Davide Barreca

The Potential of Supported Cu2O and CuO Nanosystems in Photocatalytic H2 Production

Hy wire: Supported Cu(2)O nanosystems and CuO nanowires obtained by chemical vapor deposition were used in the photocatalytic splitting of methanol/water solutions to produce hydrogen. The results obtained with these systems open appealing perspectives for the clean conversion of sunlight into storable chemical energy.

Co3O4/ZnO nanocomposites: from plasma synthesis to gas sensing applications.

Herein, we describe the design, fabrication and gas sensing tests of p-Co(3)O(4)/n-ZnO nanocomposites. Specifically, arrays of (001) oriented ZnO nanoparticles were grown on alumina substrates by plasma enhanced-chemical vapor deposition (PECVD) and used as templates for the subsequent PECVD of Co(3)O(4) nanograins. Structural, morphological and compositional analyses evidenced the successful formation of pure and high-area nanocomposites with a tailored overdispersion of Co(3)O(4) particles on ZnO and an intimate contact between the two oxides. Preliminary functional tests for the detection of flammable/toxic analytes (CH(3)COCH(3), CH(3)CH(2)OH, NO(2)) indicated promising sensing responses and the possibility of discriminating between reducing and oxidizing species as a function of the operating temperature.

Columnar CeO2 nanostructures for sensor application

CeO2 columnar nanostructures with tailored properties were synthesized by chemical vapour deposition on Si(100) and Al2O3 substrates between 350 and 450 °C and characterized in their structure, composition and morphology by means of a multi-technique approach. Their higher sensitivity in the detection of gaseous ethanol and nitrogen dioxide with respect to continuous CeO2 thin films opens interesting perspectives for the development of nanosized sensor devices.

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.

Rational Design of Ag/TiO2 Nanosystems by a Combined RF-Sputtering/Sol-Gel Approach

The present work is devoted to the preparation of Ag/TiO(2) nanosystems by an original synthetic strategy, based on the radio-frequency (RF) sputtering of silver particles on titania-based xerogels prepared by the sol-gel (SG) route. This approach takes advantage of the synergy between the microporous xerogel structure and the infiltration power characterizing RF-sputtering, whose combination enables the obtainment of a tailored dispersion of Ag-containing particles into the titania matrix. In addition, the systems chemico-physical features can be tuned further through proper ex situ thermal treatments in air at 400 and 600 degrees C. The synthesized composites are extensively characterized by the joint use of complementary techniques, that is, X-ray photoelectron and X-ray excited Auger electron spectroscopies (XPS, XE-AES), secondary ion mass spectrometry (SIMS), glancing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), electron diffraction (ED), high-angle annular dark field scanning TEM (HAADF-STEM), energy-filtered TEM (EF-TEM) and optical absorption spectroscopy. Finally, the photocatalytic performances of selected samples in the decomposition of the azo-dye Plasmocorinth B are preliminarily investigated. The obtained results highlight the possibility of tailoring the system characteristics over a broad range, directly influencing their eventual functional properties.

Vapor Phase Processing of α-Fe2O3 Photoelectrodes for Water Splitting: An Insight into the Structure/Property Interplay

Harvesting radiant energy to trigger water photoelectrolysis and produce clean hydrogen is receiving increasing attention in the search of alternative energy resources. In this regard, hematite (α-Fe2O3) nanostructures with controlled nano-organization have been fabricated and investigated for use as anodes in photoelectrochemical (PEC) cells. The target systems have been grown on conductive substrates by plasma enhanced-chemical vapor deposition (PE-CVD) and subjected to eventual ex situ annealing in air to further tailor their structure and properties. A detailed multitechnique approach has enabled to elucidate the interrelations between system characteristics and the generated photocurrent. The present α-Fe2O3 systems are characterized by a high purity and hierarchical morphologies consisting of nanopyramids/organized dendrites, offering a high contact area with the electrolyte. PEC data reveal a dramatic response enhancement upon thermal treatment, related to a more efficient electron transfer. The reasons underlying such a phenomenon are elucidated and discussed by transient absorption spectroscopy (TAS) studies of photogenerated charge carrier kinetics, investigated on different time scales for the first time on PE-CVD Fe2O3 nanostructures.

Zirconium Dioxide Thin Films Characterized by XPS

In this work we use x-ray photoelectron spectroscopy (XPS) to analyze the principal core levels of a ZrO2 thin film deposited on glass using Zr(OPri)3(dpm) (OPri=isopropoxy; hdpm=2,2,6,6-tetramethyl-3,5-heptanedione) as precursor. Besides the general survey, charge corrected binding energies for the Zr 3d5/2, Zr 3d3/2, O 1s, and C 1s photoelectrons are reported. Deconvolution of the O 1s signal reveals the presence of –OH groups and adsorbed water, whose presence can be related to the air exposure of the film between its preparation and XPS analysis.

Controlled synthesis and properties of β-Fe2O3 nanosystems functionalized with Ag or Pt nanoparticles

β-Fe2O3 nanosystems functionalized with Ag or Pt nanoparticles were synthesized by an innovative two-step procedure, based on the chemical vapor deposition (CVD) of β-iron(III) oxide matrices and the subsequent radio frequency (RF)-sputtering of metal nanoparticles. The system structure, nano-organization and chemical composition were investigated by means of X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), X-ray photoelectron/X-ray excited-Auger electron spectroscopies (XPS/XE-AES), and secondary ion mass spectrometry (SIMS). High purity nanomaterials based on the scarcely investigated β-Fe2O3 phase, and functionalized by Ag or Pt nanoparticles with tailored dispersion, were successfully obtained. Preliminary gas sensing experiments towards toxic and flammable analytes were carried out in the temperature range 100–400 °C, highlighting interesting results in the detection of H2, CH3CH2OH, and CH3COCH3. The adopted approach can be further optimized to control the diverse morphologies of iron oxide-based materials meeting the demands of a variety of applications.

Hafnium oxide thin film grown by ALD: An XPS study

Hafnium(IV) oxide thin films were synthesized by atomic layer deposition (ALD) on Si(100) substrates, using an innovative guanidinate-stabilized hafnium amide precursor, [Hf(NEtMe)2(EtMeNC(NiPr)2)2]. In the present work, our attention is focused on a detailed XPS characterization of a representative HfO2 coating grown at 350 °C. Beside the wide scan spectrum, detailed spectra for the O 1s, Hf 4f, Hf 4d and C 1s regions and related data are presented and discussed. The obtained results point out to the formation of HfO2 coatings characterized by the presence of -OH groups, whose main origin is attributed to the use of water as oxidizing agent during the preparation process.

Sol-Gel and CVD Co3O4 Thin Films Characterized by XPS

The present investigation is focused on x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XE-AES) analysis of the main core levels (O 1s, Co 2p, and Co LVV) of nanocrystalline Co3O4 coatings. The samples were obtained by CVD and sol-gel routes. Co(dpm)2 (Hdpm = 2,2-6,6-tetramethyl-3,5-heptanedione) was chosen as CVD precursor thanks to its appreciable volatility, the absence of direct Co–C bonds and the presence of thermally labile Co–O moieties. The preparation of the sol-gel films was accomplished starting from methanolic solutions of Co(OCOCH3)2⋅4H2O due to the clean conversion of cobalt acetate into cobalt oxides. The obtained Co3O4 films were bluish-brown, homogenous, crack-free, and adhered well to the substrates. The microstructural analyses revealed the formation of single-phase nanostructured layers with average crystallite dimensions ranging between 15 and 26 nm.