1,720,986 research outputs found
Sol-Gel Films containing Metal and Semiconductor Nanoparticles for Gas Sensing
No full textNanotechnology 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
Optical and conductometric gas sensing properties of sol-gel TiO2 films doped with Au nanoparticles
No full textTiO2 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 °C. Measurements
performed at 360 °C 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
Gold nanoparticles to boost the gas sensing performance of porous sol–gel thin films
No full textIn 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
Gold-nanoparticle-doped TiO2 semiconductor thin films: Optical characterization
No full textA simple procedure for creating titania sol–gel-based semiconductor thin films is described. Gold nanoparticles are doped
homogeneously into the precursor mixture and the particles are homogeneously distributed in the resultant films when prepared
using spin-coating. The effects of particle loading and annealing temperature on the optical properties of the resultant
films are characterized. Ellipsometry, X-ray diffraction, atomic force microscopy, and surface plasmon spectroscopy are used to
monitor the crystallization and porosity changes during film synthesis
TiO2 sol-gel thin films containing Au and Pt nanoparticles with controlled morphology : optical study and gas sensing properties
No full textAu and Pt nanoparticles are prepared with colloidal techniques in order to achieve high morphological quality, capped with a polymer and then embedded inside a TiO2 sol-gel matrix, resulting in a homogeneous dispersion of both metal colloids, confirmed by TEM analyses. Refractive index values measured with ellipsometry increase with the annealing temperature, with quite a linear trend, and at the same time the Au surface plasmon resonance peak undergoes a red shift: the refractive index evaluated from the Au plasmon band is slightly lower than the measured value, indicating that the refractive index just around metal particles is different from the average of the matrix, likely because of the polymeric capping agent. Optical gas sensing tests towards CO and H2 are presented as one of the possible applications of these nanocomposites.Peer reviewed: YesNRC publication: Ye
Different sensing layers for SPR sensing of organic vapours
No full textIn 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. TiO and TiO - 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
Titanium Dioxide-Based 64° YX LiNbO3 SurfaceAcoustic Wave Hydrogen Gas Sensors
Full text linkAmorphous titanium dioxide (TiO2) and gold (Au) doped TiO2-based surface acoustic wave (SAW) sensors have been investigated
as hydrogen gas detectors. The nanocrystal-doped TiO2 films were synthesized through a sol-gel route,mixing a Ti-butoxide-based
solution with diluted colloidal gold nanoparticles. The films were deposited via spin coating onto 64° YX LiNbO3 SAWtransducers
in a helium atmosphere. The SAW gas sensors were operated at various temperatures between 150 and 310 °C. It was found that
gold doping on TiO2 increased the device sensitivity and reduced the optimum operating temperature
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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