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INVESTIGATION ON ELECTRONIC-STRUCTURE OF CU CLUSTERS ON GRAPHITE BY EELS AND XPS STUDIES
No full textSTRUCTURAL INVESTIGATION OF THE CR/SI INTERFACE
No full textWe have studied the short range order around Cr atoms deposited on Si(111) surface by means of the surface electron energy loss fine structure (SEELFS) technique above the L2,3 edges of chromium. The weak oscillations superimposed on the high energy side of the edges have been analyzed using the extended X-ray absorption fine structure (EXAFS) formula. Different evaporations of very clean chromium films have been analyzed. The radial distribution function indicates the formation of a Cr/Si interface for very thin deposits (equivalent thicknesses of about 3 and 5 angstrom) of chromium. We have found that the first nearest neighbour distance Cr-Si is 2.46 +/- 0.05 angstrom supporting the formation of a CrSi2 interface at room temperature
ELECTRONIC-STRUCTURE OF CR-CLUSTERS ON GRAPHITE
No full textThe electronic structure of small chromium clusters deposited by evaporation onto clean polycrystalline graphite has been studied by means of Auger, X-ray Photoemission (XPS) and Electron Energy Loss (EELS) spectroscopies. The XPS results show an increase in the binding energy of both core levels and valence band reducing the cluster size. The EELS measurements show a variation of the intensity ratio of L3-to-L2 ionization core edges. We interpret this change as due to different redistribution, within the cluster d-band, of the empty states above the Fermi level. As a consequence the XPS results may also be attributed to sizeable change of the electronic structure of the small clusters
EXFAS STUDIES ON THE THERMAL-BEHAVIOR OF COPPER SURFACE
No full textThe crystalline structure of copper surface has been studied by means of the Extended Fine Auger Structure spectroscopy as a function of the sample temperature. The oscillating features observed beyond the Cu M2,3VV Auger transition, due to an autoionization process involving the 3p and d-valence band electrons, have been analysed following the Extended X-ray Absorption Fine Structure theory, when the sample temperature grows from 300 K to 900 K. As the temperature increases no shift of the nearest neighbour distances but a sizeable increase of the Debye-Waller factor have been observed. The results show the capability of the EXFAS technique to follow the thermal behaviour of the surface structure of solids with higher surface sensitivity than other electronic spectroscopies
Local structure of graphite by EELFS spectroscopy: influence of multiple plasmons and orientational dependence
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EXTENDED ELECTRON ENERGY-LOSS FINE-STRUCTURE AND SELECTED-AREA ELECTRON-DIFFRACTION STUDIES OF SMALL PALLADIUM CLUSTERS
No full textExtended electron energy-loss fine structure (EXELFS) and selected-area electron diffraction (SAED) techniques have both been applied to the study of the crystalline structure of Pd clusters of average diameters ranging from bulk to 24 angstrom. The combined use of these techniques gives complementary information about the crystalline structure of Pd clusters. Both techniques show the same lattice parameter expansion, about 4% for the smallest Pd cluster, with respect to the bulk. The EXELFS analysis performed on the Pd-M4,5 edge shows a sizeable increase of structural disorder in the smallest cluster. SAED gives additional information about the Pd bulk sample, showing the occurrence of crystalline regions about 50 angstrom in diameter
EXAFS LIKE OSCILLATIONS IN X-RAY EXCITED AUTOIONIZATION SPECTRA ASSISTED BY COMPTON PROCESS
No full textOscillating features have been observed in the background of the inelastic electrons excited by high energy monochromatic X-ray photons at kinetic energy above the Cr M2,3VV Auger transition. These structures are absent when X-ray photons of HBARomega less-than-or-equal-to 1.5 keV are used. We suggest that these extended features are due to an autoionization process experienced by the 3p core electron assisted by a Compton scattering with the X-ray photons. Through the inelastic Compton process the incoming photons excite the core electrons towards empty states above the Fermi level in a continuous manner up to a maximum energy, which strongly depends on the incident photon energy. These excited states are modulated in energy by the crystalline structure as it has been shown by means of the EXAFS (Extended X-ray Absorption Fine Structure) spectroscopy. These oscillating structures are compared with those obtained through electron excitation for the same Auger transition in the Extended Fine Auger Structure (EXFAS) spectroscopy
ELECTRONIC AND STRUCTURAL INVESTIGATIONS OF PALLADIUM CLUSTERS BY X-RAY ABSORPTION NEAR-EDGE STRUCTURE AND EXTENDED X-RAY ABSORPTION FINE-STRUCTURE SPECTROSCOPIES
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