At present the only surface electron microscope which allows true characteristic XPEEM (photoemission electron microscopy using synchrotron radiation) and structural characterization is the spectroscopic LEEM developed at the Technical University Clausthal in the early nineties. This instrument has in the past been used mainly for LEEM studies of various surface and thin film phenomena, because it had very limited access to synchrotron radiation. Now the microscope is connected quasipermanently to the undulator beamline 6.2 at the storage ring ELETTRA, operating successfully since the end of 1996 under the name SPELEEM (Spectroscopic PhotoEmission and Low Energy Electron Microscope). The high brightness of the ELETTRA light source, together with an optimized instrument, results in a spatial resolution better than 25 nm and an energy resolution better than 0.5 eV in the XPEEM mode. The instrument can be used alternately for XPEEM, LEEM, LEED (low energy electron diffraction), MEM (mirror electron microscopy) and other imaging modes, depending upon the particular problem studied. The combination of these imaging modes allows a comprehensive characterization of the specimen. This is of particular importance when the chemical identification of structural features is necessary for the understanding of a surface or thin film process. In addition, PED (photoelectron diffraction) and VPEAD (valence photoelectron angular distribution) of small selected areas give local atomic configuration and band structure information, respectively.

This paper reports the present stage of commissioning of the gas-phase photoemission beamline at Elettra, Trieste. The beamline is designed for atomic and molecular science experiments with high-resolution and high-flux synchrotron radiation. It consists of an undulator source, variable-angle spherical-grating monochromator and two experimental stations. The design value of the energy range is 20 to 800 eV with a specified resolving power of over 10000. The procedure adopted for calibration of this type of monochromator is discussed. At present a resolving power up to 20000 and a range up to 900 eV have been measured. Absorption spectra taken at the argon L(II,III)-edge and at the nitrogen, oxygen and neon K-edges are as sharp as, or sharper than, any reported in the literature. The instrumental broadening is well below the natural line-width making it difficult to quantify the resolution; this problem is discussed.

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