Paola Luches | Consiglio Nazionale delle Ricerche (CNR) (original) (raw)

Papers by Paola Luches

Topics in Catalysis, Sep 16, 2016

Journal of Physical Chemistry Letters, Jun 25, 2020

The ultrafast dynamics of excited states in cerium oxide are investigated to access the early mom... more The ultrafast dynamics of excited states in cerium oxide are investigated to access the early moments of polaron formation, which can influence the photocatalytic functionality of the material. UV transient absorbance spectra of photoexcited CeO2 exhibit a bleaching of the band edge absorbance induced by the pump and a photoinduced absorbance feature assigned to Ce 4f → Ce 5d transitions. A blue shift of the spectral response of the photoinduced absorbance signal in the first picosecond after the pump excitation is attributed to the dynamical formation of small polarons with a characteristic time of 330 fs. A further important result of our work is that the combined use of steady-state and ultrafast transient absorption allows us to propose a revised value for the optical gap for ceria (Eog = 4 eV), significantly larger than usually reported.

ACS Photonics, May 3, 2023

Journal of Chemical Physics, Mar 17, 2020

Journal of Physical Chemistry C, May 6, 2019

The functionality of cerium oxide, and in particular its reactivity, can be significantly altered... more The functionality of cerium oxide, and in particular its reactivity, can be significantly altered by the addition of diluted cationic species with different electronic properties as compared to cerium. We investigate the modifications induced by Ag and Cu as modifier cations in cerium oxide ultrathin epitaxial films. The reducibility is assessed by following the modifications of the oxidation state of surface Ce ions by x-ray photoemission spectroscopy, during thermal treatments in ultra-high vacuum and oxygen partial pressure. A significantly higher reducibility is observed in Ag-and Cu-modified films as compared to pure CeO 2 films of the same thickness. The thermal stability of the cation modifier concentration and the changes of the surface structure with the reducing treatments are also discussed. The modifications induced in the material are explained by comparison with density functional theory calculations, which indicate that the oxygen vacancy formation energy is significantly modified by the addition of Ag or Cu in the cerium oxide matrix. The obtained results are of help in view of a rational design of catalysts with optimized performance.

Nanotechnology, Sep 15, 2016

The initial stages of cobalt disilicide formation on Si(111) and Si(100)surfaces are studied usin... more The initial stages of cobalt disilicide formation on Si(111) and Si(100)surfaces are studied using backscattered electron imaging of the near-surface atomicstructure. Both the reactive deposition and the solid phase epitaxy are investigatedin the coverage range of 1-10 ML of Co. The evidence for CoSi2 island formation atthe earliest stages of the process is found. The epitaxial orientations of disilicidelayers grown on Si(111) and Si(100) surfaces are determined

Journal of Physical Chemistry B, Jun 30, 2017

Physica Status Solidi A-applications and Materials Science, Mar 23, 2023

Advanced Materials Interfaces, 2020

Ceramics International, 2019

Applied Surface Science, 2017

Journal of Physics: Condensed Matter

Microchimica Acta

Novel solid-phase microextraction coatings based on the use of multiwalled carbon nanotube–cyclod... more Novel solid-phase microextraction coatings based on the use of multiwalled carbon nanotube–cyclodextrin (MWCNT-CD) nanocomposites were developed for the determination of 16-priority polycyclic aromatic hydrocarbons at ultratrace levels in snow samples. The performance of both β- and γ-CD was tested to increase the detection capabilities towards the heaviest and most lipophilic compounds, i.e., five- and six-ring PAHs. To facilitate the interactions of MWCNTs with CDs, an oxidation procedure using both HNO3 and H2O2 was applied, obtaining superior results using MWCNTs-H2O2-γ-CD fiber. Detection and quantitation limits below 0.7 and 2.3 ng/L, RSD lower than 21%, and recoveries of 88(± 2)–119.8(± 0.4)% proved the reliability of the developed method for the determination of PAHs at ultratrace levels. The complexation capability of the γ-CD was also demonstrated in solution by NMR and fluorescence spectroscopy studies and at solid state by XRD analysis. Finally, snow samples collected in...

Journal of Applied Biomaterials & Functional Materials, 2016

Cerium oxide is a very interesting material that finds applications in many different fields, suc... more Cerium oxide is a very interesting material that finds applications in many different fields, such as catalysis, energy conversion, and biomedicine. An interesting approach to unravel the complexity of real systems and obtain an improved understanding of cerium oxide-based materials is represented by the study of model systems in the form of epitaxial ultrathin films or nanostructures supported on single crystalline substrates. These materials often show interesting novel properties, induced by spatial confinement and by the interaction with the supporting substrate, and their understanding requires the use of advanced experimental techniques combined with computational modeling. Recent experimental and theoretical studies performed within this field are examined and discussed here, with emphasis on the new perspectives introduced in view of the optimization of cerium oxide-based materials for application in different fields.

AIP Conference Proceedings, 1996

The possibility of using the reflection grazing angle (e,2e) technique as a binding energy and/or... more The possibility of using the reflection grazing angle (e,2e) technique as a binding energy and/or momentum spectroscopy of surface states rests on the accurate knowledge of the ionisation process. Two possible mechanisms are envisaged that can generate pairs of correlated electrons in the reflection geometry: a single inelastic collision at large momentum transfer or a double collision (elastic plus inelastic). In this paper are presented the results of (e,2e) experiments that allow to elucidate the ionisation mechanism at intermediate energies (300 eV) and asymmetric kinematics. The measurements, performed on highly oriented pyrolitic graphite, also show that an overall energy resolution as good as 1.2 eV can be achieved.

Materials & Design, 2016

The effect of phosphate on the ability of Ce-containing bioactive glasses to inhibit oxidative st... more The effect of phosphate on the ability of Ce-containing bioactive glasses to inhibit oxidative stress was studied on compositions based on Hench (46.2%SiO 2 \ \24.3%Na 2 O\ \26.9%CaO\ \2.6P 2 O 5 , mol%) and Kokubo (50.0%SiO 2 \ \ 25.0%Na 2 O\ \25.0%CaO) glasses. In particular, the reduction of catalase mimetic activity of Ce-containing glasses due to the presence: i) of P 2 O 5 in the glass compositions, and ii) of phosphate groups in the solution employed for catalase mimetic activity tests was explained and rationalized by combining SEM, XPS, XRD, DTA, FT-IR and UVvis experiments with Molecular Dynamics simulations. The results suggest that the Ce ions play a different structural role in the two series of glasses. In particular, in phosphate free glasses Ce is coordinated by non-bridging oxygens (NBOs) originated from the disruption of the silicate network, whereas in phosphate containing glasses the NBOs around Ce ions belong to orthophosphate groups. The latter groups stabilize the Ce 3+ species subtracting them from the interconversion process between Ce 3+ and Ce 4+ , which is of fundamental importance for the exhibition of the catalase mimetic activity.

Materials Science and Technology, 2016

Ultrathin films of TiO 2 were grown on a W(100)-O(261) substrate and characterised with a combina... more Ultrathin films of TiO 2 were grown on a W(100)-O(261) substrate and characterised with a combination of scanning tunneling microscopy (STM) and low energy electron diffraction. In addition to islands of rutile TiO 2 (110) with (161) termination that were reported previously, we also observed rutile TiO 2 (110) islands with a (162) film termination. A lepidocrocite-like TiO 2 nanosheet was also observed on the W(100) surface. High resolution STM images show that the nanosheet grows in the principal orthogonal directions of the W(100) substrate and forms a commensurate (167) coincident cell.

Surface Science, 2002

ABSTRACT Thin MgO films (1–20 ML) were synthesised by evaporating the metallic component in oxyge... more ABSTRACT Thin MgO films (1–20 ML) were synthesised by evaporating the metallic component in oxygen atmosphere on Ag(0 0 1). The reduced lattice misfit (3.1%) between the (0 0 1) surface unit meshes of the Ag fcc and MgO rock salt structure leads to the formation of epitaxial MgO layers with the (0 0 1)MgO∥(0 0 1)Ag and [1 0 0]MgO∥[1 0 0]Ag orientation relationships. The oxide layers were structurally characterized by LEED and modulated electron emission, while their surface morphology was studied by STM. In spite of the weak interaction between the oxide overlayer and the substrate, the occurrence of a significant tetragonal distortion of the MgO structure has been detected. We investigated in detail the strain in the oxide layer as a function of the thickness. Thin (&lt;6 ML) films exhibit an expansion along the growth axis with respect to the equilibrium phase. This vertical strain progressively reduces as the thickness increases and disappears at about 9 ML. A Poisson ratio larger than the bulk MgO value has been obtained for the 3 ML film, while the bulk value is appropriate films thicker than 6 ML. STM data indicate that an almost complete substrate coverage is obtained at 3 ML deposition.