Erzeugung und elektronische Struktur von endohedral dotierten Fullerenen

A machine devoted to the size-selected and non-destructive deposition of cluster ions has been set up. Pristine and endohedrally doped fullerenes (C$_{60}$, La@C$_{60}$ and Ce@C$_{60}$) have been deposited onto graphite and the electronic structure of individual clusters has been investigated using scanning tunneling spectroscopy (STS) and X-ray photoelectron spectroscopy. The STS-data show that deposited endohedrally doped fullerenes have considerably smaller band gaps than pristine C6o. The encapsulated atom determines the character of the electronic structure. Ce@C$_{60}$ shows a 0.5 eV band gap at the Fermi level, whereas La@C$_{60}$ is metal-like at room temperature. Below 28 K this cluster shows reversibly the opening of a 40 meV band gap. This metal-to-insulator transition at 28 K is explained by the freezing of the intramolecular "rolling mode" and the transition from a dynamical to a static Jahn-Teller effect. The spectra are interpreted in terms of free C$_{60}$ including a charge transfer and a Jahn-Teller-splitting. A systematic investigation of the production and the abundancies of metal-carbon clusters allows to draw conclusions about the geometries of these clusters. The smallest possible endohedrally doped fullerene M@C$_{n}$ (M=metal) has been found for some transition metals at n = 36, and additional density functional studies shed more light onto their electronic structure. Y$_{2}$C$_{n}$ and La$_{2}$C$_{n}$ show a distinct structural transition at n $\approx$ 70. Density functional calculations on C$_{44}$ and La@C$_{44}$ along with earlier experimental studies (by H. Kietzmann [72]) have led to the identification of ground state isomers