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Iron/iron oxide-based nanocomposites were prepared by IR laser sensitized pyrolysis of Fe(CO)5 andmethylmethacrylate (MMA) mixtures. The morphology of nanopowder analyzed by TEM indicated that mainly core-shell structures were obtained. X-ray diffraction techniques evidence the cores as formedmainly by iron/iron oxide crystalline phases. A partially degraded (carbonized) polymeric matrix is suggested for the coverage of the metallic particles. The nanocomposite structure at the variation of the laser density and of the MMA flow was studied. The new materials prepared as thick films were tested for their potential for acting as gas sensors. The temporal variation of the electrical resistance in presence of NO2, CO, and CO2, in dry and humid air was recorded. Preliminary results show that the samples obtained at higher laser power density exhibit rather high sensitivity towards NO2 detection and NO2 selectivity relatively to CO and CO2. An optimum working temperature of 200°C was found. [ABSTRACT FROM AUTHOR]

In this paper, the growth of thin and dense films of vertically aligned carbon nanotubes (CNTs) on Fe-Co/TiN/Si(100) substrates is reported. Special attention is held to the preparation of the TiN buffer layers. This layer is deposited by pulse laser deposition at high temperature with a high texturation according to [TiN(100)//Si(100)]. Further ammonia heat treatment is performed at 623 K to control a Ti:N stoichiometry and remove oxygen impurity. Fe and Co as catalysts are subsequently deposited at high temperature (923 K) at the monolayer level with two ultrahigh vacuum evaporator cells. The growth of CNTs is performed by a direct-current plasma-enhanced and hot filaments-assisted catalytic chemical vapor deposition (dc HF CCVD) process. Highly dense films of CNTs, are obtained with only 0.5 nm Fe(Co) evaporated. Observations by transmission electron microscopy show that most of the CNTs display sizes in the 2.5-6 nm range, most of them with a double-wall (DW). This is in agreement with spectral features of the Raman radial breathing modes (RBM) in the 70-130 cm-1 range. Generally, these large-diameter DWCNTs display a high defect density with morphologies partially collapsed into flattened twisted shapes. [ABSTRACT FROM AUTHOR]

Abstract: The preparation of TiO2-based nanoparticles of closely controlled sizes and purity gives rise to considerable interest in the frame of environmental applications, e.g. in photocatalysis. When nanoparticles instead of their bulk counterpart are used the synthesis method plays a fundamental role in defining specific structural properties. Between the different gas-phase synthesis techniques, the CO2 laser pyrolysis is a versatile method allowing for the preparation of nanostructures of various chemical compositions. Here we demonstrate that pure and Fe–doped TiO2 nanoparticles with rather low Fe concentration may be prepared by applying the sensitized IR laser pyrolysis to a gas mixtures containing titanium tetrachloride, air and iron pentacarbonyl (vapors). The structures of TiO2-based particles were systematically investigated by X-ray diffraction, transmission electron microscopy, high-resolution electron microscopy, selected area electron diffraction and X-ray Photoelectron Spectroscopy. Depending on the synthesis parameters, the nanoparticle system contains mixtures of anatase and rutile, with a preponderance of the anatase phase. Higher rutile proportion was found in the iron-doped samples. Mean particle diameters of around 14nm and 12nm were estimated for undoped and doped anatase titania, respectively. From UV–Vis diffuse reflectance spectra, higher absorbance and red shifted absorption were evidenced at higher amount of doped iron. Preliminary evaluation tests of the UV photoactivity of samples were performed by using the scanning electrochemical microscopy for determining the evolution of the oxygen consumption in the presence of IV-chlorophenol. They show that the undoped nano titania samples perform better than the reference P25 Degussa sample. A drop of the nano-titania photoactivity as a consequence of Fe doping was observed. Possible reasons of this effect are tentatively discussed. [Copyright &y& Elsevier]

Abstract: Nitrogen-doped TiO2 nanoparticles have been prepared by the IR laser pyrolysis technique. A sensitized mixture of TiCl4 (vapors) and N2O was used as titanium and nitrogen precursors, respectively. The structural properties of the resultant N-doped nanoparticles such as the phase formation and the average particle size and distributions were investigated by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The phase composition varied from almost pure anatase to mixtures of rutile and anatase. A decrease of the mean particle diameters from about 18nm in case of the almost pure anatase sample to about 13nm in case of the anatase–rutile mixture is observed. XPS analysis suggests and interstitial character of the doping process. [Copyright &y& Elsevier]

Abstract: The synthesis of carbon nanotubes (CNTs) by catalytic laser-induced chemical vapor deposition (C-LCVD) was investigated. C-LCVD uses both ex situ synthesized catalyst nanoparticles and the controlled decomposition of gas-phase hydrocarbon mixtures. As catalysts, Fe/C composites of the core-shell type were used. A continuous-wave CO2 laser was employed to irradiate the ethylene/acetylene hydrocarbon precursors and to simultaneously heat a silicon substrate on which the carbon nanotubes were grown. The effects on carbon nanotube growth of both the iron-based nanocomposite particles and of the ethylene concentration were studied. The analysis suggests the feasibility of the C-LCVD process, in which the core-shell Fe/C catalysts comply with the prerequisite conditions of the CNT growth namely dispersion and supersaturation. [Copyright &y& Elsevier]

Abstract: The preparation of TiO2 nanoparticles by CO2 laser pyrolysis of TiCl4 (vapor)-based gas mixtures was investigated as a function of laser power and influence of the oxidizer. Increased crystallinity and crystallite dimensions as well as increase of the rutile fraction are observed at moderate flow increase in the flow rate of the oxidizing agent. [Copyright &y& Elsevier]