Performance of the grating-crystal monochromator of the ALOISA beamline atthe Elettra Synchrotron

The new beamline ALOISA, now operational at the Elettra Synchrotron, is des igned for surface studies by means of several experimental techniques: surf ace x-ray diffraction and reflectivity, photoemission spectroscopy, photoel ectron diffraction, e(-)-Auger coincidence spectroscopy. A new monochromato r has been specifically designed and realized for this multipurpose beamlin e: 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 r ange. Both dispersive elements share the same optical system. In the low en ergy range (200-900 eV) the spectral resolving power exceeds 5000 while mai ntaining a throughput higher than 10(10) photons/s/200 mA/0.02% BW. In the case of the N-2 1s -->pi* and Ne 1s --> 3p transitions, the extremely high signal-to-noise ratio of the absorption spectra allowed a very accurate det ermination of the corresponding natural linewidth (116 +/- 2 and 250 +/- 10 eV, respectively). Moreover, the vibrational structure of the CO-oxygen 1s -->pi(*) 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 resolvi ng power of similar to 7500. (C) 1999 American Institute of Physics. [S0034 -6748(99)01410-0].