Coulomb blockade phenomena in ultrathin Langmuir-Blodgett sandwich junctions

Electrical junctions were fabricated in sandwich configuration from Langmui r-Blodgett (LB) films of two types of material, pi-conjugated, peripherally substituted ring systems or a sigma-bonded polymer. The sandwich junctions consisted of four to ten monolayers between two micro-structured gold elec trodes, corresponding to a nominal film thickness between about 8 and 20 nm . At liquid helium temperature, the current (I)/voltage (V) characteristics generally exhibited smooth exponential behaviour or irregular steps. Howev er, for a small fraction of the LB sandwiches comprising a pi-conjugated or a-bonded compound, regular staircases were observed. It was possible to fi t such Il V characteristics with curves calculated on the basis of a Coulom b blockade model. These results are accounted for by the presence of nanome tre sized gold particles formed upon evaporation of the top electrode. Sing le electron tunnelling is assumed to proceed through double tunnel barrier junctions consisting of a gold island asymmetrically located between the to p and bottom electrode.