| Focusing on the electronic states of high fullerenes C70 and C84, we have investigated the (C70, C84)/Ag(111) interfaces, valence photoemission intensity oscillations and Eu-C70 fullerides with photoemission spectroscopy (PES), X-ray absorption spectroscopy (XAS), scanning tunneling microscopy (STM), low energy electron diffraction (LEED) measurements and density functional theory (DFT) calculations.PES and XAS data of a C70 monolayer on the surface of Ag(111) (1 ML C70/Ag(111)) reveal a large amount of charge transfer,2.6-2.9 e per C70 molecule, which is only surpassed by the C60/Cu(111) interface among the various fullerene/metal interfaces. The screening effect of Ag(111) on the electronic structure of C70 is remarkable, which greatly reduces or even eliminates the on-site Hubbard energy, and makes the monolayer show metallic properties. The energy levels of C70 align with the Fermi level of the Ag(111) substrate. A close resemblance between the work functions of the C70 multilayer (4.53 eV), monolayer (4.52 eV) and the Ag(111) surface (4.50 eV) discloses that the vacuum level shift caused by the C70 adsorption is negligible. Potassium doping indicates that 1 ML C70/Ag(111) can still accommodate about 9 electrons and that the sample keeps metallic at any doping level. STM studies reveal that the 1 ML C70/Ag(111) forms the first-order commensurate ((?)13×(?))R±13.9°structure, and that the rule of lattice match is invalid here. C70 molecules take the up-right orientation on Ag(111) surface, and present temperature-dependent bright/dim contrast, which implies the pit formed at the C70/Ag(111) interface. The pit, generally say, the substrate reconstruction, is widely observed at the fullerene/metal interfaces, but its origin is still unknown. By considering both the electronic and geometric structures of 1 ML C70/Ag(111), we provide a unify interpretation of the pits at the various fullerene/metal interfaces.A similar study has been carried out on C84/Ag(111) system. Owing to the substantial difference between the energy level structures of C70 and C84 molecules, the amount of charge transfer for the 1 ML C84/Ag(111) is determined to be within the range of 1-1.6 e per molecule, which is much lower than the case of 1 ML C70/Ag(111). Potassium doping indicates that 1 ML C84/Ag(111) can accommodate～6 electrons at most (including the electrons transferred from the substrate). As a result of the substrate screening effect, the C84 monolayer also shows metallic properties before and after K doping. The energy levels of C84 also align with the Fermi level of the Ag(111) surface, but here the shift of the vacuum level caused by C84 adsorption is obvious. On the Ag(1111) surface, both the C84-C84 and C84-Ag interactions are stronger than the cases of C60 and C70, which are indicated by the Volmer-Weber type growth manner, the non-commensurate R30°structure of the 1 ML C84/Ag(111), and the fact that a annealing at 550℃can not yet completely desorbe all C84 molecules.Photoionization cross section is not only related to the occupied states (initial states of PES), but also to the ionized states (final states of PES). For molecular systems, both the initial and final states are closely related to the molecular configurations. In this thesis, we have measured the valence photoemission intensity oscillations of C84 in the photon energy range from 13.4 eV to 129.3 eV. Combining with the reported oscillating data of C60 and C70 in the literature, we raise a very simple method to elucidate the sizes of fullerenes from the oscillating data. This method uses cosine functions to fit the oscillations, and only those oscillating data measured with the photon energies smaller than 100 eV (with an interval of 2-3 eV) are needed to give satisfactory results of the molecular diameters.In the PES study of Eu-C70 fullerides, we observed substantial hybridizations between the Eu 6s states and the HOMO-n (n=6-10) orbitals of C70, which should play important role in understanding the ferromagnetic mechanism for Eu9C70. We also found a charge transfer limitation (< 6 e) in the EuxC70 (x=0-9) system. This limitation is much smaller than the 18 e as expected with all 5d6s electrons of Eu transferred to C70, also lowers than the case of K doping 1 ML C70/Ag(111) (～12 e). Based on the 6s-πhybridizing states and the electronic structure differences between Eu atom and Eu metal, the charge transfer limitation can be well understood. Our work also reveals that the deeper molecular levels of fullerenes can be crucial to some physical properties such as magnetism, in comparison with the LUMO and LUMO+1 levels that determine the transport properties.
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