ROCCA , Mario Agostino

Recent progress in experimental and theoretical investigations of surface electronic excitations of metals is reviewed with an emphasis on surface plasmon dispersion. The experimental methods applied to these studies are critically discussed, highlighting present limitations and possible future developments. Available data on the dependence of...

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A review of the most recent experimental progress in the investigation of the dynamics of the interaction of dioxygen with Ag single crystal surfaces is given. In such studies the dioxygen molecules are dosed by a supersonic molecular beam, which allows for angle and energy selectivity. Moreover the background pressure remains very low during...

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Recent results are presented of surface electronic excitations on Ag single crystals. For small q(parallel-to) the data show a linear and Positive dispersion of the surface plasmon for all faces, whose slope depends on crystallographic face, and a strong azimuthal anisotropy in case of Ag(110). This demonstrates that the centroid of the induced...

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We present EELS cross-section data of surface phonons on Ag(001) along GAMMABAR-MBAR. The inelastic intensity is due to the contribution of different modes which are not solved by the EEL spectrometer. However, the shape of the inelastic intensity shows a strong dependence on impact energy for all wave vectors, which allows tuning the EELS on...

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We discuss the influence of elastic reflectivity of the electrons for the analysis of dissociation phenomena on surfaces and adsorbate-induced reconstructions of the substrate. Two situations corresponding to the enhancement of the reflectivity induced by low-energy-electron-diffraction fine structures and by multiple scattering for O2...

Recent progress in experimental investigation of the surface plasmon for d-electron metals with angle resolved electron energy loss spectroscopy and energy loss spectroscopy - low energy electron diffraction is reviewed. The latter technique allows to greatly improve resolution in k-space which constitutes the major limiting factor for...

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We demonstrate the feasibility of a new type of electrostatic cylindrical analyzer terminated with plates with focus at 90degrees also in the presence of significant space charge. The transmission function is determined by numerical simulation of the trajectories after a full three-dimensional solution of the Poisson problem with boundary...

We report on the first observation of selective adsorption and desorption of low energy electrons, scattering off surfaces at low energy. The phenomenon, which is masked by interference effects for the elastic interaction, shows up in the energy loss spectrum. For electrons scattered inelastically off Ag(001), we observe sharp and intense...

Many reactions like the ethylene epoxidation which work readily in industrial reactors can not be reproduced under controlled laboratory conditions. This failure is ascribed to so-called "pressure" and "structure" gaps. The latter is possibly determined by an active role of defects, since surface science experiments are performed on nearly...

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Oxygen adsorption on Ag(110) is investigated as a function of coverage by high resolution electron energy loss spectroscopy. We find for the O-Ag(110) stretching frequency a value of 39.1 meV from the limit of low coverage up to the (4 x 1) structure. The frequency is then gradually shifted upwards, whereby an increase of 0.9 meV is observed...

The dependence of surface-plasmon damping versus plasmon momentum and energy has been measured for the Ag(011) surface with angle-resolved electron energy loss spectroscopy. The data are compared with previous results obtained for Ag(001). At small transferred momenta, q parallel-to, we observe a nearly linear dependence of the energy loss...

The surface plasmon dispersion of ion bombarded Ag(001) is investigated by angle resolved high resolution electron energy loss spectroscopy. We find it to be parabolic and dominated by the quadratic term, contrary to the case of flat Ag(001) where the linear term is dominant. The case is reminiscent of surface plasmon dispersion on the oxygen...