Giorgio Carraro

On the performances of CuxO-TiO2 (x = 1, 2) nanomaterials as innovative anodes for thin film lithium batteries.

CuxO-TiO2 (x = 1, 2) nanomaterials are synthesized on polycrystalline Ti substrates by a convenient chemical vapor deposition (CVD) approach, based on the initial growth of a CuxO matrix (at 400 and 550 °C for x = 1 and 2, respectively) and the subsequent overdispersion of TiO2 at 400 °C. All CVD processes are carried out in an oxygen atmosphere saturated with water vapor. The obtained systems are investigated by means of glancing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), field emission-scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and electrochemical experiments. Galvanostatic charge/discharge measurements indicate that Cu2O-TiO2 nanomaterials exhibit very attractive high-rate capabilities (∼400 mA h g(-1) at 1 C; ∼325 mA h g(-1) at 2 C) and good stability after 50 operating cycles, with a retention of 80% of the initial capacity. This phenomenon is mainly due to the presence of TiO2 acting as a buffer material, i.e., minimizing volume changes occurring in the electrochemical conversion. In a different way, CuO-TiO2 systems exhibit worse electrochemical performances as a consequence of their porous morphology and higher thickness. In both cases, the obtained values are among the best ever reported for CuxO-based systems, candidating the present nanomaterials as extremely promising anodes for eventual applications in thin film lithium batteries.

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.

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.

Supported ε and β iron oxide nanomaterials by chemical vapor deposition: structure, morphology and magnetic properties

Supported e- and β-Fe2O3 are synthesized by a chemical vapor deposition (CVD) strategy, yielding systems with controllable morphologies from nanorods (e) to square-like pyramids (β). The hard magnetic properties of e-Fe2O3 and the antiferro/paramagnetic behavior of β-Fe2O3 are directly influenced by the system morphological organization and structural orientations.

Solar H2 generation via ethanol photoreforming on ε-Fe2O3 nanorod arrays activated by Ag and Au nanoparticles

Earth-abundant, non toxic and cheap Fe2O3 can be used as photocatalyst for sustainable hydrogen production from bio-ethanol aqueous solutions, under sunlight irradiation and without the application of any external electrical bias. To this aim, supported materials are not only technologically more appealing than powders, but also of key importance to develop photoactive and stable Fe2O3-based nanostructured photocatalysts. Here we demonstrated that, while bulk Fe2O3 is unsuitable for solar hydrogen evolution, nanostructured iron(III) oxide polymorphs show promising photoactivity. In particular, a hydrogen yield of 20 mmol h−1 m−2 was obtained on e-Fe2O3 nanorod arrays supported on Si(100) under simulated sunlight irradiation, mainly due to UV solar photon absorption. The functionalization with partially oxidized Ag nanoparticles resulted in a positive performance improvement upon selective irradiation with the UV portion of the solar spectrum. Conversely, the incorporation of Au nanoaggregates into e-Fe2O3 enabled to obtain a significant H2 production even under sole Vis light.

Fe2O3–TiO2 nanosystems by a hybrid PE-CVD/ALD approach: controllable synthesis, growth mechanism, and photocatalytic properties

Supported Fe2O3–TiO2 nanocomposites are fabricated by an original vapor phase synthetic strategy, consisting of the initial growth of Fe2O3 nanosystems on fluorine-doped tin oxide substrates by plasma enhanced-chemical vapor deposition, followed by atomic layer deposition of TiO2 overlayers with variable thickness, and final thermal treatment in air. A thorough characterization of the target systems is carried out by X-ray diffraction, atomic force microscopy, field emission-scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. High purity nanomaterials characterized by the co-presence of Fe2O3 (hematite) and TiO2 (anatase), with an intimate Fe2O3–TiO2 contact, are successfully obtained. In addition, photocatalytic tests demonstrate that, whereas both single-phase oxides do not show appreciable activity, the composite systems are able to degrade methyl orange aqueous solutions under simulated solar light, and even visible light, with an efficiency directly dependent on TiO2 overlayer thickness. This finding opens attractive perspectives for eventual applications in wastewater treatment.

A plasma-assisted approach for the controlled dispersion of CuO aggregates into β iron(III) oxide matrices

β-Fe2O3/CuO nanosystems were synthesised by using a two-step plasma-assisted strategy. β-Fe2O3 nanostructures (host) were initially deposited by plasma assisted-chemical vapour deposition (PA-CVD) on indium tin oxide (ITO) substrates. Subsequently, CuO nanoparticles (NPs, guest) were over-deposited on host matrices by means of radio frequency (RF) sputtering under mild conditions. The combined use of structural, morphological and chemical analyses evidenced the formation of pure and homogeneous β-Fe2O3/CuO systems possessing a high dispersion of CuO NPs in/on β-Fe2O3hosts. The target nanomaterials were characterized by an intimate contact between the two oxides, with CuO NP size and tuneable content as a function of sputtering time. These features, along with the tailored nano-organization, make the present β-Fe2O3/CuO nanosystems attractive candidates for diverse technological applications involving solar light harvesting.

Vapor-Phase Fabrication of β-Iron Oxide Nanopyramids for Lithium-Ion Battery Anodes

The other polymorph: A vapor-phase route for the fabrication of β-Fe(2)O(3) nanomaterials on Ti substrates at 400-500 °C is reported. For the first time, the β polymorph is tested as anode for lithium batteries, exhibiting promising performances in terms of Li storage and rate capability.

Fluorine doped Fe2O3 nanostructures by a one-pot plasma-assisted strategy

The present work reports on the synthesis of fluorine doped Fe2O3 nanomaterials by a single-step plasma enhanced-chemical vapor deposition (PE-CVD) strategy. In particular, Fe(hfa)2TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N′,N′-tetramethylethylenediamine) was used as molecular source for both Fe and F in Ar/O2 plasmas. The structure, morphology and chemical composition of the synthesized nanosystems were thoroughly analyzed by two-dimensional X-ray diffraction (XRD2), field emission-scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM). A suitable choice of processing parameters enabled the selective formation of α-Fe2O3 nanomaterials, characterized by an homogeneous F doping, even at 100 °C. Interestingly, a simultaneous control of the system nanoscale organization and fluorine content could be achieved by varying the sole growth temperature. The tailored properties of the resulting materials can be favourably exploited for several technological applications, ranging from photocatalysis, to photoelectrochemical cells and gas sensing.

Aerosol assisted chemical vapour deposition of Ga-doped ZnO films for energy efficient glazing: effects of doping concentration on the film growth behaviour and opto-electronic properties

High quality Ga-doped ZnO thin films for use as energy efficient glazing coatings were deposited onto glass substrates by low cost single source aerosol assisted chemical vapour deposition (AACVD) of zinc and gallium acetylacetonates (in methanol) at a temperature of 350 °C. The effect of Ga content ranging from 0.4 at% to 6.1 at% on the structural and functional properties of ZnO films was investigated. Highly c-axis oriented films are easily formed in the case of pure ZnO with hexagonal (002) surfaces observed. This texture is gradually weakened in 0.4 at% to 3.0 at% Ga doped samples, and the deposit morphology is transformed to granular particles, irregular platelets, agglomerated particles and wedge-like structures, respectively, which may result from retarded grain boundary growth and increasing exposed non-(002) surfaces. Further gallium addition to 4.3 at% suppresses the grain growth and deteriorates the system crystallinity, with a concomitant change to a (102) preferential orientation in the heavily 6.1 at% Ga doped sample. The ZnO:Ga coatings exhibit high carrier concentration (up to 4.22 × 1020 cm−3) and limited carrier mobility (<5 cm2 V−1 s−1), and the minimum resistivity value obtained is 1.16 × 10−2 Ω cm. Due to their large band gaps (3.14–3.42 eV) and favourable carrier numbers, high visible transmittance (83.4–85.3%) and infrared reflection (up to 48.9% at 2500 nm) are observed in these films, which is one of the best AACVD ZnO reported for low emissivity application and close to the optical requirements for commercial energy saving glazing.