Skills (4)
Research experience
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Jul 2009–
presentResearch: Italian Institute of Technology (IIT)
Italian Institute of Technology (IIT)Italy · Genova
Publications (39) View all
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Article: Colloidal CdSe/Cu3P/CdSe Nanocrystal Heterostructures and their Evolution upon Thermal Annealing.
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ABSTRACT: We report the synthesis of colloidal CdSe/Cu3P/CdSe nanocrystal heterostructures grown from hexagonal Cu3P platelets as templates. One type of heterostructure was a sort of "coral", formed by vertical pillars of CdSe grown on top of a Cu3P platelet and preferentially at its edges, on both basal facets. Another type of heterostructure had a "sandwich" type of architecture, formed by two thick, epitaxial CdSe layers encasing the original Cu3P platelet. When the sandwiches were annealed under vacuum up to 450°C, sublimation of P and Cd species with concomitant interdiffusion of Cu and Se species was observed by in-situ HR- and EFTEM analyses. These processes transformed the starting sandwiches into Cu2Se nanoplatelets. Under the same conditions, both the pristine (uncoated) Cu3P platelets and a control sample made of isolated CdSe nanocrystals were stable. Therefore, the thermal instability of the sandwiches under vacuum might be explained by the diffusion of Cu species from Cu3P cores into CdSe domains, which triggered sublimation of Cd, as well as out-diffusion of P species and their partial sublimation, together with the overall transformation of the sandwiches into Cu2Se nanocrystals. A similar fate was followed by the coral-like structures. These CdSe/Cu3P/CdSe nanocrystals are therefore an example of a nanostructure that is thermally unstable, despite its separate components would be stable under the same conditions.ACS Nano 04/2013; · 10.77 Impact Factor -
Article: Plasmon Dynamics in Colloidal Au2Cd Alloy-CdSe Core/shell Nanocrystals.
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ABSTRACT: Metal-semiconductor nanocrystal heterostructures are model systems for understanding the interplay between the localized surface plasmon resonances in the metal domain and the relaxation of the excited carriers in the semiconductor domain. Here we report the synthesis of colloidal Au2Cd (core)/CdSe (shell) nanocrystal heterostructures, which were characterized extensively with several structural and optical techniques, including time-resolved fluorescence and broadband transient absorption spectroscopy (both below and above the CdSe bandgap). The dynamics of the transient plasmon peak was dominated by the relaxation of hot carriers in the metal core, its spectral shape was independent on the pump wavelength and the bleaching lifetime was about half a picosecond, comparable with the value found in the AuCd seeds used for the synthesis.ACS Nano 01/2013; · 10.77 Impact Factor -
Article: CO Oxidation on Colloidal Au0.80Pd0.20-FexOy Dumbbell Nanocrystals.
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ABSTRACT: We report a colloidal synthesis of Au0.80Pd0.20-FexOy dumbbell NCs derived from Au0.75Pd0.25 NCs by metal oxide overgrowth. We compared the catalytic activity of the two types of NCs in the CO oxidation reaction (CO+1/2O2CO2), after they had been dispersed on an alumina nanopowder support. In both cases, the surface active sites were identified by means of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The enhanced catalytic performance of the dumbbell NCs (Au0.80Pd0.20-FexOy) catalyst over that of the initial Au0.75Pd0.25 NCs could be correlated to the presence of the epitaxial connection between the FexOy and the Au80Pd20domains (as the main factor). Such connection should result in an electron flow from the metal oxide (FexOy) domain to the noble metal (Au0.80Pd0.20) domain and appears to influence favorably the nature and composition of the catalytically active surface sites of the dumbbells. Our experiments indicate indeed that, when the metal alloy domain is attached to the metal oxide domain (that is, in the dumbbell) surface Pd species are more active than in the case of the initial Au0.75Pd0.25 NCs and also Auδ- sites are formed that were not present on the initial Au0.75Pd0.25 NCs.Nano Letters 01/2013; · 13.20 Impact Factor -
Article: Influence of organic solvent on optical and structural properties of ultra-small silicon dots synthesized by UV laser ablation in liquid.
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ABSTRACT: Ultra small silicon nanoparticles (Si-NPs) with narrow size distribution are prepared in a one step process by UV picosecond laser ablation of silicon bulk in liquid. Characterization by electron microscopy and absorption spectroscopy proves Si-NPs generation with an average size of 2 nm resulting from an in situ photofragmentation effect. In this context, the current work aims to explore the liquid medium (water and toluene) effect on the Si-NPs structure and on the optical properties of the colloidal solution. Si-NPs with high pressure structure (s.g. Fm3m) and diamond-like structure (s.g. Fd3m), in water, and SiC moissanite 3C phase (s.g. F4[combining macron]3m) in toluene are revealed by the means of High-Resolution TEM and HAADF-STEM measurements. Optical investigations show that water-synthesized Si-NPs have blue-green photoluminescence emission characterized by signal modulation at a frequency of 673 cm(-1) related to electron-phonon coupling. The synthesis in toluene leads to generation of Si-NPs embedded in the graphitic carbon-polymer composite which has intrinsic optical properties at the origin of the optical absorption and luminescence of the obtained colloidal solution.Physical Chemistry Chemical Physics 10/2012; 14(44):15406-11. · 3.57 Impact Factor -
Article: The Big Impact of a Small Detail: Cobalt Nanocrystal Polymorphism as a Result of Precursor Addition Rate during Stock Solution Preparation.
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ABSTRACT: The control of nanocrystal structures at will is still a challenge, despite the recent progress of colloidal synthetic procedures. It is common knowledge that even small modifications of the reaction parameters during synthesis can alter the characteristics of the resulting nano-objects. In this work we report an unexpected factor which determines the structure of cobalt nanoparticles. Nanocrystals of distinctly different sizes and shapes have resulted from stock solutions containing exactly the same concentrations of [Co{N(SiMe(3))(2)}(2)(thf)], hexadecylamine, and lauric acid. The reduction reaction itself has been performed under identical conditions. In an effort to explain these differences and to analyze the reaction components and any molecular intermediates, we have discovered that the rate at which the cobalt precursor is added to the ligand solution during the stock solution preparation at room temperature becomes determinant by triggering off a nonanticipated side reaction which consumes part of the lauric acid, the main stabilizing ligand, transforming it to a silyl ester. Thus, an innocent mixing, apparently not related to the main reaction which produces the nanoparticles, becomes the parameter which in fine defines nanocrystal characteristics. This side reaction affects in a similar way the morphology of iron nanoparticles prepared from an analogous iron precursor and the same long chain stabilizing ligands. Side reactions are potentially operational in a great number of systems yielding nanocrystals, despite the fact that they are very rarely mentioned in the literature.Journal of the American Chemical Society 10/2012; · 9.91 Impact Factor
