E. S. LEONOV, А. Р. LUTCHNIKOV, G.L. PAKHOMOV, V.V. ТRAVKIN
Multilayered (stacked) heterostructures based on thin films of phthalocyanines (PcMet) having useful characteristics stable in air, under illumination and at different temperatures are perspective components for molecular electronics. If the thickness is small enough (few tens nanometers), then the mutual influence of interacting layers of molecules with different redox potentials may modify their original (intrinsic) properties. This would particularly concern, e.g., specific conductivity, mobility of charge carriers or their injection from adjacent contacts (work function) etc.
This work illustrates how the presence of an overlayer composed of Cl16PcCu molecules on the surface of PcCu or PcMg films affects the parameters of their in-plane J-V plots. This can be explained by combination of several factors such as: - Interlayer migration of admixtures; - Increase in concentration of electrically active admixtures; - Existence of a vertical heterojunction; - Formation of a contact complex.
Peculiar role of the top layer material is confirmed during experiments with Alq3 (tris(8-hydroxyquinolinato-) aluminum salt), almost ball-like molecules that were deposited on PcCu film in place of Cl16PcCu under the same conditions. Both Alq3 and Cl16PcCu are highly resistive n-type semiconductors having similar ionization potentials. A decrease in specific conductivity of the Alq3/PcCu two-layer structure was observed, whereas in the Cl16PcCu/PcCu structure conductivity increases substantially. The profile of J-V plot changes insignificantly.