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Electronic transport in oligothiophene based junctions

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TELEM group n collaboration with the Nanoelectrochemistry group of the ITODYS laboratory is developping i a project on the study of transport properties of molecular junctions obtained by combining electrochemestry and conventional CMOS technology.
Junctions are realized by two metallic electrodes (Au) separeted by a thin layer (5-10 nm) of oligo(1-(2-bisthienyl)benzene) (BTB).

Schéma d'une jonction à base de BTB

This molecular layer is grafted on the base electrode by electro-reduction of the corresponding diazionium salt. Such procedure results in a very strongh and stable covalent metal-molecule bond.
This molecular layer is very easly p-dopable. the top electrode is obtained by directly evaporating a thin metallic layer on the molecular film through a e-beam lithographied mask.
We analyse transport properties of such junctions in the framework of a tunnel model by density current measurements as function of the bias voltage at low (4K) and room temperature.

Caracteristiques courant tension d'une jonction planaire à base de BTB à differentes températures

First results show a strong hybridization of the molecular layer with the base electrode resulting in a tunnel barrier thickness lower than the thikness of the grafted molecular layer, mesured by atomic force microscopy (AFM).
Transport measurements at lower temperature have sown also that thermal activated transport plays a major role depending on the bias polarity. Such observation has been explained on the basis of a model where the p-dopable nature of the molecular layer is taken into account.
More recently the same molecule has been succesfully grafted on carbone nanotube in order to realize nanotube/BTB/metal junctions.