The new beamline ALOISA, now operational at the Elettra Synchrotron, is designed for surface studies by means of several experimental techniques: surface x-ray diffraction and reflectivity, photoemission spectroscopy, photoelectron diffraction, e Ϫ -Auger coincidence spectroscopy. A new monochromator has been specifically designed and realized for this multipurpose beamline: it makes use of a channel-cut Si crystal dispersive element for the 3-8 keV range and of a plane mirror-plane grating element for the 200-2000 eV range. Both dispersive elements share the same optical system. In the low energy range ͑200-900 eV͒ the spectral resolving power exceeds 5000 while maintaining a throughput higher than 10 10 photons/s/200 mA/0.02% BW. In the case of the N 2 1s →* and Ne 1s→3 p transitions, the extremely high signal-to-noise ratio of the absorption spectra allowed a very accurate determination of the corresponding natural linewidth (116Ϯ2 and 250 Ϯ10 eV, respectively͒. Moreover, the vibrational structure of the CO-oxygen 1s→* transition has been fully resolved. In the high energy range, the measured flux exceeds 10 10 photons/s/200 mA up to 6.5 keV with a resolving power of ϳ7500.

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The structure of Fe films, epitaxially grown on Ni͑001͒, has been studied in the 0-14 ML coverage range by means of photoelectron diffraction ͑PD͒ in the forward scattering regime. Quantitative analysis by a multiple scattering approach has been performed on Fe films at a coverage of 3 and 7 ML. Analysis of the 3-ML data showed that growth was not layer-by-layer but rather occurred through islands nucleation and that transition from the pseudomorphic fcc to the bcc phase was located in this early stage of growth. In fact, best fit was obtained by calculations on a 2 ML bcc͑110͒/3 ML fcc͑001͒ Fe film with the bcc͗111͘ʈfcc͗110͘ in-plane orientation. Interlayer spacings of 2.05Ϯ0.06 Å, 2.01Ϯ0.03 Å, and 1.85Ϯ0.03 Å were found in the bcc region, between bcc and fcc layers and in the fcc region, respectively. Best-fit in-plane nearest-neighbors ͑n-n͒ distance was 2.49Ϯ0.02 Å, in registry with that of the Ni substrate. To analyze the 7-ML data a 4 ML bcc͑110͒/3 ML fcc͑001͒ film was employed, varying the fitting parameters in the bcc region only. Best fit was obtained for an interlayer spacing of 2.04Ϯ0.04 Å and in plane n-n distance of 2.47Ϯ0.01 Å. At 14 ML the PD pattern collected over a 94°azimuthal range displayed symmetry around the ͓110͔ substrate direction, which was explained by the equipopulation of the 4 bcc͑110͒ domains satisfying the bcc͗111͘ʈfcc͗110͘ alignment.

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