  Immobilization of polyoxometalates (POMs) onto oxides is relevant to many
applications in the fields of catalysis, energy conversion/storage or molecular
electronics. Optimization and understanding the molecule/oxide interface is
crucial to rationally improve the performance of the final molecular materials.
We herein describe the synthesis and covalent grafting of POM hybrids with
remote carboxylic acid functions onto flat Si/SiO2 substrates. Special
attention has been paid to the characterization of the molecular layer and to
the description of the POM anchoring mode at the oxide interface through the
use of various characterization techniques, including ellipsometry, AFM, XPS
and FTIR. Finally, electron transport properties were probed in a vertical
junction configuration and energy level diagrams have been drawn and discussed
in relation with the POM molecular electronic features inferred from
cyclic-voltammetry, UV-visible absorption spectra and theoretical calculations.
The electronic properties of these POM-based molecular junctions are driven by
the POM LUMO (d-orbitals) whatever the nature of the tether or the anchoring
group.
