We have deposited Mn on the ͑110͒ surface of Ni and discover ordering into a c(2ϫ2) superstructure for coverages of 0.35-0.5 monolayer Mn. Mn 2p photoemission spectra show distinct satellite structures which disappear for higher Mn coverage. Calculations using configuration-interaction theory including multiplet effects on a model cluster representing the local geometry of a surface alloy identify the features as correlation satellites and give model parameters as follows: charge-transfer energy ⌬ϭ1 eV, Coulomb energy Uϭ3 eV, and transfer integral Tϭ1.2 eV. A detailed comparison to the case of c(2ϫ2) Mn/Cu͑100͒ leads to the conclusion that c(2ϫ2) Mn/Ni͑110͒ is a new magnetic surface alloy.

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Experimental photoelectron spectra are usually interpreted using rather crude approximations for the upper states into which the electrons are excited. Better knowledge about these excited states could substantially improve the accuracy of valence band mapping by photoelectron spectroscopy. We here demonstrate that VLEED measurements are ideally suited for accurate determination of the desired upper states. This is illustrated by model calculations including absorption and self-energy corrections. The close correspondence between so-called irregularity points of the excited-state bands and the total electron reflectivity is established, which opens up the possibility for direct mapping of irregularity points by comparison with experimental VLEED spectra, and for fitting of the whole excited-state bands between these points. The proposed scheme is finally used to determine the excited-state bands of Cu along L from measurements on Cu(111).

We have combined photoelectron spectroscopy (PES) and very-low-energy electron diffraction (VLEED) to study the electronic band structure E͑k͒ of a material with complicated unoccupied upper bands, which are incompatible with the free-electron approximation. Using VLEED, we have experimentally determined these bands, and accordingly optimized the PES experiment. PES band mapping using the VLEED upper bands enabled the first consistent resolution of the lower occupied bands, in particular, the perpendicular dispersion E͑k Ќ ͒, for a layered material. The combination of PES and VLEED is a powerful method to resolve even very complicated E͑k͒ absolutely.[S0031-9007(97)

The valence bands of the layered compound VSe 2 and the related intercalation compounds Na x VSe 2 , K x VSe 2 , and Cs x VSe 2 have been investigated by means of angle-resolved photoelectron spectroscopy, and compared to self-consistent linear augmented plane-wave ͑LAPW͒ band calculations. The intercalation compounds were prepared in situ by deposition of Na, K, and Cs on VSe 2 cleavage surfaces. The intercalation was monitored by core-level spectroscopy, and although K was found to intercalate more slowly than Na and Cs, estimated alkali concentrations of xϭ0.2-0.3 were reached for all three alkali metals. Additional depositions mainly seemed to increase the intercalation depth. Good agreement between LAPW calculations and valenceband spectra was found, in particular for the dispersion along the layers. Normal-emission spectra, obtained at different photon energies, indicated vanishing perpendicular dispersion, but in spectra measured under variation of the emission angle some band-edge signatures were seen, which suggests that some perpendicular dispersion remains, in accordance with the LAPW calculations. The lack of dispersion in the normal-emission spectra could be due to intercalation induced structural transformations, leading to stacking disorder. Also correlation effects may contribute. The rigid-band model is found inadequate, except as a crude approximation, for describing the changes during the initial phase of intercalation. It might be used to describe the continued intercalation, however, under condition that the intercalation modified bands are used. The need for studies that probe both electronic and crystallographic structure ͑including defects͒ is stressed. ͓S0163-1829͑98͒08536-1͔