Precise Measurement of Dark Bridge between Micro-gap Electrical Contacts in a State of Thermal Equilibrium Condition

Newly discovered nonluminous (dark) bridge was precisely produced and measured its size by microscopic means. Palladium (Pd) was tested as a typical contact material. The contacts separating system was constructed by using 1 (m) long steel cantilever system. The experiments were carried out with very slow opening speed and observed the bridge growing process with the microscope. The contacts were set at the bottom side of the cantilever and controlled its moving speed (contacts separating speed) by pushing the top of the cantilever, that can reduce the displacement scale with any reduction ratio but we chose it by one-thirtieth (1/30) and we reached the separation speed of 0.05 mum/s that was enough to maintain the thermal equilibrium condition. Both the bridge voltage and the displacement of electrode were monitored and recorded. The microscopic images of the bridge were stored in the computer, from which the size of the bridge was measured for each image and plotted on a graph showing the relationship between bridge length and diameter. The results showed that enough correspond to the theoretical estimation formerly presented by the authors