Showing papers by "Gaetano Granozzi published in 1995"

Xps and uv-vis study of high-purity fe2o3 thin-films obtained using the sol-gel technique

Abstract: Fe2O3 thin films obtained by the sol-gel technique from ethanolic solutions of Fe(OEt)3 have been deposited on pure silica and heat treated at two different temperatures. Preliminary thermogravimetric (TG) measurements on the precursor were carried out in order to evaluate the weight loss as a function of temperature and heat-treatment time. Chemical characterization of the films was obtained by XPS and UV–VIS spectroscopies. The bulk of the film heated at 500 °C did not show residual carbon. The corresponding UV–VIS spectrum was well structured in the 15 000–50 000 cm–1 region due to charge-transfer and inner-oxygen transitions. XRD measurements showed an amorphous pattern for the sample heated at 200 °C, whereas a diffraction peak corresponding to haematite (α-Fe2O3) nanocrystals was observed for the film heated at 500 °C.

Nanocrystalline α-Fe2O3 sol-gel thin films: a microstructural study

Abstract: The structure of α-Fe 2 O 3 sol-gel thin films, obtained from an alkoxide precursor, was investigated by X-ray diffraction, X-ray absorption spectroscopy and conversion electron Mossbauer spectroscopy. Samples heated at 300°C were amorphous, while those treated at 400 and 500°C showed the presence of crystalline hematite. The crystallites were small enough to give rise to the superparamagnetic effect. In the nanostructured films, the α-Fe 2 O 3 particles were not linked together but dispersed in a network of amorphous ferric oxide.

A theoretical and experimental investigation of the electronic structure of alpha -Fe2O3 thin films

Abstract: Ground and excited states of alpha -Fe2O3 have been investigated by determining the spin-polarized wavefunctions and eigenvalues of an embedded Fe2O912- cluster using the discrete variational Xalpha method. The computed transition energies compare reasonably well with the recorded experimental spectrum of high-purity alpha -Fe2O3 thin films obtained by the sol-gel technique. The theoretical data herein reported predict a very high valence-conduction band gap incompatible with the experimental outcomes, which were routinely interpreted as originated by an interband transition. In contrast to this, the lowest-energy optical transitions have a charge transfer nature, involving excitation of electrons from the occupied O 2p-based spin down levels to the empty Fe atom-like spin down orbitals.

A theoretical and experimental investigation of the electronic structure of α-Fe2O3 thin films

Abstract: Ground and excited states of α-Fe 2 O 3 have been investigated by determining the spin-polarized wavefunctions and eigenvalues of an embedded Fe 2 O 9 12- cluster using the discrete variational X α method. The computed transition energies compare reasonably well with the recorded experimental spectrum of high-purity α-Fe 2 O 3 thin films obtained by the sol-gel technique. The theoretical data herein reported predict a very high valence-conduction band gap incompatible with the experimental outcomes, which were routinely interpreted as originated by an interband transition. In contrast to this, the lowest-energy optical transitions have a charge transfer nature, involving excitation of electrons from the occupied O 2p-based spin down levels to the empty Fe atom-like spin down orbitals

DETERMINATION OF THE OVERLAYER/SUBSTRATE REGISTRY IN Ni(1 ML)/Pt(111) BY ANGLE-SCANNED PHOTOELECTRON DIFFRACTION

Abstract: The site (fcc or hcp) occupied by the atoms of a Ni ML deposited on Pt(111) is determined in this paper using angle-scanned photoelectron diffraction (PD). A full 2π MgKα-excited Ni-2p3/2 PD pattern from 1-ML Ni deposited on Pt(111) is compared to single scattering cluster-spherical wave (SSC-SW) simulations and the agreement between experimental and theoretical data is quantified by R-factor analysis. From the present investigation it turns out that Ni atoms occupy hcp sites. In addition, the Ni-Pt distance has been estimated to be 2.5±0.1 A.