| 1. |
- Macovez, R., et al.
(författare)
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Electronic surface reconstruction and correlation in the fcc and dimer phases of RbC60
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:19, s. 195424-
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Tidskriftsartikel (refereegranskat)abstract
- A combined photoemission and x-ray absorption study of a RbC60 crystalline film is presented. We find evidence for an electronic charge reconstruction of the film surface in both the fcc and the dimer phases of RbC60. We confirm the previous conclusion on less crystalline films that the dimer phase is insulating. Several observations, such as the presence of molecular features in the photoemission spectra, indicate that at least partial electron localization occurs in the high-temperature fcc phase. In the fcc phase, the surface consists in a half-charge C60(111) plane and appears weakly metallic, as found for the bulk. In the dimer phase, the charge reconstruction simply implies the presence of neutral C60 in the surface layer. The identification of neutral molecules in the surface layer drastically improves the agreement between calculations of the electronic density of states and photoelectron spectra in both phases.
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| 2. |
- Macovez, Roberto, et al.
(författare)
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Metal-to-insulator transition in thin-film polymeric AC(60)
- 2009
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 11, s. 023035-
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Tidskriftsartikel (refereegranskat)abstract
- We present an electron spectroscopy study of phase-pure AC(60) thin films (A = Rb, Cs) in their monomer (face-centred cubic (fcc)) and polymer phases. A surface electronic reconstruction is observed in polymeric RbC60, analogous to that reported for the fcc phase. As for pristine C-60, the occupied electronic states of AC(60) fullerides are not dramatically affected by polymerization. The energy separation between the leading feature in photoemission and inverse photoemission is similar in both stable AC(60) phases. These observations suggest that electron correlation effects are similar in the two phases, and that their different electronic behaviour is mainly related to the reduction of degeneracy of the polymer frontier states. Photoemission and electron-energy loss spectroscopy data show that the thin-film form of the RbC60 polymer is metallic at room temperature, and that it undergoes a metal-insulator transition at around 100 K. This transition temperature is much higher than that reported for the corresponding bulk phase and signals a poorer screening of Coulomb interactions at the film surface.
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