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We present a reflection energy loss investigation of the Ti L2,3 edge. The oscillations detected above the core-edge have been analyzed following the standard EXAFS-procedure in order to obtain the radial distribution function around the excited central atom.

The nature and the energy dispersion of the collective excitations of two layers of K adsorbed at 200 K on Ni(111) have been studied by high-resolution electron-energy-loss spectroscopy. At small momentum transfer parallel to the surface, q{sub {parallel}}, the loss spectrum showed two collective modes: an intense feature close to 2.70 eV, attributed to the surface plasmon, and a broad peak at 3.40 eV, interpreted as the multipole surface plasmon. Contrary to theoretical prediction for two layers of K on Al(111), present results demonstrate that in the limit of small q{sub {parallel}} the excitation of the surface plasmon for two K layers on Ni(111) is possible. {copyright} {ital 1997} {ital The American Physical Society}

The identification of features in the Local Density of States (LDOS) of carbon nanotubes (CNTs) obtained by Scanning Tunneling Spectroscopy (STS) is of great importance in order to understand their properties. In this work, Single- and Multi-Wall Carbon Nanotubes are compared with Multi-Wall CNTs filled with tin nanowires (Sn@CNTs) in order to investigate the effect on morphological and electronic properties of the CNTs metallic filling. The LDOS of CNTs, together with topology changes, is investigated by using spatially resolved STM/STS at room temperature and in air and compared to the LDOS of highly oriented pyrolitic graphite (HOPG). The LDOS of CNTs is dominated from different electronic states filling the C 2p sigma-2p sigma* band gap. The appearance of those states is linked to the diameter and the defects of the CNTs. In fact, Sn-nanowires encapsulation induces changes in the structure of the CNTs and the appearance of electronic states in the LDOS inside the band gap. A more extensive description of the samples is obtained depicting the morphological features and the vibrational structure on wider areas using Scanning Electron Microscopy (SEM) and Raman spectroscopy, respectively. Journal of Nano Research

The coadsorption of CO and NO on Ni(111) at room temperature has been studied by HREELS, LEED and angle-scanned XPD techniques. The experiments have been carried out by first exposing the clean surface to one gas up to the observation of a c(4 × 2) LEED pattern, and then by monitoring the step-wise addition of the other. CO does not modify or adsorb on a c(4 × 2)-NO layer, while 1 L NO causes the complete desorption of a c(4 × 2)-CO layer. The LEED pattern is always c(4 × 2), even if both CO and NO species are present on the surface. For NO exposures lower than 1 L of the CO-covered Ni(111) surface, XPD measurements show that NO molecules are in a bent geometry, while CO molecules are perpendicular to the surface. Our results indicate that the NONi interaction is very weakly affected by the presence of coadsorbed CO.

The coadsorption of oxygen on a potassium precovered Ni(100) surface was investigated by the high resolution electron energy loss technique. The interaction between the coadsorbate atoms takes place only for a K coverage of 0.38 ML corresponding to the completion of the first K layer. At this K coverage, an intense vibrational feature, at 180 meV, is a consequence of the oscillating motion of the atoms of the Ni–K–O clusters, particularly, of the component vibrating along the surface plane.

The coadsorption of oxygen and sodium on Ni(111) was studied by high resolution electron energy loss spectroscopy. Measurements were performed for a definite sodium precoverage, as a function of oxygen exposure and temperature. For a coverage of two layers of sodium, the loss spectra show the vibrational features related to Na– O 2 and O–O bonds of superoxide NaO 2 molecules. The annealing up to 450 K causes the decomposition of these complexes and the reappearance of the stretching frequencies of isolated Na–O and O–Ni species. At 550 K, only the oxidation of the Ni substrate occurs. The spectra are correlated to work function measurements, and the behavior of the work function versus oxygen exposure, for high alkali coverages, is ascribed to a reionization of the metallic Na layer, rather than to a penetration of oxygen atoms underneath the Na layer.

We have studied the morphology and electronic structure of cluster-assembled carbon films containing nickel and titanium nanoparticles by structural probes (transmission electron microscopy) and electronic spectroscopies (x-ray absorption, Auger spectroscopy, and electron energy loss). Vibrational characteristics of the surface have been investigated using high resolution electron energy loss spectroscopy. Nanocomposite carbon-metal films have been grown by supersonic cluster beam deposition of carbon clusters produced in the presence of finely dispersed metal catalysts. Characterization has been performed on pristine, annealed (at 560 K in vacuum), and ${\mathrm{H}}_{2}$ exposed ${(p}_{{\mathrm{H}}_{2}}=1\mathrm{mbar})$ samples. The nanocomposite films are characterized by metallic clusters embedded in a matrix of nanostructured carbon. The carbon structure at the nanoscale depend upon the type of metallic species. The electronic properties of the as-deposited films do not show any evidence of carbide formation. Thermal treatment and ${\mathrm{H}}_{2}$ exposure procedures have different effects on the electronic features inducing a certain degree of bond ordering and a decrease of the available ${\mathrm{sp}}^{2}$ sites, respectively.

Reflection electron energy loss investigation on Al samples has been carried out with an average angle collection system from 30 to 1000 eV of primary electron energy. Plasmonic structures occur always at the same energy while their lineshape broadening increases decreasing the electron kinetic energy. The ratio between surface and bulk contributions has been exploited and reproduced with a phenomenological model. The extrinsic loss mechanism for the creation of the bulk plasmon has been investigated and compared with available theories.

The oxygen-exposed Ni(110) surface has been studied at 300 K using the AES and EELFS techniques. Analysis of the radial distribution functions F(R) obtained at 2.5 and 12.5 langmuirs (L) of oxygen exposure, in comparison with results recently obtained by us on the Fe(110)+oxygen system, show that the O-Ni distance is near the sum of the covalent radii. For an exposure of 140 L, we found nickel oxide islands on the surface. The oxygen coverages obtained by analysis of the O(KLL)/Ni(L3VV) peak-to-peak intensity ratio are found to be consistent with recent nuclear reaction analysis results.

We have applied the Extended Energy Loss Fine Structure (EELFS) technique for studying the radial distribution function of iron before and after the formation of a surface carbidic iron layer. The experiment is performed in the reflection mode with a conventional CMA electron analyzer. The energy range scanned is 50–500 eV. The Fourier analysis of the structures measured above the Fe M 2,3 edge and the C K edge gives structural information around different absorbing sites on surfaces which lack long range order. The structural results are compared with the local structure of bulk Fe 3 C measured with the EXAFS technique. We have found that each carbon on the surface is coordinated to six nearest neighbours iron atoms in a trigonal prism coordination as in the crystalline iron carbide.