ELECTRICAL BREAKDOWN MEASUREMENTS OF SEMICONTINUOUS METAL-FILMS

The breakdown current I(c) of a percolating system is measured on real materials, We find I(c) is-proportional-to B(-x)., B is the weakly nonlinear response determined by third-harmonic generation. A new criterion for I(c) is suggested, defined as the current at which a hot spot reaches the melting temperature of the metallic grains, T(m). This criterion remains valid in the presence of nonlinear effects. It is also consistent with the experimental observations: At I(c) the resistance either increases to infinity or decreases, i.e., the local geometry is changed at T(m). Modeling the breakdown by hot spots yields the above power law with 0.5 greater-than-or-equal-to x greater-than-or-equal-to 0.36, in excellent agreement with the measured data: x =0.48 and 0.41 for Ag and Au films.