Chiara Manfredotti

Effect of thermal treatments on sputtered silver nanocluster/silica composite coatings on soda- lime glasses: ionic exchange and antibacterial activity

Silver nanocluster/silica composite coatings were deposited on both soda-lime and silica glasses by radio frequency (RF) co-sputtering. The effect of thermal treatments on the microstructure in the range of 150–450xa0°C were examined by UV–visible spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Time of Flight-Elastic Recoil Detection Analysis. Sodium/silver ionic exchange was evidenced for coatings sputtered on soda-lime substrates after heating at 450xa0°C; presence of silver ions and/or silver nanoclusters, nanocluster size and their position inside the sputtered layers will be discussed for as-deposited and heated coatings on both substrates. The antibacterial activity of all coatings was determined against Staphylococcus aureus and Candida albicans by disk diffusion method and colonies forming units count; in agreement with microstructural results, the antibacterial activity present on all coatings was slightly reduced after heating at 450xa0°C. All coatings have been submitted to humidity plus UV ageing and sterilization by autoclave, gamma ray and ethylene oxide gas. Tape resistance (ASTM D3359-97) tests have been done on each coating before and after ageing and sterilizations, revealing a good adhesion on soda-lime substrates, except for those aged in humidity plus UV and sterilized by autoclave. Scratch tests and nanoindentation tests have been done on each coating, as-deposited and after heating at 450xa0°C. The coating hardness was improved by heating only when coatings were deposited on silica. The heating of coatings deposited on soda-lime substrates gave opposite effect on their hardness.

Silver Nanocluster/Silica Composite Coatings Obtained by Sputtering for Antibacterial Applications

Silver nanocluster silica composite coatings were deposited by radio frequency co-sputtering technique on several substrates. This versatile method allows tailoring of silver content and antibacterial behaviour of coatings deposited on glasses, ceramics, metals and polymers for several applications. Coating morphology and composition as well as nanocluster size were analyzed by means of UV-Visible absorption, X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), electron dispersive spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM). The antibacterial effect was verified through the inhibition halo test against standard bacterial strain, Staphylococcus aureus, before and after sterilization process. Tape test demonstrated a good adhesion of the coatings to the substrates.

Supported Rhodium Nanoparticles in Catalysis: the role of stabilizers on catalytic activity and structural features

Abstract Rhodium nanoparticles supported on γ-Al 2 O 3 , derived from arene-solvated Rh atoms stabilized by trioctylamine (TOA), are valuable catalysts in hydrogenation and silylformylation reactions. They are largely more active than the analogous commercial catalyst, as well as of a sample similarly prepared in the absence of TOA. HRTEM measurements, IR studies on adsorbed CO species and extended X-ray absorption fine structure analyses evidenced the role of TOA in controlling the particle growth in the preparative process and in stabilizing the resulting Rh particles against erosion by CO and oxidation.

Synchrotron study of oxygen depletion in a Bi-2212 whisker annealed at 363 K

Direct evidence is reported of structural and electronic effects induced on a single Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi-2212) whisker during a progressive annealing process. The crystal was investigated by micro X-ray diffraction (micro-XRD), micro X-ray fluorescence and electrical characterization at the European Synchrotron Radiation Facility, during a series of three in situ thermal processes at 363 K. Each step increased the sample resistivity and decreased its critical temperature, up to a semiconducting behaviour. These data correlate with micro-XRD analysis, which shows an increase of the c-axis parameter from 30.56 A to 30.75 A, indicating an oxygen depletion mechanism. Mild temperature annealing could be an effective process to modulate the intrinsic Josephson junctions characteristics in Bi-2212 whiskers.

Tailoring and stabilization of ultrafine rhodium nanoparticles on γ-Al2O3 by troctylamine: Dependence of the surface properties on the preparation route

Abstract Rhodium nanoparticles supported on γ-AI2O3 have been prepared by Metal Vapour Synthesis (MVS), using mesitylene solvated Rh atoms as starting material and working in the absence and in the presence of trioctylamine (TOA), as stabilizer. The size and surface features of the metal particles have been studied by Transmission Electron Microscopy (TEM) and by FT-IR spectroscopy of adsorbed carbon monoxide, and they have been compared with those of a commercial Rh/γ-AI2O3 sample. The results indicated that by MVS technique nanoparticles significantly smaller in size and with a narrower size distribution than those present on the commercial sample were produced. The addition of TOA during the MVS process resulted in a further decrease in the metal particle size. IR spectra of adsorbed CO indicated that metal particles produced via MVS expose at their surface a larger fraction of Rh atoms in low coordination. They can be extracted by CO, forming volatile Rh carbonyls which migrate onto the support, where the metal atoms are oxidised to Rh(I). For Rh particles produced via MVS in the presence of TOA, such low coordinated sites appeared stabilised by adsorbed amine molecules.

Imaging at the Nanoscale: Scanning Probe Microscopies Applied to Semiconductors

The aim of this chapter is to give an overlook of the various possibilities given by scanning probe microscopy (SPM) techniques for the characterization of semiconducting nanostructures and heterostructures. A scanning probe microscope is a lensless microscope, probing the surface using the force or the tunneling current exerted between a tip and a sample surface brought in close proximity to each other. In the following paragraphs, the basics of scanning tunneling microscopy, atomic force microscopy, electrostatic force microscopy, Kelvin probe force microscopy and conductive AFM will be introduced, with the aim at giving at least a glimpse of the many different possibilities they offer for the investigation of nanostructures and heterostructures. Moreover, the key factors that must be taken into account in order to extract as much information as possible from these techniques, avoiding misinterpretation and artifacts, will be discussed. In the end, some examples of characterization of surfaces and devices will be presented.