Conductivity of tridecylammonium-Au (dmit)₂ Langmuir-Blodgett films under hydrostatic pressure

The electrical conductivity of electrochemically oxidized Langmuir-Blodgett films of tridecylmethylammonium-Au(dmit)₂and icosanoic acid has been studied. The measurements were performed at temperatures down to 3 K and hydrostatic pressures up to 17 kbar, and also at high electric fields up to 3.2 kV/cm. The results support the view that the films consist of relatively large metallic islands, separated by thin barriers, and indicate that the low-temperature conductivity with dσ/dT>0 originates from thermal-fluctuation-induced tunneling. At higher temperatures dσ/dT<0 because of the finite resistance of the metallic islands. The conductivity increased upon applied pressure, and the temperature of the maximum conductivity shifted to lower temperature without any pronounced saturation. The ambient-pressure room-temperature conductivity of the best conducting samples could be increased by a factor of about 2 at 10-kbar hydrostatic pressure and further to 140 S/cm at the temperature of the maximum conductivity at 51 K.