Negative differential resistance and sample conductivity in polypyrrole films

An unusual negative differential resistance (NDR) has been observed in I–V response in p-toluensulfonate-doped polypyrrole films, leading to a conductivity switching effect of almost four orders of magnitude. The effect appears at temperatures below 20 K for highly conducting samples while it is displaced to temperatures close to the room temperature for more resistive samples. The observed correlation between conductivity and switching phenomenon provides a fingerprint of the influence played by the sample nanostructure. The relation between the chemical structure of the material and the observed physical phenomenon is discussed.