356 research outputs found
Il Tesoro della confraternita della Madonna del Rifugio
No full textsuppellettili liturgiche e parati sacri della confraternita della Madonna del Rifugio di Polizzi Generos
Laser Ablation: An Easy Route To Obtain Gold And Silver Nanomaterials
No full textGold and silver nanoparticles (AuNP and AgNP) have a very important role in nanotechnolgy and nanoscience, due to their physical, chemical and biochemical properties. We produced colloidal solution of Au and Ag nanoparticles in a fast and inexpensive way by laser ablation of the bulk metals in a liquid buffer using the 1064 nm line of a Q -switched Nd – YAG laser. On one hand these solutions are stable without any external chemical reagent, so nanoparticles can be obtained free in solution. On the other hand we succesfully performed the laser ablation synthesis (LAS) in water and in organic solvents, so it is possible to functionalize these particles during as well as after the LAS, simply solubilizing the ligands in the appropriate solvent.[1,2] Furthermore we found that in toluene, LAS of AuNP produces a graphite – gold nanocomposite. The graphitic matrix determined the quenching of the characteristic surface plasmon absorption (SPA) of the AuNP, that can be restored by the matrix removal.[3]
The characterization of AuNP and AgNP solutions is easily achieved by UV – vis spectroscopy using the Mie Theory to fit the SPA. For free particles in solution we conveniently fitted the SPA with the Mie Model for compact spheres and the Gans model for spheroids. We verified that one can account for the isolated nanoparticles fraction using the Mie model for simple spheres and for the aggregated nanoparticles fraction using the Gans model for spheroids.[2] In the case of the graphite – AuNP composite we reproduced the SPA quenching using the Mie model extension for core@shell particles.[3] HRTEM images confirmed the results obtained with the UV-vis spectroscopy.
Finally we were able to obtain a certain control on the average size and aggregation of nanoparticles by laser treatment at 532 nm of AuNP solution.
[1] V. Amendola, G. Mattei, C. Cusan, M. Prato and M. Meneghetti; Synthetic Metals 2005; 155; 283–286
[2] Vincenzo Amendola, Stefano Polizzi and Moreno Meneghetti; J Phys Chem B 2006; 110; 7232-7237
[3] Vincenzo Amendola, Gian Andrea Rizzi, Stefano Polizzi and Moreno Meneghetti; J Phys Chem B 2005; 109; 23125-2312
Strong dependence of surface plasmon resonance and surface enhanced Raman scattering on the composition of Au–Fe nanoalloys
No full textNanoalloys of noble metals with transition metals are crucial components for the integration of plasmonics with magnetic and catalytic properties, as well as for the production of low-cost photonic devices. However, due to synthetic challenges in the realization of nanoscale solid solutions of noble metals and transition metals, very little is known about the composition dependence of plasmonic response in nanoalloys. Here we demonstrate for the first time that the elemental composition of Au–Fe nanoalloys obtained by laser ablation in liquid solution can be tuned by varying the liquid environment. Due to surface passivation and reaction with thiolated ligands, the nanoalloys obtained by our synthetic protocol are structurally and colloidally stable. Hence, we studied the dependence of the surface plasmon resonance (SPR) on the iron fraction and, for the first time, we observed surface enhanced Raman scattering (SERS) in Au–Fe nanoalloys. SPR and SERS performances are strongly affected by the iron content and are investigated using analytical and numerical models. By demonstrating the strong modification of plasmonic properties on the composition, our results provide important insights into the exploitation of Au–Fe nanoalloys in photonics, nanomedicine, magneto-plasmonic and plasmon-enhanced catalysis. Moreover, our findings show that several other plasmonic materials exist beyond gold and silver nanostructures
Laser Ablation Synthesis of Silver Nanoparticles Embedded in Graphitic Carbon Matrix
No full textWe obtained a nanocomposite of silver nanoparticles embedded in a graphitic carbon matrix by laser ablation of an Ag plate in toluene solution. The AgNP nanocomposite has been characterized by UV–vis spectroscopy, micro–Raman spectroscopy and HRTEM analysis. AgNP surface plasmon resonance (SPR) is quenched by the carbon matrix, but it can be easily restored by thermal oxidation in air of the matrix. The synthesis procedure is very fast and easy and the matrix prevents AgNP aggregation and growth. The solid nanocomposite can be obtained either as a film or as a bulk sample simply by evaporating the solvent. This technique can be easily adopted for several types of metals
Magnetic tuning of SERS hot spots in polymer-coated magnetic–plasmonic iron–silver nanoparticles
No full textPlasmonic nanostructures are intensively studied for their ability to create electromagnetic hot spots, where
a great variety of optical and spectroscopic processes can be amplified. Understanding how to control the
formation of hot spots in a dynamic and reversible way is crucial to further expand the panorama of plasmon
enhanced phenomena. In this work, we investigate the ability to modulate the hot spots in magnetic–
plasmonic iron-doped silver nanoparticles dispersed in aqueous solution, by applying an external
magnetic field. Evidence of magnetic field induction of hot spots was achieved by measuring the
amplification of surface enhanced Raman scattering (SERS) from analytes dispersed in the solution
containing Ag–Fe NPs. A polymeric shell was introduced around Ag–Fe NPs to confer colloidal stability,
and it was found that the length and density of the polymer chains have a significant influence on SERS
performance, and therefore on the formation of electromagnetic hot spots, under the action of the
external magnetic field. These findings are expected to provide an important contribution to
understanding the growing field of tuneable electromagnetic enhancement by external stimuli, such as
magnetic fields applied to magnetic–plasmonic nanoparticles
Complete sets of factors for absorption correction and air scattering subtraction in X-ray powder diffraction of loosely packed samples
No full textLa scienza dei materiali a scuola: un'azione didattica in collaborazione tra scuola e università
No full textApplication of Fitting Techniques to the Warren-Averbach Method for X-ray Line Broadening Analysis
No full textA method for fitting X-ray line profiles has been devised for application to line broadening analysis. The approximation of the profile by pseudo-Voigt functions (sum of Lorentz and Gauss terms of equal width) has been explored in different cases which frequently occur in the characteriza-tion of materials by X-ray diffraction. It has been found that such an approximation is able to give satisfactory fittings of experimental data even in cases with severe overlapping of very broadened peaks. The procedure allows peak Separation and application of the Warren-Averbach method for determining crystallite size and strain, in cases that could not be considered meaningful before. The corrected Fourier coefficients are free from “hook” effect and allow determination of physical parameters within the ränge of information content of experimental data. © 1985, R. Oldenbourg Verlag. All rights reserved
Polydisperse Analysis of Absolute Small Angle Intensities scattered by Activated Carbons
No full textThe absolute small-angle x-ray intensities, scattered by two activated carbons, are analyzed assuming that coals scatter as polydisperse distributions of uncorrelated layered cubic particles. The specific interphase surface areas and the densities of the samples are obtained by the particle populations resulting from the intensity best-fits. The values agree, within a factor two, with those obtained by different experimental techniques
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