CESYRA@GasPhase

One of the most powerful tools for the characterization of the local electronic structure, electronic density of states and correlation effects in the solid state is X-ray absorption spectroscopy (XAS) using synchrotron radiation. This technique is based on the excitation of electrons from deeply bound core levels to unoccupied levels. The core levels selected are element-specific and the spectrum is determined by the local surroundings of the excited atom.

In the case of XAS, the difficulties related to free clusters’ dilution are increased by the low absorption cross section for transition metal clusters (typically in the Mbarn range or below). To overcome these limitations the possible solutions are to increase the photon flux and to develop high intensity cluster sources.

The availability of high-brilliance, synchrotron radiation facilities has made possible the study of core-level excitation of free van der Waals and molecular clusters produced in supersonic beams, but no results have been published to date on free transition metal clusters. This is due to the fact that available cluster sources cannot provide adequate cluster densities even for third generation synchrotron light sources.

Thanks to the high-intensity of the cluster beam produced by the PMCS, the LGM laboratory was recently able to perform the first core electron spectroscopy measurements of free titanium clusters [1]. The measurements were performed at the GasPhase beamline at ELETTRA (Sincrotrone Trieste), and thanks to the approval of a "long term project" of two years at the same beamline, those measurements will be repeateated on carbon, metal and oxides clusters.

The activity of the LGM laboratory in this field was prized in 2006 by the prestigious italian institute "Accademia dei lincei", that awarded to the group the Tartufari Prize.

Apparatus developed by the LGM laboratory for the electron spectroscopy measurements on free clusters.	Interaction chamber.
Inside view of the interaction chamber for PEPICO experiments on free clusters.	Top view of the interaction chamber: channeltrons for ion detection.

[1] P. Piseri, T. Mazza, G. Bongiorno, C. Lenardi, L. Ravagnan, F. Della Foglia, F. DiFonzo, M. Coreno, M. DeSimone, K. C. Prince and P. Milani, Core level spectroscopy of free titanium and titanium oxide clusters in supersonic beams, New Journal of Physics 8, 136 (2006)