Transport properties of ion-implanted and chemically doped polyaniline films.

Abstract

The low-temperature dc conductivity and magnetoconductivity of ion-implanted (${\mathrm{Ar}}^{+}$) and chemically doped (${\mathrm{H}}_{2}$${\mathrm{SO}}_{4}$) polyaniline films have been studied. The metal-insulator transition has been observed for ion-implanted polyaniline films on increasing the irradiation dose to 3\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ions ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$. The maximum values of the room-temperature conductivity reached 800 S ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for ion-implanted and 8 S ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for chemically doped polyaniline films. In both cases, for samples on the insulator side of the metal-insulator transition, \ensuremath{\sigma}(T)=\ensuremath{\sigma}(0)exp[-(${\mathit{T}}_{0}$/T${)}^{\mathit{m}}$], where m\ensuremath{\sim}0.5, whereas for the most heavily ion-implanted polyaniline films \ensuremath{\sigma}(T)\ensuremath{\sim}T at Tg20 K; the minimum in the \ensuremath{\sigma}(T) occurs at T\ensuremath{\sim}20 K and a negative magnetoconductance \ensuremath{\Delta}\ensuremath{\sigma}(H,T)\ensuremath{\sim}${\mathit{H}}^{2}$ 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. \textcopyright{} 1996 The American Physical Society.