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ABSTRACT: Resistance and capacitance measurements, as a function of frequency, were carried out to analyze and model the electrical behavior of undoped titanium dioxide (TiO2) films. The sensing measurements were carried out in a chamber with independent temperature, pressure, gas composition, and flow rate control. With the aim of evaluating the electrical response of the sample as a function of the surrounding atmosphere, a frequency range of 100 Hz–4 MHz was used (vacuum or air at atmospheric pressure). The resistance and capacitance responses were obtained with the help of impedance spectroscopy technique. The impedance response versus frequency allows the discrimination between grain-boundary capacitance (Cgb) and resistance (Rgb) contributions. A model, taking into account the possible effects due to grain size is proposed in order to work out the permittivity of the material.
Physica Status Solidi (A) Applications and Materials 10/2010; 208(1):118 - 122. · 1.46 Impact Factor
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ABSTRACT: Impedance spectroscopy was carried out on SnO2 thick films exposed to different atmospheres. Oxygen desorption and adsorption during heating and cooling processes, respectively, onto the grain surface affects the resistance and electrical capacitance of the sensors. Double parabolic Schottky-type potential barriers at grain boundaries were assumed to analyze the tunneling and thermionic contributions to conductivity. In addition, the influence of the temperature on the oxygen diffusion into the grains annihilating oxygen vacancies was studied. It was deduced that in-diffusion substantially affects the conductivity.
Sensors and Actuators B-chemical - SENSOR ACTUATOR B-CHEM. 01/2009; 136(1):230-234.
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M. Blo,
M. C. Carotta,
S. Galliera,
S. Gherardi, A. Giberti,
V. Guidi,
C. Malagù,
G. Martinelli,
M. Sacerdoti,
B. Vendemiati,
A. Zanni
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ABSTRACT: Nanopowders of pure and of Mn-, Ta- and Zr-loaded (5wt.%) WO3 were prepared and printed as thick films. Investigation of the influence of the doping on morphology, structure and gas response versus NO2 has been performed. Pure nanometric WO3 was prepared by a modified sol–gel synthesis while loading was carried out by impregnation with Mn(II), Ta(V) and Zr(IV) chlorides. Addition of Ta resulted in grain coalescence and phase transition inhibitions in the layers with respect to pure WO3 films, being the effect strongly enhanced in the films fired at 850°C. The Ta-doped films turned out to be the most sensitive films with a response extending down to the sub-ppm domain.
Sensors and Actuators B-chemical - SENSOR ACTUATOR B-CHEM. 01/2004; 103(1):213-218.
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ABSTRACT: The photoluminescence of rutile and anatase TiO2 has been investigated in the range of 360–890 nm at several temperatures. An unexpected intense near-infrared (1.53 eV) photoluminescence band was recorded for both phases. At low temperatures, the resulting bands form a substructure of equally spaced peaks irrespective of the phase. The spectra were interpreted in the framework of the single-configuration-coordinate model as the phonon-replica effect, originating from ionization of oxygen vacancies. © 2003 American Institute of Physics.
Journal of Applied Physics 07/2003; 94(3):1501-1505. · 2.17 Impact Factor
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V Guidi,
M Blo,
M.A Butturi,
M.C Carotta,
S Galliera, A Giberti,
C Malagù,
G Martinelli,
M Piga,
M Sacerdoti,
B Vendemiati
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ABSTRACT: Different synthetical routes involving several solvents for obtaining WO3 powders, suitable for gas sensing have been studied. Aqueous and alcoholic solvents proved to be the most promising media to grow nanometric particles. Among these, a modified sol–gel route that involves ethanol and a di-chetone, highlighted a more homogeneous grain-size distribution. The structure and morphology evolution of pure WO3 powders with time and annealing temperature have been studied. The study of the energy barrier and conductance versus temperature allows to understand the reason for the high response of WO3 to oxidising gases and its lack of sensitivity to reducing agents. Films of WO3 responded to NO2, sensing as low a gas concentration as 200 ppb.
Sensors and Actuators B Chemical 100:277-282. · 3.90 Impact Factor
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ABSTRACT: Sensing of light alkanes via chemoresistive gas sensors has been addressed. Screen-printed films of a solid solution of mixed Sn and Ti oxides have been selected for the purpose. We demonstrate that the films sensitively detect 100 ppm of such gases and 500 ppm of methane, the two levels being by far lower than the alarm limits for these gases. Information about the working mechanism of chemical reactions on the surface has been discussed under either dry or wet condition.
Sensors and Actuators B: Chemical.
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ABSTRACT: A study of the sensing properties of chemoresistive metal-oxides vs. light alkanes has been undertaken under wet condition and in presence of ethanol. Screen-printed films of a solid solution of mixed Sn and Ti oxides have been selected for the purpose. We demonstrated that the films are capable of detecting 100 ppm of light alkanes or 500 ppm of methane in wet condition, two concentration levels by far lower than their alarm thresholds, respectively. Ethanol is known to be a harmful interfering gas, though its concentration can be reduced to values lower than 10 ppm by proper filtering. We show that, even in presence of 10 ppm of ethanol, the films steadily responded to alkanes.
Sensors and Actuators B: Chemical.
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ABSTRACT: Diffuse reflectance spectroscopy in the UV–vis–NIR is employed to study the electronic transitions in MoO3–WO3 mixed oxide. The spectroscopic results were then related to the temperature profile of the surface barrier. The electronic absorptions appear to increase after reducing treatments and to decrease after oxidation. This variation of oxygen-related defects changes the doping level, which in turn, affects the dependence of surface barrier on temperature. The latter is strictly connected to the sensing properties of the mixed oxide.
Sensors and Actuators B: Chemical.
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ABSTRACT: One of the main applications of metal oxide gas sensors is the environmental monitoring of urban and industrial areas, where the pollution level may become dangerously high. In this frame, environmental temperature plays a fundamental role, since it may influence the sensor signal. This work aims at measuring ambient temperature induced conductance variation, and to suggest a theoretical model to account for that.
Sensors and Actuators B: Chemical.
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M.C. Carotta,
A. Cervi,
V. di Natale,
S. Gherardi, A. Giberti,
V. Guidi,
D. Puzzovio,
B. Vendemiati,
G. Martinelli,
M. Sacerdoti,
D. Calestani,
A. Zappettini,
M. Zha,
L. Zanotti
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ABSTRACT: Nanostructured ZnO was obtained through two different synthetic processes: a traditional sol–gel (SG) route and a combination of vapor transport process and controlled oxidation methods. In SG synthesis, thermal decomposition of the precursor at 450 °C for 2 h in an oven led to pure zincite nanoparticles. Through the second method, instead, nanocrystalline structures in form of tetrapods (TP) were directly obtained during the synthesis process. Powder and film characterizations have been carried out by means of TG–DTA, SEM, TEM and XRD. Finally, electric measurements have been performed with the aim to compare conductive properties, surface barrier heights and gas sensing features, versus O3, NO2, CO and H2S. Despite the significant difference in morphology, it turned out that both types of sensors offered large responses to oxidizing gases at concentration suitable for environmental monitoring.
Sensors and Actuators B: Chemical.
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M. Blo,
M.C. Carotta,
S. Galliera,
S. Gherardi, A. Giberti,
V. Guidi,
C. Malagù,
G. Martinelli,
M. Sacerdoti,
B. Vendemiati,
A. Zanni
[show abstract]
[hide abstract]
ABSTRACT: Nanopowders of pure and of Mn-, Ta- and Zr-loaded (5 wt.%) WO3 were prepared and printed as thick films. Investigation of the influence of the doping on morphology, structure and gas response versus NO2 has been performed. Pure nanometric WO3 was prepared by a modified sol–gel synthesis while loading was carried out by impregnation with Mn(II), Ta(V) and Zr(IV) chlorides. Addition of Ta resulted in grain coalescence and phase transition inhibitions in the layers with respect to pure WO3 films, being the effect strongly enhanced in the films fired at 850 °C. The Ta-doped films turned out to be the most sensitive films with a response extending down to the sub-ppm domain.
Sensors and Actuators B: Chemical.
