Electrical properties of ultra thin polymer films

Ultra thin polyamide (PA) films (thickness : 2 similar to 3 nm) were deposited on a glass substrate by the vacuum evaporation method. PA-pellets inserted in a boron-silicated glass tube were evaporated by the heating with far infrared light under about 10(-4) Pa. The evaporating temperature is 285 degrees C. The substrate used was a micro cover slide glass. The distance between a evaporating source and a substrate was 30 cm. The glass substrate was kept at room temperature during the deposition. Evaporated PA thin film was annealed at 200 degrees C for one hour in nitrogen. The FT-IR spectrum of a ultra thin PA film (thin PA film) agreed well with that of a conventional PA film. This suggests that the thin PA film has a structure similar to a conventional PA film. The binding energies of O-18 and C-18 spectra shift to the higher energy side. This means that the thin PA film was slightly oxidized in the evaporation process. The breakdown strength and electrical conduction of a thin PA film were discussed. The conduction currents of 2.3 nm-thick film were measured under the application of DC 2.5 V which corresponds to 10 MV/cm. No self healing breakdown occurs until 8 MV/cm. This value is much higher than the breakdown strength of a conventional PA film (2.4 MV/cm). The conduction mechanism of a PA thin film annealed in vacuum were also discussed.