Reducing Gap Distance of Ag Electrodes by Oxygen Atomic Junction Formation

Electrode–electrode gap distance (GD) of Ag electrodes was measured by using scanning tunneling microscope breaking junction (STM-BJ) technique. An oxygen atom can be expected to bridge the Ag electrodes in series as Ag–O–Ag during the thinning of Ag point contacts under elongation. The GD with the oxygen junction is smaller by about 1.5 to 2 Å than the GD without the oxygen junction as soon as the Ag contact ruptures. This result is attributed to the Ag–O atomic junction formation, which is enhanced due to oxygen insertion in Ag electrodes. Furthermore, we successfully observed the longer molecular plateau length for the small GD when compared with the large GD, where a series of amine-terminated oligophenyl and alkane molecules were formed with Ag electrodes. This study may advance the understanding of the electrical and mechanical properties in single-molecule-based devices with a smallest Ag electrode gap in future.