Electronic properties of ion-implanted polymer films

Electronic properties of polystyrene-acrylonitrile (PSA) films, implanted with 20-175-keV nitrogen to a dose range of 5 × 10 ¹³-5 × 10 ¹⁶ ions/cm ², were studied. Electrical conductivity of the films increases more than 17 orders of magnitude with increasing ion dose and beam energy. Temperature dependence of the conductivity suggests a composite hopping conduction in the films. Temperature dependence of piezoresistance shows that the variable-range hopping conduction is also responsible for piezoresistivity in the films. Hall coefficient measurements show no hall voltage with the experimental limit of ∼ 1 μV, indicating that a large number of carriers (> 10 ²² cm ^-3) are present in the implanted films. Optical absorption indicates a progressive optical gap closing as ion dose increases, suggesting a gradual phase transition from insulator to semiconductor. Graphitic properties were observed in the PSA film implanted with 175-keV N ₂⁺ ions to a dose of 5 × 10 ¹⁶ ions/cm ².