Atom and Molecule Migrations between Scanning Tunneling Microscopy Tips and Surfaces

The breaking and formation of chemical bonds in nanoscale junctions are of fundamental importance in single molecule electronics. Direct visualization of junction structures is crucial for revealing structural changes and establishing an atomic-scale correlation between the structure and conductance. Here, we employ a low-temperature scanning tunneling microscope to visualize the migration of atoms and molecules in the tunneling junctions. Through tip manipulation, four types of Ag clusters are constructed on the Ag(111) surface, each containing 1-4 Ag atoms, respectively. Ag and C₆₀ functionalized tips are used to establish contact with the Ag clusters, and the atom and molecule migrations are unambiguously determined by subsequent imaging. This approach establishes a clear relationship between structure and conductance for these junctions, and the resulting insight into the structural change during junction rupture is crucial for developing reliable single molecule devices.