Electrons in a Small Particle of Gold

Before presenting experimental results concerning the electronic structure of the AU55 cluster compound, it is necessary to first examine several concepts relating to the electronic structure of small gold particles in general, and to try to see how these differ from the bulk. 

One can expect a number of changes in the system when the size of the sample becomes small. Below we will see that the gold atoms in the core of AU55 reflect many characteristics of the metallic state. For this reason we will look specifically at Aujs as an example of a small metallic system , and will later examine the validity of this approach. 

Just as the energy splitting within a band of levels will effect the physical properties of the cluster, so will the density of the sub-levels, the filling of the individual sub-levels, and the filling of the band of levels. For possible collective motion of the electrons within the cluster, the band must not be completely filled. In the case of AU55 this point is not completely clear. 

When small clusters are placed adjacent to one another, but at random with respect to inter-cluster distances and orientations, as is the case in the amorphous arrangement of the clusters of Aujj, the interactions between the individual clusters will lead to small shifts of the intra-cluster energy levels which are slightly different for each cluster. Since both macroscopic as well as microscopic 

In recent publications [120, 121, 122,123] it has been shown that both the ionization potentials and the optical properties of bare and uncharged mercury clusters in a molecular beam experiment demonstrate a gradual size dependent evolution of metallic properties, starting at about 13 atoms and already bulklike at about 70 atoms. It has been predicted theoretically [124] that plasmons should begin to develop for such mercury clusters at about Hgi5. We should keep this in mind in the discussion of the electronic properties of AU55. 

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