Sol-Gel Films containing Metal and Semiconductor Nanoparticles for Gas Sensing

Nanotechnology is an exciting modern research field encompassing the traditionally specialist disciplines of chemistry, physics and engineering. Optics and catalysis are two areas of application that will continue to benefit from the recent improvements in control of materials morphology at the nano-scale. The work presented in this thesis is focussed on the application of the Sol-Gel technique in the realization of thin inorganic layers containing metal and semiconductor nanoparticles that are capable of reversibly of detecting gas phase analytes. Three synthetic approaches were adopted, each of them characterized by a systematic increase of the final materials morphology, structure and micro-structure control. This materials engineering was essential in order for nanocomposites with the desired optical and chemical properties applicable to gas sensing devices to be obtained. The synthesized layers comprised of an inorganic porous matrix (SiO2, TiO2 and NiO) containing nanosized metal (Au, Pt) or semiconductor crystals (NiO), and were shown to be active materials for chemical recognition of H2 and CO. The films were readily deposited onto different sensing supports, leading to successful gas detection via optical, conductometric and surface acoustic wave interfaces. SiO2-NiO-Au systems are capable to selectively detect H2 using an optical interface thanks to a marked wavelength dependence of its sensitivity toward this specie. However, if a peculiar NiO-Au morphology is obtained inside the SiO2 support CO is more likely to be detected. TiO2-Au thin films are shown to be excellent conductometric sensors for H2 detection, and ideal gas-sensing dynamics have been observed in this case. This class of layers demonstrated to be effective also for H2 detection through a Surface Acoustic Wave (SAW) interface. Monolayers of Au nanoparticles covered by a thin NiO layer showed promising sensing dynamics in the optical recognition of H2. In this case the material synthesis allows for a detailed control of the single nanocomposite constituents, thus opening the possibility for a finer tuning of the sensor sensitivity

Gold nanoparticles to boost the gas sensing performance of porous sol\u2013gel thin films

In this paper we review our research work of the last few years on the synthesis and the gas sensing properties of nanocomposite thin films of sensitive materials with a large specific surface area, which consist of porous matrices containing functional nanocrystals of metal oxides and gold. The film porosity provides a path for the gas molecules to reach the active reaction sites on the nanoparticles surface undergoing chemical reactions which nature depends on the nature of the active material. The introduction of Au nanoparticles affects the reactions mechanism improving the sensing process, moreover the Au Surface Plasmon Resonance peak can be used for the realization of selective optical gas sensor. Two different synthetic approaches will be described, each of them characterized by a peculiar control of the final materials morphology, structure and micro-structure

Photonic band gap tuning through chalcogenide glass coating

Abstract not available

Nonlinear nanocomposites for three-dimensional photonic crystals using two-photon polymerization

We developed a novel nanocomposite consisting of an organic-inorganic hybrid polymer modified with PbS quantum dots. The uniformally dispersed nanocomposite has high third-order nonlinearity and has been proven to be suitable for photonic crystal fabrication

Active three-dimensional photonic crystals with high third-order nonlinearity in telecommunication

We developed a novel nanocomposite consisting of an organic-inorganic hybrid polymer modified with near-infrared emitting core-shell quantum dots. The composite has both high third-order nonlinearity and a high quantum efficiency and is suitable for photonic crystal fabrication

Engineering the refractive index of three-dimensional photonic crystals through multilayer deposition of CdS films

Woodpile photonic crystals are amongst the preferred candidates for the next generation of photonics components. However, the photocurable resists used to produce them still lack the optical properties (high-n, non-linearity) suitable for photonics applications. A chemical bath deposition protocol has been adapted to deposit high-n/non-linear chalcogenide CdS on the surface of Ormocer® woodpiles. The deposition parameters have been adjusted to obtain heterogeneous growth of CdS layers on the Ormocer® surface. The layers shift the photonic band-gap and increase its amplitude by more than 15%. Software simulation confirmed that the woodpile effective refractive index underwent an excess of 30% increase

Optical and conductometric gas sensing properties of sol-gel TiO2 films doped with Au nanoparticles

TiO2 sol-gel films have been doped with colloidal gold nanoparticles (NPs) and used as a platform for optical and conductometric gas sensors for CO and H2 detection. Optical gas sensors of this type require an operating temperature above 300 \ub0C. Measurements performed at 360 \ub0C showed a reversible gas-induced variation of absorption spectra for both CO and H2. The variation in absorbance depends on testing wavelength and film annealing temperature. Conductometric gas sensors showed excellent performances toward H2 detection with a dynamic response close to ideal

Erratum: 'Engineering the refractive index of three-dimensional photonic crystals through multilayer deposition of CdS films'

Corrects an error in Buso, D., Nicoletti, E., Li, J. and Min, G. (2010). Engineering the refractive index of three-dimensional photonic crystals through multilayer deposition of CdS films. Optics Express, 18 (2), pp. 1033-1040. For the original article, see: http://hdl.handle.net/1959.3/76702

Tuning the band gap of photonic crystals through optical-quality chalcogenide glass coating

Abstract not available

Gold nanoparticle-doped TiO\u2082 semiconductor thin films : Gas sensing properties

TiO\u2082 sol\u2013gel films doped with gold nanoparticles are used as both optical and conductometric sensors for the detection of CO and H\u2082. Tests performed at 360\ub0C show for the first time CO- and H\u2082-induced reversible variations in the optical absorption of thin TiO\u2082/Au sol\u2013gel films. The absorbance changes are strongly dependent on both the testing wavelength and the film microstructure. Together with the sensing dynamics observed through an electric interface, it is possible to obtain a better understanding of the mechanisms involved in the detection of both gases. The presence of H\u2082 elicits almost ideal, step-like dynamic responses using conductometric detection.Peer reviewed: YesNRC publication: Ye