Valentina Bello

Ultrasmall Iron Oxide Nanoparticles for Biomedical Applications: Improving the Colloidal and Magnetic Properties

A considerable increase in the saturation magnetization, M(s) (40%), and initial susceptibility of ultrasmall (<5 nm) iron oxide nanoparticles prepared by laser pyrolysis was obtained through an optimized acid treatment. Moreover, a significant enhancement in the colloidal properties, such as smaller aggregate sizes in aqueous media and increased surface charge densities, was found after this chemical protocol. The results are consistent with a reduction in nanoparticle surface disorder induced by a dissolution-recrystallization mechanism.

Colloidal approach to Au-loaded TiO2 thin films with optimized optical sensing properties

TiO2 and Au nanoparticles are synthesized by the colloidal technique and used for nanocomposite thin film preparation. The effect of thermal treatment and organic template presence is analyzed in order to tailor film microstructure. The Au-TiO2 interfaces as well as the overall porosity of the films are analyzed combining structural and morphological characterization along with spectroscopic ellipsometry and surface plasmon spectroscopy analyses. An efficient surrounding of TiO2 nanoparticles around Au colloids is obtained, leading to an extensive noble metal–metal oxide interface, improving functional properties of the films, while keeping a porous structure. Gas sensing tests are performed on these nanocomposites films: reversible sensing dynamics for CO detection are observed with high sensitivity and a correlation between response and recovery times and microstructure is reported.

Self-assembled gold nanoparticle monolayers in sol-gel matrices: synthesis and gas sensing applications

Gold nanoparticle monolayers have been deposited on amino-functionalized commercial glass and on sol–gel glass surfaces using a fast chemisorption protocol. The nanoparticle surface coverage could be tuned by varying the deposition conditions. The nanoparticle monolayers have been embedded into SiO2 sol–gel matrices to study the feasibility of this approach for the engineering of sol–gel based nano-composites. The same approach has been used for obtaining Au–NiO multilayer films which showed a reversible absorbance change when exposed to CO (100–10000 ppm) at 300 °C operating temperature.

Selective optical detection of H2 and CO with SiO2 sol–gel films containing NiO and Au nanoparticles

NiO is a p-type semiconductor widely studied for its promising implementation in chemo-optical gas sensors. Reducing/oxidizing gases induce a change in optical absorption of NiO. It has been found that Au doping induces a remarkable increase in the NiO sensitivity, and at the same time silica films obtained by the sol?gel technique have been demonstrated to be a suitable support matrix for gas-sensitive materials due to their extremely high specific surface area (up to 600?m2?g?1). The aim of this work is the synthesis of SiO2 films containing both NiO and Au nanoparticles and their morphological and functional characterization as active gas-sensing materials suitable for optical detectors. The possibility to selectively recognize H2 and CO is studied exploiting the wavelength dependence of the gas-induced optical transmittance variation.

Thermal-induced phase transitions in self-assembled mesostructured films studied by small-angle X-ray scattering

Two examples of phase transition in self-assembled mesostructured hybrid thin films are reported. The materials have been synthesized using tetraethoxysilane as the silica source hydrolyzed with or without the addition of methyltriethoxysilane. The combined use of transmission electron microscopy, small-angle X-ray scattering and computer simulation has been introduced to achieve a clear identification of the organized phases. A structural study of the self-assembled mesophases as a function of thermal treatment has allowed the overall phase transition to be followed. The initial symmetries of mesophases in as-deposited films have been linked to those observed in samples after thermal treatment. The monodimensional shrinkage of silica films during calcination has induced a phase transition from face-centered orthorhombic to body-centered cubic. In hybrid films, instead, the phase transition has not involved a change in the unit cell but a contraction of the cell parameter normal to the substrate.

Femtosecond nonlinear absorption of gold nanoshells at surface plasmon resonance

The nonlinear optical absorption of gold nanoshells (Au NSs) of different size, in water, was investigated using open aperture z-scan technique with femtosecond laser pulses at 806 nm. It is found that, in general, NSs behave as saturable absorbers. The level of saturation depends on the Au NSs structure and precisely on the ratio between the core size and shell thickness. The measured values of the nonlinear absorption coefficient show a dependence on both the repetition rate and the pulse energy. An average value of the nonlinear absorption coefficient β = -4.5 ± 1.0 × 10(-11) cm W(-1) is obtained from z-scan data of core-shell particles of inner and outer radius 95 and 110 nm, respectively, measured at 20 Hz repetition rate in the energy range 120-300 nJ.

Iridium/silicon multilayers for extreme ultraviolet applications in the 20-35 nm wavelength range.

We have developed an Ir/Si multilayer for extreme ultraviolet (EUV) applications. Normal incidence reflectance measurements of a prototype film tuned to 30 nm wavelength show superior performance relative to a conventional Mo/Si multilayer structure; we also find good stability over time. Transmission electron microscopy and electron dispersive x-ray spectroscopy have been used to examine the microstructure and interface properties of this system: we find amorphous Si layers and polycrystalline Ir layers, with asymmetric interlayer regions of mixed composition. Potential applications of Ir/Si multilayers include instrumentation for solar physics and laboratory EUV beam manipulation.

Size-dependent oxidation in ZnO nanoparticles embedded in ion-implanted silica

ZnO–SiO2 nanocomposites were synthesized by ion implanting a Zn+ beam in a silica slide and by annealing in oxidizing atmosphere at 800 °C. A detailed structural and optical characterization was performed by using glancing incidence x-ray diffraction, transmission electron microscopy combined with selected area electron diffraction and energy dispersive spectrometry, optical absorption, and photoluminescence spectroscopies. Samples obtained with three different Zn+ fluences in the range 1–2×1017 ions/cm2 have been investigated. According to the results, Zn crystalline nanoparticles were found in the as-implanted Zn–SiO2 samples. The size of the Zn nanoparticles was proportional to the implantation fluence. The annealing in oxidizing atmosphere promotes the total oxidation of the Zn nanoparticles with a preferential migration of the nanoparticles toward the surface of the sample along with an opposite and less pronounced diffusion toward the bulk of the matrix. A relatively strong excitonic peak from the Z...

De-alloying behaviour of metal nanoclusters in SiO2 upon irradiation and thermal treatments

Abstract Bimetallic Au–Cu and Au–Ag nanometer sized clusters obtained by sequential ion implantation in silica have an elemental selective de-alloying process upon thermal annealing in oxidizing atmosphere or irradiation with smaller atomic mass ions. In the case of Au–Cu alloy, the first process promotes preferentially copper extraction due to the chemical interaction (oxidation) with the incoming oxygen atoms. Irradiation with light ions promotes on the contrary a preferential extraction of gold from the alloy (either Au–Cu or Au–Ag), resulting in the formation of Au-enriched ‘satellites’ nanoparticles around the original cluster.

Transmission Electron Microscopy of Lipid Vesicles for Drug Delivery: Comparison between Positive and Negative Staining

Lipid-containing nanostructures, in the form of solid lipid nanoparticles or iron oxide nanoparticles (NPs) coated with a lipid shell, were used as case studies for assessing and optimizing staining for transmission electron microscopy structural and compositional characterization. These systems are of paramount importance as drug delivery systems or as bio-compatible contrast agents. In particular, we have treated the systems with a negative (phospshotungstic acid) or with a positive (osmium tetroxide) staining agent. For iron-oxide NPs coated with the lipid shell, negative staining was more efficient with respect to the positive one. Nevertheless, in particular cases the combination of the two staining procedures provided more complete morphological and compositional characterization of the particles.