IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM5
Electronic Structure of Epitaxial Thin NiO(100) Films Grown on Ag(100): Towards a Firm Experimental Basis

Tuesday, October 30, 2001, 9:40 am, Room 121

Session: Adsorption on Oxide Surfaces
Presenter: M. Marcon, Politecnico di Milano, Italy
Authors: L. Duò, Politecnico di Milano, Italy
M. Portalupi, Politecnico di Milano, Italy
G. Isella, Politecnico di Milano, Italy
R. Bertacco, Politecnico di Milano, Italy
M. Marcon, Politecnico di Milano, Italy
F. Ciccacci, Politecnico di Milano, Italy
Correspondent: Click to Email
In the field of electron correlations in solids NiO definitely plays a key role. A large amount of work on the electronic and magnetic properties of NiO has been done, but the longstanding problem of the full description and understanding of its electron states is still open. While for photoemission (PE) results on NiO a large set of data is available in literature, with a general consensus on the lineshapes, concerning inverse PE (IPE) only few pioneering works have been carried out in the early eighties. They gave rise to significant discrepancies, due both to the quality of the sample and to charging problems. This has relevant consequences concerning the application of model systems in terms, e.g., of the magnitude of the correlation energy and the charge transfer energy . On the other hand, very recently the possibility of growing well characterized NiO(100) monocrystalline thin films has shown up. This is achieved by evaporation of Ni in an O@sub 2@ atmosphere onto Ag(100), whose lattice parameter agrees with that of NiO. We have therefore measured IPE spectra of NiO(100) thin films (up to about 50 monolayers) grown by such a method. By studying the dispersion behavior of the various IPE features we were able to classify them as d- or sp-derived states and a d-like ligand hole structure at high energy is clearly shown. By combining these results to X-ray photoemission spectroscopy taken on the same surfaces we find that the magnitude of the gap is similar to what previously found. A new aspect is instead related to the position of the Fermi level (E@sub F@) which is near the middle of the gap. This is at variance with previous results which showed a strong pinning of E@sub F@ at the top of the valence band and were interpreted in detail as an intrinsic effect of "pure" NiO.