Fig. 4

Origin of major differences in the magnitude of the image potential for isolated ions in the gas phase vs. charge-neutral molecules on gold surfaces. a An isolated ion with a net charge of +1.0e in the gas phase induces significant charges in the metal surface that spread across several atomic layers vertically and several nanometers laterally. b In contrast, neutral water molecules in the condensed phase contain dipoles with opposite charges in close proximity, unable to induce a long-range pattern of image charges. Electrostatic interactions are screened and the image potential is more than order of magnitude smaller. The reduction in image potential in (b) also applies for metal-oxide and metal-ceramic interfaces. c Electron density difference at the interface of a water monolayer with an Au (111) surface according to DFT (blue = negative charge, isovalue −0.027e Å⁻³, red = positive charge, isovalue +0.027e Å⁻³). Induced charges are small, illustrated by visualization on the right hand side showing some negative induced charge in the vicinity of positively charged hydrogen atoms of water molecules close to the gold surface (blue = negative charge difference, red = positive charge difference)