PERCOLATIVE METAL-INSULATOR-TRANSITION IN EXCIMER-LASER IRRADIATED POLYIMIDE

The metal-insulator transition observed in excimer laser irradiated polyimide is presented as a new experimental method to study three-dimensional percolation. The conductivity critical exponent t and the percolation threshold Phi(c) are measured in situ for the transition under both Ohmic and non-Ohmic conditions. The experimental values obtained in the Ohmic case were Phi(c) = 0.31 +/- 0.06 and t = 2.00 +/- 0.05. These values are in close agreement with theory. The dependence of the critical exponent on current voltage characteristics of conducting sites is demonstrated for the first time.