Transition Voltage Spectroscopy and the Nature of Vacuum Tunneling

Transition voltage spectroscopy (TVS) has been proposed as a tool to analyze charge transport through molecular junctions We extend TVS to Au-vacuum-Au junctions and study the distance dependence of transition, voltage V-t(d) for clean electrodes in cryogenic vacuum. On the one hand, this allows us to provide an important reference. for V-t(d) measurements on molecular junctions.' On the other hand, we show that TVS forms a simple and powerful test for Vacuum tunneling models.