S. Nannarone

Flame retarding poly(methyl methacrylate) with nanostructured organic–inorganic hybrids coatings

Abstract Organic–inorganic hybrid materials were prepared starting from tetraethoxysilane and α- or α,ω-triethoxysilane terminated poly(e-caprolactone) (PCL–Si) using the sol–gel process. In all cases the formation of nanocomposites with a high level of interpenetration between organic and inorganic phases was noted. Poly(methyl methacrylate) slabs were dip-coated with PCL–Si/silica hybrids and a very strong increase of the flame resistance (also after UV irradiation) was noted for all coating compositions without marked differences with respect to hybrid compositions. This behavior was attributed to a preferential segregation of silica onto the outer surface, as evidenced by XPS analysis.

Synthesis and characterization of praseodymium-doped ceria powders by a microwave-assisted hydrothermal (MH) route

Nanocrystalline Pr-doped ceria powders were prepared for the first time by a microwave-assisted hydrothermal route. The effect of the microwave treatment in relation to the conventional hydrothermal technique was evaluated. The samples prepared were characterized in terms of composition, crystalline structure, particle shape and size distribution by X-ray diffraction, transmission electron microscopy (TEM) and specific surface area analysis (BET). The color properties of these solid solutions were also evaluated as a function of synthesis conditions and composition. Finally the oxidation state of the Pr cations and the relative quantities of Pr(IV) and Pr(III) were investigated by X-ray absorption at the M4,5 Pr absorption edge.

Catalytic oxidation of Si(100) and InP(100) surfaces

Abstract The catalytic oxidation of clean Si(100) and InP(100) surfaces in the presence of a Cs overlayer has been studied by using high resolution electron energy loss spectroscopy (HREELS), photoelectron. Auger and energy loss spectroscopy (XPS, Auger, ELS), and low energy electron diffraction (LEED). At room temperature we obtain, as a function of Cs exposure, saturation for Si(lOO) with a 2 × 1 LEED pattern whereas this is not the case for InP(100). For InP we first observe a 1× 1 structure, which is followed by an amorphous overlayer growth of Cs. This latter effect is probably related to segregation of metallic In on top of the Cs layers. As the amount of Cs actually determines the thickness of the oxide layer, subsequent oxygen exposure results, therefore, in a higher uptake of oxygen for InP compared to that of Si. Annealing the adsorbate/substrate systems at higher temperatures leads to diffusion of oxygen from adsorption sites related to Cs to the semiconductor interface. Simultaneously, different oxidation states at Si and InP are detected. A comparison to oxidation studies of clean Si and InP wafers clearly indicates a strongly enhanced oxidation when using alkali metals like Cs as a catalytic agent. Possible local bond configurations at the interface will be discussed for Si within the framework of existing models. The InP system is much more complicated, and therefore for that system only preliminary results will be presented.

First spectroscopic investigation of the Yb/Si interface at room temperature

We report the results of a preliminary synchrotron radiation photoemission and Auger experiment on the Yb/Si interface, prepared in situ by depositing monolayers of Yb onto vacuum‐cleaved Si(111) surfaces at room temperature. Spectra were taken for the Si 2p and Yb 5p core levels at several different values of escape depth. The evolution of the valence band and the Si L2,3 VV Auger line shape with coverage also were depth examined. The first monolayer of Yb is adsorbed onto the Si surface without apparent mixing or reaction. For 1.5–2 monolayers, there is evidence of chemical interaction from core level shifts and changes in the Si LVV line shape. At higher coverages, the surface becomes essentially Yb metal; the region of intermixing appears to be limited to 2–3 atomic layers at room temperature.

Els investigation of the Si-Pd interface

Abstract Energy loss and Auger spectra of Pd deposited onto Si(111) at increasing coverages are presented, together with those of pure Pd and of bulk Pd 2 Si obtained in situ. The loss evolution with coverage is interpreted with the aid of a simple model calculation of the surface loss function of an ideal Si-Pd system. The results indicate that for coverages between 1 and 7 A an intermixed phase forms at the interface, while for higher coverages pure Pd grows on the surface. In the first stage some losses seem to shift in energy with coverage due to interface mode coupling.

Azimuthal dependence of reflection high resolution electron energy loss of Si(111)(2×1)

Abstract High Resolution Electron Energy Loss Spectroscopy has been used, with low energy of the primary beam and azimuthal resolution, to study the anisotropy of surface dielectric properties of Si(111)(2 × 1), in the range of the surface electronic excitations. By eliminating the effect of the kinematic prefactor, we are able to obtain from the data the surface Loss Function. Its dependence on q ∥ and ω is discussed in term of a model of surface dielectric function.

Energy loss spectroscopy (ELS) on the Si-Au system

Abstract We report on the energy loss spectroscopy obtained on the clean cleaved Si(111) covered with different gold thickness. The results clearly indicate that in the Si-Au system the interface is characterized by a Si rich phase with a well defined electronic transition at 7.5 eV energy loss. Increasing Au thickness the main changes in the spectrum arise in the low energy loss region and a gold-like behaviour is observed for a gold coverage of 60 monolayers. The effects of annealing at 350°C are reported.

Filled and empty states of H:GaAs(110) through electron energy‐loss and photoemission spectroscopies

The energy distribution of filled and empty states of H:GaAs (100) surface is reported. The results have been obtained by the combined analysis of photoemission and energy‐loss spectra (ELS). The main emphasis is devoted to the ELS interpretation of interface plasmon losses of the H:GaAs (110) surface layer. New excitations are found at the vacuum–H:GaAs (110)–GaAs interface and the energy difference between filled and empty states is determined. Starting from filled electronic states as localized by photoemission measurements, empty states of the surface layer are located.

Adsorbate phase transformations and the coverage-dependent oscillation of electron transfer probabilities

We report a study of the effects of chlorine adsorption on the interaction of positive ions (H+, Ne+, Ar+ with a Ag(111) surface from the submonolayer Cl chemisorption to initial stages of AgCl formation. Cl adsorption on Ag(111) proceeds through different phases and we observed that the neutralization probabilities oscillate in this range, attaining an intermediate minimum at about 2/3 coverage and reach a maximum at full coverage. The subsequent appearance of AgCl phase again leads to a reduction in neutralization. These results are described in terms of changes in Auger neutralization rates due to modifications in the adsorbate density of states.

Empty states investigation of Ni2Si by photon absorption spectroscopy

We report photoabsorption spectra from the Ni-L2,3 edges in bulk Ni2Si and in pure Ni in order to investigate the d-partial density of states. The white lines observed in bulk Ni show a reduced intensity in the silicide. Moreover, we observed, in Ni2Si compound, a shift of the main feature of 1.7 eV towards higher binding energies and a new structure at about 7 eV above EF. The first feature indicates a marked shift of the maximum of the d-DOS above EF and it is interpreted in terms of the antibonding states. The feature at 7 eV can be related to the structure recently observed by Bremsstrahlung Isochromat Spectroscopy.