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The heteroepitaxial growth of C60 on GeS(001) has been studied using low-energy electron diffraction, selected-area electron diffraction, high-resolution electron microscopy, x-ray diffraction, and x-ray and ultraviolet-photoelectron spectroscopy (UPS). The simultaneous observation of diffraction spots characteristic of the substrate and the C60(111)overlayer allows us to specify the geometry of the epitaxy. The shape of the intensity curves of the C 1s and Ge 3d photoemission lines strongly suggests a layer-bylayer-type growth, confirmed by the observation in the synchrotron x-ray diffraction spectrum of finitesize oscillations on the (111)Bragg reflection peak of a thin C60(111)film. From a theoretical simulation of the C ls and Ge 3d line-intensity curves, the mean free path of a C 1s and Ge 3d photoelectron in solid C60 is estimated to about 15. 4 and 17 A. , respectively. The plot of the film thickness versus deposition time shows evidence for a small difference in sticking coefBcient between the first monolayer and the upper ones. A detailed analysis of the C 1s line shapes for normal and grazing emission suggests the existence of inequivalent carbon sites at the interface. The first valence-band feature of the substrate presents a downward band bending of about 200 meV with increasing C60 coverage. From the shift of the cutoff in the UPS spectra we deduce a work function increase of about 100 meV upon monolayer adsorption. The characteristic spectral features of C60 observed in the UPS spectra for bulk fullerite are slightly broadened and shifted to lower binding energies at submonolayer coverages and show no direct evidence for significant hybridization, indicating that the C60-substrate interaction is mainly dominated by van der Waals bonding. All these observations can be explained by a positive effective dipole of about 8 X 10 ' C m induced on the C60 molecule upon adsorption onto the GeS substrate.

We report evidence for surface plasmon excitations in concentric-shell fullerenes. A film of these concentricshell fullerenes with radii around 5-7 nm was produced by carbon bombardment of a silver polycrystalline target and measured by electron-energy-loss spectroscopy ͑EELS͒ in reflection geometry. These data were analyzed with the help of a dielectric theory developed for EELS in transmission geometry. Taking into account the concentric-shell-substrate interaction, the spectral shape can be explained as a combination of contributions from -* interband transitions ͑around 13.5 eV͒, from the surface radial (-*) and tangential (-*) plasmons ͑around 14.5 eV and 16.7 eV, respectively͒, and from the volume plasmon ͑24.5 eV͒.

Electronic-transitions and excitations in solid C-70 studied by EELS and XPS c-1s satellite structures Han, Bo-ying; Yu, Li-ming; Hevesi, K.; Gensterblum, G.; Rudolf, P.; Pireaux, J.-J.; Thiry, P.A.; Caudano, R.; Lambin, Ph.; Lucas, A.A. . (1995). Electronictransitions and excitations in solid C-70 studied by EELS and XPS c-1s satellite structures. Physical

The intramolecular vibrations of a C 70 epitaxial film have been studied by high-resolution electron energy-loss spectroscopy (HREELS). The spectral response of infrared active vibrations has been separated from the specular spectra based on a detailed angular distribution analysis of the scattered electrons. With the help of the oscillator frequencies and the damping ratios determined by optical absorption measurements, the oscillator strengths of the C 70 dipole active modes between 400 and 1500 cm −1 are accurately determined by fitting the dipole contributions of the HREELS spectrum in the framework of the dielectric theory. Moreover, our experiment confirms that there are infrared active vibrations below 400 cm −1, which were predicted by molecular dynamical calculations for C 70.