DC conductance of CuPc films prepared by plasma activated evaporation

A CuPc film with good mechanical and gas sensing properties was prepared by the plasma activated evaporation method. The conductivity of the CuPc film approximately satisfies the following equation: σ = σoexp(−E/kT) where E is the activation energy. The activation energies of the films deposited at high pressures (200 and 300mtorr) are 0.7∼0.8eV which are almost the same with Eg/2 of the sublimated CuPc film. For the films deposited at low pressures (20 and 100mtorr), the activation energies are 0.1∼0.4 eV depending on the gas environment. As the deposition pressure of the CuPc film decreases, the porosity of the film increases and thus the surface area where NOx gas molecules can be adsorbed increases. This results in the increases of the DC conductivity and the NOx gas sensing sensitivity with decreasing CuPc deposition pressure.