Thesis

These are ongoing projects with opportunities for PhD and Master students. All subjects are investigated by theoretical modelling based on parameter-free numerical simulations, in the field of Condensed Matter Physics.

Ultrafast electron transfer from adsorbed molecules

Isonicotinic/TiO2(110)

We simulate the electron transfer at the interface between an adsorbed molecule and a substrate, focusing on the resonant transfer channel. Ultra-fast transfer (on the femtosecond time scale) is one of the basic processes in organic solar cells, photocatalysis, color photography, etc.

On the left we summarize our recent findings for isonicotinic acid adsorbed at the surface of TiO2(110). An electron populating the lowest unoccupied+1 molecular orbital (LUMO+1) by absorption of 400eV photons from the N 1s core level is eventually injected into the substrate. The N1s core hole has to be taken into account in the Green's function calculations because of its lowering of molecular energy levels. Read more.

Core-level spectroscopy of organic molecules

Pentacene NEXAFS
In collaboration with experimental groups at the ELETTRA synchrotron, we study the adsorption of organic molecules at metal and semiconducting surfaces. Core-level spectroscopy is a much useful tool on analysis, both on the experimental and theoretical side. Especially, near edge X-ray adsorption (NEXAFS) allows one to determine the orientation of molecules at surfaces, which is a key factor in the functioning of organic electronic devices.

We perform simulation of X-ray absorption and photoemission spectra for molecules. Left is the case of pentacene, for which we demonstrated the presence of azimuthal dichroism (E||x vs E||y), in addition to the well-known polar one (E||z vs E||xy). Read more.

Atomic diffusion at metal and oxide surfaces

Co diffusion on Co/Fe(001) We are interested in understanding basic issues for the atomic diffusion on solid surfaces and the nucleation of structures, that play fundamental role in a large variety of physical and chemical processes, from the growth of nanosized clusters, to reactivity in heterogeneous catalysis.

Left is an example of a recent study of Co diffusion on ultrathin Co films grown on Fe(001), where we demonstrated by Density Functional Theory simulations that lattice instability of the Co film (forced by the underlying Fe substrate) yields to a softening of the film itself and in suppression of Co diffusion barriers.
This implies a different growth behaviour of Co structures at the surface, as observed by Scanning Tunnelling Microscopy experiments performed at Politecnico di Milano. Read more.
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