Gian Andrea Rizzi

Molecular oxygen interaction with Bi2O3: a spectroscopic and spectromagnetic investigation

The interaction of molecular oxygen with polycrystalline Bi2O3 was investigated by infrared (IR) and thermogravimetric (TGA) analyses, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). The results indicate the formation of “end-on” and “bridging” superoxide species, which are trapped in the β-Bi2O3 vacant oxygen sites, Bi(IV) and Bi(V) centres also being produced. O2− interacts with Bi(IV) centres giving two superoxide adducts with temperature-dependent relative amounts, Bi(IV)–O2− and Bi(IV)–O2−–Bi(III), both having a triplet spin state.

Vanadyl Precursors Used to Modify the Properties of Vanadium Oxide Thin Films Obtained by Chemical Vapor Deposition

Vanadium oxide thin films were prepared by chemical vapor deposition using as precursors a series of vanadyl complexes of general formula VO(L){sub 2}(H), where L is a {beta}-diketonate ligand. The depositions were carried out on {alpha}-Al{sub 2}O{sub 3} substrates in O{sub 2}, N{sub 2}, and N{sub 2} + H{sub 2}O atmospheres. In order to elucidate the role played by different ligands and synthesis conditions on the properties of the obtained films, the chemical composition of the samples was investigated by X-ray photoelectron spectroscopy, while their microstructure and surface morphology were analyzed by X-ray diffraction, Raman and atomic force microscopy. The thermal decomposition of the precursors, with particular attention to their reactivity in the presence of water vapor, was studied by mass spectrometry and Fourier transform infrared spectroscopy.

An angle-scanned photoelectron diffraction study on the surface relaxation of ZnO (0001)

Abstract An angle-scanned X-ray photoelectron diffraction (XPD) study of the polar Zn-terminated ZnO(0001) surface has been carried out in order to look for a hypothetical inward relaxation of the outermost Zn layer. From the comparison of the O 1s polar scan with single-scattering-cluster (SSC) simulations it is clearly evident that the surface is bulk terminated and any relaxation is ruled out. Moreover, the capability of the XPD technique in determining the surface polarity (atomic termination) by inspection of θ/φ 2D plots without the aid of theoretical simulations has been demonstrated.

MgCl2/TiCl4/AlEt3 catalytic system for olefin polymerisation: a XPS study

Abstract A variety of techniques have been applied for 40 years in order to characterise Ziegler–Natta catalysts, however, few studies report the use of surface science technologies in an effort to understand surface structure, composition and chemical bonding in MgCl2 supported catalytic system. In this paper, the synthesis and the characterisation of the MgCl2/TiCl4/AlEt3 catalyst in controlled conditions is reported. Our aim is to understand (1) the activation process of the magnesium chloride support; (2) the interaction between the magnesium chloride support and TiCl4; (3) the chemical structure of the titanium active centres formed by treatment of the procatalyst, MgCl2/TiCl4, with the co-catalyst, TEA (triethylaluminium ); (4) which Tin+ species is active in ethene and propene polymerisations. These experiments were performed in conditions as similar, as possible, to the ones used for laboratory synthesis and polymerisation. The experiment consists of different steps: (1) preparation of δ-MgCl2 under strictly inert atmosphere as previously reported [1] ; (2) activation of δ-MgCl2 in a UHV chamber by means of argon ion sputtering; (3) exposure to TiCl4 vapours; (4) exposure to TEA. The surface composition was checked during the experimental steps by means of XPS technique.

Polyvinyl alcohol electrospun nanofibers containing Ag nanoparticles used as sensors for the detection of biogenic amines

Polyvinyl alcohol (PVA) electrospun nanofibers containing Ag nanoparticles (NPs) have been deposited on glass substrates. The aim of the work was to test the feasibility of this approach for the detection of biogenic amines by using either the Ag localized surface plasmon resonance quenching caused by the adsorption of amines on Ag NPs or by detecting the amines by surface enhanced Raman spectroscopy (SERS) after adsorption, from the gas phase, on the metal NPs. Two different approaches have been adopted. In the first one an ethanol/water solution containing AgNO3 was used directly in the electrospinning apparatus. In this way, a simple heat treatment of the nanofibers mat was sufficient to obtain the formation of Ag NPs inside the nanofibers and a partial cross-link of PVA. In the second procedure, the Ag NPs were deposited on PVA nanofibers by using the supersonic cluster beam deposition method, so that a beam of pure Ag NPs of controlled size was obtained. Exposure of the PVA mat to the beam produced a uniform distribution of the NPs on the nanofibers surface. Ethylendiamine vapors and volatile amines released from fresh shrimp meat were chemisorbed on the nanofibers mats. A SERS spectrum characterized by a diagnostic Ag-N stretching vibration at 230 cm(-1) was obtained. The results allow to compare the two different approaches in the detection of ammines.

Xylene sensing properties of aryl-bridged polysilsesquioxane thin films coupled to gold nanoparticles

Surface plasmon resonance gas sensors based on organic–inorganic hybrid thin films coupled to gold nanoparticles were fabricated and tested against the detection of xylene at the concentration of 30 ppm. Such nanocomposites are prepared either by dispersing Au nanoparticles inside an aryl-bridged polysilsesquioxane system, synthesized via a sol–gel process, or by depositing an aryl-bridged polysilsesquioxane film on Au nanoparticle sub-monolayers. Ultra-high-vacuum temperature programmed desorption of xylene on both the aryl-bridged polysilsesquioxane films and the nanocomposite Au/hybrid system was investigated, resulting in an interaction energy between the sensitive film and the gas molecules in the 38–139 kJ mol−1 range. The functional activity of the nanostructured composites as xylene gas optical sensors was tested monitoring gold localized surface plasmon resonance, and was shown to be reversible. The detection sensitivity was calculated in 0.1 ppb through a calibration procedure in the 16–30 ppm range, and a threshold limit of detection of 265 ppb xylene was estimated as three standard deviations of the baseline noise. Typical response and regeneration times are of one min and about one ten of minutes, respectively.

Au nanoparticles on a templating TiOx/Pt(111) ultrathin polar film: a photoemission and photoelectron diffraction study

We present an in-depth investigation of Au nanoparticles self-assembled on a zigzag-like TiO(x)/Pt(111) ultrathin polar film, whose structure is known in great detail. The peculiar pattern of defects (picoholes) templates a linear array of size-selected (ca. 1 nm) Au nanoparticles without disruption of the titania layer, as observed by scanning tunneling microscopy. Their structure and electronic properties have been investigated by several large-area spectroscopic tools, i.e. high-resolution core and valence level photoemission and angle-scanned and energy-scanned photoelectron diffraction. The comparison between experimental data and density functional theoretical calculations indicates that the Au atoms landing on the oxide film are rather mobile, and that the picoholes can act as effective trapping and nucleation centers for the growth of the Au nanoparticles. All the experimental results are in concord in indicating that the Au NPs are flat islands with a maximum thickness of 2-3 layers exposing the (111) surface.

One step forward to a scalable synthesis of platinum–yttrium alloy nanoparticles on mesoporous carbon for the oxygen reduction reaction

In this paper, we report the synthesis and characterization of nanoparticles (NPs) of a PtxY alloy supported on a commercial mesoporous carbon (MC). The NPs were prepared following a solid state synthesis in a quartz tubular furnace under H2 flow. The influence of Pt precursors on the NP shape and alloy formation was investigated together with the temperature and reaction time. The best synthesis afforded the obtainment of small spherical PtxY NPs (4 nm diameter) on the surface and inside pores of a MC with a maximum of alloy content of 41% with respect to the whole Pt loading. The electrochemical properties of PtxY NPs were investigated with special attention to their catalytic properties. The results in ORR studies showed that the catalyst containing the highest amount of PtxY alloy exhibits higher catalytic activity expressed in terms of mass and specific activity and comparable stability, after accelerated degradation tests, for oxygen reduction as compared to a standard Pt/C catalyst.

Epitaxial TiO2 nanoparticles on Pt(111): a structural study by photoelectron diffraction and scanning tunneling microscopy

Angle-scanned X-ray photoelectron diffraction (XPD) and scanning tunneling microscopy (STM) are used to characterise the structure of TiO2 nanoparticles grown on a Pt(111) single crystal surface. The nanoparticles grow over a well-ordered oxide interfacial layer that displays a (square root 43 x square root 43) - R7.6 degrees superstructure with a unit cell (18.2 x 18.2 A), as demonstrated by STM and low-energy electron diffraction (LEED). Our XPS Ti 2p core level spectra suggest a significant contribution from reduced titanium ions within the interfacial layer. On the contrary, according to XPS binding energy data, the nanoparticles are mostly composed of Ti(IV) ions. During the initial stage of the growth, the nanoparticles are on the average 2 nm high and about some tens of nm wide, and show a flat on-top surface, while the interparticle region show the structure of the ordered interfacial layer. During later stages of the deposition, the particles become larger and they show a more irregular, globular-like shape as well as coalescence. But, even at this stage of the growth, large interparticle regions are present. Moreover, the nanoparticles produce a distinct XPD pattern which demonstrates that they grow with a preferential azimuthal orientation with respect to the substrate surface. A simple geometrical analysis of the XPD data in terms of forward scattering events suggests that the particles crystallize in the rutile TiO2 structure and expose the (100) surface. This hypothesis is supported by means of multiple scattering simulations of the XPD patterns.

DETERMINATION OF TiO2(110) SURFACE RELAXATION BY VARIABLE POLARIZATION PHOTOELECTRON DIFFRACTION

A new method to determine the surface relaxation by means 0 of photoelectron diffraction (PED) from an s-core level has been applied to the (1 × 1)-TiO2(110) surface. Complete 2π solid angle PED patterns for both oxygen 1s and titanium 3s core level peak intensities have been measured at the ALOISA beamline (Elettra Synchrotron, Italy) in two different photon polarization/electron detection geometrical configurations: one with the photon polarization vector parallel to the surface normal (TM polarization) and the other with the photon polarization vector perpendicular to the surface normal (TE polarization). In the latter case the PED sensitivity to the vertical spacing is enhanced. Because forward scattering is suppressed on the node of the primary wave along the surface normal, the relative weight of the distance-sensitive higher order interference fringes is enhanced. The opposite occurs for the TM polarization, which enhances the PED sensitivity to lateral spacing at grazing emission angles. The exper...