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Proceedings of Symposium N on Ultrathin Epitaxial Oxides, E-MRS Spring Conference, Strasbourg, France, June 5-8 2001
No full textGas-phase Uv Photoelectron-spectra and Dv-x-alpha Calculations of Bridged Organometallic Dimers
No full textAngle scanned photoelectron diffraction: Probing crystalline ultrathin films
No full textElectrons emitted from the core levels of a photon-irradiated crystalline sample undergo scattering by atoms in the vicinity of the emitting species. Subsequent interference phenomena between the electron wave portions propagating to the detector produce intensity modulations as a function of the direction of detection. This process constitutes the physical basis of the angle-scanned X-ray photoelectron diffraction (XPD) technique. The resulting modulations, properly interpreted, are rich in structural information concerning the near-surface atomic layers. In this review, after an introduction to the principles of XPD, some selected results in the field of ultrathin epitaxial films will be reported in order to outline the merits of the technique. Qualitative structural information (e. g., growth modes and lattice distortions) is directly obtained from the experimental raw data without the need for theoretical simulation. On the other hand, quantitative structural parameters, as well as the presence of stacking faults and other structural defects, may be deduced by using a trial-and-error fitting procedure based on simple scattering models
Polarization effects to enhance surface sensitivity of angle- scanned X-ray photoelectron diffraction in synchrotron- radiation-based experiments
No full textWe show that the surface sensitivity of angle-scanned photoelectron diffraction applied to bulk crystals or epitaxial multilayers can be enhanced by exploiting the angular anisotropy of the photoelectron primary wave excited by linearly polarized light, combined with the possibility of performing measurements in two different light polarization/electron detection geometries. The obtained relative photoelectron diffraction patterns of the form I1(k)/I2(k), where 1 and 2 denote the two different geometric set-ups discussed in the present paper, show an enhanced structural surface sensitivity, which should allow the determination of the presence and the extent of surface relaxation by comparing the experimental data to suitable theoretical simulations. In a set of preliminary model calculations, the best results are obtained for emission from an s-initial state. High angular resolution of the electron detectors is an additional requirement
Ultrathin V films on Pt(111): a structural study by means of X- ray photoelectron spectroscopy and diffraction
No full textA detailed structural study of V growth on Pt (111) has been performed mainly by means of angle resolved X-ray photoelectron spectroscopy and diffraction, with the aid of multiple scattering cluster-spherical wave simulations of the diffraction curves. Vanadium on Pt (111) grows with a two-domain bulk-like bcc (111) stacking largely incoherent with the substrate, at least up to a thickness of eight equivalent monolayers. For thicker layers, an orientational transition is observed, leading to a six-domain bulk-like bcc (110) structure. Although bcc (111)-oriented V is preserved in the thicker layer, we cannot exclude the fact that some of the initially (111) ultrathin film has been partially restructured to the (110) orientation when the critical thickness associated with the transition has been exceeded. Strong three-dimensional clustering of the overlayer is observed for any investigated thickness which supports a Volmer–Weber growth of the V film. Our findings are compared to literature data concerning the growth of Cr on the same substrate
Preface to the special issue on the following topic: Graphene and graphene-related materials growth on surfaces
No full textReactivity of Simple Alcohols on iron Oxide and Mixed Titanium Iron Oxide Powders: An XPS and FTIR Study
No full textPHOTOELECTRON DIFFRACTION - A STRUCTURAL PROBE FOR EPITAXIAL THIN-FILMS
No full textElectrons emitted from the surface region of a photon-irradiated sample undergo scattering by atoms in the vicinity of the emitting species. Subsequent interference between the direct electron wave (which propagates to the detector without undergoing any elastic scattering) and the scattered electron wave portion produces intensity modulations (up to 70% of the signal) as a function of either the direction of detection or the kinetic energy (Ek) of the emitted electron. This fundamental process constitutes the physical basis of Photoelectron Diffraction (PD). The resulting modulations, properly interpreted, are rich of structural information and PD has been recently applied with success to follow the epitaxial growth of thin and ultrathin films and to study the chemisorption processes over monocrystals. PD is a surface structural probe sensitive to short range order, with atomic and chemical state specificity. The short range order sensitivity is due to the lack of coherence between photoelectron waves emitted at different atomic sites because of the random nature of the emission process, coupled with the relatively short electron inelastic mean free paths at the energies typical for a PD experiment. On the other hand, the atomic and chemical state specificity is easily understood if one considers that PD is an implementation of the conventional X-ray Photoelectron Spectroscopy (XPS). In fact, a PD curve is obtained simply by selecting any spectral feature out of a full XPS spectrum of typically 1 -1.5 keV energy range from a single-crystalline sample, and by monitoring this particular spectral region as a function either of the emission direction or (once fixed the direction) of the Ek of the outgoing photoelectron. PD curves can therefore be obtained for different core levels of the same element, of various elements present on the surface, and, at higher energy resolution, even of different chemical states of the same element. Coupled with the chemical specificity of the structural information, there is the capability of observing the very surface and near surface region of the sample (up to thicknesses of 20-30 Å), due to the limited escape depths of photoelectron at the kinetic energies usually employed in PD. In this short presentation, after a brief introduction to the principles of PD, some selected results in the field of epitaxy of semiconductor compounds and of ultrathin metallic layers will be reported in order to outline the merit of the technique
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