We examined the current-voltage (I-V) characteristic of metal/polyimide/rhodamine-dendorimer/polyimide/ metal junctions prepared by the Langmuir-Blodgett (LB) technique. At a temperature of 32.8 K, a step structure was observed in the I-V characteristic, whereas it was not observed for the junctions without rhodamine-dendorimer. The step structure was very similar to that seen in so-called Coulomb staircase. On the basis of the model of Coulomb blockade, the possibility of single electron tunneling via rhodamine-dendrimer (Rh-G2) molecule as a quantum dot was discussed.

We fabricated junctions with a porphyrin polyimide (PORPI) monolayer, and then investigated the electron transport properties of the junctions from the current-voltage (I-V) and d2V/dI2-V measurements. Polyimide LB films without porphyrin were used as tunneling barriers. One large peak was seen at a voltage around 1.9 V, due to the excitation of electron transitions in PORPI molecules, whereas a step structure was not observed in the I-V characteristic.

The threshold voltage of Coulomb staircase using organic molecules was analyzed by extending our previous model with only consideration of the metal/organic film interfacial space charge to the generalized one. The generalized model is helpful to examine coupling capacitance in organic double barrier tunneling junction (DBTJ). The current-voltage (I-V) characteristic of metal/polyimide (PI)/rhodamine-dendrimer (Rh-G2)/PI/metal junction was analyzed using this generalized model. The calculation results were in good agreement with our experimental data.