Electronic and Magnetic Properties of Free Metal Particles Studied by Photoelectron and X-ray Absorption Spectroscopy
Clusters allow to follow the development of material properties from the atom to the bulk, but often exhibit characteristics far from that of the atoms or the bulk, which makes them especially interesting. Recent technologic developments make it now possible to study free clusters with well defined size and temperatures (down to a few Kelvin). Furthermore the range of spectroscopic tools has been extended, for example by the inclusion of angle resolved photoelectron spectroscopy or gas phase x-ray absorption measurements.
Photoelectron spectroscopy on free metal clusters yields is a powerful technique which in principle yields an image of the electronic density of states of the cluster, which in the case of simple metals like the alkalis or noble metals is dominated by electron shell effects, but clearly exhibits an influence of the geometric cluster structure as well . Recently we could show by angle resolved photoelectron spectroscopy that despite this perturbing influence of the ionic background the valence electrons in a close to spherical cluster strongly resemble angular momentum eigenstates .
Core shell x-ray absorption spectroscopy (XAS) is an element specific technique, which allows to study the local electronic structure of the atoms addressed . This is especially helpful in the case of doped clusters like transition metal doped silicon clusters, where it allows to characterize the interaction of the doping atom with the surrounding cluster.
Finally the measurement of x-ray magnetic circulate dichroism, which can be achieved by performing XAS-experiments with circularly polarized light on cold free size-selected clusters stored in an ion trap within a strong magnetic field, can be used to measure the spin and orbital moment of single doping atoms or whole clusters, and thus shed some light on the development of bulk magnetic behavior .
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