Dark conductivity and photoconductivity of asymmetric gold/ (Langmuir-Blodgett film)/gold tunnel junctions

We have performed measurements of the dark conductivity and photoconductivity on organic tunnel junctions. The junctions incorporate only a few monolayers of two different organic substances, transferred to the substrate by the Langmuir-Blodgett technique. Current/voltage measurements at liquid helium temperature reveal a rectifying behavior which is manifested in characteristic onsets in current, arising from resonant tunneling processes through molecular states. To emphasize that the observed effects are actually originating from the molecules, we record the photoaction spectra of the tunnel junctions and compare the results with absorption spectra measured on identical organic structures without the presence of electrodes. The photoaction spectra and the absorption spectra show characteristic bands at the same wavelengths. From this result we conclude that both organic layers in the tunnel junction are intact. Therefore, the application of electrodes affects only a small number of the outer monolayers of the organic film and does not destroy the heterostructure itself.