Electrostatic origin of multi-non-monotonic forces above single Ho, Gd, and Fe adatoms on Cu(111) revealed by atomic force microscopy
Phys. Rev. B 113, 245402 – Published 1 June, 2026
DOI: https://doi.org/10.1103/w4gy-p6mn
Abstract
In this work, we investigate the interaction between the tip of an atomic force microscope and single Ho and Gd adatoms adsorbed on Cu(111). Force-distance spectroscopy shows a pronounced long-range repulsive force that dominates at tip-sample separations larger than 700 pm and precedes the onset of measurable van der Waals attraction. In constant-height imaging, this interaction gives rise to a characteristic ring-shaped contrast. The measured force-distance curves and image features are quantitatively reproduced by a model that only includes electrostatic, van der Waals, and Pauli terms. Measurements performed with CO-terminated and bare metal tips show that the long-range repulsion is governed primarily by the electrostatic interaction between the dipole moment of the metallic tip apex and the adatom. Comparison with Fe adatoms demonstrates that the observed long-range rings are distinct from short-range chemical contrast.
