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[en] We have studied the growth of Pd thin films on W(1 1 0), by means of low-energy electron microscopy (LEEM), X-ray photoelectron microscopy (XPEEM), and microspot low-energy electron diffraction (μLEED). Real-time LEEM measurements of the evolution of the film morphology as a function of deposition time showed substantial differences in the growth mechanism at 380 and 1000 K. Imaging the valence band structure with spatial resolution of 60 nm revealed clear differences for the interfacial monolayer film and the 3D islands growing on top at 1000 K. The observed spatial variations in the electronic structure are attributed to bonding, structural and electron confinement effects

[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] The interactions of O₂ and CO with alkali covered Ni, Ru, and Pt are reviewed with emphasis on the author's own studies. It is shown that the presence of alkalis changes the coadsorbates adsorption rates, heats of adsorption, and dissociative propensity, the strength of the effect depending on the alkali nature and coverage. The differences for the three substrates are interpreted comparing the properties of the clean surface. A detailed analysis of the coadsorbate--modifier interactions suggests that they depend on the adsorption state of the alkali species and the coadsorbate--substrate bond strength. Evidence of the formation of patches of ''surface complexes'' coexisting with the unperturbed surface is given and discussed in terms of strong direct alkali--coadsorbate interactions

[en] The absorption of CO at 300 K on Ru(1010) modified with different amounts of Cu has been studied using Auger electron spectroscopy (AES), thermal desorption, electron energy loss spectroscopy (EELS), low energy electron loss diffraction (LEED) and work function (WF) measurements. It was found that the effect of the adsorbed Cu on the CO adsorption kinetics and energetics depends strongly on the actual Cu site occupation and Cu coverage θ_Cu. The presence of Cu in the submonolayer region does not not cause changes in the CO initial sticking coefficient, S_o, and initial dipole moment, μ_o, but reduces the CO saturation coverage. At θ_Cu larger than a monolayer, both S_o and μ_o are reduced, accompanied with a complete removal of the CO adsorption states at 300 K. The observed behaviour of the precursor state model for the adsorption and ensemble and ligand effects on modified surfaces. (author)

[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] FERMI-Elettra comprises two free electron lasers (FELs) that will generate short pulses (τ∼25-200 fs) of highly coherent radiation in the XUV and soft x-ray region. The use of external laser seeding together with a harmonic upshift scheme to obtain short wavelengths will give FERMI-Elettra the capability of producing high-quality, longitudinally coherent photon pulses. This capability, together with the possibilities of temporal synchronization to external lasers and control of the output photon polarization, will open up new experimental opportunities that are not possible with currently available FELs. Here, we report on the predicted radiation coherence properties and important configuration details of the photon beam transport system. We discuss the several experimental stations that will be available during initial operations in 2011, and we give a scientific perspective on possible experiments that can exploit the critical parameters of this new light source.

[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

[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