Dario Buso

Nanostructured sol–gel silica thin films doped with NiO and SnO2 for gas sensing applications

Nanoporous SiO2 thin films containing different functional oxide nanoparticles (NiO, SnO2) have been synthesized by sol–gel methods and the gas response to H2, CO and humidity has been determined by volt amperometric techniques. The structure development of the nanocomposite films has been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy and secondary ion mass spectrometry (SIMS). Films of molar composition 60SiO2–40NiO and 60SiO2–40SnO2 showed homogeneously dispersed round shaped oxide nanocrystals of 3–4 nm mean diameter. The gas response of films deposited on Si/Si3N4 substrates provided with Pt interdigital electrodes has been measured at different operating temperatures ranging from 25 to 350 °C and gas concentrations between 10 and 1000 ppm. NiO and SnO2 nanocomposite films have shown a p-type and n-type response, respectively, with greater sensitivity to H2 gas than CO in the whole range of the investigated operating temperatures.

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.

Rapid Detection of Hendra Virus Using Magnetic Particles and Quantum Dots

A proof-of-concept for the development of a fast and portable Hendra virus biosensor is presented. Hendra virus, a deadly emerging pathogen in Australia, can be co-localized, concentrated and revealed using simultaneously magnetic and luminescent functional particles. This method should be applicable for the early detection of any other virus by targeting the specific virus with the corresponding antibody.

Study of 3D composition in a nanoscale sample using data-constrained modelling and multi-energy x-ray CT

Submicrometre x-ray computed tomography (CT), referred to as x-ray nanotomography, is a research area attracting much attention nowadays. The major limiting factors in observing compositional structures and features below the micrometre scale are signal-to-noise ratio and loss of information below the x-ray detector pixel size. Conventional image segmentation techniques, such as image thresholding, are not usually sufficient for accurately resolving such microscopic compositional distributions. In this work we carried out multi-energy x-ray CT simulations on a computer generated sample of nanoporous alumina with gold nanoparticles incorporated inside some of the pores. The multi-energy CT data sets served as inputs to our in-house developed data-constrained microstructure (DCM) modelling software, which can accurately predict the 3D chemical composition of a sample from CT data. Different levels of x-ray detector noise were also added to the CT simulations and the DCM chemical phase predictions were analysed under these conditions. The pixel resolution was 15 nm, and the x-ray projection images were re-sampled to lower resolutions to simulate the effect of features smaller than the CT pixel resolution. We found that despite the simulated sample having constituents that possess vastly different x-ray absorption properties, with one constituent having a total linear absorption coefficient up to two orders of magnitude greater than the other, the DCM showed a clear advantage over image thresholding, particularly in the presence of noise.

Simultaneous microfabrication and tuning of the permselective properties in microporous polymers using X-ray lithography.

Microchannels are fabricated using a photosensitive polymer to which microporosity is tuned with different X-ray doses. Using hard X-ray irradiation, the micropattern is positioned with various geometries in a multi-level, three-dimensional structure, while controlling the pore size and transport properties of small molecules. This highly reliable fabrication process has potential for use in microfluidic devices with enhanced transport properties through microchannels.

Gold/titania nanocomposites thin films for optical gas sensing devices

Nanostructured TiO2 films and Au-TiO2 nanocomposite thin films prepared by sol-gel method have been deposited onto gold covered glass substrates and glass substrates in order to study their optical properties using Surface Plasmon Resonance and Optical Absorption measurements. Both techniques have been used to study the sensing features of both kind of films to different vapour organic compounds. A comparative study of the two techniques has allowed us to know the possible benefits than can be found when the sensing material is a nanocomposite thin film.

Different sensing layers for SPR sensing of organic vapours

In this work we present a theoretical and experimental work due to develop a performing configuration for gas-sensing through the employ of Surface Plasmon Resonance effect. Different sensing layers have been studied and tested on our optical bench assembly. Metallic (Au) and bimetallic (Ag/Au) layers have been properly designed through simulations and then have been realized through electron-beam evaporation. TiO2 and TiO2 - Au doped layers have been deposited on the top of some of the metallic samples. These layers were prepared by the sol gel route. This kind of material is expected to be suitable as a gas sensor for its nanosized structure and its stability. The optical bench configuration for the experimental exploitation of SPR is presented. It is based on a collimated beam, a rotational stage with a triangular prism and a single photodiode. Finally the sensing properties of the different sensing layers prepared was tested to some organic vapours. Preliminary results are presented.

Two-photon absorption in direct bandgap semiconductors quantum dots

We present degenerate and nondegenerate two-photon absorption spectra in a series of CdSe and CdTe quantum dots. The measurements show that the two-photon absorption (2PA) spectrum is strongly dependent on the quantum dot size and that the 2PA coefficient decreases as the quantum dot size decreases, and it is larger for the frequency nondegenerate process. Previously we had shown a theoretical analysis of these results based on a simple model using the effective mass approximation. Although this model works well for larger quantum dots, it fails for the smaller ones. Here we use the more (formula available in manuscript) model for the band structure and consider the hole band mixing in quantum dots to describe our data. This theory better describes the spectral structures for smaller quantum dots and also predicts the decrease of the 2PA coefficient with the decrease of quantum dot size. This is due to the reduction of the number of possible transitions and the blue shift of the optical bandgap from quantum confinement. This theory predicts the reduction of the 2PA coefficient with size, although our experimental results show an even stronger reduction.