1,721,106 research outputs found
Metastable He deexcitation at semiconductor interfaces
No full textA review is given of the application of metastable deexcitation spectroscopy (MDS) to the study of the interface formation between semiconductors and different materials. In particular we present an overview of the results obtained on nanostructured interfaces, where strain and reaction between the substrate and the overlayer atoms drive the growth mode and the morphology of the system. As prototypical examples we discuss the growth of CaF, on silicon and rare earths (Yb, Er) on silicon and gallium arsenide. The mechanisms and chemical reactions which bring to interface formation are examined on the basis of MDS results and their comparison with photoemission
FISICA A
No full textIl testo rappresenta un manuale di introduzione alla Fisica classica per studenti di corsi di laurea scientifici di primo livello, ingegneria in particolare. Esso presenta una quadro essenziale ma completo, che partendo dai fondamenti, copre le aree della meccanica e dell'elettromagnetismo classici. Partendo dalla scrittura dell’equazione di Newton, introducendo l’origine delle forze ed a seguire fornendo il concetto di campo vengono man mano composti gli strumenti concettuali e formali con cui si imposta e si risolve il problema del moto sotto l’azione di forze. Lungo tale costruzione, risalto viene dato alle proprietà dei campi in quanto tali, giungendo alla scrittura delle equazioni di Maxwell in forma locale
Interpretation of linear dichroism at S L2,3 x-ray absorption edges of small organic molecules at surfaces
No full textResonant soft x-ray absorption was applied at the S L2,3 (2p) edges of thin films of 1,4-benzenedimethanethiol (BDMT) on gold and of sexithiophene (6 T) on flat and patterned CaF2 surfaces. Linear dichroism effects were clearly observed depending on the orientation of the electric field vector of the incoming radiation. They were related to the organization of the molecules. For the interpretation of the angular dependencies of the spectral features, density functional theory (DFT) simulations of the absorption cross sections were calculated. It was possible to confirm the generally accepted chemisorption geometry of BDMT on Au(111), composed of molecules nearly vertical at the surface with one of the S atoms participating in the bonding with Au and the other left pending at the outermost surface and contributing mostly to the measured x-ray absorption. For 6 T on CaF2 a new chemisorption phase was identified on ridge-patterned CaF2(110), coexisting with a previously known phase given by 6 T crystallites highly oriented along the ridges. The new phase being composed of molecules oriented perpendicular to the ridges and lying on their edges
Surface electronic properties by metastable deexcitation spectroscopy
No full textMetastable deexcitation spectroscopy (MDS) is used to probe the surface electronic properties of semiconductor surfaces and different interfaces with semiconductors. Results are compared to photoemission data and calculations. The following case studies are treated: clean GaAs(110), clean Ge(111)c(2 x 8), Sb/GaAs(110), H:GaAs(110), Yb/GaAs(110), Yb/Si(100) and Ge(111) surface incomplete melting. For each system, MDS spectral features are related to surface valence band (VB) states
Surface electronic states of Yb silicide ultrathin films studied with He metastable deexcitation spectroscopy
No full textWe studied the growth of Yb silicide films on Si(100) with Metastable Deexcitation Spectroscopy (MDS) assisted by Low Energy Electron Diffraction (LEED). Different surface structure phases are observed at progressively high annealing temperature. Annealing at T<550 degreesC produces Yb-rich disordered compounds, with metallic character shown on MDS. A 3 X 1 ordered phase is observed by low energy electron diffraction (LEED) after annealing of the films at about 640 T and it is associated with the formation of a stable silicide. Correspondingly, electronic states assigned to the Yb 6s-5d hybridised band and to Si 3s and 3p bands in the compound are observed in MDS. A further increase in the annealing temperature causes the system to evolve rapidly. Above 700 degreesC, the films present a character similar to that of the Si substrate. (C) 2002 Elsevier Science B.V. All rights reserved
Studies of the interface of conducting polymers with inorganic surfaces
No full textMany of the properties of multi-material systems and relevant devices depend on the interfaces between the different components. This review focuses on characteriza- tion of the interfaces between intrinsically conducting poly- mers and inorganic materials consisting of metals and metal oxides. These materials are chosen because of their impor- tance in several analytical applications. Although use of conducting polymers and metals or metal oxides in analyt- ical systems, specifically in sensing, is well established, the number of novel materials used for analytical purposes is continuously increasing. This further increases the possible number of effective combinations of different materials within multicomponent systems. As a consequence, innova- tive characterization techniques have become as important as more conventional techniques. On the other hand, sophis- ticated characterisation techniques are increasingly wide- spread and, consequently, also readily accessible. This critical review is not an exhaustive discussion of all possible analytical techniques suitable for characterization of interfaces. It is, instead, limited to an overview of the most effective, relatively widespread techniques, emphasising their most significant recent advances. Critical analysis of the individual techniques is complemented by a few selected examples
The UHV Experimental Chamber For Optical Measurements (Reflectivity and Absorption) and Angle Resolved Photoemission of the BEAR Beamline at ELETTRA
No full textThe experimental station of the BEAR (Bending magnet for Emission, Absorption and Reflectivity) beamline at ELETTRA (Trieste, Italy) is an UHV chamber conceived to fully exploit the spectroscopic possibilities offered by the light spot produced by the beamline. Spectroscopies include reflectivity (θ-2θ and diffuse), optical absorption, fluorescence and angle resolved photoemission. The chamber can be rotated around the beam axis to select the s (TE) or p (TM) incidence conditions and/or the position of the ellipse of polarization with respect to the sample. Photon detectors (e.g. photodiodes) and electron detector (hemispherical analyzer - 1° angular resolution, 20 meV energy resolution) cover about completely the full 2π solid angle above the sample surface in any light incidence condition
Growth of Yb silicide on Si(100): structure and electronic properties as a function of annealing temperature
No full textThe growth of Yb on Si(100) from 1 to 12 ML as a function of the annealing temperature has been monitored with low energy electron diffraction (LEED) and the electronic properties were studied by He I photoemission and He metastable deexcitation spectroscopy (MDS). The annealing temperature (ranging from 590 degreesC to 640 degreesC) induces a 3 x 1 double domain LEED pattern. Correspondingly, a change in the electronic properties is observed, with the appearance of well defined s-p type features in MDS and UPS. This stage corresponds to the formation of a well ordered silicide film. At increasing temperature Yb is progressively diluted in a Si rich surface. (C) 2001 Elsevier Science B.V. All rights reserved
Lustre Ce-glazes: scientific aspects of materials having high aesthetic properties
No full textThree frits conceived for high porosity single firing tiles containing different amounts of cerium oxide and their glazes were investigated. The glazes obtained under industrial firing were studied using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersion spectroscopy (EDS). The mechanism of the lustre effect on the surface was explained. The results indicate that the glaze presents iridescent colours on the surface, mainly associated to the formation of a very thin layer of CeO2 crystals. Moreover, the CeO2 crystals present a preferential orientation and different dimensions
Structural transition in Fe ultrathin epitaxial films grown on Ni(111)
Full text linkA structural study of Fe ultrathin epitaxial films, grown at room temperature on Ni(111), has been performed in the 1.5-18 ML coverage range by angle-scanned photoelectron diffraction. Both backscattering and forward-scattering energy regimes have been employed, in order to enhance the structural sensitivity at lower and higher film thicknesses, respectively. Modeling of the experimental data has been performed with multiple scattering calculations. We found indications that Fe atoms in the first layer occupy fcc hollow sites and stack with a pseudomorphic fcc structure up to 2 ML. Concerning the growth mode at these early stages, data suggest that a good substrate wetting and a sharp Fe/Ni interface take place. Between 3 and 6 ML, transition to a bcc(110) phase develops. By quantitative R-factor analysis, we found that Nishiyama-Wassermann (NW) in-plane orientation of the bcc(110) cell (<001>(bcc)parallel to<110>(fcc)) is favored over the Kurdjumov-Sachs (<1 (1) over bar1>(bcc)parallel to<1 (1) over bar0>(fcc)) orientation. The best-fit vertical interlayer distance between bcc(110) planes is d(NW)=2.11 Angstrom (+3.9% expansion) at 6 ML and relaxes to d(NW)=2.05 Angstrom (+1.0%) at 18 ML, in agreement with the angular shift observed for the forward-focusing features. In the same coverage range, the angle between bcc(110) surface basis vectors changes from 67.7degrees to 69.0degrees, corresponding to -1.7% and -1.0% contractions of the surface cell area, respectively
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