Modulations of valence-band photowmission spectrum from C60 monolayers on Ag(111).

The photon-energy dependences of valence-band photoemission spectra have been investigated for monolayer, submonolayer, and multilayer (formula presented) films on Ag(111). The intensity ratios of the highest and next-highest occupied molecular orbitals (the HOMO and NHOMO) of the films are found to oscillate with the same period as the incident photon energy is varied, but the amplitude of the oscillation is smaller with lower film coverage. Since the characteristics of the molecular orbitals of (formula presented) in the monolayers are considerably different from those of the thick film due to the charge-transfer interaction between the metallic surface and the molecule the observation opposes the proposal in which the oscillation is entirely dependent on the nature of the empty and occupied states involved in the photoemission process. The results instead support the photoelectron interference model by Hasegawa et al. [Phys. Rev. B 58, 4927 (1998)]. Variation of the oscillation amplitude with (formula presented) coverage is explained in terms of hybridization of the HOMO and NHOMO with the surface. Depositing (formula presented) onto Ag(111) held at a high temperature produces a single-phase (formula presented) (formula presented) (formula presented) monolayer. Angle-resolved photoemission experiments reveal changes in the relative intensities of the two bands with the azimuth-emission angle, measured with respect to the symmetry axes of the ordered monolayer. The intensity modulation is due to anisotropic scattering of photoelectrons along various molecular axes. © 2003 The American Physical Society

Structural and electronic properties of ordered La@C-82 films on Si(111)

The growth of endohedral fullerene La@C82 films on Si(1 1 1) has been explored by scanning tunneling microscopy (STM). The STM images reveal the molecules are hexagonally close-packed in multilayer films with the inter-molecular separation similar to that of the La@C82 crystal. Electronic properties of the films have been investigated by ultraviolet photoelectron spectroscopy (UPS) and tunneling spectroscopy, which provide comparable results for the electronic structure of the occupied electronic states. Tunneling spectroscopy also gives an insight into the unoccupied states and shows that the edges of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) both approach the Fermi level, indicating that the film is metallic or semi-metallic. An electronic structure of the La@C82 film is proposed from the spectroscopic results

Electrostatic ordering of the lanthanum endoatom in La@C <inf>82</inf> adsorbed on metal surfaces

An investigation of the dynamic behavior of the endohedral La atom in La@C 82 adsorbed on Ag(111) or Cu(111) using the normal-incidence x-ray standing wavefield (NIXSW) technique is presented. For the surface-normal (111) reflection, NIXSW demonstrates different La absorption profiles between the La@C 82 monolayer and multilayer. Analysis of the profiles reveals significant La ordering in the monolayer; the degree of ordering increases as the film is cooled. First-principles calculations provide a description of the endohedral metal atom-cage bonding and the fullerene-surface interaction. Combined, these effects give rise to preferential binding sites for the endoatom resulting from electrostatic interactions within the adsorbed fullerene. ©2005 The American Physical Society

Electrostatic ordering of the lanthanum endoatom in La@C~8~2 adsorbed on metal surfaces

An investigation of the dynamic behavior of the endohedral La atom in La@C-82 adsorbed on Ag(111) or Cu(111) using the normal-incidence x-ray standing wavefield (NIXSW) technique is presented. For the surface-normal (111) reflection, NIXSW demonstrates