Metal point contacts and metal-oxide tunnel barriers fabricated with an AFM

We report the fabrication of atomic point contacts and lateral tunnel junctions by using anodic oxidation of thin metal films with an atomic force microscope.In situelectrical measurements were used as feedback to control the fabrication of metal nanowires that were subsequently anodized through their cross section to form point contacts and tunnel junctions. When the conductance of an Al device is reduced below 5×10⁻⁴S it starts to decrease in discrete steps of 2e²/h. In some devices we are able to stabilize the conductance at a value near 2e²/hwhich corresponds to a single, atomic-sized conducting channel. Similar experiments on Ti devices result in a continuous decrease of the conductance and the formation of stable tunnel junctions. This continuous behavior is a result of the large series resistance and the small oxide barrier height of the Ti/TiO_xsystem.