DARK CONDUCTIVITY AND PHOTOCONDUCTIVITY OF ASYMMETRIC GOLD (LANGMUIR-BLODGETT-FILM) GOLD TUNNEL-JUNCTIONS

We have performed measurements of the dark conductivity and photocondu ctivity 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 measure ments at liquid helium temperature reveal a rectifying behavior which is manifested in characteristic onsets in current, arising from resona nt tunneling processes through molecular states. To emphasize that the observed effects are actually originating from the molecules, we reco rd the photoaction spectra of the tunnel junctions and compare the res ults with absorption spectra measured on identical organic structures without the presence of electrodes. The photoaction spectra and the ab sorption spectra show characteristic bands at the same wavelengths. Fr om this result we conclude that both organic layers in the tunnel junc tion are intact. Therefore, the application of electrodes affects only a small number of the outer monolayers of the organic film and does n ot destroy the heterostructure itself.