Luisa D'Urso

Formation and characterization of high-density silver nanoparticles embedded in silica thin films by “ in situ ” self-reduction

Silver nanoparticles (10–20 nm) embedded into silica thin films have been obtained through the use of a silver organometallic precursor compound dissolved in Spin-On-Glass and subsequently spinned onto suitable substrates. In this paper we present a study of the shape, size, and distribution of silver particles through the use of microscopes, x-ray diffraction, and optical extinction. It has been observed that the obtained films are stable for annealing up to 500 °C with a progressive degradation above this temperature. Furthermore it is possible to obtain high-density silver particles up to 15% in weight without affecting the cluster size and shape.

Characterization of Graphene Nanoribbons from the Unzipping of MWCNTs

Graphene nanoribbons were obtained by oxidative unzipping reaction conducted on multi-walled carbon nanotubes (MWCNTs). The oxidized and reduced nanoribbons (after treatment with hydrazine) were characterized by FT-IR and Raman spectroscopy. Graphite oxide was used as reference material in FT-IR and highly oriented pyrolytic graphite was used as reference in the Raman study. The transmission electron microscopy (TEM) of the nanoribbons both in oxidized and reduced form show beautiful images confirming the single graphene structure of the nanoribbons. When heated in a thermobalance at 10°C/min under N2, the oxidized nanoribbons undergo an explosive decomposition at 152°C with formation of a fluffy carbon soot whose FT-IR spectrum is analogous to that of the hydrazine reduced nanoribbons.

Structure and properties of silver nanoparticles dispersed in SiO2 thin films obtained by in situ self-reduction

Abstract Recently, silver nanoparticles (10–15 nm) embedded into silica thin films have been obtained in our laboratory by in situ reduction of a suitable silver organometallic compound (precursor) dissolved in a spin-on-glass (SOG) solution and subsequently span onto a substrate. Here, we present a study of the spatial distribution of these nanoparticles as a function of deposition and post-deposition parameters by using atomic force microscopy (AFM). We find that the distribution of the Ag particles is strongly dependent on the aging of the precursor–polymer blend obtained after the spin coating procedure, giving a uniform spatial distribution only with thermal annealing performed after several hours from the organometallic–polymer blend deposition.

Size distribution and particle shape in silver colloids prepared by laser ablation in water

We have produced silver colloids by ablating metal targets in water and using two different laser wavelengths. The obtained sols have been characterized by optical spectroscopy and electron microscopy, revealing a definite double size distribution centered at a few tens and a few hundreds of nanometers with a mild difference between the two wavelengths employed. On the contrary, a marked difference in shape has been found for the biggest aggregates, revealing sharp cubic or octahedral structures when visible or infrared radiations are used, respectively. This fact is explained by the re-irradiation processes induced on the already formed colloid and taking place during the ablation.

Aggregation Phenomena and Electromagnetic Amplification Properties in Silver Nanoparticles Joined Through Highly Conjugated Carbon Chains

Silver colloids prepared by laser ablation in water have been linked using sp-hybridized carbon chains thus obtaining a plasmonic transfer between the metallic nanoparticles. It has been found that the state of the metallic surface is of fundamental importance for the plasmonic transfer. The role of the carbon �- electron system has been considered in order to justify the electromagnetic field amplification and the observed surface enhanced Raman signals. These findings open the possibility to control the electronic transfer between different metallic nanostructures for the application in future plasmonic devices.

Adsorption of Dinitrogen Tetroxide (N2O4) on Multi‐walled Carbon Nanotubes (MWCNTs)

Abstract The adsorption of dinitrogen tetroxide (N2O4) on multi‐walled carbon nanotubes (MWCNTs) has been studied by FT‐IR, Raman and X‐ray photoelectron spectroscopy (XPS). The N2O4 adsorption is fully reversible, and after the desorption there is no evidences of MWCNTs nitration. Instead, the MWCNTs have been found oxidized by the action of N2O4. By thermogravimetric analysis (TGA) about 5% by weight of oxygenated groups have been found. Thermal analysis has revealed that MWCNTs having a surface area of 275 m2/g are able to reversibly adsorb about 25% by weight of N2O4, a value comparable to that observed for certain active carbons.

The effect of polymer molecular weight on the formation and evolution of silver-polymer nanocomposite thin films

Abstract Silver-poly(methyl methacrylate) nanocomposite thin films (0.1–1 μm) have been obtained by in situ self-reduction of an organometallic compound formerly embedded in the polymer structure. The reduction has been obtained through thermal treatments, leading to the formation of Ag particles in the size range 5–50 nm, homogeneously dispersed in the film structure. Nearly monodisperse polymer macromolecules have been used to study the effect of polymer molecular weight (MW) on the formation and evolution of particles. It was found that changes in the polymer molecular weight produce different average particle size which drive the film properties.

Degradation of Assembled Silicon Nanostructured Thin Films: a Theoretical and Experimental Study

The study of the structures and properties of small elemental clusters has been an extremely active area of current research, due to the peculiar behavior of these species halfway between that of single atoms and of the bulk phase. In this work silicon nanoclusters are generated by ablation of a high purity polycrystalline rod with a pulsed laser vaporization source and then deposited on a support. Their structure is studied both in the gas phase by means of Time of Flight Mass Spectrometry and in the solid phase through in situ Raman and Infrared Spectroscopy. The spectra reveal that the as deposited clusters are hydrogenated with negligible amount of oxide. Degradation of silicon nanoclusters has been studied after gas exposure. In the gas of air a consistent modification was observed, leading to a near-infrared luminescent silicon nanoparticles. In the second part of the work, density functional theory is applied to investigate the geometrical structure of silicon clusters and their interaction, in term of structure and energy, with different gases. The calculations were performed with the Gaussian 03 program suite, adopting the B3LYP functional to calculate the exchange and correlation energy. Si 8 has been chosen as model cluster to study the degradation of silicon clusters both kinetically and thermodynamically, in order to explain the experimental evidences. Experimental and calculated infrared spectra are compared.