D. Manno

A new amperometric nanostructured sensor for the analytical determination of hydrogen peroxide

A new amperometric, nanostructured sensor for the analytical determination of hydrogen peroxide is proposed. This sensor was constructed by immobilizing silver nanoparticles in a polyvinyl alcohol (PVA) film on a platinum electrode, which was performed by direct drop-casting silver nanoparticles that were capped in a PVA colloidal suspension. UV-vis spectroscopy, X-ray diffraction and transmission electron microscopy were used to give a complete characterization of the nanostructured film. Cyclic voltammetry experiments yielded evidence that silver nanoparticles facilitate hydrogen peroxide reduction, showing excellent catalytic activity. Moreover, the cronoamperometric response of modified sensors was dependent on nanoparticle lifetime. Experiments were performed, using freshly prepared solutions, after 4 and 8 days. Results concerning the quantitative analysis of hydrogen peroxide, in terms of detection limit, linear range, sensitivity and standard deviation (STD), are discussed for each tested sensor type. Utilization of two different linear ranges (40 microM to 6mM and 1.25 microM to 1.0mM) enabled the assessment of concentration intervals having up to three orders of magnitude. Moreover, the electrode made using a 4-day-old solution showed the maximal sensitivity of 128 nA microM(-1)(4090 nA microM(-1)cm(-2)), yielding a limit of detection of 1 microuM and STD of 2.5 microAmM(-1). All of these analytical parameters make the constructed sensors suitable for peroxide determination in aqueous solution.

Physical and structural characterization of tungsten oxide thin films for NO gas detection

Abstract Tungsten trioxide (WO3) thin films were rf sputtered from a WO3 target in various oxygen/argon (O2/Ar) atmospheres and at different total pressures. A detailed structural and morphological investigation has been carried out on all obtained films by high resolution electron microscopy and nanodiffraction methods. Optical and electrical properties have been studied as function of deposition parameters. In addition, all obtained films were tested in controlled atmosphere in order to investigate their response to NO in the interval 2–100 ppm in dry air. The sputtering parameters were optimized in order to obtain the maximum sensitivity to NO gas. Finally, a close dependence between sputtering conditions, morphological features and physical properties was observed.

Titanium oxide thin films for NH3 monitoring: Structural and physical characterizations

Titanium oxide thin films have been deposited by thermal evaporation in vacuum and then have been analyzed before and after a suitable thermal annealing in order to test their application in NH3 gas-sensing technology. In particular, spectrophotometric and conductivity measurements have been performed in order to determine the optical and electrical properties of titanium oxide thin films. The structure and the morphology of such material have been investigated by high resolution electron microscopy and small area electron diffraction.

Structural and electrical properties of sputtered vanadium oxide thin films for applications as gas sensing material

A detailed structural and morphological investigation has been carried out by conventional transmission electron microscopy, high resolution electron microscopy and nanodiffraction methods on vanadium oxide films obtained by reactive rf sputter at a high power discharge (1000 W) and different O2/Ar ratio. Electrical characterization has been also performed in controlled atmosphere in order to investigate the influence of NO2 oxidizing gas on the material conductance as a function of deposition parameters. A strict relation between structure, morphology and resistance variation in controlled atmosphere has been observed.

Non-functionalized silver nanoparticles for a localized surface plasmon resonance-based glucose sensor

The optical properties of non-functionalized silver nanoparticles in ethanol solution have been analyzed and a progressive shift of localized surface plasmon resonances caused by the adding of increasing quantities of glucose has been observed. To understand this occurrence, the interaction of glucose molecules with the silver nanoparticle surface has been investigated using Raman spectroscopy. In addition, high resolution transmission electron microscopy shows the presence of superstructures on the silver nanoparticle surface that can be imputed to the presence of glucose.

Gas-sensing properties of porphyrin dimer Langmuir-Blodgett films

Abstract Langmuir–Blodgett films of a 1:4 mixture of meso,meso′-buta-1,3-diyne-bridged Ni(II) octaethylporphyrin dimer and arachidic acid have been deposited onto various substrates. The isotherm at the air/water interface and absorbance measurements using polarised light are consistent with a planar statistical orientation of the porphyrin dimers which are probably prone onto the arachidic acid tails. The presence in the dimer of the acetylenic linking group allows the formation of a large and highly conjugated molecular structure; this has suggested the use of the films in gas sensing apparatus. Electrical characterisation in controlled atmosphere and with the simultaneous presence of interfering gaseous species, such as C2H5OH, NH3, and CO, suggest that this porphyrin dimer is a promising selective NO gas sensing material.

Kinetic behavior analysis of porphyrin Langmuir–Blodgett films for conductive gas sensors

Meso, meso′-buta-1,3-diyne-bridged Ni (II) octaethylporphyrin dimer thin films have been deposited by the Langmuir–Blodgett method and, for the first time, have been considered as the active layer in resistive gas sensors. In particular, the electrical conductivities of these films undergo a remarkable variation due to exposure to small concentrations of NO in air at an operating temperature of 50 °C. To interpret the behavior of such organic films, a model has been built up and the conductivity variation as a function of test gas concentrations and time has been derived. The fitting of theoretical and experimental behavior allows us to determine the number of adsorbed gas molecules per porphyrin dimer, response and recovery times, adsorption and desorption coefficients. The reliability of the model is proved by obtained results. In particular, the determined adsorption and desorption coefficients depend only on test gas species but are unaffected by other experimental conditions such as gas concentration.

Effects of thermal annealing on optical absorption of amorphous indium selenide thin films

Abstract The thermal annealing behaviour of optical absorption in amorphous indium selenide thin films is investigated in the visible spectral range. Annealing is performed at different temperatures and for different periods of time. In all the examined cases it is found that the dependence of the absorption coefficient α on the photon energy ħω is well described by the relation α h ω = B( h ω − E opt ) 2 . The increase in the values of the optical gap Eopt for samples annealed between 300 and 550 K is ascribed to the decrease of the unsaturated bonds in the amorphous structure due to heat treatment.

Gas-sensing properties of sputtered thin films of tungsten oxide

Electrical, structural and morphological properties of thin films of deposited by the reactive RF sputtering method have been analysed. The fundamental electrical features of have been determined by Hall-effect measurements. Information about the structure and morphology of these films was obtained by transmission electron microscopy techniques. The investigations of electrical properties in a controlled atmosphere at various operating temperatures revealed that is particularly suitable for NO gas detection. In particular, the relative variation of the resistance of was found to be reversible and to follow a power-law relationship. The dependence of the electrical properties on the structure and morphology has also been discussed.

Structural and electrical properties of In2O3–SeO2 mixed oxide thin films for gas sensing applications

In2O3–SeO2 mixed oxide thin films have been obtained by thermal evaporation of a stoichiometric In–Se starting charge and subsequent thermal annealing in an oxygen flow. High-resolution transmission electron microscopy, small area electron diffraction, and digital image processing have been employed in order to investigate the structure and the morphology of the films obtained. Hall effect and resistivity measurements in a vacuum and in a controlled atmosphere have been performed to obtain information about physical properties of these films. The experimental data show evidence that the electrical conductivity of these films undergoes a remarkable variation due to exposure to small concentrations of NO in dry synthetic air or argon. To interpret the behavior of such films, an adsorption kinetic model has been developed and the conductivity variation as a function of gas concentrations, time, and temperature has been derived. The fitting of the theoretical and experimental behavior allows us to determine t...