SAVIO , Letizia

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...

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...

We demonstrate by vibrational spectroscopy that open steps are the active site for O-2 dissociation on Ag(410), and that the barrier to adsorption at defects can be measured by energy and angle resolved investigation of the dynamics of the gas-surface interaction. We identify a molecular adsorption channel with considerably reduced activation...

The active sites for catalytic reactions in heterogeneous catalysis are often minority sites related to defects at the surface. However, in most studies performed so far under controlled conditions, nearly perfect low Miller index surfaces were used, giving rise to the so-called structure gap in the surface science approach to catalysis. In...

We show with supersonic molecular beams and surface vibrational spectroscopy that, contrary to the case of Ag(100) and Ag(110), O-2 undergoes total dissociation on Ag(210) at 105 K. Moreover, metastable subsurface sites can be accessed either directly or indirectly. For the direct channel, the final configuration of the oxygen atoms depends on...

The role of defects in catalytic reactions, especially those involving low rates and high degrees of selectivity, has been debated ever since the very early days of surface science. However, most studies on gas-surface interaction and chemisorption performed under controlled laboratory conditions have dealt so far with nearly perfect...

In the present paper we review our findings on ethylene adsorption on clean and oxygen covered Ag(001) surfaces investigated by dosing the gas with a Supersonic Molecular Beam and analysing the adsorption state either by High Resolution Electron Energy Loss Spectroscopy or by High Resolution X Rays Photoemission Spectroscopy. The final...

The active role of defects in some catalytic reactions was predicted in the very early days of surface science. Most of the studies on gas adsorption at solid surfaces dealt, however, so far with nearly perfect low Miller index surfaces, which are rather unlike the active powders employed as catalysts in industrial reactors. The structure gap...

The sticking probability of C2H4 on Ag(210) is studied by the molecular beam technique and by high resolution electron energy loss spectroscopy. At a crystal temperature of 110 K, adsorption occurs initially into a stable, pi-bonded, state. At larger coverage a metastable state is populated, too. The sticking probability, S, decreases with...

One of the main goals of surface science is the understanding of the elementary steps occurring in catalytic reactions in the heterogeneous phase, in order to identify promoters and rate limiting factors at the atomic scale with the ultimate scope of designing more efficient catalysts. To reduce the complexity of the problem and focus attention...

The interaction of ethylene with Ag(410), a vicinal surface of Ag(100) characterised by a high density of open steps, is investigated. Energy and angle resolved measurements of the sticking coefficient are performed with the retarded reflector method of King and Wells using a supersonic molecular beam. We find that open steps remove the...

The effect of surface interband transitions (SIT) on surface plasmon dispersion was investigated by high-resolution electron-energy-loss spectroscopy for Ag(001). We demonstrate that the anomalous linear dispersion on this face, which is at variance with the parabolic form present for the other low Miller index surfaces, is due to a SIT between...

We report on a combined high resolution electron energy loss spectroscopy and x-rays photoelectron spectroscopy investigation of the interaction at room temperature of H2O with thin and ultra-thin MgO films grown on Ag(100). We find a strongly enhanced dissociation probability in the monolayer and sub-monolayer regime, indicative of an active...

The interaction of propene with Ag(001) is investigated by high resolution electron energy loss spectroscopy and supersonic molecular beam methods under ultra high vacuum conditions. Propene adsorbs molecularly at 110 K and desorbs intact leaving a clean surface after annealing to 160 K. Two adsorption sites, characterized by slightly different...

We show that vibrational energy can be used to tune the chemisorption state of an adsorbed molecule. When dosing C2H4 with a supersonic molecular beam on Ag(0 0 1) we demonstrate by vibrational spectroscopy that, with increasing nozzle temperature, TN, firstly no stable adsorption occurs, then a pi -bonded configuration is populated, switching...

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We present here a scanning tunnelling microscopy (STM) study on O-2 adsorption at Ag(110) at T = 175 K, i.e. in the temperature range between the onset of O-2 dissociation and the formation of the added row reconstruction. In agreement with previous studies at lower surface coverage, we observe several structures forming upon O-2 dissociation,...

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The interest in thin and ultrathin oxide films is increasing rapidly due to the new properties and the many possible technological applications of such materials. In this frame the interaction with water, a major constituent of our atmosphere, is an essential issue for a better characterization of oxide film-based devices. We report here a...

The fundamental understanding of adsorption and self-organization of biological molecules at surfaces is of greatest importance for a huge variety of possible applications, ranging from molecular electronics to the study of biocompatible materials; hygiene, and biofouling. In spite of that, the characterization of the interactions of organic...

Self-assembly of organic molecules at metal surfaces is of greatest importance in nanoscience; in fact, it opens new perspectives in the field of molecular electronics and in the study of biocompatible materials. Combining an experimental low-temperature scanning tunneling microscopy investigation with ab initio calculations, we succeeded to...

We present here a supersonic molecular beam investigation of the initial sticking probability (SO) for the O-2/Cu(410) system. Over the temperature range between 130 and 800 K adsorption occurs dissociatively and So increases up to similar to 0.7 with beam energy, indicating that the process is activated. So is larger for angles corresponding...