Gaetano Granozzi

XPS and UV-VIS study of high-purity Fe2O3 thin films obtained using the sol-gel technique

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.

Yttrium oxide/gadolinium oxide-modified platinum nanoparticles as cathodes for the oxygen reduction reaction.

Rare-earth-element (Y, Gd) modified Pt nanoparticles (NPs) supported on a carbon substrate (Vulcan XC-72) are synthesized via a water-in-oil chemical route. In both cases, X-ray diffraction (XRD) measurements show the non-formation of an alloyed material. Photoemission spectroscopy (XPS) results reveal that Y and Gd are oxidized. Additionally, no evidence of an electronic modification of Pt can be brought to light. Transmission electron microscopy (TEM) studies indicate that Pt-Y(2)O(3) and Pt-Gd(2)O(3) particles are well dispersed on the substrate-and that their average particle sizes are smaller than the Pt-NP sizes. The catalytic activity of the Pt-Y(2)O(3)/C and Pt-Gd(2)O(3)/C catalysts towards the oxygen reduction reaction (ORR) is studied in a 0.5 M H(2)SO(4) electrolyte. The surface and mass specific activities of the Pt-Y(2)O(3)/C catalyst towards the ORR at 0.9 V (vs. the reversible hydrogen electrode, RHE) are (54.3±1.2) μA cm(-2)(Pt) and MA=(23.1±0.5) mA mg(-1)(Pt), respectively. These values are 1.3-, and 1.6-fold higher than the values obtained with a Pt/C catalyst. Although the as-prepared Pt-Gd(2)O(3)/C catalyst has a lower catalytic activity for the ORR compared to Pt/C, the heat-treated sample shows a surface specific activity of about (53.0±0.7) μA cm(-2) Pt , and a mass specific activity (MA) of about (18.2±0.5) mA mg(-1) Pt at 0.9 V (vs. RHE). The enhancement of the ORR kinetics on the Pt-Y(2)O(3)/C and heat-treated Pt-Gd(2)O(3)/C catalysts could be associated with the formation of platinum NPs presenting modified surface properties.

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.

X‐ray photoelectron diffraction from the HgCdTe(111) surface

The surface polarity of a mercury cadmium telluride (MCT) (111) crystal surface has been determined by x‐ray photoelectron diffraction (XPD). Emission from the core levels of Hg, Cd, and Te gave reproducible photoelectron diffraction patterns with considerable fine structure. Comparisons between experiment and single scattering cluster calculations via R factors very well distinguished the different kinds of lattice sites of Cd, Hg, and Te, and also permitted unambiguously assigning a cationic termination to the sample studied. This is thus a demonstration of the capability of XPD to study the type of termination involved at MCT and other compound semiconductor surfaces.

X-ray photoelectron diffraction from the CdTe(111)A polar surface

Abstract Polar and azimuthal X-ray photoelectron diffraction (XPD) data on a CdTe(111)A (Cd terminated) surface are reported and discussed on the basis of a single scattering cluster (SSC) theory. Significantly distinct patterns are predicted for the two different (111)A and (111)B polar surfaces, suggesting that the XPD technique is a valid tool for the absolute determination of the surface polarity. Moreover, the azimuthal diffraction patterns obtained at grazing polar angles (so that the probed surface region is very shallow) revealed details which can be elucidaded assuming either a surface relaxation, where Cd and Te atoms of the outermost double layer are almost coplanar, or a ( 2√3×2√3 ) R30° surface reconstruction.

Polarity determination of the HgCdTe(111) surface by azimuthal X-ray photoelectron diffraction experiments

Azimuthal X-ray photoelectron diffraction (APD) experiments have been carried out on a sample of Hg0.78Cd0.22 Te (MCT) epitaxially grown by liquid phase epitaxy (LPE) on (111) CdTe. To our knowledge this is the first XPD study of the (111) face of a II-VI semiconductor. Reproducible diffraction features are seen for emission from core levels of Hg, Cd and Te both before and after minimum ion bombardment, with bombardment being done to remove the native oxide overlayer. Single scattering cluster (SSC) calculations have been carried out using a spherical wave (SW) model. From comparison between experiment and theory an absolute determination of the surface polarity is possible.