Synthesis and electrical properties of fullerene-based molecular junctions on silicon substrate

We report the synthesis and the electrical properties of fullerene-based molecular junctions on silicon substrates in which the highly pi-conjugated molecule C-60 (pi quantum well) is isolated from the electrodes by alkyl chains (sigma tunnel barriers). Initially, the Si/SiO2/sigma C-60 architecture was prepared either by sequential synthesis (3 different routes) or by direct grafting of the presynthesized C-60-sigma-Si(OEt)(3) molecule. We described the chemical synthesis of these routes and the physico-chemical properties of the molecular monolayers. Then the second s tunnel barrier was added on the Si/SiO2/sigma C-60 junction by applying a hanging mercury drop electrode thiolated with an alkanethiol monolayer. We compared the electronic transport properties of the Si/SiO2/sigma C-60//Hg and Si/SiO2/sigma C-60//sigma Hg molecular junctions, and we demonstrated by transition voltage spectroscopy that the fullerene LUMO - metal Fermi energy offset can be tailored from similar to 0.2 eV to similar to 1 eV by changing the length of the alkyl chain between the C-60 core and the Hg metal electrode (i.e. from direct C-60//Hg contact to a 14 carbon atoms tunnel barrier).