L. Mirenghi

Synthesis and Characterization of Rutile TiO 2 Nanopowders Doped with Iron Ions

Titanium dioxide nanopowders doped with different amounts of Fe ions were prepared by coprecipitation method. Obtained materials were characterized by structural (XRD), morphological (TEM and SEM), optical (UV/vis reflection and photoluminescence, and Raman), and analytical techniques (XPS and ICP-OES). XRD analysis revealed rutile crystalline phase for doped and undoped titanium dioxide obtained in the same manner. Diameter of the particles was 5–7 nm. The presence of iron ions was confirmed by XPS and ICP-OES. Doping process moved absorption threshold of TiO2into visible spectrum range. Photocatalytic activity was also checked. Doped nanopowders showed normal and up-converted photoluminescence.

Physical properties evolution of sputtered zirconium oxynitride films: effects of the growth temperature

Zirconium oxynitride (ZrNO) films were deposited by RF reactive magnetron sputtering in water vapour–nitrogen atmosphere varying the deposition temperature from RT to 600 °C. Optical analysis, x-ray diffraction, x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) are the employed characterization techniques to investigate the influence of the substrate temperature on the films physical properties. It was found that the variation of the substrate temperature from RT to 600 °C caused a structural transition from cubic phase of Zr2ON2 to ZrN one, as confirmed by TEM observations too. In particular, Forouhi–Bloomer dispersion equations for optical parameters (n and k) and deconvolution of XPS spectra allowed further chemical properties be elucidated. They also permitted identification of two oxynitride phases, γ phase (Eg = 1.94 eV) and β phase (Eg = 1.7 eV), and an over-stoichiometric nitride one. The use of [Ec − Ev] values helped to confirm further the distinction between (γ, β)-phases and N-rich zirconium nitride compound, which is unachievable by using only Eg values.

Role of Organic Additives in Hydriding Properties of Mg-C Nanocomposites

The hydrogen storage performances of Mg-C nanocomposites have been studied on materials synthesized by ball milling with and without addition of an organic additive. The main purpose of this work is to study in more detail the cooperative effect observed when both graphite and benzene are added to the milled blend. In fact, when both components are added to Mg in the ball milling process, good catalyzing properties of the composite surface allow improved sorptiondesorption behavior of the synthesized material. The processed materials have been characterized by XRD to assess the details of the phase structure by Rietveld analysis, while surface features have been studied by XPS, which evidences structural modifications of both the surface Mg oxide and the graphite particles. The hydrogen desorption behavior has been correlated with the surface structure which appears to depend on the carbon to benzene ratio. Thermal stability and hydrogen desorption properties were investigated by DSC. Experimental results on nanocomposites with the same Mg to C weight ratio (70:30) show improved performances for a proper choice of carbon to benzene ratio weight (1/3), even after manipulation of the milled material in air.

Structural, compositional, and optical characterization of thin TiOxNy coatings fabricated by dual ion beam sputtering

Titanium oxynitride (TiOxNy) thin films are of great interest for the fabrication of protective optical coatings. By varying the oxygen and nitrogen content in the films, the electrical, optical and mechanical properties of these coatings can be tailored properly. In this work, we fabricated TiN and TiOxNy films by dual ion beam sputtering technique. TiOxNy films were ion-assisted by a low energy oxygen and nitrogen mixed ion beam of variable O/N flux ratio. We observe that the incorporation of oxygen greatly improves the adhesion of the film on the glass substrate. Further, the optical extinction coefficient drastically decreases for increasing oxygen content, suggesting new applications of TiOxNy films as protective coatings on transparent substrates. The film composition by XPS analyses is in agreement with the results obtained by a simple model to describe the ion assistance phenomena. The crystallographic structure of the deposited films was characterized by using (Theta) - 2(Theta) x-ray diffraction and grazing incidence x-ray diffraction measurements. In the range up to 14 percent of the oxygen to nitrogen flux ratio, a TiN f.c.c. phase structure with preferred (111) growth-orientation of the grains is observed. For higher oxygen concentrations the absence of diffraction peaks suggests a more amorphous-like structure of the deposited film. Specular x-ray reflectivity measurements provide important and accurate information about the film-air and film-substrate interface roughness. The Kiessig fringes are caused by multiple internal interference of the x-ray beam and can be observed up to 3 degrees, which is a clear indication of the high homogeneity of the film thickness and of sharp interfaces.

CdS and ZnS nanoparticles growth in different reaction media: synthesis and characterization

In this work we report on the growth of cadmium sulfide and zinc sulfide nanocrystals by thermolysis, starting from a metal thiolate in a (i) solventless way, (ii) by a novel route in tryoctilphosphine oxide (TOPO), and (iii) by direct synthesis in a polystyrene matrix. The x-ray diffraction (XRD) and transmission electron microscopy (TEM) show that the nanocrystals fabricated by the different methods are under optimized growth conditions single crystals of zincblende structure and of regular spherical shape. The average size was estimated to be between 2.0-3.0 nm with a size dispersion that depends on the synthesis route and is in the range between 10% and 20%. The XPS results indicate that for the nanoparticles obtained via solventless strategy the sulfur is present both as bonded to the metal atom and to the organic residue, while in the TOPO synthesized nanoparticles the sulfur signal has only one component associated to the metal-sulfide bond. The photoluminescence spectroscopy (PL) analysis of CdS crystals clearly evidences the typical emissions of nanosized zincblende CdS monocrystalline particles. Furthermore, the optical spectroscopy data indicate that the size distribution of the Cdsulfide - TOPO nanoparticles seems to be generally larger than that ones grown directly in polymer matrix. For all the CdS samples, the metal-sulfide nanocrystals exhibit a trap-related radiative transition at about 2eV that can be attributed to the hole-electron recombination at particle surface defect-center.

Structural and chemical investigation of surface and interface of multilayer optical coatings deposited by DIBS

The investigation of the surface and interface of a multilayer coating is a key factor for producing high quality optical device. In this work, we present a non-destructive technique as X-ray reflectivity to study deeply the chemical and structural quality of the multilayer. XPS depth profile analysis and AFM images have been used to evaluate the chemical intermixing and the surface roughness in order to verify the X-ray results.

Fabrication of 3D carbon nanotube networks

We report on the synthesis and characterization of a hyperbranched polymer englobing single-wall carbon nanotubes (SWCNTs). This new material was obtained by using SWCNTs functionalized with carboxylic groups as starting reagent. The acid groups were firstly converted in acyl chloride moieties and afterwards were bound to hexamethylenediamine (HMDA) via formation of amide functionality. The acquired spectra of attenuated total reflectance and the analysis performed through x-ray photoelectron spectroscopy confirmed the amide bond formation. The hyperbranched polymer characterization was completed by using scanning and transmission electron microscopy, thermo-gravimetric analysis and Raman spectroscopy. The electron microscopy analyses showed the formation of an amorphous polymeric material englobing a dense network of SWCNTs without phase segregation, demonstrating that the reaction with HMDA allows a reorganization of SWCNTs in a complex three-dimensional network.