Tuning the thickness of electrochemically grafted layers in large area molecular junctions

Abstract : We have investigated the thickness, the morphology and the transport properties of oligo(1-(2-bisthienyl)benzene) (BTB) thin films grafted on evaporated Au electrodes thanks to a diazonium-based electro-reduction process. Atomic force microscope (AFM) measurements reveal that the thickness is accurately controlled by the number of electrochemical cycles in the 2-27 nm range. The thickness displays a linear dependence with the number of cycles followed by a saturation. Ultrathin (2 nm) and thin (27 nm) large area molecular junctions have then been fabricated. The current-voltage characteristics is fully consistent with a tunneling barrier model whereas for thicker molecular films a rectifying behavior is observed.