Break conductance of noble metal contacts

We have studied the instability of noble metal contacts under high biases (currents) by measuring their break conductance, a conductance just prior to the contact break. At high contact currents (greater than or similar to 1 mA), the break conductance distribution shows a broad single peak located at similar to(10-50)G(0) (G(0)equivalent to 2e(2)/h is the quantum unit of conductance). From the observed peak shift with the contact current, we showed that the contact break of noble metals most likely takes place when the contact current density reaches a critical value (6-9)x10(10) A/cm(2). Noble metal contacts thus make a current-induced break under high currents. At lower biases (currents), a contact tends to break off at one of its preferred contact geometries. We found that the 1G(0) contact is always strongly preferred at the contact break of Au, while contacts of 1G(0), 2.5G(0), 5G(0), and 7.5G(0) appear at the break of Ag and Cu contacts. Preference of these contact geometries of Ag and Cu at the contact break is weakly affected by the contact bias (current).