Competition between Coulomb and van der Waals Interactions in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>Xe</mml:mi><mml:mtext>−</mml:mtext><mml:msup><mml:mrow><mml:mi>Cs</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math> Aggregates on Cu(111) Surfaces
J. Thomas, C. Bertram, J. Daru, J. Patwari, I. Langguth, P. Zhou, D. Marx, K. Morgenstern, U. Bovensiepen
Abstract
Microscopic insight into interactions is a key for understanding the properties of heterogenous interfaces. We analyze local attraction in noncovalently bonded Xe-Cs^{+} aggregates and monolayers on Cu(111) as well as repulsion upon electron transfer. Using two-photon photoemission spectroscopy, scanning tunneling microscopy, and coupled cluster calculations combined with an image-charge model, we explain the intricate impact Xe has on Cs^{+}/Cu(111). We find that attraction between Cs^{+} and Xe counterbalances the screened Coulomb repulsion between Cs^{+} ions on Cu(111). Furthermore, we observe that the Cs 6s electron is repelled from Cu(111) due to xenon's electron density. Together, this yields a dual, i.e., attractive or repulsive, response of Xe depending on the positive or negative charge of the respective counterparticle, which emphasizes the importance of the Coulomb interaction in these systems.