Atom Transfer and Single-Adatom Contacts

TL;DR

This study investigates atomic-scale contact formation and conductance behavior between a scanning tunneling microscope tip and metal surfaces or adatoms, revealing distinct contact mechanisms and the role of dipolar bonding.

Contribution

It demonstrates the difference in conductance transition between tip-surface contact and adatom contact, highlighting the influence of dipolar interactions in adatom conductance.

Findings

Jump-to-contact is random during tip-surface approach.

Single adatoms show smooth conductance transition.

Dipolar bonding affects conductance behavior.

Abstract

The point contact of a tunnel tip approaching towards Ag(111) and Cu(111) surfaces is investigated with a low temperature scanning tunneling microscope. A sharp jump-to-contact, random in nature, is observed in the conductance. After point contact, the tip-apex atom is transferred to the surface, indicating that a one-atom contact is formed during the approach. In sharp contrast, the conductance over single silver and copper adatoms exhibits a smooth and reproducible transition from tunneling to contact regime. Numerical simulations show that this is a consequence of the additional dipolar bonding between the homoepitaxial adatom and the surface atoms.