. doi: 10.1038/s41586-018-0473-8. PubMed

Citace poskytuje Crossref.org

Interaction of surface cations of cleaved mica with water in vapor and liquid forms

Quantifying the evolution of atomic interaction of a complex surface with a functionalized atomic force microscopy tip