Welcome to the Web page of Mario Rocca and of the Surface Science Spectroscopy Group of the
Social Responsibility: Mario Rocca is a member of the scientific council of the Italian Union of Scientist for Disarmament USPID
Teaching activity: click here for Surface Science and surface nanostructuring
The research activity is performed in strict collaboration with the Genovese branch of the IMEM-CNR institute.
The current group's scientific interests deal with:
1) Surface Reactivity of metal single crystal surfaces and epitaxially grown ultrathin oxide films
Our research program is aimed at the understanding of the chemical reactivity of molecules interacting with solid surfaces and ultrathin films. This research is precious for a knowledge based control of heterogeneous catalytic reactions, used e.g. for the elimination of toxic gas emissions, and for the synthesis of novel catalysts. To this scope a wide variety of modern physical tools based on ultrahigh vacuum physics is employed to understand which intermediates form in the course of these reactions, and how compounds can be molecularly engineered via surface-mediated reaction pathways. Students in my group learn about Ultra High Vacuum and on how to apply scanning tunneling microscopy, X-Ray induced photoemission spectroscopy, low energy electron diffraction, Auger electron spectroscopy, high resolution electron energy loss spectroscopy, supersonic molecular beams and mass spectroscopy. Experiments are partly performed at synchrotron radiation facilities.
We are particularly interested in the dynamics of the gas-surface interaction, i.e. in the determination of the sticking probabilities which may give a clue for the understanding of the dependence of reactivity on surface structure and defectivity, and at performing simple chemical reactions. To this purpose we perform state resolved experiments on well-ordered metallic surfaces and on ultrathin oxide films epitaxially grown on them. The gases are exposed via a supersonic molecular beam. The effect of defects on the reactivity are mimicked by studying the effect of atomic under-coordination occurring at the steps of vicinal surfaces. The physical state of the reactants can be controlled with respect to their translational energy and angle of incidence with the surface as well as with respect to their rotational alignment with respect to the beam direction. Our most recent experiments concerned ethene dehydrogenation on Cu, CO oxidation on Pd, CO2 hydrogenation on Ni, oxide nucleation on Ag and Cu, H induced metallization of SiC surfaces, the reactivity of ultrathin MgO films towards hydroxylation and water interaction with olivine. The latter experiment is relevant for the origin of water on Earth.
2) Surface response function and acoustic surface plasmons
The interest is focussed on the newly predicted acoustic surface plasmon (ASP) connected with the electronic surface Shockley states at metallic surfaces. Its linear dispersion is promising for applications since it allows for distortion-less conversion of a light signal into a plasmonic signal at much smaller wavelength, a characteristic which may allow to develop new, nanosized optoelectronic devices. So far we found the ASP on Be, Cu and Au. The effect of surface defectivity on the ASP dispersion is currently investigated. Students joining this research field will learn about advanced electronic properties and about their application to “plasmonics”, i.e. surface plasmon based photonics, which should allow to reduce the size of optoelectronic devices to the nanometer scale.
3) Selfassembling of aminoacids at surfaces
Selfassembling of small organic molecules at surfaces governs the construction of organic electronic devices, the so called “plastic electronics”. Adsorption of organic molecules of biological relevance as aminoacids is, however, of importance also for questions of biocompatibility. We are currently investigating glutamic acid adsorption on Ag surfaces by STM and spectroscopic means. The next goal is investigating the adsorption of aminoacids dosed by seeding them in the supersonic molecular beam. Better layer formation is expected thanks to the additional energy available during the adsorption process. The layers are then characterised by the cryogenic STM and by spectroscopic methods. Students joining this research will learn about theses techniques and about the fast growing field of molecular electronics and of biocompatibility.
Experimental facilities in Genova
Three ultrahigh vacuum apparatuses are available. The first allows a combined XPS (Omicron) and HREELS (SPECS) investigation. The second permits to combine HREELS (self constructed) analysis and the deposition of the reactants via a supersonic molecular beam. The third is a liquid He cooled STM (CreaTec) for structural and spectroscopic investigation of single molecules.
Funding by the Italian ministry for research MIUR under PRIN projects, by Cassa di Risparmio di Genova ed Imperia and by Compagnia S. Paolo di Torino is acknowledged.