[en] Probed length scales of sub-micrometer dimensions have been achieved in photoemission spectroscopy owing to the high flux and brightness of the soft X-rays provided by the third generation synchrotron sources and the progress in microfabrication of focusing elements for soft X-rays. The use of multichannel detectors in the recently constructed scanning photoelectron microscopes adds speed and flexibility in data acquisition. Here we present some results obtained with the scanning photoemission microscope at ELETTRA illustrating the importance of the multichannel data acquisition for the interpretation of the data

[en] Full text: The advantage of X-ray photoemission electron microscopy (XPEEM) combined with low energy electron microscopy and diffraction (LEEM-LEED) to probe in-situ surface reactions and complex changes in the local substrate and adlayer structures was successfully combined with the better spectral resolution of scanning photoelectron microscopy SPEM for detailed characterization of the local chemical state of the substrate and the adsorbed species in studies of mass transport phenomena in model Au/Ru(110) systems, triggered by reaction fronts or exposure of confined films to different gas environment. The local composition, the adlayer structure and the reactivity of the spatially separated phases, evolved as a result of redistribution of initially uniform Au films, are thoroughly characterized. The observed dynamic rearrangements at the Au/Rh(110) surface, involving development of spatially separated phases of varying O and Au coverage and massive reconstruction and deconstruction events, affect in a rather complex manner the adsorption bond and mobility of the Au and O adatoms. In a classical approach the events occurring during the reaction can be described in terms of different minima of the potential energy surface and different mobility of the Au adatoms, corresponding to the different local arrangements of the adlayer. Similar stationary patterned surfaces triggered by propagating reaction fronts we observed very recently when instead of inert Au the Rh(110) surface was modified by Pb and Ag. This confirms that re-organization processes destroying the homogeneity of the interface are common phenomenon in bimetallic systems

[en] With respect to the other photoelectron microscopy techniques, a scanning photoemission microscope (SPEM) uses the direct approach to photoelectron spectromicroscopy, which is the use of a small focused photon probe to illuminate the surface. The SPEM at the Elettra synchrotron light source can operate in two modes: imaging and spectroscopy. In the first mode, the sample surface is mapped by synchronized scanning of the sample with respect to the focused photon beam and collecting photoelectrons with a selected kinetic energy. The second mode is photoelectron spectroscopy from a microspot. The well-known capabilities of photoemission to chemically probe the surface of conducting and semiconducting, and to a certain extent of insulating, materials can be exploited at a submicrometre level for the investigation of spatially heterogeneous or confined systems, structures measured in micro- or nanometres, etc. (author)

[en] Silicon nitride layers grown on Si (1 1 1) by atomic nitrogen exposure at elevated substrate temperatures have been investigated in situ by photoemission spectro-microsopy. From the X-ray photo emission spectra taken at various sample areas, the chemical composition of samples grown at 800 deg. C is found to be homogenous all over the surface, with a stoichiometry according to Si₃N₄. Due to attenuation of the photo electrons, the images also provide information about the morphology of the nitride films. For 800 deg. C, a smooth film is observed, whereas for growth temperatures exceeding 900 deg. C, an increased roughness is observed

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[en] The scanning photoelectron microscope (SPEM) on beam line 2.2 at the Elettra synchrotron produces small spot XPS spectra from a sub-micron radiation microprobe. It is also capable of producing surface images in terms of the energy resolved photoelectron signal. This microscope has been used to study oxidation on polycrystalline tin and lead surfaces and the variations in reactivity between different crystallite surfaces. The diffusion of gold and silver films on polycrystalline metal surfaces has also been followed

[en] A Dynamic High Pressure (DHP) system has been developed, tested and implemented in the scanning photoelectron microscope (SPEM) operated at ESCAmicroscopy beamline at Elettra synchrotron. The system consists of a compact gas injection set up that allows experiments with local pressure near the sample several orders of magnitude higher that the allowable pressure for X-ray photoelectron spectroscopy setups. The DHP setup controls the amount of gas injected toward the sample by fine tuning the time and spatial profiles using a pulsed valve and a nozzle, respectively. The DHP functionality and effectiveness has been demonstrated by in operando oxidation experiments of Ru and Si. The obtained results confirmed that using the DHP the gas exposure onto the sample is equivalent to a static pressure between 10⁻³ and 10⁻² mbar, about 3 orders of magnitude higher than the maximum gas pressure for the XPS machines under operation.

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[en] The beam-induced effects, a consequence of the high photon flux density used in soft X-ray photoelectron emission microscopes in operation at the 3rd generation synchrotron sources, are discussed and illustrated using some representative results obtained with the microscopes at the laboratory Elettra. The focus is on the photon-induced charge potential and chemical degradation, which might be a severe problem for photon-sensible specimens. The possible steps to avoid, reduce or even make use of the beam-induced effects are outlined.