The electronic structure of (C59N)2 from high energy spectroscopy

We report the results of a detailed study of the occupied and unoccupied electronic structure of dimers of the new heterofullerene C59N by means of photoemission and electron energy-loss spectroscopy. A close similarity is found between the electronic structures of pristine (C59N)2 and C60 with an additional broadening of the spectra in the former due to the distortion of the fullerene cage caused both by dimerization and the chemical substitution. Both the occupied and unoccupied electronic states, as well as the interband transitions between them, attest to the high degree of molecular character retained in the solid state. Comparison of the shake-up structures in the C1s and N1s X-ray photo emission spectra confirm that the highest lying occupied states in the heterofullerene have a strong degree of N character, whereas the lowest lying unoccupied states have mainly C character. We also present the optical conductivity of the heterofullerene (derived from the loss function), which shows an optical gap of 1.4 eV, some 0.4 eV smaller than that of C60

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 substrate in which the highly \pi-conjugated molecule C60 (\pi quantum well) is isolated from the electrodes by alkyl chains (\sigma tunnel barriers). Initially, the Si/SiO2/\sigmaC60 architecture was prepared either by sequential synthesis (3 different routes) or by direct grafting of the presynthesized C60-\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 \sigma tunnel barrier was added on the Si/SiO2/\sigma C60 junction by applying a hanging mercury drop electrode thiolated with an alkanethiol monolayer. We compared the electronic transport properties of the Si/SiO2/\sigma C60//Hg and Si/SiO2/\sigma C60//\sigmaHg molecular junctions, and we demonstrated by transition voltage spectroscopy that the fullerene LUMO - metal Fermi energy offset can be tailored from ~ 0.2 eV to ~ 1 eV by changing the length of the alkyl chain between the C60 core and the Hg metal electrode (i. e. from direct C60//Hg contact to 14 carbon atoms tunnel barrier).Comment: Single pdf file including: main text, figures, tables and supporting information