Transport properties of ion-implanted and chemically doped polyaniline films

The low-temperature dc conductivity and magnetoconductivity of ion-implanted (${\mathrm{Ar}}^{+}$) and chemically doped (${\mathrm{H}}_2$ ${\mathrm{SO}}_4$) polyaniline films have been studied. The metal-insulator transition has been observed for ion-implanted polyaniline films on increasing the irradiation dose to 3×${10}^{17}$ ions ${\mathrm{cm}}^{\mathrm{-}2}$. The maximum values of the room-temperature conductivity reached 800 S ${\mathrm{cm}}^{\mathrm{-}1}$ for ion-implanted and 8 S ${\mathrm{cm}}^{\mathrm{-}1}$ for chemically doped polyaniline films. In both cases, for samples on the insulator side of the metal-insulator transition, σ(T)=σ(0)exp[-(${\mathit{T}}_0$/T${)}^{\mathit{m}}$], where m∼0.5, whereas for the most heavily ion-implanted polyaniline films σ(T)∼T at T>20 K; the minimum in the σ(T) occurs at T∼20 K and a negative magnetoconductance Δσ(H,T)∼${\mathit{H}}^2$ has been observed. It is shown that electron-electron Coulomb interactions play an important role in charge-carrier transport in ion-implanted polyaniline films near the metal-insulator transition. © 1996 The American Physical Society.