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 Φc are measured in situ for the transition under both Ohmic and non-Ohmic conditions. The experimental values obtained in the Ohmic case were Φc=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.