Organic Molecules on Inorganic Substrates: Charge Transfer and
Adsorption Effects
Gian Paolo Brivio
ETSF, CNISM, Dipartimento di Scienza dei Materiali, Università
di Milano-Bicocca, Milano (Italy)
The adsorption of the first layer of organic molecules at the interface between inorganic substrates
and organic species is critical in electronic devices as it influences the carrier injection across the
interface. It also forms the foundation for the growth ordering of the subsequent layers, which in
turn affects the overall performance of these devices.
In this talk by density functional theory (DFT) simulations, we would like to discuss two phenomena.
First the resonant electron transfer from the excited state of an organic adsorbate to a
semiconductor surface, namely isonicotinic acid on rutile TiO2(110). We compute the resonant
charge transfer times from the lowest unoccupied molecular orbitals (LUMO) by using a density
functional theory (DFT) approach which takes into account a truly semi-infinite substrate,
benchmarking the results with experimental data [1].
Second we examine the adsorption of pentacene on Al(001) by investigating the structural,
electronic, and spectroscopic properties of this system combining DFT methods including van der
Waals interactions with measurements by x-ray photoemission (XPS), near-edge x-ray absorption
fine structure (NEXAFS), and scanning tunneling microscopy (STM). We find a major change of the
molecular backbone resulting into a peculiar V-shape bending, due to the direct anchoring of the
two central carbons atop two Al atoms underneath. In the most stable adsorption configuration,
pentacene is oriented with the long axis parallel to the substrate direction, where such anchoring is
favored by optimally matched interatomic distances.
[1] G. Fratesi, C. Motta, M.I. Trioni, G.P. Brivio and D. Sánchez-Portal: Resonant Lifetime of CoreExcited Organic Adsorbates from First Principles, J. Phys. Chem. C 118, 8775 (2014).
[2] A. Baby, G. Fratesi, S. Vaidya, L. Patera, C. Africh, L. Floreano and G.P. Brivio: Anchoring and
bending of Pentacene on Aluminum, J. Phys. Chem. C 119, 3624 (2015).