Structural studies of excimer laser-induced percolative phase transition on polyimide thin ®lm surfaces

The behavior of electrical conductivity for excimer laser irradiated polyimide ®lms in the vicinity of the critical number of laser shots was described by three-dimensional percolative phase transition model. It is found that electrical conductivity changed more rapidly than that predicted by the percolation model. Thus, the change in microstructure with increasing number of laser shots was analyzed by FT-IR Raman spectrometry and laser desorption time-of-¯ight mass spectrometry. It is demonstrated that not only the number but also the average size of graphite particles on the irradiated polyimide ®lm surfaces increased with increasing number of laser shots. These results were helpful to better understand the critical change in electrical conductivity on the irradiated polyimide ®lm surfaces. # 2001 Elsevier Science B.V. All rights reserved.