Research

The group activity is focused in determining the geometrical and electronic structure of a large variety of solid surfaces, ranging from clean and adsorbate covered transition metals, ultra-thin Oxide Films, and Surface Alloys to Epitaxial Graphene and 2D-materials. The experimental team routinely participates in experiments performed at the Elettra beamlines, in particular at the SuperESCA. The experiments are often complemented by density functional theory calculations performed by external groups, in particular at University College London-UK, SISSA, University of Trieste, and IOM-CNR DEMOCRITOS.

We are interested in how adsorbates interact on a surface, how they modify the substrate, how the formation of bonds influences the electronic structure of the systems, and what are the elementary steps in simple surface processes (atomic and molecular diffusion, subsurface penetration, surface segregation, chemical reactions). To this purpose, we use an ultra-high-vacuum chamber equipped with instrumentations for Low Energy Electron Diffraction, X-ray Photoelectron Spectroscopy, X-ray Photoelectron Diffraction and Temperature Programmed Desorption experiments. Atomic and supersonic molecular beams are also employed to study gas-surface interactions processes and surface reactivity on model systems.

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Low Energy Electron Diffraction

Since the formation of the first electron diffraction patterns in 1927 by Davisson and Germer, who explained the physical phenomenon in terms of wave nature of electrons, Low Energy Electron Diffraction has been widely used for surface crystallography studies. LEED is not only a powerful tool for the qualitative identification of surface symmetries and two-dimensional periodicities, but it is the most used technique for quantitative structure determination of ordered surfaces.

X-ray Photoelectron Diffraction

X-ray Photoelectron Diffraction is a crystallographic technique that successfully combines chemical, structural and surface sensitivity. A radiation field excites an atomic core-level, and the outgoing electron goes through a scattering process with the surrounding atoms. The quantum-mechanical interference of the directly emitted component of the photo-ejected electron wave-field with the other components, coherently scattered from neighbor atoms, produces a diffraction pattern that is characteristic for each emitter.

Temperature Programmed Desorption

Temperature Programmed Desorption is one of the most straightforward surface science experimental tools which provides information on the binding energy of the bound surface species. While increasing the sample temperature with a linear ramp in time it is possible to monitor one or more desorbing species with a mass spectrometer. The desorption temperature, the shape of the desorption peak, and how all these change with initial surface coverage and heating rate can be analyzed to provide information about  the adsorbate/substrate interaction.

X-ray Photoelectron Spectroscopy

X-Ray Photoelectron Spectroscopy is based on the photoelectric effect, which was first discovered by Albert Einstein in 1905. The photoemission process from a solid sample takes place when a highly energetic photon interacts with matter, causing an electron to be removed from an atomic orbital or from a band and to reach the vacuum level. The excitation energy must be large enough for the electrons to overcome the work function of the solid.

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Ultima modifica il Sabato, 05 Novembre 2022 19:30