Papers by Author: L. Giorgi

Abstract: Aiming at the purpose of using carbon nanotubes as secondary phase in composite materials, removal of metal catalyst, catalyst support and amorphous carbon is crucial to make the most of the required properties. A purification method was developed to remove the metal catalyst from multi-walled nanotubes grown by thermal CVD. A nanosized Fe-based catalyst, prepared by coprecipitation of iron and aluminum ions, followed by solid state reaction, was used to catalyze the growth. Carbon nanotubes were subjected to acid purification and a comparison between nitric acid and a mixture of nitric and hydrochloric acid for the removal of Fe and Fe oxides is provided. Morphological and spectroscopic analyses of the materials were performed, both before and after the purification processes.

Abstract: The achievement of nanosmooth, ultrathin diamond coatings with nanosized grains is mandatory for the successful utilization of diamond in areas such as microelectromechanical systems, field emission and surface acoustic waves devices. The bias enhanced nucleation technique (BEN) allows to achieve high nucleation density diamond films, where the average distance between diamond nuclei can be as low as 10-20nm. Moreover by diluting the gas precursors (H2 and CH4) into noble gas (Ar, He) during growth, the formation of larger crystals can be inhibited, giving rise to nanocrystalline films without a degradation of the film quality, such as the presence of more graphitic bonds. In this paper we report the growth of ultrathin, smooth, high quality nanodiamond films obtained by combining the two techniques in a HFCVD reactor. A variety of nanocrystalline diamond films with a grain size as low as 10nm and thickness up to 1μm were obtained. The nucleation process and ensuing growth of the film were monitored by SEM observation. Spectroscopic measurements were also performed to study the microstructure and to assess the quality of the deposited material.

Abstract: The proton exchange membrane fuel cells (PEMFC) have been developed mainly as a power source for vehicles, power generation and consumer electronics since they combine high energy conversion efficiency at relatively low temperatures without pollutants emission in the environment. An electrode for a PEMFC is a layered structure composed by a catalyst layer deposited on a porous carbon substrate. The substrate is usually covered by a diffusion layer that enhances the gas and water flow. Platinum nanoparticles supported by carbon microparticles are commonly employed as catalyst layer. In this work an extreme ultra-low loading of Pt catalyst (< 0.02 mg/cm2) has been deposited by magnetron sputtering on gas diffusion electrodes, with different carbon supports (Vulcan and SuperP), in order to enhance the activity of PEM fuel cells. The morphology (shape and grain size) and microstructure have been studied combining field emission scanning electron microscopy (FEG-SEM), grazing incidence synchrotron x-ray diffraction (GIXRD) and x-ray photoelectron spectroscopy (XPS). The results presented here concern the evolution of the cluster size and shape after the ageing, induced by cyclic voltammetry for methanol oxidation reaction.