We have carried out an extensive study of C 60 adsorption on Cu͑111͒ surfaces using low-energy electron diffraction, photoemission, and x-ray-absorption spectroscopy. It is found that in valence-band photoemission a state forms right below the Fermi energy for an annealed, well-ordered monolayer, similar to the case of K-doped C 60 . This peak disperses across the Fermi energy at off normal emission geometry. The spectra of carbon core-level photoemission show that the line shape is highly asymmetric with a metalliclike tail. The carbon near-edge absorption spectra show that the lowest unoccupied molecular orbital ͑LUMO͒ is attenuated, and a clear Fermi edge jump appears at the absorption onset. This evidence indicates that charge transfers from the substrate to the C 60 molecular orbitals and the overlayer becomes metallic. The amount of charge transfer can be determined to be 1.5-2 electrons per molecule from both the area of the occupied LUMO in photoemission and the peak shift in near-edge absorption spectra. It has been reported that many metal surfaces with originally different work functions covered by a monolayer of C 60 have a similar work function of about 5 eV. We suggest that the measured work functions are due to the metallic C 60 overlayers and are similar regardless of the metal substrates. This is in line with the reported alignment of monolayer energy levels to substrate Fermi energy. Since the work functions are similar, the energy levels with respect to the vacuum level are also similar. Finally we compare near-edge x-ray-absorption with inverse photoemission spectroscopy to address the screening effects.

No abstract

No abstract

The design, construction and commissioning of a beamline and spectrometer for inelastic soft X-ray scattering at high resolution in a highly efficient system are presented. Based on the energy-compensation principle of grating dispersion, the design of the monochromator-spectrometer system greatly enhances the efficiency of measurement of inelastic soft X-rays scattering. Comprising two bendable gratings, the set-up effectively diminishes the defocus and coma aberrations. At commissioning, this system showed results of spin-flip, d-d and charge-transfer excitations of NiO. These results are consistent with published results but exhibit improved spectral resolution and increased efficiency of measurement. The best energy resolution of the set-up in terms of full width at half-maximum is 108 meV at an incident photon energy tuned about the Ni L3-edge.

No abstract